section Ⅸ -...
TRANSCRIPT
Schedule for section Ⅸ
•Today------General principles, Vision
•Next Wednesday------Hearing & Equilibrium, Other senses
Clinical Investigation
After a visit to a brothel in Arles, France, on December 23, 1888, Vincent Van Gogh, the nineteenth-century French painter, returned to his room, picked up a knife, and cut off his own ear. A local physician, Dr. Felix Ray, examined Van Gogh that night and wrote that the painter had been “assailed by auditory hallucinations” and in an effort to relieve them, “mutilated himself by cutting off his ear.” A few months later, Van Gogh committed himself to a lunatic asylum. By 1890, Van Gogh was dead by his own hand. Historians have assumed that Van Gogh suffered from epilepsy. But the painter’s strange attacks of dizziness, nausea, and overwhelming tinnitus, which he recorded in desperate letters to his relatives, are more consistent with Ménière's disease, a condition that affects the inner ear.
GENERAL PRINCIPLES OF SENSORY PHYSIOLOGY
What is the Sensory System?•Part of the nervous system consisting of sensory receptors that receive stimuli from internal and external environment and conduct this information to brain that processes this information.
What is it made of?•Nose•Eyes•Ears•Tongue•Skin•Brain•Neurons•Receptors
Traditional Classification of Sensory System
General sensesTouchTemperaturePain
Special sensesVisionHearingTasteSmellEquilibrium
What Triggers These Senses
•Receptors–Specialized endings–Collect information about external and internal environment through a stimulus.
•Each receptor is specific to a certaintype of stimulus
–An exception: a receptor can be activated by a nonspecific stimulus if its intensity is sufficiently high
Events occurring within a sensation
1.stimulation of the receptor2.transduction (conversion) of stimulus into a graded potential–vary in amplitude and are not propagated3.generation of impulses when graded potential reaches threshold4. Information is sent to CNS5.integration of sensory input by the CNS
Receptors and Sense Organs
•Receptor is referred to the structure located on the body surface or within tissues to detect the changes in internal or external environments and to convert stimulus into electrical signals. •The receptor is often associated with nonneural cells that surround it, forming a sense organ.
Receptors and Sense Organs
Hair cells Ear
Receptors and Sense Organs
•Receptors detect a small range of energy levels –Ear, 20～20,000 Hz vibration–Taste buds, specific chemicals–Eye, 380～750 nM electromagnetic wave
Complexity Range of Receptors
Types of Receptors-Location
1.Exteroceptors (外感受器)–Teleceptors (距离感受器)
•Sight, hearing–Contact receptor (接触感受器)
•Pressure, temp., touch, taste2.Interoceptors (内感受器)
–Visceroceptors (内脏感受器)•Blood pressure, pain
–Proprioceptors (本体感受器)•Muscle spindle
Types of Receptors-Modalities1.Mechanoreceptors
•respond to mechanical stimulus2.Thermoreceptors
•changes of temperature can stimulate these receptors3.Nociceptors
•brings information concerning pain4.Electromagnetic receptors
•rod cells and cone cells of the eye which are stimulated by changes of intensity and wavelengths of the light
5.Chemoreceptors•respond to chemical stimulus, such as taste, smell andblood oxygen
Properties of the Receptors
1.Adequate stimulus2.Transducer function3.Coding4.Adaptation
1、Adequate Stimulus of Receptors
• Each type of receptor is highly sensitive to one type of stimulus
• The particular form of energy to which a receptor ismost sensitive is called its adequate stimulus.
• E.g. The adequate stimulus for the rods and conesis light. The threshold for their nonspecific responsesis much higher. Pressure on the eyeball will stimulate the rods and cones, but the threshold of these receptors to pressure is much higher than the threshold in the skin.
2、Transducer function
• The receptors translate the energy of the stimulusinto an electrical change in specific sensory cells orafferent nerve endings.
• In the former case the electrical change is called receptor potential, and in the later case it is called generator potential.
• Converting one type of energy into another type(bioelectrical energy) is the process of transduction
• Our brain only deals with bioelectrical impulses sotransduction must occur!
Generator (Receptor) Potential
Character: local excitation–Not all-or-none–electrotonic propagation–temporal & spatial summation
It can be summated to reach the threshold to produce AP in afferent fibers.
