Spinal Cord (Week 1 and 2--Houser and Bisley)

Question 1

Subarachnoid space

Answer 1

Deep to aracnhoid meninges

Contains CSF

Contains nerve roots that compose cauda equina

Question 2

Where are gray and white matter in the spinal cord?

Answer 2

Gray matter is the “H” in the center

White matter surrounds cord on the outside

(Note: this is opposite from the brain where gray matter is outside and white matter is inside)

Question 3

Regions of the spinal cord

Answer 3

Gray matter: dorsal/ventral/lateral horns

White matter: columns, fasciculi

Note: dorsal = posterior; ventral = anterior

Question 4

Sensory nerves with cell bodies in DRG go where?

Answer 4

Some go to dorsal horn, others go to dorsal column

(Also remember that sensory cells of DRG are pseudounipolar)

Question 5

Motor neurons with cell bodies in ventral horn go where?

Answer 5

To skeletal muscle

Question 6

Symp pre fibers from lateral horn (only T1-L2/3) go where?

Answer 6

To autonomic ganglia then to viscera

Question 7

Spinal cord segments

Answer 7

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

Question 8

Gray matter of the spinal cord–dorsal horn

Answer 8

“H” in middle of spinal cord

Somatosensory

Gets input from DRG cells and neurons that participate in further processing of sensory information

Subdivision of dorsal horn into nuclei or laminae (Rexed’s cyto-architectonic description)

Includes substantia gelatinosa (which has lots of cell bodies and is important for processing sensory information)

Question 9

Gray matter of the spinal cord–ventral horn

Answer 9

Motor neurons that control skeletal muscles

Alpha motor neurons have large axons and innervate striated muscles (“final common path” of motor system)

Gamma motor neurons are smaller and innervate muscle spindle (sensory structure within skeletal muscles that contributes to muscle tone but does not directly cause contraction of skeletal muscle)

Motor neurons organized into columns or motor pools associated with certain muscle groups: proximal muscles medially in ventral horn, distal muscles laterally in ventral horn, flexor muscles dorsally in ventral horn, extensor muscles ventrally in ventral horn

Question 10

Gray matter of the spinal cord–intermediate gray matter

Answer 10

Between dorsal and ventral horns

Contains interneurons that link sensory function to motor function

Many “polysynaptic” spinal reflexes involve interneurons in this region

Many descending pathways form contacts with neurons in this region

Note: interneurons form synaptic connections within same segment as well as in more distal segments of spinal cord

Question 11

Gray matter of the spinal cord–lateral horn

Answer 11

Within intermediate zone of gray matter

Only in thoracic and upper lumbar segments

Mediates visceral motor function

From T1-L2 or L3, sympathetic preganglionic neurons form a column of cells (intermediolateral cell column) that occupies lateral horn –> axons exit thru ventral roots

Neurons in corresponding region of S2-4 form a sacral parasympathetic nucleus but do not form a distinct lateral horn

Question 12

White matter of spinal cord

Answer 12

Contains columns (funiculi) in which axons ascend or descend

Dorsal columns: major sensory pathway divided into fasciculus gracilis (found at all levels and more medial) and fasciculus cuneatus (only in cervical and upper thoracic (to T6) levels; wedge-shaped)

Lateral and ventral columns: contain several motor and sensory tracts (location cannot be determined in conventional sections but has been shown experimentally)

Propriospinal system/fasciculus proprius: forms thin shell around gray matter; fibers interconnect different spinal cord levels

Question 13

Why is amount of white matter greatest in cervical cord?

Answer 13

Everything has to synapse in the brain so there is the highest traffic of myelinated axons in the cervical region

Question 14

Why are some ventral horns larger at some levels than others?

Answer 14

Some spinal segments innervate more muscle than others

Ex: cervical has big ventral horn because lots of muscles to supply but thoracic has small ventral horn because muscles don’t need fine detail control

Question 15

Anterior median septum

Answer 15

Break in spinal cord between two ventral horns

Where arterial supply to spinal cord is? Anterior spinal artery comes from 2 branches off vertebral artery that come together to form anterior spinal artery?

