SPINAL CORD

ANATOMY OF THE SPINAL CORD

Structure of the spinal cord

Tracts of the spinal cord

Spinal cord syndromes

The Nervous System

• Coordinates the activity of muscles, organs, senses, and actions

• Made up of nervous tissue

• Has 3 main functions:

– 1. Receives sensory Input

– 2. Integration

– 3. Dictates motor output

Spinal Cord

Copyright 2010, John Wiley & Sons, Inc.

Spinal Cord Functions • Pathways for nerve impulses within tracts

– Ascending (sensory). Example: spinothalamic

– Descending (motor). Example: corticospinal

• Reflexes: fast, involuntary sequences of actions in response to stimuli

– Can be simple (withdrawal) or complex (learned sequence such as driving car)

– Levels

• Spinal (reflex arc): simple

• Cranial: more complex

Reflex Arc 1. Sensory receptor: responds to stimulus

2. Sensory neuron: through dorsal root ganglion and root posterior horn

3. Integrating center: single synapse between sensory and motor neurons

4. Motor neuron: from anterior horn ventral root spinal nerve

5. Effector: muscle responds

Example of Reflex Arc: Patellar Reflex

1. Sensory receptor is stimulated by tap on patellar tendon

2. Sensory neuron: through dorsal root spinal cord

3. Integrating center: single synapse in spinal cord

4. Motor neuron: through ventral root spinal nerve femoral nerve

5. Effector: quads contract, extend leg

Example of Reflex Arc: Patellar Reflex

General Organization

• Spinal cord is SMALL! – 42-45 cm long

– 1 CM wide at widest point

– Does not extend all the way to the bottom of the spinal column

• Pattern of grey/white matter is reversed in the cord – White matter tracts on outside

– Grey matter on the inside

– Staining reverses this!!!

General Organization

White matter (tracts

of axons) axons)

Grey Matter

(cell bodies) )

General Organization

• Spinal cord is segmented anatomically

• Input and output occurs in groups of rootlets arranged in a series longitudinally along the cord

– Dorsal rootlets -- Input -- carry sensory information

– Ventral rootlets -- Output -- motor neurons

General Organization

• Each set of rootlets forms a spinal nerve that innervates a corresponding segment of the body, called a dermatome

General Organization

• There are 31 segments in the spinal cord:

– 8 cervical (C1 - C8)

– 12 Thoracic (T1 - T12)

– 5 Lumbar (L1 - L5)

– 5 Sacral (S1 - S5)

– 1 Coccygeal

General Organization

General Organization

• The spinal cord is housed within the vertebral column

• Each cord segment has a corresponding vertebra of the same name (e.g., C3)

• Spinal nerves enter/exit underneath their corresponding vertebral segment

General Organization

General Organization

Grey and White Matter

Grey and White Matter

Grey Matter = Cell Body

White Matter = Myelinated axon

Grey and White Matter

• Grey matter

– Cortex

– Nucleus (CNS)

– Ganglion (PNS) Exception: Basal Ganglia

Grey and White Matter

• White Matter

– Nerve (PNS)

– Tract (CNS)

– Fasciculus/Funiculus -- Group of fibers with common origin and destination

– Lemniscus -- Ribbon-like fiber tract

– Peduncle -- Massive group of fibers -- usually several tracts

Grey and White Matter

• Tracts are named with origin first, then destination – Corticospinal tract -- cortex to spinal cord

– Mammilothalamic tract -- Mammilary bodies to thalamus

– Spinocerebellar tract -- Spinal cord to cerebellum

– Corticobulbar tract -- Cortex to brain stem

DIVISIONS OF THE NERVOUS SYSTEM

• Central Nervous System (CNS)

– Brain and spinal cord

– Interprets incoming sensory signals

– Dictates motor responses

• Peripheral Nervous System (PNS)

– Ganglia

– Nerves • Cranial nerves and spinal nerves

– Communication between regions of body and CNS

- Spinal Nerve (C8, T12, L5, S5, Cx1) - Segmental Structure of Neural Tube Origin

- Comparable to Input-Output (IO) System of the Computer

Spinal Cord

Spinal cord

Spinal cord

• Internal gray matter: presence of neurons relaying and integrating motor/sensory impulses

• Fiber tracts: sensory and motor

Spinal cord

• Segmental organization derived from neural tube and somites

• Spinal segments - 31

• Spinal nerves: C8, T12, L5, S5, Co1

• Comparable to „input-output„ systemof computer

• Seat of reflexes

• Origin of ascending and descending projections

PNS

Somatic

ANS Sympathetic

Parasymp.

