Cell Biology and Integumentary System Lecture Notes
Basic Features of a Cell
Cells: The fundamental unit of life.
Common Features:
Plasma membrane
Cytoplasm
DNA/genetic material
Ribosomes
Types of Cells:
Prokaryotic Cells:
Characteristics: Lack a nucleus and membrane-bound organelles.
Eukaryotic Cells:
Characteristics: Possess a nucleus and organelles.
General Structure & Function of the Plasma Membrane
Structure:
Composed of a phospholipid bilayer.
Embedded with proteins, cholesterol, and carbohydrates.
Function:
Serves as a selectively permeable barrier regulating the entry and exit of substances.
Provides protection and structural support, and facilitates communication between cells.
Types of Plasma Membrane Proteins
Integral Proteins:
Span the bilayer and are often involved in transport or signaling as receptors.
Peripheral Proteins:
Attached to the inner or outer surfaces of the membrane, often engaged in signaling or providing structural support.
Major Roles of Membrane Proteins
Transport:
Includes channels, carriers, and pumps that facilitate movement across the membrane.
Communication:
Act as receptors involved in signal transduction pathways.
Structural Support:
Contribute to the overall shape and integrity of cells, and help anchor different cells together.
Passive Transport
Definition:
Movement of substances across a membrane down their concentration gradient without the need for energy.
Types:
Simple Diffusion:
Molecules move directly through the lipid bilayer (e.g., O₂, CO₂).
Facilitated Diffusion:
Requires the assistance of proteins (e.g., ions, glucose).
Factors Influencing Diffusion
Steepness of Concentration Gradient: Greater gradients enhance diffusion rates.
Temperature: Higher temperatures increase molecular movement, accelerating diffusion.
Size of Molecule: Smaller molecules diffuse faster than larger ones.
Membrane Permeability:
The ease with which a substance can cross the membrane.
Surface Area of Membrane: Larger surfaces permit more molecules to pass through at once.
Osmosis
Definition:
The movement of water across a selectively permeable membrane, driven by differences in solute concentration, moving from low to high solute concentration (toward the hypertonic side).
Active Transport
Definition:
Movement of substances across a membrane against their concentration gradient, requiring energy (ATP or electrochemical gradients).
Types:
Primary Active Transport:
Directly utilizes ATP (e.g., sodium-potassium pump).
Secondary Active Transport:
Utilizes the energy stored in ion gradients created by primary active transport to move other molecules.
Calcium and Sodium/Potassium Pumps
Na⁺/K⁺ Pump:
Transports 3 Na⁺ ions out and 2 K⁺ ions into the cell per ATP molecule.
Essential for maintaining the electrochemical gradient crucial for nerve and muscle function.
Ca²⁺ Pump:
Moves calcium ions out of the cell or into storage organelles, keeping cytoplasmic Ca²⁺ levels low to regulate cellular signaling.
Symport vs. Antiport (Secondary Transport)
Symport:
Mechanism where two substances move in the same direction across the membrane (e.g., glucose + Na⁺).
Antiport:
Mechanism where two substances move in opposite directions (e.g., Na⁺ in, Ca²⁺ out).
Vesicular Transport
Definition:
Process of moving large molecules in membrane-bound vesicles.
Types:
Exocytosis:
Vesicles fuse with the plasma membrane to release substances outside of the cell (e.g., neurotransmitters, hormones).
Endocytosis:
The plasma membrane engulfs materials to bring them into the cell.
Types include:
Phagocytosis: Uptake of solid particles.
Pinocytosis: Uptake of liquids.
Integumentary System
Four Types of Tissues in the Body:
Epithelial Tissue: Covers surfaces, lines organs, forms glands; functions include protection, secretion, and absorption.
Connective Tissue: Supports and binds other tissues (includes bones, cartilage, blood, fat, and tendons).
Muscle Tissue: Contracts to facilitate movement (includes skeletal, cardiac, and smooth muscles).
Nervous Tissue: Carries electrical signals, consisting of neurons and supporting cells.
Structures Associated with the Integument:
Skin (composed of the epidermis and dermis), hypodermis (subcutaneous layer), hair, nails, and various glands (sweat glands, sebaceous glands, ceruminous glands, mammary glands).
