Nervous and hormonal control (8.1–8.7) Flashcards
1
Q
How do animals increase their chances of survival?
A
By responding to changes in their external environment
2
Q
Why do animals respond to changes in their internal environment?
A
To ensure they are always optimal for their metabolism.
3
Q
What is a stimulus?
A
A change in the internal or external environment.
4
Q
What are receptors?
A
They detect stimuli and can be cells or proteins on cell surface membranes.
5
Q
What are effectors?
A
Cells that bring about a response to a stimulus to produce an effect. Include muscle cells.
6
Q
How do receptors communicate with effectors?
A
Via the nervous system or the hormonal system
7
Q
What are the 3 main types of neurone?
A
Sensory, motor, and relay.
8
Q
Sensory neurones?
A
Transmit electrical impulses form receptors to the CNS
9
Q
Motor neurones?
A
Transmit electrical impulses from the CNS to effectors.
10
Q
Relay neurones?
A
Transmit electrical impulses between sensory neurones and motor neurones.
11
Q
What is the basic process from a stimulus to an effector?
A
- Stimulus is detected by receptor cell and an electrical impulse is sent along a sensory neurone.
- When an electrical impulse reaches the end of a neurone chemicals called neurotransmitters take information across to the next neurone which sends an electrical impulse.
- CNS processes the information and sends an impulse along motor neurones to effectors.
12
Q
What happens to your eyes in dim light?
A
- Photoreceptors in your eye detect the lack of light.
- CNS processes the information
- Radial muscles in the iris are stimulated.
- Radial muscles contract to dilate your pupils.
13
Q
What happens to your eyes in bright light?
A
- Photoreceptors in your eye detect the bright light.
- CNS processes the information
- Circular muscles in the iris are stimulated by the motor neurones.
- Circular muscles contract to constrict your pupils.
14
Q
What is a gland?
A
A group of cells that are specialised to secrete a useful substance, such as a hormone.
15
Q
What are hormones?
A
Chemical messengers. Many are proteins or polypeptides. Some are steroids.
16
Q
When are hormones secreted?
A
When a gland is stimulated by a change in concentration of a specific substance.
They can also be stimulated by electrical impulses.
17
Q
How do hormones work?
A
Hormones diffuse directly into the blood. They diffuse out of the blood all over the body but only bind to specific receptors found on target cells.
18
Q
What is the basic process of hormones? in the example of low glucose levels and the release of glucagon
A
- Low glucose level concentration
- Receptors on pancreas cells detect the low blood glucose concentration
- The pancreas releases the hormone glucagon into the blood
- Target cells in the liver detect glucagon and convert glycogen into glucose.
- Glucose is released into the blood, so glucose concentration increases.
19
Q
Compare nervous communication with hormonal communication?
A
Nervous vs Hormonal
Electrical impulses vs chemicals
Faster vs slower
Localised vs widespread response
Short lived vs long lived
20
Q
What is potential difference?
A
When there is voltage across a membrane
21
Q
What is meant by receptors being specific?
A
They only detect one particular stimulus.
22
Q
How do photoreceptors convert light into an electrical impulse?
A
- Light enters the eye, hits the photo receptor and is absorbed by light sensitive pigments.
- Light bleaches the pigments causing a chemical change.
- This triggers a nerve impulse along a bipolar neurone.
- Bipolar neurones connect photoreceptors to the optic nerve, which takes impulses to the brain.
23
Q
What are the two types of receptor?
A
Rods and cones
24
Q
Where are rods mostly found?
A
In the peripheral parts of the retina
25
Where are cones found?
Packed together in the fovea.
26
What are the 3 types of cones?
Red sensitive, green sensitive and blue sensitive.
27
What do rod cells give information in?
Black and white.
28
What happens in your rod cells when its dark (not activated)?
1. **Sodium ions** are **pumped out** of the cell using active transport.
2. Sodium ions **diffuse back** in to the cell through **open sodium channels.**
3. This makes the **inside** of the cell only **slightly negative** compared to the outside. The membrane is **depolarised**.
4. This **triggers** the **release** of **neurotransmitters.**
5. The **neurotransmitters inhibit** the **bipolar neurone** so the bipolar neurone cannot fire an action potential so no information goes into the brain.
