Spinal Cord and Spinal Nerves

Flashcards covering the anatomical structures, meninges, neuronal pathways, connective tissue coverings, and functional organization of the spinal cord and spinal nerves.

Intervertebral foramen

The opening formed by the junction of the inferior notch of the vertebra above and the superior notch of the vertebra below, through which spinal nerves pass.

Meninges

The protective membrane coverings surrounding the spinal cord, consisting of three layers: dura mater, arachnoid mater, and pia mater.

Dura mater

The tough, outermost protective membrane layer covering the spinal cord.

Subdural space

The anatomical space located directly beneath the dura mater.

Arachnoid mater

The middle meninx located between the dura mater and the pia mater.

Subarachnoid space

The space located directly beneath the arachnoid mater that is filled with cerebrospinal fluid (CSF).

Pia mater

The delicate, innermost membrane layer directly adhering to the spinal cord.

Rootlets

Small divisions of nerve fibers formed as the dorsal and ventral roots get closer to the spinal cord.

Spinal nerve

A mixed nerve formed by the union of dorsal and ventral roots, containing both motor and sensory neurons.

Dorsal root ganglion (DRG)

A swelling associated with the dorsal root that contains the cell bodies of unipolar sensory neurons.

Ventral gray horn

The anterior gray matter region of the spinal cord containing the cell bodies of multipolar motor neurons.

Regeneration tube

A structure formed by Schwann cells wrapping around axons and dendrites in the peripheral nervous system (PNS) that facilitates nerve fiber regeneration.

Schwann cells (neurolemmocytes)

Glial cells in the peripheral nervous system (PNS) that produce the myelin sheath and form the regeneration tube around axons.

Oligodendrocytes

Glial cells responsible for laying down myelin in the central nervous system (CNS), where axonal regeneration tubes do not form.

Ventral root

The motor branch of a spinal nerve; transecting it causes paralysis because it carries only motor axons.

Dorsal root

The sensory branch of a spinal nerve; transecting it causes numbness because it carries sensory axons.

Gray commissure

An unmyelinated crossbar of gray matter in the spinal cord where interneurons relay electrical information across to the opposite side.

Contralateral response

A physiological response occurring on the opposite side of the body relative to an ipsilateral stimulus, mediated by crossing interneurons.

Cervical enlargement

A widened region of the cervical spinal cord containing extra neurons to innervate the sensory receptors and effectors of the upper limbs.

Lumbar enlargement

A widened region of the lumbar spinal cord containing extra neurons to innervate the sensory receptors and effectors of the lower limbs.

Conus medullaris

The cone-shaped tapering end of the spinal cord terminating at approximately the $L_1$ vertebral level.

Cauda equina

A bundle of spinal nerves resembling a horse's tail that extends inferiorly through the vertebral canal beyond the conus medullaris.

Epidural space

An anatomical area in the spinal canal located outside the dural sac containing fat and blood vessels, acting as a protective cushion between the vertebrae and spinal cord.

Nerve plexus

A complex network of interconnected, branching, and weaving spinal nerves, such as the cervical, brachial, lumbar, and sacral plexuses.

Intercostal nerves

Thoracic spinal nerves that emerge and extend as straight, unbranched pathways rather than forming a plexus.

Sciatic nerve

A large mixed nerve originating from the sacral plexus that passes near or above the piriformis muscle.

Anterior median fissure

A prominent, deep groove situated exclusively on the ventral surface of the spinal cord.

Lateral gray horn

A projection of gray matter containing extra cell bodies for autonomic nervous system (ANS) neurons, found only in specific segments of the spinal cord.

White columns (funiculi)

Regions of myelinated white matter in the spinal cord organized into ascending sensory tracts and descending motor tracts that do not regenerate if severed.

Posterior white column

A region of white matter in the dorsal spinal cord carrying sensory tracts; damage to this column results in numbness.

Nerve (organ)

A peripheral nervous system organ composed of multiple bundles of nerve fascicles, blood vessels, and connective tissue layers.

Fascicle

A discrete bundle of individual neuron fibers (axons) within a nerve.

Epineurium

The outer sheath of connective tissue that encases and protects the entire peripheral nerve.

Perineurium

The middle sheath of connective tissue that encloses each individual fascicle within a nerve.

Endoneurium

The delicate connective tissue layer that surrounds each individual axon within a fascicle.

Inhibitory interneuron

A spinal interneuron that inhibits an antagonist muscle ($-$) while the agonist muscle is being excited ($+$) during a reflex.

Contralateral reciprocal innervation

A reflex pathway arrangement in which interneurons coordinate opposite muscular excitation and inhibition on the opposite side of the body.