Cellular organisation of the nervous system Flashcards
What are the 3 main parts of the neurone
Dendrites with a cell body
-can be multiple
Axon
-always a single axon
Axon terminal
-arborisation in terminal
What is the main property of neurones
Polarised
-direction of flow is always the same
What is the main property of neurone membranes
What is the result of this
Polarized membranes maintained by NaK ATPase => resting potential (-70mV)
Results in uneven ion distribution
How is a stimulus spread from the dendrite
Stimulus => redistribution of charge
Stimulus spreads away and decays in all directions
Results in a ripple of graded potential changes (small depolarisation)
All graded potentials converge on cell body
How is an action potential initiated from the axon hillock
Axon hillock, specialized part of cell body
Many graded potentials converge on cell body
More voltage gated Na channels open => increase [Na+]
-VGNaC only in axon hillock, none in dendrites
Increase in [Na+] => reach threshold => action potential
Unidirectional => axon terminal => arborist
Name the 2 types of synapse
Electrical
Chemical
Describe how electrical synapses work
What are the 3 main properties of electrical synapses
Current carried via ion transfer directly through gap junction
- minimal delay
- bidirectional
- activity in neighboring cells is the same
Describe how chemical synapses work
What are the 3 main properties of chemical synapses
Involves presynaptic NT and postsynaptic receptors
NT stored in vesicles release across synaptic cleft
NT binds to postsynaptic receptors
Results in either
-depolarisation => many graded potentials => AP
-hyperpolarisation => harder for AP formation
-2ndary messengers
- delay of 0.3-0.5ms due to diffusion of NT
- unidirectional
- allows for learning and plasticity
What are the 4 types of neurotransmitter
What are some examples of each one
Biogenic amines
-Ach, NA, A, dopamine, seretonin
Amino acids
-glutamate, aspartate, GABA, glycine
Peptides
-somatostatin, endorphins, enkephalins, bradykinin
Other
-ATP, NO
What are the 6 types of synapses
Axodendritic, less powerful Axoaxonic, v powerful synapses that affect cell output Axiomatic Dendrodendritic Somatosomatic Somatodendritic
Describe how synapses and dendrites have plastic properties
Synapses
-efficiency of transfer can be modulated => learning
Dendrites
- integrate inputs from multiple synapses on their spines
- the thinner the spine, the harder it is for the signal to travel
Why is dendrite complexity important
3 reasons with examples
Shape dictates the way the impulses are processed
-more distant from axon hillock => less likely to reach axon
Can act as coincidence detectors
- sound heard in different ears at different times
- time difference used to work out direction and distance of stimuli
Can act as directional filters
-sustained spread of signals in amacrine cells in the eye
Describe the structure of myelinated axons
What is the benefit of myelinating axons
What happens if the axons are demyelinated
Glial cell wraps around axons
Allows for
- saltatory conduction
- rapid passive conduction over high resistance membrane segments
- AP regenerate at VGNC rich nodes
Demyelinating diseases slow down/prevent conduction
Describe the structure of the spine and brain in terms of the white matter and grey matter
In spinal cord
- Outer areas = white matter
- Inner areas = grey matter
In the brain
- Outer areas = grey matter
- Inner areas = white matter
What are the 3 ways of organising grey matter in the brain
In nuclei
-same groups of cells found in 1 place
In layers
-same groups of cells found in same layers
Functional segregation
-individual units are sensitive to different stimuli
Describe the importance of layers in grey matter organisation in the brain
- Spatially distributed info maps
- Functional units grouped within modules
- Within modules, different cells compartmentalized into different layers
Name 2 diseases of grey matter layering in the brain
Double cortex syndrome
-neurons clump together where they shouldn’t be (type of heterotopia)
Lissencephaly
-smooth cortex
Describe the importance of nuclei in grey matter organisation in the brain
Group together neurones with similar functions
Facilitets local circuit control
Maximises efficiency of connections between nuclei
Describe projection neurones
4 properties
V long axon
Connects 2 sections of CNS
Found in cortical layer 5
Interact with interneurons in the cortex
Describe local interneurons
2 properties
What are the 2 types of local interneuron
Found in the cortical layers
Controls activity of projection neurones and communicate within the brain
- excitatory
- inhibitory
Describe the route of motor neurons
Leave CNS ventrally
Efferent from projection neurones
Describe the properties of spinal ganglion
Name the main spinal ganglion here
Dorsal root ganglion
-sensory peripheral afferents have cell bodies here
Describe the properties of autonomic ganglion
What nerves are found in-between ganglia
Describe the location of sympathetic and parasympathetic ganglia
What are the alternative names for sympathetic and parasympathetic ganglia
Preganglionic neurone/spinal cord synapses in autonomic ganglion
Post ganglionic neurone efferent to ganglion
Sympathetic/paravertebral ganglia = thoracic
Parasympathetic/prevertebral ganglia = cranial/sacral
How does the CNS and PNS develop
Neural tube formed by dorsal closure in neurulation
Neural crest cells leave dorsal tube => PNS and glial cells
How do CNS cells differentiate in the neural tube
BMP and SHH are morphogens
BMP found on dorsal side
SHH found on ventral side
Cells born from inner ventricular surface receive varying amounts of BMP/SHH => allows for differentiation into motor of sensory neurones
Based on the conc of BMP and SHH received
How do cells proliferate and migrate in the brain => structure and diversity
What are the 2 methods of migration?
Daughter cells migrate up from the ventricles into the mantle from the dividing cells (radial) of the inner lining
Migrate radially and tangentially
Become neurones by differentiation
What are the 4 main glial cell types
Radial (CNS)
Oligodendrocytes (CNS) and Schwann cells (PNS)
Microglia (CNS)
Astrocytes (CNS)
What is the function of radial cells
- in adulthood
- in development
- in the injured brain
In adulthood
-structural scaffold
In development
-guide for migrating neurones
In injured brain
-source of astrocytes
What is the function of oligodendrocytes and Schwann cells
Deposit myelin
What is the function of microglia
Phagocytic, clear damaged tissue
What is the function of astrocytes
Homeostasis, links metabolism to function by attaching to both blood vessels and neurones
Refine signalling
- remove excess K at Nodes of Ranvier, prevents overstimulation
- remove NT by wrapping around Nodes of Ranvier
- insulate synapse
What 3 things can happen when astrocytes are damaged
Brain injury
Excess K and H2O absorption => brain swelling
Reactive astrocytes => glial scars, could trigger epilepsy
