Muscular System Notes

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School

University of New South Wales *

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Course

1521

Subject

Anatomy

Date

Oct 30, 2023

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pdf

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Uploaded by PresidentSardine3670

• Understand the organization and structure of muscles and how this relates to function. Skeletal Muscle Organisation: o Muscles are bound within deep fascia which is a layer of dense connective tissue. o They are arranged into functional groups separated by connective tissue septae. o Muscle fibers are organised into bundles or fascicles. o Muscle fascicle are aligned in different patterns in different muscles. Muscle Fascicle arrangement: o Muscle power is a function of the cross-section area (i.e number of fibres/fascicles). o Parallel patterns can generate a long length of contraction at the sacrifice of power. o Pennate and convergent patterns can pack in many more fibres for more power, but at the sacrifice of length of contraction. o Other arrangements allow the generation of specific movements such as pursing the lips. Muscle attachments and actions: o Muscles are connected to tendons, which anchor them to bones. o All muscles have at least two attachments: the origin and the insertion. o Most muscles cross at least one joint, with the origin and insertion on opposing bones. o In the limbs, the origin of a muscle is proximal and the insertion is distal. o Muscles can only pull; they can never push. o During contraction, the muscle insertion moves toward the origin. Roles in movement: o An agonist - also known as the prime mover, these muscles are the principle muscles in generating movement.

o An antagonist - these are the opposing muscles which slow/control the prime movement. o A synergist - these are muscles that assist the agonict in generating movement. o A fixator - stabilises/prevents unwanted movement at a joint. A movement can be categorised according to how the mucle changes: o Isotonic - the muscle tone does not change during the movement but the length does. Concentric is when the muscle shortens during the movement and eccentric is when the muscle lengthens during the movement. o Isometric - the muscle tone changes during the movement but the length does not. • Identify muscles of the head and neck and understand their functions based on their attachments. Muscles of facial expression, mastication, neck region: Muscles to know: o Occipitofrontalis - Flat muscle with 2 bellies; frontalis and occipitalis. Facial Expression o Temporalis - Origin is at the temporal fossa, insertion is at the ramus of the mandible. Mastication o Orbicularis Oculi - It has a surround orbital margin, its insertion extends into eyelids. This muscle closes the eyelids. Facial Expression o Orbicularis Oris - Its origin and insertion are within the lips. This muscle closes the mouth. Facial Expression o Buccinator - Its origin is at the mandible and maxilla, and its insertion is the angle of the mouth. This muscle helps with chewing, speaking etc. Facial Expression o Masseter - Its origin is at the zygomatic arch and its insertion is the angle of the mandible. This muscle closes the jaw and is very strong. Mastication o Sternocleidomastoid - Has a superior head which is the mastoid process. Has 2 inferior heads known as the sternum and the clavicle. This muscle flexes neck forward bilaterally and to same side when unilateral. Neck • Identify muscles of the upper limb and shoulder girdle and understand their functions based on their attachments. o Muscles of the shoulder girdle: ▪ Pectoralis Major (muscles connecting upper limb to thoracic wall) - Its origin is medial 2/3 clavicle, the body of the sternum and the costal cartilages 2-6. Its insertion is at the lateral lip of intertubercular sulcus of humerus. Its action is shoulder flexion, adduction and medial rotation. ▪ Trapezius (muscles connecting upper limb to vertebral column) - Its origin is at the superior nuchal line, external occipital protuberance, C7-T12 spinous

processes. Its insertion is at the clavicle lateral 1/3, scapular acromion and spine. The action of this muscle is elevation retraction, depression and upward rotation of the scapula and also neck extension. ▪ Latissimus Dorsi (muscles connecting upper limb to vertebral column) - Its origin is at the T7-l% spinous processes, ribs 8-12 and the thoracolumbar fascia. Its insertion is at the floor of the intertubercular sulcus of the humerus. The action of this muscle is shoulder extension, adduction and medial rotation. ▪ Deltoid (muscles connecting upper limb to scapula) - Its origin is at the lateral 1/3 of the clavicle, the scapular acromion and the spine. Its insertion is at the deltoid terosity of the humerus. The action of this muscle is shoulder abduction past 15 degrees. The anterior part is used for shoulder flexion and medial rotation, the posterior part is used for shoulder extension and lateral rotation. ▪ Teres Major (muscles connecting upper limb to scapula) - Its origin is at the inferior angle of the scapula. Its insertion is at the medical lip of the intertubercular sulcus of humerus. The action of this muscle is for shoulder extension, adduction and medial rotation. ▪ The Rotator Cuff Group (muscles connecting upper limb to scapula). ▪ Supraspinatus - Its origin is at the supraspinous fossa and its insertion is at the superior aspect of greater tubercle. Its action is shoulder adduction. ▪ Infraspinatus - its origin is at the infraspinous fossa and its insertion is at the posterior aspect of greater tubercle. Its action is the lateral rotation of arm. ▪ Teres Minor - Its origin is at the lateral border of the scapula and its insertion is at the posterior aspect of the greater tubercle. Its action is the lateral rotation of arm. ▪ Subscapularis - Its origin is at the subscapular fossa and its insertion is at the anterior aspect of the greater tubercle. Its action is the medial rotation of arm. o Muscles of the upper limb: ▪ Biceps Brachii (muscles of the anterior compartment of the arm) - Its origin is at the short head, coracoid process of the scapula, and at the long head, the supraglenoid tubercle. Its insertion is at the radial tuberosity. Its innervation is the musculocutaneous nerve. Its action is the flexion of the elbow and shoulder joint as well as the supination of the forearm. ▪ Brachialis - Its origin is at the anterior aspect of the shaft of the humerus. Its insertion is at the ulnar tuberosity. Its innervation are the musculocutaneous and radial nerves.. The action of this muscle is the flexion of the elbow joint.

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