Skeletal Muscle

Skeletal

Allows us to move/walk; moves that skeleton

Cardiac

Contracts heart which pumps blood. Found in the atria and ventricles of heart and contracts to move blood

Smooth

Covers organs and passageways. Found in numerous location including digestive tract, blood vessels and Pumps/pushes blood/fluid/food through

Produces Movement (skeletal muscles functions)

muscles pull on tendons which moves skeleton

Maintain Posture (skeletal muscles functions)

holds head up, allows you to sit upright

Support soft tissue (skeletal muscles functions)

supports the weight of organs

Guards entrances and exits (skeletal muscles functions)

Prevents unnecessary or undesired defecation, urination, swallowing

Maintains body temperature (skeletal muscles functions)

muscle contractions use energy; energy use generates or gives off heat that warms the body

Providee Nutreints Reserves (skeletal muscles functions)

proteins in the muscular system can be cannibalized to be broken down into amino acids for other uses such as synthesis of glucose and/or energy.

Epimysium (3 layers of connective tissue)

surrounds the entire muscle; a dense layer of collagen fibers, connects muscle to deep, dense connective tissue, large blood vessels and nerves enter here

Perimysium (3 layers of connective tissue)

divides the muscle into compartments called fascicles. comprised of elastic and collagen fibers

Endomysium (3 layers of connective tissue)

surrounds individual muscle cells and interconnects adjacent muscle fibers. Contains blood capillaries and satellite cells, between the endomysium and muscle fibers and “satellite cells” which are a type of stem cells that repair muscle, primarily made up of reticular connective tissue.

Fasicle

Compartment containing a bundle of muscle fibers.

Small fasiculi

Are responsible finely controlled movements

Large fasiculi

Responsible for gross movement

Tendon formation

at ends of muscle, collagen fibers of the epimysium, perimysium, endomysium come together to form a bundle called… or a broad sheet… called aponeurosis

Blood vessels and nerves

For the muscle together and go into epimysium and perimysium (larger blood vessels do not ender the endomysium but are wrapped around it) to feed the endomysium

Orgin

point of attachment of muscle normally to the non-movable bone

Insertion

point of attachment of muscle normally to the moveable bone

Skeletal muscle (classiifcation)

surrounded by Epimysium and contains/ made up of muscle fasicles

Muscle Fasicle (classification)

Surrounded by perimysium and contains/made up of muscle fibers

Muscle fibers (classification)

Surrouned by Endomysium and contains/ made up of myofibrils

Myofibrils (classification)

Surrounded by sarcoplasmic reticulum and contains/made up of sarcomeres

Sarcomeres (Classification)

Contains/made up of thick and thin filaments

Skeletal muscle characteristics

large, multinucleate, embryonic stage

Embryonic stage

during this stage a group of embryonic cells called myoblasts fuse together to form a single muscle fiber. Every nuclei in a muscle fiber represents a myoblast.

Myoblasts

That do not fuse together differentiate into a satellite cell

Parts of a Muscle Fiber (Muscle Cell)

Sarcolemma, Sarcoplasm, Transverse tubule, Myofibrils, Sarcoplasmic Reticulum, and Sarcomeres

Sarcolemma

The cell membrane of muscle fiber/cell that surrounds the Sarcoplasm.

Sarcoplasm

cytoplasm of muscle cells/fiber. Has an unequal charge across membrane due to sodium potassium pump, contains a large amount of stored glycogen and myoglobin

Glycogen

Storage form of glucose

Myoglobin

Protien that binds oxygen in muscles

Transverse Tubule (“T Tubules”)

Passageways that carry electrical impulses from the sarcolemma into the cell sarcoplasm. Surround myofibril

Myofibrils

Responsible for skeletal muscle fiber contraction. Consists of bundle of thick and then filaments. These are achored to sarcolemma and to collagen fibers of tendons. When they contract the entire cell becomes shorter. Sacttered among these are mitochondria and glycogen and myoglobin.

Thin Filaments

primarly composed of protein Actin

Thick Filaments

Composed of protein Myosin

Sarcoplamsic Reticulum

This is same or equivalent to “smooth endoplamic Reticulum”. Formed a network around each myofibril.

Terminal Cisternae

Expaned chambers of SR are called… they hold excess calcium that is pumped out of Sarcoplasm.

Triad

Made up of one “transverse tubule” and two “terminal Cisternae”

Muscle contraction

Happends when stored calcium is released into the sarcoplasm (cytosol)

Sarcomeres

Are smallest functional unit of muscle fiber/cell

Proteins of a Sarcomere

Thick filaments- myosin, thin filaments- actin, proteins that stabilize thick and thin filaments- titin, proteins that regulate interactions beteen thick and thin filaments- Troponin and tropomyosin

A Bands (components of a Sarcomere)

also called dark bands

“A” Bands contain

M-line, H Zone, Zone of overlap

M Line

connects and stabilizes thick filaments

H Zone

Contains only thick filaments. These are on sides of M Line

Zone of overlap

areas where thick and thin filaments are overlapped

I Band (components of a Sarcomere)

also called light bands

“I” bands contain the following

contain ONLY thin filaments (no thick filaments), extends for mA band of one Sarcomere to next A band of Sacromere, Z line divides the I band

Components of a Sarcomere

z lines mark ends, consist of protien “actin”, alternating dark and light bands gives skeletal muscle the striated look

When contraction occurs

H Zone & I bands get smaller, zones and areas of overlap increase, z lines move closer together, width of a bands remain constant.

