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•The Spinal Cord and Spinal Nerves Grouping of Neural Tissue • Neural tissue can be grouped according to its color: • White Matter is composed of neurons myelinated with oligodendrocytes in the CNS and Schwann cell in the PNS • Gray Matter is composed of nerve cell bodies and dendrites, or unmyelinated axons and neuroglia Nerves • Bundles of fibers (axons and dendrites) outside the CNS 1 Ganglia • Collections of nerve cell bodies outside the CNS Tract • A bundle of fiber inside the CNS Nucleus • A mass of unmyelinated nerve cell bodies in the CNS 2 Horns • Chief areas of gray matter in spinal cord Meninges Meninges Epidural space - between the dura mater and the wall of the vertebral canal - filled with adipose tissue which serves as padding Dura Mater - runs from the foramen magnum to S2 where it fuses with the filum terminale - continuous with the dura mater of the brain Subdural Space - contains serous fluid Arachnoid Mater - avascular delicate layer continuous with the arachnoid of the brain - adheres to the dura mater Subarachnoid Space - where Cerebral Spinal Fluid flows Pia Mater - adheres to the surface of the brain and spinal cord - Denticulate Ligaments - pieces of pia mater that suspend the spinal cord in the middle of the dural space and protect it against injury 3 General Features of the Spinal Cord • Enlargements in the cervical and lumbar regions the spinal cord is thicker • Conus Medullaris the pointed end of the cord near L1 – L2 • Filum Terminale pia mater strand that anchors the spinal cord • Cauda Equina nerves that arise from the lower portion of the cord occupying the space below L-2 4 The spinal cord cross-section Functions of the Spinal Cord • To convey sensory impulses from the PNS to the brain • To conduct motor impulses from the brain to the skeletal muscles, smooth muscles, heart, and glands • Integration of reflexes Reflex Center • The spinal cord is the center for some reflex actions • There are five basic components involved in a reflex 5 The components of a reflex (1) Receptor – responds to a stimulus and initiates a nerve impulse in a sensory neuron (2) Sensory Neuron – has the cell body in the dorsal root ganglion. Passes nerve impulses into the spinal cord through the dorsal root to the posterior horn of the gray matter Components continued (3) Center – region of the spinal cord where the incoming sensory information generates an outgoing motor impulse, usually contains internuncial neurons (4) Motor Neuron transmit nerve impulses to muscle or gland through the ventral root to the spinal nerve (5) Effector the organ (gland or muscle) that responds to the impulse from the motor neuron 6 Types of Reflexes • Reflexes are fast responses to certain changes in the internal or external environment the allow the body to maintain homeostasis. Several types: • Spinal reflexes carried out by the spinal cord alone • Somatic reflexes result in the contraction of skeletal muscle • Cranial reflexes involve brain centers and cranial nerves • Visceral (Autonomic) Reflexes cause contraction of smooth muscle or cardiac muscle, or secretion by glands Patellar Reflex • Knee jerk • Relates to damage to the 2nd, 3rd, or 4th lumbar vertebra • Absent in people with chronic diabetes and neurosyphilis • Exaggerated in disease or injury to corticospinal tracts Achilles Tendon Reflex • Ankle jerk • Relates damage to lumbosacral region of the spine • Absent in people with chronic diabetes, neurosyphillis, alcoholism • Exaggerated with cervical cord compression 7 Babinski Sign Reflex • Outer margin of the foot is stimulated • In children under 1 ½ years of age the great toe is extended with or without fanning of the toes – after 1 ½ years may indicate corticospinal damage • In adults response is to curl the toes under Abdominal Reflex • Stroke the side of the stomach and the belly-button deviates laterally to the opposite side • Absence indicates damage to corticospinal tracts, lesions of reflex centers in the thoracic area, or multiple sclerosis Spinal Nerves • 31 pairs of spinal nerves • Named according to region and level of the spinal cord from which they emerge - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1 coccyx 8