Muscular System Overview

These flashcards are designed to help students review key concepts related to the muscular system, including the types of muscle, their functions, and the basic mechanisms of muscle contraction and relaxation.

What are the three types of muscle tissue in the muscular system?

Skeletal muscle, Cardiac muscle, Smooth muscle.

What distinguishes skeletal muscle from the other types of muscle tissue?

Skeletal muscle is voluntary and attached to the bones.

What is the primary function of cardiac muscle?

To pump blood through the heart.

How does smooth muscle differ from skeletal muscle?

Smooth muscle is involuntary and lacks striations.

What is the role of tendons in the muscular system?

To connect muscle to bone.

What is the epimysium?

The connective tissue that surrounds the whole muscle.

What is the sarcolemma?

The cell membrane of a muscle fiber.

What is the primary function of the neuromuscular junction?

It is the site where a motor neuron and a muscle fiber interact.

What is acetylcholine?

The neurotransmitter that stimulates muscle contraction at the neuromuscular junction.

What is the sliding filament model?

It describes the process of muscle contraction whereby thick and thin filaments slide past each other.

What happens during muscle relaxation?

Calcium ions return to the sarcoplasmic reticulum, and the troponin-tropomyosin complex covers the binding sites on actin.

What is muscle fatigue?

The inability of a muscle to contract due to factors like decreased blood flow and ion imbalances.

What are the two phases of cellular respiration?

Anaerobic phase and Aerobic phase.

What distinguishes fast-twitch muscle fibers from slow-twitch fibers?

Fast-twitch fibers contract quickly and use anaerobic respiration; slow-twitch fibers are more fatigue-resistant and use aerobic respiration.

What is muscle hypertrophy?

The enlargement of skeletal muscle that is exercised.

What is the function of myoglobin in muscle cells?

To store oxygen for aerobic respiration.

What is summation in muscle response?

The process where the force of individual muscle fiber twitches combine due to increased frequency of stimulation.

What role does the troponin-tropomyosin complex play in muscle contraction?

It covers binding sites on actin until calcium ions bind to troponin, allowing contraction.

What is the origin and insertion of a muscle?

The origin is the less movable end, and the insertion is the more movable end of the muscle.

What is the effect of exercise on skeletal muscles?

Exercise stimulates muscle fibers to increase in size and improve their endurance.

What is the main characteristic of cardiac muscle?

It is striated, involuntary, and cells are interconnected by intercalated discs.

Agonist

A muscle that is the primary mover during a specific action or movement.

Synergists

Muscles that assist the agonist in performing a movement

Antagonist

A muscle that opposes the action of the agonist, often relaxing while the agonist contracts

Prime mover

Another term for agonist, indicating the muscle that provides the primary force for a specific movement.

Origin

less movable end of a muscle that remains fixed during contraction.

Insertion

the more movable end of a muscle that is attached to the bone being moved during contraction.

Cardiac Muscle

-Located only in the heart

-Striated

-Contains a single nucleus

-self exciting;Rhythmic

-Longer refractory period than skeletal muscle

-Muscle fibers joined together by intercalated disc

Fascia

Thin covering of connective tissue around a muscle.

How does smooth muscle resemble skeletal muscle contraction?

• Interaction between actin and myosin

• Both use calcium and ATP

• Both are triggered by membrane impulses

How is smooth muscle different from skeletal muscle contraction?

• Smooth muscle lacks troponin; uses calmodulin instead

• Two neurotransmitters affect smooth muscle: Acetylcholine (Ach) and norepinephrine (NE)

• Hormones can stimulate or inhibit smooth muscle

• Stretching can trigger smooth muscle contraction

• Smooth muscle slower to contract and relax

• Smooth muscle more resistant to fatigue

• Smooth muscle can change length without changing tautness

What are 2 types of smooth muscle?

Multi-unit Smooth Muscle and Visceral smooth muscle

Multi-unit Smooth Muscle

-Cells are less organized

-Function as separate units

-Fibers function Independently

-Iris of eyeballs of blood vessels

-Stimulated by neurons, hormones

Visceral Smooth muscle

-Single smooth muscle

-sheets of spindle-shaped muscle fibers

-fibers help together by gap junctions

-exhibit rhythmicity

-conduct peristalsis

-walls of most hollow organs

-More common type of smooth muscle

compared to skeletal muscle, Smooth muscle is

• Shorter

• Single, centrally located nucleus

• Elongated with tapering ends

• Myofilaments randomly organized

• Lack striations

• Lack transverse tubules

• Sarcoplasmic reticulum (SR) not well developed

Tendon

Cord-like mass of connective tissue that connects muscle to a bone

Aponeurosis

Sheet-like mass of connective tissue that connects a muscle to bone, skin, or another muscle.

Epimysium

surrounds whole muscle; lies beneath fascia

Perimysium

surrounds fascicles within a muscle

Endomysium

Surrounds muscle fibers (cells) within a fascicle

Skeletal Muscles

• Over 600 skeletal muscles in the body

• Attached to bones, and skin of face

• Under conscious control (voluntary)

• Are organs of the muscular system

What are skeletal muscles composed of?

• Skeletal muscle tissue

• Nervous tissue

• Blood

• Connective tissues

What are the order of events in Cross-Bridge Cycling?

