Animal Body Systems Lecture 10 PDF

Biol 224.3 – Animal Body Systems Lecture 10: Sensory Systems Dr Joan Forder Supplementary Textbook Reading: (5th Edition: Chapter 42, page 1139-1152) 1 Where we are going Detecting th...

Biol 224.3 – Animal Body Systems Lecture 10: Sensory Systems Dr Joan Forder Supplementary Textbook Reading: (5th Edition: Chapter 42, page 1139-1152) 1 Where we are going Detecting the environment Sensory Inputs Sensory Transduction Sensory Receptors Mechanoreceptors Photoreceptors  Detecting the Environment Animals can detect a wide variety of environmental variables Very important in context of homeostasis Basic neuronal physiology applies, with some specializations 3 Sensory Inputs: Reception Sensory systems begin with sensory receptors (transducers) that detect sensory information, convert it to neural activity, and pass the information along neurons to the central nervous system (CNS). Sensory receptors are formed by the dendrites of afferent neurons or by specialized receptor cells. Sensory Transduction Sensory transduction occurs when stimuli cause changes in membrane potentials in the sensory receptors. Stimuli may be in the form of light, heat, sound waves, mechanical stress, or chemicals. If the receptors are available to the stimulus, the cell will react Sensory Receptors Sensory receptors respond to stimuli in their receptive fields by undergoing a change in receptor potential which varies with the magnitude of the stimulus (a graded potential). Change in receptor potential is caused by changes in the rate of conduction of positive ions (Na+, K+, Ca2+) across the plasma membrane. Strength of Stimulus Intensity & Extent of a Stimulus is encoded in several ways: The frequency of action potentials that the stimulus generates in the afferent neuron (number per unit time) The number of afferent neurons sending action potentials in response to a stimulus Structural Forms of Sensory Receptors Sensory receptors occur in three structural forms: One is a specialized cell that synapses with an afferent neuron. Two involve peripheral endings of an afferent neuron Figure 42.14 Sensory Receptor: Free Nerve Endings A stimulus causes a change in membrane potential This generates AP in the axon Examples: pain receptors and some mechanoreceptors Fig. 42.14a, p. 1139  Sense Organ: Enclosed Nerve Endings A stimulus affecting the specialized structure triggers an AP in the afferent neuron Example: some mechanoreceptors Fig. 42.14b, p. 1139 Sensory Cell that Consist of Two Separate Cells Synapse with a axon of afferent neuron Stimulus causes change in MP causing release of neurotransmitter Neurotransmitter triggers an AP in the axon of an afferent neuron Examples: photoreceptors, chemoreceptors, some mechanoreceptors Fig. 42.14c, p. 1139  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 Sensory Cell Membrane Proteins Respond to Stimuli Fig. 42.15, p. 1139  Mechanoreceptors: Touch and Pressure Detect mechanical stimuli Touch and pressure Touch and pressure receptors in vertebrates Embedded in skin and other surface tissues, skeletal muscles, blood vessel walls, internal organs Four types of mechanoreceptors detect tactile stimulation in human skin  Mechanoreceptors: Propriceptors Invertebrate Statocyst Proprioceptors detect stimuli used by the CNS to monitor and maintain body and limb positions. Example: statocysts in aquatic invertebrates such as jellyfish, some gastropods, and some arthropods. Fig. 42.17, p. 1141 Sensory hair cells generate action potentials in afferent neurons when the hairs are moved. Mechanoreceptors in muscles, tendons, and joints detect changes in the pressure/tension of body parts (more about this when we look at the musculoskeletal system). Two more examples of Proprioceptors Halteres Crane flies Vestigial hind wings of flies transduce information about pitch, roll, and yaw during flight. Fig. 42.18, p. 1141 Halteres The Lateral Line System of Fishes Neuroblasts Contain a gelatinous cupula Pushed & pulled by vibrations and currents transmitted through the lateral line canal. Bends hair cells, generating AP  Vertebrate Vestibular Apparatus: Balance and Orientation Within the Inner Ear Used for balance and orientation by perceiving position and motion of head Essential for maintaining equilibrium and coordinating head and body movements Consists of 3 semicircular canals 2 chambers, utricle and saccule Human Vestibular Apparatus Fig. 42.20, p. 1143 Detection of Sound Sound is made up of Invertebrates: Mechanoreceptors in skin vibrations that travel as or other surface structures waves produced by detect sound and other vibrations. alternating compression and decompression of air or water. Vertebrates: Auditory structures of terrestrial vertebrates Water is denser than air, so transduce vibrations in sounds move about three air (sound) to sensory times faster under water. hair cells that respond by triggering action potentials.  Terrestrial Vertebrate Ear Ear consists of: Pinna (outer ear): Concentrates and focuses sound waves Middle ear Consists Malleus, Incas, & Stapes; & Oval Window Inner Ear Consists of Cochlea, Organ of Corti, and Round Window Sound waves enter auditory canal, strike a thin sheet of tissue (tympanic membrane or eardrum). and start it vibrating. Transmits vibrations through one or more bones in the middle ear to the fluid-filled inner ear.  Structures of the Human Ear Fig. 42.23, p. 1145 It is the hair cells in the Organ of Corti that, when moved, send signals to the brain through afferent neurons  Some Animals Have Pinnae; Some Don’t Whales do NOT Birds do NOT have outer ears have outer ears Bats have HUGE Reptiles do NOT outer ears have outer ears Fig. 42.24, p. 1146  Photoreceptors Detect light at particular wavelengths Convert stimuli to action potentials that move information to visual centres in the CNS or the central ganglion Signals integrated into light perception All animals use forms of a single lipidlike pigment, retinal (synthesized from vitamin A), in photoreptors to absorb light energy. The simplest eyes are capable only of distinguishing light from dark. The most complex eyes distinguish shapes and colours and focus an accurate image of objects being viewed onto a layer of photoreceptors.  Invertebrate Eyes Take Many Forms Earthworms have photoreceptors in their skin that allow them to sense and respond to light. Ocellus—simplest eye, lacking a lens and not leading to image formation Ocelli may each consist of