Chapter 3: The Synapse Flashcards
This is a unique junction that mediates the transfer of information from one neuron to another or from one neuron to an effector cell.
SYNAPSE
Most synapses occur between axonal endings of one neuron and the dendrites or the cell bodies of other neurons. This is called:
axodendritic or axosomatic synapse
The neuron conducting impulses toward the synapse is called:
presynaptic neuron
The neuron that transmits the electrical signal away from the synapse is called:
postsynaptic neuron.
True regarding Synapse. Except:
- The postsynaptic neuron sends the information and the presynaptic neuron is the information recipient.
- Most neurons function as both presynaptic and postsynaptic neurons, receiving information from one neuron and sending it to another neuron.
- Neurons have between 1000 and 10 000 axonal terminals.
- The postsynaptic cell may be either another neuron or an effector cell.
Except: number 1
Correct: 1. The presynaptic neuron sends the information and the postsynaptic neuron is the information recipient.
Synapses between neurons and muscle cells are called:
neuromuscular junctions
Synapses that between neurons and gland cells are called:
neuroglandular junctions
___________ - Bridged junctions that correspond to the gap junctions found between certain other body cells. They contain protein channels that interconnect the cytoplasm of adjacent neurons and allow the current carrying ions to flow directly from one neuron to the next.
Electrical Synapses
Communication may be ___________ or ___________ depending on the nature of the synapses.
uni-directional
bi-directional
Electrical synapses are abundant in certain non-nervous tissues, such as ________ and _________.
cardiac
smooth muscles
Specialized for release and reception of chemical neurotransmitters.
Chemical Synapses
Typical chemical synapse has two parts:
- Axonal terminal of the presynaptic neuron.
- A receptor region on the membrane of a dendrite or the cell body of the postsynaptic neuron which have (several types of) neurotransmitter receptors.
___________ - they are tiny membrane bound sacs, found in axonal terminals of the presynaptic neuron.
Synaptic vesicles
___________ - they are fluid filled spaces, that separate pre and postsynaptic neurons.
Synaptic cleft
______________________ is a chemical event that depends on the release, diffusion and receptor binding of neurotransmitter molecules and results in uni-directional communication between neurons.
The transmission of signals across chemical synapses
Chemical synapses convert the ___________ into chemical signals (neurotransmitters) that travel across the ___________ to the postsynaptic cells, where they are converted back into electrical signals.
electrical signals
synapse
There are a series of events that trigger neurotransmitter release. Once released the neurotransmitter crosses the synaptic cleft and binds to receptors on the postsynaptic membrane, causing changes in the postsynaptic membrane permeability. This process is called:
Information Transfer Across Chemical Synapses
Series of events that trigger neurotransmitter release:
- Calcium gates open in the presynaptic axonal terminal.
- Neurotransmitter is released by exocytosis.
- Neurotransmitters bind to postsynaptic receptors.
- Ion channels open in the postsynaptic membrane.
They are substances such as norepinephrine, acetylcholine and dopamine that are released when the terminal end of an axon is stimulated.
Neurotransmitters
All statements are TRUE. Except:
- The neurotransmitter then travels across the dendrite to another neuron or an effector cell to either stimulate or inhibit the effector.
- There are over 50 different chemicals that are either known neurotransmitters or are candidates.
- Neurotransmitters are classified as being present in the pre-synaptic terminal axon and are released when appropriately stimulated.
Except: 1
Some neurotransmitters can be synthesized in different areas of the nervous system. This areas are:
1) cell body of the neuron
2) Pre-synaptic terminal
What are the mechanisms in termination of neurotransmitter Effects?
- Degradation by enzymes
- Removal from the synapse by re-uptake into the presynaptic terminal where it is stored or destroyed by enzymes.
- Diffusion of the neurotransmitter away from the synapse.
Determine if the statements are True or False:
Neural transmission across a chemical synapse is slow and reflects the time required for neurotransmitter release, diffusion across the synapse and binding to receptors. This synaptic delay lasts 0.3 - 0.5 ms and is the rate-limiting step of neurotransmission; therefore transmission along short neural pathways occurs rapidly. Transmission along multi-synaptic pathways occurs more slowly.
True
Classification of Neurotransmitters:
- Acetylcholine
- Biogenic Amines
- Amino Acids
- Peptides
___________ - Types consist of dopamine, norepinephrine and serotonin. They are broadly distributed in the brain where they play a role in emotional behaviour and in the regulation of the biological clock.
Biogenic Amines
____________ - This was the first neurotransmitter to be identified. It is the best understood because it is released at the neuromuscular junction. It is synthesized and enclosed in synaptic vesicles within axonal terminals.
Acetylcholine
__________ - They are difficult to prove as neurotransmitters. They occur in all cells of the body and are important in many biochemical reactions. neurotransmitters have only been found in the CNS.
Amino Acids
Neuropeptides include a broad spectrum of molecules with diverse effects. Neuropeptide called substance P is an important mediator of pain signals.
Peptides
_________ - act as a natural euphoric and decrease our perception of pain, under certain stressful conditions.
Endorphins
Receptors on postsynaptic membranes are specialized to open ion channels which convert chemical signals into electrical signals. These chemically gated channels are not as sensitive to changes in membrane potential, unlike voltage-gated ion channels.
Postsynaptic potentials and synaptic integration
Two types of chemical synapses
- Excitatory
- Inhibitory
_______________ , neurotransmitter binding causes depolarization of the postsynaptic membrane. Here only one type of channel opens allowing Na+ ions to diffuse through the membrane.
Excitatory Synapses
If enough neurotransmitters bind, depolarization of the postsynaptic membrane can successfully cause local graded depolarization events called ___________ , which occur at excitatory postsynaptic membranes.
Excitatory Postsynaptic Potentials (EPSP)
Each EPSP lasts a few milli-seconds then membrane returns to RMP; therefore, the function of EPSP is to help trigger an __________ at the axon hillock.
action potential
All Statements are True regarding excitatory postsynaptic potentials (EPSP). Except:
- If currents reaching the axon hillock are strong enough to depolarize the axon to threshold, axonal voltage gated channels open and an action potential, is generated.
- A single EPSP cannot induce an action potential in the postsynaptic neuron. If thousands of excitatory axonal terminals fire on the same postsynaptic membrane, the probability of reaching threshold depolarization increases.
- EPSPs added together (or summated) can influence the activity of a presynaptic neuron.
Except: number 3
Correct: EPSPs added together (or summated) can influence the activity of a postsynaptic neuron.
Can result from the opening of Cl- or K+ channels. The ionic flow in either case, will cause the inside of the postsynaptic cell to hyperpolarize. Hyperpolarizing postsynaptic potential is called an __________________ .
inhibitory postsynaptic potential (IPSP)
_____________ occurs when the release of excitatory neurotransmitters by one neuron, is inhibited by the activity of another neuron, via an axo-axonic synapse.
Presynaptic inhibition
Integration of input from synapses is called _________ and occurs at the trigger zone.
summation
There are two types of summations:
Spatial summation
Temporal summation
______________ - results from a build up of neurotransmitters released by a single presynaptic end bulb, two or more times in rapid succession.
Temporal summation
___________ - results from build up of neurotransmitters released simultaneous by several presynaptic end bulbs.
Spatial summation
TRUE or FALSE
Spatial and temporal summations are usually acting together to influence the chance of a nerve impulse occurring. The sum of all the excitatory and inhibitory effects at any given time determines the effect on the postsynaptic neuron.
TRUE
