block 4 synapses Flashcards
why is synaptic integration important?
-Neurons make contact with
multiple neurons and receive
100-1000s of synaptic inputs
-synaptic integration enables
information processing in the
CNS
-integration of synaptic inputs
determines nervous system
function.
therefore synpases and there contacts are important because of the complexity of the neurone, and their ability to reach 100’s of neurones
two aspects of synaptic integration
-Single EPSP: A tiny positive signal in a neuron that briefly makes it more likely to send action potential
-Spatial Integration: Adding up signals from multiple neurons sending inputs to one neuron at the same time.
-t
temporal Integration: Adding up repeated signals from the same neuron over a short period of time.
parameters that effect synaptic integration
b -The neuron needs multiple signals from synapses, both from different places (spatial summation) and over time (temporal summation), to generate a large enough signal to “fire” and send a message. The structure of the neuron and its connections affects how these signals combine
spatial synaptic integration
A single neuron can receive signals from multiple synapses at once. When several neurons are active at the same time, they send signals to the same target neuron. The combined effect of all these signals from different synapses determines the electrical state of the target neuron’s cell body (soma). If the combined signals are strong enough, the neuron will fire and send its own signal.
purkinje cells= intergrators in the cerebellum
urkinje cells are special brain cells that receive two types of input, like getting messages from two different messengers:
Climbing fibre (big messenger):
Each Purkinje cell talks to just one climbing fibre.
That climbing fibre makes many, many connections to the Purkinje cell, so it sends a strong, focused message.
Parallel fibres (small messengers):
Each Purkinje cell gets messages from thousands of parallel fibres.
But each parallel fibre only makes one small connection with the Purkinje cell, so their messages are weaker individually.
Together, the climbing fibre gives one strong signal, while the parallel fibres work together to provide lots of small signals.
purkinjie cells-two types of synaptic inputs summary
Parallel fibre input:
Single contact
- small synaptic
current & potential
Climbing fibre input:
Many contacts
- large synaptic current & potential,
-triggers complex spike
spatial synaptic intergration and length constant
synaptic potentials spread passively from site of synapse
- The amplitude of synaptic potential change reduces with distance from synapse
- The decline in synaptic amplitude with distance from the synapse is determined by length constant
- Synaptic potential decline is
described by length constant
(lambda) and the exponential (see lecture)
- make a maths sheet block 4 lecture 2
whats the purpose of chemical synapses
-information transfer between cells: excitation, inhibition, modulation
-amplification of signals
-intergration of multiple inputs
-plasticity- learning and memory
inotropic mechanisms
- ligand-gated ion channels. When a neurotransmitter binds to the receptor, it directly causes the ion channel to open or close, altering the flow of specific ions across the membrane.
metabotrophic
Metabotropic receptors are G-protein-coupled receptors (GPCRs) that do not directly control ion channels. Instead, they initiate a cascade of intracellular signalling through second messengers.
what are the 3 ways to classify synpases:
- transmitter chemistry=e.g. acetylcholine
-transmitter mechanisms: iontropic or metabotropic
-transmitter functions: inhibitory or excitatory
what describes weather a synapses are excitatory or inhibitory?
- depends on the change in postsynaptic membrane permeability caused by the neurotransmitter
resting membrane potential
Resting Membrane Potential:
The resting membrane potential (Vm) is approximately -60 mV.
This is due to ion concentration gradients and higher permeability for K⁺ over Na⁺ (about 50 times more permeable).
Typical ion concentrations:
K⁺: Inside = 135 mM; Outside = 3 mM.
Cl⁻: Inside = 7 mM; Outside = 120 mM.
Na⁺: Inside = 18 mM; Outside = 145 mM.
Ca²⁺: Inside = 0.0001 mM; Outside = 1.5 mM.
how do neurotransmitters work?
Neurotransmitters affect the postsynaptic cell by opening ion channels, altering membrane permeability, and changing the membrane potential.
Excitatory Postsynaptic Potential (EPSP)
what happens if you make the membrane potential more permeable for K+
-more k + leaves the cell as we are making the cell more positive shifting the ratio
-therefore the membrane will become more negative causing a slight hyperpolarisation
-A more negative cell is less likely to “fire” a signal to the next cell.
-causes an inhibitory postsynaptic potential ( the nerve is less like;y to send a action potential)
