1/2- Spinal Cord Anatomy + Ascending Sensory Pathways

what are the 3 layers of meninges

outer → innermost D A P

1. dura mater

2. arachnoid

3. pia mater

T/F: the 3 meninges only surround CNS, not PNS

true

blood vessels + CSF are found between which 2 meninges

in subarachnoid space: between arachnoid + pia

how many pairs of spinal nerves

31

5 groups of spinal nerves

C T L S C

1. cervical

2. thoracic

3. lumbar

4. sacral

5. coccygeal

how many cervical spinal nerves

8

how many thoracic spinal nerves

12

how many lumbar spinal nerves

5

how many sacral spinal nerves

5

how many coccygeal spinal nerves

1-3

term for back of human body

dorsal

term for front of human body

ventral

term for towards the brain

rostral

term for towards the feet

caudal

spinal cord is increased in diameter in which 2 areas

1. cervical enlargement: C5-T1

2. lumbar (lumbosacral) enlargement: L3-S2

why does the spinal cord increase in diameter in those areas

to accommodate the neurons required for upper + lower extremities

how do you differentiate between the anterior (ventral) surface vs. posterior (dorsal) surface of the spinal cord

• ventral: 1 single spinal artery (supplies anterior 2/3 of cord)

• dorsal: pair of spinal arteries

what’s the conus medullaris

termination of the spinal cord

where is the conus medullaris

between vertebrae L1/L2

what’s the cauda equina

where spinal nerves extend inferiorly from conus medullaris

since the difference of growth between spinal cord + spinal column, length of nerve roots become

progressively longer from cervical to sacral levels

where are spinal taps performed

below L2, b/c spinal cord ends between L1/L2

spinal has _____ and _____ oragnization

segmental + longitudinal

definition of spinal cord segment

part of cord that gives rise to a pair of spinal nerves

primary sensory neurons are what type of neurons (how many processes)

pseudounipolar

primary sensory neurons are located where

dorsal root ganglion

motor neurons are located where

ventral horn of spinal cord

what does DAVE stand for

Dorsal Afferent - Ventral Efferent

where are unipolar sensory neurons located

cell bodies in dorsal root ganglion

roots of unipolar sensory neurons project where

into dorsal horn of gray matter or white matter of dorsal funiculus

where are multipolar motor neurons located

cell bodies in ventral horn of gray matter

what’s a myotome

a single nerve root innervating a muscle

spinal reflexes reveal what

segmental organization of spinal cord

gray matter is divided into what 2 regions

1. dorsal horn

2. ventral horn

white matter is divided into what 4 regions

4 funiculi:

1. dorsal

2. ventral

3. 2 lateral

what are the numbers

1. lateral funiculus

2. dorsal funiculus

3. ventral funiculus

what are the numbers

1. posterior median sulcus

2. posterior intermediate sulcus

3. posterolateral sulcus

what are the numbers

1. anterior median fissure

2. anterolateral sulcus

describe location of motor neuron bodies within gray matter

• distal-lateral muscles are lateral in ventral horn

• flexor muscles are more dorsal vs. extensor muscles are ventral

why does is there more gray matter in cervical sections than thoracic

cervical section contains brachial plexus (arm muscles) vs. thoracic contains torso nerves, which has less muscles

preganglionic sympathetic neurons originate from which vertebrae

T1-L2

preganglionic parasympathetic neurons originate from which vertebrae

S2-S4

what can you find in the bracketed areas

preganglionic sympathetic neurons

motor neurons that innervate the diaphragm are found where

phrenic nucleus, C3-C5

5 functional groups of myelinated axons

1. long ascending fibers

2. long descending fibers

3. efferent (motor) fibers

4. afferent (sensory) fibers

5. propriospinal fibers

define long ascending fibers

sensory “bottom-up” projections from dorsal root ganglion (DRG) destined to reach the cortex, thalamus, brainstem

define long descending fibers

motor fibers “top-down” from the cortex, brainstem destined to reach motor neurons in ventral horn that project to peripheral muscles

define propriospinal fibers

3 tracts (dorsal, lateral, ventral) that ascend, descend, cross, and don’t cross that stay intrinsic to the spinal cord and interconnect different levels

4 mechanisms of spinal trauma

1. hyperextension: caused by extension injury

2. hyperflexion: caused by flexion injury

3. compression

4. rotation

2 types of lesions

1. paresis: incomplete loss of muscle function

2. plegia/paralysis: complete loss of muscle function

3 types of plegia/paralysis

1. quadriplegia: C8 and above

2. paraplegia: below T1

3. hemiplegia: paralysis of ½ of body, usually brain injury

4 types of paresis

1. anterior cord syndrome

2. posterior cord syndrome

3. central cord syndrome

4. Brown-Sequard syndrome

2 important ascending pathways that are clinical testable + relays conscious sensory perception

