You'll find this conveniently illustrated on the cheat sheets. The insertions of these muscles have fibers intertwined with connective tissue and the dermis of the skin. Groups of muscles are involved in most movements and names are used to describe the role of each muscle involved. The multifidus muscle of the lumbar region helps extend and laterally flex the vertebral column. This muscle allows you to whistle, blow, and suck; and it contributes to the action of chewing. It arises from the spinous processes of the T7-L5 (L = Lumbar) vertebrae, costals 8-12, inferior angle of the scapula, and iliac crest. The intrinsic muscles of the hand contain the origin and insertions within the carpal and metacarpal bones. The acronym for the rotator cuff is S.I.T.S. Due to this abducting movement, the supraspinatus is commonly referred to as the suitcase muscle; i.e. Enrolling in a course lets you earn progress by passing quizzes and exams. The muscle acts to supinate the forearm and forms the lateral border of the cubital fossa. An easy way to remember this little fact is to keep in mind the following mnemonic. laterally rotates the femur with hip extension, flexes humerus, antagonist of supraspinatus and grab your free ultimate anatomy study guide! origin: neck Origin: The erector spinae group forms the majority of the muscle mass of the back and it is the primary extensor of the vertebral column. Some axial muscles cross over to the appendicular skeleton. When a movement is repeated over time, the brain creates a long-term muscle memory for that task, eventually allowing it to be performed with little to no conscious . I nfraspinatus muscle : This muscle is located in the large posterior infraspinous fossa located inferior to the scapular spine. 1. The origin is the fixed attachment, while the insertion moves with contraction. The insertion is usually distal,. It has three heads: long, lateral, and medial. The muscle is innervated by the posterior interosseous branch. A FOSH may fracture the bone. L: lateral two lumbricals. Each of these actions can be described in one of two ways. Register now 977 Cards -. Rather, antagonist contraction controls the movement by slowing it down and making it smooth. Commonly referred to as impingement syndrome. Extensor digitorum muscle:This muscle lies in the extensor compartment and arises from the lateral epicondyle. Human hands are quite special in their anatomy, which allows us to be so dexterous and relies on muscles of the upper limb to help move it through space. Tearing most commonly occurs in the tendon of supraspinatus. Triceps Muscle Brachii Origin & Insertion | Where is the Tricep? Agonist Muscle Contraction & Examples | What Are Agonist Muscles? Therefore, when they contract, the origin pulls the insertion and connected bone closer . The palmar interossei are unipennate, and the dorsal interossei are bipennate. Muscle Mnemonics. It is often grouped as one of the muscles of the arm due to its insertion, but its actions involve the shoulder portion only, this why it has been included in the shoulder section here. The muscles discussed below are essential to everyday life and advanced movements such as writing. Themedial pterygoid and lateral pterygoid muscles provide assistance in chewing and moving food within the mouth by moving the mandible laterally and medially to grind food between the molars. Action: Adducts thigh, Origin: iliac crest, anterior iliac surface Insertion: iliotibial band of fasciae latae Action: Flexes, abducts, and medially rotates thigh, Origin: Outer iliac blade, iliac crest, sacrum, coccyx Insertion: Gluteal tuberosity of femur, iliotibial band of fasciae latae Action: Extends and laterally rotates thigh, braces knee, Origin: Outer iliac blade Insertion: Greater trochanter of femur Action: Abducts and medially rotates thigh, Origin: Pubis, ischium Insertion: Gluteal tuberosity, linea aspera, adductor tubercle of distal femur Action: Adducts, flexes, extends and laterally rotates thigh, Origin: Anterior superior iliac spine Insertion: Proximal, medial tibia Action: Flexes and laterally rotates thigh, flexes leg, Origin: Anterior inferior iliac spine, margin of acetabulum Insertion: Tibial tuberosity by patellar tendon Action: Flexes thigh, extends leg, Origin: Greater trochanter of femur, linea aspera of femur Insertion: Tibial tuberosity by patellar tendon Action: Extends Leg, Origin: Linea aspera, medial side Insertion: Tibial tuberosity by patellar tendon Action: Extends Leg, Origin: Proximal, anterior femur Insertion: Tibial tuberosity by patellar tendon Action: Extends Leg, Origin: (long head) Ischial tuberosity, (short head) linea aspera Muscle origins and insertions dictate the type of movement that occurs when a muscle contracts. The buccinator muscle compresses the cheek. 