Neuronal control Flashcards
Why are different proteins needed in a membrane to allow diffusion of different ions?
Each protein and ion have different shapes so they need to be specific and complementary to each other
What are the roles of sensory receptors?
They are specialised cells that transduce the energy of a stimulus into electrical energy in an action potential that is transmitted in a neurone.
Generate receptor potentials on stimulation
If a threshold intensity is reached, the sensory neurone, specific to that receptor is stimulated to generate an action potential.
What is a sensory receptor?
A cell, or group of cells, in which a change in the external or internal environment, produces a nerve impulse or action potential.
What must happen for an action potential to be produced?
The stimulus must be at or above a certain threshold level
What is a transducer?
All receptors are an example of transducers, they are adapted to detect changes in particular forms of energy.
What are the 3 types of neurone?
Sensory
Relay
Motor
What are the similarities between sensory and motor neurones?
Both have:
Cell body, nucleus, dendrites, axon, (myelin sheath/nodes of Ranvier)
What are the differences between sensory and motor neurones?
Only sensory neurones are in the peripheral nervous system and have dendrons, cell body in the middle of the axon, shorter axon. Impulse goes to relay neurone.
Only motor neurones are in the central nervous system and have largest axon, short dendrites, no dendrons and a cell body before the axon. Impulse goes to effector muscle/gland.
In what direction does the dendron/dendrites take the impulse?
Towards the cell body
In what direction does the axon take the impulse?
Away from the cell body
Structure of all neurones?
Long - impulse can travel far.
Plasma membrane lots of gated ion channels to control movement of Ca2+, K+ and Na+ ions.
Na+/K+ pumps use ATP for active transport.
Neurones maintain a potential difference across their plasma membrane.
Cell body has nucleus, mitochondria and ribosomes
Dendrites connect to other neurones
Axon carries impulse away from the cell body
surrounded by fatty layer to insulate, composed of schwann cells
Description of cell body
Contains nucleus surrounded by cytoplasm
Description of dendron
Short extensions that come from the cell body
Description of axon
Elongated nerve fibres - cylindrical and consists of narrow region of cytoplasm surrounded by plasma membrane
Description of myelin sheath
Layers of membrane around axon
Description of Nerve-muscle junction
Where a nerve joins a muscle
Description of dendrites
Small branches of dendrons
Function of cell body
Cytoplasm - ER / mitochondria produce neurotransmitters
Function of dendron
Divide into smaller branches called dendrites that transmit electrical impulses to cell body
Function of axon
Transmit impulse away from cell body
Function of myelin sheath
Speed up electrical impulse (insulate axon)
Function of nerve-muscle junction
Stimulates muscle fibres to contract
Function of dendrites
Transmits electrical impulses to cell body
What is myelin sheath made of?
Schwann cells
Lipid and protein
What do Schwann cells do to myelinate a neurone?
Wrap around them so the myelin sheath consists of several layers of membrane and thin cytoplasm from the Schwann cells
What does the myelin sheath prevent?
Movement of ions across the membrane
Where does the movement of ions still occur in a myelinated neurone?
The Nodes of Ranvier
What is called when the action potential jumps from one node of ranvier to another?
Saltatory Conduction
How is impulse conduction different in unmyelinated neurones?
Impulse has to pass through all the membrane instead of jumping from one Node of Ranvier to another
How is the arrangement of Schwann cells and neurones different in an unmyelinated neurone?
Un - Axons in 1 Schwann cell that isn’t wrapped around
Myelinated - 1 Axon surrounded in a Schwann cell that is wrapped around
What happens to the speed of transmission in myelinated neurones?
Increased. means the action potential reaches the end neurone much quicker so there’s a more rapid response to a stimulus.
What happens to the distance travelled by the impulse in myelinated neurones?
Carry impulse much further, from sensory receptors to CNS to effectors
What are non-myelinated neurones normally used for?
Carry action potentials over short distances. Normally coordinating body functions like breathing and actions of the digestive system.
When is a neurone at resting potential?
When there is no impulse
What does a neurone being polarised mean?
Inside the neurone is negative with regards to the outside (about -70 mV)
What does the sodium potassium pump do at resting potential?
ATPase uses ATP energy to actively transport 3Na+ ions out of the neurone and 2K+ into the neurone
Why is the membrane more permeable to, K+ or Na+?
K+, there are more channel protein molecules for K+ ions than for Na+ ions
What does the membrane being more permeable to K+ cause?
More K+ diffuses out then Na+ diffuses in (facilitated diffusion)
What are the 2 types of channel that allow K+ and Na+ to diffuse through?
Always open channels and voltage-gated channels
Which directions are potassium ions pumped?
Into axon
Which directions are sodium ions pumped?
Out of axon
What else contributes to the negative charge?
Negative ions and negative proteins
What is the resting potential of the axon?
-70mV
What are the stages of an action potential?
Resting potential
Depolarised
Hyperpolarised
Repolarised
How does an axon become depolarised?
Voltage gated Na+ channels open.
Na+ ions diffuse into the axon by facilitated diffusion until they reach +40mV
How does an axon become hyperpolarised?
