047 The Vestibular System

Question 1

Explain what retinal slip errors result in?

Answer 1

Retinal slip errors occur when head movement is at different velocities to eye movement.

1. When compensatory eye movement is inadequate, the image on retina will move.
2. This sends retinal slip error to flocculus via climbing fibres from inferior olive.
3. Climbing fibres instruct modification of parallel fibre synaptic efficacies.
4. There is decrease in inhibitory output from purkinje cells
5. Results in compensatory movement to increase velocity.

Question 2

Explain the 2 half centre circuitary and the central pattern generator during walking

Answer 2

CPG - oscillations between 2 half centres.

1. Flexor motor neuron is stimulated, with inhibition of interneuron to the exensor motor neuron.
2. When the interneurons tire out, the inhibitor to extensor will turn off and the inhibitor to felxor turns on.
3. There is oscillation in 2 half centres.

Question 3

Explain mesencephalic locomotion region influences on the central pattern generator of spinal cord?

Answer 3

This influences the speed/ strength of the CPG (whether it is walking, running etc). It is due to stimulation of ACh and 5HT.

1. Receives inputs from basal ganglia, S1, M1, limbic system
2. Projects to medial reticular formation in midbrain
3. Reticulospinal tract passes down spinal cord to activate the system.

Question 4

Explain the descending pathway that controls the syngerstic/ oscillatory activity of the flexors and extensors in CPG?

Answer 4

Lateral vestibulospinal tract influences extensor neurons
Rubrospinal tract influences flexor neurons.
1. Cerebellum influences the rhythmic activity of lateral vestibulospinal tract and rubrospinal tract.
2. Cerebellar lesions cause uneven stepping/ataxia