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Muscular System

Terms in this set (30)

Compare and contrast the three types of muscle tissue in terms of location,
function, structure, control (voluntary or involuntary), and reproduction.
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List four important functional characteristics of all muscle tissue types.
1. Excitability, or irritability - the ability to receive and respond to stimuli
2. Contractility - the ability to shorten forcibly
3. Extensibility - the ability to be stretched or extended
4. Elasticity - the ability to recoil and resume the original resting length
List the functions of skeletal muscle tissue
- Produce movement
-Maintain posture and body position
-Stabilizing joints
-Generate heat
-Protects abdominal organs
-Link between the body and the external environment (manipulate the environment)
Describe the anatomy of a skeletal muscle (one whole muscle not cells). Be able to label these wrappings.
Fascia covers the surface of the muscle

The are 3 types of connective tissue sheaths:
1.) Epimysium
-lies beneath the fascia
-connective sheath
- *dense irregular
- becomes dense regular as tendon when there is no more muscle cells
-Histology: an overcoat of dense irregular connective tissue
-surrounds the entire muscle

2.) Perimysium
-surrounds groups of muscle fibers called fascicles
- *made of collagen fibers
-Histology: *fibrous connective tissue

3.) Endomysium
-separates each muscle fiber
-wraps around each individual muscle cell
- *made of mainly reticular fibers
- *fine sheath of connective tissue composed of reticular fibers surrounding each muscle fiber
- Histology: areolar CT
Describe the microscopic anatomy and functional roles of glycosomes,
myoglobin, myofibrils, sarcoplasmic reticulum, and T tubules of muscle
fibers.
-Each fiber is a long, cylindrical cell with multiple oval nuclei just beneath the sarcolemma
- Each cell is a syncytium produced by fusion of hundreds of embryonic cells
( *syncytium is when skeletal muscle fuse together; big cells with many nuclei)
Sarcolemma=cell membrane of muscle fiber
Sarcoplasm=cytoplasm of muscle fiber that contains nuclei and mitochondria

Sarcoplasm: *cytoplasm of cell
1.) Glycosomes
(stores sugar): are granules of stored glycogen

2.)Myoglobin
- *takes oxygen from hemoglobin and stores m it
- muscle molecules that bind oxygen and store it ( similar to hemoglobin)
- *a unique oxygen-binding protein
-Red pigment that stores oxygen

3.) The usual organelles plus three highly modified structures: myofibrils, sarcoplasmic reticulum, and T tubules.

Myofibril
: (fills the space)
-are with the cytoplasm lying parallel to each other
- rod-like contractile elements
-Make up most of the muscle volume
- hundreds to thousands of myofibrils in a single muscle fiber
- *It's arrangement within a fiber is such that a perfectly aligned repeating series of dark A bands and light I bands is evident = striations
- the arrangement gives the striations
Light=I band (striations) Dark = A band (striations)

Sarcomere
: *structual unit of cardiac muscle
-section of myfibril
-smallest contractile unit of skeletal and cardiac muscle
*Functional unit of skeletal muscle
-located between two successive Z discs
( Z discs - coin-shaped sheet of proteins that anchors the thin filaments
)
- Z line to the next Z line is a Sarcomere
composed of 3 myofilaments:
1.) Thick filament
(myosin)
- extend the entire length of an A band
-myosin and actin drive a contraction
-myosin is composed of protein

2.) Thin filament
(actin) troponin and trypomysin
-Extends across the I band and partially into the A band
- *Made of actin, troponin, and tropomyosin
- actin is composed of protein

Sarcoplasmic reticulum
(stores calcium)
-is the same as SER
- *Stores Calcium in high concentraion
-Functions in the regulation of intracellular calcium ions levels
-inner lining of perimysium

T tubule
- opens to outside of muscle fiber
-contains extracellular fluid
-continuous with the sarcolemma
-conduct impulses to the deepest regions of the muscle
-These impulses open voltage sensor proteins, which release Ca2+ from adjacent SR terminal cisternae
-The relationship between the paired SR terminal cisternae and the T tubule is called triad.
Define triad and describe the relationship that occurs in the triad of a skeletal muscle cell. (Youtube & check packet pg. 4)
The relationship between the paired SR terminal cisternae and the T tubule is called triad.
Triad= sarcoplasmic reticulum, sarcolemma and T tubules
-an electrical impulse trave,s across the sarcolemma and goes down the T tubules activating a voltage changing protein channel and makes the protein channel change shape. SR forms sac like buldges called terminal cisternae surrounding the T tubule. The T tubule and terminal cisternae are connected by a calcium release channel.Calcium is then release from the terminal cisternae into the sarcoplasm, flooring the cytoplasm with calcium. The flooding of calcium causes a contraction in the skeletal muscle fiber. Calcium is responsible for excitation and contraction. The release of calcium initiates a cross bridge
Name the smallest contractile unit of skeletal and cardiac muscle.
Sacromere
Describe the structure of the sarcomere. Be able to label one.
Sarcomere
a. smallest contractile unit of skeletal and cardiac muscle
b. Functional unit of skeletal muscle
c. located between two successive Z discs
i. Z discs - coin-shaped sheet of proteins that anchors the thin filaments
d. composed of three myofilaments:
i. Thick filament
1. myosin
2. extend the entire length of an A band
ii. Thin filament
1. Extends across the I band and partially into the A band
2. Made of actin, troponin, and tropomyosin
Explain the sliding filament mechanism
Sliding Filament Model of Contraction
The formation of cross bridge is initiated when calcium binds to triponin. The shape of troponin changes and tropomyosin moves away from myosin binding site in which the myosin head is able to
A. Proposes that changes in overall fiber length are directly associated with changes in the overlap between the two sets of filaments (thick and thin filaments).
B. This accounts for the change in the length of the fiber.
C. Accomplished by actin and myosin.

