Neuronal Communication Module 5.1.3 Flashcards
What is a description and function of dendrons and dendrites?
-Dendrons split into smaller dendrites
-They carry nerve impulses towards the cell body
What is a description and function of the axon?
-Elongated nerve fibres which can be short or long depending on the type of neuron
-Carry nerve impulses away from the cell body
What is a transducer?
-A cell that can convert one form of energy into another
What is the structure and function of a sensory neuron?
-They have short dendrites and one long dendron carries action potential from receptor cells to the cell body
-One short axon then carries the action potential to the CNS
-Specialized cells and transducers
-Each sensory receptor only responds to one type of stimulus
What is the structure and function of motor neurones?
-Short dendrites carry action potential from CNS to a cell body
-One long axon then carries cell body to effector cells
What are the structural differences between a motor and sensory neuron?
-Sensory neuron has short dendrites and long dendrons whereas motor neuron only has short dendrites
-Sensory neuron has a short axon whereas motor neuron has a long axon
What is the structure and function of Relay neurones?
-Short dendrites that carry action potential away from sensory neurones to cell body
-One axon carries action potential to motor neurones
What are the four main types of sensory receptors, their stimulus and an example of an organ they belong to?
- Mechanoreceptor- Pressure and movement- Skin
- Chemoreceptor- Chemical- Nose
3.Thermoreceptor- Heat- Tongue
4.Photoreceptor- Light- eye
What is the membrane of a sensory receptor-like when not being stimulated?
-There is a difference of charge between the inside and outside of the cell, the inside is negatively charged relative to the outside
What is a generator potential?
-When a stimulus is detected the receptor cell changes permeability ions move into and out of the cell via pumps and channels
-Ions carry a charge so there is a change in potential difference, this change due to a stimulus is a generator potential
What will happen if a stimulus is too small?
-A smaller stimulus will produce a smaller movement of ions across the membrane
-This causes a smaller change in potential difference across the membrane and the threshold level isn’t reached so there is no action potential
When is an action potential triggered and what is it?
- If the generator potential is big enough
-An action potential is a nerve impulse that travels along a neuron
What is the Pacinian Receptor?
-Sensory receptor, found in the skin
-Contains Mechanoreceptors that detect mechanical pressure and vibration
What happens when pressure is applied to the Pacinian Corpuscle?
-Stretch mediated sodium channels in the membrane of the neurone change shape and sodium ions diffuse across the membrane into the neurone.
-This creates a generator potential and if it reaches the threshold potential an action potential is triggered
Why do you not constantly receive electrical impulses from the corpuscles?
-The corpuscles only respond to changes in pressure so when it is constant they stop responding therefore you don’t receive mundane electrical impulses
How do neurones set up a resting potential?
- Sodium-potassium pumps pump more sodium out of the cell and they can’t diffuse back in as they aren’t permeable to the membrane
- Potassium inside the cell due to the pump can diffuse back out through potassium pumps
- As a result the cell is negative inside the cell as there are more positive ions outside the membrane
Describe the propagation(spread) of an action potential down the axon?
- First region becomes depolarised and sodium ions are attracted to the negative ions in the next region so diffuse sideways
2.Process continues creating a wave of depolarisation as the first area becomes repolarised.
What is the refractory period and why is it important?
-After an action potential the neurone cannot become excited straight away
-This is important as it ensures action potentials don’t overlap and are unidirectional
What are the two stages of the refractory period?
-Absolute refractory period: nothing happens
-Relative refractory period: during this period another action potential can only be initiated if stimulus is more intense than normal threshold.
What is the difference between myelinated and non-myelinated neurones?
-The axon of myelinated neurones are covered in a myelin sheath made of layers of plasma membrane, non-myelinated do not have these
Describe saltatory conduction in myelinated neurones?
- Sodium and potassium ions cannot diffuse through the myelin sheath, and the neurone is only permeable at the nodes of Ranvier
- This allows the depolarisation to ‘jump’ from node to node, the sodium ions can also diffuse rapidly, making conduction faster.
Why is saltatory conduction more efficient?
-It saves time and energy because every time a channel opens it takes time for ions to move it also requires ATP so reducing the number of times a membrane is repolarised it reduces energy.
What are two factors that affect the speed of action potentials?
-Axon diameter: bigger the axon diameter the faster the impulse due to less resistance for diffusion of ions
-Temperature: the higher the temperature the faster the nerve impulse up until the temperature at which proteins begin to denature
What is the difference in action potentials between a large and small stimulus?
-The size of the stimulus does not determine the size of the action potential instead it determines the number of action potentials in a given time
How does the brain determine the intensity of a stimulus?
-From the frequency of action potentials, the higher the frequency the higher the intensity.
What are the key features of a synapse?
-Synaptic cleft: gap between axon terminal of a neurone and dendrite of another
-Presynaptic neurone: neurone where the impulse arrives
-Postsynaptic neurone: neurone that receives neurotransmitter
-Synaptic vesicle: contains neurotransmitters
-Neurotransmitter receptors: where the neurotransmitter binds to on the postsynaptic neurone
What are the two types of neurotransmitters?
-Excitatory: result in depolarization of a postsynaptic neurone and if a threshold is reached an action potential is triggered
-Inhibitory: hyperpolarize the postsynaptic neurone, preventing an action potential
What is synaptic divergence and synaptic convergence?
-Synaptic divergence: when one neurone connects to many neurones, electrical impulse can be lessened
-Synaptic convergence: when many neurones connect to one, electrical impulse can be amplified
What is spatial summation?
-When a number of presynaptic neurones connect to one postsynaptic neurone. They all release neurotransmitters which build up to a high enough level for an action potential
What is temporal summation?
-When a single presynaptic neurone releases neurotransmitter as a result of an action potential several times, this builds up neurotransmitters in the synapse until a sufficient amount is present to trigger an action potential.
How can drugs, poisons and toxins affect synapses?
-They can inhibit the enzyme that breaks down the neurotransmitter, or the release of neurotransmitters
-Some chemicals are the same shape of Neurotransmitters so can mimic their actions or block the receptors so they can’t bind
