The central nervous system (CNS) is made up of the brain
and spinal cord. The area between the arachnoid space and the pia mater contains cerebral spinal fluid (CSF).
The spinal cord is divided into 31 segments that send nerve rootlets out into the body through intervertebral foramen.
Each segment of the spinal cord is associated with a pair of ganglia called dorsal root ganglia, which are situated just outside of the spinal cord and contain cell bodies of sensory neurons. These neurons travel into the spinal cord via the dorsal roots.
Ventral roots consist of axons from motor neurons, which bring information to the periphery from cell bodies within the CNS. Dorsal roots and ventral roots come together and exit the intervertebral foramina as they become spinal nerves.
A thick, whitish cord of nerve tissue which is a major part of the vertebrate central nervous system. It extends from the brain stem down through the spine, with nerves branching off to various parts of the body.
The conduction of impulses inwards to the
brain or spinal cord.
A lumbar puncture (spinal tap) is an example of a medical procedure that directly targets the spinal cord.
The birth defect
spina bifida is a failure of
the vertebral arch to close, exposing the spinal cord.
The spinal cord is a long, thin, tubular bundle of nervous
tissue and support cells that extends from the medulla oblongata of the brain to the level of the lumbar region. The brain and spinal cord
together make up the central nervous system (CNS). The spinal cord, protected
by the vertebral column, begins at the occipital bone and extends down to the
space between the first and second lumbar vertebrae. The spinal cord has a varying width,
ranging from 0.5 inch thick in the cervical and lumbar regions to 0.25 inch
thick in the thoracic area. The length of the spinal cord is approximately 45
cm (18 in) in men and about 43 cm (17 in) long in women.
The spinal cord is protected by three layers of tissue called meninges and divided into three regions.
Spinal Cord Tissue Layers
The dura mater is the outermost layer of spinal cord tissue, forming a tough
protective coating. The space between the dura mater and the surrounding bone
of the vertebrae is called the epidural space. The epidural space is filled
with adipose tissue and contains a network of blood vessels. The middle layer
is called the arachnoid mater. The pia mater is the innermost protective layer
and is tightly associated with the surface of the spinal cord. The space
between the arachnoid and pia maters is called the subarachnoid space and is
where the CSF is located. It is from this location at the level of the lumbar
region that CSF fluid is obtained in a spinal tap.
Spinal Cord Regions
In cross-section, the peripheral region of the cord
displays neuronal white matter tracts containing sensory and motor neurons.
Internal to this peripheral region is the gray, butterfly-shaped central region
made up of nerve cell bodies. This central region surrounds the central canal,
which is an anatomic extension of the spaces in the brain known as the
ventricles and like the ventricles, contains cerebrospinal fluid.
The spinal cord is divided into cervical, thoracic,
and lumbar regions. The cervical region is divided into eight levels that are
related to different motor and sensory functions in the neck and the arms. The
spinal nerves of the thoracic region supply the thorax and abdomen. The nerves
of the lumbosacral spinal cord supply the pelvic region, legs, and feet.
Spinal Cord Nerve Branches
Thirty-one pairs of spinal nerves (sensory and
motor) branch from the human spinal cord. Each spinal nerve is formed from the
combination of nerve fibers from its posterior and anterior roots. The
posterior root is the sensory (afferent) root that carries sensory information
to the brain from other areas of the body. The anterior root is the motor
(efferent) root that carries motor information to the body from the
The spinal nerve emerges from the spinal column
through the opening (intervertebral foramen) between adjacent vertebrae. An
exception is the first spinal nerve pair (C1), which emerges between the
occipital bone and the atlas (the first vertebra). The swelling found in the
posterior root is the posterior (dorsal) root ganglion, which contains the cell
bodies of sensory neurons. The anterior (ventral) root contains axons of motor
neurons that conduct nerve impulses from the CNS to other parts of the body
such as the muscles.
The cauda equina ("horse's tail") is the
name for the collection of nerves in the vertebral column that extends beyond
the cord. The nerves that compose the cauda equina supply the pelvic organs and
lower limbs, including motor innervation for the hips, knees, ankles, feet, and internal and external anal sphincters. In addition, the cauda equina extends to
sensory innervation of the perineum.
Primary Spinal Cord Function
spinal cord functions primarily in the transmission of neural signals between
the brain and the rest of the body, but it also contains neural circuits that
can independently control numerous reflexes and central pattern generators. The
three major functions of the spinal cord are the conduction of motor
information traveling down the spinal cord, the conduction of sensory
information in the reverse direction, and acting as the center for conducting certain reflexes. The spinal cord is the main pathway for information
connecting the brain and peripheral nervous system.