Presentation on theme: "Sensory physiology Instructor: DU Jing Office: 0850 physiological sciences Jining medical college Department of Physiology."— Presentation transcript:
Sensory physiology Instructor: DU Jing Office: 0850 physiological sciences Jining medical college Department of Physiology
Section A General Physiological Properties of Receptors Section B Special Sensory systems Sensory Receptors & Sensory Organs General physiological properties of receptors Vision Hearing Vestibular system Somatic sensation
Introduction Sensation and perception are reflection of the objective world in the subjective consciousness. Stimulus energy is transduced by Sensory Receptors/Sensory Organs into nerve impulse which travels along specific neuron pathways to specific areas in the cerebral cortex of the brain.
Receptors & Sensory Organs Section A Ⅰ Definition: 1) Receptors (Sensory receptors, not proteins) Sensory receptors is referred to the cells or structures located on the surface of the body or within tissues, the function of which is to detect changes in internal or external environment and transduce these changes to electrical response. 2) Sensory organs Sensory organ is the special organ that is composed of sensory receptor and its subsidiary structures.
For example: Receptors -- Rods and cones in the retina; the endings of sensory nerves; Sensory Organs – Eyes, ears, the vestibular apparatus in the inner ear, the taste buds on the tongue, the olfactory epithelium of the nasal cavity
Ⅱ Classification of receptors Section A Interoceptors Exteroceptors By location By types of stimuli mechanoreceptors thermoreceptors noticeptors (pain receptors) electromagnetic receptors chemoreceptors
General physiological properties of receptors 1. Adequate stimulus of receptor 2.Transducer function of receptor 3. Encoding of receptor 4. Adaptation of receptor
General physiological properties of receptors 1. Adequate stimulus of receptor: Each kind of receptors is very highly sensitive to one type of stimulus for which it is designed. This special stimulus is called adequate stimulus of the receptor. eg. electromagnetic waves with specific rangs of wavelength to the photoreceptor cells in the retina; mechanical vibration at a specific rang of frequency to the hair cells in the cochlea Section A
Receptors can also respond to inadequate stimuli; Each receptor has its own sensory threshold.
Perceptions of the world are created by the brain from action potentials (APs) sent from sensory receptors. Receptors can transduce (change) different forms of stimulus energy to electrical signals that are conducted along the specific afferent nerve pathways to CNS.
General physiological properties of receptors 2. Transducer function of receptor The process in which a stimulus energy is transduced into the electrical response is known as transducer function of receptor. Section A stimulus→ electrical response → brain
Receptor potential During the process of transducing, the receptor firstly changes the stimulus energy into a graded local electrical response across the receptor membrane or the sensory nerve ending, this transitional potential that can later initiate the action potential is known as a receptor potential.
Characters of receptor potential Slow, local potential, can summate Extends by electrotonic propagation, decreases with distance Stimulus information is reflected by the magnitude, duration and direction of receptor potential.
stimulus receptors electrical information cerebral cortex Transducer function along afferent nerves (receptor potential →AP) sensation or perception Steps of sensation
Mechanism of transducer function AP on afferent nerves StimulusReceptor Ion channel (+) Through Second Messenger Change in ion fluxes across receptor membrane Receptor potential CNS alters the release of neurotransmitter (ending of afferent neuron) (a separate cell) EPSP/IPSP
During the process in which stimulus is changed to AP by a receptor, not only the form of stimulus energy is transduced, but also the information brought by stimulus is transformed into the sequence of AP. Stimulus → AP Transducing of energy form Transformation of information
General physiological properties of receptors 3. Encoding of receptor: Section A Receptor could transfer the messages of environmental changes brought by stimuli into the information conveyed in the action potential sequence on the afferent neuron. This function of information transformation is termed as encoding of receptor.
Encoding of stimulus characteristics: Special receptor, special neuron pathway, Special CNS location. Encoding of stimulus intensity: Stimulus intensity is distinguished both by the frequency of AP generated on the afferent N and by the number of the fibers transporting the messages.