3、Coding of Sensory Information
•The quality of sensation is dependent on sensory pathway including receptor, afferent fiber and cortex, which the stimulus eventually activates.
•The quantity (intensity) of sensation is associated with the frequency of APs in afferent fibers and the number of receptors activated by stimulus. –The stronger the stimulus, the more APs are fired over a given time period
E.g. Stretch Receptors:Weak stretch causes low impulse frequency on neuron leaving receptor.Strong stretch causes high impulse frequency on neuron leaving receptor.
4、Adaptation of Receptors• Definition: When a maintained stimulus of constant
strength is applied to a receptor, the frequency ofthe action potentials in its sensory nerve declinesover time
1.Rapidly adapting receptor (Phasic Receptors):The frequency of APs diminishes or stops if the stimulusis unchanging.
2.Slowly adapting receptor (Tonic Receptors):adapt slowly or not at all.
The height of the curve indicates the frequency of the discharge in afferent nerve fibers at various times after beginning sustained stimulation.
Adaptation of Receptors
Significance of Adaptation
•The rapidly adapting receptors cease firing if strength of a continuous stimulus remains constant. Allow body to ignore constant unimportant information, e.g. Smell
•The slowly adapting receptors continue signal transmission for duration of stimulus. Monitoring of parameters that must be continually evaluated, e.g. baroreceptors.
Visual Sense Organ
• Structure of the Eye Refractive systemA lens system for focusing light on the receptors.
RetinaA light-sensitive tissue lining the inner surface of the eye.Blind spot
Function ofRefractiveSystem
Reduced EyeRefraction of Light in the Eye
Vitreous humor
Accommodation of Refractive Function
Gaze at a near object (less than 6m)：
1. Accommodation of lens
2. Accommodation of Pupils
3. Convergence of Eye Balls
Clear image on retina
Accommodation of Refractive FunctionAccommodation of Lens
Lens ligaments
A more convex shape
Accommodation of Refractive Function
Accommodation of Pupils
Sphincter pupillae contracts, the size of thepupil is decreasedPupillary light reflex
Significance: regulate the amount of lightentering the eye
Pupillary light reflexdirect light reflexconsensual light reflex
Bright light is shone on the eye light sensitive cells in the retina, including rod and cone photoreceptors---the optic nerve fiber that carry the impulses initiating pupillaryresponses end in the pretectal region and the superior colliculi--- send signals to the oculomotor nerve, which terminates on the circular iris sphincter muscle. When this muscle contracts, it reduces the size of the pupil.
Pupillary light reflex•Direct light reflex
•Consensual light reflex
Accommodation of Pupils Near reflex of the pupil: The pupil constricts when an individual looks at a near object
Near point of vision:The nearest point at which an object can be
seen distinctly by the eye
Far point of vision:The farthest point at which an object can be
seen distinctly by the eye
Abnormalities of Refractive Function andAccommodation in the Eyes
EmmetropiaAmetropia
Myopia
The anteroposterior diameter of the eyeball is too long. This defect can be corrected by the use of glasses with biconcave lenses so that parallel light rays are made to diverge slightly before they strike the eye.
• Hyperopia
The eyeball is shorter than normal and parallel rays of light are brought to a focus behind the retina. The use of glasses with convex lenses to aid the refractive power of the eye in shortening the focal distance corrects the defect.
Astigmatism
The curvature of the cornea is not uniform. When the curvature in one meridian is different from that in others, light rays in that meridian are refracted to a different focus, so that part of the retinal image is blurred.Corrected with cylindric lenses placed in such a way that they equalize the refraction in all meridians
Presbyopia
Glasses with convex lenses
The photoreceptor mechanism
Retina: A light-sensitive tissue lining the inner surface of the eye.
• The optics of the eye: create an image of the visual world on the retina, which serves the same function as the film in a camera.
• Rod cells and cone cells• Light activating rod cells and cone cells on the retina
initiates chemical and electrical events that ultimately trigger nerve impulses. These are sent to visual centers of the brain through the fibers of the optic nerve.