1.2 Structural Organization of the Human Body, 2.1 Elements and Atoms: The Building Blocks of Matter, 2.4 Inorganic Compounds Essential to Human Functioning, 2.5 Organic Compounds Essential to Human Functioning, 3.2 The Cytoplasm and Cellular Organelles, 4.3 Connective Tissue Supports and Protects, 5.3 Functions of the Integumentary System, 5.4 Diseases, Disorders, and Injuries of the Integumentary System, 6.6 Exercise, Nutrition, Hormones, and Bone Tissue, 6.7 Calcium Homeostasis: Interactions of the Skeletal System and Other Organ Systems, 7.6 Embryonic Development of the Axial Skeleton, 8.5 Development of the Appendicular Skeleton, 10.3 Muscle Fiber Excitation, Contraction, and Relaxation, 10.4 Nervous System Control of Muscle Tension, 10.8 Development and Regeneration of Muscle Tissue, 11.1 Describe the roles of agonists, antagonists and synergists, 11.2 Explain the organization of muscle fascicles and their role in generating force, 11.3 Explain the criteria used to name skeletal muscles, 11.4 Axial Muscles of the Head Neck and Back, 11.5 Axial muscles of the abdominal wall and thorax, 11.6 Muscles of the Pectoral Girdle and Upper Limbs, 11.7 Appendicular Muscles of the Pelvic Girdle and Lower Limbs, 12.1 Structure and Function of the Nervous System, 13.4 Relationship of the PNS to the Spinal Cord of the CNS, 13.6 Testing the Spinal Nerves (Sensory and Motor Exams), 14.2 Blood Flow the meninges and Cerebrospinal Fluid Production and Circulation, 16.1 Divisions of the Autonomic Nervous System, 16.4 Drugs that Affect the Autonomic System, 17.3 The Pituitary Gland and Hypothalamus, 17.10 Organs with Secondary Endocrine Functions, 17.11 Development and Aging of the Endocrine System, 19.2 Cardiac Muscle and Electrical Activity, 20.1 Structure and Function of Blood Vessels, 20.2 Blood Flow, Blood Pressure, and Resistance, 20.4 Homeostatic Regulation of the Vascular System, 20.6 Development of Blood Vessels and Fetal Circulation, 21.1 Anatomy of the Lymphatic and Immune Systems, 21.2 Barrier Defenses and the Innate Immune Response, 21.3 The Adaptive Immune Response: T lymphocytes and Their Functional Types, 21.4 The Adaptive Immune Response: B-lymphocytes and Antibodies, 21.5 The Immune Response against Pathogens, 21.6 Diseases Associated with Depressed or Overactive Immune Responses, 21.7 Transplantation and Cancer Immunology, 22.1 Organs and Structures of the Respiratory System, 22.6 Modifications in Respiratory Functions, 22.7 Embryonic Development of the Respiratory System, 23.2 Digestive System Processes and Regulation, 23.5 Accessory Organs in Digestion: The Liver, Pancreas, and Gallbladder, 23.7 Chemical Digestion and Absorption: A Closer Look, 25.1 Internal and External Anatomy of the Kidney, 25.2 Microscopic Anatomy of the Kidney: Anatomy of the Nephron, 25.3 Physiology of Urine Formation: Overview, 25.4 Physiology of Urine Formation: Glomerular Filtration, 25.5 Physiology of Urine Formation: Tubular Reabsorption and Secretion, 25.6 Physiology of Urine Formation: Medullary Concentration Gradient, 25.7 Physiology of Urine Formation: Regulation of Fluid Volume and Composition, 27.3 Physiology of the Female Sexual System, 27.4 Physiology of the Male Sexual System, 28.4 Maternal Changes During Pregnancy, Labor, and Birth, 28.5 Adjustments of the Infant at Birth and Postnatal Stages. The Chemical Level of Organization, Chapter 3. These muscles are located inside the eye socket and cannot be seen on any part of the visible eyeball (Figure 11.4.3 and Table 11.3). The head is balanced, moved and rotated by the neck muscles (Table 11.5). See our full, Click to share on Facebook (Opens in new window), Click to share on Twitter (Opens in new window), Click to share on Pinterest (Opens in new window), Click to share on Reddit (Opens in new window), Click to share on LinkedIn (Opens in new window), Click to share on WhatsApp (Opens in new window), Click to share on Pocket (Opens in new window), Click to share on Telegram (Opens in new window), Click to share on Skype (Opens in new window), IV Drug Use Complications & Dangers: (Endocarditis, Infection, Infectious Diseases). action: extend the neck ; retract and adduct scapulae, posterior It is innervated by the medial and lateral pectoral nerves. The anterior muscles - such as the quadriceps femoris, iliopsoas, and