Chapter 29 SENSORY RECEPTION © 2012 Pearson Education, Inc.

Sensory Receptors  Sensory receptors = specialized cells or neurons that detect –conditions of the external and internal world  Sensory receptors convert stimulus to action potential –This is called sensory transduction  Message of stimulus carried to CNS –Interpretation of stimulus depends on area of CNS stimulated © 2012 Pearson Education, Inc.

Fig. 27.2

Sensory transduction begins with a receptor protein that opens or closes ion channels in response to stimulus Changes in ion flow change membrane potential of sensory cell Receptor potential = membrane potential of sensory cell Notice how each stimulus binds a receptor protein to open or close ion channel.

Figure 29.UN04 Sensory receptors electromagnetic receptors pain and thermoreceptors (b)(a) are grouped into several types involved in involved in many types found in sensitive to (c) human skin taste and smell touch, hearing, balance many are (d) most common are (e) Mechano- receptors Chemo- receptors light Rods and cones Hair cells

Sensory Receptor May be Found on Plasma Membrane of a Separate Sensory Cell or on a Sensory Neuron © 2012 Pearson Education, Inc.

 Sensory receptor on Separate Sensory Cell –Vision (rods and cones) –Taste (taste buds) –Hearing (hair cells) –Balance (hair cells)  Sensory receptor on specialized sensory nerve ending –Pain –Heat –Touch –smell

–If receptor found on separate cell - stimulus triggers release of neurotransmitters from sensory cell Changes in receptor potential lead to formation of action potentials in sensory neurons © 2012 Pearson Education, Inc. “Hairs” of a receptor cell Neurotransmitter at a synapse Sensory neuron Action potentials Action potentials

Figure 29.2A Sugar molecule Sensory receptor cells Taste pore Taste bud Sensory neuron Sugar molecule (stimulus) Membrane of a sensory receptor cell Sweet receptor Signal transduction pathway Ion channels Ion Sensory receptor cell Receptor potential Neurotransmitter Sensory neuron Action potential to the brain No sugarSugar present Rates of action potentials mV Example of sensory reception – Sense of Taste Notice how binding of sugars to receptor on taste bud leads to action potential in sensory neuron Let’s look at the details….

Figure 29.2A_1 Sugar molecule Sensory receptor cells Taste pore Taste bud Sensory neuron 1 1. sugar molecules enter the taste bud

Sugar molecule (stimulus) Membrane of a sensory receptor cell Sweet receptor Signal transduction pathway Ion channels Ion Sensory receptor cell sugar molecules bind to sweet receptors 3. the binding triggers some ion channels (usually Na channels) in the membrane to close and others to open 4. Change in ion flow changes membrane potential (receptor potential) of sensory cell

Receptor potential Neurotransmitter Sensory neuron Action potential to the brain No sugar Sugar present Rates of action potentials mV Ion channels Ion Sensory receptor cell Change in receptor potential triggers release of neurotransmitter 6. AP triggered in sensory neuron

LE Tongue Taste pore Sugar molecule Taste bud Sensory neuron Sensory receptor cells G protein Adenylyl cyclase Sugar Sugar receptor Protein kinase A SENSORY RECEPTOR CELL Synaptic vesicle K+K+ Ca 2+ Sensory neuron Neurotransmitter ATP cAMP Note: Release of neurotransmitter from taste bud due to opening of Ca2+ channels!!

 Different stimuli trigger different receptors and sensory cells; which trigger different sensory neurons and travel to different parts of brain How is stimulus interpreted? “Sugar” interneuron Sugar receptor cell Taste bud Brain Sensory neurons Salt receptor cell “Salt” interneuron Taste bud No sugar No salt Increasing sweetnessIncreasing saltiness

 The stronger the stimulus, –the more neurotransmitter released by the receptor cell and –the more frequently the sensory neuron transmits action potentials to the brain.  Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly. How is INTENSITY of stimulus detected? © 2012 Pearson Education, Inc.

“Hairs” of a receptor cell Fluid movement Neurotransmitter at a synapse Sensory neuron Action potentials Action potentials Receptor cell at restFluid moving in one directionFluid moving in the other direction More neurotransmitter molecules Fewer neurotransmitter molecules Fluid movement 321  The stronger the stimulus, –the more neurotransmitter released by the receptor cell and –the more frequently the sensory neuron transmits action potentials to the brain.  Repeated stimuli may lead to sensory adaptation, the tendency of some sensory receptors to become less sensitive when they are stimulated repeatedly.