Functions of the Integument:
Protection: Acts as a physical barrier, provides UV protection, and helps prevent water loss.
Sensation: Senses touch, pressure, temperature, and pain.
Temperature Regulation: Regulates body temperature through sweat production and blood flow.
Metabolic Functions: Synthesizes vitamin D.
Excretion/Secretion: Releases substances such as sweat and sebum.
Immune Defense: Contains immune cells that combat pathogens.
Layers of the Integument and Tissues
Epidermis: Composed of stratified squamous epithelium.
Dermis: Consists of connective tissues (areolar connective tissue and dense irregular connective tissue).
Hypodermis: Contains adipose tissue and areolar connective tissue.
Cells in the Epidermis
Keratinocytes: The primary cells that produce keratin for skin protection and waterproofing.
Melanocytes: Cells responsible for the production of melanin, which contributes to skin pigmentation.
Langerhans/Dendritic Cells: Involved in immune defense within the skin.
Merkel/Tactile Cells: Act as touch receptors in the skin.
Keratinocyte Maturation
Originates in the stratum basale of the epidermis, migrates upwards, fills with keratin, flattens, undergoes programmed cell death (apoptosis), and ultimately becomes part of the stratum corneum (the outermost layer).
Functions of Keratin & Melanin
Keratin: A tough protein that provides protection and waterproofing to the skin.
Melanin: A pigment that absorbs UV radiation and protects the DNA in skin cells.
Types of Melanin:
Eumelanin: Brown/black pigment.
Pheomelanin: Red/yellow pigment.
Dermis & Hypodermis
Dermis: Comprised of dense irregular connective tissue and areolar connective tissue, providing strength and elasticity. Contains blood vessels, nerve endings, glands, and hair follicles.
Hypodermis: Primarily made of fat and areolar connective tissue, serving functions such as insulation, cushioning, energy storage, and anchoring the skin.
Markings of the Skin
Friction Ridges: Create fingerprints that enhance grip.
Flexure Lines: Folds formed at joints due to skin's mobility.
Striae: Also known as stretch marks, resulting from rapid skin expansion or contraction.
Wrinkles: Caused by aging, UV exposure, and loss of collagen.
Differences in Skin Color
Skin color is primarily influenced by the amount and type of melanin produced, the distribution of melanosomes, and the exposure to UV radiation. Factors such as blood flow and carotene levels also affect skin tone.
Epidermal Derivatives and Their Cells
Hair: Composed of keratinocytes.
Nails: Formed primarily from keratinocytes (specifically hard keratin). Also included are sebaceous and sweat glands, which develop from epithelial cells.
Hair Functions & Types
Functions:
Provides protection (against UV light and dust), aids in heat retention, serves sensory roles, and plays a role in expression.
Types:
Lanugo: Fine hair present in fetuses.
Vellus: Soft, fine body hair.
Terminal: Coarse, pigmented hair (found on the scalp, eyebrows, and beards).
Regeneration vs. Fibrosis
Regeneration: The process where damaged tissue is replaced with the same tissue type, restoring full function.
Fibrosis: Occurs when damaged tissue is replaced with scar tissue (primarily collagen), resulting in incomplete restoration of function.
Wound Healing Process
Hemostasis: Clotting mechanisms activate to stop bleeding.
Inflammation: Immune cells infiltrate to clean the wound.
Proliferation: Formation of new tissue and blood vessels occurs.
Remodeling: The tissue strengthens, and a scar may form.
Skeletal Muscle Functions
Movement: Facilitates various body movements (e.g., walking, running, facial expressions).
Posture and Stability: Continuous muscle contractions maintain body posture and stabilize joints.
Support of Soft Tissues: Protects and supports organs, especially in the abdominal region.
Guarding Body Openings: Controls the passageways of the digestive and urinary tracts via sphincter muscles.
Maintaining Body Temperature: Generates heat as a by-product of muscle contraction (e.g., shivering).
Nutrient Reserve: Muscle proteins can be catabolized into amino acids during extended periods of starvation.
Anatomy of Skeletal Muscle
Gross Anatomy:
Hierarchical structure from the whole muscle → fascicles → individual muscle fibers (cells) → myofibrils → myofilaments.
