Muscular System

Muscular System

responsible for all the types of human body movement

Skeletal
Smooth
Cardiac

THREE BASIC MUSCLE TYPES

Skeletal Muscle

striated and voluntary

Endomysium
Perimysium
Epimysium
Fascia

connective tissues that surround the skeletal muscle

Endomysium

encloses a single muscle fiber

Perimysium

wraps around a fascicle (bundle) of muscle fibers

Epimysium

covers the entire skeletal muscle

Fascia

on the outside of the epimysium

Tendons

cordlike structures; attach muscle to bone

Aponeuroses

sheet-like structure

Smooth Muscle

no striations; involuntary muscle; found mainly in the walls of hollow visceral organs

Cardiac Muscle

striation; involuntary; found only in the walls of the heart; uninucleate

Intercalated discs

branching cells joined by gap junctions

Sarcolemma

specialized plasma membrane

Myofibrils

long organelles inside muscle cell

I band and A band

banding pattern of myofibrils

I band

light band; composed of thin filaments

A band

dark band; contains the entire length of the thick filaments

Sarcomere

contractile unit of a muscle fiber

Thick filaments (myosin)

- composed of the protein myosin
- contain ATPase enzymes to split ATP to release energy for muscle contractions

Thin filaments (actin)

- composed of the contractile protein actin
- actin is anchored to the Z disc

H zone

zone that lacks actin filaments

Sarcoplasmic reticulum (SR)

specialized smooth endoplasmic reticulum, which stores and releases Ca+

Irritability (responsiveness)

ability to receive and respond to a stimulus

Contractility

ability to forcibly shorten when an adequate stimulus is received

Extensibility

ability of muscle cells to be stretched

Elasticity

ability to recoil and resume resting length after stretching

Motor unit

one motor neuron and all the skeletal muscle cells stimulated by that neuron

Neuromuscular junction

association site of axon terminal of the motor neuron and sarcolemma of a muscle

Neurotransmitter

chemical released by nerve upon arrival of nerve impulse tin the axon terminal

Synaptic cleft

gap between nerve and muscle filled with interstitial fluid

Graded responses

different degrees of skeletal muscle shortening

Muscle twitch

single, brief, jerky contraction

Summing of Contractions

- in most types of muscle activity, nerve impulses are delivered at a rapid rate
- as a result, contractions are "summed" (added) together, and one contraction is immediately followed by another

Unfused (incomplete) tetanus

when stimulations become more frequent, muscle contractions get stronger and smoother

Fused (complete) tetanus

achieved when the muscle is stimulated so rapidly that no evidence of relaxation is seen

Muscle response to stronger stimuli

- muscle force depends upon the number of fibers stimulated
- contraction of more fibers results in greater muscle tension
- when all motor units are active and stimulated, the muscle contraction is as strong as it can get

ATP (Adenosine Triphosphate)

the only energy source that can be used to directly power muscle contraction

Direct phosphorylation of ADP by creatine phosphate (CP)
Aerobic pathway/respiration
Anaerobic glycolysis and lactic acid formation

3 Pathways to Regenerate ATP

Ion imbalances (Ca2+, K+)
Oxygen deficit and lactic acid accumulation
Decrease in energy (ATP) supply

Factors that contribute to muscle fatigue include

Isotonic contractions

- myofilaments are able to slide past each other during contractions
- muscle shortens and movement occurs

Isometric contractions

- muscle filaments are trying to slide, but the muscle is pitted against an immovable object
- tension increases, but muscles do not shorten

Muscle Tone

state of partial contraction

Flexion

- decreases the angle of the joint
- brings two bones closer together
- typical of bending hinge joint

Extension

- increases angle between two bones
- typical of straightening the elbow or knee

Hyperextension

extension beyond 180 degrees

Rotation

- movement of a bone around its longitudinal axis
- common in ball and socket joints

Abduction

movement of a limb away from the midline of the body

Adduction

movement of the limb toward the midline

Circumduction

combination of flexion, extension, abduction, and adduction

Dorsiflexion

lifting the foot so that the superior surface approaches the shin (toward the dorsum)

Plantar flexion

pointing the toes away from the head

Inversion

turning the sole of the foot medially

Eversion

turning the sole of the foot laterally

Supination

movement that turns the palm up

Pronation

turning the palm downward

Opposition

movement of the thumb to touch the fingertips

Prime mover

muscle with the major responsibility for a certain movement

Antagonist

muscle that opposes or reverses a prime mover

Synergist

muscle that aids a prime mover in a movement or reduces undesirable movements

Fixator

specialized synergists that hold a bone still or stabilize the origin of a prime mover

Frontalis

raises eyebrows, wrinkles forehead

Orbicularis Oculi

Closes eyelids; used in blinking, winking, and squinting

Orbicularis Oris

kissing muscle

Buccinator

compresses the cheek to hold food

Zygomaticus

smiling muscle

Masseter

elevates mandible

Temporalis

acts as a synergist of the masseter in closing the jaw

Platysma

producing a downward sag of the mouth (the "sad clown" face)

Sternocleidomastoid

flexes neck; rotates head

Pectoralis Major

adducts and flexes humerus

Intercostal Muscles

depress the rib cage, helping to move air out of the lungs when you exhale forcibly

Rectus abdominis

flexes vertebral column

External oblique

flexes and rotates vertebral column

Internal oblique

flexes and rotates vertebral column

Transversus abdominis

compresses abdominal contents

Trapezius

elevates, depresses, retracts, and rotates the scapula

Latissimus Dorsi

extends and adducts the humerus

Erector Spinae

prime mover of back extension

Quadratus Lumborum

flexes the spine laterally

Deltoid

prime movers of arm abduction

Biceps Brachii

flexes elbow and supinates forearm

Brachialis

elbow flexion

Brachioradialis

a fairly weak muscle that arises on the humerus and inserts into the distal forearm

Triceps Brachii

it is the antagonist of the biceps brachii and brachialis

Gluteus Maximus

extends hip

Gluteus Medius

abducts thigh

Iliopsoas

acts to keep the upper body from falling backward when we are standing erect

Adductor Muscles

adduct or press thighs together

Hamstring Group

biceps femoris, semitendinosus, semimembranosus

Sartorius

most superficial muscle of the thigh

Quadriceps Group

rectus femoris, vastus lateralis, vastus medialis, vastus intermedius

Tibialis Anterior

acts to dorsiflex and invert the foot

Extensor Digitorum Longus

prime mover of toe extension

Fibularis Muscles

flexes and everts the foot, which is antagonistic to the tibialis anterior

Gastrocnemius

a prime mover for plantar flexion of the foot; for this reason it is often called the "toe dancer's" muscle

Soleus

a strong plantar flexor of the foot

Muscular Dystrophy

- weakening of the musculoskeletal system and hampers locomotion - defect in muscle proteins, death of muscle cells and tissues

Duchenne Muscle Dystrophy

- decreased gene dystrophin, prominent phenotype
- affects both male and female patients

Myotonic Muscle Dystrophy

- delayed relaxation of muscles
- followed by muscle wasting and weakness
- muscles affected are skeletal, cardiac, and internal organs esp. the GI tract