1.) Myosin head attaches to actin binding site, forming cross-bridge

2. ) Myosin cross-bridge pulls thin filament toward center of sarcomere

3.) ADP and phosphate are released from myosin

4.) New ATP binds to myosin

5.) Linkage between actin and myosin cross-bridge break

6.) ATP splits

7.) Myosin cross-bridge goes back to original position, ready to bind to another binding site on actin

Sliding Filament Model of Muscle Contraction

1.) When sarcomeres shorten, thick and thin filaments slide past each other

2.) H zones and I bands narrow

3.) Z lines move closer together

4.) Thin and thick filaments do not change length

5.) Overlap between filaments increases

Stimulus for muscle contraction

1.) Acetylcholine (ACh) is the neurotransmitter

2.) Nerve impulse causes release of ACh from synaptic vesicles

3.) ACh binds to ACh receptors on motor end plate

4.) ACh causes changes in membrane permeability to sodium and potassium ions, which generates a muscle impulse (action potential)

5.) Impulse causes release of calcium ions from SR, which leads to muscle contraction

Thick filaments

• Composed of myosin protein

• Heads form cross-bridges with thin filaments

Thin filaments

• Composed of actin protein

• Associated with troponin and tropomyosin, which prevent cross-bridge formation when muscle is not contracting

Neuromuscular Junction (NMJ)

• A type of synapse

• Also called a myoneural junction

• Site where an axon of motor neuron and skeletal muscle fiber interact

• Skeletal muscle fibers contract only when stimulated by a motor neuron

Parts of a Neuromuscular Junction

• Motor neuron: Neuron that controls skeletal muscle fiber

• Motor end plate: Specialized folded portion of skeletal muscle fiber, where fiber binds to neurotransmitter

• Synaptic cleft: Space between neuron and muscle fiber, across which neurotransmitter travels

• Synaptic vesicles: Membrane-bound sacs containing neurotransmitters

• Neurotransmitters: Chemicals released by motor neuron to deliver message to muscle fiber

Contraction of a skeletal muscle fiber:

• Requires interaction from several chemical and cellular components

• Results from a movement within the myofibrils, in which the actin and myosin filaments slide past each other, shortening the sarcomeres

• Muscle fiber shortens and pulls on attachment points

Skeletal muscle fiber (cell):

• Multinucleated

• Sarcolemma: Cell membrane of muscle fiber

• Sarcoplasm: Cytoplasm of muscle fiber

• Many myofibrils:

• Sarcoplasmic reticulum (SR): Endoplasmic reticulum of muscle; stores calcium

• Transverse (“T”) tubule: Relays electrical impulses to the SR

Compartment

Space containing group of muscles, blood vessels and nerves, enclosed by fascia

Compartment syndrome

• Fluid accumulation within a compartment

• Results in increase in pressure in compartment

• Leads to deficiency of oxygen and nutrients

• Causes severe pain

Fascia

Fascia of each muscle is part of network of fasciae

Portion surrounding muscles is deep fascia, which connects to subcutaneous fascia under skin

Network also connects to subserous fascia of serous membranes

Muscular Dystrophy

• Deficiency or abnormality/mutation in scarce muscle protein called dystrophin

• Dystrophin binds to internal side of muscle cell membranes, and holds them together during contraction

• In absence of normal dystrophin, cells lose normal structure and die

Muscular Dystrophy

• Deficiency or abnormality/mutation in scarce muscle protein called dystrophin

• Dystrophin binds to internal side of muscle cell membranes, and holds them together during contraction

• In absence of normal dystrophin, cells lose normal structure and die

Location

location: (head, neck,arm,leg)

Action

(Movement at joint) Ex:Flexion

Direction

Direction of muscle fiber

shape

Shape:(orbicularis;round),(Longus=long),(trapezius=diamond)

Number of origins

(1,2,3,4)(triceps, biceps,quadriceps)

Origins/insertion

Ex:antagonist

Relative

size

orbicularis oculi

circular (shape)

palmaris longus

longus (size)

Trapezius

diamond (shape)

Rhomboid minor

Rhombus (shape)

Rhomboid maximus

Rhombus (shape)

Latissimus dorsi

wide (shape)

Deltoid

triangle (shape)

Prontor teres

round (shape)

Gluteus maximus

largest (size)

Gluteus medius

Medium (shape)

Gluteus minimus

smallest (size)

Vatus lateralls

huge (size)

Adductor brevis

short (size)

muscles of abdominal wall

1.) external oblique

2)Internal oblique

3.)Transverse abdominus

4.) Rectus abdominus

Muscles of thigh

1.) hamstring group

2.) Bicep femoris

3.) semitendinous

4.)semimembranosus

Muscles of mouth

1.) Masseter (mastrification)

2.)temporalis

3.)medial pterygoid

4.)lateral pterygoid

Threshold stimulus

Excitatory stimulus that causes enough Na+ ions

to flow into cell that it reaches Threshold Potential of −55 mV

Depolarization

Change from negative to positive charge inside cell,

making both sides of membrane positive.

All-or-None Law

Reaching an action potential; either achieved or not

If action potential is reached, it sends signal all the way down the axon

Repolarization:

Return to resting potential after action potential;

occurs as K+ channels open and K+ ions rush out of cell; polarity

returns.

Hyperpolarization

Slight overshoot at end of repolarization, in which

potential drops below −70 mV for a moment before returning to −70

mV

Na+/K+ pump

now returns ions to original locations and concentrations