Neuroscience and Central Nervous System Review

Comprehensive set of vocabulary flashcards covering Central and Peripheral Nervous System organization, neuronal bioelectricity, ion channels, synaptic plasticity, sensory systems, motor control, muscle reflexes, and autonomic functions based on lecture notes.

Nucleus (CNS)

A group of neuron cell bodies inside the central nervous system (CNS) that share a common function.

Dura Mater

The tough, leather-like outer meningeal layer located directly underneath the skull.

Subarachnoid Space

The space between the arachnoid membrane and pia mater containing cerebrospinal fluid (CSF) that allows the CNS to float and protects it from mechanical injury.

Pia Mater

The delicate, very thin inner meningeal layer directly attached to the brain and spinal cord tissue.

Blood-Brain Barrier (BBB)

Specialized cellular structures surrounding CNS blood capillaries that protect CNS cells from bloodborne pathogens and toxins.

Dorsal Roots

Nerve structures that carry sensory information into the spinal cord.

Ventral Roots

Nerve structures that carry motor commands away from the spinal cord toward target muscles.

Dorsal Horn

The region of spinal cord gray matter responsible for sensory processing.

Ventral Horn

The region of spinal cord gray matter containing motor neurons controlling skeletal muscles and components of autonomic control.

Ascending Tracts

Axon bundles in spinal cord white matter carrying sensory information up from the spinal cord to the brain.

Descending Tracts

Axon bundles in spinal cord white matter carrying motor commands down from the brain to the spinal cord.

Pons

Brainstem structure that relays information between the cerebrum and cerebellum, contains sensory and motor neurons for the face and neck, and connects to cranial nerves.

Medulla Oblongata

Brainstem structure located below the pons that controls vital involuntary functions including breathing and heart rate.

Cerebellum

Brain region posterior to the brainstem that monitors movement, compares actual movement to intended commands, and corrects movement errors.

Vagus Nerve

The 10th cranial nerve ($\text{CN X}$) that extends beyond the head and neck to provide widespread parasympathetic innervation to thoracic and abdominal organs.

Decussation

The crossing of axon pathways over the midline of the body to the contralateral side.

Thalamus

Major subcortical relay station that receives peripheral sensory signals and routes them to the appropriate primary sensory areas of the cerebral cortex.

Cortical Functional Axis (Posterior to Anterior)

Organizational pattern of the cerebral cortex progressing from sensory processing (posterior) to motor execution (middle) to cognitive control (anterior).

Posterior Parietal Cortex (PPC)

Cortical area that integrates multi-modal sensory inputs into reference frames to transform sensory information into motor commands.

Prefrontal Cortex (PFC)

Anterior cortical area involved in top-down cognitive control, using explicit goals to guide lower-level brain processing.

Sequence of Voluntary Movement Control

Goal formation in PFC -> Movement selection in Basal Ganglia -> Command generation in Primary Motor Cortex (M1) -> Execution by Skeletal Muscles -> Error monitoring/correction by Cerebellum.

Corticospinal Tract

Major lateral motor pathway originating in M1 and synapsing in the spinal cord ventral horn to control voluntary movement of distal muscles.

Ventromedial Motor Pathways

Motor pathways controlling skeletal muscles involved in posture, balance, trunk movement, and eye movements.

Basal Ganglia

Subcortical nuclei that receive broad cortical input to select and initiate specific motor programs.

Positron Emission Tomography (PET)

Hemodynamic functional imaging technique measuring regional blood flow via radioactive tracers, offering high spatial resolution (few mm) but poor temporal resolution ($\sim 1\,\text{min}$).

Functional Magnetic Resonance Imaging (fMRI)

Hemodynamic imaging technique measuring blood oxygenation levels with high spatial resolution and moderate temporal resolution (a few seconds).

Electroencephalography (EEG)

Electromagnetic technique recording scalp electrical potentials produced by synchronized neuronal populations, providing excellent temporal resolution ($\sim 1\,\text{ms}$) but lower spatial resolution.

Magnetoencephalography (MEG)

Electromagnetic technique measuring magnetic fields generated by neuronal activity, combining excellent temporal resolution ($\sim 1\,\text{ms}$) with better spatial resolution than EEG.

