Summary physiology

MUSCLE TISSUE
A primary tissue type, divided into:
• Skeletal muscle tissue
• Cardiac muscle tissue
• Smooth muscle tissue
Skeletal muscles are organs composed mainly of skeletal muscle tissue, but they also contain
connective tissues, blood vessels, and nerves. It is an organ because it is made up of two or more
tissues that work together to perform one or more specific functions.

Muscles have three layers of connective tissues

1. Epimysium

2. Perimysium

3. Endomysium



EPIMYSIUM
The epimysium is a dense layer of collagen fibers that surrounds the entire muscle. It separates the
muscle from nearby tissues and organs. The epimysium is connected to the deep fascia, a dense
connective tissue layer

PERIMYSIUM
The perimysium divides the skeletal muscle into a series of compartments. Each compartment
surrounds a bundle of muscle fibers called a fascicle. The perimysium contains collagen and elastic
fibers as well as the blood vessels and nerves that supply the muscle fibers within the fascicles.

ENDOMYSIUM
The endomysium is delicate connective tissue that surrounds individual muscle cells, known as
muscle fibers. Endomysium is a flexible, elastic connective tissue that contains:

1. capillary networks (the smallest blood vessels) that supply blood to the muscle fibers;
2. myosatellite cells, stem cells that help repair damaged muscle tissue
3. nerve fibers that control the muscle.
The endomysium, perimysium and epimysium come together at the end of muscles to form
connective tissue attachment to bone matrix i.e. tendon.

,CHARACTERISITICS OF SKELETAL MUSCLE FIBERS
 skeletal muscle fibers are very long
 Develop through fusion of mesodermal cells called myoblasts
 Multinucleated: contains hundreds of nuclei
 The reason skeletal muscle fibers are multinucleated is because genes are necessary
to code for enzymes and structural proteins required for normal muscle contraction.

, THE SACROLEMMA AND TRANSVERSE TUBULES
The sarcolemma is the cell membrane of a muscle fiber; it surrounds the sarcoplasm. The sarcoplasm
is the cytoplasm of the muscle fiber. In a skeletal muscle fiber, a sudden change in the membrane
potential is the first step that leads to a contraction. Even though a skeletal muscle fiber is very large,
all regions of the cell must contract at the same time. The signal to contract must be distributed
quickly throughout the interior of the cell.

This signal is propagated through the transverse tubules. Transverse tubules, are narrow tubes
whose surfaces are continuous with the sarcolemma and extend deep into the sarcoplasm. They are
filled with extracellular tubules. Electrical impulses, known as action potentials, are conducted by the
sarcolemma and travel along the transverse tubules. This allows the entire muscle fiber to contract
simultaneously.

MYOFIBRILS
Myofibrils are smaller in diameter, but they are as long as the entire muscle fiber. Myofibrils consist
of bundles of protein filaments called myofilaments. There are two kinds of myofilaments:

1. Thin filaments: composed primarily out of protein actin
2. Thick filaments: composed primarily out of protein myosin
Myofibrils are responsible for muscle contraction, and ATP is needed. Mitochondrial activity and
glucose breakdown by glycolysis provide energy in the form of ATP for short-duration, maximum-
intensity muscular contractions.

THE SARCOPLASMIC RETICULUM
The sarcoplasmic reticulum is a membrane complex that forms a tubular network around each
myofibril. It is similar in structure to smooth endoplasmic reticulum in other structures. On either
side of a Transverse tubule, the tubules of the Sarcoplasmic Reticulum enlarge, fuse, and form
expanded chambers called terminal cisternae.