73 - Corticomotor Function Flashcards
What is the origin and termination of the corticospinal tract?
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
What is the function of the corticospinal tract
Sensory and motor function
Motor function includes fine control of distal extremities and coarse regulation of proximal flexors
What is the origin and termination of the corticonuclear tract?
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
What is the function of the corticonuclear tract?
Sensory and motor function of the face
What is the origin and termination of the rubrospinal tract?
Origin: Red nucleus (may or may not exist in humans)
Termination:
Intermingle with fibers of lateral corticospinal
What is the function of the rubrospinal tract?
- Control mainly distal and proximal muscles of the upper extremity
- Might enable motor cortical area to suppress spinal reflexes and spinal activity
What are the effects of lesions in the corticospinal tract in monkeys?
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
What are the effects of lesions in the corticospinal tract in humans?
- 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)
What are the cortical areas involved with motor control?
- Primary motor cortex
- Premotor cortex
- Supplementary motor aarea
- Frontal eye fields
Where is the primary motor cortex?
Broadmann’s area 4
What is the function of the primary motor area?
Motor cortical neurons control several different muscles that work together to cause a movement. (e.g. reaching forward with one arm)
Where is the premotor cortex?
Brodmann’s area 6
What is the function of the premotor area?
- 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.
Where is the supplementary motor area located?
Broadmann’s area 6
What is the function of the supplementary motor area?
- 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)
Where is the frontal eye field located?
Part of Brodmann’s area 8 and part of 6
What is the function of the frontal eye field?
- 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
What is the effect of a lesion in the primary motor cortex?
- 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.
What is the effect of a lesion in the premotor area?
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
What is the effect of a lesion in the supplementary motor area?
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.
What is the effect of a lesion in the frontal eye field?
- 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.
Describe the motor homunculus
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.
How would a lesion in the anterior cerebral artery affect motor function?
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.
How would a lesion in the middle cerebral artery affect motor function?
Middle cerebral artery supplies the trunk, hand and face area of the primary motor cortex and all of the premotor area
