Describe the Muscle type

Skeletal

Cardiac
Smooth

• Striated, Voluntary - must have nerve stimulation
• Striated, Involuntary - can function without nerve input
• Smooth, Involuntary - nervous, hormonal, mechanical & metabolic controls

How does myosin adenosine triphosphatase (ATPase) work?

The faster ATP is hydolyzed (by ATPase), the faster a muscle can shorten.

mm. for posture = slow myosin ATPase

limb mm. = myosin with a fast ATPase

The surface membrane of the muscle cell is called?

The name given to the specialized ER is?

These make up the myofibrils and are connected end to end at the Z disk?

• Sarcolemma

• Sarcoplasmic reticulum

• Sarcomere

Describe the following:

Sarcomere (1)

A band (4)

• generates force development & shortening of muscle

• interdigitated thick & thin filaments
• aka dark band
• length of band remains constant even w/ changes in sarcomere length
• determined by length of thick filaments

Define the following:

H zone (2)

M line (1)

I band (2)

Z disk (2)

• center of A band, only thick filaments
• at extremely short sarcomere lengths thin filaments extend into the H zone

• Thick filaments interconnected

• consists of only thin filaments
• adjacent parts of consecutive sarcomeres

• longitudinal boundary of a sarcomere
• region where thin filaments of adjacent sarcomeres are joined to each other

What is the composition of the thin filaments

G, globular actin mlcs. connect to form F actin strands, 2 of which intertwine into a helix.

Where does tropomyosin lay?

In the helical groove of the actin filament.

List the three troponin subunits and their functions.

What is nebulin, what role does it play?

• Troponin C (TnC) - binds Ca²⁺, cause troponin/tropomyosin complex to change shape, exposes site on actin to which myosin crossbridge head can bind 

• Troponin T (TnT) - links the troponin subunits to tropomyosin

• Troponin I (TnI) - inhibits contraction when intracellular Ca²⁺ is low

• Nebulin is a filamentous protein, attached to thin filament along its full length. May fxn to determine thin filament length.

How many myosin molecules coil around each other?

What is this called?

What is the fxn of titin?

• Two to form a dimer

• Thick filament

• it's an elastic protein that connects the ends of each thick filament to the Z disk, helps maintain precise interfilament spacing

What is another name for the myosin heads?

How many parts are there to one head?

• Crossbridges

• (1) actin binding site, (2) an ATP binding site and (3) a region with ATPase activity

What is the name of the junction between a nerve & a skeletal muscle fiber?

What kind of nerve is it?

• Neuromuscular junction

• somatic motor nerve

In the NMJ what is the presynaptic membrane?

postsynaptic membrane?

What lies between them?

• membrane of the bouton or axon terminal of the somatic motor n.

• folded sarcolemma of the motor endplate

• synaptic cleft

What NT is produced in the terminals?

How is NT packaged?

What is the purpose of the active zone/site?

• Acetylcholine

• into discrete packets of quantum

• this is where vesicles fuse with the membrane

Fill in the blanks

Arrival of the ____ results in ____ of the axon terminal (presynaptic) membrane. This results in opening of ______ Ca²⁺ channels in the presynaptic membrane. This increase in axon terminal cytoplasmic Ca²⁺ conc. causes the ______ to fuse with the internal surface of the presynaptic membrane at sites called ______ and to release their contents into the _______.

• action potential
• depolarization
• voltage-gated
• synaptic vesicles
• active zones
• synaptic cleft

What happens to ACh in the absence of an action potential?

Will this result in a muscle contraction?

• a vesicle will spontaneously release a packet of ACh at a freq of 1/sec

• It will not result in a propogated action potential or contraction but a miniature epsp can be recorded.

• T or F the density of ACh receptors is low at the crest of the folds?
• To what kind of receptors does ACh bind?
• How many ACh mlcs have to bind to cause conductance changes?
• T or F the ion channels that open are relatively non-selective?
• Which way will the ions diffuse?
• What is the net movement and what ion is most responsible?

• False - the density is high
• Nicotinic (acetylcholine)
• Two
• True - they are permeable to K⁺, Na⁺ & Ca²⁺ 
• The Na⁺ & Ca²⁺ will diffuse inward and K⁺ will diffuse outward
• The net movement is positive charge inward and Na⁺ is most responsible, depolarizes the postsynaptic membrane

• T or F the sarcolemma is excitable?

• What is the result of depolarization of the endplate region?

• F, there is no action potential at the postsynaptic membrane

• current flow to and depolarization fo the rest of the sarcomlemma. If EPSP is large enough , threshold is reached for opening fast Na⁺ channels in adjacent sarcolemma. A propagated action potential occurs, contraction is triggered.

What is the function of Acetylcholinesterase?

Does ACh stay around in the synaptic cleft?

It catalyzes the hydrolysis of ACh, it's produced in the post-syn membrane & is present at high concentrations.

No, it is present transiently and then is hydrolyzed.