Cells of the Nervous System and Neurotransmitters at Synapses Flashcards
(87 cards)
1
Q
What are nerve cells called?
A
neurons
2
Q
What do neurons do?
A
conduct nerve impulses allowing rapid communication and control within the body.
3
Q
What are the 3 types of neurons?
A
sensory
inter (relay/association)
motor
4
Q
In sensory neurons, what do the dendrites gather into?
A
one long fibre that transmits information from receptors to the cell body.
5
Q
Where do sensory neurons go to?
A
inter neurons
6
Q
Where are the cell bodies of inter neurons?
A
CNS
7
Q
Where do motor neurons receive nerve impulse from?
A
inter neurons
8
Q
In motor neurons, what can the axons be?
A
very mong (e.g. axon to toes > 1m) and each axon carries a message to an effector.
9
Q
What do dendrites do?
A
receive nerve impulses and pass them to the cell body.
10
Q
What is an axon?
A
a single nerve fibre that carries impulses away from the cell body.
11
Q
What does the cell body do?
A
- contains the nucleus
- contains most of the cytoplasm (also running down axon)
- controls the cell’s metabolism
- contains clusters of ribosomes - to make proteins e.g. enzymes needed to make neurotransmitters.
12
Q
What surrounds the axon nerve fibre?
A
myelin sheath
13
Q
What surrounds the myelin sheath?
A
thin protective membrane
14
Q
What is myelin sheath made of? (2)
A
made of fatty material
Made of tightly packed double layers of plasma membrane in a spiral around the nerve fibre
15
Q
What does the myelin sheath do?
A
increases the speed that impulses are transmitted
forms insulating jacket around nerve fibre
16
Q
Describe what happens to the myelin sheath as baby grows?
A
Not complete at birth, continues to develop as baby grows
17
Q
What is a nerve fibre without myelin sheath called?
A
unmyelinated
18
Q
What do glial cells do?
A
close around the axon and lay down tightly packed layers of plasma membrane around it, giving physical support to the axon.
19
Q
What are glial cells also responsible for?
A
maintaining a homeostatic environment around neurons as well as removing any debris by phagocytosis.
20
Q
At birth what is wrong with the hypothalamus?
A
it is not fully myelinated
21
Q
As the hypothalamus is not fully myelinated at birth what effect does this have on young babies?
A
young babies can’t regulate their body temperature very well until the myelin sheath develops at 6 months.
Babies don’t have full control of their legs
22
Q
Why do babies not have full control of their legs?
A
the neurons in the spinal cord that send impulses from the brain to the lower body are not fully myelinated until the infant is around 2 years old.
23
Q
What is poliomyelitis (polio)?
A
A virus which is transmitted by person-to-person spread mainly through faecal-oral route or, less frequently, by a common vehicle (e.g. contaminate water or food) and multiplies in the intestine, from where it can invade the nervous system and can cause paralysis.
24
Q
What is multiple sclerosis?
A
Myelin sheath around neuron is destroyed. The demyelinated nerve fibres are unable to transmit nerve impulses efficiently so muscle control is lost.
25
What are the symptoms of MS?
Numbness
Walking difficulties
Impaired vision
26
What is a synapse?
the area of functional contact between an axon ending (synaptic knob) of one neuron and the dendrite of another.
27
What is the presynaptic neuron?
neuron before the synapse
28
What is the postsynaptic neuron?
neuron after the synapse
29
Describe the sequence of events at a synapse?
- Nerve impulse arrives at the synaptic knob of the presynaptic neuron.
- Vesicles containing neurotransmitters are stimulated and move towards the surface of presynaptic knob.
- Vesicles fuse with the membrane of presynaptic knob.
- Neurotransmitter molecules are released into the synaptic cleft.
- Neurotransmitter molecules diffuse across the synaptic cleft and combine with receptor molecules on membrane of postsynaptic dendrite.
- Nerve impulse is initiated and transmitted along postsynaptic neuron.
30
How is information passed on at a synapse?
via a chemical called a neurotransmitter
31
Give 2 examples of neurotransmitter?
acetylcholine + nor-epinephrine
32
Why can an impulse only go in one direction?
