Physio Exam 1 Study Guide Part 1

Theme I: Cell Membrane Physiology

Plasma Membrane Structure and Function

The plasma membrane is a selectively permeable barrier that separates the intracellular environment from the extracellular space, playing a crucial role in cellular homeostasis and communication.

• Structure: Composed primarily of a phospholipid bilayer with embedded proteins, cholesterol, and carbohydrates.

• Functions: Regulates transport, facilitates cell signaling, and maintains structural integrity.

• Key Terms: Phagocytosis, Pinocytosis, Receptor-mediated endocytosis, Exocytosis

• Example: White blood cells use phagocytosis to engulf pathogens.

Intracellular and Extracellular Compartments

Cells maintain distinct internal (intracellular) and external (extracellular) environments, each with unique ionic compositions and functions.

• Intracellular compartment: Contains cytosol and organelles.

• Extracellular compartment: Includes interstitial fluid and plasma.

Transport Mechanisms Across the Membrane

Transport across the plasma membrane occurs via passive and active mechanisms, each with distinct energy requirements and specificity.

• Passive Transport: Movement down a concentration gradient without energy input (e.g., diffusion, osmosis).

• Active Transport: Movement against a concentration gradient, requiring ATP (e.g., Na+/K+ pump).

• Carrier-mediated Transport: Involves specific membrane proteins; can be passive (facilitated diffusion) or active.

• Simple Diffusion: Direct movement of small, nonpolar molecules.

• Facilitated Diffusion: Movement via channel or carrier proteins.

• Osmosis: Diffusion of water across a semipermeable membrane.

• Equation: $J = -D \frac{dC}{dx}$ (Fick's law of diffusion)

• Osmotic Pressure: $\Pi = iMRT$

• Example: Glucose transport into cells via GLUT transporters.

Osmosis and Tonicity

Osmosis is the movement of water across membranes, influenced by solute concentration. Tonicity describes the effect of a solution on cell volume.

• Hypotonic Solution: Lower solute concentration than the cell; cell swells.

• Isotonic Solution: Equal solute concentration; no net water movement.

• Hypertonic Solution: Higher solute concentration; cell shrinks.

Homeostasis of Plasma Osmolarity

Cells regulate osmolarity to maintain optimal function and prevent lysis or shrinkage.

• Mechanisms: Ion channels, pumps, and aquaporins.

• Example: Kidney regulation of blood osmolarity.

Equilibrium Potential and Membrane Potential

Equilibrium potential is the membrane voltage at which there is no net movement of a particular ion. Membrane potential is the overall electrical potential difference across the cell membrane.

• Equation (Nernst): $E_{ion} = \frac{RT}{zF} \ln \frac{[ion]_{out}}{[ion]_{in}}$

• Resting Membrane Potential: Typically -70 mV in neurons.

• Action Potential: Rapid change in membrane potential due to ion flux.

Receptor Proteins and Signal Transduction

Receptor proteins on cell membranes bind signaling molecules, initiating cellular responses.

• Location: Found on target cells, often specific to certain ligands.

• G Protein-Coupled Receptors: Activate intracellular signaling cascades.

Action Potentials and Conduction

Action potentials are electrical signals conducted along neurons, essential for communication in the nervous system.

• Steps: Depolarization, repolarization, hyperpolarization.

• Conduction: Faster in myelinated axons due to saltatory conduction.

• Unmyelinated vs. Myelinated Axons: Myelinated axons conduct impulses more rapidly.

Theme II: Nervous System Overview and Central Nervous System

Neurons and Supporting Cells

The nervous system consists of neurons and supporting glial cells, each with specialized functions.

• Neurons: Transmit electrical impulses; classified by structure and function.

• Glial Cells: Support, protect, and nourish neurons (e.g., astrocytes, oligodendrocytes, Schwann cells).

Myelin Sheath and Blood-Brain Barrier

Myelin sheath insulates axons, increasing conduction speed. The blood-brain barrier protects the CNS from harmful substances.

• Myelin Formation: Oligodendrocytes (CNS) and Schwann cells (PNS).

• Blood-Brain Barrier: Formed by endothelial cells with tight junctions.

Synaptic Transmission and Neurotransmitters

Neurons communicate via synapses, where neurotransmitters are released to transmit signals.

• Electrical Synapses: Direct ionic current flow via gap junctions.

• Chemical Synapses: Neurotransmitter release and receptor activation.

• Excitatory vs. Inhibitory Synapses: Excitatory (e.g., glutamate), inhibitory (e.g., GABA).

• Acetylcholine: Major neurotransmitter in neuromuscular junctions.

• G Protein-Coupled Receptors: Mediate slow synaptic responses.

Action Potentials and Postsynaptic Potentials

Action potentials are generated and propagated along neurons, while postsynaptic potentials (EPSPs and IPSPs) determine neuronal response.

• EPSP (Excitatory Postsynaptic Potential): Depolarizes membrane, increasing likelihood of action potential.

• IPSP (Inhibitory Postsynaptic Potential): Hyperpolarizes membrane, decreasing likelihood of action potential.

• Summation: Multiple EPSPs/IPSPs can combine to influence action potential generation.

Neurotransmitter Types and Functions

Neurotransmitters are classified by their effects and mechanisms of action.

• Monoamines: Dopamine, norepinephrine, serotonin.

• Amino Acids: Glutamate (excitatory), GABA and glycine (inhibitory).

• Peptides: Substance P, endorphins.

Brain Regions and Structures

The brain is divided into distinct regions, each with specialized functions.

• Major Regions: Cerebrum, cerebellum, brainstem (midbrain, pons, medulla).

• Ventricles: Fluid-filled cavities within the brain.

• Thalamus and Hypothalamus: Relay and regulate sensory/motor signals and homeostasis.

Cerebral Cortex and Hemispheres

The cerebral cortex is responsible for higher-order functions, with distinct roles for the right and left hemispheres.

• Right Hemisphere: Spatial, creative tasks.

• Left Hemisphere: Language, analytical tasks.

• Limbic System: Emotion and memory processing.

Motor Pathways and Tracts

Motor pathways transmit signals from the brain to muscles, enabling movement.

• Pyramidal Tracts: Voluntary motor control.

• Extrapyramidal Tracts: Involuntary and automatic movements.

Table: Comparison of Synaptic Types

Feature	Electrical Synapse	Chemical Synapse
Speed	Very fast	Slower
Directionality	Bidirectional	Unidirectional
Mechanism	Gap junctions	Neurotransmitter release
Example	Cardiac muscle	Neuromuscular junction

Additional info: Academic context and definitions have been expanded for clarity and completeness.