Sensory Systems The difference in perception between a

Sensory Systems

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. 1. False. My 6 th sense is telling me that this is a function of how fast the information is received by the brain. 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. 2. 3. 4. 5. 6. 7. Differentiate between sensation and perception Describe the sequence of events in general receptor function Describe how and where integration of sensory information occurs for perception and for simple behavioral responses Compare the structure and function of various receptor types (i. e. classification of receptors) Compare and contrast structure and function in the eye cups of Planaria, the compound eyes of insects, and the single-lens eyes of mollusks. Compare the systems for hearing and equilibrium in various animals Describe how chemoreceptors may function in taste and smell

Basic Function Sequence of Events in a Biological Receptor Stimulus Reception Amplification Receptor Protein Activated Enzyme Cascade (in some cases) Receptor Ion Channels affected (deplorization or hyperpolarization) Receptor Potential (graded) Transduction Change in Neurotransmitter release from Receptor Cell Transmission p. 1053 Integration Modulated Impulse Frequency in Receptor Cell Axon to CNS Modulated Impulse Frequency in Second Order Neuron to CNS

“Decoding” Sensory Information Qualitative • 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

Receptor Classification All receptors are specialized to act as transducers; transforming one type of energy into an electrical potential. Pacinian corpuscle (pressure receptor) This means that in all receptors, energy transduction results in opening or closing _____. Shown are two types of mechanoreceptors. How are their functions different? 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 Classification Photoreceptors, 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), light triggers a receptor potential that is hyperpolarization, instead of the usual depolarization. The sensory pathway is thus stimulated by a reduction in the release of inhibitory neurotransmitter. 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 separate hot and cold receptors?

Population Code Integration begins at the level of the receptor, and continues at each synapse in the sensory pathway. Has a receptor potential led to an action potential in the first (primary) sensory neuron(s)? What type of receptor has been stimulated? How many? In this example, how would the two stimuli be perceived: as one point or two points? Is the neurotransmitter between first order and second order sensory neurons excitatory or inhibitory?

Population Code (continued) Convergence of primary sensory neurons onto a single sensory neuron reduces 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: Frequency Code Weak stretch causes low impulse frequency on neuron leaving receptor. Strong stretch causes high impulse frequency on neuron leaving receptor. Membrane potential Time

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 adapt slowly 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 compound eyes is that the area of best focus is not limited to just one area (like in mammalian eyes). Explain why. The visual sensory system of mammals has a refractory period which is almost 7 x longer than that of animals with compound eyes. What does this mean in terms of visual perception? p. 1037 Which animal groups possess compound eyes?

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 light on photoreceptor cells? What is the difference in function between the pupil and the lens? http: //www. cas. vanderbilt. edu/bsci 111 b/eye/supplemental. htm Why are there pigments in photoreceptors?

Vertebrate Single-lens Eye p. 1038

Equilibrium Statocyst 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?

Hearing While statocysts may be sensitive to lowfrequency sound energy, most invertebrates 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 the function of body hairs to the function of the tympanic membrane. How is reception of sound energy similar to the function of sensory systems for balance?

Human Ear p. 1034