Because vesicles are only on one side of the synapse
33
Only once the impulse has been transmitted, the neurotransmitters need to be removed from the receptors, why?
to prevent continuous stimulation of postsynaptic neurons
34
What are the 2 main methods of neurotransmitter removal?
enzyme degradation
| Re-uptake
35
Describe enzyme degradation?
As soon as the impulse is transmitted, certain neurotransmitters are broken down into non-active products and reabsorbed by the presynaptic neuron, where they are reassembled and stored in vesicles.
36
Give an example of enzyme degradation?
Acetylcholine is broken down into non-active products by an enzyme present on the postsynaptic membrane :
acetylcholinesterase
Acetylcholine ------> Non-active products
37
How is nor-epinephrine removed?
It is reabsorbed by the presynaptic neuron which secreted it and is stored in vesicles ready to be reused
38
Why is the removal of the neurotransmitter substance after an impulse has crossed the synapse rapid?
so that many separate impulses can cross the gap each second
39
What provides the energy for each of the processes (enzyme degradation/ re-uptake)?
mitochondria, which are abundant in the cytoplasm of the presynaptic knob.
40
What do neurons in the CNS have?
several synapses
41
At synapses what are the 2 possible responses from the receptors on the postsynaptic membrane?
Excitatory
| Inhibitory
42
Describe an excitatory response?
increases the membrane's chance of transmitting a nerve impulse
43
Describe an inhibitory response?
decreases the membrane's chance of transmitting a nerve impulse
44
What happens if total excitatory effects > total inhibitory effects?
an impulse is sent
45
What does the type of response depend on?
the receptors present at the postsynaptic membrane
46
What is a neuro-effector junction?
a tiny area of functional contact between an axon-ending of a motor neuron and an effector. (it is also known as a neuro-muscular junction).
47
Describe what threshold is?
A certain minimum number of neurotransmitter molecules need to be released into the synaptic cleft and combined with receptors to allow an impulse to be passed on at a synapse
48
What happens if there is less than the minimum number of neurotransmitters required?
the impulse will not pass over the gap.
49
What are weak stimuli called and how are they filtered out by the synapse?
subthreshold stimuli, they are filtered out by the synapse acting as an undridgeable gap
50
How is the intensity of an environmental stimulus conveyed (e.g. volume)?
Each impulse is equal in size, so information about intensity is transferred by the number of impulses per second e.g. loud music = many impulses per second, soft music = few impulses per second
51
What is summation?
If many synaptic terminals of many presynaptic neurons discharge their neurotransmitter simultaneously or in rapid succession, then enough of the chemical is released to fire an impulse. This cumulative effect of a series of weak stimuli that together bring about an impulse is called summation.
52
What is a converging pathway? give example
information from many sources is transmitted to one destination e.g. stimuli from many rods (on retina of eye) that allows us to see in the dark
53
What do converging pathways do?
increase the sensitivity to excitatory or inhibitiory pathways, ensuring that the threshold is met by summation
54
What is a diverging pathway? give examples
Information from a single source is transmitted to several destinations e.g. signal from brain to muscles in the fingers allowing them to work together to let you pick up pencil and signal from hypothalamus to control body temperature by sending a signal to sweat glands, skin arterioles and skeletal muscles
55
What does a reverberating pathway allow?
nerve impulses to be recycled and to stimulate the presynaptic neurons
56
A reverbrating pathay continues to send out signals until what?
the process is brought to halt when no longer required
57
What is a reverberating pathway used for?
control of rhthmic activities such as breathing. The pathway can reverberate and transmit impulses for seconds, hours or in the case of breathing, for a lifetime.
58
Neurons in the brain undergo changes in the synaptic netwok during a persons lifetime, especially during....
early development of the brain
the learning of new skills
Response to brain injury
59
What is plasticity of response?
the brain's ability to become altered from new environmental experiences
60
Describe an example of major plasticity?
Plasticity in response to a brain injury e.g. after a stroke a persons ability to move limbs or speak could be affected. Regaining these functions is caused by neurons in other parts of the brain forming new pathways and links meaning they can take on these new jobs an allow the damaged area to be bypassed.
61
Describe an example of minor plasticity?