Structure of retina
The photoreceptor mechanism
Photoreceptors in Retina
1) Scotopic vision systemRod cell:The photosensitive pigment in the rods is called Rhodopsin
• Rod cellNot color sensitiveMainly more sensitive to light (scotopic vision)
Peripheral area of retinaNight blindness
Photoreceptors in Retina
2) Photopic vision system
Cone cell:
• Cone cellColor sensitiveLess sensitive to lightMainly fovea in retina
Visual Transduction in Rods System
Photochemistry of rhodopsin-retinal visual cycle in the rod
Rhodopsin: opsinretinene
Mechanism for Rod Receptor Potential
Generation of a hyperpolarization receptor potential
In dark In the presence of light
Ionic currents in the photoreceptor cell( The terminal releases less transmitters when
hyperpolarized )
Hyperpolarization of photoreceptor in response to light• Intensity-dependent • Saturation
Color Vision (Cone, Photopic vision)
Trichromatic theory
Color Blindness
Information Process in Retina
Other Phenomina Related with Vision
Visual acuity:
The degree to which the details and contours of objects are perceived
Snellen visual acuity chart
Other Phenomina Related with Vision Dark adaptation: If a person spends a considerable period of time
in brightly lighted surroundings and than moves to a dimly lighted enviroment, the retinas slowly become more sensitive to light. The decline in visual threshold during this process is known as darkadaptation.
Light adaptationMechanisms of adaptations:Changes in concentrations of rhodopsin or color photochemicals
to resolve fine detail
Visual field:Not circularWhite > yellow > red > greenBlind spotular
White＞yellow＞red＞green
Binocular vision and stereopsis
The central parts of the visual fields of the 2 eyes coincide; therefore, anything in this portion of the field is viewed with binocular vision. Binocular vision is often assigned an importantrole in the perception of depth to produce stereopsis.
HEARING
Outline
• Belongs to special senses• Receptors: Hair cells in the inner ear• Sense organ: Ear• Adequate stimulus: Sound wave• Coding: Pitch and loudness
Structure and function of earExternal ear-funnels sound waves from environment
Middle ear-cavity between tympanic membraneand cochlea
Inner ear-where sound is actually transmittedto nerves (It alsoreceives the changes of the position of the head to balance centers in the brain.)
1. External Ear:
–Pinna (auricle):directs sound waves into the auditory canal
–External auditory Canal:conducts sound to the eardrum
2. Middle Ear−Tympanic membrane (Eardrum): thin membrane that
vibrates in response to sound, and transfers sound energy to bones of the middle ear
−Ossicles:three tiny bones “amplify sound” and transfer sound energy to the inner ear
−Tympanic cavity: small cavity surrounding ossicles−Auditory tube: connecting the middle ear with the throat,
equalizing pressure during yawning or swallowing
Role of middle ear in sound transmission
• Sound Force Amplification by the Ossicles– Greater pressure at oval window than tympanic
membrane, moves fluid of cochlea• The Attenuation Reflex
– Response where onset of loud sound causes tensor tympani and stapedius muscle contraction
– Function: Adapt ear to loud sounds
Inward movement of the tympanicmembrane by a sound pressure wave causes the chain of ossiclesto push the footplate of the stapes into the oval window
Mechanisms involved in transformer process
1.Size difference between Tympanic Membrane and Stapes Footplate
2.Lever action
Impact of size difference on Middle Ear Transformer Action
Tympanic membrane59.4 mm2
Stapes footplate3.2 mm2
Pressure = force/area
Pressure gain: 59.4/3.2 = 18.6 (times)
Impact of Lever Action on Middle Ear Transformer Action
pressure gain: 1.3 times
Total Amount of Amplification
Pressure Gain Contribution from
18.6 Size difference1.3 Lever action24.2 Total pressure gain
(18.6 x 1.3)
The malleus takes the pressure from the inner surface of the tympanic membrane and passes it by means of the incus to the stapes in such a way that the pressure is amplified about 24 times as it moves.
3. Inner EarIncludes sense organs for hearing and balanceFilled with perilymph
Inner Ear
A maze of bony chambers•Cochlea: snail shaped fluid-filled structure•Vestibule
Oval window: thin membrane, transfers vibrations from stapes to fluid of cochleaRound window: absorbs energy and equalizes pressure in the cochlea
Cochlea•Snail-shaped organ with a series of fluid-filled tunnels. Converts mechanical energy into electrical energy•Three chambers: scala vestibuli, scala tympani, scalamedia (cochlear duct)•Basiliar and vestibular membranes
CochleaAt the end of the cochlea, the helicotrema joins the scalavestibuli and the scala tympani.