29
What happens when your rod cells are stimulated (in the light)?
1. **Light energy** causes **rhodopsin** to **break** apart into **retinal** and **opsin**. (bleaching)
2. **Bleaching** of **rhodopsin** causes the **sodium ion channels to close.**
3. So **sodium ions** are actively **transported out** of the cell, but they **cant diffuse back** in.
4. **Sodium ions build up on the outside** of the cell, making the **inside** of the membrane much **more negative** than the **outside**, the cell membrane in **hyperpolarised**.
5. When the **rod cell** is **hyperpolarised** it **stops releasing neurotransmitters**. So there is **no inhibition** of the bipolar neurone.
6. Because the **bipolar** neurone is **no longer inhibited it depolarises**. If the change in the potential difference reaches the **threshold**, an **action potential** is **transmitted** to the **brain via the optic nerve**.
30
What do all neurones have?
A cell body with a nucleus. Plus cytoplasm and all other organelles you usually get in a cell.
31
Draw and describe a motor neurone
Many short dendrites and One long axon
32
Describe the function of a motor neurone?
Carries nerve impulses from the CNS to effector cells.
33
Draw and describe a sensory neurone?
One long dendron carries nerve impulses from receptor cells to the cell body which is in the middle of the neurone.
One shot axon carries nerve impulses from the cell body to the CNS.
34
What is the function of sensory neurones?
Carrying impulses from receptor cells to the CNS.
35
Draw and describe a relay neurone?
**Many short dendrites** carry nerve **impulses** from **sensory neurones** to the **cell body.**
An **axon** carries **nerve impulses** from the **cell body to motor neurones.**
36
Describe a neurone cell membrane at rest
1. The outside of the membrane is positively charged compared to the inside.
2. As there are more positive ions outside the cell than inside.
3. So the membrane is polarised and the resting potential is -70mV.
37
How is a resting potential created and maintained in a neurone membrane?
**Sodium and potassium pumps** and **potassium ion channels.**
* The **sodium-potassium pump** uses active transport to move **3 Na+ out** for for every **2 K+ in**. ATP is needed to do this.
This creates a **sodium electrochemical gradient** because there are **more positive sodium ions outside** the cell than **inside**.
* The **potassium ion channel** allows the **movement** of **K+ down** the **concentration gradient** out of the cell.
this makes the **outside** of the cell **positively charged** compared to the inside.
38
Describe the process of cell membrane becoming depolarised when they're stimulated.
1. **_Stimulus_-** **Sodium ion channels open**. Sodium ions **diffuse into** the **neurone** down the sodium ion electrochemical gradient. This makes the **inside** of the neurone **less negative.**
2. **_Depolarisation_-** If the **PD reaches -55mV** **more** sodium channels **open** and more sodium ions diffuse into the neurone.
3. **_Repolarisation_**- At **PD of +30mV** the **sodium ion channels open**. The membrane is more permeable to potassium so potassium ions diffuse out of the neurone **down the potassium ion concentration gradient.**
4. **_Hyperpolarisation_-** Potassium ion channels are **slow to close so too many potassium ions diffuse out** of the neurone. The PD becomes **more negative** than the resting potential.
5. **_Resting potential-_** Ion channels are reset. **Sodium potassium pump** returns the membrane to its **resting potential.**
39
What is the refractory period?
When the ion channels are recovering and cant be made to open so the cell membrane cannot be excited.
40
How does action potential move along the neurone?
When action potential happens some of the sodium ions that enter the neurone diffuse sideways.
This causes the sodium ion channel in the next region of the neurone to open and sodium ions diffuse into that part.
That causes a wave of depolarisation to travel along the neurone.
The wave moves away from the parts of the membrane in refractory period because these parts cannot fire an action potential.
41
What are the benefits of the refractory period?
**Acts as a time delay** making sure that action potentials **don't overlap** but pass along as **discrete impulses.**
Ensures action potential is **unidirectional**
42
What happens to action potential if its a bigger stimulus?
Wont cause a bigger action potential but will cause them to fire more frequently.
43
How do local anesthetics work?
