EXAM 2 - Spinal Cord and PNS

Central Nervous System (CNS)

brain and spinal cord

PNS

cranial nerves, spinal nerves and ANS

PERIPHERAL NERVES

⦿ Bundles of axons outside the CNS

⦿ Most are myelinated

⦿ Myelinating cells are schwann cells/neurolemnocytes

Connective tissue coverings in peripheral nerves

Nerves arranged in bundles (fascicles)

3 covering: (outer to inner)

1. epineurium

2. perinerium

3. endoneurium

motor endplate

synapse of neuron to muscle

Ganglion

bundle of nerve cell bodies in the peripheral nervous system

plexus

network of nerves; ventral rami of sp n

(brachial plexus)

31 pairs of spinal nerves

8 cervical

12 thoracic

5 lumbar

5 sacral

1 coccygeal

2 parts of the nerve root

1. dorsal (sensory)

2. ventral (motor)

clinical application for dorsal nerve roots

viruses can lay dormant here - chicken pox, shingles, herpes viruses

clinical application of ventral nerve roots

polio virus, ALS both attack here

destroy motor neurons that innervate skeletal muscle

each Nerve then divides into

1. dorsal ramus

2. ventral ramus

characteristics of dorsal rami

small, mixed (sensory and motor), NEVER form plexuses

Characteristics of ventral rami

large & thick, mixed (sensory and motor), form plexuses

where are dorsal rootlets

where are ventral rootlets

where are dorsal roots

where are ventral roots

dorsal root ganglion location

what makes a spinal nerve

where the ventral and dorsal roots combine into the spinal nerve

Dorsal ramus

the division of posterior spinal nerves that transmit motor impulses to the posterior trunk muscles and relay sensory impulses from the skin of the back

ventral ramus

the anterior division of spinal nerves that communicate with the muscle and skin of the anterior and lateral trunk

gray ramus

unmyelinated nerves, return from sympathetic ganglion to rejoin spinal nerve (postganglionic fibers)

more medial

sympathetic ganglion

Ganglion (bundle of nerve cell bodies) that receives preganglionic sympathetic fibers. part of sympathetic nervous system that has fight or flight response

white ramus

Carries visceral motor fibers to sympathetic ganglion of autonomic nervous system (preganglionic fibers)

more lateral

Spinal cord and age

Length varies with age

◼ Foramen magnum to:

⭘ Adult: between L1 and L2

⭘ Child : L3

⭘ Fetus: Full length

General cord features

the spinal cord is CNS and continuous with brain stem

length of spinal cord

length varies with age

adult: foramen magnum to between L1 and L2

child: foramen magnum to L3

fetus: foramen magnum to full length

*shortens as you develop

Cervical & lumbosacral enlargements locations

locations:

C4-T1

T11-L1

Conus medullaris (medullary cone)

L1 - end of spinal cord

Filum terminale (terminal filament)

pia mater

anchors spinal cord to coccyx

silver/shiny

Cauda equina

collection/bunch of spinal nerves below the end of the spinal cord

"horse tail"

meninges of the spinal cord

dura mater, arachnoid mater, pia mater

Dura mater

outermost

◼ Ends at S2 - forms dural sac at that point

◼ Epidural space - continues with the epineurium of spinal n - between the dura and the bone of vert (coats the dura mater)

Arachnoid mater

◼ Delicate & avascular; impermeable; fibrous & elastic

CT; ends S2 (dural sac)

◼ Subarachnoid space - CSF flows

Pia mater

makes terminal filament

Ligamentum denticulum AKA denticulate ligaments

- looks like teeth

- serves as an anchor for the spinal cord but delicate

- fibrous bands that help separate anterior and posterior roots

Cord grows slower than column

◼ Upper cord segments adjacent to same # verts

◼ Spinal nerves L2-S4 - form cauda equina

Spinal nerves exit vertebrae via?

intervertebral foramen

Where do spinal nerves exits along the vertebrae?

◼ C1: between the occipital bone and the atlas

◼ C2-C7: above the same # vert

◼ C8: between C7 and T1 vert

◼ T1-S5: exit below same # vert

Dorsal median fissure

Defines left and right gracilis tubercles

splits dorsal white matter in half

Ventral median sulcus

splits ventral white matter in half

gray matter of spinal cord

INNER: Butterfly shaped

Surrounds the central canal of spinal cord

Contains unmyelinated mostly cell bodies neuron cell bodies (also have minimlal axons)

white matter of spinal cord

OUTER part of sp. cord

myelinated mostly axons

central canal

A tiny channel found within the spinal cord and inferior medulla oblongata for CSF to flow in

Where does the white/gray matter change happen

at the level of the medulla

Dorsal horn

termination sensory fibers

◼ integration for relay; reflex

Ventral horn

cell bodies lower motor fibers

◼ medial & lateral columns

Lateral horns

preganglionic sympathetic cell bodies

◼ Cord levels T1-L3 only

WHITE MATTER COLUMNS

⦿ Dorsal (posterior) ⦿ Ventral (anterior) ⦿ Lateral

TRACTS OR FASCICULI

⦿ Definition

groups of neuronal fibers in CNS with similar function

named for origin and termination

EXAMPLES:

- peduncles

- columns

- funiculus

Commissures

connect 2 hemispheres

TRACTS (WHITE MATTER)

⦿ Ascending

sensory

TRACTS (WHITE MATTER)

⦿ Descending

motor

***Usually a 2 neuron pathway (upper & lower)

Lateral Spinothalamic tract

sensory tract for pain and temperature sensation

ascending spinal cord tract to the thalamus

clinical app - chronic pain

dorsal column tract

2 parts:

fasciculus gracile

fasciculus cuneatus

- functions for conscious perception of position (position of limb) and 2 point discrimination

clinical application: lesion = inability to recognize form by touch (astereognosia)

Lateral Corticospinal tract

descending motor output tract...cortex to spinal cord

- functions: largest human tract; fine motor movements (writing)

clinical app: LCST hemiplegia = lesion in tract causes weakness/loss of voluntary control of muscles ipsilaterally

SPINOTHALAMIC PATHWAY

One of the smaller tracts of the anterolateral system.

- passes up the anterior and lateral columns of the spinal cord

carries signals for pain, pressure, temp, light touch, tickle, and itch

first order neurons end in posterior horn

synapse with second order neurons which decussate to other side of spinal cord and form ascending spinothalamic tract

third order neurons continue from thalamus to cerebral cortex

sends signals to the contralateral cerebral hemisphere

GRACILE FASCICULUS PATHWAY

-carries signals from the midthoracic and lower parts of the body (dorsal column ascending)

-Below T6, it composes the entire posterior column (at T6 joins cuneate fasciculus)

-First order nerve fibers end in the gracile nucleus on the ipsilateral side and synapse with second order neurons in the medulla. Second order neuron decussate in medulla forming medial lemniscus. Synapse with third order neuron at thalamus where third order carries signals to contralateral cerebral hemisphere

carries signals for vibration, visceral pain, deep and discriminative touch and proprioception (non-visual sense of position and movement of body) from lower limbs and lower trunk

CUNEATE FASCICULUS PATHWAY

Joins the Gracile Fasiculus at T6

occupies lateral portion of the posterior column

carries the same type of sensory signals

originates from the level of T6 and up (upper limb and chest)

First order nerve fibers end in the cuneate nucleus on the ipsilateral side of the medulla oblongata and synapse with second order neurons in the medulla. Second order neuron decussate in medulla forming medial lemniscus. Synapse with third order neuron at thalamus where third order carries signals to contralateral cerebral hemisphere

medial lemniscus is formed from what?

from the second order neurons of the gracile and the cuneate systems that decussate in the medulla

CORTICOSPINAL TRACTS PATHWAY

From cerebral cortex to spinal cord for precise finely coordinated limb movements

pyramids (anterior ridges) in medulla formed from fibers in this system

decussate in the lower medulla

LATERAL corticospinal tract - contralateral side of the spinal cord (the brain signals go to opposite side of spinal cord at medulla)

ANTERIOR corticospinal tract - on ipsilateral side of the spinal cord

two neuron pathway (upper and lower motor neurons)

Paresis

damage to spinal cord causing partial paralysis, weakness

Paraplegia

damage to spinal cord causing paralysis from the waist down typically

lower extremity paralysis

Quadriplegia

damage to spinal cord causing paralysis of all four extremities

Can lead to:

⭘ respiratory paralysis(ventilation), loss of sensation or motor

control

⭘ disorders of bladder, bowel and sexual function

Damage to spinal cord from strokes or

other brain injuries

hemiplegia

a R sided stroke - leads to L sided paralysis/paresis

hemiplegia

weakness or paralysis of one side of the body

not always permanent

VASCULAR ANATOMY OF CORD

⦿ Arterial

◼ 3 longitudinal arteries supply cord

⭘ 1. anterior (1) spinal artery

⭘ 2. Posterior (2) spinal arteries

VASCULAR ANATOMY OF CORD

⦿ Venous

◼ Internal & external venous plexuses

◼ Basivertebral & intervertebral veins

◼ 6 longitudianl veins drain the cord

⭘ 1. Anterior (3) spinal veins

⭘ 2. Posterior (3) spinal veins

REGIONAL DIFFERENCES WHITE VS GRAY

⦿ Observe differences in distribution of gray & white matter

⦿ Pay special attention to general progression

from cervical to sacral

⦿ Note: Amount of gray matter increases as you travel cervical to sacral (because you add lateral gray matter horns)

AUTONOMIC NERVOUS SYSTEM ( ANS)

⦿ 2 Parts of ANS

1. sympathetic

2. parasympathetic

CNS neuron

1 neuron to somatic effector (target)

ANS neuron

2 neuron pathway to target effector

- preganglionic neuron

- postganglionic neuron

two types of ANS pathways

visceral sensory afferents

Motor efferents

Visceral Sensory Afferent Pathway

◼ Somatic (body wall) poorly understood

◼ Visceral (gut) better understood clinically

⭘ Use DORSAL ROOT (sensory=dorsal)