Question 16

Classification of peripheral nerve fibers

Answer 16

Ia: sensory; muscle spindle primary endings

Ib: sensory; golgi tendon organs

alpha: motor; efferents to extrafusal muscle fibers

gamma: motor; efferents to intrafusal muscle fibers

Question 17

Do reflexes require higher brain centers to operate?

Answer 17

No!

“Spinal cord” reflexes!

Reflexes can be modulated by descending influences from more rostral brain regions, but do not require them

Question 18

How many neurons do reflexes utilize?

Answer 18

One class of spinal cord reflexes uses only one synapse between sensory and motor elements (monosynaptic reflex)

However, most reflexes involve one or more interneurons within the pathway (polysynaptic reflexes)

Question 19

Ways to classify axons within a peripheral nerve

Answer 19

Letters (for sensory and motor fibers): Group A-B are larger fibers that are myelinated and have highest conduction velocities; Group C are smallest fibers that are unmyelinated

Roman numerals (sensory fibers only): Groups I-IV

Question 20

3 basic spinal cord reflexes

Answer 20

1) Stretch reflex
2) Golgi tendon organ reflex
3) Flexor withdrawal reflex

Question 21

Major components of stretch reflex (deep tendon reflex)

Answer 21

1) Muscle spindle: connective tissue capsule that encloses intrafusal muscle fibers; receives sensory innervation from primary and secondary nerve (afferent?) fibers; receives motor innervation from small gamma motor neurons; is located within regular skeletal muscle and attached to muscle fibers by connective tissue; spindles in parallel with regular muscle fibers
2) Ia primary afferent fibers: have primary ending wrapped around intrafusal fiber; form excitatory connections with alpha motor neurons; send projections to dorsal nucleus of Clarke; send excitatory connections to motor neurons of synergistic muscles; send inhibitory (disynaptic) signals to motor neurons of antagonistic muscles
3) Gamma motor neurons: innervate polar ends of intrafusal muscle fibers so can influence sensitivity of muscle spindle; do not innervate regular muscle fibers directly; not contacted by primary sensory endings; innervated by other afferents from dorsal roots and by descending motor pathways that influence both alpha and gamma motor neurons

Question 22

4 things the Ia fiber sends signals to

Answer 22

First, the Ia fiber senses stretch of the primary endings of the muscle spindle (?), then it sends signals:

1) Alpha motor neuron to same muscle
2) Dorsal nucleus of Clarke in dorsal horn (–> alpha motor neuron goes up dorsal spinocerebellar tract); also up dorsal column for proprioception
3) Alpha motor neuron to synergistic muscle
4) Inhibitory Ia nerve –> alpha motor neuron to antagonist muscles

Question 23

Gamma motor neuron

Answer 23

Influence sensitivity of muscle spindle

Sense stretch of intrafusal fibers with sensory endings that are wrapped around intrafusal fibers

Produce contractions at polar ends of muscle spindle (this makes it easier to activate the stretch reflex, doesn’t contract the muscle itself!!)

Not contacted by primary afferent Ia fibers

Activated by descending motor pathways and other afferents from dorsal roots (cutaneous afferents)

Ensures that we can still signal length of muscle even when muscle contracted (without gamma motor neuron, would have no afferent activity coming in!)

Could contribute to hyperreflexia if over-active!

Question 24

Effects of stretch and contraction on discharge rate of Ia afferent fibers from muscle spindle

Answer 24

Stretch of muscle = stretch of spindle = increased discharge rate of Ia fiber

Contraction of muscle = decreased stretch of spindle = decreased discharge rate of afferent Ia fiber

Makes sense because muscle spindle reflex CONTRACTS the muscle

Question 25

What does the gamma motor system do during muscle contraction in the “silent” period of Ia afferents

Answer 25

Gamma motor system fills in continued discharge because it is activated by polar ends of spindle

Muscle spindle can respond to chanes in load by providing information to us about muscle length

Question 26

Roles of the muscle spindle in motor control

Answer 26

Negative feedback system that monitors muscle length

1) Participate in automatic adjustments of body to maintain posture (need something operating on a lower level to help us maintain balance)
2) Compensate for changes in load during motor activity
3) Contribute to normal muscle tone
4) Contribute to sense of limb position and movement (proprioception and kinesthesia)

Question 27

What do primary afferent fibers of the muscle spindle respond to?

