4.7: Nervous system Flashcards
0
Q
Define a stimulus.
A
A change in an organisms internal or external environment.
1
Q
What is a sense organ?
A
A aggregation of receptor cells that respond to specific stimuli.
2
Q
What is the stimulus-response control system?
A
This is the process by which an organism responds to a stimulus Stimulus → receptor/detector → coordinator → effector → response.
3
Q
What is the purpose of senses?
A
To increase your chances of survival.
4
Q
What is the function of the nervous system?
A
To detect and process information and initiate responses to stimuli.
5
Q
What is the function of sensory cells and sense organs?
A
They detect information (stimuli) and relay it to the effectors. They act as transducers - they convert from one form of energy (light, sound, pH, chemicals, pressure, temprature) into electrical energy.
6
Q
What happens to electrochemical energy which has been transduced by a receptor?
A
The electrochemical energy is sent from the sensory receptors via the peripheral nervous system (PNS) to the central nervous system (CNS).
7
Q
What is the PNS (peripheral nervous system)?
A
This is the individual neurones and ganglia that connect the receptors and effectors to the CNS.
8
Q
What is the CNS (central nervous system?)
A
The spinal chord and brain.
9
Q
What happens once the brain receives the information from the receptors?
A
It processes the information and initiates an appropriate response by communicating with the effectors.
10
Q
What are effectors?
A
These are the things that bring about a response - muscles and glands.
11
Q
What is a reflex reaction?
A
A rapid, involuntary response resulting from nervous impulses initiated by a stimulus: It is involuntary because conscious control by the brain is not involved. They are generally protective in nature because they are quick.
12
Q
What is a reflex arc?
A
The pathway of the nerve impulses along different neurones during a reflex reaction.
13
Q
Outline the reflex arc.
A
1.) a receptor detects a stimulus 2.) this sends a nerve impulse via sensory neurone to a relay neurone in the spinal cord. 3.) this sends an impulse straight back to muscles via a motor neurone. 4.) this initiates a response (muscles/glands) without going through the brain.
14
Q
Do reflex reactions bypass the brain completely?
A
No. A nervous impulse still gets sent to the brain via the spinal chord but the response happens on an independent loop - not waiting for the response from the brain to happen.
15
Q
Give a breakdown of the process of the reflex arc.
A
Stimulus → receptor → Sensory neurone → intermediate/relay neurone → motor neurone → effector → response
16
Q
Label this diagram.
A
17
Q
Complete this diagram to show a reflex arc.
A
18
Q
Give some examples of reflex reactions.
A
Flexion of the arm in response to touching a hot surface
Flexion of the leg in response to standing on an upturned plug
Knee-jerk reaction
Pupil contraction on bright light
Babinski reaction of the foot and toes.
19
Q
Why are actions such as blinking, coughing and swallowing co-ordinated by reflexes?
A
To make sure you don;’t get uncoordinated and stop halfway through the action.
20
Q
What other complications can be involved in a reflex arc?
A
Even in a simple reflex arc the brain may overcome and modify the response - it may relate the information recieved with information from other sensory input such as visual input from the eyes. e.g dropping a hot metal tray quickly whilst dropping a equally hot glass dish more gently.
21
Q
What is the function of inhibitory synapses?
A
These allow your brain to make conscious decisions about reflex reactions. The brain may transmit nerve impulses down the spinal cord via neurones that terminate in inhibitory synapses which, for example, may prevent you from dropping a hot glass dish immediately.
22
Q
in a reflex reaction what is the purpouse of also sending a neuronal signal to the brain via relay neurones.
A
This information can be used to allow you to make concious decisions about a reflex action and can be used for learning.
23
Q
What are the ascending and descending nerve fibers in the spinal cord used for?
A
They are used to transmit neuronal impulses in both reflex and voulantary actions.
24
What are the three types on neurones?
Sensory Neurones
Motor Neurones
Connectore/intermediate/relay neurones.
25
What is the function of sensory neurones
These bring impulses from the sense organs/receptors in to the CNS
26
What is the function of Motor neurones?
these carry impulses from the CNS to the effector organs (muscles or glands)
27
What is the function of relay neurones?
