Spinal reflexes

Question 1

Motor system 3 main types of movement

Answer 1

Reflexive - brain + spinal chord
Rhythmic - central pattern generators in brainstem + SC
Voluntary - with special dependence upon motor cortex.

Question 2

Reflexes

Answer 2

Protective - gag, blink, limb withdrawal
Regulatory - vestibular ocular - maintains gaze
Muscle stretch - limb position

Question 3

Motor pool

Answer 3

Total number of motor neurons that goes to a single muscle

Question 4

Motor unit

Answer 4

Small - Single motor neuron may connect to 20-30 muscle fibres.
Large - single motor neuron to 1000 muscle fibres.

Question 5

Synaptic drive

Answer 5

Smaller motor units recruited by lower synaptic drive, larger units with larger SD. Orderly recruitment is called Henneman’s size principle.
Tension produced in the whole muscle is a function of the number of motor units recruited AND their firing rates.

Question 6

Feedback receptors

Answer 6

Proprioception - sense changes in muscles inform about motor control
Muscle spindles - detect length changes in the muscle - stretch receptors.
Golgi Tendon organ - detect tension.

Question 7

Muscle spindle

Question 8

Muscle stretch reflex

Answer 8

Only monosynaptic reflex in whole NS. Spindle fibre > 1a afferent > synapse > motor neuron > Muscle.
1a afferent also splits to inhibitory neuron for triceps. (antagonist).

Question 9

H reflex

Answer 9

A spinal reflex elicited by artificial (electrical) stimulation of the nerve.
After electricity, see M wave then H wave.

Question 10

Tendon organ reflex - inverse myostatic reflex

Answer 10

‘let go reflex’ 1b afferent motor neuron to 1b inhibitory interneuron.

Question 11

Flexion withdrawal reflex

Answer 11

A painful stimulus - fast nociceptors in foot transmit to spinal interneurons.
Flexors are activated in one limb, extensors in others, to prevent falling over.