Fluids in the cochlea
Perilymph: fills the scala vestibuli and scala tympani. similar in composition to extracellular fluid (High in Na+and low in K+).
Endolymph: fills the scala media. Similar to intracellular fluid (High in K+and low in Na+).
Cochlea - Organ of Cortia structure contains approx. 16,000 cochlear hair cellslocated on basilar membrane Stereocillia, kinocilium : at apex of hair cells, embedded in tectorial membraneGel-like tectorial membrane is capable of bending stereocillia, konocilium and activating receptorsCochlear nerve attached to hair cells transmits nerveimpulses to auditory cortex
Function of Corti
Relative shearing motion of basilar membrane and tectorial membrane makes the hair cells bend and depolarize, changes transmitters release
Properties of SoundSound travels in waves as light does
•Pitch: determined by “frequency,” the number of cycles per second of a sound wave, measured in hertz (Hz)
•Loudness:determined by “amplitude” (height) of the sound wave, measured in decibels(dB)
•Timbre: determined by “complexity and shape” of the sound wave, gives each sound its unique quality
Pitch of sound
Loudness of Sound•0 dB = hearing threshold•50 dB = normal conversation•90 dB = danger zone•120 dB = Rock concert•130 dB = Pain threshold
Sound Transmission and Transduction
Sound waves
Tympanic membrane vibrations
Ossicles transmit & amplify vibration
Via oval window to perilymph then endolymph
basal membrane resonance oscillation
hair cells translate the vibration into generator potentials
auditory nerves transmits nerve impulses to auditory cortex
Conduction of Sound1. The air conduction
Air Conduction of Sound
Conduction of Sound
2. The bone conduction
Sound Transmission and Transduction
Sound waves
Tympanic membrane vibrations
Ossicles transmit & amplify vibration
Via oval window to perilymph then endolymph
basilar membrane resonance oscillation
hair cells translate the vibration into generator potentials
auditory nerves transmits nerve impulses to auditory cortex
Electrical Potentials in Cochlea1, Endocochlear Potential (EP)
–Putting the electrode in the scala media and a +80 mV potential with respect to a neutral point of perilymph in scala tympani can be discovered
Intracellular Potential (IP) or hair cell resting potential: -80 mV
Difference between extracellular and intracellular potential:
Top: 150-160mV endolymph in scala media
Base: 80mV perilymph in scala tympani
Electrical Potentials in Cochlea
Mechanoreceptor in hair cell
When the stereocilia of a hair cell move toward
the tallest cilium, the hair cell is depolarized;
when the stereocilia bend in the opposite direction,
the hair cell is hyperpolarized.
Electrical Potentials in Cochlea
Sound Transduction
• Vibrations from sound waves move tectorialmembrane
• Hair cells (stereocillia) are bent by the membrane• Generator potential is induced in hair cell• An action potential starts in the cochlear nerve
2,Cochlear Microphonic Potential (CM)–When cochlear is activated by sound, the membrane potential recorded in cochlear or near cochlear which is generated from hair cells. It reproduces frequency of a sound wave perfectly.
3, Action Potential (AP)–Electrical activity from the auditory nerve–Can be measured from anywhere in the cochlea or in the auditory nerve
Electrical Potentials in Cochlea
Coding of sound
•Coding Information About Sound Intensity–Firing rates of neurons–Number of active neurons
•Coding Information About Sound Frequency–Location of Basilar membrane activated–Frequency: Highest at base, lowest at cochlea apex
How to discriminate the frequency of the sound?
