Principles of Animal Physiology

1. Principles of Animal Physiology Nervous System

2. Principles of Animal Physiology Nervous System • Sensory cells - specialized cells for obtaining information about the environment. • Review • Mechanically gated channels • Voltage-gated channels • Chemically gated channels • Chemotaxis

3. Principles of Animal Physiology Nervous System • Three primary roles of sensors • Exteroreceptors • Detect external signals such as light, chemicals, etc • Somesthetic sensation - from body surface • Special senses - vision, hearing, taste, and smell • Interoreceptors • Detect internal body signals such as blood pressure • Proprioceptors • Detect the animal’s position in space

4. Principles of Animal Physiology Nervous System • Perception - interpretation of the external world as created by the brain from nerve impulses delivered by sensory receptors. • .Our perception of the world is incomplete, why?

5. Principles of Animal Physiology Nervous System • Our perception of the world is incomplete, because: • We (humans) can detect only a limited number of energy forms • We perceive sounds, colors, shapes, textures, smells, tastes, deformations, and temperature • We DO NOT perceive magnetic forces, electrical forces, polarized light waves, or ultraviolet light waves • Information we receive is filtered or modified • At the receptor, brainstem or cortex • The brain can hide or distort the truth

6. Principles of Animal Physiology Nervous System • The brain fills in and add lines to “complete” the picture (story).

7. Principles of Animal Physiology Nervous System

8. Principles of Animal Physiology Nervous System

9. Principles of Animal Physiology Nervous System • Receptor Physiology • Stimulus - change detectable by the body • Modality - form of energy that stimuli take • Receptor - structure that respond to a particular modality • Transduction - conversion from one form of energy to another • Adequate stimulus - modality with the lowest energy that would activate the receptor • Doctrine of specific nerve energies (Johannes Muller) - receptors would only respond to certain stimulus and not to others • Sensation perceived depends on receptor activated, not stimulus

10. Principles of Animal Physiology Nervous System • Categories of receptor by type of energy used • Photoreceptors - light • Mechanoreceptors - mechanical energy • Chemoreceptors - specific chemicals • Thermoreceptors - change in temperature • Nociceptors - pain, noxcious stimuli • Electroreceptors - electrical fields • Magnetoreceptors - magnetic fields

11. Principles of Animal Physiology Nervous System • Uses of information detected by receptors • Used for controlling efferent output • Used as input to the reticular activating system for arousal and consciousness • Gives rise to the animal’s perception of the environment • May be stored for future use

12. Principles of Animal Physiology Nervous System • A receptor may be either: • A modified nerve ending • Local change in membrane permeability • Generator potential • Another cell closely associated with the sensory neuron • Stimulation causes changes in permeability of receptor cell • Receptor potential

13. Principles of Animal Physiology Nervous System • Receptor vs generator potentials

14. Principles of Animal Physiology Nervous System • Receptors vary according to their speed of adaptation • Adaptation - diminished response to sustained stimulus strength • Tonic receptors • Do not adapt at all, or adapt slowly • E.g. Muscle stretch receptors • Phasic receptors • Adapt rapidly • Exhibit “on” “off” responses • E.g. Touch to the skin

15. Principles of Animal Physiology Nervous System • Tonic and phasic receptors

16. Principles of Animal Physiology Nervous System • The Pacinian corpuscle

17. Principles of Animal Physiology Nervous System • Sensory Adaptation • May take place in the PNS or CNS • Receptor may act as a filter • Transducer molecules may be depleted • Enzyme cascade activity may be inhibited • Electrical properties may change • Spike initiation zone may be less sensitive • Adjustments at higher brain centers may occur

18. Principles of Animal Physiology Nervous System • Somatosensory pathway is “labeled” according to modality and location • From receptor to brain perception area (somatosensory cortex) • Receptor • First order neuron (sensory/afferent neuron) • Second order neuron • Third order neuron • And so on • From a specific location to a specific portion of the cortex • From a specific receptor/modality to a specific location on cortex

19. Principles of Animal Physiology Nervous System • Photoreception: Eyes and Vision • It may be the most dominant sense • Uses photopigments • Conversion of light energy to action potentials • From eyespots to pinhole eye to camera eye to compound eye

20. Principles of Animal Physiology Nervous System • Development of invertebrate eye

21. Principles of Animal Physiology Nervous System • The mammalian eye

22. Principles of Animal Physiology Nervous System • Control of light entering the eye

23. Principles of Animal Physiology Nervous System • The Electromagnetic spectrum

24. Principles of Animal Physiology Nervous System • Focusing of diverging light rays • Cornea • Lens

25. Principles of Animal Physiology Nervous System • Focusing on near and distant objects

26. Principles of Animal Physiology Nervous System • Accomodation - ability of lens to adjust strength to focus on both near and distant objects

27. Principles of Animal Physiology Nervous System • Retinal layers

28. Principles of Animal Physiology Nervous System • Photoreceptors

29. Principles of Animal Physiology Nervous System • Photopigments - undergo chemical alternations when activated by light • Consists if opsin, an enzyme and retinene, from vitamin A • Rhodopsin - vertebrate rod photopigment • Provides vision in shades of gray • Porphyropsin - insect rod pigment • 4 cone photopigments - red, green, blue, and ultraviolet • Respond to selective wavelengths • Makes color vision possible

30. Principles of Animal Physiology Nervous System • Phototransduction • Virtually the same for all vertebrate photoreceptors

31. Principles of Animal Physiology Nervous System • The mammalian visual pathway

32. Principles of Animal Physiology Nervous System • Sound waves, ears and hearing • Uses • Early detection of predators, competitors, physical threats, potential prey • Detection of mating calls • Herding

33. Principles of Animal Physiology Nervous System • Sound properties • Compression and rarefaction of molecules • Pitch or tone • Frequency of vibration (20-20,000 Hz) • Ultrasonic > 20,000 cycles per second • Infrasonic < 20 cycles per second • Echolocation - the use of sound echoes to detect objects in the environment • Intensity (loudness) • Amplitude of sound waves • Measured in decibels (dB) • Timbre or quality • Overtones

34. Principles of Animal Physiology Nervous System • Properties of sound

35. Principles of Animal Physiology Nervous System • Anatomy of the mammalian ear

36. Principles of Animal Physiology Nervous System • Middle ear and cochlea

37. Principles of Animal Physiology Nervous System • Transmission of sound waves

38. Principles of Animal Physiology Nervous System • The organ of Corti

39. Principles of Animal Physiology Nervous System • Sound transduction

40. Principles of Animal Physiology Nervous System • End here • Next, the Endocrine System