Introduction to Human Body Anatomy

Introduction to the Human Body

• The human body consists of various systems that work together to maintain homeostasis and perform specific functions.

Anatomical Terms

• Anatomical descriptions are based on a person being in the anatomical position: standing erect, facing forward, with arms at the sides and legs together.
• Body planes:
  • Sagittal plane: divides the body into equal right and left halves.
  • Frontal (coronal) plane: divides the body into anterior and posterior portions.
  • Transverse (axial) plane: divides the body into superior and inferior portions.
• Terms of relationship:
  • Anterior (ventral): near the front.
  • Posterior (dorsal): near the back.
  • Superior (cranial): upward, or near the head.
  • Inferior (caudal): downward, or near the feet.
  • Medial: toward the midline.
  • Lateral: farther from the midline.
  • Proximal: near a reference point, closer to the trunk or point of origin.
  • Distal: away from a reference point, further from the trunk or point of origin.
  • Superficial: closer to the surface.
  • Deep: further from the surface.

Movements

• Body movements occur at joints where two or more bones or cartilages articulate with each other.
• Types of movements:
  • Flexion: decreases the angle between two bones.
  • Extension: increases the angle between two bones.
  • Abduction: movement away from the midline.
  • Adduction: movement towards the midline.
  • Rotation: movement around a longitudinal axis.
  • Circumduction: movement in a circular direction.

Skin

• The skin is the largest organ in the body, accounting for 15-20% of total body mass.
• Functions of the skin:
  • Protection: against abrasions, dehydration, and infection.
  • Temperature regulation: through fat storage and sweat gland activation.
  • Sensations: to touch, pain, and temperature.
  • Endocrine regulation: secretion of hormones and synthesis of vitamin D.
  • Exocrine secretions: secretion of sweat and sebum.
• Layers of the skin:
  • Epidermis: outer protective layer.
  • Dermis: dense connective tissue layer.
  • Subcutaneous tissue: deepest layer.
• Appendages of the skin:
  • Nails: horny covering on the tips of fingers and toes.
  • Hair follicles: sheath of cells and connective tissue surrounding the root of a hair.
  • Sebaceous glands: secrete lubricating oily matter into hair follicles.
  • Sweat glands: secrete sweat and situated in the dermis.

Skeletal System

• The skeletal system supports, protects, and provides movement for the body.
• Divided into two regions:
  • Axial skeleton: includes bones of the skull, vertebral column, ribs, and sternum.
  • Appendicular skeleton: includes bones of the limbs, pectoral and pelvic girdles.
• Functions of the skeletal system:
  • Support: provides a framework for the body.
  • Protection: vital organs are protected by the skeleton.
  • Movement: bones provide a system of levers and joints for movement.
  • Storage of calcium and other salts/growth factors.
  • Source of blood cells (bone marrow).
• Bones can be classified into 5 shapes:
  • Long bones.
  • Short bones.
  • Flat bones.
  • Irregular bones.
  • Sesamoid bones.
• Long bones have the following regions:
  • Epiphysis: ends of long bones.
  • Epiphysial plate: site of growth in length.
  • Metaphysis: site where the bone's shaft joins the epiphysis and epiphysial plate.
  • Diaphysis: shaft of a long bone.

Joints

• Joints are the sites of union or articulation of two or more bones or cartilages.
• Types of joints:
  • Fibrous joints: bones joined by fibrous connective tissue.
  • Cartilaginous joints: bones joined by cartilage and fibrous tissue.
  • Synovial joints: bones joined by a joint cavity filled with synovial fluid and surrounded by a capsule.

Muscular System

• The muscular system produces contractions that result in movement, maintenance of posture, changes in shape, or the propulsion of fluids through hollow tissues or organs.
• Three types of muscle:
  • Skeletal muscle: striated muscle fibers attached to bone.
  • Cardiac muscle: striated muscle fibers that make up the walls of the heart and proximal portion of the great veins.
  • Smooth muscle: non-striated muscle fibers that line various organ systems and attach to hair follicles.

Ligaments and Tendons

• Ligaments: fibrous connective tissue that connects bones to bones and serve to hold structures together.
• Tendons: fibrous connective tissue that attaches muscles to bone or other body structures.

Cardiovascular System

• The cardiovascular system consists of the heart, vessels, and blood.
• Functions of the cardiovascular system:
  • Transports oxygen and nutrients to cells.
  • Transports waste products away from cells.
  • Regulates body temperature.
  • Maintains healthy blood pressure.
• Pulse points: locations where the pulse can be taken.

