Human Muscular System

Muscle Cell Structure and Sliding Mechanism

The human muscular system relies on specialized cells and structures to produce movement. The sliding filament mechanism is central to muscle contraction.

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

• Actin and Myosin Filaments: Actin provides the track for myosin heads to pull, causing contraction. Myosin uses ATP to bind and pull actin filaments.

• Sliding Filament Theory: Muscle contraction occurs when myosin heads attach to actin, pulling them closer together, shortening the sarcomere.

• Order of Events in Muscle Contraction:

  1. Action potential arrives at motor neuron.

  2. Release of neurotransmitter (acetylcholine) at neuromuscular junction.

  3. Depolarization of muscle cell membrane.

  4. Release of calcium ions from sarcoplasmic reticulum.

  5. Calcium binds to troponin, exposing binding sites on actin.

  6. Myosin binds to actin, ATP is hydrolyzed, and contraction occurs.

• Electrical Impulses: Initiated by action potentials in motor neurons, leading to muscle contraction.

• Heat Generation: Most body heat is generated by muscle activity, especially during contraction.

• Major Muscle Groups: Includes biceps, triceps, quadriceps, hamstrings, pectorals, abdominals, and others.

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

• Isotonic vs. Isometric Contractions:

  • Isotonic: Muscle changes length (movement occurs).

  • Isometric: Muscle length remains the same (no movement, tension increases).

Example: Lifting a weight involves isotonic contraction; holding a weight steady involves isometric contraction.

Key Terms and Functions

• Sarcomere Function: Facilitates contraction by shortening during muscle activity.

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

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

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

Human Respiratory System

Significance of Breathing

Breathing is essential for gas exchange, supplying oxygen to tissues and removing carbon dioxide.

• Oxygen Transport: Oxygen-rich blood is pumped from the lungs to the heart, then distributed throughout the body.

• Blood Flow Through the Heart: Oxygenated blood enters the left atrium, passes to the left ventricle, and is pumped into systemic circulation.

Structures of the Respiratory System

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

• Lower Respiratory System: Includes trachea, bronchi, bronchioles, and lungs. Functions in gas exchange and air conduction.

Mechanics of Breathing

• Pressure Changes: During inhalation, lung volume increases and pressure decreases, drawing air in. During exhalation, volume decreases and pressure increases, pushing air out.

• Intercostal Muscles: Contract during inhalation to expand the rib cage; relax during exhalation.

• Inspiration: Diaphragm contracts, intercostal muscles lift ribs, lungs expand.

• Expiration: Diaphragm relaxes, intercostal muscles lower ribs, lungs recoil.

Example: During exercise, breathing rate increases to meet oxygen demand.

Respiratory Diseases and Disorders

• Common Disorders: Asthma, chronic obstructive pulmonary disease (COPD), pneumonia, and lung cancer.

Additional info: Gas exchange occurs in alveoli, where oxygen diffuses into blood and carbon dioxide is expelled.

Human Digestive System

Major Structures and Functions

The digestive system breaks down food, absorbs nutrients, and eliminates waste.

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

• Accessory Organs: Salivary glands, liver, gallbladder, pancreas. These produce enzymes and aid digestion.

• Enzymes: Catalyze breakdown of macromolecules; produced in salivary glands, stomach, pancreas, and small intestine.

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

Metabolic Rates

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

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

Digestion Process

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

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

Example: Carbohydrates are digested by amylase in the mouth and pancreas; proteins by pepsin in the stomach.

Additional info: Most nutrient absorption occurs in the small intestine.

Human Genetics and Inheritance

Genes, Chromosomes, and Genomes

Genetics is the scientific study of heredity and variation in organisms.

• Gene: Segment of DNA coding for a specific protein.

• Chromosome: Structure composed of DNA and proteins; humans have 23 pairs.

• Genome: Complete set of genetic material in an organism.

• Homologous Chromosomes: Pair of chromosomes with the same genes but possibly different alleles.

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

Genotype and Phenotype

• Genotype: Genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: Observable traits resulting from genotype and environment.

Punnett Square and Alleles

• Punnett Square: Diagram used to predict genetic crosses.

• Alleles: Variants of a gene; can be dominant or recessive.

• Dominant Allele: Expressed when present (e.g., AA or Aa).

• Recessive Allele: Expressed only when homozygous (aa).

• Homozygous: Two identical alleles (AA or aa).

• Heterozygous: Two different alleles (Aa).

Mendelian Laws

• Law of Segregation: Each parent passes one allele for each gene to offspring.

• Law of Independent Assortment: Genes for different traits are inherited independently.

Patterns of Inheritance

• Incomplete Dominance: Heterozygote shows intermediate phenotype (e.g., pink flowers from red and white parents).

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

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

• Environmental Impact: Environment can modify phenotypic expression (e.g., nutrition affects height).

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

• New Allele Combinations: Crossing over during meiosis creates genetic diversity.

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

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

Table: Comparison of Dominant and Recessive Alleles

Example: A Punnett Square can predict the probability of offspring inheriting a trait.

Additional info: Lethal dominant disorders are rare because affected individuals often do not survive to reproduce; recessive disorders can persist if carriers are unaffected.