Neuronal Communication Flashcards
What are specialised nerve cells called and what do they do?
Specialised nerve cells are called NEURONES and they transmit electrical impulses rapidly
What are the 3 key structures of a neurone?
- Dendrons
- Axons
- Cell body
Explain the structure and function of Dendrons
Dendrons are short extensions from cell body which divide into dendrites
They are responsible transmitting electrical impulses towards the cell body
Explain the structure and function of an axon
An axon is a nerve fibre that transmit impulses away from the cell body
Explain the structure and function of a cell body?
The cell body of a neurone contains the nucleus and cytoplasm
It also has lots of mitochondria and RER to produce neurotransmitters which are the chemical which pass signals across neurones
What are the three types of neurone?
- Sensory neurone
- Motor neurone
- Relay neurone
What is the function of a sensory neurone?
Transmit impulses from receptor to CNS
What is the function of a relay neurone?
Transmit impulses between sensory neurone and motor neurones
Relay neurones have lots of axons and dendrites
What is the function of motor neurones?
Relay impulses from relay and sensory neurones to an effector (muscle of gland)
What does it mean if a neurone is myelinated?
It means the Axon of the neurone have a myelin sheath which is made up of layers of SCHWANN CELLS
- every layer is a phospholipid bilayer
- acts as an insulating layer
Increases the speed of electrical impulses
What is a node of Ranvier?
A gap between each Schwann cell where electrical impulses jump across the node
What is the function of a sensory receptor? [2]
- Specific to a single type of stimulus
- Act as a transducer - convert stimulus into nerve impulses
What does a mechanoreceptor recept? E.g?
Mechanical receptors recept pressure and movement
E.g skin, pacinian corpuscle
What does a chemoreceptor recept? E.g?
Chemoreceptors recept chemicals
E.g nose
What does a thermoreceptor recept? E.g?
Thermoreceptors recept heat
E.g tongue
What does a photoreceptor recept? E.g?
Photoreceptors recept light
E.g eye
What is the pacinian corpuscle and where is it located?
The pacinian corpuscle is a receptor that detects mechanical pressure
It is located deep in the skin and is abundant in fingers and feet
Draw the structure of pacinian corpuscle
Neurone ending inside layers of connective tissues with gel
Surround capsule around entire diagram
The neurone ending in a pacinian corpuscle has a stretch mediated sodium channel, what does this mean?
This means that when they change shape, the permeability to sodium also changes
Describe the 5 step mechanism detailing how the pacinian corpuscle converts pressure into an impulse
- In the normal state, stretch mediated sodium channels are too narrow so Na+ ions cannot pass
- When pressure is applied, the corpuscle changes shape
This allows membrane around neurone to stretch - Membrane stretches allowing channel to widen so Na+ ions can now diffuse into neurone
- Influx of positive Na+ ions changes potential of membrane and it is DEPOLARISED resulting in a generator potential
- In turn, generator potential turns into action potential which is transmitted along neurones to CNS
What is resting potential?
The state of a neurone when it is not transmitting an impulse
What is true of the membrane charge of an axon when the neurone is in resting potential?
The membrane is polarised as the outside of the axons is more positively charged than the inside
How is a resting potential created in a neurone?
- Three Na+ions are transported out of the axon for every 2 K+ ions transported in the axon by a sodium potassium pump
- As there is more Na+ outside the axon it will diffuse back in and vice versa for K+ ions diffusing out
- But because gated sodium ion channels are closed whilst potassium channels are open - there is a more positively charged environment outside cell
What causes action potential in a neurone?
When a stimulus is detected and the energy causes depolarisation
What is depolarisation in a neurone?
A change in potential difference from negative to positive
What is repolarisation of a neurone and when does it occur?
Repolarisation is when the potential difference changes from positive to negative and returns to resting potential
It occurs when an impulse has passed
What are the 6 stages during an action potential
- Neurone starts at resting potential where some K+ channels are open and no Na+ voltage gated channels are open
- Energy of stimulus triggers sodium voltage channels to open, so Na+ ions diffuse in making it less negative
- Positive feedback occurs as change in charge causes more Na+ channels to open
- 40mV potential difference is reached and Na+ voltage gates close and the K+ voltage gates open
- K+ diffuse out reducing the charge making the inside more negative than the outside HYPERPOLARISATION
- Voltage gate K+ ion channels close and sodium potassium pimp causes Na+ to move OUT AND K+ to move IN - axon returns to resting potential
What is a synapse?
