Neurobiology Theme 2 Flashcards
what is the average number of neurones in a human
100 billion
what id the rate of proliferation during foetal devlepment
250,000 neurones/minute
what is the diameter of a neurone cell body
4 to 100 microns
what is the length of the longest axon
5m
what is the length of all the neurones in the body
600 miles long
what is the function of dendrites
receive and process information from other neurones and bring it to the soma
what is the function of the axon
conducts signals to other neurones via synapses at the axon terminal
what is a nerve
bundle of axons in the pns
what is a nerve tract/pathway
bundle of axons in the CNS
what is the soma (cell body)
houses the cell nucleus (genetic info)
responsible for cell metabolic maintenance
what is a ganglion
group of neurone cell bodies in the peripheral ns
what is the nucleus
group of neurone cell bodies in the cns
what are the factors that determine the function of the neurone
shape of neurones
chemicals used to communicate with other neurones
reaction to neurotransmitters
what are multipolar neurones
they have many processes emanating from the cell body (e.g. spinal motor neurones, purknje fibres)
interneurones & motor neurones
what is the function of interneurones
form all the neural wiring within the cns
what are motor neurones
cell body located in the motor cortex- carries signals from the cns to muscles or glands (efferent)
what are bipolar sensory neurones
where one axon communicates with the sense organ and one with the cns (dorsal root ganglion cells in the spinal cord)
what are glial cells & what is their function
nerve cells that do not carry nerve impulses
they digest part of dead neurones, manufacture myelin and provide physical & nutritional support
what are they types of glial cells
astrocytes
oligodendrocytes
microglia
schwann cells
what is the function of astrocytes
they help in regulating extracellular ionic concentrations.
provide physical and metabolic support to the neurones of the cns.
scar forming cells of the cns
what is the function of oligodendrocytes
form myelin around axons for electrical insulation in the cns
fewer & shorter processes
what is the function of schwann cells
form myelin in the pns
what is the function of microglia & what is their origin
phagocytic cells, they clean up dead tissue in case of damage
mesodermal origin
what are the advantages of the golgi method (silver impregnation method)
neurones can be studied in isolation from their neighbours (only 1% of cells are stained)
neurones well delineated (outlined)
what is a neurite
a projection from the cell body of a neurone
either a dendrite or axon
how many dendrites does a neurone possess
one to several
primary dendrites may branch into secondary or tertiary
some dendrites are covered with spines
how many axons does a neurone have & where does it originate
as a rule each neurone only has one axon which originates from the axon hillock
they do not taper but may branch
why are dendrites important
they receive and process info from other cells making synaptic contacts with them
how do dendrites act as neural integrators
neurones with many dendrites can fine tune synaptic inputs (no of dendrites determines no of synaptic contacts received by the same cell)
what tasks is the cerebellum concerned with? are they conscious?
“automatic” motor tasked
unconscious coordination of movement
what is the function of the cerebellar purkinje cell
makes decisions about which muscles need to be contracted & by how much to keep us in balance
what is the importance of dendrite growth
they grow, branch & prune during development allowing establishment & refinement of many connections with other neurones
what is the lipid & protein content of myelin
70-80% lipids
20-30% proteins
what is the difference in terms of location and function of oligodendrocytes & schwann cells
oligodendrocytes
cns- provide myelin to several axons
schwann cells
pns- provide myelin to only one axon
what are the 3 types of connection between axon terminals & post synaptic cells
axosomatic
axoaxonic
axodendritic
what are synaptic boutons
small, bulb shaped swellings at the end of axon or along the course of their branches
what are the three axonal transport mechanism & which element of the cytoskeleton do they use
fast anterograde
slow anterograde
fast retrograde
microtubules
where does fast anterograde transport from & to
from cell body to synaptic terminal
at what pace are chemicals and chemicals transported in fast anterograde
100-400 mm/day in mammals
why do active neurones require require fast anterograde flow
for quick supply to their axon terminals to replace used neurotransmitters or organelles
