SYNAPSES, NEUROTRANSMITTERS, HORMONES Flashcards
Define synaptic transmission
how neurons communicate
what is a synapse
the gap between neurons where signals are passed from the pre-synaptic neuron (“sending” neuron) to the post-synaptic neuron (“receiving” neuron)
what are the two types of synapses
electrical and chemical
explain electrical synapses
Action potential is always electrical, involves ion movements
Formed by gap junctions (2-4nm), which are made up by connexons (channel proteins)
Ions flow from one neuron to the other, generating changes in membrane potential of the post-synaptic neuron
Very fast transmission
Common where speed is crucial (reflexes and sensory systems)
Excitatory - **
Explain Chemical Synapses
Specialised structures for transmitting chemical signals from one neuron to another
The pre-synaptic neuron contains vesicles filled with neurotransmitters which are released in the synaptic cleft
Synaptic cleft: the gap between 2 neurons, (20-40nm)
The post-synaptic neuron has specialised structures (post-synaptic receptors) that neurotransmitters bind to
What is the process of synaptic transmission
- Action potential arrives at the axon terminal of pre-synaptic neuron
- Voltage-gated calcium channels open, they diffuse into the cell
- Synaptic vesicles fuse with the membrane, releasing the neurotransmitter molecules into the synaptic cleft
- Neurotransmitters can be excitatory or inhibitory
- Post-synaptic potential
→Excitatory: opens sodium channels = depolarisation [Excitatory Postsynaptic Potential - EPSP] can pass
→Inhibitory: opens chloride channels = hyperpolarisation [Inhibitory Postsynaptic Potential – IPSP] cannot pass
Explain the two types of summation
spatial summation: involves simultaneous signals coming from multiple presynaptic neurons being received by a single postsynaptic neuron
temporal summation: involves a single presynaptic neuron rapid-firing signals to a postsynaptic neuron
What are the two types of receptors
ionic and metabotropic
explain ionic receptors
Transmembrane proteins that have a pore or channel
When a neurotransmitter binds to the receptor, the receptor will open, allowing the ions to pass through and change the membrane potential of the post-synaptic neuron
explain metabotropic receptors
Not ion channels
They activate signals within the cell, which leads to the opening when it binds with the G protein
This can also allow other things to happen in the cell, slower and more prolonged signalling
What are neurotransmitters
chemicals released by a neutron that play a crucial role in transmitting signals between neutrons
Explain the journey of neurotransmitters
- Synthesised in the presynaptic neuron
- Localised to the vesicles in the presynaptic neuron
- Released from the presynaptic neuron
- Bind to the receptor of the post synaptic neuron, to elicit a biological response
- Rapidly removed from the synaptic cleft
Explain the reuptake of neurotransmitters
After the signal is transmitted, the neurotransmitter’s job is complete, and it is no longer needed in the synaptic cleft.
They are either:
→Recycled (reabsorbed) into the pre-synaptic cleft by cells called transporters
→The neurotransmitters are destroyed by enzymes
Explain the role of neurotransmitters in mental health
Low levels of serotonin are implicated in the aetiology of depression
SSRIs are a common treatment alongside therapy
Serotonin reuptake inhibitors will mean inhibiting is blocked and there is less reuptake, meaning there is more serotonin available to bind to receptors
What are neuromodulatory systems
A set of neural networks in the brain that use different neurotransmitters
Neurotransmitters are secreted by a small group of neurons in the brainstem and diffuse through large areas of the nervous system
Regulate different behaviours
Heavily implicated across psychiatric disorders
Name the 4 neuromodulatory systems
Noradrenergic Locus Coeruleus
Serotonergic Raphe Nuclei
Cholinergic Basal Forebrain
Dopaminergic Substantia Nigra
Explain the role of Noradrenergic Locus Coeruleus
Makes some of the most diffuse connections in the brain
Involved in the regulation of multiple functions (arousal, sleep/wake cycle, learning, memory, anxiety, pain, mood and brain metabolism)
Most known in the flight or fight response
Explain the role of Serotonergic Raphe Nuclei
Caudal nuclei innervate the spinal cord (pain sensation)
Rostral nuclei innervate the brain (sleep/wake cycles and regulation of sleep stages)
Implicated in the control of mood and emotions, mostly known for its role in depression
Explain the role of Cholinergic Basal Forebrain
General function not completely understood
Implicated in function like arousal, sleep/wake cycle, learning and memory
Mostly known for muscle contractions
Explain the role of Dopaminergic Substantia Nigra
Neurons project from the substantia nigra to thr striatum (control voluntary movements)
The ventral tegmental areea projects to the frontal cortex and areas of the imbic csystem (reward system pathway)
What is the relationship between dopamine and reward
Dopamine release is associated with the feeling of euphoria and pleasure
It signals to the brain which activities need to be replicated/repeated. It reinforces the actions, helping us to survive.
Dopamine and Drugs
Almost all abused drugs stimulate dopamine release in the ventral tegmental area (VTA)
Drugs hijack the rewards system by producing x10 higher dopamine in comparison to anything else
Nothing natural is as rewarding as this and therefore drug abuse leads to a disinterest in all other activities
After a period of use, the system adapts its sensitivity to dopamine
Some of the receptors will start to die overtime, the brain can readapt if someone stops using the drugs
Dopamine is implicated in the control of voluntary movements - Parkinsons
Parkinson’s disease is characterised by the progressive loss of dopamine producing neurons, in the substance nigra, which leads to a significant reduction in dopamine levels in the brain
As dopamine-producing neurons degenerate and die, the communication between different parts of the brain that controls movement becomes impaired.
What are hormones
Molecules secreted by endocrine glands
Travel through the blood stream to influence, the activity of organs
Control major bodily functions like hunger, reproduction and mood
Influence cells that have specific target receptors for that particular hormone
