Biology Unit 5
Differentiation and Specialization
Differentiation refers to the process by which a cell undergoes changes to acquire a specialized function. This process allows cells in multicellular organisms to take on unique roles, such as carrying oxygen or transmitting signals.
Cells within a multicellular organism are not identical in structure or function. Instead, they specialize based on the needs of the body. For example, red blood cells are adapted to carry oxygen, while nerve cells are designed to transmit electrical impulses.
Stem Cells are undifferentiated cells that have not yet specialized. Because they have the potential to transform into any type of cell, they play a crucial role in growth, healing, and development. Stem cells hold promise in treating various conditions, including degenerative diseases and injuries, by regenerating damaged tissues.
Specialized Cells:
Nerve Cells (Neurons):
Nerve cells are designed to transmit electrical signals throughout the body. They have long, thin extensions called axons and dendrites that enable them to carry signals over long distances.
Their structure allows them to efficiently carry messages from the brain to other parts of the body and vice versa, allowing for rapid responses to stimuli. This process happens almost instantaneously.
Skin Cells (Epithelial Cells):
Skin cells form epithelial tissue, which serves as a protective barrier between the body and the outside environment. This tissue is found lining surfaces such as the mouth, throat, and digestive tract.
Epithelial cells are arranged in overlapping patterns that enhance their ability to block pathogens and physical damage.
Red Blood Cells (Erythrocytes):
Red blood cells are responsible for transporting oxygen from the lungs to the rest of the body and returning carbon dioxide to be expelled.
Their biconcave shape increases the surface area for efficient gas exchange and allows them to pass easily through small blood vessels.
The protein hemoglobin, found in red blood cells, binds to oxygen and facilitates its transport.
Muscle Cells (Myocytes):
Muscle cells are specialized for contraction and allow movement within the body. They form muscle tissue, which can contract and relax in response to electrical impulses.
The heart is composed of cardiac muscle, a special type of muscle tissue that can continuously contract without tiring. This is essential for the heart’s function of pumping blood throughout a person's lifetime.
Hierarchy of an Organism
The organization of life progresses from simple to complex, with each level playing a specific role in maintaining the function of an organism:
Cells:
The basic unit of life. In unicellular organisms, one cell performs all necessary functions. In multicellular organisms, cells differentiate into specialized types to perform specific functions within tissues and organs.
Tissues:
Groups of cells working together to perform a specific function. In humans, there are four primary types of tissue:
Epithelial Tissue: Covers and protects body surfaces and cavities. It also plays a role in absorption and secretion (e.g., skin, digestive tract lining).
Connective Tissue: Provides structural and nutrient support and connects different parts of the body. Examples include bone, blood, and adipose tissue.
Nervous Tissue: Composed of neurons and supporting cells that transmit electrical signals throughout the body. This tissue is vital for communication within the nervous system.
Muscle Tissue: Specialized for contraction and movement. It includes skeletal muscle (voluntary), smooth muscle (involuntary), and cardiac muscle (heart muscle).
Organs:
Organs are composed of two or more tissue types working together to carry out a specific function. For example, the heart is made of muscle, connective, and nervous tissues, all working together to pump blood.
Organ Systems:
An organ system consists of several organs that work together to perform a major bodily function. There are 11 major organ systems, including the circulatory system, respiratory system, and nervous system.
Each system contributes to homeostasis, which is the body's ability to maintain stable internal conditions despite changes in the external environment.
Homeostasis
Homeostasis is the process by which an organism maintains a stable internal environment. It includes regulating factors like temperature, pH, and nutrient levels to ensure optimal functioning of cells, tissues, and organs.
When the body detects changes, like needing food or water, it triggers responses to bring the internal conditions back into balance. For example, hunger signals indicate that the body needs energy, prompting a search for food.
Cardiovascular System
The cardiovascular system is responsible for circulating blood throughout the body, delivering oxygen and nutrients, and removing waste products. It also plays a critical role in immune defense via the action of white blood cells.
The Heart
The heart is a muscular organ that acts as a pump to circulate oxygen-rich blood to the body and oxygen-poor blood to the lungs.
Made of cardiac muscle, the heart contracts and relaxes rhythmically without tiring, allowing it to pump blood consistently throughout a person’s lifetime.
The heart has four chambers: two atria (upper chambers) and two ventricles (lower chambers).
Atria collect blood entering the heart.
Ventricles push blood out of the heart to the lungs or the rest of the body.
