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Biology A2 > 3.8 nervous system > Flashcards

3.8 nervous system Flashcards

1
Q

3 functions of a nervous system?

A

deflecting change or stimuli inside the body + the environment
process + stores information
initiates response

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2
Q

Stimulus?

A

detectable change in the internal or external environment of an organism that produces a response in the organism

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3
Q

Sensory receptors?

A

Senses
taste
smell
touch
eyesight
hearing

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4
Q

Specialised sensory cells?

A

pressure sensors in the skin

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5
Q

Sensory receptors?

A

transducers because they detect energy in one form and convert it to electrical energy

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6
Q

Electrical impulse?

A

travel along neurones and initiate a response in an effector ( muscle or gland)

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7
Q

Central nervous system?

A

brain and spinal cord
processes information from a stimulus
brain + spinal cord are surrounded by a tough protective membrane called meninges
white matter only contains nerve fibres surrounded by myelin
Grey matter has nerve fibrous of relay neurones but the colour is provided by cell bodies of motor neurones

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8
Q

Myelin?

A

fatty + tissue which is white in colour

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9
Q

Peripheral nervous system?

A

split into 2 parts
somatic nervous system
autonomic nervous system

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10
Q

Somatic nervous system?

A

pairs of nerves that originate from the brain or the spinal cord + branch outwards
nerves contain sensory neurones which carry impulses to the CNA
motor neurones carry impulses from the CNS to the effectors

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11
Q

Autonomic Nervous system?

A

provides unconscious control for the functioning of internal organs such as heartbeat or digestion

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12
Q

Structure of sensory neurone?

A

Dendrites
Schwann cell
Myelin sheath
Axon
Nodes of ranvier
Cell Body
Synaptic bulb
direction of impulse = towards cell body

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13
Q

Motor neurone?

A

Cell body
dendrites
schwann cell
nodes of ranvier ( no myelin sheath)
Schwann cell (nucleus)
axon
synaptic bulb

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14
Q

Spinal cord?

A

Sensory neurone
cell body in dorsal root ganglion
central canal
grey matter
dorsal root gangolion
dorsal root
spinal nerves
ventral root
motor neurone

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15
Q

Reflex arc?

A

stimulus ( hot objects)
Receptors
Sensory neurone
Relay neurone
Coordinators ( Brain/spinal cord)
Motor neurone
Effector - Muscle/gland
Response

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16
Q

What is a reflex arc?

A

rapid automatic response, resulting from a nerve impulse initiated by a stimulus
The decision making area of the brain is not involved
so action = involuntary
usually protective functions

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17
Q

Withdrawal reflex?

A

stimulus = heat
sensory receptor = located in dermis of skin
responds to pain + temp

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18
Q

Sensory neurone?

A

sends the impulse up the arm of the spinal cord
CNS relays the impulse from the sensory neurone to the motor neurone
the motor neurone sends the impulse to the effector which would be muscle in arm.

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19
Q

Response?

A

the arm muscle contracts, hand = removed from heat source

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20
Q

Pupil reflex?

A

stimulus = light
sensory receptor= photo sensitive cells in the retina
sensory neurone = the optic nerve
CNS= brain
motor neurone carries impulses to the muscle pf the iris
circular - contraction
dilation - radial

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21
Q

Response?

A

iris muscle contracts, altering diameter of pupil

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22
Q

Nerve nets?

A

Phylum ponfera (sponge)
has no nervous system
Phylum Chdaria ( jellyfish)
Radial symmetry
nerve net
( nervous system)
Phylum chordata
( humans)
Bilaterally symmetrical
CNS

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23
Q

Hydra(cnidaria)?

A

nerve net= diffuse network of cells
Grouped into ganglia
(swelling of nerves )
but no brain = formed

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24
Q

2 types of cells in a nerve net?

A

Ganglian - provides connections in all directions
Sensory cells - detect light, sound, touch, temp