Answer 27

Stretch of the regular muscle fibers

Contraction of the polar ends of the spindle (intrafusal muscle fiber)

Question 28

Do gamma motor neurons contribute directly to muscle tension?

Answer 28

No

They exert their effects through the stretch reflex pathway

Question 29

What initiates the stretch reflex?

Answer 29

Tendon tap stretches the muscle

You’re tapping the tendon but it’s really the muscle that is the site of action

Question 30

Extrafusal vs. intrafusal muscle fibers

Answer 30

Extrafusal = regular muscle fibers

Intrafusal = muscle spindle = in parallel with extrafusal muscle fibers

Question 31

Why does afferent activity stop after stimulating alpha motor neuron if there is NOT gamma motor neuron there?

Answer 31

Because as soon as muscle contracts, you obviously have no stretch of the muscle anymore so those sensory afferent wrappings from the alpha motor neuron are not stimulated

Question 32

Muscle tone

Answer 32

Resistance you feel either actively or passively to movement of the limb

In normal muscles we have little contractions going on all the time so we can respond by holding up our arm if examiner drops it

Note: hypotonia if you let go of arm and totally falls down

Question 33

Golgi tendon organ

Answer 33

Found near tendinous ends of skeletal muscles

Located in series with regular muscle fibers

Info from these receptors conveyed to spinal cord by Ib afferent fibers

Cell body in DRG, comes into dorsal horn, hits Ib inhibitory interneuron INHIBITS alpha motor neuron (also hits excitatory neurons to antagonist muscles!)

Question 34

Gogli tendon organ reflex

Answer 34

Responds to muscle tension and monitors/maintains muscle force

Golgi tendon organs are sensitive to muscle contraction (and fire more when muscle contracted)

Muscle contraction stimulates golgi tendon organ afferent to inhibit muscle from contracting more and to stimulate antagonist muscles to work against original muscle

Question 35

Roles of the golgi tendon organ

Answer 35

Provides negative feedback to regulate muscle tension

Helps maintain steady level of force

Contributes to fine adjustments in the force of contraction

Prevents muscles from generating excessive tension

Question 36

What happens regarding muscle spindle and golgi tendon organ when the muscle is stretched?

Answer 36

Muscle spindle: fires more

Golgi tendon organ: fires only a little more

Question 37

What happens regarding muscle spindle and golgi tendon organ when the muscle is contracted?

Answer 37

Muscle spindle: does not fire at all

Golgi tendon organ: fires a lot more

Question 38

Flexion withdrawal reflex

Answer 38

What lets you pull your foot away after stepping on a pin before you even realize you’ve stepped on it

Mediated by somatic afferents carrying nociceptive information

Since muscles at different joints involved, this reflex involves multiple segments of the spinal cord (afferent fibers enter spinal cord and course up and down within dorsolateral fasciculus)

Question 39

How does the flexion withdrawal reflex work?

Answer 39

Polysynaptic excitation of alpha motor neurons to approppriate muscles for withdrawal of limb from stimulus

Polysynaptic inhibition of motor neurons of antagonistic muscles

Opposite pattern on contralateral side leading to a crossed extension response

Question 40

Central pattern generators

Answer 40

Local circuits within the spinal cord that can control complex, rhythmic patterns of movement, such as those in locomotion

Ex: dog had complete transection of spinal cord but if on treadmill, still got rhythmic movement of limbs

Question 41

Major MOTOR pathways of the spinal cord

Answer 41

Corticospinal pathway (lateral pathway) = major motor pathway!

