Central and Peripheral Nervous Systems

Vocabulary practice flashcards covering gross anatomy of the spinal cord, spinal nerve distribution, functional organization of the nervous system, receptor types, pathways of rami and roots, the autonomic nervous system, and reflex arcs.

Central Nervous System (CNS)

The brain and spinal cord, which contain control centers responsible for processing and integrating sensory information, planning and coordinating responses to stimuli, and providing control over the activities of other systems.

Peripheral Nervous System (PNS)

Neural tissue outside the CNS whose primary function is to link the central nervous system with sense organs and other body systems.

Sensory (Afferent) Division

The functional division of the PNS that conducts nerve impulses from somatic and visceral sensory receptors to the CNS.

Motor (Efferent) Division

The functional division of the PNS that conducts motor nerve impulses from the CNS out to effectors, which include muscles and glands.

Somatic Nervous System (SNS)

The voluntary motor division of the PNS that conducts impulses from the CNS specifically to skeletal muscles.

Autonomic Nervous System (ANS)

The involuntary visceral motor division of the nervous system that conducts impulses from the CNS to smooth muscle, cardiac muscle, glands, and adipose tissue.

Spinal Cord

A central nervous system structure measuring approximately $45\,\text{cm}$ ($18\,\text{in.}$) in length that extends from the foramen magnum of the skull to the first lumbar vertebra (L1).

Cervical Enlargement

An expanded region of the spinal cord that supplies nerves to the pectoral girdle and upper limbs.

Lumbosacral Enlargement

An expanded region of the spinal cord that supplies nerves to the pelvic girdle and lower limbs.

Conus Medullaris

The tapered, cone-shaped inferior region of the spinal cord located near L1/L2.

Cauda Equina

The bundle of long inferior nerve roots extending downward from the conus medullaris near L1/L2.

Filum Terminale

A slender strand of fibrous tissue ('terminal thread') extending from the conus medullaris at L1 to the coccyx.

Gray Matter (Spinal Cord)

The inner layer of the spinal cord surrounding the central canal, composed of dendrites and cell bodies of sensory and motor neurons.

Central Canal

An internal channel located at the center of the spinal cord that is surrounded by gray matter and contains cerebrospinal fluid (CSF).

Gray Commissures

Regions surrounding the central canal containing axons that cross (decussate) from one side of the spinal cord to the other.

White Matter (Spinal Cord)

The outer layer of the spinal cord consisting of mostly myelinated axons organized into tracts and columns.

Ascending Tracts

Axon pathways that carry sensory information upward through the posterior section of the spinal cord to the brain.

Descending Tracts

Axon pathways that carry motor information downward away from the brain via the anterior section of the spinal cord to effectors.

Spinal Nerves

$31$ pairs of mixed peripheral nerves that emerge through the intervertebral foramina of the vertebral column, each containing thousands of nerve fibers.

Cervical Plexus

A nerve network formed by spinal nerves C1–C5 that innervates neck muscles and gives rise to the phrenic nerve controlling the diaphragm.

Brachial Plexus

A nerve network formed by spinal nerves C5–T1 that innervates the pectoral girdle and upper limbs, giving rise to nerves including the radial and ulnar nerves.

Lumbosacral Plexus

A nerve network formed by spinal nerves T12–S4 that innervates the pelvic girdle and lower limbs, giving rise to the femoral and sciatic nerves.

Exteroceptors

Sensory receptors located near the body surface that detect external stimuli, including touch, pressure, pain, temperature, and special senses.

Interoceptors

Sensory receptors located within internal viscera (such as the digestive tract, bladder, and lungs) whose activation mediates sensations of pain, nausea, hunger, and fullness.

Proprioceptors

Sensory receptors located in skeletal muscles, tendons, joints, and ligaments that detect muscle stretch and inform the CNS of body position.

Dorsal Root

The posterior branch of a spinal nerve that conveys incoming sensory nerve impulses from peripheral receptors into the spinal cord.

Dorsal Root Ganglion

A swelling on the dorsal root of a spinal nerve formed by an anatomical cluster of sensory neuron cell bodies.

Ventral Root

The anterior branch of a spinal nerve that conducts outgoing motor nerve impulses away from the spinal cord toward effectors.

Dorsal Ramus

A mixed branch of a spinal nerve carrying both sensory and motor fibers that innervates the skin and muscles of the neck and back.

Ventral Ramus

A mixed branch of a spinal nerve carrying both sensory and motor fibers that supplies ventrolateral body surfaces, body wall structures, and the limbs.

Rami Communicantes

Spinal nerve branches containing visceral motor and visceral sensory neurons that connect with the sympathetic trunk ganglion.

Sympathetic Division

The thoracolumbar division of the ANS that mobilizes the body for 'fight-or-flight' emergencies by increasing heart rate and dilating pupils and bronchi.

Parasympathetic Division

The craniosacral division of the ANS that operates under restful conditions to conserve energy, promote digestive activity, and counterbalance sympathetic actions.

Reflex Arc

The five-component neural pathway mediating an involuntary, subconscious response, comprising a receptor, sensory neuron, integration center, motor neuron, and effector.

Monosynaptic Reflex

A rapid reflex involving a single synapse between just $2$ neurons (sensory and motor) that does not travel up to the brain, such as the knee-jerk reflex.

Polysynaptic Reflex

A reflex pathway involving more than $2$ neurons, utilizing one or more interneurons to trigger protective motor responses like the withdrawal reflex.