6 Responding to Change- Nervous Coordination Flashcards
What are neurones and the 3 main types? (+ description)
Neurones= cells that transmit information from receptors to effectors
Sensory neurones- carry nervous impulses from receptors into CNS
Motor neurones- carry impulses from CNS to effector organs (eg muscle/glands)
Relay neurones- intermediate neurones, receive impulses from sensory neurone & relay them to motor neurones
What is the basic structure of neurones?
-Can be myelinated/non-myelinated
-Dendrites; carry nervous impulse towards cell body
-Axons; carry nervous impulse away from cell body
-Cell body; where nucleus is normally located
What is the structure of myelinated motor neurones?
-Motor neurones in vertebrates= usually myelinated
-Schwann cells= wrapped around axon of neurone, form myelin sheath
-Nodes of Ranvier= gaps between adjacent Schwann cells
What is resting potential?
When a neurone hasn’t been stimulated
Why is there a potential difference at resting state?
-At resting potential—> diff in charge across neurone membrane: inside neurone more negatively charged than outside, as there are more positive ins outside cell than inside
-Diff in charge= potential difference
What is the resting potential maintained by and how?
-Resting potential maintained by sodium-potassium pumps in neurone membrane
-3 Na+ ions are actively transported out of neurone by pumps for every 2 K+ ions transported in
-This leads to build-up of positive ions outside of cell
How do potassium ion channels in the neurone membrane affect the sodium ions?
-Potassium ion channels are in neurone membrane—> it’s permeable to K+ ions
-When K+ ions are transported into neurones, can diffuse back
-Neurone membrane—> also impermeable to Na+ ions so ions can’t diffuse back into cell after they’ve been transported out
What actions establish the resting potential?
-Together, action of sodium-potassium pumps & potassium ion channels lead to potential diff across neurone membrane—> called resting potential (about -70mV)
-Neurone is said to be polarised
When does repolarisation happen?
When a resting neurone is stimulated, its membrane experiences a change in potential difference
What happens when a neurone is stimulated?
-Na+ ions channels in cell membrane open when neurone is stimulated
-Na+ ions flood into neurone
-Potential difference across membrane changes, becomes more positive inside neurone
How does depolarisation occur and what happens as a result?
-If potential diff increases above threshold value (about -55mV) then membrane becomes depolarised
-More sodium channels open and there’s a sharp increase in potential difference to about +30mV
Why is depolarisation called an all-or-nothing response?
-If potential diff reaches threshold, depolarisation always takes place & charge in potential diff will always be the same
-If stimulus= stronger, action potentials will be made frequently but size won’t increase
What is the process of repolarisation?
-After neurone has been depolarised to +30mV, sodium ions channels close & potassium ion channels open
-K+ ions transported back out of neurone, potential diff becomes more negative—> repolarisation
How does hyperpolarisation happen and what is the refractory period?
-Short period after repolarisation of neurone where potential diff becomes slightly more negative than resting potential—> hyperpolarisation
-Hyperpolarisation Prevents neurone from being restimulated instantly—> refractory period
What occurs after the refractory period?
-Potassium ion channels close, membrane returns to resting potential
The process where neurone= depolarised, returns to resting potential—> action potential
What is an action potential?
Stages involved in depolarisation of neurone membrane
Move along neurone in a wave
What happens when an action potential is generated?
-When action potential is generated, there’s more Na+ ions inside neurone than outside.
-Some of the Na+ ions diffuse sideways along neurone axon.
Action potential: How does a part of the neurone become depolarised?
-Presence of Na+ ions creates change in potential difference further along neurone membrane.
-If this reaches threshold value, sodium ion channels at this membrane part open.
-Na+ ions diffuse into neurone.
-This part of the neurone becomes depolarised.
Action potential: How does a wave of depolarisation and refractory period occur?
-Na+ diffuse all along neurone in this way.
-Depolarisation takes place along neurone membrane; creates a wave of depolarisation.
