descending pathways Flashcards

1
Q

what is the cortical homunculus

A

homunculus represents either the motor or the sensory distributionalong the cerebral cortex of the brain.

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2
Q

what is in the premotor cortex

A

the posterior portions of the superior, middle and inferior frontal gyri.

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3
Q

what is the function of the premotor cortex

A

the programming of and preparation for movement and in the control of posture.

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4
Q

The premotor cortex exerts its actions partly via the primary motor cortex with which it is connected by short association fibres and partly via ___________

A

via corticospinal and corticobulbar fibres.

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5
Q

what is the principal subcortical input to premotor cortical regions

A

is the ventral anterior nucleus of the thalamus

This receives fibres from the globus pallidus and substantia nigra.

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6
Q

where is the frontal eye field

A

In the middle frontal gyrus

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7
Q

where is the motor speech area

A

In the inferior frontal gyrus of the dominant hemisphere

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8
Q

what are commissural fibers

A

connect cortices of cerebral hemispheres

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9
Q

what is the largest bundle of commissural fibers

A

the corpus callosum

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10
Q

what are association fibers

A

connect regions of the cerebral cortex with one hemisphere

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11
Q

what do short association fibers connect

A

adjacent gyri

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12
Q

what do long association fibers connect

A

distant gyri (different lobes)

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13
Q

what are projection fibers

A

fibers that leave the cerebral white matter

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14
Q

what are the two categories of projection fibers

A

corticofugal and corticopedal

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15
Q

what are corticofugal projection fibers

A

terminate in the basal nuclei, brainstem or spinal cord

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16
Q

what are corticopedal projection fibres

A

originate in thalamus and terminate in cerebral cortex

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17
Q

what do motor projection fibers travel through

A

corona radiata and internal capsule

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18
Q

what are muscles innervated by

A

motor neurons in the ventral horn and motor nuclei of cranial nerves

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19
Q

what are upper motor neurons (first order neurons)

A

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.

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20
Q

where does the cell body of an upper motor neuron originate

A

originates in the cerebral cortex or brainstem

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21
Q

what are lower motor neurons (second-order neurons)

A

motor neurons that directly innervate skeletal muscle.
They constitute the so-called ‘final common pathway’ by which the nervous system controls movement.

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22
Q

where does the cell body of a lower motor neuron originate

A

originate in the grey matter of the spinal cord, brain stem or cranial nerve nuclei.

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23
Q

describe the reflex arc

A

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)

24
Q

what are the two pyramidal tracts

A

Corticospinal and corticobulbar

25
Q

what do corticobulbar fibers control

A

control the activity of motor neurons located in cranial nerve nuclei which innervates skeletal muscles of the head and neck through the cranial nerves.

26
Q

what do corticospinal fibers control

A

the activity of motor neurons in the spinal cord which innervate trunk and limb muscles.

27
Q

where are most of the cell bodies of the pyramidal tracts located

A

on precentral gyrus

28
Q

where does the corticospinal tract travel

A

brain to spinal cord
through internal capsule to the cerebral peduncles and come to lie on ventral surface of medulla (the pyramids)

29
Q

where does the corticobulbar tract travel

A

brain to crainal nerves

30
Q

what does the corticospinal tract receive input from

A

somatosensory cortex, parietal lobe and cingulate sinus

31
Q

where does the corticospinal tract originate

A

layer 5 of cortex, internal pyramidal layer

32
Q

what does the anterior/ventrak corticospinal tract control

A

trunk muscles
posture control

33
Q

where do anterior corticospinal fibers decussate

A

in the spinal cord

34
Q

where do lateral corticospinal fibers decussate

A

in the pyramids

35
Q

what does the lateral corticospinal tract control

A

appendicular muscles for fine movemnet of ipsilateral limbs

36
Q

what crainal nerves does the corticobulbar tract carry upper motor neuron input to

A

to motor nuclei oftrigeminal, facial, glossopharyngeal, vagus, accessory, and hypoglossal nerves.

37
Q

where does the corticobulbar tract synapse

A

with the motor nuceli of the cranial nerves beginning at the level of the upper pons

38
Q

name a clinical context for the pyramids

A

Upper and lower motor neuron lesions
upper: causes spastic paralysis
loweer: causes flaccid paralysis

39
Q

what are bulbar lesions

A

injuries to cranial nerve nuceli or axons of glossopharyngeal, vagus or hypoglossal nerve

40
Q

what is the function of the extrapyramidal tracts

A

involuntary and automatic control movements, posture and muscle tone

41
Q

what are 4 extrapyramidal tracts

A

vestibulospinal
reticulospinal
rubrospinal
tectospinal

42
Q

what structures are involved with the extrapyramidal

A

basal ganglia
red nucleus
substantia nigra
reticular formation
cerebellum

43
Q

where does the vestibulospinal tract axons arise from

A

vestibular nuclei located in pons and medulla

44
Q

Vestibular nuclei recieve sensory input from_________

A

the inner ear and cerebellum

45
Q

what is the function of the vestibulospinal tract

A

conveys balance information to spinal cord, ipsilateral

46
Q

where does the rubrospinal tract begin

A

red nucleus of midbrain

47
Q

what is the function of the rubrospinal tract

A

plays a role in fine control of the hand, contralateral

48
Q

where does the reticulospinal tract begin

A

reticular formation of the pons

49
Q

what is the function of the reticulospinal tract

A

medial fibres excite voluntary movements
lateral fibres inhibit voluntray movements

50
Q

what does the tectospinal tract begin

A

superior colliculi

51
Q

what is the function of the tectospinal tract

A

recieves input from optic nerves, coordinates head movement in relation to visual stimuli

52
Q

name a extrapyramidal syndrome

A

parkinsons

53
Q

describe the path of the Rubrospinal tract

A
  1. red nucleus
  2. descend through the pons and medulla oblongata to enter the lateral funiculus of the spinal cord
  3. terminate by synapsing with internuncial neurons in the anterior gray column,
54
Q

describe the path of the lateral Vestibulospinal tract

A

tract arises from the lateral vestibular nucleus and descends along the periphery of the anterior white column of the spinal cord

55
Q

describe the path of the medial Vestibulospinal tract

A

arises from the medial vestibular nucleus and descends within the medial longitudinal fasciculus of the brainstem

56
Q

describe the path of the tectospinal tract

A
  1. superior colliculus, where it receives information from the retina and cortical visual association areas. 2. project to the contralateral side of the midbrain
  2. descend within the medial longitudinal fasciculus into the ventral funiculus of the cervical spinal cord.