Animal Body Systems Lecture 11 PDF

Biol 224.3 – Animal Body Systems Lecture 11: Sensory Systems (continued) Dr Joan Forder Supplementary Textbook Reading: (5th Edition: Chapter 42, page 1153-1157) 140140140140140140 Opsins and Colour V...

Biol 224.3 – Animal Body Systems Lecture 11: Sensory Systems (continued) Dr Joan Forder Supplementary Textbook Reading: (5th Edition: Chapter 42, page 1153-1157) 140140140140140140 Opsins and Colour Vision Colour vision depends on cones in retina Most mammals—2 types of cones Humans and other primates—3 types of cones Each cone cell contains 1 of 3 photopsins in which retinal is combined with different opsins. 141 Photoreceptors of the Retina Rods—specialized for detecting low-intensity light Cones—specialized for detecting light of different wavelengths (colours) Both are linked to neurons in the retina. Perform initial integration and processing of visual information Fig. 42.31a, p. 1150 142  Converting Signals to Electrical Impulses Photoreceptor has three parts: Outer segment of stacked, flattened, membranous discs Inner segment where metabolic activities occur Synaptic terminal where neurotransmitter molecules are stored and released Photoreceptors of different animals contain different forms of retinal, a light- absorbing pigment. 143  Photopigment: Rhodopsin Photopigment Discs Found in discs of RODS Consists of the opsin protein retinal In response to light, retinal changes from a bent to a straight structure retinal inside Fig. 42.31b, p. 1150 of rhodopsin 144  Retina: Initial Integration BIPOLA e ner optic cells - process -> back of eye ↓ front ↓ Fig. 42.32, p. 1151 brain 145  Neural Pathways for Vision Half of axons carried by the optic nerves cross over at the optic chiasma. Leading to the left half of the field seen by both eyes being transmitted to the visual cortex in the right hemisphere (and reverse for right half of visual field) Results in right hemisphere seeing objects to the left of the centre of vision and left hemisphere seeing Fig. 42.33, p. 1152 objects to the right of the centre of vision 146  Major Categories of Sensory Receptors Type of Sensory Receptor Responds to Example Mechanoreceptors mechanical deformation Auditory receptors in the ears Thermoreceptors cold and heat Temperature receptors in the skin Nocioreceptors pain (tissue damage) Skin & some internal organs Electromagnetic electrical & magnetic Detect earth’s magnetic Receptors fields; infrared and field to guide movement ultraviolet light over distances Photoreceptors visible light Visual receptors in the retina of the eye Chemoreceptors various chemicals Taste buds on the tongue 147  Sensory Cell Membrane Proteins Respond to Stimuli Fig. 42.15, p. 1139 148 Chemoreceptors Provide information about taste (gustation) and smell (olfaction) Measure intrinsic levels of specific molecules in the environment (examples: oxygen, carbon dioxide, hydrogen) Work through membrane receptor proteins Stimulated when they bind with specific molecules Generate action potentials leading to CNS ↑ as channels open. 149 Defining Taste and Smell Taste involves the detection of potential food molecules in objects touched by a receptor. Smell involves the detection of airborne molecules. 150  Invertebrates In many invertebrates, same receptors for sensing smell and taste May be around mouth (ex: hydra) or distributed over body surface (ex: earthworm) 151  Terrestrial Invertebrates Some terrestrial invertebrates have clearly differentiated receptors for taste and smell. Insects Taste receptors occur inside hollow sensory bristles called sensilla usually located on the antennae, mouthparts, or feet. Pores in the sensilla admit molecules from potential food to the chemoreceptors Specialized to detect nollow mole- sugars, salts, amino acids, so cules can or other chemicals go inside. 152  Use of Pheromones Pheromones are chemicals used in communication in both animals and plants Insects are excellent examples of animals that make extensive use of pheromones Male/female attraction (ex: Silkworm Moth) Ants, bees, and wasps use odour to identify members of the same hive or nest, or to alert nestmates to danger Olfactory Receptors: Sensory Bristles on the Silkworm Moth Binding of odorant leads to membrane depolarization Fig. 42.36, p. 1154 153  Taste & Smell in Vertebrates Taste and smell receptors have hairlike extensions containing proteins that bind environmental TEST molecules Hairs of taste receptors are derived from microvilli and # contain microfilaments Processed in Parietal Lobes of the brain Hairs of smell receptors are derived from cilia and contain microtubules Processed in Olfactory Bulbs and Temperal Lobes Taste receptors form part of a structure called a taste bud, a small, pear-shaped capsule with a pore at the top opening to the exterior. 