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Physiology > Chapter 12 > Flashcards

Chapter 12 Flashcards

1
Q

What is epimysium?

A

fibrous connective tissue from tendons that form sheaths that extend around and into skeletal muscle

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2
Q

What are fascicles?

A

created by connecting tissue dividing muscle into columns

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3
Q

What is perimysium?

A

connective tissue around fascicles

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4
Q

What is endomysium?

A

thin connective tissue layer that wraps muscle fibers

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5
Q

What is sarcolemma?

A

plasma membrane of muscles

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6
Q

What’s the main difference between muscle fibers and other cells?

A

muscle fibers are multinucleate and striated

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7
Q

What is the most distinctive feature of skeletal muscle?

A

striations

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8
Q

What is part of the neuromuscular junction?

A

single synaptic ending of the motor neuron innervating each muscle fiber and underlying specializations of sarcolemma

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9
Q

Where does neuromuscular junction occur on sarcolemma?

A

motor end plate

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10
Q

What is a motor unit?

A

one motor neuron and all the fibers it innervates

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11
Q

What happens when a motor neuron is activated?

A

all muscle fibers in the motor unit contract

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12
Q

What is the innervation ratio?

A

motor neurons to muscle fibers
- according to degree of fine control capability of the muscle

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13
Q

When does fine control occur?

A

motor units are small
- 1 motor neuron innervates small amount of fibers

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14
Q

What is recruitment of motor units?

A
  • brain estimates number of motor units required and stimulates them to contract
  • keeps recruiting more units until desired movement is accomplished in smooth fashion
  • more and larger motor units are activated to produce greater strength
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15
Q

What is the structure of a muscle fiber?

A

myofibrils (extend length of fiber)
myofilaments (thick and thin filaments that give rise to bands that underlie striations)

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16
Q

What is the A band?

A

dark
- thick filaments
- mostly myosin

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17
Q

What is the H zone?

A

light area in the center of A band
- actin and myosin don’t overlap

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18
Q

What is the I band?

A

light
- contains thin filaments
- mostly actin

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19
Q

What is the Z line/dic?

A

at the center of I band
- actins attach

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20
Q

What is a sarcomere?

A

contractile units of skeletal muscle between 2 Z-discs

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21
Q

What are M lines?

A

structural proteins that anchor myosin during contraction

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22
Q

What is titin?

A

elastic protein attaching myosin to Z-disc that contributes to elastic recoil of muscle

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23
Q

What happens when muscles contract? How does it work?

A

myofibrils get shorter
- thin filaments slide over and between thick filaments towards center
- shortens distance between z discs

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24
Q

What happens during the sliding filament theory of contraction?

A

at muscle contraction
- A bands (with actin) move closer together (not shorten)
- I bands shorten
- H bands (with myosin only) shorten and disappears

