Intro to Human Anatomy and Structure Flashcards

Introduction to Anatomy and Tissue Study

• The human body can be divided structurally into specific components based on the type of tissue and organs involved.

• Osteology: The scientific study of the bones within the human body.

• Arthrology: The scientific study of the joints.

• Myology: The scientific study of the muscles.

• Neurovascular Anatomy: The study of blood vessels and nerves throughout the body.

• The human structural framework consists of bones, cartilages, joints, ligaments, muscles, tendons, organs, glands, and plaques of the nose.

The Human Skeleton: Axial and Appendicular Divisions

• The human skeleton is divided into two primary groups based on their location and function:

  • Axial Skeleton: This comprises the bones along the long axis of the body. Since humans are bipedal and stand upright (vertical), the axial skeleton provides stability and supports the body's position. It consists of the head, the neck, and the trunk (vertebral column, ribs, and sternum).

  • Appendicular Skeleton: This consists of the bones of the limbs, including both the upper limbs and the lower limbs.

Classification of Bones by Size and Shape

• Bones are categorized according to their dimensions and morphology:

  • Long Bones: Characterized by a long shaft; found in the upper and lower limbs.

  • Short Bones: Very small in size, such as the tarsals in the feet and the carpals in the hand.

  • Flat Bones: Thin and flattened bones found in the skull, the scapula (shoulder blade), and the sternum.

  • Irregular Bones: Bones with unique, complex shapes that do not fit other categories, such as the vertebrae and certain skull bones.

  • Sesamoid Bones: Bones that are not directly joined to other bones but are instead suspended within soft tissue or tendons. A primary example is the Patella (kneecap), which is suspended within the patellar tendon.

Arthrology: Structural Classification of Joints

• Joints facilitate movement where muscles pull on different parts on either side of the joint. They are classified by their structural composition:

  • Fibrous Joints: Heavily composed of fibrous tissue. Mobility is extremely limited, providing stability. Examples include the sutures between skull bones, the distal connection between the radius and ulna, and joints between carpals.

  • Cartilaginous Joints: Composed of cartilage between the articulating bones. Movement is limited but not immobile. Examples include connections between the sternum and ribs, between vertebrae (intervertebral discs), and the pelvic bone joints.

  • Synovial Joints: The most common and most movable type of joint in the human body. Defined by a synovial cavity, a small space between bones filled with synovial fluid. This fluid provides essential lubrication to reduce friction during constant movement.

Functional Types of Synovial Joints

• Synovial joints are categorized by their range of motion ($ROM$):

  • Ball and Socket Joint: Provides the highest range of motion, allowing movement in multiple planes. Examples: Shoulder and hip joints.

  • Hinge Joint: Operates like a door hinge, performing only two actions: opening (extension) and shutting (flexion). Examples: Elbow and knee joints.

  • Gliding Joint: Allows for sliding movements.

  • Saddle Joint: Provides specific bi-axial movement.

Connective Tissues: Ligaments and Tendons

• Both are string-like structures composed of fibrous connective tissue, specifically collagen (providing structural strength) and elastin (providing elasticity and stretch).

• Ligaments: Connect bone to bone ($B2B$). Their primary function is stabilizing joints.

• Tendons: Connect muscle to bone ($M2B$), muscle to muscle, or muscle to other structures. They transmit the force of muscle contraction to facilitate movement.

Anatomical Position and Directional Terminology

• All relative positions are defined based on the Anatomical Position: A person standing upright, facing forward, with arms at the sides and palms facing forward.

• Directions are described in pairs of opposites:

  • Anterior (Ventral): Toward the front of the body (e.g., the sternum is anterior to the heart).

  • Posterior (Dorsal): Toward the back of the body (e.g., the vertebrae are posterior to the heart).

  • Superior (Cranial): Toward the head or upper part of the body (e.g., the nose is superior to the chin).

  • Inferior (Caudal): Toward the feet or lower part of the body (e.g., the chin is inferior to the nose).

  • Medial: Toward the midline of the body (e.g., the sternum is medial to the shoulder).

  • Lateral: Away from the midline of the body (e.g., the shoulder is lateral to the sternum).

  • Superficial: Closer to the skin surface.

  • Deep: Away from the skin surface, more internal.

  • Proximal: For limbs, closer to the trunk (e.g., the elbow is proximal to the wrist).

  • Distal: For limbs, further from the trunk (e.g., the hand is distal to the elbow).

Sectional Anatomy: Planes of the Body

• Sectioning is used to view deep structures (organs) via X-ray, MRI, or CT scans:

  • Sagittal Plane: Slices the body into right and left parts.

