Histology and Physiology Flashcards

Flashcards based on Histology and Physiology lecture notes.

What is the origin of skeletal muscles prenatally?

Myoblasts

What is the origin of skeletal muscles postnatally?

Satellite cells (in younger age)

List three LM characteristics of skeletal muscles.

Large in diameter, deeply acidophilic; multinucleated, flat and peripheral nuclei; striations.

What connective tissue covering surrounds a single muscle fiber?

Endomysium

What connective tissue covering surrounds a bundle of muscle fibers?

Perimysium

What connective tissue covering surrounds the whole muscle?

Epimysium

Which band in the myofibril contains both actin and myosin?

A band

Which band in the myofibril contains only actin?

I band

Which band in the myofibril contains only myosin?

H band

Which band contains both actin and proteins?

M line

What happens to the H and I bands during muscle contraction?

They decrease in size.

What happens to the A band during muscle contraction?

It remains constant in size.

What is the functional contractile unit of skeletal muscle?

Sarcomere

Name three components of thin filaments.

F actin double helix, tropomyosin, troponin

What attaches the thin filament to the Z line?

Nebulin

Name three components that maintain the sarcomere.

Titin, nebulin, alpha actinin

What three components make up the triad of skeletal muscle at the A-I junction?

1 Terminal cistern, 2 T tubule, 3 terminal cistern

What happens to the Z lines during muscle contraction?

They come closer together.

What happens to the I band during muscle contraction?

It is reduced.

What happens to the A band during muscle contraction?

It remains unchanged.

What happens to the H band during muscle contraction?

It disappears.

What happens to the sarcomere during muscle contraction?

It shortens.

How does regeneration of skeletal muscle occur in young age (below 20)?

Can divide and regenerate

How does regeneration of skeletal muscle occur in old age?

By satellite cells

What is the mechanism of Duchenne muscular dystrophy?

Defect in dystrophin protein synthesis, which connects the cytoskeleton of each muscle fiber to the basal lamina.

What are the LM characteristics of cardiac muscles?

One large oval central nucleus; weak acidophilic cytoplasm; no satellite cells.

What connects adjacent cardiac muscle cells together?

Intercalated discs

Do cardiac muscles have a TRIAD or DIAD system?

DIAD

What are the two parts of the intercalated disc?

Transverse and Longitudinal

What prevents detachment of muscle fibers during contraction in cardiac muscle?

Macula adherens present in transverse part of intercalated disc.

Why are there numerous gap junctions in the longitudinal part of intercalated discs?

For ionic coupling (coordination of muscle contraction as one functional unit).

Name three special characters of the purkinji fibers of cardiac muscles.

No diad system, few intercalated disc, large in diameter with rich nerve supply, pale vacuolated cytoplasm due to large amount of glycogen and few myofilaments.

Name three special characters of smooth muscles.

Secretory function (collagen III, elastin and gags), SER poorly developed, caveolae (Ca regulator).

How do smooth muscles regenerate?

By pericytes and mitotic activity of existing muscles.

Give an example of contractile non muscles cells.

Myofibroblast or myoepithelial cells.

Describe the function of caveolea in smooth muscle.

Similar to T tubules and regulates calcium.

What is a shared characteristic between a dense body in smooth muscle and a Z line in sketetal muscle?

They're equal.

Compare the regeneration capabilities of skeletal and cardiac muscle

Skeletal muscle can regenerate via satellite cells, while cardiac muscle has no regeneration.

What is the role of calcium in neuromuscular transmission?

Helps acetylcholine release at the neuromuscular junction.

How does acetylcholine affect Na+ permeability?

Increases the permeability of Na+ ions, causing depolarization.

List the effect that prostigmine has and why.

Anti-cholinestrase as prostigmine , increase transmission .

List the effect that curare has and why.

Blocked neuromuscular transmission as curare , decrease transmission.

What is Myasthenia Gravis?

Autoimmune disease where antibodies are produced against acetylcholine receptors, leading to skeletal muscle weakness.

What is the role of cholinesterase inhibitor drugs such as neostigmine?

It will inhibit the function of cholinesterase, ultimately increasing transmission by having more acetylcholine present.

What is the function of troponin I?

Binds with actin.

What is the function of troponin C?

Binds with Ca.

What is the function of troponin T?

Binds with tropomyosin.

During which phase of excitability changes is there a complete loss of excitability?

Absolute refractory period

During which phase of excitability changes is the excitability reduced but not lost?

Relative refractory period

What is the function of tropomyosin?

Covers the myosin binding site on actin during relaxation.

What is the function of T tubules?

Spread the action potential to the interior of fibers.

What is the function of the sarcoplasmic reticulum?

Storage of Ca in skeletal muscle.

What happens when calcium binds with troponin C?

It reacts with tropomyosin to uncover myosin binding site.

What four factors affect simple muscle twitch?

Type of muscle (red or white fibers), temperature, fatigue, Starling’s law.

What is Starling's Law?

The force of contraction is directly proportional to the length of muscle fibers within limits.

What is the optimal length of muscle fibers according to Starling's Law?

2.2 micro

What is the all-or-none law?

A single muscle fiber contracts maximally or not at all provided all conditions are the same.

What causes the staircase phenomenon?

Reduced K ions inside the fibers, increased Ca ions inside the muscle, liberated heat that lead to increase of strength of contraction.

What channel is responsible for action potential in smooth muscle?

Calcium

What is the main difference between isotonic and isometric contractions?

Isotonic contractions shorten and carry weight; tension is not changed. Isometric contractions do not allow muscle to shorten; tension increases.

List four factors affecting smooth muscle contraction.

Stretch; local factors; cold; nerve supply.

Compare between visceral and multi unit smooth muscle

Visceral smooth muscle : Occurs in large sheets and has low resistance bridges “gap junctions” between the individual muscle cells.

Action potentials spread from one fiber to the adjacent ones very easily exp: its functions is syncytial fashion

3. Is found mainly in the walls of hallow visceral i.e: gut,ureters, and many blood vessels.

4. Nerve supply is confined to superficial layers. The muscle is spontaneously active and controlled by hormones, neurotransmitters.

   Multi unit smooth muscle:

   1. Is made up of individual units without interconnecting bridges.

   2. Action potential cannot spread from one fiber to the adjacent fibers.

   3. The muscle behaves like separate motor units. All or none law is obeyed only by the single muscle fiber.

   4. The muscle is densely innervated, and contraction is under neural control.

      Found in the iris of the eye, vas deferens and erector pili muscles of the skin