Motor System Flashcards
Briefly describe the general location of the upper and lower motor neurones
Upper- entirely in the CNS
Lower- cell body and proximal part of axon in CNS
- distal part of axon in the PNS
Briefly describe why the lower motor neurone is called the final path
Activation of the neurone results in activation of skeletal muscle
Briefly describe the more specific location of the UMN and LMN cell bodies
UMN- primary motor cortex (in the precentral gyrus of the frontal lobe)
LMN- ventral horn of the spinal cord
- also in motor nuclei of brainstem
Briefly describe how the lentiform nucleus is defined
Anatomically defined:
Putamen
Globus pallidus- internal and external
Briefly describe the nigrostriatal pathway
The pathway from the substantia nigra to the striatum nucleus
Briefly describe how the striatum is defined
Functionally and evolutionarily defined
Made up of:
Putamen and caudate nucleus (they are separated by the CST)
Briefly describe the structure of the cerebellum
2 cerebellar hemispheres
Midline vermis
Briefly describe how the cerebellum attaches to the brainstem
The hemispheres attach via 3 peduncles:
Superior cerebellar peduncle- attaches to midbrain
Middle cerebellar peduncle- attaches to the pons
Inferior cerebellar peduncle- attaches to the medulla
Briefly explain which cerebellar peduncle is largest and why
The middle cerebellar peduncle
It contains the corticoponto cerebellar pathway which connects the motor cortex to the cerebellum.
Briefly describe the basal ganglia direct pathway
Putamen inhibits the internal globus pallidus, which would normally inhibit the thalamus.
As the thalamus isn’t inhibited, it can continue to stimulate the cortex.
Producing a net excitatory effect on the motor cortex.
Briefly describe the basal ganglia indirect pathway
The putamen inhibits the external globus pallidus, which would otherwise have inhibited the subthalamic nucleus.
Without this inhibition, the subthalamic nucleus stimulates the internal globus pallidus, which in turn inhibits the thalamus, preventing stimulation to the cortex.
Producing a net inhibitory effect on the motor cortex.
Describe the dopaminergic effect on basal ganglia pathways
Dopamine is released from the substantia nigra.
It acts on D1 receptors at the putamen to stimulate the direct pathway, causing an excitatory effect at the cortex.
It also acts on D2 receptors at the putamen to inhibit the indirect pathway. This also has an excitatory effect on the motor cortex (by inhibiting the inhibition of the cortex).
Briefly describe the cause of Parkinson’s disease and how the mechanism links to symptoms
Degeneration of the substantia nigra reduces dopamine release.
This means the net excitatory effect of dopamine on the primary motor cortex is lost. Decreases movement.
Causes bradykinesia.
Rigidity may be due to a lack of agonist and antagonist muscle coordination.
Psychiatric features are due to similar affected loops in the frontal lobe, involved in cognition and emotion.
Briefly describe the cause of Huntington’s chorea and how the mechanism links to symptoms
Autosomal dominant inheritance.
Degeneration of inhibitory influences from the putamen to the external globus pallidus.
So, the external globus pallidus is able to inhibit the subthalamic nucleus, which is then unable to stimulate the internal globus pallidus. Thus, the thalamus is not inhibited and is able to stimulate the cortex.
Resulting in hyperkinesis and dystonia.
Briefly describe the cause of Hemiballismus and how the mechanism links to symptoms
Lesion of subthalamic nucleus.
Globus pallidus isn’t stimulated, so is unable to inhibit the thalamus. The cortex is then stimulated by the thalamus.
This leads to involuntary, explosive unilateral movements.
Are basal ganglia lesions uni or bilateral?
Sometimes unilateral but often bilateral due to neurodegeneration.
Are cerebellar lesions uni or bilateral?
Unilateral
Briefly explain if basal ganglia lesions are ipsilateral or contralateral and why
Contralateral.
The corticostriatal and pallidothalamocortical pathway do not decussate.
The UMN then decussates at the level of the pons to supply the contralateral LMN and muscle.
Briefly explain if cerebellar lesions are ipsilateral or contralateral and why
Ipsilateral
The corticoponto cerebellar and cerebello-thalamo-cortico pathway both decussate to the contralateral cerebellum.
This means the UMN on that side then decussates at the pons, supply the same side that the previous pathways originated from.
Double decussation.
Also, sensory pathways (e.g. SCT) run to the ipsilateral cerebellar hemisphere.
What are the symptoms of a lesion in the cerebellar hemisphere?
Vomiting
Vertigo
Difficulty walking
What are the symptoms of a lesion in the vermis of the cerebellum?
DANISH - affecting the trunk
Dysdiadochokinesis- can’t perform rapid alternating movement e.g. pronation to supination
Ataxia
Nystagmus- fast towards lesion
Intention tremor- opposite to Parkinson’s
Dysarthria- larynx and pharynx muscle coordination lost
Hypotonia
What produces similar symptoms to a lesion in the vermis of the cerebellum?
Occlusions of the three cerebellar arteries- may also damage brainstem so test CNs.
Briefly describe the basic function of the basal ganglia
Inhibits inappropriate movement, via the indirect pathway to the primary motor cortex
Stimulates appropriate movement, via the direct pathway to the primary motor cortex.
Briefly describe the basic function of the cerebellum
Determines sequence of movement by integrating information form the primary motor cortex, sensory motor cortex and the spinocerebellar tracts (proprioceptors) and feeding back to the primary motor cortex.