what is the role of cytoskeleton in fast anterograde axonal transport
entire length of axonal transport is threaded with microtubules
organelles/chemicals transported along microtubule tracks by small kinesin molecules
what are the two different rates of slow anterograde axonal transport
type A: 0.2-1mm/day
type B: 2-5mm/day
what is the function of fast retrograde axonal transport & what is its pace
movement of surplus membrane particles & neurotoxins and viruses into cns
200-300mm/day
what is the carrier for fast retrograde
ATPase dyenin
what is resting potential
electrical potential that exists across the membrane when cell is in resting conditions
what is nernst potential used to calculate
exact V generated by a specific ion for a known conc difference across a membrane potential permeable to that ion
what does Vnernst reflect
balance between electrical and chemical forces (electrochemical gradient) acting on a given ion)
what happens when Vm is exactly Vnernst
no net flow of that ion across the membrane
each ion will try to pull Vm to its Vnernst & the ion with the highest permeability (more open channels) will win
what influences Vrest
Pk predominantly
Pna ana Pcl to a lesser extent
why is Vrest not identical to Ek
there is leakage through Na+ and Cl- channels
what does the Goldman-Hodgkin-katz constant field equation do
combines the nernst equations for all ions and takes permeabilities into consideration
gives a better approximation of vrest
what is meant by passive propagation
that of which occurs in an electric wire where static membrane properties do not change during electrical signalling
what is meant by active propagation in neurones
unlike wires electrical properties in neurones are triggered by changes in Vm which enable conduction of electrical signals without decrement over large distances
what is the difference in signal propagation along a cable and axon
along a cable the signal decreases away from point of generation where in an axon the signal does not change with distance
what happens to the current when the axon diameter is increased
the current will propagate further
what factors influence signal propagation
larger axon
myelin
what is the all or nothing principle
if the stimulus too low there is no action potential and if over threshold its same size
how many gates do Na+ channels have
2 internal (h) - inactivation external (m)- activation
how many gates to K+ channels have
1
n gate
what is the state of the gates during resting condition of the cell
Na+
70% internal (h) open
external (m) gates closed
K+
n gates closed
do the Na+ or K+ channels contribute to Vm under resting conditons
no
Vrest is close to Ek (bc of Pleak) and far from Ena
what happens when electrical membrane potential (Vm) decreased to threshold
external (m) gates open
Na+ flows inside axon decreasing Vm causing more m gates to opening - rising phase of action potential
what is the effect of sodium permeability on action potential - goldman equation
increased Na+ permeability causes Vm to shift towards Ena. the action potential overshoots and reaches its peak value
how is further depolarisation of a membrane stopped after an action potential
internal (h) gates on Na+ channels begin to shut down
responsible for the absolute refractory period
how are K+ channels involved in repolarisation of action potential
K+ channel slowly open allowing K+ to flow out of cell
why does an undershoot of the action potential occur
Pk higher than at rest
membrane more positive on the inside
hyperpolarisation causes K+ channels to close & membrane settles back to rest
internal (h) na+ gates repopen
what does the refractory period do
limits the firing frequency
why is the refractory period important
info about strength of stimulus is encoded in the firing frequency of action potentials
what is meant by the absolute refractory period
a second AP can not be generated regardless of the strength
in which situations can a 2nd AP be generated (relative refractory period)
- increased threshold to overcome hyperpolarisation
2. reduced amplitude because there are fewer na+ channels are available to open so less na+ can flow into the cell
why does the AP only propagate forwards
ahead of ap, Na+ channels are closed ready to be opened
behind ap Na+ channels inactive and so cant be opened (spreading current has no effect)
why do membrane areas covered with myelin not become depolarised
myelin means they cannot create APs
the current is forced to travel down to nodes of ranvier where the conc of Na+ channels is high
the AP jumps from node to node
what is the benefit of saltatory conduction
