Physiology II PHL 226Sensory System

How does the central nervous system gets information about the environment?

Title

• Information contained in sensory receptor outputs:

• Duration• Intensity

• Afferent / Efferent nerves!

Fig. 38.2

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olfactory bulb

olfactory epithelium

nasal cavity

olfactory bulb

odor molecules

olfactory tractneuron

a.

b.

frontal lobe ofcerebral hemisphere

odormolecules

olfactory cilia ofolfactory cell

olfactorycell

supportingcell

olfactoryepithelium

sensorynerve fibers

Taste

• Receptors for taste are modified epithelial cell present in taste buds located on the tongue, roof of the mouth and pharynx

• Four primary types of taste receptors : sour, salt, sweet and bitter

• The binding of the receptor to a taste molecule release of neurotransmitter in a synapse with a neuron

• Taste impulses travel through nerves to a gustatory nucleus in the medulla oblongata thalamus gustatory cortex located in the parietal lobe in the mouth area.

Fig. 38.1

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b. Papillae d. One taste bud

epiglottistonsils

taste bud

supporting cell

microvillitaste cellconnective tissue

papillae

sensory nerve fiber taste pore

a. Tongue c. Taste budsb(All): © Omikron/SPL/Photo Researchers, Inc.

10 µm

Hearing

• Sounds are waves of compressed air traveling through space

• Organ of hearing and equilibrium is the inner ear

Fig. 38.10

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

round window

cochlea

earlobe

vestibule

stapes semicircular canals

incus

malleus

Outer ear Middle ear Inner ear

pinna

tympanicmembrane

auditorycanal

auditorytube

cochlearnerve

vestibularnerve

1- The sound waves enter the external auditory canal and trigger vibrations of the tympanic membrane

2- The tympanic membrane induces a vibration of the ossicles

3- The last ossicle, the stapes, transmits amplified vibrations to the oval window

4- The vibrations induce waves in the perilymph of the various inner ear chambers

5- The round window absorbs excess energy and prevent wave reverberation

6- The fluid wave is transduced into an electrical signal by the auditory receptors, the organs of Corti located on the basilar membrane

2 µm

Cochlea cross section

Organ of Corti

tectorial membrane

hair cell

stereocilia

cochlear nerve

oval window

stapes

cochlea

round window

Stereocilia

semicircularcanals

vestibularcanal

cochlearcanal

tympaniccanal

cochlearnerve

basilarmembrane

tympaniccanal

© P. Motta/SPL/Photo Researchers, Inc.

• The hair cells of the organ of Corti transduce fluid wave into an electrical signal

• The energy of the wave causes the basilar and vestibular membrane to move, thus displacing the cilia from the organ of Corti

• The louder the sound, the more the cilia bend, the stronger the signal

• The signal travels through Cochlear nerve nucleus in medulla oblongata thalamus auditory cortex in the temporal lobe

Equilibrium

• Ability to detect head position and movement (or acceleration)

- Change of speed = linear acceleration (utricle and saccule)

- Turning = rotational acceleration (semi-circular canals)

Utricle and saccule

• Sensory cells have cilia extending into a gelatinous material

• Saccule detects backward-frontward movement

• Utricle detects changes relative to gravity

Figure 10.46a–c

Semi-circular canals

• The receptors in the ampulla are hair cells with cilia extruding into a gelatinous mass (cupula)

• When the head rotates, the cupula moves cilia pulled Neurotranmitters (vestibular nerve cerebellum …)

Vision

• In order to see an object:

1- the pattern of the object must fall on the vision receptors (rods and cones in the retina) accommodation

2- the amount of light entering the eye must be regulated (too much light will “bleach out” the signals)

3- the energy from the waves of photons must be transduced into electrical signals

4- The brain must receive and interpret the signals

Accommodation• It is the process of adjusting the shape of the lens so that the external

image fall exactly on the retina

Figure 10.25

Accommodation

• Object is far the lens flattens• Object is near the lens rounds

Accommodation abnormalities

• Myopia

• Hyperopia

• Astigmatism: the cornea is irregular irregular pattern of vision

• Presbyopia: stiffening of the lens occurring with aging increased difficulty with near vision

Figure 10.27a–b

Figure 10.27c

Regulation of the amount of light entering the eye

• The iris controls the amount of light entering the eye cavities

• The contraction of radial or circular smooth muscles located within the iris permit changes in the pupil diameter

Figure 10.28a

Rods – are sensitive to light and black and white – can’t distinguish colours

Cones – allow for colour vision

cell body

cone cell

rod cell

nucleus

inner segment

outer segment

synaptic endings

membrane of disk

retinal

opsin

synapticvesicles

ion channelsin plasmamembrane

lightrays

membraneof disk

Rhodopsin molecule(opsin + retinal)

3 types of cones – red, blue, green – colour blindness usually results from a deficiency in one or more of the cones (red/green colourblindness is common)

COLOUR BLINDNESS

Colour blindness results when there is a deficiency in one or more of the cone colours (ie red/green deficiency). The patient will have difficulty differentiating between red and green colours and tend to see them all as something in between.

Colour blindness is a genetic condition and affects boys much more frequently than girls, because it is a disorder carried on the “X” chromosome. Females are XX and therefore need 2 defective Xs to have colour blindness. If a female has 1 defective X chromosome, they are a carrier. Males have XY, therefore only 1 X chromosome needs to be affected to have colour blindness.

Try this simple colour blindness test to see whether or not you have this deficiency.

This is the CONTROL