motor pathways Flashcards
what are descending tracts?
-pathways by which motor signals are sent from the brain to lower motor neurones
- the lower motor neurones then directly innervate muscles to produce mvt
what 2 groups are the motor tracts divided into?
- pyramidal tracts
-extrapyramidal tracts
what are pyramidal tracts?
-descending tracts that originate in the cerebral cortex, carrying motor fibres to the spinal cord and brain stem
-they are responsible for the voluntary control of the musculature of the body and face
what are extrapyramidal tracts?
-these tracts originate in the brain stem, carrying motor fibres to the spinal cord
-responsible for the involuntary and automatic control of muscles such as muscle tone, balance etc
are there synapses within the descending pathways?
no, except at the termination of the descending tracts, the neuron’s synapse with a lower motor neurone
what do ‘pyramidal tracts’ derive their name from?
medullary pyramids of the medulla oblongata which they pass through
what can the pyramidal tracts be subdivided into?
- pyramidal system is divided based on cranial nerves and spinal nerves
corticobulbar tracts
-corticospinal tracts
what are corticobulbar tracts?
group of upper cranial motor nerves that start in the cortex and end in the brainstem
what are the corticospinal tracts?
-group of upper motor nerves that start in the cortex and end in the spinal cord
how many neutrons are there in the descending pathways and what are they called?
- 2 neurons
-upper motor neurons
-lower motor neurons
what are upper motor neurons?
neurons from cerebral cortex too the brainstem (cranial nerve) or the spinal cord (spinal nerve)
what are lower motor neurons ?
-neurons going to innervate the muscle from the brainstem cranial nerve motor nucleus or from the anterior horn cell of the spinal cord
where do the corticospinal tracts begin and where do they receive inputs from?
-they begin in the cerebral cortex
-they receive inputs from the primary motor cortex, premotor cortex and supplementary motor area
what is the internal capsule?
a white matter pathway located between the thalamus and the basal ganglia
in the corticospoinal tract, after the neurons move from the cerebral cortex, where do they travel to?
- they go to the internal capsule
-after the IC, they pass through the crus cerebra of the midbrain, the pons and into the medulla
what happens to the cortciospinal tract once it reaches the medulla?
it divides into 2 - the lateral corticospinal tract and the anterior corticospinal tract
Describe the lateral corticospinal tract
-larger of the 2 tracts
-it descends on the lateral part of the spinal cord
-fibres then cross over to the opposite side of the body at the level pf the medulla
-the fibres then synapse with the lower motor neurons of the ventral horn of the cord
-lower motor neurons then innervate the muscles, leading to voluntary control
describe the anterior corticospinal tract
-smaller in comparison to the lateral corticospinal tract
-descends on the anterior/ventral side of the spinal cord
-fibres dont cross over like lateral pathway, but they continue to descend ipsilaterally for a distance before crossing over @ level of cord
-fibres eventually synapse with lower motor neurons in the ventral horn of cord
what is the function of the corticobulbar tracts?
-These tracts are involved in the control of movements of the head, face, and neck, as well as certain functions related to speech, swallowing, and facial expressions.
- Unlike the corticospinal tracts, which primarily control movements of the limbs and trunk, the corticobulbar tracts control movements of the head and face.
what is a upper motor neuron lesion?
-damage or dysfunction to the upper motor neurons in the brain or spinal cord
-can occur due to trauma, stroke, spinal cord injury
Describe an upper motor lesion the cerebral hemisphere
-lesions in the cerebral hemisphere (specifically the motor cortex) can lead to motor deficits on the contralateral side of the body
-ie if lesion occurs in the left hemisphere, the deficits will be on the right side of the body
describe an upper motor lesion in the spinal cord
- lesion in the spinal cord - then there is ipsilateral deficits
-lesions in the spinal cord will affect upper motor neurons as they descend from the brain to synapse with lower motor neurons of the cord
what are examples of symptoms associated with UMN lesions in the spinal cord?
- initial weakness / paralysis
-hypertonicity - increased muscle tone
-hyperreflexia (exaggerated response of reflexes)
-clonus -rhythmic, involuntary contraction & relaxation of muscle
-babinskis response (extension of the big toe and fanning of other toes)
what is a lower motor lesion?
-damage of dysfunction of the lower motor neurones which innervate muscles
- can occur at various levels eg in the spinal cord or in the peripheral nerves