Enteric

CNS

PNS

• Nervous system structures outside the brain and spinal cord

• Structural components:

– Sensory receptors

– Motor endings

– Nerves and ganglia

PNS - Nervous Tissue

• Made up of 2 cells:

–Neurons

•Conduct nervous impulses

–Supporting cells

• Surround the neurons

•Ex. Glial cells

35

The Neuron

• Nerve cells

• Transmit signals in form of nerve impulses

• Have extreme longevity

• Do not divide

• High metabolic rate

Neuron-To-Neuron Transmission

synapses

Neuronal Anatomy

• Cell body (soma)

– Most are in CNS

• Neuron processes

– Dendrites • Toward cell body

– Axons • Transmit away from

cell body

• Synapses

– Site where neurons communicate

Neuronal Anatomy

• Myelin sheath

– Fatty sheath that surrounds most nerve fibers

• Reflex arc

– Responses to a stimulus

• Interneuron

– Nerve cell that lies between a sensory neuron and motor neuron in a reflex arc

– Confined entirely within the CNS

PNS - Sensory and Motor Signals

• Divided by the body regions they serve:

• Sensory division

– Somatic sensory

– Visceral sensory

• Motor division

– Somatic motor

– Visceral motor

The Spinal Cord

• Foramen magnum to L1 or L2

• Runs through the vertebral canal of the vertebral column

• Functions 1. Sensory and motor innervation of entire body inferior to

the head through the spinal nerves

2. Two-way conduction pathway between the body and the brain

3. Major center for reflexes

• Fetal 3rd month: ends at coccyx • Birth: ends at L3 • Adult position at approx L1-2

during childhood • End: conus medullaris

– This tapers into filum terminale of connective tissue, tethered to coccyx

• Spinal cord segments are superior to where their corresponding spinal nerves emerge through intervertebral

• Denticulate ligaments: lateral shelves of pia mater anchoring to dura (meninges: more later)

Spinal cord

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The Spinal Cord

ventral root

pia mater

dura mater

arachnoid

grey matter

dorsal root

white matter

spinal nerves

The Spinal Cord

spinal cord

spinal nerve

vertebra

Nerve Pathways into the

Spinal Cord sensory pathway

motor pathway

Autonomic Nervous System

• Visceral Motor Function

• Not easily controlled by will – Get nervous and sweat

• Innervate smooth muscle, cardiac muscle, glands

• Regulate visceral function – Heart rate, blood pressure, digestion, urination

• Has 2 divisions: – Parasympathetic

– Sympathetic

ANS

• Parasympathetic – Enables body to unwind

and calm down

– Most active when body at rest

– Routine maintenance functions

– Craniosacral division

• Fibers emerge from brain and sacral spinal cord

• Sympathetic – “fight or flight”

– Mobilizes the body during extreme situations

– Becomes active when extra metabolic effort needed

– Thoracolumbar division

• Fibers arise from thoracic and lumbar parts of spinal cord

ANS

• Includes a chain of 2 motor neurons – Preganglionic neuron

• Preganglionic axon

– Ganglionic neuron

• Postganglionic axon

– Autonomic neuron synapses 2 neurons

PNS

• Somatic NS

• Autonomic NS

– Sympathetic division

– Parasympathetic division

– Enteric division

Somatic Nervous System

• Innervates skeletal muscle

• Neurons runs from CNS directly to muscle

• Consists of single neuron plus skeletal muscle cells

• Voluntary control

– Running, moving limbs, typing on a computer!

CNS – Spinal Cord

• Runs through vertebral canal of the vertebral column

• Protected by bone, meninges, and cerebrospinal fluid

• Spinal cord made of a core of gray matter surrounded by white matter

• 31 pairs of spinal nerves branch off spinal cord through intervertebral foramen

• Functions in many ways:

– Involved in sensory and motor innervation of body inferior to the head (through spinal nerves)

– Provides a 2-way conduction pathway for signals between body and brain

– Major center for reflexes

Spinal Cord Growth

• Until 3rd month of development, does not run to coccyx

• As vertebral column grows caudally, spinal cord becomes more rostral

• At birth, ends at L3

• During childhood, terminates at L1 and L2

• Adults runs from medulla oblongata to L1

Regions of the Spinal Cord

• Cervical

• Thoracic

• Lumbar

• Sacral

• Coccygeal

• Cervical + Lumbar enlargements

• Cauda equina

• Conus medullaris

• Filum terminale

Protection: Bone

Meninges

CSF (cerebrospinal fluid) 3 meninges:

dura mater (outer)

arachnoid mater (middle)

pia mater (inner)

3 potential spaces

epidural: outside dura

subdural: between dura &

arachnoid

subarachnoid: deep to arachnoid

Copyright 2010, John Wiley & Sons, Inc.