These recieve impulses from sensory neurones or other relay neurones and relay them to motor neurones (or other relay neurones)
28
What is contained within the cell body of a neurone?
Nucleus, granular cytoplasm and lots of ribosomes.
29
What do ribosomes in the cell body of a neurone from?
They group together to form Nissl granules.
30
What is the function of the ribosomes within the cell body of a neurone?
To synthesise neurotransmitters.
31
What are dendrites?
Thin extentions from the cell body of a neurone that connect to other cells. Dendrites recieve impulses from other neurones and carry them towards the cell body.
32
What are axon terminals?
At its end the axon divides into branches called axon terminals which connect to other neurones.
33
What is an axon?
A long membrane-covered extention from the cell body of a neurone. Axons transmit impulses away from the cell body. Peripheral neurones have a myelin sheath around the axon made up of schwann cells wrapped around the axon. During myelination the membrane of the schwann cells extends and wraps around the axon. The membranes of the schwann cells are rich in a lipid called myelin.
34
What is the function of the Myelin sheath?
The fatty myelin sheath acts as an electrical insulator around the neurones and speeds up impulse transmission. The schwann cells also support and protect the neurones and provide them with nutrients.
35
In what kind of organisms are these multi-layered myelin sheaths found?
They are only found in vertebrates.
36
Label this neurone.
37
What is the function of the nodes of Ranvier?
The nodes of Ranvier speed up impulse transmission.
38
39
What are neurones?
Highly specialised cells that link together to form pathways and generate and transmit nerve impulses.
40
What is a nerve?
A bundle of neurones surrounded by a protective sheath of fibrous tissue.
41
Label the parts of the spine.
42
Label the regions of the spinal cord. (ignore black arrows)
43
What is grey matter?
The grey matter resides in the central area of the spine and contains all the cell bodies and relay neurones.
44
What is white matter?
This is found around the outside of the spinal cord and consists of the myelinated axons that run up and down the spinal cord, to and from the brain. It appears white because of the presence of myelin.
45
Where do the sensory neurones enter the spinal cord?
Through the dorsal root.
46
Where are the cell bodies of the sensory neurones found?
The dorsal root ganglion.
47
Where do motor neurones exit the spinal cord?
Through the ventral root of the spiunal cord.
48
Define ventral.
on or relating to the underside of an animal or plant; abdominal
49
Define Dorsal.
on or relating to the upper side or back of an animal, plant, or organ.
50
Where are the cell bodies of the motor neurones found?
The grey matter of the spinal cord.
51
What do neurones transmit?
Electrochemical impulses.
52
What is an electrochemical impulse?
A signal which is electrical in nature but created by the movment of ions not electrons.
53
What do neurones create across their membranes?
They set up an electrochemical gradient of ions across their membranes which creates a potential difference across the membrane.
54
How to neurones create an electrochemical gradient?
By pumping ions (sodium and potassium) in and out of their membranes. 3Na+ ions are pumped out for every 2K+ ions that are pumped in to the axon. This creates an electrochemical gradient with a negative (less positive) charge on the inside of the axon and a positive charge on the outside of the axon. There are very few Na+ channels in the axon's membrane so sodium diffuses back in very slowly. There also lots of K+ channels in the axon membrane so lots of Potassium cations diffuse out fairly quickly further increasing the potential difference across the membrane.
55
What do axons have in their membrane in order to allow them to create an electrochmical gradient.
Protien channels for facilitated diffusion and protien pumps for active transport.
56
What channel protiens are present in the axon membrane?
Voltage gated K+ channel proteins and voltage gated Na+ channel proteins. - these allow potassium/Sodium cations to pass through the membrane by facillitated diffusion, but they only open when triggered by a voltage.
The membrane also has normal K+ and Na+ channel proteins that allow these ions to pass through at all times.
57
What protein pumps are present in the axon membrane?
Na+/K+ protein pumps which pump sodium and potassium cations through the membrane by active transport. These require ATP to function and can be affected by respiratory inhibitors. They can move ions against the concentration gradient.
