Muscles PDF

8/27/24, 3:48 PM Platform | Study Fetch The Muscular System: Structure and Function (00:00 - 00:12) Introduction to the muscular system (00:12 - 00:24) The muscular system gives the body strength and balance to move aroun...

8/27/24, 3:48 PM Platform | Study Fetch The Muscular System: Structure and Function (00:00 - 00:12) Introduction to the muscular system (00:12 - 00:24) The muscular system gives the body strength and balance to move around and maintain posture Overview of the lesson: Types of muscle and their structure Muscle contraction Twitch contraction and other types (00:24 - 00:37) Muscles and their structure Distinction between tendons and ligaments: Tendons connect muscle to bone Ligaments connect bone to bone Four types of tissue: Connective tissue Epithelial tissue Muscle tissue Nervous tissue (00:37 - 00:49) Three types of muscles: Smooth muscle Cardiac muscle Striated muscle All three types are derivatives of the mesoderm (00:49 - 01:01)Cardiac Muscle: Made of myofibrils and intercalated discs Intercalated discs contain desmosomes and gap junctions Contracts involuntarily but is coordinated (01:01 - 01:16)Schematic of Cardiac Muscle: Intercalated discs with desmosomes and gap junctions Gap junctions allow signals and electricity to travel through the muscle, depolarizing all cells (01:16 - 01:27) Striations are specific to cardiac muscle Cardiac muscle is located between the endocardium and pericardium (01:27 - 02:01)Smooth Muscle: Found in the walls of hollow organs (stomach, intestines, bladder, uterus, arteries, veins, respiratory tract, reproductive tract) Located throughout the body, commonly in hollow tubes Under involuntary control, primarily https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 1/6 8/27/24, 3:48 PM Platform | Study Fetch (02:01 - 02:25)Striated Muscle: Not covered in this section, will be discussed later The Autonomic Nervous System and Smooth Muscle (00:02:41 - 00:02:55) The autonomic nervous system controls blood flow and airflow by constricting or opening up the arteries and capillaries in the lungs. Smooth muscle is very important for this function, as well as for peristalsis (the movement of food through the GI tract). The autonomic nervous system modulates the activity of smooth muscle. (00:02:55 - 00:03:06) Smooth muscle is called "smooth" because it does not have the intense striations that are seen in other muscle types. Smooth muscle is found in many areas of the body that are controlled by the autonomic nervous system. (00:03:06 - 00:03:18) Mnemonic for Smooth Muscle: Smooth muscle is smooth in appearance under a microscope. (00:03:18 - 00:03:31) Skeletal Muscle Tissue: Skeletal muscle is voluntary, meaning it can be contracted at will. Skeletal muscle is striated in appearance. Skeletal muscle cells have multiple nuclei per cell. (00:03:31 - 00:03:42) Skeletal muscle cells have multiple nuclei because they need to synthesize so many proteins to make up the muscle fiber. (00:03:42 - 00:03:54) The structure of skeletal muscle includes: Sarcolemma (cell membrane) Nucleus Myofibrils (00:03:54 - 00:04:12) Within the skeletal muscle cell: Sarcolemma is the cell membrane T-tubules conduct signals Sarcoplasmic reticulum stores calcium Mitochondria provide energy https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 2/6 8/27/24, 3:48 PM Platform | Study Fetch (00:04:12 - 00:04:25) Muscle Contraction: The sarcomere is the functional unit of a myofibril that allows muscle contraction. The sarcomere structure can be seen using electron microscopy. (00:04:25 - 00:04:37) Electron micrographs of the sarcomere structure may be shown on exams, so it's important to be able to identify this structure. (00:04:37 - 00:04:49) The sarcomere structure is made up of individual units that can be seen on electron microscopy. Skeletal Muscle Structure and Function Structure Description Sarcolemma Cell membrane of the muscle fiber Nucleus Multiple nuclei per muscle fiber Myofibrils Contain the contractile proteins T-tubules Conduct signals for contraction Sarcoplasmic Reticulum Stores calcium for contraction Mitochondria Provide energy for contraction Key Points: Smooth muscle is controlled by the autonomic nervous system and is important for functions like blood flow and peristalsis. Skeletal muscle is voluntary and striated, with multiple nuclei per cell to support the high protein synthesis needs. The sarcomere is the functional unit of skeletal muscle contraction, and its structure can be seen using electron microscopy. The Sarcomere and Muscle Contraction (00:04:49 - 00:05:02) The Z line is the end of the sarcomere, with Z representing the end of the alphabet. The M line is the midpoint of the sarcomere, with M representing "mid". The H zone is the part of the