Nervous and hormonal control (8.1-8.7) Flashcards
(89 cards)
1
Q
Sensory neurone
A
A type of neurone that transmits impulses from receptors to relay neurones in the CNS.
2
Q
Motor neurone
A
Carries impulses from relay/sensory neurones to effectors (muscles/glands)
3
Q
Relay neurone
A
A type of neurone that exists in the CNS and connects sensory neurones with motor neurones.
4
Q
Structure of motor neurone
A
Cell body (situated in CNS) at one end and dendrites at the other
5
Q
Structure of sensory neurone
A
Cell body on stalk with dendron and axon either side
6
Q
Structure of relay neurone
A
Cell body in between axon with dendrites at both ends
7
Q
Neurones
A
Individual nerve cells that conduct impulses in one direction only
8
Q
Nerves
A
Bundles of neurones protected by a sheath
9
Q
Myelination
A
The formation of a myelin sheath around nerve cells by Schwann cells
It causes saltatory conduction, allowing impulses to travel faster
10
Q
Schwann cells
A
Cells that form the myelin sheath around nerve cells in the peripheral nervous system.
Contain myelin which insulates the axon, leading to saltatory conduction
11
Q
Reflex
A
A rapid involuntary response to a stimuli
12
Q
Why are reflex arcs important
A
Protect the body from harm
Fast response time
Involuntary
13
Q
What type of nervous system is the pupil reflex controlled by
A
Autonomic nervous system
14
Q
Stages of pupil contraction
A
High light intensity detected by photoreceptors on retina
Electrical impulse arises
Passes along sensory neurone to the optic nerve to the brain
The impulse travels down a parasympathetic neurone to a motor neurone
To the circular muscles which contract and decreases the pupil aperture
15
Q
Pupil dilation stages
A
Low light intensity detected by photoreceptors on retina
Electrical impulse arises
Passes along sensory neurone to optic nerve
Impulse travels down sympathetic neurone to a motor neurone
To the radical muscle which contract and increase pupil aperture
16
Q
Where are Na+ transported by co transporter pumps
A
out of the cell/axon
17
Q
Where are K+ transported by co transporter pumps
A
Into the cell
18
Q
Dendron
A
An extension from a nerve cell that carries impulses towards the cell body.
19
Q
Axon
A
An extension from a nerve cell that carries impulses away from the cell body.
20
Q
Stimulus
A
A change in internal or external conditions which brings about a response.
21
Q
Receptor
A
A structure which acts as a transducer by detecting changes in the environment and converting them into electrochemical impulses
22
Q
Effector
A
A muscle or gland which produces a response to a stimulus.
23
Q
Pupil
A
The hole in the centre of the iris which can contract and dilate using the iris to alter the amount of light which contacts the retina.
24
Q
Iris
A
The pigmented muscular ring that surrounds the pupil and controls its diameter
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Retina
The structure at the back of the eye which is composed of photoreceptors and is specialised to detect light
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Saltatory conduction
When the nerve impulse jumps from node to node, due to the myelinated sections of the neurone blocking the electrical impulse, it is extremely fast
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Nodes of Ranvier
Unmyelinated sections of nerve cells which allow for the propagation of an action potential due to their clusters of voltage gated Na+ channels
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Depolarisation
The rapid influx of sodium ions into the cell which cause it to lose its negative charge and the membrane potential to increase.
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Hyperpolarization
The drop in membrane potential below the resting potential after repolarization due to open potassium ion channels.
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Resting potential
When there is a point of electro chemical equilibrium so no ions are diffusing in or out of the neurone
Usually occurs at around -70mV
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Acetylcholine
A neurotransmitter used in the parasympathetic nervous system
Removed from the cleft by enzyme, acetylcholinesterase
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Synapse
The junction between two nerve cells or a nerve cell and an effector.
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Neurotransmitter
A chemical which diffuses across the synaptic gap to stimulate other neurones or effector cells.
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All-or-nothing principle
If the threshold is reached then the impulse will fire at the same voltage, amplitude and duration
All action potentials are equal and there is not want of controlling the degree of of depolarisation
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Rods
A type of photoreceptor found in the retina which is specialised to work in dim light.
