Muscular System Notes

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University of New South Wales *

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1521

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Anatomy

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Oct 30, 2023

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pdf

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• 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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▪ Triceps Brachii (muscles of the posterior compartment of the arm) - The origin of the long head is at the infraglenoid tubercle of the scapula, for the lateral head its the lateral shaft of the humerus and for the medial head its the posterior shaft of the humerus. The insertion is at the olecranon process of the ulna. The innervation is the radial nerve. The action of this muscle is the extension of the elbow joint (long head), and the extension of arm at the shoulder joint. ▪ Muscles of the anterior compartment of the forearm, they are arranged into three layers: ▪ Superficial layer (4) ▪ Intermediate layer (1) ▪ Deep later (3) They have a common origin which is the medial epicondyle of humerus. The insertion is at the bones of the forearm and hand. The innervations are the ulnar and median nerves. The actions of these muscles is the pronation and supination of the forearm; flexion of the hand at wrist joint; flexion of the digits. The carpal tunnel is formed by the flexor retinaculum bridging across the carpal bones of the wrist. The carpal tunnel is the passageway for the median nerve and tendons of the forearm flexor • Identify muscles of the trunk and understand their functions based on their attachments. Muscles of the back: Extrinsic group: Superficial Layer o Trapezius o Latissimus dorsi o Levator scapulae o Rhomboid muscles Intermediate layer: o Serratus posterior Intrinsic/deep group: Erector spinae group Action:

o Extension of the trunk (bilateral) o Ipsilateral lateral flexion of the trunk (unilateral) Innervation: o Dorsal rami of spinal nerves Muscles of abdominal wall Transversus abdominis Action: Compression of the abdominal wall Internal obliques Action: o Flexion of the trunk; Compression of the abdominal wall (bilateral) o Ipsilateral lateral flexion, and ipsilateral rotation of the trunk (unilateral) External obliques Action: o Flexion of the trunk; Compression of the abdominal wall (Bilateral) o Ipsilateral lateral flexion and contralateral rotation of the trunk Rectus abdominis Action: Flexion of the trunk; Compression of the abdominal wall • Identify muscles of the lower limb and pelvic girdle and understand their functions based on their attachments. Muscles of the pelvic girdle and lower limb Muscles of the Pelvic Girdle: 1. Gluteal Muscles - The origin is the gluteal surface of the ilium, sacrum and coccyx. The insertion is at the geater trochanter and gluteal tuberosity of the femur; iliotibial tract. The actions of these muscles is the extension of thigh at hip joint, abduction and lateral rotation of thigh at hip joint. ▪ Rotator group ▪ Gluteus minimus ▪ Gluteus medius ▪ Gluteus maximus

2. Hip flexor Muscles ▪ Psoas major - The origin is at the T12-L5 vertebrae. the insertion is at the lesser trochanter of femur. The action of this muscle is the flexion of thigh at the hip joint(prime mover) and the flexion of the trunk. ▪ Iliacus - the origin is at the iliac fossa. The insertion is at the lesser trochanter of femur. The action of this muscle is flexion of thigh at hip joint (prime mover). Muscles of the Anterior Thigh: 3. Sartorius - Its origin is at the anterior superior iliac spine. The insertion is at the medial proximal tibia. The innervation is the femoral nerve. The action of this muscle is the flexion and lateral rotation of thigh at hip joint; flexion of leg at knee joint. 4. Quadriceps femoris: 1. Rectus femoris - Its origin is at the anterior inferior iliac spine. Its insertion is at the quadriceps femoris tendon. Its innervation is the femoral nerve. The action of this muscle is the flexion of thigh at hip joint and the extension of leg at kneww joint. 2. Vastus medialis/intermedius/lateralis - Its origin is at the anterior aspect of the proximal femur. Its insertion is at the quadriceps femoris tendon. The innervation is the femoral nerve. Its action is the extension of leg at knee joint. Muscles of the Medial thigh: 3. Adductor group - The origin is at the pubis and ischium of the pelvis. Its insertion is at the medial aspect of the femur. The action of these muscles is the adduction of the thigh at the hip joint. The innervation is the obturator nerve. Muscles of the Posterior thigh: 4. Biceps femoris - The origin of the long head is the ischial tuberosity and the short head is the linea aspera posterior femur. The insertion is at the head of the fibula, the innervation is the sciatic nerve. The actions of these muscles is the extension and lateral rotation of the thigh at the hip joint; flexion of leg at knee joint.

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5. Semitendinosus - The origin is at the Ischial tuberosity, the insertion is at the medial aspect of the proximal tibia. The innervation is the sciatic nerve. The actions of this muscle is the extension and medial rotation of thigh at the hip joint and the flexion of leg at the knee joint. 6. Semimembranosus - Its origin is at the ischial tuberosity, the insertion is at the posteromedial aspect of the medial condyle of the tibia. The innervation is the sciatic nerve. The actions of this muscle is the extension and medial rotation of the thigh at the hip joint and the flexion of the leg at the knee joint. Muscles of the Posterior Leg: 7. Gastrocnemius - Its origin is at the medial and lateral condyles of the femur. The insertion is at the calcaneus. The innervation is the tibial nerve. The action os this muscle is the plantarflexion of foot and the flexion of leg at knee joint. 8. Soleus - The origin is at the head and posterior aspect of the fibula and the medial aspect of the tibia. The insertion is at the calcaneus. The innervation is the tibial nerve. The action of the muscle is plantarflexion of the foot. Intrinsic muscles of the foot: 9. Extensor muscle group - The action of these muscles is the extension of digits. The innervation is the fibular nerve. 10. Flexor muscle group - The action of these muscles is the flexion of digits. The innervation is the plantar nerve branches of tibial nerve. 11. Lumbricals 12. Plantar & dorsal interossei