Nervous System and Nervous Tissue

This set of flashcards covers the terminology and functional divisions of the central and peripheral nervous systems, types of neurons and glia, and the mechanisms of action potentials and synaptic transmission.

PNS

Consists of ganglia and nerves which are distinct structures.

CNS

Includes the brain and spinal cord; acts as integrative and control centers with subparts best examined with a microscope.

Gray matter

Localized areas containing cell bodies, dendrites, and axon terminals; the site of synapses.

White matter

Axon bundles connecting gray matter sections; characterized by myelin insulation.

Nucleus (CNS Context)

A localized center of function containing the cell bodies of several neurons.

Optic nerve

The bundle of fibers extending from the eye to the chiasm.

Optic tract

The bundle of fibers extending from the eye to the brain through the chiasm.

Optic chiasm

The border structure between the peripheral and central nervous systems.

Ganglia

Clusters of nerve cells specifically located in the PNS.

Sensation

Functional division involving the "big 5" senses and internal changes.

Integration

Functional division involving communication within the nervous system.

Response

Functional division involving voluntary or involuntary actions in response to stimuli.

Somatic Nervous System

The division focused on conscious, voluntary control and some reflexes.

Autonomic Nervous System

The division responsible for involuntary control and homeostatic balance.

Enteric Nervous System

The division responsible for digestion that can function independently of the CNS.

Sensory (afferent) division

Nerve fibers that conduct impulses from receptors to the CNS.

Motor (efferent) division

Nerve fibers that conduct impulses from the CNS to effectors such as muscles and glands.

Sympathetic division

Division of the ANS that mobilizes body systems during activity.

Parasympathetic division

Division of the ANS that conserves energy and promotes housekeeping functions during rest.

Neuron

Excitables cells that transmit electrical signals, consisting of a soma, axon, and dendrite.

Soma

The cell body of a neuron.

Axon

The secretory region of a neuron.

Dendrite

The reception region of a neuron.

Synapse

The space between neurons where communication occurs.

Glial cells

The supporting framework for neurons, also referred to as "glue."

Unipolar neurons

Sensory neurons in PNS ganglia with one process including both axon and dendrite.

Bipolar neurons

Neurons with two processes (one axon, one dendrite); primarily associated with special senses.

Multipolar neurons

The most abundant neuron type, especially in the CNS, containing one axon and many dendrites.

Astrocyte

Glial cell that provides support and interacts with neurons, vessels, and the pia mater to form the blood-brain barrier.

Blood-Brain Barrier (BBB)

A barrier that allows glucose, amino acids ($AA$), $H_2O$, and small particles to pass, but excludes white blood cells ($WBCs$).

Oligodendrocyte

Glial cell in the CNS responsible for insulation and myelination of axons.

Microglia

Glial cells responsible for immune surveillance and phagocytosis.

Ependymal cells

Cells that line ventricles and produce cerebrospinal fluid ($CSF$).

Choroid plexus

Area where ependymal cells meet vessels for filtration and absorption using tight junctions.

Satellite cells

Glial cells providing support for sensory and autonomic functions in the PNS.

Schwann cells

Glial cells in the PNS that wrap and insulate a single axon segment.

Myelin

Insulating layer made of phospholipids and proteins, produced by oligodendrocytes in the CNS and Schwann cells in the PNS.

Neurotransmitter

A chemical that signals other tissues via receptors; it must diffuse across the synapse to reach targets like the thalamus and cerebral cortex.

Ligand-gated channels

Ionotropic receptors that open when signaling molecules bind to them, causing a change in charge.

Mechanically gated channels

Channels that open due to physical changes in the cell membrane, such as touch or pressure.

Voltage-gated channels

Channels that open in response to changes in the electrical charge surrounding them.

Leakage channels

Channels that open and close at random, contributing to the resting membrane potential.

Membrane potential

The electrical state of the cell membrane determined by the distribution of charge from the inside to the outside.

Action potential (AP)

An "all or nothing" electrical signal of uniform size generated by nervous tissue for communication.

Refractory period

The time during an action potential when another cannot be initiated.

Absolute refractory period

A period where another AP cannot start due to the inactivation gate for $Na^+$; a stronger stimulus and outward flow of $K^+$ are required to overcome it.

Continuous conduction

Propagation in unmyelinated axons where the AP moves in one direction toward axon terminals.

Saltatory conduction

Propagation where the AP "jumps" from node to node; speed is influenced by axon diameter.

Summation

The overall change in membrane potential resulting from the addition of excitatory and inhibitory postsynaptic potentials.

Presynaptic element

The synaptic end bulb where $Ca^{2+}$ enters to trigger vesicle fusion and neurotransmitter release.