Human Anatomy and Physiology: Nervous, Muscular, Skeletal, and Respiratory Systems

Posted on Sep 18, 2024 in Biology

Nervous System

Functions

  1. Sensory: Receptors detect stimuli and send signals to the CNS.
  2. Integration: The CNS processes information and makes decisions.
  3. Motor: Decisions from the CNS are responded to.

Nerve Impulse

A signal is transmitted along a neuron. It enters through dendrites, travels along the axon, and reaches the axon terminal. Neurotransmitters (e.g., acetylcholine) are released at the synapse to communicate with the next neuron.

Neuromuscular Junction

The connection point between a motor neuron and a muscle fiber.

Motor Plate

The specific region where the axon terminal of the motor neuron comes into close contact with the muscle fiber.

Central Nervous System (CNS)

Comprises the brain and spinal cord.

Brain

Divided into four regions:

  1. Cerebrum: Responsible for voluntary actions, thoughts, and sensory perception.
  2. Diencephalon:
    • Thalamus: Relay center for sensory information.
    • Hypothalamus: Maintains homeostasis (e.g., body temperature, hunger).
  3. Cerebellum: Coordinates and fine-tunes movements.
  4. Brainstem: Controls essential functions like breathing, heart rate, and muscle tone.

Spinal Cord

Transmits information between the brain and the rest of the body. It also integrates spinal reflexes.

Peripheral Nervous System (PNS)

  1. Autonomic Nervous System: Controls involuntary functions. It has two divisions:
    • Sympathetic Nervous System: Prepares the body for “fight or flight” responses (e.g., increased heart rate).
    • Parasympathetic Nervous System: Promotes “rest and digest” functions (e.g., slows heart rate).
  2. Somatic Nervous System: Controls voluntary movements. It consists of:
    • Sensory Neurons (Afferent): Carry sensory information from the body to the CNS.
    • Motor Neurons (Efferent): Carry commands from the CNS to muscles, causing movement.

Sensorimotor Integration

Sensory Input

Sensory information is received by receptors and transmitted to the CNS (brain and spinal cord) for processing.

Motor Control

The CNS processes sensory information and generates motor commands to produce appropriate responses.

Reflex Responses

Automatic, involuntary responses to stimuli. Examples include:

  • Stretch Reflex (Myotatic Reflex): Muscle contraction in response to stretching, mediated by muscle spindles.
  • Golgi Tendon Reflex: Muscle relaxation in response to excessive tension, mediated by Golgi tendon organs.

Muscular System

Muscle Fiber Types

  1. Slow-Twitch (Type I): Resistant to fatigue, rich in mitochondria and myoglobin, suited for aerobic activities.
  2. Fast-Twitch (Type II): Generate more force, fatigue quickly, rely on anaerobic metabolism for energy.

Muscle Hypertrophy

The thickening of muscle fibers. Two main types:

  1. Sarcoplasmic Hypertrophy: Increase in sarcoplasm (muscle cell fluid), associated with increased muscle size.
  2. Myofibrillar Hypertrophy: Increase in the number of actin and myosin filaments, leading to increased muscle strength.

Muscle Contraction

Muscle Structure

  • Muscle Belly: The contractile portion of the muscle.
  • Tendons: Connect muscles to bones.
  • Fascia: Connective tissue that surrounds muscles.
  • Capillaries: Supply muscles with oxygen and nutrients.
  • Nerves: Control muscle contraction.

Muscle Fiber Structure

  • Sarcolemma: The muscle cell membrane.
  • Myofibrils: Contractile units within muscle fibers, containing actin and myosin filaments.
  • Sarcoplasm: The cytoplasm of a muscle cell.
  • Transverse Tubules (T-tubules): Invaginations of the sarcolemma that transmit nerve impulses into the muscle fiber.
  • Sarcoplasmic Reticulum (SR): A network of tubules that store and release calcium ions, essential for muscle contraction.

Sliding Filament Theory

Muscle contraction occurs when actin and myosin filaments slide past each other, shortening the sarcomere (the basic contractile unit of a muscle fiber).

