Resting Membrane Potential

Definition and Maintenance

The resting membrane potential is the electrical potential difference across the plasma membrane of a cell at rest. It is essential for the function of excitable cells such as neurons and muscle fibers.

• Ions Involved: Primarily sodium (Na+), potassium (K+), chloride (Cl-), and negatively charged proteins.

• Maintenance: Maintained by the sodium-potassium pump (Na+/K+ ATPase), which actively transports 3 Na+ ions out and 2 K+ ions into the cell, and by the selective permeability of the membrane to K+.

• Typical Value: Approximately -70 mV in neurons.

Example: In neurons, the resting membrane potential is crucial for the generation and propagation of action potentials.

Cell Biology

Functions of Organelles

Cell organelles perform specialized functions necessary for cell survival and activity.

• Mitochondria: Site of ATP (energy) production via cellular respiration.

• Ribosomes: Sites of protein synthesis.

• Endoplasmic Reticulum (ER): Rough ER synthesizes proteins; smooth ER synthesizes lipids and detoxifies chemicals.

• Golgi Apparatus: Modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.

• Lysosomes contain digestive enzymes that break down waste.

Cell Growth and Reproduction

• DNA Replication: Occurs during the S phase of the cell cycle, prior to cell division.

• Mitosis vs. Cytokinesis:

  • Mitosis: Division of the nucleus and its contents.

  • Cytokinesis: Division of the cytoplasm, resulting in two daughter cells.

Protein Synthesis

• Transcription: The process by which DNA is copied into messenger RNA (mRNA) in the nucleus.

• Translation: The process by which mRNA is decoded by ribosomes to synthesize proteins in the cytoplasm.

• Products: Transcription produces mRNA; translation produces polypeptide chains (proteins).

• Types of RNA: mRNA (messenger), tRNA (transfer), rRNA (ribosomal). Each plays a specific role in protein synthesis.

Example: Hemoglobin synthesis in red blood cells involves transcription of the hemoglobin gene and translation of the mRNA into the hemoglobin protein.

Histology

Definition of Tissue

Tissue is a group of similar cells that perform a common function.

Epithelium

• General Functions/Characteristics: Covers body surfaces, lines cavities, forms glands; functions include protection, absorption, secretion, and sensation.

• Classification: Based on cell shape (squamous, cuboidal, columnar) and number of layers (simple, stratified).

• Types of Glands: Exocrine (secrete into ducts) and endocrine (secrete into blood).

Connective Tissue

• General Functions/Characteristics: Supports, binds, and protects other tissues; contains cells, fibers, and ground substance.

• Classification: Loose (areolar, adipose), dense (regular, irregular), cartilage, bone, blood.

Nervous Tissue

• General Functions/Characteristics: Conducts electrical impulses, processes information.

• Types of Cells: Neurons (transmit impulses) and neuroglia (support neurons).

Membranes

• Types: Cutaneous (skin), mucous (lines cavities open to exterior), serous (lines closed cavities).

• Distinguishing Features: Cutaneous is dry and protective; mucous is moist and involved in absorption/secretion; serous produces lubricating fluid.

Tissue Repair

• Process: Involves inflammation, proliferation, and remodeling phases.

• Different Tissue Types: Epithelial tissues repair rapidly; connective tissues vary; nervous and muscle tissues repair poorly.

Integumentary System

Epidermis

• Cell Types: Keratinocytes (produce keratin), melanocytes (produce melanin), Langerhans cells (immune), Merkel cells (sensory).

• Layers (from superficial to deep):

  • Stratum corneum

  • Stratum lucidum (only in thick skin)

  • Stratum granulosum

  • Stratum spinosum

  • Stratum basale

Dermis

• General Characteristics/Function: Provides strength, elasticity, and houses blood vessels, nerves, and appendages.

• Layers:

  • Papillary layer (superficial, areolar connective tissue)

  • Reticular layer (deep, dense irregular connective tissue)

Pigments Involved in Skin Color

Hair

• Characteristics/Functions: Protection, sensation, reduces heat loss.

Nails

• Characteristics/Functions: Protect distal phalanges, aid in grasping objects.

Glands

• Types: Sebaceous (oil), sudoriferous (sweat), ceruminous (earwax).

• Functions: Lubrication, thermoregulation, protection.

Skin Cancer

• General Terms: Uncontrolled growth of skin cells.

• Types:

  • Basal cell carcinoma

  • Squamous cell carcinoma

  • Melanoma

Burns