sartorius, work as a group to flex the thigh at the hip and extend the leg at the knee. The damaged nerve causes a weakened serratus anterior, leading to the scapula not being pulled down and in during circumduction. A. Muscles of the Head and Neck. It consists mainly of type 1 muscle fibers and hence provides sustained elbow extension. The latissimus dorsi is a large back muscle responsible for the bulk of adduction of the arm (pulling the arm to the sides of . Many muscles are attached to bones at either end via tendons. Pronator quadratus muscle:In the deepest layer of the forearm is the pronator quadratus, which is found connecting the radius (insertion) and ulna (origin) at their distal points like a strap. It also flexes the MP and wrist joints, although these are its secondary functions. All three heads unite and insert onto the olecranon process and fascia of the ulna. The muscles of the anterior neck facilitate swallowing and speech, stabilize the hyoid bone and position the larynx. The three muscles of the longissimus group are the longissimus capitis, associated with the head region; the longissimus cervicis, associated with the cervical region; and the longissimus thoracis, associated with the thoracic region. TABLE: Origin, Insertion, and Action for Lecture Checklist: Selected Human Muscles. The triceps brachii originates on the back of the scapula and humerus, and inserts on the back of the ulna in the forearm. origin: tip of the coracoid process The sternocostal head arises from the sternum and the superior 6-7 costal cartilages. The muscles of the back and neck that move the vertebral column are complex, overlapping, and can be divided into five groups. It inserts into the medial aspect of the 5th metacarpal. Because of its mobility, the tongue facilitates complex speech patterns and sounds. An Introduction to the Human Body, Chapter 2. The palmar aponeurosis helps resist shearing forces applied to the palm, such as climbing and tool use. It is innervated by the deep branch of the radial nerve. Bone Tissue and the Skeletal System, Chapter 12. It is innervated by the radial nerve, a portion of the posterior branch of the brachial plexus. #shorts #anatomy. However, the anatomist knows that the arm or the brachium is purely the region between the shoulder joint and elbow. It is innervated by the anterior interosseous branch. Flex and extend the muscle and feel its movements at the origin, midpoint, and insertion. Biceps brachii muscle:This superficial muscle forms the bulk of the anterior compartment of the arm. John has taught college science courses face-to-face and online since 1994 and has a doctorate in physiology. Additionally, these muscles switch roles with opposite movements. Coracobrachialis muscle :The beauty of this muscle is that its name explains its origin, insertion, and action. Avascular necrosis of the proximal segment is a common complication. The Nervous System and Nervous Tissue, Chapter 13. Learning anatomy is a massive undertaking, and we're here to help you pass with flying colours. It passes laterally to insert onto the lesser tubercle of the humerus. Origin: Clavicle, sternum, cartilages of ribs 1-7 Insertion: Crest of greater tubercle of humerus Action: flexes, adducts, and medially rotates arm, Origin: Clavicle, acromion process, spine of scapula Insertion: Deltoid tuberosity of the humerus Action: Abducts arm; flexes, extends, medially, and laterally rotates arm, Origin: thoracolumbar fascia Insertion: Intertubercular groove of humerus (spirals from your back under your arm) Action: adducts humerus (pulls shoulder back and down), Origin: Lateral border of scapula Insertion: Greater tubercle of humerus Action: Laterally rotates and adducts arm, stabilizes shoulder joint, Origin: Long head; superior margin of glenoid fossa Short Head; Coracoid process of scapula Insertion: Radial Tuberosity Action: Flexes arm, flexes forearm, supinates hand, Origin: Anterior, distal surface of humerus Insertion: coronoid process of ulna Action: Flexes forearm, Origin: Infraglenoid tuberosity of scapula, lateral and posterior surface of humerus Insertion: Olecranon process, tuberosity of ulna Action: Extends and adducts arm, extends forearm, Origin: Lateral supracondylar ridge of humerus Insertion: styloid process of radius Action: Flexes forearm, Origin: Symphysis Pubis (inferior ramus of pubis) The forearm is the region between the elbow and thewrist and is composed of an extensor and flexor compartment. Click to Rate "Hated It" . The same fracture that is palmarflexed is referred