ap jump from node to node so increased conduction velocity
what is the speed of large myelinated axon conduction
120m/sec
what is the speed of small myelinated axon conduction
0.25m/sec
what would happen to axon propagation without myelin
it would be delayed
what are the two types of synapses
electrical
chemical
which type of synapse is the fastest
electrical- no chemical transduction involved
where are electrical synapses found
escape reflex neurones
cardiac muscle cells
epithelial cells
where are chemical synapses found
neurones
what are gap junctions
protein pores that bridge the gap between 2 cells
how are gap junctions different from channels
channels allow communication between the cell and the extracellular space
what are the pores in gap junctions made of
6 subunits of the protein connexin
of up to what molecular weight will gap junctions allow substances to pass through
1000
what is the distance between the membranes in an electrical & chemical synapse
electrical- 3.5nm
chemical- 20-40nm
which synapse has cytoplasmic continuity
electrical
what is the structural unit for an electrical synapse
gap-junction channel
what is the structural units for a chemical synapse
vesicles
docking/fusion proteins
channels
postsynaptic receptors
what is the transmitter for an electrical synapse
ionic current
what is the transmitter for a chemical synapse
chemical transmitter
in which synapse is there a transmission delay and by how long is it
chemical
1-5ms
what is the direction of transmission in an electrical synapse
can be bidirectional
what is the transmission direction in a chemical synapse
unidirectional
what are the two types of receptors to neurotrasmitters
ionotropic
metabotropic
what is a ionotropic receptor & give an example
one that is linked to an ion channel (ligand gated)
ionotropic nicotinic cholinergenic receptor
what is a metabotropic receptor & give an example
g-protein coupled receptors one that is not directly linked to an ion channel, uses a second messenger
metabotropic muscarinic cholinergic receptor
outline the sequence of events in synaptic transmission
ap propagated in presynaptic neurone
Ca2+ entry into synaptic knob
release of neurotransmitter by exocytosis
binding of nt to postsynaptic receptor
opening of specific ion channels in subsynaptic membrane
what is SNARE
vesicle docking and calcium sensing proteins which enable vesicle fusion with the terminal membrane
what are V-SNARE proteins
vesicle membrane protein
what are the 2 types of V-SNARE proteins
synaptobrevin
synaptotagmin
what is the function of synaptobrevin (V-SNARE)
SNARE complex binding protein
what is the function of synaptotagmin (V-SNARE)
calcium sensory which helps with the fusion when calcium enters the synaptic terminal so the vesicle with neurotransmitter can fuse with the membrane
what is a synaptic terminal
the ending of a presynaptic neurone where the electrical signal is converted into chemical
what are T-SNARE protein and name the 2
target membrane proteins
voltage transducer
syntaxin
SNAP-25
where are V-SNAREs located
on the vesicle
where are T-SNAREs located
on the membrane of the pre-synaptic membrane
what is the importance of recycling neurotransmitters
if they remained in the synaptic cleft there would be uncontrolled signalling
what does EPSP stand for
excitatory post synaptic potential
what is the main differences between AP and EPSPs
EPSP only reaches threshold
EPSP is decremental
EPSP is much longer (15-20msec)
why does temporal summation occur in EPSPs
as the time taken is much longer for a single EPSP the signals adduct at high frequency to each other reaching the threshold
why is temporal summation id EPSPs important
otherwise the EPSP would decrement allowing for an AP to generated
what is spatial summation
signals come from different inputs
this ‘collects’ signals together allowing for threshold to be met for AP
what does IPSP stand for
inhibitory post synaptic potential
what does IPSP do
causes hyperpolarisation of post synaptic neurones
what is the importance of IPSPs
makes it much harder to generate an AP as you are further away from the threshold
what neurotransmitters can cause hyperpolarisation in the post synaptic neurone
GABA
glycine
what is the function of first order neurones
conduct impulses from receptors to spinal cord or brainstem
do first order neurones enter on the same or opposite side of the body that the peripheral receptor is located
same
where are the cel bodies on first order neurones located
dorsal root ganglion of spinal nerve
trigeminal ganglion of trigeminal nerve
within the cns do 1st order neurones remain on the same side or opposite?
