lecture 16 Flashcards
upper motor neurons are a part of
the CNS
lower motor neurons are a part of
the peripheral nervous system and they project to and innervate skeletal muscle
the peripheral pathway of 1 lower motor neuron
- some that control facial muscle that live in the brain travel via cranial nerves
- most travel via spinal cord (ventral region)
when axon collaterals branch out at their distal ends
- each collateral can innervate a muscle fibre but muscle fibre can only receive input from one motor neuron
what role do shwann cells play for the neuromuscular junction
they play a supporting role by secreting paracrine to help maintain NMJ
The NMJ is the region where
the lower motor neurons synapse onto the muscle fibre
why is the motor end plate a specialized region
- 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
synaptic transmission at neuromuscular junction
- arrival of action potential at the axon terminus within the axon bulb
- voltage gated Ca2+ channels open and Ca2+ goes in
- this triggers exocytosis of neurotransmitter acetylcholine
- Ach is always excitatory at NMJ
- Ach binding to nicotinic Ach receptor which is always excitatory
the nicotinic Ach receptor is
- 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
muscle terminology
general term —> muscle equivalent
muscle cell—>
cytoplasm—>
endoplasmic reticulum—>
cell membrane—>
muscle cell—> muscle fibre
cytoplasm—> sarcoplasm
endoplasmic reticulum—> sarcoplasmic reticulum
cell membrane—> sarcolemma
contractile proteins within the myofibril are called
- myosin
- actin
what does the sarcoplasmic reticulum do
- stores Ca2+ when muscles is relaxed
- releasing it when muscle contracts as a signal
T-Tubules
- poke/indentation in sarcolemma that runs down into the interior of muscle fiber
- fill w ECF
- brings action potential in muscle fiber
A band
- Thick filament
- myosin
M-line
- middle of myosin
I band
- thin filament
- measuring distance between adjacent thick filaments
H-zone
- distance between one thin filament to the neighbouring thin filament
z disk
- middle of thin filament
- shown as a zig zag
Do thin/thick filaments shorten
no! thin/thick filaments do not shorten but any intervening distance between them will
myosin
myosin binds to actin, hydrolizes ATP and performs power stroke
each myosin head has
one actin binding site and one ATP binding site
Nebulin
is the structural support around which thin filament is formed
how do we form a thin filament
globular g-actin polymerize to form f-actin and then we have a thin filament
troponin
- is a trimeric protein complex that binds to tropomyosin and has 2 Ca2+ binding sites
- calcium dependent
tropomyosin
- 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
titin
- huge and elastic protein
- job is to help a muscle return to resting length
