neuroanatomy exam 2 (ch7-ch)

first order neuron

intial sensory neurons that detect stimuli

cell bodies are outside the spinal cord

(dorsal root ganglia [body] or cranial nerve ganglia [head/face])

second order neuron

rece

fine, discrimitative touch

for example writing

crude touch

anterolateral pathways

pain

temperature sense

crude touch

we will focus on 3 tracts (spinothalamic, spinoreticular, spinomesencephalic tract) but there is more than 3

spinoreticular tract

emotional and arousal aspects of pain

spinothalamic tract

discriminative aspects of pain and temperature → location and intensity of stimulus

posterior column - medical lemniscus pathway

proprioception

vibration sense

fine, discriminative touch

large-diametic myelinated axons

gracile fasciculus

info from legs and lower trunk (medial portion)

cuneate fasciculus

info from upper trunk, arms, neck (lateral portion)

why would something have large-diameter myelinated axons

fast conduction

For posterior column-medical lemniscal pathway, what is the first order?

sensory neurons travel to the CNS

For posterior column-medical lemniscal pathway, what is the second order?

sensory neurons

(nucleus gracilis / pathways from upper body)

(nucleus cuneatus / pathways from lower body)

synapses of the posterior column-medial lemniscal pathway

1st order neurons → 2nd order neurons → thalamus (3rd order neurons)→ post central gyrus

explain the synapses of the posterior column-medial lemniscal pathway

axons go through gracile fasculus and cuneate f

first you have small unmyelinated axons and then they synase into dorsal horn of spinal and then they dicussate at spinal cord anterior commissure where they ascend into the 3 pathways

the spinothalamic tract → thalamus (vpln + other nuclei) → primary somatosensory cortex (post-central gyrus) → 2nd assn

spinal nerve roots

initial segments of spinal nerves that connect the spinal cord to the peripheral nervous system

vertebral bones

mechanical & physical support for the body

it provides protection of spinal cord

• passes thru the nertevral foramen (spinal canal)

• posterior arch

spinal column

made of five cord sections (cervical, thoracic, lumbar, sacral, coccygeal)

arms in spinal column

C5-T1

legs in spinal column

L1-S3

Cauda equina

just nerve roots…it’s a collection of nerve roots that continue downward within the spinal cord but contians no spinal cord

Mixed Spinal Nerve

formed by when dorsal (sensory) root joins with ventral (motor) root at each segment

it occurs on both left and right side

vestigial nerve root

C1 has no cutaneous (skin) sensory roots

why do nerve roots exist through the foramina?

that’s what foramina are there for, these holes provide an opening for things to pass through

foramen magnum is where spinal roots enter

how does numbering for cervical nerve roots work?

Nerve roots exit the spinal canal above their correspondibly numbered vertebral bone for ex C6 exits below C5 vertebra and above C6 vertebra

how does numbering for thoracic and lumbosacral?

usually corresponds to the lower of the two adjacent vertebral bones in the disc space

intervertebral discs

made up of inner “juicy” component: nucleus pulpous and then an outer “fibrous” component which is the annulus fibrosus

How is the spinal cord separated?

Stacked and separated by

intervertebral discs

 Central nucleus pulposus

 Surrounded by annulus fibrosus

Spinal dura

separated from the vertebral bones by the epidural space with fat, connective tissue, and venous plexuses

What is hapenning in the Meninges and epidural space for Intervertebral discs?

— spinal dura is there but separated from the veretrabl bones by the epidural space

—- pia and arachnoid are still present

Bulging Disc

The disc extends beyond its normal space, but the other layer (annulus fibrosus) remains intact

very common and often no symptoms and people often have it and never know about it

is common and normal part of aging

you can try stretching to help with the lack of space

Herniated Disc (slipped disc)

this is where the outer layer of the disc tears of ruptues

the soft inner material (nucleus pulpous) leaks out through the tear when it shouldnt be

the structural integrity of the disc has been compromised

associatetd with pain and most likely to cause pain, numbness, weakness

more serious than a bulging disc

Rule of Thumb for disc herniation

the affected nerve root usually corresponds to the lower of the two adjacent vertebra that form the disc space

for ex: c5-c5 herniation means it effects the c6 nerve root

What direction are these herniations?

Either going out or to the side, so either lateral or posterolaterl

*the specific direction and its clinical impact depend on the regiion of the spine involved”

Thoracic Herniations

These are less common herniations as they are less mobile and stabilized by the rib cage

Radiculopathy

a condition caused by compression, inflammation, or injury to a nerve root

radicular

refers to the nerve root

What does Herniation mean?

Results in pain specific area that correspond to the impacted nerve

atypical disc herniations

lateral disc herniations and central disc herniation

lateral disc herniation

exception from the rule of thumb

can reach root at the exiting level

impacts next higher than lower nerve root

Central disc hermniation

herniation towrds the center of the spinal cord

at cauda equina, can impinge multiple nerve roots lower than the herniation level

Cauda equina syndrome

impaired function of multiple nerve roots below L1 or L2

T/F: For a typical Disc Hernation between L2 and L3, this ere is an L2 radiculopathy/

False: affected nerve root corresponds lower of the two adjacent vertebrae that form the disc space

segmental innervation

body organization into distinct regions that are primarily supplied by individual spinal nerver roots

What is a Dermatone?

sensory region of skin innervated by a nerve root

• usual locations with some variability

• primarily clinical utility = localizing nerve roots lesions and providing anatomical landmarks

• can be continuity between front and back, such as front and lateral/back of thigh

What is a myotome?

