Muscular system

• The muscular system is an organ system consisting of skeletal, smooth and cardiac muscles.
• It permits movement of the body, maintains posture and circulates blood throughout the body.
• There are more than 600 muscles in the body, which together account for about 40 percent of a person’s weight.
• There are two platysma muscles, one on each side of the neck.
• Each is a broad sheet of a muscle that covers most of the anterior neck on that side of the body.
• Under the platysma are two sternocleidomastoid muscles.
• One on each side of the neck. These muscles have two origins, one on the sternum and the other on the clavicle.
• They insert on the mastoid process of the temporal bone.
• They can flex or extend the head, or can rotate the towards the shoulders.
• The triceps brachii is innervated by the radial nerve
• The epicranius muscle is also very broad and covers most of the top of the head.
• Found over the forehead (the portion of the muscle called the epicranius frontalis;
• Back of the head (the portion of the muscle called the epicranius occipitalis;
Muscles of face
• Humans have well-developed muscles in the face that permit a large variety of facial expressions.
• The buccinator muscles, one on each side of the face, compress the cheeks when contracted.
• The two masseter muscles are also on each side of the face.
• They close the jaw when contracted.
• The zygomaticus major muscles and the zygomaticus minor muscles are found on each side of the face both have their origins on the zygomatic bone.
• They both can change the shape of the mouth by elevating it.
Muscles of arm
• The arm muscles of the upper limb act on the elbow and shoulder joints to produce the various movements of the forearm.
• Five arm muscles play a role in these movements: biceps brachii, brachialis, coracobrachialis, triceps brachii and anconeus.
• The first three are primarily involved in forearm flexion, hence they are called flexors.
• They occupy the anterior, or flexor, compartment of the arm.
• The triceps brachii is mainly involved in forearm extension, making it an extensor muscle.
• The biceps brachii is the most superficial muscle of the anterior compartment of the arm.
• Therefore, it is easily clearly visible as a round bulge when you flex your forearm against resistance.
• The muscle consists of two heads, long and short.
• The long head originates from the supraglenoid tubercle of the scapula.
• The short head starts from the coracoid process of the scapula.
• Biceps brachii traverses the shoulder and elbow so acting on both.
• However, it primarily moves the forearm around the elbow joint by pulling on the radius.
• During contraction, it causes forearm flexion and supination, exhibiting the greatest force when the forearm is close to 90 degrees.
• This muscle is also a weak arm flexor by acting on the shoulder joint.
• The biceps brachii is innervated by the musculocutaneous nerve.
• Brachiialis lies deep in the anterior compartment of the arm, underneath the biceps brachii.
• The muscle originates from the inferior half of the anterior surface of the humerus.
• The brachialis acts only on the elbow joint.
• During contraction, it flexes the forearm by pulling on the ulna.
• The brachialis is the most powerful flexor of the forearm, irrespective of the forearm position.
• It is innervated by the musculocutaneous and radial nerves.
• The coracobrachialis muscle also lies deep within the anterior compartment of the arm, in the same plane as the brachialis underneath the biceps brachii.
• It originates from the coracoid process of the scapula, passes through the axilla and inserts into the anteromedial surface of the humeral shaft.
• Therefore, the coracobrachialis acts on the shoulder joint.
• During contraction, it flexes and adducts the arm by pulling on the humerus.
• The coracobrachialis is innervated by the musculocutaneous nerve.
• The anatomy of the arm muscles would be incomplete without learning about the triceps brachii, the largest muscle of this region.
• Triceps consists of three heads: long, lateral and medial.
• The long head originates from the infraglenoid tubercle of the scapula.
• The lateral and medial heads begin from the posterior surface of the humerus, superior and inferior to the radial groove, respectively.
• The primary function of this muscle is forearm extension by pulling on the ulna.
• The triceps brachii is innervated by the radial nerve

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