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Kaitley Lopez Period 1 Muscular System - Coggle Diagram
Kaitley Lopez Period 1 Muscular System
Major functions of the muscular system
Produce Movement: Powers all external movement like walking and running, as well as internal movement like digesting food and pumping blood
Maintain Posture and Body Position: Works continuously against the pull of gravity to keep your body erect and balanced
Stabilize Joints: Maintains tension on tendons that cross over joints to keep bones properly aligned and supported
Generate Heat: Produces thermal heat as a metabolic byproduct during muscle contraction to maintain standard body temperature
Names of all the skeletal muscles (including the facial muscles)
Anterior / Superior View (Front Upper Body)
Facial & Head Muscles:
Frontalis (Epicranius frontal belly): Raises eyebrows and wrinkles forehead skin
Masseter: Chewing muscle that elevates the mandible
Orbicularis oculi: Ring muscle surrounding the eye that closes the eyelid
Orbicularis oris: Circular muscle around the mouth that closes and pouts lips
Temporalis: Fan-shaped chewing muscle on the temporal bone that elevates the jaw
Zygomaticus: Cheek muscle that raises the corners of the mouth (smiling muscle)
Neck & Trunk:
Sternocleidomastoid: Neck muscle that flexes and rotates the head
Sternohyoid: Neck muscle that depresses the hyoid bone
Pectoralis major: Large chest prime mover for arm flexion and adduction
Serratus anterior: Fan-shaped chest muscle holding the scapula against the rib cage
External obliques: Outer abdominal wall muscle for trunk rotation and compression
Rectus abdominis: Straight vertical abdominal muscle that flexes the lumbar spine
Arms & Shoulders:
Deltoid: Triangular shoulder muscle that acts as prime mover for arm abduction
Bicep brachii: Two-headed anterior arm muscle that flexes the elbow and supinates the forearm
Brachialis: Deep anterior arm muscle that flexes the forearm
Brachioradialis: Lateral forearm muscle assisting in elbow flexion
Tricep brachii: Three-headed posterior upper arm muscle that extends the forearm
Pronator teres: Anterior forearm muscle that pronates the forearm
Flexor carpi radialis: Anterior forearm muscle flexing and abducting the wrist
Flexor carpi ulnaris: Anterior forearm muscle flexing and adducting the wrist
Palmaris longus: Slender anterior forearm muscle that tenses palm fascia
Pelvis & Hips:
Iliopsoas: Composite hip flexor muscle
Pectinus (Pectineus): Anterior hip muscle flexing and adducting the thigh
Tensor fasciae latae: Anterolateral hip muscle stabilizing the knee and flexing the thigh
Trapezius: Large upper back muscle extending to the neck that stabilizes and moves the scapula
Anterior / Inferior View (Front Lower Body)
Thigh & Hip:
Adductor longus: Medial thigh muscle adducting and flexing the thigh
Gracilis: Slender medial thigh muscle adducting the thigh and flexing the leg
Rectus femoris: Anterior thigh muscle (quadriceps) flexing the thigh and extending the knee
Sartorius: Long diagonal strap muscle flexing, abducting, and laterally rotating the thigh
Vastus lateralis: Lateral quadriceps muscle extending the knee
Vastus medialis: Medial quadriceps muscle extending the knee
Iliotibial tract: Lateral connective tissue band stabilizing the hip and knee joint
Leg & Foot:
Fibularis longus: Lateral leg muscle everting the foot and assisting ankle plantar flexion
Extensor digitorum longus: Anterolateral leg muscle extending toes and dorsiflexing the foot
Gastrocnemius: Superficial calf muscle flexing the knee and plantar flexing the foot
Soleus: Deep calf muscle plantar flexing the ankle
Tibialis anterior: Anterior shin muscle dorsiflexing and inverting the foot
Posterior / Superior View (Back Upper Body)
Head, Neck, & Back:
Occipitalis (Epicranius occipital belly): Pulls scalp posteriorly
Sternocleidomastoid: Neck muscle visible posteriorly near insertion
Trapezius: Large diamond-shaped muscle extending the neck and moving the scapula
Infraspinatus: Rotator cuff muscle laterally rotating the shoulder
Latissimus dorsi: Broad lower back prime mover for arm extension and adduction
Rhomboid major: Deep back muscle retracting and stabilizing the scapula
