SENSE ORGANS (Organs of Special Sense)

From a Gray’s Anatomy-style perspective

Overview

Sense organs are specialized anatomical structures responsible for perceiving external or internal stimuli and converting them into electrical impulses, which are interpreted by the brain. They include:

• The eye (vision)

• The ear (hearing and balance)

• The nose (olfaction)

• The tongue (taste)

• The skin (touch and general sensation)

All sense organs contain receptor cells specialized for specific types of stimuli.

1. The Eye (Organ of Vision)

Location: Situated in the orbital cavity of the skull, protected by the orbital bones and eyelids.

Key Structures:

• Cornea: Transparent anterior surface; refracts light.

• Sclera: Dense connective tissue forming the “white” of the eye.

• Choroid: Vascular layer providing oxygen and nutrients to retina.

• Retina: Innermost layer containing photoreceptor cells:

• Rods: For black and white vision in low light.

• Cones: For color vision and high acuity in bright light.

• Lens: Biconvex structure that focuses light on the retina.

• Aqueous and Vitreous Humors: Maintain intraocular pressure and shape.

Neural Connection:

• Optic nerve (CN II) transmits impulses to the visual cortex (occipital lobe).

2. The Ear (Organ of Hearing and Balance)

Divided into three parts:

• External ear: Auricle and external auditory canal; gathers sound.

• Middle ear: Tympanic cavity with ossicles (malleus, incus, stapes) that amplify sound.

• Inner ear (Labyrinth):

• Cochlea: Spiral-shaped organ with Organ of Corti, the sensory organ for hearing.

• Vestibular apparatus: Includes semicircular canals, utricle, and saccule for balance and spatial orientation.

Neural Connection:

• Vestibulocochlear nerve (CN VIII) carries signals to auditory and vestibular cortices.

3. The Nose (Organ of Smell / Olfaction)

Location: Upper part of the nasal cavity.

Key Structures:

• Olfactory epithelium: Located on the superior nasal concha and septum; contains:

• Olfactory receptor neurons

• Supporting cells

• Basal cells (stem cells)

• Olfactory bulb and tract: Transmit signals directly to the olfactory cortex, bypassing the thalamus.

Neural Connection:

• Olfactory nerve (CN I) carries impulses to the olfactory cortex (temporal lobe).

4. The Tongue (Organ of Taste / Gustation)

Location: Floor of the oral cavity.

Key Structures:

• Taste buds: Found mainly on papillae of the tongue (fungiform, circumvallate, foliate).

• Contain gustatory receptor cells.

• Saliva: Dissolves substances to allow interaction with taste receptors.

Five basic tastes:

• Sweet, sour, salty, bitter, umami (savory)

Neural Connection:

• Facial nerve (CN VII): Anterior 2/3 of tongue.

• Glossopharyngeal nerve (CN IX): Posterior 1/3.

• Vagus nerve (CN X): Small area in epiglottis and pharynx.

5. The Skin (Organ of Touch / Somatic Sensation)

Receptors in skin detect:

• Mechanoreception (touch, pressure, vibration): e.g., Meissner’s corpuscles, Pacinian corpuscles

• Thermoreception (temperature)

• Nociception (pain)

• Proprioception (body position via muscle spindles and Golgi tendon organs)

Neural Connection:

• Signals travel via spinal nerves and cranial nerves (e.g., trigeminal nerve for the face) to the somatosensory cortex (parietal lobe).