Cells of the nervous system Flashcards
What is a unipolar neurone?
A neurone with 1 axonal projection
What is psuedo-unipolar neurone?
Single axonal projection that divides into two
What is a bipolar neurone?
2 projections from cell body
What is a multipolar neurone and give 3 examples
Numerous projections from cell body
Pyramidal cells: ‘pyramid’ shaped cell body
Purkinje cells: GABA neurons found in the cerebellum
Golgi cells: GABA neurons found in the cerebellum
What are neurones
Excitable cells of CNS
Heterogeneous morphology
Non-dividing cells
Share common features:
What is contained in a soma?
Contains nucleus & ribosomes
Neurofilaments for structure & transport
What is an axon?
Long process (aka nerve fibre) - originates from soma at axon hillock
Can branch off into ‘collaterals’
Usually covered in myelin
What are dendrites?
Highly branched cell body - NOT covered in myelin
Receive signals from other neurons
What is a oligodendrocyte?
Glial cell - produces myelin
What is an astrocyte?
Most abundant cell type in CNS
Involved in clearing excess neurotransmitters, stabilizing and regulating the blood-brain barrier, and promoting synapse formation.
What is a microglia?
Neuronal macrophages
What is an ependyma?
Epithelial cells lining CNS ventricles
What does membrane impermeability to Ca2+, K+, Na+ and Cl- cause?
Transport is regulated by ion pumps
This causes an uneven ion distribution:
High extracellular - Na+ & Cl-
High intracellular - K+
High concentration gradient for Ca2+
Difference in concentration → creates a potential difference across the membrane
What is the range for resting membrane potential for neuronal cells?
-40mV to -90mV
How is an action potential reached?
Membrane depolarisation - opening of VGSC → Na+ influx → further depolarisation
VGKCs opens at a slower rate and causes → efflux of K+ from cell → membrane repolarisation
How is resting potential regained after an AP?
AP leaves Na+ & K+ imbalance → need to be restored
Na+-K+-ATPase (pump) restores the ion gradients
Resting configuration - Na+ enters vestibule & upon phosphorylation → ions are transported through protein
Active configuration - Na+ removed from cell → K+ enters the vestibule
Pump returns to resting configuration → K+ is transported back into the cell
Describe the process of saltatory conduction
AP spreads along the axon by ‘cable transmission’
Myelin prevents AP spreading because it has- high resistance & low capacitance
Nodes of Ranvier - Small gaps of myelin intermittently along axon:
AP ‘jumps’ between nodes - saltatory conduction
AP is unable to ‘jump’ across the gap at the axon terminal
How does a synapse function?
Propagation of the action potential (AP)
AP is propagated by VGSCs opening
Na+ influx → membrane depolarisation → AP ‘moves along’ neurone
VGKC opening → K+ efflux → repolarisation
Neurotransmitter (NT) release from vesicles
AP opens voltage-gated Ca2+ channels at presynaptic terminal
Ca2+ influx → vesicle exocytosis
Activation of postsynaptic receptors
NT binds to receptors on post-synaptic membrane
Receptors modulate post-synaptic activity
Neurotransmitter reuptake
NT dissociates from receptor and can be:
Metabolised by enzymes in synaptic cleft
Recycled by transporter proteins
What 2 types of intercellular signalling are neurones involved in?
Paracrine and autocrine
What is an axodendritic synapse
A synapse between the presynaptic terminal and neuronal dendrite
What is an axosomatic synapse
A synapse between between presynaptic terminal and a neuronal soma
What is an axoaxonic synapse
A synapse between the presynaptic terminal and neuronal axon
What type of communication is it in a neuromuscular junction?
Paracrine
Outline what occurs at an NM junction
Action potential propagated along axon (Na+ & K+) causes Ca2+ entry at presynaptic terminal
Ca2+ entry causes acetylcholine (ACh) release into synpase
ACh binds to nicotinic ACh receptors (nAChR) on skeletal muscle causes change in end-plate potential (EPP)
What does a minimal EPP cause?
A quantal(non-continuous) ACh release
What is the location, function and effect of the sarcoplasmic reticulum?
Location: surrounds myofibrils – contractile units of muscle
Function: Ca2+ storage causes Ca2+ release following sarcolemma depolarisation
Effect: Ca2+ causes myofibril contraction & muscle contraction
What occurs in botulism?
Botulinum toxin (BTx): irreversible disruption of stimulation-induced ACh release from presynaptic nerve terminal
What occurs in myasthenia gravis?
Autoimmune disorder: antibodies directed against ACh receptor
Cause fatigable weakness (i.e. becomes more pronounced with repetitive use)
What occurs in Lambert-Eaton myasthenic syndrome (LEMS)
Autoimmune disorder: antibodies directed against VGCC