Rubrospinal (lateral pathway, origin at red nucleus)

Vestibulospinal (medial pathway, origin at lateral vestibular nucleus)

Medullary reticulospinal (medial pathway, origin at reticular formation of the medulla)

Pontine reticulospinal (medial pathway, origin at reticular formation of the pons)

Tectospinal (medial pathway)

Question 42

Where is the location in the spinal cord of the lateral corticospinal tract?

Answer 42

In the lateral column of the spinal cord (right next to rubrospinal tract!)

There is no distinction to tell you exactly where it is

Question 43

Where are the cell bodies of the corticospinal tract located

Answer 43

Pathway originates in cerebral cortex from neurons in area 4 (primary motor), 6 (supplementary motor region), 3,1,2 (primary somatosensory area), 5 (adjacent parietal area)

Many are in area 4 (primary motor area) or the precentral gyrus of the frontal lobe

Note: face and upper limb on lateral surface; lower limb on medial surface

Question 44

What movements is the lateral corticospinal tract responsible for?

Answer 44

Voluntary motor control

Question 45

Simple pathway of lateral corticospinal tract

Answer 45

Cortex

Cerebral peduncle

Basal pons

Pyramid

Pyramidal decussation

Lateral corticospinal tract in spinal cord

Question 46

Details of pathway of lateral corticospinal tract

Answer 46

1) Originate in cerebral cortex from neurons in area 4, 6, 3, 1, 2, 5
2) Axons of those neurons leave cerebral cortex and converge in posterior limb of internal capsule
3) Reach midbrain, fibers are concentrated in central part of basis pedunculi (base of cerebral peduncle)
4) Reach pons, fibers diverge and descend in small bundles (located between transverse fibers of basis pontis that enter cerebellum)
5) Reach medulla, form group of fibers again in pyramid of medulla (remember, ventral surface)
6) Reach caudal medulla, fibers cross midline in decussation of pyramids and become more dorsolateral within lateral column of spinal cord
7) In spinal cord, fibers descend within lateral corticospinal tract (in lateral columns) until they reach appropriate level of spinal cord for termination. Then they move into gray matter where they form synaptic contacts with (1) alpha motoneurons of ventral horn, (2) interneurons in intermediate zone which then contact motoneurons, (3) neurons in base of dorsal horn for modulation of somatosensory information

Question 47

Where else can the corticospinal fibers go?

Answer 47

1) Majority cross in the decussation of pyramids (85%)
2) Very small portion remain ipsilateral and descend in lateral column without crossing
3) Remaining fibers form anterior corticospinal tract and continue to be uncrossed until they reach their level of termination in the spinal cord where they cross (or bilateral termination). Note: these fibers synapse on motoneurons or interneurons that supply proximal musculature and thus are functionally related to medial pathways

Question 48

Functions of lateral corticospinal tract

Answer 48

1) Facilitatory effects on flexor muscles and distal muscles
2) Necessary for isolated and skilled movements of digits
3) Voluntary, goal-directed or skilled movements

Question 49

2 things that we consider when classifying motor disorders

Answer 49

1) Ability to produce desired movements (weakness or paralysis)
2) Muscle tone

Question 50

Muscle tone

Answer 50

Normal resistance of a muscle to active or passive stretch

Question 51

2 factors that influence muscle tone

Answer 51

1) Inherent viscoelestac properties of the muscle
2) Tension set up by contraction of a small number of skeletal muscle fibers

Note: can be influenced by alterations in local reflexes (reflex arc) and descending pathways

Question 52

Clinical terms for alterations in muscle tone

Answer 52

Absent or decreased tone: atonia, hypotonia, flaccidity

Increased tone (spasticity or rigidity): hypertonia

Question 53

Lower motor neuron signs

Answer 53

Result from damage of alpha motor neurons (cell bodies or axons) that innervate skeletal muscle

