Muscle Pt 2 (S.M contraction initiation/termination)

Question 1

what are the 2 types of motor neurons?

Answer 1

1. upper motor neuron = primary motor cotex –> spinal cord
2. alpha (lower) motor neuron = spinal cord –> muscle fibers

Question 2

the neurotransmuscular junction refers to . . .

Answer 2

area where motor neuron makes synaptic contact with muscle fiber

Question 3

The AP created by one motor neurons will cause a rxn ______ on all of its connected fibers

Answer 3

spontaneousy

Question 4

alpha motor neurons are _____ with ___ diameters that creat fast AP

Answer 4

mylenated with large diameters

Question 5

what is a nuerodegenerative motor neron disease? Ex?

Answer 5

its a death of a lower (somtimes upper) motor neuron due to disuse that results in loss of muscle control

“if you dont use it = you loose it”

Question 6

What are the 3 components of the neuromuscular junction:

Answer 6

1. Presynaptic motor neuron filled with synaptic vesicles
2. The synaptic cleft
3. Postsynaptic membrane of the skeletal muscle fiber

Question 7

T?F Input can either be inhibitory/excitatory in skeletal muscle.

Answer 7

false = only ever excitatory

Question 8

How does nueral transmission stop at the neurmuscular junction?

Answer 8

remaining Acetyl CoA in synaptic cleft will either diffuse away or be broken down by the enzyme acetylcholineresyerase into aceate & choline. choline returns to motor neuron for reuse by choline acetyltransferases to make acetylcholone

Question 9

What does autoimmune mean?

Answer 9

your body makes antibodies to ACho receptors and block them, making the synapse to be ineffecient due to decrease in receptors & therefore AP = leads to loss in muscle movement (Ex. myasthenia gravis)

Question 10

AP propogate from the sarcolemma (cell membrane) into the muscle fiber via ___________ network

Answer 10

transverse (T-tubule) network

Question 11

the T-tubules penetrate into the muscle fiber and wrap around each ____ at the __ & __ band

Answer 11

wrap around myofribril at A & I bands

Question 12

AP propogation down the T-tuble triggers __ release from the ____

Answer 12

Ca+ release from the sarcoplasmic reticulum

Question 13

The ultimate intracellular signal required to trigger contrcation in ALL muscle types is ___

Answer 13

an increase in intracellular Ca+ (wether gained from extracelllar spaace or internal release (SR))

Question 14

excitation-contraction coupling refers to . . .

Answer 14

the process by which electrical excitation of the surface membrane tiggers an increase of Ca+ in muscle

Question 14

excitation-contraction coupling refers to . . .

Answer 14

the process by which electrical excitation of the surface membrane tiggers an increase of Ca+ in muscle

Question 15

T-tubules are neighbeired by x2 __ (specialized region of SR) to form a ____

Answer 15

terminal cisternea to form a triad

Question 16

T/F T-tubules bring Ca+ into interior of muscle fiber

Answer 16

False - T-tubules bring AP into interia

Question 17

How is an AP initiated in a muscle?

Answer 17

1. Somatic motor nuerons release ACho at neuromuscular junction
2. Net entry of Na+ via ACho receptors on the motor end plate starts the muscle AP

Question 18

Where are DHP & RyR receptors located? what are they?

Answer 18

DHP = L-type Ca+ voltage channel = on sarcolemma
RyR = Ca+ release channel = on sarcoplasmic reticulum

In some muscles, this receptors are mechanically linked (not in all though, ex. cardiac)

Question 19

What alters the conformatino of the DHP receptor? What is the result?

Answer 19

AP recieved from T-tuble (depolarization) –> structural change in receptor –> pulls opens the RyR = which results in Ca entering cytoplasm {skeletal}

For the muscle types in which these receptors arn’t linked (cardiac), the RyR receptor can also be activated by Ca+ induced Ca+ releae (this is not a big factor in skeletal)

Question 20

The increase in intracellular Ca+, triggers _____ by removing the ___ of cross bridge cycling

Answer 20

triggers contraction y removing the inhibition of cross brdige cycling

Question 21

What terminates muscle contraction requires . . .

Answer 21

removal of Ca+ –> which will lead to the myosin binding sites on actin to be covered by tropomyosin

stoping AP won’t stop contraction, only once there is no excess Ca+ in the intracellular space to alow for cross-bridge cycling will contraction stop

Question 22

What are x2 intracellular Ca+ removal options?

Answer 22

1. Ca+ leaves to extracellular space via Na-Ca exchanger or Ca+ pump (doens’t happen often)
2. Ca+ is reuptaken into SR via SeRCA pump (Main destination)

High Ca+ in SR blocks the SERCA pump to stop more intake
Calsequestrin & calreticulin store Ca inside SR to allow for more CA uptake

Question 23

When Ca+ is removed, the ___ shifts to once again cover the ___

Answer 23

torpomyosin shifts to cover myosin binding sites

Question 24

What is Rigor Mortis

Answer 24

when the cross bridge cycleing remain in a latched state (due to Ca+ leake that binds to troponin), with your body unable to make more ATP to release myosin head from actin

development of rigid muscle, hours after death