SPINAL CORD ANATOMY & PHYSIOLOGY

HONORS ANATOMY & PHYSIOLOGY

Spinal Cord

w/spinal nerves contain neural circuits that mediate some of your most rapid reactions to environmental changes

Protective Structures

2 types of CT coverings surround & protect delicate nervous tissue

1. bony vertebrae2. tough CT meninges, w/cushion of CSF

Meninges

3 CT coverings that encircle spinal cord & brain:

Spinal meninges covers spinal cord Cranial meninges covers brain

Meninges Layers: Dura Mater

“tough mother” most superficial layer made of dense, irregular CT continuous with cranial meninges forms sac from foramen magnum S2 layer of adipose tissue between dura

mater & wall of vertebral cavity (epidural space)

Middle Meninges: Arachnoid Mater

“spider-like” deep to dura mater, superficial to pia

mater contiguous with cranial arachnoid between dura & arachnoid = subdural

space

Innermost Meninges:Pia mater

“delicate” thin, transparent CT adheres to spinal cord & brain between arachnoid & pia =

subarachnoid space

Spinal Tap

aka lumbar puncture long needle inserted into subarachnoid

space adults: between L3 –L4 or L4 – L5

(inferior to lowest portion of spinal cord) purpose: withdraw CSF for

diagnostic purposes insert antibiotics/contrast media for

myelography/ anesthetics/ chemotherapy

Spinal Cord

cylindrical with flattening of its AP diameter

adults:extends from medulla oblongata L2 vertebra

newborns: extends to L3 or L4 elongation of spinal cord stops ~age 3-4

but growth of vertebral column continues

Spinal Cord: External View

2 obvious enlargements noted: cervical enlargement

C4 – T1 serve upper limbs

lumbar enlargement T9- T12 serve lower limbs

Spinal Cord: External View

conus medullaris: tapered conical structure of spinal cord below lumbar enlargement ending @ L1 – L2

filum terminale: extension of pia mater extends inferiorly & anchors cord to coccyx

cauda equinae: “horse tail” nerves that arise from lumbar, sacral, & coccygeal portions of spine

Conus Medullaris

Filum Terminale

Cauda Equina

Spinal Nerves

31 pairs spinal nerves emerge thru intervertebral foramen

8 pair cervical nerves: C1 – C8 12 pair thoracic nerves: T1 - T12 5 pair lumbar nerves: L1 – L5 5 pair sacral nerves: S1 – S5 1 pair coccygeal nerves: Co1

Spinal Nerves

2 bundles of axons, called roots, connect each spinal nerve to segment of spinal cord

Spinal Cord Roots

1. posterior (dorsal) root only sensory axons each has dorsal root ganglion containing

cell bodies of sensory neurons

2. anterior (ventral) root only motor axons

Internal Anatomy of Spinal Cord

2 grooves penetrate white matter & divide it in right & left sides:

1. anterior median fissure1. deeper, wider of the 2

2. posterior median sulcus1. shallower, narrow furrow

Internal Anatomy ofSpinal Cord

gray matter shaped like “H” or a butterfly & is surrounded by white matter

gray commissure forms the “H” crossbar central canal small hole in its center

extends entire length of spinal cord filled with CSF @ superior end is contiguous with 4th ventricle

of brain

Spinal Nerves

& the nerves that branch off them are part of PNS

emerge from vertebral column thru intervertebral foramina

Spinal Nerves

typically has 2 connections to spinal cord1. dorsal root (sensory)2. ventral root (motor)

classified as “mixed”

Distribution of Spinal Nerves

Spinal Nerve Plexuses

a network of nerves (or veins, or lymphatic vessels)

Cervical Plexus

supplies skin & muscles of the head, neck, & superior portion of shoulders, chest, & diaphragm

C1 – C 5

Brachial Plexus

supplies the shoulders & upper limbs

Lumbar Plexus

supplies anterolateral abd wall, external genitals, part of lower limb

Sacral Plexus

supplies buttocks, perineum, & lower limbs

Dermatomes

cutaneous area developed from one embryonic spinal cord segment & receiving most of its sensory innervation from one spinal nerve

knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord

Reflexes & Reflex Arches

reflex: a fast, automatic, unplanned sequence of actions that occurs in response to a particular stimulus

can be:1. inborn

pulling hand away from hot stove

2. learned or acquired foot on brake when see dog run in front of

car

5 Parts of a Reflex Arc

Stretch Reflex

Pupillary Light Reflex

pupils of both eyes decrease in diameter when either eye is exposed to light

absence of a normal pupillary light refex indicates possibility of brain damage or injury

Spinal Cord Injuries

most due to trauma cervical, lower thoracic, upper lumbar most

common regions involved paralysis

depends on location, extent of damage monoplegia: 1 limb paraplegia: both lower limbs hemiplegia: upper limb, trunk, lower limb

on 1 side of body quadriplegia: all 4 limbs & trunk

Extent Muscle Paralysis

C1 – C3: no function neck down, requires ventilator to breathe

C4 – C5: diaphragm, allows breathing C6 – C7: some arm, chest, allows breathing,

moving wheelchair T1 – T3: intact arm function T4 – T9: control of trunk above umbilicus T10 – L1: most thigh muscles, walk w/long

leg braces L1 – L2: most leg muscles, walk w/short leg

braces

Shingles

acute infection of PNS caused by herpes zoster (chicken pox) virus stays in posterior root ganglion

becomes reactivated normally immune system will prevent it from spreading

reactivated virus can overcome weakened immune system leaves ganglion travels down sensory neurons supplying skin

Medical Terminology

meningitis: inflammation of meminges due to infection, bacterial (worse) or viral, vaccine protests against some bacterial causes: headache, N/V, fever, stiff neck

neuralgia: pain along a sensory nerve, trigeminal neuralgia

neuritis: inflammation of 1 or several nerves

paresthesis: abnormal sensation