Special Senses Special sensory receptors Distinct, localized - - PowerPoint PPT Presentation

Special Senses

• Special sensory receptors

– Distinct, localized receptor cells in head

• Vision - 70% of body's sensory receptors

in eye

• Taste
• Smell
• Hearing
• Equilibrium

The Eye and Accessory Structures

The Lacrimal Apparatus

Sense of Vision

Ora serrata Ciliary body Ciliary zonule (suspensory ligament) Cornea Pupil Anterior pole Anterior segment (contains aqueous humor) Lens Scleral venous sinus Posterior segment (contains vitreous humor) Diagrammatic view. The vitreous humor is illustrated only in the bottom part of the eyeball. Sclera Choroid Retina Macula lutea Fovea centralis Posterior pole Optic nerve Central artery and vein of the retina Optic disc (blind spot) Iris

Circulation of Aqueous Humor

Inner Layer: Retina

• Delicate two-layered membrane

– Outer Pigmented layer

• Absorbs light and prevents its scattering
• Phagocytize photoreceptor cell fragments
• Stores vitamin A

– Inner Neural layer

• Transparent
• Composed of three main types of neurons

– Photoreceptors, bipolar cells, ganglion cells

• Signals spread from photoreceptors to bipolar cells to

ganglion cells

• Ganglion cell axons exit eye as optic nerve

Figure 15.6c Microscopic anatomy of the retina.

Photomicrograph of retina Nuclei of ganglion cells Outer segments

• f rods and cones

Choroid Axons of ganglion cells Nuclei of bipolar cells Nuclei of rods and cones Pigmented layer of retina

Figure 15.15a Photoreceptors of the retina.

Process of bipolar cell Synaptic terminals Rod cell body Inner fibers Nuclei Cone cell body Mitochondria Connecting cilia Outer fiber Apical microvillus Discs containing visual pigments Discs being phagocytized Melanin granules Pigment cell nucleus Basal lamina (border with choroid)

Inner segment

Pigmented layer Outer segment

The outer segments

• f rods and cones

are embedded in the pigmented layer of the retina.

Rod cell body

Chemistry Of Visual Pigments

• Retinal

– Light-absorbing molecule that combines with

• ne of four proteins (opsins) to form visual

pigments – Synthesized from vitamin A – Retinal isomers: 11-cis-retinal (bent form) and all-trans-retinal (straight form)

• Bent form → straight form when pigment absorbs

light

• Conversion of bent to straight initiates reactions →

electrical impulses along optic nerve

Figure 15.18 Signal transmission in the retina (1 of 2). Slide 1

In the dark cGMP-gated channels

• pen, allowing cation influx.

Photoreceptor depolarizes. 1 Voltage-gated Ca2+ channels open in synaptic terminals. Neurotransmitter is released continuously. Neurotransmitter causes IPSPs in bipolar cell. Hyperpolarization results. Hyperpolarization closes voltage-gated Ca2+ channels, inhibiting neurotransmitter release. No EPSPs occur in ganglion cell. No action potentials occur along the optic nerve. Photoreceptor cell (rod) Bipolar Cell Ganglion cell Ca2+ −40 mV −40 mV 2 3 4 5 6 7 Ca2+ Na+

Figure 15.18 Signal transmission in the retina. (2 of 2). Slide 1

−70 mV No neurotransmitter is released. Depolarization opens voltage-gated Ca2+ channels; neurotransmitter is released. EPSPs occur in ganglion cell. Action potentials propagate along the

• ptic nerve.

cGMP-gated channels close, so cation influx

• stops. Photoreceptor

hyperpolarizes. Lack of IPSPs in bipolar cell results in depolarization. Voltage-gated Ca2+ channels close in synaptic terminals. 1 Photoreceptor cell (rod) Bipolar Cell Ganglion cell In the light Light Ca2+ −70 mV 2 3 4 5 6 7 Below, we look at a tiny column of retina. The outer segment of the rod, closest to the back of the eye and farthest from the incoming light, is at the top. Light

Figure 15.15b Photoreceptors of the retina.

