The Nervous System Structure and Function Flashcards

Vocabulary terms and definitions covering the structure, cellular components, brain divisions, and functional mechanisms of the human nervous system as presented in Basic Nursing Unit 4.

Neuron

The basic structural and functional cell of the nervous system, specialized to respond to chemical and physical stimuli.

Neuroglia (Glial Cells)

Supportive cells of the nervous system that outnumber neurons by five times; they support and connect nervous tissue but do not transmit impulses.

Central Nervous System (CNS)

The division of the nervous system comprising the brain, spinal cord, and accessory structures like the meninges and cerebrospinal fluid.

Peripheral Nervous System (PNS)

The division of the nervous system made up of cranial nerves, spinal nerves, and the autonomic nervous system.

Axon

An extension of the neuron that carries impulses away from the cell body; it may be myelinated or bare.

Dendrites

Short, highly branched extensions of the neuron cell body that receive impulses from other axons and transmit them toward the cell body.

Myelin Sheath

A fatty covering on axons that electrically insulates nerve cells from one another and allows impulses to conduct more rapidly.

Synapse

The junction or space between the axon of one neuron and the dendrites of the next where neurotransmitters allow impulses to cross.

Neurotransmitter

A chemical released by an axon, such as acetylcholine, dopamine, or serotonin, that allow nerve impulses to cross the synapse.

Sensory (Afferent) Neurons

Neurons that receive and transmit messages to the central nervous system from all parts of the body.

Motor (Efferent) Neurons

Neurons that receive and transmit messages from the central nervous system to muscles and glands.

Interneurons

Also called connectory or association neurons; they are located only within the CNS and link sensory and motor neurons.

Astrocytes

CNS neuroglia with extensions attached to blood vessels that help form the blood-brain barrier.

Microglia

CNS neuroglia that can enlarge and consume microbes through phagocytosis.

Oligodendrocytes

CNS neuroglia that have extensions forming myelin sheaths around axons in the central nervous system.

Cerebrum

The largest portion of the brain ($80\%$ of its volume), serving as the center for conscious thought and higher mental functioning.

Cerebral Cortex

The outside layer of the brain made of soft gray matter; it is responsible for learning, intelligent reasoning, and judgment.

Convolutions (Gyri)

The wrinkles or folds on the surface of the cerebral cortex that increase the brain's surface area.

Fissures (Sulci)

The crevices or grooves located between the folds (gyri) of the cerebral cortex.

Frontal Lobe

The lobe responsible for higher mental processes (intelligence, mood, planning), motor speech (Broca's area), and voluntary control of skeletal muscles.

Parietal Lobe

The sensory area of the brain that interprets touch, temperature, pain, shapes, and spatial ability.

Temporal Lobe

The lobe that controls sensations of hearing, auditory interpretation (Wernicke's area), smell, and some memory.

Occipital Lobe

The lobe where visual transmissions and interpretations occur and eye movements are integrated.

Decussation

The crossing of nerve tracts within the medulla, resulting in the right hemisphere of the brain controlling the left side of the body and vice versa.

Corpus Callosum

A band of approximately $200\text{ million}$ neurons that connects the right and left cerebral hemispheres, allowing them to share information.

Thalamus

A relay station in the diencephalon that integrates all sensory impulses except smell before they reach the cerebral cortex.

Hypothalamus

A vital center in the diencephalon that regulates body temperature, water balance, sleep, appetite, sexual urges, and the pituitary gland.

Limbic System

Consists of the hippocampus and reticular formation; responsible for learning, long-term memory, and maintaining levels of awareness/wakefulness.

Cerebellum

The second-largest part of the brain; it coordinates voluntary muscle movement, muscle tone, coordination, and equilibrium.

Midbrain

Located at the top of the brain stem; acts as a visual and auditory reflex center and houses the righting reflex.

Pons

Meaning "bridge," it carries messages between the cerebrum and medulla and contains respiratory centers for normal breathing patterns.

Medulla Oblongata

The floor of the skull; contains vital centers for cardiac (heart rate), vasomotor (blood pressure), and respiratory functions.

Reflex Arc

The circular pathway of a reflex, receiving and sending messages through nerve fibers to relieve the brain of routine work.

Meninges

Three protective membranes covering the CNS: the tough outer Dura Mater, the web-like middle Arachnoid, and the thin vascular inner Pia Mater.

Cerebrospinal Fluid (CSF)

A lymph-like fluid that forms a cushion around the CNS, carries nutrients, and removes waste.

Vagus Nerve (Cranial Nerve X)

Known as "the wanderer," it serves a large portion of the body and provides reflex control for heart rate, hunger, and abdominal viscera.

Sympathetic Nervous System

A division of the ANS that produces the "fight or flight" response, preparing the body for emergencies by increasing heart rate and diverting blood flow.

Parasympathetic Nervous System

A division of the ANS that produces responses for normal body functions at rest (feed-or-breed), such as resuming digestion and slowing heart rate.

Action Potential

An electrical signal or nerve impulse caused by the rapid exchange of sodium and potassium ions across the cell membrane.

All-or-None Law

The principle that a nerve impulse is either transmitted completely across a synapse or not at all; it cannot be partially transmitted.

Aphasia

An abnormal neurologic condition where language function is defective or absent due to injury to Broca's or Wernicke's areas.

Plexus

A group of spinal nerves, such as the Cervical, Brachial, Lumbosacral, or Pudendal plexuses.

Proprioceptors

Sensory receptors within muscles and joints that relay information to the cerebellum about balance and body position.