General Biology2 Summers

Respiration and oxygen availability Heart and Circulation/Transport Nutrition, Digestion, Metabolism Excretion and Elimination

Chemical Messengers Sexual Reproduction Neuronal Structure & Signals Sensory Reception

text:Biological Science 5th Edition - Freeman ..: Read Chap 47 for this lecture Integration of Neural Function Neuromuscular Action - Behavior syllabus Figures acronyms    end

XV. Sensory Reception 		


	A. Neural Sensory Receptors are Transducer Neurons


		1. convert external stimulus into a neural impulse


			a. stretch/displacement reception, photoreception, chemoreception


	B. Stretch and Displacement Reception


		1. associated with touch, hearing, balance, temperature


		2. specialized dendrites are placed so that mechanical changes
		   will cause them to bend


			a. bending stretches the membrane to open ion channels
			   which allows for depolarization


				i. depolarization begins the action potential


		3. phonoreception


			a. hair cells - size and length associated with
			   different frequencies of sound


		4. nociception - pain


		5. touch and balance


			a. equilibrium receptors in the vestibular apparatus of the
			   inner ear evolved from lateral line of fishes


	C. Chemoreception


		1. taste and smell


		2. chemically alter neuronal (receptor) membrane permeability


			a. ions may cross the membrane ® depolarization ®
			   Action Potential


	D. Photoreception


		1. sight, temperature, light


			a. many photoreceptors are capable of detecting light
			   without delineating images


				i. infrared sensitive heat pits of pit vipers


				ii. parietal eye of lizards


					(1) lens


					(2) connected to pineal - melatonin secretion in darkness


		2. Retina (neural lining) contains photosensitive molecules


			a. found in the rods and cones = photoreceptive neurons


				i. in membranes of flattened discs in the
				   outer segment of these neurons


					(1) away from the lens


			b. Rhodopsin


				i. pigment made from opsin (protein) and
				   retinal (vitamin A derivative)


				ii. energy from light causes a configurational
				    change in retinal, unbends it (bleaching)


				iii. activated rhodopsin binds a G protein, closing membrane
				     channels, hyperpolarizing the cell


					(1) stops the ions from leaking in or out


				iv. hyperpolarization travels down the neuron
				    just as depolarization would


				v. signal is graded
				   - more hyperpolarization with more light


					(1) depolarization in normal neurons is all or nothing:
					    graded responses come from
						the number of neurons depolarizing