Nervous System: Structure, Function, and Physiology – Study Guide Notes

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Major Divisions: The nervous system is divided into the central nervous system (CNS) and the peripheral nervous system (PNS).
Information Flow: Sensory (afferent) neurons carry information to the CNS; motor (efferent) neurons carry commands from the CNS to effectors.

Neuron Anatomy: Neurons consist of a cell body (soma), dendrites (receive signals), and an axon (transmits signals).
Ion Channels: Types include leak channels (always open), gated channels (open/close in response to stimuli), and voltage-gated channels (respond to changes in membrane potential).
Active vs. Passive Transport: Active transport (e.g., Na+/K+ ATPase) requires energy to move ions against gradients; passive transport (e.g., diffusion through channels) does not.
Resting Membrane Potential: Maintained by ion gradients and selective permeability. Typical value: -70 mV.
Electrochemical Gradient: The combined effect of concentration and electrical gradients on ion movement.
Myelin: Insulating layer around axons, produced by oligodendrocytes (CNS) and Schwann cells (PNS), increases conduction speed.

Functional Classes of Neurons: Sensory (afferent), motor (efferent), and interneurons.
Glial Cells: Supportive cells in CNS (astrocytes, oligodendrocytes, microglia, ependymal cells) and PNS (Schwann cells, satellite cells).
Membrane Potentials: Resting potential, threshold, depolarization, repolarization, hyperpolarization.
Graded vs. Action Potentials: Graded potentials are local and variable; action potentials are all-or-none and propagate along axons.
EPSP vs. IPSP: Excitatory postsynaptic potentials (EPSPs) depolarize the membrane; inhibitory postsynaptic potentials (IPSPs) hyperpolarize it.
Summation: EPSPs and IPSPs can combine (spatial and temporal summation) to influence action potential generation.
Action Potential: Rapid, transient change in membrane potential. Key phases: depolarization (Na+ influx), repolarization (K+ efflux), hyperpolarization.
Threshold: The critical level to which a membrane potential must be depolarized to initiate an action potential.
Refractory Periods: Absolute refractory period (no new AP possible), relative refractory period (AP possible with strong stimulus).
Propagation: Action potentials travel faster in myelinated (saltatory conduction) than unmyelinated axons.

Synapse Anatomy: Presynaptic terminal, synaptic cleft, postsynaptic membrane.
Types of Synapses: Axoaxonic, axodendritic, axosomatic.
Neurotransmitter Release: Triggered by Ca2+ influx; neurotransmitters bind to postsynaptic receptors.
Fates of Neurotransmitters: Reuptake, enzymatic degradation, diffusion away from synapse.
Signal Transduction: Ionotropic (direct ion channel opening) vs. metabotropic (G-protein-coupled) receptors.
Inhibitory vs. Excitatory Stimuli: Inhibitory (IPSPs, e.g., Cl- influx), excitatory (EPSPs, e.g., Na+ influx).
Summation: Temporal (same synapse, rapid succession) and spatial (multiple synapses, simultaneous).

Cholinergic Receptors: Nicotinic (ionotropic, fast) and muscarinic (metabotropic, slow).
Adrenergic Receptors: Alpha and beta subtypes, respond to norepinephrine/epinephrine.
Hydrophilic Messenger Receptors: G-protein-coupled receptors, signal via second messengers.

Sensation: Detection of stimuli by sensory receptors.
Perception: Interpretation of sensory input by the brain.
Receptor Types: Mechanoreceptors, thermoreceptors, nociceptors, photoreceptors, chemoreceptors.
Receptor Potential: Graded potential generated in response to a stimulus.
Receptor Adaptation: Decreased response to a constant stimulus (tonic vs. phasic receptors).
Receptive Fields: Area monitored by a single sensory neuron; smaller fields = greater acuity.
Stimulus Coding: Intensity coded by frequency of action potentials and number of receptors activated.

Divisions: Sympathetic ("fight or flight") and parasympathetic ("rest and digest").
Dual Innervation: Most organs receive input from both divisions, often with opposing effects.
ANS Anatomy: Two-neuron chain: preganglionic (CNS to ganglion) and postganglionic (ganglion to effector).
Neurotransmitters: Acetylcholine (ACh) and norepinephrine (NE) are primary ANS neurotransmitters.
Receptors: Cholinergic (nicotinic, muscarinic) and adrenergic (alpha, beta).
Varicosities: Swellings along autonomic axons that release neurotransmitters.
Adrenal Medulla: Modified sympathetic ganglion; releases epinephrine and norepinephrine into blood.

Structure: Single motor neuron from CNS to skeletal muscle.
Neurotransmitter: Acetylcholine acts on nicotinic receptors at neuromuscular junction.
Motor Unit: One motor neuron and all the muscle fibers it innervates.

Function: Protects brain from toxins/pathogens; maintains stable environment.
Structure: Tight junctions between endothelial cells, astrocyte end-feet.

Cerebrospinal Fluid (CSF): Cushions brain, removes waste, circulates nutrients.
Brain Regions: Frontal, parietal, occipital, temporal lobes; basal nuclei; thalamus; hypothalamus.
Functional Areas: Broca's area (speech production), Wernicke's area (language comprehension).
Learning and Memory: Short-term vs. long-term memory; procedural vs. declarative memory.

Spinal Cord Anatomy: White matter (myelinated axons), gray matter (cell bodies), ascending/descending tracts.
Reflex Arc: Sensory receptor → afferent neuron → interneuron → efferent neuron → effector.
Classes of Reflexes: Monosynaptic (e.g., stretch reflex), polysynaptic (e.g., withdrawal reflex).

Glial Cell	Location	Function
Astrocyte	CNS	Support, BBB maintenance, nutrient supply
Oligodendrocyte	CNS	Myelination of CNS axons
Microglia	CNS	Immune defense
Ependymal cell	CNS	CSF production and circulation
Schwann cell	PNS	Myelination of PNS axons
Satellite cell	PNS	Support neuron cell bodies in ganglia

Some details, such as the specific mechanisms of neurotransmitter action and the molecular structure of ion channels, can be further explored in advanced neurophysiology texts.
For exam preparation, focus on understanding the flow of information, the role of different cell types, and the mechanisms underlying action potentials and synaptic transmission.