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CHAPTER 49

CHAPTER 49. SENSORY AND MOTOR MECHANISMS. INTRO TO SENSORY RECEPTION. AN ANIMAL’S INTERACTION WITH ITS ENVIRONMENT DEPENDS ON THE PROCESSING OF SENSORY INFO AND THE GENERATION OF MOTOR OUTPUT SENSORY RECEPTORS RECEIVE INFO FROM THE ENVIRONMENT

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CHAPTER 49

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  1. CHAPTER 49 SENSORY AND MOTOR MECHANISMS

  2. INTRO TO SENSORY RECEPTION • AN ANIMAL’S INTERACTION WITH ITS ENVIRONMENT DEPENDS ON THE PROCESSING OF SENSORY INFO AND THE GENERATION OF MOTOR OUTPUT • SENSORY RECEPTORS RECEIVE INFO FROM THE ENVIRONMENT • ACTION POTENTIALS THAT REACH THE BRAIN VIA SENSORY NEURONS ARE TERMED SENSATIONS • INTERPRETATION OF A SENSATION LEADS TO THE PERCEPTION OF THE STIMULUS (SMELLS, SOUNDS) • MOTOR EFFECTORS CARRY OUT THE MOVEMENT IN RESPONSE TO THE SENSOR INFO

  3. SENSORY RECEPTORS • SENSORY RECEPTION = ABILITY OF A CELL TO DETECT THE ENERGY OF A STIMULUS • SENSORY RECEPTORS = STRUCTURES THAT TRANSMIT INFO ABOUT CHANGES IN AN ANIMAL’S INTERNAL AND EXTERNAL ENVIRONMENT • THEY ARE USUALLY MODIFIED NEURONS OR EPITHELIAL CELLS OCCURRING SINGLY OR WITHIN GROUPS IN SENSORY ORGANS • EXTERORECEPTORS DETECT EXTERNAL STIMULI, SUCH AS HEAT, PRESSURE, LIGHT, CHEMICALS • INTERORECEPTORS DETECT INTERNAL STIMULI, SUCH AS BLOOD PRESSURE AND BODY POSITION • SPECIALIZED TO CONVERT STIMULI ENERGY INTO CHANGES IN MEMBRANE POTENTIALS AND THEN TRANSMIT SIGNALS TO THE N.S. • ALL RECEPTORS CELLS HAVE THE SAME 4 FUNCTIONS: TRANSDUCTION, AMPLIFICATION, TRANSMISSION, INTEGRATION

  4. SENSORY TRANSDUCTION • SENSORY TRANSDUCTION IS THE CONVERSION OF STIMULUS ENERGY INTO A CHANGE IN THE MEMBRANE POTENTIAL OF A RECEPTOR CELL • STIMULUS ENERGY CHANGES MEMBRANE PERMIABILITY OF THE RECEPTOR CELL (VIA OPENING OR CLOSING ION CHANNEL GATES, OR INCREASING ION FLOW BY STRETCHING THE RECEPTOR CELL MEMBRANE) AND RESULTS IN A GRADED CHANGED IN MEMBRANE POTENTIAL CALLED RECEPTOR POTENTIAL

  5. AMPLIFICATION • AMPLIFICATION OF STIMULUS ENERGY THAT IS TOO WEAK TO BE CARRIED INTO THE N.S. OFTEN OCCURS • MAY TAKE PLACE IN ACCESSORY STRUCTURES OR BE A PART OF THE TRANDUCTION PROCESS

  6. TRANSMISSION • TRANSMISSION OF A SENSATION TO THE CNS OCCURS IN 2 WAYS: • 1) THE RECEPTOR CELL DOUBLES AS A SENSORY NEURON (E.G. PAIN CELLS). IN THIS CASE, THE INTENSITY OF THE RECEPTOR POTENTIAL WILL EFFECT THE FREQUENCY OF ACTION POTENTIALS THAT CONVEY SENSATIONS TO THE CNS • 2) THE RECEPTOR CELL TRANSMITS CHEMICAL SIGNALS (NEUROTRANSMITTERS) ACROSS A SYNAPSE TO A SECOND SENSORY NEURON. IN THIS CASE THE RECEPTOR POTENTIAL AFFECTS THE AMT OF NEUROTRANSMITTER THAT IS RELEASED, WHICH IN TURN INFLUENCES THE FREQUENCY OF ACTION POTENTIAL GENERATED BY THE SENSORY NEURON

