APK2100C Chapter 10 (Skeletal Muscle)

Muscle specific terms tend to have the prefix "Myo" or "Mys", what is a Myocyte?

A muscle fiber, a muscle cell

"Sarc" is the typical prefix for "flesh", and it is also used in the context of muscle cells.

Knowing this, define Sarcolemma, Sarcoplasm, and Sarcoplasmic Reticulum

- Sarolemma: plasma membrane of a skeletal muscle cell

- Sarcoplasm: the cytoplasm of a muscle fiber

- Sarcoplasmic Reticulum: Endoplasmic Reticulum of a muscle fiber

What are the four functional characteristics of all muscle fibers?

Contractility

Excitability

Extensibility

Elasticity

What does Contractility mean in reference to muscle fibers?

The ability to shorten and generate force

What does Excitability mean in reference to muscle fibers?

Responds to stimuli by producing electrical signals

What does Extensibility mean in reference to muscle fibers?

Ability to stretch without being damaged

What does elasticity mean in reference to muscle fibers?

Ability to return to original shape/length after being stretched

What are some general functions of muscle?

Movement

Posture and joint stabilization

Open/close body passages

Thermogenesis

Components of muscle are held together by connective tissue sheaths. What is the name of the sheath that holds together the entire muscle?

Epimysium

What is a bundle of individual muscle fibers called?

A fascicle

What is the name of the sheath that covers fascicles of muscle fibers?

Perimysium

What is the name of the sheath that wraps individual muscle fibers?

Endomysium

What is a tendon?

A CT attachment of skeletal muscle to the periosteum of a bone

What is an aponeurosis?

A broad/flat tendon

What is the Origin of a muscle?

The attachment to the stationary or less moveable bone

What is the insertion of a muscle?

The attachment to the mobile/more movable bone

The attachment to the bone the muscle pulls on to make movement occur

Distinguish between direct attachment and indirect attachment of muscles to bone

- Direct attachment happens when the CT strands (the tendons) involved are so short it appears that the muscle is attached directly to the bone.

- Indirect attachment is more common. It happens when the CT forms visible tendons/aponeuroses that connect the muscle to the bone.

Distinguish between sprains and strains

- A Strain is an injury to the muscle or tendons

- A Sprain is an injury to the ligament

True or False: muscles can both push and pull on bones

False, muscles ONLY pull

Explain how muscles are typically innervated

- They are typically innervated by one main nerve that branches out within the CT sheath in the muscle

- One axon will synapse (communicate) with multiple muscle cells

How is the blood supply of muscles similar to the innervation of muscles

Like with nerves, one main artery branches across the entire muscle in the CT sheath

How does the shape of capillaries in endomysium allow for the extensibility of muscle tissue?

The capillaries are wavy during rest. This creates "slack" that allows for the muscle to be stretched without damaging the capillaries

Review from chapter 4: Muscle cells are ______ and _______

Striated, multinucleate

What is a myofibril?

An organelle specific to muscle cells

They allow the muscles to contract

A _______ is a muscle cell

A ________ is a contractile organelle within a muscle cell

Myofiber

Myofibril

What is a sarcomere?

Contractile units within myofibrils

What does a Z line (Z disc) do in a sarcomere?

Serves as the dividing line between sarcomeres

Sarcomeres are composed of....

Myofilaments

There are two kinds of filaments contained in a sarcomere, what are they?

Thin Filaments

Thick Filaments

Thin Filaments are made of

Actin double strands

Thick Filaments are made of

Hundreds of myosin proteins

The H zone is the area down the middle of a sarcomere (in a lateral view), there is only ______ filament in the H zone and no _______

Thick, Thin

A bands in sarcomeres span the length of the ________ filaments. They _______ with _____ filaments.

Thick, overlap, thin

I bands in sarcomeres span from the beginning of the _______ filaments. They _______ with ________ filaments.

thin, do not overlap, thick

What is the M line in a sarcomere?

A series of proteins down the middle of a sarcomere (in lateral view)

Myofibrils (which contain sarcomeres) are made up of three kinds of proteins. What are they?

Contractile Proteins

Regulatory Proteins

Structural Proteins

What are some examples of contractile proteins? What is their function?

