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89 Cards in this Set

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How are motor circuits in the spinal cord regulated?
By input from descending motor pathways.
3 Cortical structures that regulate motor circuits in the spinal cord:
-Primary motor cortex
-Prefrontal cortex
-Somatosensory and parietal association cortex
3 Subcortical structures that regulate motor circuits in the spinal cord:
-Basal ganglia
-Cerebellum
-Thalamus
What else regulates motor circuits in the spinal cord?
The Brainstem
What did John Hughling's jackson observe about patient movement during a seizure?
That it often progressed from more distal to more proximal structures.
What did Fritsch and Hitzig observe when electrically stimulating a dog brain?
That it resulted in contralateral limb movements.
What required the least amount of stimulus to evoke a response by Fritsch and Hitzig?
The primary motor cortex
What does more intense stimulation of the premotor area do?
Evokes complex movements involving multiple joints.
What is the basis for Brodmann's subdivisions of the brain?
Cytoarchitecture
What is in Brodmann's area 4?
Primary motor cortex M1
What is in Brodmann's area 6?
-Supplementary motor area
-Premotor area
What is in Brodmann's area 3, 2 and 1?
Parietal lobe
What gyri contain the Primary Motor Cortex?
-Precentral gyrus
-Paracentral gyrus
Where do the neurons from the Primary Motor Cortex project?
To Rexed Laminae layers 6-9
What do Primary M1 neurons synapse on in laminae 6-9?
Small groups of motor neurons in the brainstem and spinal cord.
What will result from injury to M1?
Contralateral paralysis - especially loss of fine motor skills
What gyri contain the Premotor Area?
-Anterior precentral gyrus
-Posterior parts of frontal gyri
What is the function of the Premotor area?
To prepare the Primary motor cortex for an impending action.
What happens when Premotor cortex is injured?
Complex movements are slower than normal.
Where is the Supplementary Motor Area located?
On the medial surface of the cerebral hemisphere, anterior to the paracentral lobule.
What is the SMA functional in?
-Complex movements of many muscle groups, postural mvmts.
-Plans/integrates movements performed on both sides of the body simultaneously.
What is the result of a unilateral lesion of the SMA?
The inability to perform complex bi-manual tasks.
In what gyrus is Brodmann's area 3,2,1?
Postcentral gyrus - the somatosensory cortex.
Where do the neurons in the somatosensory cortex originate?
-Rexed laminae 4 and 5
-Posterior column nuclei
How is the somatosensory cortex in the parietal lobe involved in motor control?
It transmits sensory info
How is the primary motor cortex organized?
Somatotopically
What areas are biggest in the primary motor cortex?
Those areas that are used for tasks that require great precision.
Where is tongue motor control on the primary motor cortex?
Most lateral (near ear)
What is above the tongue?
The mouth, lips, face, and eye
Where is the neck?
Just above the eye
What is above the neck?
The thumb, then rest of the hand.
What is most medial on the primary motor cortex, before dipping into the longitudinal fissure?
The hip
What motor control is in the longitudinal fissure area?
Knee, ankle, and toes.
What motor control would an infarct in the middle cerebral artery most disrupt?
Movements of the face
What motor control would an infarct in the ACA most affect?
The knee, and lower limb.
What artery supplies most of the supplementary motor area?
ACA
What artery supplies the trunk, hand and face area of M1 and PMA?
MCA
Can a patient recover from a stroke? How/why?
Yes because of plasticity and the ability for some areas of the cortex to take over for others.
What happens to the motor cortex if the left forearm is amputated?
The area controlling the upper arm / biceps on the right brain will get larger.
What does the firing rate of INDIVIDUAL neurons in M1 cortex encode?
Force of contraction
What do populations of M1 neurons encode?
The DIRECTION of movement
So what do M1 neurons encode?
The VELOCITY with which a force is applied
-FORCE
-DIRECTION
What is M1 connected to?
Alpha lower motor neurons that innervate a particular skeletal muscle.
How do the M1 neurons get to the lower motor neurons?
Via the Corticospinal (pyramidal) tract
What is the function of the Corticospinal tract?
Voluntary skilled movement of distal muscles of the limbs
Where do the axons of the corticospinal tract originate?
-33% from M1
-33% from SMA & Prefrontal Cortex
-33% from Parietal lobe
What do 3% of the 33% of neurons that arise in M1 arise from?
Betz cells - the largest pyramidal cells in lamina V in the precentral gyrus.
After originating in their various areas, where do the fibers of the corticospinal tract pass through?
-Corona radiata
-Posterior limb of the internal capsule
How do the corticospinal tracts pass through the midbrain and brainstem?
By passing through the:
-Middle of crus cerebri and cerebral peduncle
-Medullary pyramids
What does the corticospinal tract split into? What percentage is each?
