Motor Tracts Flashcards
Motor neurons are part of a 2-tract system, which are…
Upper Motor Neurons (UMN)
Lower Motor Neurons (LMN)
These neurons arise and are contained within the cerebral cortex or brain stem. Axons then travel in descending tracts and synapse with the neurons and/or interneurons of the spinal cord (i.e., Corticospinal tract and Corticobulbar tract).
Upper Motor Neurons (UMN)
These neurons directly innervate skeletal muscle, and the cell body lies in the spinal cord or brainstem which synapse with skeletal muscle fibers. Examples include peripheral nerves and cranial nerves (with motor components).
Lower Motor Neurons (LMN)
There are two types of LMNs, which are…
Gamma Motor Neuron
Alpha Motor Neuron
This type of LMN is medium-sized, myelinated, and project to intrafusal fibers in muscle spindle.
Gamma Motor Neuron
This type of LMN has large cell bodies and large myelinated axons that projects to extrafusal skeletal muscle.
Alpha Motor Neuron
Somatic motor pathways can either be direct or indirect. (INDIRECT/DIRECT) pathways go from the cerebral cortex to the spinal cord and out to muscles. (INDIRECT/DIRECT) pathways include synapses in the brainstem, basal ganglia, thalamus, reticular formation, and cerebellum.
Direct
Indirect
***Some fibers from direct pathways will send fibers to indirect pathways to help modulate
For the Corticospinal Tract (CST), the UMNs arise in the cortex and synapse with LMNs in the spinal cord. The ________ CST goes to postural muscles, and the ________ CST goes to limb muscles and gives us the ability of fractionation (move fingers and do precise movements).
Medial
Lateral
***90 percent of fibers go to Lateral tract!
What is the general pathway of the CST?
Cerebral Cortex – Posterior limb of internal capsule – Cerebral peduncles (middle 1/3) – Anterior pons – Pyramids (decussation) – Lateral column of spinal cord – Synapse with LMNs in spinal cord
This is located in the precentral gyrus and initiates voluntary movement.
Primary motor cortex
The right side motor strip usually controls the (LEFT/RIGHT) side of the body, and vice versa.
Left
In the primary motor cortex, the neurons are (UMN/LMN).
UMN
At what point is the CST called the “Lateral” CST?
Once the fibers are descending in the lateral column of the spinal cord.
In the Lateral CST, the UMNs synapse with the LMNs in the _______ _______ of the spinal cord.
Ventral horn
In the Medial CST, they control postural and proximal movements (neck, shoulder, and trunk muscles). The pathway is exactly the same except…
The fibers do NOT cross in the medulla (at pyramids)
This motor tract arises from the ventral part of cortical area 4. It descends into the brainstem and influences muscles innervated by cranial nerves including motor nuclei (V, VII, IX, X, XI, XII). Axons will cross and control muscle on the contralateral side.
Corticobulbar (Corticonuclear) Tract
T/F. The Corticobulbar Tract follows the same path as the CST until it reaches the pyramids of the medulla. Some will cross over, some won’t depending on where the nuclei are for their specific CNs. The UMNs synapse in the nuclei of the CNs, which are the LMNs.
True
In the Corticobulbar Tract, CN 5 receives ________ input and Facial Nucleus receives ________ input to the forehead but only ________ for the lower face.
Bilateral
Bilateral
Contralateral
LMNs are found in the ventral horn of the spinal cord. Medial LMNs project to ______ muscles, lateral LMNs project to _______ muscles, LMNs innervating _______ muscles tend to lie ventral, and LMNs innervating ________ muscles tend to lie dorsal.
Axial
Limb
Extensor
Flexor
Indirect pathways tonically activate antigravity and axial LMNs. What are the Medial and Lateral UMN indirect tracts?
Medial UMN tracts:
- Tectospinal
- Medial reticulospinal
- Lateral vestibulospinal
- Medial vestibulospinal
Lateral UMN tracts:
- Rubrospinal
- Lateral reticulospinal
Medial LMNs are not quite as prominent, and are located in the _______ _______. They receive input from:
- Tectospinal tract
- Medial vestibulospinal tract
- Medial reticulospinal tract
- Medial corticospinal tract
- Lateral vestibulospinal tract
Anterior Fasciculus
Lateral LMNs are more prominent and receive input from…
- Rubrospinal tract
- Lateral reticulospinal tract
- Lateral corticospinal tract
***Need to know where these are within the SC!
This tract goes from the vestibular nuclei to the spinal cord and projects to the cervical and thoracic levels (neck and shoulder muscles).
Medial vestibulospinal tract
This tract goes from the vestibular nuclei to the spinal cord and projects to ipsilateral LMNs innervating the postural muscles and limb extensors (gravity, keeps upright).
Lateral vestibulospinal tract
This tract goes from the red nucleus to the spinal cord and innervates the upper limb flexors.
Rubrospinal tract
This tract goes from the pontine reticular formation to the spinal cord and projects to ipsilateral LMNs innervating the postural muscles and limb extensors (postural reflexes).
Medial (Pontine) reticulospinal tract
This tract goes from the medullary reticular formation to the spinal cord and facilitates flexor motor neurons and inhibits extensor motor neurons (you need this to not look like a statue against gravity).
Lateral (Medullary) reticulospinal tract
This tract goes from the superior colliculus to the upper spinal cord and projects to neck muscles.
Tectospinal tract
The function of this tract is fine motor control of the hand, motor neuron recruitment to increase force, and inhibition of postural reflexes.
