Signalling in NS Flashcards
what is the role of dendrites ?
receives input from other cells
what is the role of axons?
key role in transmission of nerve impulses from the cell body
what is the typical resting membrane potential in neurons and what does this mean in terms of -ve and +ve ions?
-60mV to -70mV
In neurons there are more positive ions outside the cell compared to more negative ions inside the cell
Are Na+ ions major extracellular or intracellular ions ?
extracellular
Are K+ ions major extracellular or intracellular ions ?
intracellular
Are Cl- ions major extracellular or intracellular ions ?
extracellular
define equilibrium potential
membrane potential where number of ions entering the cell = number of ions leaving cell
define an action potential
An action potential is a very brief but dramatic change in membrane potential
what occurs during depolarisation of a neuron ?
Increased permeability to Na ions into the cell
what occurs during repolarisation of a neuron ?
increased permeability of K ions out of the cell
describe the process of an action potential
Influx of Na ions into cell
Rapid opening of voltage gated Na channels
The channels close
Voltage gated K channels SLOWLY open
K+ ions leave the cell and causes repolarisation
leads to hyperpolarisation
List some examples of voltage gated Na channel drugs in medicine
These drugs are Na voltage gated channel blockers:
Local anaesthetics
Pain treatment
Epilepsy drugs
describe the propagation of action potential along an axon
Depolarisation of a patch of neurons before and after the area, so a depolarising wave travels the length of the axon as a cascade
what are two ways to increase the speed of propagation along an axon?
Increase axon diameter
Reduce number of open pores/channels in membrane to insulate axon and prevent leakage (forces )
What are node of Ranvier?
Gaps on axons between myelin sheaths
Describe saltatory conduction
The action potentials jump from node (of ranvier) to node in the myelinated axon
how does the diameter of a myelinated axon compare to an unmyelinated one?
Myelinated axons have wider diameter
Describe the causes of multiple sclerosis, its effect on action potential and symptoms
Antibodies attack myelin sheaths in CNS, forming scars (sclerosis). This delays/blocks action potentials
Symptoms: Blurred vision Muscle pain Partial paralysis Fatigue Lack of coordination
Describe the causes of guillan barre syndrome and symptoms
It is an inflammatory disease caused by previous infection/inflammation.
Causes autoimmune attack of myelin (schwann cells) in PNS
Symptoms:
Progressive motor weakness
motor and sensory loss
what effect does an EPSP (excitatory postsynaptic potential) have on a post synaptic membrane ? give an example of this
it brings it closer to the threshold (depolarisation) and increases the probability of the postsynaptic cell producing an action potential
E.g. entry of Na ions
what effect does an IPSP (inhibitory postsynaptic potential) have on a post synaptic membrane ? give an example of this
It moves the post synaptic membrane further away from threshold (hyperpolarisation) and reduces the probability of the postsynaptic cell producing an action potential
Describe temporal summation
high frequency of action potentials from one axon in the presynaptic neuron elicits postsynaptic potentials that summate with each other
Describe spatial summation
firing of action potentials at multiple sites from one or more presynaptic neurons
give an example of a cholinergic neurotransmitter
acetylcholine
give examples of a biogenic amine neurotransmitter
catecholamines: noradrenaline, adrenaline, dopamine
5-HT/serotonin
give excitatory and inhibitory examples of amino acid neurotransmitters
excitatory: glutamate
inhibitory: GABA
give an example of a neuropeptide neurotransmitter
endogenous opioids
what are two conditions associated with defective myelination?
multiple sclerosis
guillan barre syndrome
what are two conditions associated with disruption of cholinergic synaptic transmission?
botulism
myasthenia gravis
describe the cause of botulism, its effect on synaptic transmission and symptoms associated with it
Clostridium bacteria produce botulinum toxin which disrupts exocytosis and disrupts ACh release from motor neurons
symptoms:
skeletal muscle weakness
paralysis of diaphragm (respiratory failure)
describe the cause of myasthenia gravis, its effect on synaptic transmission and symptoms associated with it
this is an inflammatory disease whereby antibodies bind to ACh receptors on post synaptic membrane at motor end plate.
Symptoms:
severe muscle weakness
particularly affects eyelids, eyes, face, throat and limb muscles
2 ways in which information may spread in the NS is by divergence and convergence, describe the difference between them
Divergence: one neuron communicates with many neurons
Convergence: many neurons feed into one neuron
list 4 tests to investigate cerebral function
EEG - electro-encephalography
PET - positron emission tomography
fMRI - functional magnetic resonance imaging
TMS - transcranial magnetic stimulation
what does EEG record and how is this done?
Investigates cognitive processes in response to a stimulus, this is done by recording the electrical activity of the brain
what do PET scan and fMRI investigate and how is this done?
locates brain activity while performing a task
Do this by measuring blood flow (PET: via a small dose of radioactive material injected into the bloodstream)
what does TMS investigate and how is this done?
interrupts brain activity while performing a task
Does this by using an electromagnet to stimulate brain activity
