Upper And Lower Motor Neurones Flashcards
Where are the cell bodies of the upper + lower motor neurones located?
- upper: primary motor cortex
- lower: brain stem + ventral horn of spinal cord
Distribution of upper + lower motor neurones in CNS and PNS
- upper: only in CNS
- lower: cell bodies in CNS + axons in PNS
Where can lower motor neurones be damaged?
Severed axon
Destruction of cell body
List lower motor neurone lesion signs
- weakness
- hyporeflexia
- areflexia
- hypotonia
- muscle atrophy
- fasciculaitons
Define hyperreflexia, areflexia + hyporeflexia
- hyperreflexia: excessive reflex
- areflexia: no reflex
- hyporeflexia: reduced reflex
What are fasciciualtions?
Uncoordinated muscle contraction
Why does muscle atrophy occur in lower motor neurone lesions?
Reduce ACh to muscle at neuromuscular junction + reduction of growth factor
Why do fasciculations occur in lower motor neurone lesions?
- reduction of ACh to muscle
- upregulation of Ach receptors
- causes hypersensitivity
- uncoordinated muscle contraction
In the knee jerk reflex, for the quadriceps to contract, the hamstrings must relax. Explain the mechanism behind how this happens
- upper motor neurones at L3 cause contraction of quadriceps at
- the same UMN sends a projection to L5 + synapse at inhibitory interneurones > relaxation of hamstrings
Describe the inputs to lower motor neurones
- majority of inputs via inhibitory interneurones from upper motor neurones
- a strong excitatory input is needed to overcome inhibition to elicit a response
- net effect of UMNs on LMNs is inhibition
What pathway allows for communication between CN 3,4+6 for extra ocular eye muscle innervation?
Medial longitudinal fasciculus
What are signs of upper motor neurone lesion?
- weakness
- spasticity: hypertonia, hyper reflexia + clasp knife rigidity
- (atrophy)
- spinal shock
What is clasp knife rigidity?
- Flexed limb
- resistance to being pulled out then sudden relaxation
What is considered spasticity?
Hypertonia
Hyper reflexia
Clasp knife rigidity
What is spinal shock?
A phenomenon that occurs hours-days post upper motor neurone lesion
- initially flaccid paralysis with areflexia
- then hypertonia +hyperreflexia