Muscle Anatomy (PDF)

Chapter 11: Muscles 1. Universal Characteristics of Muscle Tissue: ○ Excitability: Muscles can react to signals from the brain or nerves. It’s like when you touch something hot, your muscles move without you thinking about it. ○ Contractility: Muscles can shorten and t...

Chapter 11: Muscles 1. Universal Characteristics of Muscle Tissue: ○ Excitability: Muscles can react to signals from the brain or nerves. It’s like when you touch something hot, your muscles move without you thinking about it. ○ Contractility: Muscles can shorten and tighten. This helps you lift, move, and do all kinds of physical activities. ○ Extensibility: Muscles can stretch or lengthen when needed. For example, when you straighten your arm after bending it. ○ Elasticity: After muscles contract or stretch, they go back to their original length. Think of a rubber band that stretches and then snaps back. 2. What is a Muscle Fiber? ○ A muscle fiber is just a muscle cell. These are long, skinny cells that can contract (get shorter). They are bundled together to form a muscle. 3. What is Endomysium, Perimysium, Epimysium and Where Are They? ○ Endomysium: A thin, delicate layer that surrounds each individual muscle fiber (cell). ○ Perimysium: A thicker layer that wraps around groups of muscle fibers (called fascicles). ○ Epimysium: The outermost layer that covers the entire muscle, like a skin around a whole muscle. 4. Structure of Muscle Fiber (Fig. 11.2): ○ The sarcolemma is the outer membrane (like the skin) of a muscle cell. ○ Inside, there are myofibrils, which are long, thread-like structures that do the actual muscle contraction. ○ The sarcoplasmic reticulum is like a storage room for calcium ions, which are important for muscle contractions. ○ Mitochondria give the muscle energy by breaking down food into ATP (fuel for the muscles). 5. Myofilaments: ○ Thick Filaments: Made of myosin (like tiny ropes). These grab onto thin filaments to make muscles move. ○ Thin Filaments: Made of actin (the ropes the myosin grabs). They also have troponin and tropomyosin to help regulate muscle contractions. 6. Motor Unit: ○ A motor unit is made up of one motor neuron (the nerve cell that tells muscles to move) and all the muscle fibers it connects to. It’s like a boss (neuron) and its workers (muscle fibers). 7. Neuromuscular Junction (NMJ): ○ This is where the nerve meets the muscle. It’s the special connection where a neuron tells a muscle fiber to contract.  ○ It uses acetylcholine (a special chemical) to send the signal across a gap called the synaptic cleft. The message reaches a special part of the muscle fiber called the motor end plate. 8. Four Stages of Muscle Contraction: ○ Excitation: A nerve sends an electrical signal to the muscle. This releases acetylcholine at the NMJ, which travels into the muscle. ○ Excitation-Contraction Coupling: The signal causes calcium ions to be released inside the muscle. These ions help the muscle contract. ○ Contraction: The calcium helps the myosin (thick filaments) pull on the actin (thin filaments). This makes the muscle shorten or contract. ○ Relaxation: Once the signal stops, the calcium goes away, and the muscle goes back to its original length. 9. Resting Membrane Potential: ○ The resting membrane potential of a muscle cell is about -90 mV. This means the inside of the muscle cell is negative compared to the outside, like a battery waiting to be used. 10. Toxins (Tetanus, Botulism): ○ Tetanus (lockjaw): Causes muscles to stay contracted (tight) all the time. This happens because the body doesn’t stop sending the contraction signal. ○ Botulism: Prevents the release of acetylcholine, so muscles can't contract properly. This makes muscles weak or unable to move (flaccid paralysis). 11. Spastic vs. Flaccid Paralysis: ○ Spastic paralysis: Muscles are tight and can’t relax, like they are stuck in contraction. ○ Flaccid paralysis: Muscles are weak and can’t contract properly, like they are floppy. 12. Length-Tension Relationship: ○ Muscles generate the most force when they are at a middle length—not too stretched, not too scrunched. If they are too stretched or too tight, they don’t work as well. 13. Myogram: ○ A myogram is a graph that shows how a muscle contracts over time. It shows things like: Threshold: The smallest signal needed to make a muscle contract. Latent period: The short time between when the muscle is first signaled and when it starts to contract. Twitch: A single contraction of the muscle. 14. Recruitment: ○ Recruitment is when your body needs more muscle fibers to help lift something heavy. So, it activates more motor units to make the muscle stronger. 15. Isotonic vs. Isometric: ○ Isotonic contractions: The muscle changes length. For example, when you lift a weight, the muscle shortens and then lengthens.  ○ Isometric contractions: The muscle stays the same length. For example, when you push against a wall, the muscle doesn't get shorter, but it is still working. Chapter 12: Nervous System 1. CNS (Central Nervous System): ○ The brain and spinal cord. It’s like the command center of your body where all the big decisions happen. 2. PNS (Peripheral Nervous System): ○ All the nerves that go from the spinal cord to the rest of your body. It’s like the body’s delivery system for messages. 3. Ganglion: ○ A ganglion is like a little “meeting spot” for nerve cell bodies, found outside the brain and spinal cord. 4. Sensory and Motor Divisions: ○ Sensory (Afferent): Nerves that send messages from your senses (like touch or heat) to your brain. ○ Motor (Efferent): Nerves that send instructions from the brain to muscles and glands (telling you to move). 5. Autonomic Nervous System: ○ This part of the nervous system controls things you don’t have to think about, like your heart beating, digestion, and breathing. It’s automatic! 6. Receptor: ○ A receptor is a sensor in your body that detects things like touch, temperature, or light. It helps your brain know what’s happening in the world. 7. Neuroglia (Support Cells): ○ These are helper cells that support and protect neurons (nerve cells). They don’t send signals, but they help neurons stay healthy. 8. Resting Membrane Potential: ○ The resting membrane potential of a neuron (nerve cell) is about -70 mV. It’s like a battery waiting to be used. The neuron is ready to send a message when needed. 9. EPSP and IPSP: ○ EPSP (Excitatory Post-Synaptic Potential): This is when a signal makes the neuron more likely to send a message. It's like telling the neuron to get ready to act. ○ IPSP (Inhibitory Post-Synaptic Potential): This is when a signal makes the neuron less likely to send a message, like telling the neuron to calm down. 10. Action Potential: Step 1: Resting state (-70 mV). Step 2: Depolarization (signal comes in, sodium ions rush in, the cell becomes positive). Step 3: Repolarization (potassium ions go out, the cell goes back to negative).  Step 4: Hyperpolarization (the cell becomes even more negative before going back to normal). 11. Neurotransmitters: ○ These are chemicals that help neurons talk to each other. Some types are acetylcholine, dopamine, and serotonin. ○ Adrenergic synapse uses norepinephrine (to speed things up). ○ Cholinergic synapse uses acetylcholine (for normal activity). ○ GABA-ergic synapse uses GABA (to calm things down). Chapter 13: Spinal Cord & Reflexes Spinal Cord: It’s like the highway that sends messages between your brain and the rest of your body. Meninges: Three protective layers around the brain and spinal cord. Dura Mater: The tough outer layer. Arachnoid Mater: The middle, web-like layer. Pia Mater: The soft layer next to the brain and spinal cord. Tracts: Bundles of nerve fibers that carry messages up (to the brain) or down (to muscles). Reflexes: When your body automatically reacts to something without thinking, like when your knee kicks after the doctor taps it. Muscle Spindle: A sensor inside your muscles that helps your brain know if the muscle is stretching. Plexuses: Nerves that come together in groups to send messages to different parts of your body.