General physiological properties of receptors 4. Adaptation of receptor: Section A Receptors have the ability to reduce the frequency of AP generated on the afferent neuron in spite of a sustained stimulus strength.
Classification according to adaptation: Rapidly adapting receptor --important for the body to detect new stimuli eg. Touch and pressure receptors in the skin Slowly adapting receptor --important for monitoring the continuous functions of the body eg. Stretch receptors in muscles participating in maintaining posture
Vision Section B Special Sensory systems
Structures in the eye involved in vision Refractive system (optical portion) Retina (photoreceptive system) Cornea Aqueous humor Lens Vitreous humor Photoreceptor cells (rods, cones) Bipolar cells Ganglion cells
Adequate stimulus: nm electromagnetic waves (visible wavelengths of light) Processes of vision: Formation of the image on the retina --refractive system Phototransduction by the photoreceptors --rods and cones Electrical signals is sent along the optic never to the visual cortex in the brain
Vision Ⅰ Refractive function of the eye and accommodation
Vision Ⅰ Refractive function of the eye and accommodation As in a camera, image is up- side down and inverted. The brain interprets this correctly.
Refractive structures of the eye Cornea Aqueous humor Lens Vitreous humor (Outside to inside)
Refractive structures of the eye fovea centralis optic nerve ← Viewed through an ophthalmoscope
It’s an imaginative artificial model which has the same refractive effect as the eye. Reduced eye Vision If all the refractive surfaces are algebraically added together and considered to be a single lens with its center placed 15cm in front of the eye, the normal eye may be schematically regarded as ‘reduced eye’.
Under the condition of non-accommodation, the focal point of normal human eye is on the retina. Lights from an object at infinite distance (>6m) can form a image on the retina.
Visual accommodation Vision When focusing at objects at different distance from the eye, some adjustments are made, especially when focusing at near objects (<6m) -- visual accommodation. Accommodation include shape changes of the lens diameter changes of the pupil convergence of two eyes Ability of lens accommodation: Near point of vision is the nearest distance distinguished by the eye.
The periphery of the lens is joined to the ciliary muscle (circular like a sphincter) by the zonular fibers. Shape changes of the lens Controlled by the zonular fibers and the ciliary muscle. Ciliary muscle Zonular fibers
Shape changes of the lens
Near object Ciliary muscle contracts Lessens tension on zonular fibers Lens becomes more spherical Far object Ciliary muscle relaxes Increases tension on zonular fibers Lens becomes more flattened Shape changes of the lens
Light rays from close objects diverge and require more accommodation for focusing.
Since the lens must be elastic to assume a more spherical shape during accommodation for near objects, the increasing stiffness of the lens that occurs with aging makes accommodation for near vision increasingly difficult --- presbyopia, a normal part of the aging process in people around 45 years old. Old people often wear corrective glasses for close work.
Diameter changes of the pupil -- The amount of light entering the eye is controlled by the diameter of the pupil, the hole in the center of the iris through which light enters the eye. -- a reflexive process (light-sensitive reflex) -- protect the retina from damage induced by too bright light -- also one of the symbols of deep anesthesia or death
Convergence of two eyes Focusing on an object moving from the distance to the near, the two eye balls convergent towards the nasal sides, so that the images could be focused on corresponding points of the two retinas.
