How can we help?

You can also find more resources in our Help Center.

396 terms

A&P Intro/Muscle/Nerve

STUDY
PLAY
anatomical position
the subject stands:
erect facing the observer with the head level
the eyes facing forward
feet flat on the floor directed forward
arms at their sides
palms forward
sagittal plane
slice going through from front to back dividing body into R and L, but not down the midline. (z axis in geometry)
frontal plane (coronal)
slice going through from ear to ear; in geometry the y axis. Separated body into front and back
transverse (axial) plane
slice from belly button to back (spans from left to right) Separates body into top and bottom in geometry the x axis
flexion/extension
narrowing the angle of the joint/making the angle of the joint straighter or wider
supination/pronation
palms up (think you can hold soup)/palm down (think you CAN'T hold soup)
abduction/adduction
to move away from midline/to move towards the midline
dorsiflexion/plantarflexion
adduction of the foot, moving upwards/abduction of the foot, moving downwards
eversion/inversion
overpronation/underpronation
pleural membrane
serous membranes that covers the lungs (visceral pleura) and the walls of the pleural cavity (parietal pleura)
pericardial membrane
serous membrane that covers the heart (visceral pericardium) and the pericardial cavity walls (parietal pericardium)
peritoneal membrane
serous membrane that covers the abdominal organs (visceral peritoneum) and the abdominal cavity walls (parietal peritoneum)
tight junctions
intracellular junctions found where a leakproof seal is needed between cells, i.e. in the stomach and bladder.
adherens junctions
intracellular junction that make an adhesion belt (from glycoprotein cadherin) that keeps tissues from separating as they stretch and contract. Ex; epithelial cells
desmosomes
intracellular junctions that act as "spot welds". They also use cadherin glycoprotein (plus intermediate filaments) to hook into the cytoplasm of other cells and CONNECT CYTOSKELTONS
hemidesmosomes
intracellular junctions that are "half-welds" that join cells to the basement membrane. ex: keratinocytes in the epidermis of skin
gap junctions
are pores (connexons) that allow small substances like ions to pass between cells. If one of the cells gets sick or dies, these seal like a hatch to prevent damage to other cells. ex: Alveoli gas diffusion
epithelial tissue
covers body surfaces, forms glands, line hollow organs, body cavities, ducts. Avascular and develops from all 3 germ layers. Free apical surface and attached basal surface.
connective tissue
protects supports and binds organs. this includes fat, RBCs, WBCs, platelets. derived from mesoderm
muscular tissue
generate the physical force needed to make body structures move. They also generate heat used by the body. derived from mesoderm
nervous tissue
detect changes in the body and respond by generating nerve impulses. develops from ectoderm
tissues develop from ___ primary germ layers. which are......
3
Endoderm, mesoderm, ectoderm
squamous epithelium
flat, wide, pavingstone cells
cuboidal epithelium
cells as tall as they are wide
columnar epithelium
cells taller than they are wide
simple epithelium
One layer. All cells in contact with basement membrane. Useful for: Diffusion, Osmosis, Filtration, Secretion, Absorption
pseudostratified epithelium
Appears to have layers, but in reality all cells go from the apex to the base. May contain cilia or goblet cells.
stratified epithelium
Two or more layers. Only basal layer in contact with basement membrane. Protect underlying tissues in locations where there is wear and tear.
simple squamous
makes up epithelial membranes and lines the blood vessels. Thin layer allows rapid passage of substances thru them (Filtration, Diffusion) as in alveoli of lungs or capillary beds. Also involved in secretion (serous membranes)
simple columnar
is common in the digestive tract, function in secretion/absorption. forms a single layer of column-like cells, ± cilia, ± microvilli, ± mucous (goblet cells)
pseudostratified ciliated columnar
is characteristic of the upper respiratory tract. May contain goblet cells
transitional
found in the bladder, cells can change shape
simple cuboidal
lines ducts and sweat glands. It is often found lining the tubules of the kidneys and many glands
Important in secretion and absorption
stratified squamous epithelium
has apical surface made of squamous cells. The other layers have different shapes, but the name is based on the apical layer
The many layers are ideal for protection against strong friction forces
May be keratinized (skin) or non-keratinized (mucosa)
stratified cuboidal epithelium
has an apical surface made up of two or more layers of cube-shaped cells.
Locations include the sweat glands and part of the ♂ urethra
endothelium
is a specialized simple squamous epithelium that lines the entire circulatory system from the heart to the smallest capillary - it is extremely important in reducing turbulence of flow of blood and decreasing surface tension.
mesothelium
is found in serous membranes such as the pericardium, pleura, and peritoneum
endocrine glands/exocrine glands
glands that secrete their contents directly into the blood/glands that secrete their contents into a lumen or duct. Ex: mucus, sweat, oil, earwax, saliva, and digestive enzymes.
Define merocrine gland
most common type of secretion (salivary glands, pancreas). the gland releases its product by exocytosis and no part of gland is lost or damaged
Define apocrine gland
glands 'bud' off their secretions through the plasma membrane through vesicles (milk fats)
Define holocrine gland
secreted by rupture of plasma membrane, releasing cell contents into lumen and killing cell itself (sebum)
Connective tissue characteristics x3
Contains collagen fibers and ground substance, highly vascular and supplied with many nerves (exception is cartilage and tendons), most abundant and widely distributed tissue in body.
Define Extracellular Matrix (ECM)
non-cellular material around cells, consists of protein fibers and ground substance
What consistency can ground substance take on?
fluid, semifluid, gelatinous, or calcified
What type of slices does a CT scan use?
Transverse (axial) sections
Medial plane
Cuts that separates the body into EQUAL R and L sides.
Oblique plane
Angled cut
Supine vs Prone
belly up vs belly down when lying on a table
External vs Internal rotation
External is lateral rotation, Internal is medial rotation
What are the regional names of the head, eye, neck, elbow, hand, knee, chest, and groin?
Cephalic/Cranial, Orbital/Ocular, cervical, cubital, carpal, patellar, thoracic, inguinal
4 body cavities
1) Cranial- brain and meninges
2) Vertebral- vertebrae and spine
3) Thorax- chest contains potential space. Pleural x2, pericardial, and mediastinum
4) Abdominopelvic- Abdomen and peic
Pericardial cavity
surrounds the heart
Mediastinum
between pleural cavities. Runs from sternum to vertebral column and first rib to diaphragm. Contains heart, esophagus, trachea, thymus and serveral large blood vessells
Pleural cavity
Two cavities on either side of heart. Each contains a lung
ASIS stands for?
Anterior superior iliac spine
How are tissues formed?
By grouping cells together using a variety of Intercellular Junctions
What do Intracelular Junctions do?
Intracellular Junctions connect adjacent cells mechanically at the cell membranes or through cytoskeletal elements within and between cells
How many types of Junctions are there?
5:
-Tight
-Adherence
-Desmosomes
-Hemidesmosomes
-Gap
What are the 4 basic tissue types?
1) Epithelial
2) Connective
3) Muscular
4) Nervous
Which tissues develope from the Ectoderm, Endoderm, & Mesoderm?
