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Biology A-Level -James > Chapter 5.3-Roles of sensory receptors > Flashcards

Chapter 5.3-Roles of sensory receptors Flashcards

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1
Q

What are sensory receptors?

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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2
Q

What is a transducer?

A

a cell that converts one form of energy into another-in this case to an electrical impulse

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3
Q

What is a stimulus?

A

change in the environment which brings about a response

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4
Q

If there is a change in light intensity what is the sensory receptor that detects this change and what energy change happens?

A
  • light sensitive cells (rods and cones) in the retina

- light to electrical energy

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5
Q

If there is a change in temperature on the skin what is the sensory receptor that detects this change and what energy change happens?

A
  • temperature receptors in the skin and hypothalamus

- heat to electrical

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6
Q

What is the Pacinian corpuscle?

A

a pressure sensor found in the skin

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7
Q

What is the structure of the Pacinian corpuscle?

A

-oval-shaped structure that consists of a series of concentrated rings of connective tissue wrapped around the end of a nerve cell

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8
Q

How does the Pacinian corpuscle carry out its function?

A
  • sensitive to changes in pressure that deform the rings of the connective tissue.
  • if pressure is constant then they stop responding
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9
Q

What is the sodium-potassium pump and how does this help generate an nerve impulse?

A
  • sodium-potassium pump: actively pump sodium ions out of the cell and potassium ions into the cell. 3 Na+ are pumped out for every 2 K+ pumped into the cell. The concentration of sodium ions outside the cell increases, while the concentration of potassium ions inside the cell increases.
  • the result of this movement is that a potential gradient is generated across the membrane. The cell is negatively charged inside compared with outside. This negative potential is enhanced by the presence of negatively charged anions inside the cell. The resting potential of the inside of the cell is -60mV.
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10
Q

What are the two different channel proteins found in the cells associated with the nervous system?

A
  • sodium channels (specific to Na+)
  • potassium channels (specific to potassium ions (k+)
  • these channels also possess a gate that can open or close the channel
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11
Q

How do the sodium channels create a nerve impulse when the Pacinian corpuscle detects pressure?

A
  • a nerve impulse is created by altering the permeability of the nerve cell membrane to sodium ions. This is achieved by opening the sodium ion channels.
  • sodium channels opne, the membrane permeability increases and the sodium ions can move across the membrane down their concentration gradient.
  • this creates a change in the potential difference (charge) across the membrane. The inside of the cell becomes less negative (compared with the outside) than usual. This is called depolarisation.
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12
Q

What happens when the potential difference across the cell membrane changes significantly?

A

initiates an impulse or action potential

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13
Q

What is the name of the change in potential across a receptor membrane caused by the influx of Na+ ions into the cell?

A

generator potential

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14
Q

What are neurones?

A

nerve cells that carry information as tiny electrical signals

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15
Q

What are the three types of neurones?

A
  • motor neurones
  • sensory neurones
  • relay neurones
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16
Q

What is the function of motor neurones?

A

carry an action potential from the CNS to an effector such as a muscle or gland

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17
Q

What is the function of sensory neurones?

A

carry the action potential from a sensory receptor to the CNS.

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18
Q

What is the function of relay neurones?

A

connect sensory and motor neurones

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19
Q

What is the structure of neurones?

A
  • very long so can transmit action potential over a long distance
  • many gated ion channels that control the entry of exit of sodium, potassium or calcium ions
  • sodium/potassium pumps which use ATP to actively transport sodium ions out of the cell and potassium ions into the cell
  • cell body that contains the nucleus, many mitochondria and ribosomes
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20
Q

What are the roles of dendrites in neurones?

A
  • numerous dendrites connect to other neurones

- they carry impulses towards the cell body

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21
Q

What are the roles of axons in neurones?

A

carries impulses away from the cell body

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22
Q

What is the specific structure of a motor neurone?

A
  • cell body is in the CNS

- long axon that carries the action potential out to the effector and is located in the PNS (peripheral nervous system)

23
Q

What is the specific structure of a sensory neurone?

A
  • long dendron carrying the action potential from a sensory receptor to the cell body, which is positioned just outside of the CNS in the PNS
  • short axon carrying potential into the CNS
24
Q

What is the specific structure of a relay neurone?

A

-many short dendrites and a short axon located in the CNS

25
Q

What is a myelinated neurone?

A

has an individual layer of myelin around it

26
Q

What is a non-myelinated neurone?

A

has no individual layer of myelin

27
Q

What are the cells that make up the fatty myelin sheath and how are they arranged in myelinated cells?

A
  • Schwann cells
  • wrapped tightly around the neurone so the sheath actually consists of several layers of membrane and thin cytoplasm from the Schwann cell
28
Q

What are the gaps called in the myelin sheath?

A

nodes of Ranvier

29
Q

What are the advantages of myelination?

A
  • increases speed of transmission of an action potential much more quickly than a non-myelinated neurone can
  • used in longer neurones (sensory and motor rather than relay neurones)
  • enable a more rapid response to a stimulus
30
Q

What is an action potential?

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

31
Q

What is the resting potential?

A

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

32
Q

What are the stages in the generation of an action potential stage one?

A
  1. the membran estrads in its resting state-polarised with the inside of the cell being -60mV compared to the outside. There is a higher concentration of sodium ions outside than inside and a higher concentration of potassium ions inside than outside
  2. Sodium ion channels open and some sodium ions diffusee into the cell
  3. The membrane depolarises-it becomes less negative with respect to the outside and reaches the threshold value of -50mV.
  4. Positive feedback causes nearby voltage-gated sodium ion channels to open and many sodium ions flood in. As more sodium ions enter, the cell becomes positively charged inside compared with outside
33
Q

What is the stages of generating an action potential part two?

