Question

List & explain the events that transpire from the time an efferent (motor) neuron is stimulated until a motor unit contracts; indicate where each event occurs; describe how spinal cord damage influences muscle activity or movement: efferent (motor) neuron, stimulus, motor end plate, calcium, ACh, ACh-ase, neuromuscular junction (synapse), synaptic vesicles

Answer 1

The events happening in between the efferent nerve stimulation and contraction

Steps involved are

• The release of acetylcholine
• The acetylcholine action
• End plate potential development
• End plate potential miniature development
• Acetylcholine destruction occur

Steps of communication in detail
1) Release of acetylcholine---when the specific action potential for the motor neuron reach the axon terminal it results in the opening of voltage gated calcium channel inside their axon terminal membrane. This cause the breakup of the specific vesicles with Ach and move out of cells by the process of exocytosis.
2) Acetylcholine action --- The nicotinic receptors site is where the ACH will bind to and form the Acetylcholine -receptor complex . The postsynaptic membrane will become permiable to stage Na+ ions by the opening of ligand gated sodium channels. As a result the sodium ion entering the ECF will cause the alteration in the resting membrane potential and cause end plate potential
3) End plate potential development
When the impulse reach the neuromuscular junction a change in RMP occur called the end plate potential. When Na+ ions enter the ECF it will result in reduction of resting membrane potential from -90mV to -60mV called end plate potential
4) miniature end plate potential development
A miniature potential of up to 0.5 mV is produced when small amount of Ach reach the post synaptic receptors. This is called miniature end plate potential. These due to this small quantum if Ach acting in receptors. All these small quanta acting in the post synaptic neuron will cause generation of action potential and end plate potential.
5) destruction of Ach
This occur with the help of the acetycholinsterase which destroy the Ach so that unwanted contraction if muscle can be avoided