Ecto- Nervous tissue and Outer Epithelium
Endo- Epithelium (GI, Lungs, and Bladder)
Meso- Muscle and CT and Epithelium
What is the time-frame for embryology?
from conception to 8 weeks gestation
What are the 3 shapes of epithelial cells?
1) Squamous- flat and wide
2) Cuboidal- thick and short
3) Columnar- long
What are the 3 types of arrangement for epithelial cells
1) simple- 1 cell deep (good for diffusion)
2) Stratified- multiple cells deep for protection
3) Pseudostratified- 1 cell deep, but looks layered due to varying nucleus heights.
What is Basement membrane? What is it made up of?
Basement membrane is a thin sheet of fibers that underlies the epithelium
1) Basal lamina
2) Reticular lamina
What tissue types secrete the basal and reticular laminas?
basal= epithelium
reticuar= CT
What are the 3 types of Pseudostratified epithelium?
1) Goblet- secrete mucus
2) Cilia- tiny hairs to move foreign bodies
3) Villi- increase surface area
What types are cell arrangement are the following made up of? Epithelium, Blood vessels, Digestive, lungs, bladder, ducts & sweat glands.
Epithelium & Blood vessels- simple squamous
GI- columnar for secretion/absorptio
Lungs- pseudostratified coumnar w/goblet cell or cilia
Bladder- transitional
Glands/ducts- cuboidal
What are goblet cells?
They are simple columnar cells that have developed the ability to secrete mucus.
What are microvilli?
They are cytoplasmic projections of the simple columnar cell's apical surface that increases surface area for absorption.
Endothelium and Mesothelium are both derived from which layer of embyonic tissue?
The middle= mesoderm
They 2 types of epithelial glands are?
1) Exocrine
2) Endocrine
The two criteria for categorizing multicellular glands?
1) Shape: tubular, acinar (round), tubuloacinar
2) Branched or unbranched
Function of CT?
Bind tissues together
Support and strengthen tissue
Protect and insulate internal organs
Compartmentalize and transport
Energy reserves
Immune responses
The main protein of CT?
Collagen
What do all types of CT have in common?
Sparse cells & Surrounded by an extracellular matrix
What cells make up CT/
Fibroblasts (most common)
Chondrocytes make the various cartilaginous C.T.
Adipocytes store triglycerides.
Osteocytes make bone.
White blood cells are part of the blood.
What are Fibroblasts?
The most numerous cell in CT. Secrete protein fibers (collagen, elastin, & reticular fibers) and a "ground substance" which varies from one C.T. to another.
5 types of WBCs?
1)Macrophages are the "big eaters" that swallow and destroy invaders or debris. They can be fixed or wandering.
2)Neutrophils are also macrophages ("small eaters") that are numerous in the blood.
3&4)Mast cells and Eosinophils play an important role in inflammation.
5)Lymphocytes secrete antibody proteins and attack invaders.
3 Fiber secreted by CT are?
Collagen fibers
Elastin fibers
Reticular fibers
What are the 2 classifications of CT?
1) Embryonic: mesenchyme & mucous
2) Mature: Loose, Dense, Cartilage, Bone, or Liquid
What are mesenchyme and mucous CT?
Mesenchyme gives rise to all other connective tissues

Mucous C.T. (Wharton's Jelly) is a gelatinous substance within the umbilical cord and is a rich source of stem cells
3 types of loose CT
1) Areolar Connective Tissue: most widely distributed in the body. Contains all 3 fiber types. STRUCTURE- It is used to attach skin and underlying tissues, and as a packing between glands, muscles, and nerves.
2) Adipose tissue:
It reduces heat loss and serves as padding and as an energy source.
3) Reticular connective tissue: is a network of interlacing reticular fibers and cells.
Makes a Scaffolding used by cells of lymphoid tissues such as the spleen and lymph nodes.
3 Types of dense CT?
1) Dense Irregular Connective Tissue: consists predominantly of fibroblasts and collagen fibers randomly arranged. STRENGTH when forces are pulling from many different directions.
2) Dense regular Connective Tissue: tendons, ligaments, and other strong attachments where the need for STRENGTH along one axis is mandatory (muscle pulling on a bone)
3) Elastic Connective Tissue: fibroblasts and freely branching elastic fibers. It allows STRETCHING of certain tissues like elastic arteries (ex: aorta)
What are the 3 types of Cartilage?
1) Hyaline- smooth surface for joint movement between 2 bones
2) Fibrocartilage- tough and strong (intervertebral spaces and meniscus)
3) Elastic- consists of chondrocytes, malleable (ears, nose, epigottis)
What is Bone?
Bone is a connective tissue with a calcified intracellular matrix.
What are the 2 types of Liquid CT?
Blood and Lymph: atypical liquid connective tissues. Blood has many cells as well as fibers (such as fibrin that makes blood clot).
chondrocytes
CT cell that make the cartilaginous CT
adipocytes
CT cell that stores triglycerides
osteocytes
CT cell that makes bone
macrophages
big eaters who swallow and destroy invaders or debris, can be fixed or wandering
neutrophils
also macrophages 'small eaters' that are in the blood
mast cells and eosinophils
play an important role in inflammation
What are lymphocytes?
secrete antibody proteins and attack invaders
What is areolar connective tissue?
a loose connective tissue that is widely distributed in the body- used to attach skin and underlying tissues and in between glands, muscles and nerves. has all 3 fiber types
What is adipose tissue?
loose connective tissue that is in the subcutaneous layer deep to the skin and around organs and joints. It functions to reduce heat loss, serve as padding and be an energy source
What is reticular CT?
network of interlacing reticular fibers and cells, forms a scaffolding used by lymphoid tissues
What is dense irregular CT?
mostly fibroblasts and collagen fibers in random arrangement, provides strength when forces are pulling from many different directions
What is dense regular CT?
found in tendons, ligaments, other strong attachments where the need for strength is along one axis
What is elastic CT?
mostly fibroblasts and freely branching elastic fibers, allows stretching of tissue (i.e. in elastic arteries like the aorta)
cartilage
tissue with poor blood supply that grows slowly and is slow to repair if injured
What is hyaline cartilage?
most abundant provides a smooth surface for joing movment and covers ends of long bones, parts of ribs, nose, trachea, bronchi and larynx
What is fibrocartilage?
thick bundles of collagen fibers, is very strong and tough. makes up intervertebral discs and knee joints
What is elastic cartilage?
made of condrocytes in a threadline network of elastic fibers, found in the malleable part of the external ear and the epiglottis
Define bone
connective tissue with calcified intracellular matrix, at times chondrocytes of cartilage are able to turn into osteocytes that make up this structure
What type of CT are blood and lymph?
atypical liquid CT
Define organ
having 2 types of tissue present, although most contain all 4 types of tissue
Define epithelial membrane
simplest organ in the body: epithelium and little bit of CT (mucous, serous, cutaneous)
Define mucous membrane
line interior surfaces that are open to the outside (digestive tract, respiratory tract, reproductive tract)
Define serous membranes
line internal surfaces (parietal layer next to body wall, serous fluid between layers, visceral layer next to organ)
Define synovial membranes
enclose certain joints and are made of CT ONLY
What is the Integumentary System?
A cutaneous membrane that covers outer surface of the body.
