Human Muscular System

Muscle Structure and Function

The human muscular system enables movement, posture, and heat production. Muscles are composed of muscle fibers, which contain myofibrils made up of repeating units called sarcomeres.

• Sarcomere: The basic contractile unit of muscle fiber, defined by the area between two Z-lines. It contains actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Actin filaments serve as tracks for myosin heads to pull, while myosin filaments have heads that bind to actin and use ATP to generate force.

• Sliding Filament Mechanism: Muscle contraction occurs when myosin heads bind to actin, pulling the filaments past each other, shortening the sarcomere.

• Major Muscle Groups: Include biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and gluteals.

• Muscles and Body Cavities: The diaphragm separates the thoracic and abdominal cavities and is essential for respiration.

Muscle Contraction Mechanism

• Action Potential: An electrical signal generated in a motor neuron that triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine) at the neuromuscular junction.

  2. Muscle cell membrane depolarizes, generating an action potential.

  3. Action potential travels along the sarcolemma and into T-tubules.

  4. Calcium ions are released from the sarcoplasmic reticulum.

  5. Calcium binds to troponin, shifting tropomyosin and exposing actin binding sites.

  6. Myosin heads bind to actin, perform a power stroke, and contract the muscle.

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (shortens or lengthens) while tension remains constant (e.g., lifting a weight).

  • Isometric: Muscle length remains the same while tension increases (e.g., holding a weight steady).

• Heat Generation: Most body heat is generated by muscle activity due to ATP hydrolysis during contraction.

Key Terms Table

Human Respiratory System

Structure and Function

The respiratory system enables gas exchange, supplying oxygen to the body and removing carbon dioxide. It consists of upper and lower respiratory tracts.

• Upper Respiratory System: Includes the nose, nasal cavity, pharynx, and larynx. Functions in filtering, warming, and humidifying air.

• Lower Respiratory System: Includes the trachea, bronchi, bronchioles, and lungs. Responsible for gas exchange.

• Significance of Breathing: Provides oxygen for cellular respiration and removes carbon dioxide, a metabolic waste product.

Mechanics of Breathing

• Inhalation (Inspiration): Diaphragm and intercostal muscles contract, increasing thoracic volume and decreasing lung pressure, causing air to flow in.

• Exhalation (Expiration): Diaphragm and intercostal muscles relax, decreasing thoracic volume and increasing lung pressure, pushing air out.

• Intercostal Muscles: Located between ribs; assist in expanding and contracting the chest cavity during breathing.

Blood Flow and Gas Exchange

• Oxygen-Rich Blood Flow: Oxygenated blood returns from the lungs to the left atrium, passes to the left ventricle, and is pumped to the body.

• Gas Exchange: Occurs in alveoli, where oxygen diffuses into blood and carbon dioxide diffuses out.

Respiratory Diseases and Disorders

• Common disorders include asthma, bronchitis, emphysema, and pneumonia.

Human Digestive System

Structure and Function

The digestive system breaks down food into nutrients for absorption and energy. It includes the alimentary canal and accessory organs.

• Major Structures: Mouth, esophagus, stomach, small intestine, large intestine, rectum, anus.

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas.

• Function of Enzymes: Enzymes catalyze the breakdown of macromolecules; produced in the mouth (amylase), stomach (pepsin), pancreas (lipase, proteases), and small intestine.

• Large Surface Area: Villi and microvilli in the small intestine increase surface area for nutrient absorption.

Digestion and Absorption

• Peristalsis: Wave-like muscle contractions that move food through the digestive tract.

• Digestion of Molecules: Carbohydrates, proteins, and fats are digested in different regions by specific enzymes.

Metabolic Rates

• Basal Metabolic Rate (BMR): The energy expended at rest to maintain vital body functions.

• Standard Metabolic Rate (SMR): The metabolic rate of an ectotherm at a specific temperature.

Nutrition Guidelines

• "My Plate": A visual guide for balanced nutrition, emphasizing fruits, vegetables, grains, protein, and dairy.

Human Genetics and Inheritance

Basic Concepts

• Gene: A segment of DNA that codes for a protein or functional RNA.

• Chromosome: A DNA molecule with part or all of the genetic material of an organism.

• Genome: The complete set of genes or genetic material in an organism.

• Genetics: The scientific study of heredity and variation.

Inheritance Patterns

• Homologous Chromosomes: Chromosome pairs with the same genes but possibly different alleles.

• Karyotype: The number and appearance of chromosomes in a cell.

• Genotype: The genetic makeup of an organism.

• Phenotype: The observable traits of an organism.

• Punnett Square: A diagram used to predict the outcome of a genetic cross.

Alleles and Laws of Inheritance

• Allele: Different forms of a gene.

• Dominant Allele: Expressed when present; masks recessive allele.

• Recessive Allele: Expressed only when two copies are present.

• Homozygous: Two identical alleles for a gene.

• Heterozygous: Two different alleles for a gene.

• Law of Segregation: Each individual has two alleles for each gene, which segregate during gamete formation.

• Law of Independent Assortment: Genes for different traits assort independently during gamete formation.

Complex Inheritance Patterns

• Incomplete Dominance: Heterozygotes show an intermediate phenotype (e.g., red x white flowers = pink).

• Codominance: Both alleles are fully expressed in heterozygotes (e.g., AB blood type).

• Polygenic Inheritance: Multiple genes influence a single trait (e.g., skin color).

• Environmental Impact: Environment can affect gene expression (e.g., temperature-sensitive fur color in rabbits).

Gene Linkage and Chromosomal Changes

• Linked Genes: Genes located close together on the same chromosome tend to be inherited together.

• New Allele Combinations: Crossing over during meiosis creates new combinations of alleles.

• Sex-Linked Genes: Genes located on sex chromosomes (e.g., color blindness on X chromosome).

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to abnormal chromosome numbers (e.g., Down syndrome).

Genetics Table

Additional info: This guide expands on the review points by providing definitions, mechanisms, and examples for each system and genetic concept, ensuring a comprehensive overview suitable for exam preparation.