Chapter 13: The Spinal Cord and Spinal Nerves Review

Comprehensive vocabulary flashcards covering the anatomy, protection, physiology, and pathology of the spinal cord and spinal nerves.

Spinal cord

The structure enclosed in the vertebral column that begins at the foramen magnum and ends at the $L1$ or $L2$ vertebra, providing two-way communication to and from the brain.

Cervical enlargement

An area of the spinal cord that is thicker than elsewhere and gives rise to nerves of the upper limb.

Lumbosacral enlargement

An area of the spinal cord that is thicker than elsewhere and gives rise to nerves of the pelvic region and lower limbs.

Medullary cone (conus medullaris)

The inferior point of the spinal cord.

Cauda equina

A bundle of nerve roots that occupy the vertebral canal from $L2$ to $S5$ and resembles a horse’s tail.

Meninges

Membranes that enclose the brain and spinal cord to protect and support the CNS and contain cerebrospinal fluid (CSF).

Dura Mater

A tough, fibrous membrane composed of dense irregular connective tissue; it is the most superficial layer of the meninges.

Epidural space

The space between the dura and vertebral bones that contains blood vessels, adipose tissue, and loose connective tissue.

Arachnoid Mater

The second layer of the meninges located between the dura mater and pia mater.

Subarachnoid space

The space between the arachnoid and pia layers that is filled with Cerebral spinal fluid (CSF) and is the site of lumbar punctures.

Pia Mater

A delicate, transparent membrane that follows the contours of the spinal cord.

Denticulate ligament

Extensions of the pia mater that pass through the arachnoid to the dura to stabilize the spinal cord.

White matter

Bright, pearly white colored bundles of myelinated axons coursing up and down the spinal cord.

Gray matter

Dull-colored tissue containing neuron cell bodies, dendrites, and proximal portions of axons; it is shaped like a butterfly in cross-section.

Posterior (dorsal) horns

Portions of gray matter that receive sensory nerve fibers and synapse with interneurons.

Anterior (ventral) horns

Portions of gray matter that contain the cell bodies of motor neurons.

Lateral horns

Gray matter segments present from $T2$ through $L1$ associated with the sympathetic nervous system.

Gray commissure

The structure that connects the left and right sides of spinal gray matter and contains the central canal.

Funiculus

Large bundles of axons in the white matter, categorized as posterior, lateral, and anterior, which are subdivided into tracts.

Ascending tracts

White matter bundles that carry sensory information up toward the brain.

Descending tracts

White matter bundles that carry motor information down from the brain.

Decussation

The crossing over of nerve fibers from one side of the body to the other.

Contralateral

Meaning the origin and destination of a tract are on opposite sides of the body.

Ipsilateral

Meaning the origin and destination of a tract are on the same side of the body.

First-order neuron

The neuron that detects a stimulus (receptor) and synapses with a second-order neuron in the spinal cord.

Second-order neuron

An interneuron with a cell body in the spinal cord whose axon extends to the thalamus or cerebellum.

Third-order neuron

An interneuron that carries sensory signals from the thalamus to the sensory area of the cerebral cortex.

Spinothalamic tracts

Ascending tracts that carry signals for pain, pressure, temperature, light touch, tickle, and itch.

Upper motor neuron

A neuron that originates in the cerebral cortex or brainstem and terminates on a lower motor neuron.

Lower motor neuron

A motor neuron with a cell body in the brainstem or spinal cord whose axon leads to a muscle or target organ.

Corticospinal tracts

Descending tracts that carry signals from the cerebral cortex for precise, finely coordinated movements.

Poliomyelitis

A disorder caused by a virus that destroys motor neurons in the brainstem and anterior/ventral horn of the spinal cord, leading to paralysis and atrophy.

Amyotrophic Lateral Sclerosis (ALS)

A condition characterized by the destruction of motor neurons and sclerosis of lateral regions of the spinal cord, often due to toxic levels of glutamate.

Nerve

A cord-like organ composed of numerous nerve fibers (axons) bound together by connective tissue.

Endoneurium

Loose connective tissue that encloses individual axons and their myelin sheaths.

Perineurium

Coarse connective tissue that bundles fibers into fascicles.

Epineurium

A tough fibrous sheath that surrounds all fascicles to form a complete nerve.

Mixed nerves

The most common type of nerves, consisting of both afferent (sensory) and efferent (motor) fibers.

Dorsal root ganglion

A structure containing the cell bodies of sensory neurons carrying signals to the spinal cord.

Anterior/ventral ramus

The larger distal branch of a spinal nerve that innervates the trunk and limbs.

Nerve plexuses

Interlacing nerve networks formed by all ventral rami except $T2$ through $T12$, found in cervical, brachial, lumbar, and sacral areas.

Phrenic nerves

Major motor and sensory nerves of the diaphragm found in the cervical plexus; spasms cause hiccups.

Sciatic nerve

The largest and longest nerve of the body, found in the sacral plexus, composed of the tibial and common fibular nerves.

Somatic reflexes

Quick, involuntary, stereotyped reactions of glands or muscle to stimulation.

Reflex arc

The pathway of a reflex involving a receptor, sensory neuron, integration center, motor neuron, and effector.

Monosynaptic reflex arc

A reflex arc with only one synapse between the afferent and efferent neurons, such as the patellar reflex.

Reciprocal inhibition

A process where sensory fibers synapse with interneurons that inhibit motor neurons of antagonistic muscles during a reflex.