Graded Potential
What is a Graded Potential
A graded potential is a small, localized change in the membrane potential of a neuron or muscle cell.
What is an action potential?
An action potential is a rapid, large, and transient change in the membrane potential of an excitable cell (such as a neuron or muscle cell).
What is action potential propagation?
Action potential propagation refers to the process by which an action potential travels along the membrane of a neuron or muscle fiber.
What is a chemical synapse?
A chemical synapse is a junction between two neurons or between a neuron and a target cell (such as a muscle or gland cell) where communication occurs via the release of neurotransmitters.
What are the main areas of the cerebral cortex, and what are their primary functions?
Where in a neuron are graded potentials most commonly generated?
Graded potentials are most commonly generated in the dendrites and cell body (soma) of a neuron.
What are the phases of an action potential?
How does an action potential propagate along an unmyelinated axon?
As the action potential depolarizes one segment of the axon, the local change in membrane potential causes adjacent voltage-gated sodium channels to open, triggering depolarization in the next segment.
What are the main components of a chemical synapse?
What is the function of the motor cortex, and where is it located?
The motor cortex is responsible for controlling voluntary movements of muscles. It is located in the precentral gyrus of the frontal lobe, just in front of the central sulcus. The motor cortex is organized in a way that different parts of the cortex control different regions of the body, and the body’s map on the motor cortex is called the motor homunculus.
What is spatial summation in relation to graded potentials?
Spatial summation occurs when multiple graded potentials from different locations on the dendrites or cell body arrive at the axon hillock simultaneously.
How does the membrane reach the threshold for an action potential?
The membrane reaches the threshold for an action potential when a graded potential depolarizes the membrane to a critical level. This critical level, known as the threshold potential, is typically around -55 mV. Once this threshold is reached, voltage-gated sodium channels open, causing a rapid depolarization that leads to the full action potential.
What is saltatory conduction and how does it affect action potential propagation?
Saltatory conduction occurs in myelinated axons, where the myelin sheath acts as an insulating layer, preventing ion flow across the membrane. The action potential "jumps" from one Node of Ranvier (gaps in the myelin) to the next, where there are high concentrations of voltage-gated sodium and potassium channels. This increases the speed of propagation, allowing the action potential to travel much faster compared to continuous conduction in unmyelinated axons.
How does neurotransmitter release occur at a chemical synapse?
Neurotransmitter release occurs when an action potential reaches the presynaptic terminal, causing voltage-gated calcium (Ca²⁺) channels to open. The influx of calcium ions triggers synaptic vesicles to fuse with the presynaptic membrane, releasing neurotransmitters into the synaptic cleft. These neurotransmitters then bind to receptors on the postsynaptic membrane, leading to a response in the postsynaptic cell.
What is the function of the somatosensory cortex, and where is it located?
The somatosensory cortex processes sensory input from the body, including sensations such as touch, temperature, pain, and proprioception (sense of body position). It is located in the postcentral gyrus of the parietal lobe, just behind the central sulcus. Similar to the motor cortex, the somatosensory cortex is organized into a map, known as the sensory homunculus, that corresponds to different body regions.
What is temporal summation in relation to graded potentials?
Temporal summation occurs when a single synapse generates multiple graded potentials in rapid succession.
What is the role of sodium (Na⁺) and potassium (K⁺) ions in generating an action potential?
What is the role of the refractory period in action potential propagation?
The refractory period plays a critical role in ensuring that action potentials propagate in one direction. During the absolute refractory period, the region of the axon that just underwent an action potential cannot fire again, preventing the action potential from traveling backward. The relative refractory period allows the axon to reset, ensuring that the signal only moves forward along the axon toward the axon terminal.
How is the neurotransmitter signal terminated at a chemical synapse?
What is Broca’s area, and what is its role in language?
Broca’s area is located in the frontal lobe, typically in the left hemisphere, and is associated with the production of speech. It helps in the planning and formation of speech, and damage to this area can lead to Broca's aphasia, which causes difficulty in speaking but usually leaves comprehension intact. It is located in the posterior part of the frontal lobe, near the lateral sulcus
What determines whether a graded potential will be depolarizing or hyperpolarizing?
The nature of the graded potential—whether it is depolarizing or hyperpolarizing—depends on the type of ion channels that are activated. If sodium (Na⁺) or calcium (Ca²⁺) channels open, the membrane potential becomes more positive, resulting in depolarization. Conversely, if potassium (K⁺) or chloride (Cl⁻) channels open, the membrane potential becomes more negative, resulting in hyperpolarization.
What is the refractory period and why is it important?
The refractory period is a period during and after an action potential in which the neuron or muscle cell is less responsive or completely unresponsive to further stimulation. It has two phases:
How does axon diameter affect the speed of action potential propagation?
Larger axon diameters generally allow for faster action potential propagation. This is because larger axons offer less resistance to the flow of ions, allowing depolarization to spread more quickly. Smaller-diameter axons have greater resistance to ion flow, which slows the speed of propagation. Myelination also plays a significant role in speeding up propagation, as it increases the efficiency of the signal transmission.
What role do synaptic vesicles play in a chemical synapse?
Synaptic vesicles are small, membrane-bound structures within the presynaptic neuron that store neurotransmitters. When an action potential reaches the presynaptic terminal, these vesicles fuse with the presynaptic membrane and release neurotransmitters into the synaptic cleft. This process is essential for signal transmission between neurons or from a neuron to a target cell.
What is Wernicke’s area, and how does it affect language comprehension?
Wernicke’s area is located in the temporal lobe, typically in the left hemisphere, and is responsible for language comprehension. It helps in understanding spoken and written language. Damage to Wernicke’s area results in Wernicke’s aphasia, a condition where a person may speak fluently and with normal grammar but have difficulty understanding language or producing meaningful speech.