Lecture 10: Spinal Cord and Brainstem Control of Motor Function II

Question 1

Pyramidal system definition

Answer 1

Tracts that pass through the medullary pyramids

Question 2

Components of pyramidal system

Answer 2

Corticospinal tract

Corticobulbar tract

Question 3

Upper motor neurons of pyramidal system decussate where and form what

Answer 3

75-85% decussate in pyramids and form the lateral corticospinal tracts
Remainder decussate near synapse with LMN and form anterior corticospinal tracts
Most synapse with association neurons in SC central gray

Question 4

Origins of corticospinal tract

Answer 4

Primary motor cortex
Premotor cortex
Somatosensory area

Question 5

Pathway of corticospinal tract

Answer 5

Site of origin–> internal capule–> medullary pyramids–> X in lower medulla (most fibers)–> lateral columns of spinal cord (lateral corticospinal tract)

Some fibers do not cross but continue down ipsilaterally in ventral corticospinal tract

Question 6

Lateral corticospinal tract made up of and supply what

Answer 6

Corticospinal fibers that have crossed in the medulla

Supply all levels of spinal cord

Question 7

Anterior corticospinal track made up of and supply what

Answer 7

Uncrossed corticospinal fibers that cross near level of synapse with LMN
Supply neck and upper limbs

Question 8

Functions of corticospinal tract divisions

Answer 8

Add speed and agility to conscious movements (especially in hand)
Provide high degree of motor control

Question 9

Giant pyramidal (Bertz) cells

Answer 9

Located in motor cortex
Large fibers
Send collaterals back to cortex
Synapse directly on LMNs

Question 10

Symptoms of cortical spinal tract lesions

Answer 10

Reduced muscle tone
Clumsiness
Weakness
Complete paralysis only occurs if both pyramidal and extrapyramidal systems are involved

Question 11

Corticobulbar tract

Answer 11

Upper motor neurons of the cranial nerves, innervating face, head and neck

Question 12

Corticobulbar tract fibers terminate where

Answer 12

In reticular formation near cranial nerve nuclei

Question 13

Association neurons of corticobulbar tract synapse where

Answer 13

Cranial nerve nuclei with lower motor neurons

Question 14

Corticobulbar tract lesions

Answer 14

Can affect hypoglossal nerve (CN XII)

Can affect facial nerve (CN VII)

Question 15

Extrapyramidal system

Answer 15

Descending motor tracts that do not pass through medullary pyramids or corticobulbar tracts

Question 16

Extrapyramidal system includes what tracts

Answer 16

Rubrospinal
Vestibulospinal
Reticulospinal
Olivospinal

Question 17

Extrapyramidal subcortical nuclei (taylor)

Answer 17

Thalamus
Red nucleus
Subthalamic nucleus
Caudate
Substantia niagra
Globus pallidus
Putamen

Question 18

Red nucleus description

Answer 18

Fibers from primary motor cortex (corticorubral pathways) and branches from corticospinal tract synapse in magnocellular portion of red nucleus

Question 19

Large neurons from magnocellular region of red nucleus give rise to

Answer 19

Rubrospinal tract which decussates in lower brain stem

Question 20

Magnocellular region has a ________ of all muscles of the body

Answer 20

Somatotopic representation

Question 21

Stimulation of red nucleus results in

Answer 21

Stimulation of flexors

Inhibition of extensors

Question 22

Red nucleus relays info from x to y (what are x/y?)

Answer 22

From motor cortex to cerebellum

Question 23

Rubrospinal tract originates, decussates, descends where

Answer 23

Originates in red nucleus
Decussates in midbrain
Descends in lateral funiculus
Function is closely related to cerebellum

Question 24

Rubrospinal tract responsible for

Answer 24

Large muscle movement and some fine motor of UE

Question 25

Lesions of rubrospinal tract cause

Answer 25

Impairment of distal arm/hand movement Intention tremors May take over for injured corticospinal tract in some animals

Question 26

Vestibulospinal tract originates, descends, synapses where

Answer 26

Originates in vestibular nuclei Descends in anterior funiculus Synapses with LMNs to extensor muscles (maintains upright posture)

Question 27

Vestibulospinal tract receives input from

Answer 27

``` Vestibular nerve (CN VIII) about changes in head position Helps maintain balance ```

Question 28

Lateral vestibulospinal tract characteristics

Answer 28

Major part of tract Ipsilateral To lumbar region of SC Upright posture/balance (extensors of LE/trunk)

Question 29

Medial vestibulospinal tract characteristics

Answer 29

Projects bilaterally

Question 30

Reticulospinal tract originates/descends

Answer 30

In reticular formation | Descends in lateral funiculus (column)

Question 31

Functions of reticulospinal tract

Answer 31

``` Mediates larger movement of trunk/limbs Excites axial extensors when standing Controls alpha/gamma motor neurons Mediates autonomic functions (breathing) Can modulate pain ```

Question 32

Pontine reticular nuclei

Answer 32

Make up anterior column | Stimulatory effect on both extensors/flexors but mostly extensors

Question 33

Medullary reticular nuclei

Answer 33

Make up lateral column | Inhibitory effect on both extensors/flexors but mostly extensors

Question 34

Semicircular canals detect ___ while utricle and saccule detect

Answer 34

Semicircular canals detect angular acceleration of head | Utricle and saccule detect linear acceleration of head

Question 35

Utricle and saccule each contain

Answer 35

Macula which contains hair cells

Question 36

Semicircular canal contains

Answer 36

Enlargement at one end called ampulla which has hair cells

Question 37

Function and plane of macula of utricle

Answer 37

Horizontal plane | Determining orientation of head when head is upright

Question 38

Function and plane of macula of saccule

Answer 38

Vertical plane | Signals head orientation when person is lying down

Question 39

Statoconia

Answer 39

Calcium carbonate crystals in macula | The weight of these crystals bend cilia in direction of gravitational pull

Question 40

Bending of stereocilia towards kinocilium does what

Answer 40

Opens hundreds of cation channels causing receptor membrane depolarization/excitation

Question 41

Bending of cilia in opposite direction of kinocilium does what

Answer 41

Closes channels and hyperpolarizes receptor membrane

Question 42

Semicircular canal fluid function

Answer 42

Fluid flows through the ampulla and causes cupula to bend to one side Hair cells within cupula detect bending and send signals via vestibular nerve

Question 43

Ampulla characteristics

Answer 43

Filled with endolymph Contains crista ampullaris Contains cupula above the crista

Question 44

Response of hair cell in semicircular canal with head rotation

Answer 44

At onset of rotation, cupula is dragged through endolymph and cilia are bent-depolarization When head stops, endolymph continues moving and cilia are bent in opposite direction causing hyperpolarization