154 Taste Receptors in the Human Tongue Taste receptors form part of a structure called a taste bud, a small, pear- shaped capsule with a pore at the top opening Fig. 42.37, p. 1154 to the exterior. 155 Taste Transduction Taste - relies on contact chemoreception Nat H Salt and Sour simple Cation inflow depolarizes cell - neurotransmitter release Sweet, bitter, and Figure 42.37 umami complex - 2nd messenger pathway Each receptor has a preferred chemical sensitivity 156 Odours as Signals Smell is a powerful receptor for memories Many mammals communicate with odours. Family or colony identification Attraction of mates Territory and trail marking 157  Smell in Water Dwelling Vertebrates Fishes and amphibian tadpoles Detects chemicals in surrounding water wo Receptors found inside nasal sacs Open to the water through nares Blind ending Not used for breathing Source: aging times https://www.hepper.com/can-fish-smell/ 158 Smell in Air Breathing Vertebrates Detects volatile (airborne) chemicals Receptors located in nasal cavities Used for both smell and breathing One end has 10 – 20 sensory hairs projecting into layer of mucus covering the olfactory area of the nose Star-Nosed Mole Molecules dissolve in the watery mucus solution Other end has olfactory receptor cells synapse with interneurons in the olfactory bulbs Communicate directly with cerebral cortex Humans: ~ 107 olfactory neurons Dogs: ~ 20 times more Moth:~ 1,000 more sensitive Fig. 42.38, p. 1155 than dog 159 Question? Why does the sense of smell contribute to the sense of taste? Look at it from a physiological viewpoint 160  Nociceptors ▪ Detect damaging stimuli interpreted by brain as pain ▪ In mammals and possibly other vertebrates ▪ Located on body surface and interior ▪ Pain receptors adapt very little, if at all, as part of their protective function. ▪ Protective mechanisms ▪ Prompts us to do something immediately to remove or decrease the damage being done 161  Pain Circuits Neurons involved are part of the Somatic Nervous System of PNS Synapse with interneurons in the grey matter of the spinal cord Cause these interneurons to release either glutamate or Substance P Glutamate releasing axons produce sharp, prickly sensations localized to a specific body part Substance P releasing axons produce dull, burning, or aching sensations more wide spread 162  Electroreception Ancient trait in vertebrates Electric fish Electroreceptors Detect electrical currents and fields Sharks, bony fishes, some amphibians Electroreceptors detect distortions of electric fields Also produce large fields (up to 600 V)for prey capture Fig. 42.41, p. 1157 163  Magnetoreception Detect and use Earth’s magnetic field as source of directional information Butterflies, beluga whales, sea turtles, homing pigeons, foraging honey bees 164  Adaptation of Receptors with Constant Stimuli In many sensory systems, the effect of a stimulus is reduced if it continues at a constant level; this reduction is called sensory adaptation. Some receptors adapt quickly and broadly (e.g., your eyes getting used to light on a sunny day); other receptors adapt only slightly (e.g., receptors detecting painful stimuli show little or no adaptation). 165 Perception Perception: the conscious awareness of our external and internal environments derived from the processing of sensory input. The action potentials from sensory receptors are the signals the brain uses to generate an interpretation—the perception—of the external and internal environments. 166  (afferent) synthesis of an output based on the sum of the Inputs plus past experiences and genetics (efferent) all these activities depend on bioelectricity 167 Something to think about How do you know that what I am seeing (or smelling, or tasting) is exactly the same thing as what you are seeing/smelling/tasting when everything is about perception and my life experiences & genetics are different from yours? … is blue really blue? 168