Neural Control

Question 1

Are the axons of the corticobulbar tract ipsilateral or contralateral? and hence the corticospinal tract?

Answer 1

Corticobulbar - ipsilateral

Corticospinal - contralateral (synapse on opp side of body)

Question 2

What is the point in the medullary-spinal border where most fibres in the corticospinal tract cross over the midline?

Answer 2

Pyramidal decussation

Question 3

Briefly outline a generic descending pathway

Answer 3

Betz cells in M1 synapse with LMN in the spinal cord or brain stem at the ventral horn. They travel the corticospinal or corticobulbar tract.

Question 4

Where is the M1 located?

Answer 4

Frontal lobe along the precentral gyrus

Question 5

What’s the difference between LMN lesion and UMN lesion?

Answer 5

LMN lesion is characterised by flaccid paralysis,

UMN lesion is characterised by spastic paralysis

Question 6

Explain the tendon jerk reflex

Answer 6

Tap stimulus stretches muscle,
The muscle spindles are stretch receptors and fire action potential along a sensory neuron,
Sensory neuron synapses at spinal cord,
Somatic motor neuron fires AP to quads to contract and hamstrings to relax.
This causes the jerk

Question 7

Outline the process of neural conduction

Answer 7

Na/K ion pump maintains resting potential,
Stimulus opens voltage gated Na ion channels to open, causing influx of Na,
If the threshold is reached, more Na channels open,
K ion channels open and cause outflux of K,
This depolarises the cell,
Na channels close at the peak of the AP,
K continues to leave the cell causing repolarisation of the cell,
K channels are slow to close causing refractory period

Question 8

What is hennemans size principle?

Answer 8

Under load, motor units are recruited from smallest to largest

Question 9

What happens at the NMJ?

Answer 9

.

Question 10

What is E-C coupling?

Answer 10

Mechanism whereby an electrical discharge at the muscle initiates chemical events at the cell surface to cause contraction