58
What is happening in the axon at rest (cytosolic face negative)?
An eloectrochemical gradient is produced by the Na+/K+ pumps by pumping out three Na+ out and two K+ ions back in and because There are very few Na+ channels in the axon's membrane sodium diffuses back in very slowly. There also lots of K+ channels in the axon membrane so lots of Potassium cations diffuse out fairly quickly.
59
What is the resting potential of the axon?
It has a potential difference of -70mV and is polarized. It is a negative value because it shows that the inside of the axon is negative. The resting potential varies from -20mV to -200mV in different cells and species.
60
What does the combination of the Na+/K+ pumps and Na+ and K- channel protiens cause?
They cause a stable imbalance of Na+ and K- ions across the membrane.
61
What does this charge imbalance create?
This charge imbalance creates a potential difference across animal cell membranes known as the membrane potential.
62
What is a potential difference?
A charge gradient that could drive a voltage if hooked up to a complete circuit,
63
Why are neurones and muscle cells electrically excitable?
Because they have voltage-gated channel protiens which open and close depending on the voltage across the membrane. This allows these cells to change their membrane potential.
64
How long does an action potential last?
1-3ms.
65
What happens during depolarization?
The axon is stimulated causing a change in the membrane potential. The voltage gated Na+ channels detect this change and when the potential reaches -30mV the Na channels open for 0.5ms. The Na+ ions rush into the axon down the electrochemical gradient and the inside of the axon becomes tempoarally more positive than the outside (cytosolic face positive).
66
What is the potential difference across the membrane during depolarization? ( The action potential)
+40
67
What is an action potential.
The change in electrical potential across a cell membrane associated with the passage of an impulse along the membrane of a muscle cell or nerve cell.
68
What happens when the membrane potential reaches 0V during depolarization?
The voltage gated K+ channels open for 0.5ms
69
What happens once the voltage gated K+ channels open?
K+ ions move out of the neurone down their concentration gradient making the inside more negative again. This is repolarization and restores the original polarity
70
What is the significance of the refactory period?
* Another action potential cannot be generated during the refractory period, until the resting potential is restored
* This ensures a unidirectional impulse & prevents impulses from merging
71
What is the ‘all-or-nothing’ law?
* The size of the impulse is independent of the size of the stimulus
* Stimuli need to be above the threshold to generate an action potential
* Any increase over the threshold produces a greater frequency of action potentials, but all of the same size
* This means the signal is never attenuated
72
How can you measure the resting potential of a neurone?
you put one microelectrode inside the axon and another into the surrounding fluid
73
How can you measure the action potential as it moves along the neurone?
74
What is the overall change in p.d across the axon membrane during an action potential
120mV (
75
What are the three factors that affect the speed of an impulse?
* Temperature
* Diameter of the axon
* Presence/absence of a myelin sheath
76
What is the range across which the speed of an impulse can vary?
0.5ms - 120ms
77
How is the speed of the impulse affected by temprature?
As the temprature increases up to about 40oC The speed of transmission increases because the process is enzyme controlled (active transport). Also active transport requires energy in the form of A.T.P from respiration which also happens faster at a higher temperature. Above 40oC the speed starts to decrease as enzymes become denatured.
78
How does the speed of impulse transmission depend on the diameter of the axon?
In axons, speed of transmission depends on the longitudinal resistance. of the cytoplasm of the axon (axoplasm). The lager the diameter of the axon, the lower the resistance of the cytoplasm.
79
What is the myelin sheath made out of?
It is made up of cells called Schwann cells, wrapped around the axon. The membranes of these cells are rich in a lipid called myelin
80
What is myelination?
This is the process by which the myelin sheath is formed. During myelination, the membrane of the Schwann cells extends & wraps around the axon.
81
What are the functions of the Myelin sheath?
* It acts as an electrical insulator because ions cannot pass through it.
* It speeds up the transmission of electrical impulses
82
How does the myelin sheath speed up impulse transmission?
