Muscle Tissue: Types, Structure, and Function 1/2

contractility

Muscle tissue is specialized for

Types of muscle tissue

Skeletal, cardiac, smooth

Cell lengthening

&

Synthesis of myofibrillar proteins actin and mysoin

Differentiation of muscle tissue entails

Verly long fibers (cells)

Multinucleated cells

Cross-striations

Skeletal muscle has what features?

Fast and strong, voluntary control

How are the contractions of skeletal muscle?

Cardiac muscle

What muscle tissue has branched cells with intercalated discs & cross-striations

Vigorous, rhythmic, and involuntary

Describe the contractions of the cardiac muscle tissue

Spindle-shaped (fusiform) cells, involuntary, no striations.

What are the features of smooth muscle tissue?

SM contractions are slow and involuntary

Are smooth muscle contractions fast or slow?

Wall of hollow, internal organs (except the heart)

Smooth muscle tissue lines the walls of what

muscle fiber

muscle cell =

sarcolemma

cytoplasmic membrane =

sarcoplasm

cytoplasm =

sarcoplasmic reticulum

Smooth ER =

Surrounds myofibrils and creates proteins for sequestration

Location and function of the sarcoplasmic reticulum?

Sarcomere

Functional unit of contraction between Z discs.

Myoblasts -> form myotubes -> muscle fiber

How does skeletal muscle develop?

Epimysium

What is the dense connective tissue surrounding the ENTIRE muscle?

Perimysium

What is the thin tissue surrounding muscle fascicles.

Endomysium

What are the reticular fibers and fibroblasts that surround INDIVIDUAL muscle fibers?

P = perimysium

En = endomysium

E = epimysium

Identify the parts of the skeletal muscle

It carries a rich vascular network that surrounds each muscle fiber

What's an important trait of the endomysium?

Striations

Alternating dark and light bands

Myofirbrils run parallel to long axis of the cell. Consists of repetitive sarcomeres.

How are myofibrils organized?

Mitochondria and sarcoplasmic reticulum

What cell structures are found in between myofibrils?

from z disc to z disc

What are the boundaries of one sarcomere?

A bands (anisotropic)

Dark bands in muscle fibers containing myosin.

I bands (isotropic)

Light bands in muscle fibers containing actin.

Z disc

What is the dissection of the I band?

H zone

Central lighter zone in A band, no actin.

Sarcomere

What is the functional unit of contractile apparatus between two Z discs?

T tubules (transverse tubules)

Extensions of that sarcolemma (plasma membrane) that penetrate muscle fibers.

T tubules encircle each myofibril close A- and I- band boundaries of sarcomeres

What structure is surrounded by t-tubules?

Triad

One T-tubule and two terminal cisternae.

Depolarization triggers Ca2+ release by the sarcoplasmic reticulum into the sarcoplasm

How does depolarization of t-tubules affect sarcoplasmic reticulum?

Initiates contraction of sarcomeres

Presences of Ca2+ in the sarcoplasm causes what?

Thick and thin (myosin and actin)

What two myofilaments make up myofibrils?

Two identical heavy chains, two pairs of light chains

What do thick filaments (myosin) consist of?

They are twisted as myosin tails b/c they have thin, rod-like motor proteins.

How do the heavy chains of myosin function?

End in globular projections, formed at the head of each heavy chain.

Describe the structure of the 2 pairs of light chains.

Bind to actin (forming cross-bridges) and ATP (actomyosin ATPase activity).

What do the light chains bind?

Thin filaments: F-actin

This type of filament is composed of monomers of G-actin and are located between thick filaments

Each monomer has a binding site for myosin

Each monomer of thin filaments contain a what?

Tropomysoin and Troponin

What two regulary proteins are associated with thin filaments?

Tropomyosin

Protein that blocks actin binding sites. Located in the grove of actin strands.

TnT

TnC

TnI

What are the 3 subunits that make up troponin?

TnT: attaches to tropomyosin

TnC: binds Ca2+

TnI: regulates actin-myosin interaction

List the functions of the 3 subunits

Causes a change in confirmation of troponin

Which causes a movement of tropomyosin from the site

Exposing the active site of globular actin so myosin can bind

Describe what happens when Ca binds to a subunt:

Thin filaments not overlapping thick filaments, contains Titin

Describe the structure of the I band

Titin anchors myosin to Z disc

Titin is the largest protein of the body and has what function in the I band?

alpha actin

What protein anchors actin filaments to Z discs?

Thick filaments that have overlapping portion of thin filaments and an H zone in the center

How is the A band organized?

NO, the H zone has no thin filaments; it is just the lighter central zone

Does the H zone contain thn filamets?

the -M line-—containing myomesin and creatine kinase

What bisects the A band?

Actomyosin ATPase

Enzymatic activity of myosin during contraction.

ACh is released from the synaptic lobe into the synaptic cleft. 2 molecules of Ach binds to the motor end plate.

During the 1st step of a contraction, describe the path of ACh?

Binding of AcH initiates a muscle impulse in the sarcolemma of the muscle fiber.

What gets initiated when ACh binds at the motor end plate?

in the neuromuscular junction

the motor end plate is found where?

Muscle impulse spreads quickly from the sarcolemma along T tubules.

How does the muscle impulse spread after the binding of ACh? (step 2)

calcium ions are released from terminal cisternae into the sarcoplasm.

During the spreading of the muscle impulse, calcium ions are released from?

Calcium ions bind to troponin.

where do calcium ions bind after being released into the sarcoplasm? (step 3)

troponin will change shape and ultimately the active site on actin is exposed (thin filaments)

Describe the conformational change that calcium ions cause

myosin heads of thick filaments attach to form crossbridges

when the active site of actin is exposed, what attaches to it? (step 3)

the repeating cycle of attatch-pivot-detach-return slides thick and thn filaments past each other

How do myosin heads cause the shortening of sarcomeres? (step 4)

ATP

ATP binds myosin heads = ADP +Pi

what high energy molecule is involved in the pivoting of myosin heads?

1. calcium ions ACTIVELY transported into the sarcoplasmic reticulum

2. active sites no longer exposed

3. filaments relax

what happens once the muscle impulse stops? (step 5)

A band same length

During sarcomere shortening/muscle contractions, what band stays the same length?

I band is reduced, and overlapping zones increase in size

Which band is reduced in size during contraction?