Vision The normal condition, in which the eyes has the full adjustment range that allows the maximum capacity for accommodation to keep objects in focus as they get nearer and nearer, is termed as emmetropia. The eyes of many individuals don’t achieve this ideal. Errors of refraction include myopia, hyperopia, astigmatism and cataract (opacity of the lens with aging). Errors of refraction
Concave lens Convex lens Cylindrical lens
Ⅱ Phototransduction of the retina fovea centralis optic nerve
Structure of the retina – four layers Pigment cells Photoreceptor cells Bipolar cells Ganglion cells outside →inside Back → front Ⅱ Phototransduction of the retina
ganglio n cell
Structure of the photoreceptor cell retinal opsin photopigment mitochon dria nucleus Synaptic terminal Inner segment Stacked layers of membrane--discs lipid bilayer with proteins mosaiced in it
Comparison of rods and cones rodscones more sensitiveless sensitive highest density--6mm from the fovea centralis highest density--center of the fovea centralis, only cones more convergent connections to neurons more single connections to neurons one type (no color vision)three types (color vision)
Photochemistry of vision Chemical composition of photopigment a photopigment four types-- one called rhodopsin in the rods and one in each of three different cones an opsin (membrane protein binding to retinal) chromophore (retinal, derivative of Vit A)
Photochemistry of vision -- a reversible chemical reaction
In bright light, decomposing of rhodopsin excels composing; in the dark,composing excels decomposing. Vitamin A can derive 11-cis retinal which can bind to opsin to produce rhodopsin. The amount of retinal lost during the process of decomposing and composing of rhodopsin is replaced by Vit A from foods. Serious Vit A deficiency leads to nyctalopia, (night blindness, impaired vision in dim light and in the dark.)
Phototransduction of the retina Electrical response Light stimlus (by photoreceptors) A unique character: hyperpolarized receptor potential, all-trans retinal AP
1. Inhibits release of neurotransmitter (glutamte) is depolarized Hyperpolarized receptor potential
(a) In light (b) In darkness
2. Information modification of the retina Local potential on bipolar cells
Optic nerve carries information to thalamus Some processing edits information Visual cortex interprets information Creates visual image Visual pathways
phototransduction by the cones and color vision Trichromatic theory (different)
Color blindness It’s a condition in which certain colors cannot be distinguished, and is most commonly due to an inherited condition. It is caused by missing of one or more of the cones, or by poor function of the cones. Red/Green color blindness is the most common form, about 99%, and causes problems in distinguishing reds and greens.
Ⅲ Some vision phenomena
Landolt arc Snellen map 2)
4) Binocular Vision and Stereopsis Binocular vision: The ability to maintain visual focus on an object with both eyes, creating a single visual image. Lack of binocular vision is normal in infants. Adults without binocular vision experience distortions in depth perception and visual measurement of distance. Monocular Vision-- with no overlapped optic fields Binocular Vision – with overlapped optic fields
4) Binocular Vision and Stereopsis Stereopsis is one of the processes of the human visual system that extracts depth information from a viewed scene and builds a three dimensional understanding of that scene. It makes use of the slight difference in perspective of one eye relative to the other.
Hearing Section B Special Sensory systems
Hearing ~1000 dyn/cm 2 most sensitive: 1000~3000Hz
Hearing threshold and hearing range
Middle ear cavity separated from external ear by eardrum and from internal ear by oval & round window Auditory tube leads to nasopharynx--helps to equalize pressure on both sides of eardrum Membranous labyrinth contains cochlea (organs of hearing) and vestibular apparatus (equilibrium) Structure of the ear
Hearing Sound waves are conducted through the auditory canal and cause vibration of the eardrum Sound waves are conducted and amplified by moving of the ossicular chain in the middle ear Vibration of sound waves is converted into receptor potential by hair cells in the organ of Corti of the cochlea. Receptor P triggers release of neurotransmitter and then cause AP which travels along the afferent nerves to the auditory cortex of the brain.
