5.3 Neuronal communication Flashcards
(144 cards)
1
Q
What is a motor neurone?
A
A neurone that carries an action potential from the CNS to the effector?
2
Q
What is the function of the motor neurone?
A
The motor neurone carries an action potential from the CNS to an effector (e.g. a muscle or a gland).
3
Q
What is a myelinated neurone?
A
A neurone with an individual layer on myelin around it.
4
Q
What is a non-myelinated neurone?
A
A neurone that has no individual layer of myelin.
5
Q
What is the relay neurone?
A
The relay neurone joins the sensory neurone to the motor neurone.
6
Q
What is the sensory neurone?
A
A neurone that carries an action potential from the sensory neurone to the CNS.
7
Q
What are the 3 types of neurone?
A
- Motor neurone
- Sensory neurone
- Relay neurone
8
Q
What is the function of the sensory neurone?
A
The sensory neurone carries an action potential from the sensory receptor to the CNS.
9
Q
What is the function of the relay neurone?
A
The relay neurone is in the CNS, it connects the sensory and the motor neurone.
10
Q
What are some features all neurones have?
A
- Long so can transmit action potential over long distances.
- Plasma membrane has many gated ion channels.
- Sodium/ potassium pumps use ATP to actively transport sodium ions out of the cell and potassium ions into the cell.
- Maintains a potential difference across plasma membrane.
- Cell body contains nucleus, many mitochondria and ribosomes.
- Many dendrites.
- Axon carries impulses away from the cell body.
- Neurones surrounded by a fatty layer made up of schwann cells which insulate the cell from electrical activity in other nerves nearby.
11
Q
What is the structure of a motor neurone?
A
12
Q
What is the structure of a sensory neurone?
A
13
Q
What is the structure of a relay neurone? (labelled diagram)
A
14
Q
What is different about a motor neurone?
A
Motor neurones have their cell bodies in the CNS and have a long axon that carries the action potential out to the effector.
15
Q
What’s different about a sensory neurone?
A
They have a long dendron carrying the action potential from the sensory receptor to the cell body, which is just outside the CNS. They have a short axon carrying the action potential to the CNS.
16
Q
Whats different about relay nurones?
A
They connect the sensory and the motor neurones together. They have many short dendrites and a short axon.
17
Q
Why is the myelin sheath tightly wrapped around the sensory and motor neurones?
A
The myelin sheath prevents movement of ions across the neurone membranes, this means movement of ions can only occur at the nodes of Ranvier. This means that the action potential, jumps from one node to the next, making it a very fast process.
18
Q
What are the cells called that make up the myelin sheath?
A
Schwann cells.
19
Q
Whats different between myelinated neurones and non-myelinated neurones?
A
Myelinated neurones are wrapped tightly in a myelin sheath while a non-myelinated neurone may olny be surrounded in one loosely wrapped Schwann cell.
20
Q
What is an advantage of myelination?
A
Myelinated neurones can transmit an action potential much more quickly then non-myelinated neurones can.
21
Q
What is the typical speed of an action potential to be transmitted in a myelinated neurone and a non-myelinated neurone?
A
- Myelinated neurone: 100- 120 ms-1
- Non-myelinated neurone: 2- 20 ms-1
22
Q
Are myelinated or non-myelinated neurones usually longer or shorter compared to each other? why
A
Non-myelinated neurones are usually shorter as they carry action potentials over short distances.
23
Q
What are non-myelinated neurones usually used for?
A
They’re often used in coordinating body functions such as breathing and the action of the digestive system.
24
Q
What is the structure of a Schwann cell?
A
25
In a myelinated neurone, how does the action potential move across it?
The action potential wave **jumps from node to node.**
26
In a non-myelinated neurone, how does the action potential move across it?
The action potential moves along the neurone as a **wave**.
27
What is an action potential?
Action potential- a brief **reversal of the potential across the membrane** of a neurone causing a **peak of +40 mV** compared to the **resting potential of -60 mV.**
28
What is positive feedback?
A mechanism that **increases a change** taking the **system further away from the optimum**.
