Human Muscular System

Muscle Cell Structure and Function

The human muscular system enables movement, generates heat, and supports body structure. Muscle cells (fibers) contain specialized structures that facilitate contraction.

• Sarcomere: The basic contractile unit of muscle, composed of actin (thin) and myosin (thick) filaments.

• Actin and Myosin: Proteins responsible for muscle contraction. Myosin heads bind to actin, pulling the filaments and shortening the sarcomere.

• Sliding Filament Mechanism: Muscle contraction occurs as myosin heads "walk" along actin filaments, powered by ATP.

• Substructures: Includes Z-lines (define sarcomere boundaries), A-band (myosin), I-band (actin), and M-line (center).

• Major Muscle Groups: Examples include biceps, triceps, quadriceps, hamstrings, pectorals, and abdominals.

Muscle Contraction Mechanisms

Muscle contraction is initiated by electrical impulses from motor neurons.

• Action Potential: A rapid change in membrane potential in motor neurons triggers muscle contraction.

• Order of Events:

  1. Motor neuron releases neurotransmitter (acetylcholine).

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

  3. Calcium ions released from sarcoplasmic reticulum.

  4. Calcium binds to troponin, exposing actin binding sites.

  5. Myosin binds to actin, ATP hydrolysis powers contraction.

• Heat Generation: Most body heat is produced by muscle activity (thermogenesis).

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle tension increases, but length does not change (no movement).

• Muscles and Body Cavities: Diaphragm separates thoracic and abdominal cavities.

Key Terms and Functions

• Sarcomere Function: Facilitates contraction and force generation.

• Actin: Thin filament, provides binding sites for myosin.

• Myosin: Thick filament, motor protein that pulls actin.

Example: During running, quadriceps contract isotonicly to extend the knee.

Additional info: ATP is required for both contraction and relaxation of muscle fibers.

Human Respiratory System

Significance and Structure

The respiratory system enables gas exchange, supplying oxygen and removing carbon dioxide. It consists of upper and lower structures.

• Upper Respiratory Structures: Nose, nasal cavity, pharynx, larynx. Functions: filter, warm, and humidify air.

• Lower Respiratory Structures: Trachea, bronchi, lungs, alveoli. Functions: conduct air, gas exchange.

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

Mechanics of Breathing

• Inhalation: Diaphragm and intercostal muscles contract, increasing thoracic volume, decreasing lung pressure, air flows in.

• Exhalation: Muscles relax, thoracic volume decreases, lung pressure increases, air flows out.

• Pressure Changes: ; air moves from high to low pressure.

Blood Flow and Gas Exchange

• Oxygen-rich Blood: Flows from lungs to left atrium, left ventricle, then systemic circulation.

• Order of Flow: Pulmonary veins → left atrium → left ventricle → aorta → body.

Respiratory Diseases and Disorders

• Examples: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia.

Example: During exercise, breathing rate increases to supply more oxygen.

Additional info: Alveoli provide a large surface area for efficient gas exchange.

Human Digestive System

Structure and Function

The digestive system breaks down food, absorbs nutrients, and eliminates waste. It includes primary and accessory organs.

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

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

• Enzymes: Biological catalysts produced in salivary glands, stomach, pancreas, small intestine; speed up digestion.

• Large Surface Area: Villi and microvilli in small intestine increase absorption efficiency.

Metabolic Rates

• Basal Metabolic Rate (BMR): Energy used at rest.

• Standard Metabolic Rate (SMR): Energy used under specific conditions (e.g., fasting, resting).

Digestion Process

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

• My Plate: USDA guideline for balanced nutrition.

Example: Amylase in saliva breaks down starch into sugars.

Additional info: The liver produces bile, which emulsifies fats for digestion.

Human Genetics and Inheritance

Basic Concepts

Genetics is the scientific study of heredity and variation. Genes are DNA segments coding for traits, located on chromosomes.

• Gene: DNA sequence coding for a protein or trait.

• Chromosome: DNA molecule with associated proteins; humans have 23 pairs.

• Genome: Complete set of genes in an organism.

• Homologous Chromosomes: Chromosome pairs with same genes, one from each parent.

• Karyotype: Visual representation of chromosomes; used to detect abnormalities.

Inheritance Patterns

• Genotype: Genetic makeup (allele combination).

• Phenotype: Observable traits.

• Punnett Square: Diagram predicting genetic crosses.

• Dominant Allele: Expressed trait when present.

• Recessive Allele: Expressed only when homozygous.

• Homozygous: Two identical alleles.

• Heterozygous: Two different alleles.

Mendelian Laws

• Law of Segregation: Alleles separate during gamete formation.

• Law of Independent Assortment: Genes on different chromosomes assort independently.

Complex Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

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

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

• Environmental Impact: Environment can affect phenotypic expression.

• Linked Genes: Genes close together on a chromosome tend to be inherited together.

• Sex-linked Genes: Genes on sex chromosomes (e.g., X-linked traits).

• Nondisjunction: Failure of chromosomes to separate during meiosis, leading to abnormal chromosome numbers.

Genetic Disorders

• Dominant Disorders: Often lethal if homozygous.

• Recessive Disorders: Can persist in populations due to carriers.

Allele Combinations and Meiosis

• New Combinations: Crossing over and independent assortment during meiosis create genetic diversity.

Example: Cystic fibrosis is a recessive genetic disorder; Huntington's disease is dominant.

Additional info: Punnett squares can be used to predict probabilities of offspring genotypes and phenotypes.