BIO 3324 1nd Edition Lecture 11Outline of Last LectureI. Receptor signalsII. Somatosensory pathwaysIII. SmellIV. TasteV. PainVI. EarVII. visionOutline of Current Lecture I. vision lightII. photopigmentIII. visual transductionIV. nervesV. PNSVI. ReceptorsVII. musclesCurrent LectureLight must pass through several retinal layers before reaching the photoreceptorsVisual Transduction:the players• Photopigment: Responsible for transducing light energy into a membrane potential– Rods = rhodopsinThese notes represent a detailed interpretation of the professor’s lecture. Grade Buddy is best Used as a supplement to your own notes, not as a substitute.– Cones = three different pigments that are maximally excited at different wavelengths of light• Consists of a retinal molecule (ligand) and an opsin molecule (GPCR)• Light absorption results in retinal isomerization and thus activation of the opsin molecule and transduction pathway• Responsible for transducing light energy into a membrane potential– Rods = rhodopsin– Cones = three different pigments that are maximally excited at different wavelengths of light• Consists of a retinal molecule (ligand) and an opsin molecule (GPCR)• Light absorption results in retinal isomerization and thus activation of the opsin molecule and transduction pathwayVisual Transduction:darknessVisual Transduction:Visual Transduction:lightInitiation of an action potential in the visual pathway• Termination of the light respons The transducin a particle catalyzes the bound GTP to GDP thus “turning itself off”• cGMP levels rise resulting in opened ion channels causing depolarization of the outer segment• All trans-retinal diffuses to the pigment epithelium and is converted by an isomerase into 11-cis-retinal which can then bind opsin, thus “resetting” the photopigment.Visual processing:• The image detected on the retina at the onset of visual processing is upside down and backwards (due to the bending of light rays).• Retinal neuronal layers beyond the photoreceptors are responsible for processing the signal• Bipolar cells connect the photoreceptor cell to the ganglion cell; either light-on (inhibited in dark) or light-off (inhibited in light); form either inhibitory or excitatory synapses with ganglion cells• Ganglion cells reinforce and suppress visual information to enhance contrast• Lateral inhibition - strongly excited cone pathways suppress weakly excited pathwaysVisual processing:ganglion cell• The receptive field of a cone ganglion is determined by the field of light detection of the cone with which it is linked.• On-center ganglion - most responsive when the center of the receptive field is illuminated• Off-center ganglion - most responsive when the periphery of the receptive field isilluminated• By emphasizing differences in relative brightness, this mechanism helps define contours of images, but at the expense of determining absolute brightness• Form, color, depth and movement are separated and projected in parallel pathways to different regions of the visual cortex then integrated in the higher visual processing centers to create a perceived imageNerves:• Bundle of peripheral neuronal axons• Contain only the axon portion of the many neurons• Do not have any influence on each other (e.g. the fibers travel together for convenience)• As spinal nerves emerge from the spinal cord, they supply a particular regionThe efferent division of the PNS:• Two branches:– Autonomic system – involuntary branch• Cardiac & smooth muscles, most exocrine glands, some endocrine glands & adipose tissues– Somatic system – voluntary branch• Skeletal musclesAutonomic system innervates visceral organs:• Two systems, Sympathetic and Parasympathetic branches general exert opposite effects on a particular organ• Both systems are always active but the dominant level of activity is dependent on the homeostatic need at a given time• Tonic activity = basal level of activityDominance:• Dominance – when one system is increased above its tonic level with a simultaneous decrease in the other system• Sympathetic dominance– Prepare the body for strenuous physical activity in an emergency or stressful situations– “Fight or Flight” response• Parasympathetic dominance– Concerned with general housekeeping– “Rest and digest” responseAdvantages of two systems:• System is called dual reciprocal innervation• Like having a brake and accelerator• Some exceptions to the rule– Innervated blood vessels – only sympathetic• Changes occur by in/decreasing firing rate above/below normal– Sweat glands – sympathetic but post-ganglionic fibers secrete ACh– Salivary glands – innervated by both but activity is not antagonisticAutonomic nerve pathway consists of two-neuron chains:• Cell body of 1st neuron is located within the CNS– Synapses with cell body of 2nd neuron located in a ganglion• Axon of 2nd neuron (post-ganglionic fiber) innervates the effector organ• High degree of divergence in the ganglion, a single neuron synapses with 8-32 neurons– Results in multiple targets being stimulated siumltaneouslyAutonomic system has two subdivisions:• Sympathetic– Fibers originate in the thoracic & lumbar regions of the spinal cord– Preganglionic fibers are fairly short– Postganglionic fibers are long and terminate on the effector organ• Parasympathetic– Originate in the cranial & sacral areas of the CNS– Preganglionic fibers are long & terminate at terminal ganglions– Postganglionic fibers are short and terminate on the effector organNeurotransmitters of the ANS:• Cholinergic – fibers that release Acetylcholine (Ach)• Adrenergic – fibers that release Norepinephrine (NorE)• Preganglionic fibers - ACh is released by both sympathetic and parasympathetic• Postganglionic fibers –– Parasympathetic release ACh– most Sympathetic release NorEThe neuroeffector junction:• Autonomic synapses consist of varicosities, swellings found at the branched ends of autonomic neurons• On the post-synaptic side, NT bind to GPCRs resulting in slower but long lasting responsesReceptors:• Cholinergic receptors– Nicotinic receptors • located on post-ganglionic cell bodies• Activated by ACh from both sympathetic & parasympathetic preganglionicfibers– Muscarinic receptors• Located at effector cell membranes• Activated by ACh from parasympathetic postganglionic