descending pathways Flashcards
what is the cortical homunculus
homunculus represents either the motor or the sensory distributionalong the cerebral cortex of the brain.
what is in the premotor cortex
the posterior portions of the superior, middle and inferior frontal gyri.
what is the function of the premotor cortex
thought to function in the programming of and preparation for movement and in the control of posture.
The premotor cortex exerts its actions partly via the primary motor cortex with which it is connected by short association fibres and partly via ___________
via corticospinal and corticobulbar fibres.
what is the principal subcortical input to premotor cortical regions
is the ventral anterior nucleus of the thalamus
This receives fibres from the globus pallidus and substantia nigra.
where is the frontal eye field
In the middle frontal gyrus
where is the motor speech area
In the inferior frontal gyrus of the dominant hemisphere
what are commissural fibers
connect cortices of cerebral hemispheres
what is the largest bundle of commissural fibers
the corpus callosum
what are association fibers
connect regions of the cerebral cortex with one hemisphere
what do short association fibers connect
adjacent gyri
what do long association fibers connect
distant gyri (different lobes)
what are projection fibers
fibers that leave the cerebral white matter
what are the two categories of projection fibers
corticofugal and corticopedal
what are corticofugal projection fibers
terminate in the basal nuclei, brainstem or spinal cord
what are corticopedal projection fibres
originate in thalamus and terminate in cerebral cortex
what do motor projection fibers travel through
corona radiata and internal capsule
what are muscles innervated by
motor neurons in the ventral horn and motor nuclei of cranial nerves
what are upper motor neurons (first order neurons)
are the neurons that control the activity of lower motor neurons and do not transmit impulses directly to muscles.
They form a number of descending tracts that run through the brainstem and spinal cord. Among the most important of these are the corticospinal and corticobulbar tracts.
where does the cell body of an upper motor neuron originate
originates in the cerebral cortex or brainstem
what are lower motor neurons (second-order neurons)
motor neurons that directly innervate skeletal muscle.
They constitute the so-called ‘final common pathway’ by which the nervous system controls movement.
where does the cell body of a lower motor neuron originate
originate in the grey matter of the spinal cord, brain stem or cranial nerve nuclei.
describe the reflex arc
a receptor picks up a stimulus (e.g. pain from hot iron) > Sensory neuron sends afferent signal to the Integration centre (interneuron) in spinal cord > Lower motor neuron then sends an efferent signal > effector (muscle to move hand away from hot iron)
what are the two pyramidal tracts
Corticospinal and corticobulbar
what do corticobulbar fibers control
control the activity of motor neurons located in cranial nerve nuclei which innervates skeletal muscles of the head and neck through the cranial nerves.
what do corticospinal fibers control
the activity of motor neurons in the spinal cord which innervate trunk and limb muscles.
where are most of the cell bodies of the pyramidal tracts located
on precentral gyrus
where does the corticospinal tract travel
brain to spinal cord
through internal capsule to the cerebral peduncles and come to lie on ventral surface of medulla (the pyramids)
where does the corticobulbar tract travel
barin to crainal nerves
what does the corticospinal tract receive input from
somatosensory cortex, parietal lobe and cingulate sinus
where doe sthe corticospinal tract originate
layer5 of cortex, internal pyramidal layer
what does the anterior/ventrak corticospinal tract control
central axial and proximal muscles involoved in postural control
where do anterior corticospinal fibers decussate
in the spinal cord
where do lateral corticospianl fibers decussate
in the pyramids
what does the lateral corticospinal tract control
appendicular muscles for fine movemnet of ipsilateral limbs
what crainal nerves does the corticobulbar tract carry upper motor neuron input to
to motor nuclei oftrigeminal, facial, glossopharyngeal, vagus, accessory, and hypoglossal nerves.
where doe sthe corticobulbar tract synapse
with the motor nuceli of the cranial nerves beginning at the level of the upper pons
name a clinical context for the pyramids
Upper and lower motor neuron lesions
upper: causes spastic paralysis
loweer: causes flaccid paralysis
what are bulbar lesions
injuries to cranial nerve nuceli or axons of glossopharyngeal, vagus or hypoglossal nerve
