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Questions and Answers
What channels are responsible for the rapid depolarization during an action potential?
K+ channels close during the absolute refractory period.
False
What happens to Na+ channels after they close during action potential?
They reset to their original position.
Myelinated axons are generally _____ than unmyelinated axons.
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What effect does myelin degeneration have on neuronal function?
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What determines membrane potential in cells?
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What factor influences the speed of action potential propagation in neurons?
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What hormones are involved in endocrine regulation?
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What is the main function of trophic hormones?
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The hypothalamus-anterior pituitary axis involves a portal system.
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Which hormone is released by the anterior pituitary that stimulates growth?
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What is hypersecretion?
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What does hyposecretion mean?
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Changes in membrane permeability do not influence the action potential.
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What primarily determines resting membrane potential?
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Match the following phases of action potential with their characteristics:
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What causes depolarization in the rising phase of action potential?
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What is the threshold potential?
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What happens to Na+ channels during the absolute refractory period?
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Myelinated axons propagate action potentials slower than unmyelinated axons.
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What determines membrane potential in cells?
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Myelin degeneration can result in significant loss of function, such as in the disease _____ .
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Which of the following factors influence the speed of action potential propagation?
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What is the role of graded potential in action potential generation?
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What is the role of trophic hormones in hormonal regulation?
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Which hormone functions to stimulate growth?
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Hypersecretion refers to a deficiency in hormone secretion.
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What impact does myelination have on action potentials?
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Match the following phases of action potential with their descriptions:
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The ______ system provides rapid but short-lasting shifts in physiology.
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What equation is associated with membrane potential?
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Changes in membrane permeability can lead to action potentials.
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Which hormone is primarily associated with the stress response?
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Study Notes
Hypothalamus-anterior pituitary Axis
- The hypothalamus synthesizes and releases trophic hormones into the portal system, which carries them directly to the anterior pituitary.
- The anterior pituitary, upon receiving trophic hormones, releases its own hormones, which are then distributed throughout the body.
Endocrine Pathologies
- Hypersecretion occurs when there is excess hormone secretion due to a loss of feedback regulation or excess hormone production.
- Hyposecretion occurs when there is a deficient hormone secretion due to a loss or deficiency of hormone production.
- Target cell pathologies involve issues with the ability of the target cell to receive or interpret a hormonal signal due to loss of receptors or signal transduction issues.
Homeostasis and Communication
- Negative feedback loops are fundamental for regulating physiological functions by counteracting changes in the system.
- Local communication influences the state of nearby cells via paracrine or autocrine signaling.
- The nervous system provides rapid short-lasting effects on physiology, while the endocrine system produces slower but longer-lasting effects.
- Peptide and steroid hormone permeability across membranes influences their action mechanisms and the speed of their actions.
- Endocrine responses often involve complex cascades that can be regulated at different steps.
Cells of the Nervous System
- Glial cells provide support and maintain the neural environment. They include astrocytes, oligodendrocytes, Schwann cells, and stem cells.
- Neurons are the signaling units of the nervous system, receiving input signals, integrating them, and transmitting output signals via action potentials.
Chemical Disequilibrium
- Sodium (Na+) is highly concentrated outside the cell, while potassium (K+) is highly concentrated inside the cell.
- The membrane permeability of ions plays a critical role in establishing membrane potential.
- The Nernst equation helps to predict the equilibrium potential for a specific ion based on its concentration gradient and permeability..
Resting Membrane Potential
- At rest, the membrane is more permeable to potassium than sodium.
- The resting membrane potential (around -70mV) is mainly determined by potassium permeability.
Phases of the Action potential
- Resting phase: K+ permeability dominates, determining the membrane potential.
- Rising phase (depolarization): Voltage-gated Na+ channels open, allowing Na+ influx and rapid depolarization.
- Overshoot (peak): Na+ inactivation gates close, while K+ channels open, causing a reversal of membrane potential.
- Falling phase (repolarization): K+ flows out of the cell, leading to repolarization.
- Recovery phase (undershoot): K+ channels close slowly, leading to temporary hyperpolarization until resting membrane potential is restored.
Action Potential initiation through positive feedback
- Depolarization triggers the opening of voltage-gated Na+ channels, leading to more Na+ influx and further depolarization.
- This creates a positive feedback loop that initiates the action potential.
- The cycle is terminated by the inactivation of Na+ channels and the opening of K+ channels.
- K+ efflux leads to repolarization, ending the action potential.
Action Potential Propagation
- Action potentials are triggered by local current flow, which is a graded potential.
- The strength of graded potentials depends on the resistance to current flow.
- The rate of action potential propagation depends on the resistance of the axon to current loss.
- Increased resistance to current loss across the membrane maintains signal strength over a longer distance.
Refractory Periods
- During the absolute refractory period, sodium channels are inactivated.
- The sodium channels reset to their original position during the relative refractory period.
- Potassium channels remain open during the relative refractory period.
Propagation Rates
-
Factors influencing the speed of action potential propagation in neurons:
- Diameter of the axon: larger axons are faster.
- Resistance of the axon membrane to ion leakage out of the cell.
- Myelination: Myelinated axons are faster.
Saltatory Conduction
- Action potentials jump between nodes of Ranvier due to myelination.
Myelin Degeneration
- Degeneration of myelin can lead to significant loss of function.
- Diseases associated with myelin degeneration: Multiple Sclerosis, Meylitis, Leukodystrophy.
Review
- Ion concentration gradients and membrane permeability determine membrane potential in cells.
- Dynamic changes in membrane permeability (Na+ & K+) cause the development of an action potential.
