Week 4: Somatic Motor Pathways

Question 1

what are lower motor neurons ?

Answer 1

the only neurons that directly control skeletal muscle.

Question 2

what are local circuit neurons ?

Answer 2

neurons that are close to and synapse with lower motor neurons.
- these are important for coordination and gait.
- often found in the brain stem and spinal cord.

Question 3

what are upper motor neurons ?

Answer 3

neurons that synapse with local circuit neurons and rarely with lower motor neurons.
- generally found in the cerebral cortex.

Question 4

what is the basal nuclei ?

Answer 4

large group of central nervous system neurons that are implicated in emotion and behavior.

Question 5

the lower motor neurons ultimately are ?

Answer 5

responsible for receiving information from all other neuron types and they are the only neurons that are able to directly control the skeletal muscles.

Question 6

the signal usually comes from local circuit neurons ?

Answer 6

stimulate the lower motor neuron which stimulate the skeletal muscles.

Question 7

the local circuit neurons receive information from?

Answer 7

all other upper motor neurons and basal nuclei. the local circuit neurons in the brain or spinal cord interpret the higher signals and focus them into a single signal that stimulate the lower motor neurons that ultimately control the skeletal muscles.

Question 8

what are the two main upper motor neuron pathways called ?

Answer 8

direct motor pathways and indirect motor pathways.

Question 9

what are the direct motor pathways ?

Answer 9

direct linkage of axons from cerebral cortex to lower motor neurons.

Question 10

what are the indirect motor pathways ?

Answer 10

input to lower motor neurons from basal nuclei, cerebellum, and the cerebral cortex.

Question 11

where is the primary motor area ?

Answer 11

it is in the precentral gyrus in the frontal lobe.

Question 12

what is the location of the upper motor neurons ? what do they control ?

Answer 12

primarily located in the primary motor area. these neurons control voluntary movements.

Question 13

what are corticospinal pathways ?

Answer 13

the corticospinal pathways are responsible for voluntary motor control, with axons from the primary motor cortex travelling down two tracts to reach the spinal cord.
- lateral corticospinal tract : hands fingers toes, etc
- anterior corticospinal tract : shoulder , upper arms
both tracts carry signals from the brain to lower motor neurons in the spinal cord which then stimulate muscles to produce movement.

Question 14

lateral corticospinal pathway ?

Answer 14

1. the pathway starts in the primary motor cortex of the frontal lobe.
2. the upper motor neuron send their axons through the brainstem into the medulla oblongata.
3. the axons then reach the pyramids of the medulla oblongata, the pyramids decussate. the axon then travels down to the appropriate area of the spinal cord where eventually it will reach the posterior gray horn of the spinal cord.
4. synapse with a lower motor neuron whos axons project out of the anterior root of the spinal cord and will then send signals to to the skeletal muscles to initiate voluntary movement.

Question 15

the corticobulbar pathway ?

Answer 15

1. start with the upper motor neuron in the primary motor area in the frontal lobe.
2. motor neuron will project axons down the cerebral peduncles into the brainstem where they will decussate, in the pons/medulla.
3. the upper motor neurons then synapse with lower motor neurons in cranial nerve nuclei.
4. the lower motor neurons in the cranial nerves will then send signals to the right muscles for movement.