spinal motor output

Question 1

three types of motor units (all fibers within that unit are same type)

Answer 1

S (1)-slow, weak contraction but resist fatigue. FF (2x or 2b)- strongest and fastest but fatigue in seconds. FR (2a)- in between

Question 2

two components to motoneurons translating electrical to firing patterns

Answer 2

recruitment (more motor units) and rate modulation (firing rate increases if stimulus continues after threshold is reached)

Question 3

Hennemans size principle: what does it say? based on what law?

Answer 3

motoneurons are recruited in order of increasing size, S before FR before FF. Ohms law (V=IR, where V is voltage threshold for spike initiation, I sis current generated by synaptic inputs, R is resistance of neuron (S has HIGHEST R)

Question 4

how does conduction speed relate to neuron diameter

Answer 4

direct correlation

Question 5

input from brainstem on motoneurons

Answer 5

5HT and NE metabostropic synapses are all over motoneuron dendrites (with axons originating in brainstem). Generates persistent inward Ca current which stimulates the motoneuron. Increases recruitment and rate modulation.

Question 6

why do you want brainstem input on motoneurons

Answer 6

reflexes change with state of arousal. More active fight or flight response

Question 7

how is posture affected by neuromodulators

Answer 7

monoamines make cell more difficult to turn off.

Question 8

what kind of recruitment and brainstem neuromodulation do you see in posture? walking? running? sprinting? weight lifting?

Answer 8

s, moderate monoamines. same. S and FR, moderate monoamines. S, FR, FF, high monoamines. Same