Unit 4: Neurons, Neurotransmitters, and Neuroimaging Techniques

Comprehensive vocabulary flashcards covering neuron anatomy, action potential dynamics, neurotransmitter systems, nervous system divisions, and modern neuroimaging methods from Unit 4.

Biological Psychology (Neuroscience)

The branch of psychology rooted in physiology that examines how genetics, the nervous system, and the endocrine system influence human behaviors and mental processes.

Neurons

Specialized cells serving as the primary building blocks of the nervous system, exceeding $100\text{ billion}$ in the human brain, that receive, integrate, and transmit electrical and chemical information.

Glial Cells (Glia)

Supportive cells comprising roughly $50\%$ of the brain's total volume that provide nourishment, insulation, and protection for neurons, defend against toxins, and produce myelin.

Soma (Cell Body)

The central body of a neuron containing the nucleus with genetic DNA and mitochondria that convert oxygen and glucose into energy to power the cell.

Dendrites

Branch-like extensions branching off the neuronal soma that receive chemical messages (neurotransmitters) from adjacent neurons via specialized receptor sites.

Axon

A long, thin, tube-like fiber extending from the soma that carries outgoing electrical impulses (action potentials) away from the cell body toward target cells.

Axon Hillock

The specialized conical region at the junction of the soma and axon where the action potential or nerve impulse is initiated.

Myelin Sheath

A white, fatty, insulating layer produced by glial cells that encloses certain axons, allowing impulses to transmit up to $50\text{ times}$ faster than unmyelinated fibers.

Nodes of Ranvier

Gaps along the myelin sheath of an axon that permit the action potential to jump from node to node, speeding up transmission and facilitating repolarization during the refractory period.

Multiple Sclerosis (MS)

An autoimmune disorder characterized by the immune system destroying the myelin sheath on axons, which degrades electrical impulse propagation and leads to muscle weakness, tremors, fatigue, and paralysis.

Myasthenia Gravis (MG)

An autoimmune neuromuscular disease where the immune system destroys acetylcholine receptors at the neuromuscular junction, impairing muscle contraction and leading to profound muscle fatigue and weakness.

Axon Terminal Buttons

Knob-like structures at the distal branches of an axon that contain synaptic vesicles filled with chemical neurotransmitters awaiting release into the synapse.

Synaptic Vesicles

Tiny membranous sacs contained inside axon terminal buttons that store neurotransmitters and release them into the synaptic cleft when triggered by an action potential.

Synapse (Synaptic Cleft)

The microscopic, fluid-filled physical gap separating the axon terminal button of a sending presynaptic neuron from the receptor sites on the receiving postsynaptic neuron; it is not part of the neuron itself.

Microglia

A specialized subtype of glial cells that cleans and protects the central nervous system by digesting metabolic cellular waste and dead neurons.

Astrocytes

A class of glial cells that forms structural bridges between neurons and cerebral blood vessels, regulating nutrients and maintaining the neural environment.

Resting Potential

The polarized electrical state of an inactive neuron, wherein the fluid-filled interior maintains a negative charge of approximately $-70\,\text{mV}$ relative to the positively charged exterior.

Action Potential

A rapid, temporary shift in a neuron's electrical membrane voltage from $-70\,\text{mV}$ past a $-55\,\text{mV}$ threshold up to $+40\,\text{mV}$ that propagates section by section down the axon.

Threshold

The minimum level of depolarization (approximately $-55\,\text{mV}$) required to trigger the opening of voltage-gated ion channels and initiate an action potential.

All-or-None Law

The principle stating that an action potential fires at complete, invariant strength if the threshold is met, or does not fire at all; stimulus intensity is encoded solely by firing frequency.

Depolarization

The phase of the action potential during which gated sodium channels open and positive sodium ions ($\text{Na}^+$) flood into the axon, turning the intracellular charge positive.

Repolarization

The restorative process in which potassium ions ($\text{K}^+$) exit the axon and sodium-potassium pumps work to return the intracellular charge back to its resting negative level.

Refractory Period

The recovery interval following an action potential during which a neuron temporarily cannot fire another impulse while resetting its resting ionic concentrations.

Presynaptic Neuron

The transmitting neuron whose terminal buttons release neurotransmitters into the synaptic cleft in response to an arriving action potential.

Postsynaptic Neuron

The receiving neuron whose dendrite receptor sites capture neurotransmitters crossing the synaptic cleft, altering its own electrical charge.

Reuptake

The biological recycling mechanism by which excess neurotransmitters in the synaptic gap are drawn back into the presynaptic terminal buttons.

Excitatory Neurotransmitters

Chemical messengers that open receptor channels to depolarize the postsynaptic membrane, increasing the probability that an action potential will fire.

Inhibitory Neurotransmitters

Chemical messengers that hyperpolarize the postsynaptic membrane, decreasing the probability that the receiving neuron will fire an action potential.

Dopamine

A neurotransmitter regulating voluntary movement, posture, reward pathways, pleasure, and attention; deficits cause Parkinson's disease, while excessive activity is linked to schizophrenia.