  7. INTEGRATION • RECEPTOR SIGNALS ARE INTEGRATED THROUGH SUMMATION OF GRADED POTENTIALS • SENSORY ADAPTATION IS A DECREASE IN SENSITIVITY DURING CONTINUED STIMULATION; A TYPE OF INTEGRATION THAT RESULTS IN SELECTIVE INFO BEING SENT TO THE CNS • THE THRESHOLD FOR TRANSDUCTION BY RECEPTOR CELLS VARIES WITH CONDITIONS RESULTING IN A CHANGE IN RECEPTOR SENSITIVITY • SENSORY INFO INTEGRATION OCCURS AT ALL LEVELS IN THE N.S.

  8. CATEGORIES OF SENSORY RECEPTORS • RECEPTORS CAN BE GROUPED INTO 5 TYPES DEPENDING ON THE TYPE OF ENERGY THEY DETECT • 1) MECHANORECEPTORS ARE STIMULATED BY PHYSICAL DEFORMATION CAUSED BY PRESSURE, TOUCH, STRETCH, MOTION, SOUND- ALL FORMS OF MECHANICAL ENERGY • BENDING OF THE PLASMA MEMEBRANE INCREASES ITS PERMEABILITY TO NA+ AND K+ RESULTING IN A RECEPTOR POTENTIAL • IN THE HUMAN SKIN, PACINIAN CORPUSCLES DEEP IN THE SKIN RESPOND TO STRONG PRESSURE, WHILE MEISSNER’S CORPUSCLES AND MERKEL’S DISCS, CLOSER TO THE SURFACE, DETECT LIGHT TOUCH • MUSCLE SPINDLES ARE STRETCH RECEPTORS ( A TYPE IF INTERORECEPTOR) THAT MONITOR THE LENGTH OF SKELETAL MUSCLES, AS IN THE REFLEX ARC • HAIR CELLS DETECT MOTION

  9. SENSORY RECEPTORS IN THE SKIN

  10. 2) NOCICEPTORS • NOCICEPTORS ARE A CLASS OF NAKED DENDRITES THAT FUNCTION AS PAIN RECEPTORS • DIFFERENT GROUPS RESPOND TO EXCESS HEAT, PRESSURE, OR SPECIFIC CHEMICALS RELEASED FROM DAMAGED OR INFLAMED TISSUE • PROSTAGLANDINS INCREASE PAIN BY LOWERING RECEPTOR THRESHOLDS; ASPIRIN AND IBUPROFEN REDUCE PAIN BY INHIBITING PROSTAGLANDIN SYNTHESIS

  11. 3) THERMORECEPTORS • THERMORECEPTORS RESPOND TO HEAT OR COLD AND HELP REGULATE BODY TEMPERATURE • THERE IS STILL DEBATE ABOUT THE IDENTITY OF THERMORECEPTORS IN THE MAMMALIAN SKIN. MAY BE TWO RECEPTORS CONSISTING OF ENCAPSULATED, BRANCHED DENDRITES OR THE NAKED DENDRITES OF CERTAIN SENSORY NEURONS • THE INTEROTHERMORECEPTORS IN THE HYPOTHALAMUS FUNCTION AS THE PRIMARY TEMP. CONTROL OF THE MAMMALIAN BODY

  12. 4) CHEMORECEPTORS • CHEMORECEPTORS INCLUDE GENERAL RECEPTORS THAT SENSE TOTAL SOLUTE CONCENTRATION (E.G. OSMORECEPTORS OF THE MAMMALIAN BRAIN), RECEPTORS THAT RESPOND TO INDIVIDUAL MOLECULES, AND THOSE THAT RESPOND TO CATEGORIES OF RELATED CHEMICALS (E.G. GUSTATORY AND OLFACTORY RECEPTORS)

