Human Anatomy: Sensory, Skeletal, Muscular & Reproductive Systems

Human Sensory Organs

The Eye: Structure and Function

The eyeball consists of the globe itself and attached structures. Key parts include:

• Enveloping Membranes:
  • Sclera: The outermost, opaque, white part.
  • Cornea: The transparent front part.
  • Choroid: A dark-colored layer carrying nutrients to the eye.
  • Iris: A colored disk that regulates the amount of light entering.
  • Pupil: The opening in the center of the iris that controls light entry.
  • Retina: Formed by photoreceptor cells. Contains two types:
    • Cones: Responsible for color vision.
    • Rods: Appreciate light intensities (more numerous in the periphery).
  • Blind Spot: The area where the optic nerve exits the eye.
• Internal Structures:
  • Lens: Focuses images onto the retina.
  • Aqueous Humor: Fluid maintaining the eye's shape in the front chamber.
  • Vitreous Humor: Jelly-like substance filling the main globe cavity.

The eye's internal components act as transparent media for light.

The Ear: Hearing and Balance Mechanisms

The ear is divided into three main sections:

• External Ear:
  • Auricle (Pinna): Cartilage covered with skin folds.
  • Ear Canal: Passageway where earwax (cerumen) is produced, ending at the eardrum.
• Middle Ear (Tympanic Cavity):
  • Contains three cavities obscured by membranes: the eardrum (tympanic membrane), the oval window, and the round window.
  • The Eustachian tube connects the middle ear to the pharynx (throat).
  • A chain of small bones (ossicles) transmits vibrations between the eardrum and the oval window: Malleus (hammer), Incus (anvil), and Stapes (stirrup).
• Internal Ear (Labyrinth):
  • Located within the bony labyrinth.
  • Contains the Vestibule, Semicircular Canals, and the Cochlea.
  • Filled with fluids: Perilymph and Endolymph.

Audition (Hearing)

The ear is responsible for hearing. Sound is transmitted as waves through the auricle and ear canal. When waves reach the eardrum, it vibrates. These vibrations move the ossicles (hammer, anvil, stirrup). The stapes transmits the signal to the oval window. This causes the fluid inside the inner ear (cochlea) to move, stimulating auditory receptors. The round window compensates for pressure changes.

Equilibrium (Balance)

When you move, the fluid (endolymph) filling the semicircular canals shifts position. Specialized cells within these canals detect this movement and inform the brain via nerve impulses. If the internal fluid moves abnormally, the brain receives conflicting information, which can cause vertigo.

The Sense of Touch: Skin Layers and Receptors

The skin is the primary organ for touch:

• Epidermis: The outer layer, composed of epithelial tissue. The outermost cells are dead and contain keratin (a protective protein).
• Dermis: The lower layer, made of connective tissue, providing elasticity. It houses blood vessels, nerve endings, and various tactile receptors that provide information about touch, pressure, temperature, and pain.

The interaction of these receptors produces the sense of touch.

The Sense of Smell: Olfactory System

The sense of smell originates in the nasal cavity:

• The interior nasal passages are lined by a specialized mucous membrane called the olfactory epithelium.
• This membrane has two areas:
  • A vascular area (rich in blood vessels) that warms inspired air.
  • An olfactory area containing numerous olfactory receptors.
• These receptors form the olfactory bulb, which transmits smell information to the brain.

The Sense of Taste: Gustatory System

Taste is detected on the tongue's surface:

• The tongue features taste papillae, which contain taste buds.
• Within the taste buds are chemoreceptors that detect the basic tastes (e.g., sweet, sour, salty, bitter).
• Each taste bud is connected to a nerve ending that transmits taste information to the brain.

The Musculoskeletal System

This system is formed by the skeletal and muscular systems.

Skeletal System: Bones and Joints

• Predominant tissue is bone tissue, forming the bones of the skeleton.
• Bones connect at joints, which allow for varying degrees of movement:
  • Fixed Joints: Immobile (e.g., skull sutures).
  • Semi-mobile Joints: Allow limited movement (e.g., vertebrae).
  • Mobile Joints: Allow free movement, often connected by ligaments.
• Bones can be classified by shape: Flat (e.g., skull), Long (e.g., femur), and Short (e.g., carpals).
• Tendons are connective tissues that attach muscles to bones.

Muscular System: Muscle Types and Attachments

• The predominant tissue types are striated muscles.
• Muscles can be categorized by form or function:
  • Flat Muscles: Often provide protection (e.g., abdominal wall).
  • Sphincter Muscles: Circular muscles that close and open passages (e.g., around the mouth or anus).
  • Elongated Muscles: Typically joined to bones by tendons for movement (e.g., biceps).

Human Reproductive Systems

Principles of Human Reproduction

• Humans reproduce sexually.
• Females produce female gametes called ova (eggs).
• Males produce male gametes called sperm.
• Gametes meet during fertilization to form a zygote.
• Gametes are produced in the gonads: ovaries in females, testes in males.
• Fertilization is internal, meaning the egg and sperm unite within the female reproductive tract.
• Humans are viviparous, meaning the development of the new being occurs inside the mother's body.
• Reproduction involves several processes:
  • Gamete Production: Occurs in specialized reproductive organs and tracts.
  • Fertilization: The union of the nuclei of the gametes. Can be external (e.g., fish) or internal (requires a copulatory organ in many species). Forms the zygote, containing the complete genetic information.
  • Zygote Development: The process from zygote formation until birth. Includes:
    • Embryonic Development: Occurs inside the egg (oviparous) or mother (viviparous).
    • Post-embryonic Development: Stages after birth/hatching (e.g., childhood, puberty).
    • Mitosis: The process by which cell number increases during development.
  • Birth/Delivery: Occurs when the individual is fully formed.

Male Reproductive System Anatomy

• Testes (Testicles): Glands located in the scrotum where sperm are produced.
• Prostate Gland: A walnut-sized gland surrounding the urethra. Produces prostatic fluid, which protects sperm from the acidity of the urethra and vagina.
• Urethra: The tube that carries both urine and semen (at different times) to the exterior. Its walls contract during ejaculation to propel sperm.
• Epididymis: A long, tightly coiled tube located on the surface of each testis where sperm mature and are stored.
• Vas Deferens (Ductus Deferens): A tube that continues from the epididymis, transporting sperm towards the urethra. It meets the duct from the seminal vesicle.
• Seminal Vesicles: Glands that produce seminal fluid, a component of semen that nourishes sperm. Their ducts join the vas deferens to form the ejaculatory duct, which empties into the urethra.
• Penis: The external cylindrical male reproductive organ. The end, called the glans, is enlarged and covered by the prepuce (foreskin) unless circumcised.
• Scrotum: A pouch of skin hanging below the penis that contains the testes and epididymis. It has sebaceous glands and helps regulate testicular temperature.