preguntas exámenes Flashcards
Explain what would happen to the passive movement of Na+ ions in these cases:
a) There is a depolarization but the membrane potential is still negative
b) The action potential reaches its maximum peak and the cell voltage is positive
Explain what would happen to the passive movement of Na+ ions in these cases:
a) There is a depolarization but the membrane potential is still negative
When there is a stimulus and Na+ ionic channels open, they will depolarize the membrane. However, if this stimulus is not high enough to open voltage dependent Na+ ionic channels, the influx of Na+ will stop at a certain moment, as its would be a local potential (filled action potential). However, if the threshold is reached, Na+ voltage dependent ionic channels will open and the depolarization in form of action potential could happen. So therefore, it depended on the threshold that the influx of Na+ ionic channels continue or not. Depending on the negativity of the membrane, it will be more excitable or not and therefore an action potential is more or less likely to happen.
b) The action potential reaches its maximum peak and the cell voltage is positive
Na+ ionic channels (voltage-dependent) would close, as at this positive voltage, they are inactivated. Also, at the same time, K+ ionic channels open, so the depolarization stops and now hyperpolarization will happen.
Explain the differences between an action potential and a local potential, according also if the axon is myelinated or not.
A local potential is a failed action potential. This happens when the stimuli is not high enough to reach the threshold voltage, which in deed is the voltage needed to trigger an action potential because all the mechanisms start at this point. An action potential will be triggered without exception when that threshold is reached, as it is the voltage in which Na+ ionic channels open and can depolarize totally the membrane. In the case of myelinated axons, the action potential travels by saltatory conduction as myelin works as a perfect insulator. The current or ion for created in myelinated axons is so effective, that ions don’t get lost along the way. However, in unmyelinated axons, some ions can be lost and therefore, the possibility that the voltage is not the correct to trigger more action potentials is higher.
Neurotransmitters (fill in a table with neurotransmitter, type of receptor, pathway and effect):
- alpha 1
- NMDA
- 5 HT 1
- D2
- GABA A
- alpha 1: adrenaline and noradrenaline; metabotropic, posphatases; IP3 pathway, Ca2+ release
- NMDA: glutamate; ionotropic,mostly Ca2+, but also Na+; slow depolarization, slow influx Ca2+
- 5 HT 1: serotonin; ionotropic (Na+, K+ and Ca2+); depolarization
- D2: dopamine; metabotropic, adenylate cyclase; inhibitory, inhibit a.c., decrease cAMP
- GABA A: GABA; inotropic, Cl-; inhibitory, hyperpolarization
In muscle contraction, what is a tetanus and an incomplete tetanus.
Tetanus is a event that only can happen in skeletal and smooth muscle, not in cardiac muscle cells (at they have a really long refractory period). To understand this event, we need to explain first of all what summation of waves is. Muscle cells are excitable cells, that when an action potential a contraction can happen. Action potentials can not happen at the same time, as they have refractory periods. Unlike this, contraction can we added up, as there is no need to relax before another contraction happens. Therefore, the frequency of actions potentials can make contractions to be separated in time, or not. When there is no relaxation, or a not completed relaxation, another contraction can happen. When the frenzy of action potentials is high and between two contraction there is a little relaxation, we call this incomplete tetanus. A complete tetanus is reached when the action potentials reach their maximum frequency so that between contraction there is no relaxation. Just after some myofilaments contract, other are also stimulate and also contracted.
Mechanisms of regulation in the hypothalamus-hypophysis axis
The hypothalamus and hypophysis axis is the main point in which the endocrine and nervous system interconnect between each other. The communication between each other is mainly mediated by releasing hormones secreated in the hypothalamus and received in the anterior pituitary gland (in the case of the posterior pituitary gland, the stimuli an electrical signal as the axon of the heron originated in the hypothalamus ends up in this gland). This axis has a very complex regulation. Mostly all af the hormones secreted in an organism can create cycle events, as positive or negative feedback mechanisms, that can inhibit or activate the axis to stop or potentiate (respectively)
Definition of positive and negative feedback. Examples.
A feedback system is a biological cycle of events where a condition or stimulus is monitorized and sent to the control center to create a response, which may amplify or inhibit the initial stimulus or the system itself. In a positive feedback, the response increases the original stimulus, whereas in a negative feed-back system, the response is inverse to the original stimulus.
An example of positive feedback is blood clotting. When some platelets are activated, more molecules and chemicals are released into the blood, and consequently, more platelets are activated. This is a cascade reaction in which the effect of one condition (in this case, the effect of one platelet trying to stop the bleeding), activates other adjacent platelets.
As example of negative feedback system is the effect of insulin. The stimulus is the high levels of glucose after a food intake. When these blood levels are monitorized in the organisms, insulin is secreted by the pancreas as a response to lower the glucose levels in blood.