They **bind to sodium ion channels** in the membrane.
This **stops** sodium **ions** from **moving into** the **neurones** so their membranes will not depolarise.
This **prevents action potentials** from being conducted along the neurones and stops information about pain reaching the brain.
44
What is the structure of a myelinated neurone?
Myelin sheath made of Schwann cell. Tiny patches of bare membrane called the nodes of Ranvier.
45
What is saltatory conduction?
In myelinated neurone depolarisation only happens at the nodes of Ranvier as sodium ion channels are concentrated there.
The neurone (Schwann cell) cytoplasm conducts enough electrical charge to depolarise the next node so the impulse jumps from node to node.
Its very fast.
46
What is the speed at which an impulse moves along a neurone called?
The conduction velocity. Higher = quicker.
47
What is the role of acetylcholine?
A neurotransmitter involved in muscle contraction and the control of heart rate.
48
How do neurotransmitters transmit nerve impulses between neurones? (short)
1. An **action potential** triggers **calcium influx**
2. **Calcium influx** causes **neurotransmitter release.**
3. The neurotransmitter **triggers** an **action potential** in the post synaptic neurone.
49
What happens for an action potential to trigger a calcium influx?
1. **Action potential arrives** at the synaptic knob of the presynaptic neurone.
2. The action potential **stimulates voltage gated calcium ion channels** in the presynaptic neurone to **open**.
3. Calcium ions **diffuse** into the synaptic **knob**.
50
What happens to cause the calcium influx to cause neurotransmitter release?
1. **Influx of calcium ions** into the synaptic knob causes the **synaptic vesicle** to **move** to the **presynaptic membrane**. They then **fuse** with the presynaptic **membrane**.
2. The vesicle **release** the **neurotransmitter** into the **synaptic cleft** (exocytosis)
51
What causes the neurotransmitter to trigger an action potential in the postsynaptic neurone?
1. **Neurotransmitters** diffuse **across** the **synaptic cleft** and **binds** to **specific receptors** on the post synaptic membrane.
2. Causing **sodium ion channels** in the **post synaptic neurone** to **open**.
3. The **influx** of **sodium ions** into the post synaptic membrane **causes depolarisation**. An **action potential** on the post synaptic membrane causes **depolarisation**. An action potential on the post synaptic membrane is generated if the **threshold** is **reached**.
4. The **neurotransmitter** is **removed** from the **synaptic cleft** so the response doesn't keep happening.
52
What is synaptic divergence
When one neurone connects to many different neurones information can be dispersed to different parts of the body.
53
What is synaptic convergence?
When many neurones connect to one neurone information can be amplified.
54
What is summation?
Where the effect of neurotransmitters released from many neurones is added together.
55
What is tropism?
The response of a plant to a directional stimulus
56
What is positve tropism?
Growth towards the stimulus
57
What is negative tropism?
Growth away from the stimulus.
58
What is phototrophism?
Growth of a plant in response to light.
59
What is geotrophism?
The growth of plants in response to gravity.
60
What is IAA?
It is an auxin that's produced in the tips of shoots in flowing plants. When it enters the nucleus of a cell, its able to regulate the transcription of genes related to cell elongation and growth.
61
How does IAA move around plants?
Moves by diffusion and active transport over short distances and via the phloem over longer distances.
62
What does uneven distribution of IAA mean?
There's uneven distribution of IAA there will be uneven growth in the plant.
63
How do plants detect light?
Using phytochromes (photoreceptors)
64
What are the two states of phytochromes?
Red light and far red light
65
What are the different states phytochromes are converted to and from when exposed to light?
**Red light phytochrome** is _converted_ to **Far red light phytochrome** when exposed to **red light.**
**Far red light phytochrome** is _converted_ to **red light phytochrome** when exposed to **far red light**
66
What is converted in darkness?
Far red light is converted slowly into red light in darkness.
67
What does daylight contain more of?
Red light (not far red light)
68
How do phytochromes influence growth in plants?
The amount of FRL and RL changes depending of the amount of light eg day or night, summer or winter.
So differing amounts of RL and FRL control the responses to light by regulating the transcription of genes involved in these responses.