29
Define resting potential.
Resting potential- the **potential difference** across the membrane while the **neurone is at rest.**
30
In the simplest terms, what is a neurone doing when it is resting?
When a neurone is resting, it is **actively pumping ions** across it's cell surface membrane.
31
Describe what is happening while a neurone is at rest?
* **Sodium/ potassium ions pump** uses **ATP** to pump **3 sodium ions** out of the cell for every **2 potassium ions** that are pumped in.
* Sodium ion channels are kept **closed**.
* Plasma membrane is **more permeable** to potassium ions than sodium ions.
* Potassium ions diffuse out of the cell by **facilitated diffusion** through potassium ion channels.
* Cell cytoplasm contains **large organic anions** so the interior of the cell is kept at a negative potential compared to the outside of the cell.
* Cell membrane is said to be **polarised**.
32
What do sodium/potassium ion pumps require to use?
ATP
33
When a neurone is at rest, what ion channels are kept closed?
Sodium ion channels are kept closed.
34
When a neurone is at rest, what ion channels are kept open? What effect does this have?
**Potassium ion channels** are kept open. This means **some potassium ions diffuse out** of the cell via **facilitated diffusion**. Therefore, the cell membrane is **more permeable to potassium ions** compared to sodium ions.
35
What would you find in the cell cytoplasm of a neurone cell which means the interior of the cell is maintained at a negative potential compared to the outside?
Large organic anions (negatively changed ions).
36
When the neurone id at rest, what word can you use to describe the cell surface membrane?
The cell surface membrane is polarised.
37
When a neurone is at rest, what is the potential difference across the cell membrane?
-60mV (milivolts). This is called the **resting potential**.
38
When a neurone is at rest, Where is the concentration of sodium ions highest, on the inside or the outside?
The concentration is higher outside than inside.
39
When a neurone is at rest, Where is the concentration of sodium ions highest, on the inside or the outside?
Concentration of ions is higher on the inside than the outside.
40
What causes depolarisation of the cell membrane of a neurone?
If some of the **sodium ion channels are opened** , then the sodium ions will quickly **diffuse** down their concentration gradient **into the cell from the surrounding** tissue fluid.
41
What are most of the sodium channels opened by in a neurone? What are they called?
Most sodium region of a neurone are opened by changes in the potential difference across the membrane- they are called **voltage-gated channels.**
42
What does the opening of voltage-gated sodium ion channels allow?
It allows **a large influx of sodium ions** and the depolarisation reaches **+40mV** on the inside of the cell.Once this value is reached, the neurone **will transmit the action potential**.
43
What word can we use to describe an action potential, which describes how once it starts at one point in the neurone, it will continue along to the end?
Self-perpetuating
44
How are action potential described, meaning they all reach the same magnitude? (+40mV)
They are referred to as an **‘all-or-nothing’ responce.**
45
Describe the stages of an action potential?
1. Membrane starts at it's **resting state**- **polarised** with the inside of the cell being **-60mV**.
2. **Sodium ion channels open** and some sodium ions diffuse into the cell.
3. The membrane **depolarises**- reaches a threshold value of **-50mV**.
4. **Positive feedback** causes nearby **voltage-gated sodium ion channels to open** and many **sodium ions flood** into the cell, causing the cell to become more **positively charged.**
5. Potential difference across the plasma membrane reaches **+40mV**
6. Sodium ion channels **close** and potassium channels **open**.
7. **Potassium ions diffuse out** of the cell bringing the potential difference back to negative inside compared to the outside (**repolarisation**).
8. **Potential difference overshoots** slightly, making the cell **hyperpolarised**.
9. Original potential difference is restored so that the cell **returns to its resting state**.
46
What is a happening at this stage of forming an action potential?
**Membrane starts in its resting state**- **polarised** with the inside of the cell being **-60mV** compares o=to the outside of the cell. There i a higher concentration of sodium ions outside than inside and a higher concentration of potassium ions inside than outside the cell.
47
What is a happening at this stage of forming an action potential?