Acetylcholine (ACh)

A neurotransmitter critical for voluntary muscle contraction and memory formation; deficiency is seen in Alzheimer's disease, while blocking its transmission induces muscular paralysis.

Serotonin

A monoamine neurotransmitter responsible for regulating mood, sleep, appetite, and sensory perception; chronically low transmission is strongly linked to clinical depression.

Endorphins

Endogenous opioid neuropeptides that act as natural internal painkillers to alleviate physical discomfort and induce feelings of pain relief during times of intense stress, injury, or vigorous exercise.

Norepinephrine

A chemical messenger functioning as a neurotransmitter in the brain and an adrenal hormone (noradrenaline) that triggers mental vigilance, physical arousal, and fight-or-flight reactions.

Glutamate

The most abundant excitatory neurotransmitter in the central nervous system, central to long-term potentiation (LTP), memory encoding, and cognitive functioning.

GABA (Gamma-Aminobutyric Acid)

The primary inhibitory neurotransmitter in the central nervous system that slows neural excitability, induces relaxation and sleep, and mitigates feelings of anxiety.

Substance P

A neuropeptide mediator of nociception (pain perception) that transmits pain signals from sensory nerve endings to the brain.

Agonist

A drug or chemical substance that mimics or strengthens the action of a neurotransmitter by binding directly to its postsynaptic receptor site and activating it.

Antagonist

A drug or substance that binds to a postsynaptic receptor site without activating it, thereby blocking the endogenous neurotransmitter from stimulating the cell.

Selective Serotonin Reuptake Inhibitors (SSRIs)

Antidepressant medications that function as indirect agonists by blocking the presynaptic transporter proteins, leaving more serotonin molecules available to stimulate postsynaptic receptors.

Central Nervous System (CNS)

The core division of the human nervous system encased in protective bone (the skull and spinal column), composed exclusively of the brain and spinal cord.

Peripheral Nervous System (PNS)

The division of the nervous system encompassing all neural nerves and ganglia situated outside the skull and spinal cord that convey sensory and motor signals to and from the CNS.

Gray Matter

Nervous tissue in the brain and spinal cord composed primarily of unmyelinated neuron cell bodies, dendrites, and capillaries, forming the outer cerebral cortex.

White Matter

Nervous tissue in the central nervous system composed largely of myelinated axonal pathways that facilitate fast communication across neural regions.

Blood-Brain Barrier

A specialized semipermeable boundary formed by capillary endothelial cells that prevents toxins, bacteria, and foreign chemicals from entering brain tissue while admitting necessary nutrients.

Cerebrospinal Fluid (CSF)

A protective, shock-absorbing liquid that circulates through the brain's ventricles and around the spinal cord, providing mechanical cushioning, delivering nutrients, and removing waste.

Spinal Reflex Arc

A rapid, involuntary circuit where sensory receptors stimulate afferent neurons, which synapse on spinal interneurons that directly activate motor neurons to execute movement prior to conscious awareness by the brain.

Somatic Nervous System

The voluntary subdivision of the peripheral nervous system that delivers sensory feedback to the CNS and conducts motor commands from the CNS to voluntary skeletal muscles.

Autonomic Nervous System

The involuntary division of the peripheral nervous system that regulates smooth muscles, cardiac muscle, internal organs, and endocrine glands to sustain homeostasis.

Autonomic Nervous System Divisions

The two opposing branches of autonomic regulation: the sympathetic division, which initiates emergency fight-or-flight reactions, and the parasympathetic division, which conserves energy and manages rest-and-digest states.

Sensory Neurons (Afferent Neurons)

Nerve cells equipped with afferent fibers that carry sensory information from environmental receptors inward toward the central nervous system.

Motor Neurons (Efferent Neurons)

Nerve cells equipped with efferent fibers that transmit outgoing signals away from the central nervous system to target muscles, organs, and glands to initiate voluntary or involuntary movements.

Interneurons

The most abundant category of neurons, located exclusively within the brain and spinal cord, that form internal communicating pathways linking sensory and motor neurons.

Phineas Gage

A historic neurological case study of a railroad supervisor whose frontal lobes and limbic connections were severed by an iron tamping rod in $1848$, resulting in profound emotional and personality changes.

Lesioning

The process of observing or experimentally creating targeted damage to specific neural tissue to determine localized brain functions based on resulting behavioral deficits.

Transcranial Magnetic Stimulation (TMS)

A noninvasive technique using a magnetic coil held against the scalp to temporarily enhance or suppress neural firing in targeted surface cortical regions, creating a reversible 'virtual lesion.'

Electroencephalogram (EEG) Tracing

A real-time graphic readout of electrical wave potentials recorded by scalp electrodes, capturing frequency and amplitude variations across neurological states like normal resting and hypsarrhythmia.

Functional Magnetic Resonance Imaging (fMRI)

A noninvasive imaging technique that monitors blood oxygen level-dependent (BOLD) changes via magnetic fields, providing real-time maps of both anatomical brain structure and active neural function.