9 25 Lecture 7 Ch 6 Neurotransmitter Systems Ch 15 482 483 490 507 Ch 17 543 545 Chemical Control of Behavior Transmitter Gated ACh receptor Sequence of events o 1 ACh binds to receptor o 2 Pore opens o 3 Pore is permeable to Na and K o 4 At RMP driving force on Na is larger than K so Na influx K efflux and Vm depolarizes o 5 ACh unbinds and channel closes o 6 Vm returns to resting value Excitatory postsynaptic potential EPSP Neurotransmitter gated ion channels permeable to Na tend to bring membrane potential toward threshold o Resulting in an excitatory postsynaptic potential EPSP o ACh and glutamate gated ion channels result in EPSPs Note that Na influx is partly offset by K efflux Inhibitory postsynaptic potential IPSP Neurotransmitter gated ion channels permeable to Cl tend to clamp membrane potential below threshold ECl is about 65 mV o Results in an IPSP o GABA gated ion channel receptors IPSPs also produced by other transmitters that open K channels Neurotransmitter removal from synaptic cleft After its effect neurotransmitter cleared from synaptic cleft so neuron can be prepared for subsequent responses 1 Reuptake into presynaptic axon terminal or glia o Neurotransmitter specific transporter proteins in axon terminal and glia plasma membranes The antidepressant Prozax inhibits serotonin reuptake transporter greater accumulation of serotonin in synaptic cleft and prolonged interaction with serotonin receptors 2 Enzymatic breakdown o ACh cleared from neuromuscular junction by acetylcholinesterase nerve gases inhibit this enzyme Sarin o After reuptake monoamine oxidase MAO metabolizes monoamines serotonin norepinephrine and dopamine MAOis used to treat Parkinson s disease and also as antidepressants Neurotransmitter released in packets 1 vesicle 1 quanta EPSPs usually represent response to more than 1 vesicle Miniature postsynaptic potentials minis spontaneous release of 1 vesicle o Size of mini reflect number of neurotransmitter molecules in a vesicle and number of postsynaptic receptors Comparing size of EPSP to minis can calculate number of vesicles released by an action potential This is called quantal analysis o At neuromuscular junction 200 vesicles released by an action potential giving EPSP of 40 mV large enough to reach threshold o In the brain each action potential releases only a few vesicles and the EPSP is usually less than 1 mV Summation of many EPSPs is necessary to reach threshold the Summation of PSPs Synaptic currents are passive decremental o EPSP is attenuated at a distance from synapse Summation of many EPSPs is necessary to reach threshold for an action potential at axon hillock EPSP summation produces a larger EPSP Spatial summation EPSPs from different synapses Temporal summation EPSPs produced in quick succession at same synapse 9 30 Lecture 8 Ch 6 15 17 Transmitters Ch 7 Structure of the Nervous System Glutamate Major CNS excitatory transmitter about 90 of synapses 3 ionotropic glutamate receptors AMPA main glutamate receptor NMDA and Kainate o AMPA receptors responsible for EPSPs at most CNS excitatory synapses o NMDA and Kainate receptors implicated in synapse formation during early development learning in the mature nervous system Metabotropic glutamate receptors GABA GABA major inhibitory neurotransmitter 2 types of GABA receptors GABAA main type and GABAB o GABAA are inhibitory receptors with channels permeable to Cl Nernst potential for Cl is below threshold for action potential o GABAB G protein coupled receptor many located on axon terminals can inhibit vesicle exocytosis GABAA receptor has several sites where substances besides GABA affect opening Benzodiazepines barbiturates and ethanol enhance GABA induced opening of the Cl channel o Used as sedatives and anxiolytics treatment for epilepsy Nervous System Anatomy Ipsilateral same side Contralateral opposite side Anatomical planes of section Sagittal vertical slice from front to back midsagittal if down midline Coronal aka frontal Vertebrate Nervous System Organization 1 Central Nervous System CNS o Brain within the skull o Spinal cord within the vertebrae 2 Peripheral Nervous System PNS o Peripheral Nerves axons and Ganglia cell bodies Somatic division conscious sensation voluntary control of movement Sensory afferents from skin skeletal muscle bones and joints Motor efferents nerves innervating skeletal muscle Autonomic division visceral involuntary motor system Sympathetic branch more active during arousal and stress Parasympathetic branch more active during relaxation Sympathetic Parasympathetic Divisions of the Peripheral Autonomic Nervous System ANS are Most organs glands and smooth muscle cells innervated by both divisions of the ANS sympathetic and parasympathetic Increased NE release from postganglionic neurons of sympathetic nervous system during stress Increased ACh release from postganglionic neurons of parasympathetic nervous system during periods of relaxation Ultimate control comes from the hypothalamus Early Development of Vertebrate CNS Neurualation o Edge of neural plate bulges up induced by notochord factors o Folds meet and fuse at top to form closed neural tube CNS o Neural crest pinches off at top becomes PNS Endoderm internal organs kidneys gut Mesoderm muscle Ectoderm nervous system skin bone notocord Segmentation Major Divisions of the Brain 1 Telencephalon cerebral hemisphere forebrain 2 Diencephalon thalamus and hypothalamus forebrain 3 Mesencephalon tectum and tegmentun midbrain 4 Rhombencephalon pons medulla and cerebellum hindbrain brainstem Segmentation of the neural tube during early brain development controlled by proteins coded by Hox genes Major Divisions Rat brain and human brain compared Structurally similar The Spinal Cord Cell bodies located in center of spinal cord gray unmyelinated Axon bundles located outside of spinal cord white myelinated Peripheral nerves split at dorsal ventral root o Dorsal root sensory axons afferents come in from body and go to brain o Ventral root motor axons efferents go out from brain and go to body Cerebral Hemispheres 85 of human brain is cerebral cortex Rat s cerebral cortex is flat evolution for humans necessitates folds for surface area o Cerebral cortex comprises outer surface Layered structure neocortex outermost area olfactory cortex and hippocampus memory Gyrus ridge Sulcus fissure groove Gray matter cell bodies unmyelinated White matter bundles of axons myelinated Most axons are underneath cerebral cortex gray