Muscle Physiology

Muscles are — tissues able to contract

soft

Name three different muscle types:

• Skeletal

• Smooth

• Cardiac

Skeletal muscles are usually attached to —- on each end by —

bones;tendons

Connective tissue within the tendons forms the:

epimysium

The epimysium subdivides the muscle into —, which are surrounded by the —

muscle fascicles;perimysium

A muscle fascicle is made of several muscle cells, also named:

muscle fibers

The plasma membrane of the muscle fibers is called the —- and their cytoplasm is the —

sarcolemma;sarcoplasma

Muscle fibers are surrounded by a thin layer of connective tissue called the:

endomysium

True or false: muscle fibers are multinucleated

true

Muscle fibers contain —, which are made up of —, responsible for muscle contraction

myofibrils; myofilaments

Skeletal muscle fibers are —

striated

Dark bands are called —bands and the light bands are called —bands. In the middle of the I bands, dark lines are visible: they are named — bands.

A;I;Z

Each muscle fiber receives a single terminal bouton from a somatic motor neuron, or —

motor neuron

The motor end plate is rich in ACh receptors and voltage-gated Na+ channels (VGSCs). The depolarization is called — —- potential

end plate

Each motor neuron and its innervated muscle fibers is called a — —

motor unit

The A band contains — filaments primarily made of myosin. The I band contains thin filaments primarily made of —

thick; actin

The central region is called the — band and it only contains thick filaments

H

In the middle of the A bands, in the center of each H band is an - line. Produced by protein filaments made of myomesins and titin

M

Sliding of the filaments is produced by the action of numerous —- — extending out from the thick filaments towards the thin filaments

cross-bridges

Describe the cross-bridge cycle:

• Myosin heads are able to hydrolyze ATP into ADP and inorganic phosphate (Pi)

• Then, Pi is released and the myosin head becomes unphosphorylated, triggering a power stroke

• After the power stroke, the bound ADP is released: myosin and actin are tightly bound to each other

• Rigor state

• Then, a new ATP molecule can bind to the myosin head, allowing it to break its bond with actin

True or false: In order for a muscle to relax, cross-bridge formation must be prevented

true

Troponin complex proteins:

Troponin I. Inhibits the binding of myosin to actin

Troponin T. Binds to Tropomyosin

Troponin C. Binds to Ca2+

In a relaxed muscle, —- physically blocks the myosin heads from bonding to actin

tropomyosin

In order for a —- —— to occur, troponin C binds to Ca2+

Conformational change

The — — is made of interconnected tubules and terminal cisternae

sarcoplasmic reticulum

Muscle fibers have extensions of the cell membrane called — —-

transverse tubules

For muscle contraction regulation, the receptors open and Na+ enters the cell, causing a depolarization:

end plate potential

For muscle contraction regulation, the T tubules have —- —- that respond to action potentials.

They undergo a conformational change and they are coupled to the —— —- — in the sarcoplasmic reticulum

This process is called: —- —- —-

voltage-gated Ca2+ channels; Ca2+ release channels; excitation-contraction coupling

To stop muscle contraction, the production of action potentials muscle cease, closing the Ca2+ release channels.

Ca2+ now needs to be pumped back into the sarcoplasmic reticulum by — —

SERCA pumps

Name

Incomplete tetanus

Name

Complete tetanus

Name

Treppe or stairway effect

Muscle contraction strength is influenced by:

• Number of stimulated fibers

• The frequency of the stimulation

• The thickness of each muscle fiber

In skeletal muscles, the maximum relative tension is achieved when the muscle is — to — of its resting length

100%;120%

Exercise stimulates the production of — — into the sarcolemma

glucose transporters

Muscle cells combine ADP with a Pi derived from a high energy molecule called ——

phosphocreatine/creatine phosphate

Describe slow-twitch fibers:

• Also known as type I fibers, reach their maximal tension in up to 100 msec

• Slow oxidative fibers or red fibers

Describe fast-twitch fibers:

• AKA type II fibers, reach their tension in 7.3 msec

• White fibers

Type II fibers can be subdivided into two categories:

• Fast glycolytic, or type IIX fibers. They have the greatest rate of ATP and phosphocreatine consumption.

• Fast oxidative-glycolytic, or type IIA fibers. They have a high oxidative capacity and are more resistant to fatigue.

Sensory feedback is provided by the —— and —-

Golgi tendon organ; muscle spindle

Muscle spindles are stretch receptors (—-) located in the muscles

proprioceptors

— — —-, loosely arranged nuclei and — — —, nuclei arranged in rows

nuclear bag fibers; nuclear chain fibers

Skeletal muscles are mainly innervated by two types of neurons:

• Alpha motor neurons, innervating the extrafusal fibers

• Gamma motor neurons that innervate the intrafusal fibers

Stimulation by gamma neurons, causes an — — in the spindle

active stretch

Alpha and gamma neurons are usually stimulated simultaneously by upper motor neurons, this is termed:

coactivation

Stretch and activation of the spindles triggers a reflex contraction to maintain a normal resting muscle length:

the muscle tone

The simplest type of reflex is:

monosynaptic

Neurons from the Golgi tendon organ synapse between a sensory neuron and a spinal interneuron: —-. This system prevents any dangerous tension on a tendon from excessive muscle contraction

disynaptic reflex

During a stretch reflex, — — takes place

reciprocal innervation

On the opposite limb, the extensor muscles contract and the flexor relax to support weight:

Contralateral reflex

Unlike skeletal muscles, cardiac and smooth muscles are —- and are regulated by autonomic motor neurons

Involuntary

— cells are short, branched and interconnected

cardiac muscle

In skeletal muscle cells, —— —- are mechanistically coupled to the —- —- —

the voltage-gated Ca2+ channels; Ca2+ release channels

True or false: in myocardiac cells, the two channels DO interact

False

— — can be found in the walls of hollow organs. They can be arranged in circular and longitudinal layers

Smooth muscles

Smooth muscles are —- and involuntary

non-striated

Thin filaments attach their ends to the plasma membrane or to structures called — —

Dense bodies

In skeletal muscles, the myosin proteins of the thick filaments are stacked

horizontally

In smooth muscles, the myosin proteins of the thick filaments are stacked

vertically

Smooth muscles can be grouped in two functional categories:

• Single-unit

• Multiunit

In smooth muscle, neurotransmitters are released from regions of the autonomic axon named:

varicosities

Unlike single-unit smooth muscles, the cells of the multiunit must be stimulated —- by neurons

individually

True or false: In smooth muscles, Ca2+ does not bind to troponin: smooth muscle cells do not express that protein

True

—- phosphorylates the myosin light chains, allowing them to interact with actin filaments and cause contractions in smooth muscles

MLCK

To relax a smooth muscle, — cytoplasmic levels are brought back to their basal concentration

Ca2+