Neuron Structure and Function

Neuron Structure

• Neurons are specialized cells that transmit electrical signals.
• The cell body (soma) contains the nucleus and organelles, maintaining cell functions.
• Dendrites receive incoming signals and carry electrical impulses toward the cell body.
• The axon is a long extension that transmits electrical signals away from the cell body.
• Axons can be quite long, enabling communication across different body parts.
• A myelin sheath, a fatty substance, covers the axon and speeds up signal transmission.
• Axon terminals convert electrical impulses into chemical signals to communicate with other neurons.
• The synapse is a gap between two neurons where neurotransmitters facilitate communication.

Myelin Sheath and Nodes of Ranvier

• The myelin sheath insulates the axon, speeding up electrical signal transmission.
• Nodes of Ranvier are gaps in the myelin sheath where electrical signals are amplified.
• Signals jump from node to node, increasing transmission speed.

Synaptic Transmission

• Neurotransmitters are released from the axon terminal of one neuron.
• Neurotransmitters bind to receptors on the dendrites of the next neuron.
• Binding continues the signal.

Transmission of Nervous Messages

• Electrical impulses travel along neurons to transmit nervous messages.
• Neuron stimulation causes a change in electrical charge, creating an action potential.
• The action potential is an electrical impulse that moves down the axon.
• When an electrical impulse reaches the axon terminals, neurotransmitters are released into the synapse.
• Neurotransmitters cross the synaptic gap and bind to receptors on the next neuron's dendrites.
• Binding causes a change in electrical charge in the next neuron.
• This process continues along the chain of neurons.

Types of Neurons

• Sensory neurons detect environmental changes and carry signals to the brain and spinal cord.
• Interneurons are located in the brain and spinal cord and act as bridges between sensory and motor neurons.
• Interneurons process sensory information and determine the appropriate response.
• Motor neurons carry electrical impulses from the brain and spinal cord to muscles or glands, triggering a response.

Neurotransmitters in Synapses

• Neurotransmitters transmit signals between neurons.
• Electrical impulses reaching axon terminals cause the release of neurotransmitters into the synapse.
• Neurotransmitters travel across the synaptic gap and bind to receptors on the next neuron.
• Binding generates an electrical signal in the receiving neuron.
• The process enables the brain to send and receive information rapidly.

Central Nervous System (CNS)

• The CNS consists of the brain and spinal cord.
• The CNS serves as the control center for the body.
• The CNS processes incoming sensory information and sends out motor commands.

Peripheral Nervous System (PNS)

• The PNS includes all the nerves outside the CNS.
• The PNS connects the CNS to the rest of the body, including organs, limbs, and skin.
• The PNS transmits sensory information to the CNS and relays motor commands from the CNS to muscles and glands.

Somatic Nervous System

• The somatic nervous system controls voluntary actions.
• It allows conscious control over muscle contractions, like walking.

Autonomic Nervous System (ANS)

• The ANS regulates involuntary functions, like heart rate, digestion, and breathing.
• The sympathetic nervous system activates the body for "fight or flight" responses.
• The parasympathetic nervous system promotes "rest and digest" functions.

Stimulus-Response Model

• The stimulus is any change or signal from the environment.
• The receptor is a sensory organ or specialized cell that detects the stimulus.
• The effector is an organ or tissue (like a muscle or gland) that responds to the stimulus.
• The response is the action or behavior resulting from the stimulus.

Applying the Stimulus-Response Model

• Touching something hot: heat is the stimulus.
• Skin receptors detect the temperature and send signals to the brain.
• The brain processes information and sends a response to arm muscles via motor neurons.
• The muscle is the effector, and pulling away is the response.

Sensory Receptors

• Mechanoreceptors detect touch, pressure, vibration, and sound, found in skin and ears.
• Chemoreceptors respond to chemicals, involved in taste and smell, detecting molecules like food particles or odorants.
• Thermoreceptors sense changes in temperature found in the skin .
• Photoreceptors detect light, enabling vision, located in the eyes.

