Anatomy Lab 4 Quiz

Spinal cord

CNS structure connecting brain and peripheral nerves; recognize its position within the vertebral canal.

Cervical enlargement

Increased neural tissue associated with upper-limb innervation and the brachial plexus.

Lumbosacral enlargement

Increased neural tissue associated with lower-limb innervation and the lumbar/sacral plexuses.

Conus medullaris

Tapered inferior end of the adult spinal cord, typically near the L1-L2 vertebral level.

Cauda equina

Descending lumbar and sacral nerve roots inferior to the conus; roots travel within the lumbar cistern before exiting.

Filum terminale

Slender continuation from the conus that contributes to longitudinal stabilization of the spinal cord.

Lumbar cistern

CSF-containing subarachnoid region containing cauda equina; lumbar puncture is performed below the adult cord to reduce risk of cord injury.

Gray matter

Contains neuronal cell bodies, dendrites, and local circuitry; organize into dorsal, ventral, and—at appropriate levels—lateral horns.

White matter

Primarily myelinated axons organized into funiculi; carries ascending sensory and descending motor information.

Dorsal (posterior) horn

Receives/processes sensory information entering through dorsal roots.

Ventral (anterior) horn

Contains somatic motor neuron cell bodies whose axons leave through ventral roots.

Lateral horn

Visceral motor/autonomic region, especially prominent in T1-L2 spinal cord segments for sympathetic outflow.

Central canal

Small CSF-containing channel within the spinal cord; lined by ependymal cells.

Posterior, lateral & anterior funiculi

White-matter regions containing ascending and descending tracts; recognize organization rather than individual tract detail.

Posterior (dorsal) rootlets

Sensory axons enter the spinal cord through posterior rootlets and diverges from the dorsal root.

Posterior (dorsal) root

Carries afferent sensory fibers toward the spinal cord.

Dorsal root ganglion (spinal ganglion) (DRG)

Contains sensory neuron cell bodies; enlargement on the dorsal root. A lesion may affect sensory input without directly interrupting ventral-root motor axons.

Anterior (ventral) rootlets

Motor axons leave the spinal cord through anterior rootlets and converge into the ventral root.

Anterior (ventral) root

Carries efferent motor fibers away from the spinal cord.

Mixed spinal nerve

Formed by union of dorsal and ventral roots; contains sensory, somatic motor, and autonomic fibers, forms just distal to DRG.

Posterior (dorsal) ramus

Mixed branch supplying intrinsic back muscles, vertebral joints, and overlying skin.

Anterior (ventral) ramus

Mixed branch supplying anterolateral trunk and limbs; forms major nerve plexuses except in much of the thoracic region.

Meningeal branch

Re-enters the vertebral canal to supply structures within/around the canal.

Intervertebral foramen

Passage through which spinal nerves/roots and associated vessels enter or leave the vertebral canal; clinically relevant to nerve-root compression.

Peripheral nerve

Bundle of PNS axons carrying sensory, motor, and/or autonomic signals between the CNS and peripheral targets.

Nerve fascicle

Bundle of axons within a peripheral nerve.

Endoneurium

Connective tissue surrounding individual peripheral nerve fibers.

Perineurium

Connective-tissue sheath surrounding a nerve fascicle; contributes to the protected internal environment of the fascicle.

Epineurium

Outer connective-tissue sheath surrounding the entire peripheral nerve and its fascicles.

Cervical plexus

Network formed primarily by anterior rami of upper cervical spinal nerves; recognize as a ventral-ramus plexus.

Brachial plexus

Anterior-ramus plexus distributing spinal nerve fibers to the upper limb.

Lumbar plexus

Anterior-ramus plexus contributing peripheral nerves to the lower trunk and lower limb.

Sacral plexus

Anterior-ramus plexus contributing major peripheral nerves to the pelvis and lower limb.

Neuron cell body (soma)

Metabolic/integrative region containing the nucleus; motor neuron somata may be recognized in spinal gray matter.

Dendrites

Receive synaptic input and conduct graded signals toward the cell body.

Axon

Conducts action potentials away from the cell body toward another neuron or effector.

