Olfaction

• Link between smell, memory, and emotion • Vomeronasal organ (VNO) in rodents – Response to sex pheromones • Olfactory sensory neurons – Olfactory epithelium in nasal cavity • Odorants bind to odorant receptors, G protein–linked membrane receptors

© 2016 Pearson Education, Inc. Figure 10.13a The Olfactory System

Olfactory Pathways The olfactory epithelium lies high within the nasal cavity, and its olfactory neurons project to the olfactory bulb. Sensory input at the receptors is carried through the olfactory cortex to the cerebral cortex and the limbic system. Cerebral cortex

Limbic system

Olfactory bulb Olfactory tract Olfactory cortex

Cranial Nerve I

Olfactory neurons in olfactory epithelium

© 2016 Pearson Education, Inc. Figure 10.13b The Olfactory System

The olfactory neurons synapse with secondary sensory neurons in the olfactory bulb.

Olfactory bulb

Secondary sensory neurons Bone

Olfactory sensory neurons Olfactory epithelium

FIGURE QUESTION Multiple primary neurons in the epithelium synapse on one secondary neuron in the olfactory bulb. This pattern is an example of what principle?

© 2016 Pearson Education, Inc. Figure 10.13c The Olfactory System

Olfactory neurons in the olfactory epithelium live only about two months. They are replaced by new neurons whose axons must find their way to the olfactory bulb.

Olfactory neuron axons (cranial nerve I) carry information to olfactory bulb. Capillary Lamina propria

Basal cell layer includes Olfactory (Bowman’s) gland stem cells that replace olfactory neurons.

Developing olfactory neuron Olfactory sensory neuron

Supporting cell

Olfactory cilia (dendrites) contain odorant receptors.

Mucous layer: Odorant molecules must dissolve in this layer. © 2016 Pearson Education, Inc. Gustation

• Closely linked to olfaction • Taste is a combination of five basic sensations: sweet, sour, salty, bitter, umami. • Additional taste sensations may be linked to TRP pathways, same as thermoreceptors and nocireceptors: minty, hot spicy

© 2016 Pearson Education, Inc. Gustation

• Taste receptor cells are non-neural epithelium. • Each taste cell is sensitive to only one taste. • Taste transduction – Gustducin • Humans and animals may develop specific hunger, such as salt appetite.

© 2016 Pearson Education, Inc. Figure 10.14a Taste

Taste Buds. Each taste bud is composed of taste cells joined near the apical surface with tight junctions. Taste ligands create Ca2+ signals that release serotonin or ATP.

Sweet Umami Bitter Sour

Tight junction

Type I support cells Taste buds are located may sense salt when on the dorsal surface Na+ enters through of the tongue. channels.

Taste pore Salt?

(Based on Tomchik et al., J Presynaptic Neurosci 27(40): cell (III) 10840–10848, 2007.)

ATP

Serotonin Receptor cells (type II)

Light micrograph of a taste bud Primary sensory neurons

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 1

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, Signal sweet, or umami ligands and release transduction ATP as a signal molecule. ? Ligands activate the taste cell.

Ca2+ Various intracellular pathways Ca2+ are activated. Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits Ca2+ Ca2+ signal in the cytoplasm Umami T1R1 + 3 subunits triggers exocytosis or ATP formation. Bitter T2R

Neurotransmitter or ATP is ATP released.

Primary Primary sensory neuron fires gustatory and action potentials are neurons sent to the brain.

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 2

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, sweet, or umami ligands and release ATP as a signal molecule. Ligands activate the taste cell.

Ca2+ Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits

Umami T1R1 + 3 subunits

Bitter T2R

Primary gustatory neurons

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 3

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, Signal sweet, or umami ligands and release transduction ATP as a signal molecule. ? Ligands activate the taste cell.

Ca2+ Various intracellular pathways are activated. Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits

Umami T1R1 + 3 subunits

Bitter T2R

Primary gustatory neurons

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 4

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, Signal sweet, or umami ligands and release transduction ATP as a signal molecule. ? Ligands activate the taste cell.

Ca2+ Various intracellular pathways Ca2+ are activated. Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits Ca2+ Ca2+ signal in the cytoplasm Umami T1R1 + 3 subunits triggers exocytosis or ATP formation. Bitter T2R

ATP

Primary gustatory neurons

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 5

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, Signal sweet, or umami ligands and release transduction ATP as a signal molecule. ? Ligands activate the taste cell.

Ca2+ Various intracellular pathways Ca2+ are activated. Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits Ca2+ Ca2+ signal in the cytoplasm Umami T1R1 + 3 subunits triggers exocytosis or ATP formation. Bitter T2R

Neurotransmitter or ATP is ATP released.