  13. 5) ELECTROMAGNETIC RECEPTORS • ELECTROMAGNETIC RECEPTORS RESPOND TO ELECTROMAGNETIC RADIATION SUCH AS LIGHT (PHOTORECEPTORS), ELECTRICITY, AND MAGNETIC FIELDS (MAGNETORECEPTORS) • A GREAT VARIETY OF LIGHT DETECTORS HAS EVOLVED IN ANIMALS, FROM SIMPLE CLUSTERS OF CELLS TO COMPLEX ORGANS • MOLECULAR EVIDENCE INDICATES THAT MOST, IF NOT ALL, PHOTORECEPTORS IN ANIMALS MAY BE HOMOLOGOUS

  14. PHOTORECEPTORS • A BROAD ARRAY OF PHOTORECEPTORS HAS EVOLVED AMONG INVERTEBRATES • THE EYE CUP OF PLANARIANS IS A SIMPLE LIGHT RECEPTOR THAT REPONDS TO LIGHT INTENSITY AND DIRECTION WITHOUT FORMING AN IMAGE • AN OPENING ON ONE SIDE OF THE CUP EMITS LIGHT TO ENTER; THE OPENING TO ONE CUP FACES LEFT SLIGHTLY FORWARD, THE OTHER CUP OPENS RIGHT AND SLIGHTLY FORWARD • LIGHT ENTERS THE OPENING AND STIMULATES PHOTORECPETORS THAT CONTAIN LIGHT-ABSORBING PIGMENTS • PLANARIA MOVE AWAY FROM LIGHT SOURCES TO AVOID PREDATORS • THE BRAIN COORDINATES AND INTERPRATES NERVE IMPULSES AND MOVEMENTS

  15. EYE CUP OF PLANARIAN

  16. INVERTEBRATE EYES • 2 TYPES OF IMAGE-FORMING EYES HAVE EVOLVED IN INVERTABRATES: • 1) COMPOUND EYE - CONTAINS THOUSANDS OF LIGHT DETECTORS CALLED OMMATIDIA, EACH WITH ITS OWN CORNEA AND LENS • FOUND IN INSECTS, CRUSTACEANS AND SOME POLYCHAETE WORMS • RESULTS IN A MOSAIC IMAGE • MORE ACUTE AT DETECTING MOVEMENT PARTLY DUE TO RAPID RECOVERY OF PHOTORECEPTORS • 2) SINGLE-LENS EYE- ONE LENS FOCUSES LIGHT ONTO THE RETINA, WHICH CONSISTS OF A BILAYER OF PHOTOSENSITIVE RECEPTOR CELLS • FOUND IN SOME JELLIES, POLYCHAETES, SPIDERS AND MANY MOLLUSKS

  17. COMPOUND EYES

  18. VERTEBRATE EYES-SINGLE LENS • THE PARTS OF THE VERTEBRATE EYE ARE STRUCTURALLY AND FUNCTIONALLY DIVERSE • CONSISTS OF A TOUGH OUTER LAYER OF CONNETIVE TISSUE, THE SCLERA, AND A THIN INNER PIGMENTED LAYER, THE CHOROID. • A THIN LAYER OF CELLS, THE CONJUNCTIVA, COVERS THE SCLERA AND KEEPS THE EYES MOIST • THE CORNEA IS LOCATED IN FRONT AND IS A TRANSPARENT AREA OF THE SCLERA; IT ALLOWS LIGHT TO ENTER THE EYE AND ACTS AS A FIXED LENS

