Neurotransmitters, Synapses, Neural Communication and Hormones Flashcards
Outline the electrical synapse
“Gap junctions”
Very small gap between two neurones (2-4 nm)
§
The facing membranes have large channels that allow ions to move directly from one cell to the other
Transmission from one neuron to the next is similar to action potential conduction along the axon
Very fast –no time delay
Rare in human CNS (eye movements)
NEAR-INSTANTANEOUS TRANSMISSION
outline the chemical synapse
There is a gap between the axon of one neurone and the dendrite of the next one
Small gap but much larger than gap junctions (20-40 nm)
Each neurone has many (typically ca 1000) synapses
Slower (ca 1ms)
Chemical synapses Specialized structures for transmitting chemical signals from one neuron (presynaptic neuron) to another (postsynaptic neuron) Neurons are separated by small gap = synaptic cleft
How does the chemical synapse work?
- Action potential arrives at presynaptic membrane
- Voltage-gated Ca2+ channels open, Ca2+ diffuses into cell
- Synaptic vesicles fuse with membrane, releasing neurotransmitter molecules into synaptic cleft 4. Transmitter binds to postsynaptic receptors, opening ion channels
- If channel is for Na+: → depolarization= excitatory postsynaptic potential (EPSP) If channel is for Cl-: → hyperpolarization= inhibitory postsynaptic potential (IPSP)
- EPSP/IPSP propagated along membrane
what is a receptor in terms of neurones?
Receptors are membrane proteinsthat bind neurotransmitters
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
Fast= Ionotropic receptors
These control the ion channel directly § When bound to the transmitter the ion channel opens and ions flow across the membrane § Also known as ligand-gated ion channels
slow= metabrotropic receptors
These also bind with the neurotransmitter but do not open the ion channel
They activate G-Proteins that subsequently control the ion channel
what i the differecne between tempral and spatial summation
temporal: many EPSPs/IPSPs occur at the same time
spatial: many axons converge on one neuron
what happens when EPSPS/IPSPS reach the axon hilllock?
If net charge (sum of EPSPs+IPSPs) is below threshold (
what is a neurotransmitter?
A chemical released by one neuron that affects another neuron or an effector organ (e.g., muscle, gland, blood vessel)
where are neurotransmitters qualities?
. Synthesized in the presynaptic neuron
- Localized to vesicles in the presynaptic neuron
- Released from the presynaptic neuron under physiological conditions
- Rabidly removed from the synaptic cleft by uptake or degradation
- Presence of receptor on the post-synaptic neuron
- Binding to the receptor elicits a biological response
give the 7 steps to neurotransmitters
neurotransmitters are synthathised from precursors under the influence of enzymes
- stored in vesicles
- neurotransmitter molecules that leak from their vescicles are destroyed by enzymes
- Action potential cause vesicles to fuse wit hsynpase and release neurotransmitters
- some of it binds with auto receptor and inhibit subsequent neurotransmitter release
- rest of it binds to receptors
- released neurotransmitters are deactivated either by uptake orenzyme degredation
give some excitatory neurones in the CNS
Acetylcholine Aspartate Dopamine Histamine Norepinephrine Epinephrine Glutamate Serotonin
give some inhibitory neurones in the CNS
GABA Glycine
explain the many types of communication in the CNS
Point-to-point= Restricts synaptic communication
hormonal communication= Secretes chemicals into the blood stream to affect the entire body
interconnected neurones in the ANS= Simultaneously controls responses in many internal organs.
Diffuse modulatory systems:
Specific neurotransmitter. Regulate arousal, mood, motivation, sexual behavior, emotion, sleep, etc.
what is a DMS
diffuse modulatory systems
Modulatory system affect wide areas to make them more or less excitable or more or less synchronously active etc.
Messages that must be widely broadcast through the brain use diffuse modulatory systems
The brain uses many of these mechanisms each requiring a specific neurotransmitter
Connections are widely dispersed throughout the brain
Important in motor control, memory, mood, motivation, and metabolic state
Heavily involved in many psychiatric disorders
outline DMS within the brain
Core of each system has a small number of neurons § Neurons of the diffuse system arise from this central core
The core is in the brain stem
Each neuron has tremendous affect because it can connect to as many as 100,000 neurons
Neurotransmitters are released into the extracellular fluid and can diffuse to many neurons
what is the Noradrenergic Locus Coeruleus
Makes some of the most diffuse connections in the brain
Involved in regulation of attention, arousal, sleep wake cycles, learning and memory, anxiety, pain, mood and brain metabolism
Activated by new, unexpected, non-painful sensory stimuli
General arousal to interesting events in the outside world
Increase brain responsiveness, speeding information processing