muscle physiology

Question 1

what is the purpose of the neuromuscular junction

Answer 1

where the nerves and muscle elements meet

• required for muscle contraction

Question 2

what is the importance of acetycholiesterase

Answer 2

takes Ach out of the synaptic clef

would be constant firing of Ach action potential in the muscle cell

Question 3

what are the structural components of skeletal muscle

• muscle fiber

Answer 3

whole muscle- fascicle- muscle fibre- myofibrils- thick and thin filaments

• muscle fiber

Question 4

describe characteristics of skeletal muscle cell

Answer 4

• striated- thick and thin filaments
• many nucleus- have a lot of microcndira

Question 5

myofibril

Answer 5

composed of bundles of myofillaments

Question 6

sacrocomeres

Answer 6

contrile unit of myofibril

Question 7

how is action potential in a skeletal muscle cell different than action potential in a neuron

Answer 7

in skeletal muscle-
graded potential

RMP -85- (-90)
more leaky potassium channels
more cl channels

no real hyper polarization phase

— harder to meet action potential (-90, -55)
— take longer

neuron-
RMP: -70, -55

Question 8

how does the excitement
contraction coupling work

Answer 8

azon terminal
down t tubal

VOLTAGE SENSOR- on t tubal, detects action potential and changes shape

causes ca to be realeased from SR

binds to troponin, pulling tropomyosin off the actin myosin binding sites

Question 9

why is ATPase important

Answer 9

it pumps Ca2+ back into SR

• this is what allows the muscle to relax
  -without the pump ca would be still bonded on troponin and the muscle would be constantally contracted

Question 10

explain the stages of ATP on the actin/myosin cycle

Answer 10

when ATP- is attached
- myosin not attached to actin

ADP + P
- energy transferred to myosin head
- how actin and myosin WANT to bind

• ca is realeased because of action potential
• Ca2+ binds to troponin and pulls off tropymosin
• Myosin attaches to actin- CROSSBRIDGE

PI RELEASED
- now power stroke triggered (muscle contraction)

ADP RELEASED
- crossbridge still formed

NEW ATP
- cross bridge breaks

Question 11

what is needed to release the cross bridge after a powerstoke

Answer 11

a new ATP molecule only way to break cross bridge

Question 12

what happens when you have rigor mortis

Answer 12

• stiffening of muscles after death
• begins 3-4 hours after
• max 12h
• slowly disappears 24-48h after

cause:
- no oxygen, no atp
- no ATP: nothing to break the crossbridge (of actin and myosin)
(muscles permanently fused)
- no ATP: Ca can’t be pumped back into SR, cross bridge forms

Question 13

what does the motor unit do

Answer 13

motort unit
- one motor unit and the muscle fibres it innervates

Question 14

what is a muscle twitch

Answer 14

contraction in response to ONE action potential on motor neuron

Question 15

how to increase force of contraction

Answer 15

more motor unit requirement:

more motor units are recruited, more muscle fibers contract- high contractile force

summation of twitch contractions:

increased stimulus frequency

Question 16

how does summation work for muscle cells

Answer 16

summation AP- frequency is increased
- each muscle twitch has LESS TIME TO RELAX before the next one occurs

• twitches BUILD on each other causing MORE FORCEFUL CONTRACTIONS

Question 17

What can you change about an action potential

Answer 17

-CANNOT change magnitude
- can only change frequency

Question 18

what is unfused tetanus

Answer 18

smaller amount of relaxation period between twitches

med-high frequency

Question 19

fused tetanus

Answer 19

at very high frequencies

• no time for muscle to relax between twitches
• produce smooth sustained contraction

Question 20

what does arborization stand for

Answer 20

branching of smooth muscle
- like branches of tree sticking out from the trunk- axon

Question 21

how is smooth muscle arranged

Answer 21

longitudinal- dilation and shortening

circular layer-

Question 22

difference in smooth muscle than skeletal muscle

Answer 22

• only one nucleus per cell
• actin and myosin arranged in a diagonal arrangement

-filaments attached to dense bodies- act like a z-line, filaments pull on the dense body and the muscle contracts

• cavelolae

Question 23

the role of calcium in smooth muscle vs skeletal muscle

Answer 23

smooth muscle-
has caveoloe:
important for

Question 24

what is the importance of cavaeloe

Answer 24

• important in take up concentrate ca 2+ from the ECF
• Ca 2+ concentrated from ECF , than needed for muscle contraction
• close to SR in proximity

-in smooth muscle very little ca 2+ comes from SR

• in smooth muscle SR is smaller, as its not as important for muscle contraction as it is in skeletal muscle

Question 25

difference between neuromuscular junction vs neuroeffector junction

Answer 25

neuroeffector junction
- no motor end plate
- AP travels down varicosities instead
- NT: norepinephrine, acetycholine

Question 26

how are neurotransmitters released onto the smooth muscle

Answer 26

travel through neuro effector junction

• diffuse through varicosities

VARICOSITIES- have neurotransmitters in them
- norepinephrine
- acetylcholine

• neurotransmitters diffuse from the varicosities
• innervate a large number of muscle cell

Question 26

what is the neuroeffector junction

Answer 26

CNS (pre-sympatic neuron)- ganglion- post sympatic neuron- target tissues- diffusion through varicosities (smooth muscle)

this is how smooth muscles communicate

Question 27

what’s the important of calmodulin?
in what muscle is it important

Answer 27

calmodulin is important in SMOOTh muscle contraction

• ca 2+ binds and activates calmodulin
• activated calmodulin than activates myosin light-chain kinase

-

Question 28

smooth muscle- slow wave vs pacemaker potential

Answer 28

slow wave-

smooth muscle- generate contractions without innervation n
- depolarizes due to changes in permeability
- passive movement of ions, AP will be generated

AP- muscle contracts