The Nervous System: Spinal Cord and Spinal Nerves

Introduction –Spinal cord  Truly the pathway between body and mind  Conducts impulses to and from the brain  Carries out spinal reflexes –Spinal nerves  31 pairs  All are mixed nerves

Gross Anatomy of the Spinal Cord

Coverings of the Spinal Cord –3 layers called meninges –Dura mater  Outer layer  Dense irregular connective tissue –Arachnoid  Middle layer  Encloses cerebrospinal fluid –Pia mater  Adheres tightly to the surface of the spinal cord

Meninges of the Spinal Cord

Sectional Anatomy of the Spinal Cord –Inner part consists of gray matter –Outer part consists of white matter

Sectional Anatomy of the Spinal Cord

Example of Ascending Nerve Tracts

Spinal Nerves – Connect to the spinal cord via roots –The roots unite into the spinal nerve  Dorsal root  Ventral root –Spinal nerves exit through holes between the vertebrae –Split into branches  Supply muscles and skin

Spinal Nerves

Dermatomes

Nerve Plexuses –Plexus = “braid” –Nerves supplying the limbs form plexuses when they leave the spinal cord  Cervical –Innervates neck and shoulder  Brachial –Innervates shoulder and arm  Lumbosacral –Innervates abdomen, hip, thigh, leg, genital region –Sciatic nerve

Nerve Plexuses

Cervical Plexus

Brachial Plexus

Lumbar Plexus

Sacral Plexus

Spinal Reflexes –Reflexes are automatic responses to stimuli –Spinal reflexes result from the stimulation of a spinal reflex arc. –Basic elements of a reflex arc  Receptor  Afferent pathway (sensory)  Synapse in spinal cord (integrating center)  Efferent pathway (motor)  Response (effector)

A Reflex Arc

Stretch Reflex