Largest organ by surface area and weight.
Functions of skin/integument x6
it protects, regulates body temp, allows sensory perception, synthesis of vitamin D, emotional expression, reservoir of blood.
What are the 3 layers of the Integumentary System?
1) Epidermis
2) Dermis
3) Subcutaneous
Define epidermis
outermost of the 3 layers of skin, consists of epithelial tissue, composed of keratinized stratified squamous epithelium, functions to resist damage and offers protection to underlying tissues
Define dermis
middle of the 3 layers of skin, consists of CT, is thicker than othe layers, provides temperature stability and prevents dehydration
Define subcutaneous layer (hypodermis)
innermost of 3 skin layers, loose areolar/adipose CT that attaches skin to underlying tissues and organs, contains pacinian corpuscles that detect external pressure applied to skin, also has blood vessels and nerves in transit to upper layers of skin. functions to insulate and store fat and serve as anchor for skin
Define Langer lines. What are they determined by and what happens is you cut perpendiculat to them?
aka tension lines-> patterns we should follow when making incisions into the skin to ensure there is no gaping when sutured back together (hint to remember: story about the circle cut in the forehead)
-They correspond to the natural orientation of collagen fibers in the dermis and epidermis.
-If you cut perpendicular to them you will leave a gap.
The epidermis is made up of what type of epithelium and what 4 cells?
-Stratified squamous epithelium
-keratinocytes, melanocytes, langerhans cells, & merkel cells
Define keratinocytes
make up 90% of cells in epidermis, produce keratin, and a water repellant sealant. Found in all layers of Epithelium.
Define melanocytes
provide pigment melanin, found in stratum basale
Define langerhans cells
macrophages that originated in red bone marrow, involved in immune response
Define merkel cells
function in the sensation of touch along with other adjacent tactile discs/receptors. Found in Stratum basale.
The epidermis is composed of ___ layers in thin skin and ___ layers in thick skin. What are the layers?
4, 5
From base to surface: Stratum Basale-->Stratum Spinosum-->Stratum Granulosum--> Stratum Lucidum (only in thick skin like on heels)-->Stratum Corneum
What is the stratum basale?
bottom deepest layer of epidermis, continuous cell division occurs here and this layer produces all other layers of epidermis. Contains Melanocytes
What is the stratum spinosum?
layer of 8-10 keratinocytes, sits above stratum basale
What is the stratum granulosum?
3rd layer of epidermis contains non-dividing cells and granules of keratin
What is the stratum lucidium?
layer of epidermis between granulosum and corneum in thick skin of the fingertips, palms and soles
What is the stratum corneum?
outermost layer of epidermis, composed of 20 layers of flat cell-remnants (dead keratinocytes filled with keratin protein) these layers are continuously shed and replaced
What is keratinization?
process of replacing viable cells in the stratum basale with waxy keratin protein as cells move from deepest layer to surface layer
Define thin (hairy) skin
covers all regions of body except palms, palmar surfaces of digits and soles
Define thick (hairless) skin
covers palms, palmar surfaces of digits and soles
What is Melanin? Types x2
produced by melanocytes: eumelanin (brown to black) & pheomelanin (yellow to red)
What are Freckles?
Freckles are clusters of concentrated melanin triggered by exposure to sunlight
Define albinism
congenital disorder characterized by the complete or partial absence of pigment in skin, hair or eyes due to defect of an enzyme involved in producing melanin
Define vitiligo
chronic disorder that causes depigmentation patches in the skin, unknown cause (proposed combo of genetic factors and autoimmune disease)
What is the papillary region of dermis?
just below epidermis consists of areolar CT, dermal papillae, corpuscules of touch, free nerve endings
What is the reticular region of dermis?
sits above subQ. consists of dense irregular CT, adipose cells, hair follicles, nerves, sebaceous glands, sudoriferous (sweat) glands. tears in this region cause stretch marks (striae)
What are epidermal ridges?
reflect contours of underlying dermal papillae and form basis for fingerprints (function to increase firmness of grip by increasing friction)
What are the superficial sensory receptors in skin?
1) Merkel cells (stratum basale)
2) Free nerve endings
3) Meissner corpuscles (in dermis at border of epidermis)
4) Hair root plexuses
What are the deep sensory receptors in skin?
Pacinian corpuscles-used for sensitivity to vibration and pressure. Located in Dermis right above hypodermal region.
What is hair? (composition, function, components)
-made of dead keratinized epidermal cells, -functions in touch sensation and protection (sun exposure/heatloss)
-3 parts: shaft, follicle, root (epithelial and dermal root sheath)
What is lanugo?
fine non-pigmented downy hairs that cover the body of the fetus
What are vellus hairs?
short, fine, pale hairs barely visible to the naked eye
What are terminal hairs?
long, coarse, heavily pigmented hairs
What are sebaceous (oil) glands?
connected to hair follicles, secrete sebum.
What are eccrine sweat glands?
most numerous of the sudoriferous, secrete a watery solution that helps to cool the body and eliminates small amounts of waste. sweat in response to an emotional stressor and is responsible for thermoregulation
What are apocrine sweat glands?
located mainly in the skin f the axilla, groin, areolae, and bearded facial regions (in adult males). secrete a slightly viscous sweat. responsible for body odor, active during emotional sweating, sexual activity, NOT responsible for thermoregulation.
What are ceruminous glands?
modified sweat glands in the ear canal
What are nails?
composed of hard, keratinized epidermal cells. located over the dorsal surfaces of the ends of fingers and toes
What are the structures of a nail? x4
includes free edge, transparent nail body/plate, whitish lunula at proximal base of nail body, and the nail root embedded in a fold of skin.
What is epidermal wound healing?
occurs following superficial wounds that only affect the epidermis, usually returns to normal function
What is deep wound healing?
occurs when an injury extends to the dermis and subcutaneous layer, may result in some loss of function and/or development of scar tissue
What is the process of epidermal wound healing?
basal epithelial cells migrate across wound, epidermis thickens
What is the process of deep wound healing? 2 phases
inflammatory phase: blood clot forms, epithelium migrates across wound and inflammatory process involving neutrophils & monocytes occurs in dermis/hypodermis.
Maturation phase: scar tissue has formed in dermis/hypodermis, epithelium has come together in epidermis and is working its way to thickening and forming normal layers under a surface scab.
Define burns
-Tissue damage caused by excessive heat, electricity, radioactivity or corrosive chemicals that denature the proteins of the skin cells.
-Destroys the skins ability to protect against bacteria and microbes and to regulate temperature
What is a first degree burn?
involves only the epidermis, characterized by mild pain and erythema. lacks blisters and skin function remains intact.
What is a second degree burn?
destroys epidermis and part of the dermis. characterized by redness, blister formation, edema and pain
What is a third degree burn?
full thickness (destroys epidermis, dermis and subq) most skin functions are lost and area is numb due to nerve ending damage
A major burn is classified as?
3rd degree over 10% of body OR
2nd degree over 25% of body OR
3rd degree on face, hands, feet, or perineum
Burns exceeding ___% of body have ___% mortality
70% of body = 50% mortality
What is the Rule of Nines for burns?
