Neuroscience: Key Concepts in Neurons, Synapses, and CNS

Neuron

Specialized cell that conducts electrical and chemical signals

Action Potential

All-or-none electrical signal that propagates along an axon

Graded Potential

Local change in membrane potential that varies in magnitude

Postsynaptic Potential (PSP)

Voltage change in the dendrite or cell body of a postsynaptic neuron

EPSP (Excitatory Postsynaptic Potential)

Depolarizing graded potential that moves membrane potential toward threshold

IPSP (Inhibitory Postsynaptic Potential)

Hyperpolarizing graded potential that moves membrane potential away from threshold

Depolarization

Membrane potential becomes less negative

Hyperpolarization

Membrane potential becomes more negative

Threshold

Membrane potential (-60 mV) required at the axon hillock to trigger an action potential

Axon Hillock

Initial segment of the axon where action potentials are generated

Temporal Summation

Summation from rapid repeated stimulation of one synapse

Spatial Summation

Summation from simultaneous input from multiple synapses

Frequency Coding

Information encoded by the rate of action potential firing

Central Nervous System (CNS)

Brain and spinal cord

Peripheral Nervous System (PNS)

All neural tissue outside the CNS

Enteric Nervous System (ENS)

Neural network controlling the digestive tract

Sensory (Afferent) Division

Carries information from receptors to the CNS

Motor (Efferent) Division

Carries commands from the CNS to effectors

Somatic Nervous System

Controls voluntary skeletal muscle movement

Autonomic Nervous System (ANS)

Controls involuntary visceral functions

Sympathetic Division

ANS division that prepares the body for stress ("fight or flight")

Parasympathetic Division

ANS division that conserves energy ("rest and digest")

Dual Innervation

Control of an organ by both ANS divisions

Chain Ganglia

Sympathetic ganglia arranged alongside the spinal cord

Collateral Ganglia

Sympathetic ganglia located near target organs

Terminal (Intramural) Ganglia

Parasympathetic ganglia located in or near target organs

Vagus Nerve (CN X)

Parasympathetic cranial nerve innervating most thoracic and abdominal organs

Adrenal Medulla

Releases epinephrine into the bloodstream during sympathetic activation

Epinephrine (Adrenaline)

Hormone that produces widespread sympathetic effects

Homeostasis

Maintenance of internal balance through shifting ANS activity

SA Node

Pacemaker cells that set intrinsic heart rate (80-100 BPM)

Sympathetic Effects

Increased heart rate, bronchodilation, reduced digestion

Parasympathetic Effects

Decreased heart rate, bronchoconstriction, increased digestion

Neuroglia

Supporting cells of the nervous system

Astrocytes

CNS glial cells that maintain the BBB and regulate the neural environment

Oligodendrocytes

CNS glial cells that myelinate axons

Schwann Cells

PNS glial cells that myelinate axons

Microglia

CNS immune cells that protect against pathogens

Satellite Cells

PNS glial cells that surround neuron cell bodies

Ependymal Cells

Glial cells that line ventricles and circulate CSF

Cerebrospinal Fluid (CSF)

Fluid that cushions, protects, and supports the CNS

Choroid Plexus

Structure that produces CSF in the ventricles

Ventricles

Fluid-filled cavities in the brain

Subarachnoid Space

Area where CSF circulates around the brain and spinal cord

Arachnoid Villi

Structures that reabsorb CSF into venous blood

CSF Buoyancy

Reduces effective brain weight by ~97%

CSF Circulation

Lateral ventricles → 3rd ventricle → 4th ventricle → subarachnoid space → blood

Blood-Brain Barrier (BBB)

Selective barrier that restricts substances from entering the CNS

Tight Junctions

Seals between capillary endothelial cells in the CNS

Astrocyte Foot Processes

Structures that help maintain the BBB

BBB-Permeable Substances

Lipid-soluble molecules (O₂, CO₂, alcohol)

Transported Across BBB

Glucose, amino acids, L-dopa

Excluded from BBB

Proteins, metabolic wastes, K⁺

Regions Without BBB

Hypothalamus and vomiting center

Gray Matter

Regions containing neuron cell bodies and dendrites

White Matter

Regions containing myelinated axons

Wallerian Degeneration

Axon degeneration process following injury in the PNS

PNS Regeneration

Possible due to Schwann cells

CNS Regeneration

Limited due to inhibitory environment