- Actin myofilaments, myosin myofilaments

- Controlling contraction in the muscle

What are some examples of regulatory proteins? What is their function?

- Troponin, tropomyosin

- Restrict myosin binding, allowing the cell to only contract at specific times

What are some examples of structural proteins? What is their function?

- Titin and Dystrophin

- Titin anchors myosin in place in the sarcomere and creates slack in the sarcomere to allow stretching to occur. Dystrophin anchors the sarcomere in the sarcolemma.

Thick Filaments contain what proteins?

Thin Filaments contain what protins?

Thick: myosin

Thin: Actin, troponin, and tropomyosin

How does contraction occur? Explain the steps.

- Actin molecules in thin filaments contain myosin binding sites

- The binding sites are covered tropomyosin, which is held in place by troponin

- Ca2+ changes the shape of troponin, which results in tropomyosin moving out of the way of the binding site

- Myosin in thick filaments bonds and the cell contracts

Where is the sarcoplasmic reticulum in a muscle cell? What function does it perform?

- Covering the myofibrils

- Releases Ca2+ to allow muscle contraction to happen

What are T Tubules? Where are they? What is their function?

- Invaginations of the sarcolemma

- Covering myofibrils with the Sarcoplasmic reticulum

- Helps with innervation

During contraction, I bands _______ in size while A bands ________

decrease, stay the same

What is a motor unit?

A nerve fiber and all the muscle fibers it controls

True or false: muscle fibers are innervated by multiple nerves

False, nerves can innervate multiple muscle fibers but a muscle fiber will always be innervated by one nerve

What is the neuromuscular junction? What are the three components?

The communication center between the neuron and the muscle cells

Axon terminal, junctional folds of the sarcolemma, synaptic cleft

What is the axon terminal?

The end of an axon branch, also called a terminal bouton

What is the junctional fold of the sarolemma?

Folds in the sarcolemma that increase the surface area, allowing more receptors to be packed in

What is the synaptic cleft?

A small gap between the folds of the sarcolemma and the axon terminal

True or False, the synaptic cleft makes it so that there is no direct contact between the sarcolemma and the axon terminal

True

Describe the process from an electrical signal to contraction.

- Motor neuron transmits an electrical signal down to the axon terminal

- Signal causes the release of the neural transmitter inside the terminal into the receptors in the sarcolemma

- When the transmitters bind to the receptors it causes an electrical signal to be transferred across the muscle fiber (end plate potential)

- The signal moves across the surface of the sarcolemma until it falls into a t tubule

- It moves down the T Tubule and stimulates the terminal cisternae of the sarcoplasmic reticulum on either side to open

- This causes calcium to be released, which binds to troponin, moving tropomyosin and allowing myosin to bind

What are the three types of Skeletal Muscle fibers?

Slow Oxidative Type 1

Fast Ox-Glycolytic Type 2a

Fast-Glycolytic Type 2b/2x

"Fast Twitch" muscles are more likely to contain which fibers?

Fast OG 2a

Fast G 2b

"Slow Twitch" muscles are more likely to contain which fibers?

Slow O 1

Which fibers are more likely to be red?

Slow O 1 (Red)

Fast OG 2a (Pink)

Myoglobin is a protein that carries oxygen in muscles. What kinds of fibers are more likely to contain high amounts of myoglobin

Red/pink muscle fibers

Slow O 1

Fast OG 2a

Muscle fibers are either Aerobic or Anaerobic. Which fibers are aerobic or anaerobic?

Slow O 1 = Aerobic

Fast OG 2a = Aerobic or Anaerobic

Fast G 2b/2x = Anaerobic

Muscle fibers that are "slow twitch" or have slower contraction velocity are more likely to be fatigue resistant. What are the fatigue resistance levels of the three fiber types?

Slow O 1 = High

Fast OG 2a = Intermediate

Fast G 2b/2x = Low

What is the primary function of Slow Oxidative Type 1 fibers

Maintaining posture and endurance activities

What is the primary function of Fast Ox-Glycolytic Type 2a fibers?

Walking and Sprinting

What is the primary function of Fast-Glycolytic Type 2b/2x fibers?

Rapid, intense movements of short duration

Does training-induced "fiber type switching" actually switch the fibers in the muscles?

No, it only changes the characteristics of your muscle cells to be more like a certain type