Nervous System Divisions and Neuron Physiology

These vocabulary flashcards cover the divisions, functions, and cellular structures of the nervous system, as well as the physiological mechanisms of membrane potentials and nerve impulses.

Nervous System

A system that uses electrical signaling (neural impulses) to provide swift, brief responses to stimuli and integrates all body activities.

Endocrine System

A system that uses chemical signaling (hormones produced by glands) to adjust metabolic operations and direct long-term changes.

Neuron

The basic unit of the nervous system that controls and integrates body activities.

Neuroglia (glia cells)

Non-neuronal supportive tissue that maintains homeostasis, forms myelin, and provides protection for neurons; these cells are smaller than neurons, $50 \times$ more numerous, and capable of division.

Sensory Function

One of the three basic functions of the nervous system involving the sensing of changes with sensory receptors.

Integrative Function

The function of the nervous system responsible for interpreting and remembering changes sensed by receptors.

Motor Function

The function of the nervous system that reacts to changes with effectors, such as muscular contractions or glandular secretions.

Central Nervous System (CNS)

The division of the nervous system consisting of the brain and the spinal cord.

Peripheral Nervous System (PNS)

The division consisting of cranial and spinal nerves that connects the CNS to different body parts using sensory and motor fibers.

Somatic Nervous System (SNS)

A voluntary subdivision of the PNS that carries sensory neurons from the skin and special receptors to the CNS, and motor neurons to skeletal muscle tissue.

Autonomic Nervous System (ANS)

An involuntary subdivision of the PNS that carries sensory neurons from visceral organs to the CNS, and motor neurons to smooth muscle, cardiac muscle, and glands.

Sympathetic Division

A division of the autonomic nervous system responsible for energy demanding reactions.

Parasympathetic Division

A division of the autonomic nervous system responsible for energy conserving responses.

Reflex Arc

The simplest, primitive, and inborn stimulus-response pathway where the spinal cord makes the 'decision' without involving the brain.

Gliomas

Tumors formed by the rapid mitosis of neuroglial cells.

Membrane Potential

A localized electrical gradient or voltage difference across the plasma membrane of a cell.

Action Potentials

Rapid, short-lasting, 'all-or-none' changes in membrane potential that propagate down an axon for long-distance communication.

Graded Potentials

Local membrane changes occurring in dendrites and the cell body that vary in amplitude and can be either excitatory (depolarizing) or inhibitory (hyperpolarizing).

Principal Intracellular Cation

$K^+$.

Principal Extracellular Cation

$Na^+$.

Resting Membrane Potential

The potential energy difference across the membrane of a polarized cell at rest, typically valued at $-70 \text{ mV}$.

$Na^+/K^+$ pump

A mechanism that maintains resting potential by removing $3 \text{ Na}^+$ to the outside and moving $2 \text{ K}^+$ to the inside of the cell.

Leakage Channels

Ion channels that are always open; nerve cells have more for $K^+$ than for $Na^+$.

Voltage-gated Channels

Ion channels that open and close in response to a change in membrane voltage.

Ligand-gated Channels

Ion channels that open and close in response to chemical stimuli, such as hormones or neurotransmitters.

Hyperpolarization

A change where the membrane potential becomes more negative, often caused by gated $K^+$ channels opening and $K^+$ diffusing out of the cell.

Depolarization

A phase where the membrane potential becomes less negative, caused by gated $Na^+$ channels opening and $Na^+$ rushing into the cell.

Threshold

The critical membrane potential level, typically $-55 \text{ mV}$, required to trigger an action potential.

Absolute Refractory Period

The period of time during which a neuron cannot generate another action potential, even with a strong stimulus, because inactivated $Na^+$ channels must return to the resting state.

Synapse

The 'gap' or synaptic cleft, ranging as small as $20 \text{ nm}$, between the axon of one neuron and the dendrite or effector of another.

Electrical Synapse

A type of synapse where ionic current spreads through gap junctions, allowing faster, two-way transmission and synchronization of neuron groups.

Chemical Synapse

The most common type of synapse involving one-way information transfer from a presynaptic neuron to a postsynaptic membrane.