The Corticospinal Tract Flashcards
Motor circuits in the spinal cord are regulated by input from
descending motor pathways:
Cortical structures
primary motor cortex
prefrontal cortex
somatosensory and parietal association cortex
Subcortical structures
basal ganglia
cerebellum
thalamus
Reflexes
Stereotyped responses to stimuli
Voluntary
Goal-directed Internally generated Improve with practice
Three types of movement
Reflexes
Voluntary
Automatic Postural Adjustments
How many neurons are in the corticospinal tract
one upper motor neuron!
The corticospinal tract projects to_______
Lower Motor Neurons LMN in the ventral horn of ALL levels of the spinal cord
Function of the corticospinal tract
voluntary movement of the distal extremities
Upper motor neuron route of corticospinal tract
corona radiata
posterior limb of internal capsule
the middle of the cerebral peduncle (crus cerebri)
ventral pons
medullary pyramids (pyramidal decussation).
lateral funiculus
Where do the fibers of the corticospinal tract decussate adn then what happens
90% of fibers decussate in pyramidal decussation and descend in lateral funiculus to all sp cd levels
Description of the corticospinal tract
Primary Motor Cortex connects to alpha lower motor neurons that innervate a particular skeletal muscle via the corticospinal tract (CST).
Function of the corticospinal tract
Descends to all spinal cord levels for voluntary control of motor neurons that
innervate muscles in the distal extremities. Allows for skilled movements. Excites flexor m.’s,
inhibits extensor m.’s
Lesions ABOVE the pyramidal decussation result in
CONTRALATERAL weakness
Lesions BELOW the pyramidal decussation result in
IPSILATERAL weakness bc it has already decussated
Upper Motor Neuron (UMN) Lesion:
Paresis (weakness) or paralysis Spasticity Hyperreflexia Loss of abdominal reflexes Babinski sign
What is the babinski sign
stroking the plantar surface of the foot along the lateral border leads to dorsiflexion of the great toe (normal response is plantar flexion) indicative of an upper motor neuron problem
Lower Motor Neuron (LMN) Lesion:
Muscle atrophy, Fasciculations, Hypotonia, Hyporeflexia
Corticospinal tract lesion: Lesion in the Cortex
Contralateral paresis of a particular body part corresponding to area of cortical damage
Corticospinal tract lesion: Lesion in the Posterior Limb of Internal Capsule
Contralateral hemiplegia
Corticospinal tract lesion: Lesion in the Cerebral Peduncle (Crus cerebri): Webers syndrome
Weber Syndrome Possible Cause: Occlusion of PCA
Corticospinal tract lesion: Lesion in the cerebral peduncle crus cerebral
Contralateral paralysis of lower face, tongue, arm and leg
Corticospinal tract lesion: Lesion in the cerebral peduncle crus cerebral CNIII lesion
Ipsilateral oculomotor palsy (eye deviates laterally, ptosis, pupil is dilated and fixed)
Lesion in the Medullary Pyramid: Medial Medullary Syndrome
Possible Cause: occlusion of vertebral a. or anterior spinal a.
Lesion in the Medullary Pyramid:Corticospinal Tract lesion
Contralateral hemiparesis of arm and leg, face is spared
Lesion in the Medullary Pyramid: CN XII injury
Ipsilateral paralysis and atrophy of tongue
Lesion in the Medullary Pyramid: Medial Lemniscus injury
Contralateral loss of touch, vibration and joint position sensation from half of the body
Lesion in the Spinal Cord
Ipsilateral spastic paralysis Ipsilateral Babinski sign
What is a physical sign of an upper motor neuron lesion
Babinski sign
the central part of the crus cerebri contains fibers involved in which function
Voluntary movements
when CN III emerges from the brainstem, its fibers pass in close proximity to which structure?
Red Nuclei
Hoffman’s sign
flick nail of middle finger, index finger and thumb come together in a patient with an upper neuron lesion
