Download Title: Muscles

Title: Muscles
1- Introduction – Bones provide the framework and leverage of the body, however,
they cannot move by themselves. Locomotion results from the alternating
contraction and relaxation of muscle
a- Muscles make up approximately 45-50% of the body’s total weight
b- Muscle strength reflects the three prime function of muscle which is to
convert chemical energy into mechanical energy to generate force,
perform work and produce movement
c- Muscle tissue helps to stabilize the body’s position, regulate organ
volume, generates heat and propels fluids and food throughout the body
2- Muscle Structure
a- There are three types of muscle and while they share many properties they
differ from one to another in their microscopic anatomy, location in the
body and control by nervous and endocrine systems
1- Skeletal-
2- Smooth
3- Cardiac –
3- Functions of Skeletal Muscle –
a- Through sustained relaxation and contraction muscle tissue has four key
functions
1- Producing body movement –
2- Stabilizing body position –
3- Sharing, storage and moving substances within the body –
a- Contraction of ring-like bands of smooth muscles called
sphincters prevent the outflow of contents of hollow organs
such as the stomach and rectum
b- Temporary storage of food and urine is made possible by
closing these sphincters
c- Cardiac muscle contraction pumps blood out of the heart and
through the vessels
d- Contraction and relaxation in smooth muscles in blood vessels
adjust their diameter, regulate flow, help to regulate blood
pressure
e- Smooth muscle contractions move food, bile and enzymes
through the digestive tract and push gametes through the
reproductive system
f- Skeletal muscle contraction promotes the flow of lymph and
returns blood to the heart
4- Heat Generation –
4- Properties of Muscle Tissue – Muscle tissue has four special properties that
enable them to function and contribute to homeostasis
a- Electrical excitability – A shared property of neurons and muscle cells is
the ability to respond to certain stimuli by producing electrical signals
known as action potentials or nerve impulses. These impulses travel along
the plasma membrane in ion channels
1-
b- Contractility – The ability to contract and produce force is due to its
ability to respond to an action potential. When the muscle contracts it
generates tension by pulling on attachment points (tendons inserted on
bone)
c- Extensibility –
d- Elasticity -
Questions:
1- Which type of muscle is controlled consciously and which is controlled
unconsciously?
2- What properties do muscle tissue and neurons share in common?
3- How are extensibility and elasticity related?
Title: Muscles Continued
1- The most important component of skeletal muscle are the muscle fibers
2- The diameter of mature muscle fibers range from 10 – 100  (10-6 or 1/25,000
inch)
3- A typical length of a muscle fiber is about 10 cm (4 in)
4- Embryologically, 100’s of myoblasts (muscle forming cells) fuse to form a single
fiber. Therefore a mature fiber is a single cell with 100’s of nuclei
5- Skeletal muscles do not undergo mitosis – In general you are born with all the
muscle fibers you are ever going to have.
a- Hypertrophy –
b- Hyperplasia –
c- Hypertrophy results from the production of HGH and the muscles
response to it and to increased levels of testosterone (primarily in men) at
puberty
d- Atrophy –
6- Satellite cells –
a- Fibrosis – Replacement of skeletal muscle with scar tissue
7- Sarcolemma, Transverse tubules (T-tubules) and Sarcoplasm
8- Myofibrils – High magnification of the sarcoplasm shows parallel threads about 2
micron in diameter running the entire length of the fiber. These threads are called
myofibrils
9- Within each myofibril are smaller structures called filaments. The filaments are
directly involved with contraction. These filaments are set up as alternating thin
filaments (8nm) and thick filamemts (16nm) a nanometer is 10-9 or .0001
10- Filament Structure – Thick and thin filaments overlap each other to a greater or
lesser extent depending on whether the muscle is relaxed, contracted or stretched.
a- A Band –
b- H Zone –
c- I Band –
d- Z Disc –
e- M line –
11- Muscle Proteins
a- Myosin –
b- Actin
c- Myosin acts as a protein motor that pushes or pulls other structures to provide
movement by converting the chemical energy of ATP into mechanical energy
that can produce force
d- Actin – contains a myosin binding site. When a muscle contracts the myosin
attaches to the binding site of the actin and shortens its length, pulling it closer to
the M-Line.