Muscle, Chapter 6 Microanatomy

What is the function of myoepithelial cells?

Expel secretions from glandular acini

What are pericytes?

Smooth muscle-like cells that surround blood vessels

What are myofibrils?

Cells that have a contractile role

What is the function of myofibrils?

Secrete collagen

important following tissue damage during the process of healing and repair (leading to a scar)

Muscle cells can divided into 3 types:

1. Skeletal

2. Smooth

3. Cardiac

What is the external lamina propria?

1. Surrounds the cells of all three types

2. Contractile forces are transmitted to the external lamina via link proteins

What are some characteristics of skeletal muscle?

1. Responsible for the movement of the skeleton and organs (tongue, globe of eye)

2. Voluntary movement

3. Striated muscle (prominent cross-striations)

The sarcolemma is:

the plasma membrane or plasmalemma

The sarcoplasm is the:

cytoplasm

The sacroplasmic reticulum is:

the endoplasmic reticulum

What are some characteristics of smooth muscle?

1. Smooth, no appearance of cross-striations

2. Forms the muscular component of visceral structures (blood vessels, GI tract, uterus, urinary bladder)

3. Involuntary muscle (autonomic and hormonal control)

What are some characteristics of cardiac muscle?

1. Intermediate between skeletal and smooth muscle (structural and functional characteristics)

2. Provide continuous rhythmic contractility of the heart

3. Striated in appearance ONLY

What are the 4 characteristics of muscle tissue?

1. Excitability (respond to stimuli)

2. Contractility (ability to shorten)

3. Extensibility (ability to stretch)

4. Elasticity (ability to return to original shape

What are the key features of skeletal muscle?

1. Large cell with multiple peripheraly located nuclei

2. Arranged in fascicles

3. Three layers (endomysium, perimysium, epimysium)

These are elongated, multinucleate contractile cells bound together by collagenous supporting tissue

Muscle fibers

Atrophy of muscle fibers is caused by:

nerve damage

This is the synapse between motor neuron and muscle fibers, ACh is a neurotransmitter, and a signal transmission process occurs.

Neuromuscular junction

Individual nerve fibers branching within the muscle to supply a group of muscle fibers, collectively described as:

motor unit

Individual muscle cells (muscle fibers) grouped together into elongated bundles

Fasciculi/fascicles

Delicate supporting tissue that occupy the spaces between individual muscle fibers

Endomysium

Loose collagenous tissue that surrounds each fascicle

Perimysium

Dense collagenous sheath surrounding the entire muscle mass

Epimysium

These muscles are responsible for fine, highly controlled movements

Small fasciculi (more perimysial tissue)

Muscles that are responsible for gross movements only:

Large fasciculi (little perimysial tissue)

The connective tissue framework contains both kinds of fibers:

Collagen and elastic fibers

What are the steps of skeletal muscle embryogenesis?

1. Mesenchymal cells differentiate into myoblasts (by mitosis)

2. Myoblasts fuse end to end forming elongated multinucleate cells called myotubes

3. Myotubes synthesize contractile proteins to form myofilaments

True or false: Mature muscle cells can regenerate if damaged by proliferation of stem cells, which remain in adult cells

TRUE

Atrophy occurs by:

1. Shrinkage of cells

2. Reduction of cytoplasmic components

3. Organelles and enzyme proteins

4. Loss of cells by apoptosis

Increase in size of individual muscle fibers (NO INCREASE IN THE NUMBER OF MUSCLE CELLS)

Hypertrophy

Increase in the number of cells

HYPERPLASIA

An increase of bulk smooth muscle can occur to the combination of:

Hypertrophy and hyperplasia

This is pure hypertrophy, without the co-exisitng of hyperplasia

Hypertrophic myocardium

When can myocardium become hypertrophic?

Become hypertrophic when it is subjected to an increased hemodynamic load over a period of time (systemic hypertension or valvular stenosis)

Hyperplasia of endometrium occurs when:

There is abnormal estrogenic stimulation

The sarcomere consists of two types of myofilaments:

Thick and thin filaments

thick filaments are composed mainly of:

myosin

thin filaments are composed mainly of:

actin

Where is actin attached?

attached to the Z line

Where is myosin attached?

Attached to the M line

What are the I and H bands?

1. Areas of where thick and thin filaments do not overlap one another

2. areas of low electron density

What are the steps of the sliding filament mechanisms?