The SA node (sinoatrial node) is a cluster of cells in the right atrium that serves as the heart’s natural pacemaker, regulating the heart's rhythm by sending electrical signals to stimulate contraction.
Circulation
Veins and Vena Cava: The upper vena cava carries blood from the upper body (from the head and arms) back to the heart. The lower vena cava returns blood from the lower body (from the legs and abdomen).
Pulmonary Circulation: Oxygen-poor blood is pumped from the right ventricle to the pulmonary arteries, which lead to the lungs. In the lungs, the blood is oxygenated.
Systemic Circulation: Oxygen-rich blood returns to the heart through the pulmonary veins, entering the left atrium. From there, it moves to the left ventricle, which pumps it out to the body through the aorta.
The left side of the heart handles oxygenated blood, while the right side deals with deoxygenated blood.
The AV node (atrioventricular node) works with the SA node to ensure proper coordination of heartbeats.
Arteries, Veins, and Capillaries
Arteries: Arteries carry oxygen-rich blood away from the heart to the body. They have thick walls to withstand high pressure generated by the heart's contractions.
Veins: Veins carry oxygen-poor blood back to the heart and have thinner walls because they operate under lower pressure. Many veins, especially in the legs, have valves to prevent blood from flowing backward.
Capillaries: These tiny vessels connect arteries to veins. Their extremely thin walls allow for the exchange of gases, nutrients, and waste products between the blood and tissues.
Blood
Blood pressure: Regulated by the heart's pumping action and skeletal muscles, which contract and help push blood through the veins.
Components:
Plasma: The liquid part of blood, primarily water, carrying nutrients, waste, and proteins like clotting factors.
Red blood cells: These are the most abundant cells in blood, containing hemoglobin, which binds to oxygen and facilitates its transport.
Platelets: Small fragments of cells responsible for blood clotting.
White blood cells: Part of the immune system, produced in response to infections and pathogens.
Lymph: Extra fluid that accumulates between cells, which is collected by the lymphatic system. Lymph nodes filter this fluid, especially during infections.
Blood Types
Blood Types: Blood can be classified as type A, B, AB, or O based on antigens on red blood cells.
The Rh factor indicates whether the blood type is positive or negative, based on the presence of a specific protein on the red blood cells.
Cardiovascular and Blood Diseases
Atherosclerosis: A condition where fatty deposits accumulate in the arteries, narrowing and hardening them, which can lead to heart attacks.
Hypertension: Chronic high blood pressure that puts strain on the heart and blood vessels.
Hemophilia: A genetic disorder where blood doesn't clot properly, leading to excessive bleeding.
AIDS: A disease caused by the HIV virus that attacks the immune system.
Anemia: A condition where there are not enough red blood cells or hemoglobin to carry sufficient oxygen to the body’s tissues.
Leukemia: A cancer of the blood or bone marrow that results in the production of abnormal white blood cells.
Respiratory System
The respiratory system facilitates gas exchange, where oxygen is absorbed into the bloodstream and carbon dioxide is expelled from the body.
Parts of the Respiratory System
Lungs: The primary organs where gas exchange takes place. They are the site of oxygen absorption and carbon dioxide removal.
The respiratory system is divided into the upper and lower respiratory systems for organizational purposes.
Upper Respiratory System
Air enters the body through the nose, where nasal hairs trap debris like pollen.
The pharynx (throat) connects the nose to the mouth, and the larynx (voice box) contains the vocal cords and aids in sound production.
The trachea (windpipe) directs air to the lungs and is lined with cilia to filter out foreign particles.
Air travels from the trachea into bronchi (major airways), which branch into smaller bronchioles, eventually leading to tiny air sacs called alveoli for gas exchange.
The epiglottis is a flap that closes off the windpipe during swallowing, preventing food or liquid from entering the lungs.
Lower Respiratory System
The bronchioles continue to branch into alveoli, which are surrounded by tiny blood vessels where oxygen and carbon dioxide are exchanged between the lungs and bloodstream.
Inhalation and Exhalation
Inhalation: The diaphragm contracts and flattens, increasing the chest cavity's volume, allowing air to rush into the lungs.
Exhalation: The diaphragm relaxes and moves upward, decreasing the chest cavity’s volume, and pushing air out of the lungs.
Hyperventilation: Rapid, shallow breathing that increases oxygen intake and expels more carbon dioxide.
