Descending Pathways Flashcards
Outline the difference in pathways between the UMN from cerebral cortex and UMN from the brainstem. Also mention the LMNs these will synapse, the muscles involved and the main functions involved.
UMN in cerebral cortex travel in the lateral white matter of the spinal cord to synapse with LMNs in the lateral ventral horn. These supply the distal limb muscles.
- involved in skills movement
UMN in brainstem travel in the anterior medial white matter of spinal cord to reach the LMNs in the medial ventral horn bilaterally. These supply the axial muscles and the proximal limb muscles.
- involved in posture, balance and locomotion.
In which lobe is the motor cortex located?
Frontal lobe
What is the motor cortex made up of?
- where do these receive input from?
Pre central gyrus and premotor cortex
Receive input from thalamus (VA and VL) and from the primary somatosensory and sensory association fibres
What is the role of Betz cells in primary motor cortex?
Play an important role in activation of LMN that control muscle activities in distal extremities
Which parts of the body does corticospinal and corticobulbar tract innervate?
Corticospinal - trunk, upper and lower extremity
Corticobulbar - face
What are the functions of the premotor cortex?
Influences motor behaviour both directly and indirectly
Where does the premotor cortex receive inputs from?
Receives input from sensory areas in the parietal lobe and other complex inputs come from the prefrontal cortex
Describe the pathway of the Corticospinal tracts.
The UMN leaves the motor cortex and pass through through the posterior limb of the internal capsule to then enter the cerebral peduncle in the midbrain.
Fibres continue to descend through the pons and travel on the ventral surface of the medulla where they form the medullary pyramids.
80-90% of the fibres decussate at the medullary pyramids and descends in the lateral spinal cord
- this forms the lateral corticospinal tract
- controls detailed movements of the distal muscles
10-20% descends ipsilaterally in the ventral spinal cord
- this forms the anterior corticospinal tract
- supplies axial and proximal muscles
Both terminate at the ventral horn of spinal cord
This tract has collaterals to the red nucleus (in the midbrain) and to the reticular formation (in the medulla)
Where does does the corticobulbar tract terminate? And why is this important clinically?
At the motor nucleus of the trigeminal nerve (V) and the hypoglossal nuclues
This is NB clinically because most fibres in nerve the motor neurons bilaterally. However, these nuclei are the exception.
- UMN for facial nerve have contralateral innervation (only affects the muscles in the lower quadrant of the face below the eyes)
- UMN for hypoglossal nerve only provide contralateral innervation (affects taste over posterior 1/3 of tongue)
Which 2 tracts constitute the pyramidal pathway?
Corticospinal tracts
Corticobulbar tract
Which tracts constitute the extrapyramidal pathway?
Vestibulospinal and reticulospinal tract
Where does the vestibulospinal tract originate from? And how does it travel to the spinal cord?
There are 2 pathways:
- lateral
- medial
Originates from the lateral and medial vesticular nucleus
- they travel ipsilaterally
Where does the reticulospinal tract originate from? And how does it travel to the spinal cord?
Originate from the pontine and medullary reticular formation
- travels ipsilaterally
Upper motor neurons vs Lower motor neurons lesions
- strength
- muscle bulk
- reflexes
- special signs and symptoms
Lower motor neurons syndrome
- strength: weakness or paralysis
- muscle bulk: severe atrophy develops
- reflexes: hypo active superficial and deep reflexes
- special signs and symptoms: initial signs and symptoms persist; fasciculations and fibrillations; geographic distribution of impairment (reflecting distribution of affected spinal segments, cranial nuclei or spinal/cranial nerves); impairments of reflexive and gross and or fine voluntary movements
Upper motor neuron syndrome
- strength: weakness
- muscle bulk: mild or no atrophy develops
- reflexes: hyperactive deep reflexes after initial period of spinal shock
- special signs and symptoms: initial period of spinal shock then spasticity ensues; babinski’s sign and clonus; more widespread (non geographic)distribution of impairment in body regions; impairment of fine voluntary movements and gross movements relatively unimpaired
What is a positive babinski sign and what does it indicate?
Normal plantar response - toes down (flexion)
Positive sign results in an extensor plantar response (fanning of the toes)
- also positive in infants as their corticospinal pathway has not matured therefore incomplete control of UMN