Schwann Cells

Glial cells responsible for forming myelin sheaths around axons in the peripheral nervous system (PNS).

Oligodendrocytes

Glial cells responsible for myelinating multiple axon segments within the central nervous system (CNS).

Astrocytes

Glial cells that regulate the extracellular chemical environment, maintain ion homeostasis, and support the blood-brain barrier.

Microglia

Specialized glial cells that act as the primary immune defense and phagocytes within the CNS.

Resting Membrane Potential ($V_{\text{rest}}$)

Baseline electrical potential across a neuron's membrane at rest, typically around $-70\,\text{mV}$, determined predominantly by high resting $\text{K}^+$ permeability.

Inward Current

Flow of positive ions into the cell (or negative ions out of the cell), producing membrane depolarization.

Outward Current

Flow of positive ions out of the cell (or negative ions into the cell), producing membrane hyperpolarization.

Membrane Capacitance ($C_m$)

The property of the lipid bilayer to separate and store electrical charge between the cytosol and extracellular fluid.

Membrane Time Constant ($\tau_m$)

Calculated as $\tau_m = R_m \times C_m$; dictates how rapidly membrane potential changes in response to current, where a larger time constant enhances temporal summation.

Length Constant ($\lambda$)

Distance parameter determined by $\text{High } R_m$ and $\text{Low } R_a$; dictates how far passive voltage changes travel down a dendrite, where a larger length constant enhances spatial summation.

Equilibrium Potential ($E_{\text{ion}}$)

The specific membrane potential at which electrical driving force exactly balances the concentration gradient for a given ion, resulting in net zero current.

Driving Force

The net electrical voltage acting on an ion species, calculated as $V_m - E_{\text{ion}}$.

Modified Ohm's Law for Neurons

Equation relating ionic current flow to membrane conductance and driving force: $I_{\text{ion}} = g_{\text{ion}}(V_m - E_{\text{ion}})$.

Sodium Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase)

Active transport protein that utilizes ATP to pump $3\,\text{Na}^+$ ions out of the cell for every $2\,\text{K}^+$ ions in, maintaining resting concentration gradients.

Hyperkalemia

Elevated extracellular potassium concentration ($[\text{K}^+]_e$) that reduces $\text{K}^+$ efflux, depolarizes $V_{\text{rest}}$, and makes neurons hyper-excitable.

Channel Inactivation

Functional closure of a voltage-gated ion channel caused by a structural inactivation gate while the membrane remains depolarized, distinct from activation gate closure.

Absolute Refractory Period

Time window during an action potential when voltage-gated $\text{Na}^+$ channels are inactivated, making it physically impossible to fire another action potential.

Relative Refractory Period

Time window following an action potential where some $\text{Na}^+$ channels have recovered but $\text{K}^+$ channels remain open, requiring a stronger-than-normal depolarizing stimulus to reach threshold.

Saltatory Conduction

Rapid mode of action potential propagation in myelinated axons where electrical signals jump passively between unmyelinated Nodes of Ranvier.

Synaptic Vesicle Exocytosis Trigger

Action potential arrival -> terminal depolarization -> opening of voltage-gated $\text{Ca}^{2+}$ channels -> $\text{Ca}^{2+}$ influx -> binding to synaptotagmin -> SNARE-mediated membrane fusion.

Neurotransmitter Clearance Mechanisms

Three primary processes that clear transmitter from the synaptic cleft: presynaptic/glial reuptake, enzymatic breakdown, and passive diffusion.

Ionotropic Receptors

Ligand-gated ion channels that open directly upon neurotransmitter binding to produce fast, brief postsynaptic potentials.

Metabotropic Receptors

G-protein-coupled receptors (GPCRs) that indirectly alter ion channel gating or intracellular biochemical cascades via second messengers, producing slower, longer-lasting effects.

AMPA Receptors

Ionotropic glutamate receptors permeable to $\text{Na}^+$ and $\text{K}^+$ with a linear I-V curve and reversal potential near $0\,\text{mV}$.

NMDA Receptors

Ionotropic glutamate receptors permeable to $\text{Na}^+$, $\text{K}^+$, and $\text{Ca}^{2+}$ that require both glutamate binding and postsynaptic depolarization to clear a voltage-dependent $\text{Mg}^{2+}$ block.

