Bio 2160 exam 4

what are the three types of muscles types, are they voluntary and how do they look under a microscope

smooth - involuntary - unstriated

cardiac - involuntary - striated

skeletal - voluntary - striated

how is a muscle body held together

-held together by numberous fascicles that are held together by connective tissue

-the fascicles contain several muscle fibers

—the muscle fibers is a single muscle cell that has a lot of nuclei in order to make a lot of protein (nucleus directs protein synthesis)

—muscle fibers alse incases myofibril which incases protein filaments

how do you muscles get bigger

-in adulthood, muscle cells don’t divide and you can’t make more of them BUT protein makes more myofibirls- thats what makes your muscles grow

what defines a cell

-the cell membrane, NOT the cell nucleus, because you can have none, but in this case you have multiple

what does multinucleated mean

refers to one muscle fiber having many nuclei

how are myofibrils shaped

in a rod like shape

what is the T tubule

-part of the skeletal muscle cell membrane

-extends deep into the muscle fiber

-they transmit action potentials down into the skeletal muscle cell

what is the sarcoplasmic reticulum

-aka SR

-exactly like the endoplasmic reticulum in a normal cell but “Sarc” means “muscle”

its filled with calcium

explain the neuromuscular junction

-the synapse between a motor neuron and a muscle cell

*neurotransmitters carries signal from the brain and tells the muscle to contract

-the motor end plate is on the muscle membrane, not the neuron

—this is where nicotinic acetylcholine receptors are found

*most well studied synapse on the planet

on the motor plate, why are the nicotinic acetylcholine receptors all in one spot

because diffusion only happens over short distances, these receptors need to be in one place for the neurotransmitters to be able to bind to them

explain what EPP (end plate potential) is

-when the acetylcholine binds to the nicotinic receptors, it opens up the ion channels which is permeable to both Na and K

-however, at rest of -70mv, it is closers to -94 of K and the closer the membrane potential is to the ion equilibrium potential, the smaller the current is

-meaning that Na will enter the cell in larger amounts than K is leaving the cell which causes EPSP (depolarization-going up)

-once threshold is reached, the EPP produces an action potential in the muscle cell

what is a Z line and explain the sliding

-at the end of a sarcomere *boundaries between one sarcomere and another

-contains thick filaments (myosin) and thin filaments (actin)

-when the myosin head touches the actin they make a crossbridge

-the head then moves back towards the center of the sarcomere and the filaments slide on top of each other therefore making the sacromere length shorter aka skeletal muscle contractions

what is the order of the skeletal muscle

muscle body - connective tissue - fascicle - muscle fiber - myofibril - protein filaments

*sarcolemma is the area surrounding the myofibrils

what are the two sites of a myosin head

-actin binding site: forms a crossbridge with actin

-ATPase site: where an enzyme breaks downs ATP

what is the site of the actin

-myosin binding site: where it makes a crossbridge with myosin

-when the muscle is relaxed, this site is covered up by tropomyosin (a protein fiber)- keeps the crossbridge from forning

-Tropomyosin is controlled by Troponin which is calcium sensitive

*myosin biding site on G actin - G actin molecule - F actin - double helical actin strands - portion of thin filament

all muscle contractions require what two things

calcium and ATP

what happens when calcium levels are low vs high

low: troponin keeps tropomyosin on top of myosin and it keeps the muscle relaxed - no crossbridges are being formed

high: calcium binds to troponin when then moved tropomyosin out of the way so that crossbridges can be formed- contracts the muscle

how does an action potential increase calcium levels

-Ryanodine receptors (hold back calcium) that are on the SR (sarcoplasmic reticulum) membrane are physically connected to DHP receptors that are on the T tubules

-these DHP receptors detect action potentials that are flowing down the T tubules

-when the DHP receptors change shape, they physcially pull the ryanodine channel open, which lets calcium flow out

*this is a mechanically gated channel

-this calcium then goes to activated troponin which moves the tropomyosin and the crossbridges can be formed *calcium allows the muscle to contract

explain the cross bridge cycling

step 4: after a contraction, the myosin head will stay in contact with the actin until a new atp binds to it

once atp binds to the myosin head, it develops a low affinity for actin so it disconects and the muscle relaxes

step 5: the ATP then gets hydrolized and broken down into ADP and PI (ATP hydrolysis), this makes the myosin head cock

step 1: When the myosin head is bout to ADP, it develops a high affinity for actin and forms a crossbridge (it connects to the actin)

step 3: the Pi gets released and this is a state of rigor

how do you turn off muscle contraction

-you have to stop thinking about it first which will then make the motor neuron input stop

-it will stop sending action potentials down motor neurons which means that no more acetylcholine is being relased- so no more EPP (end point potentials) on the muscle cell

-negative feeback from high levels of calcium, shuts the ryanodine channels

-SERCA (Saroplasmic or Endoplasmic Reticulum Calcium ATPase) is a pump on the SR or ER membrane that transports calcium back in

-the calcium has to disconnect from the troponin which makes the tropomyosisn cover back over the biding sites on actin

what is a twitch and whats the difference between isotonic twitch and isometric twitch

-smallest muscle contraction possible

-isotonic: you generate enough energy to move something (lifting a book)

-isometric: you don’t generate enough energy to move something (pushing against a brick wall)

what is the latent period

-the time between when the action potential first reaches the muscle and the that the muscle is full contrac