Each muscle is encapsulated in epimysium; fascicles are wrapped in perimysium; individual fibers (myofibrils) are wrapped in endomysium.
Microscopic Anatomy:
Muscle Fiber: A long, multinucleated cell containing myofibrils which are the contractile units of the muscle.
Key organelles include the sarcolemma (plasma membrane of the muscle cell), sarcoplasm (cytoplasm), sarcoplasmic reticulum (SR, involved in calcium storage and release), and T-tubules (involved in action potential propagation).
Function of Connective Tissue, Blood Vessels, and Nerves in Skeletal Muscle
Connective Tissue: Provides structural integrity, transmits the force of contraction, and prevents damage from overstretching.
Blood Vessels: Deliver oxygen and nutrients while removing waste products from muscle tissue.
Nerves: Stimulate contractions, coordinate muscle activity, and regulate force generation.
Organelles and Structures in Skeletal Muscle
Multiple Nuclei: Necessary for high rates of protein synthesis.
Mitochondria: Organelles responsible for ATP production through aerobic respiration.
Sarcoplasmic Reticulum (SR): Stores calcium ions necessary for muscle contraction.
T-tubules: Extension of the sarcolemma that facilitate the conduction of electrical impulses deep into the fiber.
Myofibrils: Composed of myofilaments (actin and myosin) which are essential for muscle contraction.
Glycogen & Myoglobin: Serve as energy reserves and oxygen storage, respectively.
Excitable Cells & Resting Membrane Potential
Excitable Cell: Any cell (like neurons or muscle fibers) capable of generating an electrical impulse.
Resting Membrane Potential (RMP):
The electrical charge difference across the membrane, typically around -70 mV in neurons and -90 mV in muscle cells.
Maintained primarily by Na⁺/K⁺ pumps and selective ion permeability, resulting in a negative charge inside relative to the outside.
Pathway of Force Production
A motor neuron stimulates the muscle fiber at the neuromuscular junction.
Action potential spreads across the sarcolemma and down the T-tubules.
Calcium ions are released from the sarcoplasmic reticulum and bind to troponin.
Troponin shifts tropomyosin, exposing binding sites on actin.
Myosin heads bind actin, initiating the cross-bridge cycling.
Repeated cycles result in sarcomere shortening and production of force.
Motor Units
Definition: Each motor unit consists of a single motor neuron and all the muscle fibers it controls.
Small Motor Units: Contain a few fibers and allow for precise control (e.g., in eye muscles or fingers).
Large Motor Units: Comprise many fibers, producing stronger but less precise force (e.g., in quadriceps).
Neuromuscular Junction (NMJ), Sarcolemma, T-Tubules, and SR
NMJ: The interface where a motor neuron communicates with a muscle fiber through the release of acetylcholine (ACh).
Sarcolemma: The membrane surrounding a muscle cell, responsible for generating action potentials.
T-Tubules: Invaginations of sarcolemma that propagate electrical signals into the muscle fiber.
Sarcoplasmic Reticulum (SR): Organelle responsible for the storage and release of calcium ions during contraction and relaxation phases.
Proteins in a Sarcomere
Thin Filaments:
Actin: Provides binding sites for myosin.
Tropomyosin: Blocks binding sites on actin at rest.
Troponin: Binds calcium ions, initiating muscle contraction.
Thick Filaments:
Myosin: Forms cross-bridges with actin during contraction.
Structural Proteins:
Titin: Provides elasticity to the sarcomere.
Nebulin: Stabilizes actin filaments.
Sarcomere: The functional unit from Z-disc to Z-disc, fundamental to muscle contraction.
Excitation-Contraction Coupling
Excitation:
A nerve impulse leads to the release of ACh at the NMJ, binding to receptors on the sarcolemma, thus generating an action potential.
Signal Transmission:
The action potential travels along the sarcolemma and down the T-tubules.
Calcium Release:
Voltage sensors trigger the SR to release Ca²⁺ into the cytoplasm.
Contraction:
Ca²⁺ binds to troponin, causing a shift of tropomyosin and allowing myosin to bind to actin.
ATP hydrolysis powers the myosin pulls actin, leading to sarcomere shortening.
Relaxation:
ACh is broken down, Ca²⁺ is pumped back into the SR, and tropomyosin re-blocks the binding sites.