A quick means for estimating the surface area affected by a burn in an adult:
9% if both ant/post surfaces of head and neck
9% for both ant/post of an arm
36% for ant/post surfaces of trunk (includes buttocks)
9% anterior of a leg
9% for posterior of a leg
Parenchymal cells of an organ
consist of that tissue which conducts the specific function of the organ
Stroma cells of an organ
everything that does NOT conduct specific function of the organ (CT, blood vessels, nerves)
What is granulation tissue?
actively growing connective tissue created during repair of parenchymal cells and stroma by: rapid division of fibroblasts, manufacture of new collagen fibers and new capillary supply for healing.
Aging and tissue healing
tissue heals faster the younger you are (surgery of fetus usually leaves NO scar!), young tissue has better nutritional state, blood supply and metabolic rate
Aging changes on Integumentary system x7
1) wrinkles develop
2) dehydration and cracking
3) sweat production increases
4) changes in melanocytes result in gray hair and atypical skin pigmentation
5) Subq fat is lost/general decrease in skin thickness
6) nails may become brittle
7) increased susceptibility to pathological conditions
Why are Muscle and Neural tissue considered excitable?
They exhibit electrical excitability--->the ability to respond to certain stimuli by producing electrical signals such as action potentials
What can stimulate Keratinization?
Constant friction can stimulate the process and produce a callus (an even thicker buildup of keratinocytes in the stratum corneum)
What is Dandruff?
Dandruff is an excess of keratinized cells shed from the scalp
What is Keratin?
A tough fibrous protein that helps protect the skin and underlying tissues from heat, microbes, and chemicals.
What are nevi?
Nevi ("birthmarks" or moles) are chronic lesions of the skin - they are, by definition, benign
What is melanoma?
Malignant melanoma is a cancer of melanocytes
What are the 2 regions of the Dermis?
Papillary and Reticular
What is the Dermis made of?
connective tissue containing collagen and elastic fibers
Stretch marks (striae) are caused by?
Tears or excessive stretching in reticular region of dermis.
Why does the skin have different types of sensory receptors?
To differentiate between the different tactile ("touch") sensations:
Light touch, pressure, vibration, itch and tickle
How is hair color determined?
by the amount and type of melanin
What type of gland opens onto the hair shaft?
Sebaceous gland
What is the function of Sebum?
sebum prevents dehydration of hair and skin and inhibits bacterial growth
What shape/type of gland are the sweat glands?
coiled tubular glands
What are the 2 types of Sweat glands?
apocrine and eccrine
Function of Muscular tissue x4
1. Create motion - muscles work with nerves, bones, and joints to produce body movements
2. Stabilize body positions and maintain posture.
3. Store substances within the body using sphincters.
4. Move substances by peristaltic contractions.
5. Generate heat through thermogenesis
Electrical Excitability
generate action potentials in response to electrical or chemical stimuli
Contractility
generates tension
Extensibility
ability to stretch without being damaged
Elasticity
ability to return to its original shape/length after contraction or extension
How does a skeletal muscle fiber form?
many small spindly myoblasts fuse to form a single muscle fiber. Explains why there are so many nuclei in a skeletal muscle cell.
The myosin binding site is covered by
tropomyosin
Epimysium
outermost layer of the muscle, continuous with tendon
Perimysium
surrounds groups of 10-100 fibers separating them into bundles (fascicles)
Endomysium
Like endothelium, penetrates into each fascicle and separates individual muscle fibers from one another continuous with the connective tissues that form tendons and ligaments
Sarcolemma
plasma membrane of the muscle cell
Transverse T tubules
invaginations of the sarcolemma that tunnel in from the surface toward the center of each muscle fiber
Sarcoplasm
cytoplasm of the muscle fiber, rich in glycogen and myoglobin
Myofibrils
contractile organelles within sarcoplasm, prominent striations. Contain actin and myosin surrounded by sarcolemma
Sarcoplasmic reticulum
encircles each myofibril, stores Ca2+, terminal cisterns butt against T tubule, triad: transverse tubule and 2 terminal cisterns on either side
Thin filaments vs Thick filaments
actin( protiens strung together like beads) vs myosin (proteins boud together that look like golf clubs)
Connectin
another name for the muscle protein titan
Myoglobin
holds O2 in muscle cell
What are the 3 proteins Myofibrils are built from?
1) Contractile proteins- the part of the muscle that generates force during contraction (actin & myosin)
2) Regulatory proteins- help switch the contraction process on and off (troponin & tropomyosin)
3) Structural proteins- keep the thick and thin filaments in proper alignment and link the myofibrils to the sarcolemma and ECM (titin, dystrophin)
The sarcomere starts and ends at?
z-disc
The binding sites for myosin located on actin or covered by? How are they uncovered?
Tropomyosin
-Ca2+ binds Troponin (sitting on top of tropomyosin) which moves tropomyosin out of the way
The movement of the Tropomyosin/Troponin complex depends on?
Intracellular Ca2+
This filaments are anchored to what structure?
Z disks
Where do muscle contractions occur?
Sarcomere
M line
region at center of H zone that contains proteins that hold thick filaments together at the center of the sarcomere
H zone
Narrow region in center of each A band that contains thick filaments but no thin filaments
I band
lighter, dense area of sarcomere that contains remainder of thin filaments but NO THICK filaments. A Z disc passes through center of I band
A band
dark, middle part of sarcomere that extends entire length of THICK FILAMENTS!! and includes those parts of thin filaments that overlap thick filaments
Z disc
narrow, plate-shaped regions of dense material that separate one sarcomere from the next.
What occurs with overstretching of a muscle?
If there is overstretching there is not enough overlap between the actin binding sites and the myosin to get a good contraction.
What is the Motor End Plate?
The plasma membrane of the muscle cell on post synaptic side of the NMJ.
What is the Neuromuscular junction? What are the pre and post components?
is where transmition of the electrical events of a neuronal action potential into the electrical events of a muscle action potential occurs.
-Presynaptic membrane is on the neuron
-Postsynaptic membrane is on the muscle cell.
Describe the neuromuscular junction process in detail (8 steps)
1) The motor end plate on the muscle cell is rich in ACh-gated sodium channels
2) Nerve impulse causes Ca2+ channel in synaptic end bulb to open and Ca2+ flows inward.
3) Intra-axonal Ca2+ causes synaptic vesicles to undergo exocytosis, liberating ACh into synaptic cleft.
4) Released ACh crosses cleft and binds with Na+ channel- Na+ channel opens and Na+ flows into muscle cell
5) now muscle cell is +. This change in membrane potential triggers an action potential
6) action potential then propagates along sarcolemma to the T tubules.
7) SR then releases stored Ca2+ into sarcoplasm and the muscle contracts.
8)Ach is rapidly broken down by acetylcholinesterase attached to extracelluar matrix of synaptic cleft.