  19. VERTEBRATE EYE

  20. THE ANTERIOR CHOROID FORMS THE IRIS, WHICH REGULATES THE AMOUNT OF LIGHT ENTERING THE PUPIL. THE IRIS IS PIGMENTED AND GIVES THE EYE COLOR; THE PUPIL IS THE HOLE IN THE CENTER OF THE IRIS • THE RETINA IS THE INNERMOST LAYER OF THE EYEBALL; IT CONTAINS PHOTORECEPTOR CELLS WHICH TRANSMIT SIGNALS FROM THE OPTIC DISC, WHERE THE OPTIC NERVE ATTACHES TO THE EYE • THE LENS AND CILIARY BODY DIVIDE THE EYE INTO 2 CHAMBERS; A SMALL CHAMBER BTW. THE LENS AND THE CORNEA AND A LARGE CHAMBER WITHIN THE EYEBALL • THE CILIARY BODY PRODUCES AQUAEOUS HUMOR THAT FILLS THE CAVITY BTW. THE LENS AND CORNEA • VITREOUS HUMOR FILLS THE CAVITY BEHIND THE LENS AND COMPRISES MOST OF THE EYE’S VOLUME • BOTH AQUEOUS HUMOR AND VITREOUS HUMOR HELP TO FOCUS LIGHT ONTO THE RETINA

  21. THE LENS • THE LENS IS A TRANSPARENT, PROTEIN DISC THAT FOCUSES AN IMAGE ONTO THE RETINA BY CHANGING THE SHAPE (ACCOMMODATION) • IS NEARLY SPHERICAL WHEN FOCUSING ON NEAR OBJECTS AND FLAT WHEN FOCUSING AT A DISTANCE • CONTROLLED BY THE CILIARY MUSCLE

  22. FOCUSING THE MAMMALIAN EYE

  23. PHOTORECEPTORS OF THE EYE • THE PHOTORECEPTORS OF THE EYE ARE ROD CELLS AND CONE CELLS • THEIR RELATIVE NUMBERS IN THE RETINA ARE PARTLY CORRELATED WITH WHETHER AN ANIMAL IS DIURNAL OR NOCTURNAL • ROD CELLS ARE SENSITIVE TO LIGHT BUT DO NOT DISTINGUISH COLORS • FOUND IN GREATEST DENSITY AT PERIPHERAL REGIONS OF THE RETINA; COMPLETELY ABSENT FROM THE FOVEA (CENTER OF VISUAL FIELD) • CONE CELLS ARE RESPONSIBLE FOR DAYTIME COLOR VISION • MOST DENSE AT THE FOVEA

  24. PHOTORECEPTORS IN THE EYE

  25. LOOK AT THE FOVEA

  26. RHODOPSIN • THIS LIGHT ABSORBING PIGMENT OPERATES VIA SIGNAL TRANSDUCTION • CELLS IN THE RETINA TRANSDUCE STIMULI (CAUSED BY THE LENS FOCUSING A LIGHT IMAGE ONTO THE RETINA) INTO ACTION POTENTIALS • EACH ROD CELL OR CONE CELL HAS AN OUTER SEGMENT WITH A STACK OF FOLDED MEMBRANES IN WHICH VISUAL PIGMENTS ARE EMBEDDED • THE VISUAL PIGMENTS CONSISTS OF LIGHT-ABSORBING RETINAL, WHICH IS MADE FROM VITAMIN A, BONDED TO A MEMBRANE PROTEIN OPSIN

  27. LOOK AT VISUAL PIGMENTS

  28. RODS • RODS CONTAIN THEIR OWN TYPE OF OPSIN, AND WHEN COMBINED WITH RETINAL, MAKES UP RHODOPSIN • WHEN RHODOPSIN ABSORBS LIGHT, ITS RETINAL COMPONENT CHANGES SHAPE. THIS TRIGGERS A CHAIN OF METABOLIC EVENTS THAT HYPERPOLARIZES THE PHOTORECEPTOR CELL MEMBRANE; THUS, A DECREASE IN CHEMICAL SIGNAL TO THE CELLS WITH WHICH PHOTORECEPTORS SYNAPSE SERVES AS THE MESSAGE • LIGHT-INDUCED CHANGE IN RETINAL IS REFERRED AS “BLEACHING” OF RHODOPSIN; IN BRIGHT LIGHT, RODS BECOME UNRESPONSIVE AND THE CONES TAKE OVER • IN THE DARK, ENZYMES CONVERT RETINAL BACK TO ITS ORIGINAL FORM