Traveling Wave Theory
The Traveling Wave Theory
• Sound wave entering at the oval window is to cause the basilar membrane to vibrate
• different frequencies cause vibrations at different locations (places) along basilar membrane
• higher frequencies at base, lower frequencies at top
The Traveling Wave Theory
Hearing impairments
• Deafness • Conduction deafness • Sensorineural deafness
• Tinnitus • Ménière's syndrome
• attacks of dizziness, nausea, caused by excess endolymph in the media canal
Deafness Conduction deafness • Transmission of sound waves through middle ear is impaired. • Impairs all sound frequencies. • May be caused by damage to ossicles by an infection of the middle ear or immobilization of the stapes in otosclerosis. • Treatment: Hearing aids- amplify sounds
Sensorineural/perceptive deafness• Transmission of nerve impulses anywhere from the cochlea to the auditory cortex is impaired. • Often impairs ability to hear some pitches more than others. • May be caused by many pathological processes or exposure to extremely loud sounds. • Treatment: Cochlear implants- electrically stimulate nerve fibers in response to sound
Outline
• Belongs to special senses • Receptors: Hair cells in the inner ear • Sense organ: Vestibular organ in the
inner ear • Adequate stimulus: Rotational and
linear acceleration
Structure of vestibular organ
Ability to detect head position and movement (or acceleration) to maintain a steady balance when it is still or moving
• Semicircular canals • Utricle • Saccule
Semicircular canals• Three semicircular canals on one side on three
directions, helps sense all possible head-rotation angles• Receptors in the semicircular canals
– Crista ampullaris, located in the expanded end (ampulla) of the canal
– Consists of hair cells – Cupula (gelatinous cap) covers the hair cells
Utricle and saccule•Receptors in the Utricle and saccule: OtolithicOrgan (Maculae)•Hair cells are embedded in the otolithic membrane•Otoliths (tiny stones) float in a gel around the hair cells
Function of Semicircular canals•Detects rotational acceleration•To maintain balance while turning
Function of Utricle•Detects changes relative to gravity (linear acceleration) from vertical movement
Function of Saccule•Detects backward-frontward (horizontal)movement (linear acceleration) from acceleration
Vestibular reaction
•Vestibular autonomic reaction–Motion sickness: “mismatch” betweenvisually perceived movement and the vestibular system's sense of movement
– Dizziness, fatigue and nausea
–Treatment: Antimotion drugs (e.g. Dramamine), depression of vestibular inputs
Vestibular reaction
• Nystagmus (The Vestibulo-Ocular Reflex, VOR)–When spinning is suddenly stopped, eyes continue to move inthe direction opposite of the spin, then jerk rapidly back to themidline.When a person begins spinning, the cupula bends in the opposite direction,and eyes slowly drift in opposite direction, then jerk rapidly back to the midline.
–If the spining suddenly stops, inertia of endolymph causes it tocontinue moving in the direction of spin,and eyes movement isopposite to those at the begining .
–This is a normal phenomenon that helps maintain balance during spinning.
Otoscopy is used to have a visual examination of the earAudiometer measures various frequencies to test hearingA tuning fork compares the conduction of sound in one ear or between the two ears.
Summary
• Each type of receptor is excited most effectively byonly one modality of stimulus known as the adequate stimulus.
• The stimulus is converted into an electrical potential.• The intensity of the stimulus is associated with frequency of APs and the number of receptors activated by stimulus.
• Ear is the sense organ for both hearing and equilibrium, both use hair cells in the inner ear as receptors.
Ear care Day
March 3rd
Olfaction-the sense of smell•The sense of smell is activated by neurons called olfactory receptors which are covered with cilia.•Olfactory receptors are yellowish-brown masses along the top of the nasal cavity.•Responds to molecules dissolved in mucus or lipids
Gustation-the sense of taste
•Humans perceive five types of taste: bitter, sour, salty, sweet, and umami(meaty flavor) .•Papillae are structures on the surface of the tongue that contain the taste buds.•Taste Buds are organs that sense the taste of food, contain receptor cells called taste cells responsive to each of the taste categories.
Somatic senses1.Pain
•Fast pain: The nervous system quickly responds to a pain initiating event to the central processing unit •Slow pain: persistent, indistinct source
•Referred pain is a phenomenon of pain perceived at a site adjacent to or at a distance from the site ofan injury's origin.
(during ischemia brought by a myocardial infarction where pain is often felt in the neck, shoulders, and back rather thanin the chest.)
2. Warmth and cold• Changes in temperature in dermis, skeletal muscles, liver and hypothalamus
• Free nerve endings• Cold receptors are much more than warm receptors
3.Touch-pressure
• Unencapsulated receptors: free nerve endingsMerkelsdics-fine touch
• Encapsulated receptors: Meissners corpuscles -fine touchPacinian corpuscles -deep pressure
4. Proprioception
monitors of muscle stretch
•Muscle spinder
•Tendon organ