73 - Corticomotor Function

Question 1

What is the origin and termination of the corticospinal tract?

Answer 1

Origin:
60% from frontal lobe (Brodman’s area 4, 6, 8)
40% from primary somatosensory complex (9% from posterior parietal complex and 9% from cingulated gyrus)

Termination:
Sensory portion from the dorsal horn of the spinal cord
Motor portion directly through monosynaptic connections OR indirect through interneurons

Question 2

What is the function of the corticospinal tract

Answer 2

Sensory and motor function

Motor function includes fine control of distal extremities and coarse regulation of proximal flexors

Question 3

What is the origin and termination of the corticonuclear tract?

Answer 3

Origin:
Primary motor cortex (4, 6, 8)

Termination:

• Direct control of cranial motor nerve nucle and thus facial muscles (bilateral and contralateral)
• Fibers also terminate in sensory cranial nerve nuclei in the brainstem and dorsal column nuclei

Question 4

What is the function of the corticonuclear tract?

Answer 4

Sensory and motor function of the face

Question 5

What is the origin and termination of the rubrospinal tract?

Answer 5

Origin:
Red nucleus (may or may not exist in humans)

Termination:
Intermingle with fibers of lateral corticospinal

Question 6

What is the function of the rubrospinal tract?

Answer 6

• Control mainly distal and proximal muscles of the upper extremity
• Might enable motor cortical area to suppress spinal reflexes and spinal activity

Question 7

What are the effects of lesions in the corticospinal tract in monkeys?

Answer 7

Monkeys who have had their corticospinal tracts cut at the medullary pyramids:
• Cannot grasp an object between two fingers or make isolated movements of wrist or elbow
• Monkeys can maintain balance and walk and climb
• Animals do not develop spasticity

Question 8

What are the effects of lesions in the corticospinal tract in humans?

Answer 8

• Cannot perform similar experiment in human subjects!!! Any spinal cord lesion in humans would affect multiple descending motor tracts so cannot be sure of effect of just lesioning the corticospinal cord. Believed that spasticity caused by spinal cord lesions might be due to damage to reticulospinal tracts.
• Thought that lesion of the corticospinal tract in humans can cause weakness and extensor plantar reflex (Babinski Sign)

Question 9

What are the cortical areas involved with motor control?

Answer 9

• Primary motor cortex
• Premotor cortex
• Supplementary motor aarea
• Frontal eye fields

Question 10

Where is the primary motor cortex?

Answer 10

Broadmann’s area 4

Question 11

What is the function of the primary motor area?

Answer 11

Motor cortical neurons control several different muscles that work together to cause a movement. (e.g. reaching forward with one arm)

Question 12

Where is the premotor cortex?

Answer 12

Brodmann’s area 6

Question 13

What is the function of the premotor area?

Answer 13

• Goal directed movements require that sensory information about the environment be used to plan and carry out the desired motor task
• So one function of the premotor area is to use visual information about objects to control a motor task like grasping.

Question 14

Where is the supplementary motor area located?

Answer 14

Broadmann’s area 6

Question 15

What is the function of the supplementary motor area?

Answer 15

• SMA has a role in planning or preparing for sequential motor acts (especially those initiated or controlled by internal, remembered or self-determined stimuli)
• Supplementary motor cortex important for coordinating movements on both sides of the body. Unilateral SMA lesions were found to limit monkeys’ abilities to perform complex tasks requiring both hands. (NO paralysis though)

Question 16

Where is the frontal eye field located?

Answer 16

Part of Brodmann’s area 8 and part of 6

Question 17

What is the function of the frontal eye field?

Answer 17

• Influences eye movements through projections to the brainstem vertical and horizontal gaze centers and the superior colliculus.
• It is important for voluntary and memory guided eye movements

Question 18

What is the effect of a lesion in the primary motor cortex?

Answer 18

• Weakness (voluntary muscle weakness is called paresis)
• Lesions restricted to the primary motor cortex can cause persistent hypotonia. Spasticity though can occur if other motor cortical areas are also damaged
• Lesions caused by cerebrovascular disease cause motor losses that correspond to territory of artery.
• Lesions can cause permanent deficit in control of fine, fractionated, finger movements.

Question 19

What is the effect of a lesion in the premotor area?

Answer 19

Different aspects of motor planning and motor learning are controlled by the premotor area (PM) and the supplementary motor area (SMA) with the PM more important for movements activated or guided by external stimuli.

***When monkeys had lesions in their PM they were unable to learn new tasks involving associating a specific stimulus with a movement they were to make

Question 20

What is the effect of a lesion in the supplementary motor area?

Answer 20

Supplementary motor cortex important for coordinating movements on both sides of the body. Unilateral SMA lesions were found to limit monkeys’ abilities to perform complex tasks requiring both hands.

Question 21

What is the effect of a lesion in the frontal eye field?

Answer 21

• Permanent deficit in the ability to make saccades that are not guided by an external target. Subject would not be able to make a saccade to the remembered location that is no longer visible.
• Patients with FEF lesions cannot voluntarily direct their eyes away from a stimulus in their visual field.

