Nervous System—Spinal Cord and Spinal Nerves
Lecture 9
Today we’re going to talk about the major pathways that get impulses
to and from the brain to the rest of the body. And we’re going to be
dealing with the spinal chord and the spinal nerves.
T
his lecture examines the anatomy and functions of the spinal cord,
including the outer coverings and layers of the cord, the spinal
uid, and the internal
components of the cord. Next,
we review the re ex arc, which
allows the body to react rapidly
to changes in the external
environment, bypassing the brain.
Finally, the lecture examines the
categories and locations of the
spinal nerves.
The spinal cord is still part of the
central nervous system. It begins
at the foramen magnum, the large
hole at the base of the skull. It
connects the brain with the rest
© Hemera/Thinkstock.
of the body. Ascending (afferent)
bers bring sensory input to the
brain from the body. Descending
(efferent) bers send motor signals
to the body. The spinal re ex arc The spinal cord connects the brain with
the rest of the body.
receives sensory signals from
the body and relays immediate
responses via the motor neurons to take action without intervention from
the brain. The brain modulates the re ex, which is why a severed cord
(interrupting the brain’s modulation) causes hyperre exia.
47
, Spinal cord anatomy
The spine runs from the base of the skull to the tailbone. At the top of the
spine, the atlas holds the skull up and the axis allows it to rotate. It is divided
into four sections.
Eight spinal nerves exit the cervical (neck) section.
Twelve spinal nerves exit the thoracic (chest) section.
Five spinal nerves exit the lumbar (back) section.
Five spinal nerves exit the sacrum, in which the vertebrae are fused
together.
The spine is curved in an anterior-posterior (front to back) direction, and the
curves alternate between convex (kyphosis) and concave (lordosis), allowing
Lecture 9: Nervous System—Spinal Cord and Spinal Nerves
the spine to act as a spring.
The coverings of the spinal cord are completely analogous to those of the
skull and brain. The vertebral column is analogous to the skull. The meninges
of the spinal cord are analogous to the meninges of the brain. There are
three meninges:
The dura mater
The arachnoid
The pia mater, which is adherent to the cord
The spaces are the same (epidural, subdural, and subarachnoid). The CSF in
these spaces is continuous with the CSF of the brain. Thus CSF analysis from
a spinal tap gives information about the brain as well as the cord. Anesthesia
can be introduced into these spaces to aid surgery. However, anesthesia that
ascends too high in the spine can stop respiration. Missing CSF can cause
the brain and cord to sag and produce severe headaches. Spinal nerves near
the end of the spine simply fan out at the end of the cord, forming the cauda
equina (“horse’s tail”).
48
Lecture 9
Today we’re going to talk about the major pathways that get impulses
to and from the brain to the rest of the body. And we’re going to be
dealing with the spinal chord and the spinal nerves.
T
his lecture examines the anatomy and functions of the spinal cord,
including the outer coverings and layers of the cord, the spinal
uid, and the internal
components of the cord. Next,
we review the re ex arc, which
allows the body to react rapidly
to changes in the external
environment, bypassing the brain.
Finally, the lecture examines the
categories and locations of the
spinal nerves.
The spinal cord is still part of the
central nervous system. It begins
at the foramen magnum, the large
hole at the base of the skull. It
connects the brain with the rest
© Hemera/Thinkstock.
of the body. Ascending (afferent)
bers bring sensory input to the
brain from the body. Descending
(efferent) bers send motor signals
to the body. The spinal re ex arc The spinal cord connects the brain with
the rest of the body.
receives sensory signals from
the body and relays immediate
responses via the motor neurons to take action without intervention from
the brain. The brain modulates the re ex, which is why a severed cord
(interrupting the brain’s modulation) causes hyperre exia.
47
, Spinal cord anatomy
The spine runs from the base of the skull to the tailbone. At the top of the
spine, the atlas holds the skull up and the axis allows it to rotate. It is divided
into four sections.
Eight spinal nerves exit the cervical (neck) section.
Twelve spinal nerves exit the thoracic (chest) section.
Five spinal nerves exit the lumbar (back) section.
Five spinal nerves exit the sacrum, in which the vertebrae are fused
together.
The spine is curved in an anterior-posterior (front to back) direction, and the
curves alternate between convex (kyphosis) and concave (lordosis), allowing
Lecture 9: Nervous System—Spinal Cord and Spinal Nerves
the spine to act as a spring.
The coverings of the spinal cord are completely analogous to those of the
skull and brain. The vertebral column is analogous to the skull. The meninges
of the spinal cord are analogous to the meninges of the brain. There are
three meninges:
The dura mater
The arachnoid
The pia mater, which is adherent to the cord
The spaces are the same (epidural, subdural, and subarachnoid). The CSF in
these spaces is continuous with the CSF of the brain. Thus CSF analysis from
a spinal tap gives information about the brain as well as the cord. Anesthesia
can be introduced into these spaces to aid surgery. However, anesthesia that
ascends too high in the spine can stop respiration. Missing CSF can cause
the brain and cord to sag and produce severe headaches. Spinal nerves near
the end of the spine simply fan out at the end of the cord, forming the cauda
equina (“horse’s tail”).
48
