Descending Motor Tracts Flashcards
Name the pyramidal tracts
Corticospinal
Corticobulbar
Name the extrapyramimdal
Vestibulospinal
Reticulospinal
Tectospinal
Rubrospinal
Briefly what is the function of the vesitubulospinal tract?
Balance reflexes
Briefly what is the function of the tectospinal tract?
Eye-body coordination
Breifly what is the function of the reticulospinal tract?
Medullary (lateral) = flexor reflex facilitation and extensor reflex inhibition
Pontine (Medial) = extensor reflex facilitation
Functions of the corticospinal tract?
- Descending control of afferent inputs
- Selection, gating and gain control of spinal reflexes
- Excitation and inhibition of motor neurons
- Autonomic control
What are the inputs to the corticospinal tract?
30% SMA
30% M1
~40% S1
What do inputs from S1 to the CST do?
Descending modulation of inputs from priopceptors generated by moving. Fibres from S1 in the CST terminate on the dorsal horn and filters irreverent sensory signals
Where does decussation of the CST occur?
~85% in caudal medulla
The rest decussate on the spinal level of the motor neuron they innervate
What does the 85% that decussate form?
The lateral CST
What does the 15% which remain ipsilateral form?
The ventral CST
What does the CST pass through in the brain?
The internal capsule?
Genu of IC = face
Going outwards = arms, trunk , legs
What do neurons on the CST synapse on?
Directly to alpha
To alpha via interneurons
What does the lateral corticospinal tract innervate?
Distal musculature
What do neurons of the ventral corticospinal tract innervate?
Musculature of the pelvic and pectoral girdle
Where does the corticobulbar tract originate?
M1 - the face region of the motor homunculus
What does the corticobulbar tract innervate?
cranial nerves which contain motor nuclei for general somatic efferents and special visceral efferents motor components. This is mostly bilateral i.e. A motor nuclei will receive bilateral innervation
What cranial nerves have a motor modality to them?
occulomotor Trochlear Trigeminal Abducens Facial Glossopharyngeal Vagus Spinal accessory hypoglossal
What muscle groups are innervated by the corticobulbar tract?
Muscles of facial expression Tounge Extraoccular Vocal cords Mastication
What CN nuclei are not bilaterally innervated?
The motor nuclei for the muscle of facial expression of the lower face (why an UMN causes contralateral face paralysis but is forehead sparing)
The hypoglossal nerve motor nuclei 9UMN points tongue to contralateral side, LMN points it towards side of lesion)
Which extrapyramidal tracts do not decussate?
Vestibulospinal
Recticospinal
Which extrapyramidal tracts do decussate immediately/
Rubrospinal
Tectospinal
Where does the reticospinal tract originate/
Pontine (medial) in the nucleus reticularis pontis oralis and caudalis
Medullary (lateral) in the nucleus reticularis giantocellularis
The pontine (medial) reticulospinal tract does what?
Extensor reflex facilliatation and synapses on alpha and gamma MN to increase muscle tone
The medullary (lateral) reticospinal tract does what?
Flexor reflex facilitation and extensor reflex inhibition
What are the inputs to the vesiculospinal tract?
The balance organs of the vestibular apparatus and cerebellum
Wat does the vestibulospinal tract orginate from?
Medial and lateral vestibular nuclei
Where does the vestibulospinal tract terminate?
Interneurons which synapse to muscle of balance and posture
What does the medial VST control?
Muscles of the neck e.g. Spinal accessory nerve to cause rotation and uplifting of head and neck (stabilise neck and head when walking)
What does the lateral VST control?
Innervate extensor antigravity muscles. Alpha and gamma MN of lower limb muscles important for posture and balance
Where does the tectospinal tract orginate?
The superior collicus within the tectum
Where does the tectospinal tract decussate?
The midbrain at the ventral tegmental decussation
Where does the tectospinal tract terminate?
Neurons within the upper cervical spine
What is the function of the tectospinal tract?
Coordinates head movements towards visual stimuli
How is the red nucleus organised?
Somatotopically
What inputs into the red nucleus?
Input from M1 and premotor cortex
Where does the rubrospinal tract decussate?
The ventral tegmental area
Where does the RubroST terminate?
In higher animals within the C spine
In lower animals within the lumbar spine
Why is the rubrospinal tract a ‘parallel’ system to the CST?
Both receive inputs from the cortex
Both somatotopically organised
Both mainly facilitate flexors
What is the difference between positive and negative signs?
\+ = emergence of feature - = loss of function
Name some lower motor neuron signs?
Flaccid paralysis Hypotonia Hyporeflexia Muscle weakness Fasiculuations Denervation atrophy
Why do you get fasiculuations?
Increase sensitivity to Ach at NMJ so that single muscle fibres spontaneously contract
Why do you get denervation atrophy?
Loss of trophies factors from presynaptic neuron in the NMJ
Causes of LMN signs
MND
Diabetic neuropathy
Trauma (e.g. Laceration of the median nerve)
What are some UMN signs?
Hypertonia Hyperreflexia Clonus \+ babinski sign Disuse atrophy Spastic hemiplegia Clasp knife rigidity Pronator drift
Why do you get spastic hemiplegia?
There is an increase in tone of agonist and antagonist across a joint
What is clasp knife rigidity?
Increase in stretch reflex = increase in tone
Tone continues to increase until eventually gives way
Dependant on how fast a limb is moved (the fast moved the more pronounced)
Function of rubrospinal and rubrobulbar
distal flexor muscle tone
