Muscular System A+P OAT Prep

What does a muscle do?

• Transfer of what into what

It converts chemical energy into mechanical energy

• This of course happens through muscle contraction

What is a contraction

Pulling

Skeletal Muscle

• Function

Moves the body, maintains the body posture, and the body temperature

Cardiac Muscle

• Main function

Contracts the heart to pump blood throughout the body.

Smooth Muscle

• Main function

Aids the organ systems like the gastrointestinal, digestive, and circulatory system

Striated muscles meaning

• Also striated vs nonstriated muscles

Appearance

• Striated or nonstriated

A muscle with dark and light band differences. (they have sarcomeres)

Striated: Cardiac, Skeletal

Nonstriated: Smooth

Involuntary vs Voluntary muscles

• Control type

  • Involuntary or voluntary

Concious or non concious use.

Cardiac and Smooth are involuntary.

Skeletal are voluntary.

Multinucleated vs mononucleated muscles

• Nuclei

  • Single (one) or multinucleated

Mononucleated: Cardiac and smooth

Multinucleated: Skeletal muscles

Skeletal Muscle

• Function (again)

• Locations

• Characteristics (striated/nonstriated, voluntary/involuntary, nucleated/multinucleated)

Function: Moves our bodies and maintains posture and body temperature. Also stabilizes joints

Locations:

● Bones

● Tongue and esophagus

● Diaphragm

● Eye socket

Characteristics:

● Nuclei: multinucleated

● Appearance: striated (sarcomeres)

● Control: voluntary

Cardiac Muscle

• Function

• Locations

• Characteristics (striated/nonstriated, voluntary/involuntary, nucleated/multinucleated)

• What do they contain that makes them special

Function: Contracts the heart to pump blood

throughout the body

Locations:

● Walls of the heart

Characteristics:

● Nuclei: one

● Appearance: striated (sarcomeres)

● Control: involuntary

They have intercalated discs

• These guys have coordinated electrical impulse propagation.

• They consist of desmosomes (which hole cells together) and gap junctions (which connect cytoplasms for ion exchange)

Smooth Muscle

• Function

• Locations

• Characteristics (striated/nonstriated, voluntary/involuntary, nucleated/multinucleated)

Function: Aids organ systems like the GI, digestive, and the circulatory systems

Locations:

• Organs

• Airways

• Blood vessels

  • Can undergo vasoconstriction and vasodilation

Characteristics:

• Nuclei: one

• Appearance: nonstriated

• Control: involuntary

Label the order from largest to smallest skeletal muscle anatomy parts starting with the skeletal muscle.

• Skeletal Muscle

• Muscle Fascicles

• Muscle Fibers

• Myofibrils

Skeletal Muscle

• What is it surrounded by

• What is it made of

• Largest bundle

○ Surrounded by: protective sheath, epimysium

○ Composed of: fascicles

Muscle Fascicle

• What is it surrounded by

• What is it made of

• Second largest bundle

  • Surrounded by: protective sheath, perimysium

  • Composed of: fibers

Muscle Fibers

• What is it surrounded by

• What is it made of

• Second smallest bundle (muscle cell)

  • Surrounded by: protective sheath, endomysium and cellular membrane, sarcolemma

  • Composed of: myofibrils

Myofibrils

• What is it surrounded by

• What is it made of

Smallest bundle

○ Surrounded by: sarcoplasm

(cytoplasm, not protective sheath)

○ Composed of: contractile proteins

What are sarcomeres?

• What do they consist of?

• Sarcomeres are the functional unit of skeletal muscle cells (muscle fibers)

  • Located in the myofibrils

• Sarcomeres contain myofilaments which have:

  • Actin

  • Myosin

sliding filament model of muscle contraction

Actin Def

• Actin (thin filaments)

Myosin Def

• Myosin (thick filaments)

Sarcolemma def

Cell membrane

Sarcoplasmic reticulum

Regulates calcium

Sarcoplasm

cytoplasm of skeletal and cardiac muscle

Actin and Myosin’s role in sliding filament theory

They are the contractile filaments

Troponin

Regulatory protein (the lined one)

Troponin

Regulatory Protein

What is the neuromuscular junction?

• How does contraction occur here?

• PT 1 of contraction

• NMJ is a connection between a motor neuron and a muscle cell

• Muscle contraction:

1. Action potential reaches the end of motor neuronʼs axon

2. Acetylcholine (ACh) is released

3. ACh binds to ligand-gated sodium channels; channels open (graded potentials), causing EPSP

4. If threshold is reached, voltage-gated sodium channels open → action potential

Sliding Filament theory part of contraction

5. Action potential goes down the T-tubles

6. Action potential triggers the sarcoplasmic reticulum to release calcium

7. Calcium binds to troponin, which stimulates a power stroke

8. Muscle fiber shortens and the muscle contracts.

Cross Bridge cycle (sliding filament theory in depth.

1. ADP-bound myosin head is cocked and ready to bind to actin (high energy state).

2. In the presence of Ca²⁺, Ca2+ binds to troponin, which exposes a binding site for myosin.

3. The bound myosin rotates its head, producing a “power stroke”

4. Then ADP is released and an ATP molecule binds to the myosin head

5. The actin and myosin detach

ATP is then hydrolyzed to ADP, which cocks back the myosin head.

Rigor Mortis

Muscles stiffen after death

This is since it requires ATP to relax the muscle

Contractile Unit of the muscle

• What is it?

Sarcomere

Z lines

Ends of sarcomeres

○ Thin actin filaments

M lines

Middle of the sarcomere

• Thick myosin filaments

I band

Only has actin present (I is thin just like actin)

Vowels = band

H zone

only has myosin present

(H is thick like myosin)

constanants are a zone

A band

Spans the length of myosin, while also having actin and myosin overlap.

Vowels = band

Which bands shrink when the muscle contracts

Which band stays the same

I and H shrink

A band stays the same

What is a motor unit

Muscle fibers innervated by a single neuron

• i.e. variable number of muscle cells to one motor neuron

Small motor units

• What are they used for

• example

• Only a few muscle fibers innervated by a motor neuron

• Used for precise movements (i.e. fine motor control)

Example: extraocular eye muscles

Large Motor Units

• Many muscle fibers innervated by a motor neuron

• Used for powerful movements

EX: Thigh muscles

Twitch Contraction

• Neuron stimulates contraction of ALL muscle fibers belonging to its motor unit

• Each twitch has the same size and duration

Acetylcholinosterase use

It is used to stop acetylcholine from passing the NMJ. It is hydrolyzes Acetycholine.