Motor Efferents Pathway

◼ Message for action at target organ

⭘ Use VENTRAL ROOTS (motor=ventral)

BASIC COMPARISON DIVISIONS - SNS & PSNS

⦿ Location of Pre-ganglionic cell bodies (CNS

connections)

⦿ Location of fibers

⦿ Pre & post-ganglionic fiber length

⦿ Ratio of pre to post ganglionic fibers

⦿ Neurotransmitters & Fate of NT

⦿ General function(s)

LOCATION OF PRE- GANGLIONIC CELL BODIES (SNS)

⦿ SNS

◼ Thoracolumbar division

◼ Spans - T1-L2 (lateral gray column)

LOCATION OF PRE- GANGLIONIC CELL BODIES (PSNS)

⦿ PSNS: Craniosacral division

⭘ Brainstem

-Contains - axons of CN III, VII, IX, X (nuclei in brainstem=cell bodies)

⭘ Sacral

-Spans - S2-S4 (lateral gray column)

LOCATION OF FIBERS (SNS) (postganglionic fibers)

⦿ SNS

◼ Chain of ganglia on each side of vertebral column

-paravertebral

◼ # ganglia per chain = 31

-also prevertebal ganglion and splanchic nerve

LOCATION OF FIBERS (PSNS) (postganglionic fibers)

⦿ PSNS

◼ Ganglia run uninterrupted from CNS to terminal

ganglia close to organ they innervate

◼ ***No ganglia chain (cannot see it with being so close to target)

-near or in walls of viscera

FIBER LENGTH (SNS)

⦿ SNS

◼ Pre-gang = SHORT

◼ Post-gang = LONG

FIBER LENGTH (PSNS)

⦿ PSNS

◼ Pre-gang = LONG

◼ Post-gang = SHORT

RATIO OF PRE TO POST (SNS and PSNS)

⦿ SNS

◼ 1 pre- to many post-

◼ Ratio 1:25

⦿ PSNS

◼ 1 pre- to few post-

◼ Ratio 1:5

NEUROTRANSMITTER SNS

⦿ SNS

◼ Pre-gang = Ach

◼ Post-gang = NE - Norepinephrine

NEUROTRANSMITTER PSNS

⦿ PSNS

◼ Pre-gang = Ach

◼ Post-gang = Ach

CHOLINERGIC FIBERS - secrete

ACh

CHOLINERGIC FIBERS - seen in

SNS and PSNS

CHOLINERGIC FIBERS - types of receptors

◼ 1. nicotinic

⭘ Fxn: always stimulatory

◼ 2. muscarinic

⭘ Fxn: inhibitory or stimulatory

Where are muscarinic receptors stimulatory or inhibitory

they are in PSNS:

stimulatory in smooth muscle

inhibitory in cardiac muscle

ADRENERGIC FIBERS - Secrete

Norepinephrine (NE)

ADRENERGIC FIBERS - found

in SNS

ADRENERGIC FIBERS - types of receptors

◼ (1) alpha (α): mostly stimulatory

⭘ 2 types:

◼ (2) beta (β): mostly inhibitory

⭘ 2 types:

2 types of alpha adrenergic receptors

A1 - constrict blood vessels

A2 act on platelets - stimulate blood clotting

2 types of Beta Adrenergic Receptors

B1 - stimulatory on the heart

B2 - inhibit respiratory structures

FATE OF NEUROTRANSMITTER in SNS

⦿ SNS

◼ NE is retrieved - active transport which takes energy and time

◼ Length of effect - prolonged effect

FATE OF NEUROTRANSMITTER in PSNS

⦿ PSNS

◼ Ach destroyed - quickly by enzyme acetylecholinesterase

◼ Length of effect - short lived

SUMMARY OF PARASYMPATHETIC EFFERENT DISTRIBUTION (CN III, CN VII, CH IX, CN X, S2-S4

Know that PSNS has craniosacral division

⦿ CN III: paravertebral chain- to orbital area

⦿ CN VII: para- to lacrimal area; submandibular &

sublingual gland

⦿ CN IX: para- to parotid gland

⦿ CN X: Para- to heart, lungs, upper gut

⦿ S2-S4: para- to distal gut

SYMPATHETIC MOTOR DISTRIBUTION

-thoracolumbar division

⦿ Throughout body (blood vessels)

⦿ L/R paravertebral chains

◼ Rami communicantes:

⭘ White -carry preganglionic fibers

⭘ Gray - carry post ganglionic fibers

⦿ Prevertebral ganglia & splanchnic nerves

Prevertebral ganglia & splanchnic nerves

◼ Def - paired nerves carrying ANS fibers to the visceral organs

***Thoracolumbar Division SYMPATHETIC PATHWAYS

⦿ Once a sympathetic preganglionic fiber has entered

the paravertebral chain, it can do one of 4 things to

synapse with a postganglionic fiber:

1. End at level it entered

2. Run up the chain

3. Run down the chain

4. Pass out to a prevertebral ganglion via a splanchnic nerve that goes directly to organ