Spinal Cord and Peripheral Nervous System Anatomy

Comprehensive vocabulary flashcards covering the gross and cross-sectional anatomy of the spinal cord, meninges, spinal nerve branches, cervical, brachial, lumbar, and sacral plexuses, and reflex arcs.

Conus Medullaris

The tapered, cone-shaped inferior end of the spinal cord located at the level of the L1 and L2 vertebrae.

Cauda Equina

A bundle of nerve roots resembling a horse's tail occupying the vertebral canal from L2 to S4 vertebrae that innervates the pelvic organs and lower extremities.

Anterior Median Fissure

The deep longitudinal groove running along the midline of the anterior surface of the spinal cord.

Posterior Median Sulcus

The shallow groove running along the midline of the posterior surface of the spinal cord.

Cervical Enlargement

A thickened, wider region of the superior spinal cord that gives rise to nerves supplying the upper limbs.

Lumbar Enlargement

A widened region of the lower spinal cord that gives rise to nerves supplying the pelvic region and lower limbs.

Spinal Nerve

A mixed nerve formed by the fusion of anterior (ventral) and posterior (dorsal) spinal nerve roots, carrying both motor and sensory fibers.

Anterior Spinal Nerve Root

A root formed by 6 to 8 rootlets that carries motor axons and efferent signals away from the spinal cord to the body.

Posterior Spinal Nerve Root

A root formed by 6 to 8 rootlets that transmits sensory axons and afferent signals inward toward the spinal cord.

Posterior Root Ganglion

A bulbous enlargement on the dorsal root housing the neurosomas (cell bodies) of sensory neurons heading to the spinal cord.

Central Canal

A cerebrospinal fluid-filled longitudinal passage situated in the center and midline of the spinal cord; open in children and closed in adults.

Anterior Horn

The ventral projection of spinal gray matter containing the cell bodies of somatic motor neurons (lower motor neurons).

Posterior Horn

The dorsal projection of spinal gray matter that receives incoming sensory axons from neurons in the dorsal root ganglia.

Lateral Horn

A gray matter region found exclusively in the thoracic and lumbar segments containing cell bodies of the sympathetic division of the autonomic nervous system.

Gray Commissure

A central bridge of gray matter surrounding the central canal that connects the left and right sides of the spinal gray matter.

Funiculi

Three pairs of white matter columns (anterior, lateral, and posterior) composed of tracts carrying ascending sensory or descending motor signals.

Denticulate Ligaments

Lateral, tooth-like extensions of the pia mater that attach to the dura mater to anchor the spinal cord and restrict side-to-side displacement.

Epidural Space

The space located between the dura mater and the vertebral wall containing adipose tissue, loose connective tissue, and blood vessels.

Filum Terminale

A fibrous extension of the pia mater extending inferiorly from the conus medullaris to anchor the spinal cord to the coccyx.

Meningitis

An inflammation of the meninges caused by bacterial, viral, or fungal pathogens, presenting with severe headache, fever, neck stiffness, and photophobia.

Cervical Spinal Nerves

Eight pairs of spinal nerves originating from the cervical spinal cord, with the first pair emerging superior to the C1 vertebra.

Posterior Ramus

The dorsal branch of a spinal nerve that innervates the deep muscles, joints, and skin of the posterior trunk.

Anterior Ramus

The ventral branch of a spinal nerve that innervates the anterior and lateral trunk, the limbs, and forms somatic nerve plexuses.

Intercostal Nerves

Eleven pairs of anterior rami arising from thoracic spinal nerves (T1–T11) that course between the ribs to supply thoracic/abdominal muscles and skin.

Cervical Plexus

A somatic nerve network formed by anterior rami of C1–C4 with contributions from C5, primarily innervating the head, neck, and upper chest.

Lesser Occipital Nerve

A branch of the cervical plexus (C2–C3) that travels along the posterior border of the sternocleidomastoid to provide sensory innervation to the external ear, lateral scalp, and upper neck.

Ansa Cervicalis

A loop formed by C1–C3 anterior rami lying anterior to the internal jugular vein that provides motor supply to the omohyoid, sternohyoid, and sternothyroid muscles.

Supraclavicular Nerve

A sensory branch of the cervical plexus (C3–C4) emerging near the middle third of the sternocleidomastoid that supplies the skin over the clavicle, shoulder, and upper chest.

Transverse Cervical Nerve

A cutaneous branch of the cervical plexus (C2–C3) that travels horizontally across the sternocleidomastoid to supply the anterior and lateral neck skin.

