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 bony vertebrae 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 posterior (dorsal) root anterior (ventral) root only sensory axons each has dorsal root ganglion containing cell bodies of sensory neurons anterior (ventral) root only motor axons

Internal Anatomy of Spinal Cord 2 grooves penetrate white matter & divide it in right & left sides: anterior median fissure deeper, wider of the 2 posterior median sulcus shallower, narrow furrow

Internal Anatomy of Spinal 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 cord dorsal root (sensory) 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: inborn pulling hand away from hot stove 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 paralysis 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