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Biology > Chapter 13 - Neuronal Communications > Flashcards

Chapter 13 - Neuronal Communications Flashcards

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1
Q

What are sensory receptors?

A

Specialised cells that can detect changes in our surroundings
- energy transducer that convert one form of energy to another

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2
Q

What sensory receptors detect change in light intensity?

A
  • Light sensitive cells (rods and cones) in the retina
    (light -> electrical)
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3
Q

What sensory receptors detect change in temperature?

A
  • Temperature receptors in the skin and hypothalamus
    (heat -> electrical)
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4
Q

What sensory receptors detect change in pressure on the skin?

A
  • Pacinian corpuscles in the skin
    (movement -> electrical)
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5
Q

What sensory receptors detect change in sound?

A
  • Vibration receptors in the cochlea of the ear
    (movement -> electrical)
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6
Q

What sensory receptors detect change in movement?

A
  • Hair cells in inner ear
    (movement -> electrical)
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7
Q

What sensory receptors detect change in length of muscle?

A
  • Muscle spindles of skeletal muscles
    (movement -> electrical)
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8
Q

What sensory receptors detect change in chemicals in the air?

A
  • Olfactory cells in epithelium lining the nose
    (receptors detect the presence of a chemical and create an electrical nerve impulse)
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9
Q

What sensory receptors detect chemicals in food?

A
  • Chemical receptors in taste buds on tongue
    (receptors detect the presence of a chemical and create an electrical nerve impulse)
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10
Q

What is a Pacinian corpuscle?

A
  • pressure sensor that detects change in pressure on the skin
    corpuscle = oval-shaped structure that consists of a series of concentric rings of connective tissue wrapped around the end of a nerve cell.
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11
Q

What is the corpuscle sensitive to ?

A
  • ONLY to changes in pressure that deform the rings of connective tissues.
    when pressure is constant, they stop responding
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12
Q

Membrane stuff

A
  • if channel proteins are permanently open the ions can diffuse across the membrane and will keep going till conc on both side of the membrane are equal
  • if the channels can be closed, the action of the active pumps can create a conc gradient across the membrane
  • sodium channels + potassium channels possess a gate that can open or close the channel
  • sodium channels are sensitive to small movements of the membrane, so when the membrane is deformed by changing pressure, sodium channels open
  • allows Na+ to diffuse into the cell, producing a generator potential
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13
Q

What do the membranes contain? (generating nerve impulse)

A
  • sodium/ potassium pumps actively pump sodium ions out of the cell and potassium ions into the cell
  • 3 Na+ out for every 2 K+ in
  • channel proteins closed = sodium pumps work to create a conc gradient
  • conc of Na+ outside the cell increases, more than conc of K+ inside the cell
  • movement of ions via the sodium-potassium pumps establishes an electrochemical gradient
    -membrane is more permeable to K+ ions and less to Na+ ions
  • negatively charged on inside of axon
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14
Q

What is the cell membrane when the cell is inactive?

A
  • polarised
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15
Q

How is a nerve impulse created?

A
  • altering the permeability of the nerve cell membrane to sodium ions by opening sodium ion channels
  • as Na+ channels open, membrane permeability increases and Na+ can move across the membrane
    down conc gradient into the cell
  • creates a change in potential difference across the membrane
  • inside of the cell becomes LESS NEGATIVE = depolarisation
  • if a small stimulus is detected, only a few sodium channels will open
  • the larger the stimulus, the more gated channels will open
  • if enough Na+ enter the cell and enough gates are opened, potential difference across the cell membrane changes significantly + will initiate an action potential/ impulse
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16
Q

What are the 3 different types of neurones?

A
  • motor neurones
  • sensory neurones
  • relay neurones
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17
Q

Motor neurones

A
  • carry an action potential from the central nervous system (CNS) to an effector such as a muscle or a gland
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18
Q

Sensory neurones

A
  • carry the action potential from a sensory receptor to the CNS
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19
Q

Relay neurones

A
  • connect sensory and motor neurones
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20
Q

What features do neurones have? (8)

A
  • long so they can transmit the action potential over a long distance
  • cell surface membrane has many gated ion channels that control the entry/exit of Na, K and Ca
  • Na/K pumps uses ATP to actively transport 3 Na+ out the cell and 2 K+ into the cell
  • maintain a potential difference across their cell surface membrane
  • cell body contains the nucleus, mitochondria, ribosomes
  • dendrites connect to other neurones: carry impulses towards the cell body
  • axon carries impulses away from the cell body
  • surrounded by a fatty layer that insulates the cell from electrical activity (composed of Schwann cells associated with the neurone)
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21
Q

What are the differences between types of neurone?

