Overview of Special Senses

Special Senses Overview

• Students will be able to describe the eye and vision, the chemical senses (smell and taste), and the ear.

Lecture Outline

• The eye and vision
• Chemical senses: smell
• Chemical senses: taste
• The ear

The Eye and Vision

• Eyes are located within the skull orbits, providing protection and anchoring for supporting tissues.
• Eyelids and lashes protect the eye from abrasions.
• Conjunctiva is a mucus membrane covering the eye's inner surface.
• Tears are produced by lacrimal glands, washing away particles.
• Tears flow through nasolacrimal ducts to the nasal cavity.
• The eye is a hollow sphere composed of three layers: fibrous tunic (sclera and cornea), vascular tunic (choroid), and neural tunic(retina). The sclera accounts for most of the fibrous tunic and is not visible.
• The cornea is the transparent anterior portion allowing light to pass through.
• The vascular tunic is composed of the choroid, supplying blood. The ciliary body focuses light onto the retina.
• The iris regulates light entry through the pupil.
• The Retina is the innermost layer, containing photoreceptors (rods and cones).
• The macula lutea is a spot where visual acuity is highest (the fovea).
• The optic disc is the blind spot.
• The eye is divided into anterior and posterior chambers.
• The anterior chamber is between the cornea and iris, filled with aqueous humor.
• The posterior chamber is between the iris and lens, also filled with aqueous humor.
• The vitreous chamber is behind the lens, filled with vitreous humor.
• Eye movement is controlled by six extraocular muscles.
• Accommodation is the process the lens uses to change shape, focusing light on the retina.
• The cornea and lens refract light rays.
• The retina located at the back of the eye, converts light into signals.
• Photoreceptors convert light into signals processed by ganglion cells.

Chemical Senses: Smell

• Olfaction (sense of smell) occurs when odors bind to receptors in the nasal cavity.
• Olfactory receptor neurons are in the superior nasal cavity (olfactory epithelium).
• Odorants dissolve in mucus, stimulating olfactory cilia.
• Olfactory axons pass through the cribriform plate to the olfactory bulb.
• Smell is complex, with thousands of odor molecules potentially triggering different combinations.
• Dissolved odorants stimulate olfactory receptors via G-Protein.
• Receptor cells release neurotransmitters to sensory neurons.
• Olfactory signals are processed through olfactory bulb, hypothalamus, limbic cortex, and olfactory cortex.

Chemical Senses: Taste

• Gustation (sense of taste) involves dissolved molecules interacting with taste buds.
• Basic tastes: sweet, salty, sour, bitter, umami.
• Taste buds are located in papillae on the tongue's surface.
• Taste stimuli are dissolved in saliva, activating receptor cells in taste buds.
• Receptor cells release neurotransmitters to sensory neurons, sending signals to the brain.
• Taste information is processed through sensory neurons, the medulla, thalamus, and gustatory cortex of the brain.

The Ear

• The ear is the organ for hearing and balance, with three major areas: external, middle, and inner ear.
• External ear includes the pinna (auricle) and auditory canal (external acoustic meatus).
• Cerumen (earwax) traps foreign matter and deters insects.
• The middle ear contains ossicles (malleus, incus, stapes) that amplify vibrations from the Tympanic membrane (eardrum) and transmit them to the inner ear.
• The inner ear contains the cochlea, responsible for hearing.
• The cochlea is filled with fluid, vibrations cause the basilar membrane to move, stimulating hair cells.
• Hair cells convert vibrations to electrical signals for the brain.
• Vestibular apparatus (utricle, saccule, semicircular canals) are responsible for balance.
• The vestibular apparatus contains hair cells that detect head position and movement.
• Hair cells send signals to the brainstem and cerebellum for balance control.
• Auditory transduction occurs in the Organ of Corti within the cochlea, and is processed in the brainstem and primary auditory cortex of the temporal lobe of the brain.