Spinal reflexes

Question 1

What are features of a spinal reflex?

Answer 1

• Require stimulation
• Fast, due to few synapses
• Involuntary, intact even if spinal cord severed
• Stereotyped, occur in the same way each time. Underlying basic circuitry

Question 2

What is the patellar reflex and why does it occur?

Answer 2

‘Knee jerk’

• Due to stretching of the thigh extensor muscle
• Tries to correct stretching

Question 3

What are monosynaptic reflexes?

Answer 3

Involve one synape (very quick)

• Patellar reflex
• Myotactic reflex

Question 4

Describe what happens during the ‘pint pouring’ reflex in both the bicep and the tricep

Answer 4

• As glass gets heavier, sensory fibre detects stretch in the bicep
• Action potentials from the spinal cord cause the bicep to contract
• Tricep muscles simultaneously relax due to an inhibitory inter-neuron inhibiting the firing of the motor neuron to the tricep

Question 5

What is ‘reciprocal inhibition’?

Answer 5

Muscles on the opposite side of the limb relax to accommodate contraction on the other side

Question 6

What do proprioceptors do and what are 2 examples?

Answer 6

They detect body position and movement in time and space

• Muscle spindle
• Golgi tendon organ

Question 7

Where are muscle spindles located in the body and what do they detect?

Answer 7

• Deep within the muscle fibres of striated muscle

- Detect stretch

Question 8

What do the Ia sensory muscle fibres in a muscle spindle do?

Answer 8

• Innovate the muscle spindle with their ends wrapping around the spindle fibres
• Detect stretch of the muscle spindle
• Provide feedback to alpha motor neurons about the degree of stretch occuring

Question 9

What do the gamma motor neurons in a muscle spindle do?

Answer 9

• Stimulate intrafusaal muscle fibres to adjust tension to prevent slack
• Maintain muscle length by making the muscle spindle contract when surrounding muscle contracts

Question 10

Where are golgi tendon organs located in the body and what do they detect?

Answer 10

• Wrap around tendons

- Detects muscle tension due to contraction and counteracts it

Question 11

How do golgi tendon organs conteract stretch?

Answer 11

• Activation of sensory Ib afferents activate inhibitory interneurons and this inhibits alpha motor neurons that innovate the same muscle
• Negative feedback prevents damage

Question 12

What is the parallel after-discharge circuit?

Answer 12

• Multiple parallel pathways of different numbers of excitatory interneurons
• Immediate response but also sustained response

Question 13

What reflex uses the parallel after-discharge circuit?

Answer 13

Flexor (withdrawal) reflex