Corticospinal tract
The function of this tract is control of muscles of face, chewing, speech, and swallowing.
Corticobulbar tract
The function of this tract is the facilitation of upper limb flexors.
Rubrospinal tract
The function of this tract is the facilitation of extension against gravity.
Lateral vestibulospinal tract
The function of this tract is the coordination of head movements.
Medial vestibulospinal tract
The function of this tract is the facilitation of postural reflexes.
Pontine (Medial) reticulospinal tract
The function of this tract is the inhibition of spinal segmental reflexes.
Medullary (Lateral) reticulospinal tract
The function of this tract is the coordination of head with eye movements.
Tectospinal tract
If there is a lesion in the (UMN/LMN) then it will present as:
- Flaccid Paralysis
- Wasting or atrophy
- Hyporeflexia or areflexia due to denervation
- Hypotonia (decreased muscle tone)
- Denervation hypersensitivity (fasciculations)
LMN
***CNs
UMN syndrome is a combination of the loss of the _________ tract (direct pathway) and the loss of regulation from the indirect brainstem motor control pathways.
Corticospinal
***i.e., Pronator drift
If there is a lesion in the (UMN/LMN) then it will present as:
- Loss of distal extremity strength and dexterity
- Babinski sign (inverted plantar reflex)
- Hypertonia
- Hyperreflexia (may be seen as clonus)
- Clasp-kine phenomenon and spasticity
UMN
***Loss of distal extremity strength and dexterity and babinski sign are a result of CST. All the others are from indirect pathway.
LMNs result in clinical signs on the (SAME/OPPOSITE) side as the lesion. LMNs will tell you exactly what level is involved with the lesion!
Same
For UMNs, if the lesion is above the lower medulla (where CST crosses) then clinical signs will be (IPSILATERAL/CONTRALATERAL). In the spinal cord, clinical signs will be (IPSILATERAL/CONTRALATERAL).
Contralateral
Ipsilateral
This is due to an UMN lesion above the level of the red nucleus. The thumb is tucked under flexed fingers in a fisted position, pronation of forearm, flexion at elbow with the LE in extension with foot inversion all occur.
Decorticate posture (rigidity)
- **Above midbrain, it is still intact!
- **Remember, red nucleus is rubrospinal tract!
This is due to an UMN lesion below the red nucleus, but above the reticulospinal and vestibulospinal nuclei. The UE is in pronation and extension and the LE is in extension.
Decerebrate posture (rigidity)
- **Down past midbrain and includes it!
- **Remember, red nucleus is rubrospinal tract!
What can cause decorticate or decerebrate posture?
Central herniation
If there is a lesion in the UMN and the LMN, what will take precedence?
The LMN lesion, it will mask any other problems.
What type of lesion presents with the following?
- All sensation 1 or 2 levels below lesion is lost
- Bladder and bowel control are lost
- Spinal shock (loss of tendon reflexes)
- UMN signs at level below the lesion (after period of time)
- LMN signs at the level of the lesion
Complete transection of the spinal cord
What type of lesion presents with the following?
- Loss of pain and temp from contralateral side body
- Loss of ipsilateral discriminative touch and proprioception
- LMN signs at level of lesion
- UMN signs on ipsilateral side of lesion
Hemisection of spinal cord
***Specifically called Brown-Sequard’s Syndrome
This occurs from the formation of cysts in the central canal within the spinal cord. Pain and temp are affected first due to the anterior white commissure being affected. Results in pattern of “cape”. May also have LMN signs if ventral horns are affected, or UMN signs if the lateral CST is affected.
Syringomyelia
The spinal cord syndrome is due to the compression or damage to the anterior part of the spinal cord. Usually due to spinal cord infarction, intervertebral disc herniation, and radiation myelopathy.
Anterior Cord Syndrome
This spinal cord syndrome is due to compression and damage to the central portion of the spinal cord. Mechanism of injury is usually cervical hyperextension.
Central Cord Syndrome
This can occur due to a lesion of the CBT involving CN VII. Muscles of the upper face are controlled by equal numbers of fibers from both hemispheres. Muscles of the lower face are controlled by the contralateral hemisphere. Lesion rostral to facial motor nucleus results in drooping of muscles at the corner of the mouth (on opposite side of lesion).
Central Seven Palsy
***Remember, forehead gets bilateral input and lower face gets contralateral input.
This can occur due to ipsilateral flaccid paralysis of the upper and lower face.
Bell’s Palsy
This is a movement dysfunction that has abnormal supraspinal influences, failure of normal neuronal development, and consequent aberrant muscle development (damage to CST).
Spastic Cerebral Palsy
This motor disorder presents with the following:
- Paresis
- Abnormal tonic stretch reflexes (at rest and with movement)
- Reflex irradiation
- Lack of postural preparation prior to movement
- Abnormal co-contraction of muscles
- Scissor walk
Spastic Cerebral Palsy
This disease destroy only somatic motor neurons (UMNs and brainstem and spinal cord LMNs). It leads to paresis, myoplastic hyper stiffness, hyperreflexia, Babinski’s sign, atrophy, fasciculations, and fibrillations. Cranial nerve involvement leads to difficulty breathing, swallowing, and speaking.
Amyotrophic Lateral Sclerosis (ALS)
This is the involvement of sensory, motor and autonomics. It progresses form distal to proximal and is due to dying-back or impaired axonal transport. Demyelization may also contribute.
Polyneuropathy
***Autoimmune or metabolic (like diabetes). “Glove” or “stocking”