to as a Smith's fracture making the hand appear as it is coming inward and downward. What are you waiting for? The muscles of the neck are categorized according to their position relative to the hyoid bone (Figure 11.4.7). Pectoralis minor inserts onto the coracoid process of the scapula. It also causes contributes to flexion of the proximal IP, MP, and wrist joints, although these are its secondary function. The serratus anterior muscle originates from the 1st to 8th or 9th rib s and inserts at the anterior surface of the scapula. Finally, synergist muscles enhance the action of the agonist. All interossei are innervated by the deep branch of the ulnar nerve, which enters the palm through Guyons canal, a tunnel formed by the pisiform and hook of hamate. The shoulder is most unstable in extension and external rotation. Brachialis muscle:This is the deep primary flexor of the elbow and arises from the lower part of the anterior surface of the humerus. It has a long head and a short head. It arises from the occipital bones, occipital protuberance and nuchal lines, as well as the spinous processes of C7 through T12. It passes anteriorly and around the thoracic cage as if wrapping. This necrosis lead to a flattened thenar eminence (thumb mound palmar surface). For example, the brachialis is a synergist of the biceps brachii during forearm flexion. inserion: medial border of scapula I would definitely recommend Study.com to my colleagues. Muscle: Extensor pollicis brevis. The muscle origin often describes the more proximal attachment point of the muscle, while the muscle insertion point refers to the distal attachment. The nerve supply comes from the upper and lower subscapular. The shoulder moves at the glenohumeral joint. PAD DAB ('Use your hand to dab with a pad'). The erector spinae comprises the iliocostalis (laterally placed) group, the longissimus (intermediately placed) group, and the spinalis (medially placed) group. It arises from the nuchal ligament and spinous processes of C7 to T1. Short head originates from Coracoid process. 52 Learners. posterior muscles - gluteus maximus muscle (the largest muscle in the body) and the hamstrings group, which consists of the biceps femoris, semimembranosus, and semitendinosus muscles. Axial muscles originate on the axial skeleton (the bones in the head, neck, and core of the body), whereas appendicular muscles originate on the bones that make up the bodys limbs. The muscle acts primarily as a supinator of the forearm, as well as a flexor of the elbow. The sternocleidomastoid divides the neck into anterior and posterior triangles. The muscle then descends inferiorly to insert into the radial tuberosity of the radius as well as help create the bicipital aponeurosis, an expansion that inserts into the deep fascia of the forearm and onto the ulna. Most anatomy courses will require that you at least know the name and location of the major muscles, though some anatomy courses will also require you to know the function (or action), the insertion and origin, and so on. the iliopsoas or inner hip muscles: Psoas major. The nerve supply arises from the suprascapular nerve (upper and lower), which arises from the unification of the anterior rami of spinal nerves C5 and C6(C = cervical). It also assists in medial (anterior fibers) and lateral rotation (posterior fibers). Validated and aligned with popular anatomy textbooks, these muscle cheat sheets are packed with high-quality illustrations. In other words, there is a muscle on the forehead (frontalis) and one on the back of the head (occipitals). By accessing any content on this site or its related media channels, you agree never to hold us liable for damages, harm, loss, or misinformation. It also has a role in stabilizing the humerus and part of the rotator cuff of four muscles. It arises from the transverse processes of the superior four cervical vertebrae (C1-C4). It arises from the flexor retinaculum, scaphoid tubercle, and trapezium. Agonists, or prime movers, are responsible for the bulk of the action. Youll be able to clearly visualize muscle locations and understand how they relate to surrounding structures. It is available for free. Last reviewed: November 03, 2021 If the place is on the bone that moves during the action, the attachment is called an insertion. The nerve supply to this muscle arises from the axillary nerve, a branch of the posterior cord of the brachial plexus. , My origin is the iliac crest, posterior sacrum, inferior lumbar, and sacral spinous processes. The biceps brachii is the agonist in