Differences between the contraction of the skeletal muscle and smooth muscle
From one side, the skeletal muscle is a completely voluntary movement (without taking into consideration reflexes), whereas the smooth muscle contraction is totally involuntary. This is due to their nervous innervation. While the skeletal muscle is inverted by the somatic PNS, the smooth muscle is innervated by the autonomic or vegetative PNS. Secondly, the shape and organization of the singles cells are completely different. Smooth muscle cells or myofibers are large and striated, as they have myofibrils inside with miofilaments arranged in sarcomeres. However, myofilaments are not arranged in myofibrils nor sarcomeres in the smooth muscle, so only the skeletal muscles has a striated appearance. Another difference is that in skeletal muscle cells, we find T-tublues, whereas in the smooth muscle cells we find invaginations of the membrane called caveolaes. Both of them increase the surface of the membrane as to allow the excitability. Also, the endoplasmic reticulum is different between these to type of cells. In the skeletal muscle the RE is really big and contains a lot of Calcium. However in the smooth muscle, the RE is smaller and therefore, Ca2+ is mainly taken from the extracellular fluid. Finally, thin myofilament in the skeletal muscle have a regulatory protein called troponin, which is where calcium binds to move the tropomyosin and therefore Strat the contraction cycle. An important difference is that smooth muscle cells (thin filaments) do not have troponin. As a consequence, the tropomyosin (which needs to be moved to Strat the contraction cycle) is not displaced by calcium, but calcium attached to calmodulin.
Brief explanation about the sympathetic and parasympathetic nervous system: neurotransmitters, receptors and length of the pre and post ganglionic neurons
The autonomic nervous system is part of the efferent division of the peripheral nervous system. It is the efferent division of involuntary responses. The sympathetic and parasympathetic have antagonistic responses. From one side, the sympathetic nervous sytem activates the fight or flight response during a danger or need to survival, whereas the parasympathetic nervous system responses are related to a calmed and relaxed state.
Both have a preganglionic and postganglionic neurons, and in both cases, the synapse between these are by acetylcholine and its inotropic nicotinic receptor that depolarizes the postsynaptic neuron. The main difference between the sympathetic and parasympathetic nervous sytem is the length of the neurons and the neurotransmitter released by the postganglionic neuron.
In the case of the sympathetic nervous system, ganglia are located in every spinal cord level, so the postganglionar neuron has normally the same or bigger length that the preganglionar. The main neurotransmitter released by the second neurons is noradrenaline, which activates alfa (1 and 2) or beta (1 and 2) receptors in smooth muscles and glands. However, there is an exception in the case of sweat glands, which have muscarinic receptors for acetylcholine. There is also an exception for the adrenal medulla.
In the case of the parasympathetic nervous system, the neurotransmitter released is always acetylcholine and the receptor is a muscarinic receptor from smooth muscle and glands. In this case, the ganglia are really close to the target organ, or are even in the wall of the organ itself. That is because this part of the vegetative NS has only preganglionic neurons in the brain stem (some in the sacral plexus), and they are very long. They travel through the body until they reach the ganglia, which are normally close to the innervated target cell.
Definition of the membrane resting potential and explain what mechanisms maintain it.
The membrane resting potential is the point of electrochemical equilibrium between the intercellular and extra cellular fluid, in which the first is more negative than the second one. At this point, a cell is able to maintain a more negative interior in relation to the exterior thanks to some mechanisms. It is called resting potential at it referees to the state of no excitation of a cell. In fact, when a cell is excitated by an action potential, the resting potential must be reestablished as to try to excitate another time that membrane.
The resting membrane potential is mainly determined by the permeability of the membrane for K+ and Na+ ions. The equilibrium is reached although concentrations are not equal. At this point, the membrane prevents the flow of ions in favor of their gradient although they are not equally concentrated in both sides of the membrane due to the electric potential that maintain it like this.
The diffusion potential is the chemical gradient. Ions will tend to move by simple diffusion in favour of gradient (from more to less concentrated). The potential or electric gradient is capable of preventing the further movement of ions cross the membrane. K+ is much more abundant inside the cell, so if ionic channels open, there will be an important outflux of these ions. However, this process can be stoped. As K+ go out the cell, the interior is be aiming more and more negative, and the ECF more and more positive. The negative charges inside the cell will prevent more positives charges going outside the cell, and also, so many positive charges outside will repell positive charges coming from inside.
Explain the different types of nervous cells and their functions
Nervous cells are not only neurons. We find also other types. Neurons however are the main nervous cells and are in charge of conducting the actions potentials and generate and receive action potentials.
