Neurotransmitters I Lecture Powerpoint Flashcards
90% of neurons in the body are what type? Where do they reside?
Interneurons/association neurons, between sensory and motor pathways in the CNS
Cerebellum acts as a ____ between movement ____ vs movement ____ to modify actions
Comparer, intended, actualized
Majority of all sensory information is….
….ignored (for example the constant noise in surroundings)
Spinal cord level circuits that do not require simple conduit of signals from periphery of body to brain and vise versa (4)
- Walking circuits
- withdrawal reflexes
- support against gravity circuits
- other reflex control of organ function such as defecation and micturition
2 divisions of afferent division of PNS
Visceral sensory division and somatic sensory division
2 divisions of efferent division of PNS
Viceral motor division to cardiac, smooth muscle, and glands (autonomic, sympathetic and parasympathetic) and somatic motor division to skeletal muscle
Electrical synapses definition and locations they are found (3)
Electrical current passing from cell to cell often thru gap junctions that is not common in the CNS or the body except in certain areas, useful to rapidly recruit and conduct more quickly than thru chemical synapses
- retina
- olfactory bulb
- smooth and cardiac muscle
Chemical synapses
More common method of synapse in the body thru release of neurotransmitters (chemical messengers)
Neurotransmitters
One of over 40 compounds that are used in neuron communication thru release into the synapse that can then excite/inhibit postsynaptic neuron at a receptor, one way and thus allows signals directed toward a specific goal, must be present in nerve terminal, released during action potential, and have reproducible effect
2 structures important to function of synapse
- presynaptic vesicles housing the neurotransmitter
- mitochondria to provide energy to produce neurotransmitter
Axodendritic, axosomatic, and axoaxonic synapses
- Where the axon of one neuron synapses on the dendrite of the other
- Where the axon of one neuron synapses on the body of the other
- Where the axon of one neuron synapses on the axon of another
Number of synapses on a postsynaptic cell is variable based on…
….decision making capacity of that postsynaptic cell (for example cerebellum receives many more than a spinal motor neuron)
Quantum
Several thousand molecules of neurotransmitter stored in synaptic vesicles at the nerve terminals kept relatively constant thru reabsorption or degradation to maintain a relative constant amount
Neuropeptides vs small molecule neurotransmitters
Neuropeptides are stored in larger granules that act at lower conc. and have longer lasting effects, with some functioning hormonally as well and being released from other tissue unlike small molecule neurotransmitters
Lock and key fit
Idea that only specific neurotransmitters or very closely related substances can bind to a specific receptor
What determines if a neurotransmitter is excitatory or inhibitory?
The receptor it binds (heart ones may be inhibitory while skeletal muscle are excitatory for the same neurotransmitter)
Neuromodulators and an example
Hormones, neuropeptides, or other messengers that modify synaptic transmission, act pre or postsynaptically to influence likelihood an AP will result in production of an AP in post synaptic terminal (ex - nitric oxide released by postsynaptic neurons diffuses into presynpatic neurons and stimulates release of more neurotransmitter)
Ca2+ mech of neurotransmitter release
Depolarization of presynpatic membrane by action potential opens voltage gated Ca2+ channels, influx of Ca2+ induces release of neurotransmitter thru unknown mechanism resulting in exocytosis via fusion of the vesicle to the membrane
Transmitters that open ____ excite postsynaptic neuron (depolarization), transmitters that are open ___ inhibit the postsynaptic neuron (hyperpolarization)
sodium channels, chloride channels
Secondary messenger activators
Cause prolonged changes in activity of neurons from seconds to months, some processes like memory require long term changes in neuronal activity in function, about 75% transduced via G protein coupled receptors, upon binding a portion of G protein dissociates and perform different functions
4 changes G protein bring about in post synaptic membrane
- Opening specific ion channels in the post synaptic membrane
- activation of an enzye system in cells membrane
- activation of one or more intracellular enzymes
- activate gene of transcription
Inactivation of ___ is acheived by phosphodiesterase
cAMP
Ways neurotransmitters are removed from synaptic cleft and ensure short term effect on post synpatic terminals
- Catabolism of enzymes located near receptor
- active transport(quickly pump back in nerve terminals)
- diffusion (into extracellular fluid
More ___ a neuron has the greater its info processing capability
-Synapses
Excitatory postsynaptic potential (EPSP) and 2 examples
A positive voltage change causing postsynaptic cell to become more likely to fire (depolarization) resulting from Na+ flowing into cell,
-glutamate and aspartate
Inhibitory postsynaptic potential (IPSP) and 2 examples
A neg voltage change causing postsynaptic cell to be less likely to fire (hyperpolarization) resulting from Cl- flowing into cell or K+ leaving the cell
-glycine and GABA
What 2 neurotransmitters can be either EPSP or IPSPs?