Sliding Filament Theory
Steps:
Nerve Impulse: A motor neuron releases ACh at NMJ.
Sarcolemma Depolarization: ACh binds to receptors, resulting in the action potential spreading across the sarcolemma and down T-tubules.
Calcium Release: The action potential triggers the SR to release calcium.
Troponin Activation: Ca²⁺ binds to troponin, which results in the shifting of tropomyosin, exposing actin binding sites.
Cross-Bridge Cycle:
Myosin heads bind to actin, undergo a power stroke, detach with ATP binding, and reset for another cycle, leading to actin sliding over myosin, resulting in sarcomere shortening.
Relaxation: Breakdown of ACh and reuptake of Ca²⁺ into the SR occurs, with tropomyosin AGAIN blocking binding sites.
Key Proteins & Molecules
Important components in contraction include: Actin, myosin, troponin, tropomyosin, ATP, Ca²⁺, and acetylcholine.
Supplying ATP & Exercise Intensity/Duration
ATP Supply Pathways:
Phosphagen System:
Immediate ATP source (0-10 seconds of high intensity, e.g., sprinting, heavy lifting).
Anaerobic Glycolysis:
Fast, short-term energy (30-60 seconds, e.g., 400m sprint).
Aerobic Cellular Respiration:
Provides ATP through the use of oxygen and substrates for longer duration activities (minutes to hours, e.g., distance running).
Oxygen Debt & EPOC (Excess Post-exercise Oxygen Consumption)
Rationale for Heavy Breathing Post-Exercise:
Restoring homeostasis requires:
Replenishing oxygen in blood and myoglobin within muscle.
Converting lactic acid into pyruvate or glucose.
Resynthesizing ATP and creatine phosphate.
Maintaining elevated body temperature, heart rate, and breathing until full recovery is achieved.
Fiber Types in Skeletal Muscle
Slow Oxidative (Type I):
Characteristics: Red fibers with high mitochondria and myoglobin content.
Traits: Fatigue resistant, low force output.
Activities: Endurance-based (e.g., marathon running).
Fast Oxidative-Glycolytic (Type IIa):
Characteristics: Intermediate fibers.
Traits: Moderate fatigue resistance and moderate force output.
Activities: Suited for activities like middle-distance running and cycling.
Fast Glycolytic (Type IIb/IIx):
Characteristics: White fibers with low mitochondria and myoglobin.
Traits: Fatigues quickly but can produce high force.
Activities: Effective for short bursts of activity (e.g., sprinting, weightlifting).
Types of Muscle Contractions
Isotonic Contractions:
Muscle length changes while maintaining constant tension.
Concentric: Muscle shortens (e.g. lifting a weight).
Eccentric: Muscle lengthens under tension (e.g. lowering a weight).
Isometric Contractions:
Muscle length remains constant while tension increases (e.g., holding a plank).
Delayed-Onset Muscle Soreness (DOMS)
Definition: Muscle soreness experienced 24-72 hours post-exercise.
Causes: Mainly due to microscopic tears in muscle fibers, frequently from eccentric contraction activities, followed by an inflammation and repair process that leads to pain and stiffness.
Muscle Fatigue
Definition: The inability to maintain force of contraction over time.
Causes:
ATP Depletion: Insufficient energy for continued contraction.
Ion Imbalances: Disruption in concentrations of Na⁺, K⁺, and Ca²⁺.
Lactic Acid Accumulation: Leads to an acidic environment and drops pH, affecting contractile ability.
Central Fatigue: Nervous system signals diminish, reducing stimulation of muscle fibers.
Oxygen Depletion: Consequence of prolonged aerobic activity without adequate oxygen supply.
Nervous System
Homeostasis: The capacity of the body to maintain a stable internal environment in the face of external changes.
Components of a Homeostatic System:
Receptor: Detects changes or stimuli.
Control Center: Processes information and determines the response (typically the brain or spinal cord).
Effector: Executes the response (muscles or glands).
Forms of Energy
Kinetic Energy: Energy resulting from motion (muscle contraction and nerve impulses).
Potential Energy: Stored energy, as found in chemical bonds or concentration gradients.
General Functions of the Nervous System
Sensory (Input): Detects internal and external stimuli.