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Rhodopsin
A protein found in rod cells that converts dim light into an electrochemical
impulse.
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Opsin
A GPCR that forms part of rhodopsin along with retinal and is involved in converting detected photons into electrochemical signals
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Retinal
A protein that makes up rhodopsin along with opsin and forms the light sensitive part of the complex.
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Phytochrome
Light sensitive pigments found in plants used to detect changes to external light conditions.
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IAA
A type of auxin mainly produced at growing plant tips which is used to promote cell growth and elongation
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Action potential stages
- Stimulus excites the neurone membrane causing voltage gated NA+ channels to open
- NA+ diffuse into axon down their electrochemical gradient making inside of the axon less
negative - DEPOLARISATION
- When the potential difference reaches the threshold potential of around -50mV then more NA+
ions move in triggering more NA+ channels to open
- Depolarisation continues until the potential difference has been reversed from -70mV to +40mV
(action potential)
- The NA+ channels close and voltage gated K+ channels open
- K+ ions diffuse out of axon causing REPOLARISATION
- The voltage gated K+ channels return the membrane to its resting potential
42
Refractory period
The time taken to return from the peak to the resting potential
- This gives a delay between impulses
- Ensures that impulses only travel in one direction so the membrane in the refractory period cannot be depolarised
43
What is the intensity of the stimulus determined by
- Frequency of impulses
| - Number of neurones in a nerve that are conducting impulses
44
What is the speed of conduction determined by
Determined by axon diameter
- Travels faster along larger diameter axons
- There is less resistance to ion flow in the cytoplasm
- So depolarisation reaches other parts of the cell membrane quicker - There is less leakage of ions back across the membrane
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Myelin
Acts as an electrical insulator
| Stops the diffusion of Na+ and K+ ions
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Impulse travelling along synapse stages
- Action potential arrives at the synaptic knob which causes the opening of voltage gated ion channels
- The influx of ions causes the vesicles continuing neurone transmitters to move and fuse with the presynaptic membrane
- Released neurotransmitters diffuse across the synaptic cleft and bind to complementary receptors on the post synaptic membrane
- The binding of the neurotransmitters increase the permeability of the post synaptic neurone to NA+
- This initiates depolarisation of post synaptic neurone
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What are neurotransmitters inactivated by
- Taken back up presynaptic knob
- Broken down by enzymes and reabsorbed
- Diffuse away and taken up by another neurone
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Why do neurotransmitters have to be removed
So that there is not a prolonged action potential and so that the receptors are available for future use
49
Excitory synapses
Associated with a process called summation
They make the post synaptic membrane more permeable to NA+ but sometimes a single impulse is not enough to cause neurotransmitters to be released so no AP is formed so summation has to occur
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Inhibitory synapses
Block transmission making a generation of an impulse less likely
This occurs when neurotransmitters open up different ion channels that are not NA+ This leads to hyperpolarisation which makes it difficult to depolarise the membrane
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Summation
Adding together the effects of a number of weak AP at a synapse to reach a threshold because sometimes there isn’t enough neurotransmitters diffusing across to reach the threshold and bring about an action potential
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Spacial summation
The convergence of a number of presynaptic neurones and synapses and one synaptic neurone Needs enough neurotransmitters to diffuse across to achieve an AP
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Temporal summation
Where a single presynaptic neurone fires a number of times in quick succession so that the neurotransmitters build up in the synaptic cleft
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What reflex are the circular muscles controlled by
Parasympathetic because they relax to let in more light
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What reflex are radial muscles controlled by
Sympathetic reflex, because they contract to let in more light
56
Stages of pupil constriction
- High light intensity detected by photoreceptors on retina
- Electrical impulse arises
- Passes along sensory neurone to the optic nerve to the brain
- The impulse travels down a parasympathetic neurone to a motor neurone - To the circular muscles which contract and decreases the pupil aperture
57
stages of pupil dilation
- Low light intensity detected by photoreceptors on retina
- Electrical impulse arises
- Passes along sensory neurone to optic nerve
- Impulse travels down sympathetic neurone to a motor neurone
- To the radical muscle which contract and increase pupil aperture
58
Structure of retina
Consists of 2 layers
| - Photoreceptor cells (roads and cones) at the back - Neurones at the front connecting to the topic nerve
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Cones
Located in the fovea and used to detect colour and in high visual acuity
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Photoreception in rod cells in light
- When rhodopsin absorbs light the retinal component changes shape
