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Muscular System Genesis Dominguez period: 3 - Coggle Diagram
Muscular System
Genesis Dominguez
period: 3
Major Functions of the Muscular System
Posture
: Muscles maintain body position and stabilize joints.
Movement
: Muscles work with the skeletal system to move the body and internal organs.
Circulation and Digestion
: Smooth and cardiac muscles help move blood and food through the body.
Heat Production
: Muscle contractions produce heat, helping maintain body temperature.
3 Types of Muscles & Their Functions
Cardiac Muscle
Function
: Pumps blood through the heart.
Appearance
: Striated, branched cells with one nucleus.
Control
: Involuntary (autonomic nervous system).
Smooth Muscle
Function
: Moves substances through hollow organs (stomach, intestines, blood vessels).
Appearance
: Non-striated, single nucleus.
Control
: Involuntary.
Skeletal Muscle
Function
: Voluntary movements (walking, lifting).
Appearance
: Striated (striped) and multinucleated.
Control
: Under conscious control (somatic nervous system).
Sarcomere
Structure
Actin (
thin
filament)
Myosin (
thick
filament)
A band
: Dark area where actin and myosin overlap.
I band:
Light area with only actin.
H zone
: Center area with only myosin.
Function
: Sarcomeres shorten during contraction — the basis of muscle movement.
The sarcomere is the
basic functional unit of a muscle
fiber.It’s the segment between
two Z-lines or Z-discs.
Neuromuscular Junction
Definition
: The NMJ is where a motor neuron connects with a muscle fiber.
Steps at the NMJ:
1
. A nerve impulse (action potential) reaches the end of the motor neuron.
2
. Acetylcholine (ACh), a neurotransmitter, is released into the synaptic cleft.
3
. ACh binds to receptors on the muscle fiber membrane (sarcolemma).
4
. This triggers an action potential in the muscle fiber.
5
. ACh is broken down by acetylcholinesterase, ending stimulation.
Sliding Filament Theory of Muscle Contraction
Steps
1. Action potential
travels down the T-tubule into the muscle fiber.
2. Calcium ions (Ca²⁺)
are released from the sarcoplasmic reticulum.
3.
Calcium binds to
troponin
, causing
tropomyosin
to move and expose binding sites on actin.
4. Myosin heads
attach to actin, forming
cross-bridges
.
5.
Myosin heads
pull actin
toward the center of the sarcomere (power stroke).
6. ATP
binds to myosin, causing it to release actin and reset for another cycle.
7.
When stimulation ends, calcium returns to storage, and the muscle relaxes.
Action Potential in a Muscle Fiber
-A muscle action potential is an electrical signal that triggers contraction.
STEPS
1.
The sarcolemma depolarizes when ACh binds to receptors, allowing Na⁺ ions to enter.
2.
Depolarization spreads through T-tubules.
3.
Calcium ions are released, starting contraction.
4.
After contraction, repolarization occurs, and the muscle returns to resting state.
Muscle Coverings (Connective Tissue Coverings)
Endomysium
: Surrounds each muscle fiber (cell).
Perimysium
: Surrounds bundles of fibers called fascicles.
Epimysium
: Surrounds the entire muscle.
These layers come together to form
tendons
, which attach muscles to bones.
Disorders Associated with the Muscular System
Fibromyalgia
: Chronic pain and tenderness in muscles without clear cause.
Myasthenia Gravis
: Autoimmune disease that blocks ACh receptors, causing muscle fatigue.
Muscular Dystrophy:
A genetic disorder causing progressive muscle weakness.
Cerebral Palsy
: A neuromuscular disorder caused by brain damage that affects muscle control, coordination, and posture.
Myositis
: An inflammation of the muscles that causes weakness, pain, and fatigue.
Skeletal Muscles
Platysma – tenses skin of neck
Sternocleidomastoid – rotates and flexes head
Temporalis – elevates and retracts jaw
Levator labii superioris – elevates upper lip
Masseter – elevates jaw (chewing)
Depressor anguli oris – frown muscle
Buccinator – compresses cheeks
Depressor labii inferioris – lowers bottom lip
Zygomaticus major & minor – smiling
Pectoralis major – adducts and rotates arm
Orbicularis oris – puckers lips
Serratus anterior – protracts scapula
Orbicularis oculi – closes eyelids
Rectus abdominis – flexes spine (“abs”)
External oblique – rotates and flexes trunk
Frontalis – raises eyebrows
Trapezius – elevates, retracts, rotates scapula
Latissimus dorsi – extends, adducts, rotates arm
Deltoid – abducts arm
Biceps brachii – flexes elbow, supinates forearm
Brachialis – flexes elbow
Triceps brachii – extends elbow
Supinator – supinates forearm
Flexor carpi radialis – flexes and abducts wrist
Flexor carpi ulnaris – flexes and adducts wrist
Gluteus maximus – extends and laterally rotates thigh
Hamstrings (Biceps femoris, Semitendinosus, Semimembranosus) – flex knee, extend hip
Gastrocnemius – plantar flexes foot, flexes knee
Soleus – plantar flexes foot
Tibialis anterior – dorsiflexes and inverts foot
Gracilis – adducts thigh, flexes knee
Transversus abdominis – compresses abdomen