Sensory Physiology Notes PDF

Sensory Physiology Kevin Johnston, PhD Department of Physiology and Pharmacology Western University Overview of this Section 1. General properties of the sensory systems, smell, taste 2. Somatic Senses: touch, temperature and pain 3. Vision 4. Hearing 5. Spinal cord and motor cortex Sensati...

Sensory Physiology Kevin Johnston, PhD Department of Physiology and Pharmacology Western University Overview of this Section 1. General properties of the sensory systems, smell, taste 2. Somatic Senses: touch, temperature and pain 3. Vision 4. Hearing 5. Spinal cord and motor cortex Sensation and Motor control 81 Basic Principles of Sensation The afferent division of the peripheral nervous system tells us about our internal and external environment Only certain types of energies, or stimulus modalities, can be detected by our bodies Afferent division of the peripheral nervous system has specialized receptors that transduce stimuli into action potentials, which are relayed to the CNS 82 General Overview Stimulus How is a physical ??? stimulus converted into Receptor a response? Neuron CNS Receives, interprets and responds 82  Types of Sensory Receptors 1. Photoreceptors: wavelengths in visible spectrum 2. Mechanoreceptors: mechanical energy (e.g., stretch, deformation, bending) 3. Chemoreceptors: sensitive to specific chemicals 4. Nociceptors (pain receptors): tissue damage 5. Thermoreceptors: heat and cold 6. Osmoreceptors: solute concentration and osmotic activity 83 Two Classes of Sensory Receptors Complex Neural Special Senses Receptors Receptor Specialized receptor Specialized nerve ending Synapse Myelinated axon Myelinated axon Cell body Cell body OLFACTION VISION SOMATIC SENSES HEARING BALANCE TASTE 84 Transduction at Complex Neural Receptor 1 1. Application of Stimulus 2 2. Alteration of receptor membrane 3 (e.g., usually Na+ channels open) 4 3. Local current flow within receptor (Receptor potential – graded potential) 5 4. Change in frequency of action potentials 5. AP Propagation to central nervous system 85 Transduction at Special Senses Receptor 1 1. Application of Stimulus 2 3 2. Alteration of receptor membrane (in photoreceptors Na+ channels close in response to light) 4 3. Local current flow within receptor (Receptor 5 potential – graded potential) 4. Release of Neurotransmitter 6 5. Change of post-synaptic membrane potential 7 6. Change in frequency of action potentials (AP) 7. AP Propagation to central nervous system 86 Action potentials versus Receptor potentials Remember that receptor potentials are very different from action potentials! Action potentials are all-or-none à Once initiated, they will flow down the entire axon Receptor potentials are graded à they can differ in amplitude and dissipate over time and distance 87 What about the intensity and duration of the stimulus? At an individual receptor, a stronger, longer stimulus produces a larger and longer receptor potential. This is transduced into a higher frequency of action potentials that lasts longer. Transduction site Trigger zone Myelinated axon Cell body Axon terminal Stimulus This leads to the Membrane potential (mV) Smaller Stimulus, Short Duration 20 0 release of more Amplitude - 20 - 40 - 60 Threshold neurotransmitters. - 80 0 5 10 0 5 10 0 5 10 Duration Time (sec) Longer and 20 Stronger Stimulus 0 - 20 - 40 - 60 - 80 0 5 10 0 5 10 0 5 10 88  Receptive fields The part of sensory space that can change the activity of a neuron. 89 Smell Taste  Smell The receptor cells for olfaction are neurons (primary sensory neurons) They synapse with secondary neurons in the olfactory bulb Olfactory bulb Olfactory bulb Olfactory epithelium Secondary Bone sensory neurons Olfactory primary Olfactory Sensory neurons epithelium 89  How do we perceive different smells? We have about 350 different odor receptors The combination of signals coming from different olfactory sensory neurons creates the perception of different smells Banana Pear Rose 89  Taste Taste is currently believed to be a combination of five sensations: sweet, sour, salty, bitter, and umami. We have about 2000-5000 taste buds. Each taste bud contains 50-150 taste cells. Each taste cell is a non-neural epithelial cell, responsible for taste transduction 90  Important structures of the CNS for Sensory Physiology: 1. Cerebrum – Cortex, Basal ganglia, Limbic System 2. Cerebellum 1 3. Brain stem – Medulla Oblongata, Pons, and Midbrain 4 4. Diencephalon – Thalamus, Hypothalamus, 3 Pineal gland, Pituitary gland 2 5. Spinal Cord (central nervous system) 5 90  Cortical anatomy Central sulcus Frontal Lobe Parietal Lobe (movement & (sensation) cognition) Occipital Lobe (vision) Temporal Lobe (hearing, object perception) 91 Smell OLFACTORY CORTEX OLFACTORY BULB 92 Taste GUSTATORY CORTEX THALAMUS BRAIN STEM 92  Touch – somatic sense SOMATOSENSORY CORTEX THALAMUS BRAIN STEM 92 Vision THALAMUS VISUAL CORTEX 92 Hearing THALAMUS AUDITORY CORTEX MEDULLA 92 Balance THALAMUS THE VESTIBULAR APPARATUS 92