Lec 15

Question 1

Describe the monosynaptic stretch reflex (pathway and what does)

Answer 1

Ia afferents connect directly to alpha motor neurons. This mediates the muscle contraction in response to stretch.

Question 2

Describe H-reflex purpose and how each component plays a role (m wave, h wave)

Answer 2

Artificially stimulate nerve half way down. This stimulates both the Ia afferent and the alpha motor neuron.

Purpose - to measure the excitability of the motor neuron pool.

This is because afferent info may play role in how sensitive your motor neuron pool is (e.g. if you are at height). By using m wave as a reference of stimulus intensity, you can more accurately guage the excitability of the pool.

Question 3

Describe H-reflex in depth

Answer 3

• stimulate nerve. This will activate both the Ia afferents and the motor neurons. For each, there will be an orthodromic and antidromic response.
• M-wave - appears first (in relation to muscle)
• H-reflex appears second, but appear at lower stimulus before m-wave.
• As stim gets stronger, M-wave increases while H-wave decreases due to the antidromic potential, there is a refractory period in the nerves preventing another action potential in short succession. As the stim increases, more neurons are recruited an have refractories, until there is is no h reflex.

Question 4

Orthodromic vs antidromic

Answer 4

Orthodromic - correct/forward direction of travel for action potential propagation.

Antidromic - backwards

Question 5

Which responds first to artificial stimulation along a nerve, Large or Small neurons?

What happens once the reflex passes through a synapse.
What happens as you increase the stimulus size.

Answer 5

Large are recruited first when artificially stimulated (opposite of size principle).

Once pass through monosynaptic connection, size principle applies again.

This causes activation (NOT RECRUITMENT) of larger neurons but recruitment of smaller neurons with smaller stimulus.

As stimulus increases, larger neurons get recruited for the h reflex, then eventually in the middle sized neurons, there can be no larger h-wave because the larger neurons are recovering from the antidromic potential, therefore, h wave decreases as m wave continues to increase.

Question 6

nerve vs neuron

Answer 6

nerves are made up of many neurons

Question 7

Practical application of the H reflex and T reflex.

what happen to both in different danger conditions.

Answer 7

Can use H to test the excitability of motor neuron pools.

Can use T to test the integrity of the entire monosynaptic reflex as it connects to spindles as well.

Both reflexes increase when at height/Increased danger or alertness compared to when at low risk. Due to info from descending pathways and peripheral input

Question 8

Similarities and differences between T reflex and H reflex

Answer 8

Similarities
- Both cause contraction of the muscle via the monosynaptic reflex arc

Difference
- H if via artificial electrical stim, T is due to tendon tap causing a stretch reflex from the muscle spindles.