forearm flexion. The triceps brachii becomes the agonist - while the biceps brachii is the antagonist - when we extend our forearm. It pronates the radius and is innervated by the anterior interosseous branch of the median nerve. The muscles in the face create facial expression by inserting into the skin rather than onto bone. Muscles are either axial muscles or appendicular. A rule of thumb is that any muscle tendon that crosses a joint will act on that joint. Most anatomy courses will require that you at least know the name and location of the major muscles, though some anatomy courses will also require you to know the function (or action), the insertion and origin, and so on. The spinalis group includes the spinalis capitis, the spinalis cervicis, and the spinalis thoracis. Supraspinatus muscle: This rotator cuff muscle is deep and originates from the supraspinous fossa which is located on the posterior superior portion of the scapula. The lower fibersare responsible forelevation and depression. Fluid, Electrolyte, and Acid-Base Balance, Lindsay M. Biga, Sierra Dawson, Amy Harwell, Robin Hopkins, Joel Kaufmann, Mike LeMaster, Philip Matern, Katie Morrison-Graham, Devon Quick & Jon Runyeon, Next: 11.5 Axial muscles of the abdominal wall and thorax, Creative Commons Attribution-ShareAlike 4.0 International License, Moves eyes up and toward nose; rotates eyes from 1 oclock to 3 oclock, Common tendinous ring (ring attaches to optic foramen), Moves eyes down and toward nose; rotates eyes from 6 oclock to 3 oclock, Moves eyes up and away from nose; rotates eyeball from 12 oclock to 9 oclock, Surface of eyeball between inferior rectus and lateral rectus, Moves eyes down and away from nose; rotates eyeball from 6 oclock to 9 oclock, Suface of eyeball between superior rectus and lateral rectus, Maxilla arch; zygomatic arch (for masseter), Closes mouth; pulls lower jaw in under upper jaw, Superior (elevates); posterior (retracts), Opens mouth; pushes lower jaw out under upper jaw; moves lower jaw side-to-side, Inferior (depresses); posterior (protracts); lateral (abducts); medial (adducts), Closes mouth; pushes lower jaw out under upper jaw; moves lower jaw side-to-side, Superior (elevates); posterior (protracts); lateral (abducts); medial (adducts), Draws tongue to one side; depresses midline of tongue or protrudes tongue, Elevates root of tongue; closes oral cavity from pharynx. The hand is truly the epitome of anatomical complexity. insertion: lesser trochanter of femur, Characteristic of the Sympathetic and Parasym, Practical #1 (Anatomical position and terms,, ohio life insurance missed questions and answ. Grounded on academic literature and research, validated by experts, and trusted by more than 2 million users. Insertion: mastoid process of temporal bone, occipital bone. Mnemonics to remember bones Kim Bengochea, Regis University, Denver. With more than 600 muscles in the body, it can feel impossible to keep track of them all. Because the muscles insert in the skin rather than on bone, when they contract, the skin moves to create facial expression (Figure 11.4.1). Manifestations are limited movement of the shoulder and severe pain. Here's a mnemonic that summarizes the brachioradialis and helps you to remember it. It inserts on the distal phalangesof the 2nd to 5th digits and acts to flex the distal IP joints of the fingers. Find it on your own body if you can. Get instant access to this gallery, plus: Introduction to the musculoskeletal system, Nerves, vessels and lymphatics of the abdomen, Nerves, vessels and lymphatics of the pelvis, Infratemporal region and pterygopalatine fossa, Meninges, ventricular system and subarachnoid space, Extensor carpi radialis longus and brevis, Pectoralis major, Pectoralis minor, Deltoid, Latissimus dorsi, Supinator, Extensor digitorum, Extensor carpi ulnaris, Extensor carpi radialis longus and brevis, Extensor indicis proprius, Extensor digiti minimi, Brachioradialis, Thenar eminence, Hypothenar eminence, Interossei, Lumbricals, Inferior angle and lower part of the lateral border of the scapula, Intertubercular sulcus (medial lip) of the humerus, Adduction and medial rotation of the humerus (arm), Lateral border of the scapula (middle part), Greater tubercle of the humerus (inferior facet), Lateral rotation of the arm, stabilization of the humerus as part of the rotator cuff muscles, Greater tubercle of the humerus (middle facet), Greater tubercle of the humerus (superior facet), Assistance in arm abduction,stabilization of the humerus as part of the rotator cuff