Muslces innervated by a single nerve root

• strength training and reflex testing for individual muscles, nerves, and nerve roots

  • serves as diagnostic tools in the neuroexam

cervical flexion

C2: look at your shoe (upper myotome)

cervical lateral flexion

C3: fallen tree (upper myotome)

shoulder elevation/shrug

c4: i’m not sure: (upper myotome)

shoulder abduction

c5: arms out wide (upper myotome)

wrist extension (elbow extension in arms out zombie style)

c7: no zombies in heaven (upper myotome)

Differences between Mapped dermatones versus myotomes

Dermatones are surface map

• overlapping innverations

Myotomes are functional/muscle groups

• most muscles get input from multiple nerve roots

Muscles migrate more than skin during development → dont align/match

• can be a rough alighment of limbs

• Bigger mismatch of trunk

A single root lesion can show up as sensory loss in one area and weakness in muscles located somewhere quite different.

• can also have positive symptons like parathesia

T/F: The function of spinal nerves can be checked using general assessments

False: segmental organization means that each nerve is associated with a distinct region

PNS disorders

disorders can affect nerve, neuromuscular junction or muscle

• distinguished from central nervous system dysfunction

• based on anatomical apttern of deicits

• presence of lower motor neurons suggest pns dysfinction

lower motor neuron signs

atrophy, fasciculations, decreased tone, decreased reflexes

What is the site of pathology for Neuropathies (nerve disorders)

include axons and/or myelin; large of small diameter fibers

Where are neuropathies located? What types are there?

there are 3 types located in 3 diff places

focal = sognal nerve

multifocal = individual non-contiguous nerves - patchy effects

generalized = diffuse, symmetical nerve effects

spinal nerve root neuropathy

caused by radiculopathy (compression of irritation of nerve root)

Most common kind of Diabetic neuropathy?

It’s generalized = distal symmetical polyneuropathy (glove & stocking pattern for sensory loss)

Mechanism for Diabetic Neuropathy?

Multiple possible mechanisms: most common = compromised microvascular and blood supply of peripheral nerves

Common single neuropathies

specific sensorimotor deficits, possibly with painful paresthesia

what is the recovery like for diabetic neuropathY?

Often partial or complete recovery with diabetes control, diet, activity, medical

treatment (pain, interventions at the spinal cord)

What are the Mechanical causes of nerve energy?

extrinsic compression, traction, laceration, entrapment of intrisic structures, mild mechanism disruption, wallerian degeneration, potential axonal regeneration

Mild mechanical disruption

a little bit of compression

can lead to neuropaxia which is temporary, has temporary effects

sometimes can resolve itself

Potential axonal regeneration →

occasional complications incl. incomplete/aberrant reinnervation, complex regional pain syndrome

sometimes there is pain

Guillain-Barre syndrome

acute inflammatory demyelinating polyneuropathy; AIDP

autoimmune neuropathy → immune-mediated demyleination of peripheral nerves (can affect axons of modes of ranvier”

Plasmapheresis

filtering blood out

plexus

bundle of intersecting nerves

Successive segments of nerve fibers

start with spinal roots → join to form trunks (upper, middle, lower)→ divides into a division (anterior, posterior) → divdes into cords (ant→lateral cord & post→posterior or medial cord) → and then the cords divide into branches called peripheral nerses

branchial plexus

upper extremities (think arms, neck, shoulder)

c5,c6,c7,c8, t1 roots go into trunks then → anterior and posterior division → then goes from ant→lateral cord and posterior→posterior. then lateral cord goes into musculocutaneous and other nerves. posterior cord goes into radial, axillary, other nerves. and then the medial cord goes into ulnar and other nerves

*three nerves leave at root and trunk level (shoulder)

Lumbosacral plexus

lower extremities and pelvis

L1-L5, S1-S4 and then goes into upper trunk, middle trunk and lower trunk.

from upper and middle trunk it goes into anterior division → then goes into obturator, sciatic, tibial, other nerves

from middle and lower trunk it goes into posterior division → femoral, fibural (peroneal), other nerves

THIS ONE HAS NO CORDS

Radial nerve

it’s an extension of all nerve, wrist, and proximla finger joints below the shoulder

responsible for foream supination and thumb abduction in plane or palm

What can the Radial nerve run?

You can straighten elbow (extend your arm)

bend your wrist back (like signalling “stop”)

turn palm up (like holding a bowl)

move your thumb away from your palm (same level as palm)

Median nerve

thumb flexion and opposition

flexion of digits 2 and 3

wrist flexion and abdicion

forearm pronation

What can the median nerve do?

Bend thumb and touch to fingertips (like “OK” sign)

Bend index and middle fingers at the knuckles

Bend wrist forward (like revving a

motorcycle) and angle towards your

pinky side)

Turn palm down

ulnar nerve

finger abduction and abduction other than thumb

thumb addict