Teres major: Inferior scapular muscle extending and adducting the arm
Shoulder, Arms, & Gluteal:
Deltoid: Posterior fibers assist in arm extension
Tricep brachii: Posterior arm muscle extending the elbow
Brachioradialis: Lateral forearm muscle
Extensor carpi radialis: Posterior forearm muscle extending and abducting the wrist
Extensor carpi ulnaris: Posterior forearm muscle extending and adducting the wrist
Flexor carpi ulnaris: Anteromedial forearm muscle visible posteriorly
Gluteus maximus: Large gluteal prime mover for thigh extension
Gluteus medius: Lateral gluteal muscle abducting and medially rotating the thigh
Posterior / Inferior View (Back Lower Body)
Thigh (Hamstrings & Adductors):
Bicep femoris: Lateral hamstring muscle extending the thigh and flexing the knee
Semitendinosus: Medial hamstring muscle extending the thigh and flexing the knee
Semimembranosus: Deep medial hamstring muscle extending the thigh and flexing the knee
Adductor magnus: Large medial thigh muscle adducting and extending the thigh
Gracilis: Medial thigh muscle
Leg & Calcaneal Tendon:
Gastrocnemius: Calf muscle visible posteriorly
Soleus: Deep calf muscle
Fibularis longus: Lateral leg muscle
Calcaneal (Achilles) tendon: Strong fibrous tendon anchoring gastrocnemius and soleus muscles to the calcaneus heel bone (Note: A tendon, not a muscle)
Neuromuscular junction
Definition:The specialized anatomical junction where a motor neuron's axon terminal meets a single muscle fiber
Anatomical Components:
Axon Terminal: Enlarged end of the nerve containing vesicles filled with the neurotransmitter acetylcholine (ACh)
Synaptic Cleft: Gel-filled microscopic space separating the nerve end from the muscle membrane
Junctional Folds: Deep infoldings of the sarcolemma housing millions of ACh receptors
Sequential Events at the NMJ:
Calcium Influx: Voltage-gated calcium channels open on the neuron terminal, allowing calcium to enter
ACh Release: calcium entry triggers synaptic vesicles to fuse with the membrane and dump ACh into the synaptic cleft via exocytosis
Nerve Impulse:An action potential travels down the motor neuron axon to the axon terminal
ACh Diffusion: ACh diffuses across the cleft and binds to chemically gated ACh receptors on the junctional folds
Ion Flux & EPP: Receptor binding opens ion channels, allowing rapid sodium influx into the cell to create a local depolarization called an End Plate Potential (EPP)
ACh Termination:The enzyme acetylcholinesterase (AChE) rapidly destroys remaining ACh in the cleft to prevent non-stop muscle stimulation
Muscle coverings (connective tissue coverings)
Function: Layers of fibrous connective tissue that reinforce, protect, and support the muscle organ as it pulls on bones
Epimysium: Dense irregular connective tissue wrapped around the entire muscle organ
Perimysium: Fibrous connective tissue wrapped around each fascicle (a discrete bundle of muscle fibers)
Endomysium: Fine, delicate areolar connective tissue wrapped around each individual muscle fiber cell
Disorders associated with the Muscular system
Duchenne Muscular Dystrophy (DMD):
Cause & Mechanism: Sex-linked recessive inherited disease caused by a defective gene for dystrophin
Pathophysiology: Lacking functional dystrophin, the sarcolemma tears easily during contraction, allowing excess calcium to enter and destroy contractile fibers
Myasthenia Gravis:
Cause & Mechanism: Autoimmune condition where self-antibodies attack and destroy ACh receptors at the neuromuscular junction
Symptoms: Causes a shortage of functional ACh receptors, leading to drooping eyelids, difficulty talking/swallowing, and generalized muscle weakness
Rigor Mortis:
Cause & Mechanism: Postmortem muscle stiffening occurring 3–4 hours after death due to a complete lack of ATP production
Pathophysiology: Without ATP, active calcium pumping back into the sarcoplasmic reticulum stops. Calcium stays in the sarcoplasm, keeping cross bridges locked in place until muscle tissue decomposes
Fibromyalgia:
Definition: A chronic disorder characterized by widespread musculoskeletal pain, fatigue, sleep disturbances, and heightened pain sensitivity at specific tender points.
