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OCR Biology A Level Module 5 Communication, homeostasis and energy > 5.3 Neuronal Communication > Flashcards

5.3 Neuronal Communication Flashcards

1
Q

What are sensory receptors?

A

detect stimuli and are energy transducers, converting one form of energy to electrical energy as a nerve impulse

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2
Q

What receptors respond to changes in pressure? How? What are some features?

A

Pacinian Corpuscles

  • when pressure on skin changes, it deforms the ring. Sodium channels open, allowing them to diffuse into the cell and produce a generator potential.
  • the movement across the membrane creates a change in potential difference.
  • if a large enough stimulus is detected and enough gates are opened, the potential difference changes significantly = depolarisation and an action potential.
  • rings of connective tissue around end of nerve cell
  • fibroblasts producing connective tissue
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3
Q

What is the function of the motor neurone?

A

carry action potentials from CNS to an effector

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4
Q

What is the structure of a motor neurone?

A
  • cell body with dendrites
  • axon hillock
  • very long axon with myelin sheath
  • synaptic endings/ axon terminals
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5
Q

What is the function of the relay neurone?

A

connect sensory and motor neurones

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6
Q

What is the structure of a relay neurone?

A
  • cell body with dendrites
  • VERY short axon, with synaptic endings
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7
Q

What is the structure and function of sensory neurones?

A
  • carry APS from receptors to CNS
  • may have dendrites to sensory receptor
  • dendron with myelin sheath
  • cell body
  • axon with myelin sheath
  • synaptic endings
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8
Q

What are similarities in the structures of all the neurones?

A
  • plasma membrane has many gated ion channels and Na+/K+ pumps
  • cell body with nucleus, mitochondria and ribosomes
  • ## dendrites carry impulses towards body, and axons away
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9
Q

What are the differences between the neurones?

A
  • motor: cell body in CNS and has LONG axon to effector, sensory has LONG dendron to cell body which is outside of CNS. Short axon into CNS
  • relay: short dendrities + short axon. CNS
  • third of peripheral nervous system neurones MYELINATED. Rest in PNS, and the CNS, ARE NOT.
  • sensory and motor contain nodes of ranvier, relay dont
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10
Q

What does myelination look like on a neurone? What is the purpose?

A
  • Schwann cells that make up fatty sheath. Cytoplasm wrapped around axon.
  • Gaps are nodes of Ranvier. The movement of ions can only occur here
  • Jumping of impulse = rapid = increased speed of transmission over long distances
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11
Q

What occurs in non myelinated neurones? What is the purpose?

A
  • AP moves along in a wave
  • Schwann cells loosely wrapped around multiple axons instead
  • Shorter distances, coordinating functions where speed isn’t so important
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12
Q

What is happening when neurones are at rest?

A
  • Gated sodium ion channels are kept closed
  • ATP is used to actively pump 3 Na+ ions out for every 2K+ ions inside
  • Some potassium channels are open meaning the membrane is more permeable to them, and they tend to diffuse out.
  • The cell cytoplasm also contains many large anions
  • Membrane is POLARISED - more negative compared to outside = resting potential at about -60mV
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13
Q

What are the stages of an action potential?

A
  1. Resting potential
  2. A few sodium ion channels open (due to a stimulus in receptor cells, or diffusion in neurones) and some sodium ions diffuse into the cell
  3. Membrane reaches about -50mV - the THRESHOLD
  4. Positive feedback causes nearby voltage gated sodium ion channels to open and loads of ions flood in = DEPOLARISATION
  5. Potential difference reaches +40mV, where the sodium ion channels now close and potassium channels open.
  6. Potassium ions diffuse OUT of the cell bringing the potential difference back to negative = REPOLARISATION
  7. The potential difference overshoots slightly = HYPERPOLARISATION
  8. K+ ion channels close. Original resting potential is restored via the pump.
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14
Q

What is the refractory period?

A

after each AP it is impossible to reach another for some time -> allows the cell to recover and ensures APs are transmitted in one direction.

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15
Q

How are local currents formed?

A
  1. Sodium ion channel opens during depolarisation allowing Na+ to diffuse into the neurone
  2. Localised increase in conc of Na+ inside the neurone -> AP
  3. Sodium ions diffuse sideways along the axon/dendron away to a region of lower concentration.
  4. Causes slight depolarisation of the membrane further down and causes opening of Na+ channels further down the neurone at a node of Ranvier.
  5. The open channels allow rapid influx of sodium ions in, causing a full depolarisation along the neurone = another AP.
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16
Q

What is saltatory conduction? What are the advantages?

