Muscle Overview

Three types of muscle tissue are skeletal, cardiac and smooth

Muscle contraction depends on two types of myofilaments – actin and Myocin

TYPES OF MUSCLELOCATION MICROSCOPIC

APPEARANCERELATIONSHIP

WITH THE NERVOUS SYSTEM

NEUCLEUS GENERAL FUNCTION

SKELETAL STRIATED VOLUNTARY MULTIPLE PRODUCE MOVEMENT

SMOOTH NONSTRIATED INVOLUNTARY SINGLE MOVEMENT OF FOOD AND URINE

CARDIAC STRIATED INVOLUNTARY SINGLE PUMPING BLOOD TO THE BODY

SKELETAL MUSCLE ORGAN

A WHOLE MUSCLE

CONSISTS OF A LARGE

NUMBER OF MUSCLE

FIBERS (CELLS) , PLUS

CONNECTIVE

TISSUE WRAPPINGS,

BLOOD VESSELS,

AND NERVE FIBERS.

SKELETAL MUSCLE ORGAN

THE OUTERMOST LAYER,

WHICH ENCIRCLES THE

WHOLE MUSCLE ORGAN,

IS THE EPIMYSIUM.

IT IS COMPOSED OF

CONNTECTIVE TISSUE.

SKELETAL MUSCLE ORGAN

THE NEXT LAYER IS

THE PERIMYSIUM.

IT SURROUNDS

GROUPS OF 10 TO

200 MUSCLE FIBERS,

SEPARATING THEM

INTO BUNDLES

CALLED FASCICLES.

SKELETAL MUSCLE ORGAN

THE DEEPEST LAYER

IS THE ENDOMYSIUM.

IT SURROUNDS EACH

MUSCLE FIBER

SEPARATING ONE

FROM ANOTHER. IT IS

COMPOSED OF LOOSE

CONNECTIVE TISSUE.

SKELETAL MUSCLE ANATOMY

A MUSCLE FIBER OR CELL IS

ELONGATED, MULTINUCLEATED,

AND IS STRIATED.

Parts of a Muscle

SKELETAL MUSCLE ANATOMY

SKELETAL MUSCLE CELL ANATOMY

Internal structure of skeletal muscle cell Nucleus: Contain the genetic material of the cell Sarcolemma: Plasma membrane of muscle cell Sarcoplasmic Reticulum: The endoplasmic reticulum of the

muscle cell T Tubule: Invagination of the Sarcolemma project deep into

Muscle cells interior Terminal cisternae: Serve as specialized reservoirs for Ca

ions Triad: Consist of one T-Tubule laying between two terminal

cisternae Mitochondria: The site of ATP synthesis Myofibril: Bundle of contractile filaments

Myofibrils Structure Myofibrils -cylindrical structures within muscle fiber

Are bundles of protein filaments Two types of myofilaments

1. Actin filaments (thin filaments)2. Myosin filaments (thick filaments)

At each end of the fiber, myofibrils are anchored to the inner surface of the sarcolemma

When myofibril shortens, muscle shortens (contracts)

Myofibrils Structure

MYOFIBRILS ACCOUNT

FOR ABOUT

80% OF THE CELLULAR

VOLUME OF

A SKELETAL MUSCLE

FIBER. THEY ARE THE

CONTRACTILE ORGANELLE

OF SKELETAL MUSCLE FIBERS.

Myofibrils Structure

WITHIN THE MYOFIBRIL,

ARE THICK AND THIN

MYOFILAMENTS.

THESE MYOLFILAMENTS

ARE ARRANGED IN A

REGULAR PATTERN, A

SARCOMERE,WHICH

PRODUCES A REPEATING

SERIES OF DARK AND LIGHT BANDS.

The Thick Filament (Myosin)

Consists of the protein called myosin.

A myosin molecule is shaped a bit like a golf club, but with 2 heads.

The heads stick out to form the cross bridge

Many of these myosin molecules stick together to form a thick filament

Each head contains two binding sites, one for actin and one for ATP.

one m yosin m olecule

m yosin heads(cross bridges)

m yosin tails

Thin Filament (Actin) The thin filament consists of a protein called actin. It

compose of actin subunit twisted into double helical chain. Actin has specific binding site to which the myosin head binds

The thin filament also contains tropomyosin. The position of tropomyosin cover the binding sites on the actin during unstimulated muscle

The third component is troponin. Attached along the tropomyosin strand. Which expose the binding site of actin to myosin

actin monom ers tropomyosin

Arrangement of Myofilament The arrangement of thick and thin myofilaments forms light and dark

alternating bands (striation). A band: Dark region, correspond to the length of thick filament I band: light region, only thin filaments, correspond to distance between

adjacent thick filaments In the middle of the light band is the Z-line: Protein disc anchor the thin

filaments The repeating unit from one Z-line to the next is called the sarcomere H zone: Light stripe in the center of the dark (A) band, region between thin

filaments M line: Line in the center of H zone, Protein connect myosin filaments Sarcomere: Contractile unit, extends from one Z line to the next, include the

entire A band and half I band on each side of A band

MYOSIN

ACTIN, TROPOMYSOIN, TROPONIN

SARCOMERE

MOTOR UNIT

A MOTOR UNIT IS A MOTOR NEURON AND ALL OF THE MUSCULE CELLS IT INNERVATES.

THE NUMBER OF MUSCLE FIBERS PER MOTOR UNIT MAY BE AS HIGH AS SEVERAL HUNDRED OR A FEW AS FOUR.

MOTOR UNIT

STIMULATION OF A

SINGLE MOTOR UNIT CAUSES A WEAK

CONTRACTION OF THE

ENTIRE MUSCLE, OR A NUMBER OF MOTOR UNITS MAY CAUSE A STRONG

CONTRACTION OF THE ENTIRE MUSCLE.

NEUROMUSCULAR JUNCTION

CONSISTS OF:

1. THE AXON TERMINAL: The distal end of an axon, contains neurotransmitter substance within synaptic vesicles

2. SYNAPTIC CLEFT: The space between the axon terminal and the folded region of the muscle cell membrane

3. THE MOTOR END PLATE: The folded portion of the sarcolemma

NEUROMUSCULAR JUNCTION

NEUROMUSCULAR JUNCTION

Excitation contraction coupling

Transmission of action potential along transverse tubules (T tubules)

T tubules action potentials caused release of Ca ions inside the muscle fiber.

Ca ions caused contraction Overall process called Excitation

Contraction Coupling

Axon Terminal

Opening of Voltage gated Calcium channels

Entry of Calcium ions from Extracellular fluid

Opening of vesicles & release of Ach

Synaptic cleft

Binding of Ach with Receptor and formation of Ach-Receptor complex

Opening of the ligand gated sodium channels

& entry of sodium ions from ECF

Development of end plate potential

Passage of Ach

Postsynaptic membrane

Muscle Fiber

Generation of Action Potential

Excitation contracting coupling

Muscular contraction

Neuromuscular transmission

The function of neuromuscular junction is to transmit the impulses from the nerve to the muscle.

When the impulses are transmitted from nerve to the muscle, a series of events occur in the neuromuscular junction:

1. Release of acetylcholine 2. Action of acetylcholine 3. Binding with receptors 4. Miniature end plate potential 5. Destruction of acetylcholine

Action Potential through motor nerve fiber