-Lateral corticospinal tract 90%
-Antero/ventral corticospinal tract 10%
What happens to the lateral corticospinal tract?
Its 90% fibers decussate in the pyramidal decussation and descend in the lateral funiculus to all spinal cord levels.
What happens to the anteroventral corticospinal tract?
Its 10% fibers DO NOT decussate; they descend in the anterior funiculus and decussate in ventral white commissure
How low do the anterior/ventral corticospinal tracts descend?
To thoracic spinal cord levels.
What is the goal function of the corticospinal tract?
-Excites flexor muscles
-Inhibits extensor muscles
What are the pyramids?
2 elongated swellings on the ventral aspect of the medulla.
What does each pyramid contain?
A million CORTICOSPINAL AXONS
What are the corticospinal tract fibers?
Upper motor neurons
What are the skeletal muscle nerve fibers upon which the corticospinal tract fibers synapse?
Lower motor neurons
Where does the lateral corticospinal tract begin?
At the pyramidal decussation
What will a lesion of the Internal Capsule result in?
Contralateral hemiparesis
What is hemiparesis?
Weakness
So a lesion to the left internal capsule will cause:
Right hemiparesis
What will a lesion to the left brainstem above the pyramidal decussation at the level of the midbrain result in?
-Right hemiplegia of all extremities
-Left paralysis of most eye movements
What will a lesion to the left brainstem above the pyramidal decussation at the level of the pons result in?
-Right hemiplegia of all extremities
-Left paralysis of most eye movements AND facial or lateral rectus muscles
What will a lesion to the left brainstem above the pyramidal decussation at the level of the medulla result in?
-Right hemiplegia of all extremities
-Left paralysis of most eye movements AND facial or lateral rectus muscles AND tongue mvmt
What will happen if there is a rostral lesion the brainstem AT the level of the pyramidal decussation?
Bilateral paresis of the upper extremities
What will happen if there is a caudal lesion the brainstem AT the level of the pyramidal decussation?
Bilateral paresis of the lower extremities
What will result from a unilateral cervical spinal cord lesion?
Ipsilateral weakness or paralysis of both the upper and lower limbs.
What will result from a bilateral cervical spinal cord lesion?
Bilateral weakness/paralysis of both upper and lower limbs.
What is bilateral weakness/paralysis of both the upper and lower limbs called?
Quadriplegia
When patients have hemiplegia or hemiparesis due to a unilateral lesion of the cervical spinal cord, what develops later?
Signs of UMN lesions - spacticity
What will result from a unilateral lesion of the thoracic spinal cord?
Paralysis of the lower limb on one side
What will result from a bilateral lesion of the thoracic spinal cord?
Paraplegia - loss of both lower limbs.
Lesions above the pyramidal decussation result in:
Contralateral weakness
Lesions below the pyramidal decussation result in:
Ipsilateral weakness
5 cardinal signs of an UMN lesion:
-Paresis or paralysis
-Spasticity
-Hyperreflexia
-Loss of abdominal reflexes
-Babinski sign
What is the babinski sign?
Stroking of the plantar foot results in big toe dorsiflexion instead of plantarflexion
4 cardinal signs of a LMN lesion:
-Muscle atrophy
-Fasciculations
-Hypotonia
-Hyporeflexia
3 examples of Corticospinal tract lesions:
1. Weber syndrome
2. Medial Medullary Syndrome
3. Brown-Sequard syndrome
What causes Weber syndrome?
Posterior cerebral artery occlusion - loss of blood supply to the midbrain.
What major nerve tracts are injured in Weber syndrome?
-CN III
-corticospinal tract
What deficits result in Weber Syndrome?
-Ipsilateral oculomotor palsy
-Contralateral paralysis of the lower face, tongue, arm, and leg
What will ipsilateral oculomotor palsy consist of?
-Lateral deviation of the eye
-Ptosis
-Pupil fixed and dilated
What major nerve tracts are injured in Medial Medullary syndrome?
-Cn XII
-Corticospinal tract
-Medial Lemniscus
What deficits result in Medial Medullary Syndrome?
-Ipsilateral paralysis and atrophy of the tongue
-Contralateral hemiparesis of the arm and leg, but the face is spared
-Contralateral loss of touch, vibration and proprioception from half the body
What is Brown Sequard syndrome?
A lesion of the spinal cord
So where will deficits be seen in Brown Sequard syndrome?
On the ipsilateral side of the body b/c you're below the pyramidal decussation.
What will be seen in a lower motor neuron lesion?
MUSCLE ATROPHY
What will be seen in a Corticospinal tract lesion at the level of the spinal cord?
-Ipsilateral spastic paralysis
-Ipsilateral babinski sign
-Ipsilateral loss of abdominal and cremasteric reflexes