Download 26: Spinal Cord, Spinal Nerves, White and Grey Matter

THE HUMAN BODY 1
The dura mater
(of the meninges)
wraps the spinal
cord
26: Spinal Cord,
Spinal Nerves, White
and Grey Matter
Cauda
equina
Spinal cord
The spinal cord runs down through the vertebral
foramina (singular: vertebral foramen, a hole
between the body and vertebral arch of a
vertebra) of the vertebrae.
It is covered in three layers of connective tissue
called the meninges, which are continuous
with the brain.
Conus
medullaris
(end of spinal
cord proper).
At L1
Filum
terminale
The spinal cord itself ends at the conus
medullaris, situated at the first lumbar (L1)
vertebra.
It is important to learn all of the names on
Figure 3.26.
Note that ventral is essentially another way
of saying anterior, and dorsal is essentially
interchangeable with posterior.
Spinal nerves
The ventral root branches off the anterior
aspect of the spinal cord and carries fibres
from efferent neurons (which carry information
If we took a transverse section of the spinal
cord, we would see something like this:
Dorsal
(sensory) root
ganglion
Posterior
horn
Figure 3.25
away from the central nervous system [CNS])
out to effectors in the periphery. These neurons
are also known as motor neurons.
The dorsal root branches off the posterior
aspect of the spinal cord and carries fibres
from afferent neurons (which carry information
towards the CNS) from sensors in the
periphery. These neurons are also known as
sensory neurons, and their cell bodies are
located in the dorsal root ganglion.
The ventral root and dorsal root come together
and form a spinal nerve. Spinal nerves are
always mixed nerves, as they carry both
sensory and motor fibres.
Posterior
median
sulcus
These nerves join to make
one mixed nerve
Posterior column
(where the dorsal
column tract travels)
Lateral
column
Afferent fibres
(from body)
Efferent fibres
(to body)
Nervous
The nerves continue in a structure called the
cauda equina that terminates at the filum
terminale.
Anterior
column
Anterior
horn
Anterior
median fissure
Figure 3.26
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Nervous
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THE HUMAN BODY 1
Spinal nerves branch again into dorsal rami
and ventral rami (singular: ramus).
Dorsal rami innervate the back and ventral
rami innervate most other regions of the body
except for the head.
The ventral rami communicate with the
sympathetic chain via sympathetic rami (the
white ramus communicans and grey ramus
communicans).
These axons are arranged into fascicles that
are covered in a second layer of connective
tissue known as the perineurium.
A tough fibrous sheath of connective tissue
surrounds collections of fascicles and is called
epineurium.
Perineurium
(wrapping a
fascicle)
Epineurium
Spinal nerves come in pairs, with one nerve on
either side of the spinal cord.
Nerves exit the spinal cord by passing through
spaces between the vertebrae (intervertebral
foramina between adjacent vertebral arches).
There are 30 vertebrae, but 31 pairs of
spinal nerves as there are 8 cervical nerves
(in the cervical region nerves exit above the
vertebrae, but this changes at the C7 vertebra,
below which the C8 nerve exits, therefore the
extra cervical nerve).
Nervous
Dorsal ramus
(supplies
posteriorally)
Axon
Endoneurium
(wrapping axon)
Figure 3.28
White and grey matter
Spinal nerve
White matter:
•Contains myelinated axons (that appear
white because of the lipid material in
myelin).
•Found in the periphery of the spinal cord in
regions known as columns (See Figure 3.26
on page 1).
•Located in the central region of the brain.
Grey matter:
White ramus communicans
(myelinated/preganglionic)
Ventral ramus
(supplies
anteriorally)
Grey ramus communicans
(unmyelinated/postganglionic)
Figure 3.27
•Contains the cell bodies of neurons and
non-myelinated axons.
•Found in the centre of the spinal cord in the
regions known as horns (See Figure 3.26 on
page 1).
•Located in the peripheral regions of the
brain, and the ganglia (term for a group
of cell bodies in the peripheral nervous
system) or nuclei (term for same thing in
central nervous system).
Nerve composition
Nerves are made of nervous tissue, and are
structurally supported by connective tissue,
which also provides stretch resistance.
A layer of connective tissue called endoneurium
surrounds individual axons.
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Nervous
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