Nervous system + action potential Flashcards
What is dorsal root known as…
What is the ventral root known as…
Dorsal - Sensory
Ventral - motor
Multipolar neurons have extensive dendritic network attached to their cell bodies. These are the most common types of neuron found within the nervous system
Bipolar neurons have an extended dendritic arm, which is often associated with sensory organs such as the retina and olfactory system
Pseudounipolar neurons are similar to bipolar neurons but the dendritic extension and the axon has been fused during development. These neurons are sensory and tend to be found associated with visceral sensations (such as the sensation of stomach fullness)
The arrival of an action potential triggers what on pre synaptic neurone
It causes voltage gated Ca2+ channels to open to enable an influx of Ca2+ which causes neurotransmitter vesicles to fuse to the presynaptic membrane
On the post synaptic receptor I what happens when neurotransmitters bind to it
It opens the channels allowing an influx of ions into the post synaptic neurone
What happens in excitatory neurotransmission
The neurotransmitter binds to a receptor on the post synaptic membrane which allows positive ions through i.e Na+ which has a depolarises the membrane. If the membrane then reaches the threshold potential then an action potential is triggered
What happens in inhibitory neurotransmission
The neurotransmitter binds to a receptor on the post synaptic membrane which allows negative ions through i.e Cl- which hyperpolarises the membrane. Which moves it away farther from the threshold potential so more excitatory input is required to trigger an action potential.
What is the autonomic nervous system responsible for
Involuntary processes
Autonomic system is comprised of 1.sympathetic and 2.parasympathetic
- Fight or flight
- Rest and digest
How do sympathetic neurones transmit information
Pre-ganglionic sympathetic neurons release acetylcholine onto nicotinic receptors. Post-ganglionic neurons release noradrenaline onto adrenergic receptors (salivary glands are the exception, where post-ganglionic neurons release acetylcholine)
How to parasympathetic neurones transmit information
Parasympathetic neurons also have their cell bodies in the spinal cord. These pre-ganglionic neurons project to the target organ where they synapse on post-ganglionic neurons either within or very close to the target organ. Pre-ganglionic neurons release acetylcholine onto nicotinic receptors and post-ganglionic neurons release acetylcholine onto muscarinic receptors
How do somatic neurones transmit information
the somatic nervous system, which also has cell bodies in the spinal cord, which project directly to the target organ. In the case of somatic motor neurons innervating muscle, these neurons release acetylcholine onto nicotinic receptors
What is the somatic system responsible for
Voluntary processes
Photoreceptive ganglion cells in the retina detect Light, transmit the information to an area of the brain called the…
Edinger-westphal nucleus which activates parasympathetic nervous system to constrict the pupil - does not require conscious control.
The medulla function in autonomic system
Has many regions which directly connect with parasympathetic and sympathetic nerves, receives information from hypothalamus as well as sensory information from the viscera
What does an action potential diagram look like
How is an action potential triggered
There will sensitive ion channels that will open in response to a change e.g mechanoreceptors are pressure sensitive and when opened will allow an influx of positive ions
This makes the membrane depolarised if the amount of depolarisation reaches the threshold potential an action potential will be generated
When the threshold potential is reached…
The voltage gated sodium channels open at -55mv allowing a great influx of Na+ so the membrane becomes positive relative to the outside
The level of depolarisation is so high it activates neighbouring voltage gated sodium channels allowing for Na+ so the action potential can propagate down the axon
How does lidocaine work as an anaesthetic
Blocks voltage gated sodium channels preventing propagation of action potentials in pain sensing fibres
At peak potential…
The voltage gated sodium channels close into a voltage insensitive state so it is in the absolute refractory period (during depolarisation and repolarisation) - no more action potentials can be fired
At the same time voltage gated k+ channels open so k+ leaves down its conc gradient
What happens during repolarisation
The reflux of k+ ions leaves which makes the membrane potential more negative
There is an undershoot that occurs - hyperpolarisation - as the voltage gated k+ channels stay open longer than required
Once it reaches -70 to -75mv the voltage gated channels become sensitive again
During hyperpolaristaion it is called the relative refractory period as theoretically an action potential can be triggered but the amount of depolarisation required is much greater
What happens if there was not a refractory period
The second sodium channel would trigger the first channel again which means the action potential will be moving backwards
So with the refractory period we can ensure it is only moving in one direction - towards the sodium channels that are still voltage sensitive
After an action potential has fired how do we reset back to normal
Na-K-ATPase re-establishes correct concentration balance by moving 2k+ inside and 3Na+ out
What happens to the resting potential in a person with hyperkalaemia
We can see from the Goldman-Hodgkin-Katz equation when k+ conc increases from 4 to 10mmol/l the resting membrane potential decreases coming closer to the threshold potential so action potentials can start firing spontaneously
In myelinated neurones voltage gated Na+ channels only exist at the…
Nodes of ranvier as the myelin acts as an insulator so Na+ cannot be discharged through Na-k-ATPase nor can k+ leak from leak channels
Therefore the action potential jumps from node to node known as saltatory conduction
The larger diameter neurone will
will express a higher number of voltage gated sodium channels compared with a small diameter neuron, meaning the sodium conductance is greater, thus increasing the speed of depolarisation
There will also be less resistance
What is temporal and spatial summation
Spatial summation – where multiple synapses fire simultaneously, leading to a large influx of sodium across the whole body of a neuronal soma
Temporal summation – where a single synapse fires multiple times within a very short time space