- Myelination increases the speed of action potential propagation.
Hormonal Control
- Trophic hormones regulate endocrine hormone release
- Often involved in the hypothalamus-anterior pituitary axis
Hypothalamus-anterior pituitary axis
- Hypothalamus releases trophic hormones through the portal system, which carry hormones directly to the anterior pituitary.
- Anterior pituitary then secretes hormones into the bloodstream, targeting specific organs.
- Key hormones released by the anterior pituitary include:
-
Growth Hormone (GH)
- Stimulates growth and development of the body
-
Adrenocorticotropic Hormone (ACTH)
- Stimulates release of cortisol from adrenal glands
-
Thyroid-Stimulating Hormone (TSH)
- Stimulates release of thyroid hormones
-
Luteinizing Hormone (LH) and follicle-stimulating hormone (FSH)
- Regulate sex hormone production and gamete formation
-
Prolactin
- Stimulates breast growth and milk production
-
Growth Hormone (GH)
Endocrine Pathologies
-
Hypersecretion: Excess hormone secretion due to:
- Loss of feedback regulation
- Excess hormone production
-
Hyposecretion: Deficient hormone secretion due to:
- Loss/deficiency of hormone production
-
Target cell pathologies:
- Loss/down-regulation of target cell receptors
- Disruptions in signal transduction within target cells
Homeostasis and Communication
- Negative feedback control loops regulate physiological function
- Local communication regulates nearby cells
- Nervous system provides rapid and short-lasting shifts in physiology, while the endocrine system produces slower but longer-lasting effects
- Peptide hormones and steroid hormones have different mechanisms of action depending on their membrane permeability
- Endocrine responses often involve complex cascades regulated at various steps
Nervous System
- Afferent neurons carry signals from sensory receptors to the central nervous system
- Efferent neurons carry signals from the central nervous system to muscles and glands
- Central nervous system (CNS) is comprised of the brain and spinal cord
- Peripheral nervous system (PNS) is composed of the nerves that connect the CNS to the rest of the body
Cells of the Nervous System
-
Glial cells support neuron function:
- Astrocytes maintain extracellular fluid.
- Oligodendrocytes (in the CNS) and Schwann cells (in the PNS) produce myelin to insulate axons.
-
Neurons are responsible for transmitting information:
- Dendrites receive input signals.
- Cell body integrates input signals.
- Axon transmits output signals.
- Myelin sheath insulates the axon, increasing the speed of signal transmission.
Chemical Disequilibrium
- Ion concentration gradients across the cell membrane create a membrane potential.
- Membrane permeability determines how readily ions can cross the membrane.
- Nernst equation calculates the equilibrium potential for a single ion based on its concentration gradient.
Resting Membrane Potential
- At rest, the inside of the cell is negatively charged compared to the outside.
- This is due to the higher permeability of the cell membrane to potassium (K+) compared to sodium (Na+).
- Potassium leaks out of the cell, contributing to the negative charge inside.
Action Potential (AP)
- Dynamic changes in membrane permeability to Na+ and K+ cause action potentials.
- Depolarization: Na+ channels open, causing a rapid influx of Na+ ions, making the inside of the cell more positive.
- Repolarization: Na+ channels close, and K+ channels open, allowing K+ to flow out of the cell, restoring the negative membrane potential.
- Undershoot: K+ channels close slowly, leading to a temporary hyperpolarization.
Phases of the Action Potential
- Resting phase: The membrane is at resting potential, determined by K+ permeability.
- Rising phase: Na+ channels open, causing depolarization.
- Overshoot: Na+ channel inactivation gates close, K+ channels open, and the membrane potential reaches its peak.
- Falling phase: K+ flows out of the cell (repolarization).
- Recovery phase: K+ channels close slowly, restoring the resting membrane potential.
AP Initiation
- Positive feedback is essential for AP initiation.
- Depolarization leads to the opening of Na+ channels, which further depolarizes the membrane, leading to more Na+ channels opening.
- This cycle continues until Na+ inactivation gates close, and K+ channels open, allowing K+ to flow out of the cell and repolarize the membrane.
Action Potential Propagation
- The rate of action potential propagation depends on the resistance of the axon to current loss.
- Increased resistance to current loss across the membrane maintains signal strength over longer distances.
- Absolute refractory period: Na+ channels are inactivated and cannot be reopened, no action potential can be generated.
- Relative refractory period: Na+ channels reset to original position, but K+ channels remain open, only a strong stimulus can trigger another action potential.
Propagation Rates
- Speed of action potential in neuron is influenced by:
- Diameter of axon: Larger axons are faster.
- Resistance of axon membrane to ion leakage out of the cell: Myelinated axons are faster.
Saltatory Conduction
- Myelin acts as an insulator, preventing ion leakage.
- Action potentials jump between nodes of Ranvier, increasing speed of propagation.
Myelin Degeneration
- Myelin degeneration can lead to significant loss of function.
- Diseases associated with myelin degeneration include Multiple Sclerosis, Meylitis and Leukodystrophy.
Review
- Membrane potential is determined by ion concentration gradients and membrane permeability.
- Dynamic changes in membrane permeability (Na+ & K+) lead to the development of an action potential.
- Action potentials are triggered by local current flow (graded potential).
- Graded potential strength depends on resistance to current flow.
- Myelination increases the speed of action potential propagation.
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Description
This quiz covers the hypothalamus-anterior pituitary axis and its role in endocrine pathologies such as hypersecretion and hyposecretion. It also explores the significance of negative feedback loops in maintaining homeostasis and local communication in physiological functions.