Reflex Arc

• A reflex arc is a quick, automatic response to a stimulus.
• Touching something hot: sensory neurons send a signal to the spinal cord.
• Interneurons in the spinal cord process the signal, sending a message to motor neurons.
• Muscles contract and pull your hand away.
• The response occurs without brain involvement.

Brain Function

• The brain processes sensory information, controls motor functions, and manages cognitive functions.

Brain Parts

• The cerebrum controls thinking, decision-making, movement, and emotions.
• The cerebellum coordinates muscle movements and helps with balance and motor control.
• The medulla (brainstem) controls involuntary functions like breathing, heart rate, and blood pressure.

Brain Lobes

• The frontal lobe is responsible for reasoning, planning, movement, and problem-solving.
• The parietal lobe processes sensory information related to touch, temperature, and spatial awareness.
• The occipital lobe processes visual information.
• The temporal lobe is involved in auditory processing, memory, and emotional responses.

Hormones

• Hormones are chemical messengers produced by endocrine glands.
• Hormones are released into the bloodstream and travel to target cells.
• Hormones bind to receptors on target cells, triggering changes in metabolism, growth, or mood.
• Hormones regulate body functions.

Homeostasis

• Homeostasis maintains a stable internal environment despite external changes.
• Temperature regulation is an example: the body maintains a temperature around 37°C (98.6°F).
• Maintaining a constant internal environment ensures optimal cell function.

Blood Glucose Regulation

• The pancreas regulates blood glucose levels.
• When glucose levels are high, the pancreas releases insulin, which helps cells absorb glucose and lowers blood sugar.
• When glucose levels drop, the pancreas releases glucagon, which signals the liver to release stored glucose.

Disease

• A condition that disrupts the normal functioning of the body.
• Can be caused by pathogens (infectious) or other factors like genetics and lifestyle (non-infectious).

Symptoms

• The physical or physiological signs that indicate illness.
• Fever, fatigue, pain, or swelling.

Transmission

• The way a disease spreads from one organism to another.
• Includes direct contact, airborne particles, bodily fluids, or contaminated food and water.

Infectious vs. Non-Infectious Diseases

• Infectious diseases are caused by pathogens and can be transmitted.
• Non-infectious diseases are not caused by pathogens and cannot be transmitted.
• Examples: diabetes, cancer, heart disease.

Pathogens

• Bacteria are single-celled organisms that can reproduce on their own.
• Viruses are non-living particles that invade host cells and replicate.
• Fungi are organisms like molds and yeasts that infect skin, nails, or internal organs.

Lines of Defenses

• First line: physical and chemical barriers prevent pathogens from entering.
• Second line: non-specific immune responses fight off invaders.
• Third line: specific immune responses target and eliminate pathogens.

Specific vs. Non-Specific Immunity

• Non-specific immunity provides general protection against all pathogens (innate).
• Specific immunity targets particular pathogens (adaptive).

First Line of Defense Components

• Physical barriers: skin, mucus, and cilia prevent pathogens from entering.
• Chemical barriers: stomach acid, saliva, and tears destroy microbes.
• Biological barriers: beneficial bacteria outcompete harmful microbes.

Fever and Inflammation

• Fever: raises body temperature to slow down pathogen reproduction and boost immune cell activity.
• Inflammation: increases blood flow to infected areas, bringing white blood cells.

Phagocytes

• Phagocytes (macrophages and neutrophils) engulf and digest pathogens.
• They recognize foreign invaders and break them down through phagocytosis.

Disease Control

• Hygiene (washing hands, clean drinking water)
• Vaccination (stimulating immunity against specific diseases)
• Antibiotics & Antivirals (treat bacterial and viral infections)
• Quarantine & Social Distancing (reducing spread of contagious diseases)
• Insect Control (reducing mosquito populations to prevent malaria)`

B Cells and T Cells

• B cells: produce antibodies that bind to and neutralize pathogens.
• T cells: directly attack infected cells (killer T cells) or help activate other immune cells (helper T cells).

Vaccines

• A vaccine contains a weakened or inactive form of a pathogen.
• Vaccines stimulate the immune system to produce memory B and T cells.
• The immune system can respond quickly and effectively if the real pathogen enters the body later.