L1 - Sensory Physiology PDF

Special senses Sensory physiology H U M A N A N AT O M Y & P H Y SI O LO G Y – B I O L - 1 1 1 2 W I N T E R 2 02 5 R E A DI N G S: C H A P T E R 1 7 Membrane physiology recap  Membrane transport Pas...

Special senses Sensory physiology H U M A N A N AT O M Y & P H Y SI O LO G Y – B I O L - 1 1 1 2 W I N T E R 2 02 5 R E A DI N G S: C H A P T E R 1 7 Membrane physiology recap  Membrane transport Passive diffusion of lipid-soluble molecules Facilitated diffusion by channels & carrier proteins Active transport (primary or secondary) – energy requiring Moyes & Schulte 2015 Fig. 3.40  Transport proteins – channels Ligand-gated channel Voltage-gated channel Mechano-sensitive channel Butler et al. 2021 Fig. 3.5, 3.16, 3.17  G protein-coupled receptor signal transduction G protein-coupled receptor ◦ Receptor coded for a specific ligand/stimulus ◦ Associated with a G protein Stimulus triggers conformational change in G protein-coupled receptor Activated receptor → activates G protein → activates amplifier enzyme Amplifier enzyme modifies second messenger → activates or inhibits cellular pathway Moyes & Schulte 2015 Fig. 4.27  Graded potential Occur in excitable cells – neuron & non-neuron cells Any local change in membrane potential ◦ Depolarization – less negative; excitatory ◦ Hyperpolarization – more negative; inhibitory Vary in magnitude & duration Travel short-distance – decays over distance Moyes & Shulte 2015 Fig. 5.7  Action potential Occur in neurons & some specialized non- neuronal cells (e.g., muscle cells) Triggered if net graded potential at trigger zone exceeds threshold potential All-or-none phenomena ◦ Propagates rapidly & without degradation Involves voltage-gated channels (e.g., VG-Na+ channels) that open in response to changes in membrane potential Moyes & Shulte 2015 Fig. 5.9 Reminder The special senses Special senses ◦ Gustation (taste) & olfaction (smell) ◦ Hearing & equilibrium ◦ Vision Sensory receptor cells – distinct receptor cells localized in the head region ◦ Usually in complex organs – e.g., eyes & ears; olfactory epithelium & taste buds Sense of touch – one of the general senses, mediated by general receptors (modified nerves)  Sensory system example: Visual system Photoreceptors Organization of Accessory tissues (e.g., iris & cornea) Primary visual cortex sensory systems Sensory receptor cell Visual field Visual field of right eye ◦ Excitable cell specialized to detect of left eye Binocular visual field incoming stimuli (e.g., photoreceptor) Sense organ Optic (II) ◦ Receptor cells + accessory non-neural nerves Optic chiasm tissues (e.g., eyes) Midbrain Lateral geniculate nucleus of thalamus Sensory system Optic tracts Optic radiation ◦ Sense organ + afferent sensory neurons + associated CNS processing Primary visual cortex areas (e.g., visual system) in occipital lobe of cerebum Moyes & Shulte 2015 Fig. 7.39; Tortora Fig. 17.17 Reception Overview of Transduction sensory reception 1) Reception of a stimulus ◦ Requires specialized sensory receptor proteins sensitive to a particular sensory stimulus Transmission 2) Transduction of the signal ◦ Sensory receptor cells transduce incoming stimuli into changes in membrane potential (graded potential) 3) Transmission of signal to integrating center Perception 4) Perception of the stimulus at integrating center Moyes & Schulte 2015 Fig. 5.23, 7.2, 8.17  Sensory receptor cells Excitable cells (neuron or non- neuron) that are specialized to detect incoming stimuli (form of external energy that a receptor responds to) ◦ Have specialized sensory receptor proteins to detect stimuli Classified by stimulus modality ◦ Photoreceptor (light) ◦ Chemoreceptor (chemical stimuli) ◦ Mechanoreceptor (mechanical stimuli) A sufficient stimulus can overcome specialization Moyes & Schulte 2015 Fig. 7.2  Sensory receptor proteins Ion channels ◦ Salty, sour gustatory receptors Mechanically-gated ion channels ◦ Hair cells (hearing & equilibrium) G protein-coupled receptors ◦ Sweet, bitter, umami gustatory receptors ◦ Photoreceptors Moyes & Schulte 2015 Fig. 7.2  Sensory receptor cells (receptor potential) Stimulus triggers a conformational change in receptor protein that leads to a graded potential known as a receptor potential Sensory receptor neuron ◦ Receptor potential → opens voltage-gated Na+ channels → action potential Epithelial sensory receptor cell ◦ Receptor potential → ↑ intracellular Ca2+ → neurotransmitter release ◦ Neurotransmitter acts on afferent neuron to trigger an action potential Note that the trigger zone of the afferent neuron is not at the axon hillock, it is adjacent to the receptor region Moyes & Schulte 2015 Fig. 7.3 Check your knowledge Compare & contrast the ways in which neuronal and epithelial sensory receptor cells receive, transduce, & transmit their signals. True OR false – sensory receptor cells are excitable cells that can be both neuronal or non- neuronal. True OR false – a receptor potential is an action potential that occurs within a sensory receptor cell True OR false – stimulation of an epithelial receptor cell results in the generation of an action potential at the trigger zone.