The Muscular System

The Muscular SystemThe Muscular System Myology = The study of muscles

Functions of muscle tissue:

Move the body by pulling bones

Maintain body positions by continuous muscle contraction (ex. Neck holding up the head)

Move substances within the body such as blood, reproductive cells and food.

Produce heat- muscle contraction generates thermal energy

Regulate organ volume (controls opening from the bladder, stomach, and rectum)

There are 3 types of muscle tissueThere are 3 types of muscle tissue

Skeletal

Smooth

Cardiac

Skeletal Muscle CharacteristicsSkeletal Muscle Characteristics Most are attached by

tendons to bones

Cells- called muscle fibers- are multinucleate

Striated – have visible banding

Voluntary – subject to conscious control

Cells are surrounded and bundled by connective tissue = great force, but tires easily

Smooth Muscle CharacteristicsSmooth Muscle Characteristics Has no striations

Spindle-shaped cells

Muscle fibers have a single nucleus

Involuntary – no conscious control

Found mainly in the walls of hollow organs and structures

Slow, sustained and tireless

Cardiac Muscle CharacteristicsCardiac Muscle Characteristics Has striations

Muscle fibers branch and contain a single nucleus

Joined to another muscle cell at an intercalated disc

Involuntary

Found only in the heart

Steady pace!

Naming of Skeletal MusclesNaming of Skeletal Muscles

Location of the muscles origin and insertion

Example: sterno (on the sternum)

Shape of the muscle

Example: deltoid (triangular)

Action of the muscle

Example: flexor and extensor (flexes or extends a bone)

Naming of Skeletal MusclesNaming of Skeletal Muscles

Direction of muscle fibers

Example: rectus (straight)

Relative size of the muscle

Example: maximus (largest)

Naming of Skeletal MusclesNaming of Skeletal Muscles

Location of the muscle

Example: many muscles are named for bones (e.g., temporalis)

Number of origins

Example: triceps (three heads)

Connective Tissue Wrappings ofConnective Tissue Wrappings ofSkeletal MuscleSkeletal Muscle

Epimysium – covers the entire skeletal muscle

Fascia – on the outside of the epimysium

Connective Tissue Wrappings ofConnective Tissue Wrappings ofSkeletal MuscleSkeletal Muscle

Perimysium – around a fascicle (bundle of fibers)

Endomysium – around single muscle fiber (cell)

Microscopic Anatomy of SkeletalMicroscopic Anatomy of SkeletalMuscleMuscle Sarcolemma – specialized plasma

membrane of a muscle fiber

Sarcoplasm- cytoplasm of the muscle fiber

Sarcoplasmic reticulum – network of tubules in the muscle fiber that store calcium ions for muscle contraction

Myoglobin- pigment in the sarcoplasm that stores oxygen

Microscopic Anatomy of Skeletal Microscopic Anatomy of Skeletal MuscleMuscle Myofibril- Cylindrical structure within a

muscle fiber

Bundles of thick and thin filament (makes muscle striated)

I band = light band (thin)

A band = dark band (thick)

Microscopic Anatomy of Skeletal Microscopic Anatomy of Skeletal MuscleMuscle

Sarcomere Contractile units of a muscle fiber which are

separated by Z discs

Microscopic Anatomy of Skeletal MuscleMicroscopic Anatomy of Skeletal Muscle Organization of the sarcomere

Thick myofilaments = myosin filaments= have extensions called “heads”

Thin myofilaments = actin filaments

Myosin and actin somewhat overlap

Actin are anchored at the z-disc

Quick Review1. For cardiac, smooth and skeletal muscle, indicate if

they are: striated or not; voluntary or not; multinucleated or not

2. What are the differences in shape between the different muscle cells?

3. What is the outermost connective tissue layer of skeletal muscle?

4. What are bundles of muscle fibers called?

5. What tissue layer surrounds each muscle fiber?

Quick Review cont…..6. What is the plasma membrane of a muscle fiber called?

7. What is the cylindrical unit inside a muscle cell?

8. What are the 2 myofilaments in a muscle fiber?

9. What is another term for the thick band?

9. What is another term for the thin band?

10.What is the region between z-discs called?