Thick filaments protein

myosin

Thin filaments proteins

actin

Protein that stabilize thick and thin filaments

titin

Proteins that regulate interactions between thick and then filaments

troponin and tropomyosin

Thick filaments

Made up of 500 myosin molecules; each made up of a pair of mysoin subunits.

Thick filaments characteristics

Has a tail that binds to other myosin molecules in thick filament. A head that interacts with thin filaments; free head is made up of two subunits which pivot. When myosin “head” binds to thin filaments it forms “cross bridge”

Titin

Very large protein found in I band. Attaches to one end of thick filament and to Z line. Helps to keep thick and thin filament aligned.

Thin filaments proteins

F Actin, G actin, Nebulin, active site.

G Actin

Has an active site were the thick filament binds to it. There also is two rows of G Actin and that creates F actin.

Nebulin

A strand of nebulin spiral between two rows of G actin holding F Actin together

Tropomyosin

This protein strand covers “G actin” “active site” preventing Actin/Myosin from interacting. 1 tropomyosin covers 7 active sites and binds to troponin

Troponin

Has 3 subunits. One subunit binds to tropomyosin( forms troponin-tropomyosin complex). One subunit binds to G Actin which allows the complex to block the active site. One subunit binds to Calcium molecule.

Excitation

The nerve (boss) must send a command to the skeletal muscle to contract.

Excitation-Contraction Coupling

The impulse/command must be transferred into the inter portions of the cell.

Contraction

The skeletal muscle/Sarcomere must contract.

Excitation: Neural stimulation of muscle

This is how the Motor Neuron “excites” the skeletal muscle (NOT cardiac or smooth) causing it to contract.

synapse

An area where cells meet to “communicate”

“neuromuscular junction” or NMJ

A specific synapse where the nerve and muscle meet

muscle contraction.

An impulse from a Motor Neuron (nerve) starts the Excitation Process and will lead to a…

synaptic terminal

The location on a nerve ending where the communication takes place

“motor neuron”

sends impulse down its membrane until it reaches the “synaptic terminal”

calcium channels.

Once the electrical impulse (called action potential) reaches the synaptic terminal it causes the membrane to open…

ACH

a neurotransmitter.

The calcium entering the nerve

causes “vesicles” (containers) filled with the chemical Acetylcholine (ACH) to fuse to the nerve membrane.

“synaptic cleft”

The gap between the muscle and neuron

Motor Neuron vesicles

release ACH into the “synaptic cleft”

“motor end plate”

The section of the muscle that holds the “nACH receptors” (nicotinic ACH receptors)

“nACH receptors”

ACH floats across synaptic cleft to the muscle and binds to receptors on outside of muscle

Motor End Plate also contains junctional folds

which increases the surface area for more nACH receptors to be located

Sodium/Potassium ATPase Pump.

The inside of muscle cell is more negative as compared to the ECF

Polarized

When ICF is negative the cells is… meaning that it is resting

Na

Where ever the higher concentration of… it is going to be positive.

pump transports

in 2 K+ and 3 Na+ out, creating a polar difference in charge. The Muscle cell is now “polarized”

When ACH is diffusing

There will be more Na outside than inside; and there will be more K+ inside than outside.

When ACH binds to nACH receptors

causes Na+ channels in the nACH receptor to open.Two forces causes NA+ ions to move inside, which changes the charge on inside of cell to positive.

Diffusion

Sodium moves from a high to a low concentration

The muscle cell becomes

depolarized when enough Na+ has laterally diffused across skeletal muscle fiber

Excitation-Contraction Coupling

The period between the generation of the “action potential” and start of the muscle contraction

Excitation contraction coupling occurs at the…

Triad

Action potential

The change in charge on inside the muscle causes…

Muscle cell

The action potential passes across the entire surface of…

T tubule

Action potential travels along each… until reaching the sarcoplasm containing the sarcoplasmic reticulum

Sarcoplamsic Reticulum

When Action potential reaches each… it causes the terminal Cisternae to release calcium

Released Calcium

Binds to troponin, which causes the troponin-tropomyosin complex to move allowing the “Active site” of actin to be exposed

Contraction cycle step one (Contraction cycle begins)

the arrival of calcium ions begins the contraction cycle

Step two Exposure of the active site (Contraction cycle)

Troponin is attached to tropomyosin blocking the active site during muscle relaxation. Calcium released from S.R. binds to troponin, which causes troponin-tropomyosin complex to move away from actins “active site” leaving it exposed

Step 3formation of a crossbridge (contraction cycle)

When Actin “active site” is exposed “myosin head” binds to the actin forming a “cross bridge”

Step 4 Pivoting (contraction cycle)

Myosin head is cocked and moved to M line. This is called the “power stroke” and ATP is required; after the power stroke and ADP and phosphate group are released

Step 5 Detachment of Cross bridge (contraction cycle)

A second ATP binds to myosin head causing it to release from the Actin “Active site” which causes the cross bridge to be broken