the neuromuscular junction Flashcards
what do nerve signals trigger
muscle action potential
how are nerve signals delivered
by a motor neuron
what can 1 neuron trigger
trigger 1 or more fibres at the same time
whats a motor unit
Neuron plus triggered fibres
what does a Neuromuscular Junction do
This contacts the muscle fibre by contraction of the muscle
what is a Neuromuscular junction
A neuronal ending to a muscle fibre
where are synaptic end bulbs found and what do they do
(at neuron terminal)
Release neurotransmitter that they contain into the synaptic cleft ( = the gap that separates the synaptic and bulb of the neuron that’s supplying stimulus to the tissue and motoring plate)
what is the motor end plate
muscle area
whats the gap between the motor end plate called
synaptic cleft
explain the Events at the Neuromuscular Junction
Release of the neurotransmitter, acetylcholine (ACh)
- This Diffuses across cleft
Activation of ACh receptors on sarcolemma by it binding to these receptors on the sarcolemma (motor end plate)
Generation of Muscle Action Potential as sodium channels open, to move sodium into channel.
- Repeats with each nerve action potential
Breakdown of ACh by the enzyme acetylcholinesterase, to bring it to a stop
explain how the contraction is initiated
Muscle action potential
- brings about, Ca2+ released from Sarcoplasmic Reticulum (SR) (which is specifically designed for the holding and storing of calcium ions)
4 Ca2+ bind to troponin to being about muscle contraction
This Moves tropomyosin off actin sites
Myosin then binds to actin and starts contraction cycle
explain the contraction cycle
summary:
This cycle is active in nature and so depends upon ATP availability, the phosphate released allows formation of across bridge between myosin and actin
Swivels and ADP go back into sarcoplasm and can be regenerated by gaining a phosphate
The movement of myosin head causes shortening of sarcomere , this is called a power stroke
from PowerPoint:
Myosin binds to actin & releases phosphate group (forming crossbridges)
Crossbridge swivels releasing ADP & shortening sarcomere (power stroke)
ATP binds to Myosin => release of myosin from actin
ATP broken down to ADP & Pi => activates myosin head to bind and start again
Repeats as long as Ca2+ concentration is high
explain the process of relaxation
Breakdown of ACh to stop muscle action potentials by acetylcholinesterase as conc of ACh drops.
Once Ach is removed from synaptic cleft, Ca2+ ions transported back into SR (sarcoplasmic reticulum) lowering concentration
- This process involves active transport and the use of ATP
- when ca not present, Tropomyosin covers actin binding sites
what is muscle tone
Even at rest some motor neuron activity occurs
when would muscle tone be lost
If nerves are cut the fibres becomes flaccid (very limp)