Voltage-gated Na+ channels close, voltage-gated K+ channels open.
K+ ions diffuse out of the axon by facilitated diffusion so axon becomes more negative than at resting potential (hyperpolarised)
How does an axon become repolarised?
K+ and Na+ pump returns change to resting potential
Is an impulse passing along the axon during an action potential?
Yes
What initiates an action potential?
Stimuli
How is the impulse transmitted along an axon?
Local reversal of charge
What is the refractory period?
Follows an action potential, Na+ voltage-gated channels are closed so another impulse cannot be generated/conducted.
Resting potential needs to be restored by K+ and Na+ ions being redistributed
Why is a refractory period important?
Ensures impulses are separate
Ensures impulses pass in one direction only.
When is a threshold level reached?
When a certain number of sodium ions have moved into the axon
What happens when a threshold level is reached?
Voltage-gated sodium channels open.
More sodium ions move into the axon
What is the sodium ions entering the axon and causing voltage-gated sodium channels to open an example of?
Positive feedback
What is the all or none principle?
A stimulus has to be at/above a threshold level for an action potential to be made.
Past the threshold level, an action potential is always the same size.
What factors speed up action potential conduction?
Myelination
Large axon diameter
Higher temperature
How does myelination speed up action potential conduction?
Insulation of axon allows for faster conduction.
Longer local circuits
How does a large axon diameter speed up action potential conduction?
Less resistance to the flow of ions when larger diameter.
Less resistance means depolarisation reaches other parts of the neurone cell membrane quicker
How does a higher temperature speed up action potential conduction?
Ions diffuse faster at higher temperature but, like proteins, channels will denature above 40 degrees.
What is the definition of synaptic cleft?
Gap separating the axon of one neurone from the dendrite of another. 20-30nm across.
What is the definition of Presynaptic neurone?
Neurone along which the impulse has arrived
What is the definition of postsynaptic neurone?
Neurone that receives the neurotransmitter
What is the definition of synaptic knob?
The swollen end of the presynaptic neurone. It contains many mitochondria and large amounts of ER to enable it to manufacture the neurotransmitter.
What is the definition of synaptic vesicles?
Vesicles containing neurotransmitters. They fuse with the presynaptic membrane and release their contents into the synaptic cleft.
What is the definition of neurotransmitter receptors?
Receptor molecules that the neurotransmitter binds to in the post synaptic membrane
What are the 2 types of neurotransmitter?
Excitatory
Inhibitory
What are excitatory neurotransmitters?
Neurotransmitters that result in the depolarisation of the postsynaptic neurone. If the threshold is reached in the post-synaptic membrane, an action potential is triggered. Eg Acetylcholine.
What are inhibitory neurotransmitters?
Neurotransmitters that result in the hyperpolarisation of the post synaptic membrane. Prevents an action potential being triggered. Eg Gamma-aminobutyric acid (GABA) - found in some synapses in the brain.
What is summation?
Each stimulus causes the release of a certain amount of neurotransmitter. A single impulse may not release enough neurotransmitter to trigger an action potential so more than one impulse is needed.
What are the 2 types of summation?
Spatial
Temporal
What is spatial summation?
A number of presynaptic neurones connect to one postsynaptic neurone. Each releases neurotransmitter which builds up to trigger an action potential
What is temporal summation?
When a single presynaptic neurone releases neurotransmitter as a result of an action potential several times over a short period. This builds up in the synapse until the quantity is enough to trigger an action potential
What are the roles of a synapse?
Ensure impulses are unidirectional
A single stimulus creating a number of simultaneous responses.
Stimuli from different receptors interacting to produce a single result.
How does a synapse create a single stimulus creating a number of simultaneous responses.
An impulse from one neurone to be transmitted to a number of neurones at multiple synapses.
How does a synapse have a stimuli from different receptors interacting to produce a single result.
Number of neurones may feed into 1 synapse with a single postsynaptic neurone
How does a synapse ensure that an impulse is unidirectional?
Neurotransmitter receptors are only on the postsynaptic membrane.
What are the 2 effects drugs can have on synapses?
Stimulation
Inhibition
How can drugs cause stimulation?
Mimicking the shape of a neurotransmitter
Stimulating the release of more neurotransmitters
Inhibiting enzymes responsible for breaking down neurotransmitters
How does mimicking the shape of a neurotransmitter cause stimulation of a synapse?
Bind to neurotransmitter receptor on postsynaptic membrane and trigger action potentials.
What is an example of a drug that stimulates the release of neurotransmitters?
Amphetamines
How does inhibiting enzymes that break down neurotransmitters cause stimulation in a synapse?
Prevents neurotransmitters being broken down so they stay in the synapse longer
What are the 2 ways to inhibit nervous stimulation?
Blocking receptors
Binding to specific receptors
How does blocking receptors inhibit nervous stimulation?
Neurotransmitters can no longer bind and activate the receptor
How does binding to specific receptors inhibit nervous stimulation?
Changes shape of receptor so active site isn’t complementary to neurotransmitter