Primary gustatory neurons

© 2016 Pearson Education, Inc. Figure 10.14b Taste Slide 6

Sweet, umami, Sour Taste Transduction. Each taste cell or bitter ligand H+ senses only one type of ligand. Gustducin GPCR ? Presynaptic cells sense sour taste (H+) apparently when H+ enters the cell through channels. Receptor cells with G protein–coupled H+ membrane receptors bind either bitter, Signal sweet, or umami ligands and release transduction ATP as a signal molecule. ? Ligands activate the taste cell.

Ca2+ Various intracellular pathways Ca2+ are activated. Taste GPCR Family Ca2+

Sweet T1R2 + 3 subunits Ca2+ Ca2+ signal in the cytoplasm Umami T1R1 + 3 subunits triggers exocytosis or ATP formation. Bitter T2R

Neurotransmitter or ATP is ATP released.

Primary Primary sensory neuron fires gustatory and action potentials are neurons sent to the brain.

© 2016 Pearson Education, Inc. The Ear: Hearing

• Perception of energy carried by sound waves • Frequency is translated into pitch • Loudness is an interpretation of intensity, a function of wave amplitude

© 2016 Pearson Education, Inc. Figure 10.15 The Ear The Ear

EXTERNAL EAR MIDDLE EAR INNER EAR

The pinna The oval window and the round window separate directs sound the fluid-filled inner ear from the air-filled middle ear. waves into the ear. Malleus Semicircular Oval Incus canals window Nerves

Stapes

Cochlea Vestibular apparatus

Ear canal

Tympanic Round membrane window To pharynx

Eustachian tube © 2016 Pearson Education, Inc. Figure 10.16a Sound waves

Sound waves alternate peaks of compressed air and valleys where the air is less compressed.

Wavelength

Tuning fork

© 2016 Pearson Education, Inc. Figure 10.16b Sound waves

Sound waves are distinguished by their frequency, measured in hertz (Hz), and amplitude, measured in decibels (dB).

(1) 1 Wavelength

Intensity Amplitude (dB) (dB)

0 0.25 Time (sec)

(2)

FIGURE QUESTIONS Intensity Amplitude 1. What are the frequencies of the (dB) (dB) sound waves in graphs (1) and (2) in Hz (waves/second)? 2. Which set of sound waves would be interpreted as having lower pitch? 0 0.25 Time (sec)

© 2016 Pearson Education, Inc. Sound Transduction

• Sound waves to mechanical vibrations when striking the tympanic membrane (ear drum) • Three middle bones vibrate and transfer to membrane in oval window • Vibrations generate fluid waves in the cochlea • Hair cells bend in the cochlea and ion channels open • Action potential travel to the brain

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 1

Sound waves The sound The stapes is The fluid waves push on Neurotransmitter Energy from the waves strike the wave energy is attached to the the flexible membranes release onto sensory transfers across the tympanic transferred to membrane of the oval of the cochlear duct. Hair neurons creates action cochlear duct into the membrane the three bones window. Vibrations of cells bend and ion potentials that travel tympanic duct and is and become of the middle the oval window channels open, creating an through the cochlear dissipated back into vibrations. ear, which create fluid waves electrical signal that alters nerve to the brain. the middle ear at the vibrate. within the cochlea. neurotransmitter release. round window.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 2

Sound waves strike the tympanic membrane and become vibrations.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 3

Sound waves The sound strike the wave energy is tympanic transferred to membrane the three bones and become of the middle vibrations. ear, which vibrate.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 4

Sound waves The sound The stapes is strike the wave energy is attached to the tympanic transferred to membrane of the oval membrane the three bones window. Vibrations of and become of the middle the oval window vibrations. ear, which create fluid waves vibrate. within the cochlea.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 5

Sound waves The sound The stapes is The fluid waves push on strike the wave energy is attached to the the flexible membranes tympanic transferred to membrane of the oval of the cochlear duct. Hair membrane the three bones window. Vibrations of cells bend and ion and become of the middle the oval window channels open, creating an vibrations. ear, which create fluid waves electrical signal that alters vibrate. within the cochlea. neurotransmitter release.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 6

Sound waves The sound The stapes is The fluid waves push on Neurotransmitter strike the wave energy is attached to the the flexible membranes release onto sensory tympanic transferred to membrane of the oval of the cochlear duct. Hair neurons creates action membrane the three bones window. Vibrations of cells bend and ion potentials that travel and become of the middle the oval window channels open, creating an through the cochlear vibrations. ear, which create fluid waves electrical signal that alters nerve to the brain. vibrate. within the cochlea. neurotransmitter release.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Figure 10.17 Sound transmission through the ear Slide 7

Sound waves The sound The stapes is The fluid waves push on Neurotransmitter Energy from the waves strike the wave energy is attached to the the flexible membranes release onto sensory transfers across the tympanic transferred to membrane of the oval of the cochlear duct. Hair neurons creates action cochlear duct into the membrane the three bones window. Vibrations of cells bend and ion potentials that travel tympanic duct and is and become of the middle the oval window channels open, creating an through the cochlear dissipated back into vibrations. ear, which create fluid waves electrical signal that alters nerve to the brain. the middle ear at the vibrate. within the cochlea. neurotransmitter release. round window.

