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BiologyF2144 > Nervous System > Flashcards

Nervous System Flashcards

1
Q

What is the role of a sensory receptor?

A

Specialised calls that detect changes in surroundings, energy transducers, change in energy level on environment is stimulus, convert this into sl from of electrical energy - nerve impulse

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2
Q

What are some common sensory receptors?

A 
In eyes for light intensity and colour
Olfactory cells for volatiles 
Taste buds for soluble chemicals
Pressure receptors 
Sound receptors 
Muscle receptors for length of muscle fibres
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3
Q

Why does permeability of membrane change during a nerve impulse?

A

Protein channels allow movement of ions across the membrane, neurones have gated channels that allow permeability of membrane to differ t ions to be altered. Nerve impulse generated by altering permeability if cell membrane to sodium ions.

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4
Q

What is the role of carrier proteins in nervous membranes?

A

Actively transport sodium ions out if the cell, and potassium ions into the cell, Na/K+ pumps. 3 Na out for every 2K in, inside of cell is negatively charged with respect to the outside

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5
Q

What is a polarised membrane?

A

One that had a potential difference across it, this is the resting potential

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6
Q

How is a nerve impulse generated?

A

Created by altering permeability of nerve cell membrane to sodium ions. Permeability increases and sodium ions can move across membrane down gradient into cell, created change in potential difference across the membrane, depolarisation

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7
Q

What is depolarisation?

A

The loss of polarisation across a membrane, refers to period when sodium ions are entering the cell and making it less negative with respect to the outside

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8
Q

What is a generator potential?

A

A small depolarisation caused by sodium ions entering the cell. Receptor cells respond to change and sodium gated channels open, allowing sodium to diffuse across membrane into the cell, small change in potential by opening of one or two sodium ion channels

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9
Q

What is an action potential?

A

Achieved when the membrane is depolarised to a value of about +40mV. All or nothing response, in events leading up to action potential m, membrane depolarises and reaches threshold level, lots of sodium ions enter axon and action potential is reached

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10
Q

What are the different types of neurones?

A

Sensory neurones that can carry an action potential from sensory receptor to CNS
Motor neurones that carry action potential from CNS to effector
Relay neurones that connect sensory and motor neurones

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11
Q

What is the function of a neurone?

A

To transmit action potential for one part of the body to another

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12
Q

What are general features of a neurone?

A

Long so can transmit over long distance
Plasma membrane has many hated ion channels
Sodium/potassium pumps
Maintain potential difference across the membrane
May be surrounded by myelin sheath, that insulates neurone
Cell body that contains nucleus, mitochondria and ribosomes
Numerous dendrites connected to other neurones

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13
Q

What are the differences between sensory and motor neurones?

A

Motor burned have cell body in CNS, sensory have cell body just outside of CNS.
Motor neurones have long axon, carry action potential to effector
Sensory buries have long sense on to carry action potential to cell body. Short axon to carry action potential into CNS

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14
Q

Why do neurones need to possesses large number of mitochondria?

A

Mitochondria produce ATP by respiration, needed to maintain resting potential and for exocytosis of neurotransmitter at synapses

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15
Q

Why do membranes need special channels for diffusion of ions?

A

Charged ions cannot diffuse across phospholipid bilayer, so can it diffuse directly across membrane, need protein channel to produce hydrophilic channel for facilitated diffusion

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16
Q

What is resting potential?

A

Potential difference or voltage across the neurone cell membrane while neurone is at rest, about -60mV inside cell compared with outside. Mains atoned by sodium potassium pumps, membrane also more permeable to potassium ions diffuse out again

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17
Q

How is action potential generated?

A

Gates sodium channels closed at rest, actively transported out, if sodium channels opened, quickly dissolves across down concentration gradient, depolarisation of membrane. In generator potential gates opened by energy changes in the environment, cause hates further along neurones to open by change in voltage, voltage gated channels

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18
Q

What is a voltage gated channel?

A

Channels in the cell membrane that allow the passage of charged particles or ions. Gate mechanism that opens and closes in response to changes in voltage

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19
Q

What is a threshold potential?

