Overview of Special Senses

Special Senses Overview

• The four major special senses are taste, smell, hearing, and vision.
• The presentation covers the anatomical structures associated with these senses, the transmission of nerve impulses, the neuron names & locations for each special sense, components of the ear (hearing and balance), and extraocular structures.

Taste

• Taste buds are chemical taste receptors.
• Most are on the sides of papillae on the tongue, some in the mouth and pharynx.
• Taste buds are small, rounded structures composed of gustatory cells and supporting cells.
• Each taste bud has a taste pore (opening) where tiny hair-like processes (dendrites) receive stimulus.
• Humans perceive sweet, sour, salty, and bitter tastes.
• Some animals have different taste perception (e.g., cats lack sweet receptors).

Smell (Olfaction)

• Olfaction, a chemical sense, features a stronger perception in animals than in humans.
• Olfactory epithelium, located deep in the nasal passages, contains two patches.
• Sensory olfactory cells, interspersed with supporting cells, have hair-like dendrites that project into the mucus layer of the epithelium.

Vomeronasal Organ

• Present in multiple species.
• Located in the rostroventral portion of the nasal cavity.
• Detects pheromones (chemical communication signals).
• Demonstrates the flehmen response (specific facial expression) in some species when detecting pheromones.

Hearing

• Hearing is an auditory sense.
• Hair cells are the sensory receptors for auditory impulses.
• The auditory system has components:
  • External ear: gathers sound waves and funnels them.
  • Middle ear: amplifies and transmits vibrations.
  • Inner ear: contains the actual sensory receptors for hearing (and equilibrium).
• Most structures are within the temporal bone.
• Membranes cover bony cavities.

External Ear

• The pinna is made of elastic cartilage and skin, often able to move toward a sound source.
• The external auditory canal (external acoustic meatus) is a soft membrane-lined tube from the pinna to the eardrum.
• Many domestic species have an L-shaped external auditory canal.
• The tympanic membrane (eardrum) is a thin membrane that separates the external auditory canal from the middle ear.

Middle Ear

• The middle ear is a hollowed-out area in the temporal bone, lined with soft tissues, and filled with air.
• It contains ossicles (malleus, incus, stapes) that transmit and amplify vibrations.
• It also has an opening for the eustachian tube, connecting to the pharynx.
• The eustachian tube equalizes air pressure on both sides of the tympanic membrane.

Ossicles

• The malleus (hammer) connects to the tympanic membrane and transmits vibrations.
• The incus (anvil) connects to the malleus and stapes.
• The stapes (stirrup) connects to the incus and the membrane covering the oval window.

Function of Ossicles

• The ossicles act as levers, transmitting sound waves from the tympanic membrane to the cochlea.
• They decrease vibration amplitude but increase force.

Eustachian Tube

• The eustachian tube connects the middle ear cavity to the pharynx.
• Its function is to equalize air pressure on both sides of the tympanic membrane.

Inner Ear - Cochlea

• The cochlea is a complex, snail-shell-shaped spiral in the temporal bone
• The organ of Corti is the sensory organ for hearing within the cochlea. It's composed of hair cells and supporting cells.
• The cochlear duct is a tube within the cochlea filled with fluid (endolymph).
• This area also contains perilymph.

Cochlea Continued

• The oval and round windows, located at the base of the cochlea, play roles in pressure relief during sound transmission.
• The organ of Corti has a tectorial membrane on top of hair cells, which helps translate movements into nerve impulses.

How Sound is Transmitted

• Sound waves enter the ear, the tympanic membrane vibrates. Ossicles vibrate to increase force, and push on the oval window.
• Perilymph vibrates and causes movement in the cochlear duct, triggering responses in hair cells.
• The round window acts as a pressure relief mechanism to prevent damage.
• Tectorial and hair cells in the organ of Corti rub together, generating nerve signals.

Equilibrium Controls - Balance

• Receptors that control balance and equilibrium are located in the vestibule and semicircular canals within the inner ear.
• The vestibule: senses linear motion and the head's position.
• The semicircular canals: sense rotary motion and head movements.

