BIOL 1030 – TOPIC 20 LECTURE NOTESTopic 20: Neurons and Synapses (Ch. 48)I. functionA. receive information about the external and internal environmentB. process and integrate that informationC. store information as necessaryD. command responses (mainly by signals to muscles and glands)II. how neurons receive and conduct signalsA. review of neuron structure: dendrites, cell body, axonB. neurons keep a resting membrane potential (polarized membrane)1. many negative ions (anions) are trapped inside the cell2. sodium-potassium pumps in the plasma membrane actively pump out 3 Na+ ions and bring in 2 K+ ions – makes inside even more negative3. active pumping sets up diffusion gradients- higher K+ concentration in the cell- higher Na+ concentration outside the cell- diffusion occurs to try and correct the imbalances- work must constantly be done to maintain the ion gradientsC. incoming signals generate action potentials by changing membrane potential beyond a threshold1. plasma membrane also has voltage-gated channels for Na+ and K+2. small amounts of depolarization do not affect these channels3. depolarization beyond a threshold leads to an action potential- first, Na+ channels open: Na+ rushes in- leads to a rapid change in membrane potential, all the way from about-70 mV to about +30 mV- K+ channels open: K+ rushes out- leads to a rapid repolarization- neurons have a refractory period between possible action potentials, because it takes time for the sodium-potassium pump to reestablish the ion gradientsD. action potentials propagate along dendrites, usually through the cell body, and down axons to the synapse(s)III. how neurons transmit signalsA. synapses are intercellular junctions between an axon and either a muscle cell, gland cell, or dendrites of another neuronB. cell sending signal: presynaptic cell; cell receiving signal: postsynaptic cellC. neurotransmitters carry the signal to the next cell1. action potential at end of axon leads to opening of voltage-gated Ca++ channels: Ca++ rushed in2. Ca++ stimulates vesicles filled with neurotransmitters to fuse with plasma membrane3. neurotransmitters are released into the synapse4. neurotransmitters bind with receptors in the cell membrane of the postsynaptic cell5. binding causes different effects depending on neurotransmitter type and postsynaptic cell type6. example: ACh binding to ion channel in muscle cell allows Na+ in and K+ out, starting an action potential in the muscle cellD. some know neurotransmitters and their major functions1. glutamate – excitatory (transmits action potentials)2. glycine and GABA – inhibitory (reduce likelihood of action potentials)3. dopamine – control of body movements4. serotonin – regulation of sleep and emotional stateE. neurotransmitters must be reabsorbed or destroyed, and receptor number can be modified1. the normal body responds to unusually high or low amounts of neurotransmitters- if neurotransmitter level stays too high, receptor number is reduced and reuptake or destruction mechanisms are increased- the opposite occurs if level stays too low- neurological disorders are often associated with problems in these responses (including psychiatric disorders)2. drug addiction is caused by body responses to drug exposure- example: cocaine leads to keeping too much dopamine around too long- eventually, dopamine receptor number is reduced- cocaine now needed just to feel normal, and higher dose needed to get high1 of 2BIOL 1030 – TOPIC 20 LECTURE NOTESIV. the role of supporting cellsA. called neuroglia in central nervous system (CNS – brain and spinal cord)B. 10x more of them than neurons in CNSC. major role is to produce myelin sheaths around axons1. myelin sheaths are layers of membrane, insulating the axon2. sheaths are interrupted every 1-2 mm by small gaps called nodes of Ranvier3. action potentials do not move along myelin-coated regions; instead, they “jump” to the next node of Ranvier4. thus, action potentials propagate quicker along myelinated axonsD. not all neuron cells have myelin sheathsV. comparison of animal nervous systemsA. sponges do not have a nervous systemB. radiata have neural netsC. echinoderms have a neural net with a central neural ringD. bilataria typically have a central nervous system, with a centralized control center (brain) located in the headVI. vertebrate nervous system organizationA. central nervous system (CNS) – brain and spinal cord; mainly association neuronsB. peripheral nervous system (PNS) – everything else; mainly sensory and motor neurons1. somatic motor neurons – control skeletal muscles2. autonomic motor neurons – regulate smooth and cardiac muscle, and glandsVII. vertebrate brain – selected regionsA. medulla oblongata (brain stem) – integrates brain with spinal cord; controls breathingB. cerebellum – associated with medulla oblongata; involved in coordination and motion memoryC. cerebrum – greatly enlarged in humans, generally larger in mammals relative to body mass; motor control, memory, emotion, higher functions (in cerebral cortex)1. left cerebral hemisphere controls right side of body, and vice-versa2. corpus callosum integrates the hemispheres 3. hemispheres divided into lobes with different main functions2 of