Nerves Flashcards
Name the depression & raised folds of brain matter?
Gyrus - Raised folds
Sulcus - Depression between folds
What makes up forebrain?
Cerebrum & diencephalon
What makes up the cerebrum?
Frontal Lobe
Parietal Love
Occipital Lobe
Temporal Lobe
What makes up the diencephalon?
Thalamus
Hypothalamus
What makes up the brainstem?
Midbrain
Pons
Medulla Oblongata
What other brain structure controls automatic motor function?
Cerebrum
How many pairs of spinal nerves are there? (split them up)
31 pairs:
- 8 cervical
- 12 thoracic
- 5 lumbar
- 5 sacral
- 1 coccygeal
What matter contains the cell bodies & axons?
In spinal corD:
- White matter contains axons
- Grey matter contains cell bodies
Where in the neurone are things syntehsised?
The cell body
When in a neuron are signals recieved?
Dendrites (post-synaptic)
What is the axon hillock?
Section just after cell body where info for APs is gathered & theyre fired from
What do axon terminals do?
Convert an axon-potential to a chemical signal for synapse.
How much of the CNS is glia?
Around 90% of CNS cells are Glia
NAme the 3 types of GLia?
Astrocytes
Microglia
Oligodendrocytes
What do astrocytes do?
Astrocytes:
- Maintain external enviroment for neurones
- Surround blood vessels & produce the blood-brain barrier
What do oligodendrocytes do?
- Dorm myelin sheafs around CNS fibres
What do microglia do?
Produce phagocytes
What is the value of the resting membrnae potential?
-70mV. Basically the inside is 70mV negative to the outside
How is the RMP produced?
- K+ pumped in/Na+ pumped out
- Leaky potassium channels let K+ out
Why doesnt half the K+ move out the cell through the leaky channels to form a chemical equilibirum?
- Because it creates an electrical gradient
- This is eventually = & opposite ot hte chemical gradient
- So the electrochemical gradient = 0
Define equilibirum potential?
The membrane potential at which electrical gradient is equal & opposite to the conc. gradient.
How does hyperkalemia cause ventricular fibrillation?
- High K+ external conc.
- Lower conc. gradient
- Lower eectrical gradient maintained at equilibirum
- Cell depolarised
- Random APs fire
- Ventricular fibirllation
Why doesnt the brain experience the effects of hyperkalemia?
Its protected by the blood brain barier
Why is the blood brain barrier protectivE?
Its capillaires are espeicially tight due to:
- Astrocytes
- Tight junctions
The astrocytes prevent ion movement into the brain ISF
What other ions have a small effect on the RMP?
Na+
Cl-
Both are small intracellular conc. & large extracellular concs.
If the potassium equilibirum potential would be -90mV. Why is the RMP closer to -70mV?
- Electrogenic nature of the Na+/Cl- pump
- Other leaky ion channels
- Large intracellular -ve molecuels
Name the 4 types of graded potentials:
- Generator (sensory receptors)
- Postsynaptic
- Endplate (NMJ)
- Pacemaker
Other names for graded potentials?
- Electrotonic potential
- Decremental
- Non-propagated
- Local potential
What are the properties of a graded ptenital?
- Decremental
- Hyper- or Depolarising
- Graded
- Can Summate
Why are graded potentials decremental?
They leak out the membrane.
Furhter from the initial site of depolarisation the weaker the current
How do graded potentials transmit stimulus intensity?
In their amplitude
Whats the process behind graded potentials being graded?
- Stronger stimulus
- More channels opened
- Bigger current
- Larger potential
Whats an EPSP?
Excitatory Post Synaptic Potential
Depolarises the membrane
Whats an IPSP?
Inhibitory Post Synaptic Ptential
Hyperpolarizes the cell
How does a fast IPSP occur?
Chlorine channels open and Cl- ions flood the cell
How does a slow IPSP occur?
Potassium channels open & K+ leaves cell
Slow because K+ channel is seperate the the receptor
What transmitter vauses both fast & slow IPSPs?
GABA
How does a fast EPSP occur?
Non-specific monovalent cation channels open.
Some k+ leaves but lots of Na+ enters
Cell depolarises
How does a slow EPSP occur?
Leaky potassium channels are closed
K+ builds up even higher in cell
What kind of gated channels ar einolved in graded potentials?
Ligand-gated
What gated channels are involved in APs?
Voltage gated
What are the 2 types of summation (or integration)?
Temporal summation
Spatial summation
What is temporal summation?
Triggering the same graded potential multiple times to build up.
What is spatial summation?
Triggering different gradient potentials
Whats differnet about postsynaptic potentials generated at differnet dendrites?
They are diffent distances from the axon hillock
Therfore they decay different amounts before summating
What is usually the threshold for an AP to be triggered?
-55mV
How far does an AP overshoot?
Usually around +30/40mV
How does an AP occur?