Botulinum toxin
blocks exocytosis of synaptic vesicles at the NMJ, therefore ACh is not released, leading to skeletal (respiratory) muscle paralysis (Botox)
Curare
binds and blocks Ach receptors, therefore ion channels don't open and can't contract skeletal muscles
Many OR drugs are curare based
Neostigmine
slows enzymatic activity of achetylcholinesterase, can strengthen weak muscle contractions such as in myasthenia gravis and treat curare poisoning or reverse curare-like drugs used for anesthesia
3 sources of muscle energy
1) Creatine phosphate: CP->C = 1 ATP, yields 15 sec of energy
2) anerobic glycolysis: glycogen breakdown = 2 ATP and lactic acid; yields 30-40 sec of energy
3) aerobic cellular respiration: in mitochondria break down AAs, Pyruvic acid from glycolosis, FAs from adipose, or O2 from Hgb = 36 ATP, yields minutes to hours of energy
Oxygen Debt
is the amount of O2 repayment required after exercise in skeletal muscle to: 1. Replenish ATP stores. 2. Replenish creatine phosphate and myoglobin stores. 3. Convert lactic acid back into pyruvate so it can be used in the Krebs cycle to replenish ATP
Motor Unit
is composed of a motor neuron plus all of the muscle cells it innervates
Less innervations= higher precision
Always the same type of muscle fiber
Neuron will fire only to same type of muscle fibers
Red muscle fibers
(the dark meat in chicken legs) have a high myoglobin content, more mitochondria, more energy stores, and a greater blood supply because they are more active
White muscle fibers
(the white meat in chicken breasts) have less myoglobin, mitochondria, and blood supply
Slow oxidative fibers (SO) -
small, appear dark red (myoglobin), least powerful type. Generate ATP by aerobic cellular respiration. Very fatigue resistant. Used for endurance like running a marathon and for maintaining posture.
Fast oxidative-glycolytic fibers (FOG)
are intermediate in size, appear dark red (myoglobin), and are moderately resistant to fatigue. Fast ATPase. Generate ATP by anaerobic glycolysis. Used for walking.
Fast glycolytic fibers (FG)
are large, white, and powerful. Contain large amounts of glycogen. Generate ATP by glycolysis. Stong and quick contractions. Suited to intense anaerobic activity of short duration, i.e. weight-lifting.
Isotonic contractions- 2 types
results in movement . tension remains unchanged and the muscle's length changes. Lifting an object at a constant speed is an example of isotonic contractions.
-concentric and eccentric
Concentric isotonic
is a type of muscle contraction in which the muscle shorten while generating force
Eccentric isotonic
is a contraction in which muscle tension is less than the resistance (the muscle lengthens)
Isometric contractions
results in no movement. Muscle force and resistance are equal, supporting objects in a fixed position and posture
Spasm
A sudden involuntary contraction of a single muscle within a large group of muscles - usually painless
Cramp
Involuntary and often painful muscle contractions caused by inadequate blood flow to muscles (such as in dehydration), overuse and injury, and abnormal blood electrolyte levels
Fibrosis (myofibrosis)
Replacement of muscle fibers by excessive amounts of connective tissues (fibrous scar tissue)
Myosclerosis
Hardening of the muscle caused by calcification from the excess calcium that was in the blood at the site of injury
Myasthenia Gravis
autoimmune disorder- produces Ab to ACh receptors Presents often in women, thymic tumors, first sxs are double vision, dysphagia
Neuroglia (glial cells)
play a major role in support and nutrition of the brain, but they do not manipulate information
Ganglia
are small masses of neuronal cell bodies located outside the brain and spinal cord, usually closely associated with cranial and spinal nerves.They are divided into three catagories somatic, autonomic, and enteric.
Nissl bodies
Rough endoplasmic reticulum in neurons, it imparts a striped "tiger appearance". Granular bodies of variable size that occur in cell bodies and dendrite, but not axons of neurons (contain RNA and polyribosomes)
Slow axonal transport
conveys axoplasm slowly in one direction only - from the cell body toward the axon terminals. (ex. Nutrients, lysosomes)
Fast axonal transport
moves materials quickly in both directions.
Nodes of Ranvier
are the gaps in the myelin sheath.
White matter
of the brain and spinal cord is formed from aggregations of myelinated axons from many neurons.The lipid part of myelin imparts the white appearance.
Gray matter of the brain & spinal cord
composed entirely of neuronal cell bodies and dendrites(gray because it lacks myelin)
Action potentials
allow communication over long distances within the body.
Voltage-gated channels
These channels respond to changes in the transmembrane electrical potential and are mainly located along the neuronal axon.
Mechanically-gated channels
respond to mechanical deformation (applying pressure to a receptor).
"Leakage" channels
these channels are gated but they are not active, and they open and close randomly.
An agonist
is any chemical that enhances or stimulates the effects at a given receptor.
An antagonist
is a chemical that blocks or diminishes the effects at a given receptor
Excitatory postsynaptic potential (EPSP)
is a depolarization of the postsynaptic cell, bringing it closer to threshold
Inhibitory postsynaptic potential (IPSP)
hyperpolarizes the postsynaptic cell taking it farther from threshold
Spatial summation
occurs when postsynaptic potentials arrive near the same location.
Temporal summation
occurs when postsynaptic potentials arrive close to the same time & add up to create an action potential.
What are the 3 types of muscle?
1) Skeletal
2) Cardiac
3) Smooth
What type of control are muscles under?
Voluntary and Involuntary
What are the 4 characteristics of Skeletal Muscle?
1) Electrical excitability
2) Contractility
3) Extensibility
4) Elasticity
What are satellite cells?
-Small mononuclear progenitor cells with virtually no cytoplasm found in mature muscle. They are found sandwiched between the basement membrane and sarcolemma (cell membrane) of individual muscle fibers.
-They can differentiate and fuse to augment existing muscle fibers and form new fibers.
-Oldest known adult stem cell niche, and are involved in the normal growth of muscle, as well as regeneration following injury or disease.
What is a somatic motor neuron?
Neurons located in the CNS that project their axons outside the CNS and directly or indirectly control muscles. The motor neuron is often associated with efferent neuron.
What are large muscle groups encased in?
Superficial- found in most regions of the body, blending with the reticular layer of the dermis
Deep fascia-surrounds the muscles, bones, nerves and blood vessels of the body.
What is the Linea Alba?
White line down middle of Rectus Abdomini where fascia from multiple muscles comes together.
3 components of Muscle CT
1) Epimysium
2) Perimysium
3) Endomysium
What is the sliding filament mechanism?
myosin hydrolyzes ATP--> Myosin binds actin--> Myosin power stroked in towards M line shortening sarcomere--> ATP bind myosin head to detach my acting.
With the exposure of the myosin binding site on the actin (in the presence of Ca2+), the thick and thin filaments "slide" over one another and the sarcomere is shortened.
What is Excitation Contraction Coupling?
Muscle AP causes release of Ca2+ from terminal cistern of SR which then binds to Troponin and allows the sliding filament mechanism to take place.
Muscle action potential basic steps
RMP -70mV
Depolarization: Na+ gates open +40 mV
Repolarization: K+ gates open -80mV
Na+/K+ pump brings RMP back to -70mV
What contributes to the negative RMP inside of the muscle cell?
Negatively charged proteins
Generating an AP on the muscle involves? x3
1) Transfer of info from electrical signal down neuron
2) To a chemical signal at the NMJ
3) To an electrical signal that causes depolarization of the sarcolemma
The Latent period is?
the brief delay as the AP sweeps over the sarcolemma and Ca2+ id released from the SR
What is the Relaxation phase?
