First lecture: Cells of the nervous system and how their use of electrical signlling Break Second lecture: Chemical communication between neurons (neurotransmission) MAIN POINTS of first lecture: 1. Structure of neurons allows them to use electrical signals 2. Electrical signals may be graded or all or none Study Question: 1. What features of a neuron allow it to have a negative resting potential? Why, if you stimulate the middle of an axon, will an AP travel in both directions? Why, under normal circumstances, does an AP not travel backwards? Why don't dendrites typically use APs? READING: 1.2; 2.1-2.2; 3.1-32! http://www.youtube.com/watch? v=zxlejfu57wg! Neurons (nerve cells)!!information processing units! Glia (glial cells)!!support cells!!more numerous than neurons!
Axon collaterals! Fig. 2-7, p. 31!
Nucleus and ganglion -- Two terms to be clarified! Nucleus has two meanings! 1. Chromosome containing unit of cell! 2. Group of neurons packed together in central nervous system! e.g., suprachiasmatic nucleus (SCN biological clock)! Ganglion means group of neurons packed together in peripheral nervous system! Retinal ganglion in eye! NOTABLE EXCEPTION Basal Ganglia!
Ion channels usually described functionally! e.g., Voltage-gated Sodium Channel! Actually. 10+ versions of this!!mutations in different forms!!!e.g., one leads to infant epilepsy!!can find drugs that affect some or all of them! Fig. 2-3, p. 30!
Neural electrical signaling! 1. Membrane Resting Potential! 2. Graded potentials! 3. Action Potential: Information Unit! Why is the resting potential negative?! 1. Selective permeability of membrane!!ion-specific channel proteins!!at rest, K+ channels are open!!k+ flows out of cell! 2. Diffusion along concentration gradient (move from high to low concentration)! Cell loses positive inside becomes negative with respect to outside!
electrical gradient! Similar charges repulse! K+ stops flowing when electrostatic charge opposes movement! outside of cell becomes too negative! Other facts:! leaky sodium channel! 4. Na+/K+ pump restores charge! Active transport!!na+ leaks into cell!!pump Na+ out and K+ in!!na+:k+ = 3:2! uses LOTS of energy! Drugs can block! Neural electrical signaling! 1. Membrane Resting Potential! 2. Graded potentials! 3. Action Potential: Information Unit!
1. Voltage-gated sodium channel opens at threshold! 2. Na+ gate closes after 0.5 msec for at least 1 msec! 3. K+ opens more to restore potential!
http://www.youtube.com/watch?v=vao62y4hqjo&feature=related! http://outreach.mcb.harvard.edu/ animations/ actionpotential_short.swf! Summary 1. Neurons are specialized cells structurally and functionally 2. Neurons expend energy to be ready to communicate an electrical signal -- an Action Potential 3. AP depends on gradients, selective permeability, active transport and voltage-gated channels Study Questions: 1. What features of a neuron allow it to have a negative resting potential? Why, if you stimulate the middle of an axon, will an AP travel in both directions? Why, under normal circumstances, does an AP not travel backwards? Why don't dendrites typically use APs?!
MAIN POINTS: 1. Neurons summate the signals from afferent neurons 2. Brain uses many different neurotransmitters that are differentially distributed through the brain 3. Drugs act on any of several steps of neurotransmission Study Questions: 1. At what sites in or around the synapse might a new drug "Y alter neurotransmission and how? http://www.youtube.com/watch? v=_chkzzvfvoq&feature=related! http://www.youtube.com/watch? v=cizlnbkvihm&feature=related! 2. What are some differences between neurotransmitters and drugs that resemble them chemically?! 1-4 mm!
http://www.youtube.com/watch? v=olsmncem2x0&feature=related!
Very different RETROGRADE signaling by endocannabinoids!
Several classes of NTs! Monoamines (dopamine DA; norepinephrine NE; serotonin 5-HT)! Acetylcholine (ACh -- control of every muscle)! Amino acids (GABA - inhibition, glutamate -- excitation)! Peptides (Endorphins -- natural opiates)! Others! Serotonin! Acetylcholine! Norepinephrine!
Dopamine!
Summary 1. Electrical - chemical - electrical signalling 2. Neurons are integrators 3. Drugs interact at myriad stages with endogenous chemical transmission Study Questions: 1. At what sites in or around the synapse might a new drug "Y alter neurotransmission and how? 2. What are some differences between neurotransmitters and drugs that resemble them chemically?!