Neuronal Communication Flashcards
1
Q
What are neurons
A
- specialised nerve cells
- transmit electrical impulses rapidly around the body so that an organism can respond to changes in its internal and external environment
2
Q
Outline the structure of a neuron
A
- cell body; contains a nucleus surrounded by cytoplasm which contains large amounts of mitochondria and endoplamsic reticulum which are involved in the production of neurotransmitters
- dendron; short extensions which divide into dendrites and transmit electrical impulses towards the cell body
- axon; singular, elongated nerve fibres that transmit impulses away from the cell body, it is long and has a cylindrical shape consisting of a narrow region of cytoplasm surrounded by a plasma membrane
3
Q
Name the 3 types of neuron
A
- sensory - transmits impulses from sensory receptors to the CNS
- relay - transmits impulses between sensory neurons and motor neurons
- motor - transmits impulses from CNS to effectors
4
Q
What are myelinated neurons
A
- neurones surrounded by a myelin sheath which is made from Schwann cells
- acts as an insulating layer which allows myelinated neurons to conduct the electrical impulse at a much faster speed
- gaps in between the myelin sheath are the nodes of ranvier
5
Q
How do the nodes of ranvier contribute to the speed of an impulse?
A
- they allow the impulse to jump from one node to the next node as it travels along the neurone which causes it to be transmitted much faster rather than it transmitting continuously along the nerve fibre which would be slower
6
Q
What are sensors receptors?
A
- transducers which detect stimuli and convert it into a nerve impulse, producing a generator potential
- each specific to a single type of stimulus
7
Q
Give the 4 main examples of sensory receptors in animals
A
- mechanoreceptors ; detect pressure and movement, found in the skin (e.g Pacinian Corpuscles)
- chemoreceptors ; detect chemicals, found in the nose (e.g olfactory receptors)
- thermoreceptors ; detect heat, found in the tongue (e.g end-bulbs of Krause)
- photoreceptors; detect light, found in the eyes (e.g cone cell)
8
Q
Outline what Pacinian Corpuscles are
A
- sensory receptors which detect mechanical pressure
- found deep within the skin
- contain a sensory nerve ending
9
Q
How do sensory receptors work?
A
- during resting potential, when a stimulus is detected the cell
membrane is excited and becomes more permeable allowing more ions to move in/out of the cell, altering the potential difference - this change in potential difference caused by a stimulus is known as the generator potential
- the bigger the stimulus, the bigger the generator potential produced
- if the generator potential reaches the threshold then an action potential will be triggered
10
Q
Describe how Pacinian Corpuscles work
A
- during resting state, the stretch mediated sodium ion channels in the sensory neurone membrane are too narrow for ions to pass through
- when pressure is applied to the Pacinian Corpuscles, it changes shape and causes the membrane surrounding its neurone to stretch
- this widens the sodium ion channels and ions diffuse into the neurone
- the influx of positive sodium ions changes the potential of the membrane; it becomes depolarised and results in a generator potential
- generator potential creates an action potential which is transmitted along neurones to the CNS
11
Q
What is resting potential?
A
- usually -70mV
- when the outside of the membrane is more positively charged
- the membrane is polarised due to the difference in charge
12
Q
How is a resting potential created?
A
- Sodium ions are actively transported out of the axon and Potassium ions in using the sodium potassium pump (an intrinsic protein)
- every 3 sodium ions pumped out, 2 potassium ions are pumped in
- there are more sodium ions outside of the membrane than in the axon cytoplasm so sodium ions diffuse back into the axon down the electrochemical gradient
- the gated sodium channels close and potassium channels open so potassium ions can diffuse out of the axon
- there are more positively charged ions outside of the axon creating a resting potential
13
Q
What is an action potential?
A
- the sequence of events that occur due to the rapid movement of sodium and potassium ions across the axon membrane through voltage gated ion channels
14
Q
Name the 5 stages involved in an action potential
A
- stimulus
- depolarisation
- repolarisation
- hyperpolarisation
- resting potential
15
Q
Discuss the first stage of an action potential
A
- stimulus
- excites the cell membrane causing some sodium ion channels to open, means the membrane becomes more permeable to sodium ions so sodium ions diffuse down their electrochemical gradient into the neurone, making the inside of the neurone less negative
16
Q
Describe the second stage of an action potential
A
- depolarisation
- if the potential difference reaches a threshold then the voltage gated sodium ion channels will open so more sodium ions diffuse into the neurone
- this is positive feedback
17
Q
Describe the third stage of an action potential
A
- repolarisation
- at around 30mV, all the voltage gated sodium channels close and voltage gated potassium ion channels open membrane becomes more permeable to potassium ions allowing them to diffuse out of the neurone down their conc gradient, starts to get membrane back to its resting potential
- this is negative feedback
18
Q
Describe the 4th stage of an action potential
A
- hyperpolarisation
- the potassium ion channels are too slow to close causing a slight overshoot of potassium ions where too many diffuse out of the neurone
- potential difference is more negative than the resting potential
19
Q
Describe the 5th stage of an action potential
A
- resting potential
- once all potassium ion channels are closed, the sodium-potassium pump restores the resting potential
20
Q
what is the refractory period?
A
- occurs when the sodium ion channels close and when the potassium ion channels are closed (between repolarisation and hyperpolarisation)
- because the ion channels are recovering and can’t be made to open
- ensures that action potentials are separate and that the impulse only travels in one direction
21
Q
Discuss the all or nothing principle
A
- idea that an impulse will only be transmitted if the initial stimulus is sufficient enough that increase the membrane potential above a threshold
22
Q
what is the speed of conduction
A
- how quickly an impulse is transmitted along a neurone
- affected by myelination, the diameter of an axon and temperature
23
Q
how does myelination affect the speed of conduction?
A
- increase the speed that action potentials travel
- depolarisation cannot occur at the myelin sheath
- action potentials only occur at the nodes
- schwann cells allow the impulse to jump from one node to the next (saltatori conduction)
24
Q
How does the diameter of the axon affect the speed of conduction?
A
- thicker the axon is, the higher speed the impulse travels at
- axon membrane has a greater surface area
- increases the rate of diffusion of ions which increases the rate of action potentials
- greater volume of cytoplasm reduces electrical resistance and action potential moves faster
25
Q
How does temperature affect the speed of conduction?
A
- impacts ectotherms more
- cold conditions will slow down nerve impulses/warmer conditions will speed them up
- colder means less kinetic energy available for the facilitated diffusion if sodium and potassium ions
26
Q
what is the synaptic cleft?
A
- the gap between two neurones that depresses the axon of one neuron from the denture of the next
27
Q
what is the presynaptic neurone?
A
the neurone where the impulse arrives
28
Q
what is the postsynaptic neurone?
A
- neurone that received the neurotransmitter
29
Q
what are synaptic vesicles
A
- vesicles containing neurotransmitters that fuse with the presynaptic membrane and release the contents into the synaptic cleft
30
Q
what do excitatory neurotransmitters do? give an example
A
- result in depolarisation of the postsynaptic neurone
- if threshold is met than an action potential is triggered
- example is acetylcholine
31
Q
what do inhibitory neurotransmitters do?
A
- result in hyperpolarisation of the postsynaptic membrane
- prevents an action potential being triggered