The Vestibule

• The utricle and saccule are two sac-like spaces within the vestibule.
• They detect head movements and position, using hair cells with supporting cells and otoliths to generate nerve impulses as the head moves.
• Hair movements are driven by gravity's effects on the gelatinous matrix with otoliths.

The Semicircular Canals

• These canals are located at right angles to each other and detect angular head movements.
• The crista ampullaris inside an ampulla is sensitive to endolymph movement during head rotation, generating nerve impulses.
• The cupula, a gelatinous area atop the crista, detects endolymph movement.

The Eye

• The eye has layers: fibrous (outer), vascular (middle), and nervous (inner).

Vision Overview

• Photoreceptors are the neurons within the retina responsible for vision.
• Photoreceptors are in two types: rods (black and white vision) and cones (color vision).
• The fibrous layer includes the cornea (clear front window), and the sclera (protective outer layer).

Fibrous Layer

• The cornea is a transparent window that allows light to enter the eye.
• The sclera is the protective outer layer.
•  The limbus is the juncture of the sclera and the cornea, where the cornea bends the light that enters the eye, and gives it its shape.

Vascular Layer: The Uvea

• The uvea comprises the iris, ciliary body, and the choroid.

Vascular Layer: Iris

• This is the colored part of the eye, a pigmented diaphragm that controls the pupil's size, regulates light intake.

Vascular Layer: Ciliary Body

• The ciliary muscles adjust the lens shape for near and far vision using suspensory ligaments and their attachment to the periphery of the lense.

Vascular Layer: Choroid

• This layer is located between the sclera and retina, supplying nutrients to the retina.
• Some animals have a reflective layer of cells (tapetum lucidum) that amplifies light in low-light conditions.

Nervous Layer: Retina

• The retina lines the back of the eye and is the location of photoreceptors (rods and cones), the structures associated with vision.
• Rods are for light detection and provide black and white vision, while cones are for color perception.

Retina Continued

• Nerve fibers converge at the optic disc.
• The optic disc is a point on the retina lacking photoreceptors and is blind.

Eye Compartments: Aqueous & Vitreous

• The aqueous compartment holds watery fluid in front of the lens (anterior and posterior chambers).
• The vitreous compartment is behind the lens, is filled with a gelatinous fluid, and provides support to the eye.

Aqueous Compartment

• Aqueous humor is produced and drained constantly.
• It is produced in the ciliary body and passes through the pupil, then anterior chamber, and exits through iridocorneal angle via Schlemm's canal.

Clinical Disease: Glaucoma

• Glaucoma is a disease of elevated intraocular pressure due to aqueous humor not draining properly. This can cause permanent vision loss.

Lens

• A soft, transparent biconvex disc, the lens can change shape (accomodation).
• Ciliary muscles contract for near vision and relax for distant vision.

How an Image is Formed

• Incoming light bends (refracts) through the cornea, aqueous humor, lens, and vitreous, ultimately refracting an upside-down image onto the retina. The brain then inverts that image for us to perceive it correctly.

Extraocular Structures - Conjunctiva

• A mucus membrane lining the inner eyelids and the surface of the eye (bulbar conjunctiva).
• It enables interactions between the eyelids and the eye's surface.
• Conjunctival sac accommodates placement of eye drops.

Extraocular Structures - Eyelids

• Folds of skin with conjunctiva, and medial and lateral canthi.
• Contain meibomian glands producing a waxy substance to prevent tear overflow.
• A third eyelid (nictitating membrane) for supplemental protection and lubrication.

Extraocular Structures - Lacrimal Apparatus

• Tears are produced by lacrimal glands (located dorsolateral to each eye).
• Tears drain through lacrimal puncta and ducts, passing the lacrimal sac then nasolacrimal ducts, to reach the nasal cavity.

Tear Film

• Tear film has three layers: inner mucus layer (antimicrobial), middle tear layer (moisture), and outer oily layer (reduces evaporation).

Eye Muscles

• Six extraocular muscles (4 rectus and 2 oblique muscles) control eye movement and position.
• Some eye muscles, like the retractor bulbi, are involved in eye movements and shape.

This quiz explores the four major special senses: taste, smell, hearing, and vision. It covers the anatomical structures, nerve impulse transmission, and specific characteristics and functions of each sense. Ideal for students studying human anatomy and physiology.