Introduction to Human Anatomy PDF

INTRODUCTION DEPARTMENT OF HUMAN ANATOMY Assistant Professor: Dr. Ahmed Almusawi  Introduction | Ahmed Almusawi What is Anatomy? Anatomy: is a descriptive science that studies the structure of living organism...

INTRODUCTION DEPARTMENT OF HUMAN ANATOMY Assistant Professor: Dr. Ahmed Almusawi  Introduction | Ahmed Almusawi What is Anatomy? Anatomy: is a descriptive science that studies the structure of living organisms. It includes two major branches: Gross anatomy and Microscopic anatomy. A. Gross Anatomy: is the study of body structures visible to the naked eye. This can be approached in a Systemic Pattern where an entire system (like the respiratory system) is studied at different regions. It may also be studied in a Regional Pattern where the body is divided & studied in regions; each region containing parts of different systems. The study of anatomy in a comprehensive regional pattern is the most useful approach for medical students. For descriptive reasons, the body is divided into the following regions [figure 1]: The head & neck The trunk which consists of: 1. From behind: The back 2. From front: a- The thorax (chest) b-The abdomen: consisting of the abdomen proper and the pelvis. The upper limbs. The lower limbs. Sub-branches of gross anatomy include: Surface Anatomy which describes the external body features & relates them to internal structures; and Anatomic Imaging which involves the use of different imaging techniques e.g. X-ray to reveal inner structures without dissection. How to Study Anatomy? Studying anatomy involves lots of memorization. For instance, the human body contains 206 bones and over 600 muscles. Learning these structures requires time, effort, and good memorization skills. The following tips will help make learning and memorizing body structures easier: 1  Introduction | Ahmed Almusawi Know the language. The most important thing to understand when studying anatomy is the terminology. Using standard anatomical terminology ensures that physicians have a common method of communicating to avoid confusion when identifying structures. Use anatomy study aids. Anatomy is almost impossible to understand without visual aids. The more pictures, diagrams, flash cards & atlases you study, the more you’ll grasp the subject. Important anatomical terms The anatomical position The anatomical position is the standard reference position of the body used to describe the location of structures. The body is in the anatomical position when standing upright with feet together, hands by the side and face looking forward. The mouth is closed and the facial expression is neutral. The rim of bone under the eyes is in the same horizontal plane as the top of the opening to the ear, and the eyes are open and focused on something in the distance. The palms of the hands face forward with the fingers straight and together and with the pad of the thumb turned 90° to the pads of the fingers. The toes point forward. The other positions are: The prone position: the body is lying on the face. The supine position: the body is lying on the back. The lateral decubitus position: the body is lying on one side. Anatomical planes Three major groups of planes pass through the body in the anatomical position Coronal planes are oriented vertically and divide the body into anterior and posterior parts. Sagittal planes also are oriented vertically but are at right angles to the coronal planes and divide the body into right and left parts. The plane that passes through the center of the body dividing it into equal right and left halves is termed the median sagittal plane. Transverse, horizontal, or axial planes divide the body into superior and inferior parts. 2  Introduction | Ahmed Almusawi Terms to describe location Anterior (ventral) and posterior (dorsal), medial and lateral, superior and inferior Three major pairs of terms are used to describe the location of structures relative to the body as a whole or to other structures. Anterior (or ventral) and posterior (or dorsal) describe the position of structures relative to the “front” and “back” of the body. For example, the nose is an anterior (ventral) structure, whereas the vertebral column is a posterior (dorsal) structure. Also, the nose is anterior to the ears and the vertebral column is posterior to the sternum. Medial and lateral describe the position of structures relative to the median sagittal plane and the sides of the body. For example, the thumb is lateral to the little finger. The nose is in the median sagittal plane and is medial to the eyes, which are in turn medial to the external ears. Superior and inferior describe structures in reference to the vertical axis of the