Paralysis or paresis

Decreased strength

Hyporeflexia

Hypotonia

Atrophy of muscles

Fibrillations and fasciculations

Question 54

Upper motor neuron signs

Answer 54

Result from damage of multiple descending motor pathways (both excitatory and inhibitory on spinal cord circuitry)

Reflect loss of normal balance of excitatory and inhibitory inputs to motor neurons in favor of increased excitability of spinal level reflexes (must be increased excitation (facilitation) or decreased inhibition of alpha or gamma motor neurons)

Paralysis or paresis

Decreased strength

Hyperreflexia

Hypertonia (spasticity)

Minimal (disuse) atrophy

Babinski response (extenxor plantar response): toes go up instead of pointing/plantarflexion

Question 55

Causes of lower motor neuron syndromes

Answer 55

Poliomyelitis: affects anterior horn cells themselves

Peripheral nerve injuries: interrupt axons of motor neurons

Question 56

Causes of upper motor neuron syndromes

Answer 56

Cerebral vascular accidents (stroke)

Multiple sclerosis

Question 57

Spasticity

Answer 57

1) Increased sensitivity of stretch reflex (hyperreflexia)
2) Increased muscle tone (hypertonia) with increased resistance to passive movement (may be greater on one side of joint than other, greatest in antigravity muscles (flexor of upper limb and extensors of lower limb) velocity dependent)
3) Clasp-knife or lengthening reaction (maybe; could be explained by golgi tendon reflex)
4) Clonus (variable)
5) Stereotyped patterns of movement (unable to “fractionate” movements at individual joints)

Question 58

Fibrillations

Answer 58

Spontaneous contraction of single muscle fibers

Results from sensitization of single muscle fibers that are denervated and contract individually

Because single fibers contract asynchronously, fibrillations are not visually detectable (except in the tongue) but can be revealed by EMG recording

Question 59

Fasciculations

Answer 59

Spontaneous contraction of groups of skeletal muscle fibers resulting in localized twitching which can be seen under the skin

Caused by spontaneous discharges of irritated motor neurons

Involve motor units as a whole so are visible

Most often seen in patients with chronic disease that affects the motor neurons, such as progressive muscular atrophy

Question 60

Babinski sign (Extensor Plantar Response)

Answer 60

Dorsiflexion of the great toe instead of normal plantar flexion in response to plantar stimulation (stroking of sole of foot with blunt instrument)

Indicative of abnormalities (or incomplete development) of descending motor pathways

Question 61

2 important ascending sensory pathways

Answer 61

Dorsal column-medial lemniscus system: fine touch, position sense

Anterolateral system: temperature, coarse touch, pain

Question 62

Dorsal column-medial lemniscus system

Answer 62

Conveys mechanosensory information from periphery to cortex

Cutaneous mechanoreceptors for fine touch

Proprioception and kinesthesia for position

Question 63

Kinesthesia vs. proprioception

Answer 63

Kinesthesia: awareness of body position and movement

Proprioception: sub-conscious information used in the feedback control of posture and precise movements

Question 64

Where does position sense information come from?

Answer 64

Muscle spindles (stretch)

Golgi tendon organs (tension)

Joint receptors (extreme joint movements)

Cutaneous mechanoreceptive afferents (fine touch)

Efference copy (corollary discharge)

Question 65

What is special about first, second and third order neurons in the pathway?

Answer 65

First order neurons are pseudounipolar

Second order neurons are where the crossing occurs in sensory pathways

Third order neurons not special

Question 66

Two general primciples about motor and sensory pathways in the spinal cord

Answer 66

1) Most motor and sensory pathways cross the midline at some region of the CNS
2) There are topographic representations of the body at all levels of the pathways