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25
About Hydra?
studied as they have the simplest nervous system Can regenerate rapidly e.g if they lost a tentacle Hydra's nets are in its ectoderm ( outer layer of the 2 layers of the body wall. sensitive to light, physical contact + chemicals) In response, it can contract, perform locomotion, hunt and feed has no brain but has complex movements + behaviour
26
Comparison of Human + Hydra?
Hydra nerve net 2 cell types rapid regeneration no myelin sheath conduction speed = 5ms-1 Human CNS numerous cell types very slow regeneration myelin sheath on all axons conduct speed - 120 ms-1
27
Sensory neurone?
carries impulses from the sense receptors to the CNS
28
Motor neurone?
carries impulse from the CNS to the effectors ( muscles or glands )
29
Relay neurone?
receives impulses from sensory neurone and transmit to motor neurone
30
structure and function of neurone?
31
cell body - function - contains a nucleus + granular cytoplasm
function - contains a nucleus + granular cytoplasm
32
cytoplasm?
contains ribosome for protein synthesis
33
Granules?
made of ribosomes grouped on rough ER
34
Dendrite?
thin fibre carrying impulses towards a cell body
35
Axon?
thin fibre carrying impulses away from cell body
36
Schwann cell?
wrap around the axon, many times + withdraw their cytoplasm, leaving a multi layered phospholipid myelin sheath
37
Myelin sheath?
an electrical insulator which speeds up the transmission of an impulse
38
Nodes of ranvier?
1 nanometre in the myelin sheath where adjacent schwann cells meet and the membrane is exposed at these points, the membrane is exposed at these points, the impulse can leave the axon and jump to the next node - known as saltatory conduction
39
What does saltatory conduction do?
speeds up the rate of conduction
40
synaptic bulb?
a swelling at the end of an axon, where a neurotransmitter is synthesised
41
axon terminal?
secretes a neurotransmitter onto the synaptic cleft, so a nerve impulse can be transmitted to an adjacent neurone
42
Nerve impulse?
a neurone is an excitable cell which means it can change its resting potential ( potential difference)
43
Resting potential?
the potential difference across the membrane of the cell when no nerve impulse is being conducted
44
Potential difference across the membrane?
usually 70 mV membrane = more negative inside so resting potential = -70 mv as there is pd, membrane is described as polarised (difference in charge)
45
why is resting potential?
due to negative ions of large proteins or organic acids such as pyruvate in the cytoplasm
46
The process of K + and Na+
Inside of a cell has a high concentration of K+ ions but low concentration of Sodium ions than outside K+ ions tend to diffuse out and Na+ diffuse in Specific channels which allow K+ ions to diffuse out while the channels for Na+ ions are closed Makes the axon 100 x more permeable to k+ ions which diffuse out faster than sodium diffuses in Sodium Potassium pumps pump k+ ions back into the cell and Na+ ions back out
47
How is it moved along by active transport?
These transmembrane proteins are fuelled by ATP and the enzyme ATP synthetase which allows K+ and Na+ to be moved along the concentration gradient by active transport.
48
Action potential?
the rapid rise and fall of the electrical potential across a nerve cell membrane as a nerve impulse passes
49
Nerve impulse?
the transmission of a change in potential along a nerve fibre due to the movement of sodium ions At the site of an action potential, sodium ions diffuse into the axon because the Na+ channels are open K + ions diffuse out through the channels which remain open Na+ ions have faster than K+ ions, so there is a reversal of the potential difference between the inside and outside of the membrane. Known as depolarisation
50
What happens to the depolarisation?
opens, the voltage gated sodium channels, so even more Na+ ions flood in Na+ ions diffuse further down the axon, creating a wave of depolarisation Known as the absolute refractory period
51
What is the absolute refractory period?
period when no new action potential can be intiated and lasts 1 millisecond
52
Why is there an absolute refractory period?
it ensures the action potential = not propagated back in the direction from which it came and the nerve impulse will only travel in 1 direction
53
What is hyper polarisation?
fora period of 5-10 milliseconds, if the impulse is strong enough, a new action potential may be generated Known as the absolute refractory period + occurs when the sodium and potassium pumps try to restore the resting potential
54
What is repolarization?
Restoring the original charge to the membrane, positive on the outside and negative on the inside The potassium channels open + K+ ions diffuse out down a concentration gradient The cell becomes + inside asm more ions diffuse out, known as repolarization The Na+ and K+ pump, pump K+ ions back in and Na+ back out, restoring resting potential
55
Depolarization?
the temporary reversal of the potential across the membrane of a neurone such that the inside becomes less negative than the outside as an action potential is transmitted
56
Action refractory potential?
period at which no new action potential can be intiated
57
When an action potential is generated?
Na+ ions diffuse into the axon This created localised circuits as Na+ move laterally along the axon The Na+ ions depolarise the adjacent section of the membrane the voltage gated sodium channels open and Na+ flood in, depolarising the axon This creates a self perpetuating ( goes on) wave of depolarisation along the axon At the site of the initial action potential, Na+ channels cannot open until a resting potential = established known as the absolute refractory period, lasting 1 millisecond
58
What's the purpose?
to ensure that the wave is not propagated in the wrong direction for the next 5-10 milliseconds, Hyper polarisation occurs + if it the impulse, strong enough, it will pass and is known as the relative refractory period
59
when does the relative refractory period occur?
