1. Spinal Cord and Nerves
Nervous System

2. Gross Anatomy of the Spinal Cord
Adult spinal cord is 18 inches long and 14 mm wide
Spinal cord does not continue in length with the vertebrae; stops at L1 and L2
Entire spinal cord can be divided into 31 segments on the basis of the origins of the spinal nerves

3. Spinal Cord Anatomy
Amount of gray matter is greatest in those areas that deal with sensory and motor neuron control of the limbs.
Inferior to the lumbar the spinal cord becomes tapered and conical. This region ends in branching off of the nerves in an area called the cauda equina (horse’s tail).

4. Gross Anatomy of the Spinal Cord
Every spinal segment is associated with a pair of dorsal root ganglia. The ganglia contain the cell bodies of sensory neurons. The axons of the neurons make up the dorsal roots. Ventral roots contain axons of motor neurons. The sensory and motor roots are bound together into a single spinal nerve.

5. Gross Anatomy of Spinal Cord
Dorsal root
Ventral root

6. Gross Anatomy of Spinal Cord
Spinal nerves are classified as mixed nerves – contain both afferent (sensory) and efferent (motor) fibers.
Spinal cord continues to enlarge and elongate until an individual is 4 years old.
After that time vertebral column continues to grow, but spinal cord does not. Vertebra growth moves the intervertebral foramen and nerves further from their original positions, thus elongating the dorsal and ventral roots.

7. Spinal Meninges
Spinal meninges is a series of specialized membranes surrounding the spinal cord to provide protection (shock absorption)
Consists of three layers:
(1) dura mater
(2) arachnoid
(3) pia mater
These layers are continuous with the cranial meninges that surround the brain.

8. Spinal Meninges Layers
Pia mater
Arachnoid
Dura mater

9. Spinal Meninges
Between the dura mater and the walls of the vertebral canal lies the epidural space, a region with loose connective tissue and adipose
Anesthetics are often injected into the epidural space. The drug should only affect spinal nerves in the area of the injection. Result is an epidural block-temporary sensory loss or motor paralysis (depending on anesthetic) used to control pain during childbirth.

10. Arachnoid
A narrow region between the arachnoid and the pia mater is called the subarachnoid space that is filled with cerebrospinal fluid (CSF). The withdrawal of the CSF occurs in a procedure called a spinal tap. Spinal taps are done to diagnose CNS infection, severe back pain, disc problems, and some types of strokes.

11. Spinal Nerves
Every segment of the spinal cord is attached to a pair of spinal nerves. A series of connective tissue layers surrounds each spinal nerve and continues along its branches.

12. Spinal Nerves Epineurium surrounds several bundles of fascicles
Perineurium surrounds a fascicle
Endoneurium surrounds individual myelin sheaths and axons

13. Spinal Reflexes
A reflex is a rapid, automatic response to a specific stimuli.
Most reflexes occur in the spinal cord rather than the brain for faster response time. The wiring of a single reflex is called a reflex arc.