D. H zone disappears
Name and describe the components of the neuromuscular junction.
Neuromuscular junction is formed by:
1. axon terminal
a. end of the neuron's axon , it contains synaptic vesicles that contain the neurotransmitter acetylcholine.
i. Neurotransmitter = chemical that is released from a nerve cell which thereby transmits an impulse from a nerve cell to another nerve, muscle, organ, or other tissue.
2. Synaptic cleft
a. Space separating the axonal terminals and muscle fibers

3. Motor end plate
a. specific part of the sarcolemma looking towards the axon terminal
b. contains ACh receptors
Explain the steps taking place at the neuromuscular junction.
Step 1: action potential travels down a motor neuron toward an axon terminal
Step 2: voltage gated calcium channels open and calcium ions enter the terminal
Step 3: synaptic vessels are activated by calcium causing ACH to release
Step 4: ACH diffuses across synaptic c,eft and binds to ACH receptors (which contain ligand - gated ction channels)
Step 5: ligand - gated channels (ACH receptors) open
Step 6: sodium (Na+) enters, potassium (k+) exists. The exchange causes membrane to be positive
Step 7: once membrane potential reaches a threshold value an action potential goes through sarcolemma
Step 8: neuro transmitter to muscle fiber stops in two ways :
1.) ACH diffuses away from synapse
2.) ACH is broken down by Acetylcholinesterase (enzyme) to acidic acid and choline. Choline is transported through axon terminal for later use.
Define neurotransmitter. What does it do at the skeletal muscle fiber level?
Neurotransmitter (synaptic vescles) are tiny vesicles that store chemicals and release them at the end of a nerve fiber

Neurotransmitters stimulate impulse in another neuron at the skeletal muscle fiber level
Name the neurotransmitter used for skeletal muscle contraction.
Acetylcholine
(Myofibril ---> sacromere)
How do you terminate the effect of the neurotransmitter used?
-By the reuptake of neurotransmitter/ when molecules are broken down
-ACH diffuses away from synapse / ACH is broken down by Acetylcholinesterase (enzyme) to acidic acid and choline. Choline is transported through axon terminal for later use.
Define resting potential. Explain how the resting potential is generated.
The difference in electrical change between tge inside and outside of an undesturbed nerve cell membrane. The potential difference (-70mv) across the membrane of a resting neuron or skeletal muscle.

The outside (extracellular) face is positive, while the inside face is negative.
- Generated by different concentrations of Na+, K+, and Cl-, and proteins anions.
- The predominant extracellular ion is Na+
- The predominant intracellular ion is K+
-there are more potassium (k+) channels than there are sodium (Na+) channels

Polarized=negatively charged
Define and explain the depolarization and repolarization processes
2. Depolarization
a. The inside of the membranes becomes less negative
1. Change from -70mV to -65mV or more
b. If threshold (-55mV) is reached, an action potential is ignited.
i. AP = Constant electrical signal that can be propagated over long distances without decay.
ii. 3The AP spreads in both directions from the neuromuscular junction by opening voltage-gated channels.
iii. Once initiated, the action potential is unstoppable, and ultimately results in the contraction of a muscle.
iv. All or nothing phenomenon
3. Repolarization
a. The membrane returns to its resting membrane potential (-70mV)
b. After depolarization, the sarcolemma permeability changes by:
i. Closing the Na+ channels
ii. Opening of K+ channels
1. K+ diffuses from the cell, restoring the electrical polarity of the sarcolemma
c. Repolarization occurs in the same direction as depolarization
4. Hyperpolarization
a. K+ voltage channel close slower than sodium channels causing the mm potential to go beyond -70mV.
5. Refractory period
a. Before the muscle can be stimulated again, repolarization must occur.
b. Absolute refractory period
i. Allows Na+ channel to reset
ii. Another AP cannot be generated
c. Relative refractory period
i. A second action potential can be generated
ii. The ionic concentration of the resting state is restored by the Na-K pump
6. Repolarization only restores the electrical membrane potential (-70mV)
a. However, the ionic concentration of the resting state is restored by the Na+ - K+ pump
i. 3 Na+ out
ii. 2 K+ in
Describe how an action potential is formed and spread (including the types of
gated channels involved). Why is it an "all or nothing" event?
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How is the electrical and ionic balances restored?
Repolarization only restores the electrical membrane potential (-70mV)
a. However, the ionic concentration of the resting state is restored by the Na+ - K+ pump
i. 3 Na+ out
ii. 2 K+ in
Define the absolute and relative refractory periods.
Refractory period
: Before the muscle can be stimulated again, repolarization must occur.