11.What is the region where the actin filaments are anchored?

12.Where are calcium ions stored in a muscle fiber?

The Sliding Filament Theory of Muscle The Sliding Filament Theory of Muscle ContractionContraction

1. Activation by a nerve causes myosin heads to attach to binding sites on the adjacent thin filament.

2. Myosin heads flex inward then reach ahead to attach to the next site of the thin filament.

3. This continued forward grabbing causes a sliding of the myosin along the actin.

4. The result is that the sarcomere shortens, thus shortening the entire muscle.

5. Myosin heads attach and detach to actin due to ATP (energy stored in mitochondria) and Ca+

(stored in sarcoplasmic reticulum).

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Neuromuscular junctions – Where motor neurons (nerve cells) and muscle fibers associate

Nerve Stimulus to MusclesNerve Stimulus to Muscles

Synaptic cleft – gap between nerve and muscle Nerve and

muscle do not make contact

Area between nerve and muscle is filled with fluid

Transmission of Nerve Impulse to Transmission of Nerve Impulse to MuscleMuscle Neurotransmitter – chemical released by a nerve

to communicate with another nerve or muscle

The neurotransmitter for skeletal muscle is acetylcholine (ACh)

ACh attaches to receptors on the sarcolemma

Sarcolemma allows sodium (Na+) to enter the muscle fiber

Sodium rushing into the cell initiates muscle contraction by causing the release of Ca+ from the sarcoplasmic reticulum.

Contraction of a Skeletal MuscleContraction of a Skeletal Muscle

• What happens if NMJs are blocked?

–No muscle contraction!!• Why would someone want to purposely

block NMJs?–No muscle contraction= No wrinkles!!

• What is a drug that does that?–BOTOX!!

Botox “before” and “after”Botox “before” and “after”

What causes a muscle to relax after contraction?

• The enzyme acetylcholinesterase rapidly breaks down acetylcholine in the synaptic cleft, preventing it from continuing to signal to the muscle fiber.

• Ca2+ ions are transported from the sarcoplasm back into the sarcoplasmic reticulum for storage.

• The actin filaments slide back to their relaxed positions

Muscle Fatigue and Oxygen DebtMuscle Fatigue and Oxygen Debt

Muscle fatigue is the inability to contract after prolonged activity.

What are some possible reasons for why this happens?

The common reason for muscle fatigue is oxygen debt

Oxygen debt is the amount of oxygen taken into the body after exercise to “repay” what was taken from the myoglobin.

Muscle Fatigue and Oxygen DebtMuscle Fatigue and Oxygen Debt Under anaerobic (low oxygen) conditions (during

exercise when not taking in enough oxygen), muscle cells go through fermentation to produce energy. This results in a build up of lactic acid in the muscles. This is a very inefficient energy producing process.

Increasing acidity (from lactic acid) and lack of ATP causes the muscle to contract less.

The body uses oxygen debt to remove lactic acid and produce more ATP.

Muscles and Body MovementsMuscles and Body Movements

Slide 6.30a

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Movement is attained due to a muscle moving an attached bone

Figure 6.12

Muscles and Body MovementsMuscles and Body Movements

Slide 6.30b

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Muscles are attached to at least two points

Point of Origin –attachment to an immovable bone

Point of Insertion –attachment to a moveable bone

Figure 6.12

Types of MusclesTypes of Muscles

Prime mover – muscle with the major responsibility for a certain movement

Antagonist – muscle that opposes or reverses a prime mover

Synergist – muscle that aids a prime mover in a movement and helps prevent rotation

Flexor- bends a joint

Extensor- straightens a joint

Example:Example:

Biceps curl-

Prime mover- Biceps brachii

Antagonistic muscle- Triceps brachii

Synergist muscle- Pectoralis major

Flexor- Biceps brachii

Extensor- Triceps brachii

Disorders relating to the Muscular System

• Muscular Dystrophy: inherited, muscle enlarge due to increased fat and connective tissue, but fibers degenerate and atrophy

• Duchenne MD: lacking a protein to maintain the sarcolemma

• Myasthemia Gravis: progressive weakness due to a shortage of acetylcholine receptors