-The period of hyperpolarisation in action potential= refractory period, ion channels recovering here
-This means an action potential cannot be stimulated again instantly.
-Ensures wave of depolarisation travels in 1 direction.
How does myelination speed up transmission of nerve impulses?
- Schwann cells wrap around axon of neurones to create a myelin sheath, which acts as an electrical insulator as it’s impermeable to ions (Na+ & Ka+).
- Depolarisation & action potentials can’t occur at myelinated parts of axon, only in gaps between (nodes of ranvier)
- The nervous impulse jumps from one node to next → saltatory conduction
How does temperature speed up the transmission of nerve impulses?
- Increase in temperature → increase in kinetic energy
- Ions move across membrane more rapidly with more kinetic energy
How does axon diameter speed up transmission of nerve impulses?
- Giant axons → found in giant squid, allow it to have rapid escape respond
- Greater axon diameter = greater surface area for movement of ions across cell membrane
What is a synapse?
A junction between 2 neurones (eg relay) or between a neurone & effector (eg motor neurone & muscle cell)
What is a synaptic cleft and its use?
-A gap between the cells in a synapse
-When an action potential reaches a synapse,it must be transmitted across it
What is the presynaptic neurone & its use?
-Neurone before synapse
-When action potential reaches end of neurone, its transmitted across presynaptic membrane to postsynaptic membrane or to effector cell
What is the synaptic knob and its uses?
-End of axon of the presynaptic neurone
-Swelling, contains synaptic vesicles
-Location where nerve impulse is transmitted across synaptic cleft
-Lots of mitochondria here; lots of energy needed to synthesise neurotransmitters
What are synaptic vesicles and their uses?
-Located in synaptic knob
-Contains neurotransmitters
-Fuse w/ presynaptic membrane, release neurotransmitters into synaptic cleft
What are neurotransmitters and their uses?
-Chemicals allowing action potential to be transferred across synapse
-When are released from synaptic vesicles into synaptic cleft, bind to specific receptors on postsynaptic membrane
What is the postsynaptic membrane and its use?
-Membrane of postsynaptic neurone/effector cell
-Its receptors have complementary shape to neurotransmitters released from synaptic knob
-When neurotransmitters bind to their receptors, action potential continues
-Only receptors on here; ensures nerve impulses only moves in 1 direction
What is the function of excitatory neurotransmitters? + eg
-Generate action potential in postsynaptic cell
-When they bind to receptors on postsynaptic membrane, membrane is depolarised
Eg- when acetylcholine binds to receptors on postsynaptic membrane in CNS; action potential is established
What is the function of inhibitory neurotransmitters? +eg
-Prevent action potential from being generated in postsynaptic cell.
-When neurotransmitters bind to receptors on postsynaptic membrane, membrane= hyperpolarised.
E.g. when acetylcholine binds to receptors on postsynaptic membrane in heart, potassium ion channels are open in membrane; prevents action potential from being established.
What is summation and its 2 types?
-Process where neurotransmitters from multiple neurones are summed together to produce a response.
-Spatial & temporal summation
When does spatial summation occur and how?
-Takes place when multiple presynaptic neurones form junction w/ single neurone
-Each presynaptic neurone releases neurotransmitters. Overall= many neurotransmitters binding to receptors on 1 postsynaptic membrane.
-Together, neurotransmitters can establish generator potential that reaches threshold value, action potential is generated.
When does temporal summation occur and how?
-Takes place when multiple nerve impulses arrive at same synaptic knob within short period of time.
-More neurotransmitter released into synaptic cleft—> more neurotransmitter available to bind to receptors on postsynaptic membrane.
-Together, neurotransmitters can establish generator potential that reaches threshold value, action potential is generated.
What is a neuromuscular junction and its use?
-A synapse between a motor neurone & muscle cell
-An action potential is transmitted across the synapse using the neurotransmitter acetylcholine
Action potential being transmitted across synapse using acetylcholine 1; What does the arrival of an action potential at the synaptic knob cause?
