Sensory Systems

1. False. My 6th sense is telling me that this is a

function of how fast the information is received

by the brain.

The difference in perception between a strong smell and a weak smell is due to differences in the strength of the action potential sent from the receptor.

3. False. My spidy-sense interprets sensory

information based on how large the action potential is.

2. False. Action potentials are always the same strength, so the difference must be due to how many smell receptors

are stimulated.

4. When I smell fear, my brain is combining information from more than one receptor type. (I don’t know what I’m

talking about.)

Learning Objectives (3/9/09)

1. Differentiate between sensation and perception2. Describe the sequence of events in general receptor

function3. Describe how and where integration of sensory

information occurs for perception and for simple behavioral responses

4. Compare the structure and function of various receptor types (i.e. classification of receptors)

5. Compare and contrast structure and function in the eye cups of Planaria, the compound eyes of insects, and the single-lens eyes of mollusks.

6. Compare the systems for hearing and equilibrium in various animals

7. Describe how chemoreceptors may function in taste and smell

Sequence of Events in a Biological ReceptorStimulus

Receptor Protein Activated

Enzyme Cascade (in some cases)

Receptor Ion Channels affected (deplorization or hyperpolarization)

Receptor Potential (graded)

Modulated Impulse Frequency in Second

Order Neuron to CNS

Basic Function

Reception

Amplification

Transduction

TransmissionModulated Impulse

Frequency in Receptor Cell Axon to CNS

Change in Neurotransmitter release from Receptor Cell

p. 1053Integration

“Decoding” Sensory InformationQualitative

• What kind of stimulus…i.e. what kind of receptor?• What is the destination for the resulting nerve

impulses?

Quantitative • How “important” is the stimulus?

The population code= number of similar neurons activated

The frequency code= number of impulses per unit time

All receptors are specialized toact as transducers; transformingone type of energy into anelectrical potential.

This means that in all receptors,energy transduction results inopening or closing __________.

Shown are two types ofmechanoreceptors. How aretheir functions different?

Receptor Classification

Pacinian corpuscle(pressure receptor)

Hair cell receptor

Receptor Classification

Pain receptors (nociceptors) are specialized sensory neurons that may respond to a variety of noxious stimuli. This composite taste cell represents an example of a chemoreceptor.

Review the variety of signal transduction pathways employed.

Receptor ClassificationPhotoreceptors, like chemoreceptors often employ G-proteins to regulate ion

channels, and thus may respond to the direction of change as well as magnitude of the stimulus.

In vertebrate photoreceptors(rods and cones), lighttriggers a receptor potentialthat is hyperpolarization,instead of the usualdepolarization.

The sensory pathway is thusstimulated by a reduction inthe release of inhibitoryneurotransmitter.

Is this a level of integration?

Pit Vipers detect infrared radiation

(heat).

Receptor Classification

Thermoreceptors are specialized to respond to the physical stress of temperatures either above or below the animal’s normal body temperature.

It is unclear whether these receptors are more like mechanoreceptors, or operate by some other mechanism.

Why do you think that there are separatehot and cold receptors?

Population CodeIntegration begins at the level of the receptor, and continues

at each synapse in the sensory pathway.Has a receptor potential led toan action potential in the first(primary) sensory neuron(s)?

What type of receptor has beenstimulated? How many?

In this example, how would thetwo stimuli be perceived:as one point or two points?

Is the neurotransmitter betweenfirst order and second ordersensory neurons excitatory orinhibitory?

Population Code (continued)

Convergence of primary sensory neurons onto a single sensory neuronreduces sensory acuity.

How many receptors have been stimulated? (How is the sensation different than in the previous figure?)

How many first order neurons are conducting action potentials?

How is perception changed by this convergence?

Muscle Stretch Receptors:Weak stretch causes low impulse frequency on neuron leaving receptor.

Strong stretch causes high impulse frequency on neuron leaving receptor.

Time

Membrane potential

Frequency Code

Sensory Adaptation is one form of Integration

Phasic receptors quickly adapt. The frequency of action potentials diminishes or stops if the stimulus is unchanging.

Tonic receptors adaptslowly or not at all.

Most exteroreceptors (receptors that monitor the external environment) are _________receptors.Why?

Photoreceptors in Invertebrates

Explain the difference between the function of screening pigment in this flatworm and visual pigments. Describe the integration of information from these two receptor organs.

Image-forming Eyes in Invertebrates

One advantage to compoundeyes is that the area of bestfocus is not limited to justone area (like in mammalianeyes). Explain why.

The visual sensory system ofmammals has a refractoryperiod which is almost 7xlonger than that of animalswith compound eyes. What does this mean in terms of visual perception?

Which animal groups possess compound eyes?

p. 1037

The number of ommatidia per eye varies from species to species with only a few in ants, to 800 in fruit flies, to as many as 10,000 ommatidia in the compound eye of the horsefly. The compound eye provides information about patterns in the environment and is very good at detecting movement. The world looks different to an insect because of the compound nature of its eyes, and also because it is sensitive to different wavelengths of light than our eyes are.

Invertebrate Single-lens Eye

How do these animals focus lighton photoreceptor cells?

What is the difference in functionbetween the pupil and the lens?

http://www.cas.vanderbilt.edu/bsci111b/eye/supplemental.htm

Why are there pigments in photoreceptors?

Vertebrate Single-lens Eye

p. 1038

EquilibriumStatocyst of an invertebrate: Lateral line system in fish:

What are the common structures among all receptor systems for equilibrium in animals?

The Vestibuluar Apparatus in Mammals

What other sensory systems are important in the maintenance of balance and the coordination of skeletal muscle contraction?

HearingWhile statocysts may be sensitive to low-frequency sound energy, mostinvertebrates live in a “silent” world. Only crustaceans, insects, and spiders have developed true sound-receptor organs.

Which animal groups have a tympanic membrane associated with their hearing apparatus?

Compare and contrast thefunction of body hairs to the function of the tympanic membrane.

How is reception of soundenergy similar to thefunction of sensory systems for balance?

Human Ear

p. 1034