By revibrating the sides and the end of the external auditory canal, sound is amplified. When sound waves arrive the eardrum, the intensity is increased almost 10 desibel (dB). Ⅰ Functions of the external ear
Middle ear eardrum, ossicular chain, auditory tube Functions: Conduct sound waves Amplify the sound pressure Protect auditory apparatus in the inner ear Equilibrate the pressure Ⅱ Functions of the middle ear
Conduct sound waves The eardrum vibrates as the same frequency as the sound waves conducted from the the auditory canal. With the vibration of the eardrum, the ossicular chain moves forward and backward. Ⅱ Functions of the middle ear
Amplify the sound pressure Ossicular chain--Three flexibly linked ossicles include malleus (hammer), incus (anvil) and stapes (stirrup). The ossicles form a ‘lever’ which can conduct sound waves with high effectiveness when moving with vibration of the eardrum. Ⅱ Functions of the middle ear
Amplify the sound pressure Oval window The sound force of per unit is increased when conducted from the eardrum to the oval window. The area of eardrum is 17 times larger than that of oval window and the long arm of the ossicles is 1.3 times longer than the short arm. Thus total amplification is about 22 times. Ⅱ Functions of the middle ear
Protect the apparatus in the inner ear The amount of the energy transmitted to the inner ear is lessened reflexively by the contraction of two small skeletal muscles in the middle ear. This alter the intension of the eardrum and the position of the stapes in the oval window. The delicate receptor apparatus in the inner ear is protected from continuous intense sound stimuli. Ⅱ Functions of the middle ear
Equalize the pressure on both sides of the eardrum The auditory tube which connects the middle ear to the nasopharynx helps to equalize the pressure on both sides of the eardrum. Ⅱ Functions of the middle ear
Sound conduction to the inner ear Air conduction -- normally, main way of sound conduction. canal Middle ear cavity The round window
Less sensitive than air conduction. Bone conduction plays very minor role in normal hearing. Sound conduction to the inner ear
Identify the causes of hearing loss: Conductive Hearing Loss is caused by pathologies in the eardrum or middle ear -- the sensitivity of air conduction is obviously lessened. While the bone conduction is still normal and eventually more sensitive than air conduction. Sensorineural Hearing Loss is caused by pathologies in the cochlea or the auditory nerve – the sensitivity of air conduction and bone conduction are both lessened.
Ⅲ Functions of the inner ear The inner ear is also called labyrinth ---- a system of coiled, membranous tubes filled with fluid. cochlea for hearing vestibular apparatus for equilibrium Transducer function Sound conduction
Structure of the cochlea Three coiled tubes side by side which are separated by two layers of membranes ---- Scala vestibuli (filled with perilymph, connected with oval window ) Scala media (filled with endolymph) Scala tympani (filled with perilymph, connected with round window)
The cross section of the cochlea (Reinssner’s membrane)
Transducer function of the cochlea 1. Vibration of basilar membrane
Waves in the fluid of the cochlea caused by movement of the stapes produce distortions of the basilar membrane.
Traveling wave theory of sound 1. Vibration of basilar membrane Transducer function of the cochlea
The region nearest to the middle ear vibrates most easily in response to high-frequency tones (undergoes the greatest movement). Progressively more distant regions of the basilar membrane vibrate maximally in response to progressively lower tones.
2. Excitation of hair cells and receptor P Transducer function of the cochlea
2. Excitation of hair cells and receptor P Transducer function of the cochlea Vibration of basilar membrane Bending of the stereocilia of the hair cells (receptors) K + channel (mechanically gated ion channel) is opened Influx of K + depolarizes the hair cells Receptor P (Bending in the other direction hyperpolarizes the hair cells)
3. Receptor P of the hair cells to AP Transducer function of the cochlea Receptor P opens Ca2 + channel (voltage-gated, on the flank membrane of hair cells) Ca2+ influx triggers release of neurotransmitter (Glutamate) Glutamate binds to and activates protein binding sites on the terminals of the afferent neurons AP Auditory cortex in the temporal lobe Auditory nerve
Section B Special Sensory systems Vestibular system Somatic sensation Please study by yourself.
You need to know the following content: 1.Types of receptor 2.The refractive system of the eye 3.The structure characters of retina 4. Information transforming in retina 5.Color blindness 6.Binocular vision and stereoscopic vision 7. Function of outer ear Objectives
You need to know well the following content: 1.Color vision 2.Light adaptation and dark adaptation 3.Visual field 4.Visual acuity 5.Functions of the middle ear Objectives
You need to hold the following content: 1.The general properties of receptors: adequate stimulus, transducer function, encoding, and adaptation 2. visual accommodation 3. Phototransduction of rods 4.Air conduction and bone conduction. 5.Transducer function of the cochlea Objectives