-Action potential arrives at synaptic knob at end of motor neurone
-Action potential depolarises membrane of synaptic knob. Causes voltage-gated calcium (Ca²+) ion channels to open
-Ca²+ ions diffuse → synaptic knob
Action potential being transmitted across synapse using acetylcholine 2; What causes acetylcholine to be released and what is this process called?
- Ca²+ ion concentration inside synaptic knob start to increase
- causes synaptic vesicles to more & fuse w/ presynaptic membrane
- acetylcholine (neurotransmitter inside vesicles) released → synaptic cleft
- this = exocytosis
Action potential being transmitted across synapse using acetylcholine 3; what happens as a result of acetylcholine binding to receptors, how can an action potential be generated?
-Acetylcholine binds to specific receptors (nicotinic cholinergic receptors) on postsynaptic membrane
- binding of neurotransmitters opens sodium ion channels in postsynaptic muscle cell
- as Na+ ions diffuse → cell, membrane= depolarised
- if potential difference reaches threshold value, action potential generated + flows along motor cell
Action potential being transmitted across synapse using acetylcholine 4; How is acetylcholine removed and why is this important?
- acetylcholinesterase (AChE) enzyme breaks down acetylcholine in synaptic cleft
- products of break down reabsorbed by presynaptic neurone & reused to synthesise more acetylcholine
-It’s important that acetylcholine = removed from receptors as this stops action potentials from being continuously generated in postsynaptic cell
What are cholinergic synapses?
Synapses that use acetylcholine as a neurotransmitter
How do cholinergic synapses and neuromuscular junctions differ in terms of type of postsynaptic cell?
Cholinergic synapses = between 2 neurones
Neuromuscular junctions = between motor neurone & muscle cell
How do cholinergic synapses and neuromuscular junctions differ in terms of number of receptors?
Less receptors in postsynaptic membrane at cholinergic synapse than at neuromuscular junction
How do cholinergic synapses and neuromuscular junctions differ in terms of type of response?
- Cholinergic synapse can trigger inhibitory/ excitatory response in postsynaptic membrane
- action potential at neuromuscular junction always triggers excitatory response in muscle cell
How do cholinergic synapses and neuromuscular junctions differ in terms of result of depolarisation?
Cholinergic synapse = depolarisation of post synaptic membrane results in action potential
Neuromuscular junction = depolarisation of postsynaptic membrane results in muscle contraction
Where is acetylcholinesterase stored in the cholinergic synapses vs the neuromuscular junctions?
Cholinergic synapses - enzyme located in synaptic cleft
Neuromuscular junction - enzyme stored in clefts in postsynaptic membrane
What do excitatory drugs do?
Stimulate nervous system, producing more action potentials on post-synaptic membrane
How can excitatory drugs mimic neurotransmitters? + example
Drugs w/similar shape to neurotransmitters can mimic their function;
-They bind to receptors on postsynaptic membrane → produce action potential
-The drugs are called agonists
-Eg nicotine can bind to nicotinic choinergic receptors in brain to mimic acetylchoire
How can excitatory drugs inhibit enzymes? + example
-Drugs can bind → enzymes = prevents breakdown of neurotransmitter, which would continue to generate action potential in postsynaptic membrane
- eg. nerve gas inhibits acetylcholinesterase, stops breakdown of acetylcholine → loss of muscle control
How can excitatory drugs cause the release of neurotransmitters?
-Drugs can cause presynaptic neurones to release neurotransmitters
-More neurotransmitters → more receptors activated → action potential more likely to be created
What do inhibitory drugs do?
Inhibit nervous system to fewer action potentials produced
How can inhibitory drugs block calcium ion channels & what does this result in?
Drugs can block calcium ion channels in presynaptic membrane → prevent release of neurotransmitters from presynaptic membrane
How can inhibitory drugs block receptors and what does this result in?
Drugs (called antagonists) can block receptors on postsynaptic membrane → neurotransmitters can’t bind & action potential not generated postsynaptic neurone
