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Alanna Garcia P.5 Muscular System - Coggle Diagram
Alanna Garcia P.5 Muscular System
Action potential in a muscle fiber
End plate potential
– ACh released from motor neuron binds to ACh receptors on sarcolemma
– Causes chemically gated ion channels (ligands) on sarcolemma to open
– 𝑁𝑎 + diffuses into muscle fiber
▪ Some 𝐾 + diffuses outward, but not much
– Because 𝑁𝑎 + diffuses in, interior of sarcolemma becomes less negative (more positive)
– Results in local depolarization called end plate potential
Depolarization: generation and propagation of an action potential (AP)
– If end plate potential causes enough change in membrane voltage to reach critical level called threshold, voltage-gated 𝑁𝑎 + channels in membrane will open
– Large influx of 𝑁𝑎 + through channels into cell triggers AP that is unstoppable and will lead to muscle fiber contraction
– AP spreads across sarcolemma from one voltage-gated 𝑁𝑎 + channel to next one in adjacent areas, causing that area to depolarize
Repolarization: restoration of resting conditions
– 𝑁𝑎 + voltage-gated channels close, and voltage-gated 𝐾 + channels open
– 𝐾 + efflux out of cell rapidly brings cell back to initial resting membrane voltage
– Refractory period: muscle fiber cannot be stimulated for a specific amount of time, until repolarization is complete
– Ionic conditions of resting state are restored by 𝑁𝑎 + −𝐾 + pump
▪ 𝑁𝑎 + that came into cell is pumped back out, and 𝐾 + that flowed outside is pumped back into cell
Sarcomere (myofibril feature)
– Smallest contractile unit (functional unit) of muscle fiber
– Contains A band with half of an I band at each end
▪ Consists of area between Z discs
– Individual sarcomeres align end to end along myofibril
• Striations: stripes formed from repeating series of dark and light bands along length of each myofibril
– A bands: dark regions
▪ H zone: lighter region in middle of dark A band
– M line: line of protein (myomesin) that bisects H zone vertically
– I bands: lighter regions
▪ Z disc (line): coin-shaped sheet of proteins on midline of light I band
Actin myofilaments: thin filaments
▪ Extend across I band and partway in A band
▪ Anchored to Z discs
– Myosin myofilaments: thick filaments
▪ Extend length of A band
▪ Connected at M line
– Sarcomere cross section shows hexagonal arrangement of one thick filament surrounded by six thin filaments
Major functions of the muscular system
• Muscles can only pull; never push
• What one muscle group “does,” another “undoes”
• 3 main functional groups:
– Prime mover (agonist)
▪ Major responsibility for producing specific movement
– Antagonist
▪ Opposes or reverses particular movement
– Prime mover and antagonist are located on opposite sides of joint across which they act
– Synergist helps prime movers
▪ Adds extra force to same movement
▪ Reduces undesirable or unnecessary movement
▪ Fixators: type of synergist that immobilizes bone or muscle’s origin rather than enhancing movement of prime movers
– Gives prime mover stable base on which to act
Sliding filament theory of muscle contraction
during contraction, thin filaments slide past thick filaments, causing actin and myosin to overlap more
– Neither thick nor thin filaments change length, just overlap more
• When nervous system stimulates muscle fiber, myosin heads are allowed to bind to actin, forming cross bridges, which cause sliding (contraction) process to begin
• Cross bridge attachments form and break several times, each time pulling thin filaments a little closer toward center of sarcome in a ratcheting action
– Causes shortening of muscle fiber
• Z discs are pulled toward M line
• I bands shorten
• Z discs become closer
• H zones disappear
• A bands move closer to each other
Muscle coverings (connective tissue coverings)
• Each skeletal muscle, as well as each muscle fiber, is covered in connective tissue
• Support cells and reinforce whole muscle
• Sheaths from external to internal:
– Epimysium: dense irregular connective tissue surrounding entire muscle; may blend with fascia
– Perimysium: fibrous connective tissue surrounding fascicles (groups of muscle fibers)
– Endomysium: fine areolar connective tissue surrounding each muscle fiber
Neuromuscular junction
AP(action potential) arrives at axon terminal
after the ap enter the motor neuron then voltage gate open the calcium ions diffuse into motor neuron
Calcium entry causes release of ACh(acetylcholine) neurotransmitter into synpatic cleft
ACh diffuses across to ACh receptors (𝑁𝑎 + chemical gates) on sarcolemma
ACh binding to receptors(ligand-gated cation channel), opens gates, allowing sodium and potassium ions (𝑁𝑎 +) to pass which causes end plate potential (acetylcholine) starting Depolarization the positive and negative change
Ca is a trigger
Acetylcholinesterase degrades ACh allowing the sodium and potassium ions to enter and exit the muscle fiber
after the all the ions reach the membrane potential that reaches the threshold value, ap starts to spread along the sarcolemma myosin head detaches ending the neuromuscular junction then transitions to the start of the cross-bridge cycling
Disorders associated with the Muscular system
Myasthenia Gravis
neuromuscular disorder that blocks neurotransmitters
Cerebral Palsy
spastic paralysis causing muscle weakness
Fibromyalgia
muscle pain
Myositis
inflammation at the muscle
Muscular Dystrophy
muscle weakness and atrpohy
3 types of muscles & their functions
– Skeletal
– Cardiac
– Smooth
4 most important functions:
Produce movement: responsible for all locomotion and manipulation ▪ EX: walking, digesting, pumping blood
Maintain posture and body position
Stabilize joints
Generate heat as they contract
All the skeletal muscle names (including facials)
anterior/superior view:
● Bicep brachii
● Brachialis
● Brachioradialis
● Deltoid
● External obliques
● Flexor carpi radialis
● Flexor carpi ulnaris
● Frontalis (Epicranius frontal belly)
● Iliopsoas
● Masseter
● Orbicularis oris
● Orbicularis oculi
● Palmaris longus
● Pectinus
● Pectoralis major
● Pronator teres
● Rectus abdominis
● Serratus anterior
● Sternocleidomastoid
● Sternohyoid
● Temporalis
● Tensor fasciae latae
● Trapezius
● Tricep brachii
● Zygomaticus
anterior/inferior view:
● Adductor longus
● Fibularis longus
● Extensor digitorum longus
● Gastrocnemius
● Gracilis
● Iliotibial tract
● Rectus femoris
● Sartorius
● Soleus
● Tibialis anterior
● Vastus lateralis
● Vastus medialis
posterior/superior view:
● Brachioradialis
● Deltoid
● Extensor carpi radialis
● Extensor carpi ulnaris
● Flexor carpi ulnaris
● Gluteus maximus
● Gluteus medius
● Infraspinatus
● Latissimus dorsi
● Occipitalis (Epicranius occipital belly)
● Rhomboid major
● Sternocleidomastoid
● Teres major
● Trapezius
● Tricep brachii
posterior/inferior view:
● Bicep femoris
● Adductor magnus
● Gastrocnemius
● Gracilis
● Soleus
● Fibularis longus
● Semitendinosus
● Semimembranosus
● Calcaneal (Achilles) tendon (not a muscle)