A

A potential difference of about -50mV. If depolarisation doesn’t reach these old than no action potential is generated, if depolarisation does reach it, then an action potential is generated

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20
Q

What is an all or nothing response?

A

If depolarisation is large enough, it will open nearby voltage gated channels, causes large influx of sodium ions and depolarisation reaches +40mV which is an action potential, self perpetuating, will continue along to end of the neurone

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21
Q

What are the stages of an action potential?

A

Membrane polarised, -60mV
Sodium ion channels open, some sodium ions diffuse into the cell
Membrane depolarises, reaches threshold, -50mV
Voltage gated open, cell becomes positively charge w respect to outside +40mV
Sodium ion channels close, potassium open
Potassium ions diffuse out if cell, repolarisation
Original difference overshoots, hyperpolarised
Potential difference restored to resting state
Sodium potassium pump works to restore concentrations of ions in cell

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22
Q

What is the refractory period?

A

For short time after each action potential another one cannot be stimulated, allows cell to recover and ensures action potential only transmitted in one direction

23
Q

What is role of organic anions inside the neurones?

A

Help to ensure that outside of the cell remains negative compared to the outside

24
Q

What is the difference between gated channels in generator region and those further along the neurone?

A

Generator have dates operated by energy from the stimulus, in rest of neurone, gates opened by movement of ions in local circuit or by depolarisation

25
Q

Why can neurone not be stimulated when hyperpolarised?

A

Greater potential difference exists, so more difficult to depolarise, so threshold is not reached, sodium ions that caused action potential would still be in cell, so reduced influx of sodium ions. Potassium gates still open, so potassium going out

26
Q

What are local currents?

A

Movement of ions along the neurone, flow of ions caused by increase in concentration at one point, which causes diffusion away from the region of higher concentration where channels are open, diffuse sideways away from region of increases concentration

27
Q

How do voltage gated ion channels cause transmission of action potential?

A

Opened by changes in voltage, as ions diffuse down axon cause more voltage gated channels to open further down

28
Q

What sort of feedback is operating in transmission if action potential?

A

Positive feedback

29
Q

What is the myelin sheath?

A

Insulating layer of fatty material, ions cannot diffuse through this layer

30
Q

How does the presence of the myelin sheath affect transmission of action potentials?

A

Ions for action potential cannot diffuse through layer so not possible along much of the neurone, only at gaps between the Schwann cells - nodes of ranvier. Action potentials only occur here, so local currents are elongated, sodium diffuses along neurone from one node to another, saltatory conduction

31
Q

What is saltatory conduction?

A

Jumping conduction,refers to the way action potential appears to jump from one node of Ranvier to the next

32
Q

What are the advantages of saltatory conduction?

A

Action potential can only occur at intervals along neurone, speeds up transmission, much faster than non myelinated

33
Q

How is diffusion gradient created in the neurone?

A

Gradient created by sodium potassium pump, sodium actively transported out, so conc low inside,

34
Q

What is a synapse?

A

A junction between two or more neurones. Where one can communicate with another. Ends in synapse at it increases surface area for more vesicles containing acetylcholine to fuse. Allows it to stimulate more than one postsynaptic neurone

35
Q

What is the synaptic cleft?

A

Gap between two neurones,

36
Q

What is the role of synaptic cleft?

A

Action potential Connor bridge gap between neurones so presynaptic releases a chemical that diffuses across gap and generates new action potential in the postsynaptic neurone.

37
Q

What is a cholinergic synapse?

A

Those that use acetylcholine as their transmitter substance

38
Q

What is a neurotransmitter?

A

A chemical that diffuses across the cleft of the synapse to transmit a signal to the postsynaptic neurone

39
Q

What is the presynaptic knob?

A

End of presynaptic neurone, specialised ratites such as many mitochondria for active processes, large amount of SER
vesicles containing acetylcholine transmitter substance
Voltage gated calcium ion channels

40
Q

How are sodium ion channels in postsynaptic membrane specialised?