  • Mid-sagittal Plane: Slices exactly down the midline into equal right and left halves.

  • Para-sagittal Plane: Slices parallel to the midline but off-center (e.g., through a shoulder joint).

  • Transverse/Cross-sectional Plane: Slices the body into superior and inferior parts.

  • Frontal/Coronal Plane: Slices the body into anterior and posterior parts.

Vertebrate Characteristics and Embryology

• Humans share four characteristic features with all vertebrate species (e.g., fish, snakes, birds) during embryonic development:

  • Dorsal Hollow Nerve Cord: Develops into the brain and spinal cord.

  • Notochord: A long axial support system in the embryo. It eventually fragments and is incorporated into the intervertebral discs (as the nucleus pulposus).

  • Pharyngeal Arches and Pouches: Develop into bones and muscles of the head and neck.

  • Vertebrae: The primary repeating skeletal structures along the longitudinal axis.

• Humans are segmental animals, featuring serially repeating structures (ribs, vertebrae) derived from Somites. Somites are paired clusters of embryonic cells that develop into bones, cartilages, skin, and muscles of the body wall.

The Vertebral Column: Regions and Count

• The vertebral column is divided by body region:

  • Cervical: $7$ vertebrae ($C1-C7$), forming the neck.

  • Thoracic: $12$ vertebrae ($T1-T12$), attached to the ribs.

  • Lumbar: $5$ vertebrae ($L1-L5$), supporting the lower back.

  • Sacral: $5$ vertebrae, fused into a single unit (the Sacrum).

  • Coccygeal: $2$ to $4$ vertebrae, fused into the Coccyx (tailbone).

• Typical Vertebral Anatomy:

  • Vertebral Body: The anterior, thick, weight-bearing mass.

  • Vertebral Arch: The posterior portion consisting of the Pedicle (junction to the body) and Lamina (smooth surface).

  • Vertebral Foramen: The central hole in a single vertebra; when stacked, these form the Vertebral Canal for the spinal cord.

  • Intervertebral Foramina: Openings created by superior and inferior notches of adjacent vertebrae, serving as exit points for Spinal Nerves.

  • Spinous Process: The posterior, pointy process.

  • Transverse Processes: Bilateral processes extending from the arch.

  • Articular Facets: Superior and inferior surfaces where adjacent vertebrae join.

Regional Identification of Vertebrae

• Cervical: Feature a Transverse Foramen in the transverse processes for the passage of the vertebral artery. $C1$ (Atlas) lacks a body and features anterior/posterior arches. $C2$ (Axis) features the Dens (odontoid process) for head rotation.

• Thoracic: Feature Costal Facets for rib attachment on the body and transverse processes.

• Lumbar: Lack transverse foramina and costal facets; they possess large, thick bodies and large facets.

Vertebral Ligaments and Discs

• Intervertebral Discs: Function as cartilaginous joints providing stability and cushioning. They consist of an outer fibrous Annulus Fibrosus and an inner gelatinous Nucleus Pulposus (a notochord remnant).

• Major Ligaments:

  • Anterior Longitudinal Ligament: Connects anterior surfaces of vertebral bodies.

  • Posterior Longitudinal Ligament: Connects posterior surfaces of vertebral bodies.

  • Ligamentum Flavum: Connects laminae; high in elastin, giving it a yellow color.

  • Interspinous Ligament: Between spinous processes.

  • Supraspinous Ligament: Along the tips of spinous processes.

  • Nuchal Ligament: Continuation of the supraspinous ligament in the cervical region, supporting the head.

Curvatures of the Spine

• Primary Curvatures: Present at birth; include Thoracic and Sacral (forming a $C$-shape).

• Secondary Curvatures: Develop later for weight support and balance; include Cervical (develops when a baby lifts its head) and Lumbar (develops when a child starts walking).

• Clinical Abnormalities:

  • Scoliosis: Abnormal lateral deflection.

  • Kyphosis: Exaggerated thoracic curvature ("hunchback").

  • Lordosis: Exaggerated lumbar curvature (temporary in pregnancy or associated with abdominal weight).

Muscle Tissue Classification

• Skeletal Muscle: Voluntary, striated; moves bones at joints.

• Smooth Muscle: Involuntary, unstriated; found in tubular organs (intestines, bladder).

• Cardiac Muscle: Involuntary, striated; found only in the heart.

• Somatic Structures: Refers to skeletal muscles and skin derived from somites. Segmental muscles occur in pairs on both sides of the body.