The junction between two neurones
How are impulses transmitted between two neurones?
Using chemicals called neurotransmitters
What is the synaptic cleft?
The gap between the axon and next dendrite, approximately 20-30nm long
What is the presynaptic neurone?
The neurone where the impulse is coming from?
What is the synaptic knob and some of its feature?
The synaptic knob is the swollen end of the presynaptic neurone
It contains lots of mitochondria and endoplasmic reticulum to make lots of neurotransmitter chemicals
What are the synaptic vesicles?
Vesicles containing neutrotransmitters that fuse with presynaptic membrane and release contents into synaptic cleft through exocytosis
What is the post synaptic neurone?
The neurone receive in the neurotransmitters
What is an excitory neurotransmitter?
Results in the depolarisation of the post synaptic neurone
E.g acetylcholine
What is an inhibitory neurotransmitter?
Results in hyper-polarisation of post synaptic membrane (becomes more negative)
STOPPING action potential being triggered
What is an example of inhibitory neurotransmitter?
E.g GABBA
GABBA results in the opening of chloride channels on post synaptic membrane so that Cl- ions diffuse in and potassium channels open so K+ ions move out
Describe the 6 stages of transmission across a cholinergic synapse
- Action potential arises in presynaptic neurone - this trigger Ca2+ ion channels to open
- Ca2+ ions diffuse into synaptic knob, the increased concentration triggers vesicles to bind to presynaptic membrane
- Acetylcholine is released into synaptic cleft by exocytosis
- Acetylcholine diffuses across cleft and bind with Na+ ion channels on post synaptic membrane triggering them to open
- Na+ ions move into post synaptic membrane triggering action potential
- Enzyme acetylcholinesterase hydrolyses acetylcholine into ethanol acid and chlorine
- Na+ channels in post synaptic membrane close as acetylcholine is gone
Why is it essential that acetylcholine is hydrolysed?
If not it could trigger multiple action potentials
What happens to acetylcholine after it is hydrolysed?
It returns to synaptic knob and uses energy from ATP to recycle it
What are the main 3 roles of synapses?
- Ensure impulses are unidirectional
- Allow impulse at one neurone to be transmitted to a number of neurones
- To allow lots of neurones to feed into one synapse so that we produce a single response to a stimuli
What is temporal summation?
When a build up of neurotransmitters cause a trigger of action potential when incoming action potentials are quick in succession
What is spatial summation?
When multiple presynaptic neurones bind to one post synaptic neurone and together they release enough neurotransmitter to trigger an action potential
What is a refractory period?
Period of time where an axon cannot be ‘excited’ so sodium gates remain closed so they cannot enter axon
What 3 factors affect speed of neurone transmission?
- Weather the cell is myelinated or not
- The axons diameter
(The bigger the faster as there is less resitance) - Temperature
(Higher temperature means faster as ions diffuse at a faster rate in higher temperatures)
Does the size of a stimulus affect the size of the action potential?
No, small and large stimuli produce the same action potential
What affect will a large stimulus have on the action potential?
It will increase the frequency of action potentials
What is the all or nothing principle?
Action potential is only triggered when threshold is reached
How is a stimulus propagated down a non-myelinated cell?
- In the resting state, the axon has a negative charge (in comparison to outside environment) with more K+ ions inside and more Na+ ions outside
- A stimulus will cause membrane to depolarise allowing Na+ ions to diffuse in, in once section of axon
- Na+ ions are attracted to negative environment along axon so will move in a localised electrical circuit, causing more Na+ voltage gates to open in that area
- As Na+ ions move across axon the Na+ voltage gates close and K+ voltage gates open allowing repolarisation to occur so that axon can return to resting state
What is an advantage of myelinated cells during propagation?
Less ATP is required to repolarise axon as only the parts at the nodes of Ranvier are depolarised
What is saltatory conduction?
In myelinated cells, only the sections by the nodes of Ranvier are depolarised during propagation