In myelinated axons ions can only pass through the membrane at the nodes of Ranvier. The local electrical circuits for ion movement are therefore only set up at the nodes of Ranvier. This means that Charge spreads unimpeded until it reaches an unmyelinated node of Ranvier, which is packed full of Na+ channels so electrical signals can move down a myelinated axon much faster than an unmyelinated one as
83
How do the nodes of ranvier speed up impulse transmission?
Nodes of Ranvier speed up impulse transmission… by allowing the action potential to jump from node to node - not bothering to move any ions at the in-between bits
84
What is Saltatory conduction?
This is the name given to the way in which the myelin sheath speeds up impulse transmission. Saltatory conduction increases the distances over which local currents can bring about depolarisation
85
What is another advanatage of saltatory conduction?
Since myelinated neurones only move ions at the nodes of Ranvier, they only have Na+/K+ pumps working at the nodes of Ranvier so they use less energy & ATP than unmyelinated ones (of the same diameter) where ions are pumped all the way along the neurone.
86
In what group of animals are myelinated axons found?
Vertebrates.
87
What is a synapse?
A junction between 2 neurones (or a neurone & an effector).
88
What kind of transmission occurs across a synapse?
Chemical transmission
89
How big is the gap between the synaptic knobs?
20um.
90
What is the name of the chemicals used to transmit a sinal across the synapse?
Neurotransmitters
91
What are the two main types of neurotransmitters?
1. Acetylcholine
2. Noradrenaline
92
Name some other neurotransmitters.
dopamine, serotonin, GABA, endorphins.
93
What is the function of a synapse?
Synapses connect the axon of one neurone to the dendrites of another neurone.
94
Label this diagram of a synapse.
95
What is contained in the synaptic knob?
* Synaptic vesicles containing neurotransmitters.
* Lots of Mitochondria to produce A.T.P for resynthesis of neurotransmitter molecules and active transport (Na+/K+ Pump).
96
Where are mitochondria needed in a neurone and why?
97
Outline the state of a cholinergic acetylcholine synapse before transmission occurs.
* The synaptic knob is full of synaptic vesicles, ready to go.
* The synaptic knob has a resting potential just like the rest of the neurone - the inside is negative compared to the outside.
98
How is a cholinergic acetylcholine synapse stimulated?
An impulse arrives from the axon and this depolarises the pre-synaptic membrane.
99
What happens when the pre-synaptic membrane in a cholinergic acetylcholine synapse is stimulated (is depolarised)?
The voltage gated Ca2+ ion channels open in the presynaptic membrane. This allows Ca2+ from the synaptic cleft to diffuse in through the pre-synaptic membrane.
100
What does the influx of Ca2+ ions into the synaptic knob of a cholinergic acetylcholine synapse cause?
This triggers the synaptic vesicles to move towards the membrane and fuse with it, releasing acetyl choline into the synaptic cleft by exocytosis.
101
What happens to the acetylcholine molecules once they have entered the synaptic cleft in a cholinergic acetylcholine synapse.
The acetylcholine diffuses across the synaptic cleft and binds to receptors on the post-synaptic membrane. These receptors are also gated Na+ channels which open when acetylcholine binds.
102
What happens when the receptor gated Na+ Channels open in a Cholinergic acetylcholine synapse?
This opening of the receptor gated Na+ channels allows Na+ to diffuse INTO the post-synaptic dendrite which triggers an action potential in the post-synaptic neurone, as long as it is above the threshold.
103
What happens once the action potential has depolarised the post-synaptic neurone in a cholinergic acetylcholine synapse?
Once the action potential has depolarised the post-synaptic neurone an enzyme called acetylcholinesterase, in the post-synaptic membrane hydrolyses the acetylcholine resetting the system & preventing impulses merging.
104
What happens after the hydrolysis of acetylcholine in a cholinergic acetylcholine synapse?
After hydrolysis by acetylcholinesterase, the breakdown products of acetylcholine choline & ethanoic acid diffuse back through the synaptic cleft and back into the synaptic knob by active transport.
105
What happens to the breakdown products of acetyl choline in the synaptic knob?
They are recycled to produce acetyl choline again using energy from A.T.P
106
Why are synapses unidirectional?