Rod discs Rhodopsin, the visual pigment in rods, is embedded in the membrane that forms discs in the outer segment. Visual pigment consists of

• Retinal
• Opsin

Rhodopsin Dark Light 2H+ 2H+

11-cis-retinal

Vitamin A Oxidation Reduction 11-cis-retinal

All-trans- retinal

All-trans-retinal

Opsin and

Figure 15.17 Events of phototransduction. Slide 6 Recall from Chapter 3 that G protein signaling mechanisms are like a molecular relay race. Retinal absorbs light and changes shape. Visual pigment activates. Receptor G protein Enzyme 2nd messenger Visual pigment 1 Light 11-cis-retinal Transducin (a G protein) All-trans-retinal 2 3 Visual pigment activates transducin (G protein). Transducin activates phosphodiesteras e (PDE). 4 5 PDE converts cGMP into GMP, causing cGMP levels to fall. As cGMP levels fall, cGMP-gated cation channels close, resulting in hyperpolarization. cGMP-gated cation channel

• pen in

dark cGMP-gated cation channel closed in light Phosphodiesterase (PDE) Light (1st messenger)

Visual Pathway to the Brain and Visual Fields, Inferior View

Olfactory Epithelium and the Sense of Smell

• Olfactory epithelium in roof of nasal

cavity

– Covers superior nasal conchae – Contains olfactory sensory neurons

• Bipolar neurons with radiating olfactory cilia
• Supporting cells surround and cushion olfactory

receptor cells

– Olfactory stem cells lie at base of epithelium

• Bundles of nonmyelinated axons of
• lfactory receptor cells form olfactory

nerve (cranial nerve I)

Figure 15.20a Olfactory receptors.

Olfactory epithelium Olfactory tract Olfactory bulb Nasal conchae Route of inhaled air

Figure 15.20b Olfactory receptors.

Olfactory tract Olfactory gland Olfactory epithelium Mucus Mitral cell (output cell) Olfactory bulb Cribriform plate

• f ethmoid bone

Filaments of

• lfactory nerve

Lamina propria connective tissue Olfactory stem cell Olfactory sensory neuron Dendrite Olfactory cilia Route of inhaled air containing odor molecules Glomeruli Olfactory axon Supporting cell

Figure 15.21 Olfactory transduction process.

cAMP opens a cation channel, allowing Na+ and Ca2+ influx and causing depolarization. Adenylate cyclase converts ATP to cAMP. G protein activates adenylate cyclase. Receptor activates G protein (Golf).

Odorant G protein (Golf) Adenylate cyclase

Receptor

cAMP cAMP Open cAMP-gated cation channel GDP

Odorant binds to its receptor. 2

Slide 1

1 3 4 5

Taste Buds and the Sense of Taste

• Receptor organs are taste buds

– Most of 10,000 taste buds on tongue papillae

• On tops of fungiform papillae
• On side walls of foliate and vallate papillae

– Few on soft palate, cheeks, pharynx, epiglottis

Figure 15.22a Location and structure of taste buds on the tongue.

Epiglottis Palatine tonsil Lingual tonsil Foliate papillae Fungiform papillae Taste buds are associated with fungiform, foliate, and vallate papillae.

To taste, chemicals must

– Be dissolved in saliva – Diffuse into taste pore – Contact gustatory hairs

Location and Structure of Taste Buds on the Tongue

Figure 15.22c Location and structure of taste buds on the tongue.

Gustatory hair Connective tissue Taste fibers

• f cranial

nerve Basal epithelial cells Gustatory epithelial cells Taste pore Stratified squamous epithelium

• f tongue

Enlarged view of a taste bud (210x).

Basic Taste Sensations

• There are five basic taste sensations
• 1. Sweet—sugars, saccharin, alcohol, some

amino acids, some lead salts

• 2. Sour—hydrogen ions in solution
• 3. Salty—metal ions (inorganic salts)
• 4. Bitter—alkaloids such as quinine and

nicotine; aspirin

• 5. Umami—amino acids glutamate and

aspartate

Basic Taste Sensations

• Possible sixth taste

– Growing evidence humans can taste long- chain fatty acids from lipids – Perhaps explain liking of fatty foods

• Taste likes/dislikes have homeostatic

value

– Guide intake of beneficial and potentially harmful substances

The Gustatory Pathway

The Ear: Hearing and Balance Three major areas of ear

• 1. External (outer) ear – hearing only
• 2. Middle ear (tympanic cavity) – hearing only
• 3. Internal (inner) ear – hearing and

equilibrium

• Receptors for hearing and balance respond to

separate stimuli

• Are activated independently

Structure of the Ear (1 of 2)

Figure 15.24a Structure of the ear.