- voltage-gated Na+ channels open
- cell flooded with Na+
- Rapid depolarisation
How is an AP resolved?
- Na+ chanells close
- Voltage-gated K+ open
- K+ floods out
- repolarisation
- Na+/K+ pump slowly restores normal concs & RMP
What is the period just after an AP called?
Refractory period
Why is there a refractory period?
This time is needed for the Na+ channels to recover (they are blocked temporarily)
What other things block Na+ channels & why?
Anaesthetics, Tetrodotoxin, Saxitoxin
To cause paralysis
Where is tetrodotoxin found?
In puffer fish
What are the properties of APs?
- Voltage-gated chanell mediated
- Threshold
- All or nothing
- Self-propagating
- refractory period
How do APs code stimulus intensity?
Firing frequency
How do APs self-propagate?
- First AP opens first Na+ channel
- Depolairses membrane just enough to open the next Na+ channel
- so on and on
Why do APs only self-propagate in one direction?
When an Na+ channel causes the next one to open, it itself closes entering its refractory period till after the AP has moved on.
What is the time consuming part of AP movement?
The opening of the voltage gated Na+ channels
How do Large axons increase AP travel speed?
- Larger axons = lower axial resitance
- depolarisation travels further
- Na+ channels spread further & less
- Time reduced
What is myelin?
The folds of the membrane from schwann cells or oligodendrocytes
Where are oligodendrocytes & schwann cells?
Scwann cells form myelin in PNS
Olgiodendrocytes form myelin in CNS
What does myelin do?
Decreases the leakage of the current allowing it to pass further
How does myelin improve AP movement speed?
- Reduces decrementation
- Na+ channels can be spread further
- faster travel
What are the Gaps between myelin sheafs called?
Nodes of Ranvier
Where Na+ channels are found
Name some de-myelinating diseases:
- Guillan-Barre
- Multiple Sclerosis
What is the compound action potential?
A summation of various almost (but not quite) simultaneous APs.
They arnt simultaneous because due to some fibres being differnet sizes/myelinated the various APs travel at differnt speeds
How are action potentials classifed?
alphabetically from fastest to slowest
Why fibres are most sensitive to presssure? (Anoxia)
The largest ones (As)
Which fibres are most senstitive to local anaesthetics?
The smallest ones (Cs)
What do Aalpha fibres do?
70-120ms
Proprioception/Motorneurones
Abeta fibre speed/function?
30-70ms
Touch, pressure
Agamma fibre speed/function?
15-30ms
muscle spindle motorneurones
Adelta fibre speed/function?
12-30ms
Touch, cold, fast pain
B fibre speed/function?
3-15ms
Preganglionic Autonomic fibres
C fibre speed/function?
0.5-2ms
Heat, slow pain
What are the steps of an endplate potential?
- Motor neuron AP arrives
- Triggers Ca2+ voltage-gated channels
- Calcium triggers vesicle fusion
- Ach released & crosses synaptic cleft
- Ach acts on receptors in sarcolemma
- Opens ligand gated Na+/K+ channels
- Evokes end palte potential
- Opens voltage gated Na+ channels evoking new AP
How is Ach removed after the enplate potential is trigerd?
Its broken down by acetylcholinesterase
Then the products taken up by the sarcolemma & cell
What does Ca2+ trigger at the NMJ?
Vesicle Fusion
How does Tetrodotoxin affect NMJ?
Blocks Na+ channels
So blokcs APs
How does Joro Spider toxin affect NMJ?
Blocks Ca2+ channels
Stops transmitter release
How does botulinum toxin affect NMJ?
Disrupts vesicle fusion
Prevents Ach release
How do Curare affect NMJ?
Blocks Ach receptors
So prevents Endplate potential
How do anticholinesterases affect NMJ?
Block Ach breakdown
So increases NMJ transmission
In what ways are CNS synapses more complex than NMJ?
- Multiple neurotransmitters & receptors
- Range of Post-synaptic potentials
- Anatomical arrnagemtn of the synapses
- Synapse connectivity
- Inhibitory synapses
Name some neurotransmistters used in the CNS?
Acetylcholine Norepinephrine Serotonin (5hydroxytryptamine) GABA ATP Peptides NO
What kind of post synaptic potentials are there in the CNs?
EPSPs & IPSPs
Fast & slow
What are the types of anatomical arrangement of synapses?
- Axo-dendritic
- Axo-Somatic
- Axo-axonal
- Gating
What does axo-dendritic mean?
Synapse between axon & dendrites
What does Axo-somtic mean?
Synapse between Axon & cell bdy
What does Axo-axonal mean?
Synapses between axon & axon
What is Axonal gating?
One neuron gates the synapse between two others
What are the types of synaptic connectivity?
Convergence (many neurons synapse to one)
Divergence (one neuron with multipl axons synapses to many neurons)
Feedback inhibition (Every AP this neuron fires also inhibits itself from sending anymore)
MonovsPolysynaptic pathway
