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A Level (A2) OCR Biology > Unit 5.3- Neuronal Communication > Flashcards

Unit 5.3- Neuronal Communication Flashcards

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1
Q

Motor neurones definition:

A

Neurones that carry an action potential from the CNS to effector

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2
Q

Relay neurones definition:

A

Join sensory and motor neurones

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3
Q

Sensory neurones definition:

A

Neurones that carry an action potential from the sensory receptor to CNS

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4
Q

Dendron/ dendrites definition:

A

The bit before the cell body that’s like the axon

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5
Q

Structure of neurones:

A
  • Many are long
  • Plasma membrane has many gated ion channels that control the entry or exit of sodium, potassium or calcium ions
  • Sodium potassium pump actively transports sodium ions OUT of the cell and potassium ions INTO the cell
  • Neurones maintain a potential difference across their plasma membrane
  • The cell body contains the nucleus, and many mitochondria and ribosomes
  • Neurone dendrites connect to other neurones and carry impules TOWARDS the cell body
  • The axon carries imulses AWAY from the cell body
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6
Q

What is the myelin sheath made of?

A

Schwann cells

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7
Q

Lengths of dendron and axon in sensory neurone:

A
  • Long dendron
  • Cell body just outside of CNS
  • Short axon
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8
Q

Lengths of dendron and axon in relay neurone:

A
  • Many short denrites

- Short axon

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9
Q

Lengths of dendron and axon in motor neurone:

A
  • Cell body inside CNS

- Long axon

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10
Q

Why do impulses travel faster in myelinated neurones?

A
  • The myelin sheath is wrapped tightly around the neuron, preventing the movement of ions across the neurone membrane
  • The movement of ions can only occur at the node of Ranvier
  • This means the action potential jumps from one node to the next
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11
Q

Where are the Schwann cells in non-myelinated neurones?

A

Several neurones may be enshrouded in one loosely wrapped Schwann cell, meaning that the action potential moves in a wave

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12
Q

What are non -myelinated neurones often used in?

A

Coordinating body functions such as breathing and the action of the digestive system. They do not need to be so quick for this.

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13
Q

Pacinian corpuscle definition:

A

A pressure sensor found in the skin

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14
Q

Sensory receptors definition:

A

Cells/ sensory nerve endings that respond to a stimulus in the internal or external environment of an organism and can create action potentials

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15
Q

Structure of a Pacinian corpuscle:

A
  • Oval shaped

- Series of concentric rings of connective tissue wrapped around the end of a nerve cell

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16
Q

What happens to the Pacinian corpuscle when there is pressure on the skin?

A

It deforms the rings of connective tissue, which push against the nerve ending. When pressure is constant, the corpuscle stops responding because the rings are not being deformed any more

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17
Q

What happens to sodium channels when the membrane of a nerve cell is deformed by changing pressure?

A

They open

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18
Q

What does the sodium/ potassium pump do on a nerve cell membrane

A
  • Actively pump three sodium ions out of the cell for every two potassium ions actively pumped in
  • This is when the channel proteins are closed and the neurone is at rest
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19
Q

Why do some potassium ions leak out of the nerve cell when it is at rest?

A

The membrane is more permeable to potassium ions

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20
Q

What is the negative charge inside nerve cells enhanced by?

A

The presence of negatively charged anions inside the cell

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21
Q

What is a nerve impulse created by?

A
  • Altering the permeability of the nerve cell
  • Sodium ion channels are opened and sodium ions rush in
  • This creates a change in the potential difference and causes depolarisation
  • If it is a small stimulus, only a few sodium channels will open, (generator potential)
  • If more are open, the potential difference across the cell membrane will change significantly and will cause an action potential
22
Q

Action potential definition:

A

A brief reversal of the potential across the membrane of a neurone, causing a peak of +40mV compared to the resting potential of -60mV

23
Q

Resting potential definition:

A

The potential difference across the membrane while the neurone is at rest

24
Q

What is the resting potential of a neurone at rest?

A

-60mV

25
Q

What are voltage gated channels opened by?

A
  • Changes in the potential difference across the membrane
  • When there are sufficient generator potentials to reach the threshold, the voltage gated channels open
  • Positive feedback
26
Q

What happens when generating an action potential, once the sodium ions have rushed in and the depolarisation reaches +40V on the inside of the cell?

A

The neurone will start to transmit the action potential

27
Q

Stages of an action potential:

A
  • Starts off in resting state (-60mV)
  • Sodium ion channels open and sodium diffuses into cell
  • Membrane depolarises (threshold of -50mV)
  • Positive feedback causes nearby voltage gated channels to open
  • Potential difference across plasma membrane reaches +40mV
  • Sodium ion channels close and potassium ion channels open
  • Potasium ions diffuse out of the cell, bringing back the resting potential (repolarisation)
  • Potential difference overshoots slightly, making the cell hyperpolarised
  • Original potential difference restored
28
Q

Why can another action potential not be stimulated straight after another one?