Ach and norepi
Normal resting membrane potential and general distribution of Na, K, Cl, and protein anions
-65mV due to excess Na+ outside, K+ inside, Cl- outside, and proteins and such inside (neg charged)
Nernst potential
Potential that exactly electrically opposes the movement of an ion across the neuronal membrane down its conc. gradient (electrochemical equilibrium of a particular ion), determined by the balance when conc. gradient and electric gradient directly oppose each other (61mV for Na+ to prevent influx, -87mV for K+ to prevent efflux, and -69mV in Cl- to prevent influx)
Threshold value for neuronal AP
Potential required for opening of voltage gated sodium channels causing rapid movement of Na+ inward in a neuron
Excitatory cholinergic synapse mech of action
- Ach crosses synapse
- Ach receptors trigger opening of Na+ channels producing local potential
- Upon reaching -55 mV see AP triggered
Inhibitory post synaptic potential mech of action
-Inhibitory synapses open K+ or Cl- channels causing hyperpolarization of neuron, cell membrane potential becoems more negative resulting in inhibitory post synaptic potential (-65 to -90mV)
Presynaptic inhibition, what neurotransmitter does this?
- Activation of presynaptic synapses decreasing ability of Ca2+ channels to open on the presynaptic terminals resulting in reduced neurotransmitter release
- Typically facilitated by GABA
When action potentials from peripheral baroreceptors begin firing very frequently due to high pressure, this is relayed to the brain to cause what physiologic response?
Vasodilation
Criteria for a chemical to be considered a neurotransmitter (3)
- chemical must be present in nerve terminal
- chemical must be released from nerve terminal by action potential
- chemical when applied experimentally to receptor must produce identical effect
Example of a small molecule neurotransmitter and example of a neuropeptide
- GABA
- cholecystokinin or B endorphins
2 components of receptors on postsynaptic membranes
- Binding component
- Ionophore component (opens an ion channel or activates 2ndary messenger system
75% of second messenger activators are ____. How do these systems work?
G protein coupled receptors, work thru dissociation with alpha portion moving about cytoplasm and either oopening an ion channel, activating an enzyme system, or allowing gene transcription
Ability to process, store, and recall info is due to…
….neural integration
Neural integration is based on…
….types of postsynaptic potentials produced by neurotransmitters (excitatory or inhibitory)
Excitatory adrenergic synapse mech of action
- NE binds receptor on post synaptic cell
- activates cAMP
- wide variety of effects such as activating enzymes and opening ligand gates
- post synaptic potential formed
GABA is ____ through producing ___polarization
inhibitory, hyper
Facilitation of neurons
When a neuron potential is closer to threshold than normal but not yet to firing level that can be easily stimulated by summated by subsequent input
2 types of summation of postsynaptic potentials
Spatial - multiple terminal excitation simultaneously by an EPSP exceeding threshold for inducing action potential
Temporal summation - when post synaptic neuron is stimulated repeatedly by the same presynaptic neuron, with more rapid firing of EPSP in shortened period of time can exceed threshold for inducing action potential
Macro example of summation in action
- Accidentally touching a hot pan on stove results in EPSPs in motor neurons causing hand to jerk back quickly
- Intentionally touching a hot pot of coffee keeps you from withdrawing and dropping it by having IPSP’s dominating effect overriding the EPSPs
Synaptic fatigue
Occurs when exhaustion of stores of transmitter in synaptic terminals occurs
Post tetanic facilitation
Enhanced responsiveness following repetitive stimulation due to build up of Ca2+ ions in presynaptic terminals causing more vesicular release of transmitter
Synaptic delay
Depending on length of delay of neurotransmission, can calculate number of neurons in a circuit
Effect of acidosis, alkalosis, and hypoxia on neuronal activity
- depresses
- increases excitability (seizures)
- can’t go long without!
Neural coding of qualitative vs quantitative info
- Qualitative depends on which neurons are fired
- quantitative depends on # of neurons recruited with stronger stimuli causing more rapid firing rate
Threshold, maximal, submaximal, supramaximal stimuli
Threshold causes AP, maximal is max # of AP that can be generated per unit time, submaximal is between threshold and maximal, supramaximal sees no more frequency than max in # of AP that can be generated
