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Chapter 14
Central Nervous System: Spinal cord and Brain
Spinal Cord
 45 cm (18in) in length
 Posterior median sulcus- shallow groove on the dorsal surface
 Anterior median fissure- deep crease on the ventral surface
 Each region of the spinal cord contains tracts involved with that particular segment and
those inferior to it
 Enlargements areas of coordination of incoming and outgoing messages
o Cervical enlargement
o Lumbar enlargement
 Conus medullaris + filum terminale = cauda equina
 The spinal cord is divided into 31 segments, each associated with a pair of
o Dorsal root ganglia- contain cell bodies of sensory neurons
o Dorsal root- contain axons of sensory neurons in the dorsal root ganglia
o Ventral root- leaves spinal column contains axons of somatic and visceral motor
neurons that control peripheral effectors
 Distal to each dorsal root ganglion, sensory and motor fibers form a single spinal nerve.
Classified as a mixed nerve because it contains both afferent (sensory) and efferent
(motor) fibers.
 Shingles
Spinal Meninges
 Provide protection, physical stability and shock absorption
 Cover spinal cord and surrounding nerve roots
 3 Layers:
1. dura mater- dense irregular connective tissue
2. arachnoid- simple squamous epithelium
3. pia mater- elastic and collagen fibers
 At the foramen magnum the spinal meninges are continuous with the cranial meninges
that surround the brain.
 Cerebrospinal fluid (CSF)- acts as a shock absorber diffusion medium for dissolved
gases, nutrients, chemical messengers and waste products
 In subarachnoid space
 Accessible between L3 and L4
Sectional Anatomy of Spinal Cord
 Anterior median fissure and posterior median sulcus divide the cord into left and right
sides
 Gray matter- cell bodies of neural and glial cells
 Central canal
 Horns of gray matter
 White matter- myelinated and unmyelinated axons
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Organization of gray matter
 Sensory nuclei- touch receptors
 Motor nuclei- issue motor commands to peripheral effectors
 Posterior gray horns- somatic and visceral sensory nuclei
 Anterior gray horns- neurons concerned with somatic motor control
 Lateral gray horns- found in the thoracic and superior lumbar segments contain visceral
motor neurons
 Gray commissures- contain axons crossing from one side of the cord to the other before
reaching a destination within the gray matter.
Organization of white matter
 Divided into region or columns
 Posterior white column
 Anterior white column
 Lateral white column
 Each column contains tracts- convey sensory data or motor commands
o Ascending tracts – carry sensory information toward the brain
o Descending tracts – Convey motor commands into the spinal cord
Spinal Nerves
 31 Pair
 Cervical nerves C1-C8
 Thoracic nerve T1-T12
 Lumbar nerves L1-L5
 Sacral nerves S1-S4
 Each peripheral nerve has 3 concentric layers of CT
1. epineurium
2. perineurium
3. endoneurium
Peripheral distribution of the spinal nerves
 Autonomic ganglion- associated with the sympathetic division of the ANS
 Preganglionic axons are myelinated = white ramus
 Unmyelinatd postganglionic fibers that innervate glands and smooth muscle form the
gray ramus
that rejoins the spinal nerve
 Gray ramus + white ramus = rami communicantes (communicating branches)
 Dorsal ramus- provides sensory innervation from and motor innervation to a specific
segment of
the skin and muscles of the back
 Ventral ramus- supplies the ventrolateral surface of the body- structures in the body wall
and
limbs
 Dermatome- an area of the body surface that is monitored by a pair of spinal nerves
 Nerve plexus- interwoven network of nerves. 4 major plexuses
1. cervical
2. brachial
3. lumbar
4. sacral