SPINAL CORD
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.