1. dorsal column medial lemniscus pathway

2. spinothalamic pathways (anteriolateral system)

dorsal column medial lemniscus pathway relays what kind of info

position/vibration sense, discriminatory touch from the periphery to the cortex

spinothalamic pathways relay what kind of info

pain/temp + crude touch from the periphery to the cortex

important pathway that relays unconscious sensory perception

spinocerebellar pathways

2 divisions of dorsal column medial lemniscus pathway

1. fasciculus gracilis

2. fasciculus cuneatus

2 divisions of spinothalamic pathway

1. anterior spinothalamic tract

2. lateral spinothalamic tract

long tracts that bring info to/from cortex must

decussate (cross to the other side of the nervous system) during their ascent/descent

both clinically relevant ascending pathways are considered

3 neuron pathways:

1. 1st order neuron: dorsal root ganglion (DRG)

2. 2nd order neuron: its axons cross midline (spinal cord or brainstem)

3. 3rd order neuron: thalamus-VPL

all info going to cortex must stop at thalamus except what

olfaction info, goes directly to cortex

what are the 3 modalities of the dorsal column medial lemniscus pathway

1. position sense

2. vibration sense

3. 2-point discrimination

distinguish the origins of the 2 divisions of the dorsal column medial lemniscus pathway

1. fasciculus cuneatus: T5 + above

2. fasciculus gracilis: from T6 + below

distinguish the tracts of the 2 divisions of the dorsal column medial lemniscus pathway

1. fasciculus cuneatus: lateral portion of dorsal funiculus

2. fasciculus gracilis: medial portion of dorsal funiculus

distinguish the nuclei of the 2 divisions of the dorsal column medial lemniscus pathway

within caudal medulla (lower part of brainstem)

1. fasciculus cuneatus: cuneate nucleus

2. fasciculus gracilis: gracile nucleus

T/F: pathways from both gracile + cuneate nucleus cross the midline before heading to the thalamus

true

after crossing the midline, pathways from gracile + cuneate will form the

medial leminiscus

this patient has

demyelination of dorsal column pathway → loss of proprioception of lower extremities

this patient has

loss of proprioception of their lower extremities

this patient has

loss of proprioception on left side

what are the 2 modalities of spinothalamic pathway

1. localization of pain + temp

2. crude touch

describe the 1st + 2nd order neurons of spinothalamic pathway

1. 1st order: DRG

2. 2nd order: in dorsal horn of gray matter in spinal cord

describe the pathway from 2nd → 3rd neuron of spinothalamic pathway

from 2nd, pathways crosses midline → ascends to thalamus

T/F: info passed through spinothalamic pathway ascends contralaterally to cortex

true

purple arrow is pointing to

ventral white commissure

this patient has

loss of pain + temp perception on left side of body

main differences between dorsal column medial lemniscus pathway vs. spinothalamic pathway

1. dorsal column medial lemniscus: lesions → ipsilateral loss + has very myelinated axons

2. spinothalamic: lesions → contralateral loss + poorly/non-myelinated axons

a lesion here would lead to

deficit in dorsal column medial lemniscus pathway

a lesion here would lead to

deficit in spinothalamic pathway

a lesion here would lead to

blocking dorsal root → suspended sensory loss at the level the lesion occurred since it does not involve the long tracts

a lesion here would lead to

lesion in ventral white commissure → bilateral suspended sensory loss at the level the lesion occurred since it doesn’t involve the long tracts

this patient has

lesion in ventral white commissure → bilateral loss of pain/temp only at level of lesion

3 pathways that go to the cerebellum

spinocerebellar pathways:

1. posterior (dorsal) spinocerebellar tract

2. anterior (ventral) spinocerebellar tract

3. cuneocerebellar tract

T/F: all 3 spinocerebellar pathways end ipsilaterally in cerebellum

true

this lesion would cause which paresis syndrome

occlusion of anterior spinal artery → bilateral loss of spinothalamic pathway + motor neurons → anterior cord syndrome

symptoms of this lesion

• motor: bilateral paralysis/weakness

• fine touch: normal

• pain/temp: bilateral loss

this lesion would cause which paresis syndrome

occlusion of posterior spinal artery → bilateral loss of dorsal column → posterior cord syndrome

describe symptoms of this lesion

• motor: normal

• fine touch, vibration: bilateral loss

• pain/temp: normal

this lesion would cause which paresis syndrome

damage to central area of spinal cord → bilateral loss of spinothalamic pathway → central cord syndrome

describe symptoms of this lesion

• motor: progressive bilateral paralysis by direct damage on motor neurons

• fine touch: normal

• pain/temp: immediate bilateral loss

this lesion would cause which paresis syndrome

damage to ½ of spinal cord → ipsilateral loss of dorsal columnar + contralateral loss of spinothalamic → Brown-Sequard syndrome

describe symptoms of this lesion

• motor: ipsilesional paralysis (same side lesion)

• fine touch: ipsilesional loss

• pain/temp: contralesional loss