Structure of the Ear (2 of 2)

Figure 15.24b Structure of the ear.

The Three Auditory Ossicles and Associated Skeletal Muscles

Figure 15.25 The three auditory ossicles and associated skeletal muscles.

Membranous Labyrinth of the Internal Ear

Anatomy of the Cochlea

Anatomy of the Cochlea

Anatomy of the Cochlea

Transmission of Sound to the Internal Ear

• Sound waves vibrate tympanic membrane
• Ossicles vibrate and amplify pressure at
• val window
• Cochlear fluid set into wave motion
• Pressure waves move through perilymph
• f scala vestibuli

Transmission of Sound to the Internal Ear

• Waves with frequencies below threshold of

hearing travel through helicotrema and scali tympani to round window

• Sounds in hearing range go through

cochlear duct, vibrating basilar membrane at specific location, according to frequency

• f sound

Pathway of Sound Waves

• HIGH frequency sound

detected here LOW frequency sound detected here

Excitation of Hair Cells in the Spiral Organ

• Stereocilia

– Protrude into endolymph – Longest enmeshed in gel-like tectorial membrane – Sound bends these toward kinocilium

• Opens mechanically gated ion channels
• Inward K+ and Ca2+ current causes graded

potential and release of neurotransmitter glutamate

• Cochlear fibers transmit impulses to brain

Anatomy of the Cochlea

Bending of Stereocilia Opens or Closes Mechanically Gated Ion Channels in Hair Cells

Figure 15.32 Pivoting of stereocilia (hairs) opens or closes mechanically gated ion channels in hair cells.

Generating Signals

Equilibrium and Orientation

• Vestibular apparatus

– Equilibrium receptors in semicircular canals and vestibule – Vestibular receptors monitor static equilibrium – Semicircular canal receptors monitor dynamic equilibrium

Vestibule

• Central egg-shaped cavity of bony

labyrinth

• Contains two membranous sacs
• 1. Saccule is continuous with cochlear duct
• 2. Utricle is continuous with semicircular

canals

• These sacs

– House equilibrium receptor regions (maculae) – Respond to gravity and changes in position

• f head

Figure 15.33 Structure of a macula.

Macula of utricle Macula of saccule Stereocilia Kinocilium Otoliths Otolith membrane Hair bundle Hair cells Supporting cells Vestibular nerve fibers

Activating Maculae Receptors

• Hair cells release neurotransmitter

continuously

– Movement modifies amount they release

• Bending of hairs in direction of kinocilia

– Depolarizes hair cells – Increases amount of neurotransmitter release – More impulses travel up vestibular nerve to brain

Activating Maculae Receptors

• Bending away from kinocilium

– Hyperpolarizes receptors – Less neurotransmitter released – Reduces rate of impulse generation

• Thus brain informed of changing position
• f head

Structure and Function of a Macula

Semicircular Canals

• Three canals (anterior, lateral, and

posterior) that each define ⅔ circle

– Lie in three planes of space

• Membranous semicircular ducts line each

canal and communicate with utricle

• Ampulla of each canal houses equilibrium

receptor region called the crista ampullaris

– Receptors respond to angular (rotational) movements of the head

The Crista Ampullares (Crista)

• Sensory receptor for rotational

acceleration

– One in ampulla of each semicircular canal – Major stimuli are rotational movements

• Each crista has supporting cells and hair

cells that extend into gel-like mass called ampullary cupula

• Dendrites of vestibular nerve fibers

encircle base of hair cells

Figure 15.35a–b Location, structure, and function of a crista ampullaris in the internal ear.

Crista ampullaris Membranous labyrinth Crista ampullaris Fibers of vestibular nerve Hair bundle (kinocilium plus stereocilia) Hair cell Supporting cell Endolymph Ampullary cupula Anatomy of a crista ampullaris in a semicircular canal Scanning electron micrograph

• f a crista ampullaris (200x)

Section of ampulla, filled with endolymph Cupula Fibers of vestibular nerve Flow of endolymph At rest, the cupula stands upright. During rotational acceleration, endolymph moves inside the semicircular canals in the direction

• pposite the rotation (it lags behind due

to inertia). Endolymph flow bends the cupula and excites the hair cells. As rotational movement slows, endolymph keeps moving in the direction of rotation. Endolymph flow bends the cupula in the opposite direction from acceleration and inhibits the hair cells. Movement of the ampullary cupula during rotational acceleration and deceleration