Myology: Muscle Mechanics and Terms

• Origin: The fixed, immovable attachment point of a muscle.

• Insertion: The mobile attachment point pulled toward the origin during contraction.

• Movement Types:

  • Flexion: Bending at a joint; reducing the angle.

  • Extension: Straightening at a joint; increasing the angle.

  • Bilateral Action: Both left and right muscles contract together (e.g., trunk flexion).

  • Unilateral Action: Only one side contracts, causing lateral flexion or rotation.

Back Muscles: Epaxial and Hypaxial Divisions

• Epaxial Muscles: Located dorsal to the transverse processes; they are the true back muscles, innervated by Dorsal Rami. Examples include:

  • Superficial Layer: Splenius.

  • Intermediate Layer: Erector Spinae (divided into Iliocostalis (lateral), Longissimus (middle), and Spinalis (medial)).

  • Deep Layer: Semispinalis (spans $4-6$ vertebrae) and Multifidus (spans $2-3$ vertebrae; extends the full length of the spine).

• Hypaxial Muscles: Located ventral to the transverse processes; include limb muscles and anterior/lateral body wall muscles, innervated by Ventral Rami.

• Note: The Trapezius and Latissimus Dorsi are superficial muscles of the back but belong to the upper limb group; they must be removed to see true epaxial muscles.

The Nervous System: Central and Peripheral Divisions

• Central Nervous System ($CNS$): Comprises the Brain and Spinal Cord. It serves as the integration and command center.

• Peripheral Nervous System ($PNS$): Comprises all Nerves (Cranial and Spinal). It acts as the communication pathway.

• Meninges (Coverings of the $CNS$):

  • Dura Mater: Outermost, tough, protective layer.

  • Arachnoid Mater: Middle layer with web-like projections.

  • Pia Mater: Innermost, delicate layer clinging to the tissue.

  • Subarachnoid Space: Between arachnoid and pia, filled with Cerebrospinal Fluid ($CSF$) for cushioning and nutrient exchange.

Spinal Cord Anatomy and Nerves

• The spinal cord organized into White Matter (outer; myelinated axons for fast signal transmission) and Gray Matter (inner, butterfly-shaped; cell bodies and non-myelinated neurons).

• Gray Matter Horns:

  • Dorsal Horn: Sensory input.

  • Ventral Horn: Motor output (voluntary/somatic).

  • Lateral Horn: Motor output (involuntary/autonomic).

• Structure of a Spinal Nerve:

  • Dorsal Root: Carries sensory fibers toward the spinal cord. Features the Dorsal Root Ganglion (collection of sensory cell bodies).

  • Ventral Root: Carries motor fibers away from the spinal cord; cell bodies are located inside the ventral horn.

  • Spinal Nerve: Fusion of dorsal and ventral roots; contains mixed (sensory and motor) fibers.

  • Dorsal Ramus: Innervates epaxial muscles and skin of the back.

  • Ventral Ramus: Innervates hypaxial muscles and anterior/lateral skin.

Autonomic Nervous System ($ANS$)

• Regulates involuntary functions (smooth muscle, heart, glands). It always utilizes a two-neuron pathway:

  • Preganglionic Neuron: Cell body in the $CNS$ ($Brain$ or $Spinal Cord$).

  • Ganglion: Site of synapse between the first and second neuron.

  • Postganglionic Neuron: Cell body in the ganglion; axon travels to the target organ.

• Sympathetic Division: "Fight, Flight, or Fright." Preganglionic cell bodies located in lateral horns of $T1-L2$ (Thoracolumbar). Synapses occur in Paravertebral Ganglia (Sympathetic Trunk) or Prevertebral Ganglia (near major abdominal arteries).

• Parasympathetic Division: "Rest and Digest." Preganglionic cell bodies in the Brain (via Vagus Nerve) or Sacral Spinal Segments ($S2-S4$). Synapses occur at or near the target organ.

Thoracic Anatomy: Skeleton and Muscles

• Thoracic Cage: Formed by the $12$ thoracic vertebrae, sternum, and ribs.

• Sternum: Composed of the Manubrium, Body, and Xiphoid Process.

• Ribs: $12$ pairs.

  • True Ribs ($1-7$): Attach directly to the sternum via individual costal cartilages.

  • False Ribs ($8-10$): Indirectly attach to the sternum by merging with the $7^{th}$ cartilage.

  • Floating Ribs ($11-12$): Do not attach to the sternum; end in the abdominal wall.