Shunting Inhibition

Inhibitory mechanism (such as via $\text{GABA}_A$ receptors) where increased membrane conductance reduces input resistance and short-circuits nearby excitatory voltage changes without necessarily hyperpolarizing the membrane.

Temporal Summation

Addition of successive postsynaptic potentials occurring in rapid sequence at a single synapse, promoted by a large membrane time constant ($\tau_m$).

Spatial Summation

Addition of simultaneous postsynaptic potentials originating from multiple distinct dendritic locations, promoted by a large length constant ($\lambda$).

Synaptic Efficacy Formula

Quantifies transmission strength as $E = n \times p \times q$, where $n$ is release sites, $p$ is release probability, and $q$ is quantal response size.

Synaptic Depression

Short-term synaptic plasticity where repeated high-frequency stimulation depletes the readily releasable vesicle pool, decreasing postsynaptic responses and acting as a low-pass filter.

Synaptic Facilitation

Short-term synaptic plasticity where high-frequency action potentials lead to residual terminal $\text{Ca}^{2+}$ accumulation, increasing release probability ($p$) and acting as a high-pass filter.

Long-Term Potentiation (LTP)

Persistent enhancement of synaptic strength triggered by correlated presynaptic and postsynaptic activity, driven by $\text{NMDA}$ receptor activation, $\text{Ca}^{2+}$ influx, and increased $\text{AMPA}$ receptor density or conductance.

Associativity of LTP

Feature of LTP wherein a weakly active synapse undergoes potentiation if it is active simultaneously with a strongly active depolarizing pathway on the same cell.

Synapse Specificity of LTP

Feature of LTP where potentiation occurs exclusively at synapses that released glutamate during postsynaptic depolarization, leaving inactive neighboring synapses unpotentiated.

Ocular Dominance Plasticity

Experience-dependent competitive refinement of visual cortex connections during critical periods, demonstrated by monocular deprivation leading to loss of deprived-eye cortical inputs.

Primary vs Secondary Sensory Neurons

Primary sensory neurons directly transduce environmental energy into electrical signals; secondary sensory neurons are one synapse downstream in the central pathway.

Receptive Field

The specific region of physical space or abstract stimulus parameter in which a stimulus alters the firing rate of a sensory neuron.

Center-Surround Receptive Field

Receptive field structure where stimulus presentation in the center produces the opposite electrical response to stimulus presentation in the surrounding zone.

Lateral Inhibition

Circuit design where active primary neurons excite inhibitory interneurons that suppress neighboring sensory pathways, sharpening contrast and spatial resolution.

Meissner's Corpuscles

Tactile mechanoreceptors with small receptive fields and rapid adaptation rates, specialized for detecting light touch and low-frequency vibration.

Merkel's Disks

Tactile mechanoreceptors with small receptive fields and slow adaptation rates, specialized for detecting fine details and steady pressure.

Pacinian Corpuscles

Tactile mechanoreceptors with large receptive fields and rapid adaptation rates, specialized for detecting high-frequency vibration.

Ruffini's Endings

Tactile mechanoreceptors with large receptive fields and slow adaptation rates, specialized for detecting skin stretch.

Nociception vs Pain

Nociception is the sensory neural encoding of noxious stimuli; pain is the subjective perceptual experience constructed by the brain.

\text{A}\delta Fibers

Small, loosely myelinated nerve fibers that conduct fast, sharp, localized nociceptive signals.

\text{C} Fibers

Unmyelinated nerve fibers that conduct slow, dull, aching nociceptive signals.

Tactile vs Nociceptive Spinal Pathways

Tactile fibers ascend ipsilaterally in dorsal columns and decussate in the medulla; nociceptive fibers synapse in the dorsal horn and decussate immediately in the spinal cord.

Referred Pain

Perception of visceral pain on the skin surface, caused by visceral and somatic nociceptive inputs converging onto shared second-order spinal neurons.

Middle Ear Function

Mechanical transformer system using ossicles to amplify sound pressure waves from air into fluid pressure waves inside the cochlea.