1.) Absolute refractory period
-Allows Na+ channel to reset
-Another AP cannot be generated

2.) Relative refractory period
-A second action potential can be generated
-The ionic concentration of the resting state is restored by the Na-K pump
Explain the importance of calcium ions and ATP in the muscle contraction.
For example, what is the function of calcium in muscle contraction? What molecule does it bind to? Where is it stored? What happens to calcium concentrations when nervous stimulation ceases?
Calcium is released and binds to troponin. Troponin removes tropomyosin blockage of myosin binding site. Myosin binding site moves actin toward M line (slicing)
Calcium is stored in sarcoplasmic reticulum
Calcium is pumped back into SR thus lowering the cytoplasmic concentration of normal level 10 ^-7 mol

*when myosin and actin bind together there's a contraction. Calcium is removed in order to relax
Putting everything together: Name the steps involved in a contraction of a
muscle cell. Make sure you include the neuromuscular junction (and neurotransmitter used), the triad (T tubules and sarcoplasmic reticulum) and the molecules/ions involved. When I say molecules, I say troponin, ATP, actin,
myosin, etc.
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Define motor unit, muscle tone and muscle twitch.
Muscle twitch-a brief muscular contraction followed by relaxation; a single contraction that lasts only a fraction of a second; the response of all muscle fibers to a single action potential of its motor neuron

Motor unit the number of muscle fibers innervated by one motor neuron

Muscle tone
-constant contracted state
-keeps muscle firm, healthy, and ready to respond
-spinal reflexes activate groups of motor units in response to input from stretch receptors in muscles
Define twitch and be able to draw a muscle twitch myogram and label the
latent period, period of contraction, and period of relaxation. Explain briefly
what happens in each phase.
There are 3 phases:

1.) latent period (myogram)
-takes 3-4 seconds
-first few sec after stimulus
- from depolarization to release of calcium

2.) period of contraction
-cross bridges form
-muscle shortens

3.) period of relaxation (when calcium goes back to sarcoplasmic reticulum)
- calcium is reabsorbed
-muscle tension goes to zero
Describe three ways in which ATP is regenerated during skeletal muscle
contraction.
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Muscle fatigue notes.
-muscle has reached a limit so it cannot lift anymore
-point when muscle stops contraction
-inability of a muscle to maintain force of contraction

Reasons:
- low Ca+2 levels in cytoplasm
-depletion of creatine phosphate
-insufficient oxygen
-depletion of oxygen
-build up of lactic acid
-failure of motor neuron to release enough ACh
Frequency of stimulation
- *if there's a a second action potential muscle Wil not relax
- *each action potential releases calcium, the move calcium the more force or tension
Infused=a little relaxed
Fused= holding action potential with no relaxation

1.) wave summation - stimuli arriving at different times cause larger contractions

2.) unfused tetanus - fiber stimulated 20 - 30 times per second, can only partially relax

3.) fused tetanus - fiber stimulated 80 - 100 times per second, does not relax at all, sustained contraction
Contrast Isotonic and isometric contractions
Isotonic=movement
Isometric=holding (no movement)
Concentric=going against gravity (having more calcium)
Eccentric=resisting the tension

*isotonic - tension stays the same but muscle changes in length
a.) concentric isotonic - tension is great enough to overcome the resistance of the object, muscle shortens, pulls on a tendon to produce movement
b.) eccentric isotonic - resist movement, slows down the lengthening process.

*isometric - tension is not enough to exceed the resistance of the object, muscle doesn't change in length, maintaining posture, holding an object.
The force of contraction is affected by what?
1.) number of muscle fibers contracting (motor unit recruitment)
- the more motor fibers in a muscle, the stronger the contraction

2. )The relative size of the muscle
-the bulkier the muscle, the greater its strength

3.) Degree of muscle stretch
- muscles contract strongest when muscle fibers are 80-120% of their normal resting length

*growth in cells mean more sacromere
Know the origin, insertion, and action of the skeletal muscles in the muscle lecture notes table.
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The sequence of action potential into a muscle fiber is known as
Excitation-contraction couplin
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