How nerves work Flashcards
Name the parts of the brain!!
Front - frontal lobe Middle - parietal lobe Back - Occipital lobe Bottom lobe - temporal Cerebellum - controls basic function - at the bottom too
what are low and high grooves in the brain called?
low - sulcus
high - gyrus
what nerves go to and from the brain - not via the spinal cord ?
cranial nerves
name the 3 subdivisions of the nervous system
autonomic, somatic, enteric
What nerves are sensory and what are motor?
Sensory - afferent
Motor - efferent
Describe what each part of the nerve does from the dendrite to the axon terminal
dendrite - receives information
cell body (soma) - makes things
Axon hillock (initial segment) - triggers action potential
Axon - sends action potential
Axon terminal - releases neurotransmitter
what roots does the sensory information come in, and what root does the motor information leave?
In - dorsal root (back)
Out - ventral root (front)
What is grey matter and what is white matter- which one makes the cross shape?
white - axons
grey - cell bodies
Grey is the middle bit
What does glia do - and how much of the CNS is it?
Cells that keep nerves happy - 90% of the central nervous system.
What do astrocytes do?
Maintain a good environment and protect the blood brain barrier.
what do oligodendrocytes do?
make myline sheaths
what do microglia do?
Phagocytotic hoover - mop up infection
What do ependyma cells do?
On surface - produce cerebral spinal fluid
name the three parts of the brain stem
midbrain
poms
medulla oblongata
what are the hypothalamus and the thalamus called together?
diencephalon
What causes the resting membrane potential -describe steps.
- 70v
Na K pump pumps 3 Sodium out and 2 potassium in. (charge still equal on both sides)
Leaky potassium channels cause potassium to leave the cell due to its concentration gradient.
Reaches equilibrium potential (when electrical gradient and conc gradient are exactly opposite and equal)
Should be -90 but its -70 due to a few other leaky channels E.g calcium etc.
What does the action potential do?
Transmits signals over a distance
what does the graded potential do?
decides when to fire the action potential
what does the resting membrane potential do?
Gets the cell ready to respond
If the extracellular potassium concentration increases - this causes depolarisation. (it will be less negative as outside is more negative). How does this fail to cause damage?
Blood brain barrier - network of blood vessels that can block substances. So the tight capillaries in the brain does not get affected - however, the heart might
there is a high level of potassium within the cell. What ions have a high level outside the cell?
Na +
Cl -
Ca 2+
When will an action potential fire?
If the threshold is reached -55v.
This occurs due to sodium channels opening - and sodium rushing into the cell down it’s concentration gradient.
What is an action potential? and what occurs after it?
A massive depolarisation
over shoot to about +30
Then repolarisation
Hyperpolarisation
What is the purpose of the myline sheath?
Insulation - less current leaks out of the membrane so Na+ channels can be far apart . - faster signal
Action potentials are not graded - they are all the same high (amplitude). So how does a bigger stimulus provide a bigger reaction?
More frequency - not amplitude - so there are more action potentials that spend more time above the threshold.
Why can action potentials only travel forward??
refractory states - the ones that sodium has just depolarised are recovering.
Action potentials self propagate - what does this mean?
they spread and promote themselves.
lots of different axons work in a slightly different way. (Compound action potential??) How do big axons compare to small axons??
big axons - more sensitive to pressure and anoxia (lack of oxygen)
Small axons - More sensitive to local anaesthetic
Are action potentials decremental or non decremental?
Non - decremental - do not loose steam as such
graded potentials can summate. what does this mean?
they can add together - build up.
Integration to meet the threshold.
May be ISPS and ESPS - ISPS might cancel out ESPS - need to add them all up
What is temporal summation and what is spatial summation?
Temporal - multiple from a single neuron
Spatial - multiple from different neurones
What is an ESPS?
Excitatory post synaptic potential
What is an ISPS?
Inhibitory post synaptic potential
Where on the neurone would ESPS have a larger effect?
If they are closer to the axon hillock
Are graded potentials decremental or non-decremental ?
Decremental - fade as u go along further away from the stimulus
Name 4 different types of graded potentials and where they are found.
Pacemaker ps -in pacemaker tissue - they rymthically fire action potentials
Generator ps - at sensory receptors
Postsynaptic ps - at synapses
Endplate ps - at neuromuscular junctions
How is the size of the stimulus accounted for in graded potentials??
Amplitude !!
Large stimulus = bigger amplitude
Large stimulus - more current flow - bigger potential
Describe ESPS. (fast and slow)
fast - neurotransmitter opens channel. Na goes in, Potassium goes out. (more Na+ goes in)
slow - g protein coupled. shuts potassium leaky channels - slow depolarisation.
Describe ISPS (fast and slow)
fast - neurotramitter opens channel - cl- goes in, cell hyper polarises.
slow - g protein opens potassium channel - potassium
goes comes out .
what is a synapse?
Connection between one neurone and the other.
Or neuromuscular junction is between a motor neurone and a muscle fibre.
is a chemical or an electrical synapse more common?
Chemical
In vague terms - why does the muscle contract at the neuromuscular junction?
Action potential comes down the axon.
Passes across synaptic cleft.
Stimulates response in the SARCOLEMMA (cell membrane of the striated muscle fibre)
Muscle contracts.
Describe the action potential going down the motor neurone and stimulating muscle contraction - in detail.
Action potential in motor neurone ,
Opens voltage gated calcium channels in the presynaptic terminal
This triggers fusion of vesicles
Acetylcholine is released
They diffuse across the synaptic cleft
They bind to aCH (nicotinic) receptors
This opens ligand gated Sodium potassium channels
This evokes a graded local potential - end plate potential
Depolarises adjacent membrane to the threshold
Opens voltage gated Na channels -
Action potential
Acetylcholinesterase removes Ach to stop the action potential.
How do tetrodotoxin, jorospider toxin, botulinum toxic, curare affect the neuromuscular junction?
blocks the signal from occurring.
How does anti cholinesterase work?
IT blocks the Ach breakdown - so increases the transmission at the NMJ.
How does tetrodotoxin work?
Blocks Na+ channels - near the end of the process - action potential is not fired.
How does toro spider toxin work?
It blocks the Ca+ channels at the start of the process - stops vesicle fusion and transmitter release
how does botulinum toxin work?
disrupts the release machinery - transmitter is not released.
How does curare work?
Blocks Ach receptors - end plate potential does not occur.
how does the neuromuscular junction and the CNS synapses differ in terms of neurotransmitters?
CNS has lots of neurotransmitters with lots of receptors.
E.g Ach, ATP, Peptides, Dopamine, Seretonin, Histamine, Glycine etc.
neuromuscular junction - just has one
Name a fast ESPS and A fast ISPS neutrannsmitter in the CNS synapse.
ESPS - Glutamate
ISPS - GABA
How does the neuromuscular junction and the CNS synapse differ in terms of post synaptic potential .
Neuromuscular junction just has one end plate potential.
CNS hasFAST EPSP (ionotrophic - ligand gated)
FAST EPSP (metabotropic)
SLOW IPSP
FAST IPSP
this enables complex synaptic integration
Central nervous system synapses have different arrangements. Name some.
Axo-Somatic
Axo-Dendritic
Axo-axonal
CNS synapses display divergence and convergence. Do neuromuscular junctions do anything like this?
Only a tinnnnyyyy bit of divergence.
CNS synapses also can do feedback inhibition, and can have monosynaptic and polysynaptic pathways. What do polysynaptic pathways lead too?
more modulation.
Why do CNS system synapses have more synaptic integration?
They fire smaller potentials than Neuromuscular junction.