Cochlear nerve Incus Oval Ear canal Malleus Stapes window

Vestibular duct (perilymph)

Movement Cochlear duct of sound (endolymph) waves Tympanic duct (perilymph)

Tympanic Round membrane window

© 2016 Pearson Education, Inc. Anatomy Summary: The Cochlea

• Perilymph in vestibular and tympanic duct – Similar to plasma • Endolymph in cochlear duct – Secreted by epithelial cells – Similar to intracellular fluid • Cochlear duct contains organ of Corti – Hair cell receptors and support cells – Sits on basilar membrane – Partially covered by tectorial membrane, which bends stereocilila on non-neural hair cells

© 2016 Pearson Education, Inc. Figure 10.18-2 The Cochlea

Oval Vestibular Cochlear Organ of window Saccule duct duct Corti Cochlea

Uncoiled Helicotrema

Round Tympanic Basilar window duct membrane

© 2016 Pearson Education, Inc. Figure 10.18-3 The Cochlea

Cochlea

Bony cochlear wall

Vestibular duct

Cochlear duct

Tectorial membrane

Organ of Corti

The cochlear nerve transmits action potentials from Basilar Tympanic the primary auditory membrane duct neurons to cochlear nuclei in the medulla, on their way to the auditory cortex. © 2016 Pearson Education, Inc. Figure 10.18-4 The Cochlea

Bony cochlear wall

Vestibular duct

Cochlear duct

Tectorial membrane

Organ of Corti

The cochlear nerve transmits action potentials from Basilar Tympanic the primary auditory membrane duct neurons to cochlear nuclei in the medulla, on their way to the auditory cortex. © 2016 Pearson Education, Inc. Figure 10.19 Signal transduction in hair cells

At rest: About 10% of the ion Excitation: When the hair cells bend in Inhibition: If the hair cells bend in the channels are open, and a tonic signal one direction, the cell depolarizes, which opposite direction, ion channels close, is sent by the sensory neuron. increases action potential frequency in the cell hyperpolarizes, and sensory the associated sensory neuron. neuron signaling decreases.

Tip link

Stereocilium Some More channels Channels closed. channels open. Less cation entry open. Cation entry hyperpolarizes cell. Hair cell depolarizes cell.

Primary sensory neuron

Action potentials Action potentials increase. No action potentials

mV

Action potentials in primary sensory neuron Time

0

mV

30

Release Release

Membrane potential Excitation opens Inhibition closes of hair cell ion channels. ion channels.

© 2016 Pearson Education, Inc. Auditory Pathways

• Cochlea transforms sound waves into electrical signals • Primary auditory neurons to brain in medulla oblongata • Secondary sensory neurons project to nuclei – Synapse in nuclei in midbrain and thalamus before projecting into auditory cortex • The localization of a sound source requires simultaneous input from both ears.

© 2016 Pearson Education, Inc. Figure 10.20 Sensory coding for pitch

The basilar membrane has variable sensitivity to sound wave frequency along its length.

Low frequency High frequency (low pitch) (high pitch) Basilar membrane

Stiff region near Flexible region round window near helicotrema (distal end)

The frequency of sound waves determines the displacement of the basilar membrane. The location of active hair cells creates a code that the brain translates as information about the pitch of sound.

Eardrum Oval Basilar Helicotrema window membrane

Stapes

3

100 Hz

m) m) 

0 0 10 20 30

3 400 Hz

0 0 10 20 30

3 1600 Hz Relative motion of basilar membrane ( membrane basilarmotionof Relative

0 0 10 20 30 Distance from oval window (mm)

© 2016 Pearson Education, Inc. Figure 10.21 The auditory pathways

Right auditory Left auditory cortex Right Left cortex thalamus thalamus

MIDBRAIN

To cerebellum To cerebellum

Right cochlea Left cochlea

MEDULLA Cochlear branch of Cochlear branch of right vestibulocochlear Cochlear nuclei left vestibulocochlear nerve (VIII) nerve (VIII)

Sound waves

© 2016 Pearson Education, Inc. Hearing Loss

• Conductive – No transmission through either external or middle ear • Central – Damage to neural pathway between ear and cerebral cortex or damage to cortex itself • Sensorineural – Damage to structures of inner ear

© 2016 Pearson Education, Inc.