A
  • the jumping of action potentials from one node to the next
  • the local currents are elongated, and then the ionic movements occur at the Nodes
  • speeds up transmission
17
Q

How is the intensity of a stimulus transmitted?

A
  • all action potentials are the same intensity
  • FREQUENCY of APs arriving at the sensory region of the brain.
  • higher frequency = more intense stimulus
18
Q

What are cholinergic synapses?

A
  • junction between two neurones -> synaptic cleft
  • a synapse that uses acetylcholine as the neurotransmitter released from the pre-synaptic neurone which diffuses across the cleft to the post-synaptic neurone
19
Q

What specialised features does the pre-synaptic bulb contain?

A
  • many mitochondria for ATP
  • SER to package neurotransmitter into vesicles
  • large numbers of vesicles with acetylcholine
  • number of voltage gated calcium ion channels
20
Q

How is the post-synaptic membrane specialised?

A
  • many sodium ion channels that respond to neurotransmitter, with 5 polypeptide molecules
  • two of these have a special receptor site specific to acetylcholine, complementary
  • binding causes Na+ ion channels to open
21
Q

Describe the transmission across a synapse process

A
  1. AP arrives at synaptic bulb
  2. Voltage gated Ca2+ ion channels open
  3. Ca2+ ions diffuse into the synaptic bulb
  4. They cause the vesicles to move to and fuse with the pre-synaptic membrane
  5. Acetylcholine is released by exocytosis and diffuses across cleft
  6. It binds to receptor sites on sodium ion channels on post-synaptic membrane and causes them to open
  7. Sodium ions diffuse into the post-synaptic neurone
  8. EPSP is created (excitatory post synaptic potential)
  9. If threshold then an AP is generated, which passes down.
22
Q

What is the role of acetylcholinesterase?

A
  • Found in synaptic cleft
  • Hydrolyses the acetylcholine to ethanoic acid and choline, which are recycled.
  • they reenter the bulb by diffusion and endocytosis and are recombined to acetylcholine using ATP
  • Stops over-transmission of signals
23
Q

What is an excitatory post-synaptic potential vs an inhibitory post-synaptic potential?

A
  • EPSP: the small depolarisation across the post-synaptic membrane, when a relatively small number of acetylcholine molecules diffuse and bind
  • IPSP: reduce the effect of summation and prevent an AP in the post-synaptic neurone
24
Q

What is summation? Describe the two types

A

when the effects of several impulses are added together

several APs in same pre-synaptic neurone = TEMPORAL

AP’s arriving from several different pre-synaptic neurones = SPATIAL

25
Q

How is communication controlled at synapses?

A
  • several pre-synaptic neurones might converge to one post-synaptic neurone -> could be useful when diff stimuli are warning us of danger
  • one pre-synaptic neurone might diverge to several post-synaptic neurones -> useful in reflex arc
  • synapses ensure APs go one way
  • synapses can filter out low level, unwanted signals, or summation can amplify them
  • after repeated stimulation a synapse might run out of neurotransmitter = habituation.
26
Q

The sensory neurone was stimulated electrically and the FURA-2 fluorescence in the
synaptic bulb was measured. At the same time, an electrode recorded the membrane
potential in a postsynaptic neurone.
The results of this study are shown i
Strength of electrical
stimulation
low
medium
high

FURA-2 fluorescence in
synaptic bulb
low
medium
high

Highest membrane
potential in postsynaptic
neurone (mV)
–60
+40
+40

The intensity of FURA-2 fluorescence is proportional to the concentration of Ca2+ ions.
The scientists concluded that changes in the concentration of Ca2+ ions in the presynaptic
neurone caused an action potential in the postsynaptic neurone.
Evaluate and explain the scientists’ conclusion.
.

A

conclusion is valid because:
1 concentration of Ca2+ is proportional to strength
of stimulus 
2 Ca2+ change from low to , medium / high , causes increase in (membrane) potential 
3 action potential in , presynaptic neurone / synaptic
bulb leads to , opening of Ca2+ channels / entry of Ca2+
4 Ca2+ , causes / AW , release of neurotransmitter 
5 neurotransmitter causes , Na+ / sodium ion channels to open in (post-synaptic) neurone 
6 if threshold is exceeded this causes action potential in (postsynaptic) neurone / depolarises (postsynaptic) membrane 

conclusion may not be valid because:
7 changes in Ca2+ concentration may not be thecause of (postsynaptic) action potential
8 Ca2+ change from medium to high but no change in (membrane) potential 

OCR Biology A Level Module 5 Communication, homeostasis and energy (7 decks)

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