Muscle Tissue:An Introduction

Muscles make up close to half of the body mass and are unique in transforming chemical energy (ATP) into mechanical energy

Muscle Types

Skeletal muscles have obvious stripes and are called striated. They are long, multinucleated and are voluntary or under conscious control. It reacts quickly but fatigues easily.

Skeletal Muscle

Muscle Types

Cardiac muscles are also striated but are uninucleated and branch. They are involuntary muscles and react quickly and do not fatigue easily.

Muscle Types

Smooth muscle is not striated and is uninucleated. It is involuntary, reacts slowly and does not fatigue easily.

Characteristics of Muscle Tissue

1. Excitability (responsiveness or excitability) this is the ability to respond to a stimulus.

Characteristics of Muscle Tissue

1. Excitability (responsiveness or excitability) this is the ability to respond to a stimulus. The stimulus is hormonal or a neurotransmitter and the response is the generation of an electrical impulse.

Characteristics of Muscle Tissue

2. Contraction is the ability to shorten. This is a unique property of muscle tissue.

Characteristics of Muscle Tissue

3. Extensibility is the ability to extend beyond their resting length.

Characteristics of Muscle Tissue

4. Elasticity is the ability to recoil back to its original shape.

Gross Anatomy

1. Each muscle is served by one nerve and one artery. The nerve end controls contraction while the artery supplies blood to provide O2 and remove CO2 and heat.

Gross Anatomy

2. Connective tissue sheaths support each cell and reinforce the muscle tissue as a whole. There are three types:

Connective Tissue

A) Epimysium is the outermost layer and is composed of dense irregular connective tissue.

Connective Tissue

A) Epimysium is the outermost layer and is composed of dense irregular connective tissue.

– It surrounds the “belly” of the muscle.

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Figure 9.1a Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium.

Bone

Perimysium

Endomysium(between individualmuscle fibers)

Muscle fiber

Fascicle(wrapped by perimysium)

Epimysium

Tendon

Blood vessel

Fascicle

Connective Tissue

B) Perimysium and Fascicles: Muscle cells are organized into groups called fascicles. Each fascicle is wrapped in a connective tissue sheath called the Perimysium.

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Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium.

Bone

Perimysium

Endomysium(between individualmuscle fibers)

Muscle fiber

Fascicle(wrapped by perimysium)

Epimysium

Tendon

Epimysium

Muscle fiberin middle ofa fascicle

Blood vessel

Perimysium

Endomysium

Fascicle(a)

(b)

Connective Tissue

C) Endomysium is a layer of areolar connective tissue that surrounds each fiber or cell

Connective Tissue

These three connective tissue sheaths become continuous with each other and the tendons and collectively form the fascia.

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Figure 9.1b Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium.

Epimysium

Muscle fiberin middle ofa fascicle

Perimysium

Endomysium

(b)

Attachments

Muscles have two attachments, the origin and the insertion. The origin lies proximal to the insertion and is typically less moveable.

Attachments

Muscles have two attachments, the origin and the insertion. The origin lies proximal to the insertion and is typically less moveable.

1) Direct attachments are the fleshy attachments.

Attachments

Muscles have two attachments, the origin and the insertion. The origin lies proximal to the insertion and is typically less moveable.

1) Direct attachments are the fleshy attachments.

2) Indirect attachments the muscles connective tissue forms a tendon or an aponeurosis.

Attachments

An aponeurosis is a large sheet of tendon, examples include the abdominal aponeurosis which cover the abdominal muscle and help form the “six pack”.

Microscopic Anatomy

A muscle fiber is the muscle “cell”. It is a long cylinder with multiple nuclei which lie just below the cell membrane or sarcolemma. The endomysium lies just above the sarcolemma.

Microscopic Anatomy

The muscle fiber is a large cell. Their diameter is 10 to 100 microns and can have a length of 30 cm.

Microscopic Anatomy

The muscle fiber is a large cell. Their diameter is 10 to 100 microns and can have a length of 30 cm. The cytoplasm of the muscle cell is called the sarcoplasm.

Microscopic Anatomy

The muscle fiber is a large cell. Their diameter is 10 to 100 microns and can have a length of 30 cm. The cytoplasm of the muscle cell is called the sarcoplasm.The cell membrane is called the sarcolemma.

Microscopic Anatomy

The sarcoplasm contains glycosomes, granules of glycogen and myoglobin, a red protein that stores oxygen. It is similar to hemoglobin and gives muscle its color.

Microscopic Anatomy

In addition there are structures unique to the muscle, myofibrils, sarcoplasmic reticulum (endoplasmic reticulum), mitochondria and T tubules.

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NucleusLight I bandDark A band

Sarcolemma

Mitochondrion

(b) Diagram of part of a muscle fiber showing the myofibrils. Onemyofibril is extended afrom the cut end of the fiber.

Myofibril

Figure 9.2b Microscopic anatomy of a skeletal muscle fiber.

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Figure 9.5 Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle.

Myofibril

Myofibrils

Triad:

Tubules ofthe SR

Sarcolemma

Sarcolemma

Mitochondria

I band I bandA band

H zone Z discZ disc

Part of a skeletalmuscle fiber (cell)

• T tubule• Terminal

cisternaeof the SR (2)

M line

Myofibrils

Each muscle fiber is made up of rod like myofibrils that run parallel to the length of the muscle fiber. They contain the contractile elements of the muscle.

The Sarcomere

Because muscle fibers are very long, they are divided up into small contractile units called a sarcomere.

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Figure 9.2c Microscopic anatomy of a skeletal muscle fiber.

I band I bandA bandSarcomere

H zoneThin (actin)filament

Thick (myosin)filament

Z disc Z disc

M line

(c) Small part of one myofibril enlarged to show the myofilamentsresponsible for the banding pattern. Each sarcomere extends fromone Z disc to the next.

The Sarcomere

This makes up the contracting unit of the muscle.

Its structure and function will be discussed later.

Questions?