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Gabriela Samson P:1 Muscular System - Coggle Diagram
Gabriela Samson P:1 Muscular System
Types of muscles & their functions
Smooth, walls of hollow viscera, blood vessels. Movement of viscera, peristalsis, vasoconstriction. Absent single nucleus single nucleus lacks transverse tubules. Involuntary. Contracts and relaxes slowly; single unit type is self exciting; rhythmic.
Cardiac wall of the heart. Pumping action of the heart. Present single nucleus well-developed traverse tubule system; interrelated disc separations adjacent cells. Involuntary. Network of cells contracts as a unit; self-exciting rhythmic.
Skeletal, movement of bones at joint, maintenance of posture. Present many nuclei well-develop transverse tubule system. Voluntary. Contracts and relaxes rapidly when stimulated by a motor neuron.
Sarcomere
In the center of the A band is the H zone which consists of myosin filaments only.
The M line in the center of the H zone, consists of proteins that hold the myosin filaments in place.
A bands (dark bands) are made up of overlapping thick and thin filaments.
Beneath the sarcolemma of a muscle fiber lies a network of membranous channels, called the sarcoplasmic reticulum (SR) which is the endoplasmic reticulum of a muscle cell.
I bands (light bands) are made up of actin filaments, which are anchored to the z lines
The SR is associated with transverse (T) tubules, invaginations of the sarcolemma.
Striations consist of an alternating pattern of light and dark bands.
Each T tubule lies between 2 cistern of the sarcoplasmic reticulum; T tubules are open to the outside of the muscle fiber.
A sarcomere extends from one z line to the next
The sarcoplasmic reticulum and transverse tubules activate the muscle contraction mechanism when the fiber is stimulated.
Myofibrils are made up of many units called sarcomeres, joined end-to-end
Sliding filament theory of muscle contraction
Actin is a globular protein arranged in twisted filaments, containing myosin binding sites.
Troponin and Tropomyosin are 2 proteins associated with the surface of the actin molecules; these 3 proteins form the thin filaments.
A group of myosin molecules forms a thick filament.
According to the sliding filaments model of muscle contraction, during muscle contraction, a myosin attaches to a binding site on the actin filament, forming a cross-bridge.
Myosin consists of two twisted strands, which globular heads projected outward along the strands.
This binding causes the head to bend, pulling on the actin filament, and moving it toward the center of the sarcomere.
The head then releases, and attaches to the next binding site on the actin, pulling this site toward the center.
As this occurs again and again, the filaments increase their overlap, and the sarcomere shortens from both ends.
When many sarcomeres shorten at the same time, the muscle fiber shortens.
Energy from the conversion of ATP to ADP is provided to the cross-bridges by the enzyme ATPase: ATP breakdown causes the causes the heads to return to the "cocked" position, ready to bind to another actin binding site.
Disorders associated with the Muscular system
Myasthenis Gravis- Neuromuscular disorder that blocks neurotransmitters.
Cerebral Palsy- Spastic paralysis causing muscle weakness.
Fibromyalgia- Muscle pain.
Myositis- Inflammation of the muscle.
Muscular Dystrophy- Muscle weakness and atrophy.
Muscle coverings (connective tissue coverings)
The Perimysium extends inward from the epimysium; it surrounds bundles of Skeletal muscle fibers, called fascicles within each muscle.
Each muscle cell (fiber) is covered by connective tissue layer called endomysium.
Fascia blends with the epimysium the layer of connective tissue around each skeletal muscle.
Major functions of the muscular system
Hormones can stimulate or inhibit contraction of smooth muscle, but not skeletal muscle.
Smooth muscle is slower to contract and relax.
Both acetylcholine (Ach) and epinephrine stimulate and inhibit smooth muscle contraction, while only Ach stimulates skeletal muscle.
Smooth muscle maintain a contraction longer with the same amount of ATP.
Differences from skeletal muscle contraction:
Smooth muscle can change length without change in tautness.
Both types are stimulated by membrane impulses, require an increase in calcium ions in the cells, and use ATP energy.
Cardiac muscle is only found in the heart.
Both types involve reaction between actin and myosin.
Cardiac muscle consists of branching, striated cells that interconnect in three-dimensional network.
Similarities to skeletal muscle contraction:
Cardiac muscle is self-exciting (involuntary).