1. Contraction occurs by a sliding movement of the thick and thin filaments over one another

2. Myosin molecules possess ATP-activated side projections of head groups, which bind to actin to form cross-bridges

3. Myosin head groups generate movement by a change in protein configuriation

4. Myosin thick filaments are pulled over the thin actin filaments

5. Another ATP molecule binds to the myosin head group

These are transmitted across the neuromuscular junction via release of ACh, which binds to nicotinic receptors, which leads to the depolarization of the muscle fiber

Action potentials

In the resting state, the cross-bridge binding sites on the actin molecules are masked by this filamentous protein:

Tropomyosin

this is the system of tubular extensions of the muscle cell plasma membrane (sarcolemma)

T tubule system

A pair of terminal cisternae and a T tubule is called a:

Triad

What is continuous muscle contraction?

Involved in the maintenance of posture, contract almost continuously

What is an example rapid-short lived muscle movements?

Extra-ocular muscles

These fibers are slow red fibers, contain abundant mitochondria, large content of myoglobulin, accounts for the red color of such fibers.

Aerobin (Type 1) muscle fibers

These fibers are fast white fibers, contain few mitochondria, relatively little myoglobin, rich in glycogen and glycolytic enzymes.

Anaerobic (type 2) muscle fibers

What are the 3 causes of muscular dystrophy?

1. Gene mutations, affecting proteins of the membrane linkage complex

2. Mutation in other genes coding for contractile and other structural proteins

3. Mutation in the gene of dystrophin (muscle cannot function properly)

this protein has a role in connecting the cytoskeleton of muscle of the extracellular matrix

Dystrophin

The mutation sin the dystrophin gene are responsible for these two common forms of muscular dystrophy:

1. Duchenne (DMD), early childhood, death in early adult life

2. Becker (BMD) muscular dystrophies, symptoms at later age, less aggressive

As muscular dystrophy progresses the muscle is replaced by what?

replaced by fibrosis and adipose tissue

this occurs due to failure of the neuromuscular junction, causing weakness and rapid muscle fatigue upon voluntary movement

Myasthenia gravis

What is an autoantibody?

An immunoglobulin incorrectly produced by the patient’s immune system that targets the patient’s own tissue

This muscle type is mostly found in the walls of hollow viscera (gut, ureter, fallopian tube)

Smooth muscle

What are the muscle movements like of smooth muscle?

Produces diffuse movements through contraction of the whole muscle mass

How is smooth muscle contractility modulated?

Accommodated changing functional demands

1. ANS

2. Hormones

3. Local metabolites

What are some functional characteristics of smooth muscle?

1. Involuntary, autonomic innervation

2. No striations

3. Cells shorten and broaden on contraction

Smooth muscle has an arrangement where bundles or contractile protiens:

Criss-cross the cell

The intermediate filaments of smooth muscle insert on focal densites

Desmin

In the relaxed state, the smooth muscle cell is:

elongated

In contraction, the smooth muscle cell is:

globular shape

What is tonic smooth muscle?

1. Slow contraction

2. No APs

3. Low content of fast myosin

What is phasic smooth muscle?

1. Rapid contraction associated with an AP

2. ANS innervation precisely controls contraction (iris of the eye)

Benign tumors of smooth muscles:

Leiomyomas

Malignant tumors of smooth muscle:

Leiomyosarcomas

What do cardiac myocytes look like?

Long, branching cells with central nuclei

When does heart failure occur?

1. Occurs when the muscle of the heart is unable to pump effectively, cannot deliver enough blood to meet the body’s metabolic needs

What are some symptoms of cardiac failure?

Fatigue

Breathlessness

Peripheral edema

This disease is the leading cause of morbidity and mortality worldwide

Heart disease

In developed countries, what is the root cause of the majority of cardiac pathology?

Coronary artery atheroma

What is the electrical pathway of the heart?

1. Allows ventricular depolarizaiton and contraction to spread from the apex of the heart towards the ventricular outflow tracts

2. Runs thru the interventricular septum of the heart

What is an issue that can stem from issues of the electrical pathways of the heart?

Arrhythmia

The SA node is known as the:

Pacemaker cells

What is a myocardial infarction?

The conduction of depolarization for contraction runs along the muscle cells, which is interrupted in the area of infarction