Vertebrate Muscle AnatomyMuscles: convert the chemical energy of ATP into mechanical work.

Three different kinds of muscles are found in vertebrate animals

1. Skeletal2. Cardiac3. Smooth

voluntary, striated

multi-nuleated

involuntary, non-striatedevolved first

digestive systemarteries, veins

moves bone

involuntary, striated

auto-rhythmic

heart

Anatomy of Skeletal Muscle• Muscle attaches at the origin

• At its other end, the insertion, the muscle tapers into a glistening white tendon

• As the muscle contracts, the insertion is pulled toward the origin and the arm is straightened or extended at the elbow. Thus the triceps is an extensor.

• skeletal muscle exerts force only when it contracts, a second muscle — a flexor — is needed to flex or bend the joint.

• antagonistic pair of muscles work across other joints, provide for almost all the movement of the skeleton.

Muscles movement • Muscles do work by contracting

– skeletal muscles come in antagonistic pairs• flexor vs. extensor

– contracting = shortening• move skeletal parts

– tendons• connect bone to muscle

– ligaments• connect bone to bone

Skeletal Muscle: The striated appearance of the muscle fiber is created by a pattern of alternating dark A bands and light I bands.

Closer look at muscle cell

multi-nucleated

Mitochondrion

Sarcoplasmicreticulum

Transverse tubules(T-tubules)

Fig. 50-29a

Sarcomere Ca2+ released from SR

Synapticterminal

T tubule

Motorneuron axon

Plasma membraneof muscle fiber

Sarcoplasmicreticulum (SR)Myofibril

Mitochondrion

Muscle cell organelles• Sarcoplasm

– muscle cell cytoplasm– contains many mitochondria

• Sarcoplasmic reticulum (SR)– organelle similar to ER

• network of tubes– stores Ca2+

• Ca2+ released from SR through channels• Ca2+ restored to SR by Ca2+ pumps

– pump Ca2+ from cytosol– pumps use ATP

ATP

Structure of striated skeletal muscle • Muscle Fiber

– muscle cell• divided into sections = sarcomeres

• Sarcomere– functional unit of muscle contraction – alternating bands of

thin (actin) & thick (myosin) protein filaments

Muscle filaments & Sarcomere

• Interacting proteins– thin filaments

• braided strands – actin– tropomyosin– troponin

– thick filaments• myosin

Thin filaments: actin• Complex of proteins

– braid of actin molecules & tropomyosin fibers• tropomyosin fibers secured with troponin molecules

Thick filaments: myosin

• Single protein– myosin molecule

• long protein with globular head

bundle of myosin proteins:globular heads aligned

Thick & thin filaments• Myosin tails aligned together & heads pointed

away from center of sarcomere

Fig. 50-25b

TEM

Thickfilaments(myosin)

M line

Z line Z line

Thinfilaments(actin)

Sarcomere

0.5 µm

Cardiac Muscle• Cardiac or heart muscle resembles skeletal muscle

in some ways: it is striated and each cell contains sarcomeres with sliding filaments of actin and myosin.

•

Throughout our life, it contracts some 70 times per minute pumping about 5 liters of blood each minute.

Cardiac Muscle: Structure = Function

• Striated• Different electrical and

membrane properties form skeletal

• Cardiac cells have ion channels in their plasma membranes that cause rhythmic depolarization = triggering action potentials with no input form NS

Unique traits of cardiac muscle relate to function of pumping blood• myofibrils of each cell are branched.

The branches interlock with those of adjacent fibers by adherens junctions. These strong junctions enable the heart to contract forcefully without ripping the fibers apart.

• Smooth muscle is found in the walls of all the hollow organs of the body (except the heart). Its contraction reduces the size of these structures. – regulates the flow of blood in the arteries – moves your breakfast along through your

gastrointestinal tract – expels urine from your urinary bladder – sends babies out into the world from the

uterus – regulates the flow of air through the lungs

• The contraction of smooth muscle is generally not under voluntary control.

Fig. 50-33Circularmusclecontracted

Circularmusclerelaxed

Longitudinalmuscle relaxed(extended)

Longitudinalmusclecontracted

BristlesHead end

Head end

Head end

No striations , single cell has spindle shape

• The contraction of smooth muscle tends to be slower than that of striated muscle.

• often sustained for long periods.

Gap junction allows for coordinated behavior= contractions

• Smooth muscle (like cardiac muscle) does not depend on motor neurons to be stimulated.

• However, motor neurons (of the autonomic system) reach smooth muscle and can stimulate it — or relax it — depending on the neurotransmitter they release (e.g. noradrenaline or nitric oxide, NO)

• Smooth muscle can also be made to contract by other substances released in the vicinity (paracrine stimulation) – Example: release of histamine causes contraction of

the smooth muscle lining our air passages (triggering an attack of asthma)by hormones circulating in the blood

– Example: oxytocin reaching the uterus stimulates it to contract to begin childbirth.