body. For example, the head is superior to the shoulders and the knee joint is inferior to the hip joint. Proximal and distal, cranial and caudal, and rostral Other terms used to describe positions include proximal and distal, cranial and caudal, and rostral. Proximal and distal are used with reference to being closer to or farther from a structure’s origin, particularly in the limbs. For example, the hand is distal to the elbow joint. The glenohumeral joint is proximal to the elbow joint. These terms are also used to describe the relative positions of branches along the course of linear structures, such as airways, vessels, and nerves. For example, distal branches occur farther away toward the ends of the system, whereas proximal branches occur closer to and toward the origin of the system. Cranial (toward the head) and caudal (toward the tail) are sometimes used instead of superior and inferior, respectively. Rostral is used, particularly in the head, to describe the position of a structure with reference to the nose. For example, the forebrain is rostral to the hindbrain. 3  Introduction | Ahmed Almusawi Other terms Superficial is nearer the skin. Deep is away from the skin. Middle (medius) indicates a position between superior & inferior or anterior & posterior. Intermediate usually describes a position between medial & lateral Internal & External are used to describe structures nearer or away from the interior of the body; respectively e.g. muscles are internal to the skin but external to bones. The above terms can be combined e.g. anteromedial, posteroinferior, superolateral…..etc. Terms of Movements Movements occur around joints and are referred to them e.g. Flexion of the shoulder. The following are the anatomical terms of movements: Flexion & Extension: to flex a joint is to fold it (i.e. decrease the angle) and to extend a joint is to unfold it (i.e. increase the angle). In the trunk and neck lateral flexion refers to bending the neck or trunk to the right or left. Abduction and adduction: to abduct is to move away from the median plane (increasing the angle) and to adduct is to move towards the median plane (decreasing the angle). Rotation: this movement occurs around a longitudinal axis either towards the midline (Medial or Internal Rotation) or away from the midline (Lateral or External Rotation). In the forearm medial rotation is substituted by Pronation and lateral rotation by Supination. Circumduction: is a conical rotatory movement creating an arc around a longitudinal axis and represents the combination of flexion, abduction, extension & adduction. ❖ Special movements At the wrist & hand: In the wrist the term abduction may be replaced by radial deviation and adduction by ulnar deviation. In the hand, the axis of the middle finger acts as the midline and to abduct the fingers is to spread them apart from the middle finger. Abduction of the thumb is moving it away from the fingers & palm so that it makes right angles with the index (pointing finger) and the palm. To adduct the fingers is to bring them together to the line of the middle finger and to bring the thumb beside the index. 4  Introduction | Ahmed Almusawi In the hand, to flex the fingers is to fold them in the palm and to flex the thumb is to bring it on the palm below the other fingers. To extend the thumb is to move it away from the palm making a right angle with the index finger but parallel to the palm. Opposition: is moving the thumb so its tip touches the tips of other fingers. Reposition is moving the thumb from opposition back to the neutral position. ❖ Special movements at the ankle: Flexion is replaced by dorsiflexion and refers to upward movement of the foot while extension is replaced by plantar flexion and refers to downward movement of the foot (standing on the toes). Adduction is replaced by inversion while abduction is replaced by eversion. In the foot the line of adduction and abduction of the toes is the second toe (the one next to the big toe). ❖ Other movements: Elevation (Lifting up), depression (Pulling down), Protraction or Protrusion (sliding forward) and Retraction or Retrusion (sliding backward) occur at the scapula and jaw, respectively. 5  Introduction | Ahmed Almusawi Basic Anatomical Structures The basic anatomical structures are structures that are met during dissection in almost every region of the body. The Skin The skin is composed of two layers: the superficial avascular epidermis and the deeper dermis with blood vessels and fibers. Anatomical importance of the epidermis: A. According to the thickness of the epidermis (which varies from one part of the body to another) the skin is divided into: 1. Thick skin: which is present at any area subject to pressure or friction (i.e. tear & wear) like the palms, soles, back. 2. Thin skin: is especially present in highly sensitive areas like the lips, eyelids & gentalia. B. The epidermal appendages are structures derived from the epidermis but are invaginated into the dermis. They include: 1. Nails. 