Chapter 14: The spinal cord and spinal nerves

Posterior gray horns

"Dorsal" Contain somatic and visceral sensory nuclei; receive sensory input.

Lateral gray horns

"Intermediate" contain visceral motor neurons; direct motor output to internal organs, smooth muscle, cardiac muscle, and glands.

Anterior gray horns

"Ventral" Contain somatic motor neurons; direct motor output to effectors.

Cerebrospinal fluid

Acts as a shock absorber as well as a diffusion medium for dissolved gases, nutrients, chemical messengers, and waste products.

Ventral root

Contains the axons of somatic motor neurons and at some levels, visceral motor neurons that control peripheral effectors.

Dorsal root

Contains the axons of the sensory neurons in the dorsal root ganglion.

Descending tracts

Convey motor commands into the spinal cord.

Pia mater

Deepest meninx, consists of elastic and collagen fibers which adheres to spinal cord.

Spinal nerve

Distal to each dorsal root ganglion, the sensory and motor fibers form a single nerve. Pass through intervertebral foramina.

Cauda equina

Group of spinal nerves that extend caudal from the conus medullaris; runs inside vertebral foramina branching off through intervertebral foramina; horse's tail.

Reflex

Is an immediate involuntary motor response to a specific stimulus.

Lumbosacral enlargement

Provides in innervation to structures of the pelvis and lower limbs

Phrenic nerve

Provides sensory information from, and motor innervation to, the diaphragm.

Spinal meninges

Specialized membranes that provide protection, physical stability, and shock absorption.

Thoracic, lumbar, sacral, coccygeal

Spinal nerves caudal to the first thoracic vertebra take their names from the vertebra immediately preceding them.

Arachnoid mater

The middle meningeal layer, consists of simple squamous epithelium.

Lateral white column

The white matter on either side between the anterior and posterior columns.

Steps in neural reflex

1. Arrival of stimulus and activation of receptor 2. Activation of a sensory neuron 3. information processing in CNS 4. Activation of a motor neuron 5. Response by effector

Spinal nerves

31 pairs: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal.

Cervical spinal nerves

C1, Exits between the skull and the first cervical vertebra. Cervical nerves take their names from the vertebra immediately following them.

White ramus communicans

Carry nerve fibers from spinal nerve to sympathetic (autonomic) ganglion

Gray ramus communicans

Carry nerve fibers from sympathetic (autonomic) ganglion to spinal nerves.

Ascending tracts

Carry sensory information toward the brain.

Gray matter

Central, H-shaped mass, dominated by the cell bodies of neurons and glial cells.

Mixed nerve

Classification of spinal nerve because they contain both afferent (sensory) and efferent (motor) fibers.

Cervical plexus

Composed of cutaneous and muscular branches of the ventral rami of spinal nerves C1-C4 and some nerve fibers from C5. Innervates skin and muscles of the neck.

Anterior and posterior gray commissures

Contain axons crossing from one side of the cord to the other side; Allow one side of the spinal cord to communicate with other side.

Dorsal root ganglion

Contain the cell bodies of sensory neurons. Carries sensory input only. Sensory ganglia lie between the pedicles of adjacent vertebrae.

Sacral plexus

Formed by the ventral rami of L4-S4.

Brachial plexus

Formed by the ventral rami of spinal nerves C5-T1 and innervates the pectoral girdle and upper limb. The ventral rami converge to form the superior, middle, and inferior trunks.

Lumbar plexus

Formed by the ventral rami of spinal nerves L1-L4.

Conus medullaris

Inferior to the lumbosacral enlargement, the spinal cord tapers to a conical tip, at or inferior to the level of the first lumbar vertebra.

Common fibular nerve

Innervates muscles and skin on the anterior surface of the leg.

Obturator nerve

Innervates the adductor group, gracilis, and obturator externus muscles, and the adductor Magnus, brevis, and longus muscles. Receives sensory information from the medial surface of the thigh.

Tibial nerve

Innervates the flexors of the knee and plantar flexors of the ankle; flexors of the toes; and skin over the posterior surface of the leg and the plantar surface of the foot.

Femoral nerve

Innervates the quadriceps, sartorius, pectineus, and iliopsoas muscles. receives sensory information from the skin of the anteromedial surface of the thigh and medial surface of the leg and foot.

Spinal cord

Integrates and processes information on its own, in addition to relying information to and from the brain.

Sciatic nerve

Largest nerve in the human body. Innervates the hamstrings, semimembranosus, semimtendinosus, and adductor Magnus muscles.

Anterior white column

Lie between the anterior gray horns and the anterior median fissure.

Central canal

Narrow canal that is surrounded by gray matter, which is located in the horizontal bar of the H.

Subdural space

Narrow space separating the dura mater from deeper meningeal layers.

Reflex arc

Neuro pathway that allows reflex to occur. Begins at a receptor and ends at a peripheral effector, such as a muscle or gland cell.

Sciatica

Pain resulting from the compression of the roots of the sciatic nerve.

White matter

Peripherally situated, contains large numbers of myelinated and unmyelinated axons organized in tracts and columns (funiculus)or regions.

Ventral ramus

Ramus of each spinal nerve receives sensory innervation from, and sends motor innervation to the ventrolateral body surface, body wall structures, and limbs.

Dorsal ramus

Ramus of each spinal nerve receives sensory innervation from, and sends motor innervation to, a specific segment of the skin and muscles of the neck and back.

Posterior white column

Sandwiched between the posterior gray horns and the posterior median sulcus.

Filum terminale

Slender strand of fibrous tissue, extends from the inferior tip of the conus medullaris along the length of the vertebral canal as far as the dorsum of the coccyx

Subarachnoid space

Space contains cerebrospinal fluid (CSF)

Denticulate ligaments

Strips of connective tissue that run along the length of the spinal cord, paired extensions of the pia mater that connect the pia mater and arachnoid mater to the dura mater. Collectively help prevent side to side and inferior movement of the spinal cord.

Epidural space

Superficial most space, contains areolar tissue, blood vessels, and adipose tissue.

Cervical enlargement

Supplies nerves to the pectoral girdle and upper arms

Dura mater

Tough, fibrous meninx which forms outermost covering of the spinal cord and brain. Consists of a layer of dense irregular connective tissue whose outer and inner surfaces are covered by a simple squamous epithelium.

Nerve plexus

Ventral rami of adjacent spinal nerves blend their fibers to produce a series of compound nerve trunks.