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Chapter 13

Anatomy and Physiology HAP101 Chapter Notes - Chapter 13: Intervertebral Foramina, Spinal Canal, Peripheral Nervous System

Anatomy and Physiology
Course Code
Anatomy and Physiology HAP101
Tania Killian

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HAP101 Chapter 13: Central Nervous System ~ The Spinal Cord
13.1: Spinal Cord Anatomy
The first layer of protection for the CNS is the skull and the vertebral column
o The skull encases the brain and the vertebral column surrounds that spinal cord, providing strong
protective defenses against damaging blows or bumps
The second layer of protection for the CNS is the meninges, three membranes that lie between the body
encasement and the nervous tissue in both the brain and the spinal cord
The third layer of protection for the CNS is the space between two of the meningeal membranes
o This space contains cerebrospinal fluid, a buoyant liquid that suspends the CNS tissue in weightless
environment while surrounding it with a shock-absorbing, hydraulic cushion
Vertebral Column
o The spinal cord is located within the vertebral canal of the vertebral column
o The surrounding vertebra provide a sturdy shelter for the enclosed spinal cord. The vertebral ligaments,
meninges, and cerebrospinal fluid provide additional protection
o These are three protective, connective tissue coverings that encircle the spinal cord and the brain.
o Dura mater: this is the most superficial of the three. It is a thick, strong layer composed of dense
irregular connective tissue. It forms a sac from the level of the foramen magnum in the occipital bone,
where it is continuous with the dura mater of the brain, to the second sacral vertebra. It is also continuous
with the epineurium, the outer covering of the spinal and cranial nerves
o Arachnoid mater: this layer is a thin, avascular covering comprised of cells and thin, loosely arranged
collagen and elastic fibres. It is named as such because of its spider’s web arrangement of collagen and
elastic fibres. It is continuous through the foramen magnum with the arachnoid mater of the brain.
Between the dura mater and the arachnoid mater is a thin subdural space (contains interstitial fluid)
o Pia mater: this layer is a thin, transparent connective tissue that adheres to the surface of the spinal cord
and brain. Within the pia mater are many blood vessels that supply oxygen and nutrients to the spinal
cord. Between the arachnoid mater and the pia mater is a space, the subarachnoid space, which contains
shock-absorbing cerebrospinal fluid
External Anatomy of the Spinal Cord
o It extends from the medulla oblongata, the inferior part of the brain, to the superior border of the second
lumbar vertebra.
o Spinal nerves: are paths of communication between the spinal cord and specific regions of the body.
o There are 8 pairs of cervical nerves
o There are 12 pairs of thoracic nerves
o There are 5 pairs of lumbar nerves
o There are 5 pairs of sacral nerves
o There is 1 pair of coccygeal nerves
o Roots are two bundles of axons that connect each spinal nerve to a segment of the cord by even smaller
bundles of axons called rootlets
o The posterior (dorsal) root and rootlets only contain sensory axons to the CNS
o The posterior (dorsal) root ganglion contains the cell bodies of sensory neurons.
o The anterior (ventral) root and rootlets contain axons of motor neuron, which conduct nerve impulses
from the CNS to effectors
o The spinal cord is shorter than the vertebral column, thus nerves that arise from the lumbar, sacral, and
coccygeal regions of the spinal cord do not leave the vertebral column at the same level they exist the
cord. The roots of these nerves are called cauda equine (horse’s tail)
Internal Anatomy of the Spinal Cord
o A transverse section of the spinal cord reveals regions of white matter than surround an inner core of gray
o White Matter: consists of bundles of myelinated axons of neurons. It is organized in three major regions:
anterior white columns, posterior white columns, and lateral white columns. Each column consists of
bundles of axons having a common origin or destination and carrying similar information. These bundles
are called tracts. Sensory tracts consist of axons that conduct nerve impulses towards the brain. Motor
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