Motor Tracts Flashcards
Apraxia
-inability to perform learned movements on command
recognize position of limb but cannot perform correct motor sequence
Agnosia
- loss of the ability to recognize objects, faces, voices, or places
- right-left disorientation
- can still do things with dominant hand (autonomic-voluntary dissociation)
Encephalization
dominant influence of primary motor cortex on subcortical systems
Primary Motor Cortex
- corticospinal fibers
- precise movements of digits/distal extremities
- pre-central gyrus
Pre-Motor Cortex
- anterior to precentral gyrus
- Broca’s Area
- ideation and programming of movement patterns
- receives input from cerebellum via ventral anterior nucleus of thalamus
Upper Motor Neurons
- arise from cerebral cortex or brainstem
- axons travel in descending tracts
- synapse with lower motor neurons or interneurons of spinal cord
ex. Corticospinal tract and corticobulbar tract
Lower Motor Neurons
-directly innervate skeletal muscles
-cell body in spinal cord or brainstem and synapses on skeletal muscle fibers
classified as:
1. Gamma motor neuron - medium sized, myelinated, project to intrafusal fibers in muscle spindle
2. alpha motor neuron - large cell bodies and large myelinated axons project to extrafusal muscle fiber
Lesions of Lower Motor Neurons
affects nerve fibers traveling from the anterior horn of the spinal cord to the associated muscle
- flaccid paralysis: limp muscle with no resistance to passive movement
- areflexia: loss of efferent component of reflex arc/no muscle reflex
- atonia: absence of muscle tone due to destruction of gamma motor neurons
- atrophy: denervated muscle atrophies due to loss of stimulation from motor neurons
- fasciculations: twitchings of denervated muscle due to hypersensitivity of motor end plate
Lesions of Corticospinal Tract
unilateral lesions = contralateral spastic hemiplegia or hemiparesis
Lesions of Lateral Corticospinal Tract
unilateral lesions = ipsilateral paralysis or paresis of distal limb musculature innervated by the spinal segments below level of lesion
Lesions of Upper Motor Neurons
lesion of the neural pathway above the anterior horn of the spinal cord or motor nuclei of the cranial nerves
- spastic paralysis of axial and proximal limb muscles and some spastic paralysis of distal limb muscles esp in UE
- hypertonia
- hyperreflexia
- Babinski sign
- clonus
- rigidity
- disuse atrophy
Corticospinal Tract
- arise from pyramidal Betz cells in primary motor and pre motor cortices = UMNs
- UMNs arise in cortex and synapse on LMNs in spinal cord
- CST descends through corona radiata > internal capsule > cerebral peduncles > pons > upper medulla
- decussation of most fibers in lower medulla = lateral CST
- continuation of remainder of fibers that don’t cross = anterior CST
Occlusion of the Lenticulostriate Arteries
- lenticulostriate arteries of the MCA supply internal capsule
- weakness of face, arm, leg
- hyperreflexia
- Babinski sign
- Clonus
- Spasticity
- contralateral weakness and sensory loss
Central Seven Palsy/Central Facial Paralysis
- lesion of corticobulbar tract involving CN VII
- muscles of upper face are controlled by equal number of fibers from both hemispheres
- muscles of lower face controlled by contralateral hemisphere
- lesion rostral to facial motor nucleus results in drooping of muscles at corner of mouth on OPPOSITE side of lesion
Bell’s Palsy
ipsilateral flaccid paralysis of upper and lower face
Corticobulbar Tract Function
controls muscles of face, chewing, speech, swallowing
Corticobulbar Tract Blood Supply
lentriculostriate arteries of MCA and anterior choroidal arteries
Corticispinal Tract Function
fine motor control of hand, motor neuron recruitment to increase force, inhibition of postural reflexes
Corticospinal Tract Blood Supply
anterior and posterior spinal arteries, vertebral arteries, paramedian branches of caudal portions of basilar artery
Corticobulbar Tract
- arises in premotor and primary motor cortex
- descends into brainstem and influences muscles innervated by cranial nerves V, VII, IX, X, XI, XII including motor nuclei
- axons will cross and control muscles on contralateral side
- when descending will travel through genu of internal capsule
- continues passing through cerebral peduncles, anterior pons, and pyramids
- stops at specific motor nucleus
Oculomotor N Motor Components
- medial rectus
- superior rectus
- inferior rectus
- inferior oblique
- levataor palpebrae superioris
Trochlear N Motor Components
superior oblique
Trigeminal N Motor Components
- muscles mastication
- mylohyoid
- ant belly digastric
- tensor tympani
- tensor veli palatini
Abducens N Motor Components
lateral rectus
Facial N Motor Components
- muscles of facial expression
- posterior belly of digastric
- stapedius
Glossopharyngeal N Motor Components
stylopharyngeal muscle
Vagus N Motor Components
pharyngeal muscles
laryngeal muscles
Spinal Accessory N Components
trapezius and SCM
Hypoglossal N Components
intrinsic and extrinsic muscles of tongue
Amytrophic Lateral Sclerosis
- LMN deficits: anterior horn cells, hypoglossal nucleus, nucleus ambiguus, facial motor nucleus
- UMN deficits: chronic progressive degeneration of corticospinal tracts
- ALS causes LMN paresis and atrophy of upper extremity muscles
- dysarthria, dysphagia, tongue paresis
- involvement of CST causes spastic paralysis, hyperreflexia, Babinski sign
- no sensory deficits of ALS but there can be sensory deficits from other diseases
- death happens bc of bulbar paralysis (resp centers)
Decorticate Posturing
- UMN lesion
- regidity
- lesion above red nucleus above midbrain
- thumb tucked under flexed finers in fisted positoon
- pronated forearm
- flexion at elbow
- LE in extension with foot inverted
Decerebrate Posturing
- UMN lesion
- lesion below red nucleus but above reticulospinal and vestibulospinal nuclei
- UE pronation and extension
- LE extension
Complete Spinal Transection
- all sensation lost 1 or 2 levels below lesion
- hyperactive reflexes, clonus
- Babinski
- spasticity
- LMN signs at level of lesion
Syringomyelia
- most often at C4/5
- associated with Chiaris Type 1
- formation of cyst within SC
- pain and temp first affected (ant white commissure, resulting pattern is caped shaped)
- motor loss (LMN signs if ventral horns affected; UMN signs if lateral corticospinal tract affected)
Frontal Lobe
attention in motion
Pre-Frontal Lobe
motivation and memory in motion
Ideomotor Apraxia
inability to correctly mimic hand gestures due to lesions in left parietal lobe and premotor cortex
Pyramidal System
corticospinal and corticobulbar tracts
Lenticulostriate Infarct
- ischemia within areas supplied by branches of Middle cerebral artery or internal carotid artery
- secondary to cardiac embolisms
- clinical signs: motor/sensory deficits and cognitive dysfunction
Spasticity
- caused by lesions in the pyramidal tract (UMN of CST)
- weakness present
- more resistance in one direction vs other
- velocity dependent (more noticeable with fast motions)
Rigidity
- Seen in extrapyramidal lesions (i.e. Parkinson’s) such as the rubrospinal or vestibulospinal tracts
- Same resistance in all directions
- Not velocity dependent – does not vary with speed of movement of muscle groups involved