Greater Auricular Nerve

A branch of the cervical plexus (C2–C3) ascending vertically over the sternocleidomastoid to supply the skin over the parotid gland, mastoid region, and external ear.

Phrenic Nerve

A vital nerve originating from C3, C4, and C5 that descends over the anterior scalene muscle to provide motor innervation to the diaphragm.

Brachial Plexus

A complex nerve network formed by anterior rami of C5–T1 that divides into trunks, divisions, and cords to innervate the upper limb.

Musculocutaneous Nerve

The terminal continuation of the lateral cord that innervates anterior arm flexors (biceps brachii, brachialis, coracobrachialis) and lateral forearm skin.

Axillary Nerve

A posterior cord branch innervating the deltoid and teres minor muscles and shoulder skin; prone to damage in surgical neck fractures of the humerus.

Radial Nerve

The continuation of the posterior cord traveling down the radial groove to supply upper limb extensors; injury causes wrist drop.

Median Nerve

A nerve formed by both lateral and medial cords that courses beneath the flexor retinaculum; compression leads to carpal tunnel syndrome.

Ulnar Nerve

The continuation of the medial cord passing behind the medial epicondyle to innervate forearm flexors and intrinsic hand muscles; damage causes claw hand.

Lumbar Plexus

A plexus formed by the anterior rami of L1–L4 with a T12 contribution, situated near the psoas major and quadratus lumborum muscles.

Iliohypogastric Nerve

A branch of the lumbar plexus (T12, L1) supplying the transversus abdominis, internal oblique, and skin of the lower abdomen and superior gluteal region.

Ilioinguinal Nerve

A lumbar plexus branch (L1) lying inferior to the iliohypogastric nerve that supplies abdominal muscles and skin of the superomedial thigh and external genitalia.

Genitofemoral Nerve

A lumbar plexus branch (L1, L2) that pierces the psoas major muscle to supply the cremaster muscle and the skin of the external genitalia and anteromedial thigh.

Obturator Nerve

A lumbar plexus nerve (L2–L4) passing through the obturator foramen to innervate the medial thigh adductor muscles and proximal medial thigh skin.

Lateral Femoral Cutaneous Nerve

A sensory nerve from the lumbar plexus (L2, L3) that passes over the iliacus muscle to innervate the skin of the anterolateral thigh.

Femoral Nerve

A major lumbar plexus nerve (L2–L4) supplying anterior thigh muscles responsible for knee extension, as well as anterior/medial thigh skin.

Saphenous Nerve

A cutaneous branch of the femoral nerve that passes the medial knee to supply the knee joint, medial leg, and medial foot.

Sacral Plexus

A nerve network formed by anterior rami of L4–S4 that innervates the gluteal area, pelvis, posterior thigh, leg, and foot.

Superior Gluteal Nerve

A sacral plexus branch (L4, L5, S1) innervating the gluteus medius, gluteus minimus, and tensor fasciae latae muscles.

Inferior Gluteal Nerve

A sacral plexus branch (L5, S1, S2) exiting near the piriformis muscle to supply motor innervation to the gluteus maximus muscle.

Pudendal Nerve

A sacral plexus nerve (S2–S4) providing motor innervation to the pelvic floor muscles and external sphincters, and sensory innervation to the perineum.

Posterior Femoral Cutaneous Nerve

A cutaneous branch of the sacral plexus (S1–S3) running superficial to the biceps femoris to supply the skin of the posterior thigh.

Sciatic Nerve

The largest nerve in the human body (L4–S3) that traverses the posterior thigh before bifurcating into the tibial and common fibular nerves.

Tibial Nerve

A branch of the sciatic nerve (L4–S3) descending down the posterior leg to innervate the posterior thigh, posterior leg, and plantar foot muscles.

Common Fibular Nerve

A branch of the sciatic nerve (L4–S2) wrapping laterally around the neck of the fibula to supply the lateral and anterior compartments of the leg.

Sural Nerve

A purely sensory nerve formed by uniting branches of the tibial and common fibular nerves, supplying the posterior leg and lateral foot.

Reflex Arc

The five-component neural pathway of a reflex: receptor, sensory afferent neuron, CNS integration center, motor efferent neuron, and effector.

Muscle Spindles

Specialized stretch receptors embedded within skeletal muscles that detect changes in length to initiate stretch reflexes.

Stretch Reflex

A rapid, involuntary contraction of a muscle in response to being stretched, serving to maintain posture, equilibrium, and joint stability.

Patellar Tendon Reflex

A monosynaptic stretch reflex triggered by tapping the patellar tendon, which stretches the quadriceps and causes knee extension.