Neurons and related cells Flashcards
What is a neuron?
- Sends information and instructions throughout the brain and body via electro-chemical signals known as action potentials that travel down the length of a neuron and activate terminal branches.
What is axonal transport?
- Carry peptide neurotransmitters and catecholamines e.g., serotonin to the terminal branches of the neuron to be released into the next cell.
What are peptide neurotransmitters?
- Produced in the nucleus and are transmitters that travel to the terminal branches.
What are kinesin molecules?
- Move across the microtubules of an axon using ATP, moving transmitters and catecholamines.
What are the three functional classes of a neuron?
- Sensory neuron
- Interneuron
- Motor neuron
What is depolarization?
- When the membrane potential is more positive than it is at the resting membrane potential then it is depolarized.
What is hyperpolarization?
- When the membrane potential is more negative than it is at the resting membrane potential then it is hyperpolarized.
Explain the typical chemical synapse
- Presynaptic neurons release chemical transmitters e.g., ACH which activates ion channels.
- These transmitters diffuse across the synaptic cleft
- They then activate post synaptic receptors on the dendrites of post-synaptic cells.
- This leads to local transient changes on the membrane potential.
What is an AP and the key ion for triggering the AP?
- A regenerative wave of electrical excitation.
- Key ion that triggers AP is the voltage gated sodium channel.
What are the 4 phases of AP?
- Resting state- before opening of ion channels.
- Depolarization- opening of sodium channels.
- Repolarization- opening of potassium channels.
- Hyperpolarization- changes in cell membrane making it more negative, then back to resting state.
What is the refractory period? What are the two phases?
- Is a period where a cell is incapable of repeating an action potential.
- Phase 1 is absolute refractory period= Time where a neuron is not able to send additional AP caused by shutting of sodium channels for short time.
- Phase 2 is relative refractory period= Time where a second AP can be initiated but more stimulus is required. Caused by inactivation of sodium channels.
What is the conduction velocity of an AP dependant on?
- Axon diameter (larger diameter, less resistance so faster the AP)
- Myelination (myelin acts as an insulator speeding up AP)
What is a pre-synaptic terminal (bouton)?
- Forms a synapse with the dendrites, cell body or other part of neighbouring cell.
What are the key features of a pre-synaptic terminal?
- Synaptic vesicles
- Microtubules
- Voltage gated calcium channels
What is the SNARE complex?
- Calcium activates the SNARE complex which causes the release of neurotransmitters from vesicles into the synaptic cleft.
What is the role of botulinum toxin and tetanus toxin in the SNARE complex?
- They both target SNARE proteins which prevents the release of acetylcholine
- Can be used for medical reasons (Botox) to relax the muscles.
How are neurotransmitters removed?
- Diffusion
- Enzymatic degradation
- Uptake by cells
What are graded potentials? How are they different to action potentials?
- Graded potentials occur in dendrites, cell bodies and sensory receptors. They are small changes in the membrane potential of a neuron in response to neurotransmitter binding at a synapse. They diffuse passively.
- Whereas action potentials occur when a graded potential reaches the axon hillock at a certain level of depolarization. They have consistent amplitude and duration and can regenerate.
What are glial cells?
- Surround and support neurons
- Provide electrical isolation
- Supply nutrients
- Maintain chemical environment
- Destroy/ remove dead cells & pathogens
What are the glial cells associated with the CNS?
- Astrocytes= Main cell type. Control uptake of neurotransmitters, provide energy for neurons and secrete growth related hormones to stabilise the network of neurons.
- Microglial= Monitor health of nerve cell and orchestrate local inflammatory response.
- Ependymal= line ventricles of brain, help move CSF through ventricles
- Obligondrocytes= Help maintain networks by releasing growth hormones.
What are the glial cells associated with the PNS?
- Satellite cells= Maintain chemical environment and control concentration of neurotransmitters.
- Schwann cells= Release growth factors helping to maintain growth and regeneration of axons.
What are the three main features of nerve cells?
- Cell body
- Axons
- Dendrites
Explain the arrangement of the smaller constituent parts of nerves into larger structures.
- Axons= conduct electrical impulses down the neuron to terminal branches.
- Endoneurium= is a connective tissue surrounding the axons
- Fascicles= are bundle of axons grouped together in nerve
- Perineurium= is the middle layer of tissue enclosing each fascicle
- Epineurium= is the outermost layer of tissue
- Nerve is a bundle of fascicles along with blood vessels
What blood vessel do nerves get their blood supply from?
- Vasa nervorum
Describe the three stages of the Seddon’s classification scheme.
- Neuropraxia= blunt trauma to axon sheath
- Axonotmesis= damage to axons
- Neurotmesis= sharp trauma to nerve
What are the effects of nerve ageing centrally?
- Neuronal atrophy
- Loss of myelination
- Noisy processing
- Loss of dopamine
What are the effects of nerve ageing peripherally?
- Declined axonal transport
- Axonal atrophy
- Myelin loss
- Impaired regeneration
