Spinal Cord Extends from foramen (base of brain) magnum to second lumbar vertebra Segmented Cervical Thoracic Lumbar Sacral Gives rise to 31 pairs of spinal nerves Not uniform in diameter throughout length

The spinal cord and spinal nerves

Cross Section of Spinal Cord White matter: Myelinated axons forming nerve tracts Gray matter: Neuron cell cell bodies, dendrites, axons In the spinal cord, the grey matter is found in the center (the butterfly shape) and the white matter surrounds it. The opposite arrangement is found in the cortex of the brain.

Spinal Meninges Three membranes surround all of CNS 3) Pia mater 1) Dura mater - "tough mother", strong 2) Arachnoid meninx - spidery looking, carries blood vessels, etc. Subarachnoid space filled with cerebral spinal fluid (CSF) 3) Pia mater - "delicate mother", adheres tightly to surface of spinal cord 3) Pia mater 2) Arachnoid 1) Dura mater

Spinal Cord Anatomy Central canal filled with cerebrospinal fluid Figure 7.19 Slide 7.53c Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Dermatomal Map Skin area supplied with sensory innervation by spinal nerves

spinal cord brain CNS PNS The Organisation of the Nervous System spinal nerves (31p) cranial nerves (12p) PNS sensory motor motor sensory Sensory information has to be passed on from the spinal cord to the brain ascending pathways (red) Commands from the brain have to be sent out to the PNS descending pathways (green)

Peripheral Nervous System Nerves and ganglia outside the central nervous system (brain and spinal cord) Nerve = bundle of neuron fibers Neuron fibers are bundled by connective tissue Slide 7.55 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Structure of a Nerve Endoneurium surrounds each fiber Groups of fibers are bound into fascicles by perineurium Fascicles are bound together by epineurium Figure 7.20 Slide 7.56 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Classification of Nerves Mixed nerves – both sensory and motor fibers Afferent (sensory) nerves – carry impulses toward the CNS Efferent (motor) nerves – carry impulses away from the CNS Slide 7.57 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Spinal Nerves There is a pair of spinal nerves at the level of each vertebrae for a total of 31 pairs Slide 7.63 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings