Biology 211 Anatomy & Physiology I Dr. Thompson The Special Senses

Special Senses 1. All located in the head 2.All special senses reach the brain through cranial nerves 3. Highly specialized cells form receptors 4.These specialized receptor cells are located in sensory organs which are also specialized for a particular function.

Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

The last laboratory exercise dealt with vision and hearing so Let’s start with taste and smell

Special Senses Specialized Receptor Cells Specialized Organ..... TASTE:Gustatory Cells Taste Buds

Most, but not all, taste buds are located on projections from the surface of the tongue called papillae Some taste buds are also located on the palate and the oropharynx,as far down as the epiglottis

Each taste bud contains three types of cells: Gustatory cells (50-100) Supporting cells Basal cells Each taste bud also has a small hole, or taste pore, on its free surface (facing the inside of the mouth).

Each gustatory cell has long microvillus, called a gustatory hair, which extends out of the taste pore into the saliva of the mouth. This gustatory hair contains receptors on its plasma membrane which can detect specific chemicals in the saliva. At the other end, each gustatory cell is surrounded by dendrites of sensory neurons which form part of a cranial nerve

Gustatory cells within taste buds can detect thousands of different types of molecules, but these are grouped into five general categories: a)Sweet tastes: sugars (glucose, fructose, lactose, sucrose) saccharin, aspartame, sucralose, xylitol, etc. b)Salty tastes: sodium, potassium, lithium, many others c) Sour tastes: citric acids, carbonic acid, hydrochloric acid, malic acid, tartaric acid, many others d)Bitter tastes: quinine, fatty acids, many others e)Umami taste: glutamate

Substances must be dissolved in saliva or other liquid before they can stimulate the gustatory cells. Each gustatory cell can respond to only one substance (sodium, glucose, etc.) BUT each taste bud contains many different types of gustatory cells. We used to think that taste buds on certain regions of the tongue were specialized for particular tastes, but we now know that taste buds with gustatory cells for different types of tastes are located in all regions of the tongue.

Each gustatory cell has a separate threshold: concentrations below this do not stimulate the receptors. In general: Sweet & salty substances have high thresholds Sour and umami substances have moderate thresholds Bitter substances have low thresholds

Taste signals from the anterior part of the tongue travel in the facial nerve. Taste signals from the posterior part of the tongue travel in the glossopharyngeal nerve. Taste signals from the palate and pharynx travel in the vagus nerve. From the thalamus, these signals get relayed to the “gustatory region” on the parietal lobe of the cerebral cortex. Taste signals in all three nerves reach a nucleus in the medulla oblongata, then get sent to the thalamus

These afferent neurons carry information for conscious perception of tastes. They also form afferent limbs of reflexes whose efferent limbs stimulate saliva production, secretion of enzymes by stomach, liver, pancreas if necessary, gagging & vomiting

Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

Olfactory receptor cells are part of the olfactory epithelium (mucosa) located high in the nasal cavity, just inferior to the cribriform plate of the ethmoid bone.

Each olfactory cell has long microvillus, called an olfactory hair, which extends into a layer of mucous on its free surface This olfactory hair contains receptors on its plasma membrane which can detect specific chemicals in the mucous.

The axons of these olfactory cells (neurons) pass through the cribriform plate to synapse with neurons in the olfactory bulb of the brain. These axons are the olfactory nerve (cranial nerve I)

Substances must dissolve from the air into the mucous before they can stimulate the olfactory cells. Each olfactory cell appears to be able to respond to many different substances. Each olfactory cell has a separate threshold, but these are generally very low: just a few molecules of a substance may stimulate the olfactory cells.

Olfactory Pathways: Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it.

Olfactory Pathways: Axons of olfactory receptor cells pass through the cribriform plate of the ethmoid bone as the olfactory nerve, then synapse with afferent neurons in the olfactory bulb which lies just superior to it. Axons of these afferent neurons pass through the olfactory tract to: - The thalamus and the olfactory cortex on the medial surface of the temporal lobe. This provides conscious perception and interpretation of smells -The hypothalamus and the brainstem. This provides reflexes (salivation, avoidance, etc.) and "associative responses" (activation of autonomic pathways, sexual responses, emotional responses, etc.)

Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

Pupil Sclera Iris Lateral angle (canthus) Medial angle (canthus) Anterior view of the eye

The eyeball has three layers or "tunics: Fibrous Tunic: Strong connective tissue Protects the eye Holds shape of eye Insertion of extraoccular muscles Vascular Tunic: Contains blood vessels Pigmented Contains smooth muscle cells Sensory Tunic: Contains rod and cone cells and Other neurons to transmit visual information to brain

Layers ("tunics") of the eyeball Fibrous Layer Cornea Sclera Vascular Layer Choroid Iris Ciliary Body Sensory Layer Retina

Internal Structure of the Eye

Lens Ciliary Body Suspensory Ligaments ("Zonules") Aqueous Humor Vitreous Humor

Focus: Majority of light refraction (bending) occurs in cornea. Not adjustable "Fine tuning" of light refraction occurs in lens: Thicker = more refraction Thinner = less refraction

Rods: Cones: Black & white High sensitivity Low resolution Detect motion Color Lower sensitivity High resolution

Optic Nerve Optic Tract Optic Chiasm Optic Radiations

Next: Hearing Specialized Receptor Cells Specialized Organ. HEARINGHair Cells Cochlea Located in inner ear. Outer ear and middle ear serve to transmit and regulate the volume of sound

Outer Ear Middle Ear Inner EarAuricle or Pinna

Outer ear channels air vibrations (sound) to the tympanic membrane (eardrum) The middle ear is an air-filled chamber containing three ossicles: the malleus, the incus, & the stapes The inner ear contains a complex fluid-filled structure, the membranous labyrinth, which is embedded in the temporal bone.

Tympanic membrane Malleus Incus Stapes (attaches to oval window of inner ear)

The tympanic membrane is attached to the malleus, which is attached to the incus, which is attached to the stapes, which is attached to the oval window of the membranous labyrinth of the inner ear. The membranous labyrinth is fluid-filled. Therefore: Vibrations of air (sound) in the outer ear vibrate the tympanic membrane Which makes the ossicles vibrate Which makes the oval window vibrate Which makes the fluid of the membranous labyrinth of the inner ear vibrate This is how the vibrations get transmitted from the air of the outer ear to the receptor cells of the cochlea in the inner ear

The membranous labyrinth of the inner ear actually consists of two sets of tubes, one inside the other. The outer tube is filled with a fluid called perilymph, while the inner tube is filled with fluid called endolymph.

At one end of inner ear, these two tubes (one inside the other) coil about 2 & 2/3 times to form the cochlea. Vibrations of the oval window make the perilymph vibrate. This must be transmitted to the endolymph within the cochlea before the hair cells can detect it.

Structure of cochlea if it could be uncoiled

Vibration of oval window causes vibration of perilymph of scala vestibuli and scala tympani, which causes vibration of endolymph in cochlear duct

Vibration of the cochlear duct causes bending of hair cells within it. When these hair cells bend, they send electrical signals through the vestibulocochlear nerve to the brain

Hearing involves two aspects of bending hair cells: Which hair cells bend determines the pitch of the sound How far hair cells bend determines volume of the sound

The membranous labyrinth of the inner ear also houses the specialized receptor cells for equilibrium - both position of the head ("static equilibrium") and movement of the head ("dynamic equilibrium").

Special Senses Specialized Receptor Cells Specialized Organ..... TASTE: SMELL: VISION: HEARING: EQUILIBRIUM: Gustatory Cells Taste Buds Olfactory Cells Olfactory Epithelium Rods & Cones Eye (Retina) Hair Cells Cochlea Hair Cells Vestibular Apparatus

The parts of the membranous labyrinth responsible for equilibrium are the saccule, the utricle, and three semicircular canals which lie at right angles to each other. Semicircular Canals Utricle Saccule

The saccule and the utricle are responsible for detecting the position of the head ("static equilibrium"). Each of them contain a region of hair cells called a macula

The tips of these hair cells project into a gelatinous mass called the otolithic membrane, in which are embedded small crystals of calcium carbonate called otoliths.

When the head changes position, gravity pulls on the otoliths, which causes the otolithic membrane to bend the hair cells (receptors) When these hair cells bend, they send electrical signals to the brain through the vestibulocochlear nerve, telling it the new position of the head

Semicircular Canals A very similar situation tells your brain about movement of the head (“dynamic equilibrium”) when hair cells of the semicircular canals bend.

Ampullae of Semicircular Canals Each semicircular canal has an enlargement, or ampulla, at one end where the hair cells (receptors) are located

The tips of these hair cells in an ampulla of a semicircular canal project into a gelatinous mass called the cupula, in which otoliths are also embedded

When the head moves in any direction, movement of the endolymph in the semicircular pulls on the otoliths, which causes the cupula to bend the hair cells (receptors) When these hair cells bend, they send electrical signals through the vestibulocochlear nerve to the brain, telling it which direction the head moved.