Transcript 8 Sensory - bloodhounds Incorporated

PHYSIOLOGY
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