Muscle Characteristics: Direction, Size, Shape, Action, and Location, Study notes of Nursing

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CHARACTERISTICS USED TO NAME MUSCLES Direction – orientation of muscle fascicles relative to the body’s midline Rectus Parallel to midline Rectus abdominis Transverse Perpendicular to midline Transverse abdominis Oblique Diagonal to midline External oblique Size – relative size of the muscle Maximus Largest Gluteus maximus Minimus Smallest Gluteus minimus Longus Long Adductor longus Brevis Short Adductor brevis Latissimus Widest Latissimus dorsi Longissimus Longest Longissimus capitis Magnus Large Adductor magnus Major Larger Pectoralis major Minor Smaller Pectoralis minor Vastus Huge Vastus lateralis Shape – Relative shape of the muscle Deltoid Triangular Deltoid Trapezius Trapezoid Trapezius Serratus Saw-toothed Serratus anterior Rhomboid Diamond-shaped Rhomboid major Orbicularis Circular Orbicularis oculi Pectinate Comblike Pectineus Piriformis Pear-shaped Piriformis Platys Flat Platysma Quadratus Square, four-sided Quadratus femoris Gracilis Slender Gracilis Action – Principal action of the muscle Flexor Decreases joint angle Flexor carpi radialis Extensor Increases joint angle Extensor carpi ulnaris Abductor Moves bone away from midline Abductor pollicis longus Adductor Moves bone closer to midline Adductor longus Levator Raises or elevates body part Levator scapulae Depressor Lowers or depresses body part Depressor labii inerioris Supinator Turns palm anteriorly Supinator Pronator Turns palm posteriorly Pronator teres Sphincter Decreases size of an opening External anal sphincter Tensor Makes body part rigid Tensor fasciae latae Rotator Rotates bone around longitudinal axis Rotatore Number of Origins – number of tendons of origin Biceps Two origins Biceps brachii Triceps Three origins Triceps brachii Quadriceps Four origins Quadriceps femoris Location – Structure near which a muscle is found Example: Temporalis, muscle near temporal bone Origin and Insertion – sites where muscle originates and inserts Example: Sternocleidomastoid, originating on sternum and clavicle and inserting on mastoid process or temporal bone SKELETAL MUSCLE STRUCTURE STRUCTURE AND ORGANIZATIONAL LEVELS OF SKELETAL MUSCLE 1. Pectoralis major – this muscle is a large fan-shaped muscle covering the upper part of the chest. The adduction and the flexion of the axilla is the action of this muscle. It forms the anterior wall of the axilla. 2. Intercostals muscles – these muscles are located deep between the ribs. The external intercostals muscles help raise the rib cage for breathing air in, making it a vital structure in breathing. The internal intercostals ribs, on the other hand, help air to move out the lungs when an individual exhales forcibly. 3. Muscles of the abdominal girdle – muscles of the abdominal girdle are subdivided into two categories – the anterior and posterior abdominal muscles. The anterior muscles serve as reinforcement of the body trunk. Both of these muscles are suitable for containing and protecting the abdominal contents. Anterior Abdominal Muscles  Rectus abdominis muscle – this paired strap-like muscle is the most superficial muscle of the abdomen. The MAIN FUNCTION of the rectus abdominis muscle is to flex the vertebral column. During defecation and childbirth, this muscle compresses the abdominal contents. Aside from that, it is also involved in forced breathing.  External Oblique muscle – this paired muscle makes up the lateral walls of the abdomen. The MAIN FUCNTION of this muscle is to flex the vertebral column like the rectus abdominis muscle. However, they also rotate the trunk and bend it laterally.  Internal oblique muscle – this paired muscle serves the same function as that of the external oblique muscles. Posterior Muscles 1. Trapezius muscles – these muscles are the most superficial muscles of the posterior and upper trunk. They serve as the antagonists of the sternocleidomastoids and they can elevate, depress, adduct ad stabilize the scapula. When seen together, the trapezius muscle forms a diamond or kite-shaped muscle mass. 2. Latissimus Dorsi muscle – this is a large and flat pair of muscle that covers the entire lower back. Latissimus dorsi muscle extends and adducts the humerus. This muscle plays a vital role in bringing down the arm in a power stroke when swimming or striking a blow. 3. Erector Spinae muscle – this group of muscle is a prime movers of back extension. Aside from acting as powerful back extensors, erector spinae muscle also helps control the action of bending over at the waist. When an injury to back structure occurs, these muscles go into spasms which are a common source of lower back pain. Each erector spinae muscle is composed of three muscle columns that cover the entire length of the vertebral column. The three muscle columns are longissimus, iliocostalis and spinalis. 