SENSORY RECEPTION © 2012 Pearson Education, Inc.

Ch. 46 Opener 1 Sensing Infrared Radiation

Ch. 46 Opener 2 Echolocating around an Obstacle Course

Fig. 27.2

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.

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

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

Figure 46.6 The Skin Feels Many Sensations

 Sensory receptor on Separate Sensory Cell –Vision –Taste –Hearing –balance  Sensory receptor on specialized sensory nerve ending –Pain –Heat –Touch –smell

 If receptor found on sensory neuron - stimulus triggers action potentials in receptor cell itself Changes in receptor potential lead to formation of action potentials in sensory neurons © 2012 Pearson Education, Inc.

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 in the membrane to close and others to open 4. Change in ion flow change in membrane potential (receptor potential) of sensory cell

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

 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.

Figure 29.3B_3 Fluid moving in the other direction Fewer neurotransmitter molecules Fluid movement 3

LE 49-2a Muscle Weak muscle stretch Receptor potential Action potentials Membrane potential (mV) Time (sec) –70 –50 0 Stretch receptor Dendrites Axon Crayfish stretch receptors have dendrites embedded in abdominal muscles. When the abdomen bends, muscles and dendrites stretch, producing a receptor potential in the stretch receptor. The receptor potential triggers action potentials in the axon of the stretch receptor. A stronger stretch produces a larger receptor potential and higher frequency of action potentials. Strong muscle stretch Time (sec) –70 –50 0

Chemoreceptors  Olfaction (smell) –Pheromones and VNO  Gustation (taste) © 2012 Pearson Education, Inc.

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Figure 46.5 Taste Buds Are Clusters of Sensory Cells

Figure 46.4 Olfactory Receptors Communicate Directly with the Brain

Mechanoreceptors  Hearing and Balance –Hair cells  Lateral line in fish  Pain, touch, muscle movements –Stretch receptors © 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

Figure Hair Cells Have Mechanosensors on Their Stereocilia

LE 49-2b Vertebrate hair cells have specialized cilia or microvilli (“hairs”) that bend when surrounding fluid moves. Each hair cell releases an excitatory neurotransmitter at a synapse with a sensory neuron, which conducts action potentials to the CNS. Bending in one direction depolarizes the hair cell, causing it to release more neurotransmitter and increasing frequency of action potentials in the sensory neuron. Bending in the other direction has the opposite effects. Thus, hair cells respond to the direction of motion as well as to its strength and speed. No fluid movement Fluid moving in one direction Receptor potential Axon “Hairs” of hair cell Neuro- trans- mitter at synapse Fluid moving in other direction More neuro- trans- mitter Less neuro- trans- mitter Time (sec) –70 –50 0 Action potentials Membrane potential (mV) Time (sec) –70 –50 0 Membrane potential (mV) Time (sec) –70 –50 0 Membrane potential (mV)

Figure 46.9 Sensing Pressure Waves in the Inner Ear

Figure 46.9 Sensing Pressure Waves in the Inner Ear (Part 1)

Figure Organs of Equilibrium

Figure The Lateral Line Acoustic System Contains Mechanosensors

Photoreceptors  Detect various regions of electromagentic spectrum –Visible light –Infra-red –UV © 2012 Pearson Education, Inc.

Figure Convergent Evolution of Eyes

Figure The Human Retina

Figure Rods and Cones

Figure Light Changes the Conformation of Rhodopsin

LE Outer segment Disks Rod Inside of disk Cell body Synaptic terminal Rhodopsin Cytosol Retinal Opsin trans isomer LightEnzymes cis isomer

Figure Absorption Spectra of Cone Cells

Figure A Rod Cell Responds to Light (Part 2)

Figure Light Absorption Closes Sodium Channels

LE Light INSIDE OF DISK CYTOSOL PDE Transducin Inactive rhodopsin Disk membrane Active rhodopsin Plasma membrane cGMP Na + GMP Na + Membrane potential (mV) EXTRACELLULAR FLUID Light Hyper- polarization Time –70 Dark 0 –40

LE Light Responses Rhodopsin active Na + channels closed Rod hyperpolarized Bipolar cell either hyperpolarized or depolarized, depending on glutamate receptors No glutamate released Dark Responses Rhodopsin inactive Na + channels open Rod depolarized Bipolar cell either depolarized or hyperpolarized, depending on glutamate receptors Glutamate released

LE Retina Optic nerve To brain Cone Photoreceptors Retina Rod Neurons Pigmented epithelium Bipolar cell Amacrine cell Horizontal cell Optic nerve fibers Ganglion cell