5.3- Roles of sensory receptors

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  • Created by: McTighe
  • Created on: 25-09-18 16:05
What are sensory receptors?
Cells/ sesory nerve endings that responds to a stimulus in the internal or external environment of an organism and can create action potentials
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How does the body detect stimuli?
Using sensory receptors located in sense organs
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What are transducers?
A cell that converts one form of energy into another (e.g. light --> electrical impulse)
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What type of stimulus does a photoreceptor detect?
Light
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Give an example of a photoreceptor
Rod/Cone cells in eyes
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What type of receptor detects chemicals?
Chemoreceptor
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Give an example of a chemoreceptor
Olfactory cells in mouth/eyes
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What receptor detects temperature?
End bulbs of Krause
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What receptor detects pressure/sound?
Mechanoreceptors
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Give an example of a mechanoreceptor
Pacinian Corpuscles
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What are Pacinian Corpuscles?
Pressure receptors in skin to detect pressure and vibrations
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Describe the structure of a pacinian corpuscle
Oval-shaped structure that consists of concentric rings of connective tissue, wrapped around the end of a nerve cell. IN the centre in the sesonry nerve tube (fibre). Fibroplasts produce the connective tissue
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What happens when pressure is exerted on the Pacinian Corpuscles?
The lamellae of pacinian corpsucles deforms and push against nerve endings. Na+ channels are open, so Na+ diffuse out creating a generator potential.
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What does it mean by a large nerve frequency?
A larger stimuli
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What produces a generator potential?
A stimulus will cause sodium channels to open, allowing sodium to diffuse into the cell. This depolarises the membrane slightly, causing a generator potential to form
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What is the purpose of the sodium-potassium pump?
It actively pumps out 3 Na+out of cell, and two K+ into the cell. This is used to maintain a concentration gradient, which is more positive outside than inside
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Why is the membrane more negative inside the cell?
There are negatively charged anions
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Why is the cell more permable to K+ than Na+?
The K+ channels remain open
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What is it called when the cell is resting?
Polarised
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How does a nerve impulse form?
The permability of membrane to Na+ is changed by Na+ channels opening. Na+ move down concentration gradient into cell which makes cell less negative (Depolarises)
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Name the three types of neurones?
Motor neuron, Sensory, Relay
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What is the function of the motor neurones?
Carry action potential from CNS to effector
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Where is the cell body for the motor neurone?
In the CNS
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What do the sensory neurones do?
carry potential from the receptors to the CNS
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Where is the cell body on the sensory neurone?
On the side of the axon
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What do relay neurones do?
They transport the signal from the sensory neurone to the motor neurone
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What is the structure of a relay neurone?
Lot of short dendrites and a short axon
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What does the cell body contain?
Nucleus, Mitochondria, Ribsomes
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What is the fatty layer that surrounds neurones?
Myelin Sheath
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What does the myelin sheath consist of?
Schwann cells
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What is the function of the Myelin Sheath?
Insulates cell from electrical activity in other nerve cells
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How many of vertebrate neurones are myelinated?
1/3
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What is the section between each schwann cell that is unmyelinated?
Nodes of Ranvier
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How long are Nodes of Ranvier?
2-3um long
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What are unmyelinated neurones are used for?
Breathing and action of digestive system
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What channels are open during resting potential?
Potassium ion channels open; sodium ion channels closed
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What is the potential difference at resting potential?
-60mV
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What happens when a stimulus occurs?
Na+ channels open causing sodium to move into cell, making it becomes depolarised.
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What potential is the threshold potential?
-50mV
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What happens when the threshold potential is reached?
It causes sodium voltage-gated channels to open, causing an influx of sodium ions
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Why is this seen as positive feedback?
Small depolarisation of membrane causes a change that increases depolarisation further
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When does depolarisation stop?
+40mV
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What happens when +40mV is reached?
Sodium voltage-gated channels close and potassium voltage-gated channels open so K+ move out of the cell making it more negative.
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WHat is this process knwon as?
Repolarisation
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When does repolarisation stop?
-65mV
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What is it called when the potential moves passed resting potential?
Hyperpolarisation
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Why does hyperpolarisation occur?
Slightly too many K+ move out
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What is refractory period?
When the membrane is unable to stimulate another action potential. This ensures only one way transmission.
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How are the concentrations of sodium/potassium concentrations fix?
Sodium-potassium pump
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What are local currents?
Movement of ions across a neuron
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How does a local current form?
When stimulus occurs, sodium ions channels open, so influx of sodium occurs. They then diffuse along the neuron, away from high concentration. This allows one way transmission. This causes depolarisation further along neuron, causing voltage-gated cg
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Why can depolarisation not occur when the neuron is surrounded by fatty sheath?
Sodium and potassium cannot diffuse through it
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What does the nodes of ranvier have?
Lots of voltage-gated channels
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Why are the local currents known as elongated?
The movement of ions move from one node of ranvier to another
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What is the transmission of an electrical impulse called along a myelinated neurone?
Saltatory conduction
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Why do myelinated neurones speed up rate of transmission?
action potential can only be induced at the gaps between the myelinated areas, the transmission of the action potential will be sped up, as it goes further in less time.
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What is the 'all or nothing rule?'
This term describes the idea of anything below that voltage not generating an action potential at all, whereas if it does reach that value – a full action potential is generated, which will travel along a nerve cell as a nerve impulse.
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What shows a higher stimulus?
More frequent action potentials
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What is a cholinergic synapse?
A synapse that uses acetylcholine as its neurotransmitter
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What is the gap called between two neurones?
Synaptic cleft
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How wide is the synaptic cleft?
20nm
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What is swelling called on the pre-synaptic neurone?
Pre-synaptic bulb (or 'knob')
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What is found in the pre-synaptic neurone?
Lots of mitochondria and golgi apparatus
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What type of channels are found on the post-synaptic neurone?
Sodium ion ligand-gated channels
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What is acetylcholinesterase?
An enzyme found in the synaptic cleft which breaks down
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What does acetylcholinesterase break down acetylcholine into?
Ethanoic acid and chloine
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What is the role of acetylcholinesterase?
Stop transmission of signals, so synapse does not continue to produce action potentials in post-synaptic neuron.
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What does depolarisation of the pre-synaptic bulb cause?
Calcium voltage-gated channels to open, leading to an influx of calcium into synaptic bulb
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What do the calcium ions trigger?
Movement of synaptic vesicles to membrane and fuse to membrane. Neurotransmitter molecules are released by exocytosis and diffuse across cleft.
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What happeneds when the neurotransmitter binds to the receptor?
Opens ligand-gated channels and allows influx of Na+ (depolarisation)
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Give some roles of a synapse
-Cell signalling -One direction transmission -allows convergence -allows divergence -filters out low level stimuli -prevents fatigue -permits memory/learning
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What is a excitatory postsynaptic potential?
A small stimulus cause small depolarisation (small number of neurotransmitter released) but not enough to cause action potential in post-synaptic neurone
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What is summation?
Lots of excitatory postsynaptic potential added together
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What is temporal summation?
Lots of action potentials from one neurone
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What is spatial summation?
Lots of action potentials from lots of neurones
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What is an inhibitor postsynaptic potential?
Reduce effect of summation and prevent an action potential in post-synaptic neurone.
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what is divergence?
One neurone transmits to lots of different nervous systems (Useful in a reflect arc)
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What is convergence?
Lots of neurones go into one neurone
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