Sodium ion channels in the plasma membrane open. Sodium ions diffuse into the membrane. This is **depolarisation**.
48
What is a happening at this stage of forming an action potential?
It becomes less negative with respect to the outside and reaches the **threshold value of -50mV.**
49
What is a happening at this stage of forming an action potential?
**Positive feedback** causes nearby **voltage-gated sodium ion channels to open** and **many sodium ions flood in.** As more sodium ions enter, the **cell becomes positively charged** inside compared to the outside.
50
What is a happening at this stage of forming an action potential?
The potential difference across the plasma membrane reaches +40mV. The inside of the cell in positive compared to the outside.
51
What is a happening at this stage of forming an action potential?
The sodium ion channels close and the potassium ion channels open.
52
What is a happening at this stage of forming an action potential?
**Potassium ions diffuse out** of the cell bringing the **potential difference back to the negative** inside compared to the outside - this is **repolarisation**.
53
What is a happening at this stage of forming an action potential?
The potential difference overshoots slightly, making the cell **hyperpolarised**. The potassium ion voltage gated- channels close.
54
What is a happening at this stage of forming an action potential?
The **sodium/potassium ion pumps** restore the resting potential.
55
Why do neurones need to contain large numbers of neurones?
Transmitting action potentials is an **active process** – need to pump ions to create concentration gradients.
56
In which cells are nodes of Ranvier present?
Myelinated neurones
57
What is a pacinian corpsule?
A pressure sensor found in the skin.
58
What are sensory receptors?
Cell/ sensory nerve endings that respond to a stimulus in the internal or external environment of an organism that creates action potentials.
59
What is a transducer?
A cell that converts one form of energy to another.
60
What is a stimulus to a sensory receptor?
A change in the energy level or the presence of a new chemical.
61
How do sensory receptors respond to a stimulus?
They respond by **creating a signa**l in the form of an **electrical impulse**. This is a nerve imluse.
62
What do receptors in the retina detect and what is the energy changes involved?
They detect change in light intensity and convert light energy to electrical energy.
63
What is the energy change involved in detecting a change in temperature?
Heat energy to electrical.
64
What is the energy change involved in detecting a change in pressure on the skin?
Mechanical to electrical
65
What is the energy change involved in detecting a change in sound?
Sound energy to electrical.
66
What is the energy change involved in detecting a change in chemicals in the air and chemicals in food?
These receptors detect a presence of a chemical and create an electrical impulse.
67
What is a pacinian corpsule?
A pressure sensor that detects changes in pressure on the skin.
68
What is the structure of a pacinian corpuscle?
The corpuscle is an **oval-shaped** structure that consists of a **series of concentric rings** of **connective tissue** wrapped around the end of a nerve cell.
69
Why, when pressure is constant, a pacinian corpuscle stops responding?
The corpuscle is only sensitive in pressure that deforms the rings of connective tissue, so when pressure is constant they stop responding.
70
How does a pacinian corpuscle produce an action potential?
When the membrane becomes deformed by the **changing pressure**, it allows **sodium channels to open**. This allows **sodium ions to diffuse into the cell,** producing a generator potential.
71
When can we describe a nerve cell as polarised?
When the cell is inactive.
72
When can we describe a nerve cell as depolarised?
When sodium channels have opened and sodium ions are diffusing into the cell, causing the inside of the cell to become less negative making a change in the potential difference.
73
When will an action potential be initiated?
An action potential will only be initiated if the stimulus is large enough as more channels will open causing enough sodium ions to enter to pass the threshold potential and open more voltage gated channels causing the action potential.
74
What happens if the stimulus isn't big enough to initiate an action potential?
If a small stimulus is detected only a few sodium channels will open and the threshold potential won't be reached.
75
Diagram of a pacinian corpuscle.
76
What is a generator potential?
When a **few sodium channels open** they allow a few sodium ions into the cell causing a small depolarisation- this is a **generator potential.** However, when more channels are opened the **generator potential are combined to cause a larger depolarisation**. If they depolarisation reaches a particular magnitude it passes a threshold and will cause an action potential.
