Muscle Topics Lesson

Muscle Topics Lesson

Muscle actions, Muscle shapes, Muscle Lever systems and How muscles are named

Muscle Shapes

Muscles have varying shapes for the job they perform.

Shapes

Circular Muscles-

These muscles appear circular in shape and are normally sphincter muscles which surround an opening such as the mouth, surrounded by Obicularis Oris and Obicularis Oculi surrounding the eyes

Convergent Muscles

These are muscles where the origin (the attachment to a fixed bone, usually the proximal attachment) is wider than the point of insertion. This fibre arrangement allows for maximum force production. An example is Pectoralis Major. Convergent muscles are also sometimes known as triangular muscles.

Parallel Muscles

Parallel muscles have fibres which, as the name suggests, run parallel to each other and are sometimes called strap muscles.

They are normally long muscles which cause large movements, are not very strong but have good endurance. Examples include Sartorius and Sternocleidomastoid. Some textbooks include Fusiform muscles in the parallel group.

Pennate Muscles

Pennate muscles have a large number of muscle fibres per unit and so are very strong, but tire easily. They can be divided into:

Unipennate: These muscles have their fibres arranged to insert in a diagonal direction onto the tendon, which allows great strength. Examples include the Lumbricals (deep hand muscles) and Extensor Digitorum Communis (wrist and finger extensor) Bipennate: Bipennate muscles have two rows of muscle fibres, facing in opposite diagonal directions, with a central tendon, like a feather. This allows even greater power but less range of motion. An example is the Rectus Femoris Multipennate: As the name suggests Multipennate muscles have multiple rows of diagonal fibres, with a central tendon which branches into two or more tendons. An example is the Deltoid muscle which has three sections, anterior, posterior and middle.

Fusiform Muscles

Sometimes, included in the parallel muscle group, these muscles are more spindle-shaped, with the muscle belly being wider than the origin and insertion. Examples are, Biceps Brachii and Psoas major.

Multiple Choice

Which of the following is a convergent triangular muscle?

• psoas major

• biceps brachii

• pectoralis major

• rectus femoris

Multiple Choice

Muscles with circular forms tend surround openings of the body.

• True

• False

Multiple Choice

Muscles with many dense fibers are usually weaker but have endurance.

• True

• False

Multiple Choice

A muscles shape affects its function.

• True

• False

Muscle actions

Muscle actions are the same as muscle movements and muscle functions. Refer to your movement handouts for these questions. and the video!!!

Multiple Choice

moving a part (scapula) forward

• depression
• elevation
• protraction
• retraction

Multiple Choice

Pointing your toe

• dorsiflexion
• plantar flexion
• flexion
• extension

Multiple Choice

Rotation of the forearm until the palm faces DOWN is called __________.

• supination
• pronation
• flexion
• dorsiflexion

Multiple Choice

The lateral motion TOWARDS the midline is called ______.

• adduction
• abduction
• internal rotation
• external rotation

Multiple Choice

Which of the following best describes extension?

• The straightening of a joint where the angle of movement increases
• The bending of a joint where bones get closer together
• The rotation of a joint or spinning of one bone on another
• The lateral movement away from the midline

Multiple Choice

Turning the foot so the plantar surfaces faces medially.

• plantar flexion
• eversion
• inversion
• dorsiflexion

Multiple Choice

Turning the hand so that the palm is upward or facing anteriorly (in anatomical position).

• supination
• pronation
• flexion
• dorsiflexion

Multiple Choice

Movement away from the mid-line is called _____________.

• abduction
• adduction
• internal rotation
• external rotation

Muscle lever systems

LeversA lever is composed of three parts: a fixed rod which is attached to a fulcrum (pivot) and a load. Depending on the relative position of the three components, levers can move heavy loads or move loads further or faster when a force is applied.

If a load is close to a pivot and the force is applied far from the pivot, then the lever is said to operate at mechanical advantage. A large but relatively small force can move a heavy object. The classic example of such a lever is a car jack. With big movements of the lever, the heavy car is lifted in small increments off the ground.

If a load is far from a pivot and a force is applied near to the pivot, then the lever is said to operate at a mechanical disadvantage. A large force is required to move a relatively small load, but the speed and distance at which that load can be moved is greatly increased. An example of this is a spade combined with forceful movements of the muscles in the arm, which results in large movements of the spade head.

In muscles, the joints are the pivots and the bones are the fixed rods. The load is the weight of the bone, associated tissues, and other objects being moved, and the force is applied by the muscle at its insertion point.

