Chapter 13: The Spinal Cord, Spinal Nerves, and Spinal Reflexes

Vocabulary terms and definitions from Chapter 13 covering the anatomy of the spinal cord, spinal meninges, white and gray matter, peripheral nerves, neuronal pools, and neural reflex classifications.

Central Nervous System (CNS)

The structural division of the nervous system consisting of the brain and spinal cord, which serve as processing centers.

Peripheral Nervous System (PNS)

The structural division of the nervous system consisting of cranial nerves and spinal nerves that contain sensory input and motor response pathways.

Spinal Reflexes

Quick, automatic nerve responses triggered by specific stimuli that are controlled by the spinal cord alone without input from the brain.

Posterior Median Sulcus

A groove located on the posterior side of the spinal cord that helps divide it into left and right halves.

Anterior Median Fissure

A deeper groove located on the anterior side of the spinal cord dividing it into left and right halves.

Central Canal

An internal channel within the spinal cord that contains cerebrospinal fluid (CSF).

Cervical Enlargement

A wider area of the spinal cord containing increased gray matter that supplies nerves to the shoulder and upper limbs.

Lumbosacral Enlargement

A wider region of the spinal cord containing increased gray matter that supplies nerves to the pelvis and lower limbs.

Conus Medullaris

The tapered, conical distal end of the spinal cord located below the lumbosacral enlargement.

Cauda Equina

The collection of spinal nerve roots extending below the conus medullaris, named for its resemblance to a horse's tail.

Filum Terminale

A thin thread of fibrous tissue at the end of the conus medullaris that attaches to the coccygeal ligament.

Anterior Root (Ventral Root)

The branch of a spinal nerve that contains axons of motor neurons.

Posterior Root (Dorsal Root)

The branch of a spinal nerve that contains axons of sensory neurons.

Spinal Ganglia (Dorsal Root Ganglia)

Structures located between pedicles of adjacent vertebrae containing cell bodies of sensory neurons that form the posterior root.

Mixed Nerves

Nerves that contain both afferent (sensory) and efferent (motor) nerve fibers.

Posterior Ramus

A branch of a spinal nerve that innervates and supplies the skin and muscles of the back.

Anterior Ramus

A branch of a spinal nerve that supplies most of the body wall, skin, and limbs.

Dura Mater

The tough, outermost layer of the spinal meninges composed of dense collagen fibers.

Epidural Space

The space located between the vertebrae and the dura mater containing loose connective tissue and adipose tissue.

Arachnoid Mater

The middle layer of the spinal meninges consisting of a simple squamous epithelial membrane and a network of collagen and elastic trabeculae.

Subarachnoid Space

The space between the arachnoid mater and pia mater filled with cerebrospinal fluid (CSF) carrying dissolved gases, nutrients, and wastes.

Pia Mater

The innermost meningeal layer made of a mesh of collagen and elastic fibers firmly attached to the underlying neural structures.

Denticulate Ligaments

Paired structures that anchor the pia mater to the dura mater to prevent lateral movement of the spinal cord.

Gray Matter

Regions of the central nervous system composed mainly of neuron cell bodies, neuroglia, and unmyelinated axons.

White Matter

Regions of the central nervous system composed mainly of myelinated and unmyelinated axons.

Nuclei

Functional masses of gray matter surrounded by white matter within the Central Nervous System.

Gray Commissures

Narrow bands of gray matter surrounding the central canal where axons cross from one side of the spinal cord to the other.

Tract

A bundle of axons in the Central Nervous System that relays the same type of information in the same direction.

Epineurium

The outermost connective tissue layer of a spinal nerve consisting of a dense network of collagen fibers.

Perineurium

The middle connective tissue layer surrounding a nerve that divides it into bundles of axons called fascicles.

Endoneurium

The innermost connective tissue layer of a nerve that surrounds individual axons.

Dermatome

A specific bilateral region of skin supplied by a single pair of spinal nerves.

Nerve Plexus

A complex, interwoven network of nerve fibers formed from blended fibers of the anterior rami of adjacent spinal nerves.

Phrenic Nerve

A major nerve of the cervical plexus originating from spinal segments $C_3-C_5$ that controls the diaphragm.

Interneurons

Neurons located entirely within the Central Nervous System (numbering about 20 billion) that interpret, plan, and coordinate sensory inputs and motor outputs.

Divergence

A neural circuit pattern in which information spreads from one neuron or neuronal pool to many neurons or pools.

Convergence

A neural circuit pattern where several neurons synapse on a single presynaptic or motor neuron.

Serial Processing

A neural circuit pattern where information moves sequentially along a single path from one neuron or neuronal pool to the next.

Parallel Processing

A neural circuit pattern where several neurons or neuronal pools process the exact same information simultaneously.

Reverberation

A neural circuit arrangement utilizing collateral branches that extend back to continue stimulating presynaptic neurons in a positive feedback loop.

Monosynaptic Reflex

The simplest reflex arc consisting of a single synapse where a sensory neuron synapses directly with a motor neuron.

Polysynaptic Reflex

A reflex arc that includes at least one interneuron between the sensory neuron and the motor neuron.

Innate Reflexes

Basic, genetically programmed neural reflexes present at birth.

Acquired Reflexes

Rapid, automatic learned motor patterns enhanced through repetition.

Stretch Reflex

A monosynaptic reflex that regulates skeletal muscle length throughout the body.

Muscle Spindle

Sensory receptors involved in stretch reflexes consisting of small, specialized intrafusal muscle fibers innervated by sensory and motor neurons.

Reciprocal Inhibition

The reflexive process where stimulation of flexor muscles causes interneurons to simultaneously inhibit antagonistic extensor muscles.

Ipsilateral Reflex Arc

A reflex arc where the motor response occurs on the same side of the body as the stimulus.

Crossed Extensor Reflex

A polysynaptic reflex involving a contralateral arc that straightens the opposite limb to support weight while a flexor reflex lifts the injured limb.

Babinski Reflex

An abnormal response in adults (fanning of toes) when the lateral sole is stroked, which is normal in infants but indicates CNS damage in adults.