Component 3 - Topic 3.2 - The Nervous System (COMPLETED) Flashcards
(9 cards)
Resting & Action Potentials:
a) What detects a STIMULUS?
b) Why can we describe sensory receptors as TRANSDUCERS?
c) A stimuli creates a SHIFT…or a ___________ where to where? Provide an example using a glass of water.
d) The direction of this shift is ALWAYS in what direction?
a) The stimulus is detected by a sensory receptor (a nerve).
b) Sensory receptors are TRANSDUCERS becasue they detect energy in one form and convert that energy into electrical energy.
c) The stimulus creates a shift/movement in charge down an effector which is what responds to the stimuli…(an example: a stimuli could be a glass of water which is detected and as a result an electrical charge runs down an effector, the muscles, causing a contraction.
d) Movement of charge is always AWAY from the receptor and always moving TOWARDS the EFFECTOR.
Resting & Action Potentials:
a) Zooming into the axon of a neurone you will find that there is CYTOPLASM (Called ___________) that is surrounded by the _______. The movement of charge earlier discussed occurs inside the ____________. This movement of charge _________ the ___________ is called a _______ _________.
b) Concentration of IONS: We mentioned in (a) that a movement of charge within the __________ of a neurone is called a _______ ___________. This moving area of charge is always __________. This is due to TWO __________ charged IONS, ___________ions and _________ions. They’re BOTH found inside the __________. IN general, you shall find that there are ______ of the ions in total on the outsdide of the axoplasm rather than the inside of the axoplasm - thus, the outside is _______ ___________than the inside during RESTING POTENTIAL. To specify further, the concentration of _________ ions during resting potential on the ___________is _________ than on the inside. Despite there being _______________ ions on the outside too, they’re are relatively ________ of them in comparison to the __________ of the AXOPLASM.
d) As the _________ ions MOVE INSIDE the axoplasm, DOWN their ______________ gradient, the inside becomes increasingly ___________. Now, we already know that the inside of the axoplasm contains more ______________ ions, the entry of the ____________ ions causes the axoplasm’s internal charge to rise. Repulsion between the ___ ions and ___ ions causes the ____ ions to go down their ______________ gradient. Therefore moving outside. To maintain the more ___________ charge on the outside, the membrane has a ______-____________ _______. This utilises ATP for _________ _____________ in which 3 _____ ions from the _________ are moved to the ___________ of the axoplasm. Then, once the ‘doors’ of the protein face the outside, 2 _____ions move into the axoplasm and due to ____________change, they protein flips the other way depositing the 2 _____ ions back inside the axoplasm.
a) Zooming into the axon of a neurone you will find that there is CYTOPLASM (Called AXOPLASM) that is surrounded by the AXON. The movement of charge earlier discussed occurs inside the AXOPLASM. This movement of charge INSIDE the AXOPLASM is called a NERVE IMPULSE.
b) We mentioned in (a) that a movement of charge within the axoplasm of a neurone is called a nerve impulse. This moving area of charge is always POSITIVE. This is possible due to TWO positively charged IONS, potassium ions and sodium ions. They’re BOTH found inside the AXOPLASM. IN general, you shall fidn that there are more of the ions in total on the outisde of the axoplasm rather than the inside of the axoplasm - thus, the outside is MORE POSITIVE than the inside during RESTING POTENTIAL. To specify further, the concentration of Na+ ions during resting potential on the outside is greater than on the inside. Despite there being K+ ions on the outside too, they’re are relatively less of them in comparison to the inside of the AXOPLASM.
c) The ions can’t diffuse in an out of the AXOPLASM. Instead, they require specific transmembranal channel proteins that allows for FACILLITATED diffusion to occur. Na+ ion channels allow only Na+ ions to move DOWN their concentration gradient and INTO the axoplasm. K+ channels, similarly, allow K+ ions to diffuse but only OUTWARDS (i.e. down THEIR concentration gradient). We MUST recall that the overall charge outiside is POSITIVE and therefore the overall internal charge is relatively MORE negative. Therefore, we can say that there is a CHARGE gradient for both IONS, more specifically, an electrochemical gradient.
d) As the Na+ ions MOVE INSIDE the axoplasm, DOWN their electrochemical gradient, the inside becomes MORE positive. Now, we already know that the inside of the axoplasm contains K+ ions, the entry of the Na+ ions causes the axoplasm’s internal charge to rise. Repulsion between the Na+ ions and K+ ions causes the K+ ions to go down their electrochemical gradient. Therefore moving outside. To maintain the move positive charge on the outside, the membrane has a sodium-potassium pump. This utilises ATP for active transport in which 3 Na+ ions from the inside are moved to the outside of the axoplasm. Then, once the ‘doors’ of the protein face the outside, K+ ions move in and due to conformational change, they protein flips the other way depositing majority of the K+ ions back inside the axoplasm.