Cause & Mechanism: Thought to involve abnormal central nervous system pain processing (central sensitization), where the brain amplifies pain signals without direct structural damage to the muscle tissue itself.
Myositis:
Definition: Inflammation of skeletal muscle tissue that leads to muscle weakness, swelling, tenderness, and pain.
Cause & Mechanism: Can be caused by autoimmune conditions (where the immune system mistakenly attacks muscle fibers), viral or bacterial infections, severe physical trauma, or side effects from certain medications.
3 types of muscles & their functions
Skeletal Muscle:
Function: Attaches to bones or skin to generate voluntary body movements
Structure: Composed of single, long, cylindrical cells with obvious striations (stripes) and multiple nuclei. Formally referred to as muscle fibers
Cardiac Muscle:
Function: Located exclusively in the heart walls to involuntarily pump blood through the body
Structure: Composed of branching chains of cells with striations and 1–2 nuclei. These cells are not formally called muscle fibers
Smooth Muscle:
Function: Lines the walls of hollow organs (like the stomach, intestines, and blood vessels) to involuntarily squeeze substances through internal pathways
Structure: Composed of single, spindle-shaped cells with one nucleus and no striations. Formally referred to as muscle fibers
Action potential in a muscle fiber
Stage 1: End Plate Potential (EPP): ACh binding at the NMJ opens chemically gated channels, letting sodium rush in to depolarize the local membrane.
Stage 2: Depolarization & Propagation: EPP reaches threshold voltage, opening adjacent voltage-gated sodium channels. A massive influx of sodium generates an all-or-none action potential that propagates along the entire sarcolemma and down T tubules
Resting State:The sarcolemma rests in a polarized state where the interior is negative relative to the outside
Stage 3: Excitation-Contraction Coupling:
Electrical voltage changes at the Triad (one central T tubule flanked by two SR terminal cisterns) trigger the Sarcoplasmic Reticulum (SR) to release stored calcium into the sarcoplasm.
Released calcium binds to troponin, causing troponin to shift tropomyosin off actin's active sites so myosin heads can attach.
The action potential travels deep into the cell interior via T tubules
Stage 4: Repolarization: Voltage-gated sodium channels close and voltage-gated potassium channels open. Rapid potassium efflux restores the resting negative membrane voltage. The sodium-potassium pump subsequently restores original ion balances.
Sarcomere
Definition: The microscopic functional, contractile unit of a muscle cell located inside a myofibril, running from one Z disc to the next
Z Discs (Z Lines): Coin-shaped protein sheets anchoring thin filaments at both ends of a sarcomere
A Band (Dark Band): The dark central region spanning the full length of thick filaments
I Band (Light Band): The light outer region containing thin filaments only, bisected by the Z disc
H Zone: The lighter central gap within the A band containing thick filaments only when relaxed
M Line: A vertical line of proteins in the exact center of the H zone holding thick filaments together
Thick Filaments (Myosin): Protein filaments with flexible tails and two globular heads that bind actin and ATP to form cross bridges
Thin Filaments (Actin & Regulatory Proteins):
Actin: Strands of globular proteins with active sites for myosin attachment
Tropomyosin: Spiral protein band covering myosin-binding sites on actin in a relaxed muscle
Troponin: Three-protein complex binding to actin, tropomyosin, and calcium ions
Elastic Filaments (Titin): Structural spring-like proteins anchoring thick filaments to Z discs, allowing muscle recoil after stretching
Sliding filament theory of muscle contraction
Core Concept:
During contraction, thin actin filaments slide past thick myosin filaments toward the center of the sarcomere, pulling Z discs closer together without any filaments changing their physical length
Structural Banding Changes:
Z Discs: Pulled inward toward the M line, shortening the whole sarcomere
I Bands: Shorten significantly
H Zone: Disappears completely
A Band: Width remains unchanged
The 4 Steps of the Cross Bridge Cycle:
Cross Bridge Formation:Energized myosin head attaches to the exposed active site on actin
Working (Power) Stroke: ADP and inorganic phosphate are released, causing the myosin head to pivot and pull the thin filament toward the M line
Cross Bridge Detachment: A fresh ATP molecule binds to the myosin head, weakening its link and causing it to detach from actin
Cocking of Myosin Head: ATP is hydrolyzed into ADP and Pi by myosin ATPase, re-cocking the head into its high-energy position for the next stroke