Motor System Flashcards
What are the 2 primary components of the Somatic motor system
Upper and lower motor neurones
Describe the location of the UMNs and LMNs in relation to the CNS and PNS
How is this relevant clinically?
- Entire UMN is in CNS
- LMN cell body is in CNS
- Proximal LMN axon is in PNS
Poorer prognosis for neurone damage if in CNS
Where are most UMN cell bodies found?
In the Primary Motor Cortex
Where are most LMN cell bodies found?
Where can the other be found?
Ventral horn of the spinal cord
Brainstem
Are there any upper motor neurones in the Basal Ganglia or Cerebellum?
No
What do the Cranial Nerve nuclei contains?
Cell bodies of lower motor neurones that distribute along the nerve
(Not CN VIII nucleus as it is purely sensory)
Which cranial nerves share an elongated nucleus?
Name the nucleus
9, 10, 11
Nucleus Ambiguus
Describe the Patellar Reflex
- Patellar ligament stretch causes stretch of Quadriceps fibres, detected by Muscle spindles
- Muscle spindles send impulses via 1st Order neurones to L3 level, where the neurones synapse with LMNs in the Ventral Horn
- LMNs leave via Ventral Root to synapse with Quadriceps fibres causing knee extension
Describe how the Hamstrings are inhibited in the Patellar Reflex
- 1st order neurones descend from L3 to L5, synapsing with inhibitory interneurons in the grey matter
- In the Ventral Horn, inhibitory interneurones synapse with LMNs innervating the Hamstring fibres
How are the Descending modulatory inputs from the brain clinically relevant with regards to reflexes?
Damage to them (during stroke) can lead to an altered/ abnormal reflex response
- Toe extension, rather than flexion in Babinski reflex
- Babies have immature descending modulatory fibres so their reflexes change as the get older
What is the Internal Capsule?
A white matter pathway that runs between the Thalamus (circular) and the Lentiform Nucleus (triangular)
List the contents of the Internal Capsule (Convergence of the Corona Radiata)
- Descending motor fibres (Axons of UMNs)
- Ascending sensory fibres (Axons of 3rd Order neurones)
(Internal Capsule contains the Medial Lemniscus)
Compare the Cerebellar and Cerebral peduncles
Cerebral Peduncle: White matter connecting a cerebral hemisphere to the Brainstem
Cerebellar Peduncle: White matter connecting a cerebellar hemisphere to the Brainstem
Describe the route of the Corticospinal Tracts up-to where it decussates
- Begin on Primary Motor Cortex
- Descend through the Corona Radiata then enter and travel through the Internal Capsule
- Continue descending to enter the Brainstem through the Cerebral Peduncle
- Descend through the Pons, enter and pass through Medullary Pyramids, then MOST AXONS decussate at The Decussation of The Pyramids
Describe the topography of the Corticospinal Tracts supplying the Upper and Lower limbs
- Corticospinal Tract fibres supplying the Upper Limbs lie Medially
- Corticospinal Tract fibres supplying the Lower Limbs lie Laterally
The decussated Corticospinal Tract fibres descend the cord, forming the Lateral Corticospinal Tract.
Which Funiculus is this within?
The Lateral Funiculus
What proportion of Corticospinal Tract fibres do not decussate at The Decussation of The Pyramids?
Where do they decussate instead?
What do they form as they descend the cord ipsilaterally ?
- 15%
- At the level of their corresponding LMN, in the Ventral Horn
- The Ventral Corticospinal Tract
Describe the fibres of the Corticospinal Tract that leave the CS pathway and synapse within the Brainstem
- These are the fibres of the Corticonuclear Pathway
- They supply LMNs present in the Cranial Nerve nuclei
What are the 2 components of the Corticospinal System?
Which is larger?
- Lateral Corticospinal Tract
- Ventral Corticospinal Tract
- Lateral is larger
Compare the musculature supplied by the Lateral and Ventral Corticospinal Tracts
Lateral: Supplies distal muscle (fine movements, such as hand/ foot/ arm/ leg)
Ventral: Supplies proximal muscle (such as at limb girdles)
Do the Cranial Nerve motor nuclei receive a Bilateral or Unilateral innervation from the Cerebral cortex?
Bilateral
Except facial nerve nucleus, whose upper half ONLY has a bilateral innervation
The Facial Nerve motor nuclei are split into 2 halves.
Compare the area innervated by each half
Upper half supplies upper face
Lower half supplies lower face
Describe the innervation of the Upper half of the Facial Nerve nuclei.
What is its clinical significance?
- Bilateral innervation, one UMN from each Cerebral Cortex
- In stroke, upper half of face is spared
Describe the innervation of the Lower half of the Facial Nerve nuclei.
What is its clinical significance?
- Only receives innervation from the Contralateral Cerebral cortex
- In stroke, lower half of face is not spared
List the 3 visible parts of the Internal Capsule on a transverse view (V shaped)
- Anterior Limb
- Genu (the ‘bend’)
- Posterior Limb
List the contents of the Anterior Limb of the Internal Capsule
- Fibres from Thalamus to Frontal Lobe (in Anterior Thalamic Radiation)
- Fibres connecting the Lentiform and Caudate nuclei
- Fibres connecting the Cortex and Corpus Striatum
List the contents of the Posterior Limb of the Internal Capsule
- Corticospinal fibres
- Sensory fibres (in Superior Thalamic Radiation)
- A few Corticobulbar fibres
List the contents of the Genu of the Internal Capsule
- Corticobulbar fibres (Between Brainstem and Cortex)
Where are the Facial Nerve Nuclei found, with reference to the Internal Capsule?
Found in the Corticobulbar Tract, within the Genu of the Internal Capsule
Compare UMN and LMN lesion with regards to;
- Power in muscles innervated
- Tone
- Rigid/ flaccid
UMN;
- Reduced (No input to LMN)
- Increased (as most are actually inhibitory)
- Rigid (due to increased tone due to decreased inhibition)
LMN;
- Reduced (No ACh at end-plate)
- Decreased
- Flaccid
Compare Fasciculations and Fibrillations
Fasciculations;
- Visible
Fibrillations;
- Detectable using electromyography
Other than impulses what is delivered to muscle fibres by LMNs?
Growth factors (hence can atrophy in LMN lesion)
An UMN lesion can lead to Hypertonia.
How may this present?
Spasticity
In Upper Limb during Hypertonia, why do we get a Flexed posture?
Flexors are more powerful than extensors, but both are affected equally
Compare UMN and LMN lesion with regards to;
- Reflexes
- Presence of fasciculations/ Fibrillations
- Atrophy
UMN;
- Increased (after Spinal Shock-after initial period of decreased reflex activity)
- Both are absent (as LMN is spared)
- Mild if present (majorly due to disuse)
LMN;
- Decreased/ absent
- Both are present (possibly due to aberrant activity/ AChR changes)
- Present