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25
What are cross bridges formed by?
heads of myosin molecules that extend toward and interact with actin
26
What is the sliding of filaments produced by?
actions of cross bridges - each myosin head contains an ATP-binding site which functions as an ATPase
27
How does myosin work with actin?
- must be cocked by ATP - after binding, myosin undergoes conformational change (power stroke) which exerts force on actin - after power stroke, myosin detaches
28
How is cross bridge attachment to actin controlled?
troponin-tropomyosin system - switch for muscle contraction and relaxation
29
Where is tropomyosin found?
in grove between double row of g-actins (make up actin thin filament)
30
Where is troponin?
attached to tropomyosin at intervals of every 7 actins
31
What dose tropomyosin do in relaxes muscles?
blocks binding sites on actin so cross bridges can't occur - Ca++ levels are low
32
When can muscle contraction occur?
when binding sites are exposed
33
What happens when Ca++ levels rise?
Ca++ binds to troponin causing conformational change which moves tropomyosin and exposes binding sites - allows cross bridges and contraction to occur
34
When does the cross bridge cycle stop?
when Ca++ levels decrease
35
Where does Ca++ go?
continually pumped back into the sarcoplasmic reticulum - mostly in terminal cisternae (T tubules are alongside)
36
What causes depolarization of end-plate potentials and action potentials in muscle?
release of ACh at NMJ
37
How are dihydropyridine receptors stimulated?
action potentials race over sarcolemma and down into muscle via T tubules
38
How do action potentials in T tubules cause release of Ca++?
Voltage-gated (ryanodyne receptor) and Ca++ induced release channels - electromechanical release
39
What is the mechanism for muscle relaxation?
Ca++ from sarcoplasmic reticulum diffuses from troponin to initiate crossbridge cycling and contraction - when action potential stops, muscles relax
40
What is a twitch?
single rapid contraction and relaxation of muscle fibers
41
What is summation?
2nd stimulus occurs before muscle relaxes from the 1st - 2nd twitch is greater
42
What are graded contractions?
contrations of varying strength
43
What is incomplete tetanus?
muscle is stimulated by increasing frequency of electrical shocks - tension increases to maximum
44
What is complete tetanus/tetany?
frequency is so fast = no relaxation - smooth sustained contration
45
What is the strength of muscle contraction influenced by?
- frequency of stimulation - thickness of muscle fibers - initial length of muscle fiber
46
What is the relationship between tension and cross bridges?
less tension = fewer cross bridges formed - no overlap force = no cross bridges formed
47
What are the lower motor neurons and final common pathway?
ventral horn of spinal cord with motor neuron cell bodies - axons leave at ventral root
48
What is neural control influenced by?
sensory feedback from muscles and tendons - faciliatory and inhibitory activity from upper motor neurons
49
How does the nervous system receive continuous sensory feedback?
- length/stretch of muscle from muscle spinal apparatus - tension from golgi tendon organs
50
What is the muscle spindle apparatus made of?
- modified thin muscle cells (intrafusal fibers) - regular muscle fibers (extrafusal fibers) - spindles are arranged in parallel with extrafusal fibers (insert into tendons at each end of muscle)
51
What are the alpha motor neurons?
fast conducting - innervate extrafusal fibers - cause muscle contraction
52
What are the gamma motor neurons?
slower conducting - innervate and induce tension in intrafusal fibers - increase sensitivity of muscle to passive stretch
53
What do upper motor neurons stimulate?
alpha and gamma motor neurons - coactivation
54
What does stimulation of alpha neurons result in? How about gamma neurons?
- alpha neurons = muscle contraction and shortening - gamma neurons: intrafusal fibers to take up slack, provide continued information of stretch length of extrafusal fibers (maintains normal muscle tone)
55
What does the monosynaptic-stretch reflex consist of?
1 synapse within CNS
56
What happens when the knee is hit with reflex hammer?
- stretches spindles to activate annulospiral sensory neurons - synapse on alpha neurons causing them to stimulate extrafusal fibers
57
What does the golgi tendon organ consist of?
2 synapses in CNS - disynaptic reflex
58
How does the golgi tendon organ reflex happen?
- sensory axons from golgi tendon organ synapse on interneurons - make inhibitory synapses on motor neurons - prevents excessive muscle contraction or passive muscle stretching
59
How does cardiac muscle work?
involuntary contraction - branches, adjacent myocardial cells joined by intercalated disks (gap junctions) - allows action potentials to spread throughout cardiac muscle
60
What are the characteristics of smooth muscle?
- no sacromeres - gap junctions - contains 16x more actin than myosin (allows greater stretching and contracting - actin filaments are anchored to dense bodies
61
What is smooth muscle contraction controlled by?
controlled by Ca++ (but has little SR and no troponin/tropomyosin)
62
What is the mechanism of smooth muscle contraction?
- Ca++ enters through voltage gated Ca++ channels in plasma membrane to let in extracellular Ca++ - binds to calmodulin - complex activates myosin light chain kinase to phosphorylate and activate myosin - myosin forms cross bridges with actin - myosin ATPase is slow
63
How does smooth muscle relaxaiton work?
- Ca++ concentration decreases - myosin is dephosphorylated by myosin phosphatase - myosin can no longer form cross bridges - smooth muscle has slower contractions than striated - can form state of prolonged binding of myosin to actin (latch state) - maintains force using little energy
64
What are the characteristics of single smooth muscle?
single unit is spontaneously active - pacemakers - gap junctions to spread electrical activity
65
What are the characteristics of multiunit smooth muscle?
requires nerve stimulation by ANS - neurotransmitter released along a series of synapses (varicosities) = synapses en passant

Physiology (13 decks)

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