Sensory Systems

Gustatory Receptors

Taste or Gustation The sensation following the stimulation

of oral chemoreceptors Chemoreceptors are surrounded by

supporting cells Chemoreceptors are shed every 10-14

days and are renewed by division of the supporting cells.

Tastes

Four basic tastes Sweet

Glucose, fructose, amino acids Sour

H+ concentrations Salty

Na+ concentration

Bitter Quinine, caffeine, nicotine, strychinine, etc.

Umami Produced by compounds like monosodium

glutamate Not a classic taste

Gustatory Transduction

Chemicals enter the pores of taste buds and react with the gustatory hairs

Chemicals may open sodium gates directly or may stimulate membrane receptors and G proteins and the second messenger system

Olfaction

Olfactory cells lie in a specialized region in the roof of the nasal cavity The olfactory epithelium

Odors combine to produce depolarization and impulse activity 80% of taste is smell Olfactory neurons are bipolar neurons

Olfactory Receptors

Supporting cells secrete mucus Continual degeneration and

replacement of neurons Every 60 days Basal cells differentiate into olfactory

neurons

Olfaction

Humans can detect about 104 different smells

Odiferous compounds are mainly organic Containing 3-20 carbon atoms Odiferous compounds reach the olfactory

epithelium, aided by sniffing The molecules must dissolve in the mucus

layer (water soluble) to react with the receptors on the olfactory cilia

Odorant receptors

One receptor per olfactory neuron 1000 different receptors cAMP system is used for smells

Glomeruli

Olfactory neurons synapse with the olfactory bulb in regions called glomeruli From the olfactory bulb to the temporal lobe Each olfactory neuron synapses with only

one glomerulus Each glomerulus receives input from several

thousand olfactory neurons in the epithelium

Each glomeruli receives input from neurons expressing the same receptor

Disorders of smell and taste Anosmia

Inability to detect odors Ageusia

Inability to detect tastes Uncinate Fits

Hallucinations of smell

Vision

Functional Anatomy of the Eye Three peripheral layers

Tough fibrous outer layer Sclera and cornea

Middle layer The choroid or pigmented layer

Absorbs light rays

Inner neural layer The retina

Vitreous Humor

In the posterior chamber of the eye Used to

Maintain the shape of the eye Holds the retina in place

Produced in the fetal stage of development

Aqueous Humor

Produced by the ciliary muscles into the anterior chamber of the eye

Drains into the canal of Schlemm or Scleral Venous Sinus ½ teaspoon is produced per day and this

much drains per day Clog of the canal may cause Glaucoma

Constriction of the Pupil Miosis

Results in a better depth of focus Light rays pass only through the central part

of the lens Sympathetic Nervous System

Dilator control Mydriasis

Parasympathetic Nervous System Constrictor control

Pupils are consensual

Lenses

Concave Light bends outward

Convex Light bends inward

Lens Focuses Light on the Retina Light passes through the cornea and

lens prior to striking the retina Light must refract

Focal Point The single point where the rays

converge Focal Length

Distance from the center of a lens to its focal point

Vision Problems

Hyperopia Far-sightedness

The focal point falls behind the retina

Myopia Near-sightedness

The focal point falls in front of the retina

Astigmatism Caused by a cornea and/or lens that is not

perfectly dome shaped

Convergence

The eye muscles pull eyes so that both eyes see one fused image

Accommodation

The process by which the eye adjusts the shape of the lens to keep objects in focus

Presbyopia Hardening of the lens with age due to

addition of layers to the lens Focused at Infinity

The lens is pulled flat by tension in the ligaments

Close Up The lens rounds up after the ciliary muscles

contract and the suspensory ligaments relax

Eye

Optic Disc Axons of the ganglion cells all form the

optic nerve The optic nerve leaves the eye at the

optic disc No rods or cones at the optic disc

Blind spot

Rods and Cones

Rods More numerous than cones by a ratio of

20:1 Function well in low light Nighttime vision

Cones High-acuity vision Color vision during the daytime High levels of light

Light

Each cone contains visual pigments that are excited by different wavelengths of light

Visual pigment Bound to cell membranes of dendrites The transducers that convert light energy

into a change in membrane potential

Rods Visual pigment is rhodopsin

Cones

Red, green, blue, yellow(?) cones Each cone type is stimulated by a

range of light wavelengths but is most sensitive to a particular wavelength

Colorblindness Lack of cones X-chromosome

Photoreceptors

Light passes the ganglion cells and does not stimulate them Ganglion cells have action potentials

Light passes the bipolar cells and does not stimulate them Bipolar cells only have graded response