4. Deltoid muscles – these are fleshy and triangle-shaped muscles that form the round shape of the shoulders. They are bulky and have been the most common and most favorite injection site. The deltoid muscles are the prime movers of arm abduction. Muscles of the Upper Limb Muscles of the upper limbs are divided into three groups. 1. First group – muscles arising from the shoulder girdle and cross the shoulder joint to insert into the humerus. These muscles move the arm. 2. Second group – muscles that encloses the humerus and insert on the forearm bones. These muscles cause movement at the elbow joint. 3. Third group – includes muscles of the forearm that cause their movement. Muscles of the Humerus that Act on the forearm 1. Biceps Brachii – this muscle bulges when the elbow is flexed. It is a powerful prime mover for the flexion of the forearm and acts to supinate the forearm. 2. Brachialis – this muscle plays an essential in elbow flexion. It lies deep to the biceps muscle. 3. Brachioradialis – this is a fairly weak muscle. It arises on the humerus and inserts into the distal forearm. 4. Triceps brachii – this is the only muscle fleshing out the posterior humerus. It is the powerful prime mover of elbow extension. Other term for this muscle is the “boxer’s muscle” as it can deliver a straight arm knock-out punch. This muscle is also the antagonist of the biceps brachii muscle. Muscles of the Lower Limb Characteristic of the muscles of the lower limb: 1. These muscles cause movement at the hip, knee and foot joints. 2. They are one of the largest and strongest muscles in the body. 3. These muscles play a vital role in walking and balancing the body. Muscles causing movement at the hip joint 1. Gluteus Maximus Muscle – this is a superficial hip muscle that shapes the buttocks. Gluteus maximus muscle is a very powerful hip extensor that is responsible in bringing the thigh to a straight line. 2. Gluteus medius Muscle – this is a hip abductor muscle. Gluteus medius muscle is very important in stabilizing the pelvis when an individual is walking. When more than 5 ml of medication is administered intramuscularly, the gluteus medius muscle is used. However, the medial part of each buttock overlies the large sciatic nerve, hence; this area must be used carefully. Because of this reason, the fleshy gluteus maximus would be a better choice. In cases, where the gluteus medius is used for IM injection, the nurse should divide the buttocks into four equal parts mentally. The upper outer quadrant is a very safe site for an IM injection. 3. Iliopsoas – this muscle is composed of two muscles – the iliacus and psoas major. Iliopsoas is a prime mover of hip flexion and it also acts to keep the upper body from falling backward when a person is standing erect. 4. Adductor muscles – as their name indicate, these muscles adduct or press the thighs together. However, since gravity does most of the work for them, these muscles tend to become flabby very easily. Muscles causing movement at the knee joint 1. Hamstring group – these muscles form the muscle mass of the posterior thigh. This group is composed of three muscles – the biceps femoris, semimembranosus and semitendinosus muscles. 2. Sartorius – this thin and strap-like muscle is not very significant because it is a very weak flexor of the thigh. However, this muscle is the most superficial muscle of the thigh. The Sartorius muscle is often referred to as the tailor’s muscle because it acts as a synergist to bring about the cross-legged position in which old-time tailor’s is often shown. 3. Quadriceps group – four muscles compose this muscle group. Namely, the rectus femoris and the three vastus muscles. These muscles flesh out the anterior thigh. Quadriceps group acts to extend the knee powerfully. Muscles causing movement at the ankle and foot 1. Tibialis anterior – this is a superficial muscle of the anterior leg that acts to dorsiflex and invert the foot. 2. Extensor digitorum longus – this muscle inserts into the phalanges of toes 2 to 5. It is a prime mover of toe extension and a dorsiflexor of the foot. 3. Fibularis muscles – there are three fibularis muscles namely, the longus, brevis and tertius. These muscles are found on the lateral part of the leg and working as a group, they are responsible for the plantar flexion and the eversion of the foot. 4. Gastrocnemius – this muscle forms the curved half of the posterior leg. It is a prime mover for plantar flexion of the foot. 5. Soleus – this muscle lies deep to gastrocnemius. It has no effect on knee movement but it is a string plantar flexor of the foot.