Muscles Intro

Muscle

Introduction

Three types

Cardiac, Smooth, Skeletal

Cardiac muscle:

Found only in the heart, cardiac muscle consists of short, branching fibers that fit together at intercalated disks. It appears striped, or striated, when viewed under a microscope. It is known as involuntary muscle because it contracts automatically.

Smooth muscle:

• Found in the digestive tract, blood vessels, bladder, airways, and uterus, skeletal muscle is nonstriated. It is known as involuntary muscle because it contracts automatically (such as when the digestive tract processes food).

Skeletal muscle:

Is attached to bone and causes movement of the body. It appears markedly striated when examined with a microscope. It is known as voluntary muscle because it can be contracted at will.

Multiple Select

Which muscle types are involuntary?

• cardiac

• smooth

• skeletal

Skeletal Muscle Structure

• A skeletal muscle cell is called a muscle fiber. Skeletal muscle consists of bundles of tiny fibers that run the length of the muscle. Most fibers are about 1 1/5 inches (3 cm) long and 1/500 inch (0.05 mm) wide.

• A delicate connective tissue called endomysium covers each muscle fiber

Skeletal Muscle Structure

• Muscle fibers are grouped in bundles called fascicles. A sheath of tougher connective tissue called the perimysium encases the fascicles. Another layer of connective tissue, called the epimysium, surrounds the muscle as a whole and binds all the muscle fibers together.

Skeletal Muscle Structure

• Connective tissue called fascia surrounds the muscle outside the epimysium. (Deep fascia lies between muscles, whereas superficial fascia [hypodermis] resides just under the skin.)

Multiple Choice

Muscle cells are called

• fasicles

• fibers

• bundles

Multiple Choice

The tough connective tissue surrounding the fascicle is called

• endomysium

• perimysium

• epimysium

Skeletal Muscle Attachment to Bone

• Direct: muscle fibers merge with the periosteum of the bone forming a strong attachment.

• Indirect: epimyseum extends past the muscle as a tendon. The tendon merges with the periosteum.

• If the muscle attaches to another muscle instead of a bone the tendon is a broad flat structure known as an aponeurosis and it attaches to the other muscle.

Multiple Choice

A broad, flat, tendon like material that connects two muscles is called

• ligament

• fascia

• aponeurosis

Structure of Muscle Fibers

• The membrane surrounding each muscle fiber (or cell) is called a sarcolemma.

• The cytoplasm of the cell is called sarcoplasm.

• Long protein bundles called myofibrils fill the sarcoplasm. (Myofibrils store glycogen and oxygen.)

Structure of Muscle Fibers

• Sarcoplasmic reticulum (SR) surrounds each myofibril. (This is where calcium ions are stored.)

• Transverse (T) tubules extend across the sarcoplasm. (T tubules allow electrical impulses to travel deep into the cell.)

Structure of Muscle Fibers

• Myofibrils consist of even finer fibers, called myofilaments. There are two types of myofilaments: thin and thick.

  •Thick myofilaments are made of a protein called myosin.

  •Thin myofilaments consist of a protein called actin.

• The arrangement of actin and myosin gives skeletal muscle its striated appearance.

Multiple Choice

The arrangement of the myofibrils gives skeletal muscle its __________ appearance.

• strong

• striated

• bumpy

Multiple Choice

The cell membrane of a muscle fiber is called the

• sarcoplasm

• sarcolemma

• sarcoplasmic reticulum

Multiple Choice

What is stored in the sarcoplasmic reticulum?

• oxygen

• carbon dioxide

• iron

• calcium