Ca2+ is taken back into SR and myosin binding sites are covered back up
What is the Refractory Period?
a temporary loss of excitability where the motor unit will not respond to ANY level of stimulus
What is a muscle twitch? what causes it?
when a stimulus that results in contraction (force) of a single muscle fiber is measured over a very brief millisecond time frame
when a muscle fiber generates tension through the action of actin and myosin cross-bridge cycling. While under tension, the muscle may lengthen, shorten or remain the same.
Increasing the # of APs to a muscle fiber can result in ?
fusion of contractions called tetanus
1/2 of the fibers in a typical skeletal muscle are which type?
Slow oxidative fibers
Why does Ca2+ take longer to reach smooth musce fibers than skeletal muscle fibers?
smooth muscle has not T tubules
Smooth muscle has a ___ capacity for ATP generation. Gap junction in smooth muscle are only found in?
-low
-visceral (single-unit) hollow organs
Cardiac Muscle has what extra features that skeletal muscle lacks?
1) intercalated discs- transverse thickenings that connects ends of cardiac muscle fibers
2) desmosomes- hold fibers together
3) gap junctions- allow muscle action potentials to spread from one cardiac muscle fiber to another
Is the contraction in cardiac muscle AP shorter or longer than contraction in skeletal muscle? Why?
cardiac muscle contracts 10-15 times longer than skeletal muscle due to prolonged delivery of Ca2+
Cardiac muscle 2 main energy supplies are?
1) rich supply of O2 delivered by the extensive coronary circulation to generate ATP through aerobic respiration
2) lactic acid to generate ATP
more numerous mitochondria
Which CT layer does Cardiac muscle not have?
has endomysium and perimysium but no epimysium
Smooth muscle contraction is slower or faster than skeletal muscle? Why?
Contraction starts more slowly and lasts longer.
muscle shortens, stretches to a greater extent.
calmodulin binds to Ca2+ and activates myosin light chain kinase (uses ATP to place PO4 group on myosin head)
-takes longer for Ca2+ to leave giving smooth muscle its tone
characteristics/ properties of skeletal
1. located on the skeleton
2. functions to promote movement, heat, posture
3. striated, multi-nucleated
4. under voluntary (somatic) controls
characteristics/ properties of cardiac muscle
1. located on the heart
2. functions to pump blood continuously
3. striated, one central nucleus
4. autonomic nervous system control (involuntary)
Visceral (smooth muscle) characteristics
1. GI, uterus, eye, blood vessels
2. peristalsis, blood pressure, pupil size, erects hair
3. NO striations, central nuclei
4. autonomic controls (involuntary)
skeletal muscle is derived from which type of embryonic cell layer?
mesoderm (middle)
On one skeletal muscle, how many nerves, arteries and veins?
1 somatic motor neuron (with branching axons)+ 1 artery + 2 veins & lots and lots of capillaries- which is why it bleeds so much when you cut into SM!
Fascia that lies between the inner surface of the Transversus abdominis and the extraperitoneal fascia?
tranversalis fascia
Where would you find muscular fascia?
Major muscular groups usually have both a superficial fascia covering and a deep fascia covering
Felate a fascicle to a muscle fiber
A fascicle contains bundles of muscle fibers
Relate a tendon to the various coverings of the muscle fibers
a tendon is continuous with all the muscle layers
Contained within the myofibril?
actin and myosin
Relate myofibril to muscle fiber
muscle fiber contains many myofibrils
Where is the sarcoplasmic reticulum located?
around each individual myofibril
Describe each component of the muscle tissue- starting with the outermost covering and working your way in
1.Outermost covering: epimysium
2. perimysium (surrounds groups of muscle fibers)- surrounds the fascicle
3. endomysium separates each muscle fiber
4. Sarcolemma covers each muscle fiber (cell membrane)
5. sarcoplasm= cytoplasm of each muscle fiber
6. sarcoplasmic reticulum- encircles each myofibril
7. myofibril- bundles of which reside within the muscle fiber (heavily striated, contain actin and myosin)
What is the purpose/ where are glycogen granules located?
Also within the muscle fiber, glycogen granules are sources of energy for the cell
What is the function of Titan?
Structural protein- responsible for the correct alignment, stability, elasticity, and extensibility of myofibrils. They connect the Z disc to the M line. Largest known protein and third most abundant in muscle cells
What is dystrophin and what disease is it best associated with?
structural protein that links the filaments of the sarcomere with the integral membrane proteins in the sarcolemma, which are attached in turn to proteins in connective tissue matrix that surrounds muscle fibers. A defect in dystrophin causes muscular dystrophy (x-linked), because the muscle is slowly replaced with fibrosis.
What steps are involved in muscle contraction?
1. Ca2+ is released from the sarcoplasmic reticulum and binds to troponin, thus making the troponin-tropomyosin change shape to reveal the myosin binding site.
2. myosin hydrolyses ATP and gets oriented and energized
3. myosin heads bind to actin, forming cross-bridges
4. "power-stroke" where the myosin heads rotate towards the center of the sarcomere
5. the myosin heads bind ATP and detach from the actin filaments. The process could happen again
what is happening inside the muscle fiber during relaxation phase of muscle?
the trop-trop complex is blocking the myosin-binding site- in the absence of Ca2+
Where do excitation-contraction coupling (EC coupling) events take place?
at the junction between the somatic motor neuron and a skeletal muscle fiber.
What kind of channels exist on the motor end plate of the muscle cell?
ligand-gated ACh receptor sites (gated sodium channels) populate much of the motor end plate
what occurs within the muscle fiber once the AP is generated? (steps involved)
1. Muscle AP travels along the transverse tubule to open the Ca2+ release channels in the SR membrane, allowing the Ca2+ ions to be released into the sarcoplasm.
2. Ca2+ binds the trop/trop complex on the thin filaments and opens up the myosin binding site
3. myosin binds, power stroke, release (with the binding of ATP)--> contraction. Thin and thick pushed together.
4. Ca2+ channels on the SR close and Ca2+ active transport pumps use of ATP to restore low levels of Ca2+ in sarcoplasm (by pumping the Ca2+ from the sarcoplasm into the SR via active transport pumps)
5. trop-trop complex slides back into place
6. muscle relaxes
What occurs during depolarization of the muscle fibers?
Na+ channels are open because of ACh binding to the Cholinergic receptors on the sarcolemma. Na+ floods inside the cell (where it normally isn't)
What occurs during repolarization of the muscle fibers?
the release of Na+ in the cell triggers the release (gate opening) of the K+ ions outside of the cell.
During the marathon, why wouldn't you have tons of lactic acid building up?
Because you're aerobically respiring, thus able to intake O2 and convert that lactic acid into pyruvate and feed the energy system again
What are the different phases in muscle tension cycle?
