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Neuroscience
Any of the sciences that deal with the functions of the human nervous system and brain -- perception, memory, consciousness and learning.
1,771 Questions
In muscle contraction and impulse conduction, important ions include calcium (Ca2+), sodium (Na+), and potassium (K+). Calcium plays a key role in triggering muscle contraction by binding to troponin, sodium influx starts the action potential at the synapse, while potassium efflux helps repolarize the membrane after the action potential passes.
What is the primary action during depolarization of an action potential?
Sodium ions flow into the neuron via voltage-gated sodium ion channels, driving the membrane potential into the positive. Beyond the threshold, more sodium ion channels are opened, causing the influx of sodium further downstream, and the process repeats, propagating the action potential down the axon.
What happens when a resting neuron's membrane depolarizes?
When a resting neuron's membrane depolarizes, it becomes more positive due to an influx of positively charged ions like sodium. This change in membrane potential triggers an action potential, leading to the propagation of electrical signals along the neuron.
What goes on when an action potential is transferred from one neuron to the next through a synapse?
When an action potential reaches the axon terminal of the presynaptic neuron, it triggers the release of neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic neuron, leading to changes in its membrane potential. This process either excites or inhibits the postsynaptic neuron, depending on the neurotransmitter and receptor type involved.
What part of the of the neuron receives impulses?
The dendrites of a neuron receive impulses from other neurons and transmit them to the cell body.
How does the spinal column work with the nervous system?
The brain generates efferent signals for the body.
Efferent signals travel down the spinal cord, and out to target areas of the body.
Afferent feedback signals travel back to the spinal cord, and back up to the brain for processing.
What happens to the membrane potential of a neuron during an action potential?
1. A neurotransmitter (NT) released from another cell (or in some cases the same cell) will diffuse across the synaptic cleft and bind to a recipient receptor.
2. The receptor will then change it's permeability to certain ions in the extracellular fluid, allowing the ions to flux into the cell (the exception here would be pharmacological agents designed to occupy the receptor without leading to a conformation change)
3. The influx of ions will alter the membrane potential. If the NT is inhibitory (e.g. GABA), then the GABA receptor that it binds to will increase its permeability to negatively charged ions (chloride) and thereby lower the local resting membrane potential (which is normally -70mV). If the NT is excitatory (e.g. glutamate) then the glutamte receptor (AMPA or NMDA) will increase its permeability to positively charged ions (sodium) which will increase the resting membrane potential from -70mV.
4. If enough NTs bind then the local membrane potentials will summate - and in the case of excitatory NTs - cause the membrane potential to change (by opening of voltage-gated ion channels) to around 0-20mV leading to an action potential
5. The action potential, which is generated in an 'all or none fashion' at the axon hillock, will then propagate all the way down the axon to the axon terminal causing the release of stored NTs (although not all NTs are stored - e.g. NOS)
6. NTs released from the presynaptic cell will then diffuse across the synaptic cleft and bind their postsynaptic receptor (normally located on a dendrite, although also located on the cell body themselves) and the whole process starts all over again
During repolarization, potassium channels open and potassium ions exit the cell, causing the inside of the cell to become more negative. This process restores the cell's resting membrane potential. It follows the depolarization phase, where sodium channels open and sodium enters the cell, causing the inside of the cell to become more positive.
The potential benefit lost by choosing a specific action from 2 or more alternatives?
The potential benefit lost by choosing a specific action from 2 or more alternatives is known as opportunity cost. It refers to the value of the next best alternative that is forgone when a decision is made. Understanding opportunity cost helps in making more informed decisions by considering the trade-offs involved in choosing one option over another.
WHAT system works along with the nervous system?
1) The endocrine system works with the NS (via the hypothalamus and pituitary)
2) The musculoskeletal system works with the NS (via motor neurons)
3) The cardiopulmonary system works with the NS (via the sinoatrial node of the heart interfacing with cardiac muscle)
Which cells cause resting membrane potentials to continually depolarize?
Cells with unstable resting membrane potentials, such as pacemaker cells in the heart or neurons in the brain, can continually depolarize due to the presence of a "funny" current (If) that slowly depolarizes the cell until it reaches the threshold for an action potential to be generated.