Skeletal System

Bone Structure

  • Epiphysis: The ends of a long bone.
  • Diaphysis: The shaft of a long bone.

Types of Joints

  • Fibrous Joints (Synarthrosis): Immovable joints, e.g., sutures in the skull.
  • Cartilaginous Joints (Amphiarthrosis): Slightly movable joints, e.g., intervertebral discs.
  • Synovial Joints (Diarthrosis): Freely movable joints, e.g., knee, shoulder.

Metabolism

The sum of all chemical reactions that occur within an organism.

ATP (Adenosine Triphosphate)

The primary energy currency of cells. Muscle contraction requires ATP.

Energy Systems for ATP Production

  1. Phosphagen System: Uses creatine phosphate to rapidly produce ATP. Supports short-duration, high-intensity activities (2-7 seconds).
  2. Anaerobic Glycolysis: Breaks down glucose without oxygen, producing lactic acid as a byproduct. Supports short-duration, high-intensity activities (30-60 seconds).
  3. Aerobic Respiration: Uses oxygen to break down glucose and fatty acids for ATP production. Supports long-duration activities.

Respiratory System

Functions

  • Intake of oxygen (O2).
  • Removal of carbon dioxide (CO2).
  • Filtration, warming, and humidification of inhaled air.

Components and Structure

  • Upper Respiratory Tract:
    • Nostrils and Mouth
    • Pharynx (Throat)
    • Larynx (Voice Box)
  • Lower Respiratory Tract:
    • Trachea (Windpipe)
    • Bronchi and Bronchioles (Airways)
    • Alveoli (Air Sacs): Sites of gas exchange
  • Lungs: Contain the bronchi, bronchioles, and alveoli.

Respiratory Function

  1. Pulmonary Ventilation: Movement of air into and out of the lungs (inspiration and expiration).
  2. Pulmonary Diffusion: Exchange of O2 and CO2 between the alveoli and pulmonary capillaries.
  3. Gas Transport: Transport of O2 to tissues and CO2 to the lungs via the bloodstream.
  4. Tissue Respiration: Exchange of O2 and CO2 between the blood and tissues.

Regulation of Respiration

Controlled by both voluntary (cerebral cortex) and involuntary (brainstem) mechanisms.

Lung Volumes and Capacities

  • Tidal Volume: Volume of air inhaled or exhaled during a normal breath.
  • Respiratory Rate: Number of breaths per minute.
  • Residual Volume: Volume of air remaining in the lungs after a forced expiration.
  • Vital Capacity: Maximum volume of air that can be exhaled after a maximum inspiration.
  • Inspiratory Reserve Volume: Volume of air that can be inhaled beyond a normal inspiration.
  • Expiratory Reserve Volume: Volume of air that can be exhaled beyond a normal expiration.

Circulatory System

Cardiac Cycle

  • Systole: Contraction phase of the heart.
  • Diastole: Relaxation phase of the heart.

Functions of the Heart

  • Distribution: Delivers oxygen and nutrients to tissues.
  • Elimination: Removes waste products from tissues.
  • Maintenance: Regulates body temperature and pH.
  • Protection: Transports immune cells and antibodies.
  • Transportation: Carries hormones and other signaling molecules.

Functional Parameters

  • Heart Rate (HR): Number of heartbeats per minute.
  • Cardiac Output (Q): Volume of blood ejected by the heart per minute.
  • Blood Pressure (BP): Force exerted by blood against artery walls.
  • Blood Flow: Distribution of blood to different organs and tissues.

Components

  • Heart: The pump that circulates blood.
  • Blood Vessels: Arteries, veins, and capillaries that carry blood throughout the body.
  • Blood: Composed of plasma (liquid portion) and formed elements (red blood cells, white blood cells, and platelets).
    • Erythropoietin (EPO): A hormone that stimulates red blood cell production.
  • Capillaries: Microscopic vessels that connect arteries and veins, facilitating the exchange of nutrients, gases, and waste products between blood and tissues.