Phisology Exam 3

Why is the skeletal muscle put together side by side?

so they can work together and contract the same direction

Epimysium

surrounds the entire muscle and attaches it to the bone

Perimysium

wraps a fascicle

Endomysium

lies between individual muscle fibers

What is the structural order of a muscle?

Epimysium —> Fascicle —> Perimysium —> Endomysium/muscle fibers —> Myofibrils

What is the hierarchical organization of Skeletal muscles?

Whole muscle —> Muscle fiber —> Myofibril —> Myofiliaments

What makes up myofilaments?

actin and myosin

Sarcolemma

plasma membrane of muscle fibers

What does the Sarcolemma contain?

T-tubules

T-tubules

• tunnels in the myofibrils

• act as pathways, transporting action potentials from the surface into the cell interior

Sarcoplasmic Reticulum

a calcium reservoir that joins with T-tubules to form terminal cisternae

Triad

T-tubule with terminal cisternae on each side

How do muscles work?

by sliding of actin filaments driven by myosin

Who are the main players in muscles working?

• actin

• myosin

• tropomyosin

• troponin

• titin

• nebulin

• myomesin

• alpha-actinin

• obscurin

Which players are the Force Generators?

Actin and Myosin

Which players are the Regulators?

Tropomyosin and Troponin

Which players are for Structure?

Titin, Nebulin, Myomesin, Alpha-actinin, and Obscurin

Sarcomere

contractile unit of the muscle fiber (z-line to z-line)

What are the main parts of a sarcomere?

• I band

• A band

• H zone

• M line

• Z line

I Band

• light under the microscope

• only actin

A Band

• dark under the microscope

• myosin present with actin

H Zone

• lighter region of the A band

• only myosin

M Line

where the tails of the myosin connect together

Z Line

Darker region of thge I band, where the actin is anchored

Costamere

physically connects the Z disks to the Sarcolemma and the ECM

What is the main function of the Costamere?

serves as a bridge that facilitates the transmission of force laterally

What are the key molecular components of a Costamere?

• Dystrophin-Glycoprotein Complex (DGC)

• Integrin-Vinvulin-Talin Complex

Dystrophin-Glycoprotein Complex (DGC)

the primary link between the actin and the external laminin of the ECM

Integrin-Vinvulin-Talin Complex

Adhesion and mechoanosignaling - signals the cell to adapt in response to mechanical load

Sliding Filiament Theory

muscles shorten and produce force as thin filaments slide across thick filaments. The sarcomere shortens, not the filaments

Why aren’t all cross-bridges attached at the same time (not in synchrony)?

more fluid movement, faster to contract, doesn’t allow it to go back to the original state, constant force.

What is the major role of calcium in cross-bridges?

the on/off switch for contraction

What steps in cross-bridge cycling are affected during rigor mortis?

Loss of ATP and Calcium. Without ATP, the myosin heads remain attached, and with no ATP there is no transportation of Ca to activate a contraction

What might occur to reverse the state of rigor mortis?

Decomposition

How does an action potential lead to muscle shortening?

• muscles are excitatory

• change in volatge leads to change in Ca permeability

Excitation-contracting Coupling

the process of converting electrical stimuli from neurons into mechanical muscle contraction

How do we get such a big [Ca'] gradient?

1) Ca ATpases

2) Calsequestrin

Ca ATPase

active transport into sarcoplasmic reticulum

Calsequestrin

in sarcoplasmic reticulum

DHP Receptor

• on the T-tubule membrane, a voltage sensor, and a Ca channel

• AP causes a change to mechanically pull the RyR1

Ryanodine Receptor (RyR1)

on sarcoplasmic reticulum, plugs that hold back the Ca

Why is there a latent period before the completion of contraction in skeletal muscle?

wating for calcium

Types of Muscle Contraction

1) Concentric 2) Eccentric 3) Isometric

Tension and Load

The force exerted on an object (the load) by the contracting muscle

What happens when tension > load?

movement

What happens when tension < load?

no movement

Concentric Contraction

shortening of muscle

Eccentric Contraction

lengthing of muscle

Isometric Contraction

muscle contracts but does not shorten (holding your arm at 90 degrees)

Muscle Twitch

mechanical response of a muscle to a single AP

What happens during the latent period?

excitation-contraction coupling - Ca is moving into cytosol

What happens during the Period of Contraction?

cross-bridge cycling, tension is generated

What happens during the period of Relaxation?

tension decreases because Ca levels decrease in sarcoplasm during to SERCA pumps

Is there a way to change the tension created?

Tension changes depending on what the object is that your picking up

Length-Tension Relationship

Tension produced depends on sarcomere starting length

What are two passive forces that affect contraction?

1) Serial Elastic Elements 2) Parallel Elastic Elements

Serial Elastic Elements

• Tendons

• act like a spring, absorbing force during contraction and releasing it when the muscle relaxes, helping smooth force transmission

Parallel Elastic Elements

• connective tissue structures

• store and release elastic energy, prevent overstretching

Treppe

staricase pattern observed when muscle fibers stimulated to contract

How does a staircase pattern happen?

• increasing amounts of Ca available in sarcoplasm

• heat generated from muscle increases enzyme efficiency in muscle

Tetanus

maintains contraction in response to repetitive stimulation

Unfused Tetanus

partial Ca removal and dissipation of elastic tension between subsequent stimuli

Fused Tetanus

No time for Ca removal or dissipation of elastic tension between stimuli

Motor Unit

a motor neuron and all of the muscle fibers it controls

What are the key features of Motor Units?

• Each muscle fiber is innervated by a single axon terminal

• The number of fibers/motor unit varies by muscle

• Each motor unit is all or none

How do you increase the strength of muscle contraction?

motor unit recruitment

What are the two ways muscle contraction can be graded?

1) Changing the strength of stimulus 2) Changing the frequency of stimulation