This is because:
* They ONLY release neurotransmitter from the PRE-synaptic neurone
* They ONLY have RECEPTORS on the POST-synaptic neurone.
107
What is a Tropsim?
a plant growth response TOWARDS or AWAY from a unidirectional stimulus
108
When are the females of most species fertile?
Most female animals are only fertile once a year - the breeding season. This is the most suitable season usually with favourable environmental conditions (temperature, seasonal rains and winds) abundant food and water which lead to breeding success & rearing of offspring
109
Why is it necessary to coordinate the breeding season?
To ensure that everyone knows when the breeding season is, can identify it and plan for it. This also has advantages as breeding at the same time results in the young being born at the same time, prodicing a glut of babies which increases the rate of survival.
110
How do animals coordinate breeding seasons?
Animals use daylength to coordinate their breeding seasons. They measure daylength against their own internal day-night rhythm using circadian rhythm genes.
111
What is photoperiodism?
This is the means by which plants coordinate their breeding seasons - by comapring the relative lenghts of day and night. it is defined as: A response controlled by relative length of light & dark periods of the day.
112
When do long day plants flower?
They flower when light periods are long.
113
When do short day plants flower?
They flower when the light periods are short.
114
What are day-neutral plants?
Plants for which day length has no effect on flowering time.
115
What kinds of plants would flower in this situation?
116
What kinds of plant would flower in this situation?
Day-neutral plants and short day plants.
117
What do plants use to detect photoperiod?
They use a photoreceptor called phytochrome. Phytochrome is a blue-green pigment that absorbs red and far red light. It is present in very minute quantities in the leaves of plants.
118
What are the two forms in which phytochrome exists?
Phytochrome Pr:
•Absorbs red light
Wavelength 660 nm
Phytochrome Pfr:
* Absorbs far-red light
* Wavelength 730 nm
119
How is phytochrome red converted into phytochrome far red?
By absorbing red light
120
How is phytochrome far red converted to phytochrome red?
By absorbing Far red light.
121
What happens to the phytochromes during the day?
Sunlight contains more red light and so during the day more red light is absorbed and so more phytochrome red is converted to phytochrome far red and so Phytochrome Pfr accumulates in the cell.
122
What happens to the phytochromes during the night?
At night the unstable Phytochrome Pfr that accumulated during the day reverts back to Pr SLOWLY.
123
How do plants use Phytochromes to measure photoperiod?
Plants use the relative amounts of the two forms, Pr & Pfr, to measure the photoperiod
124
In terms of phytochromes, what causes flowering in short day plants?
low levels of phytochrome far red induce flowering in short day plants
125
In terms of phytochromes what causes flowering in long day plants?
High levels of phytochrome far red induce flowering in short day plants.
126
What happens to the phytochromes during long summer days?
During long summer days lots of Pr is converted into Pfr during the day and due to the short night period very little of this Pfr converts back into Pr. So plants detect High levels of Pfr. Short day plants will not flower. Long day plants will.
127
What happens to the phytochromes during short winter days?
some Pr is converted into Pfr during the day. But due to the longer night period most of this Pfr converts back into Pr. Plants detect low levels of Pfr so long-day plants will NOT flower and short-day plants will flower.
128
If you have a short day plant and turn on a light in the middle of a winter night for one minute what will happen?
This short burst of light is enough to activate the Pr to Pfr conversion which is very rapid and undo the slow nightime Pfr to Pr conversion as Plants detect HIGH levels of Pfr the plant will not flower.
N.B Under these conditions long day plants will now flower. Horticulturalists can use this to manipulate flowering, by interrupting the photoperiod. They can also breed new hybrid varieties of plants by cross-pollinating flowers that would not usually flower at the same time, forcing the breeding/flowering seasons to overlap.
129
What light is most effective at disrupting photoperiod?
Red light. You can overcome this effect by immediately exposing the plant to infrared light.
130
How many leaves are required to detect photoperiod?
One.
131
What happens whenyou graft a short-day plant onto a long-day plant & expose both to short-days and what does this experement show?
Both plants flower.
132
What is the name of the chemical messenger that causes flowering?
Florigen.