Voltage-Gated Ion Channels:
a) Majority of the ion channels are usually __________ when the neurone is at REST. When a nerve impulse ARRIVES, the movement of ___________ IONS causes the ________ ion channels to OPEN - this is because these specific ion channels are ___________ ACTIVATED! As a result, sodium ions are able to diffuse ACROSS the membrane ________ the AXON (the axoplasm) _______ their ELECTROCHEMICAL gradient. There are some__________-_________ sodium channels and there are some_________-_________ POTASSIUM channels…
Establishing An ________ Potential:
b) When the inside of the axoplasm is at its _______ positive charge, we say an __________ POTENTIAL has been generated. The extreme positive charge causes an __________ to take ACTION.
Reestablishment of Resting Potential:
c) Re-establishing resting potential - In response to the ________positive charge being reached, the _________-__________ Na+ ions ________. Simultaneously, some _____ channels begin to _______ allowing some ______ ions to diffuse _______of the AXON. Over time, the inside becomes _____ POSITIVE as the _____ ions _________ down their electrochemical gradient. However, the voltage gated ____ channels ________ VERY slowly, allowing ____ ions to still escape. This causes a state called ____________________TION. The charge inside the axoplasm is _______ positive than USUAL. The _________-_____________then RESTORES the relative concentrations, bring about RESTING POTENTIAL.
a) Majority of the ion channels are usually CLOSED when the neurone is at REST. When a nerve impulse ARRIVES, the movement of the positive IONS causes the CLOSE ion channels to OPEN - this is because these specific ion channels are VOLTAGE ACTIVATED! As a result, sodium ions are able to diffuse ACROSS the membrane inside the AXON (the axoplasm) down their ELECTROCHEMICAL gradient. There are some voltage-gated sodium channels and there are some voltage gated POTASSIUM channels…
b) When the inside of the axoplasm is at its peak positive charge, we say an ACTION POTENTIAL has been generated. The extreme positive charge causes an effector to take ACTION.
c) Re-establishing resting potential - In response to the max. positive charge being reached, the voltga egated Na+ ions CLOSE. Simultaneously, some K+ channels begin to OPEN allowing some K+ ions to diffuse OUT of the AXON. Over time, the inside becomes LESS POSITIVE as the K+ ions escape down their electrochemical gradient. However, the voltage gated potassium channels close VERY slowly, allowing K+ ions to still escape. This causes a state called HYPERPOLARISATION. The charge inside the axoplasm is less positive than USUAL. The sodium-potassium pump then RESTORES the relative concentrations, bring about RESTING POTENTIAL.
a) What is depolarisation?
b) What is repolarisation?
c) What is hyperpolarisation?
d) As there is a potential difference across the cell membrane, it is described as being?
a) Depolarisation occurs when the voltage gated sodium channels open causing an influx of soidum ions into the axoplasm which INCREASES the positivity within this region. Once the maximum positive value has been reached, an action potential is initiated.
b) Repolarisation occurs when the voltage gated potassium channel opens. This causes potassium ions to go down their electrochemical gradient entering the outside of the axoplasm. Due to the nature of the channel (it closes VERY slowly), potassium ions are able to essentially continue to leak out which eventually causes HYPER-POLARISATION.
c) Hyperpolarisation is the state the axoplasm finds itself in when the inside becomes extremely negative (more negative than usual).
d) Polarised
a) What is the use of an oscilloscope and microelectrode?
b) Why do we say that the area behind an action potential ‘resets’? Why does the nerve do this?
c) The SPEED OF CONDUCTANCE - What do we mean when we use this term?
d) There are 2 features that impact the SPEED OF CONDUCTANCE. Factor one has 2 explainantion points. Explain the draw-back of one of the factors that is supposed to RAISE the speed of conductance.
a) A microelectrode is inserted into the axon. The oscilloscope is a device used to investigate the transmission of nervous impulses. It can show how voltage changes over time.
b) Once the action potential leaves, the area behind the action potential ‘resets’ to a resting potential. This is done so that the nerve can then recieve a new impulse.
c) The ‘speed of conductance’ is the rate at which a nerve transmission TRAVELS…
d)
1.) The first feature is the AXON’s diameter. The larger the diameter, the quicker the speed of conductance. This is becuase the Na+ ions experience LESS resistance moving thorugh the axoplasm. Reason number 2 = the smaller the diameter the MORE K+ diffuse OUT of the axon. This is because the positive particles are in frequent contact in a smaller space and so they repel more. This leads to an increase in K+ ions diffusing down their electrochemical gradient and OUT of the axoplasm meaning it’s HARDER to MAINTAIN resting potential.