  29. THE EFFECT OF LIGHT

  30. COLOR VISION • COLOR VISION INVOLVES MORE COMPLEX SIGNAL PROCESSING THAN THE RHODOPSIN MECHANISM IN RODS • COLOR VISION RESULTS FROM THE PRESENCE OF 3 SUBCLASSES OF CONES: RED CONES, GREEN CONES, AND BLUE CONES, EACH WITH ITS OWN TYPE OF OPSIN ASSOCIATED WITH THE RETINAL FOR FORMING VISUAL PIGMENTS (PHOTOPSINS)

  31. THE RETINA • THE RETINA ASSISTS THE CEREBRAL CORTEX IN PROCESSING VISUAL INFO • INTEGRATION OF VISUAL INFO BEGINS AT THE RETINA • ROD AND CONE CELL AXONS SYNAPSE WITH NEURONS CALLED BIPOLAR CELLS, WHICH IN TURN SYNAPSE WITH GANGLION CELLS • HORIZONTAL CELLS AND AMACRINE CELLS ARE NEURONS IN THE RETINA THAT HELP INTERGRATE THE INFO, AFTER WHICH THE GANGLION CELL AXONS CONVEY ACTION POTENTIALS ALONG THE OPTIC NERVE TO THE BRAIN

  32. ROD AND CONE CELL SIGNALS MAY FOLLOW VERTICAL OR LATERAL PATHWAYS • VERTICAL PATHWAYS INVOLVE INFO PASSING DIRECTLY FROM RECEPTOR CELLS TO BIPOLAR CELLS TO GANGLION CELLS • LATERAL PATHWAYS INVOLVE: HORIZONTAL CELLS CARRYING SIGNALS FROM ONE ROD OR CONE TO OTHER RECEPTOR CELLS AND SEVERAL BIPOLAR CELLS; AMARCRINE CELLS SPREAD THE SIGNALS FROM ONE BIPOLAR CELL TO SEVERAL GANGLION CELLS • HORIZONTAL CELLS, STIMULATED BY ROD OR CONE CELLS, STIMULATE NEARBY RECEPTORS BUT INHIBIT MORE DISTANT RECEPTORS AND NON-ILLUMINATED BIPOLAR CELLS, THUS SHARPENING IMAGE EDGES AND ENHANCING CONTRAST (LATERAL INHIBITION) • OCCURS AT ALL LEVELS OF VISUAL PROCESSING

  33. THE RETINA

  34. OPTIC NERVES • OPTIC NERVES FROM EACH EYE MEET AT THE OPTIC CHIASM • THE OPTIC CHIASM HAS NERVE TRACTS ARRANGED SO THAT WHAT IS VIEWED IN THE LEFT FIELD OF VIEW IS TRANSMITTED TO THE RIGHT SIDE OF THE BRAIN AND VICE VERSA • GANGLION AXONS USUALLY CONTINUE THROUGH THE LATERAL GENICULATE NUCLEI OF THE THALAMUS, AND THESE NEURONS CONTINUE BACK TO THE PRIMARY VISUAL CORTEX IN THE OCCIPITAL LOBE OF THE CEREBRM • ADDITIONAL NEURONS CARRY INFORMATION TO MORE SOPHISTICATED VISUAL PROCESSING CNETERS IN THE CORTEX

  35. VISUAL CENTERS

  36. HEARING & EQUILIBRIUM • HEARING AND EQUILIBRIUM ARE RELATED IN MOST ANIMALS AND INVOLVE MECHANORECEPTORS • THE MAMMALIAN HEARING ORGAN IS WITHIN THE INNER EAR • SOUND WAVES ARE COLLECTED BY THE OUTER EAR (THE EXTERNAL PINNA AND THE AUDITORY CANAL) AND ARE CHANNELED TO THE TYMPANIC MEMBRANE OF THE MIDDLE EAR

