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NROSCI lecture 8-10 - Lecture 8 I Review a)An A.P on a...

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Lecture 8 - January 31, 2008 I. Review a)An A.P. on a single presynaptic axon will produce only a 0.1 - 2mV EPSP in the postsynaptic neuron. b)An A.P.(axon)-->A.P.(synaptic terminal)-->exocytosis of NT-->some NT binds to postsynaptic receptors-->small EPSP c)Since a 15 - 25mV depolarization is needed to elicit an A.P. in the postsynaptic neuron, an A.P. in a single presynaptic axon will be insufficient to elicit a large enough EPSP to trigger a postsynaptic A.P. d)Larger EPSPs are elicited in a postsynaptic neuron by simultaneously producing A.P.s in many axons synapsing on the postsynaptic neuron (assuming all these axons elicit EPSPs in the postsynaptic neuron.) This is called summation . e) At some synapses presynaptic A.P.s result in hyperpolarization of the postsynaptic cell. These synaptic potentials are called IPSPs, inhibitory postsynaptic potentials. f)Like EPSPs, IPSPs generated at 2 different synapses can summate in the postsynaptic neuron. g)Finally EPSPs and IPSPs can summate resulting in an EPSP of smaller amplitude which is less likely to elicit an A.P. h)EPSPs and IPSPs are constantly being produced in neurons by A.P.s on axons synapsing on them. The summation of these collective synaptic inputs is referred to as integration . II. The neural basis of sensation a)We see with our eyes; we hear with our ears; we taste with our tongue; we feel with our fingers;... b)All these sensors are located outside our brain. c)The brain itself contains no receptors for physical stimuli coming from outside the body. d)All the information sent to the brain from the sensory organs must be carried on axons in nerves connecting the sensory organs to the brain. e) From this observation we can conclude (with the Materialistic Monist) that All Sensation is produced by action potentials(neural activity). III. What peripheral nerves carry this sensory information?
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a)The peripheral nervous system can be subdivided into 2 components: the cranial nerves (attached to the brain) and the spinal nerves (attached to the spinal cord). b) There are 12 pairs of cranial nerves . The important cranial nerves from the standpoint of sensory input are: (See Figure 9A.) o Nerve 1 - Olfactory Nerve which conveys our sense of smell. o Nerve 2 - Optic Nerve which conveys our sense of vision. o Nerve 5 - Trigeminal Nerve which conveys sensation from the face(including pain senation). o Nerve 7 - Facial Nerve which conveys our sense of taste. o Nerve 8 - Acoustic Nerve which conveys our sense of hearing and balance. c)Axons coming into the spinal cord also extend up to the brain and convey our skin senations to us. d)The brain itself does not feel anything because it has no exteroreceptors for the stimuli. o 1)Thus a woman whose brain was being electrically stimulated to treat her depression did not feel pain or anything in particular.
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