same
what is the function of second order neurones
carry signals from the spinal cord/brainstem to the thalmus
what are afferent nerves
sensory nerve fibres travelling towards the cns from sensory modalities such as pain, touch, temp etc
what afferent nerves
motor nerve fibres travelling away away from the cns to effector organs
what are the two types of peripheral neurones
multipolar
unipolar
what are multipolar neurones
more than 2 processes emanating from the neurone cell body
located in the cns
what are unipolar neurones
sensory neurones with cell bodies located in the dorsal root ganglion that enters the spinal cord
are sensory neurones myelinated?
both myelinated and unmyelianted
where are the cell bodies of motor neurones
spinal cord
where are the cell bodies of sensory neurones
dorsal root ganglion
does the letter system include sensory or motor fibres
both
does the roman numeral system include sensory or motor fibres
sensory
what properties do both the roman numeral and letter system include
size of fibres
conduction velocity
what do Ia (Aα) fibres do
sensory from muscle spindle to the CNS
What do Ib (Aα) fibres do?
golgi tendon organ to CNS
What do II (Aβ) fibres do?
muscle spindle, touch pressure, to CNS
What do III fibres (Aδ) do?
pain, pressure, temperature to cns
What do IV fibres (C) do?
pain, touch, temperature to cns
What do B fibres do?
part of the ANS, preganglionic autonomic fibres towards effector organ
what do C fibres do
part of ANS
postganglion autonomic fibres towards effector organ
What do Aα fibres do?
signals from cns to skeletal muscles
What do Aγ fibres do?
signals from cns to muscle spindle
Whats the difference between B and C fibres in parasympathetic ANS.
B fibres are preganglionic longer than C fibres
Whats the difference between B and C fibres in sympathetic ANS.
B fibres are shorter than C fibres as the preganglionic axons in the SNS synapse close to the spinal cord
What are golgi tendon organs?
sensory receptor organ sensing changes in muscle tension
How can you tell if a fibre is sensory/motor based on its name?
if its in the letter system its both but in the roman numeral its sensory only
what does sensation mean
conscious/subconscious awareness of external environment
what does perception mean
interpretation of sensation
what are the 2 types of sensory modalities
general senses
special senses
what are the types of general senses
somatic- tactile, thermal, pain, proprioceptive
visceral- conditions of internal organs
what is involved in special senses
smell, taste, hearing, eqm, balance
what are the microscopic features of peripheral nerves
free nerve endings
encapsulated nerve endings
separate cells
what are the the types of sensory receptors based on location
exteroreceptors- outiside of body
interceptors- inside the body
proprioceptors
what are the the types of sensory receptors based on stumi detected
mechanoreceptors thermoreceptors nociceptors chemoreceptors photoreceptors osmoreceptors
what modalities does the dorsal column-medial lemniscus (DC-ML) pathway sense
touch/proprioception
the first order neurones of the DC-ML pathway terminate and synapse in the medulla, which nuclei do they synapse in
cuneate- upper half of body
gracile- lower half
what is the dorsal column
the pathway on the same side that arises from the brainstem from touch/proprioception where the 1st order neurones ascend uninterruptedly
what is the medial lemniscus
the pathway on the opposite side from second order neurones after synapsing with 2nd order neurones
what modalities are received in the anterolateral system (ALS)
pain/temperature
what happens to first order neurones in ALS
they terminate at the level of the brainstem & synapse with 2nd order neurones
what happens to second order neurones in ALS
they decussate to the contralateral side and ascend to the thalamus (spinothalamic tract)
where does the pain pathway cross over
spinal cord
where do fine touch pathways cross over
brainstem
what nerve senses facial sensory info and what is the name of the pathway
trigeminal nerve
trigeminothalmic
at what level do first order neurones enter when sensory info is received from the face
enter through trigeminal ganglion at the level of the brainstem. they terminate here
where do second order neurones cross over in the trigeminothalmic pathway
brainstem
in what part of the thalamus do 2nd order neurones of the trigeminothalmic pathway cross synapse with third order
ventral posterior medial nucleus
