(4) Neurotransmitters, synapses, neuronal communication and hormones Flashcards
What is a neuron?
Information processing device, transfers information
What type of signals flow via a neuron (within)
Information flows within a neuron via electrical signals, through action potential
How does information flow between neurons?
Information flows between neurons via chemical signals
Where do neurons communicate?
Synapses
What is a synapse?
The gap between neurons where signals are passed from one to another, from pre to post synaptic neuron
What are the two types of synapses?
-Electrical and chemical synapses
How big is the gap between neurons? (electrical)
Very small gap between two neurones (2-4 nm)
What type of channels do facing membranes have? (electrical)
The facing membranes have large channels that allow ions to move directly from one cell to the other
What is transmission similar to? (electrical)
Transmission from one neuron to the next is similar to action potential conduction along the axon
How fast is transmission at electrical synapses?
Very fast – no time delay
What is Near-Instantaneous Transmission ?
Giving a current injection into the pre synapse to see how fast the post synapse responds, Artificial action potential
What did Eric Kandel do?
Eric Kandel: experiments with Aplysia (sea slug) which led to the understanding of short and long term memory
What is a chemical synapse?
The gap between the axon of one neurone and the dendrite of the next one
How big is the gap between neurons in chemical synapses?
Small gap but much larger than gap junctions (20-40 nm)
How many synapses does a neuron have? (chemical)
Each neurone has many (typically ca 1000) synapses
What are neurons separated by? (chemical)
Neurons are separated by small gap –the synaptic cleft
Are chemical synapses slower or faster than electrical?
slower
What are receptors?
Receptors are membrane proteins that bind neurotransmitters
(post synaptic receptors) Receptors can only bind to specific ________________?
Each receptor type can bind only a specific neurotransmitter – lock-and-key principle: when a transmitter molecule binds to the receptor, the receptor changes shape, causing an ion channel to open
What are ionotropic receptors?
These control the ion channel directly, when bound to the transmitter the ion channel opens and ions flow across the membrane,
What are ionotropic receptors also known as?
also known as ligand-gated ion channels (FAST)
What are Metabotropic receptors?
These also bind with the neurotransmitter but do not open the ion channel, they activate G-Proteins that subsequently control the ion channel (SLOW), needs another messenger to open the channel
What happens if net charge in EPSP and IPSP is below threshold when it reaches the axon hillock?
If net charge (sum of EPSPs+IPSPs) is below threshold (
What happens if net charge in EPSP and IPSP is at threshold when it reaches the axon hillock?
If net charge (sum of EPSPs+IPSPs) is at threshold (-40 mV):AP is elicited
What is the net charge in EPSP and IPSP threshold when it reaches the axon hillock?
-40mV
What happens when an action potential is elicited?
The AP travels along the axon to the axon terminal The AP causes release of neurotransmitter, passing the signal to the next postsynaptic neuron, etc.
What is a neurotransmitter?
A chemical released by one neuron that affects another neuron or an effector organ
Neurotransmitters can be _____ or _____
Neurotransmitters can be excitatory or inhibitory (can be both)
How many neurotransmitters does a neuron typically synthesize and release?
Each neurone typically synthesizes and releases one neurotransmitter
Examples of excitory neurotransmitters?
Acetylcholine, Aspartate, Dopamine, Histamine, Norepinephrine, Epinephrine, Glutamate and Serotonin
Examples of inhibitory neurotransmitters?
GABA and Glycine
What is hormonal communication?
secretes chemicals into the blood stream to affect the entire body, not just brain
What are Interconnected neurons of the ANS
simultaneously controls responses in many internal organs, chain of neuron
what are Diffuse modulatory systems
specific neurotransmitter, regulate arousal, mood, motivation, sexual behaviour, emotion, sleep, etc
Modulatory system affect wide areas to make them…
more or less excitable or more or less synchronously active etc.
The brains modulatory systems use mechanisms requiring….
The brain uses many of these mechanisms each requiring a specific neurotransmitter
What does the diffuse modulatory systems control?
Important in motor control, memory, mood, motivation, and metabolic state, heavily involved in many psychiatric disorders.
How many neurons can a neuron connect to?
Each neuron has tremendous affect because it can connect to as many as 100,000 neurons
Where are neurotransmitters released?
Neurotransmitters are released into the extracellular fluid and can diffuse to many neurons
Where do neurons in the diffuse system arise from?
Neurons of the diffuse system arise from a central core, in the brainstem
what is the Noradrenergic Locus Coeruleus involved in?
involved in regulation of attention, arousal, sleep wake cycles, learning and memory, anxiety, pain, mood and brain metabolism
What activates the Noradrenergic Locus Coeruleus?
Activated by new, unexpected, non-painful sensory stimuli, general arousal to interesting events in the outside world
Noradrenergic Locus Coeruleus increases…
Increase brain responsiveness, speeding information processing
The Serotonergic Raphe Nuclei fires most…
Fire most during wakefulness
The Serotonergic Raphe Nuclei is involved in…
Involved in sleep wake cycles and stages of sleep, control of mood and emotional behaviours
The Serotonergic Raphe Nuclei is part of what activating system?
Part of reticular activating system
In the Dopaminergic Substantia Nigra, neurons project from…
Neurons project from Substantia Nigra to striatum
Dopaminergic Substantia Nigra is involved in…
Control voluntary movements, degeneration results in Parkinson’s disease
What is the Colinergic Basal Forebrain involved in?
Implicated in arousal, sleep wake cycles, learning and memory
What is the general function of the Colinergic Basal Forebrain?
General function not completely understood, first cells to die in the course of Alzheimer’s disease
How do psychoactive drugs work?
Many psychoactive drugs work by binding to specific receptors in the brain
Why might depression be caused?
Some types of depression may be due to lack of serotonin
How do SSRIs (selective serotonin reuptake inhibitors) work?
e.g., Prozac – work by increasing the amount of serotonin that can bind to postsynaptic receptors
Drugs either ____ or ____ activity at the synapse
facilitate or inhibit activity at the synapse
What are Antagonistic drugs?
drugs block the effects of neurotransmitters (novacaine, caffeine)
What are Agonist drugs?
drugs mimic or increase the effects of neurotransmitters (receptors in the brain respond to heroin, LSD and cocaine)
Almost all abused drugs stimulate…
dopamine release in the nucleus accumbens
What are Stimulant drugs?
increase excitement, alertness, motor activity and elevate mood amphetamines, cocaine, MDMA (Ecstasy), nicotine Stimulant drugs directly stimulate dopamine receptor
What are Opiate drugs?
derived from the opium poppy (or similar) Opiates decrease sensitivity to pain and increase relaxation morphine, heroin, methadone
What does alcohol alter?
It alters membranes, ion channels, enzymes, and receptors
Alcohol binds directly to receptors for…
Acetylcholine, Serotonin, GABA and Glutamate
