Page 3 - class-XI-ch.8-Lesson notes

(a) Gliding joints between bones that meet at flat or nearly flat articular surfaces.
(b) Hinge joints one rounded surface fits into another in such a way that movement is only possible in one plane, as
in elbow joint.
(c) Condyloid joints allow an angular movement in 2 direction-flexion, extension, abduction, adduction,
circumduction.as in the wrist joint but not rotation.
(d)Saddle joints this joint permits great freedom of movement, enabling the thumb to be opposed to the fingers
(e) Ball & socket joint One rounded extremity fits into a cavity of another bone, permitting movement in all
directions e.g., the hip joint and the shoulder joint.
(f) Pivot joints Joints with rotary movement in one axis, ring rotates around a pivot e.g. atlas & axis bones at the top
of neck, forearm

Properties of Muscles Muscle:
Also known as muscle fibers or myocytes are the fundamental units of our muscles. Following 4 properties distinguish
them from other cells
1. Excitability Capable of stimulation by nerves thru chemical signals
2. Contractility Capable of contracting when stimulated by neural input
3. Extensibility Possess extensibility or the capacity to stretch
4. Elasticity Capable of returning to its original resting length after being stretched

Functions of Muscles:
We know that there are three types of muscles in our body, viz., skeletal, smooth and cardiac. Each type of muscle
performs specific function in our body. Along with this, there are two types of skeletal muscle fibres in a human body,
namely, red fibres and white fibres. They are also called slow twitch fibres and fast twitch fibres, respectively. The
various types of muscles and fibres perform the following functions.

I. Muscle contractions usually carry out one of the two things—either they maintain a posture or they cause movement.
2. Skeletal muscles provide the force for movement of the skeletal system. These muscles perform movements at our
will.

3. Cardiac muscles perform pumping action of the heart.
4. Smooth muscles are concerned with the movements of internal organs, such as those of the stomach, intestines,
visceral and blood vessels.
5. The two types of skeletal muscle fibres, i.e., slow twitch fibres and fast twitch fibres perform different types of
functions. Slow twitch fibres contract at a slow rate, These fibres play a vital role in endurance activities or aerobic
activities, such as in cross country race or long distance races. The fast twitch fibres contract at a fast rate. These fibres
produce explosive power. These fibres perform fast repetitive contractions. These fibres are usually at work in 100 m
race or sprint races, high jump, weightlifting, basketball, football, etc. These fibres play a vital role while performing
anaerobic activities.
6. Muscles also provide shape to the human body.

7. Some muscles help in increasing the range of movements.

8. Big muscles provide protection to the bones.