Spinal Meninges and Spaces • Epidural space: between vertebrae and dura

mater • Dura mater- tough ,dense connective tissue

– Extends to vertebra S2 (well beyond spinal cord)

• Arachnoid mater: resembles spider’s web – Extends into subarachnoid space

• Subarachnoid space – CSF circulates in this space

• Pia mater: thin, delicate layer – Adheres to surface spinal cord (and brain) – Contains blood vessels

Copyright 2010, John Wiley & Sons, Inc.

Spinal Meninges

and Spaces

Meninges of Brain and Spinal Cord

• Dura mater (superficial) – Spinal dural sheath – Does not attach to bone

• Epidural space – Fat and veins – Between dura mater and

vertebra • Subdural space

– Between dura mater and arachnoid

Meninges of Brain and Spinal Cord

• Arachnoid mater (middle) – Impermeable layer = barrier – Raised off pia mater by

rootlets • Subarachnoid space

– Between arachnoid and pia mater

– Contains CSF • Pia mater (deep)

– Highly vascular – Adheres to brain/spinal cord

tissue

Meninges of

the spinal cord

• Dura mater

• Arachnoid membrane

• Pia mater

Denticulate ligament

- specilization of the pia

mater

- landmark for cordotomy

Meninges of the spinal cord

Meninges of the spinal cord

Gray Mater

• Consists of neuron cell bodies, unmyelinated axons, dendrites, and neuroglia

• Shaped like an “H”

– Gray commissure (crossbar)

– Central canal

• Posterior horns

• Anterior horns

Gray Mater

• Posterior horns – Consist of interneurons that transmit in from outside spinal cord into it – Dorsal root contain sensory fibers

• Somatic Sensory (SS) • Visceral Sensory (VS)

– Dorsal root ganglia - swelling in dorsal root that these interneurons pass through • Anterior horns

– Cell bodies of motor neurons send info out of spinal cord to muscles and glands – Ventral Root contains Motor Fibers

• Visceral Motor • Somatic Motor

Arc reflex

• Arc reflex (fast and involuntary)

White Mater

• Surrounds gray matter

• Composed of myelinated and unmyelinated axons

• Divided into white columns (funiculi)

• Posterior funiculus

• Anterior funiculus

• Lateral funiculus

• Allow for communication between

– Parts of the spinal cord

– Spinal cord and brain

White Mater

• 3 types of nerve fibers: – Ascending

• Carry sensory info from sensory neurons of body to brain

• touch, pressure, pain, temperature

– Descending • Carry motor instructions from brain to

spinal cord • Contraction of muscles and secretion

of glands • control precise, skilled movement =

writing, maintain balance, create movement

– Commissural • Cross from one side of cord to the

other

Gray and White Matter • Like spinal cord but with

another layer of gray outside the white – Called cortex

– Cerebrum and cerebellum have

• Inner gray: “brain nuclei” (not cell nuclei) – Clusters of cell bodies

Remember, in PNS clusters of cell bodies were called “ganglia”

More words: brains stem is caudal (toward tail)

to the more rostral (noseward) cerebrum

Copyright 2010, John Wiley & Sons, Inc.

Gross Anatomy of Spinal Cord • Extends from medulla of brain to L2 vertebra

• Cauda equina (horse’s tail) – Extends inferior to end of spinal cord

– Consists of roots of lumbar, sacral and coccygeal spinal nerves

• Left and right halves partially separated by – Anterior median fissure and posterior median

sulcus

– Small central canal (filled with CSF) in middle

• Enlargements: cervical and lumbar regions – Points of origins of nerves to upper and lower limbs

Copyright 2010, John Wiley & Sons, Inc.

Gross Anatomy of Spinal Cord

Copyright 2010, John Wiley & Sons, Inc.

Internal Structure of Spinal Cord

• Dura mater

• Arachnoid mater

• Pia mater

Spinal cord

coverings

and spaces

http://www.eorthopod.com/images/ContentImages/pm/pm_general_esi/pmp_g

eneral_esi_epidural_space.jpg

Spinal cord anatomy

• Posterior median sulcus (“p”)

• Anterior median fissure (“a”)

• White matter (yellow here)

• Gray matter (brown here)

“p”

“a”

Gray/White in spinal cord

• Hollow central cavity (“central canal”)

• Gray matter surrounds cavity • White matter surrounds gray

matter (white: ascending and descending tracts of axons)

• “H” shaped on cross section • Dorsal half of “H”: cell bodies of

interneurons • Ventral half of “H”: cell bodies of

motor neurons • No cortex (as in brain)

Dorsal (posterior)

white

gray

Ventral (anterior)

Central canal______

Spinal cord anatomy

• Gray commissure with central canal

• Columns of gray running the length of the spinal cord

– Posterior (dorsal) horns (cell bodies of interneurons)

– Anterior (ventral) horns (cell bodies of motor neurons)

• Lateral horns in thoracic and superior lumbar cord

* *

*

*

White matter of the spinal cord (myelinated and unmyelinated axons)

• Ascending fibers: sensory information from sensory neurons of body up to brain

• Descending fibers: motor instructions from brain to spinal cord – Stimulates contraction of body’s muscles

– Stimumulates secretion from body’s glands

• Commissural fibers: white-matter fibers crossing from one side of cord to the other

• Most pathways cross (or decussate) at some point

• Most synapse two or three times along the way, e.g. in brain stem, thalamus or other

Sensory tracts

Motor tracts

The spinal

cord provides

a vital link

between the

brain and the

rest of the

body, and yet

it exhibits

some

functional

independence

from the

brain.

The adult

spinal cord

travels from

the foramen

magnum

and

terminates

within the

vertebral

foramen of

the first

lumbar

vertebra

(L1) in

adults.

The spinal cord

can be

subdivided into

five regions:

cervical region,

thoracic region,

lumbar region,

sacral region,

and coccygeal

region (which

has only one

pair of nerves).

Don’t be confused and think

that the sacral “region” of the

spinal cord is surrounded by

sacral vertebrae. It is NOT!

The diameter of the

spinal cord is the

largest in the cervical

region and there is a

larger proportion of

white matter

compared to gray

matter.

The diameter of the sacral

region of the spinal cord

(which is surrounded by the

T12/L1 vertebrae) is the

smallest and the proportion of

gray matter is largest in the

spinal cord.

The cervical enlargement

contains the neurons that

innervate the upper limbs

The lumbar

enlargement contains

the neurons that

innervate the lower

limbs.

General Organization

Cervical enlargement

C5 - T1

Lumbar enlargement

L2 - S3

Cervical enlargement

C5 - T1

The tapering end of

the spinal cord is

called the conus

medullaris.

The conus

medullaris is

surrounded by L1

in and adult and

L2 in a child.

The adult spinal cord

terminates at the level of

the first lumbar vertebra

(L1)

In a developing child,

the spinal cord can

extend to the level of

the second lumbar

vertebra (L2)

The cauda

equina

(horse’s tail)

is composed

of nerves that

arise from

the conus

medullaris

and extend

inferiorly.

The filum terminale,

which is composed of

pia mater, extends from

the conus medullaris to

the coccyx. Note the

subarachnoid space also

continues for some

distance.

There are 31

pairs of spinal

nerves that

serve defined

segments of the

human body.

There are 8 pairs of

cervical spinal nerves.

This is possible because

the first pair (C1 spinal

nerves) exits the spinal

column between the

occipital bone and the

atlas (C1). The

remaining 7 pairs (C2-

C8 spinal nerves) exit

below each of the 7

cervical vertebrae via

the intervertebral

foramina. All the

spinal nerves are mixed

nerves.

The spinal cord

is surrounded by

the dura,

arachnoid, and

pia maters (the

meninges)

The epidural space is between the vertebra and the dura mater

Epidural

anesthesia

LP (lumbar puncure) = spinal tap (needle introduced into subdural space to collect CSF)

Lumbar spine needs

to be flexed so can go between spinous processes

Epidural space is external to dura

Anesthestics are often injected into epidural space

Injection into correct space is vital; mistakes can be lethal

Originally thought to be a narrow

fluid-filled interval between the

dural and arachnoid; now known

to be an artificial space created by

the separation of the arachnoid

from the dura as the result of

trauma or some ongoing

pathologic process; in the healthy

state, the arachnoid is attached to

the dura and a naturally occurring

subdural space is not present.

http://cancerweb.ncl.ac.uk/cgi-

bin/omd?subdural+space

Lumbar Puncture – lumbar (terminal) cistern

Lumbar Puncture (= Spinal Tap)

For clinical examination of CSF or

administration of radiopaque dyes,

drugs and sometimes anesthetics

However: mostly “epidurals” for

anesthetics

L3

L4

Epidural

anesthesia

Effect of epidural

anesthesia

A person who needs an epidural!

