Cell communication. Gated ion channels. Allow specific ions to pass only when gates are open

Transcription

1 increase decrease Cell communication Gated ion channels Allow specific ions to pass only when gates are open Triggered by: potential change, chemical binding, temperature change, stretching 1

2 Voltage-Gated Na + Channel ECF Activation gate Inactivation gate Closed but capable of opening Open (activated) ICF Slow closing Inactivated Voltage-Gated K + Channel ECF ICF Delayed opening Closed Open Potentials and gated channels Depolarization causes: Na + gates to open, then slowly close Delayed opening of K + gates 2

3 Graded potentials Below threshold Signal dies out over distance Graded potentials Graded potential Resting potential Time Magnitude of stimulus Stimuli applied Graded potentials Loss of charge Initial site of potential change Loss of charge Current flow Current flow 3

4 Triggering an action potential Na + equilibrium potential At threshold, Na+ channels briefly open, which causes a large depolarization Triggering event K + open during spike, and slowly close, resting potential returns Threshold potential Resting potential K + equilibrium potential 1) Input zone receives incoming signals from other neurons. Dendrites Axon hillock 2) Trigger zone initiates AP s 3) Conducting zone conducts action potentials Axon terminals Dendrites Cell body Axon 4) Output zone releases neurotransmitter that influences other cells. 4

5 Conduction of signal interstitial fluid cytoplasm Conduction of signal Na + Na + Na + Conduction of signal K + K + K + Na + Na + Na + 5

6 Conduction of signal K + K+ K + Na + K + Na + Na + Na + All or nothing Action potentials No degradation of signal over distance Conduction in one direction Refractory period Action potentials travel in one direction bc of the refractory period 6

7 Myelination unsheathed node axon Schwann cells of a myelin sheath Na + action potential resting potential resting potential K + Na + resting potential restored action potential resting potential Chemical Synapse Voltage-gated Ca 2+ channels Chemically gated Na +, K +, or Cl - channels 7

8 Calcium influx causes vesicles to perform exocytosis Neurotransmitters A synapse will use only one type of neurotransmitter Ex: dopamine, serotonin, epinephrine, GABA Neurotransmitters are quickly removed once they bind to receptors Reuptake or inactivated Neurotransmitters activate gated ion channels Excitatory synapse: Na+ channels Inhibitory synapse: K+ or Cl- channels 8

9 Signal at the synapse excites or inhibits the postsynaptic neuron Excitatory synapse: Causes an influx of Na + into postsynaptic neuron. This produces an EPSP and depolarizes the neuron. Inhibitory synapse: Causes an outflow of K + from the postsynaptic neuron. It can also cause an influx of CL - This produces an IPSP and hyperpolarizes the neuron. Excitatory synapse Inhibitory synapse Activation of synapse EPSP Activation of synapse IPSP PSP= Postsynaptic potential 9

10 Temporal summation: PSPs occur close together in time from a single presynaptic neuron. Spatial summation: PSPs originate from several presynaptic inputs. Some neuron shapes Hippocampus neuron Pyramidal neurons Purkinje neurons Bipolar neurons - retina 10

11 Drug effects If a drug affects the nervous system, it usually changes synapse function Drug molecules can: mimic neurotransmitters falsely stimulate neurotransmitter release block neurotransmitters, or their reuptake These drugs all mimic natural endorphin How stimulants and sedatives work In a part of the brain stem (RAS), excitatory synapses (norepinephrine) cause wakefulness, inhibitory synapses (GABA) cause drowsiness Caffeine, amphetamines, ecstasy (MDMA) norepinephrine in RAS Alcohol, valium, barbiturates, & marijuana activate GABA receptors. Physiology of additive drugs Cocaine, methamphetamine, marijuana, and opiates influence the neurotransmitter dopamine. 11

12 Neurotransmitter: dopamine Dopamine - a neurotransmitter associated with several functions, including muscle control and feelings of reward Schizophrenia, manic depression are associated with too much dopamine. Antipsychotic drugs block dopamine receptors. reward pathways Dopamine and reward To signal the pleasure center here Neurons here use dopamine Neurotransmitter: dopamine Cocaine and methamphetamines prevent reuptake of dopamine. 12

13 Neurotransmitter: serotonin Neurons using serotonin are associated with mood, sleep, & appetite Antidepressants often enhance levels of serotonin (Zoloft, Prozac, Paxil) Three main neurotransmitters of mood All are monoamines Neurotransmitter: serotonin Ecstasy temporarily increases serotonin, but body makes less serotonin in response ecstasy blocking reuptake of serotonin 13

14 Cannabis effects THC binds to cannabinoid (CB) receptors, mimicing anandamide (from body) CB receptors are in pleasure pathway (VTA), and areas of motor coordination (cerebellum) and memory (hippocampus) Signaling b/w neurons in hippocampus is affected (GABA neurons w CB1 receptors) 14