2.) TEMPERATURE. The greater the temperature, the greater the speed of conductance. This is because there’s a higher rate of diffusion occuring. Particles possess MORE kinetic energy and move across the AXON FASTER. A draw back to a LARGE temperature is that the resting potential cannot be maintained since ATP synthesis STOPS. This means the sodium-potassium pump is hindered. It can’t utilise ATP to fease active transport.
a) What cells WRAP around the axon to form a….?
b) Every 2nm there are depressions found. What are these depressions formally known as?
c) Where are the voltage-gated Na+ ion channels found? It’s only in this area where an action potential can be generated.
d) What is saltatory conduction?
e) Whta is the purpose of the myelin sheath?
a) Schwann cells wrap around the axon to form the myelin sheath.
b) Roughly every 2nm, there are GAPS. These gaps are exposed, with no myelin sheath wrapped around. These ‘depressions’ are called the ‘Nodes of Ranvier’.
c) Only the exposed parts of the axon contain voltgae-gated Na+ channels (i.e the Nodes of Ranvier). Therefore, an action potential can only be triggered in these regions.
d) Saltatory-conduction is the rapid travel of a nerve impulse across a myleinated axon. Action potenials jump to the adjacent node of ranvier.
e) The myelin sheath acts as an electrical insulator because ions can’t diffuse across the membrane. Na+ ions essentially ‘jump across the non-myelinated region and therefore transmit across the axon at a faster rate.
Myelin SHEETH and Conductance Speed:
a) For myelinated axons SPECFICALLY, there’s 1 additional factor that impacts the ________ __ ______________. Like any cell membrane, the cell membrance of ____________cells comprises of LIPIDS. __________ cells REPEATEDLY _______ around eachother. This essentially, stacks the ________ layers. These layers _____ allow the exchange of charged ____________ as a result (namely in this instance Na+ and K+ ions). Ions cannot therefore ________ or _________the axoplasm via the myelin sheeth. It’s therefore called an __________ __________ (in Greek this term is called ‘insulare’ meaning to make an ‘_________’. By therefore forming areas like this, electrical charges must travel in the ______-_____________ region.
If we look at a ______-___________ axon. It’s clear that an action potential must be generated across the whole length of the axon. The formation of action potentials takes ______! So a myelinted axon allows a reduce number of ________ __________. Results in a GREATER ________ ___ ___________. Because the sodium-potassium pumps only exist at the nodes of ranvier LESS _______ is used.
b) What are the 2 purposes of the absolute refractory period?
c) How does a large stimuli impact the number of action potentials generated? Do more get created or do action potentials increase in their size/magnitude?
a) For myelinated axons SPECFICALLY, there’s 1 additional factor that impacts the speed of conductance. Like any cell membrane, the cell membrance of SCHWANN cells comprises of LIPIDS. Schwann cells REPEATEDLY wrap around eachother. This essentially, stacks the lipid layers. These layers DO NOT allow the exchange of charged particles as a result (namely in this instance Na+ and K+ ions). Ions cannot therefore LEAVE the axoplasm via the myelin sheeth. It’s therefore called an electrical insulator (in Greek this term is called ‘insulare’ meaning to make an ‘island’. By therefore forming areas like this, electrical charges must travel in the non-myelinated region.
If we look at a NON-myelinated axon. It’s clear that an action potential must be generated across the whole length of the axon. The formation of action potentials takes TIME! So a myelinted axon allows a reduce number of action potentials. Results in a GREATER speed of conductance. Because the sodium-potassium pumps only exist at the nodes of ranvier LESS ATP is used.
b) The absolute refractory period is a section of time during which NO new action potential can be generated. The purpose of the absolute refractory period is to ensure UNIDIRECTIONALITY (action potentials only travel in ONE direction), towards the effector! It also allows discrete action potentials (different action potentials cannot merge together).
c) The strength of a stimuli impacts the FREQUENCY of the action potentials generated. A strong stimuli causes a high frequency of action potentials to be generated. A weak stimuli causes LESS action potentials to be generated.
Cholinergic Synapses:
a) What type of chemical synapse is most abundant? Why are cholinergic synapses in particular called ‘cholinergic’? Think about the neurotransmitter found/ involved in these synapses.
b) When an action potential arrives just before the synaptic end-bulb. On the membrane at the start of the synaptic end bulb the Na+ ions enter (influx) due to the opening of the voltage-gated Na+ channels which cause an action potential to generate.