Nervous System
The nervous system coordinates the body's response to stimuli and processes information to control bodily functions.
Central Nervous System (CNS)
The brain is the body's control center, processing sensory information, regulating motor functions, and making decisions.
It has four major regions: the frontal lobe (higher functions like decision-making), parietal lobe (sensory processing), occipital lobe (vision), and temporal lobe (hearing, memory).
The cerebrum controls voluntary actions, while the cerebellum coordinates balance and motor skills.
The brainstem and medulla control involuntary actions like heart rate and breathing.
Spinal Cord
The spinal cord is the communication pathway between the brain and the rest of the body, protected by vertebrae. It controls reflex actions and coordinates movement.
Peripheral Nervous System (PNS)
The PNS includes all nerves outside the CNS and is responsible for both voluntary and involuntary functions.
Autonomic nervous system: Controls involuntary actions like heartbeat and digestion.
Somatic nervous system: Controls voluntary movements.
Neurons are specialized cells that transmit electrical signals throughout the body.
Dendrites receive signals, and axons transmit them to other neurons.
Synapses are gaps between neurons where chemical signals are passed.
Action potential: The electrical impulse that travels along neurons, triggered by a stimulus.
Types of Neurons
Sensory neurons carry information from sensory receptors to the brain.
Interneurons process information within the CNS.
Motor neurons transmit signals from the CNS to muscles and glands to initiate a response.
Digestive System
The digestive system enables the body to consume food, break it down into smaller molecules, and absorb the nutrients for energy and growth. The process involves several phases: ingestion, digestion, absorption, and elimination.
Ingestion
Ingestion is the process of taking food into the body through the mouth. The food is physically broken down by the teeth (mechanical digestion) and chemically broken down by enzymes in saliva. Saliva contains enzymes like amylase, which begin the breakdown of starches and sugars into simpler molecules.
The tongue helps manipulate food, forming it into a bolus (a ball of chewed food) to be swallowed.
As food is swallowed, it passes into the pharynx, and the epiglottis closes the windpipe to prevent food from entering the lungs.
The esophagus uses peristalsis—rhythmic muscle contractions—to push food toward the stomach.
Digestion
Mechanical digestion continues as food moves through the digestive tract, being churned and broken down further by the stomach.
In the stomach, chemical digestion takes place due to gastric juices, which contain hydrochloric acid and digestive enzymes like pepsin. These substances help break down proteins.
The stomach's folds (rugae) and villi (tiny hair-like structures) increase surface area for digestion.
The cardiac sphincter regulates food entry into the stomach, while the pyloric sphincter controls food exit from the stomach into the small intestine.
Chyme, the partially digested food mixed with gastric juices, enters the small intestine.
Absorption
The small intestine is the primary site for nutrient absorption. It is long, with villi and microvilli lining its walls, which increase surface area for absorption.
The pancreas secretes digestive enzymes into the small intestine to break down carbohydrates, proteins, and fats.
The liver produces bile, which is stored in the gallbladder and helps emulsify fats, making them easier to digest.
As chyme moves through the small intestine, the nutrients (amino acids, sugars, fatty acids) are absorbed into the bloodstream through the villi.
Remaining undigested material moves into the large intestine.
Elimination
The large intestine absorbs water and any remaining nutrients. It also houses bacteria that help break down some undigested material.
Unused food and waste are compacted into feces and move to the rectum, where they are stored until elimination.
The final step is defecation, where waste is expelled through the anus.
Muscular System
The muscular system controls the movement of the body and the contraction of organs. It includes three types of muscle: skeletal, smooth, and cardiac muscles.
Voluntary vs. Involuntary Muscles
Voluntary muscles are under conscious control and are used for movements like walking, lifting, and sports.
Involuntary muscles function automatically without conscious control, regulating processes such as digestion and heartbeat.
Skeletal Muscles
Skeletal muscles are attached to bones and are responsible for voluntary movements. They are controlled by the somatic nervous system and can tire quickly.
These muscles work in antagonistic pairs, meaning one muscle contracts while the other relaxes.
When you engage in activities like weightlifting, you break down muscle fibers, which then rebuild and grow in size during recovery.
Anterior Muscles
Biceps: Located in the upper arm, these muscles flex the forearm.
Quadriceps: The large muscles in the front of the thighs that extend the knee.
Sartorius: The long muscle that runs diagonally across the thigh, aiding in leg rotation.