sarcomere. (00:05:02 - 00:05:15) The H zone has only thick myosin filaments, as H is a thick letter. The I zone is the part of the sarcomere where there are only thin actin filaments, as I is a thin letter. (00:05:15 - 00:05:28) https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 3/6 8/27/24, 3:48 PM Platform | Study Fetch The A band is the area where actin and myosin overlap. (00:05:28 - 00:05:40) The A band is the area where actin and myosin overlap. (00:05:40 - 00:05:58) Acetylcholine is released from the nerves innervating the muscle, opening ligand-gated sodium channels. Sodium flow into the muscle fiber causes depolarization and an action potential. (00:05:58 - 00:06:09) The neuromuscular junction is where the signal from the nerve attaches to the muscle. (00:06:09 - 00:06:34) The sarcoplasmic reticulum stores calcium ions. Depolarization travels down the T-tubules and opens voltage-gated calcium channels, releasing calcium ions into the sarcoplasm. (00:06:34 - 00:06:48) The release of calcium ions into the sarcoplasm causes depolarization and contraction of the muscle fiber. In rigor mortis, the lack of ATP prevents actin and myosin from dissociating, keeping the muscles in a contracted state. Muscle Contraction and the Cocking Mechanism (00:07:04 - 00:07:19) The myosin heads on the myosin muscle fibers are going to bind ATP and undergo hydrolysis to release energy, allowing the heads to cock back and bind actin tightly. Troponin Binding Sites (00:07:19 - 00:07:31) The A site is where troponin binds and exerts its action. The C site is where troponin binds calcium. The T site is where troponin binds tropomyosin. Myosin Binding and Troponin/Tropomyosin Complex (00:07:31 - 00:07:50) The myosin bound to ADP is going to be locked in the tram, and troponin and tropomyosin are going to work together to block the myosin binding site. Calcium Binding and Muscle Contraction https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 4/6 8/27/24, 3:48 PM Platform | Study Fetch (00:07:50 - 00:08:12) The troponin and tropomyosin complex is currently unbound, blocking access from the myosin head to the actin filament. Once the calcium ion is bound to the troponin, the troponin and tropomyosin complex is going to move, allowing the cocked myosin to lock onto the actin filament. Motor Units and Twitch Contraction (00:08:12 - 00:09:13) Muscles are made up of motor units, which are a motor neuron that innervates a few muscle fibers. A single neuron will activate a muscle unit, which is the unit of muscle cells activated by that specific neuron. The size of the motor unit dictates whether the movement will be fine (small motor units) or powerful (large motor units). There are three phases of twitch contraction, which occurs when a single action potential stimulates a muscle. Table: Comparison of Motor Unit Size and Movement Type Motor Unit Size Movement Type Small Fine movement Large Powerful movement "If you say your whole hamstring is firing, that's a larger motor and it's gonna be powerful. Whereas there's small individual muscles in your hands, which are gonna be for fine movement, motor skills, those are going to be still innervated by a single neuron." Muscle Contraction and Types (00:09:13 - 00:09:24) Motor units are all-or-none, meaning a single nerve innervates a motor unit, and the entire motor unit will fire all at once. (00:09:24 - 00:09:41) Summation of multiple motor units can produce differences in movement, strength, and power, but this is dependent on how many motor units are activated, not on varying activation of a single motor unit. (00:09:41 - 00:10:12) Wave Summation: The effect of successive stimuli to create a stronger muscle contraction. Increased stimulation of a motor unit by the nerve will lead to a stronger and stronger contraction until it is maximally stimulated. Certain toxins can cause a muscle to fire maximally and become completely locked up. (00:10:12 - 00:10:36) https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 5/6 8/27/24, 3:48 PM Platform | Study Fetch Types of Muscle Contractions: Isotonic Contraction: Muscle length changes, with constant tension. Concentric: Muscle shortens. Eccentric: Muscle lengthens. Isometric Contraction: Muscle length does not change. (00:10:36 - 00:10:49) Concentric Contraction: Muscle shortens, like a bicep curl. Eccentric Contraction: Muscle lengthens, like slowly lowering a weight. Isometric Contraction: Muscle length remains the same, no movement, but the muscle holds a position. (00:11:21 - 00:11:36) Mnemonic for Isotonic vs. Isometric: Isotonic: Same tension, muscle length changes. Isometric: Same muscle length, no change. https://www.studyfetch.com/platform/studyset/66cd116dd279f5220d947c66/material/66ce2cbbf069b6d6b89c5eb1/document?go=note 6/6