77
What is a local current?
A local current is when **sodium ions move** in the **cytoplasm** of the neurone **towards** the **regions** where their **concentration** is **lower**.
78
What do local currents cause?
They cause a **light depolarisation** of the membrane and cause sodium ion channels further along the membrane to open (positive feedback).
79
What are the steps included in the formation of a local current?
1. When an action potential occurs, sodium ion channels open at a point on the neurone.
2. This allows sodium ions to diffuse into the neurone, allowing voltage-gated sodium ion channels to open.
3. Sodium ions diffuse sideways along the neurone, away from the region of increased concentration (this movement of charged particles is called a local current)
4. The local current causes a small depolarisation further along the neurone which affects the voltage-gated sodium ion channels, causing them to open. The open channels allow rapid influx of sodium ions causing full depolarisation (action potential) further along the neurone. The action potential has therefore moved along the neurone.
80
Why can't ionic movements occur over much of the length of a myelinated neurone?
The **myelinated sheath** on the myelinated neurone is **impermeable to sodium and potassium ions.** These ionic movements can only occur at the **nodes of Ranvier.**
81
Describe an action potential in a myelinated neurone?
In myelinated neurones, the local currents are **elongated** as the sodium ions move from one **node of Ranvie**r to another- this means the action potential appears to **jump** from one node to the next (**saltatory conduction)**
82
What is saltatory conduction?
Where the action potential appears the jump from one node of Ranvier to the next.
83
What are the advantages of saltatory conduction? How does this occur?
Saltatory conduction means **action potentials travel faster** along the neurone. Because action potentials can only occur at the gaps between Schwann cells that make up the myelin sheath, it action potential appears to jump from one node of Ranvier to the next.
Myelinated neurones conduct action potentials more quickly than non-myelinated neurones.
84
What do all action potentials have in common?
All action potentials are the **same magnitude.** Everyone produces a depolarisation of +40mV.
85
How can we detect stimuli of different intensities if all action potentials are the same magnitude?
Our brains detect determine the intensity of the stimulus from the **frequency of action potentials arriving in the sensory religion of the brain**. A higher frequency of action potentials means a more intense stimulus.
86
When a stimulus is at a higher intensity, what happens in our neurones?
**More sodium channels are opened** in the sensory receptor, which **produces more generator potentials,** therefore, there are **more frequent action potentials** in the sensory neurone and entering the CNS.
87
Why immediately after an action potential is it impossible to stimulate another action potential?
After an action potential, the concentration of sodium and potassium ions inside and outside the neurone must be restored by the sodium/potassium ion pumps. This is known as the refractory period.
88
What does the refractory period allow?
It allows the cell to recover after an action potential and ensures that the action potentials only travel in one direction.
89
Why do membranes need special channel proteins to enable the movement of ions?
Ions are charged particles and cannot diffuse through the phospholipid bilayer.
90
Explain why a constant sound will become unnoticeable after a short time?
Sensory receptors respond to changes in the environment. A constant sound is no longer a change. The receptor or the sensory neurone will become habituated to the sound and an impulse no longer reaches the brain.
91
Why is energy required to produce a concentration gradient?
Particles must be moved against their concentration gradient. This requires active transport – which requires energy in the form of ATP.
92
Why is a concentration gradient is needed to ensure sodium ions more rapidly into the cell?
Sodium ions will diffuse rapidly down a concentration gradient even without the immediate availability of ATP.
93
What is facilitated diffusion?
the passive movement of molecules along their concentration gradient, guided by the presence of another molecule – usually an integral membrane protein forming a pore or channel.
94
What is a cholinergic synapse?
A synapse that uses **acetycholine** as its **neurotransmitter**.
95
What is a nerotransmitter?
A **chemical** used as a **signalling molecule** between two neurones in a synapse.
96
What is a synapse?
A **junction** between 2 or more neurones.
97
What is the gap between neurines called?
Synaptic celft
98
What does the action potential in the [re-synaptic neurone cause?