Abdominal muscles (Abs): These muscles in the abdomen help with trunk movement and posture.
Obliques: Located on the sides of the abdomen, these muscles are involved in twisting motions.
Pectorals (Pecs): Located on the chest, they are responsible for pushing movements like pushing or lifting.
Posterior Muscles
Triceps: Located on the back of the upper arm, these muscles extend the forearm.
Trapezius: Found in the upper back and neck, it helps move the head and shoulder blades.
Gluteus Maximus: The largest muscle in the buttocks, responsible for movements like standing up, climbing stairs, and squatting.
Achilles Tendon: The tendon connecting the calf muscle to the heel bone.
Smooth Muscles
Smooth muscles are involuntary and line internal organs like the stomach, intestines, and blood vessels. They help regulate organ movements like peristalsis in the digestive system.
These muscles tire more slowly than skeletal muscles and are controlled by the autonomic nervous system.
Cardiac Muscles
Cardiac muscles are found exclusively in the heart. They contract rhythmically and are involuntary, meaning they work without conscious control.
Cardiac muscles do not tire, which is crucial because the heart must beat continuously throughout life.
Cardiovascular exercise strengthens the cardiac muscles, improving the heart's efficiency.
Skeletal System
The skeletal system serves multiple vital functions, providing both structure and support for the body, protecting internal organs, facilitating movement, storing minerals and energy, and producing blood cells. It is a complex system made up of bones, cartilage, ligaments, tendons, and joints that work together to maintain homeostasis and enable the body to function properly.
Primary Functions of the Skeletal System:
Support: The skeleton forms the framework that supports the body, giving it shape and structure. It supports soft tissues, such as muscles, and holds organs in place.
Movement: The bones act as levers, with muscles attached to them, allowing for movement. Joints between bones enable flexibility and motion.
Protection: The skeletal system protects vital organs, such as the brain, heart, and lungs. For example, the skull protects the brain, and the rib cage shields the heart and lungs.
Mineral Storage: Bones are key storage sites for essential minerals, particularly calcium and phosphorus, which can be released into the bloodstream as needed for various body functions.
Blood Cell Production: Inside bones, particularly in the bone marrow, new blood cells are produced. The red bone marrow creates red blood cells, white blood cells, and platelets, essential for oxygen transport, immune function, and clotting.
Bones
Bone Composition:
Bones are living tissues, meaning they are constantly being remodeled and repaired. They are composed of osteoblasts (bone-forming cells), osteocytes (mature bone cells), and osteoclasts (bone-resorbing cells). These cells work together to maintain bone density and strength.
Bones are also vascularized, meaning they contain blood vessels that nourish the bone tissue and help transport nutrients and oxygen. The central part of bones contains bone marrow, which is crucial for blood cell production.
Bone Development and Ossification:
Bones begin as soft cartilage in the early stages of development. Ossification is the process in which this cartilage is gradually replaced with bone tissue. This process starts early in fetal development and continues into adolescence as the body matures. Ossification hardens bones, making them strong enough to withstand physical stress and pressure, but they remain somewhat flexible due to the presence of collagen fibers.
Bone Shapes
Bones can be classified into several shapes, each of which plays a specific role in the body:
Long Bones: These are longer than they are wide and typically found in the limbs (e.g., femur, tibia, humerus). Long bones support weight and facilitate movement.
Short Bones: These are roughly cube-shaped and provide stability with limited motion. Examples include the carpals (wrist bones) and tarsals (ankle bones).
Flat Bones: These bones are thin and flat and provide protection for internal organs. Examples include the skull, sternum, ribs, and pelvis.
Irregular Bones: These bones do not fit into the other categories and have complex shapes. The vertebrae in the spine and bones of the pelvis are irregular bones, providing both protection and support for various body structures.
Types of Bones
Axial Skeleton: This part of the skeleton forms the central axis of the body and includes the skull, vertebral column, and rib cage.
Skull (Cranium): The cranium is made up of multiple fused bones, which encase and protect the brain.
Vertebral Column (Spine): Composed of 26 vertebrae, the spine provides structural support, flexibility, and houses the spinal cord.
Ribs: The rib cage consists of 12 pairs of ribs that protect the heart, lungs, and other vital organs. The ribs also assist in respiration by expanding and contracting during breathing.
Appendicular Skeleton: This part of the skeleton includes the limbs and the bones that connect them to the axial skeleton.