1. latent period (between signal and contraction)
2. contraction
3. relaxation period- as the Ca2+ ions get sequestered into the SR, myosin binding sites are covered by the trop-trop complex
4. refractory period- temporary loss of excitability- where all the muscle fibers in a motor unit will not respond to stimulus during this time. (needs time to return back to resting state- where the receptors are ready to receive signal)
Twitch
recorded when a stimulus that results in a contraction (force) of a single muscle fiber is measured over a very brief millisecond of time (graph of latent period, contraction, relaxation, refractory period)
tetanus
when lots of action potentials are generated in a short time span, this leads to fusion of the contractions
How can someone's blood protein indicate muscle damage?
When there is a ruptured sarcolemma or Zdisc disruption, could cause the release of proteins normally contained within the muscle fibers. If myoglobin and creatine kinase are in the blood, this would indicate muscle damage (these proteins are supposed to only be in muscle)
Hypertrophy vs Hyperplasia
"bulking up" or thickening of the muscle vs actual formation of new cells, tumor, etc
Examples of multi-unit muscle
1. large arteries
2. muscles of the iris
3. airways for breathing
Calmodulin
Found in the smooth muscle, calmodulin binds to Ca2+, and activates myosin light chain kinase (uses ATP to place phosphate group on myosin head)
What does it mean to "bulk up" from lifting weights?
just means an increase in the muscle size (thickening of the muscle), does not mean an increase in muscle cells
What characteristics of nervous tissue makes for a quick response to detect environmental changes that impact the body?
excitability characteristic of nervous tissue- allows for generation of nerve impulses.
Two main subdivisions of the nervous system:
PNS, CNS
Peripheral Nervous System (PNS)
all nervous tissue outside the CNS- ganglia, nerves, enteric plexuses, and sensory receptors
Central Nervous System (CNS)
brain and spinal cord
Which are more plentiful, the neuroglia or the neurons?
there are 100 B neurons and 10-50x that of neuroglia
Neuron
receives, processes, transmits info by manipulating the flow of charge across their membranes (electrochemical)
Neuroglia
"glue" (glial cells) major role in support and nutrition of the brain, but they do not manipulate information
Where do most signals for muscle contraction and gland secretion originate?
CNS
How is the PNS divided?
SNS (somatic nervous system), the autonomic nervous system (ANS), enteric nervous system (ENS)
What does the SNS consist of?
innervates skeletal muscle.
1) somatic sensory (afferent) neurons that convey information from sensory receptors in the periphery towards the CNS.
2) Somatic motor neurons (efferent) neurons that conduct impulses away from the CNS towards the skeletal muscles under voluntary control.
Autonomic Nervous System (ANS)
Predominately Efferent:
1. Sensory neurons that convey info from autonomic sensory receptors located primarily in visceral organs like the stomach or lungs, to the CNS
2. Motor neurons under involuntary control conduct nerve impulses from the CNS to smooth muscle, cardiac muscle, and glands.
Branches of the motor aspect of the ANS
sympathetic division (fight/flight)
Parasympathetic division (rest/digest)
Function of the ENS (enteric nervous system)
"brain of the gut"- involuntarily controls the GI propulsion, acid and hormonal secretions. Usually function independently of the ANS though they interact with the sympathetic/parasympathetic neurons
anatomical parts of a neuron
1. cell body (soma)
2. axon
3. dendrites- branch off of cell body
4. axon terminals (synaptic bulbs at the end of these)
Size of a neuron relative to other body cells
largest in the body- can reach up to 1meter in size
Neuronal dendrites
"little trees" are the receiving end of the neuron. Short, highly branches structures conduct impulses towards the cell body, contain organelles.
Cell body
nucleus surrounded by cytoplasm. Organelles such as mitochondria, lysosomes, Golgi, ER, RER= Nissl bodies, but-unlike a "typical cell", NO MITOTIC APPARATUS!!!!
Axons
Conduct impulses away from the cell body toward another neuron or effector cell. Also contain organelles.
axon hillock
where the axon joins the cell body
initial segment
beginning of the axon
trigger zone
junction between the axon hillock and the initial segment
axon terminals (telodendria)
Where the axon ends and branches off into many fine processes
synaptic end bulbs
bulb-shaped structures at the end of some of the axon terminals.
synapse
site of communication between two neurons or between a neuron and another effector cell
Synaptic cleft
gap between the pre and post-synaptic cells
Function of the synaptic end bulbs
contain many tiny membrane-enclosed sacs called synaptic vesicles. These vesicles contain packets of neurotransmitter chemicals (e.g. ACh)
How many types of neurotransmitters can be contained within one neuron?
Many neurons contain 2-3 types of neuro-transmitters, each with different effects on the post-synaptic cell
Neurotransmitter-function
to generate action potential in post synaptic cell since the AP cannot "jump" the gap.
two types of transport systems that carry materials from the cell body to the axon terminal and back
1. slow axonal transport
2. fast axonal transport
What sorts of signals are transmitted from the axon terminals to the cell body? (fast retrograde transport)
Could be harmless (nerve growth factor), or could be harmful (tetanus toxin, viruses that cause rabies and polio)
Why is a deep cut/puncture wound to the head/neck area more dangerous than a cut of the same nature in the leg?
In head/neck region, it's a shorter transmit time for the harmful substance to reach the brain (Tx must begin quickly), whereas neurons to the legs have long axons, thus signal is transmitted slower
Two ways to classify neurons
1. structural characteristics and 2. functional characteristics
What ways can you classify the structural aspects of neurons?
based on the number of processes (axons and dendrites) extending from the cell body.
1. anaxonic
2. bipolar
3. unipolar (pseudounipolar)
4. multipolar (multiple dendrites to 1 axon)
Functional characteristics of neurons
1. sensory afferents
2. interneurons
3. motor efferents
In structural classifications, the "processes" may be?
axons and dendrites
Multipolar neurons
have several dendrites and only one axon and are located throughout the brain and spinal cord.
-cell body is located within the dendrite network
-majority of neurons in the human body are multipolar.
bipolar neurons-structure
one main dendrite and one axon. The cell body is located at a distance from the dendrites.
bipolar neurons- function
bipolar neurons are found in retina of the eye, inner ear, olfactory area of the brain. Used to convey sight, smell, hearing, balance, retina information.
unipolar neuron-structure
contains one process that extends from the body and divides into a central branch that functions as an axon and as a dendritic root.
unipolar neuron-function
often employed for sensory neurons that conveys touch and stretching information from the extremities.
sensory or afferent neurons
convey action potentials INTO the CNS through cranial or spinal nerves. Most are unipolar
motor or efferent neurons
convey AP AWAY FROM the CNS to effectors (muscles/glands) in the periphery via cranial and spinal nerves. Most are multipolar
interneurons or association neurons
located within the CNS between the sensory and motor neurons. Process incoming sensory information from sensory neurons, then elicit a motor response by activating the appropriate motor neuron response. Most are multipolar in structure.
What makes neuroglia different from neurons? x2
1. do not generate or conduct nerve impulses
2. are able to mutiply
How do neuroglia support neurons?
1. forms the BBB
2. forms the myelin sheath around neuronal axons
3. making the CSF that circulates around the brain and spinal cord
4. phagocytosis
5. smaller, more numerous, can multiply
Four types of neuroglia in the central nervous system?
