Central Nervous System Plus Spinal and Cranial Nerves

Central Nervous System Consists of Brain and Spinal Cord

Spinal Cord Protection and Covering Vertebral Colum Ring of bone formed by vertebral foramina protect the spinal cord

Spinal Cord Protection and Covering Meninges – connective tissue covering that protect the spinal cord. They are found in 3 layers

Meninges Dura Mater – outer layer of meninges Composed of tough connective tissue

Meninges Arachnoid Mater – middle layer of meninges Composed of collagen and elastic fibers that resemble a spider’s web

Meninges Pia Mater – inner layer of meninges Composed of transparent collagen and elastic fibers that adhere to the spinal cord and brain

Subarachnoid Space Area between the arachnoid mater and pia mater containing CSF Spinal Tap (lumbar puncture) – a long needle is inserted into the subarachnoid space (generally between L3 & L4 or L4 & L5) to withdraw CSF for diagnostic purposes or to introduce medication.

External Structure The adult spinal cord is only about 16-18 inches long…it ends around L2

Cauda Equina Nerves on the lower portion of the cord angled downward through the vertebral canal.

Enlargements Cervical Enlargement – contains nerves that supply the upper limbs Lumbar Enlargement – contains nerves that supply the lower limbs

Indentations/divisions Anterior Median Fissure & Posterior Median Sulcus – divide the cord into right and left halves

Central Canal Space down the center of the spinal cord containing CSF

Internal Structure Gray Matter Anterior Horns – contain cell bodies of somatic motor neurons Posterior Horns – contain cell bodies of somatic and autonomic sensory neurons Lateral Gray Horns – present only in lower portion of the spinal cord. Contains cell bodies of autonomic nervous system

Ventral Horn Lateral Horn Dorsal Horn

Posterior White Column White Matter Organized into columns containing myelinated and unmyelinated axons of sensory and motor neurons Posterior White Column Lateral White Column Anterior White Column

White Matter Tracts – bundles of axons having a common origin or destination carrying similar information Sensory (ascending) tracts – consist of axons that conduct nerve impulses toward the brain Motor (descending) tracts – consists of axons that carry nerve impulses down the spinal cord

Tracts

Spinal Nerves Paths of communication between the spinal cord and the nerves that serve the specific regions of the body

Roots Connect each spinal nerve segment to the spinal cord Posterior (dorsal) root – contains only sensory axons Dorsal Root Ganglion – swollen area containing sensory cell bodies Anterior (ventral) root – contains both somatic motor and autonomic motor neurons

Spinal Reflexes A fast, involuntary sequence of actions that occurs in response to a particular stimulus in which integration takes place in the gray matter of the spinal cord

Reflex Arc Sensory Receptor Sensory Neuron Integrating Center Motor Neuron Effector