Vander’s Human Physiology

The Mechanisms of Body FunctionTenth Edition

Chapter 7

by

Widmaier • Raff • Strang© The McGraw-Hill Companies, Inc.

Figures and tables from the book, with additional comments by: John J. Lepri, Ph. D.,

The University of North Carolina at Greensboro

Sensory transduction depends on neural activity being

specifically influenced by particular stimulus characteristics.

Introduction for Chapter 7Sensory Physiology

Sensory systems covered in this chapter:

• Somatosensation

• Vision

• Audition

• Gustation

• Olfaction

Figure 7-1

Sensory receptors are either specialized endings of afferent neurons or separate cells that signal the afferent neuron.

Produces variable patterns of

action potentialsin the CNS

Produces variable receptor potentials

Figure 7-2

Variable stimulusintensity

A simplified model showing a possiblerelationship between the intensity of peripheral stimuli and CNS activity.

Figure 7-3

As presented here, adaptation is a reduction in response (the number of action potentials) in response to the continuous presence of a stimulus; this mechanism helps prevent sensory overload.

Figure 7-4

Where should the cell body be located?

Activity in a sensory unit is altered by peripheral events and communicates information into the CNS.

Figure 7-5

The number of action potentials generated by ahypothetical, pressure-sensitive, sensory afferentneuron, as shown here, is directly proportional to stimulus intensity.

Figure 7-6

Sensory afferent neuron (a) has a finer, more spatially limited receptive field than sensory afferent neuron (b).

Figure 7-7

Weak stimulus at A =Strong stimulus at B[i.e. location & intensity are ambiguous]

Stimulus A occurs in an area of the receptive field that hasgreater density of nerve endings than the area where Stimulus Bis delivered, so it is predicted that Stimulus A will generatea greater number of action potentials than will Stimulus B.

Figure 7-8

Overlapping stimulation between neighboring receptive fieldsprovides general information about the location of a stimulus.

Central Nervous System

Figure 7-9Because neuron B is firing at thehighest freq.,it inhibits Aand C viainhibitorypathways toa greater extent thanA and C

Lateral inhibition “sharpens contrast” in the pattern of action potentials received by the CNS, allowing a finer resolution of stimulus location.

inhibit B.

Lateral inhibition allows the CNS to more accurately locate the source of stimulation, which can help guidep gnecessary or beneficial responses.

Figure 7-11

The offResponseIs shown.

e.g. touch

Different sensory units vary in their speed of adaptation to stimuli.

e.g. pain

Figure 7-12

e.g.Battlefieldanalgesia

CNS activity can screen out certain types of sensory information by inhibiting neurons in the afferent pathway.

e.g.Cochlear response

to loud noise

Divergence of sensory

input to the CNS

Convergence of sensory

input to the CNS

Figure 7-13

e.g. from optic nerve to cortex for image processing, and to

e.g. from visual system and somatosensory system to parietal p g,

brainstem for eye movements

cortex, for eye-hand co-ordination

Neural processingof sensory input occurs at specialized locations

Figure 7-14

locations in the brain.

Non-specific pathwaysprovide background information about touch and temperaturefrom the periphery.

Specific pathways deliver information about location-specific changesin touch and temperature in the periphery.

Figure 7-15

What,Where,How

Something’shappening!

How much

What can we NOT sense?

Figure 7-16

Specific types of mechanosensory stimulation are transduced by specific types of receptor cells.

Painful stimuli evoke protective reflexes as well as sensations & emotions

Painful stimuli evoke CNS responses.

Figure 7-17

Descendinganalgesic system.

From: Payne R, Allen RR (1998) Pain. Scientific American Medicine

Fig. 7-18

Regions of the body surface where we typically perceive referred pain from visceral organs

Figure 7-19

RIGHT spinal lesion:Loss of touch & position

Afferent pain pathways differ from afferent “non-pain” sensory pathways.

RIGHT spinal lesion:Loss of pain & temperatureon the LEFT below the lesion

pon the RIGHT below the lesion

Figure 7-20

Somatosensory areas in the cortex of the brainare anatomically organized in relation to the source of information, with larger areasdedicated to parts of the body that processfine discriminations.

These wavelengths constitute the stimuli transduced by the visual system.

Light has wave-like properties.

Vitreous humor

Visual transductionoccurs on the retina

Figure 7-22

is a clear filtrateof the blood.

the retina,and is based on the imagesfocused there by the cornea and the lens.

The retina is an extension of the brain, directly visible with an ophthalmoscope

Figure 7-23b

Images formed on the retina are upside down andare only a small fraction of the object’s actual size.

Corrective glasses and contact lensesalter the location of image focusto correct for

Figure 7-26

to correct for problems of eyeball length (and lost elasticity in the lens of the eye).

