Lecture 12

1. Lecture 12 Senses

2. Where are sensory receptors located? • Autonomic – internal - interoceptors • Somatic – external - exteroceptors • Structure of sensory receptors: what it does - • Free nerve ending or modified nerve endings • Specialized receptors • What do we respond to: stimuli? • Chemical • pain • Mechanical • Electro-magnetic • temperature

3. Some terms: • Sensation: conscious perception of change in the environment • Receptor: specialized nerve ending capable of response to stimulus • Adaptation: loss of perception or lessended perception of a stimulus in spite of constant strength or intensity of stimulus (getting used to something) • Most adapt • Pain receptors do not adapt – selective advantage • Projection: localization stimulus (where is it?)

4. General Senses – • Mechanical: touch and pressure • Temperature • Heat: + 27C • Cold: 10-20C • Rapid adptation • Pain

6. Pain – A Chemical Response • Injured tissue releases chemicals: • Bradykinin • Histamine • Prostaglandin • nerve endings respond • What is the benefit of pain? • Bee venom – same chemical(s) • Impact of Aspirin, ibuprofen: inhibit synthesis of some injury associated chemicals • Referred Pain: pain feels as if it comes from another location – common neural pathways • Acute vs. chronic – different pathways, different speeds of transmission

7. Proprioceptors Mechanoreceptors – located in muscle Help determine relative position of limbs Information sent to CNS and back via reflex arc Maintain muscle tone – thus position, equilibrium, posture

9. Smell - Olfactory • Olfactory cells - epithelium in the upper nasal cavity • bind to specific odor molecules • cerebral cortex processes input • Limbic associations occur (‘It smells like…’)

13. Taste – Chemoreception – Tongue – Swallow it? • Four responses: • Sweet – okay • Salty - okay • Sour ?? • Bitter ?! – poison? • Receptors located in different areas of the tongue • Operation: • Compound dissolves – binds receptor on in taste cell • Specificity depends on receptor – 5+ • Integration from different receptors  various taste perceptions

15. Ear – Mechanical Sensations: • Hearing – cochlea • Equilibrium • Dynamic – semicircular canals • Static: vestibular organs – utricle and saccule • All involved distortion of hair cells to establish neural signal

18. Sense of Hearing • Vibrating objects create pressure waves in the air or water= sound. • Pressure waves vary in • Amplitude- volume. • Frequency- pitch.

19. Partitions that separate the channels are Y shaped • bony shelf of central modiolus • vestibular membrane above & basilar membrane below form the central fluid filled chamber (cochlear duct) • Fluid vibrations affect hair cells in cochlear duct

21. Equilibrium and Motion • Mechanoreceptors located in semicircular canals of inner ear • Rotation equilibrium – semicircular canals • Gravitational (up and down motion) Determination of motion due to bending of hairs of inner ear which are embedded in a cap or gelatinous material - the capula

23. Detection of Rotational Movement • When head moves, the attached semicircular ducts and hair cells move with it • endolymph fluid does not and bends the cupula and enclosed hair cells in ampulla • Nerve signals to the brain are generated indicating which direction the head has been rotated

26. Motion Sickness Mismatch of sensory input from vestibular apparatus (semi circular canals and vestibule) and eyes Example – on a boat the inner ear says motion, all sorts of it but the deck looks level to your eye – brain is confused and you suffer!

28. Eye • Lens focuses image on receptor cells • Iris restricts amount of light admitted • Receptor cells on retina • Posterior and anterior cavities • Extrinsic structures • Muscles • Lacrimal gland • Eyelids • Lining - conjuncitiva

29. Conjunctiva palpebrae

31. Eye ball- 25 mm in diameter (1 inch). • Three layers: (tunics) • Sclera + cornea- (fibrous – outer layer) the white of the eye. • Choroid- (vascular- middle layer) contains melanin that absorbs light + cilary body, iris & lens • Retina- (nervous)contains photoreceptors - 70% of all the sensory receptors in the human body • The retina contains 2 types of photoreceptors. • Rods- responsible for black and white vision. • Cones- responsible for color vision. • Lens and Cornea focuses image on receptor cells • Iris restricts amount of light admitted

32. Eyeball: Three Tunics • Fibrous Tunic (outer layer) • Sclera and cornea • Vascular Tunic (middle layer) • Iris and choroid • Nervous Tunic (inner layer) • Retina Cavities • Anterior cavity – aqueous humor • lens • Posterior cavity (vitreous chamber) – vitreous humor

33. Cataracts • Leading cause worldwide of blindness. • A lens becomes cloudy or opaque. • Caused by • Natural aging. 50 or over. • Drug reactions. • Injury. • Diabetes. • UVB damage. • At risk • Smokers (2X). • Guys named “Phil” or “Rupert”. • Treatment- surgery, removal and replacement of the lens.

35. Proper functioning of eye depends on formation of image on retina – impact of age, etc. • Nearsightedness (myopia) • Farsightedness (hyperopia) • Astigmatism – due to irregularities in cornea or lens so that light is not focused evenly on retina

38. Constrictor pupillae (circular) are innervated by parasympathetic fibers while Dilator pupillae (radial) are innervated by sympathetic fibers. • Response varies with different levels of light

39. How rod and cone cells work: Pigment (rhodopsin) in cell is modified by light Nerve impulse generated as modified pigment causes Na gates to close Color response in Cone cells due to presence of absorption of specific light wavelengths by different forms of pigment (3 kinds - different cells)

40. Cone cells contain three forms of Opsin which respond to different wave lengths of light – giving color vision

42. Color blindness – associated with genetic mutation affecting structural genes for visual pigments .. Red-green color blindness due to opsin gene mutation

43. Abnormalities of the Eye #2 • Color blindness • Colors cannot be distinguished. • 75% of people have poor green perception. • 8-10% of males, <1% females. • X-Linked. • A lack of or reduced number of one of the cone types.

44. Color Blindness Test – do you see pink elephants?

46. The End.