A
  1. The potential difference across the plasma membrane reaches +40mV. The inside of the cell is positive compared with the outside.
  2. The sodium ion channels close and potassium channels open
  3. Potassium ions diffuse out of the cell bringing the potential difference back to negative inside compared with the outside-this is called depolarisation
  4. the potential difference overshoots slightly, making the cell hyperpolarised
  5. The original potential difference is restored so that the cell returns to its resting state.
34
Q

What is the refractory period?

A
  • Na+ channels are closed so theres no way to generate a generator potential
  • the Na+ and K+ ions are in the wrong places after the action potential -this needs to be rectified by the Na/K pump
35
Q

How is a nerve impulse along an axon?

A
  1. When an action potential occurs the sodium ion channels open at that point in the neurone
  2. The open sodium ion channels allow sodium ions to diffuse across the membrane from the region of higher concentration outside the neurone into the neurone. The conc of sodium ions inside the neurone rises at the point where the sodium ion channels are open
  3. Sodium ions continue to diffuse sideways along the neurone, away from the region of increased concentration. This movement of charged particles is a current called a LOCAL CURRENT.
  4. the local current causes a slight depolarisation further along the neurone which affects the voltage-gated sodium ion channels, causing them to open. The open channels allow rapid influx of sodium ions causing a full depolarisation (action potential) further along the neurone. The action potential has therefore moved along the neurone.
36
Q

Why does the action potential move in the same direction?

A

this is because the conc of sodium ions behind the action potential is still high so it won’t diffuse that way

37
Q

What is saltatory conduction?

A
  • myelin sheath is an insulating layer of fatty material, composed of Schwann cells tightly wrapped around the neurone. Na+ and K+ cannot diffuse through this fatty layer. In-between the Schwann cells are small gaps-the nodes of Ranvier.
  • therefore ionic movements only occur at the nodes of Ranvier and this means that the local currents are therefore elongated and sodium ions diffuse along the neurone from one node of Ranvier to the next. This means that the action potential appears to jump from one node to the next (saltatory conduction)
38
Q

What is the ‘all or nothing’ rule?

A
  • There are no big or small action potentials in one nerve cell - all action potentials are the same size
  • therefore, the neurone either does not reach the threshold or a full action potential is fired
39
Q

What is a cholinergic synapse?

A

a synapse that uses acetylcholine as its neurotransmitter

40
Q

What is a synapse?

A

junction between two or more neurones, where one neurone can communicate with, or signal to, another neurone

41
Q

What is a neurotransmitter?

A

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

42
Q

What is the synaptic cleft?

A

gap between the two neurones (usually about 20nm in width)

43
Q

What is the pre-synaptic bulb?

A

the end of a neurone which is a swelling nad contains a number of specialised features

44
Q

What specialised features does the pre-synaptic bulb contain?

A
  • many mitochondria
  • large amount of smooth endoplasmic reticulum, which packages the neurotransmitter into vesicles
  • large numbers of vesicles containing molecules of a chemical called acetylcholine, the transmitter that will diffuse across the synaptic cleft
  • voltage-gated calcium ion channels on the cell surface membrane
45
Q

What does the post-synaptic membrane contain?

A
  • specialised sodium ion channels that can respond to the neurotransmitter
  • channels consist of five polypeptide molecules, two of which have a special receptor site that is specific to acetylcholine. The receptor sites have a shape that is complimentary to the shape of the acetylcholine molecule
46
Q

How many molecules of acetylcholine do you need to bind to one sodium ion channel in order to open it?

A

2

47
Q

What are the sequence of event in the transmission of a signal across the synaptic cleft?

A
  1. action potential arrives at the synaptic bulb
  2. change in the membrane potential causes voltage gated Ca^2+ channels to open
  3. Ca^2+ ions diffuse into the synaptic bulb
  4. Ca^2+ causes vesicles to move towards and fuse with the pre-synaptic membrane
  5. Acetylcholine is released by exocytosis
  6. Acetylcholine molecules bind to the receptor sites on the sodium ion channels in the post-synaptic membrane and causes them to open
  7. Na+ ions diffuse across the post-synaptic membrane into the post-synaptic neurone, generating an excitatory post-synaptic potential
  8. If sufficient generator potentials combine then the potential across the post-synaptic membrane reaches the threshold potential
  9. A new action potential is created in the post-synaptic neurone
48
Q

What is the role of acetylcholinesterase in synapses?

A
  • enzyme that is found in the synaptic cleft which breaks down unused acetylcholine
  • it hydrolyses the acetylcholine to ethnic acid (acetic acid) and choline, therefore stopping the transmission of signals, so that the synapse does not continue to produce an action potential in the post-synaptic neurone.
  • ethanoic acid and choline re-enter the synaptic bulb by diffusion and are recombined to acetylcholine using ATP from respiration in the mitochondria.
49
Q

What is summation?

A

occurs when the effects of several excitatory post-synaptic potentials (EPSPs) are added together

50
Q

What is temporal summation?

A

summation which results from several action potentials in the same pre-synaptic neurone

51
Q

What is spatial summation?

A

summation which results from action potentials arriving from several different pre-synaptic neurones

52
Q

What are IPSPs?

A
  • pre-synaptic neurone which can produce inhibitory post-synaptic potential
  • reduce the effect of summation and prevent an action potential in the post-synaptic neurone
53
Q

What is the excitatory post-synaptic potential (EPSP)?

A

the depolarisation that happens in the synaptic cleft when the relatively small number of acetylcholine molecule diffuse across the cleft.

Biology A-Level -James (18 decks)

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