Next to the Na+ voltage channels are Ca2+ voltage gated channels. These open due to the arrival of the action potential to the pre-synaptic end-bulb. Ca2+ ions diffuse down their electrochemical gradient. In a synaptic-end-bulb you shall find VESICLES. Now, specifically in a cholinergic synapse these vesicles contain a neurotransmitter called ACETYL CHOLINE. The initial influx of the Ca2+ ions cause these vesicles to move DOWN to the synaptic end bulb. They fuse with the synaptic membrane (the vesicles do) and via exocytosis they release the acetyl choline neuro-transmitters across the synaptic cleft.
The concentration of acetyl choline molecules is HIGHER near the pre-synaptic membrane than the POST synaptic membrane , acetyl choline molecules diffuse until they reach the Na+ channels on the POST syntaptic membrane. These Na+ channels have TWO RECEPTOR sites. The receptor sites are specific to acetyl choline ONLY. So, when acetyl is present, they bind, triggering these Na+ ion channels to change their shape. The channels OPEN and so Na+ ions diffuse into the POST-synaptic membrane. The synaptic cleft is SHORT in distance and so transmission is RAPID.
c) End of Synaptic transmission - To close the Na+ gates/channels, the acetyl choline molecules are REMOVED by acetylcholinesterase enzyme. Once an action potential is triggered at the POST synaptic membrane, the acetyl choline molecules are PULLED towards the acteylcholinestarase enzyme where they’re boken down into chlline and acetic acid. Water is needed and this is therefore a HYDROLYSIS reaction.
a) A cholinergic synapse is one of the most common types of chemical synapses. They’re referred to as cholinergic synapses because of the neurotrasnmitter found at these synapses called ACETYL CHOLINE.
b) When an action potential arrives just before the synaptic end-bulb. On the membrane at the start of the synaptic end bulb the Na+ ions enter (influx) due to the opening of the voltage-gated Na+ channels which cause an action potential to generate.
Next to the Na+ voltage channels are Ca2+ voltage gated channels. These open due to the arrival of the action potential to the pre-synaptic end-bulb. Ca2+ ions diffuse down their electrochemical gradient. In a synaptic-end-bulb you shall find VESICLES. Now, specifically in a cholinergic synapse these vesicles contain a neurotransmitter called ACETYL CHOLINE. The initial influx of the Ca2+ ions cause these vesicles to move DOWN to the synaptic end bulb. They fuse with the synaptic membrane (the vesicles do) and via exocytosis they release the acetyl choline neuro-transmitters across the synaptic cleft.
The concentration of acetyl choline molecules is HIGHER near the pre-synaptic membrane than the POST synaptic membrane , acetyl choline molecules diffuse until they reach the Na+ channels on the POST syntaptic membrane. These Na+ channels have TWO RECEPTOR sites. The receptor sites are specific to acetyl choline ONLY. So, when acetyl is present, they bind, triggering these Na+ ion channels to change their shape. The channels OPEN and so Na+ ions diffuse into the POST-synaptic membrane. The synaptic cleft is SHORT in distance and so transmission is RAPID.
c) End of Synaptic transmission - To close the Na+ gates/channels, the acetyl choline molecules are REMOVED by acetylcholinesterase enzyme. Once an action potential is triggered at the POST synaptic membrane, the acetyl choline molecules are PULLED towards the acteylcholinestarase enzyme where they’re boken down into chlline and acetic acid. Water is needed and this is therefore a HYDROLYSIS reaction.
Recycling Acetyl Choline:
a) What is the product of the hydrolysis reaction that the enzyme acetylcholinesterase deals with?
b) These COMPONENTS are ___________ by sending them to the synaptic ______ _______where acetyl choline is formed and they’re put into ____________. To achieve this, the choline and ethanoic acid diffuse back to the pre-synaptic _________. Choline is charged as opposed to ethanoic acid. This means to PASS into the PRE-SYNAPTIC neurone via facilitated diffusion, through a transport protein. Ethanoic acid simply _________. Once they reform the acetyl choline neurotransmitter, they’re re-packaged into vesicles using ATP. Therefore, this region is populated with __________________.
a) The product of the hydolysis reaction are choline and ethanoic acid (acetic acid).
b) These COMPONENTS are RECYCLED by sending them to the synaptic end bulb where acetyl choline is formed and they’re put into vesicles. To achieve this, the choline and ethanoic acid diffuse back to the pre-synaptic neurone. Choline is charged as opposed to ethanoic acid. This means to PASS into the PRE-SYNAPTIC neurone via facilitated diffusion, through a transport protein. Ethanoic acid simply diffuses. Once they reform the acetyl choline neurotransmitter, they’re re-packaged into vesicles using ATP. Therefore, this region is populated with mitochondria.