Yes, Vyvanse (lisdexamfetamine) has been associated with an increased risk of seizures in some individuals, especially those with a history of seizures or other predisposing factors. It is important to talk to your healthcare provider if you have concerns about this risk when using Vyvanse.
Where do upper neurons descend on lower neurons?
Movement is controlled by motor neurons that innervate muscles. Motor neurons can be classified by their location as upper motor neurons or lower motor neurons.
Upper motor neurons have cell bodies in the somatosensory and motor cortex of the brain that send axons down to the spinal cord or brainstem. Upper motor neurons descend through the posterior limb of the internal capsule in the cerebrum, through the crus cerebri of the midbrain, through the basilar pons, through the medullary pyramids, crossing midline at the pyramidal decussation in the caudal medulla, and descending through the anterior and lateral corticospinal tracts of the spinal cord to terminate at their respective ventral horn levels. Corticobulbar fibers are upper motor neurons that innervate brainstem nuclei for cranial nerves. They descend through the genu of the internal capsule of the cerebrum to various brainstem cranial nerve nuclei or reticular formation nuclei that innervate brainstem cranial nerve nuclei.
Lower motor neurons have cell bodies in the ventral horns throughout the spinal cord. These motor neurons receive excitation information from the upper motor neurons as well as a large amount of modulating input from a variety of other neuronal sources. For cranial nerves the lower motor neurons are located within the brainstem cranial nerve nuclei: occulomotor nucleus, trochlear nucleus, abducens nucleus, trigeminal motor nucleus, facial nucleus, spinal accessory nucleus, hypoglossal nucleus, & nucleus ambiguous.
Where does many upper motor neurons synapse with lower motor neurons?
Many upper motor neurons synapse with lower motor neurons in the ventral horn of the spinal cord. This is where the cell bodies of lower motor neurons are located, allowing for the direct control of muscle function.
Will a hyperpolarization graded potential lead to an action potential?
No, hyperpolarization graded potentials do not lead to action potentials. Hyperpolarization makes the membrane potential more negative, which inhibits the generation of an action potential by increasing the distance from the threshold potential needed to trigger an action potential.
What is the origin of the sympathetic nervous system?
The sympathetic nervous system has long been recognized as being active in correlation with excitation, but the origin of the term sympathetic was coined by Galen. He identified the sympathetic system as part of the nervous system, noted that the sympathetic chain follows the spinal cord 'in sympathy' and named it as such. It was only much later that Langley in the early 1800's first used the term para-sympathetic and took until Dale and Eccles to discovery something of it's function.
The term octology was introduced 8 March 2010 by Dr. Andrej Poleev in his book of the same title to denominate a new scientific discipline, which should unify morphogenetic linguistics and neurobiology to investigate the development of the words, cognition and behavior.
Reference: A. Poleev. Octology, 2010, ISBN 9781007171184. URL: see related links.
What characterize repolarization the second phase of the action potential?
Repolarization is the phase in which the cell's membrane potential returns to its resting state after depolarization. This is achieved through the efflux of potassium ions from the cell, restoring the negative internal charge. Repolarization is essential for maintaining the cell's ability to generate subsequent action potentials.
How does a neuron restore a membrane potential following the generation of an action potential?
The hyperpolarization of the membrane potential relative to the resting potential (the undershoot) causes voltage-dependent Potassium conductance (and any Sodium channels not yet inactivated) to turn off, allowing the membrane potential to return to resting level.
What is the name of suicide bag of the cell?
Lysosome contain digestive enzymes for almost all type of organic material. If their covering membrane breaks as it happens during injury to cell, the digestive enzymes will spill over cell content and digest the same. As lysosomes are organelles which on bursting can kill cells possessing them ,they are called suicide sacs.
-70 mV, or -70 millivolts, is a unit of measurement used to quantify electrical potential difference. It represents a negative charge or voltage. In biological systems such as neurons, -70 mV is a common resting membrane potential.
What does ach do at a neuromuscular junction?
ACh (acetylcholine) binds to receptors at the NMJ (neuromuscular junction) to induce contraction of muscle.