The dura mater

extends along the

entire length of the

vertebral canal and

surrounds the spinal

cord. It also extends

along the initial

portion of the

radiating spinal

nerves

The subarachnoid

space is a real

space filled with

CSF

In this midsagittal picture #3 is the dura mater, #5 is the spinal cord,

# 4 is the epidural space, and #6 is the subarachnoid space where

CSF is located (#1 is an intervertebral disc and #2 is the body of a

vertebrae).

Needle for

spinal tap

Spinal taps are done

between the third and

fourth lumbar

vertebrae because

there is no spinal cord

at that location

The tip of the

needle is

inserted into the

subarachnoid

space outside the

cauda equina and

spinal fluid is

removed for

testing.

The entering

pressure can

be

determined

when the

needle is

inserted into

the

subarachnoid

space during

a spinal tap.

Spinal fluid is normally

crystal clear like water.

Cloudy spinal fluid, like

the specimen shown, is a

sign of white blood cells

(pus). The most common

cause for white blood

cells in the spinal fluid is

viral or bacterial

meningitis.

The pia mater

directly adheres to

the spinal cord

The cross-sectional view

shows that the gray

matter is central and

the white matter is

peripheral

The peripheral

white matter

contains ascending

and descending

tracts of nerves

traveling to and

from the brain.

The central gray

matter serves as a

center for spinal

reflexes.

The central canal runs the entire length of the spinal cord, is

contiguous with the brain and contains cerebrospinal fluid (CSF)

The spinal cord

develops as 31

segments, each of

which gives rise to a

pair of spinal nerves that

emerge from the cord

through the

intervertebral foraminae

Nerves can be sensory, motor, or mixed (sensory and motor)

Mixed nerves carry both types of information and some axons are

transmitting impulses in one direction, while other axons are

transmitting impulses in the opposite direction. All spinal nerves

are mixed nerves.

There are 8 pairs of

cervical spinal nerves.

This is possible because

the first pair (C1 spinal

nerves) exits the spinal

column between the

occipital bone and the

atlas (C1). The

remaining 7 pairs (C2-

C8 spinal nerves) exit

below each of the 7

cervical vertebrae via

the intervertebral

foramina. All the

spinal nerves are mixed

nerves.

Most of the

spinal nerves are

associated with

specific

dermatomes (an

area of skin

innervated by all

the cutaneous

neurons of a

certain spinal or

cranial nerve).

Dermatome

map. Note

the trigeminal

nerve has

dermatomes

on the face.

trigeminal

Dermatomes of the trigeminal nerve (cranial nerve V) are seen

on the face

Note that the

trigeminal nerve

has dermatomes

on the face (see

white area) and

that the first pair

of cervical spinal

nerves (C1

spinal nerves)

are not

represented on

the surface at all.

The bony vertebral column

(dark line shown) grows

faster than the spinal cord.

A newborn’s spinal cord

extends to about the level of

L3. A child’s spinal cord

may extend to the level of

L2. An adult’s spinal cord

typically terminates at the

level of L1.

Bony vertebral column

The inner delicate

spinal cord terminates

in an adult, as the

conus medullaris, at

the level of the

L1vertebra.

Damage to the spinal cord

can lead to paralysis or death

ANTERIOR VIEW OF THE SPINAL CORD

CERVICAL CORD

(8 nerves)

THORACIC CORD

(12 nerves)

LUMBAR CORD

(5 nerves)

SACRAL CORD

(5 nerves)

The spinal cord begins at the base

of the medulla oblongata and

extends to about the 2nd lumbar

vertebra. The cord is divided into

four regions each of which has

branches called spinal nerves.

SAGITAL SECTION OF LOWER SPINE

The inferior, terminal portion of the

spinal cord is at the level of the 2nd

lumbar vertebra. Branches from

the lumbar region pass downward

from the cone-shaped tip (conus

medullaris) of the spinal cord

forming the cauda equina (horse’s

tail). Cauda equina

cranial nerves- 12 pr

spinal nerves- 31 pr

Spinal Nerves (31 Pairs)

• Part of the PNS (Somatic)

• Lie in intervertebral foramina

– Send lateral branches to body

• Named according to their point of issue from the vertebral column

– 8 pairs of cervical spinal nerves; C1-C8

– 12 pairs of thoracic spinal nerves; T1-T12

– 5 pairs of lumbar spinal nerves; L1-L5

– 5 pairs of sacral spinal nerves; S1-S5

– 1 pair of coccygeal spinal nerves; C01

Spinal nerves

• Part of the peripheral nervous system

• 31 pairs attach through dorsal and ventral nerve roots

• Lie in intervertebral foramina

Damage below

C3 also results in

quadriplegia,

but the person

can still utilize

their diaphragm

for breathing via

their intact

phrenic nerves.