Organelles and Muscles PDF

Organelles Functions of Organelles: Organelles are specialized structures within cells that perform specific functions. For example: o Nucleus: Stores genetic information and coordinates cell activities (growth, metabolism, protein synthesis, etc.). o...

Organelles Functions of Organelles: Organelles are specialized structures within cells that perform specific functions. For example: o Nucleus: Stores genetic information and coordinates cell activities (growth, metabolism, protein synthesis, etc.). o Mitochondria: Generate energy (ATP) through cellular respiration. o Ribosomes: Synthesize proteins. o Endoplasmic Reticulum (ER): Transports proteins and other materials (smooth ER is involved in lipid synthesis, while rough ER is involved in protein synthesis). o Golgi Apparatus: Modifies, sorts, and packages proteins for secretion or delivery to other organelles. o Lysosomes: Break down waste materials and cellular debris. o Peroxisomes: Break down fatty acids and detoxify harmful substances. o Cytoskeleton: Maintains the cell's shape and facilitates movement within the cell. Characteristics of Life An organism is considered alive if it demonstrates the following characteristics: 1. Metabolism: Chemical reactions that occur within the body to maintain life, including catabolic and anabolic processes. 2. Reproduction: The ability to reproduce and pass on genetic material to offspring. 3. Circulation: Movement of substances (e.g., nutrients, gases, waste) throughout the organism. 4. Digestion: Breakdown of food into simpler molecules for absorption. 5. Ingestion: Taking in food and liquids. 6. Absorption: Uptake of nutrients into cells or tissues. 7. Excretion: Removal of waste products from the body. Other Important Concepts Homeostasis: The ability of an organism to maintain a stable internal environment despite external changes. It includes processes such as temperature regulation, pH balance, and blood sugar regulation. Planes of the Body 1. Transverse Plane: Divides the body into upper (superior) and lower (inferior) parts. 2. Sagittal Plane: Divides the body into right and left halves. 3. Frontal (Coronal) Plane: Divides the body into front (anterior) and back (posterior) portions. Muscle Tissue 1. Skeletal Muscle: Voluntary muscle that moves bones and is striated (has a striped appearance). 2. Cardiac Muscle: Involuntary muscle found in the heart, striated but with unique features like intercalated discs. 3. Smooth Muscle: Involuntary muscle found in walls of organs (e.g., intestines, blood vessels), non-striated. Smooth Muscle Properties: Involuntary control, non-striated, spindle-shaped cells. Found in hollow organs like the stomach, intestines, and blood vessels. Responsible for involuntary movements such as peristalsis. Skeletal Muscle Contractions 1. Motor Unit: A motor unit consists of a motor neuron and all the muscle fibers it controls. More fibers recruited = stronger contraction. 2. Types of Contractions: a. Isometric: Muscle contracts but does not change length. b. Isotonic: Muscle changes length during contraction, can be concentric (shortening) or eccentric (lengthening). Motor Unit Definition: A motor unit is the functional unit of muscle contraction, consisting of a single motor neuron and all the muscle fibers it innervates. Neurological and Physiological Components: A motor neuron transmits signals from the central nervous system to muscle fibers. When stimulated, it triggers a contraction. Muscle Movement Important Components: o Myofibril: Long, threadlike structures within muscle fibers containing sarcomeres (the contractile units). o End Plate: The area where the motor neuron connects with the muscle fiber, part of the neuromuscular junction. o Motor Neuron: Transmits signals from the central nervous system to the muscle. o Actin & Myosin: Filaments within the sarcomere responsible for muscle contraction. Myosin binds to actin to produce movement during cross-bridge cycling. o Chemicals: Acetylcholine is released at the neuromuscular junction to stimulate muscle contraction. Calcium ions and ATP are critical for muscle contraction. Agonist vs. Antagonist Muscles Agonist: The muscle that initiates the contraction (prime mover). Antagonist: The muscle that opposes the action of the agonist, helping to stop or control the contraction. Motor Neuron Recruitment Recruitment: As the load (weight) increases, more motor units are recruited to generate more force, allowing muscles to handle heavier loads. Origin vs. Insertion Origin: The fixed point where a muscle attaches to a bone, usually the proximal end. Insertion: The movable point where a muscle attaches to a bone, usually the distal end. Sarcomere Structure and Function: The sarcomere is the smallest functional unit of muscle contraction. It is made up of repeating units of actin and myosin filaments, which interact to shorten the muscle fiber during contraction. Summation Summation: The process by which repeated stimuli (if delivered before the muscle has relaxed) result in a stronger contraction. This can lead to tetanic contraction, where the muscle remains in a constant state of contraction. Layers of Skeletal Muscle 1. Epimysium: Outer layer surrounding the whole muscle. 2. Perimysium: Surrounds individual fascicles (bundles of muscle fibers). 3. Endomysium: Surrounds individual muscle fibers. Periods of a Muscle Twitch 1. Latent Period: Time between the stimulus and the onset of contraction. 2. Contraction Period: Time during which the muscle contracts. 3. Relaxation Period: Time during which the muscle relaxes after contraction. Steps in Muscle Contraction 1. Neural signal (action potential) reaches the muscle. 2. Acetylcholine is released and binds to muscle receptors. 3. Action potential travels along the sarcolemma and into T-tubules. 4. Calcium ions are released from the sarcoplasmic reticulum. 5. Calcium binds to troponin, exposing myosin-binding sites on actin. 6. Cross-bridge forms between myosin and actin. 7. Power stroke occurs, causing muscle contraction. 8. Myosin heads detach and reattach for continued contraction (cross-bridge cycling). 9. Muscle relaxes when the neural signal stops and calcium is pumped back into the Cross-Bridging Steps in Cross-Bridging:  1. Calcium ions bind to troponin, causing tropomyosin to move, exposing binding sites on actin. 2. Myosin heads bind to actin forming cross-bridges. 3. Power stroke: Myosin heads pivot, pulling actin filaments towards the center of the sarcomere. 4. ATP binds to myosin, detaching it from actin. 5. ATP is hydrolyzed to reset myosin. Enzymes in Muscle Contraction Acetylcholinesterase: Breaks down acetylcholine at the neuromuscular junction to stop stimulation. · Myosin ATPase: Hydrolyzes ATP to provide energy for the power stroke. · Creatine Kinase: Regenerates ATP from creatine phosphate during short bursts of intense activity. · Phosphofructokinase (PFK): Catalyzes glycolysis to produce ATP from glucose. · Myokinase: Converts ADP to ATP to maintain energy during intense exercise. · Calcium ATPase (SERCA): Pumps calcium ions back into the sarcoplasmic reticulum for muscle relaxation. · Troponin C: Binds calcium to initiate muscle contraction by exposing the actin-myosin binding sites. Skeleton 1. Skeletal Regeneration: Every 10 years 2. Hematopoiesis: The process of blood cell production, occurring in the red bone marrow, where new blood cells (red blood cells, white blood cells, platelets) are created. ,