A
  • motor neurones have their cell body in the CNS + have a long axon that carries the action potential out to the effector
  • sensory neurones have a long dendron carrying the action potential from a sensory receptor to the cell body, which is just outside the CNS
    (short axon carrying the action potential into the CNS)
  • relay neurones connect the sensory + motor neurones together
    (many short dendrites + short axon)
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22
Q

What are myelinated neurones?

A
  • insulated by an individual myelin sheath (is formed by specialised cells known as Schwann cells which wrap themselves around the axon)
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23
Q

What make up the myelin sheath?

A
  • Schwann cells
24
Q

What are the gaps in the myelin sheath called?

A
  • nodes of Ranvier (each node is very short)
25
Q

What does the myelin sheath do?

A
  • it prevents the movement of ions across the neurone membranes, so it can only occur at the nodes of Ranvier
26
Q

What are non-myelinated neurones?

A
  • has no individual layer of myelin - so impulse travels more slowly as it moves through the entire length of the axon
27
Q

How does action potential move in myelinated neurones?

A
  • action potential jumps from node to node
28
Q

How does action potential move in non-myelinated neurones?

A
  • action potential moves along the neurone in a wave
29
Q

What are the advantages of myelination?

A
  • transmit an action potential much quicker than non-myelinated neurones
  • myelinated neurones carry action potentials from sensory receptors to the CNS and from the CNS to effectors
  • carry action potentials over long distances - increased speed of transmission= action potential reaches the end of the neurone much more quickly
30
Q

What is it called when a neurone is not transmitting?

A
  • action potential is said to be at rest
31
Q

What is action potential doing while it is at rest?

A
  • it is actively pumping ions across its cell surface membrane
32
Q

How can an action potential be generated?

A
  • when neurone is at rest, it maintains a conc gradient of Na+ across its plasma membrane
  • Na+ channels open = Na+ will diffuse down conc gradient into cell from tissue fluid -> causes depolarisation of the membrane
  • in the generator region, the gated channels are opened by the action of the synapse
33
Q

What is a generator potential?

A
  • gated channels open + allow Na+ into the cell and produce a small depolarisation
34
Q

What is a voltage-gated channels?

A
  • Na+ channels in a neurone are opened by changes in the potential difference across the membrane
35
Q

What are the stages of an action potential?

A
  • Membrane starts in its resting state - polarised with the inside being 60mV compared to the outside
    ⇡ conc of Na+ outside than inside
    ⇡ conc of K+ inside than outside
    -Na+ channels open and some Na+ diffuse into the cell
  • Membrane depolarises- becomes less -ve and reaches the threshold value of -50mV
  • positive feedback causes nearby voltage-gated Na+ channels to open and many Na+ flood in -> as more Na+ enter, cell becomes +vely charged inside compared with outside
  • A potential difference across the plasma membrane reaches +40mV : inside of the cell is +ve compared with outside
  • Na+ channels close and K channels open
  • K+ diffuse out the cell bringing the potential difference back to -ve inside compared with outside (repolarisation)
36
Q

What is the refractory period?

A
  • For a short time after each action potential it is impossible to stimulate the cell membrane to reach another action potential
  • allows the cell to recover after an action potential
  • ensures action potentials are transmitted in only 1 direction
  • limits number of impulse transmission which prevents over reaction to stimulus
36
Q

What are the steps in the formation of local currents + transmission of a nerve impulse?

A
  • When an action potential occurs, the Na+ channels open at that point in the neurone
  • open Na+ channels allow Na+ to diffuse across the membrane from the region of ⇡ conc. outside the neurone into the neurone
    -conc. of Na+ inside rises at the point where the Na+ channels are open
  • Na+ continue to diffuse sideways along the neurone, away from the region of ⇡ conc
  • local current causes a slight depolarisation further along the neurone which affects the voltage-gated Na+ channels, causing them to open
  • the open channels allow rapid influx of Na+ causing a full depolarisation further along the neurone
  • action potential has moved along the neurone
37
Q

What is a local current?

A

-the movement of charged particles:

38
Q

What is saltatory conduction?