Plasticity in suppression of reflex responses. plasticity of response can allow you to over-ride the reflex responses e.g. blinking. If the brain receives 2 conflicting message (blink and dont blink) they meet in the same converging neural pathway. If the overall effect is excitatory then a nerve impulse is fired and they blink. If the overall effect is inhibitory then no impulse is fired and they don't blink. So some people can stare people out but others cannot resist blinking.
62
What do special inter neurons in the spinal cord allow ?
short circulating of normal response times in occasions of danger
63
What are endorphins?
chemicals that function like neurotransmitters and act as natural painkillers by combining with receptors at synapses and blocking the transmission of pain signals
64
Where are endorphins produced?
in the hypothalamus
65
What are endorphins produced in response to?
physical and emotional stress
severe injury
lengthy periods of exercise
foods e.g. chocolate
66
What is dopamine?
a neurotransmitter produced in many parts of the brain
67
What are regions of the brain releasing dopamine known as?
pleasure centres
68
What are pleasure centres generally connected by and when stimulated what are they called?
neural circuits and when stimulated are called reward pathways
69
What have reward pathways evolved to reinforce?
behaviours that ensure survival such as satisfying hunger, thirst and sexual need.
70
What happens when a need is satisfied? (stages)
Centre V releases dopamine when a need is satisfied.
It is then transferred to centre N
Centre N then releases dopamine
This stimulates a pleasurable feeling in the frontal area of the cerebral cortex.
71
What can each neurotransmitter directly or indirecly influence?
neurons in a specific portion of the brain, thereby affecting behaviour and function of the brain
72
What can the lack of certain neurotransmitter lead to?
certain diseases or conditions of the brain
73
Give examples of diseases cause by problems with neurotransmitters?
Alzheimers = lack of acetylcholine
Parkinson's = lack of dopamine
Schizophrenia = overactive dopamine systems
Depression = low serotonin, a neurotransmitter that regulates mood, behaviour, appetite and sleep
General anxiety disorders
74
What are many drugs used to treat neurotransmitter diseases similar to?
neurotransmitters
75
What kind of durgs can be used to treat neurotransmitter diseases?
agonists
antagonists
inhibitors
76
What do agonists do?
Bind to and stimulate receptors by mimicking the normal neurotransmitters (enhance cellular activity)
77
What do antagonists do?
block receptor sites (cellular actvity blocked)
78
What do inhibitors do?
inhibit enzymes that would degrade the neurotransmitter or inhibit re-uptake
79
What do many drugs affect?
the transmission of nerve impulses in the reward circuit of the brain, this can lead to changes in mood, thinking ability, perception and behaviours
80
Many drugs affect the transmission of nerve impulses in the reward circuit of the brain, this can lead to changes in mood, thinking ability, perception and behaviours. Discuss how drugs cause this effect? (5)
1. stimulating release of neurotransmitter e.g. MDMA (ecstasy)
2. Acting as an agonist (e.g. morphine, cannabis)
3. Acting as an antagonist (e.g. ketamine)
4. Inhibiting re-absorption of neurotransmitter e.g. cocaine
5. Inhibiting breakdown of neurotransmitter by an enzyme
81
What is drug addiction?
a chronic disease when the sufferer compulsively seeks out and uses the drug regardless of the consequences.
82
What is sensitisation?
when the number of receptors in neurons increase and the drug has greater effect on the receptors that are present. Less of the drug is needed to stimulate the receptors.
83
What can sensitisation lead to?
cravings and addiction
84
What are the causes of sensitisation/drug addiction?
- repeated use of a drug which is an antagonist
- nervous system compensates by increasing the receptor number on the neurons
- receptors become more sensitive to drug
- increased number and sensitivity changes wanting of drug to craving and addiction
85
When is a user said to have a tolerance?
when their reaction to the drug has decreased in intensity
86
What is desensitisation?
receptors in neurons become less sensitive to the drug and the number present in the neurons decrease. A user will need a higher dose to feel the same effects.
87
What are the causes of desensitisation/drug tolerance?
- repeated use of a drug which is an agonist
- nerves compensate by reducing their receptor number
- remaining receptors become less sensitive to the action of the drug
- more of drug is needed to produce same effects
