Nerves Flashcards
What is a soma?
Cell body, contains the nucleus
What is the function of dendrites?
Transfer information between neurones
What is the function of the initial segment?
Arranges all the information for making action potentials
What is the function of an axon?
Takes the action potential elsewhere
What is the function of axon terminals?
Transfers the action potentials to other nerves or muscles. They relates neurotransmitters
What is the typical value of the resting membrane potential?
-70mV
What generates the resting membrane potential?
Na+/K+ pump and K+ specific ion channels
What is the function of the Na+/K+ pump?
Separates Na+ and K+ by pumping K+ into the cell and Na+ out
What is the function of K+ specific ion channels?
They allow K+ to flow down their concentration gradient by facilitated diffusion, which creates an electrochemical gradient which pulls the K+ back into the cell. Equilibrium is eventually reached
Why is the resting membrane potential -70mV and not -90mV?
Leaky channels and the membranes permeability depolarise the cell slightly
What are graded potentials?
They are decremental potentials which are denoted by their amplitude and can only travel over short distances. Their intensity varies with the intensity of the stimulus. They can be inhibitory or excitatory and can undergo temporal or spatial summation
What does inhibitory mean?
Hyperpolarisation
What does excitatory mean?
Depolarisation
What determines wether or not a graded potential is inhibitory or excitatory?
Which channels are open
What is temporal summation?
Intense stimulation form one presynaptic neurone which causes EPSPs to spread from one synapse to a trigger zone
What is spatial summation?
Simultaneous stimulation by several presynaptic neurones which causes EPSPs to spread from several synapses to a trigger zone
How do neurones communicate?
Action potentials
What is required before an action potential can be fired?
The graded potential must reach a significant level
What are action potentials?
Large all or nothing signals that can self-propagate, which are denoted by their frequency
What is the process by which action potentials function?
An action potential is fired when a graded potential reaches the correct threshold. This causes the charge of the neurone to change to +40mV., which opens voltage gated Na+ channels which causes Na+ to come rushing through the membrane. This causes great depolarisation which cases K+ channels to open. This results in repolarisation followed by hyperpolarisation
What is self-propogation?
The charge due to the large increase in Na+ spreads up the axon which opens channels along the axon which caused further influx and propagation of the signal
What are afferent neurones?
They are sensory neurones that detect changes or sensory stimuli
What are interneurones?
They are contained with the spinal cord and decide what to do with the stimulus
What are efferent neurones?
They are motor neurones that carry the signal to effector tissue or cells if the interneurones decides an excitatory response is needed
What is conduction velocity?
The speed of nerve transmission
What increases connection velocity?
Larger axons and myelination
Why do lager axons have a large conduction velocity?
They have less resistance so the charge can travel further up the axon when Na+ channels are open so there are less Na+ channels which take up a lot of time in order to open
How does myelination increases conduction velocity?
It causes saltatory propagation which increase conduction by providing insulation so the signal can travel further
What is myelin?
It is a lipid sheath that surrounds the axon which is formed from Schwann cells.
Where are the Na+ channels found in myelin?
In the nodes of Ranvier between the sheath
What replaces Schwann cells in the CNS?
Ogliodendrocytes
What are the affects of demyelination?
Rapid decay of action potentials which prevents them from reaching the next node and prevents them from propagating. This results in failure of conduction
How is a neuromuscular junction formed?
When the motor end plate form the neuronal axon comes to the muscle and forms a synapse
What is the sarcolemma?
A post-synpatic membrane that consist of junction folds which holds ACh receptors which allows deeper contractions
What is the function of the neuromuscular junction?
Muscle contraction
How do neuronal synapses differ from the NMJ?
Wide range of neurotransmitters, range of postsynaptic fibres, anatomical arrangement and synaptic connectivity
What are the range of postsynaptic fibres?
Fast/slow EPSPs and IPSPs
How are synapses anatomically arranged?
Axo-somatic, axo-dendritic and oxo-axonal
What are the 2 different ways in which synapses connect?
Convergence and divergence