when the K+ and Na+ pumps restoring the potential
60
The all or nothing law?
a nerve impulse is either initiated or not + is always the same size
61
Purpose of the all or nothing law?
allows the action potential to act as a filter to prevent the brain being overloaded with information
62
Graph of a very weak stimulus?
flat
63
Graph of a weak stimulus?
up then down
64
Graph of a strong stimulus?
3 x up then down
65
Very strong stimulus?
5 x up then down
66
As stimulus increases?
frequency also increases all action have a max pd of + 40 mv
67
Factors affecting speed of conduction?
Temperature The diameter of the axon Myelination
68
Temperature?
the ions move faster at higher temp, so have more kinetic energy, so birds + mammals are warm blooded, so transmit nerve impulses faster
69
Diameter of the axon?
the wider the diameter, the greater the volume, so more Na+ ions flow through so impulse is faster Humans have none myelinated axons of 0.2 - 1.5 nanometres this allows slow transmission of an impulse. Marine invertebrates live in water close to 0 degrees such as squids, which have giant axons of 1 mm Earthworms have evolved giant axons up to 700 nanometres for rapid response
70
Myelination?
speeds up the rate of transmission of the impulse as there is faps in the myelin called nodes of ranvier
71
Nodes of ranvier?
at the nodes, na+ can enter, creating a change in voltage which allow the action potential to jump between the nodes , known as saltatory conduction, making transmission more rapid. nodes of ranvier = 1 mm apart myelinated nerve fibres have a transmission rate of 120m/s. whereas non myelinated = 0.5m/s
72
Neurotransmitter?
a chemical secreted in response to an action potential which carries a chemical signal across a synapse from 1 neurone to the next, allowing an action potential to be initiated
73
What are neurones separated by?
a synapse which allows nerve impulses to pass in only 1 direction
74
2 types of synapse?
electrical synapse chemical synapse
75
electrical synapse?
3 nanometre junction which is small enough for an electrical impulse to jump from 1 neurone to the next
76
chemical synapse?
20 nanometre junction which is too large for the nerve impulse to jump, so neurotransmitter is secreted and diffuses across the synaptic cleft from the presynaptic membrane to the presynaptic membrane
77
Diagram?
Mitochondria Post synaptic membrane Receptor sites Myelin sheath Axon Vesicles containing neurotransmitter Receptor sites Postsynaptic membrane Synaptic cleft Action potential ( nerve impulse) moves to the right
78
Process?
arrival of an impulse at a synaptic bulb alters the membrane permeability The voltage gated calcium channels open and ca2+ ions diffuse into the bulb. ( down a concentration gradient) The Ca2+ ions cause the vesicles to fuse with a presynaptic membrane The vesicles release the neurotransmitter acetylcholine into the cleft by exocytosis Acetylcholine attaches to the intrinsic proteins / receptor cyles on the postsynaptic membrane The receptor proteins change shape, opening Na+ channels in the post synaptic membrane Na+ ions flood to the post synaptic membrane, causing depolarisation when the depolarisation is strong enough, the action potential can be transmitted between the neurones
79
Removing acetylcholine from the cleft?
Active transport of Ca2+ ions out of the bulb prevents exocytosis of Acetylcholine AcetylCholine is hydrolysed by the enzyme acetyl cholinesterase The products of hydrolysis = choline + ethanoic acid These diffuse back into the presynaptic neurone + reform acetylcholine using acetyl coenzyme A this is an energy requiring process, so requires mitochondria
80
Properties of a synapse?
Transmit information between neurones Pass impulses in 1 direction act as a junction Protect the nervous system from over stimulation They filter out low level stimuli and an action potential - only generated when the depolarisation reaches a threshold value of -55 milivolts
81
Temporal summation?
depolarisation which builds up over to reach a threshold at which an action potential is generated
82
Spatial summation?
several presynaptic neurones contribute to the depolarization which generate an action potential
83
Drug?
a molecule that has physiological effects on the body when ingested, inhaled, absorbed or infection
84
What do drugs act as?
synapses and disrupt the functioning of neurotransmitters
85
4 Main Neurotransmitters?
Acetyl Choline ABA Monomaines ( dopamine + serotonin) Neuropeptide (endorphins)
86
Sedatives?
creates a fewer action potentials in the postsynaptic neurone
87
Stimulant?
allows more action potentials to reach the postsynaptic neurone e.g amphetamines
88
Drug action?
drugs mimic the action of neurotransmitters have the same shape + bind to post synaptic neurone, increasing frequency of action potentials
89
Nicotine?
increases the frequency of impulses but unlike acetylcholine, it is not hydrolysed, so continues to initiate impulses body becomes habituated by nicotine and will only function its presence to achieve desired effects, more nicotine must be taken in
90
If excess nicotine is taken in?
person experiences withdrawal
91
Organo phosphates?
found in insecticides, herbicides, nerve gas These drugs prevent the breakdown of neurotransmitters by cohibiting the enzyme Acetylcholinesterase AcetylCholine is not hydrolysed and remains in the cleft this causes repeated firing of the action potential This can be inhaled, absorbed or ingested, causing long term health problems nerve gas inhibits acetylcholinesterase, causing uncontrollable muscle contractions which are strong enough to break bones
92
Psychoactive drugs?
act on the CNA to outer brain function Alters perception, mood, consciousness + your behaviour Therapeutic drugs such as Ritalin ( ADHD) Prozac(depression)and Paxil (anxiety) recreational drugs (nicotine, alcohol, cannabis,cocaine, heroin, amphetamine, ecstasy)
93
what does these cause?
these cause euphoria and increased alertdnes
94
Negatives?
dependency and impaired health

Biology A2 (9 decks)

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