HEARING AND BALANCE Both hearing and balance use hair cells as sensory cells Hair cells = type of mechanoreceptor © 2012 Pearson Education, Inc.

LE 49-8 Outer ear Middle ear Inner ear Pinna Auditory canal Tympanic membrane Eustachian tube Middle ear Stapes Incus Malleus Skull bones Semicircular canals Auditory nerve, to brain Tympanic membrane Oval window Round window Cochlea Eustachian tube Auditory nerve Tympanic canal Cochlea duct Organ of Corti Vestibular canal Bone To auditory nerve Axons of sensory neurons Basilar membrane Hair cells Tectorial membrane You do not need to all the parts of the ear

Outer earMiddle ear EardrumBones Inner ear Organ of Corti (inside the cochlea)  Pressure waves transmitted to the fluid of the cochlea –bend hair cells in the organ of Corti against the basilar membrane and –trigger nerve signals to the brain.  Louder sounds generate more action potentials.  Various pitches stimulate different regions of the organ of Corti.

LE 49-9 Oval window Cochlea Tympanic canal Basilar membrane Vestibular canal Perilymph Stapes Axons of sensory neurons Apex Base Round window

LE Cochlea (uncoiled) Basilar membrane Apex (wide and flexible) Frequency producing maximum vibration Base (narrow and stiff) 16 kHz (high pitch) 8 kHz 4 kHz 2 kHz 1 kHz 500 Hz (low pitch)

Healthy ear (cilia intact)

Ear damaged by loud music (cilia destroyed)

29.5 The inner ear houses our organs of balance  The three semicircular canals detect changes in the head’s rotation or angular movement. © 2012 Pearson Education, Inc.

Figure 29.5 Semicircular canals Nerve Cochlea Saccule Utricle Flow of fluid Cupula Flow of fluid Cupula Hairs Hair cell Nerve fibers Direction of body movement

VISION © 2012 Pearson Education, Inc.  All animal light detectors are based on cells called photoreceptors that contain pigment molecules that absorb light.

Figure 29.7A Don’t you wish you had eyes like this?

Figure 29.7B Or this?

29.10 The human retina contains two types of photoreceptors: rods and cones  The human retina contains two types of photoreceptors. 1. Rods –contain the visual pigment rhodopsin, which can absorb dim light, and –can detect shades of gray in dim light. 2. Cones –contain the visual pigment photopsin, which absorbs bright colored light, and –allow us to see color in bright light. © 2012 Pearson Education, Inc.

Cones provide for color vision. 3 types of cones absorb red, blue, and green light

Can you tell what number is hiding in here? If not – you might have trouble with your cones

29.10 The human retina contains two types of photoreceptors: rods and cones  When rhodopsin and photopsin absorb light, –they change chemically, and –the change alters the permeability of the cell’s membrane to ions –The resulting receptor potential triggers a change in the release of neurotransmitter © 2012 Pearson Education, Inc.

Figure 29.10B Retina Optic nerve Retina NeuronsPhotoreceptors RodCone Optic nerve fibers To the brain The rods and cones are located at the back of the eye

LE Outer segment Disks Rod Inside of disk Cell body Synaptic terminal Rhodopsin Cytosol Retinal Opsin trans isomer LightEnzymes cis isomer When light hits a rod or cone, the pigments change conformation, triggering our sense of vision

TASTE AND SMELL © 2012 Pearson Education, Inc.

Figure 29.12

29.11 Taste and odor receptors detect chemicals present in solution or air  Taste and smell d epend on chemoreceptors that detect specific chemicals in the environment.  Chemoreceptors –in taste buds detect molecules in solution and –lining the nasal cavity detect airborne molecules.  Taste and smell interact. Much of what we taste is really smell.  Taste buds are specialized cells that detect chemicals in our food, while chemoreceptors for smell are located directly in sensory neurons. © 2012 Pearson Education, Inc.

 Taste receptors –are located in taste buds on the tongue and –produce five taste sensations: 1.sweet, 2.salty, 3.sour, 4.bitter, and 5.umami (the savory flavor of meats and cheeses) Taste and odor receptors detect chemicals present in solution or air © 2012 Pearson Education, Inc.

Figure Brain Nasal cavity Odorous substance Mucus Cilia Sensory neuron (chemo- receptor) Epithelial cell Bone Olfactory bulb A c t i o n p o t e n t i a l s Chemoreceptors for smell are located on cilia of nerve endings. These sensory nerves are directly connected to olfactory bulb