MUSCULAR SYSTEM

Contractility

the ability of the muscle to shorten

forcefully,or contract.

Excitability

capacity of the muscle to respond to stimulus.

Extensibility

the muscle can be stretched beyond resting length but still be able to contract.

Elasticity

the ability of the the muscle to recoil to its original resting length after it has been stretched

Skeletal Muscle

(voluntary control)

■ Comprises the great mass of somatic

musculature (10%)

■ It has well-developed cross-striations

■ Cannot contract on their own

■ Its cells are strong and cylindrical with

multiple nuclei

Smooth Muscle

(Visceral) Involuntary muscle

■ lacks cross-striation

■ found in most hollow organs

■ can contract on their own

■ contains a single centrally located

nuclei

Cardiac Muscle

Cardiac (Heart) intermediate

■ It has cross-striations and is

involuntary with cylindrical cells and

branched with only one nucleus

■ Contracts rhythmically even in the

absence of external stimulus

Actin Filament

(THIN -3000)

Light band - isotropic

● I band

● F-actin ( backbone )

Globular (G) actin & ATP

Myosin Filament

(THICK - 1500)

● Dark band

● A band – anisotropic

● Has projections at the sides

called cross-bridges or

myosin heads that link actin

and myosin together during

contraction

Z-line (Z-disc)

a dark zig-zag boundary that marks the start and end of each sarcomere, actin are anchored to these lines.

I-band

lighter region surrounding the Z-line, consists exclusively of actin.

H-band

an area in the exact center of sarcomere, only myosin is present.

M-line

the line at the center of sarcomere to which myosin bind

Titin

anchored between Z-disc and M-line, it provides the muscle with elasticity, maintains alignment

Sarcoplasmic Reticulum

A specialized network of SER that wraps around every myofibril in skeletal muscle.

Longitudinal SR ( T- tubules)

a network of fine tubules that surrounds the contractile filaments of the sarcomere.

Terminal cisternae

an expanded sac-like regions that sit closely alongside T-tubules

Calcium receptors and pumps

regulate calcium movement

Ryanodine receptors

trigger release of calcium

SERCA pumps

actively transport calcium back into SR

myofibril

a rod-like, contractile organelle found within muscle cells (muscle fibers).

Neuromuscular Junction

● A highly specialized chemical synapse bridging motor neurons and skeletal muscle fibers.

● Converts nerve electrical impulses into muscle contractions

Presynaptic terminal

the end of motor neuron axon and loaded with mitochondria and Acetylcholine (Ach)

Synaptic cleft

a narrow fluid-filled gap separating the nerve and muscle membrane and embedded with acetylcholinesterase.

Motor end plate

a deeply folded postsynaptic region of the muscle fiber sarcolemma packed with nicotinic Ach receptors

Action Potential

● A rapid and temporary shift in a cell’s membrane voltage

● The primary electrical signals that cells used to transmit information

-90 mv

resting membrane potential of skeletal muscle

-70 mv

resting membrane potential of neuron

2.0 - 2.2 microns

Length of Sarcomere (Tension) - (highest degree of contraction)

less contraction

Stretch - too much

Strength of Stimulus

directly proportional

Velocity

inversely proportional

Fast Fibers (Type II) White Muscle

Much larger fibers for great strength of contraction.

Examples: eyes, gastrocnemius, arm muscle

Slow Fibers (Type 1) Red Muscle

Smaller fibers

Examples: soleus, back muscles, calf

Isotonic Contraction

● Requires much sliding among

myofibrils (Shortening)

● Contraction lasts longer

● Performs external work

● Has same fusion

● Move limbs in running

(REFLEXES)

Isometric Contraction

● Does not require much sliding

of myofibrils (no shortening)

● Same length

● Contraction shorter in duration

● No work

● Doesn't move load

● Keep limbs stiff when legs hit

the ground in running

(STRETCH)

Muscle Hypertrophy

● total muscle mass enlarges in response to contraction of muscles at maximal levels

● Characterized by hyperplasia, the enlargement and splitting of fibers already present in the muscle

Muscle Atrophy

occurs when muscles are not used

Rigor Mortis

(after death) a state of rigidity caused by the loss of ATP which is required in separation of cross bridges from actin

● muscles remain rigid until the proteins will be destroyed by enzymes released by lysosomes

Familial Periodic Paralysis

recurring, sudden episodes of severe muscle weakness or temporary paralysis Attacks can last for hours to days

Muscle Fibrillation

(Fine irregular contractions)

○ Causes:

■ destruction of nerve supply

■ increased sensitivity to circulating acetylcholine

Acetylcholine

a primary neurotransmitter that enables communication between neurons and muscles.

Muscle fasciculation

involuntary muscle twitches or ripples and are mostly harmless

Triggers: stress, fatigue, high caffeine or alcohol intake, strenuous exercise, low magnesium and potassium.

Muscle Fatigue

● Is a temporary state of reduced work capacity

● It prevents complete exhaustion of ATP reserves

Muscular Dystrophy

male): an inherited disorder that cause progressive weakness and degeneration of of muscle fibers; fibers are replaced by collagen and fatty tissue

Duchenne muscular dystrophy (DMD)

Absence of dystrophin, characterized by muscle weakness that begins in early childhood and rapidly progresses, wheelchair by age 12 and often die before age 30 due to respiratory failure.(X linked).

Becker muscular dystrophy (BMD)

lesser number of dystrophin, a protein that protects muscle fibers from breakdown when exposed to enzymes, but has a later onset and longer survival.

Myasthenia Gravis

●Muscle weakness caused by the inability of the neuromuscular junction to transmit enough signals from the nerve to muscle fibers.

● An autoimmune disease in which patients have

● developed antibodies that block or destroy their own acetylcholine receptors.

● If the disease is intense enough,the patient will die of respiratory failure as a result of severe weakness of respi.muscles.