Question 67

Pathway of dorsal column-medial lemniscus system

Answer 67

1) Larger diameter afferents from receptors in skin, joints, muscles have cell bodies in DRG. They enter dorsal horn through medial division of dorsal root and their collaterals proceed to dorsal columns without a synapse
2) Afferents from lower limbs and lower trunk (below T6) ascend within medial column (gracile fasciculus/tract); afferents from upper trunk and upper limbs (above T6) ascend in lateral column (cuneate fasciculus/tract)
3) FIbers continue in ipsilateral dorsal column until lower medulla where they synapse on second order neurons in either gracile nucleus or cuneate nucleus
4) At caudal medulla, axons of second order neurons curve ventromedially as internal arcuate fibers and cross midline in the decussation of medial lemniscus to become contralateral medial lemniscus (on midline of ventral medulla)

[5) Note that as medial lemniscus heads rostrally, it rotates so that topographic representaton matches that in the thalamus]

6) Medial lemniscal fibers form synapses onto third order neurons in ventral posterior lateral (VPL) nucleus of the thalamus
7) Fibers from thalamus project to primary somatosensory cortex of parietal lobe (areas 3a, 3b, 1, 2) via the posterior limb of the internal capsule

Question 68

Do you always have both cuneate and gracile tract?

Answer 68

Whenever you have cuneate tract, you will have gracile tract

Remember, cuneate tract is info from upper limbs and body (above T6) and gracile tract is from lower limbs and body (below T6)

Question 69

How do fine touch and position sense from head and face get processed?

Answer 69

Principal (sensory) Tact of V

1) Afferents from receptors in skin of face have cell bodies in trigeminal ganglion and enter brainstem through trigeminal nerve.
2) All afferents synapse on second order neurons in principal (sensory) nucleus of trigeminal complex in mid-pons
3) Axons from second order neurons decussate in pons and join trigeminothalamic tract (which runs adjacent to medial lemniscus)
4) Axons in trigeminothalamic tract form synapses on third order neusons in ventral posterior medial (VPM) nucleus of the thalamus
5) Fibers from the thalamus project to same areas of primary somatosensory cortex via posterior limb of internal capsule

Question 70

Two different locations for cell bodies of afferents from receptors from the face

Answer 70

1) Receptors in skin have cell bodies in trigeminal ganglion
2) Receptors in joints and muscles (for proprioception!) have cell bodies in mesencephalic nucleus of trigeminal complex (within CNS!)

Question 71

How is the whole body represented in the ventral posterior (VP) complex?

Answer 71

VPM of thalamus: face

VPL of thalamus: body

Question 72

Areas 3a, 3b, 1, 2

Answer 72

Area 3a: primarily proprioception input (note: closest to area 4 which is motor)

Area 3b: primarily tactile input

Area 1: primarily tactile input but receptive fields usually cover several digits

Area 2: combination of tactile and proprioception; hand configuration and stimulus shape are both important

Question 73

In the somatosensory homunculus, why are the hands and lips (for example) so big?

Answer 73

Because there are a lot of sensory receptors so a lot of information coming in from there

Question 74

Anterolateral system

Answer 74

Conveys pain, temperature, coarse touch information from the periphery to the cortex

Question 75

Pathway of anterolateral system

Answer 75

1) Smaller diameter fibers from skin and deeper structures have cell bodies in DRG and enter spinal cord through dorsal roots and may ascend or descend 2-3 segments to form Lessauer’s tract (dorsolateral tract) before penetrating deeper into dorsal horn
2) The fibers synapse on second order neurons in several lamina of the dorsal horn in the spinal cord
3) Axons of second order neurons cross midline of spinal cord in anterior white commissure and assemble in spinothalamic/anterolateral tract on the contralateral side
4) Fibers of spinothalamic/anterolateral tract remain in lateral locations throughout brainstem and are eventually located dorsolateral to the medial lemniscus
5) Reach thalamus and axons synapse with third order neurons in VPL of thalamus. In addition, some axons also have synapses in other thalamic nuclei that include the intralaminar and posterior nuclei
6) Neurons in VPL project to primary somatosensory cortex

Question 76

On their way through the brainstem, where else do fibers of the anterolateral system send collaterals?