what happens to 1st order neurones in the pain and temp system for the trigeminothalmic pathway
they first pass down the brainstem to find their point in the trigeminal nucleus before they ascend
what is acute pain
short term pain
what is chronic pain
long term pain
where is somatic pain and visceral pain
somatic- body
visceral- thorax =abdomen
what are nociceptors
pain receptors
where are nociceptors found
skin
muscle
joints
what are the two types of pain fibres
a delta
c fibres
which pain fibre is myelinated
a delta
which pain fibres has the faster conduction
a delta (20m/s)
c fibres only 2m/s
what is the size of a delta fibres
1-5 micrometers
what is the size of c-fibres
2.5 micrometers
what is the difference between the type of pain between the pain fibres
a delta
- sharp fast
c fibres
- dull, slow, ache
what do a delta fibres & c fibres respond to
mechanical stimulation (pin prick) , painful heat/cold
what else do c fibres respond to that a delta fibres dont
substances from damaged tissue
what laminae do a delta fibres synapse in
1 and 5
what laminae do c fibres synapse
1 and 2 (toward top)
which laminae correspond to the marginal zone
1
which laminae correspond to the substantia gelitinosa
2 and 3
which laminae correspond to nucleus proprius
4 and 5
what is peripheral sensitisation
usually nociceptors have a high threshold and only respond to noxious stimuli however after damage they become sensitised
- threshold is lowered
- responsiveness increased
why is peripheral sensitisation important
reduced likelihood of further damage
after damage & inflammation of nociceptors, chemicals are released causing sensitised nociceptor, what are these chemicals?
atp histamine seretonin cytokines bradykinin neuropeptides
where can central sensitisation occur
spinal cord
thalamus
amygdala
anterior cingulate cortex
what is central sensitisation and what can it lead to
cns receives prolonged stimulus of pain & becomes sensitised
it overacts pain pathways so non painful signals are amplified and the patient feels pain
how does central sensitisation alter synaptic strength
more AMPA and NMDA receptors are added to the . membrane so more responsiveness to neurotransmitter. this is due to increased intracellular calcium activation 2nd msg system. TFs are activated causing an upregulation of proteins
where does central sensitisation occur
lamina 1 and 5 (spinal cord)
thalamus
amydala
anterior cingulate cortex
what is likely to occur in patients with TMJ disorders
increased pain sensitivity after contraction of facial muscles
increased likelihood of referred pain (head/ neck/ ear)
bilateral pain sensitivity- myofascial pain
what does the gate theory of pain suggest
non noxious stimuli is able to close gates to painful input preventing pain sensation travelling up the cns
what is the role of collateral branches in the gated theory of pain
act on interneurones to feedback on pain pathways to inhibit ascending pain pathways
in which areas is pain perceived
thalamus - ventral posteromedial - ventral posterolateral somatosensory cortex hypothalamus limbic system
what is referred pain
feeling pain away from the area of damage
how does referred pain occur
convergence of sensory input from second order neurones due to signals from the viscera as well, as there are very few sent from spinal cord, causing confusion of the source of pain
what are the components of the central control of pain- descending system
periaqueductal grey matter
locus coeruleus
raphe nucleus
what is the function of the periaqueductal grey matter (around the cerebral aqueduct)
receive signals from hypothalamus, medulla and cortex
what does the locus coerules do
secrete noradrenaline
what does the raphe nucleus do
release serotonin
what is the centrifugal pathways
descending system acting to reduce the pain response (release endorphins)
where is sensory info received in the centrifugal pathway
sensory cortex
frontal limbic cortex
at which point are endorphins released in the centrifugal pathways
spinal cord
what is released at the synapse between the interneurones and the centrifugal pathway
gaba- an inhibitory neurotransmitter controlling centrifugal pathways
what do opioids do
inhibit interneurones and stop the inhibition of the descending pathways
what is an example of opioid
morphine, codeine
what local anaesthetics block na channels in dental treatmetn
lidocaine
mepivincaine
articaine
what are the COX enzyme inhibitors used to treat tooth aches
paracetamol
ibuprofen
