LS 2 Lec 9 Sensory

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Life Sciences 2

Sensory Systems

Chapter 41

Dr. Joseph Esdin

Sensory Cells

Sensory cells transduce physical or

chemical stimuli into action potentials

Receptor cells

Modified neurons


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Types of Receptors

Photoreceptors

Mechanoreceptors

Chemoreceptors

Thermoreceptors

Nociceptors

Electroreceptors

Magnetoreceptors

Mechanoreceptors & Sound

Sound is the vibration of air molecules

Waves of vibrations can have

High amplitude (loudness)

Frequency (pitch)


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Anatomy of the EarOuter Middle Inner

Pinna

Auditory canal

Tympanic membrane

Oval windowRound window

Cochlea

Auditory nerve

MalleusIncus

Stapes

How Is Sound Transmitted?

Vibration of air molecules goes through

the pinna, passing through the external

auditory canal

The waves then vibrate the tympanic

membrane which causes the three

ossicles to move


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How Is Sound Transmitted?

The ossicles cause the oval window to

vibrate

This leads to stimulation of hair cells

inside the cochlea

The Cochlea

Cochlea

Auditory nerve


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The Cochlea

Auditory nerve

Scala

vestibuli

Cochlear duct

(endolymph)

Scala

Tympani

Organ of Corti

Organ of Corti

Hair cells Tectorial membrane

Basilar membrane AxonsTo auditory nerve


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Hair CellStereocilia Kinocilium

Sensory neuron

Stretch gated channels

Hair Cell

Hair cellBasilar membrane

Tectorial membrane

Cochlear nerve

Stereocilia


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Hair Cells At Rest


Protein bridgeK+

Ca2+

Voltage gatedcalcium

channels

K+

K+

NT

K+

Hair Cells Depolarized


Protein bridge

K+

Ca2+

Voltage gatedcalcium

channels

K+

K+

NT

K+

Ca2+

Ca2+


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Hair Cells

Movement of the stereocilia towards the

kinocilium activates the stretch activated

channels

Movement of the stereocilia away from

the kinocilium closes the stretch

activated channels

Neural Pathway of Hearing

Cochlear nerve fibers synapse on

neurons in the cochlear nuclei in the

medulla oblongata

The signal is then sent to the thalamus

From the thalamus, the information

travels to the auditory cortex of thetemporal lobe


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The Eyes

Composed of an optical portion

Focus the image on sensory cells

Transform the image to the brain

through series of action potential

Have receptors that are sensitive to light

Layers of the Eyes

Fibrous

VascularNeural


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Fibrous Layers

Cornea

Sclera

Vascular Layer

Choroid

Zonular fibers

Ciliary muscles

Iris

Pupil


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Vascular Layer

Choroid

Pigmented layer that contain blood vessels

Ciliary muscles

Zonular fibers

Hold the lens in place

Iris

Accommodation

The ciliary muscles allow objects to be

focused on the retina no matter how

near or distant they are

The lens can change shape


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AccommodationCiliary muscles relaxed

Ciliary muscles contracted

Lens flat to focus distant objects

Lens thick to focus near objects

Zonular fibers are pulled

Zonular fibers are loose

Iris

Dim light

Bright light

Radial smooth muscles

Circular smooth muscles

Pupil

radial smooth musclescontract, pupil dilates

circular smooth musclescontract, pupil is constricts


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Neural Layer

Retina

Retina

The retina contains photoreceptors to

receive the light and send it to the brain

through the optic nerve

Contains the fovea centralis (high visual

acuity)


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Retina

Have different types of cells

Ganglion cells

Amacrine

Bipolar

Horizontal

Photoreceptors (rods and cones)

Retina

Light

Ganglion cells

Amacrine

Bipolarcells

Horizontal Rod

Cones


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Photoreceptor

Rods

Sensitive to light

Respond to low illumination

Cones

Less sensitive to light

Respond to high illumination

Both types of photoreceptors containpigments that absorb light

Pigments

Rods

Rhodopsin

Cones

S, M, and L pigments

Photopsin

These proteins contain a pigment called________


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Rods in the DarkcGMP levels are high

Na+channels are open

Na+influx causes depolarization

Ca2+channels open

Ca2+Influx occurs

NT release causes graded

potential in bipolar cells

Rods

Bipolar cells

Na+

K+

Ca2+

Rods

Membrane

Rhodopsin

Retinal

Transducin

Phosphodiesterase! " # !

cGMP Breakdown


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Rods When Exposed to Light

Rods

Bipolar cells

When cGMP levels are low

Na+channels are closed

Hyperpolarization occurs

No NT release

No graded potential

Neural Pathway of Vision

Nasal retina

Temporal retina

Optic nerve

Visual cortex

Optic chiasm

Optic tract

Left visual field Right visual field

Binocular vision


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Neural Pathway of Vision

The two optic nerves meet to form theoptic chiasm

Some axons cross to the opposite sideof the brain forming optic tracts

Fibers pass to the thalamus

Signals are sent from the thalamus to

the visual cortex

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LS 2 Lec 9 Sensory