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Sensory System

Sensory System

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Sensory System

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  1. Sensory System • Transmits sensory information collected by receptors to the CNS

  2. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  3. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  4. 1- General Principles of Sensory Physiology • Receptor physiology • Sensory pathways • Sensory coding

  5. Somatic -- Chemoreceptors (taste, smell, smell) -- Thermoreceptors (temperature) -- Photoreceptors (vision) -- Baroreceptors (sound, balance) -- Proprioreceptors (muscle stretch) Visceral -- Chemoreceptors (chemicals in blood, osmoreceptors) -- Baroreceptors (blood pressure) Sensory receptors

  6. Receptors transform an external signal into a membrane potential Two types of receptor cells: - a nerve cell - a specialized epithelial cell Sensory transduction

  7. Two types of sensory receptors Figure 10.2

  8. Tonic receptors -- slow acting, -- no adaptation: continue to for impulses as long as the stimulus is there (ex: proprioreceptors) Phasic receptors -- quick acting, adapt: stop firing when stimuli are constant (ex: smell) Receptor adaptation

  9. A receptor must convey the type of information it is sending  the kind of receptor activated determined the signal recognition by the brain It must convey the intensity of the stimulus the stronger the signals, the more frequent will be the APs It must send information about the location and receptive field, characteristic of the receptor Sensory coding

  10. The sensory pathways convey the type and location of the sensory stimulus The type: because of the type of receptor activated The location: because the brain has a map of the location of each receptor Sensory pathways

  11. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  12. The Somatosensory System • Types of receptors - Mechanoreceptors: -- Proprioreceptors in tendons, ligaments and muscles  body position -- Touch receptors in the skin: free nerve endings, Merkel’s disks and Meissner’s corpuscles (superficial touch), hair follicles, Pacinian corpuscles and Ruffini’s ending - Thermoreceptors: Warm receptors (30-45oC) and cold receptors (20-35oC) - Nociceptors: respond to noxious stimuli Figure 10.6

  13. Skin touch receptors Figure 10.13

  14. Figure 10.15

  15. Pain perception • Fast pain: sharp and well localized, transmitted by myelinated axons • Slow pain: dull aching sensation, not well localized, transmitted by unmyelinated axons • Visceral pain: not as well localized as pain originating from the skin  pain impulses travel on secondary axons dedicated to the somatic afferents  referred pain

  16. Referred pain Figure 10.16a

  17. Figure 10.16b

  18. What is Phantom pain?

  19. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  20. Specialized neurons present in the olfactory epithelium in the nose. They project cilia into a mucus layer. The cilia are able to bind to odorant molecules  the binding triggers an AP which is transmitted to the olfactory area of the olfactory bulb  olfactory cortex (lower frontal area and limbic system of the brain Each olfactory receptor is specialized for 1 odorant molecule Olfaction

  21. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  22. Receptors for taste are modified epithelial cell present in taste buds located on the tongue, roof of the mouth and pharynx Taste

  23. Four primary types of taste receptors : sour, salt, sweet and bitter (and a new one: umami) • The binding of the receptor to a taste molecule triggers the entry of calcium in the cell  release of neurotransmitter in a synapse with a neuron

  24. Taste receptors

  25. Neural pathway • Taste impulses travel through nerves VII, IX and X to a gustatory nucleus in the medulla oblongata (cross over)  thalamus  gustatory cortex located in the parietal lobe in the mouth area.

  26. What is the flavor of food?

  27. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  28. Hearing - Equilibrium Figure 10.37

  29. Hearing • Sounds are waves of compressed air traveling through space - sound intensity wave height - pitch  wave frequency

  30. Cochlea Vestibular apparatus Organ of hearing (and equilibrium) – inner ear

  31. 1- The sound waves enter the external auditory canal and trigger vibrations of the tympanic membrane 2- The tympanic membrane induces a vibration of the ossicles 3- the last ossicle, the stapes, transmits amplified vibrations to the oval window 4- The vibrations induce waves in the perilymph of the various inner ear chambers 5- the round window absorbs excess energy and prevent wave reverberation 6- the fluid wave is transduced into an electrical signal by the auditory receptors, the organs of Corti located on the basilar membrane Hearing

  32. The hair cells of the organ of Corti transduce fluid wave into an electrical signal The energy of the wave causes the basilar and vestibular membrane to move, thus displacing the cilia from the organ of Corti Receptors for sound: the organ of Corti

  33. Movements of the cilia open or close potassium channels  changes in the state of polarization of the hair cell Changes in potassium leakage due to cilia bending trigger changes in neurotransmitters exocytosis The neurotransmitters send an electrical signal to an afferent neuron of the cochlear nerve The louder the sound, the more the cilia bend, the more numerous are the APs produced Signal transduction

  34. The location of the organs of Corti on the basilar membrane codes for pitch - Organs of Corti located near the oval window are more sensitive to high pitch sounds while the ones located toward the tip of the cochlea respond more readily to low pitch sound Coding for pitch

  35. Coding for sound intensity

  36. Neural pathway for sounds • Cochlear nerve  nucleus in medulla oblongata  thalamus  auditory cortex in the temporal lobe • So, how do we perceive the direction from which a sound is coming from?

  37. Ability to detect head position and movement (or acceleration) Change of speed = linear acceleration (utricle and saccule) Turning = rotational acceleration (semi-circular canals) Equilibrium

  38. Sensory cells have cilia extending into a gelatinous material topped by otoliths Saccule detects backward-frontward movement Utricle detects changes relative to gravity Utricle and saccule

  39. Figure 10.46a–c

  40. The receptors in the ampulla are hair cells with cilia extruding into a gelatinous mass (cupula) When the head rotates, the cupula moves  cilia pulled APs (vestibular nerve  cerebellum …) Semi-circular canals

  41. So why does a person become dizzy after he/she stops spinning?

  42. Outline 1- General principles of sensory physiology 2- The somatosensory System 3- Olfaction 4- Taste 5- Hearing and Equilibrium 6- Vision

  43. Vision

  44. The eye can only perceive a small portion of the spectrum of electromagnetic waves

  45. Vision • In order to see an object: - 1- the pattern of the object must fall on the vision receptors (rods and cones in the retina)  accommodation - 2- the amount of light entering the eye must be regulated (too much light will “bleach out” the signals) - 3- the energy from the waves of photons must be transduced into electrical signals - 4- The brain must receive and interpret the signals

  46. Accommodation • It is the process of adjusting the shape of the lens so that the external image fall exactly on the retina

  47. Accommodation • Object is far  the lens flattens • Object is near  the lens rounds Figure 10.25

  48. Accommodation abnormalities • Myopia • Hyperopia • Astigmatism: the cornea is irregular  irregular pattern of vision • Presbyopia: stiffening of the lens occurring with aging  increased difficulty with near vision