Human Anatomy and Physiology - Fundamentals of the Nervous System

Flashcards about the nervous system, neurons, and neuroglia.

Nervous System

Master controlling and communicating system of the body.

Sensory Input

Information gathered by sensory receptors about internal and external changes.

Integration

Processing and interpretation of sensory input.

Motor Output

Activation of effector organs (muscles and glands) produces a response.

Central Nervous System (CNS)

Brain and spinal cord of dorsal body cavity; interprets sensory input and dictates motor output.

Peripheral Nervous System (PNS)

The portion of the nervous system outside the CNS; consists mainly of nerves that extend from the brain and spinal cord.

Somatic sensory fibers

Convey impulses from skin, skeletal muscles, and joints to CNS.

Visceral sensory fibers

Convey impulses from visceral organs to CNS.

Motor (efferent) division

Transmits impulses from CNS to effector organs (muscles and glands).

Somatic nervous system

Somatic motor nerve fibers conduct impulses from CNS to skeletal muscle; conscious control of skeletal muscles.

Autonomic nervous system

Consists of visceral motor nerve fibers; regulates smooth muscle, cardiac muscle, and glands; involuntary nervous system.

Involuntary nervous system

Regulates smooth muscle, cardiac muscle, and glands.

Neuroglia (glial cells)

Small cells that surround and wrap delicate neurons.

Neurons (nerve cells)

Excitable cells that transmit electrical signals.

Astrocytes

Most abundant, versatile, and highly branched of glial cells in the CNS.

Microglial cells

Defensive cells in the CNS.

Ependymal cells

Line cerebrospinal fluid-filled CNS cavities.

Oligodendrocytes

Have processes that form myelin sheaths around CNS nerve fibers.

Satellite cells

Surround neuron cell bodies in PNS; function similar to astrocytes of CNS.

Schwann cells (neurolemmocytes)

Surround all peripheral nerve fibers and form myelin sheaths in thicker nerve fibers.

Neurons (nerve cells)

Large, highly specialized cells that conduct impulses.

Neuron Cell Body

Also called the perikaryon or soma; biosynthetic center of neuron.

Nuclei

Clusters of neuron cell bodies in CNS.

Ganglia

Clusters of neuron cell bodies in PNS.

Tracts

Bundles of neuron processes in CNS.

Nerves

Bundles of neuron processes in PNS.

Dendrites

Receptive (input) region of neuron; convey incoming messages toward cell body as graded potentials.

Axon terminal

Region that secretes neurotransmitters, which are released into extracellular space; can excite or inhibit neurons it contacts.

Anterograde

Away from cell body. Examples: mitochondria, cytoskeletal elements, membrane components, enzymes.

Retrograde

Toward cell body. Examples: organelles to be degraded, signal molecules, viruses, and bacterial toxins.

Myelin sheath

Composed of myelin, a whitish, protein-lipid substance; protects and electrically insulates axon and increases speed of nerve impulse transmission.

Myelinated fibers

Segmented sheath surrounds most long or large-diameter axons.

Nonmyelinated fibers

Do not contain sheath; conduct impulses more slowly.

Myelin sheath gaps

Gaps between adjacent Schwann cells; sites where axon collaterals can emerge.

White matter

Regions of brain and spinal cord with dense collections of myelinated fibers.

Gray matter

Mostly neuron cell bodies and nonmyelinated fibers.

Multipolar

Three or more processes (1 axon, others dendrites); most common and major neuron type in CNS.

Bipolar

Two processes (one axon, one dendrite); rare (ex: retina and olfactory mucosa).

Unipolar

One T-like process (two axons); also called pseudounipolar.

Sensory neurons

Transmit impulses from sensory receptors toward CNS; almost all are unipolar; cell bodies are located in ganglia in PNS.

Motor neurons

Carry impulses from CNS to effectors; multipolar; most cell bodies are located in CNS (except some autonomic neurons).

Interneurons

Also called association neurons; lie between motor and sensory neurons; shuttle signals through CNS pathways; most are entirely within CNS; 99% of body’s neurons are interneurons.