Download Organization of the Nervous System

Organization of the Nervous System
1. Describe the basic anatomical organization of the nervous system. (p.7)
Anatomical organization divides the nervous system into the central and periphery nervous systems. CNS contains
the brain and the spinal cord. PNS contains the 12 pairs of cranial nerves (attaching brain with structures of head and
neck) and the 31 pairs of spinal nerves (attaching spinal cord with structures of the limbs and trunk).
2. Diagram a typical neuron, list its parts. Identify distinguishing characteristics of motor and sensory
neurons. (p.7)
Neuron has a cell body (soma), cell processes (axons and dendrites), and a synapse. Neurons may be
multipolar with many processes (motor neurons) ore pseudounipolar with a single axon/dendrite processes outside
of the soma (primary sensory neurons).
3. Describe the gross anatomical features of the spinal cord. (p.8)
Spinal cord connects the brain to the body through sensory and motor neurons. Sensory neurons send afferent
information ascending to the brain and motor neurons send efferent information descending away from the brain.
There are also spinal reflexes carred out at the spinal cord level only.
The spinal cord is cylindrical and 16-28 inches long and attached superiorly and continuously with the brain with its
inferior end tappering off in a cone. The cervical and lumbar enlargements refer to areas where the spinal cord is
bigger due to extra connections to the upper and lower limbs, respectively. The conus medullaris is the tappered end
of the spinal cord which is followed by the cauda equina, the continuation of dorsal/ventral roots of spinal nerves
below the L2 vertebrae.
4. Describe the location, organization and structure of the spinal meninges. (p.8)
Meninges are three connective tissues that cover the brain and spinal cord. From the outside in, they are the dura
mater, arachnoid mater, and pia mater.
The dura mater is the outermost layer and very tough; it forms a long tubular sheath continuous with the dura mater
around the brain and enters the sacrum. It tapers to an end as the ligament attaches to the coccyx.
The arachnoid mater has 2 parts: the transpartent layer that is indise the dura mater and web-like extensions
extending toward the pia mater.
The pia mater is very delicate and very closely invested in the brain and spinal cord. It contains the filum terminale
which inferiorly extends from the conus medullaris to attach to dura mater (vertical anchor) and the denticulate
ligaments which are laternal extensions through arachnoid mater to dura mater, actinga s a laternal anchor.
The epiderual space is above the dura mater between the dura mater and vertrebral foramen. It is a real space with
fat and the venus plexus.
The subdural space is below the dura mater and above the arachnoid mater. It is a potential space that is normally
not there. Same as the epiarachnoid space.
The subarachnoid space is below the arachnoid and above the pia mater. It holds the cerebralspinal fluid (CSF)
which provides protection as cushioning and chemical balance. It is a real space and the same as the epipial space.
There is no subpial space because the pia mater is intimately associated with the spinal cord.
5. Diagram a cross section through the spinal cord. Be able to label all of the parts as described in class.
(p.14)
The cross sectional spinal cord shows the dorsal and ventral horns which contain grey matter surrounded by white
matter. There is also a laternal horn between the dorsal and ventral horns at select levels and function as part of the
autonomic nervous system. The dorsal horn contains primary sensory neurons and the dorsal root ganglion. The
ventral horn contains the nucleus of motor neurons. The spinal nerve is where dorsla and ventral roots meet and join
up; it contains a mixed motor/sensory nerve.
6. Describe the components of a typical spinal nerve and explain the normal branching pattern. (p.15)
Diagrammed on pages 14 and 15 and explained on pages 9 (IV-F) and 10.
7. Explain the numbering of spinal nerve pairs.
The spinal nerves are numbered according to the spinal cord segment from their all of their fibers originate.
There are 31 pairs: 8 Cervical (C1-C8), 12 Thoracic (T1-T12), 5 Lumbar (L1-L5), 5 Sacral (S1-S5), and 1
Coccygeal (Co 1).
The spinal cord segment and the vertebral level are not the same because the spinal cord stops at the conus
medullaris (which is adjacent to the L2 vertebra), and because the spinal nerves descent down from the spinal cord
until they find their appropriate vertebral level and exit from the appropriate intervertebral foramina.
This concept is diagrammed on page 16 (page 49, Moore & Dalley).
8. Explain the composition of a nerve plexus, give some examples.
A nerve plexus is when the rami of several spinal nerves fuse and mix their fibers between one another, producing
peripheral nerves.
This concept is diagrammed on pages 54-55 in Moore & Dalley.
9. Define the term dermatome and state its clinical significance.
A dermatome is a section of skin supplied by a single spinal nerve (pair). The sections of skin are present in bands
on the body surface, were discovered from clinical observation and have a considerable amount of overlap between
adjacent spinal nerve contributions.
Clinically, these are significant because the can be used to assess the extent of spinal cord injury or impingement. If
the spinal cord is injured, often the dermatomes of spinal nerves below that injury will lose some or all sensation.