Classes of Levers In the human body

Levers can also vary based on the relative position of the load, pivot and point of force application. Classes of levers include:

First-class Lever

In a first class lever, the load and force sit on either side of the pivot like a seesaw. First-class levers are relatively uncommon in the body, but one example is the triceps brachii muscle of the upper arm which acts to extend the forearm. The force is applied at its point of insertion on the ulna in the forearm, the elbow is the pivot, and the load is the humerus in the upper arm. Thinking of the relative distance between the points of attachment, the triceps brachii can be said to act at a mechanical disadvantage.

Second-class Lever

In a second-class lever, the force is applied at one end with the pivot at the other and the load in between. Second-class levers are also relatively uncommon in the body. One example is raising yourself up on your toes. The pivot is based at the front of the foot, the load is the weight of the body, and the force is applied through the Achilles tendon in the heel. All second-class levers in the body act at a mechanical advantage since the force is always applied closer to the load than to the pivot.

3rd Class Levers are by far the most common in the human body...

In a third-class lever the force is applied between the load and the pivot. The majority of muscles in the body are third-class levers and all act at a mechanical disadvantage as the force is applied closer to the pivot than the load. An example of a third-class lever in the body is the biceps brachii, which flexes the forearm towards the shoulder. Originating at the scapula, the pivot is the elbow, with the force applied immediately after the elbow at the point of insertion on the radius of the forearm. The load is the forearm and any objects a person carries.

To sum up

Every lever system has a bar or rod which in our case is our bone, a fulcrum or pivot which is our joints, a force which is applied by our muscle and a resistance which is whatever we are trying to lift or move.

Multiple Choice

All lever systems are equally strong.

• true

• false

Multiple Choice

Which class of lever system is like a "seesaw", or "teetertotter"?

• 1st class

• 2nd class

• 3rd class

Multiple Choice

In a lever system in our body the "rigid bar " or arm is our

• joint

• muscle force

• bone

• Load or resistance

Multiple Choice

In a lever system the fulcrum in our body are the

• bones

• joints

• muscles

• load or resistance

How muscles are named...

There are well over 600 muscles in the human body and there criteria that are followed when they are named.

Location of or body part covered by the muscle 

Frontal bone

Tibia

Frontalis

Tibialis anterior

Direction of muscle fascicles relative to muscle midline. 

Rectus – parallel

Transverse – perpendicular

Oblique – at a 45° angle

Rectus abdominis

Transversus abdominis

Relative size      

Maximus – largest

Longus – longest

Brevus – shortest

Examples of using relative size to name

Gluteus maximus

Palmaris longus

Peroneus longus

Teres major

Teres minor

# of origins also called heads

Number of origins           

Biceps – two origins

Triceps – three origins

Biceps brachii

Triceps brachii

Location of origin or insertion    

origin at sternum

origin at clavicle

insertion at mastoid process

Sternocleidomastoid

The shape of the muscle

Shape  

Deltoid – triangular

Trapezius – trapezoidal

Serratus – saw-tooth edge

Orbicularis – circular

Deltoid

Trapezius

Serratus anterior

Orbicularis oris

Action of muscle, also called movement or function

Flexion

Extension

Adduction

Flexor carpi radialis

Extensor digitorum

Adductor longus

Many muscles are named by a combination of these terms...sometimes there are 3 or even four

levator labii superioris alaeque nasi muscle

The levator labii superioris alaeque nasi muscle is, translated from Latin, the "lifter of both the upper lip and of the wing of the nose". It has the longest name of any muscle in an animal.

Multiple Choice

The rectus femoris is named by what criteria?

• Direction of fiber and relative size

• shape and number of origins

• Direction of fibers and location

• Location and action

Multiple Choice

The sternocleidomastoid is named based on what criteria?

• Shape

• origins and insertions

• number of origins

• location

Multiple Choice

Which muscle would close or elevate your jaw?

• sternocleidomastoid

• massester

• pectineus

• sartorius

Multiple Choice

Intercostal muscles are named by what criteria?

• Relative size

• location

• how tasty they are

• number of origins

Multiple Choice

The sternocleidomastoid is named based on what criteria?

• Shape

• origins and insertions

• number of origins

• location

Multiple Choice

The infraspinatus muscle is named by what criteria?

• size and shape

• Shape only

• location

• none of these

Multiple Choice

The infraspinatus muscle is named by what criteria?

• size and shape

• Shape only

• location

• none of these

Multiple Choice

Muscles have 2 or more attachments what are they called?

• agonists and antagonists

• origins and insertions

• isotonic and isometric

• none of these

Multiple Choice

The muscle in green is the

• rectus femoris

• biceps brachii

• biceps femoris

• gluteus maximus

Multiple Choice

This muscle has how many origins?

• 1

• 2

• 6

• 3

Multiple Choice

Does this muscle pass 2 joints?

• yes

• no

Multiple Choice

Is this the largest tendon in the body?

• yes

• no