Cellular and Nervous System Fundamentals: Study Notes for Anatomy & Physiology

Cellular Structure and Function

Genetic Information

Genetic information is the blueprint for protein synthesis and cellular function.

• Gene: A segment of DNA that codes for a specific protein.

• Genome: The complete set of genes in an organism (humans have ~23,000 genes).

• Genetic Code: The method used to interpret a sequence of nucleotide bases into amino acids for protein synthesis.

Cell Division

When and Why Cells Divide

Cells divide once they are large enough to split cytoplasm into two daughter cells. Growth factors signal when to divide.

• Inhibition of Division: Occurs when there are no growth factors, nutrients are low, or space is limited.

Chromatin and Chromosomes

Definitions and Structure

• Chromatin: DNA coiled around histone proteins (semi-condensed form). The base unit is a nucleosome.

• Chromosomes: Form after DNA replication; made of two sister chromatids joined at a centromere. Spindle fibers attach and pull chromatids apart during cell division.

Cell Cycle

Phases and Processes

• Interphase: G1 (growth), S (DNA synthesis), G2 (prep for division).

• Mitosis: Prophase → Metaphase → Anaphase → Telophase.

• Cytokinesis: Division of cytoplasm.

• High mitotic rate: Cells that constantly replicate (skin, GI tract).

• Low mitotic rate: Long-lived cells (neurons, muscle cells).

DNA Replication

Mechanism

• Semi-conservative: Each new DNA molecule has one old and one new strand.

• Helicase: Unzips strands.

• DNA Polymerase: Adds complementary nucleotides.

Mitosis Phases

Stages of Mitosis

• Prophase: Chromatin condenses into visible chromosomes.

• Metaphase: Chromosomes line up along the middle (metaphase plate).

• Anaphase: Sister chromatids pulled apart to opposite poles.

• Telophase: Chromosomes uncoil back into chromatin; cleavage furrow forms.

• Cytokinesis: Cytoplasm divides.

Cancer

Definition and Mechanisms

• Definition: Uncontrolled division of abnormal cells.

• Gene Involved: TP53 mutation prevents production of p53, which normally activates p21 to stop abnormal replication.

• Steps: Abnormal cell divides → Primary tumor forms → Metastasis = Secondary tumor forms.

• Benign: Slow-growing, encapsulated.

• Malignant: Fast-growing, unencapsulated, spreads (metastatic).

Cell Differentiation

Specialization of Cells

• All cells start as stem cells and specialize by turning genes on/off to become specific types (skin, blood, etc.).

Plasma Membrane

Structure and Function

• Structure: Semi-permeable phospholipid bilayer with proteins, enzymes, and receptors.

• Selectively Permeable: Controls what enters and leaves the cell.

• Protein Types: Pores (always open), Gates (open/close), Pumps (require energy).

Transport Mechanisms

Types of Transport

• Passive Transport: Diffusion (simple/facilitated) and osmosis.

• Active Transport: Requires ATP (primary and secondary).

• Carrier-Mediated: Specific binding and transport.

• Transport Maximum: Max rate a carrier system can work.

• Vesicular Transport: Endocytosis (phago-, pino-) and Exocytosis.

Nervous System Overview

Divisions and Functions

• Divisions: CNS (brain, spinal cord) and PNS (everything else).

• Effector Divisions: Somatic (voluntary) and Autonomic (involuntary).

• Autonomic: Sympathetic ("fight or flight") and Parasympathetic ("rest and digest").

• Function: Communication and coordination via electrochemical signals.

• Endocrine System: Works with hormones instead of electrical signals.

Neurons

Structure and Types

• Structure: Soma (cell body), Dendrites (receive), Axon (send), Axon Hillock (trigger zone), Synaptic Terminals (neurotransmitters).

• Myelin: Insulating sheath (80% lipid) that speeds conduction by saltatory propagation.

Membrane Potentials

Electrical Properties of Membranes

• Transmembrane Potential: Charge difference across the membrane.

• Resting Potential: About -70 mV, maintained by Na+/K+ pump.

Electrical Activity

Action Potentials and Channels

• Gated Channels: Chemically, voltage, and mechanically gated.

• Graded Potentials: Local, variable strength; can be excitatory or inhibitory.

• Action Potentials: All-or-none signals that travel along the axon.

• Refractory Period: Absolute (no AP possible) and Relative (AP harder).

• Propagation: Unmyelinated (continuous) vs. Myelinated (saltatory).

Synapses

Structure and Function

• Structure: Presynaptic → Cleft → Postsynaptic.

• Cholinergic Synapse: Uses acetylcholine (ACh) for neuromuscular signaling.

• Acetylcholinesterase: Breaks down ACh to stop signal.

• Synaptic Delay: ~0.5 ms between action potential and response.

• Synaptic Fatigue: Neurotransmitter supply temporarily depleted.

• Norepinephrine (NE): "Noradrenaline," increases alertness and blood pressure.