Integrative (Processing): Processes information and formulates responses.
Motor (Output): Activates effectors to produce reactions (muscle movements or glandular secretions).
Structural Organization of the Nervous System
Central Nervous System (CNS): Comprises the brain and spinal cord.
Peripheral Nervous System (PNS): Comprises nerves and ganglia, further divided into:
Somatic Nervous System: Voluntary control over skeletal muscles.
Autonomic Nervous System: Involuntary control, further split into sympathetic (fight-or-flight) and parasympathetic (rest-and-digest) systems.
Tissues Associated with a Nerve
Epineurium: Tough, outer layer made of dense connective tissue surrounding the entire nerve.
Perineurium: Layer that encloses fascicles (bundles of axons).
Endoneurium: Surrounds each individual axon and its myelin sheath.
Three Basic Features of Neurons
Cell Body (Soma): Contains the nucleus and organelles.
Dendrites: Extend from the cell body to receive signals from other neurons.
Axon: Conducts signals away from the cell body to other cells.
Structural Categories of Neurons
Unipolar Neurons: Have a single process; typically sensory neurons.
Bipolar Neurons: Feature one dendrite and one axon; are relatively rare (e.g. in the retina and olfactory system).
Multipolar Neurons: Possess many dendrites and one axon; are the most common type (e.g., motor neurons).
Functional Categories of Neurons
Sensory (Afferent) Neurons: Transmit signals from sensory receptors to the CNS.
Motor (Efferent) Neurons: Relay signals from the CNS to effectors (muscles or glands).
Interneurons: Connect neurons within the CNS; responsible for processing and integration.
Pumps & Channels on Neuron Membrane
Na⁺/K⁺ Pumps: Maintain resting membrane potential by exchanging Na⁺ and K⁺.
Leak Channels: Allow constant passive ion flow across the membrane.
Voltage-Gated Channels: Open/close in response to changes in membrane potential (e.g., Na⁺, K⁺, Ca²⁺ channels).
Ligand-Gated Channels: Open upon binding of neurotransmitters.
Segment Functions:
Receptive Segment: Dendrites and soma, involving ligand-gated channels resulting in graded potentials.
Initial Segment: Axon hillock where voltage-gated channels generate action potential.
Conductive Segment: Axon propagation of action potential.
Transmissive Segment: Involves the axon terminals and trigger of neurotransmitter release through calcium channels.
Excitation vs. Inhibition of Neurons
Excitatory Neurotransmitters: Promote depolarization by opening Na⁺ channels, making it easier for neurons to fire action potentials.
Inhibitory Neurotransmitters: Promote hyperpolarization by opening Cl⁻ or K⁺ channels, decreasing the likelihood of an action potential firing.
Physiological Events at Neuron Segments
At the Receptive Segment: Graded potentials are formed.
At the Initial Segment: Summation occurs at the axon hillock; if threshold is reached, an action potential is generated.
During the Conductive Segment: The action potential propagates down the axon.
At the Transmissive Segment: Neurotransmitters are released into the synaptic cleft in response to action potentials.
Action Potential (AP)
Resting Potential: Approximately -70 mV with Na⁺/K⁺ pump actively maintaining ion gradients.
Depolarization Phase: Opening of voltage-gated Na⁺ channels causes rapid influx of Na⁺ ions, reducing the membrane's negative charge.
Repolarization Phase: Voltage-gated K⁺ channels open, allowing K⁺ ions to leave the cell, restoring the negative charge.
Hyperpolarization Phase: Slow closure of K⁺ channels leads to a brief undershoot below resting potential.
Return to Resting Potential: Restoration of resting membrane potential through the action of Na⁺/K⁺ pumps.
Propagation of Action Potential
Unmyelinated Axons: Action potentials propagate through continuous conduction, moving step-by-step down the axon.
Myelinated Axons: Action potentials undergo saltatory conduction, jumping between the Nodes of Ranvier, which results in faster transmission.
Events at the Transmissive Segment
The action potential reaches the axon terminal.
Voltage-gated Ca²⁺ channels open, allowing Ca²⁺ to enter the cell.
Voltage increases trigger vesicles to bind with the presynaptic membrane, leading to neurotransmitter release.
Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic cell.