Natalia Hernandez P.2
Muscular System

Major Functions

Muscle Coverings: CT sheaths support cells & reinforce whole muscle

Types of Muscles

Name of all the Skeletal Muscles

Disorders associated with the Muscular system

Action potential in a muscle fiber

Neuromuscular Junction (also called motor end plates)

Sliding filament theory of muscle contraction

Sarcomere: smallest contractile unit of muscle fiber

  1. Produce movement: all locomotion & manipulation (ex:walking, digesting, pumping blood)
  1. Maintain posture and body position (ex:upright)
  1. Stabilize joints: muscle tendons stretch over joints & contribute to joint stability
  1. Generate heat as they contract (ex: shivering)

Skeletal muscle

Function: allow for voluntary movement

Location: attached to bones or skin

Description: long & cylindrical, cells have multiple nuclei, there are striations (linear marks); have nerve &
blood supply, connective tissue sheaths, & attachments

Cardiac muscle

Description: tissue branches, have striations, usually one nucleus; interrelated discs (where cells connect)

Function: propels blood into circulation through contraction; involuntary

Location: walls of the heart

Smooth muscle

Description: cells taper at ends (spindle shape), have central nuclei, no striations, close to one another

Function: propels substances or objects (baby) along internal passageway; involuntary

Location: walls of hollow organs

*All muscles have excitability (responsiveness), contractility (ability to shorten), extensibility (ability to be stretched), & elasticity (ability to recoil).

Head & Neck

Upper limbs

Lower Limb

Torso

Frontalis (muscle of forehead)

Temporalis (temporal muscle)

Orbicularis oculi (eyelid muscles)

Zygomaticus

Masseter ( thick, rectangular facial muscle)

Orbicularis oris (muscle around mouth

Occipitalis (muscle arising from occipital bone)

Sternohyoid (flat muscle extending between sternum & hyoid bone)

Sternocleidomastoid (superficial and largest muscle in front neck)

Trapezius (extends from back of neck & shoulders trapezoid-shaped)

Deltoid (muscles in shoulder

Biceps brachii (large anterior muscle in upper arm)

Brachialis (muscle just beneath beneath the biceps brachii muscle)

Triceps brachii (large muscle on dorsal part of upper arm

Brachioradialis (superficial, lateral forearm muscle)

Flexor carpi radialis (superficial forearm msucle responsible for wrist flexion & abduction)

Palmaris longus (between radialis & ulnaris

Flexor carpi ulnaris (adducts and flexes wrist)

Extensor carpi radialis longus (posterior compartment)

Extensor digitorum (muscle of the posterior forearm)

Extensor carpi ulnaris (posterior compartment)

Pectoralis major (large, superficial muscle found in anterior chest wall

Serratus anterior (fan-shaped muscle below armpits)

External oblique

Rectus abdominis (ab muscles)

Trapezius

Infraspinatus (thick triangular muscle located at back of shoulder

Teres major (rectangular muscle attaching to scapula)

Rhomboid major (quadrangular muscle connecting scapula with the vertebrae

Latissimus dorsi ( flat muscle on back)

Gluteus maximus

Gluteus medius

Iliopsoas (muslce connecting spine to lower limbs)

Pectineus (flat quadrangular muscle situated in the upper thigh

Tensor fasciae latae (muscle in lateral portion of upper thigh)

Sartorius (long, superficial muscle running down anterior thigh

Adductor longus (large, fan-shaped muscle located in medial part of thigh.

Gracilis (thin muscle located in medial thigh)

Vastus lateralis (lateral side of the thigh, a quadricep)

Rectus femoris (middle quadricep)

Vastus medialus (medial quadricep)

Iliotibial band (band of tissue that runs down outside of thigh)

Biceps femoris (long muscle in posterior, a hamstring)

Semitendinosus (hamstring)

Semimembranosus (medial hamstring)

Tibialis (long muscle in anterior compartment of leg)

Extensor digitorum longus (lateral muscle in anterior)

Fibularis longus (also lateral)

Gastrocnemius (chief calf muscle)

Soleus (just below knee to the heel)

Calcaneal (Achilles) tendon

A band (dark regions)

1/2 of I band (lighter region)

Z line (sarcomere ends here): coin-shaped sheet of proteins

H zone (lighter region): only thick myosin filament & M line (myomesin)

overall, consists of myosin, thin actin filament & myomesin

Thin actin filament (tropomyosin, troponin, actin)

Titin (elastic filament)

Synaptic cleft: gel-filled space separating axon terminal & muscle fiber

Junctional folds: infoldings of sarcolemma

Axon terminal: end of axon (extensions of motor neurons)

Synaptic vesicles: sac-like structures containing neurotransmitter acetylcholine (ACh)

Mitochondria: cell organelles; powerhouses that generate chem. energy

Acetylcholine (ACh) floating around

contain millions of ACh
receptors

Epimysium: dense irregular CT surrounding entire muscle; may blend w/ fascia

Endomysium: fine areolar CT surrounding each muscle fiber

Perimysium: fibrous CT surrounding fascicles (groups of muscle fibers)

States that during contraction, thin actin filaments
slide past thick myosin filaments, causing actin & myosin to overlap more (in relaxed state, overlap only slighty @ ends)

Contraction: the activation of cross bridges to generate force; shortening occurs when tension generated by cross bridges on thin filaments exceeds forces opposing shortening

Cross bridges form when nervous system stimulates muscle fiber (by sending an impulse) & then myosin heads bind to actin; thin filaments pulled little closer toward center of sarcomere

binding site revealed when calcium attaches to troponin, which causes tropomyosin to move & expose binding site

Muscular Dystrophy: genetic disease that damages muscle fibers; symptoms include muscle atrophy; treatment = no known cure, but surgery is a possibility

Fibromyalgia: pain & tenderness of the muscle, joints, & tissues; can be caused by physical trauma and infection; more common in women; symptoms include depression; treatment: physical therapy

Myasthenia Gravis: autoimmune disease that causes muscle weakness; more common in women; can cause facial paralysis & drooping eyelids; no known cure, thymectomy an option

Cerebral Palsy: injury/abnormality to brain resulting in disconnect between brain & muscle movement; hypoxia a cause; can cause seizures and abnormal gait; no cure but surgical intervention possible

Myositis: inflammation of skeletal muscles caused by an infection; autoimmune; can cause muscle weakness & myalgia; treatment includes antibiotics

Rigor mortis: muscle stiffening after death (3-4 hours after); peak rigidity about 12 hours post.; due to increase of calcium levels b/c ATP no longer synthesized

End plate potention: ACh binds to ACH receptors, causes chem. gated ion channels to open so Na+ diffuses (some K+ too), interior of sarcolemma becomes postive; local depolarization called end plate potential

Depolarization: generation & propagation of action potential; voltage-gated Na+ channels open when end plate potential causes enough change in membrane voltage to reach threshold (30); Na+ triggers AP for contraction, AP depolarizes sarcolemma

Repolarization: restoration of resting conditions; Na+ v-gates close (Na+ pumped back) & K+ v-gates open, efflux of K+ brings cell back to initial resting membrane voltage; restored by 𝑁𝑎+ −𝐾+ pump

Refractory period: muscle fiber cannot be stimulated for a specific amount of time, until repolarization complete