Spinal Cord and Meninges

Objectives:1. Describe the segmental nature and external structure

of the spinal cord. 2. Indicate the relationship of spinal roots/nerves to

intervertebral discs (what cord levels will be affected with a disc protrusion in cervical or lower lumbar levels?)

3. Describe the blood supply and venous drainage of the spinal cord.

4. Describe the structure of the meninges and the associated spaces.

A 18-year-old female presents with pain in her neck and in her right arm. Physical exam reveals pain along the lateral arm, involving the thumb. Grip strength is normal. Her upper limb reflexes on the right side are:

•biceps = 1/4 •brachioradialis = 0/4• triceps = 2/4

What is the most likely etiology for these findings?

CLINICAL CONCEPT

Muscle Strength is measured on a scale of 0 to 5.

> Normal strength is 5/5> Paralysis is 0/5

Reflexes are measure on a scale of 0 to 4.

> Normal is 2/4> PNS lesions are 0 or 1/4> CNS lesions are 3 or 4/4

Spinal Cord

The spinal cord:

• occupies the vertebral canal

• in infants the spinal cord extends into the sacrum

• in the adult the cord extends from the cranial border of the atlas to L2

• level is slightly higher when the column is flexed

Spinal Cord

The spinal cord is:

• part of the central nervous system.

• segmental in nature

What is a spinal cord segment?

How many segments are there?

Note the relationship of the “nerves” to the spinal cord:

Dermatomes, Myotomes and Sclerotomes

Coracobrachialis

Latissimus Dorsi

Anconeus

Triceps

Serratus Anterior

Subscapularis

Pectoralis Major

Pectoralis Minor

Biceps

Brachialis

T1

Teres Minor

Supraspinatus

Rhomboids

Infraspinatus

Deltoid

C5 C6 C7 C8

Teres Major

“The Heavenly Seven”

Spinal Cord Enlargements

Cervical Enlargement

• the larger and more pronounced of the enlargements

• extends from about C3 to T2

Lumbar Enlargement

• extends from L1 to S3

Below the lumbar enlargement, the cord tapers to the conus medullaris.

Nerve Roots

Nerve Roots

Cauda equina:

Nerve Roots and IV Discs

Position of spinal segments relative to vertebra• Cervical – tip of the spine corresponds to the succeeding segment (C6 spine = C5

cord level)• Upper Thoracic – tip of the spine corresponds to 2 segments lower in number (T4

spine = T6 segment)• Lower Thoracic – 3 segments difference (T10 spine = L1 segment)

A 43-year-old female presents with abdominal pain of gradual onset. Physical exam reveals a non-tender, pulsating mass on the left side of the abdomen.

An MRI and angiography reveals an aortic aneurysm. She elects for surgical repair.

Physical exam following the surgery reveals on the left: a hypoactive patellar reflex [1/4] and weakness in the quadriceps [3/5].

What happened? artery of Adamkiewicz is blocked

Blood Supply to the Spinal Cord• Branches from the Vertebral Artery – 1 Anterior and 2 Posterior Spinal

Arteries • Feeder Vessels – highly variable; artery of Adamkiewicz (lumbar)• Radicular arteries – supply the roots

Blood Supply to the Spinal Cord

Spinal arteries Postcentral Radicular arteries

= supply the dorsal and ventral roots, some branches (feeder vessels) join the anterior and posterior spinal arteries

Prelaminar

Blood Supply to the Spinal Cord

Venous Drainage of the Spinal CordSpinal Veins:Internal Venous Plexus:Intervertebral veins:

Venous Drainage of the Spinal CordExternal Spinal Venous Plexus:Basivertebral Veins:

Venous Drainage of the Spinal Cord

BATSON’S PLEXUS*Know 2 facts…see notes

below

Spinal Meninges

The spinal cord (in fact the entire CNS) is enclosed in three layers of tissue, the meninges.

The meninges are from external to internal:

1.Dura mater2.Arachnoid mater3.Pia mater

Spinal Meninges

The dura mater:• is the outermost covering of the

spinal cord.

• is a thick and dense inelastic membrane

• forms a loose sheath around the cord

• attaches around the foramen magnum and to the bodies of the 2nd and 3rd cervical vertebrae

• has tubular extensions for the roots of the spinal nerve as they pass thorough the IV foramen

Spinal Meninges

Epidural space: • between the dura and the

periostium of the vertebrae

• fluids put into the sacral hiatus can spread to the base of the skull

Subdural space:• potential space between dura and

the arachnoid that contains only a serous fluid

• the arachnoid is not attached to the dura, but held to it by the normal pressure of CSF

• ends at the level of S2

Spinal Meninges

The arachnoid is a delicate membrane, that is separated from the dura by a potential subdural space.

Subarachnoid space: A REAL SPACE, NOT A POTENTIAL SPACE!

• between the arachnoid and the pia

• contains cerebrospinal fluid (CSF), blood vessels and connective tissue

• surrounds the cord and spinal nerves, ends at the level of S2

Spinal Meninges

The arachnoid is only loosely related to the underlying pia mater.

• the spinal cord ends at L2• the dural sac and arachnoid end at S2

As a result there is a large space between the arachnoid and pia in the lumbar region:

Lumbar Cistern: Go below L3 w/needle, which will push nerve roots out

of the way and will penetrate the subarachnoid space to get a CSF sample.

Sampling CSF:Lumbar puncture and intracranial pressure:- What about a newborn? Extends into sacrum in newborn.

Lumbar Cistern

Lumbar Puncture

Spinal Meninges

The pia mater:

• faithfully invests the spinal cord and brain

• is a vascular membrane• Contains denticulate ligaments,

delicate little transparent-like tissue that look like teeth coming off. ..see next slide.

Spinal Meninges

Denticulate ligaments:

• continuous with the pia on the cord, between the dorsal and ventral roots

• tooth-like process, 21 in number, stops at the T12 level

• serves to stabilize the cord within the dura

Spinal Meninges

The filum terminale:

• is a fine filament of pia and connective tissue that descends from the conus medullaris

• descends to the level of S2 where it is joined by dura (filum terminale internum)

• descends to coccygeal levels and anchors the spinal cord in the dura sac (filum terminale externum)

Spinal MeningesSpinal block: Epidural block:

Spinal Meninges