What is the hyperpolarization that occurs after repolarizing phase of action potential?
Hyperpolarization occurs because some of the K+ channels remain open to allow the Na+ channels to reset. This excessive amount of K+ causes hyperpolarization so the Na+ channels open to bring the potential back up to threshold.
What is the purpose of the action potential?
An action potential can also be called a nerve impulse which is known to be stimulated by an external stimuli or upon internal excitation.
This action potential travels through a neuron and involves charged ions (the key ones are sodium ions and potassium ions) that cross the membrane barrier of the neuron.
In the longitudinal section of the axon of the neuron (the part that carries the signal which may be covered in Schwann cells to protect the it) the action potential cycle occurs.
There are four main stages: The Resting Membrane Potential, Depolarization, Repolarization, and the Refractory Period.
In the Resting Membrane Potential Stage there is an active force that maintains the resting membrane potential at -70 mV. This active force is the Sodium Potassium Pump where three sodium ions leave the nerve cell and two potassium ions enter. With the Sodium Potassium Pump, it transports these ions actively and so ATP is required. In addition to the Sodium Potassium Pump, there are voltage-sensitive potassium slow leak channels that are involved with passive transport and there are also voltage sensitive sodium gates that are passive sodium channels. They are normally impermeable to sodium however it can't pass through unless there is an electrical current to open it.
In the Depolarization Stage, an external stimuli occurs altering the tertiary structure of sodium gates allowing the nerve cell membrane to become more permeable to sodium than potassium. Therefore, sodium floods in passively making the extracellular fluid (ECF) more negative and the intracellular fluid (ICF). Now the voltage inside the cell is +50 mV compared to the previous stage where it was -70 mV.
Once the cell has reached a voltage of +50 mV, sodium gates close and so the inflow of sodium ions into the cell are discontinued. Because of the altered concentration gradient of ions in the Depolarization Stage, it causes the potassium channels to alter their shape. As a result, there is an inflow of potassium ions outside of the cell and the inside becomes negative again. This stage is known as the Repolarization Stage. This prevents the signal from going backwards. The voltage inside the cell is now at -80 mV.
In the last stage, Refractory Period, the Sodium Potassium Pump actively re-establishes the resting membrane potential. It takes time to reestablish the sodium and potassium concentrations to -70 mV.
Please note that depolarization cannot occur until the resting membrane potential is reached (-70 mV).
As an aside, the action potential follows the All or None Principle. This means that larger signals do not create larger action potentials. A neuron must always reach -70 mV before the signal is passed along a neuron. Therefore, the action potential will occur fully or not at all.
The action potential is an electrical event occurring when a stimulus of sufficient intensity is applied to a neuron or muscle cell, allowing sodium to move into the cell and reverse the polarity.
Normally neurones (neurons, or nerve cells) maintain a resting potential of -70mV across their membrane by the active pumping of 3Na+ ions out of the cell for every 2 K+ ions pumped into the cell by a Na+/K+ pump. When the neurone is stimulated, sodium ion channels open in the membrane and sodium ions flood in to the cell down an electrochemical gradient by diffusion, increasing the potential of the cell to +40mV. This is called depolarisation. At this point the sodium channels close, and potassium ion channels open. Potassium ions flood out of the cell down their electrochemical gradient, decreasing the cell's membrane potential. This is called repolarisation. There is a slight overshoot where too many potassium ions diffuse out of the cell, and there is hyperpolarisation where the cell's membrane potential falls below its normal -70mV, but this is corrected and the resting potential is once again restored. This is the sequence of events that makes up a single action potential. Action potentials are transmitted by saltatory conduction in the neurone, and impulses jump from node to node along the axon of the neurone.
Why are most action potentials generated in response to a long stimulus that is above threshold?
Action potentials are generated in response to a long stimulus above threshold because it allows for the full development of the depolarization phase. This prolonged depolarization leads to the activation of voltage-gated sodium channels, triggering the rapid influx of sodium ions and initiating the action potential. A sustained stimulus ensures that the membrane potential remains above threshold for a sufficient time to generate an action potential.
