Motor Neurone disease Flashcards
What is a neuron?
A nerve cell
What is a motor neuron?
A nerve CELL that forms part of a nerve that transmits information from the motor cortices in the brain to the muscles
Are motor neurons afferent or efferent?
Efferent
They take information FROM the spinal cord to the muscles
What 2 types of motor neuron are there? Describe the difference?
Upper motor neuron: from the motor cortex to the level of exit from the spinal cord
Lower motor neuron: from the spinal cord to the muscle
Describe the journey of a motor impulse from the motor cortex to the muscle?
Which parts of the journey involve upper and lower motor neurons?
UPPER MOTOR NEURON:
Motor cortex
Corona radiata
Internal capsule
Through the brainstem
Into spinal cord where it travels down in it’s tract, e.g. corticospinal tract
Synapses with a lower motor neuron
LOWER MOTOR NEURON
Leaves the spinal cord and travels to the muscle
Define paresis?
Weakness
Impaired ability to move a body part in response to will
Define paralysis?
Complete inability to move a body part in response to will
Define ataxia?
Incoordination
Willed movements are clumsy, ill-directional
Define involuntary movement?
A spontaneous movement of a body part, independently of will
Define apraxia?
Difficulty with the motor planning needed to perform tasks or movements
It’s a bit confusing, motor neurons are actually the cell rather than the nerve, but there is misuse of the word.
Where are the lower motor neuron CELL bodies found?
Either in the anterior horn of spinal cord
Or in the cranial nuclei in the brainstem
How is muscle tone regulated?
Draw out a diagram.
By muscle spindles - stretch receptors in cells
They detect stretch and send information to spinal cord via sensory neurons
There it synapses with interneuron
Which synapses with the (gamma) motor neuron which goes back to the muscle and makes it contract
Which motor neuron’s innervate muscle spindles?
Gamma motor neurons
What problems occur in lower motor neuron disorders?
Everything goes down
Muscle tone goes down
Muscle wasting
Reflexes depressed
Also, fasciculation
What problems occur in upper motor neuron disorders?
Everything goes up
Muscle tone increase
Tendon reflexes increase
Emotional lability increased
Which motor tract controls the muscles of the head and neck?
Corticobulbar tract
Define spasticity?
When certain muscles are continuously contracted.
This causes stiffness or tightness of the muscles
It can interfere with normal movement, speech, and gait.
Define flaccidity?
No muscle contraction is occurring so there is no muscle tone
This causes weakness, floppiness and paralysis
Why does an upper motor neuron lesion causes spasticity?
UMN lesion prevents impulses getting from the brain to the muscle via the cort-spin tract
BUT it will not prevent impulses getting to muscle from the reflex arc
ALSO since the cort-spin tract is not working, it is not able to inhibit excess reflexes caused by the reflex arc
SO you get continual muscle contraction caused by the now uninhibited reflex arc = spasticity
Why does a lower motor neuron lesion cause flaccidity?
LMN lesion prevents impulses getting from the brain to the muscle via the cort-spin tract
AND it prevents impulses getting to the muscle from the reflex arc, since the LMN is part of the reflex arc
SO the muscles receive no impulses at all, no muscle contraction = flaccidity