Spinal Cord Anatomy
Spinal Cord Sections
Spinal Cord Overview
The Spinal Cord is connected to the brain and is
about the diameter of a human finger. From the brain the spinal
cord descends down the middle of the back and is surrounded and
protected by the bony vertebral column. The spinal cord is surrounded
by a clear fluid called Cerebral Spinal Fluid (CSF), that acts as
a cushion to protect the delicate nerve tissues against damage from
banging against the inside of the vertebrae.
The anatomy of the spinal cord itself, consists of
millions of nerve fibres which transmit electrical information to
and from the limbs, trunk and organs of the body, back to and from
the brain. The nerves which exit the spinal cord in the upper section, the neck, control breathing and the arms. The nerves which exit the spinal cord in the mid and lower section of the back, control the trunk and legs, as well as bladder, bowel and sexual function.
The nerves which carry information from the brain to muscles are called Motor Neurones. The nerves which carry information from the body back to the brain are called Sensory Neurones. Sensory Neurones carry information to the brain about skin temperature, touch, pain and joint position.
The brain and spinal cord are referred to as the Central
Nervous System, whilst the nerves connecting the spinal cord to
the body are referred to as the Peripheral Nervous System.
Ascending and Descending Spinal Tracts
The nerves within the spinal cord are grouped together
in different bundles called Ascending and Descending tracts.
Ascending tracts within the spinal cord carry sensory information
from the body, upwards to the brain, such as touch, skin temperature,
pain and joint position.
Descending tracts within the spinal cord carry
information from the brain downwards to initiate movement and
control body functions.
Nerves called the spinal nerves or nerve roots, branch
off the spinal cord and pass out through a hole in each of the vertebrae
called the Foramen. These nerves carry information from the spinal cord
to the rest of the body, and from the body back up to the brain.
There are four main groups of spinal nerves, which
exit different levels of the spinal cord.
These are in descending order down the vertebral
Cervical Nerves "C" : (nerves
in the neck) supply movement and feeling to the arms, neck and
upper trunk. Also control breathing.
Thoracic Nerves "T" : (nerves
in the upper back) supply the trunk and abdomen.
Lumbar Nerves "L" and Sacral
Nerves "S" : (nerves in the lower back) supply the
legs, the bladder, bowel and sexual organs.
Spinal Cord Level Numbering System
The spinal nerves carry information to and from different
levels (segments) in the spinal cord. Both the nerves and the segments
in the spinal cord are numbered in a similar way to the vertebrae.
The point at which the spinal cord ends is called the conus medullaris,
and is the terminal end of the spinal cord. It occurs near lumbar
nerves L1 and L2. After the spinal cord terminates, the spinal nerves
continue as a bundle of nerves called the cauda equina. The upper
end of the conus medullaris is usually not well defined.
There are 31 pairs of spinal nerves which branch
off from the spinal cord. In the cervical region of the spinal cord,
the spinal nerves exit above the vertebrae. A change occurs with
the C7 vertebra however, where the C8 spinal nerve exits the vertebra
below the C7 vertebra. Therefore, there is an 8th cervical spinal
nerve even though there is no 8th cervical vertebra. From the 1st
thoracic vertebra downwards, all spinal nerves exit below their
equivalent numbered vertebrae.
The spinal nerves which leave the spinal cord are
numbered according to the vertebra at which they exit the spinal
column. So, the spinal nerve T4, exits the spinal column through
the foramen in the 4th thoracic vertebra. The spinal nerve L5 leaves
the spinal cord from the conus medullaris, and travels along the
cauda equina until it exits the 5th lumbar vertebra.
The level of the spinal cord segments do not relate
exactly to the level of the vertebral bodies i.e. damage to the
bone at a particular level e.g. L5 vertebrae does not necessarily
mean damage to the spinal cord at the same spinal nerve level.
Spinal Cord Nerve Levels
Showing The Relationship Between Spinal Nerve Roots and Vertebrae
Support : Types
of Paralysis : Vertebral Column : Spinal
Cord : Myotomes & Dermatomes
: Autonomic Dysreflexia : Spasticity
& Spasms : Temperature Regulation
: Respiratory System : Pressure
Sores : Spinal Cord Injury