1. astrocytes- support neurons in the CNS, make BBB, maintains the chemical environment (Ca2+ &K+)
2. Oligodendrocytes- production of myelin in the CNS
3. Microglia- participate in phagocytosis
4. Ependymal cells- form and circulate CSF
Types of neuroglia in the PNS?
1. satellite cells- support neurons in the PNS
2. schwann cells- produce myelin in the PNS
Schwann cells
Cells that coat the axons and produce myelin sheath. Myelin wraps around the axons and increases nerve impulse speed. Each Schwann cell wraps around the axon between two Nodes of Ranvier. Even unmylenated cells have a Schwann cell in proximity.
In the CNS, what cells myelinate the nerve cells?
Oligodendrocytes in the CNS, Schwann cells in the PNS
Multiple Sclerosis (MS)
autoimmune destruction of the myelin sheath- leading to nerve impulses not being correctly transmitted and dysfunction of bodily functions (seeing, walking, etc)
Why are infants' responses to stimuli neither as rapid nor as coordinated as older child or adult?
because their myelination is still in progress
Nerve tissue regeneration
only in the PNS and the Schwann cells are largely the main cell responsible for this. Regeneration just doesn't occur in the CNS (astrocytes just form scar tissue)
neurolemma
outermost layer of the nerve fibers in PNS. Nucleated cytoplasmic layer of Schwann cells. Unlike the axon and the myelin sheath, the neurolemma does not degenerate after a nerve has been cut or crushed
How does the neurolemma aid in the regeneration of nervous tissue in the PNS?
When an axon is injured, the neurolemma aids regeneration by forming a regeneration tube that guides and stimulates regrowth of the axon.
Why can't regeneration happen in the CNS
Schwann cells are not located in the CNS, thus there is no neurolemma to create the regeneration tube
Qualifications for regeneration
1. must be located in the PNS
2. intact cell body
3. be myelinated by functional Schwann cells having a neurolemma
Demyelination
the loss or destruction of myelin sheaths around axons (could be disease, or medical treatments) Any single episode of demyelination could result in deterioration of affected nerves
Signals (electrical) that make neurons electrically excitable like muscle fibers?
1. Graded potentials
2. Action potentials
What does the production of electrical signals in a neuron depend on?
the existence of a resting membrane potential (RMP) (similar to the electrical potential of a 9v battery which has a gradient of 9 v from one terminal to another
Ion channels purpose in neuron?
Present in the plasma membrane of all cells in the body. Used to create a gate so that negative RMP stays within the cell, as compared to the outside of the cell.
In the ECM of the cell compared to the cytosol what is the distribution of + and - ions?
they are equal on both side. The slightly - electrochem gradient forms because the charge is slightly negative on the inside of the cell directly next to the membrane, but not in the actual cytosol of the cell
What is the chemical portion of the "electro-chemical gradient"?
when ions move from areas of high concentration to low concentration
What is the "electric" portion of the "electro-chemical gradient"?
When - ions move from [-] areas to [+] areas (to try to balance out), so - ions move out of the cell, and + ions move from [+] to [-] areas (into the cell)
Three types of active gated channels
1. ligand-gated
2. voltage-gated
3. mechanically-gated
ligand-gated channels
usually located at the synapse, they respond to neurotransmitters
reasons why the inside of the cell remains slightly negative
1. more K+ channels cause the K+ to leak out more than Na+ leaks in
2. negatively charged proteins that always remain in the cytosol
3. Na+/K+ pums uses 1 ATP tp move 3 Na+ outside and 2 K+ inside
Qualifications of a cell to be "polarized"?
A cell that exhibits RMP
Why must graded potentials be produced in a cell?
It needs to take the "polarized" primed cell and depolarize the cell to threshold. A graded potential occurs whenever ion flow in mechanically gated or ligand-gated channels produce a current that is localized- it spreads to adjacent regions for a short distance and then dies out within a few mm of its point of origin.
depolarizing graded potential
a stimulus that causes the cell to be less negatively charged with respect to the extracellular fluid (opens Na+ channels) and allows an AP to begin
hyperpolarizing graded potential
stimulus that causes the cell to be more negatively charged and thus harder to have an AP
Where do graded potentials usually occur?
in the dendrites and cell bodies but do NOT travel down the axon
What net result can graded potentials generate (positive or negative)?
have different names depending on the type of stimulus and where they occur. Voltage variable aptitudes that can be added together (summate) or cancel each other out- the net result is a larger or smaller graded potential. (more positive, neutral, less positive, etc)
Difference between graded potentials and action potentials
1. graded are voltage-dependent, action have a constant voltage and are impulse signals
2. graded are local signal-transduction whereas action can travel the length of the neuron
3. graded potentials do not exhibit a refractory period
action potential-mechanism
membrane potential reverses and then eventually is restored to its resting state. If a neuron receives a threshold (liminal) stimulus, a full strength nerve impulse is produced and spreads down the axon of the neuron to the axon terminals. If stimulus is not strong enough (subliminal or subthreshold), no nerve impulse will result.
Two main phases of action potential
1. depolarizing (Na+ channels open, K+ shut)(resulting from graded potentials)
2. repolarizing (K+ channels open, Na+ shut)
depolarization step of action potential
Na+ voltage gated channels open during this phase, Na+ rushes in to make the cell more progressively more positive
after-hyperpolarizing phase of the action potential
During this phase voltage-gated K+ channels remain open and the membrane potential becomes even more negative (-90mV), as the voltage-gated K+ channels close, the membrane potential is restored to -70mV
Absolute refractory period
follows immediately after action potential has just been generated. No matter how large the stimulus, the cell will not generate another AP, no matter how strong the stimulus. This period coincides with the period of Na+ channel inactivation (inactivated Na+ channels must first return to the resting state).
Relative refractory period
period of time during which a second action potential can be initiated, but only by larger-than-normal stimulus. Coincides with period when the voltage-gated K+ channels are still open after inactivated Na+ channels have returned to their resting state.
Where does the propagation of the AP begin in the neuron?
in the "trigger zone" which is between the initial segment of the axon and the axon hillock (where the axon meets the cell body).
two types of conduction associated with propagation of the AP down the neuron?
1. continuous conduction-by passive spread the current proceeds down the axon
2. saltatory conduction (much faster process)- whIch occurs in the myelinated axons, as the AP jumps from one Node of Ranvier to the next
Factors that allow saltatory conduction to be faster
1. Jumping along the Nodes of Ranvier
2. Axon diameter (larger surface area, faster it will go)
3. amount of myelination (more myelin, better the signal will transmit)
4. temperature- colder always slows things down
Fiber types of the neuronal axon
A, B, C fibers
A fibers
large, fast (130m/sec), myelinated neurons that carry touch and pressure sensations, many motor neurons are also of this type. E.g. Burns, if you got burned, you want to know ASAP!!!
B fibers
medium sized, 15m/sec speed, comprise myelinated visceral sensory and autonomic preganglionic neurons. Somewhat slower transmission. Carry sensory impulses from the viscera to the brain and are the axons of the ANS that extend from the CNS to the autonomic ganglia
C fibers
smallest and slowest (2m/sec) and comprise unmyelinated sensory and autonomic motor neurons from the viscera and from ganglia to viscera (heart, smooth muscle, glands, etc). Probably slowest because they are unmyelinated!