Motor Tracts Flashcards
What are motor Tracts?
- Descending tracts
- start in CNS/made of UMNs
- Project from cortical and brain stem centers to LMN’s (alpha and gamma) and to interneurons in the spinal cord and brain
- different descending motor tracts control different types of movements, depending on where they synpse
General Classification of Motor Tracts
- Fine volitional motor control
- automatic postural control
- Background control
General Classification of Motor Tracts
Fine volitional motor control motor tracts
- located laterally in the spinal cord
- control distal muscles usually flexors
- lateral - fractioned movements, face and neck
General Classification of Motor Tracts
Automatic postural control tracts
General
- located medially in the spinal cord
- control postural muscles, usually extensors
- medial UMNs = postural and girdle
General Classification of Motor Tracts
Background Control
- located throughout the ventral horn
- background levels of excitation in the cord and facilitate local reflex arcs
Unilateral tract
- influences LMNs on ONE side of the body
- either ipsliateral or contralateral to the origin of the tracts fibers
Bilateral tract
- excites LMNs bilterally from each side of the tracts origin
- some fibers cross and some stay ipsilaterally
Hemiparesis vs hemiplegia
- Hemiparesis = 1 side is weak
- Hemiplegia = 1 side is paralysed
What are the lateral descending tracts
- Lateral corticalspinal tract (LCST)
- cortiobrainstem tract
Lateral corticospinal tract
- important for fractionation of movement of the limbs (selective motor control/activating specific muscles)
- most important pathway controlling voluntary movement
- activates inhibitory interneurons to prevent unwanted muscles from contracting
Lateral corticospinal tract pathway
- starts in motor areas of cortex such as: primary motor cortex, premotor cortex, supplementary motor area (all have somatotopic representation)
- through internal capsule
- through the cerebral peduncles in the midbrain through ventral pons
- through the pyramids in the medulla (crosses) and then through the lateral column of the spinal cord to the ventral horn of the spinal cord
Functions of
- primary motor cortex
- premotor area
- supplementary motor area
Primary Motor Cortex - Voluntarily controlled movements
Premotor area - Control of trunk and girdle muscles, anticipatory postural adjustments
Supplementary motor area - Initiation of movement, orientation planning
Where does the LCST decussate and what does it control
- the first axon crosses in the medulla
- left motor cortex controls right-sided voluntary movement and vice-versa
- 10% of fibers do stay on the same side
What would happen with a lesion to the LCST above the pyramids
- symptoms contralateral to the lesion side
- body and face affected with some cranial nerve involvement
What would happen with a lesion to the LCST below the pyramids
same side of the body is affected
LCST synapes
- none in the brain
- first synpase is in the spinal cord
- the motor neurons then travel to their target structure (muscles)
What are some pyramidal/LCST lesion signs
- pyramidal flaccid paralysis
- hypertonia and spastic paralysis
- babinski
pyramidal signs = UMN signs
Corticobrainstem tract
pathway
- Originates in the motor cortex (where face, tongue, throat and largest muscles the move the head are represented)
- initially travels with lateral corticospinal tract
- ends in differnt regions of the brainstem on cranial nerve nuclei
Function of the corticobrainstem tract
- provides input to muscles of the face, tongue, pharynx, larynx, trapezius and SCM muscles
- most cranial nerve nuclei receive bilateral input (CN VII is the exception)
- CN I, II are in CNS and are not receiveing input from here
- Projection usually:
Bilateral (therefore, upper facial mm’s often spared with CVA) - Exception – CN VII: Projection to lower face muscle mns Contralateral
LMN to mm’s of lower face are controlled by contralateral corticobrainstem fibers; LMN’s to muscles of the upper face are bilaterally controlled by corticobrainstem fibers
Corticobrainstem tract pathway
- originates in motor coretx
- initially travels with LCST
- ends in different regions of brainstem on cranial nerve nuclei
Differentatie between bells palsy and a CVA
- UMN lesion with a stoke will lose voluntary control of lower muscles of fascial expression due to the unilateral expression
- forehead muscles will be spared due to bilateral innervation
- with Bells palsy CN 7 is affected (LMN) and therefore affects both upper and lower parts of the face
Medial descending tracts
- Medial corticospinal tract
- reticulospinal tract
- medial vestibulospinal tract
- lateral vestibulospinal tract
Describe how medial and lateral tracts generally travel in the spinal cord
- Medial UMNs descend in the anterior column of the spinal cord and synapse with LMNs and interneurons located in the anteromedial gray matter
- Lateral corticospinal tract descends in the lateral column of the spinal cord and synapses with LMNs located in the anterolateral gray matter
Medial corticospinal tract
function
- innervates muscles of trunk, neck, shoulder
Desribe the pathway for the medial corticospinal tract
- first axon travels from the cortex
- through internal capsule
- through cerebral peduncles in midbrain
- through ventral pons
- through medulla
- descends medially in spinal cord
- to ventral horn of spinal cord (cervical and thoracic only)
- some fibers cross in the spinal cord/Some will stay
Reticulospinal tract
what it is important for
- important in postural control and gross limb movemetns
- coordinates gait
- involved in reaching for objects
- postural control
- neck reflexs
- anticipatory postural control
What does the reticulospinal tract get input from
- cerebral cortex
- cerebellum
- sensory information from the body
Pathway of the reticulospinal tract
- starts in the reticular formation of the PONS and medulla
- through medulla
- through anterior column of spinal cord
- ventral horn of the spinal cord
- descends bilaterally synapses on LMN
- goes cervical, thoracic and lumbar
Flexion synergy
abnormal
- one arm is unale to combine shoulder flexion with elbow extension during reaching
- action of reticulospinal tracts unopposed by corticospinal tracts
Medial vestibulospinal tract pathway
also what do the LMN in this pathyway faciliate
- starts in medial vestibular nuclei in medulla and pons
- descends bilaterally from upper medulla
- to anterior column of the spinal cord
- to lower motor neurons in cervical and thoracic spinal cord (ventral horn)
- lower motor neurons facilitate back and neck muscles
- information about head movement and position
Lateral vestibulospinal tract
pathwayand what LMNs will faciliate
- starts in lateral vestibular nucleus of pons and medulla
- travels ipsilaterally to anterior column of the spinal cord
- to ventral horn of spinal cord
- goes cervical, thoracic, lumbar
- LMNs facilitate extensors and inhibit flexors important to keep use upright
Non-specific motor tracts
Ceruleospinal tract
raphespinal tract
ceruleospinal tract
- starts in locus ceruleus of brain stem
- release NE
- facilitates spinal motor neurons
raphespinal tract
- starts in raphe nucleus of brainstem
- releases serotonin
- helps modulate activity of spinal motor neurons
