Unit 2 Part 3: Synapses, Neuromuscular Junction, and Neurotransmitters PDF

Unit 2 Part 3-Synapses, Neuromuscular Junctions, and Neurotransmitters Readings: p. 197-203, 207- 212  The big picture Cells tissue Organs Organ systems Organ systems Neurons and...

Unit 2 Part 3-Synapses, Neuromuscular Junctions, and Neurotransmitters Readings: p. 197-203, 207- 212  The big picture Cells tissue Organs Organ systems Organ systems Neurons and Requires work together to AP’s communication maintain homeostasis Action potentials/cellular Communication between response determined neurons and effector cells by interaction btwn NT via action potentials and receptor  How does the message continue past an individual neuron? What happens when the impulse reaches the axon terminals? A synapse occurs  Synapses Presynaptic neuron-The neuron before the synapse takes place Postsynaptic neuron-The neuron after the synapse takes place  Types of Synapses (Message transfer) Transfer of information from one neuron to the next or to an effector organ (skeletal muscle, or glands) Types of synapses 1) Electrical Synapses Not as abundant Found in brain and heart Signal travels through gap junctions 2) Chemical Synapses Abundant Found throughout the entire body Neurotransmitter (chemical) released from one neuron opens/closes ligand gated ion channels on neighbouring neurons A Chemical Synapse Events occurring at a chemical synapse Events occurring at a chemical synapse  Ion passageways across membranes 4 types of ion channels can exist on a membrane Leakage Voltage gated Ligand-gated Mechanically gated Usually ion Open/close in Open/close in Open/close in specific response to response to response to a Are always open changes in chemical mechanical event voltage across messenger on the cell membrane attaching to receptor on membrane Note: Understanding how these work provides the basis of how nerve signals are propagated and how muscle contractions are initiated  Chemical synapses and Postsynaptic potential (PSP) Change in membrane potential of post synaptic membrane Can be either an inhibitory postsynaptic potential (IPSP) or excitatory post synaptic potential (EPSP)  Excitatory and inhibitory neurotransmitters Excitatory Inhibitory neurotransmitter neurotransmitter Increases likelihood of an AP Decreases likelihood of an AP occurring on post synaptic neuron occurring on post synaptic neuron Leads to an excitatory post Leads to an inhibitory post synaptic synaptic potential (EPSP) potential (IPSP) Most abundant is Acetylcholine Most abundant in brain is GABA Acetylcholine works via opening GABA works via the opening of Cl- Na+ ion channels ion channels  Na+ and K+ are not the only ions responsibl e for changing membrane potential Neurotransmitters Select Neurotransmitters Many different types Common ones: Acetylcholine Norepinepherine Dopamine Serotonin GABA (gamma aminobutyric acid) Note: All neurotransmitters have specific receptors. All receptors have varied distributions. Some may be more abundant in some regions compared to others.  Acetylcholine Both CNS and PNS Binds to muscarinic receptors (mainly CNS, and some organs) and also nicotinic receptors (mainly PNS) Can have both excitatory or inhibitory actions depending on the type of receptor it binds to (In muscle it is excitatory) Major neurotransmitter at neuromuscular junction  Nicotinic and Muscarinic receptors  Norepinepherine Both CNS and PNS A “feel good” neurotransmitter in the brain Can be both excitatory or inhibitory A major neurotransmitter of the sympathetic nervous system Low levels can lead to depression  Dopamine Mainly in CNS Excitatory or inhibitory neurotransmitter A “feel good” neurotransmitter Cocaine blocks the re-uptake of dopamine similar to the effects it has on Nepi Amphetamines interfere with re-uptake of dopamine via the dopamine transporter (DAT) and also interfere with filling of vesicles with dopamine. Dopamine neurotransmission is increased in schizophrenia.  Serotonin CNS Mainly inhibitory role Implicated in sleep regulation, migraines, appetite, and mood regulation  GABA Main inhibitory neurotransmitter in CNS Binding of GABA to GABAA receptor opens up Chloride channels (Cl-) Chloride ion (negative) rushes into cell and makes inside of cell more negative (an IPSP)