Upper Limbs: The clavicle (collarbone), scapula (shoulder blade), and bones of the arms (humerus, radius, ulna) and hands (carpals, metacarpals, phalanges) enable flexibility and movement.
Lower Limbs: The femur (thigh bone), tibia (shin bone), fibula, and bones of the feet (tarsals, metatarsals, phalanges) provide support for standing, walking, and running.
Bone Connections
The skeletal system is connected by ligaments, tendons, and cartilage:
Ligaments: These are strong, fibrous tissues that connect bones to other bones. They stabilize joints and prevent excessive movement that could lead to injury. For example, the anterior cruciate ligament (ACL) in the knee connects the femur to the tibia.
Tendons: Tendons are connective tissues that attach muscles to bones. They play a crucial role in movement by transmitting the force generated by muscles to bones, facilitating joint movement. For instance, the Achilles tendon connects the calf muscles to the heel bone.
Cartilage: Cartilage is a flexible, rubbery tissue that covers the ends of bones in joints, providing a cushion and reducing friction. It is also found in the nose, ears, and ribs.
Types of Joints
Joints allow bones to move relative to one another and are classified by the types of movement they permit:
Fixed Joints: These joints do not allow movement. The bones are fused together by dense connective tissue. For example, the sutures in the skull.
Pivot Joints: These joints allow rotational movement. The neck allows the head to rotate, facilitated by the pivot joint between the first and second cervical vertebrae (the atlas and axis).
Gliding Joints: These joints allow bones to glide past each other in a sliding motion. An example is the joints between the bones of the wrist and ankle.
Hinge Joints: These joints allow movement in one direction, similar to a door hinge. Examples include the elbow and knee.
Ball and Socket Joints: These joints allow for the greatest range of movement in all directions. They consist of a rounded ball at the end of one bone that fits into a cup-like socket of another bone. Examples include the shoulder and hip joints.
Saddle Joints: The thumb has a saddle joint, which allows it to move in two directions and provides a wide range of motion for grasping and manipulating objects.
Ellipsoid Joints: These joints allow for a range of motion similar to ball and socket joints but with some limitations. The wrist joint is an example, allowing movement in two planes, such as up/down and side to side.
Bone Marrow and Blood Cell Production
Bone marrow is the spongy tissue found inside some bones, primarily in the femur, sternum, and pelvis. It is the site of hematopoiesis, the production of blood cells, which includes red blood cells (for oxygen transport), white blood cells (for immune defense), and platelets (for clotting). Bone marrow can be classified into two types:
Red Bone Marrow: Actively involved in blood cell production.
Yellow Bone Marrow: Primarily stores fat, which can serve as an energy reserve.
Conclusion
Immune System
The immune system is a sophisticated network of cells, tissues, and organs working together to defend the body against harmful invaders like bacteria, viruses, fungi, and parasites. This system is crucial for maintaining health and preventing diseases by identifying and destroying pathogens, as well as keeping the body safe from internal threats like cancerous cells.
Overview of Immune Defense
The immune system operates through two main mechanisms of defense: nonspecific defenses and specific defenses.
Skin: The skin acts as the first line of defense. Its outer layer is a physical barrier that blocks pathogens from entering the body. Additionally, the skin produces oils and sweat that contain antimicrobial properties, which help neutralize invaders.
White Blood Cells: Once pathogens breach the skin and mucous membranes, white blood cells (leukocytes) are activated. These cells play a key role in fighting infections, including attacking pathogens directly and producing antibodies.
Types of Diseases
Infectious Diseases: These diseases are caused by pathogens (bacteria, viruses, fungi, parasites) that can be transmitted from person to person. Examples include the flu, common cold, and HIV.
Non-Infectious Diseases: These diseases are not caused by pathogens and cannot be spread between individuals. They include genetic conditions, autoimmune disorders, and cancer.
The Immune System in Action
The immune system consists of several components that work in tandem to protect the body. Some of the main parts include:
Lymphatic System: This network includes lymph nodes, lymph vessels, and lymph, a fluid that transports immune cells throughout the body. Lymph nodes filter out harmful substances and contain large numbers of immune cells, including macrophages and lymphocytes (such as T-cells and B-cells).
Spleen: The spleen helps in filtering blood and recycling iron from old red blood cells. It also contains immune cells that help fight infections, acting as a backup for the lymphatic system.
