Spinal Cord and Spinal Nerves October 28 2013

Spinal Cord and Spinal Nerves October 28, 2013 Chapter 14: 534 – 540, 548 - 553 Dr. Diane M. Jaworski 77

Spinal Cord Circuitry 1. Peripheral receptors bring in sensory information from body to spinal cord - somatic from skin/muscle, visceral from organs 2. Sensory neuron enters dorsal part of spinal cord to synapse on gray matter neuron 3. Information integration by interneurons (not required for reflexes) 4. Motor neurons exit ventral part of spinal cord 5. Effector (muscle, gland) responds 78

Arrows indicate direction of information flow Green indicates autonomic outflow to viscera 79

Anatomy of the Spinal Cord Ventral root: motor/efferent axons Dorsal root: Sensory/afferent axons Dorsal root ganglion: Cell bodies of afferents Spinal nerve = Sensory + Motor axons (& autonomic in some) 80 © Mc. Kinley et al. A & P 2013

Spinal nerves leave the spinal cord in small spaces between the vertebrae 81 © Mc. Kinley et al. A & P 2013

Why Position Matters: Partial crushing of the vertebral column leads to compression of the spinal cord, but symptoms will vary depending on which part of spinal cord is injured 82

What will be more affected motor or sensory information? 83 © Mc. Kinley et al. A & P 2013

84 © Mc. Kinley et al. A & P 2013

Dorsal root ganglion Ventral root 85

Composition of a Peripheral Nerve © Mc. Kinley et al. A & P 2013 86

Connective Tissue Components of a Peripheral Nerve Epineurium: - outer layer Perineurium: - middle layer - divides nerve into fascicles (axon bundles) Endoneurium: - inner layer - surrounds individual axons 87

Anatomy of the Spinal Cord Unlike the cerebral cortex, where the cell body containing gray matter is located on the outside and white matter axons are deep within the brain, in the spinal cord the gray matter is located deep and white matter on the outside 88 © Mc. Kinley et al. A & P 2013

Anatomy of the Spinal Cord Gray Matter: area containing neuron cell bodies, dendrites, synapses 89 © Mc. Kinley et al. A & P 2013

Gray Matter Anatomy 90 © Mc. Kinley et al. A & P 2013

91 © Mc. Kinley et al. A & P 2013

Gray Matter Anatomy Somatic and Visceral afferents and efferents are located in different regions of the gray matter Remember, spinal nerves contain both sensory and motor axons AND both somatic and autonomic axons © Mc. Kinley et al. A & P 2013 92

Gray matter consists of columns of cells 93

Anatomy of the Spinal Cord White matter Myelinated axon tracts: - Ascending sensory info - Descending motor info 94 © Mc. Kinley et al. A & P 2013

White Matter Anatomy Sensory tracts Motor tracts The white matter has: ascending tracts carrying sensory info to the cortex and descending tracts carrying motor info from the cortex 95

The spinal cord does not look exactly alike at all levels: More gray matter in cervical and lumbar enlargements because more motor neurons to innervate arm & leg More white matter at the cervical level because of all motor axons descending and all sensory axons ascending 96

97

Spinal Cord Segments 31 Pairs of Spinal Nerves: 8 cervical, 12 thoracic, 5 lumbar 5 sacral, 1 coccygeal Cervical Enlargement Upper extremity Lumbar Enlargement Lower extremity 98

99 © Mc. Kinley et al. A & P 2013

Two regions of the spinal cord are enlarged due to motor neurons innervating the upper and lower extremities Cervical Enlargement Upper extremity © Mc. Kinley et al. A & P 2013 Lumbar Enlargement Lower extremity 100

101 © Mc. Kinley et al. A & P 2013

Dermatome • A map of the body • Region of skin innervated by one spinal nerve - Face = cranial nerve V - Arm = cervical Thumb = C 6 - Body = thoracic Nipples = T 4 Navel = T 10 - Leg = lumbar/sacral 102 © Mc. Kinley et al. A & P 2013

Why dermatomes matter 103 © Mc. Kinley et al. A & P 2013

Spinal segments do not coincide with vertebral level Due to differences in growth rates of the spinal cord and vertebrae during development, the spinal cord ends at the L 1 vertebra as a structure called the conus medullaris 104

The spinal cord ends at L 1 vertebra as the conus medullaris The spinal nerves below this level form the cauda equina “horse’s tail” Conus medullaris Cauda equina Filum terminale The conus medullaris is anchored to dura via the filum terminale 105

Lumbar Puncture to Obtain CSF The cauda equina is located in a sac (dura) filled with fluid (CSF). Since there is no spinal cord, CSF can be drawn from here. 107

Some peripheral nerves (e. g. , sciatic nerve) are formed from the union of branches of several spinal nerves © Pearson 2005 108

Nerve Plexuses • Complex, interwoven networks of spinal nerves, formed from blended fibers of adjacent spinal nerves • Four major plexuses: - Cervical - Brachial - Lumbar often combined - Sacral as lumbosacral } 109