Cardiac MuscleCardiac MuscleInvoluntaryInvoluntary – heart onlyheart only

Contracts & relaxes continuously Contracts & relaxes continuously throughout lifethroughout life– Contracts without nervous stimulation!Contracts without nervous stimulation!– A piece of cardiac A piece of cardiac

muscle can even continue muscle can even continue to contract for a while to contract for a while outside the body! outside the body!

StriatedStriated - alternating - alternating light and dark bandslight and dark bandsEach cell has Each cell has 1 nucleus1 nucleus

Smooth MuscleSmooth MuscleInvoluntaryInvoluntary– internal organs, blood vesselsinternal organs, blood vessels

Controlled by ANS (& partly by endocrine Controlled by ANS (& partly by endocrine system)system)– Many can function without nervous Many can function without nervous

stimulationstimulation

Smooth muscle is Smooth muscle is not striatednot striated

Each cell has Each cell has 1 nucleus1 nucleus

Skeletal MuscleSkeletal MuscleMuscle fiber= skeletal muscle cellMuscle fiber= skeletal muscle cell– Skeletal muscles- skeletal muscle fibers, connective Skeletal muscles- skeletal muscle fibers, connective

tissues, blood vessels & nervestissues, blood vessels & nervesVoluntaryVoluntaryStriatedStriatedSkeletal muscle cells Skeletal muscle cells can develop can develop multiple multiple nucleinuclei– Cells don’t divide after Cells don’t divide after mitosis, when muscles mitosis, when muscles grow, they are not getting grow, they are not getting more muscle cells, they are more muscle cells, they are getting more nuclei, getting more nuclei, mitochondria, & mitochondria, &

cytoskeleton!cytoskeleton!

Muscle ContractionMuscle ContractionMuscle fibers are arranged into bundles Muscle fibers are arranged into bundles that contract in response to a nerve that contract in response to a nerve impulse. impulse.

Muscle tone- constant slight contraction Muscle tone- constant slight contraction in musclesin muscles– postureposture

Sliding filament theorySliding filament theory- when thin - when thin filaments slide over thick filaments, you filaments slide over thick filaments, you get muscle contractionget muscle contraction

Muscle FilamentsMuscle FilamentsFilaments- small units that make up myofibrilsFilaments- small units that make up myofibrils– Myofibrils= cytoskeleton (majority of muscle cell)Myofibrils= cytoskeleton (majority of muscle cell)

Thick filaments- contain protein called myosinThick filaments- contain protein called myosin– Rods & headsRods & heads

Thin filaments- contain protein called actinThin filaments- contain protein called actin– GlobularGlobular, also contain tropomyosin & troponin, also contain tropomyosin & troponin

Sliding Filament ContractionSliding Filament Contraction

Thick & thin filaments arrange in units Thick & thin filaments arrange in units called called sarcomeressarcomeres– Striations are from alternating thick & thin Striations are from alternating thick & thin

filaments filaments

When muscle is relaxed, no thin filaments When muscle is relaxed, no thin filaments are in the center are in the center

of the sarcomeres,of the sarcomeres,

when it contracts,when it contracts,

they move into the they move into the

centercenter

Sarcomere Shortening (499.0K)

Membrane PotentialMembrane PotentialResting potentialResting potential- partial negative - partial negative charge inside cell rest charge inside cell rest – More KMore K++ inside & Na inside & Na ++ outside outside

When muscle cell is stimulated, what When muscle cell is stimulated, what opens?opens?– NaNa+ + channels just like neuron!channels just like neuron!– DepolarizationDepolarization- change of charge- change of charge– RepolarizationRepolarization- return to resting charge- return to resting charge

Membrane

Outside the cell

Cytoplasm

Na+ Na+Na+

Na+Na+

Na+

Na+ Na+ Na+K+

K+ K+

K+K+ K+

K+

K+

K+K+ K+

-

Na+

K+ K+K+ K+

Action potential

-

-- -

-

- - -

-

--

-

Motor UnitMotor UnitAxons on motor neurons branch out & Axons on motor neurons branch out & form junctions with muscle fiberform junctions with muscle fiber– A synapse called the A synapse called the Neuromuscular Neuromuscular

junctionjunction

Motor unit- single motor neuron & all Motor unit- single motor neuron & all muscle fibers associated with itmuscle fibers associated with it

Acetylcholine- neurotransmitter released Acetylcholine- neurotransmitter released by axon to excite muscle cellsby axon to excite muscle cells– Binds to NaBinds to Na++ channels in muscle fibers to channels in muscle fibers to

begin action potential begin action potential (just like in nerve (just like in nerve cells!)cells!)

– Impulse in muscle cell membrane causes the Impulse in muscle cell membrane causes the release of Carelease of Ca2+2+ Excitation-Contraction Coupling Excitation-Contraction Coupling 2

Why do muscles need calcium?Why do muscles need calcium?It makes the filaments slide!It makes the filaments slide!CaCa2+2+ binds to the thin filament binds to the thin filament (to troponin)(to troponin), , exposing active site on actin proteinsexposing active site on actin proteinsMyosin attaches to active sites to form “cross-Myosin attaches to active sites to form “cross-bridges”bridges”Energy from ATP in the thick filament moves Energy from ATP in the thick filament moves the myosin head, the movement causes the the myosin head, the movement causes the actin filament to slide over topactin filament to slide over topATP binds to myosin head, actin filament is ATP binds to myosin head, actin filament is releasedreleased

Actin Myosin Bridge