Week 4 formative quiz questions Flashcards
All the questions are true/false as they are in the formative quizzes with a subsequent explanation
:)
The depolarising phase of the action potential is mediated by ligand-gated Na+ channels
False. They are Na+ channels, but they are voltage-gated Na+ channels. When the cell reaches threshold of about -55mV, they open and allow Na+ to rush in down its concentration and electrical gradient to cause the fast depolarising phase of the action potential.
The compound action potential recorded in a patient with multiple sclerosis would be predicted to have a smaller A alpha wave but a normal C wave
True. Multiple sclerosis is a demyelinating disease. A alpha fibres are the largest myelinated fibres and would therefore be affected. C fibres are unmyelinated and therefore would no
Interneurones are found only in the peripheral nervous system
False. Whilst the major parts of afferent and efferent neurones extend through the peripheral nervous system, the interneurones are found only the central nervous system. You can think of their job being to look at the sensory information coming in, to decide what to do about it, and to control the motor neurones appropriately
Motoneurones integrate signals from incoming afferent nerves and from descending efferent axons
True - This explains why you can consciously override reflexes, because descending motor information changes the firing patterns of motoneurones in spinal reflex circuits by altering the balance of excitatory and inhibitory synaptic inputs.
It also underpins the process called facilitation which enhances the effectiveness of sensory inputs. If you burn your hand on a hotplate, your biceps stretch reflex would be exaggerated greatly. Here, pain fibre activity facilitates the muscle spindle activity by maintaining nearby a-motoneurones in a more depolarised state
Depolarising blockers at the neuromuscular junction have high affinity and high efficacy at nicotinic ACh receptors
True. They bind to the nicotinic cholinergic receptors on the muscle membrane and activate them. They then keep the muscle in a depolarised sate which prevents it firing further action potentials.
The action of most neurotransmitters is terminated by enzymatic breakdown in the synaptic cleft.
False. The action of most neurotransmitters (eg glutamate, GABA, glycine, noradrenaline, serotonin, dopamine, histamine) is terminated by uptake into neurones or glia. ACh and the peptides are the exceptions which are inactivated by enzymatic breakdown
The effects of the sympathetic and parasympathetic systems are always antagonistic
False. They are often are, but some targets are only innervated by one division of the autonomic nervous system (eg the vast majority of blood vessels are only innervated by the sympathetic system), and on some occasions where there is dual innervation the effects are complementary (the classic example is the reproductive tract)
Inhibitory postsynaptic potentials can be generated by Cl- channels or by K+ channels.
True. The equilibrium potential for Cl- is -75mV and the equilibrium potential for K+ is -90mV. So if a cell is sitting at a resting membrane potential of -70mV, a transmitter opening ligand-gated Cl- channels or ligand gated K+ channels, will hyperpolarise the cell, take it away from its firing threshold, and inhibit it
Concerning smooth muscle: Smooth muscle is exclusively dependent on extracellular Ca2+ for contraction
False. Contraction in smooth muscle is triggered by an increase in cytosolic Ca2+ concentration but this Ca2+ can come from extra cellular sources (eg via voltage-gated Ca2+ channels in the cell membrane), or from intracellular stores
Concerning skeletal muscle: It fails to relax if the [ATP] falls well below normal.
True. And this explains the phenomenon of rigor mortis
The function of the initial segment is to determine when a neurone fires an action potential
True - This region has the highest density of voltage-gated Na+ channels and is therefore the important site in determining if membrane potential of a cell has reached threshold
Gamma amino-butyric acid (GABA) is the principle inhibitory transmitter in the central nervous system.
True. GABA acts on ionotropic and metabotropic receptors to generate fast and slow inhibitory postsynaptic potentials throughout the brain. Glycine seems to do the same job in the spinal cord
A drug with a high affinity but zero efficacy is described as an agonist
False. A drug that has a high affinity (ie binds to the receptor) but does not activate it (ie has a low efficacy) would be described as an antagonist.
Ionotropic receptors evoke fast postsynaptic potentials and metabotropic receptors evoke slow postsynaptic potentials
True. Ionotropic receptors have an integral ion channel so there is a very short delay between the neurotransmitter binding and the channel opening. Metabotropic receptors have no integral ion channel and instead have to persuade a G protein to gate the channel for them. This takes time. Hence, you can get fast and slow EPSPs and IPSPs.
Concerning skeletal muscle: Hydrolysis of ATP by myosin energises cross-bridges, providing the energy for force generation
True. ATP is used to energise the cross bridge
A stronger stimulus causes a larger action potential
False. Action potentials are “all or none”, and once one is evoked at threshold, they are all approximately the same amplitude. ie they cannot encode stimulus intensity (whether that is pressure on a sensory receptor, or amount of transmitter released at a synapse) in their amplitude
G protein coupled receptors linked to phospholipase C (PLC) produced cAMP as a 2nd messenger which regulates the activity of protein kinase A.
False. G protein coupled receptors linked to adenylyl cyclase produce cAMP as a 2nd messenger which regulates the activity of protein kinase A. The PLC-coupled ones produce inositol trisphosphate (IP3) and diacylglycerol (DAG) as 2nd messengers
In the central nervous system, a single EPSP is unlikely to reach threshold
True. In the CNS the EPSP evoked at a single synapse is likely to be in the order of 1-5mV. It is therefore not going to let the cell reach threshold. Instead, summation of EPSPs from many synapses is required. This is the concept of synaptic integration. Note the situation is very different at the neuromuscular junction in the peripheral nervous system
The equilibrium potential for an ion occurs when the concentration gradient for the ion is matched by an equal and opposite electrical gradient
True. I could not have put it better myself
Large diameter axons conduct electrical potentials better than small diameter axons
True. Large diameter axons have a lower axial resistance than small diameter axons. That means current can flow passively further along the axon, ie they decay slower so you can spread your voltage-gated Na+ channels out further along the membrane ad still have them reach threshold.
Concerning smooth muscle: Relaxation of smooth muscle occurs through the action of myosin light chain kinase.
False. Activation of myosin light chain kinase (also known as CamKinase II) causes contraction of smooth muscle
Postsynaptic potentials are generated by voltage-gated channels
False. Postsynaptic potentials, an example of a graded potential, are generated by ligand-gated channels. The neurotransmitter is the ligand that binds to receptors on the postsynaptic membrane and gates the channel.
Precision in localizing a stimulus is greatly increased by lateral inhibition
True - Lateral inhibition allows neurones to inhibit their parallel neighbours. The sensory neurones most stimulated at the centre point of a stimulus on the skin inhibit their neighbours most and this helps to sharpen localisation of the stimulus