• Intercostal Muscles: Hypaxial muscles in three layers:

  • External Intercostals: Fiber direction is "hands in pockets" (inferior-anterior). They elevate the ribs during inspiration.

  • Internal and Innermost Intercostals: Fiber direction is "hands in prayer" (inferior-posterior). They depress the ribs during forceful expiration.

  • Transversus Thoracis: Located on the inner surface of the anterior wall; depresses ribs during forceful expiration.

Body Cavities and Serous Membranes

• Cavities are lined by serous membranes: Parietal Layer (lines the wall) and Visceral Layer (clings to the organ).

  • Pleura: Surrounds the lungs ($Pleural Cavity$).

  • Pericardium: Surrounds the heart ($Pericardial Cavity$).

• Mediastinum: The central space between the lungs containing the heart, esophagus, trachea, and great vessels.

• Lungs:

  • Right Lung: $3$ lobes (Superior, Middle, Inferior); $2$ fissures (Horizontal and Oblique).

  • Left Lung: $2$ lobes (Superior, Inferior); $1$ fissure (Oblique). Features the Cardiac Notch and Cardiac Impression due to the heart's position.

  • Hilum: Medial region where bronchi, pulmonary arteries, and pulmonary veins enter/exit.

Cardiovascular System: The Heart

• Layers: Endocardium (inner lining), Myocardium (middle muscle layer), Epicardium/Visceral Pericardium (outer covering).

• Chambers:

  • Atria (Right and Left): Receiving chambers; thin-walled.

  • Ventricles (Right and Left): Pumping chambers; thick-walled (Left is thicker as it pumps to the whole body).

• Valves: Prevent backflow.

  • Atrioventricular ($AV$) Valves: Tricuspid (Right) and Bicuspid/Mitral (Left). Supported by Chordae Tendineae and Papillary Muscles.

  • Semilunar Valves: Pulmonary and Aortic (half-moon shaped).

• Blood Flow Pathway: $SVC/IVC$ → Right Atrium → Tricuspid Valve → Right Ventricle → Pulmonary Semilunar Valve → Pulmonary Trunk → Pulmonary Arteries → Lungs (oxygenation) → Pulmonary Veins → Left Atrium → Bicuspid Valve → Left Ventricle → Aortic Semilunar Valve → Ascending Aorta → Body.

Abdominal Wall and the Gut Tube

• Abdominal Wall Muscles: Three lateral layers (External Oblique, Internal Oblique, Transversus Abdominus) and one anterior layer (Rectus Abdominus). All are hypaxial and innervated by ventral rami. They insert onto the Linea Alba via the Rectus Sheath (an aponeurosis).

• Gut Tube Regions:

  • Foregut: Esophagus, stomach, first half of duodenum, liver, pancreas, spleen. Supplied by the Celiac Trunk.

  • Midgut: Rest of small intestine, cecum, appendix, ascending colon, part of transverse colon. Supplied by the Superior Mesenteric Artery.

  • Hindgut: Rest of transverse colon, descending colon, sigmoid colon. Supplied by the Inferior Mesenteric Artery.

• Accessory Organs: Liver (produces bile), Gallbladder (stores bile), Pancreas (produces digestive enzymes and insulin).

Hepatic Portal System

• Unlike other veins that drain directly to the heart, veins from the gut tube (Superior/Inferior Mesenteric, Splenic) join to form the Hepatic Portal Vein. This vein carries nutrient-rich but potentially toxin-laden blood to the Liver for filtration and detoxification before it enters the Inferior Vena Cava via the Hepatic Veins.

Pelvis and Perineum

• Pelvic Girdle: Formed by the Sacrum, Coccyx, and Os Coxae (Ilium, Ischium, Pubis). Bony landmarks include the Acetabulum (hip socket) and Ischial Tuberosity (sitting bone).

• Pelvic Diaphragm: Formed by Levator Ani and Coccygeus muscles; separates the pelvic cavity from the perineum.

• External Genitalia: Developed from homologous embryonic precursors.

  • Male: Scrotum (holds testes; cooler for sperm viability), Penis (Corpus spongiosum, Corpora cavernosa).

  • Female: Labia Majora, Clitoris.

• Descent of the Gonads: Ovaries descend into the pelvis; testes descend through the Inguinal Canal into the scrotum along the Gubernaculum. In females, the gubernaculum becomes the Round Ligament of the Uterus.

Reference Materials

• Comprehensive Human Anatomy Study Notes Link: https://knowt.com/note/016fa447-4a52-43ff-925c-b580e50da0bd/Comprehensive-Human-Anatomy-Embryology