In the centra, nervous system, apart from neurons, we also find other types of cells. For example astrocytes are highly important in the protection of the CNS. They create the blood brain barrier, which is a key point in the protection of the CNS environment as they create a barrier around blood vessels, as to prevent toxic and damaging substances to affect neurons. These are called podocytes (they have a like feet surrounding blood vessels), but we also find other types such us ependymal astrocytes. Other types of nervous cells are oligodendocytes, which create myelin sheets around the axons of the CNS neurons. Finally, microglial cells are phagocytes that are key for the defence of the CNS. They phagocyte whatever not normal substance that could harm the CNS.
In the peripheral nervous system we find another type of glial cells, a part from neurons. For example, satellite cells wrap the somas of neurons that are in the ganglia. Finally, Schwann cells are individual cells that surround the axons in the PNS and create the myelin sheets to increase the speed thanks to the saltatory conductance.
How is the action potential generated in a neuron without myelin? Which are the main differences with myelinated neurons?
Dendrites are prolongations of the soma of a neuron, where the stimulus is received. If this stimulus depolarizes enough the membrane, the positive charges will reach (traveling trough the soma) the axonic cone, which is the staring point of the action potential that travels through the axon. If the voltage reaches the threshold in this part, the action potential will be transmitted to the whole axon until the axon terminal. In a unmyelinaed neuron, the depolarization of an specific part of the membrane, will create adjacent parts of the membrane to depolarize as well. In this type of conduction (continuous conduction), the action potential happens in all the membrane, in every single ionic channel that is in the path. Unlike this, in myelinated neurons the conduction is much more rapid as not all the parts of the axon are stimulated, but only those that are able to create an action potential because they are in contact with the extracellular fluid. This is called saltatory conduction and happens thanks to cells that create a myelin sheet around the axon. Myelin is a very insulating, so prevents ion flow in the area it covers. In these places, ions from outside and inside are not able to cross the membrane and therefore action potentials are not able to be created. The fact that this insulator created action potentials to be faster is because they also leave some spaces without myelin, called Ranvier nodes. These are unmyelinated ring in the axons that allow the influx or exilic of ions through the membrane. When an action potential happens, the positive ions that will trigger it though all the axon will pass vastly through the insulated areas until the Ranvier nodes, making a saltatory conduction that is much more efficient.
What is the adaptation of a receptor? How many types are there?
A sensory receptor is a cell, tissue or gland, capable of receiving signals and creating action potentials that travel through the afferent nervous system until the CNS where it will be monitorizadme and a response will be made. They adaptation means that, although the stimulus is still existing at the same strength, the electric signals that are sent to the CNS are in decline. Phasic cells can adapt, while tonic receptors do never adapt (for example pain receptors).
Main differences between the autonomic and somatic nervous system.
Both are part of the efferent division of the peripheral nervous system, and therefore, send responses. The main difference between these systems are the consciousness of the acts or responses. While the somatic nervous system is completely voluntary (with the exception of reflexes), the autonomic nervous system, also called vegetative, is completely involuntary. Also, this last one, is divided into other 2 system, the sympathetic and parasympathetic nervous system, which antagonistic responses, as the first one prepares the body for action and for fight or flight responses, and the second one is in charge or relaxing and calming the body.
Other important differences between these two system is their composition. The somatic nervous system is composed by single motor neurons, that release acetylcholine into the neuromuscular junction to active the skeletal muscles. On the other hand, the autonomic nervous system is composed by 2 neurons, the pre and postganglionic. As the name says, ganglia can be found in the VNS (vegetative ns) and the synapse between these neurons is always mediated by acetylcholine. However, the synapse between the postganglionic neuron and the innervated tissue can be mediated by acetylcholine or noradrenaline.
Describe the fluid compartments in the body.
The body is mostly made up by water. In fact, the 70% in male and the 65% in women of the weight correspond to water. Water trough the body is distributed through compartments. 2/3 parts of that total water corresponds to intracellular fluid (inside cells), and the rest, 1/3 in extracellular fluid (outside cells but in the internal environment). This ECF can be plasma or interstitial fluid, which are respectively 20% and 80%.
Difference between local and action potential.
Not every stimulus is able to create an action potential. A threshold needs to be reached as to trigger an action potential and this is due to the presence of voltage dependent ionic channels. When a stimulus depolarizes a membrane, a minimum voltage is requiere to open the voltage dependent ionic channels responsible for creating what we know as an action potential. These are Na+ ionic channels, which open only at the threshold.Once they are opened, the following steps are inevitable. We know that it is an action potential when there is a refractory period and the adjacent parts of the membrane depolarize as well- However, in a local potential, the depolarization only happens in that unique part of the membrane. The stimulus created that some positive charges entered the cell, but the depolarized voltage was not enough to open the voltage dependen Na+ ionic channels that continue the depolarization. It is local as it does not reach the threshold.