A
  • The sodium and potassium ions are in the wrong place and have to be moved back to their correct places by the sodium/ potassium pump
  • Known as the refractory period
  • Ensures that action potentials are only stimulated in one direction
29
Q

What causes local currents?

A

Sodium ions flooding into the neurone, causing depolarisation

30
Q

Formation of local currents:

A
  • Sodium ion channels open
  • Localised increase in concentration of sodium ions inside neurone (the action potential)
  • Sodium ions diffuse along axon/ dendron
  • Sodium gates further along will open because of movement of sodium ions.
  • Action potential moves further along neurone as more sodium ions enter and set up another action potential
31
Q

What happens with local currents in myelinated neurones?

A
  • The ion exchanges can only happen at the nodes of Ranvier
  • The local currents are elongated and sodium ions diffuse from one node of Ranvier to the next
  • This means they appear to jump from one node to the next
  • This is saltatory conduction
32
Q

How do our brains determine the intensity of a stimulus?

A

From the frequency of action potentials arriving at the sensory region of the brain

33
Q

Cholinergic synapse definition:

A

A synapse that used acetylcholine as its neurotransmitter

34
Q

Neurotransmitter definition:

A

A chemical used as a signalling molecule between two neurones in a synapse

35
Q

What is the small gap between two synapses called?

A

The synaptic cleft

36
Q

How big is a synaptic cleft?

A

20nm

37
Q

What does the action potential do in order to continue on the other side of the synaptic cleft?

A

Causes the release of neurotransmitters in the pre-synaptic neurone. This defuses across the cleft and causes a new action potential in the post synaptic neurone

38
Q

What is the swelling at the end of the pre-synaptic neurone called?

A

pre-synaptic bulb (knob)

39
Q

What specialised features does the pre-synaoptic bulb contain?

A
  • Many mitochondria
  • Large amounts of SER, which packages the neurotransmitters into vesicles
  • Large number of vesicles containing acetylcholine
  • Large number of voltage gated calcium ion channels on the cell surface membrane
40
Q

What does the post-synaptic membrane contain?

A

Specialised sodium ion channels

41
Q

What do the sodium ion channels on the post-synaptic membrane contain?

A
  • Five polypeptide molecules
  • Two of these have a special receptor site that is specific to acetylcholine
  • When acetylcholine is present in the synaptic cleft, it binds to the two receptor sites and causes the sodium ion channels to open
42
Q

How does transmission across a synapse work?

A
  • Action potential arrives at the synaptic bulb
  • Voltage-gates calcium ion channels open
  • Calcium ions diffuse into synaptic bulb
  • Calcium ions cause the vesicles to move to and fuse with the pre-synaptic membrane
  • Acetylcholine is released by exocytosis and diffuses across the cleft
  • Acetylcholine molecules bind to the receptor sites on the sodium ion channels in the post-synaptic membrane, causing the sodium ion channels to open
  • Sodium ions diffuse across the post synaptic membrane into the post-synaptic neurone
  • Generator potential or excitatory post-synaptic potential (EPSP) is created
  • If sufficient generator potentials combine to reach the threshold, it creates an action potential in the post-synaptic neurone
43
Q

What does acetylcholinesterase do?

A
  • Found in the synaptic cleft
  • Hydrolyses the acetylcholine to ethanoic acid and choline
  • This stops the transmission of signals
  • The ethanoic acid and choline are recycled. They re-enter the synaptic bulb by diffusion and are recombined to form acetylcholine using ATP
44
Q

Summation definition:

A

Occurs when the effects of several excitatory post-synaptic potentials (EPSP) are added together

45
Q

What is temporal summation?

A

When there is a series of action potentials travelling along a neurone so that they can creating EPSPs that come together to create an action potential

46
Q

What is spatial summation?

A

When there are several pre-synaptic neurones that each bring action potentials, creating EPSPs that come together to create an action potential

47
Q

What prevents the combination of several EPSPs producing an action potential?

A

An IPSP

48
Q

How is one pre-synaptic neurone diverging into several post synaptic neurones beneficial?

A

One action potential can be transmitted to several parts of the nervous system. Useful in a reflex arc where one post-synaptic neurone elicits the response and the other informs the brain

49
Q

How do synapses ensure the action potential travels in the correct direction?

A

Only the pre-synaptic bulb contains the vesicles of acetylcholine

50
Q

What does it mean if we have become habituated to a stimulus?

A

After repeated stimulation, a synapse may run out of vesicles containing the neurotransmitter. We no longer notice the stimulus

A Level (A2) OCR Biology (13 decks)

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