Respiratory System: The respiratory system plays an immune function by trapping pathogens in mucus and expelling them through coughing and sneezing. The cilia (tiny hair-like structures) in the airways help sweep mucus and trapped pathogens out of the lungs.
Nonspecific Defenses
These defenses are the body’s initial responses to invading pathogens and are not targeted to any particular pathogen but instead respond to all types of threats.
Physical Barriers: The skin and mucous membranes form the first physical barriers against pathogens. The mucus in the respiratory and digestive tracts traps pathogens, which are then removed by coughing, sneezing, or swallowing.
Chemical Barriers: Substances like stomach acid, lysozyme in saliva, and oil on the skin help neutralize harmful organisms.
Inflammatory Response: When an infection occurs, the body produces inflammation as a defensive response. This includes increased blood flow to the infected area, causing redness and heat. Inflammation also triggers the release of chemicals like histamine, which attract immune cells such as phagocytes (white blood cells) to the site of infection. These immune cells engulf and destroy the invading pathogens.
Fever: Fever is another nonspecific response, often triggered by infection. It creates a less hospitable environment for pathogens by raising body temperature, which can slow down the replication of some microbes.
Specific Defenses
Once the immune system recognizes an invader, it mounts a more targeted defense through adaptive immunity, which is tailored to specific pathogens.
Antibodies: Specialized proteins produced by B-cells that specifically recognize and bind to pathogens. Once an invader is identified, antibodies neutralize it by binding to it or marking it for destruction by other immune cells.
Antigens: Antigens are molecules found on the surface of pathogens that signal the immune system to initiate a response. Antigens are unique to each pathogen and allow the immune system to specifically target and recognize an invader.
Lymphocytes: These immune cells play a crucial role in recognizing and responding to pathogens:
B-cells produce antibodies after recognizing antigens on the surface of pathogens.
T-cells have specialized functions: Helper T-cells activate other immune cells, while Cytotoxic T-cells directly kill infected cells.
Immunity
Immunity refers to the body’s ability to recognize and defend against pathogens. There are two main types of immunity:
Active Immunity: This occurs when the body is exposed to a pathogen and produces its own antibodies. It can occur through natural exposure (e.g., getting sick) or vaccination.
Humoral Immunity: This is mediated by B-cells that produce antibodies specific to an infection.
Cell-Mediated Immunity: This involves T-cells that destroy infected cells and regulate the immune response.
Passive Immunity: Passive immunity occurs when antibodies are transferred from another source, such as from mother to baby through breast milk or through an injection of antibodies (e.g., from a donor).
Vaccination helps stimulate the immune system to create an immune response without causing the disease, leading to active immunity without the illness.
Immunological Memory
Once the immune system has encountered a specific pathogen, it creates memory cells (both B and T cells) that “remember” how to fight that particular pathogen. If the same pathogen invades the body again, these memory cells enable a much faster and stronger response.
This is why you generally don’t get sick from the same disease twice. However, because pathogens like the flu virus can mutate rapidly, the immune system may not recognize new strains, which is why annual flu shots are recommended.
Homeostasis
Homeostasis refers to the body’s ability to maintain a stable internal environment despite changes in the external environment. The immune system plays a significant role in homeostasis by responding to infections, injuries, and changes in the body.
Positive Feedback Loops: These loops amplify a response. For example, during childbirth, contractions lead to the release of oxytocin, which in turn increases the intensity of contractions, moving the process forward.
Negative Feedback Loops: These loops help return the body to equilibrium. For instance, if body temperature rises, the body sweats to cool down, and if blood pressure is too high, the heart rate adjusts to lower the pressure.
Stimulus and Response
All living organisms respond to stimuli in their environment. A stimulus is any change in the environment that can trigger a response. Organisms detect stimuli using specialized cells called sensory receptors. These receptors are sensitive to physical, chemical, or olfactory (smell-related) stimuli.
Physical Stimuli: These include sensations like touch, temperature, and pressure. The skin has receptors that detect these sensations.
Chemical Stimuli: These stimuli can trigger fight-or-flight responses, such as when the body detects harmful chemicals, such as from an injury or stress.
Neurons and Response: Interneurons relay signals between sensory and motor neurons, processing and deciding how to respond to the stimuli. Motor neurons transmit the response to muscles or glands that act on it.
The body’s response to stimuli is a fundamental aspect of maintaining homeostasis and health, involving both innate reflexes (like withdrawing from pain) and learned responses (such as avoiding certain harmful substances).