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Spinal Cord

primary communication link between the brain and the peripheral nervous system, integration of incoming info, reflex mechanisms, form foramen magnum to L2

Spinal Nerves

31 pairs, exit the vertebral column through the intervertebral and sacral foramina, not uniform in diameter

Cervical and Lumbosacral Enlargements

larger diameter of cord, give rise to the spinal nerves of the limbs

Conus Medullaris

cone like region of the spinal cord inferior to the lumbosacral enlargement, have caudal equina off of it

Cauda Equina

roots of nerves that extend from the end of the spinal cord


connective tissue membranes that surround the brain and spinal cord

Dura Mater

form a thecal sac that surrounds the spinal cord, attaches to the rim of the foramen magnum and ends at the level of the second sacral vertebra, most superior

Arachnoid Mater

thin wispy meningeal layer deep to the dura mater

Pia Mater

deepest meningeal layer that is bound tightly to the surface of the spinal cord

Epidural Space

between the periosteum of the vertebral canal and the dura mater, contains blood vessels, areolar tissue and fat

Subdural space

between the arachnoid mater and the dura mater, serous fluid

Subarachnoid space

between the arachnoid mater and the pia matter, cerebrospinal fluid

Anterior Median Fissure

deep cleft partially separating right and left halves, on anterior side

Posterior Median Sulcus

deep cleft partially separating right and left halves, on posterior side

White Matter

consist of myelinated axons forming tracts, located peripherally, organized into three columns ventral, dorsal, lateral


Funiculi or columns of white matter subdivided into tracts know as ____

Tracts (fasiculi)

composed of axons ascending to the brain or desending from the brain, axons within carry same type of info

Gray Matter

dominated by the cell bodies of neurons, neuroglia, and unmyelinated axons

Dorsal (posterior) Horns

gray matter, contains somatic and visceral sensory nuclei

Ventral (anterior) Horn

gray matter, contains somatic motor nuclei

Lateral Horns

gray matter, contains visceral motor nuclei

Gray and White Commissures

connect each half of the spinal cord

Central Canal

located in the center of the gray commissures


spinal nerves arise as rootlets then combine to form roots, located along the dorsal and ventral surfaces of the spinal cord

Dorsal Root

root containing sensory axons

Dorsal Root Ganglion

collections of cell bodies of the sensory neurons

Ventral Root

contains motor axons

Spinal Nerve

dorsal and ventral root merge laterally to form, contain sensory and motor axons


basic functional unit of the nervous system, simplest portion capable of receiving a stimulus and producing a response, stereotypic, unconscious, and involuntary responses to stimuli, maintains homeostasis


response to stimulus is always the same


no awareness is necessary for the reflex to occur


one cannot will the reflex to happen

Somatic Reflexes

mediated through the somatic motor nervous system, responses; remove for painful stimuli, keep from falling suddenly, cause movement because of external forces

Autonomic Reflexes

mediated through the autonomic nervous system, responsible for maintaining variables within their normal ranges; blood pressure, carbon dioxide levels, water intake

Sensory Receptors

respond to stimuli and produce action potentials in sensory neurons

Sensory Neurons

propagate action potentials to the CNS

Interneurons in the CNS

synapse with sensory neurons and with motor neurons

Motor Neurons

carry acton potentials from the CNS to effector organs

Effector Organs

part of body that responds to the action potentials

Stretch Reflex

muscles contract in response to a stretching force applied to them, innervated by specific motor neurons, sensory neurons innervate the non contractile centers of the muscle spindle cells, synapse with alpha motor neurons, and intern innervate the muscle with spindle

Muscle Spindles

specialized muscle cells that respond to stretch

Gamma Motor Neurons

specific motor neurons that control sensitivity of muscle spindles

Golgi Tendon Reflex

reflex preventing contracting muscles from applying excessive tension to tendons, prevents damage to tendons, produces sudden relaxation of muscles

Golgi Tendon Organ

encapsulated nerve endings that have at their ends numerous terminal branches with small swelling associated with bundles of collagen fibers in tendon, located in tendon near muscle

Withdrawal Reflex

reflex function to remove a body limb from a painful stimulus, have reciprocal innervation and crossed extensor reflex

Reciprocal Innervation

causes relaxation of extensor muscle when flexor muscle contracts in withdrawal reflex, also involved in stretch reflex

Crossed Extensor Reflex

when a withdrawal reflex is initiated in one lower limb, the crossed extensor reflex causes extension of opposite lower limb

Spinal Nerve Structure

consist of axon bundles, schwann cells and connective tissue, have endoneurium, perineurium and epineurium layers


surrounds individual axons and their Shcwann cell sheath


surrounds groups of axons (fascicles)


surrounds the entire nerve

Dorsal Ramus

branches of nerves that innervate deep muscles of the trunk responsible for movements of the vertebral column and the CT and skin near the midline of the back

Ventral Ramus

branches of nerve, what they innervate depends on what part of the spinal cord is considered

Thoracic Region

part of ventral ramus, form intercostal nerves that innervate the intercostal muscles and the skin over the thorax


organization produced by the intermingling of the nerve, five in the body

Cervical Plexus

C1-C4 innervate superficial neck, structures, skin of neck, posterior portion of head, have ansa cervicalis, and phrenic nerve

Ansa Cervicalis

in cervical plexus, loop between C1 and C3

Phrenic Nerve

in cervical plexus, C3-C5, part of both cervical and brachial plexus, innervates diaphragm

Brachial Plexus

C4, C5-T1, five ventral rami form three trunks, separate into six divisions of cords giving rise to beaches/nerves; axillary, radial, musculocutabeous, ulnar, median, and small nerves that innervate muscles action on scapula and arm

Lumbar and Sacral Plexus

ventral rami of L1-L4 and L4-S4, considered together because of close relationship, major nerves;obturator, femoral, tibial, common fibular

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