- The rhodopsin breaking down into retinal and opsin
- The opsin binds to the cell surface membrane and activates a cascade of reactions that close
the cation channels and decrease the permeability of the plasma membrane
- Therefore less NA+ ions can diffuse into the rod cell
- This leads to a change in the potential difference of the rod membrane which becomes
hyperpolarised
- If the hyperpolarisation is large enough then no neurotransmitter is released and the bipolar cell
membrane depolarises and an action potential is sent to the sensory neurone of the optic nerve
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Photoreception in rod cells In the dark
- NA+ diffuse into the outer segment of the rod cell via non specific cation channels
- NA+ diffuses within the rod cell down its concentration gradient to the inner segment where
sodium ions are continuously and actively pumped out of the cell
- The influx of NA+ causes there membrane to be slightly depolarised
- The neurotransmitter binds to the bipolar cells stopping its membrane from depolarising leading
to no action poetical in the optic nerve
62
Plant growth substances
Used for when a stimuli needs to bring about a direction of growth Produced in the apical meristem regions
Transported by diffusion or the phloem
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How IAAs stimulate cell elongation
- Produced in the meristem and diffuses away from the tip building up a zone of elongation - Results in active transport of H+ into the cell wall
- This acidification of the cell wall weakens the H bonds and weakness the cell wall
- This also increases the potential difference across the cell - Water molecules enter as a result by osmosis
- Turgor pressure increases and the cell elongates
64
How phytochrome and IAAs alter development in plants
- They bind to receptors in target cells or interact with other proteins/enzymes
- This leads to the activation of intracellular second messenger signal molecules
- Pfr can directly enter the nucleus and bind to transcription factors
- The second messenger molecules enter the nucleus and activate transcription factors which
bind to DNA
- Leads to transcription of light regulated genes
- The proteins translated lead to metabolic changes that result in response
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What reflex are radial muscles controlled by
Sympathetic reflex
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What reflex are the circular muscles controlled by
Parasympathetic reflex
67
Why is the resting potential of a cell -70mV
The co transporter pumps move 3 Na+ out of the neurone for every 2 K+ moved in
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Why do K+ ions move back into the neurone
The membrane is around 50X more permeable to K+ ions than Na+ ions so K+ passively diffuses back down its concentration gradient
Co transporter pumps also transport K+ back into the neurone
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Action potential
The change in potential difference across an axon membrane which occurs during the passage of a nerve impulse, where the inside becomes more positive than the outside
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Refractory
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Why do action potentials move in only one direction
The refractory period ensures that Na+ channels behind the action potential don't open and trigger depolarisation, instead the Na+ channels ahead of the action potential are stimulated to open
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Role of mitochondria in the synapse
Pumps the ions back across the membrane to reset the knob
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Importance of synapses
Control the nerve pathways (allowing for flexibility) and integrate information from different neurones (allowing coordinated responses)
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How do synapses achieve flexible and coordinated responses
They are unidirectional (one direction)
They filter out low levels of stimuli
They are modifiable
Involved with divergence
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Unidirectional
Travel in one direction
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Filtration of stimuli
There is a maximum level of stimulation before a neurotransmitter is released
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Modifiable
Synaptic connections are not fixed especially to the CNS
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Divergence
A single stimuli in one neurone results in a number of complex responses in several other neurones
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Convergence
Where several stimuli come together to cause one single response
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Receptor for light
Photoreceptors
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Receptor for stretching and compression
Mechanoreceptors
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Receptors for temperature
Thermoreceptors
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Receptors for chemicals
Chemoreceptors
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How does an electrical impulse arise
The stimulus causes a change in the permeability of the receptor membrane to Na+, and the receptor is able to convert the energy of the stimulus into electrical energy of the nerve impulse
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Nature of receptors
Specific so only respond to one stimulus
86
Structure of the retina
Inverted and consisting of 2 layers, with rods and cones at the back, and neurones in front of them
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Structure of rod cells
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Photoperiodism
Plant response to light duration
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Phytochrome
The light sensitive pigment found in plants
