Special Senses and Endocrine System Review

Special senses will be the primary focus of the seminar; endocrine system to be reviewed independently via the learning module.

General vs. Special Senses

Two major sense types:

• General senses.
• Special senses.

Five special senses:

• Sight (vision).
• Taste (gustation).
• Smell (olfaction).
• Hearing (audition).
• Balance (equilibrium).

General senses:

• Nociception (pain).
• Thermoception (temperature).
• Proprioception (body position).
• Pressure.
• Touch (tactician).

Characteristics of Special Senses

Special senses have unique sensory receptors housed within specific complex sensory organs (e.g., eye for vision, ear for hearing and balance).

Sensory information transmitted to the brain via specific cranial nerves.

Characteristics of General Senses

General senses are widespread throughout the body and do not have specific sensory organs.

Divided into somatic senses (touch, temperature, pain, proprioception, pressure) and visceral senses (nociception, pressure, stretch).

Neurons carrying impulses for each sense type only carry information for that specific sense (e.g., touch receptor only carries touch information).

Conditions for Sensation

3. Stimulus: A change in the environment activates sensory receptors (e.g., light, sound, pressure).
4. Conversion: Sensory receptor converts the stimulus into electrical energy to produce a nerve impulse.
5. Conduction: Nerve impulse is conducted along neuronal pathways to specific brain area.
6. Integration and Perception: Brain region receives and integrates the information, allowing perception of the sense.

Olfaction (Smell)

Receptors located within the olfactory epithelium covering the superior nasal conchae and upper nasal septum.

Olfactory epithelium: Pseudostratified columnar epithelium containing olfactory receptor cells.

Odorant molecules dissolve in the mucus layer and are absorbed by cilia on olfactory cells.

Information passes through olfactory cells, attached to olfactory nerve (cranial nerve I).

Axons travel through the cribriform plate to synapse in the olfactory bulb.

Olfactory bulb sends information along the olfactory tract to:

• Temporal lobe (primary olfactory area) for processing.
• Limbic system for emotional and memory responses.
• Orbitofrontal cortex for identification and differentiation of smells.

Gustation (Taste)

Gustatory receptors (taste receptors) are located within taste buds on the tongue's mucosa, pharynx, cheeks, epiglottis, and soft palate.

Taste buds are found within papillae (projections) on the tongue's surface.

Taste receptor cells have microvilli (gustatory hairs) that project through a taste pore on the tongue's epithelium.

Saliva dissolves taste molecules, which stimulate the hair cells.

Receptor cells generate a nerve impulse within sensory nerves (cranial nerves).

Information is sent to the primary gustatory cortex (insula) for taste perception.

Four types of papillae:

• Filiform.
• Fungiform.
• Foliate.
• Vallate (prominent V-shape at the posterior tongue).

Vision (Sight)

Eye Layers:

• Fibrous tunic (outermost): protective layer.

• Sclera (whites of the eye): Shape and protection.

• Cornea: Clear, rounded, focuses light rays onto the retina.

• Vascular tunic (middle): structural functions.

• Choroid: Thin membrane with blood vessels, contains melanocytes that secrete melanin to absorb stray light and prevent scattering within the eyeball.

• Ciliary body: Consists of ciliary muscle and ciliary process; ligaments attach to the lens, helps to shape the lens for viewing objects at different distances.

• Lens: Focuses light rays for clarity of vision.

• Iris: Colored part, contains sphincter and dilator pupillae muscles controlling pupil size (amount of light entering the eye).

• Retina (innermost).

• Pigmented layer: Contains melanin to prevent light scattering and absorb extra light.

• Neural layer: Contains photoreceptors (rods and cones).

• Rods: Dim light vision, shades of grey

• Cones: Color vision, visual acuity.

• Fovea centralis: Highest concentration of cones; clearest point of vision.

Eye Chambers:

• Anterior chamber: Anterior to the lens; filled with aqueous humor.

• Posterior chamber: Posterior to the lens; filled with vitreous humor.

Visual Pathway

Light rays (stimulus) enter the eye and hit the retina.

Photoreceptors convert light energy into electrical impulses.

Impulses are sent along the optic nerve (cranial nerve II) to the optic chiasm.

Information travels through the optic tract to the thalamus.

From the thalamus, information travels through optic radiations to the primary visual area (occipital lobe).

Binocular vision (seeing with both eyes) crosses at the optic chiasm to the opposite side of the brain.

Monocular vision (seeing with one eye) stays on the same side of the brain through the optic chiasm.

Audition (Hearing) and Equilibrium (Balance)

Ear:

• External ear: Hearing only.

• Auricle (pinna): Gathers, funnels and amplifies sound and helps determine the sound direction.

• External acoustic meatus (ear canal): Channel lined with hairs (vibrissae), sebaceous glands, and ceruminous glands (secrete earwax).

• Middle ear: Hearing only.

• Tympanic membrane (eardrum): Vibrates in response to sound waves.

• Auditory ossicles (malleus, incus, stapes): Tiny bones that transmit vibrations.

• Oval window: Stapes articulates with it, leads to inner ear.

• Round window: Way for excess sound from inner ear to absorb out.

• Auditory tube (Eustachian tube/pharyngotympanic tube): Connects middle ear to pharynx, equalizes air pressure.

• Stapedius and tensor tympani muscle: Absorb and control sounds.

• Inner ear: Hearing and equilibrium.

• Bony labyrinth: Series of cavities (semicircular canals, vestibule, cochlea).

• Perilymph: Fluid within the bony labyrinth.

• Membranous labyrinth: Membranous sacs within the bony labyrinth (semicircular ducts, cochlear duct, utricle, saccule).

• Endolymph: Fluid within the membranous labyrinth.

Equilibrium

• Semicircular canals and semicircular ducts: Detect rotational movements of the head; ampulla, hair cells.

• Utricle and saccule (within vestibule): Detect static position of the head (standing upright) and linear movement (straight plane).

Hearing

• Cochlear duct contains sensory receptors where sounds waves get converted into electrical impluses.

Sent through the vestibulocochlear nerve through the