Basilar Membrane Tonotopic Map

Frequency mapping along the cochlea where the narrow, stiff base responds to high frequencies and the wide, floppy apex responds to low frequencies.

Inner Hair Cells

Primary mechanoreceptive sensory cells of the auditory system located within the Organ of Corti that release neurotransmitter upon stereocilia deflection.

Auditory Hair Cell Depolarization Mechanism

Stereocilia deflection pulls tip links open -> $\text{K}^+$ enters from high-$\text{K}^+$ endolymph -> cell depolarizes -> voltage-gated $\text{Ca}^{2+}$ channels open -> transmitter release.

Superior Olive

Brainstem nucleus where auditory information from both ears first converges to calculate interaural time and intensity differences for sound localization.

Pigmented Epithelium

Retinal layer located behind photoreceptors that absorbs stray light, prevents reflections, and maintains photopigment/photoreceptor health.

Rods

Highly sensitive photoreceptors located in the peripheral retina with high synaptic convergence and large receptive fields, specialized for low-light non-color vision.

Cones

Photoreceptors concentrated in the fovea with low convergence, high acuity, and three distinct photopigments enabling color vision under brighter conditions.

Phototransduction Cascade (Light)

Light absorption by rhodopsin -> transducin activation -> PDE activation -> $\text{cGMP}$ converted to $\text{GMP}$ -> closure of $\text{cGMP}$-gated $\text{Na}^+$ channels -> hyperpolarization -> decreased glutamate release.

Photoreceptor State in Darkness

High intracellular $\text{cGMP}$ levels keep $\text{Na}^+$ channels open -> continuous dark current -> membrane depolarization -> high tonic glutamate release.

OFF Bipolar Cells

Retinal interneurons expressing AMPA receptors that depolarize in response to darkness (high glutamate release from photoreceptors).

ON Bipolar Cells

Retinal interneurons expressing metabotropic Group III mGluRs that depolarize in response to light (decreased glutamate release from photoreceptors).

Labeled Line Coding (Taste)

Sensory coding scheme where specific, dedicated receptor cells and primary afferents directly signal individual taste qualities (salty, sour, sweet, bitter, umami).

Combinatorial Coding (Olfaction)

Sensory coding scheme where distinct odor identities are encoded by unique activity patterns across combinations of olfactory receptor types and glomeruli.

Olfactory Sensory Neuron Depolarization Mechanism

Odorant binding opens $\text{Ca}^{2+}$ channels -> $\text{Ca}^{2+}$ opens $\text{Ca}^{2+}$-gated $\text{Cl}^-$ channels -> $\text{Cl}^-$ exits due to high intracellular $[\text{Cl}^-]$ -> inward current -> depolarization.

Motor Unit

A single $\alpha$-motor neuron together with all individual skeletal muscle fibers it innervates.

Motor Pool

The complete group of all $\alpha$-motor neurons that innervate a single anatomical muscle.

Innervation Number

The number of muscle fibers controlled by a single $\alpha$-motor neuron; low numbers allow fine motor control, whereas high numbers generate coarse force.

Excitation-Contraction Coupling

Sequence where muscle action potentials propagate down T-tubules to trigger ryanodine receptor activation and $\text{Ca}^{2+}$ release from the sarcoplasmic reticulum into the cytoplasm.

Role of ATP in Muscle Contraction

ATP binding is strictly required to dissociate actin and myosin filaments from one another, permitting cross-bridge resetting for repeated contraction cycles.

Fast vs Slow Motor Units

Fast units have large $\alpha$-motor neurons and white fatigue-prone muscle fibers for burst power; slow units have small $\alpha$-motor neurons and red fatigue-resistant muscle fibers for sustained posture.

Muscle Spindles

Intrafusal proprioceptors arranged in parallel with extrafusal muscle fibers that detect changes in muscle length and rate of stretch.

\gamma-Motor Neurons

Motor neurons that innervate intrafusal muscle fibers to maintain spindle tension and sensitivity during extrafusal muscle contraction.

Myotatic Reflex

Monosynaptic reflex where sudden muscle stretch activates muscle spindle afferents to excite $\alpha$-motor neurons, causing contraction of the stretched muscle.