A
  • when action potential appears to jump from one node to the next
39
Q

What does a higher frequency of action potentials mean?

A
  • a more intense stimulus -> more Na channels are opened in the sensory receptor -> produces more generator potentials -> more frequent action potentials in the sensory neurone -> more frequent action potentials enters the CNS
40
Q

What is a synapse?

A
  • a junction between 2+ neurones, where 1 neurone can communicate with, or signal to, another neurone
41
Q

What does the action potential in the pre-synaptic neurone cause?

A
  • release of a neurotransmitter that diffuses across the synaptic cleft + generates a new action potential in the post- synaptic neurone
42
Q

What are cholinergic synpases?

A
  • synapses that use acetylcholine as the neurotransmitter
43
Q

What are 4 specialised features of a pre-synaptic bulb?

A
  • many mitochondria
  • large amount of SER, which packages the neurotransmitter into vesicles
  • large number of vesicles cont. molecules of acetylcholine
  • a number of voltage-gated ca+ channels on the cell surface membrane
44
Q

What is acetylcholine?

A
  • molecules of a chemical -> transmitter that will diffuse across the synpatic cleft
45
Q

What does post-synaptic membrane contain?

A
  • specialised Na+ channels that can respond to the neurotransmitter
  • channels consist of 5 polypeptide molecules
  • 2 have a special receptor site that is specific to acetylcholine + shape that is complementary to shape of acetylcholine molecule
  • when acetylcholine is present in the synaptic cleft it binds to the 2 receptor sites + causes Na+ channel to open
46
Q

How does transmission occur across the synaptic cleft (synapse)?

A
  • action potential arrives at the synaptic bulb
  • voltage-gated Ca+ channels open
  • Ca+ diffuse into the synaptic bulb
  • Ca+ cause the synaptic vesicles to move to + fuse with the pre-synaptic membrane
  • acetylcholine is released by exocytosis
  • acetylcholine molecules diffuse across the cleft
  • acetylcholine molecules bind to the receptor sites on the Na+ channels in the post-synaptic membrane
  • Na+ channels open
  • Na+ diffuse across the post-synaptic membrane into the post-synaptic neurone
  • generator potential is created
  • if sufficient generator potentials combine = potential across the post- synaptic membrane reaches the threshold potential
  • new action potential is created in the post-synaptic neurone
47
Q

What are the final steps to transmission occurring across the synapse?

A
  • Na+ channels open
  • Na+ diffuse across the post-synaptic membrane into the post-synaptic neurone
  • generator potential is created
  • if sufficient generator potentials combine = potential across the post- synaptic membrane reaches the threshold potential
  • new action potential is created in the post-synaptic neurone
48
Q

What is acetylcholinesterase?

A
  • it is an enzyme found in the synaptic cleft
  • hydrolyses the acetylcholine to ethanoic acid (acetic acid) and choline
  • stops the transmission of signals -> synapse doesn’t continue to produce action potentials in the post-synaptic neurone
49
Q

What happens to the ethanoic acid and choline?

A
  • recycled
  • re-enter the synaptic bulb by diffusion and recombined to acetylcholine using ATP from respiration in the mitochondria
  • recycled acetylcholine is stored in synaptic vesicles for future use
50
Q

What is the main role of syanpses?

A
  • connect 2 neurones together so a signal can be passed from 1 to the other
51
Q

What is an excitatory post-synaptic potential?

A
  • acetylcholine molecules diffuses across the cleft produces a small depolarisation
52
Q

What is summation?

A
  • occurs when effects of several EPSPs are added together
53
Q

What is a temporal summation?

A
  • result from several action potentials in the same pre-synaptic neurone
54
Q

What is a spatial summation?

A
  • result from action potentials arriving from several different pre-synaptic neurones
55
Q

What is inhibitory post-synaptic potentials (IPSPs)?

A
  • reduce effect of summation + prevent an action potential in the post- synaptic neurone
56
Q

Control of communication

A
  • combo of several EPSP’s could be prevented from producing an action potential by 1 IPSP
  • 1 pre-synaptic neurone might diverge to several post-synaptic neurones -> allows 1 action potential to be transmitted to several parts of the nervous system - useful in a reflex arc -> 1 post-synaptic neurone elicits the response, while another informs the brain
  • synapses ensure that action potentials are transmitted in the correct direction - only the pre-synaptic bulb cont. vesicles of acetylcholine

Biology (25 decks)

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