Myelin sheath

Electrical insulation around selected axons that increases conduction efficiency.

Node of Ranvier

Gap between myelin segments where action potentials are regenerated during saltatory conduction.

Schwann cell

PNS glial cell responsible for myelination/ensheathment of peripheral axons.

Oligodendrocyte

CNS glial cell responsible for myelinating CNS axons.

Satellite cell

PNS glial cell surrounding neuronal cell bodies in peripheral ganglia, including the dorsal root ganglion.

Astrocyte

CNS support cell involved in structural/metabolic support and regulation of the neural environment.

Microglia

Resident immune/phagocytic cells of the CNS.

Ependymal cells

Line the ventricles and central canal; specialized ependymal cells contribute to choroid plexus CSF production.

Lateral horn / intermediolateral cell column

Contains preganglionic sympathetic neuron cell bodies in T1-L2 spinal cord segments.

White ramus communicans

Carries myelinated preganglionic sympathetic fibers from a spinal nerve into the sympathetic trunk; present only at T1-L2 levels.

Sympathetic trunk (chain)

Paired longitudinal chains alongside the vertebral column that allow sympathetic fibers to synapse, ascend, or descend.

Paravertebral (sympathetic trunk) ganglion

Contains sympathetic postganglionic neuron cell bodies.

Gray ramus communicans

Carries unmyelinated postganglionic sympathetic fibers from the sympathetic trunk back to a spinal nerve; gray rami occur at all spinal nerve levels.

Thoracic splanchnic nerve

Carries primarily preganglionic sympathetic fibers toward prevertebral ganglia; distinguish from gray rami returning fibers to spinal nerves.

Prevertebral ganglion

Sympathetic ganglion anterior to the vertebral column/aorta where many abdominopelvic preganglionic fibers synapse.

Adrenal medulla

Modified sympathetic ganglion receiving preganglionic sympathetic fibers directly; releases catecholamines into the bloodstream.

Peripheral receptor → peripheral nerve → anterior/ventral ramus (when applicable) → mixed spinal nerve → dorsal root ganglion → dorsal root → dorsal horn/CNS.

General sensory (somatic) signal pathway

Somatic motor signal pathway

Ventral horn motor neuron → ventral rootlets → ventral root → mixed spinal nerve → dorsal or ventral ramus → peripheral nerve → skeletal muscle.

Basic spinal nerve formation

Dorsal root + ventral root → mixed spinal nerve → dorsal and ventral rami.

Sympathetic route returning to a spinal nerve

Lateral horn (T1-L2) → ventral root → spinal nerve → white ramus → sympathetic trunk/ganglion → gray ramus → spinal nerve → peripheral target.

Lateral horn (T1-L2) → ventral root → spinal nerve → white ramus → sympathetic trunk → splanchnic nerve → prevertebral ganglion → visceral target.

Sympathetic splanchnic route

Saltatory conduction

Action potential is regenerated at successive nodes of Ranvier along a myelinated axon; myelin increases conduction efficiency.

Dorsal-root or dorsal-root-ganglion injury

Primarily disrupts sensory input.

Ventral-root injury

Primarily disrupts motor output.

Injury distal to root union

Because spinal nerves and both dorsal and ventral rami are mixed, injury here can produce both sensory and motor deficits.

C1-C7 exit above their corresponding vertebrae; C8 exits between C7 and T1; T1 and below exit inferior to the corresponding vertebra.

Cervical vs Thoracic spinal nerve exit levels

Disc herniation or foraminal narrowing

Can compress a spinal nerve/root and produce radicular pain, sensory change, weakness, or altered reflexes according to the affected level.

Peripheral nerve injury

Produces deficits according to the fibers and targets carried by that nerve; due to plexus organization, a named nerve may contain fibers from multiple spinal levels.

Loss of myelin

Reduces efficient saltatory conduction and can slow or block signal transmission.

Sympathetic pathway interruption

May produce findings such as Horner syndrome when the pathway supplying the head/neck is affected.

Lower motor neuron (LMN) lesions

Lesions involving the ventral horn, root, or peripheral motor axon (anatomically distinct from upper motor neuron lesions located within descending CNS pathways).