Figure 7-24

The contraction state of the ciliary muscles determines theamount of tension that the zonular fibers exert on the lens:

contracted = lower tension and more rounded lens,relaxed = higher tension and more flattened lens.

Figure 7-32

Movements of the eyes are tightly regulated by skeletal muscles whose neural controls are influenced by head position and operated inways that assure convergent image formation.

Light penetrationpast theganglion,bipolar, and othercells occursprior to transduction

Figure 7-23

transduction by the

androds

cones

Figure 7-30

Each of the three types of cones has a photopigmentthat absorbs light in a specific range of wavelengths.In dim light, only rods respond.

In the dark, production of cGMP opens cation channels; in the light, activation of photopigment decreases cGMP & closes cation channels

9-16: Comparison of events triggered by activation of (a) a G-protein-coupled neurotransmitter receptor & (b) a photopigment.

9-17: Hyperpolarization of photoreceptors in response to light. Photoreceptors are continuously depolarized in the dark because of an inward Na+ current (a). Light activates an enzyme that destroys cGMP, shutting of the Na+ current & hyperolarizing the cell.

Figure 7-31

Patterns of neural activity in a color-sensitive ganglion cell that is affected by three different “colors” of light.

This is the neuroanatomicalneuroanatomicalpathway responsiblefor processingvisual information;

the visual associationcortex is responsiblefor visual illusions.

10-3: Ganglion cells that receive stimuli from the right visual hemifield project axons into the left optic tract, and vise versa.

10-4: Pathway for conscious visual perception.

10-5: Deficits from lesions in the pathway.(a) L optic nerve cut: L eye blind, R eye sees some of L

visual field.(b) L optic tract cut: R visual field of both eyes lost.(c) Optic chiasm split: both eyes lose peripheral

vision.

Figure 7-33

# cycles/sec. = frequency = pitch

Sound waves are the zones of atmospheric rarefaction andcompression that initiate the sequence leading to audition.

Amplitude = loudness

Figure 7-34

The pinna and external auditory canal focus sound waves on the tympanic membrane, which rocks the malleus, incus, and stapes, causing ripples in the cochlear fluid and auditory transduction.

Figure 7-35

The vibrations in the stapes are transmitted to the oval window,which sets off the ripples in the cochlear fluid.

Force per unit area multiplied ~20x from tympanic membrane to oval window

Figure 7-36

Ripples in the cochlear fluid are transmitted to movements of the basilar membrane.

11-10: (a) High frequencies dissipate near the narrow, stiff base of the basilar membrane. (b) Low frequencies propagate to the apex. (c) There is a place code on the basilar membrane where each frequency produces a maximal deflection.

Figure 7-37

Ripples in theRipples in the cochlear fluidcause the rasping of the tectorial membraneacross the hair cells,altering ion movementsinto those cells, andincreasing neurotransmitter release.

11-15: (a) K+ channels at the tips of the stereocilia open when the tip links joining them are stretched. (b) K+ entry depolarizes the cell, which opens Ca2+ channels. Ca2+ entry causes vesicles to release neurotransmitter, which diffuses to the postsynaptic spiral ganglion neurite.

Figure 7-39

The vestibular system detects changes in the motion and position of the head by the use of fluid-filled tubes near each ear. This system isconnected to the cochlear duct.

The flat sheets indicatethat the plane of each of the three semicircular canals

Figure 7-40

are perpendicular toone another.

Figure 7-41

The position of the cupula is such that fluid movements will rasp the hair cells against the ampulla wall, altering ion movements and neurotransmitter release by the hair cells.

Figure 7-42

Bending of stereocilia in opposite directions has opposite effects on their membrane potentials.

Otolith organ: utricle.a. Upright position, hair cells not bentb. Head tilts forward, gravity bends hair cells

8-2: Tongue map. The centre lacks taste buds& is relatively insensitive to taste.

Gustatory transduction involves the interaction of tastant molecules in saliva with the receptor cells in the taste buds on the papillae of the tongue; these receptor cells undergoonly graded potentials during gustatory transduction.

8-4: Responses in taste cells & gustatory axons. (a) Each taste cell has different sensitivity to salt (NaCl), bitter (quinine), sour (HCl) & sweet (sucrose). (b) The sensitivity is converted into action potentials in each axon.

Figure 7-45

Olfactory transduction involves the interaction of odorant molecules in nasal mucus with receptors on the ciliated endings of olfactory neurons.

Olfactory neurons rarely persist more than two months;stem cells undergo mitosis and differentiation to assure that there is no loss of smell ability.

R & G cone pigment genes located onX chromosome, so R-G color blindness more common in men (1/12) than women (1/200)

A typical pedigree of inheritance of red-green color blindness shows the pattern of transmission.

The End.