  37. THE EAR

  38. SOUND WAVES • SOUND WAVES CAUSED THE TYMPANIC MEMBRANE TO VIBRATE AT THE SAME FREQUENCY; THE TYMPANIC MEMBRANE TRANSMITS THE WAVES TO THREE SMALL BONES - THE MALLEUS, INCUS, STAPES - WHICH AMPLIFY AND TRANSMIT THE MECHANICAL MOVEMENTS OF THE MEMBRANE TO THE OVAL WINDOW, A MEMBRANE OF THE COCHLEA SURFACE • THE MIDDLE EAR OPENS INTO THE EUSTACHIAN TUBE, A CHANNEL TO THE PHARYNX TO AID IN PRESSURE EQUALIZATION ON BOTH SIDES OF THE TYMPANIC MEMBRANE • OVAL WINDOW VIBRATIONS PRODUCE PRESSURE WAVES IN THE FLUID (ENDOLYMPH) IN THE COILED COCHLEA OF THE INNER EAR

  39. PRESSURE WAVES • PRESSURE WAVES VIBRATE THE BASILAR MEMBRANE (FORMS THE FLOOR OF THE COCHLEAR DUCT) AND THE ATTACHED ORGAN OF CORTI, WHICH CONTAINS RECEPTOR HAIR CELLS • THE BENDING OF THE HAIR CELLS AGAINST THE TECTORIAL MEMBRANE DEPOLARIZES THE HAIR CELLS ANC CAUSES THEM TO RELEASE A NEUROTRANSMITTER THAT TRIGGERS AN ACTION POTENTIAL IN A SENSORY NEURON, WHICH THEN CARRIES SENSATIONS TO THE BRAIN THROUGH THE AUDITORY NERVE • THE PRESSURE WAVE CONTINUES THROUGH THE TYMPANIC CANAL AND IS DISSIPATED AS IT STRIKES THE ROUND WINDOW

  40. VOLUME • VOLUME IS DETERMINED BY THE AMPLITUDE OF THE SOUND WAVE; PITCH IS A FUNCTION OF SOUND WAVE FREQUENCY • THE GREATER THE AMPLITUTDE OF A SOUND, THE MORE VIBROUS THE VIBRATIONS; THIS RESULTS IN MORE BVENDING OF THE HAIR CELLS AND MORE ACTION POTENTIALS • DIIFERENT SOUND FREQUENCIES AFFECT DIFFERENT AREAS OF THE BASILAR MEMBRANE, THUS SOME RECEPTORS SEND MORE ACTION POTENTIALS THAN OTHERS

  41. SENSATIONS OF THE EAR

  42. THE INNER EAR • SEVERAL ORGANS IN THE INNER EAR DETECT BODY POSITION AND BALANCE • BEHIND THE OVAL WINDOW IS A VESTIBULE THAT CONTAINS 2 CHAMBERS, THE UTRICLE AND THE SACCULE • THE UTRICLE OPENS INTO 3 SEMICIRCULAR CANALS

  43. ORGANS OF EQUILIBRIUM

  44. EQUILIBRIUM CON’T • HAIR CELLS IN THE UTRICLE AND SACCULE RESPOND TO CHANGES IN HEAD POSITION WITH RESPECT TO GRAVITY AND MOVEMENT IN ONE DIRECTION • HAIR CELLS ARE ARRANGED IN CLUSTUERS WITH THEIR HAIRS PROJECTING INTO A GELATINOUS MATERIAL CONTAINING NUMEROUS OTOLITHS (SMALL CALCIUM CARBONTE PARTICLES) • THE OTOLITHS ARE HEAVIER THAN ENDOLYMPH IN THE SACCULE AND UTRICLE; GRAVITY PULLS THEM DOWN ON THE HAIRS OF THE RECEPTOR CELLS, THUS CAUSING A CONSTANT SERIES OF ACTION POTENTIALS INDICATING POSITION OF THE HEAD • SEMICIRCULAR CANALS DETECT ROTATION OF THE HEAD DUE TO ENDOLYMPH MOVEMENT AGAINST THE HAIR CELLS

