Descending Pathways Flashcards
What are the two modes of motor control?
External and internal control
What is external motor control?
Sensory guided control of movement
Which parts of the brain are involved in external motor control?
Parietal cortex, premotor cortex, cerebellum
What is internal motor control?
Non-sensory guided motor control
Which parts of the brain are involved in internal motor control?
Prefrontal cortex, supplementary motor area, basal ganglia
Where do the motor projection fibers that originate in the motor travel through to enter the spinal cord?
Through the corona radiata and the internal capsule
What the axons that join cerebral hemispheres called?
Commissural fibres
What are association fibres?
Axons that connect different parts of the same cerebral hemisphere
What are motor projection fibres?
Axons that originate in the motor cortex and leave the cranium
What are upper motor neurons?
Neurons where the cell body originates in the cerebral cortex or brain stem
What are the characteristics of upper motor neurons?
Do not transmit impulses directly to the muscles
Glutamatergic
What are lower motor neurons?
Motor neurons where the cell body originates in the anterior grey column of the spinal cord, the brainstem, or cranial nerve nuclei
What are the characteristics of lower motor neurons?
Transmit impulses directly to muscles
Cholinergic
Which type of motor neuron is a first order neuron in descending tracts?
Upper motor neurons
Which type of motor neuron is a second order neuron in descending tracts?
Lower motor neurons
What is the transduction of sensory fibres that results in muscular action without the input of the brain called?
Reflex arcs
Where do pyramidal tracts synapse?
Cranial nerves or neurons in the anterior horn of spinal cord
What do pyramidal tracts control in terms of movement?
Voluntary movement
Where do most pyramidal tracts originate?
Motor cortex
Do most pyramidal tracts decussate?
Yes
What do extra-pyramidal tracts control in terms of movement?
Coordination of movement, posture control, muscle tone
Where do most extra-pyramidal tracts originate?
Brain stem
What are the two subtypes of pyramidal tracts?
Corticospinal or corticobulbar
Where are most cell bodies of pyramidal tracts located?
Precentral gyrus - primary motor cortex
Where do pyramidal tracts receive input from?
Supplementary motor area, premotor cortex fibres, parietal lobe, cingulate gyrus
Where do corticospinal pyramidal tracts originate from?
Pyramidal neurons of layer 5 of cortex
Where does the corticospinal tract receive input from?
Motor and pre-motor cortical areas
Where does the corticospinal tract travel through on its way to the spinal cord?
From cerebral cortex to the internal capsule to the cerebral peduncles to the medullary pyramids
What are the two divisions of corticospinal tracts?
Anterior corticospinal
Lateral corticospinal
What do anterior corticospinal tracts control in terms of movement?
Postural control in central axial and proximal muscles
What do lateral corticospinal tracts control in terms of movement?
Fine movement of ispilateral limbs via control of appendicular muscles
Where do anterior corticospinal tracts decussate?
Spinal cord
Where do lateral corticospinal tracts decussate?
Medullary pyramids
How do corticobulbar pyramidal tracts differ from corticospinal tracts?
Initially follows same pathway but synapses with motor nuclei of cranial nerves in upper pons
Some fibres decussate and others do not
What do corticobulbar pyramidal tracts control in terms of movement?
Voluntary muscle movement in face
What are the four extrapyramidal tracts?
Vestibulospinal
Reticulospinal
Rubrospinal
Tectospinal
What function are the extrapyramidal tracts involved in, in terms of movement?
Involuntary and automatic control of movements, posture, and muscle tone, gross motor movements
What symptoms are associated with an upper motor neuron lesion?
Spastic paralysis, hypertonia
What symptoms are associated with a lower motor neuron lesion?
Flaccid paralysis, hypotonia, muscle atrophy, loss of reflexes
A lesion on which nuclei cause bulbar palsy?
Glossopharyngeal or vagus nuclei
Hypoglossal nuclei
A lesion on which nerve causes Bell’s palsy?
Lower motor neuron lesion of the facial nerve
