The Spinal Cord & Nerves: Structure, Function, and Major Pathways

The Spinal Cord & Nerves

Overview

The spinal cord and nerves are essential components of the central and peripheral nervous systems, responsible for transmitting signals between the brain and the rest of the body. This section covers the anatomy of the spinal cord, cranial nerves, spinal nerves, nerve plexuses, and major nerves of the human body.

The Spinal Cord

Anatomical Features

• Conus Medullaris: The tapered, lower end of the spinal cord, typically found near the first or second lumbar vertebra.

• Filum Terminale: A fibrous extension of the pia mater that anchors the spinal cord to the coccyx.

• Cauda Equina: A bundle of spinal nerves and nerve roots extending from the lower end of the spinal cord, resembling a horse's tail.

Gray Matter Organization

• Anterior (Ventral) Median Fissure: A deep groove along the anterior midline of the spinal cord.

• Posterior (Dorsal) Median Sulcus: A shallow groove along the posterior midline.

• Anterior (Ventral) Column: Contains motor tracts.

• Lateral Column: Contains both motor and sensory tracts.

• Posterior (Dorsal) Column: Contains sensory tracts.

Gray Matter Horns

• Central Canal: A small channel in the center of the spinal cord containing cerebrospinal fluid.

• Ventral (Anterior) Horn: Contains motor neuron cell bodies.

• Dorsal (Posterior) Horn: Contains sensory neuron cell bodies.

• Lateral Horn: Present in thoracic and upper lumbar regions; contains autonomic motor neurons.

Cranial Nerves

Overview and Functions

Cranial nerves are twelve pairs of nerves that emerge directly from the brain. Each has a specific function, including sensory, motor, or both.

• I. Olfactory (I): Smell (sensory)

• II. Optic (II): Vision (sensory)

• III. Oculomotor (III): Eye movement, pupil constriction (motor)

• IV. Trochlear (IV): Eye movement (motor)

• V. Trigeminal (V): Facial sensation, chewing (both)

• VI. Abducens (VI): Eye movement (motor)

• VII. Facial (VII): Facial expression, taste (both)

• VIII. Vestibulocochlear (VIII): Hearing, balance (sensory)

• IX. Glossopharyngeal (IX): Taste, swallowing (both)

• X. Vagus (X): Parasympathetic control of heart, lungs, digestive tract (both)

• XI. Accessory (XI): Head and shoulder movement (motor)

• XII. Hypoglossal (XII): Tongue movement (motor)

Mnemonic for cranial nerves order: "On Occasion Our Trusty Truck Acts Funny—Very Good Vehicle Any How"

Spinal Nerves

Nerve Roots

• Dorsal (Posterior) Root: Contains sensory (afferent) fibers; transmits sensory information to the spinal cord.

• Dorsal Root Ganglion: Contains cell bodies of sensory neurons.

• Ventral (Anterior) Root: Contains motor (efferent) fibers; transmits motor commands from the spinal cord to muscles.

• Spinal Nerve: Formed by the joining of dorsal and ventral roots; contains both sensory and motor fibers.

Nerve Plexuses

• Cervical Plexus: Supplies the neck and diaphragm.

• Brachial Plexus: Supplies the shoulders and upper limbs.

• Lumbar Plexus: Supplies the lower abdomen, anterior and medial thigh.

• Sacral Plexus: Supplies the pelvis, posterior thigh, and most of the lower leg and foot.

Major Nerves of the Human Body

Upper Extremity

• Radial Nerve: Supplies the posterior arm and forearm muscles.

• Ulnar Nerve: Supplies muscles of the hand and some forearm muscles.

• Median Nerve: Supplies most of the anterior forearm muscles and some hand muscles.

• Musculocutaneous Nerve: Supplies the anterior arm muscles.

• Axillary Nerve: Supplies the deltoid and teres minor muscles.

Lower Extremity

• Femoral Nerve: Supplies the anterior thigh muscles.

• Lateral Femoral Cutaneous Nerve: Supplies the skin of the lateral thigh.

• Obturator Nerve: Supplies the medial thigh muscles.

• Sciatic Nerve: The largest nerve in the body; supplies the posterior thigh, leg, and foot.

• Tibial Nerve: Supplies the posterior leg and foot muscles.

• Common Fibular Nerve: Supplies the anterior and lateral leg muscles.

Additional info:

• The spinal cord is organized into 31 segments, each giving rise to a pair of spinal nerves.

• Damage to specific nerves or plexuses can result in characteristic patterns of sensory or motor loss.