Answer 76

1) Reticular formation (so may influence level of arousal) so referred to as spinoreticular tract
2) Terminate within brainstem rather than continuing to thalamus
3) Terminate in mesencephalon (tectum and periaqueductal gray) so referred to as spinomesencephalic tract

Question 77

Differences between dorsal column and anterolateral column

Answer 77

Dorsal: light touch, vibration, 2 point discrimination, sense of position; decussation at caudal medulla

Anterolateral: pain, temperature, coarse touch; decussation at spinal cord

Question 78

What happens if you destroy an entire half of the spinal cord?

Answer 78

Get deficit in touch on one side (dorsal column-medial lemniscus tract; ipsilateral) and pain on the other side (anterolateral tract; contralateral)

Question 79

Pathway for pain, temperature and coarse touch from head and face in the brainstem

Answer 79

Spinal Tract of V

1) Afferents from face have cell bodies in trigeminal ganglion and ganglia associated with CN VII, IX, X and enter brain stem via those nerves
2) Afferents from trigeminal nerve descend in spinal trigeminal tract to medulla to synapse on second order neurons in spinal nucleus of trigeminal complex (primarily pas caudalis). Afferents from IX and X enter through medulla and synapse in spinal nucleus of trigeminal complex also
3) Axons from second order neurons decussate in caudal medulla and join anterolateral tract in brainstem
4) Fibers in anterolateral tract synapse on third order neurons in VPM of thalamus
5) Fibers from thalamus project to same areas of primary somatosensory cortex

Question 80

What other brain areas receive information about pain, and what do they do with it?

Answer 80

Cortex: localization of pain

Sub-cortical: perception of pain

Paleospinothalamic pathways: suffering component of pain (reduced by benxodiazepines)

Question 81

Spinocerebellar tracts

Answer 81

Both dorsal and ventral spinocerebellar tracts are located in the lateral part of the lateral columns of the spinal cord

These pathways transmit proprioceptive information (non-conscious) from muscle spindles and Golgi tendon organs and some exteroceptive information from cutaneous mechanoreceptors to the cerebellum

For both tracts there are slight differences in specific pathways for upper and lower parts of the body

Question 82

Descending pathways in the modulation of pain

Answer 82

Multisynaptic, descending pathways from PAG in midbrain to dorsal horn of spinal cord (or pars caudalis of spinal nucleus of trigeminal complex) can decrease painful sensation by inhibiting nociceptive transmission in the dorsal horn

Two important areas of the brain: PAG and Raphe nuclei

Question 83

Local and descending control of pain

Answer 83

1) A-alpha and A-beta fibers excite interneurons that reduce the transmission of pain information (local, use dorsal column ascending system to distract; rubbing after a sharp pain)
2) Descending fibers excite interneurons that reduce the transmission of pain information (in dorsal horn or pars caudalis–pain fibers come in but descending fibers from raphe use enkephalin to inhibit dorsal horn/pars caudalis fibers to reduce pain)

Question 84

Symptoms of a patient with right-sided hemisection (destroy entire right half of spinal cord at one level)

Answer 84

Decreased touch and proprioception on right (ipsilateral) because damaged dorsal column-medial lemniscus tract

Decreased pain and temperature sensation on the left (contralateral) because damaged anterolateral tract

Paralysis on right side (ipsilateral) because damaged lateral corticospinal tract

(This is Brown-Sequard Syndrome)

Question 85

Symptoms of a patient with lesion ventral to central canal (anterior white commissure) in cervical region

Answer 85

Affect upper limbs because lesion above T6

Interrupt anterolateral tract because those fibers cross at anterior white commissure

Deficit in pain and termperature sensation in a cape-like pattern over arms and shoulders

(Syringomyelia is fluid filling the spinal cord at C3, C4 that causes damage)

Question 86

Symptoms of patient with complete transection at T10

Answer 86

Can still move upper limbs (paraplegic)

No voluntary motor control of lower limbs

No pain felt in lower limbs

Short-term would have decreased reflexes

Long-term would have increased reflexes