  45. FISH • THE INNER EAR OF A FISH HAS NO EARDRUM, DOES NOT OPEN TO THE OUTSIDE OF THE BODY, AND HAS NO COCHLEA, BUT A SACCULE, UTRICLE, AND SEMICIRCULAR CANAL ARE PRESENT • SOUND WAVES ARE CONDUCTED THRU THE SKELETON OF THE HEAD TO THE INNER EAR. THIS SETS OTOLITHS IN MOTION, STIMULATING THE HAIR CELLS • SOME FISH HAVE A WEBERAIN APARATUS, A SERIES OF 3 BONES WHICH CONDUCTS VIBRATIONS FROM THE SWIM BLADDER TO THE INNER NEAR • FISH CAN HEAR HIGHER FREQUENCIES DUE TO THEIR INNER EARS • IN TERRESTRIAL AMPHIBIANS, REPTILES AND BIRDS, SOUND IS CONDUCTED FROM THE TYMPANIC MEMBRANE TO THE INNER EAR BY A SINGLE BONE, THE STAPES

  46. LATERAL LINE SYSTEM • FISH AND AQUATIC AMPHIBS HAVE A LATERAL LINE SYSTEM RUNNING ALONG BOTH SIDES OF THE BODY • MECHANORECEPTORS CALLED NEUROMASTS CONTAIN HAIR CELL CLUSTERS WHOSE HAIRS ARE EMBEDDED IN A GELATINOUS CAP, THE CAPULA • WATER ENTERS THE SYSTEM THRU NUMEROUS PORES ON THE ANIMAL’S SURFACE AND FLOWS ALONG THE TUBE PAST THE NEUROMASTS • PRESSURE OF MOVING WATER BENDS THE CUPULA CAUSING AN ACTION POTENTIAL IN THE HAIR CELLS • THIS PROVIDES INFO ABOUT THE BODY’S MOVEMENT, DIRECTION, AND VELOCITY OF WATER CURRENTS, AND MOVEMENTS OR VIBRATIONS CAUSED BY PREDATORS AND PREY

  47. LATERAL LINE SYSTEM • FISH AND AQUATIC AMPHIBS HAVE A LATERAL LINE SYSTEM RUNNING ALONG BOTH SIDES OF THE BODY • MECHANORECEPTORS CALLED NEUROMASTS CONTAIN HAIR CELL CLUSTERS WHOSE HAIRS ARE EMBEDDED IN A GELATINOUS CAP, THE CAPULA • WATER ENTERS THE SYSTEM THRU NUMEROUS PORES ON THE ANIMAL’S SURFACE AND FLOWS ALONG THE TUBE PAST THE NEUROMASTS • PRESSURE OF MOVING WATER BENDS THE CUPULA CAUSING AN ACTION POTENTIAL IN THE HAIR CELLS • THIS PROVIDES INFO ABOUT THE BODY’S MOVEMENT, DIRECTION, AND VELOCITY OF WATER CURRENTS, AND MOVEMENTS OR VIBRATIONS CAUSED BY PREDATORS AND PREY

  48. THE LATERAL LINE SYSTEM

  49. INVERTEBRATES • MOST INVERTS HAVE MECHANORECPEPTORS CALLED STATOCYSTS THAT FUNCTION IN THEIR SENSE OF EQUILIBRIUM • GRAVITY CAUSES STATOLITHS (DENSE GRANULES) TO SETTLE TO THE LOW POINT IN A CHAMBER, STIMULATING HAIR CELLS IN THAT LOCATION • STATOCYSTS ARE LOCATED ALONG THE BELL FRINGE OF MANY JELLIES AND AT THE ANTENNULE BASES IN LOBSTERS AND CRAYFISH • MANY INSECTS ALSO HAVE “EARS,” LOCATED ON THEIR LEGS, CONSISTING OF A TYMPANIC MEMBRANE STRETCHED OVER AN INTERNAL AIR CHAMBER CONTAINING RECEPTOR CELLS THAT SEND NERVE IMPULSES TO THE BRAIN

  50. STATOCYST

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