Module 7-Muscle Physiology Slidedeck 1

What are the three types of muscle

skeletal, cardiac, smooth

What does skeletal muscle cell look like

single, very long, cylindrical, multinucleated, striations

What does smooth muscle look like

single, fusiform, uninucleate, no striations

What does cardiac muscle look like

branching chains of cells; uni or binucleate, striations

4 characteristics of muscle

excitability, contractility, extensibility, elasticity

Muscle functions

produce movement, maintain posture and body position, stabilize joints, generate heat, generate electricity

3 layers of muscle superficial to deep

epimysium, perimysium, endomysium

What is a fascicle

bundle of muscle fibers

What wraps around the fasicles

perimysium

What wraps around the muscle fibers

perimysium

What is the A band

actin and myosin

What is the Z disk

filamentous network of protein. Serves as attachment for actin myofilaments

What is a sarcomere

contractile unit of a muscle fiber

What are myosin fibers

thick filaments

What are Actin fibers

thin filaments

What is the M line

supporting proteins that hold the thick filaments together in the H zone

What is the H zone

myosin only

What is the I band

actin only

What makes up myosin

A tail and two myosin heads bound to Z-line by titin

What is found on actin

troponin and tropomyosin

What do elastic filaments contain

titin

What does myosin contain

ATP binding site as well as actin binding site

When does myosin bind to actin and vice versa

during muscle contraction

What filamentous protein is actin made up of

globular subunits (G-actin), 2 filaments strands braid together to form thin filament.

What is tropomyosin

filamentous protein that is spiraled around actin

What does tropomyosin do

acts as an inhibitor to myosin by blocking the myosin binding site on actin

What is troponin

multisubunit protein that interacts with tropomyosin

What are the three subunits of troponin

Tnl, TnT, TnC

What is Tnl

subunit of troponin; inhibitory and covers the myosin binding site on actin filament

TnT

troponin subunit that binds to tropomyosin

TnC

troponin subunit; calcium binding subunit

What is Dystrophin

stabilizing protein that anchors thin filament to sarcolemma, aids in membrane stability

what does titin do

binds thick filament to Z-disc of sarcomere, allows extensibility

What is the sarcoplasmic reticulum

elaborate smooth E.R.

What runs along the axis of myofibrils in sarcoplasmic reticulum

tubules

What run perpendicular to A-band/I-band junction

terminal cistern

What does the Sarcoplasmic reticulum regulate

intracellular Ca2+ levels

What does the T-tubule do

brings action potentials into interior of muscle fiber

What is the triad

terminal cisterns + T-tubule

What are T-tubules

deep invaginations of the sarcolemma

What do T-tubules increase

surface area

What does the T-tubule do for the sarcolemma

places it in close association with sarcoplasmic reticulum

What do T-tubules carry

A.P.'s deep within the muscle fiber

What spans the sarcolemma of t-tubules and sarcoplasmic reticulums

integral proteins

What do the integral proteins of the t-tubule act as

voltage sensor (DHP receptor)

What do the integral proteins of the SR act as

Ca2+ channel (RY receptor)

What receptor is connect to the SR receptor

DHP receptors

What is the sliding filament model

during contraction the myosin filament grabs the actin filament and the actin filament "slides" over the top of the myosin filament increasing the degree of overlap

Where must a signal be sent to tell a skeletal fiber to contract

from the brain as an action potential

Where is the neuromuscular junction

synapse between a somatic motor neuron and muscle fiber

What is the synaptic bulb

portion of motor neuron at NMJ is enlarged

What is the portion of the myofiber that receives the synaptic bulb

motor end plate

What is the synaptic cleft

space between motor end plate and synaptic cleft

What is the motor end plate

depression in sarcolemma

What does a highly folded sarcolemma do

increase surface area

What is Doyere's eminence

lateral edges are raised and meets Schwann cell of motor neuron

What's present in the motor end plate

numerous proteins present

what type of channel is found on the motor end plate

ligand gated sodium channels with Ach receptors

Where are the voltage gated channels located on the motor end plate

at the periphery of motor end plate

What are found in the synaptic bulb

synaptic vesicles containing acetycholine

Give the steps of AP at the synaptic bulb

1. AP reaches axon terminal

2. v.g. Ca2+ channels open

3. Calcium influx

4. Calcium binds to Ach containing vesicles

5. Vesicles fuse with neurolemma

6. exocytosis of Ach into the synaptic cleft

7. Ach binds to ligand gated sodium channels

8. ligand gated Na+ channels open and there's an influx of sodium

9. Graded potential at motor end plate

10. Threshold is reached at peripheri of MEP (doyere's eminence)

11. Activation gate on vg. Na+ channel opens

12. Na+ influx and action potential occurs in myofiber

What is excitation-contraction coupling

process of an AP leading to sliding filaments

Explain SR Foot Protein Propogation

1.action potential propogates down sarcolemma (same process as action potential propogation already discussed)

2. action potential reaches voltage receptor (dihydropyridine receptor) in T-tubule

3. Voltage change causes conformational change in DHP receptor

4. DHP receptor connected to ryanodine (Ry) receptor on sarcoplasmic reticulum

5. Conformational change in DHP receptor causes conformational change in Ry receptor

6. Ry receptor acts as gated channel and gate opens

Ca2+ in SR effluxes from SR to sarcoplasm

How does cross-bridge formation work

1. Ca2+ released from SR binds to TnC receptor on troponin

2. Troponin undergoes conformational change

3. Conformational change in troponin causes conformational change in tropomyosin

4. tropomyosin slides around actin filament exposing myosin binding site on actin filament

5. when binding site exposed, myosin binds to actin

Myosin-actin interaction causes the cross-bridge

What has a high affinity for actin

myosin

What is released when myosin binds to actin

Pi

What does myosin have on it before attaching to actin

ADP and Pi

What does the release of Pi from myosin cause

myosin to undergo conformational change and "bend" at the elbow, pulling on the actin filament

What does the conformational change on myosin cause

ADP to be released and freeing up the ATP binding site on myosin

Cross-bridge cycling steps

1. myosin binds to actin and Pi is released

2. release of pi causes myosin to undergo conformational change and "bend" at the elbow, pulling on the actin filament

3. this conformational change cuases ADP to be released and frees up the ATP binding site on myosin

4. ATP binds to myosin causing myosin to detach from actin

5. ATP is hydrolyzed into ADP+Pi and myosin returns to "cocked position"

What happens if a cell signal is still present

the cross-bridge cycle repeats

When one myosin head releases...

another is attached holding the actin in place

Where does myosin goes to rebind

further up on the actin filament

Stopping the cycle

1. when a signal is no longer present an AP is not generated in the somatic motor neuron

2. Ach is cleared from the synaptic cleft through uptake by neighboring cells, the motor neuron itself, or broken down by acetylcholinesterase

^this stops AP in myofiber

3. Calcium stops being released from ST

4. Calcium is PUMPED back into SR using Calcium and ATPase

5. Calcium is no longer bound to troponin

6. Tropomyosin can return to original conformation blocking myosin binding site