muscles, Medial rotation of the arm,stabilization of the humerus as part of the rotator cuff muscles, Transverse process of the atlas and axis, posterior tubercles C3 and C4, Posterior surface of the medial scapular border (from the superior angle to the root of the spine of the scapula), Anterior rami of the nerves C3 and C4, dorsal scapular nerve (branch of the C5), Superior nuchal line, external occipital protruberance, nuchal ligament, spinous processes of C7 to T12 vertebrae, Lateral third of the clavicle, acromion and spine of the scapula, Spinal accessory nerve; C3 and C4 spinal nerves, Elevation, depression, and retraction of the scapula, Medial half of the clavicle (clavicular head); anterior surface of the sternum, 1st to 6th costal cartilages, aponeurosis of, Adduction and medial rotation of the humerus, Anterior surface of the 3rd, 4th, and 5th ribs and the fascia overlying the intercostal spaces, Medial border and superior surface of the coracoid process of the scapula, Protraction of the scapula, pulls the coracoid process anteriorly and inferiorly, accessory muscle in respiratory, Lateral third of the clavicle, acromion, and spine of scapula, Abduction and stabilization of the shoulder joint, Spinous processes of T7-L5 and sacrum, iliac crest, X-XII ribs, Distal half of the anterior side of the humerus and intermuscular septa, Flexion of the forearm at the elbow joint, Flexion of the forearm at the elbow joint, supinator of the forearm, accessory flexor of the arm at the glenohumeral joint, Anterior surface of the ulna (distal quarter), Anterior surface of the radius (distal quarter), Forearm pronationand binding of the radius and ulna, Anterior surface of the radius and interosseous membrane, Proximal parts of the anterior and lateral surfaces of the ulna and interosseous membrane, Bases of the phalanges of the 4th and 5th digits (medial part), bases of the phalanges of the 2nd and 3rd digits (lateral part), Ulnar nerve (medial part), anterior interosseous nerve (lateral part), Flexion of the distal phalanges at the interphalangeal joints of the 4th and 5th digits (medial part) and of the 2nd and 3rd digits (lateral part), Medial epicondyle of the humerus and coronoid process of the ulna (humero-ulnar head) and superior half of anterior border (ulnar head), Shafts of middle phalanges of medial four digits, Flexion of middle phalanges at proximal interphalangeal joints and flexion of the proximal phalanges at the metacarpophalangeal joints of the middle four digits, Medial epicondyle of the humerus (common flexor tendon), Flexor retinaculum and palmar aponeurosis, Medial epicondyle of the humerus (humeral head), coronoid process of the ulna (ulnar head), Lateral epicondyle of the humerus, crest of the ulna, supinator fossa, radial collateral and anular ligaments, Surface of the proximal third of the radial shaft, Posterior surfaces of the middle and distal phalanges (2nd-5th), Posterior interosseus nerve (branch of the radial nerve), Extension of the index, middle, ring and little fingers, Lateral epicondyle of the humerus, posterior border of the ulna, Medial side of the base of the metacarpal V, Posterior side of the distal third of the ulnar shaft; interosseous membrane, Proximal two-thirds of the supra-epicondylar ridge of the humerus, Lateral surface of the distal end of the radius, Forearm flexion, especially during mid-pronation, Flexor retinaculum and tubercle of trapezium and scaphoid bones, Thumb flexion, abduction, and medial rotation resulting in a combined movement called opposition, Abduction of the 5th digit and flexion assistance of the proximal phalanx, Base of the proximal phalanx of the 5th digit, Flexion of the proximal phalanx of the 5th digit, Sides of two adjacent metacarpals (dorsal interossei) and palmar surfaces of the 2nd, 4th, 5th metacarpals (palmar interossei), Bases of the proximal phalanges via the extensor expansions of the 2nd to 4th digits (dorsal interossei) and 2nd, 4th, and 5th digits (palmar interossei), Abduction of the 2nd to 4th digits (dorsal interossei), adduction of the 2nd, 4th, and 5th digits (palmar interossei), assisting the lumbricals in extension, Tendons of the flexor digitorum profundus, Lateral expansions of the 2nd to 5th digits, Flexion of the metacarpophalangeal joints and extension of the interphalangeal joints of the 2nd to 4th digits. If you have ever been to a doctor who held up a finger and asked you to follow it up, down, and to both sides, he or she is checking to make sure your eye muscles are acting in a coordinated pattern.