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Muscular System study guide

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3 Major Groups Of Muscle
1. Skeletal Muscle
2. Cardiac Muscle
3. Smooth Muscle
Skeletal Muscle
Voluntary; attached to bone; moves the skeleton
Cardiac Muscle
- Involuntary; found only in the heart
- Each cardiac muscle cell contracts rhythmically all by itself. The cell or group of cells that is contracting the fastest sets the rate for all of the other cardiac cells. A group of cardiac cells in the wall of the right atrium beats the fastest;
Smooth Muscle
Involuntary; found in organs such as the stomach, intestines, urinary
bladder, uterus, etc; eyes, air passageways, blood vessels
Myo
refers to muscle - myositis, myometrium, myocardium, etc.
Sarco
refers to muscle cells - sarcolemma, sarcoplasmic reticulum, etc
Fibers or Skeletal Muscle Cells
are striated, multinucleated, and long. There can be as many as 100 or more nuclei per cell. A muscle fiber can be several inches long, or 25,000 times longer than other cells!
what does Previously Voluntary mean
under control of the conscious mind
what is Straited
comes from the muscle cell's appearance - striations consisting of light and dark Bands
Gross Anatomy Of A Skeletal Muscle
Well defined groups of muscle cells surrounded by fibrous connective tissue
Muscle Belly
Muscles can have a variety of shapes and sizes; most have a muscle belly + two or more attachment sites. .
Attachment Sites
connect the muscles to whatever they are supposed to move.
Tendons
A band of tough connective tissue that attaches muscle to bone; generally cord-like
Aponeuroses
Sheets of connective tissue that attach muscle to bone or to other muscles
Linea alba
- Most prominent aponeurosis; White line; runs lengthwise on ventral midline between the muscles of the abdominal wall.
- Most common site of surgical entry into the abdomen
Origin - Attachments
Most stable attachment site; doesn't move much when muscle contracts
Insertion
most mobile attachment site; undergoes the most movement
Muscle Actions
Skeletal muscles contract in response to a nerve impulse
Antagonist
works opposite the prime mover; can smooth out the action of the prime mover
Synergists
help the prime movers
Fixators
stabilize movement across a joint
Flexion
bending or decreasing the angle of a joint
Extension
straightening or increasing the angle of a joint
Adduction
moving limbs closer together toward midline
Abduction
moving limbs away from midline, further apart
Skeletal Muscle Cells
. Size - long and thin, up to 25,000 times the length of average cells
. Striated
. Multinucleated - up to 100 per cell
. Lots of mitochondria
Sacrolemma
the muscle cell membrane
Myofibrils
- composed of contractile protein filaments\
- two types of protein filaments are present: actin and myosin
Sarcoplasmic reticulum
Endoplasmic reticulum
Transverse or T tubules
extensions of the sarcolemma that extend into the cell
Actin Filaments
are thin and attach to Z-lines
Myosin Filaments
are wide or thick
Thick and Thin Filaments
give skeletal muscle fibers their striated appearance
A Band
myosin filaments = dark
I Band
actin filaments = light
Z Band
look like discs and are the attachment sites for actin filaments; appear as dark line in the I-band
Sacromere
- the basic contracting unit of skeletal muscle
- measures from one Z-line to the next. The actin filaments attach to the Z-lines and the myosin filaments are in the middle. When a sarcomere contracts, the actin filaments slide in over the myosin filaments
Connective Tissue Layers
- Endomysium, Perimysium, Epimysium
- All three layers come together and are continuous with tendons or aponeuroses
Endomysium
surrounds each individual muscle cell or fiber
Perimysium
surrounds a fascicle, which consists of a bundle of muscle cells
Epimysium
surrounds the entire muscle, which consists of bundles of fascicles
Neuromuscular Junction
Nerve impulses are essential in order for skeletal muscles to contract
Atrophy
the shrinking of muscle due to lack of use or lack of nerve innervation
Synaptic space
the space between the end of a nerve fiber and the sarcolemma
Synaptic vesicles
tiny sacs in the end bulb of a nerve that contain the neurotransmitter
Acetylcholine
a neurotransmitter, or chemical messenger. Released from the vesicles, it diffuses across the synaptic space in response to a nerve impulse and binds to receptors on the sarcolemma. This is the trigger for muscle contraction
Acetylcholinesterase
an enzyme that breaks down acetylcholine so that muscle contraction will stop
Motor Unit
- each nerve fiber innervates more than one muscle fiber. A motor unit is one nerve fiber and all the muscle fibers it innervates
- Muscles that have to make delicate or fine movement have a low motor unit
- Large muscles generally have a high motor unit. With a low motor unit, the nerve fiber innervates only one or a few muscle fibers
- With a high motor unit, the nerve fiber innervates a large number of muscle fibers.
Stages of Initiation of Muscle Contraction and Relaxation
1. Nerve impulse reaches the end bulb at the neuromuscular junction
2. Acetylcholine is released from the synaptic vesicles and diffuses across the synaptic space
3. Acetylcholine binds to receptors on the sarcolemma
4. Impulse then travels along the sarcolemma and through the T-tubules into the cell interior
5. When the impulse reaches the sarcoplasmic reticulum, it causes the release of stored calcium ions (Ca++)
6. Ca++ enters the sarcoplasm (cytoplasm) and diffuses into the myofibrils
7. Ca++ diffusing into the myofibrils starts the contraction process and is powered by ATP
8. Ca++ begins being pumped back into the sarcoplasmic reticulum almost immediately after its release. ATP is used to pump Ca++ back into the sarcoplasmic reticulum.