The action potential causes the release of neurotransmitters that diffuse across the synaptic cleft and generate a new action potential in the pot-synaptic neurone.
99
Structure of a synapse (labelled diagram).
100
What features does the pre-synaptic bulb contain?
* Many mitochondria
* Large amount of smooth endoplasmic reticulum
* Large number of vesicles.
* A number of voltage gated calcium ion channels.
101
Why is there a large amount smooth endoplasmic reticulum in the pre-synaptic bulb?
The SER packages the neurotransmitters into vesicles.
102
What does the post-synaptic membrane contain?
Specialised sodium ion channels.
103
Describe the structure of a sodium ion channel of the post-synaptic neurone?
These channels are made up of **5 polypeptide molecules, 2 of these polypeptides have a species receptor site** that is specific to acetycholine (they're complimentary)/
104
Why would the sodium ion channels open in the post-synaptic membrane?
Once the acetylcholine has diffused across the synaptic cleft, it binds to the 2 receptor sites and causes the sodium ion channels to open.
105
What first happens when an action potential arrives at the synaptic bub?
The voltage-gated calcium ions open.
106
What does calcium ions diffusing into the synaptic bulb cause?
The calcium ions cause the synaptic vesicles to move to, and fuse with the pre-synaptic membrane.
107
How does acetylcholine go from being in a vesicle in the pre-synaptic vesicle to being in the synaptic cleft.
The calcium ions cause the vesicles to move and fuse to the pre-synaptic membrane, acetylcholine is released by **exocytosis**. (requires ATP)
108
What happens after acetycholine diffuses across the synaptic cleft?
The acetycholine binds to the **receptors** on the **sodium ion channels** in the post-synaptic membrane, causing the sodium ion channels to **open**.
109
What happens after the sodium channels have been opened in the post-synaptic membrane?
Sodium ions diffuse across the post-synaptic membrane into the post-synaptic neurone. A generator potential is created, if sufficient generator potentials combine, then the potential across the post-synaptic membrane reaches the threshold potential and a new action potential is created.
110
What is acetylcholinesterase?
An enzyme found in the synaptic cleft?
111
What is the role of acetylcholinesterase?
Acetylcholinesterase hydrolyses the acetycholine to ethanoic acid and choline. This stops the transmission of signals.
112
What happens after acetycholine is hydrolysed?
**The ethanoic acid and choline are recycled**. They re-enter the synaptic bulb by diffusion and are combined to aacetylcholine using ATP from respiration in the mitochondria.
113
What is summation.
Summation occurs when the effects of **several** excitatory post-synaptic potentials **(EPSPs) are added together.**
114
In cholinergic synapses, what molecule does the signal consist of?
Acetycholine.
115
What word can we use to describe several neurones coming to one neurone?
Converging.
116
What word can we use to describe one neurone sending out signals to several neurones?
Diverging.
117
What is an excitatory post-synaptic potential (EPSP)?
When a relatively small number of acetycholine molecules diffuse across the cleft, producing a small depolaristion.
118
What happens when several EPSPs combine together?
When several combine together, it increases the membrane depolarisation until it reaches the threshold. This combined effect is **summation.**
119
What can summation occur from?
Summation can result from several action potentials in the same pre-synaptic neurone (**temporal summation**), or from action potentials arriving from several different pre-synaptic neurones (**spatial summation**).
120
What are 2 types of summation?
* Temporal summation
* Spatial summation
121
Via temporal summation, how is an action potential formed?
One action potential in the pre-synaptic neurone does not produce an action potential in the post-synaptic neurone- it **requires a series of action potentials** in the presynaptic neurone.
122
Via spatial summation, how is an action potential formed?
Several pre-synaptic neurone contribute to producing an action potential on the post-synaptic neurone.
123
What are inhibitory post-synaptic potentials (IPSPs)?
Produced in the pre-synaptic neurone, IPSPs can **reduce the effect of summation** and prevent an action potential in the post-synaptic neurone.
124
What do synapses ensure about action potentials?