Light is the ligand for either rods or cones This depends on the kinetic energy of the

light

Photoreceptors

Photoreceptors in the retina transduce light energy into electrical signals

The Fovea Centralis The point on which light focuses

Phototransduction

Rhodopsin Opsin plus 11cis retinal

Purple and “kinked” in shape

Visual pigment for rods When activated by as little as one photon of

light the 11cis retinal can be bleached

Bleaching Light Changes 11 cis retinal to all trans

retinal All trans retinal is clear and a “straight” chain

Phototransduction

When a rod is in darkness Rhodopsin is not active cyclicGMP levels in the rod are high Sodium channels are open Depolarization of the rod

Phototransduction

Kinetic Energy of light transforms 11 cis retinal to all trans retinal

All trans retinal and Opsin separate Opsin moves horizontally in the

membrane and binds with transducin Transducin is a G protein

Transducin binds to phosphodiesterase PDE converts cGMP to GMP Sodium gates close

Binocular Vision

Visual Field Each ganglion cell receives signals from a

particular area of the retina

Binocular Zone Where the visual fields overlap Provides 3-D Vision Medial aspect crosses over Lateral aspect stays on same side of the

brain

Ear

Outer Ear Pinna

Collects sound waves Ear Canal

Sends sound waves to tympanic membrane

Tympanic Membrane Ear Drum Vibrates at the same frequency and

amplitude as the original wave

Middle Ear

Eustachian Tube Normally collapsed Opens transiently to equlibrate middle ear

pressure and atmospheric pressure Ossicles

Used to amplify the original sound wave by as much as 20X on the oval window Malleus Incus Stapes

Sound

Frequency The number of waves that pass a

particular point in a second The longer the wave lengths the lower

the frequency The units of frequency is Hertz

The higher the frequency the higher the pitch of the sound

Sound

Amplitude The height of the wave Amplitude is measured in decibels The higher the amplitude the louder the

sound

Inner Ear

Cochlea Scala vestibuli

Top canal Filled with Perilymph

Scala Media Middle canal Cochlear duct

Contains neurons for hearing Filled with Endolymph Organ of Corti

Scala tympani Bottom canal Filled with Perilymph

Cochlear Duct

Tectorial Membrane Dendritic hairs are embedded in the

tectorial membrane Basilar Membrane

Supporting cells are embedded in the basilar membrane

Supporting cells surround auditory neurons

Sound Transduction

Sounds waves become mechanical vibrations, then fluid waves, then chemical signals and finally action potentials

Phonotransduction

First Transduction Sound waves strike the tympanic

membrane and become vibrations The sound wave energy is transferred to

the three bones of the middle ear, which vibrate

Phonotransduction

Second The stapes is attached to the membrane of the oval

window The Stapes strikes the oval window and increases

the force of the original wave 20X Vibrations of the oval window creates waves in the

perilymph at the same frequency and amplitude as the original sound wave

Third The fluid waves push on the flexible tectorial and

basilar membranes of the cochlear duct. Hair cells bend and release neurotransmitter

Phonotransduction

Fourth Neurotransmitter is released, creating

action potentials that travel through the cochlear nerve to the brain

Energy from the waves transfers across the cochlear duct is dissipated at the round window

Organ of Corti

The bending or shearing of the neurons indicates pitch and loudness The bending of the neurons in the first third

of the neuron signals high pitch sounds to the brain

The bending of neurons in the first and second third of the neuron signals medium pitch sounds

The bending of neurons in the first, second and third part of the cochlea signals a low pitch sound to the brain

The Organ of Corti

The higher the amplitude of the wave the more the kinetic energy The high amplitude waves cause a

greater shearing force which opens more sodium gates

The more sodium gates that open the more the action potentials This creates a louder sound

Equilibrium

Equilibrium

Static Equilibrium Little to no movements Uses the vestibular region of the inner

ear Dynamic Equilibrium

Greater body movements Uses the semicircular canals

Static Equilibrium

The Vestibular Apparatus senses Linear Acceleration

Vestibular Apparatus Two saclike otolith organs

The utricle and the saccule The sensory receptors of the utricle and saccule

The maculae The macula consists of a gelatinous mass known as the

otolith membrane Otolithic crystals are embedded in the membrane

Made of calcium carbonate crystals Shearing or bending of the dendrites sends signals to

the brain

Dynamic Equilibrium

Semicircular Canals sense rotational acceleration

Endolymph within the semicircular canals are in three different planes

Endolymph moves and moves the gelatinous cupula to activate receptor cells