Chapter 14

This set covers spinal cord anatomy, gray and white matter organization, nerve construction, the reflex arc, and major peripheral nerves of the human body.

Spinal Cord

A long, cylindrical structure of nervous tissue located within the vertebral canal, extending from the foramen magnum to approximately the $L1$–$L2$ vertebrae.

Posterior/ Dorsal ramus

Small branch that intervates muscles and skin of back

Anterior ramus

Large branch splits into other branches that connects the muscle and causes sensation in the skin

Spinal cord and brain stem

Where do reflexes take place?

Cervical enlargement

A region of the spinal cord that gives rise to nerves supplying the upper limbs.

Lumbar enlargement

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

Conus medullaris

The tapered inferior end of the spinal cord.

Cauda equina

A bundle of spinal nerve roots extending below the conus medullaris.

Filum terminale

A fibrous strand that anchors the spinal cord to the coccyx.

Anterior median fissure

A deep groove located on the front of the spinal cord.

Posterior median sulcus

A shallow groove located on the back of the spinal cord.

Gray matter

folio which means leaves, ridges on the outside of cerebellum

• cerebral cortex, In the nuclei

White matter

The outer region of the spinal cord containing myelinated axons that form ascending and descending tracts.

• inside the cerebellum: arbor vitae

Central canal

A small channel in the spinal cord filled with cerebrospinal fluid (CSF).

Dorsal Horn

The section of gray matter containing sensory interneurons that receive incoming sensory information.

Ventral Horn

The section of gray matter containing somatic motor neuron cell bodies that control skeletal muscles.

Lateral Horn

Found mainly in thoracic and upper lumbar segments; contains autonomic motor neurons involved in sympathetic nervous system functions.

Ascending Pathways

Sensory pathways that carry information (pain, temperature, touch, etc.) from receptors in the body to the brain.

Descending Pathways

Motor pathways that carry commands from the brain to muscles and glands for voluntary movement and posture regulation.

Quadriplegia (Tetraplegia)

Paralysis of all four limbs, usually caused by injury to the cervical spinal cord.

Paraplegia

Paralysis of the lower limbs, usually caused by injury below the cervical region.

Peripheral Nerve

A bundle of nerve fibers (axons) located outside the central nervous system that carries sensory and/or motor information.

Endoneurium

Delicate connective tissue surrounding each individual nerve fiber.

Perineurium

Connective tissue surrounding bundles of nerve fibers called fascicles.

Epineurium

Tough outer connective tissue surrounding the entire nerve that protects it and contains blood vessels.

Mixed Nerves

Nerves containing both sensory and motor fibers, allowing bidirectional communication; most spinal nerves are of this type.

Reflex Arc

The neural pathway that produces a rapid, automatic, involuntary response to a stimulus without requiring conscious thought.

Integration Center

The component of a reflex arc located in the CNS that processes information and determines the appropriate response.

Wallerian Degeneration

The process where the portion of the axon distal to an injury degenerates and is removed by macrophages.

Schwann Cell Activity

Proliferation of Schwann cells to form a regeneration tube that guides new axonal growth during nerve repair.

Dorsal Root

Structure containing sensory (afferent) nerve fibers entering the spinal cord.

Ventral Root

Structure containing motor (efferent) nerve fibers leaving the spinal cord.

Ventral Ramus

The larger branch of a spinal nerve supplying the anterior trunk and limbs and forming major nerve plexuses.

Rami Communicantes

Branches connecting spinal nerves to the sympathetic trunk of the autonomic nervous system.

Nerve Plexus

A network of interweaving ventral rami from spinal nerves that redistribute fibers to form peripheral nerves.

Brachial Plexus

A nerve plexus formed by spinal nerves $C5$–$T1$ supplying the shoulder, arm, forearm, and hand.

Median Nerve

Controls many forearm and hand muscles and provides sensation to the palm and fingers; often involved in carpal tunnel syndrome.

Sciatic Nerve

The largest nerve in the body, originating from the sacral plexus ($L4$–$S3$) and supplying the posterior thigh and most of the leg.

Dermatome

map for nerve to see where nerves are connected to

• useful for spinal injury or degeneration disease

Monosynaptic Reflex

A reflex involving only one synapse between a sensory neuron and a motor neuron, such as the Patellar reflex.

Crossed Extensor Reflex

A reflex where one leg withdraws from a painful stimulus while the opposite leg extends to maintain balance.