Human Biology: Auditory, Visual, Olfactory, Gustatory & Tactile Senses
Organs
Auditory System
The ear consists of three parts: the outer ear, middle ear, and inner ear.
Outer Ear
Composed of the pinna, ear canal, and eardrum, the outer ear collects and transmits sound waves to the middle ear. The ear canal contains small hairs and wax-producing glands for protection. The eardrum is a membrane separating the outer and middle ear.
Middle Ear
This section contains the tympanic cavity with three openings: one closed by the eardrum, and two inward openings called the oval window and round window. The Eustachian tube connects the middle ear to the pharynx, equalizing air pressure. The ossicles (hammer, anvil, and stirrup) transmit and amplify sound waves to the inner ear.
Inner Ear
Filled with endolymph fluid, the inner ear has two chambers: the utricle (connected to the semicircular canals) and the saccule (connected to the cochlea). Sound waves cause endolymph movement, stimulating sensory cells connected to the auditory nerve. Sensory cells in the semicircular canals contribute to balance.
Visual System
The eye has three layers: sclera, choroid, and retina.
Sclera
This opaque, whitish outer layer forms the transparent cornea at the front, allowing light to enter.
Choroid
Located beneath the sclera, the choroid contains the iris (responsible for eye color) and the pupil (which controls light entry).
Retina
The innermost layer containing rods (for black and white vision) and cones (for color vision).
The optic nerve exits where these layers converge. The eyeball also has two chambers:
- Vitreous Body/Humor: A gelatinous structure in the posterior chamber.
- Aqueous Humor/Anterior Chamber: Filled with a colorless liquid.
The crystalline lens separates these two chambers.
Olfactory System
The nostrils contain:
- Respiratory Mucosa (Red): Warms and filters inhaled air.
- Olfactory Mucosa (Yellow): Contains bipolar cells with cilia that detect odors and axons connecting to the olfactory bulb, which transmits signals to the olfactory nerve.
Gustatory System
Taste buds are located in the pharynx, palate, and tongue. Each taste bud contains taste cells (connected to nerve fibers) and support cells. This sense interacts with the olfactory system to perceive flavors.
Tactile System
Skin has three layers:
Epidermis
The outermost layer, composed of epithelial tissue. Deep within are germ cells that produce new skin cells. Outer cells are keratinized and dead. Melanin provides protection from sun radiation. Sebaceous glands produce waterproofing oils.
Dermis
Connective tissue provides strength and flexibility. Contains free nerve endings (for pain) and encapsulated nerve endings (for other sensations). Also contains sweat glands, hair follicles, and blood vessels.
Subcutis (Hypodermis)
Adipose tissue provides thermal insulation and shock absorption.
Digestive System
Structure
The digestive system consists of the digestive tract and accessory glands.
- Mouth: Contains lips, teeth, tongue, and palate.
- Pharynx: Connects the mouth and nose to the esophagus and larynx.
- Esophagus: Connects the pharynx to the stomach.
- Stomach: Composed of the fundus, cardia, gastric body, and pyloric area.
- Small Intestine: About 7 meters long, with folds, villi, and microvilli. Divided into the duodenum, jejunum, and ileum.
- Large Intestine (Colon): Includes the cecum (with the appendix).
- Rectum and Anus: The final parts of the digestive tract.
Accessory Glands:
- Salivary Glands: Parotid, sublingual, and submaxillary glands lubricate food.
- Liver: Produces bile, stored in the gallbladder, which helps dissolve fats.
- Pancreas: Produces insulin and pancreatic juices for digestion.
Function
Digestion transforms complex insoluble food into simpler soluble molecules.
Stages of Digestion:
- Chewing: Mechanical breakdown of food, mixed with saliva containing ptyalin (which breaks down starch).
- Swallowing: The bolus moves from the mouth to the esophagus.
- Gastric Digestion: Food mixes with gastric juices (mucin, hydrochloric acid, and enzymes) in the stomach, forming chyme.
- Intestinal Digestion: Chyme enters the duodenum and mixes with bile and pancreatic juices, becoming chyle. Absorption of nutrients occurs mainly in the small intestine (jejunum and ileum).
- Elimination: Undigested material moves to the large intestine, where bacteria further break it down. Waste is then expelled through the rectum and anus.