Neuromuscular And Spinal Cord Movements

Question 1

Describe the two ways to alter directions by inputs

Answer 1

1. It can be made less negative via excitatory post synaptic potential (EPSP)
2. It can be made more negative via inhibitory post-synaptic potential (IPSP)

You get graded effects depending on the summation of the various inputs, the degree of summation will determine how readily a neurone can reach thereshold to produce action potential.

Question 2

Describe the basic structure of the neuromuscular junction

Answer 2

A specialised synapse between the motor neurone and the motor end plate, the muscle fibre cell membrane.

Activation of NMJ: when AP arrives calcium influx causes ACh release, ACh binds to receptors on motor end plate, ion channels open and causes Na+ influx resulting in AP in muscle fibres (excitable)

Question 3

Describe the role and function of Alpha motor neurones

Answer 3

These are lower motor neurones of the Brainstem and spinal cord. They innervate the extrafusal muscle (create tension and thus movement) fibres of the skeletal muscles. Their activation causes muscle contraction.

Alpha motor neurones are also called ventral horn cells, anterior horn cells because they are found in the anterior/ ventral horn of grey matter. They flex muscle and allow you to curl up into a ball. They also expense and stretch tall.

Question 4

Define a motor unit and the different types.

Answer 4

A single motor neurone together with all the muscle fibres that it innervates, it is the smaller function unit which produces force. One alpha motor neurone can innervate many muscle fibres but one muscle fibre can only be innervates by one motor neurone.

1. Slow (s, type 1): smallest diameter cell bodies, small dendritic trees, thinnest axons, slowest conduction velocity. Slow twitch, low tension, fatigue resistant.
2. Fast, fatigue resistance (FR, type IIa): larger diameter cell bodies, lathe dendritic trees, thick axons, fast conduction velocity. Fast twitch, moderate tension.
3. Fast, fatiguable (FF type IIb): large diameter cell bodies, large dendritic trees, thicker axons, faster conduction velocity. Fast twitch, high tension, high fatigue

Question 5

Explain the 2 mechanisms used to regulate muscle force.

Answer 5

1. Recruitment: smaller motor units ecruited first (slow twitch), this allows for fine control (under low levels or force).
2. Rate coding: slow units fire at low frequency, as firing rates increase the force produces by the unit increases, summation occurs when firing is too fast.
   S>FR>FF (force increases from S to FF)

Question 6

Describe the plasticity and neurotrophic factors affecting type of muscle of fibre.

Answer 6

Fibre types can change properties under conditions, type IIb becomes type IIa under athlete train gin (less fatigue). Type I to Type II under severe deconditioning or spinal cord injury.

Neurotrophic factors are like growth factors that prevent neuronal death after injury, muscle fibres cross innervate and switch types.

Question 7

Describe the organisation of the spinal cord.

Answer 7

1. Rubrospinal - brain to spine, automatic movements of the arm in response to posture balance changes.
2. Reticulospinal - coordinated automated movements of locomotion and posture (eg to painful stimuli)
3. Vestibulospinal - regulates posture, maintain balance and fascilitates mainly alpha motor neurones of the posture and antigravity extensors muscles,

Question 8

Describe a method of measuring synapses

Answer 8

Sensory nerve is stimulated, record a volley in recorder, get a monosynaptic connection and …

Question 9

Describe the Hoffman reflex

Answer 9

Stimulus is identical each time (same intensity and duration) therfore any changes is not due to input but the reflex pathway..

Stimulate back of the knee: m wave (contraction) and H wave (reach spinal cord) .

Question 10

Describe post synaptic felxiom withdrawals

Answer 10

More than one motor unit involved in contraction/ flexion of the muscle, there also reflexes that cross the spinal cord such that one limbs do something to keep us upright

Question 11

Describe the effect of surpaspinal control of reflexes.

Answer 11

Really important look at lecture slides.

Question 12

Describe the effects of upper motor neurone lesions

Answer 12

Strokes lead to loss of descending inhibtion of reflexes so you get hyper reflexia.

Clonus - muscular spasm involving repeated, often rhythmic contractions

Babinskis sign - if you stroke the bottom of their foot you will see planter extension where the toes fan out