Question 22

Describe the motor homunculus

Answer 22

No real motor homunculus analogous to the somatic sensory homunculus. There are broad areas of cortex devoted to control of arm, leg, etc. but firing of any one cortical cell affects several muscles and any one muscle is controlled by many different cortical cells.

Question 23

How would a lesion in the anterior cerebral artery affect motor function?

Answer 23

Anterior cerebral artery supplies the leg area of the primary motor cortex and most of the supplementary motor area. It also supplies the cingulate gyrus.

Question 24

How would a lesion in the middle cerebral artery affect motor function?

Answer 24

Middle cerebral artery supplies the trunk, hand and face area of the primary motor cortex and all of the premotor area

Question 25

Quadriplegia

Answer 25

Paralysis caused by illness or injury to a human that results in the partial or total loss of use of all their limbs and torso

Caused by a high cervical transection

Question 26

Tetraplegia

Answer 26

Another name for quadriplegia

Question 27

Paraplegia

Answer 27

Paraplegia is an impairment in motor or sensory function of the lower extremities

Caused by transection of the spinal cord below the cervical level

Question 28

Paresis

Answer 28

Weakness of voluntary movement - Not total paralysis

Question 29

Quadreiparesis

Answer 29

Muscle weakness affecting all four limbs

Question 30

Hemiparesis

Answer 30

Weakness on one side of the body. You can still move the affected side of your body, but with reduced muscular strength

Question 31

Monoplegia

Answer 31

Paralysis of a single limb, usually an arm. It is frequently associated with cerebral palsy.

Question 32

Describe the crossed pattern of some brainstem lesions

Answer 32

Crossed paralysis characteristic of brainstem lesion. It is another term for the alternating hemiplegia.

Brainstem lesions cause different types of alternating hemiplegia depending on location of lesion. All types of “alternating hemiplegia” consist of cranial nerve signs on one side and corticospinal signs on the “alternate” side. So they are examples of a crossed-palsy or crossed paralysis pattern.

Question 33

What is superior alternating hemiplegia?

Answer 33

Superior alternating hemiplegia is caused by lesions in the midbrain which affect the corticospinal tract and exiting rootlets of the oculomotor nerve.

Question 34

What is middle alternating hemiplegia?

Answer 34

One type of middle alternating hemiplegia is caused by pontine lesions which involve corticospinal tract fibers and fibers from the abducens nucleus.

Question 35

What is inferior alternating hemiplegia?

Answer 35

Inferior alternating hemiplegia results from medullary lesions affecting the corticospinal tract and fibers from the hypoglossal nerve. Patient has ipsilateral flaccid paralysis of the tongue (due to lower motor neuron lesion) and contralateral hemiparesis of the extremities.

Question 36

What are the effects of lower motor neuron disorders?

Answer 36

• Muscle atrophy
• Decreased muscle tone
• Weak or absent stretch reflexes
• Fasciculations
• Fibrillations
• Possible paralysis
• Flaccid paralysis

Question 37

What are the effects of upper motor neuron disorders?

Answer 37

• Spasticity
• Overactive deep tendon reflexes (DTR)
• Extensor plantar response (Babinski sign)
• Spastic paralysis or spastic paresis
• Immediate, short term effect of spinal cord transection though is flaccid paralysis

Question 38

Describe the manifestations of Brown-Sequard Syndrome

Answer 38

It is caused by damage to one half of the spinal cord, resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion.

Question 39

Describe lesions of the internal capsule

Answer 39

• Corticobulbar (corticonuclear) fibers are found in the genu of the internal capsule.
• Corticospinal fibers are found close together in the posterior limb of the internal capsule.
• A stroke involving one of the lenticulostriate arteries can produce pure motor signs contralateral to the lesion.

Question 40

Describe motor control of the upper face

Answer 40

Volitional movements of the upper face are controlled bilaterally by fibers from cortical motor areas

There is bilateral “backup”

Question 41

Describe motor control of the lower face

Answer 41

Volitional movements of the lower face are controlled primarily by contralateral motor cortices.

This is unilateral, so there is no “backup”

Question 42

Describe sensation of the face

Answer 42

Like the corticospinal tracts, the corticonuclear tracts have both motor and sensory cortex origins. The sensory component originates in the somatosensory cortex and projects to the sensory relay nuclei of the trigeminal nerve and the dorsal column nuclei.

Question 43

Describe the effect on the face in a lower motor neuron facial nerve lesion

Answer 43

With a facial nerve lesion, the lower motor neurons are innterrupted, preventing control of the ipsilateral muscles of facial expression. Therefore a person cannot close the eye or contract the muscles that move the lips on the same side as the lesion.

Question 44

Describe the effect on the face in an upper motor neuron lesion

Answer 44

Example:
An upper motor neuron lesion prevents information from the left cortex from reaching the facial nerve nuclei. Because the contralateral cortex controls the muscles of the lower face, the person is unable to generate a smile on the right side. However, because the upper face is innervated bilaterally, the person with an upper motor neuron lesion can close both eyes.

(diagram on slide 20)