They ensure action potentials are transmitted in the **correct direction**- only the pre-synaptic bulb contains vesicles of acetycholine.
125
How do synapses filter out unwanted low-level signals?
If a low level stimulus creates an action potential in the pre-synaptic neurone it is unlikely to pass across a synapse to the next neurone, because several vesicles of acetycholine must be released to create on action potential in the post-synaptic neurone.
126
By what process can low-level action potentials be amplified by?
Summation
127
IF a low-level stimulus is persistent what ill occur in the pre and post synaptic neurone?
It will generate several successive action potentials in the pre-synaptic neurone. The release of many vesicles of acetycholine over a short period will enable the post-synaptic EPSPs to combine together to cause an action potential.
128
When may a neurone be described as being fatiged?
After repeated stimulation a synapse may run out of vesicles containing the neurotransmitter- this means the nervous system no longer responds to the stimulus- we have become habituated.
129
How can post-synaptic neurones become more sensitive?
Synaptic membranes are adaptable, therefore more receptors on the post-synaptic membrane would make the neurone more sensitive to acetyocholine.
130
Why is a neurone active while it is said to be resting?
The neurone is using ATP to pump ions. Sodium ions are pumped out as potassium ions are pumped into the cell. This creates and maintains the resting potential across the plasma membrane.
131
Why is it essential to maintain a concentration gradient across the neurone cell membrane?
The concentration gradient will enable rapid movement of ions across the membrane when the ion channels open. Sodium ions can move in quickly and potassium ions can move out.
132
What is the role of organic anions along the inside of the neurone?
To ensure that the inside of the cell remains negative compared with outside.
133
What is the difference between the sodium channels in the generator region and those elsewhere along the neurone?
In the generator region the sodium ion channels are opened by the presence of acetylcholine; elsewhere they are charge-gated – opened by changes in potential across the membrane
134
Explain why it is not possible to stimulate a neurone immediatly after an action potential?
After an action potential the neurone membrane becomes hyperpolarised – more negative inside than at rest. The sodium ions and potassium ions need to be moved back to their original positions in order to reverse this hyperpolarisation.
135
Explain the role of positive feedback in the generation of an action potential?
When the membrane begins to depolarise this causes more sodium ion channels to open allowing more sodium ions to flow into the neurone, increasing the depolarisation.
136
What causes the sodium ion channels to open?
They are voltage-gated. A small change in the potential across the membrane caused by the local currents inside the cell opens the gates.
137
How does the myelin sheath cause saltatory conduction?
The myelin sheath is closely bound to the membrane of the neurone: this prevents movement of ions across the membrane. Movement of ions across the membrane can only occur where there are gaps in the myelin sheath. These gaps occur at the nodes of Ranvier. The local currents are extended to carry the impulse between the nodes of Ranvier
138
Why does saltatory conduction make conduction more rapid?
Only a few ions need to move along the neurone to alter the charge at the next node. The ions can move along very quickly.
139
Why is the maximum frequency of an action potential limited?
Each action potential lasts 2–3 ms and is followed by a short refractory period while the membrane is hyperpolarised and ions are pumped back to their original locations.
140
Why does the pre-synaptic nerve end in a bulb?
The swelling at the end of the neurone provides more space to store vesicles of the neurotransmitter and a larger surface area for exocytosis of the neurotransmitter.
141
Why does the pre-synaptic bulb contain many mitochondria?
Many mitochondria produce ATP, which is required to synthesise the neurotransmitter and move the vesicles
142
Why does the pre-synaptic bulb have lots of smooth reticulum?
Smooth endoplasmic reticulum is where the acetylcholinesterase is synthesised and placed into vesicles
143
Why are calcium ion channels voltage-gated?
Because an action potential arriving at the pre-synaptic bulb will cause changes to the potential across the membrane – these will then open the voltage-gated calcium ion channels.
144
Why is it important that the synaptic cleft contains acetycholinesterase?
Acetylcholinesterase hydrolyses the acetylcholine. If the acetylcholine remained in the synaptic cleft it would keep stimulating the post-synaptic neurone.
