Muscle lecture (excitation contraction coupling)

Skeletal muscle is attached to

Bone

Myofiber

Individual muscle cell

Why are muscle cells multinucleated

In utero, when the fetus develops, single muscle cells begin to fuse together

Muscle cell is surrounded by

Enomysium

Endomysium job

Hold all muscle cells together so when they contract, they all contract together

Muscle is grouped in

Fascicles

Fascicles are surrounded by

Perimysium

Epimysium on muscle turns into the

Tendon

Sarcolemma

Cell membrane of a muscle cell

Myo/ sarco are prefixes for

Muscle

Lemma is a suffix for

Cell membrane

myofibril

Long rods of proteins inside of muscle cell

Myofiber

Muscle cell

Does all the heavy lifting and contraction of muscle

Myofibril

Z lines and M lines are

Anchoring proteins

Z lines are at the

End

M lines are in the

Middle

One sarcomere consists of

Z line to Z line (with M line in the middle)

What attaches (anchors) to Z lines and M lines

Filaments

Filaments are a type of

Proteins

Myosin

Thick filament

Actin

Thin filament

Myosin is attached to

M line

In resting state of skeletal muscle, all myosin heads are pointed towards

Nearest Z line

Myosin has both

Heads and tails

G (globular) actin

One of the proteins that is involved in actin; which is attached to the Z line

Strand of pearls protein in actin

G actin

G actin has a binding site on each “pearl”, why binds to it?

Myosin head

Myosin has a super high affinity for

G actin

If myosin head can bond to G actin, what will occur?

Muscle contraction

Since G actin and myosin head have a super high affinity towards each other, and are right next to each other, which protein can thinly come between them in order to inhibit them from binding to inhibit constant tetani and allow us to relax?

Tropomyosin

If you have tropomyosin between myosin head and g actin, you can have

Relaxation of muscles

Troponin has the ability to

Move tropomyosin back and forth

If troponin allows tropomyosin to slide in between G actin and myosin head,

Muscle will be relaxed

If tropomyosin pulls troponin out from in between G actin and Myosin head,

Muscle will contract

Troponin is like a “”

Handle

How does troponin know when to remove tropomyosin?

Ca++ binds to troponin

Calcium causes

Contraction

If calcium is present,

Muscle will contract

What happens if Ca++ binds to troponin

Troponin changes shape and removes tropomyosin so that it’s not between G actin and Myosin head anymore. Muscle will contract

How does Ca++ know when to bind to troponin a where does it come from?

Rough er 2 major functions

Protein synthesis and stores calcium

The Ca++ that we need to bind to troponin is stored inside the

Rough er

Rough er has been modified, how does it look now?

It is wrapped around myofibril in a spiderweb-like shape

Modified rough er is now called

Sacroplasmic reticulum

Motor neuron neurotransmitter to muscle cell sarcolemma

Ach-acetylcholine

Which neurotransmitter stimulates skeletal muscle contraction

ACh-acetylcholine

Underneath surface of cell membrane (sarcolemma) of muscle cell is

Sarcoplasmic reticulum

Where does sarcoplasmic reticulum sit

Right on top of actin and myosin

Where neuron comes into close proximity of sarcolemma

Neuromuscular junction

Colinergic receptors

Where ACh-acetylcholine binds to

When ACh-acetylcholine binds to cholinergic receptors on muscle cells,

Action potentials begin to move across surface of skeletal muscles

As K+ is being repelled across surface of cell membrane, it will fall into and accumulate in

Transverse Tubules/ T tubules

When K+ accumulates in T tubules, it increases cell membrane voltage to

-50mV

When K+ accumulates in T tubules, and increases membrane potential to -50mV, what happens?

Ca++ regulates gates on sarcoplasmic reticulum will open, and Ca++ will diffuse out and bind to troponin to allow muscle contraction

Sarcoplasmic reticulum is directly on top of

Troponin

Ca++ has a high affinity for

Troponin

Cholinergic receptors are located on

Sarcolemma

Ach-acetylcholine is stored in

Terminal butons of motor neuron

When Ach_acetylcholine binds to cholinergic receptors on sarcolemma, it creates action potentials; which most importantly

Repels K+

At -50 which gates open

Ca++ regulated gates on sarcoplasmic reticulum

Any antigravity movement stimulates

Protein synthesis in the muscles

When you re doing anti gravity movements like weight lifting, at the cellular level, you are building ?

More actin and myosin

Why do muscles get bigger

Because we’ve built more protein (actin and myosin)

Why do people take steroids like testosterone

It also stimulates protein synthesis

The more actin and myosin in each individual muscle cell,

The Stronger the cell, and the more u can lift up

Testosterone also increases

Mitosis

Any time you increase the mitotic rate in the body, you increase susceptibility to

Cancer

Myastenia gravis

Autoimmune disease where persons immune system destroys COLINERGIC RECEPTORS, so overtime they do not exist anymore; no muscle contraction

Myastenia gravis symptoms

Very droopy; eyes droopy, no posture

Myastenia gravis does not allow a person to

Bind Acetyl choline due to destruction of cholinergic receptors, and they cannot make their muscles contract

Excitation-contraction coupling

The physiological process where an electrical signal from a motor neuron triggers a muscle contraction by causing the release of calcium ions from the sarcoplasmic reticulum, ultimately leading to the interaction between actin and myosin.

Which three major proteins make up actin?

The three major proteins that make up actin are G actin, tropomyosin, and troponin.

What is the sliding filament theory?

The sliding filament theory explains that muscle contraction occurs when the thin filaments (actin) slide over the thick filaments (myosin), shortening the sarcomere, which leads to overall muscle contraction.

During the sliding filament theory, what is happening to Z lines?

They are being pulled in towards M line by myosin which is pulling actin (which are attached to Z lines), and sarcomere is getting shorter and bulges in the middle because myosin heads are binded to actin, and are pulling (contracting)