Neurons and related cells Flashcards
where is the motor map and the sensory map in the homonculus ?
Motor- precentral gyrus
sensory-postcentral gyrus
Name the structures in a typical neuron
-dendrites
-dendritic spines
-axon
-axon hillock
-soma
-terminal branches
-terminal boutons
-main intracellular components
What is the function of dendrites?
recieves information signals via chemical or electrical synapses
What is the function of the soma?
-contains genetic info
-maintains neuron structure
-provides energy
What is the function of dendritic spines?
-protrusions from dendrites
-form functional contact with neighbouring axons
What are Nissl granules?
-site of short chain amino acid production
What is the function of the axon hillock?
-controls the initiation of electrical impulses from neuronal input
What are terminal boutons?
-specialized apparatus to release neurotransmitters
What is the function of terminal branches?
change action potentials into chemical messengers in the form of neurotransmitters
How are resting potentials maintained?
-Na+ leak channels
-K+ leak channels
-ATPase
k+- high inside
Na+-low inside
Describe the events that occur in a typical chemical synapse
1) presynaptic neurons release chemical transmitters e.g ACh
2)diffuse across synaptic cleft
3)activate post synaptic receptors on the dendrites of the post synaptic cell
4)leads to local transient changes in the membrane potential
How are APs triggered at the axon hillock?
-Once the signal reaches the threshold value
-APs are regenerative waves of electrical excitation, all or nothing events
Describe voltage gated ion channels
-detect passive changes in membrane potential
-trigger for APs to travel longer distances
-gated Na+, Ca2+, K+ channels
What are the 4 phases of the AP?
-resting stage -70mV
-depolarisation
-repolarisation
-hyperpolarisation
AP is caused by permeability changes in the plasma membrane
Why do APs only travel in one direction?
due to the refractory period
What is the refractory period?
Can’t excite inactive voltage gated Na+ channels
What is conduction velocity dependent on?
-Axon diameter
-myelination
Explain why axon diameter effects conduction velocity
Thicker axon diameters have a higher conduction velocity to send signals faster due to less resistances to ion flow
What are schwann cells?
-found in the peripheral NS
-type of glial cell
-wraps around the axon forming the mylein sheath -acts as insulation
-directional guidance of neurons
-eliminate cellular debris
What is the function of Nodes of ranvier?
APs jump from node to node- increasing rate of propogation of APs
Name the components of the presynaptic terminal/bouton
-voltage gated calcium channels
-microtubules
-vesicle transports
-vesicle fusion
-transmitter release
What are SNARE proteins?
mediates the fusion of vesicles with the target membrane
What is the SNARE complex?
-Calcium activates a set of SNARE proteins which binds to the SNARE complex
-pulls vesicle close to membrane
What toxins can stop the SNARE complex from working?
tetanus toxin- causes maximal contraction/full body stiffness
-botulinum toxin/botox
Name 3 ways neurotransmitters are removed
1) diffusion - released in the synaptic cleft and then diffuses away
2)enzymatic degradation- broken down by enzymes
3)uptake by cells-returned to neuron and transported to neighbouring cells
Describe temporal summation
-single presynaptic neuron
-rapid signals to postsynaptic neurons
Describe spatial summation
-signals coming from multiple presynaptic neurons
-recieved by a single postsynaptic neurons
Describe graded potentials
1-depolarising or hyperpolarising
2-amplitude is proportional to the strength of the stimulus
3-No refractory period
4-can be temporal or spatial
5-travel by passive spread- electronic spread to neighbouring membrane regions
6-amplitudes diminish as graded potentials travel away from initiation site-decremental
7-short distances
Describe AP’s
1-always lead to depolarisation
2-amplitude is all or none- once triggered get a full AP
3-has refractory periods
4-summation is not possible with AP’s
5-AP propagation is regenerative- active process
6-amplitude does not diminish as AP’s propagate along neuronal projections-non decremental
7-long distances
Features of electrical synapses
connexins- bridges between cells
direct electrical connection
-functional syncytium
Name parts of the integration on the neuron
-axodendritic synapses
-axosomatic synapses
-axonaxonal synapses
-inputs can be negative or positive
-location effects significance
Name the four main neuroglia that support CNS neurons
-astrocytes
-microglial cells
-ependymal cells
-oligodendrocytes
Name the two main neuroglia seen in the PNS
-satellite cells
-Schwann cells
What is the general role of glial cells?
-surround and support neurons
-electrical insulation
-supply nutrients
-maintain chemical environment
-destroy/remove dead cells and pathogens
What features do PNS glia contain?
-satelite cells
-schwann cells
-nerve fibres
-cell body of neuron
Describe the function of astrocytes
-produce scar tissue
-stabilizing and regulating the blood brain barrier
-promote synapse formation
-clear excess neurotransmitters
-perform metabolic,homeostatic, structural and neuroprotective functions
Describe the function of oligodendricytes
-wrap around several axons
-make cell membranes fatty in the brain
-release nerve growth factors
-stabilizing the connections between nerve cells
-development of brain tissue-scafold
-fast saltatory impulse propagation
Function of ependymal cells
-cillia like projections beat to circulate CSF around
-base of cells interact with astrocytes- to transmit nutrients and CSF
-modified ependymal cells-choroid plexus- produce CSF
Function of microglia
-Act like macrophages
-can remove dead neurons
-can end up damaging tissues
Describe Nerve anatomy
-axon
-mylein sheath
-endoneurium- damaged difficult for axon to grow
-perineurium-surrounds fascicles
-epineurium
-blood vessels
-fasicles
-vasi nervorum
List some nerve ageing effects in the central NS
central:
-neuronal atrophy-mitrochondria function becomes disrupted
-loss of myelination
-noisy processing
-dopamine loss
Name some nerve ageing effects in the peripheral NS
Peripheral:
-declined axonal transport
-axonal atrophy
-mylein loss
-impaired regeneration
