Human Body Organization and Cell Physiology

Organisation of the Human Body

• The human body is composed of cells, tissues, organs, and systems.
• Cells are the smallest functional units of the body.
• A group of cells with similar functions form a tissue.
• Primary types of tissues: Muscle, Nervous, Epithelial, and Connective.
• Two or more types of tissues come together to form an organ.
• Types of organs: Tubular/hollow and Compact/parenchymal.
• A group of organs working together to carry out specific functions form a system.

Systems of the Human Body

• Digestive System: responsible for digestion of food.
• Excretory System: responsible for elimination of unwanted substances.
• Cardiovascular System: responsible for transport of substances between organs.
• Respiratory System: responsible for supply of oxygen and removal of carbon dioxide.
• Reproductive System: responsible for reproduction.
• Muscoskeletal System: responsible for stability and movement.
• Nervous System: controls locomotion and bodily function, including intellectual function.
• Endocrine System: responsible for growth and regulation of body functions.

The Cell

• The cell membrane is a semi-permeable and fluid-like structure composed of hydrophobic and hydrophillic components.
• The cell membrane has integral proteins that interact with the lipid bilayer to form passive transport pores and channels, active transport pumps and carriers, and membrane-linked enzymes, receptors, and transducers.
• Sterols, such as cholesterol, stabilize the lipid bilayer.

Cell Organelles

• Nucleus: contains chromatin, DNA, and a nucleolus.
• Mitochondria: responsible for generating energy for the cell through the conversion of food into ATP.
• Endoplasmic Reticulum: site where cell membrane and exported materials are made.
• Golgi Apparatus: receives and modifies materials, and directs new materials to their destinations.
• Lysosomes: responsible for intracellular digestion and breakdown of waste.
• Peroxisomes: generate and degrade hydrogen peroxide.
• Cytosol: a water-based gel where chemical reactions take place.
• Cytoskeleton: composed of filaments, such as actin, intermediate, and microtubules, and provides structure and movement to the cell.

Homeostasis

• Homeostasis is the ability of the body to maintain a stable internal environment despite changes in the external environment.
• Homeostasis is crucial for maintaining health and preventing disease.
• The body has mechanisms to regulate various physiological processes, such as heart rate, blood pressure, and body temperature.

Physiology of the Nervous System

• The nervous system is composed of the central nervous system (CNS) and peripheral nervous system (PNS).
• The CNS consists of the brain and spinal cord, while the PNS consists of nerves that connect the CNS to the rest of the body.
• Neurons are the basic units of the nervous system, responsible for transmitting electrical impulses.
• Dendrites carry information to the cell body, while the axon sends information to the next unit.

The Neuron

• The neuron has three main parts: dendrites, cell body, and axon.
• Dendrites receive information from other neurons.
• The cell body integrates information and generates an action potential.
• The axon transmits the action potential to the next neuron.

The Synapse

• The synapse is the junction between two neurons.
• The synapse allows for communication between neurons through the release of neurotransmitters.
• Neurotransmitters bind to receptors on the postsynaptic neuron, generating an action potential.

Sensory Systems

• Each sensory system is specialized to detect a specific type of stimulus.
• Sensory systems have a specific region of the cortex dedicated to processing information.
• There are regions of overlap between sensory systems, known as association areas.

Action Potentials and the Synapse

• Action potentials are signals transmitted along axons.
• Action potentials are generated by a rapid change in the membrane potential of the neuron.
• The synapse is the site of transmission of action potentials from one neuron to another.
• Neurotransmitters are released from the presynaptic neuron and bind to receptors on the postsynaptic neuron, generating an action potential.

Muscle Physiology

• Muscles are responsible for movement and contraction.
• The motor unit is the functional unit of the muscle, consisting of a motor neuron and the muscle fibers it innervates.
• Muscle contraction is regulated by the frequency of action potentials and the number of functional motor units.