increase decrease Cell communication Gated ion channels Allow specific ions to pass only when gates are open Voltage-Gated Na + Channel Activation gate ECF Triggered by: change, chemical binding, temperature change, stretching Inactivation gate ICF Slow closing Closed but capable of opening Open (activated) Inactivated 1
Voltage-Gated K + Channel ECF Potentials and gated channels Depolarization causes: Na + gates to open, then slowly close Delayed opening of K + gates ICF Delayed opening Closed Open Graded s Graded s Below threshold Graded Resting Signal dies out over distance Time Magnitude of stimulus Stimuli applied 2
Graded s Initial site of change Loss of charge Loss of charge Triggering an action Na + equilibrium At threshold, Na+ channels briefly open, which causes a large depolarization K + open during spike, and slowly close, resting returns Threshold Current flow Current flow Triggering event Resting K + equilibrium 1) Input zone receives incoming signals from other neurons. Dendrites Axon hillock 2) Trigger zone initiates AP s 3) Conducting zone conducts action s Axon terminals Dendrites Cell body 4) Output zone releases neurotransmitter that influences other cells. Axon 3
Conduction of signal Conduction of signal interstitial fluid cytoplasm Na + Na + Na + Conduction of signal Conduction of signal K + K + K + K + K+ K + Na + Na + Na + Na + K + Na + Na + Na + 4
All or nothing Action s No degradation of signal over distance Conduction in one direction Refractory period Action s travel in one direction bc of the refractory period Myelination unsheathed node Schwann cells of a myelin sheath axon Na + action resting resting K + Na + resting restored action resting 5
Chemical Synapse Voltage-gated Ca 2+ channels Calcium influx causes vesicles to perform exocytosis Chemically gated Na +, K +, or Cl - channels Neurotransmitters A synapse will use only one type of neurotransmitter Ex: dopamine, serotonin, epinephrine, GABA Neurotransmitters activate gated ion channels Excitatory synapse: Na+ channels Neurotransmitters are quickly removed once they bind to receptors Reuptake or inactivated Inhibitory synapse: K+ or Cl- channels 6
Signal at the synapse excites or inhibits the postsynaptic neuron Excitatory synapse Inhibitory synapse 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. Activation of synapse Activation of synapse EPSP IPSP PSP= Postsynaptic Temporal summation: PSPs occur close together in time from a single presynaptic neuron. Spatial summation: PSPs originate from several presynaptic inputs. 7
Some neuron shapes Hippocampus neuron Pyramidal neurons Purkinje neurons Bipolar neurons - retina 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. 8
Physiology of additive drugs Cocaine, methamphetamine, marijuana, and opiates influence the neurotransmitter dopamine. 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 To signal the pleasure center here Dopamine and reward Neurons here use dopamine Neurotransmitter: dopamine Cocaine and methamphetamines prevent reuptake of dopamine. 9
Neurotransmitter: serotonin Neurons using serotonin are associated with mood, sleep, & appetite Three main neurotransmitters of mood All are monoamines Antidepressants often enhance levels of serotonin (Zoloft, Prozac, Paxil) Neurotransmitter: serotonin Ecstasy temporarily increases serotonin, but body makes less serotonin in response ecstasy blocking reuptake of serotonin 10
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) 11