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 O 2 and remove CO 2 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.

Copyright © 2010 Pearson Education, Inc. Figure 9.1a Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Bone Perimysium Endomysium (between individual muscle 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.

Copyright © 2010 Pearson Education, Inc. Figure 9.1 Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Bone Perimysium Endomysium (between individual muscle fibers) Muscle fiber Fascicle (wrapped by perimysium) Epimysium Tendon Epimysium Muscle fiber in middle of a 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.

Copyright © 2010 Pearson Education, Inc. Figure 9.1b Connective tissue sheaths of skeletal muscle: epimysium, perimysium, and endomysium. Epimysium Muscle fiber in middle of a 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.

Copyright © 2010 Pearson Education, Inc. NucleusLight I bandDark A band Sarcolemma Mitochondrion (b) Diagram of part of a muscle fiber showing the myofibrils. One myofibril is extended afrom the cut end of the fiber. Myofibril Figure 9.2b Microscopic anatomy of a skeletal muscle fiber.

Copyright © 2010 Pearson Education, Inc. Figure 9.5 Relationship of the sarcoplasmic reticulum and T tubules to myofibrils of skeletal muscle. Myofibril Myofibrils Triad: Tubules of the SR Sarcolemma Mitochondria I band A band H zoneZ disc Part of a skeletal muscle fiber (cell) T tubule Terminal cisternae of the SR (2) M line

Microscopic Anatomy

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.

Copyright © 2010 Pearson Education, Inc. Figure 9.2c Microscopic anatomy of a skeletal muscle fiber. I band A band Sarcomere H zone Thin (actin) filament Thick (myosin) filament Z disc M line (c) Small part of one myofibril enlarged to show the myofilaments responsible for the banding pattern. Each sarcomere extends from one 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?