A

Channels that respond to transmitter substance, made from 5 polypeptides, two of these have special receptor site that is specific to acetylcholine, receptors have complimentary shape to acetylcholine so it will fit and bind to site, when it binds it causes sodium ion channels to open

41
Q

What’s are the stages of transmission across the synapse?

A

Action potential array synaptic knob
Voltage gated calcium ion channels open
Calcium ions diffuse in
Calcium causes synaptic vesicles to move and fuse with presynaptic membrane
Acetylcholine released by exocytosis, diffuses across cleft
Acetylcholine molecule bind to receptors on postsynaptic
Sodium channels open
Sodium diffuses across into postsynaptic neurone
Generator potential created EPSP
If sufficient combine then potential across postsynaptic reaches threshold
New action potential is generated

42
Q

What is acetycholinesterase?

A

Enzyme in synaptic cleft that breakdown acetylcholine neurotransmitter. Hydrolysis to ethanoic acid and choline, recycled as renter presynaptic knob by diffusion and recombined using ATP, stored in vesicles for future use. Presence means acetylcholine us removed so doesn’t continue to stimulate postsynaptic neurone and create action potentials

43
Q

What is the role of SER in synaptic knob?

A

Associated with the metabolism of the neurotransmitter and packaging it into vesicles

44
Q

What is the role if mitochondria in the presynaptic knob?

A

Supply ATP needed to recycle acetylcholine, make the vesicles and move them to presynaptic membrane

45
Q

Why are calcium channels voltage gated?

A

Action potential in pre causes on in post, achieved by releasing neurotransmitter. Released by action of calcium ions, that enter synaptic knob through channels. Channels voltage gate so respond to depolarisation caused by original action potential. If responded to any other stimulus would release neurotransmitter at wrong time.

46
Q

What is the all or nothing response?

A

Refers to the fact that a neurone either conducts an action potential or it doe not, all are of the save magnitude, +40mV

47
Q

What are the roles of synapses?

A

Connect two neurones together
Convergence of several presynaptic neurones, signals fro different parts create same response
Presynaptic divergence, so signal can be transmitter to different parts of the nervous system
Ensures transmission in only one direction, only pre has vesicles of acetylcholine
Filter out low level signals- one action potential arrival doesn’t produce one in post, need series of action potentials in presynaptic
Summation, low level signals amplified, if persistent over short period of time
Acclimatisation repeated stimulation, may run out of vesicles, I get used to it, may help avoid overstimulation
Creation of specific pathways

48
Q

Role of synapses (short version)

A 
Memory pathways 
Summation
Filter out low level signals
Convergence 
Divergence
Only one direction 
Acclimatisation 
Connect neurones
49
Q

How does the brain determine the intensity of the stimulus?

A

Higher intensity stimulus will produce more generator potentials, causing more frequent action potentials, more vesicles released, which means higher frequency of action potentials in the postsynaptic, brain can determine intensity of stimulus from the frequency of signals arriving

50
Q

What is a myelinated neurone?

A

Neurone insulated by an individual myelin sheath, created by series of separate Schwann cells, wrapped around the neurone so consists of several layers of membrane and thin cytoplasm. Gaps along neurone at nodes of ranvier

51
Q

What is the advantage of a myelinated neurone?

A

Can transmit action potential much more faster than non myelinated, non myelinated ions diffuse in all along the murine not via saltatory conduction, carry signals from sensory receptors to CNS and from CNS to effectors over long distances, rapid response. Non myelinated are shorter

52
Q

Why are non myelinated neurones used for?

A

Coordinating body functions such as breathing and action if the digestive system so increased speed of transmission is not important

53
Q

What is the demyelination?

A

Loss of myelin from neurones that are normally myelinated, cause of degenerative diseases due to loss of myelination if certain neurones, involved with movement is ms, auto immune disorder, immune system attaches myelin sheath

54
Q

Speed of transmission?

A

Myelinated is fast, 100-120

Unmyelinated is slower 0.5-10

BiologyF2144 (11 decks)

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