Nervous System: Organization, Cytology, and Neurophysiology

Comprehensive vocabulary flashcards covering anatomical divisions, neuron cytology, glial cell functions, neurophysiology, ion channels, action potentials, and synaptic transmission from the lecture notes.

Central Nervous System (CNS)

The structural division of the nervous system comprising the brain and spinal cord, responsible for processing information and coordinating responses.

Peripheral Nervous System (PNS)

The structural division of the nervous system consisting of nerves and ganglia that connects the CNS with the rest of the body.

Ganglia

Clusters of neuronal cell bodies located along nerves in the peripheral nervous system.

Somatic sensory

The component of the sensory division that detects stimuli we consciously perceive, such as touch.

Visceral sensory

The component of the sensory division that detects internal stimuli that are not typically consciously perceived, such as signals from the heart or kidneys.

Somatic motor

The component of the motor division that transmits voluntary motor commands to skeletal muscles.

Autonomic motor (visceral motor)

The component of the motor division that transmits involuntary commands to cardiac muscle, smooth muscle, and glands; divided into sympathetic and parasympathetic divisions.

Excitability

A characteristic of neurons defined as the ability to respond to a stimulus by changing membrane potential.

Conductivity

A characteristic of neurons defined as the ability to propagate an electrical signal along the plasma membrane.

Amitotic

The characteristic describing how most neurons lose the ability to divide by mitosis after fetal development.

Perikaryon

The cytoplasm located within the cell body (soma) of a neuron.

Nissl bodies (chromatophilic substance)

Clusters of free and bound ribosomes within the neuron involved in protein synthesis.

Dendrites

Short, branching, usually unmyelinated neuronal processes that receive signals and carry input toward the cell body.

Axon hillock

The specialized triangular region of the neuron where the axon attaches to the soma and where incoming signals are summed.

Axon

A single long process that conducts action potentials away from the cell body toward another cell or effector.

Axolemma

The plasma membrane surrounding the axon of a neuron.

Synaptic knobs

Terminal expanded endings of an axon that contain synaptic vesicles filled with neurotransmitters.

Multipolar neuron

The most common structural type of neuron, possessing many dendrites and one axon, characteristic of motor neurons and most interneurons.

Bipolar neuron

A relatively uncommon neuron possessing one dendrite and one axon extending from the soma, found in specialized locations such as the retina.

Unipolar (pseudounipolar) neuron

A structural type of neuron featuring a single process that emerges from the soma and branches into a peripheral process and a central process, typical of most sensory neurons.

Interneurons (association neurons)

Neurons located entirely within the CNS that integrate and process information between sensory and motor neurons, making up approximately $99\%$ of all neurons.

Epineurium

A thick layer of dense irregular connective tissue enclosing the entire nerve.

Perineurium

A layer of dense irregular connective tissue that surrounds individual bundles of axons known as fascicles.

Endoneurium

A delicate layer of areolar connective tissue surrounding each individual axon that provides electrical insulation.

Electrical synapse

A type of synapse where cells are connected directly by gap junctions, allowing rapid electrical current flow without synaptic delay.

Chemical synapse

The most common synapse type, where presynaptic and postsynaptic cells are separated by a synaptic cleft and communication is mediated by neurotransmitters, involving a synaptic delay.

Astrocytes

The most abundant glial cells in the CNS that support the blood-brain barrier via perivascular endfeet, regulate potassium and the chemical environment, and provide structural support.

Ependymal cells

Ciliated CNS glial cells lining internal fluid-filled cavities (ventricles) of the brain and central canal of the spinal cord that assist in producing and circulating cerebrospinal fluid (CSF).

Microglia

Phagocytic immune defense cells of the CNS that replicate during infection to engulf cellular debris and infectious agents.

Oligodendrocytes

CNS glial cells that produce myelin sheaths around segments of multiple adjacent axons, accelerating action potential propagation.

Satellite cells

PNS glial cells that encircle and electrically insulate neuronal cell bodies within ganglia while regulating nutrient and waste exchange.

Neurolemmocytes (Schwann cells)

PNS glial cells responsible for myelinating a single segment of an axon and forming the outer neurilemma.

Neurilemma

The delicate outer cytoplasm and nucleus-containing layer of a neurolemmocyte (Schwann cell) that facilitates PNS axon regeneration.

Nodes of Ranvier

Gaps in the myelin sheath along an axon where voltage-gated ion channels are concentrated.

Multiple sclerosis (MS)

An autoimmune disorder characterized by progressive demyelination of neurons within the CNS due to immune attack on oligodendrocytes.

Guillain-Barré syndrome (GBS)

An inflammatory condition causing loss of myelin in peripheral nerves, typically starting with distal limb weakness that advances proximally.

Wallerian degeneration

The breakdown and degeneration of the distal segment of a severed axon and its myelin sheath following injury.

Resting membrane potential (RMP)

The electrical potential difference across the plasma membrane of a non-signaling neuron, typically valued at $-70\,\text{mV}$.

Depolarization

A change in membrane potential that makes the inside of the cell less negative (or more positive) relative to the resting potential, typically mediated by entry of $\text{Na}^+$.

Hyperpolarization

A change in membrane potential that makes the inside of the cell more negative than the resting potential, caused by either $\text{K}^+$ exit or $\text{Cl}^-$ entry.

Excitatory postsynaptic potential (EPSP)

A graded local depolarization of the postsynaptic membrane caused by cation entry, moving the membrane potential closer to threshold.

Inhibitory postsynaptic potential (IPSP)

A graded local hyperpolarization of the postsynaptic membrane caused by cation exit or anion entry, moving the membrane potential farther from threshold.

Threshold

The minimum membrane potential (typically $-55\,\text{mV}$) required at the initial segment to trigger the opening of voltage-gated sodium channels and initiate an action potential.

Spatial summation

The integration of postsynaptic potentials generated simultaneously from multiple different presynaptic inputs across the receptive membrane.

Temporal summation

The integration of postsynaptic potentials generated in rapid succession by repeated signals from a single presynaptic neuron.

All-or-none law

The principle stating that an action potential is either generated and propagated at full amplitude if threshold is reached, or not initiated at all if threshold is not reached.

Action potential

A rapid, transient reversal of membrane potential propagating along the conductive segment (axon), consisting of depolarization via $\text{Na}^+$ influx followed by repolarization via $\text{K}^+$ efflux.

Absolute refractory period

The period following action potential initiation during which voltage-gated $\text{Na}^+$ channels are either open or inactivated, preventing any subsequent stimulus from triggering another action potential.

Relative refractory period

The interval after the absolute refractory period during which an action potential can be triggered, but only by a stronger-than-normal stimulus because the cell is hyperpolarized.

Continuous conduction

The sequential, unmyelinated propagation of an action potential along each adjacent segment of axolemma, resulting in slower conduction speed.

Saltatory conduction

The rapid propagation of action potentials along myelinated axons, where electrical current travels under myelin and regenerates only at unmyelinated nodes of Ranvier.

Acetylcholinesterase (AChE)

An enzyme located in the synaptic cleft that terminates acetylcholine signaling by breaking it down into acetate and choline.