descending pathways

Question 1

what is the cortical homunculus

Answer 1

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

Question 2

what is in the premotor cortex

Answer 2

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

Question 3

what is the function of the premotor cortex

Answer 3

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

Question 4

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

Answer 4

via corticospinal and corticobulbar fibres.

Question 5

what is the principal subcortical input to premotor cortical regions

Answer 5

is the ventral anterior nucleus of the thalamus

This receives fibres from the globus pallidus and substantia nigra.

Question 6

where is the frontal eye field

Answer 6

In the middle frontal gyrus

Question 7

where is the motor speech area

Answer 7

In the inferior frontal gyrus of the dominant hemisphere

Question 8

what are commissural fibers

Answer 8

connect cortices of cerebral hemispheres

Question 9

what is the largest bundle of commissural fibers

Answer 9

the corpus callosum

Question 10

what are association fibers

Answer 10

connect regions of the cerebral cortex with one hemisphere

Question 11

what do short association fibers connect

Answer 11

adjacent gyri

Question 12

what do long association fibers connect

Answer 12

distant gyri (different lobes)

Question 13

what are projection fibers

Answer 13

fibers that leave the cerebral white matter

Question 14

what are the two categories of projection fibers

Answer 14

corticofugal and corticopedal

Question 15

what are corticofugal projection fibers

Answer 15

terminate in the basal nuclei, brainstem or spinal cord

Question 16

what are corticopedal projection fibres

Answer 16

originate in thalamus and terminate in cerebral cortex

Question 17

what do motor projection fibers travel through

Answer 17

corona radiata and internal capsule

Question 18

what are muscles innervated by

Answer 18

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

Question 19

what are upper motor neurons (first order neurons)

Answer 19

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.

Question 20

where does the cell body of an upper motor neuron originate

Answer 20

originates in the cerebral cortex or brainstem

Question 21

what are lower motor neurons (second-order neurons)

Answer 21

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

Question 22

where does the cell body of a lower motor neuron originate

Answer 22

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

Question 23

describe the reflex arc

Answer 23

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)

Question 24

what are the two pyramidal tracts

Answer 24

Corticospinal and corticobulbar

Question 25

what do corticobulbar fibers control

Answer 25

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

Question 26

what do corticospinal fibers control

Answer 26

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

Question 27

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

Answer 27

on precentral gyrus

Question 28

where does the corticospinal tract travel

Answer 28

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

Question 29

where does the corticobulbar tract travel

Answer 29

brain to crainal nerves

Question 30

what does the corticospinal tract receive input from

Answer 30

somatosensory cortex, parietal lobe and cingulate sinus

Question 31

where does the corticospinal tract originate

Answer 31

layer 5 of cortex, internal pyramidal layer frontal cortices

Question 32

what does the anterior/ventrak corticospinal tract control

Answer 32

trunk muscles posture control

Question 33

where do anterior corticospinal fibers decussate

Answer 33

in the spinal cord

Question 34

where do lateral corticospinal fibers decussate

Answer 34

in the pyramids

Question 35

what does the lateral corticospinal tract control

Answer 35

appendicular muscles for fine movemnet of ipsilateral limbs

Question 36

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

Answer 36

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

Question 37

where does the corticobulbar tract synapse

Answer 37

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

Question 38

name a clinical context for the pyramids

Answer 38

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

Question 39

what are bulbar lesions

Answer 39

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

Question 40

what is the function of the extrapyramidal tracts

Answer 40

involuntary and automatic control movements, posture and muscle tone

Question 41

what are 4 extrapyramidal tracts

Answer 41

vestibulospinal reticulospinal rubrospinal tectospinal

Question 42

what structures are involved with the extrapyramidal

Answer 42

basal ganglia red nucleus substantia nigra reticular formation cerebellum

Question 43

where does the vestibulospinal tract axons arise from

Answer 43

vestibular nuclei located in pons and medulla

Question 44

Vestibular nuclei recieve sensory input from_________

Answer 44

the inner ear and cerebellum

Question 45

what is the function of the vestibulospinal tract

Answer 45

conveys balance information to spinal cord, ipsilateral

Question 46

where does the rubrospinal tract begin

Answer 46

red nucleus of midbrain

Question 47

what is the function of the rubrospinal tract

Answer 47

plays a role in fine control of the hand, contralateral

Question 48

where does the reticulospinal tract begin

Answer 48

reticular formation of the pons

Question 49

what is the function of the reticulospinal tract

Answer 49

medial fibres excite voluntary movements lateral fibres inhibit voluntray movements

Question 50

what does the tectospinal tract begin

Answer 50

superior colliculi

Question 51

what is the function of the tectospinal tract

Answer 51

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

Question 52

name a extrapyramidal syndrome

Answer 52

parkinsons

Question 53

describe the path of the Rubrospinal tract

Answer 53

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,

Question 54

describe the path of the lateral Vestibulospinal tract

Answer 54

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

Question 55

describe the path of the medial Vestibulospinal tract

Answer 55

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

Question 56

describe the path of the tectospinal tract

Answer 56

1. superior colliculus, where it receives information from the retina and cortical visual association areas. 2. project to the contralateral side of the midbrain 3. descend within the medial longitudinal fasciculus into the ventral funiculus of the cervical spinal cord.