Neuro 9 - Neuromuscular Junctions and SC Flashcards
What are the 2 directions that a membrane potential can be altered to?
- EPSP - excitatory - membrane potential brought closer to threshold (i.e. less negative)
- IPSP - inhibitory - membrane potential brought further away from membrane potential (i.e. more negative)
PSP = post synaptic potential
What neurotransmitter is used at the NMJ?
ACh
Explain how an AP is brought about in a muscle fibre
- AP arrives at NMJ
- Ca influx causes ACh release
- ACh binds to receptors on motor end plate
- Ion channel opens - Na influx causes AP in muscle fibre
What type of motor neurone is connected to the motor end plate?
Alpha motor neurone (aka lower motor neurone)
What do alpha motor neurones innervate?
Extrafusal muscle fibres of SkM
What is meant by motor neurone pool?
All of the alpha motor neurones innervating a single muscle
Never eat shredded wheat, what is the alpha motor neurone configuration in the butterfly section of the vertebrae?
Flexors
Proximal Distal
Extensors
What is a motor unit?
A neuron and all of the muscle fibres innervated by that neurone
Smallest functional unit to produce force
What are the types of motor unit?
- Slow (S, Type 1)
- Fast, fatigue resistant (FR, Type 2A)
- Fast, fatiguable (FF, Type 2B)
What are the 2 regulatory mechanisms of force production by a muscle
- Recruitment - governed by “size principle”. Small units recruited first (usually slow twitch). More force required = more units recruited.
Recruitment allows fine control when low forces are required.
- Rate coding - Firing rate increases to accommodate for larger force production. Summation = when units fire too quickly to allow muscle to relax between APs
What do neurotrophic factors do?
Prevent neuronal death, promote growth of neurons after injury
What is the most common conversion of muscle fibre type?
Type 2B to 2A after training
If severe reconditioning (e.g. spaceflight) or spinal cord injury occurs, what muscle fibre type change can occur?
Type 1 to type 2
Ageing can result in loss of type 1 and type 2 muscle fibres, but which type is lost preferentially?
Type 2
Pyramidal tracts are crossed for limbs and uncrossed for?
Trunk muscles
What is the Hoffman reflex?
Means of stimulating a nerve without using physical stretch of a tendon.
M-wave = initial direct contraction of the motor neurone that has been stimulated
Short while after, H-wave = AP in sensory neurone that has been stimulated excites a motor neurone
Flexion withdrawal reflexes ensure that other muscles maintain correct posture (Eg)
T
Supraspinal centres (higher CNS) centres exert inhibitory and excitatory regulation on stretch reflexes. Inhibitory control dominates usually.
T
In reflexes, there is usually an inhibitory signal to the antagonist as well as a excitatory signal to the agonist (i.e. quadriceps excited, hamstrings inhibited)
T
Which neurones are more amenable to electrical impulses?
Sensory neurones. Which is why, in Hoffmans reflex, easier to get a response from a H wave than a M wave
What are the 2 polysynaptic reflexes called?
Flexion withdrawal and crossed extensor
What does removing descending inhibitory control do?
Causes brisk reflexes and spasticity in muscles
What do strokes lead to?
Loss of descending inhibition of reflexes - causes HYPER-REFLEXIA
What is a clonus?
Repeated, rhythmic muscular spasmic contractions
What is babinskis sign?
Stroking the bottom of their foot causes plantar extension -
How is hypo-reflexia often caused?
By lower motor neurone lesions
Give an example of a monosynaptic reflex
Stretch
