lecture 16

Question 1

upper motor neurons are a part of

Answer 1

the CNS

Question 2

lower motor neurons are a part of

Answer 2

the peripheral nervous system and they project to and innervate skeletal muscle

Question 3

the peripheral pathway of 1 lower motor neuron

Answer 3

• some that control facial muscle that live in the brain travel via cranial nerves
• most travel via spinal cord (ventral region)

Question 4

when axon collaterals branch out at their distal ends

Answer 4

• each collateral can innervate a muscle fibre but muscle fibre can only receive input from one motor neuron

Question 5

what role do shwann cells play for the neuromuscular junction

Answer 5

they play a supporting role by secreting paracrine to help maintain NMJ

Question 6

The NMJ is the region where

Answer 6

the lower motor neurons synapse onto the muscle fibre

Question 7

why is the motor end plate a specialized region

Answer 7

• it has receptors and enzymes —> the stuff we need for synaptic transmission is there
• the stuff we need to pass a signal from the motor neuron to the muscle fibre
• lots of nicotinic Ach receptors
• lots of surface area

Question 8

synaptic transmission at neuromuscular junction

Answer 8

1. arrival of action potential at the axon terminus within the axon bulb
2. voltage gated Ca2+ channels open and Ca2+ goes in
3. this triggers exocytosis of neurotransmitter acetylcholine
4. Ach is always excitatory at NMJ
5. Ach binding to nicotinic Ach receptor which is always excitatory

Question 9

the nicotinic Ach receptor is

Answer 9

• ligand gated
• relatively non-specific
• when channels open K+ flows out but not to a huge extent and Na+ and Ca2+ flow in
• Na+ will have a greater driving force because we’re further from Ena causing depolarizing end plate potential

Question 10

muscle terminology
general term —> muscle equivalent

muscle cell—>
cytoplasm—>
endoplasmic reticulum—>
cell membrane—>

Answer 10

muscle cell—> muscle fibre
cytoplasm—> sarcoplasm
endoplasmic reticulum—> sarcoplasmic reticulum
cell membrane—> sarcolemma

Question 11

contractile proteins within the myofibril are called

Answer 11

• myosin
• actin

Question 12

what does the sarcoplasmic reticulum do

Answer 12

• stores Ca2+ when muscles is relaxed
• releasing it when muscle contracts as a signal

Question 13

T-Tubules

Answer 13

• poke/indentation in sarcolemma that runs down into the interior of muscle fiber
• fill w ECF
• brings action potential in muscle fiber

Question 14

A band

Answer 14

• Thick filament
• myosin

Question 15

M-line

Answer 15

• middle of myosin

Question 16

I band

Answer 16

• thin filament
• measuring distance between adjacent thick filaments

Question 17

H-zone

Answer 17

• distance between one thin filament to the neighbouring thin filament

Question 18

z disk

Answer 18

• middle of thin filament
• shown as a zig zag

Question 19

Do thin/thick filaments shorten

Answer 19

no! thin/thick filaments do not shorten but any intervening distance between them will

Question 20

myosin

Answer 20

myosin binds to actin, hydrolizes ATP and performs power stroke

Question 21

each myosin head has

Answer 21

one actin binding site and one ATP binding site

Question 22

Nebulin

Answer 22

is the structural support around which thin filament is formed

Question 23

how do we form a thin filament

Answer 23

globular g-actin polymerize to form f-actin and then we have a thin filament

Question 24

troponin

Answer 24

• is a trimeric protein complex that binds to tropomyosin and has 2 Ca2+ binding sites
• calcium dependent

Question 25

tropomyosin

Answer 25

• a long protein that attaches to actin and cover myosin binding sites so that myosin can’t properly bind
• this causes the muscle to be relaxed and in the relax state there is no calcium so there is no signal from troponin to move tropomyosin so tropomyosin stays in the way blocking myosin binding site on actin so no contraction can occur

Question 26

titin

Answer 26

• huge and elastic protein
• job is to help a muscle return to resting length