1.8 Motor and Sensory Pathways

Question 1

What are the three types of motor movements?

Answer 1

• Reflexive
• Rhythmic
• Voluntary

Question 2

Give two examples of rhythmic movement

Answer 2

• Walking
• Breathing

Question 3

Explain the role of the primary motor cortex in motor movement

Answer 3

• Receives input from premotor and association areas
• Projects to spinal cord through corticospinal tract

Question 4

Explain the role of the basal ganglia in motor movement

Answer 4

• Modifies movement indirectly through planning areas
• Initiates movement and postural adjustments

Question 5

Explain the role of the cerebellum in motor movement

Answer 5

Compares planned action to actual action, and corrects disparity to aid coordination

Question 6

True or false: motor neurons and interneurons integrate sensory inputs from the periphery during motor movement

Answer 6

True.

Question 7

What are the three levels of the hierarchy of motor control?

Answer 7

• Highest level: planning (cortical association areas, basal ganglia, cerebellum)
• Middle level: commanding (motor cortex and descending pathways)
• Lowest level: executing (spinal interneurons and motor neurons)

Question 8

Which areas of the parietal lobe are important for integrating sensory information to inform motor movement?

Answer 8

Posterior parietal cortex

Question 9

What is the role of the premotor cortex?

Answer 9

Selection of appropriate motor plans

Question 10

What is the role of the supplementary motor area?

Answer 10

Active during the planning and coordinating of internally-guided movements (and coordinating bilateral movements)

Question 11

True or false: somatotopic organization of the motor cortex is plastic (i.e. it can be changed)

Answer 11

True; this is how we learn physical skills

Question 12

The cell bodies of motor neurons that are proximal are ___ in the ventral horn, and those of motor neurons that are more distal are more ___in the ventral horn.

Answer 12

Proximal muscle: medial soma
Distal muscle: lateral soma

Question 13

What is the name given to neurons that interconnect motor nuclei across vertebral segments?

Answer 13

Propriospinal neurons.

Question 14

What occurs if there is a lesion in motor association areas? What is this called?

Answer 14

• Called apraxia
• Strength is intact, but higher-order planning and execution is disrupted

Question 15

True or false: rhythmic movements can be generated at the level of the spinal cord

Answer 15

• True
• This is how they disconnected a cat’s brain, and got it to walk on a treadmill

Question 16

What neurotransmitter do lower motor neurons release?

Answer 16

Acetylcholine

Question 17

Isotonic vs isometric contractions

Answer 17

Isometric: no change in muscle length
Isotonic: change in muscle length

Question 18

What is a motor nucleus?

Answer 18

A group of motor neurons that are all responsible for the control of a specific muscle/muscle group.

Question 19

Describe the arrangement of muscle fibres, motor neurons, and motor units in a muscle

Answer 19

• There are multiple muscle fibres in a muscle
• Each motor neuron innervates multiple muscle fibres
• The combo of all muscle fibres innervated by a motor neuron is called a motor unit

Question 20

What is meant by innervation ratio? How does it change in finer movements?

Answer 20

• The number of muscle fibres innervated by a single neuron
• The finer the movement, the smaller the ratio

Question 21

Which of extra/intrafusal muscle fibres are innervated by alpha/gamma motor neurons?

Answer 21

Extrafusal: alpha
Intrafusal: gamma

Question 22

What’s the deal with Renshaw cells

Answer 22

• The axons of alpha motor neurons not only attach to extrafusal muscle fibres, but also interneurons called Renshaw cells
• These Renshaw cells are inhibitory
• This creates a negative feedback loop, preventing overcontraction of muscle

Question 23

In which area of the internal capsule does the corticospinal tract travel?

Answer 23

Posterior

Question 24

Would an UMN vs LMN result in ipsilateral/contralateral side?

Answer 24

UMN: Contralateral
LMN: Ipsilateral

(Anything in the lateral corticospinal tract would be ipsilateral)

Question 25

What’s the deal with the DCML pathway?

Answer 25

• Sensory neurons transmit information about fine touch and vibration from the lower limb (fasiculus gracilis) and upper limb (fasiculus cuneatus) in the dorsal columns
• In the medulla, they synapse at the nucleus gracilis/cuneatus, and deucssate to form the medial lemniscus (upper + lower in one bundle on each side)
• Synapse at thalamus + head out to primary somatosensory cortex

Question 26

What’s the deal with the spinothalamic tract?

Answer 26

• Carries information about crude touch (anterior) and temp/pain (lateral).
• First order neurons immediately synapse, decussate, and head up to the thalamus.
• Head out into the primary somatosensory cortex.

Question 27

How does the sensory cortical map change in response to amputation or training?

Answer 27

Areas grow/shrink depending on how much they are needed (amputation: gone, trained to use, increased in size)

Question 28

Explain phantom limbs

Answer 28

• When cortical areas are remapped in response to loss of body parts, adjacent areas on the homunculus grow bigger
• Touching these adjacently-mapped areas can lead to the feeling of an adjacent limb