9. Ca++ leaves the myofibrils and contraction process starts shutting down
10. Muscle fiber begins to relax and return to its original length
Muscle contraction And Relaxtion require what
Require ATP
Mitchondria
- immediate energy source that powers the sliding of actin filaments over myosin filaments
- Energy is released when a phosphate group splits off ATP to form ADP
Creatine phosphate (CP)
in the sarcoplasm then donates a phosphate group
to convert the ADP back to ATP
Glycogen
stored glucose. Glucose, which comes from the breakdown of carbohydrates, is the primary energy source for most cells (energy needed to produce ATP and CP) A working muscle uses available glucose first; then glycogen
Mechaniacs of Muscle Contraction
. Initiated by a nerve impulse and requires calcium (Ca++)
. Contraction is at the level of the actin and myosin filaments
. As the filaments slide over each other, the sarcomere shortens
Myoglobin
stored oxygen
Aerobic metabolism
most efficient; requires oxygen
Anaerobic metabolism
not as efficient as aerobic metabolism; kicks in after available O2 and myoglobin are used up; produces lactic acid. A build-up of lactic acid in muscle causes muscle fatigue and pain
Some Characteristics of Muscle Contraction
- All-or-none principle: when stimulated by a nerve impulse, an individual muscle fiber contracts completely or not at all
- Contraction of skeletal muscle generates heat. Shivering is a mechanism that the body uses in cold conditions to avoid hypothermia
Cardiac Muscle
Involuntary striated - found only in the heart
Gross Anatomy of cardiac muscle
. Makes up most of the heart
. Not defined groups as we see in skeletal muscle; very involved networks
. Starts contracting while the fetus is still in the embryonic phase
. Maintains constant contraction
SA Node (sinoatrial node)
this group of cells is the pacemaker for the heart
Microscopic Anatomy of cardiac muscle
. Striated
. Much smaller than skeletal muscle cells
. One nucleus per cell
. Branched
Intercalated disks
- strong end-to-end attachments between cardiac muscle cells; transmit impulses from cell to cell which allow large groups of cells to function as one coordinated unit
- found in cardiac muscle
Nerve Supply
Nerves are not needed to initiate contraction of cardiac muscle
Sympathetic nerve fibers
- cause the heart to beat harder and faster
Parasympathetic nerve fibers
allow resting cardiac function
Visceral Smooth Muscle
- Found in the walls of many internal organs such as stomach, intestine, urinary bladder, and uterus.
- Cells are arranged in large sheets.
- Large, rhythmic waves of contraction.
- Nerve supply not necessary for contraction.
- Stretching causes visceral smooth muscle to contract more strongly
Multiunit Smooth Muscle
- Found where small delicate contractions are require such as the iris of the eye, walls of small blood vessels, and small air passageways in the lungs.
- Single smooth muscle cells or small groups of cells
Contractions of Multiunit Smooth Muscle
- are NOT automatic
- require specific impulses from autonomic nerves to contract. However, function is still involuntary. Think of a bright light (triggering impulse) that causes the pupil of the eye to constrict (involuntary, multiunit smooth muscle).
Smooth Muscle Cells
Spindle shaped, single nucleus
Actin and myosin filaments crisscross instead of being linear as in skeletal muscle cells. Attached at both ends to dense bodies which correspond to the Z-lines found in skeletal Muscle.
Cells shorten more than cardiac or skeletal muscle cells
Cutaneous Muscles
located in the connective tissue just beneath the skin
Masseter muscle - Head and Neck Muscles
biggest strongest chewing muscle
Splenius, Trapezius
helps to raise the head
Brachiocephalic
helps to extend the head and neck and pull the front leg forward
Sternocephalic
flexes or lowers the head and neck
External abdominal oblique muscle - Abdominal Muscles
runs in a caudoventral direction
Internal abdominal oblique muscle
runs in a cranioventral direction
Rectus abdominis (straight abdominal)
abdominal wall floor ("six pack")
Transversus abdominis muscle
deepest abdominal muscle
Latissimus dorsi muscle - Thoracic Limbs
flexes the shoulder
Pectoral muscles
adductors of the front limb
Deltoid muscle
abducts and flexes the shoulder
Biceps brachii (brachialis)
flexes the elbow joint
Triceps brachii (brachial triceps)
extends the elbow joint
Gluteal muscles - Pelvic Limbs
extend the hip joint
Biceps femoris muscle (femoral biceps)
extends the hip and flexes the stifle
Semimembranosus muscle
extends the hip and flexes the stifle
Semitendinosus muscle
extends the hip and flexes the stifle
The three muscles that together are called the hamstring group.
Biceps femoris muscle, Semimembranosus muscle, Semitendinosus muscle
Quadriceps femoris (femoral quadriceps)
actually four muscles; they extend the stifle joint
Gastrocnemius muscle
extends the hock
External intercostal muscles
inspiratory muscles
Internal intercostal muscles
expiratory muscles