2. Hairs. (not all skin has hairs, e.g.: the palms, soles and lips are hairless). 3. Arrector pili muscles (which cause hair erection in response to cold or fear; giving the skin a goose-flesh appearance). 4. Sebaceous glands are related to hairs and secrete an oily material (sebum) that moisturizes hair. 5. Sweat glands secrete excess water & electrolytes from the body. Anatomical importance of the dermis: A. The fibers of the dermis (collagen & elastic fibers) maintain their elasticity and strength. B. The dermis contains the nerve endings and receptors for skin (general) sensation. These receptors can detect five modalities of cutaneous sensation: touch, pressure, pain, temperature & vibration. 6  Introduction | Ahmed Almusawi Fascia Fascia is a connective tissue that surrounds the body and all its inner structures & is divided into 2 types: 1) Superficial fascia This is also called the subcutaneous tissue or hypodermis because it lies immediately deep to the skin but it is NOT part of the skin. It is composed of loose areolar connective tissue rich with fat. It functions to store fat, insulate the body temperature & connect the skin above to the deeper structures below. The superficial fascia contains veins called superficial veins, the cutaneous nerves passing to the dermis, superficial lymphatic vessels and occasionally skeletal muscles. 2) Deep fascia This is a membranous connective tissue that surrounds and invests inner structures and takes its name according to the structure it surrounds. For example: deep fascia which separates muscles from each other into compartments is the septum, at joints deep fascia thickens and extends from one articulating bone to another and is called ligament. Muscles There are three types of muscles: skeletal, smooth and cardiac. Skeletal muscles These are voluntary striated muscles that have at least one attachment to the skeleton (whether bone or cartilage). Skeletal muscles are made up of bundles of striated fibers. The power of a skeletal muscle depends on the number & diameter of its bundle fibers. A skeletal muscle is composed of the following parts: o Origin is the part that moves the least (almost fixed). o Insertion: the part which moves the most (mobile). o Belly: the fleshy part between the origin & insertion. o Tendon: the fibrous band which attaches the muscle to the bone. The tendons of some muscles form a flat sheet called aponeurosis that anchor the muscle to the skeleton. o Neurovascular bundle: is composed of the nerve & vessels that supply the muscle. The nerve reaches the muscle at the neuromuscular junction. Skeletal muscles are named according to different categories. They may be named according to: - Shape: e.g. Teres (round), Deltoid (triangular). 7  Introduction | Ahmed Almusawi - Size: e.g. Minor (small), Major (Large), Longus (Long). - Position: e.g. Brachii (in the arm). - Depth: e.g. Profundus (Deep), Superficialis (Superficial). - Action: e.g. Extensor (Performs extension). - Number of heads: e.g. Biceps (two heads). - Number of bellies: e.g. Digastric (two bellies). - Points of attachment: e.g. Brachioradialis. Many muscles are named in combinations, e.g. Abductor Pollicis Longus (The long abductor of the thumb). Smooth muscles These are involuntary non-striated muscles related to internal structures e.g. arteries, gut, urinary bladder…etc. & are controlled by autonomic nerves &/or hormones. They're arranged in either of two forms: o Circular and longitudinal fibers producing a combination of constrictive & propulsive action. This action produces pulsation in arteries and peristalsis in the gut & urinary tubes. Circular smooth muscles may be thickened at the entrance or exit parts of some organs and form sphincters that control the emptying of these organs. o Interlacing fibers in the wall of a hollow viscus e.g. uterus, urinary bladder; producing an evacuator function. The cardiac muscle This is the involuntary striated muscle of the heart that contracts on its own but under autonomic nervous control. Blood Vessels 1. Arteries: An artery is a blood vessel that carries blood (away) from the heart to all body tissues. Arteries are mostly deep vessels. According to their diameter, arteries may be Large, Medium-sized or small, most of which have rich smooth muscles in their walls making them capable of constriction and dilatation (i.e., Pulsation). When the small arteries reach a diameter of