Flashcards in Chemical Neurotransmitters Deck (80)
A specialised junction between the axon terminal and post synaptic cell
What are the two types of synapses?
Why is synaptic transmission important?
Synaptic transmission is important to understand how the nervous system operates the following:
- cognition, learning & memory
- actions of psychoactive drugs
- causes of psychiatric and neurological disorders
What is a gap junction composed of?
6 connexins (gap junction protein) which make a connexon.
The pore size is 2nm
What is an electrical synapse? Expand on its transmission and where it is found. (7 points)
- It allows the direct transfer of ionic current from one cell to the next.
- Gap junctions are composed of 6 connexins; that make up 1 connexon. The pore size is 2nm.
- Ions can flow bidirectionally.
- The cells are said to be electrically coupled.
- The conduction speed is very fast (0.3milliseconds) unlike the delay seen in chemical transmission.
- It is found in neuronal pathways that are associated with escape reflexes (fight or flight --> amygdala) or in neurones that need to be synchronised (cardiomyocytes that make up the heart muscle - you want the propagation of the action potential to proceed smoothly and uninterrupted from one cell to another to provide a uniform contraction of the heart)
- they are common in non-neuronal cells (glial cells - maintain homeostasis, form myelin)
Explain the information flow through neurones
Dendrites collect electrical signals.
Cell body integrates incoming signals and generates an outgoing signal to axon (through axon hillock)
Axon passes electrical signals to dendrites of another cell or to an effector cell
The study of the drugs on the nervous system
How are neurological and psychiatric disorders often caused by?
An imbalance of chemical transmitters in the brain
How can chemical synaptic transmission be modulated?
Drugs and Toxins
What do receptor agonists do?
They mimic the action of a neurotransmitter e.g. Morphine activates u-opioid receptors in the brain and spinal cord
What do receptor antagonists do?
They inhibit the normal action of a neurotransmitter e.g. ketamine blocks the action of glutamate at the NMDA receptor
Excitatory receptor + agonist = ____ signal
Inhibitory receptor + antagonist = ____ signal
Excitatory receptor + antagonist = ____ signal
Inhibitory receptor + agonist = ____ signal
What is an axon hillock?
The part of the neurone where the cell body meets the axon
What is the resting membrane potential and what is this due to?
-70mV - this is due to the concentration of ions (+vely or -vely charged particles) inside and outside the cell
What is on the outside of the cell?
High concentration of +vely charged Na ions and some -vely charged Cl ions
What is on the inside of the cell?
Low concentration of +vely charged K ions and high concentration of -vely charged protein ions
If enough +vely charged ions enter the cell, thereby resulting in more excitatory post synaptic potentials. Then the membrane potential reaches a threshold of excitation at the axon hillock. This will trigger an action potential. What is an action potential?
A brief increase in the permeability of the membrane to Na+ (in), immediately followed by a brief increase in the permeability of the membrane to K+ (out). Once an action potential is generated, it propagates all the way down to axon to the terminal buttons. While EPSP's are small, local and contained graded changes in the membrane potential from more -ve to more +ve, an AP is a brief but larger reversal in the membrane polarity. Once the AP reaches the terminal buttons this change in membrane polarity causes Ca channels which are normally held closed to open, and let Ca into the cell. Ca acts as a signal to release the neurotransmitter substance which is docked at the presynaptic membrane via exocytosis. The neurotransmitter then binds to the post-synaptic receptor and the cycle begins again.
Neurotransmitters are released in _____
Summarise synaptic signal integration
Neurotransmitters are released in quanta. Each neurone can receive thousands of inputs in the form of ion channel and G protein-coupled receptor activation.
Neurones perform sophisticated computation by adding together EPSPs to produce a significant post synaptic depolarisation.
Types of Summation: Spatial and Temporal summation
These complex inputs give rise to discrete outputs in the form of action potentials a.k.a neural computation.
What are the two types of EPSP summation?
Name two excitatory neurotransmitters (Na+ enters):
What will a single presynaptic action potential give rise to?
a small EPSP in a post synaptic neuron
What is and what will SPATIAL summation of EPSPs give rise to?
When two or more presynaptic inputs are active at the same time, their individual EPSPs are added together. It is better than TEMPORAL because it is quicker in generating an AP
What is and what will TEMPORAL summation of EPSPs give rise to?
When the same presynaptic input fibre fired APs in quick succession, the individual EPSPs add together. Not as good as SPATIAL because it takes longer to generate an AP.
Name two inhibitory neurotransmitters (Cl- enters):