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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
Q

What are cross bridges formed by?

A

heads of myosin molecules that extend toward and interact with actin

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26
Q

What is the sliding of filaments produced by?

A

actions of cross bridges
- each myosin head contains an ATP-binding site which functions as an ATPase

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27
Q

How does myosin work with actin?

A
  • must be cocked by ATP
  • after binding, myosin undergoes conformational change (power stroke) which exerts force on actin
  • after power stroke, myosin detaches
28
Q

How is cross bridge attachment to actin controlled?

A

troponin-tropomyosin system
- switch for muscle contraction and relaxation

29
Q

Where is tropomyosin found?

A

in grove between double row of g-actins (make up actin thin filament)

30
Q

Where is troponin?

A

attached to tropomyosin at intervals of every 7 actins

31
Q

What dose tropomyosin do in relaxes muscles?

A

blocks binding sites on actin so cross bridges can’t occur
- Ca++ levels are low

32
Q

When can muscle contraction occur?

A

when binding sites are exposed

33
Q

What happens when Ca++ levels rise?

A

Ca++ binds to troponin causing conformational change which moves tropomyosin and exposes binding sites
- allows cross bridges and contraction to occur

34
Q

When does the cross bridge cycle stop?

A

when Ca++ levels decrease

35
Q

Where does Ca++ go?

A

continually pumped back into the sarcoplasmic reticulum
- mostly in terminal cisternae (T tubules are alongside)

36
Q

What causes depolarization of end-plate potentials and action potentials in muscle?

A

release of ACh at NMJ

37
Q

How are dihydropyridine receptors stimulated?

A

action potentials race over sarcolemma and down into muscle via T tubules

38
Q

How do action potentials in T tubules cause release of Ca++?

A

Voltage-gated (ryanodyne receptor) and Ca++ induced release channels
- electromechanical release

39
Q

What is the mechanism for muscle relaxation?

A

Ca++ from sarcoplasmic reticulum diffuses from troponin to initiate crossbridge cycling and contraction
- when action potential stops, muscles relax

40
Q

What is a twitch?

A

single rapid contraction and relaxation of muscle fibers

41
Q

What is summation?

A

2nd stimulus occurs before muscle relaxes from the 1st
- 2nd twitch is greater

42
Q

What are graded contractions?

A

contrations of varying strength

43
Q

What is incomplete tetanus?

A

muscle is stimulated by increasing frequency of electrical shocks
- tension increases to maximum

44
Q

What is complete tetanus/tetany?

A

frequency is so fast = no relaxation
- smooth sustained contration

45
Q

What is the strength of muscle contraction influenced by?

A
  • frequency of stimulation
  • thickness of muscle fibers
  • initial length of muscle fiber
46
Q

What is the relationship between tension and cross bridges?

A

less tension = fewer cross bridges formed
- no overlap force = no cross bridges formed

47
Q

What are the lower motor neurons and final common pathway?

A

ventral horn of spinal cord with motor neuron cell bodies
- axons leave at ventral root

48
Q

What is neural control influenced by?

A

sensory feedback from muscles and tendons
- faciliatory and inhibitory activity from upper motor neurons

49
Q

How does the nervous system receive continuous sensory feedback?

A
  • length/stretch of muscle from muscle spinal apparatus
  • tension from golgi tendon organs
50
Q

What is the muscle spindle apparatus made of?

A
  • 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
Q

What are the alpha motor neurons?

A

fast conducting
- innervate extrafusal fibers
- cause muscle contraction

52
Q

What are the gamma motor neurons?

A

slower conducting
- innervate and induce tension in intrafusal fibers
- increase sensitivity of muscle to passive stretch

53
Q

What do upper motor neurons stimulate?

A

alpha and gamma motor neurons
- coactivation

54
Q

What does stimulation of alpha neurons result in? How about gamma neurons?

A
  • 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
Q

What does the monosynaptic-stretch reflex consist of?

A

1 synapse within CNS

56
Q

What happens when the knee is hit with reflex hammer?

A
  • stretches spindles to activate annulospiral sensory neurons
  • synapse on alpha neurons causing them to stimulate extrafusal fibers
57
Q

What does the golgi tendon organ consist of?

A

2 synapses in CNS
- disynaptic reflex

58
Q

How does the golgi tendon organ reflex happen?

A
  • sensory axons from golgi tendon organ synapse on interneurons
  • make inhibitory synapses on motor neurons
  • prevents excessive muscle contraction or passive muscle stretching
59
Q

How does cardiac muscle work?

A

involuntary contraction
- branches, adjacent myocardial cells joined by intercalated disks (gap junctions)
- allows action potentials to spread throughout cardiac muscle

60
Q

What are the characteristics of smooth muscle?

A
  • no sacromeres
  • gap junctions
  • contains 16x more actin than myosin (allows greater stretching and contracting
  • actin filaments are anchored to dense bodies
61
Q

What is smooth muscle contraction controlled by?

A

controlled by Ca++ (but has little SR and no troponin/tropomyosin)

62
Q

What is the mechanism of smooth muscle contraction?

A
  • 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
Q

How does smooth muscle relaxaiton work?

A
  • 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
Q

What are the characteristics of single smooth muscle?

A

single unit is spontaneously active
- pacemakers
- gap junctions to spread electrical activity

65
Q

What are the characteristics of multiunit smooth muscle?

A

requires nerve stimulation by ANS
- neurotransmitter released along a series of synapses (varicosities) = synapses en passant

Physiology (18 decks)

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