Lymphatic System

• The lymphatic system protects the body against infection, collects tissue fluids, and returns them to the circulatory system.
• Components of the lymphatic system:
  • Lymph: a colorless, watery fluid that contains lymphocytes.
  • Lymphocytes: cellular components of lymph, including T cells and B cells.
  • Lymph vessels: an extensive network of vessels and capillaries in the peripheral tissues.
  • Lymphoid organs: collections of lymphoid tissues, including lymph nodes, aggregates of lymphoid tissue, tonsils, thymus, spleen, and bone marrow.

Respiratory System

• The respiratory system provides oxygen to the body and eliminates carbon dioxide.
• Components of the respiratory system:
  • Nose and paranasal sinuses.
  • Pharynx and its subdivisions.
  • Larynx and trachea.
  • Bronchi, bronchioles, alveolar ducts/sacs, and alveoli.
  • Lungs.
• Functions of the respiratory system:
  • Filters and humidifies the air.
  • Provides a large surface area for gas exchange.
  • Helps regulate the pH of body fluids.
  • Participates in vocalization.
  • Assists the olfactory system.

Nervous System

• The nervous system integrates and regulates many body activities.
• Divided into two divisions:
  • Central nervous system (CNS): includes the brain and spinal cord.
  • Peripheral nervous system (PNS): includes the somatic, autonomic, and enteric nerves.
• Functions of the nervous system:
  • Controls and coordinates body functions.
  • Interprets and responds to sensory information.
  • Regulates body temperature.
  • Maintains homeostasis.### Nervous System
• The nervous system consists of the central nervous system (CNS) and peripheral nervous system (PNS)
• CNS: brain and spinal cord
• PNS: cranial nerves, spinal nerves

Neurons

• Neurons are called nerve cells
• Information comes to neurons through tree-like processes called dendrites or the neuronal body (soma)
• Neurons convey efferent (motor or output) information via action potentials that course along a single axon
• All neurons can be classified into three functional types:
  • Sensory neurons: convey afferent impulses from peripheral receptors to the CNS
  • Motor neurons: convey efferent impulses from the CNS to target cells (e.g., muscle cells)
  • Interneurons: convey impulses between sensory and motor neurons in the CNS, forming integrated networks

Glial Cells

• Glial cells provide physical and metabolic support for CNS neurons
• Types of glial cells:
  • Astrocytes: provide physical and metabolic support, release growth factors, and contribute to the formation of the blood-brain barrier
  • Oligodendrocytes: responsible for the formation and maintenance of myelin in the CNS
  • Microglia: phagocytic cells that participate in inflammatory reactions, remodel and remove synapses, and respond to injury
  • Ependymal cells: line the ventricles of the brain and the central canal of the spinal cord, containing cerebrospinal fluid
  • Schwann cells: surround all axons, provide trophic support, facilitate regrowth of PNS axons, and clean away cellular debris

Peripheral Nervous System

• Network of nerves that carry messages to and from the brain and spinal cord (CNS)
• Peripheral nerves include:
  • 12 pairs of cranial nerves arising from the brain
  • 31 pairs of spinal nerves arising from the spinal cord

Cranial Nerves

• 12 pairs of cranial nerves identified by name and Roman numerals I to XII
• Cranial nerves possess multiple functional components, including motor, sensory, and both

Spinal Nerves

• 31 pairs of spinal nerves form two major branches:
  • Posterior (dorsal) ramus: small branch that courses dorsally to the back, conveying motor and sensory information to and from the skin and intrinsic back skeletal muscles
  • Anterior (ventral) ramus: larger branch that courses laterally and ventrally, innervating all remaining skin and skeletal muscles of the neck, limbs, and trunk

Somatic Nervous System

• Sensory and motor fibers to skin, skeletal muscle, and joints
• One-neuron motor system: motor neuron in CNS, axon projects to peripheral target (e.g., skeletal muscle)
• Sensory (afferent) neuron resides in a peripheral ganglion (spinal ganglion) and conveys sensory information from skin, muscle, or joint to CNS (spinal cord)
• Dermatomes: areas of skin innervated by specific spinal root nerves (30 total, excluding the 1st cervical spinal nerve)

Autonomic Nervous System

• Sensory and motor fibers to smooth muscle (viscera, vasculature), cardiac muscle, and glands
• Two-neuron motor system: first neuron in CNS, second neuron in peripheral autonomic ganglion
• Preganglionic neuron: axon of the first neuron, postganglionic neuron: axon of the second neuron, then sends axon to target (smooth muscle, cardiac muscle, and glands)

Autonomic Nervous System Divisions

• Sympathetic nervous system: controls the body's "fight, flight, or fright" response
• Parasympathetic nervous system: helps control the body's response during times of rest ("rest and digest")
• These two systems balance each other out