ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Spinal cord
Functions:
1. Conduction pathway
2. Reflex center
Gross structure (a longitudinal view)
 Filum Terminale - the meningeal layers that anchor that spinal cord to the sacrum
 Cauda equina = collection of spinal nerves that hang below the spinal cord
 Conus medullaris = cone-shaped ending of the spinal cord
 Cervical and lumbar enlargements
At what level of the vertebral column does the spinal cord terminate?
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Meninges (connective tissue covering around the spinal cord and brain)
 Dura mater = superficial
 Arachnoid mater
 Pia mater = deepest; lies closest to the spinal cord
Cross section
(These structures can be viewed at a gross level. However, they are easier to see at the microscopic
level.)
1. Central canal = where CSF flows
2. Gray matter = collection of cell bodies, dendrites, and unmyelinated axons
 anterior, posterior and lateral horns
 commissure
3. White matter = myelinated axons
 arranged in columns
4. Spinal nerves
a. Dorsal root
b. Dorsal root ganglion =bundle of cell bodies in PNS
c.
Ventral root
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Conduction pathways (spinal tracts)
1. Ascending (sensory) tracts
2. Descending (motor) tracts
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Spinal nerves
Function - All are mixed nerves. They carry both sensory and motor fibers.
Number - 31 pairs (total of 62 spinal nerves)
1. Cervical - 8 pairs
2. Thoracic - 12 pairs
3. Lumbar - 5 pairs
4. Sacral - 5 pairs
5. Coccygeal - 1 pair
Structure
1. Roots
a. Dorsal root - sensory fibers
b. Ventral root- motor fibers
2. The two roots unite to form each spinal nerve and it passes through the intervertebral
foramen.
Plexuses
Main portions of spinal nerves form plexuses (networks of nerve fibers) in all regions but the
thoracic region. Nerves emerge from these plexuses.
1. Cervical plexus
a. Most nerves from this plexus go to the skin and muscles of the head, neck and
shoulders.
b. MAJOR NERVES: R & L phrenic nerves - Fibers from C3-C5 nerves form phrenic
nerves. Supply diaphragm.
2. Brachial plexus
a. Branches from this plexus go to the upper limb.
b. MAJOR NERVES: Ulnar and radial nerves - Supply arm, forearm and hand. (Ulnar
nerve passes between medial epicondyle and olecranon process = funny bone).
3. Intercostal nerves (T1-T11)
a. Emerge from thoracic region. No plexuses.
b. Supply intercostal muscles.
4. Lumbosacral plexus
a. Branches from this plexus go to the lower abdominal wall and and the lower extremity.
b. MAJOR NERVES:
1) R & L femoral nerves- Supply anterior thigh (Quadriceps femoris, Sartorius)
2) R & L Sciatic nerve - Supply posterior thigh (Hamstrings) and anterior and posterior
leg (Gastrocnemius) plus foot.
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Reflex center
What Is a reflex?
Fast, unplanned, automatic sequence of actions that occur in response to a
stimulus
They can be spinal or cranial in location, and somatic and autonomic in function
Components of spinal reflex arc:
1.
2.
3.
4.
5.
Receptor
Sensory (afferent) neuron
Interneuron
Motor (efferent) neuron
Effector
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
Examples of spinal reflexes: (We will perform some of these in lab.)
a. Withdrawal reflex
b. Patellar reflex
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ANAT41 - Lecture Outline
CENTRAL NERVOUS SYSTEM - Spinal Cord
PNS -Spinal Nerves
c.
Corneal reflex
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