Topic 6c Muscular System- Dr. Basu’s Easy Anatomy & Physiology Lecture

Topic 6c Muscular System- Dr. Basu’s Easy Anatomy & Physiology Lecture


Hi everyone. This is the lecture 3 of topic
six. We are continuing with the muscular system. In this slide we are going to learn the two
types of muscle contraction. The first one is Isotonic contraction, and the next one
is isometric contraction. In isotonic contraction force is generated by changing the muscle
length. Unlike the isometric contraction, force is generated without changing the muscle
length. So in isotonic contraction the muscle shortens, concentric, or lengthens, eccentric.
For example, when you are bending your knee. In isometric contractions, the muscle is unable
to shorten or produce movement. For example, you push against a wall with bent elbows.
This figure shows isotonic and isometric types of muscular contractions. Muscle tone is generated
by different muscle fibers contracting at different times. I think we all know the effects
of exercise on muscles. Exercise increases the muscle mass, as well as endurance. There
are two types of exercise, aerobic which builds endurance and resistance which increases muscle
mass. Some examples of aerobic exercises are biking, and jogging. An example of Resistance
exercise is weight lifting. This is a list of five golden rules of skeletal muscle contraction.
The important one from here is that all skeletal muscles have at least two attachments. There
is the origin and the insertion. When a muscle contracts the insertion moves towards the
origin. Body movements are caused by a muscle moving an attached bone. Muscles have two
points of attachments. The first one is origin, which is stationary. The other type is insertion,
which is movable and usually during contraction, insertion moves towards the origin. The origin
is proximal to the insertion. Here is an example of origin and insertion from forearm flexion
at the elbow. So the origin is the attachment of brachialis muscle to the anterior surface
of the humerus. Insertion is the attachment to the coronoid process of the ulna. Body
movements occur in sets of two opposite movements. For example, flexion, versus extension. Flexion
is the movement that decreases the angle of the joint, bringing two bones closer together.
Extension is opposite of flexion, increasing the angle between two bones. When the extension
is beyond 180 degrees it is considered hyperextension. This slide shows you different examples of
flexion extension and hyper extension. Rotation is movement of a bone around its longitudinal
axis. For example, when you shake your head no, you move the atlas around the dens of
the axis. Abduction versus adduction. Abduction means movement of a limb away from the midline.
While adduction is opposite. Meaning movement of the limb toward the midline. You can remember
abduction as somebody taking something away. Circumduction is a combination of flexion,
extension, abduction, and adduction. For example, when you rotate your upper limb at the shoulder
joint. This is very common in ball and socket joints. Dorsiflexion versus plantar flexion.
Dorsiflexion means walking on your heels while plantar flexing is standing on toes, like
a ballerina. Inversion versus eversion. Inversion means turning the sole of the foot medially.
While eversion is Turing the sole laterally. Pronation versus supination. In supination
the radius and ulna are parallel. The forearm rotates laterally, so the palm faces anteriorly.
In pronation the radius and ulna cross each other like an x. The forearm rotates medially
so the palm faces posteriorly. This figure shows how in supination the radius and ulna
are parallel. While the in pronation the radius rotates over the ulna. Opposition vs reposition.
Opposition means movement of the thumb and other fingers on the same hand towards each
other. Reposition means return to anatomical position. Classification of skeletal muscles
bases on their action. The first type of muscles are known as the prime mover. These are the
muscles with major responsibility for a particular type of movement. For example when you are
doing a forearm flexion. It is the bicep brachii prime mover. This is the main protagonist
of the muscular contraction. The second type of muscle is the antagonist. The villain or
the one that is opposing the action of the prime mover. For example, in the forearm flexion
the triceps brachii they extend the forearm. So they are opposing the action of the bicep
brachii. The third type of muscle is the synergist muscle. This is the muscle that is helping
the prime mover in its action. For example in the bicep curl the synergist muscles are
the brachioradialis and the brachialis. This figure shows the location of the muscles that
we just discussed in the previous slide. The last catagorie of skeletal muscles is the
fixator muscle, which stabilizes or fixes the origin of the prime mover. For example
in a bicep curl the fixator muscles are a group of muscles known as the rotator cuff
muscles. These muscles connect the humerus and the scapula. The rotator cuff muscles
include the teres minor, subscaoularis, supraspinatus, and infraspinatus. Muscles are named in a
wide variety of ways. For example, by the direction of or orientation of muscle fibers.
That would be rectus. By the size of the muscle for example Maximus or medius. By location
of the muscle for example temporalis, since its close to the temporal bone. By the number
of origins, for example, triceps with three heads. By locations of the muscle’s origin
or insertion, for example sternal, means on the sternum. By the shape of the muscle for
example deltoid, which is a triangular muscle. By the action of the muscle, for example flexor
or extensor. Its flexing or extending a bone. This slide shows the different types of muscles
as for their names.

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