Class 11 Phys

Motor end plate

Specialized region of the skeletal muscle membrane Post-synaptic side of the NMJ -muscle plasma membrane opposite the pre-synaptic terminal -region where ACh receptors are located -has junctional folds

Nebulin

"template" for actin filament length; anchors thin filaments to the Z discs

6. contraction: myosin heads bind to actin, undergo ... and release; thin filaments are pulled toward center of sarcomere (full contraction)

6. contraction: myosin heads bind to actin, undergo power strokes and release; thin filaments are pulled toward center of sarcomere

Whole muscle

A bundle of muscle fascicles

Muscle Fascicle

A bundle of muscle fibers (cells)

4. A muscle action potential traveling along a ... triggers a change in the .... receptors that causes the .... release channels to open, allowing the release of .... into the .... (full contraction 8 steps)

A muscle action potential traveling along a transverse tubule triggers a change in the dihydropyridine receptors that causes the calcium release channels to open, allowing the release of calcium ions into the sarcoplasm

Electrical excitability

A property of both neurons and muscle cells Ability to respond to stimuli by producing action potentials

2. ACh binds to receptors in the ...., triggering an ...., which in turn generates a .... (full contraction 8 steps)

ACh binds to receptors in the motor end plate, triggering an end plate potential, which in turn generates a muscle action potential

Contraction cycle (4 steps) 1. ATP hydrolysis

ATP hydrolysis: myosin is "energized" and "perpendicular" to the thin filament. ADP and phosphate are still attached.

Elasticity

Ability of a muscle to return to its original length and shape after a contraction or extension

Contractility

Ability of muscle to contract forcefully when adequately stimulated When a muscle contracts, it generates tension, and possibly movement

Extensibility

Ability of muscle to stretch without being damaged

Generating heat.

As muscle contracts, it produces heat This process is known as thermogenesis.

2. Attachment of myosin to actin (Contraction cycle (4 steps))

Attachment of myosin to actin: myosin head attached to the binding site on actin. The phosphate group is released. This is a Crossbridge.

5. Ca binds to ... on the filament exposing the .... on actin (full contraction 8 steps)

Ca binds to troponin on the filament exposing the myosin binding sites on actin

Ryanodine receptor (RyR) (where is it found and what does to do?)

Calcium release channel Found in the SR membrane Opens to release Ca2+when the DHP receptor moves

Myofibril

Contractile assembly of proteins in a muscle cell

End plate potential (EPP)

Depolarization generated at the muscle membrane due to binding of the neurotransmitter Acetylcholine (ACh). Triggers an action potential if the EPP exceeds the threshold for voltage-gated sodium channels.

4. Detachment of myosin from actin (Contraction cycle (4 steps))

Detachment of myosin from actin: Crossbridge remains attached to actin until it binds another ATP - then myosin heads detach.

Sarcoplasmic Reticulum Calcium-ATPase (where is it found and what does to do?)

Found in the SR membrane Pumps Ca2+ from the cytoplasm into the SR against its concentration gradient

Sarcoplasmic Reticulum

Intracellular calcium ions storehouse of calcium ions

Dihydropyridine receptor (DHP or DHPR) (where is it found and what does to do?)

L-type voltage-gated Calcium channel family Found in the T-tubule membrane Moves in response to action potentials

Sarcomere shortening leads to....

Myofibrils shortening which leads to Whole muscle shortening

sliding filament mechanism

Myosin heads attach to the thin filaments and pull on them in both halves of the sarcomere The thin filaments slide inward and towards the center of the sarcomere Contraction results in the Z- discs coming closer together and sarcomere shortening occurs.

Transverse Tubules

Network of tubular passages within striated muscle that are an extension of the plasma membrane

Pre-synaptic terminal

Neuronal axon terminal -somatic motor neuron axon -clusters of synaptic end bulbs -contains ACh

3. Power stroke (Contraction cycle (4 steps))

Power stroke: myosin head pivots and pulls the thin filament toward the center of the sarcomere. This generates force. ADP is released.

Regulatory protein (Tropomyosin)

Tropomyosin: blocks myosin binding sites on the thin filament during relaxation Moves out of the way during muscle contraction 7 actin subunits per tropomyosin molecule

regulatory proteins (troponin)

Troponin: 3 subunit complex on the thin filament Calcium sensor that triggers muscle contraction Locks Tropomyosin in place when muscle is relaxed

skeletal muscle functions (Producing body movements)

Walking and running, localized movements -striated -voluntary -attached to bone

Muscle Fiber

a muscle cell

3. .... destroys ACh so another ..... does not arise unless more ACh is released from the somatic motor neuron (full contraction 8 steps)

acetylcholinesterase destroys ACh so another muscle action potential does not arise unless more ACh is released from the somatic motor neuron

7. calcium release channels ... and .... use ATP to restore low level of calcium in the sarcoplasm (full contraction steps)

calcium release channels close and Ca-ATPase pumps use ATP to restore low level of calcium in the sarcoplasm

Sarcomere

contracting subunit of skeletal muscle

Cardiac muscle

contractions of the heart pump blood through the blood vessels of the body. -striated -involuntary -heart

sliding filament mechanism (do the width of the I-band change?)

it appears to narrow

Dystrophin

links/connects the Z-disc to the internal/membrane cytoskeleton

Alpha-actinin

major/primary structural protein of the Z-disc

Myomesin

major/primary structural proteins of the M-line

1. nerve action potential in a .... triggers the release of ... (Full contraction 8 steps)

nerve action potential in a somatic motor neuron triggers the release of acetylcholine

sliding filament mechanism (do the individual lengths of the thick and thin filaments change?)

no

sliding filament mechanism (do the width of the A-band change?)

no

Contractile proteins (myosin)

primary protein of the thick filament ATP-driven molecule motor for muscle contractions

Contractile proteins (actin)

primary protein of the thin filament

Synaptic Cleft

region between the pre-synaptic terminal and motor end plate

Titin

spring-like connector of the thick filament to the Z-disc

Smooth Muscle

storage is accomplished by sustained contractions of ring-like bands of smooth muscle called sphincters Prevent outflow of the contents of a hollow organ. Temporary storage of food in the stomach or urine in the urinary bladder -not striated -involuntary -hollow organs

8. tropomyosin slides back into position where it blocks the .... on...(full contraction)

tropomyosin slides back into position where it blocks the myosin binding sites on actin

Stabilizing body positions

Skeletal muscle contractions stabilize joints maintain body positions, such as standing or sitting Postural muscles contract continuously when you are awake sustained contractions of your neck muscles hold your head upright

isometric

Activation of muscle but muscle shortening is prevented. Change in tension and rate of force development can be measured

isotonic contraction

Activation of muscle when muscle shortening is allowed. Change in length and rate of shortening can be measured

Triad

The junction of the Transverse Tubule with the Sarcoplasmic Reticulum