Contain thick and thin filaments, but they are arranged more randomly.
Complex membrane junctions, called intercalated discs join cells and transmit the force of contraction from one cell to the next.
Smooth muscle cells are elongated with tapered ends, lack striations (look "smooth"), and have a relatively underdeveloped sarcoplasmic reticulum.
Neuromuscular junction
The cytoplasm of the distal end of the motor neuron contains numerous mitochondria and synaptic vesicles storing neurotransmitters.
The muscle fiber membrane in this area contains a specialized region called the motor end plate, in which the sarcolemma is tightly folded.
Neuromuscular Junction: A synapse between a motor neuron and a muscle fiber that it regulates.
The motor end plate contains specific receptors for the neurotransmitter.
The neuron communicates with the muscle fiber by way of chemicals called neurotransmitters which are released at the synapse.
When an electrical impulse reaches the end of the axon of a motor neuron, synaptic vesicles release neurotransmitter into the synaptic cleft, the gap between the membranes of the neuron and muscle fiber.
Each skeletal muscle fiber (cell) is functionally (not Physically) connected to the axon of a motor neuron, creating a synapse.
The neurotransmitter diffuse across the cleft, bind to the motor end plate, and stimulate the muscle fiber to contract.
Skeletal muscle fibers contract only when stimulated by a motor neuron.
Action potential in a muscle fiber
Cross-bridges now form, and pull on the actin filaments using the energy of ATP; this cause the sarcomere to shorten.
After the nerve impulse stops, these events lead to relaxation of the muscle.
The contraction continues as long as the nerve impulse continues.
The high concentration of calcium in the sarcoplasm interacts with the troponin and tropomyosin molecules, which move aside exposing the myosin binding sites on the actin filaments.
The enzyme acetylcholinesterase in the motor end plate, rapidly decomposes the acetylcholine.
Upon receipt of the muscle impulse, the sarcoplasmic reticulum releases its stored calcium to the cytosal of the muscle fiber.
Calcium is returned to the sarcoplasmic reticulum, using ATP as an energy source.
Acetylcholine is released into the synaptic cleft in response to an impulse in the motor, it then stimulates the muscular fiber.
ATP now binds to the myosin heads, and the linkages between myosin and actin are broken.
Acetylcholine is produced in the motor neuron and stored in the synaptic vesicles at the distal end of the neuron.
The actin returns to its original position and the muscle relaxes.
Acetylcholine is the neurotransmitter for skeletal muscle fiber contraction at the neuromuscular junctions.
Names of all the skeletal muscles (including the facial muscles)
Example: extension of the arm at the elbow straightens the arm skeletal muscles usually function in groups:
The muscle that causes on action, and does the majority of the work is the agonist ( prime mover).
Extension: Increase in the angle between bones at a joint.
Muscle that assist the prime mover are called synergistic.
Example: flexion of the arm at the elbow bends the arm.
Muscles that oppose an action are called antagonists.
Flexion: Decrease in the angle between bones at a joint
The relationships between muscles depends on the actin; a muscle can be a synergistic for one action and an antagonists for another action.
Common changes in the angle & opposing movement between bones at a joint:
Skeletal muscles are named according to any of these: size, shape, location, action, number of attachments, direction of its fibers, or combinations of the above. Examples:
Action is flexion of the forearm at the elbow.
Pectoralis major: named for size and location; large size, located in chest.
Muscle is located on the anterior surface of humerus.
Deltoid: named for shape, shape like a triangle.
Insertion is the radial tuberosity of the radius.
Extensor Digitorum: named for action; extends digits (fingers, toes).
Both heads attach to portions of the scapula (coracoid process and tubercle above the glenoid cavity).
Biceps Brachii: named for numbers of attachments and location; has 2 origins , heads, and is found in the arm (brachium).
Example: Biceps brachii in the arm. "Biceps" means 2 origin or heads
Sternocleidomosteid: named for attachments; attaches to sternum, clavicle, and mastoid process.
Insertion: The more movable end of a skeletal muscle. Muscle contraction pulls the insertion toward the origin some muscles have more than one insertion or origin.
External oblique: named for location and direction of fibers; located near outside of body, and fibers run at a slant.
Origin: The less movable end of a skeletal muscle