Excitable Cells and Membrane Potential

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Questions and Answers

Which of the following statements correctly describes the electrochemical forces acting on potassium ions (K+) across the cell membrane?

The concentration gradient of K+ moves outward, while the electrical gradient moves inward. (correct)

Both the concentration gradient and electrical gradient of K+ move inward.

Both the concentration gradient and electrical gradient of K+ move outward.

The concentration gradient of K+ moves inward, while the electrical gradient moves outward.

What is the primary reason why the resting membrane potential (RMP) of a cell is closer to the equilibrium potential of potassium (EK) than the equilibrium potential of sodium (ENa)?

The concentration of sodium ions (Na+) is higher inside the cell than outside the cell.

The concentration of potassium ions (K+) is higher outside the cell than inside the cell.

Potassium ions (K+) are more permeable across the cell membrane than sodium ions (Na+). (correct)

Sodium ions (Na+) are more permeable across the cell membrane than potassium ions (K+).

What is the main difference between a ligand-gated channel and a voltage-gated channel?

Ligand-gated channels open in response to the binding of a specific molecule, while voltage-gated channels open in response to changes in membrane potential. (correct)

Ligand-gated channels are activated by changes in membrane potential, while voltage-gated channels are activated by binding to specific molecules.

Ligand-gated channels are responsible for generating action potentials, while voltage-gated channels are involved in maintaining the resting membrane potential.

Ligand-gated channels are found in excitable tissues, while voltage-gated channels are found in non-excitable tissues.

Which of the following statements accurately describes the relationship between membrane potential and the separation of charges?

The membrane potential is directly proportional to the number of charges separated across the membrane. (D) Signup and view all the answers

What is the primary function of the Nernst equation in the context of membrane potentials?

To calculate the equilibrium potential for a specific ion based on its concentration gradient. (B) Signup and view all the answers

Which of the following ions has the highest relative permeability across the cell membrane?

Potassium (K+) (D) Signup and view all the answers

Why is the intracellular fluid (ICF) more negative than the extracellular fluid (ECF)?

Due to the presence of negatively charged proteins inside the cell. (C) Signup and view all the answers

Which of the following is NOT a characteristic of an excitable cell?

Exhibit a constant membrane potential that does not change in response to stimuli. (D) Signup and view all the answers

Which of the following is true regarding the regeneration of nerve fibers in the peripheral nervous system (PNS)?

Schwann cells phagocytize debris and form regeneration tubes. (C) Signup and view all the answers

What is the primary function of the chemical messenger released at a chemical synapse?

To alter the activity of the postsynaptic cell by binding to receptors. (A) Signup and view all the answers

Which of the following is NOT a characteristic of an excitatory postsynaptic potential (EPSP)?

Results in hyperpolarization of the postsynaptic membrane. (D) Signup and view all the answers

What is the primary difference between an excitatory postsynaptic potential (EPSP) and an inhibitory postsynaptic potential (IPSP)?

EPSPs increase the likelihood of an action potential, while IPSPs decrease the likelihood. (B) Signup and view all the answers

Which of the following is an example of temporal summation?

Action potentials from the same presynaptic neuron occur in rapid succession. (D) Signup and view all the answers

Which of the following is TRUE about neuromodulators?

They can influence the level of enzymes involved in neurotransmitter production. (A) Signup and view all the answers

Which of the following conditions involve the loss of myelin sheaths?

Multiple Sclerosis and Guillain-Barre Syndrome. (D) Signup and view all the answers

Which of the following types of synapses allows charge-carrying ions to flow directly between two cells in either direction?

Electrical synapses (B) Signup and view all the answers

What happens to the activation gate of a voltage-gated sodium channel during an action potential?

The activation gate opens when the membrane potential reaches threshold and stays open until the inactivation gate closes. (A) Signup and view all the answers

What is the primary factor that determines the speed of action potential propagation?

The diameter of the axon and whether it is myelinated. (D) Signup and view all the answers

What is the primary role of the inactivation gate of voltage-gated sodium channels during an action potential?

The inactivation gate ensures that the action potential only lasts for a brief period of time. (A) Signup and view all the answers

How does the GHK equation (Goldman-Hodgkin-Katz equation) relate to the membrane potential of a cell?

The GHK equation calculates the resting membrane potential of a neuron, taking into account the permeability of the membrane to potassium and sodium. (B) Signup and view all the answers

What is the difference between contiguous conduction and saltatory conduction?

Saltatory conduction is faster than contiguous conduction, because the action potential jumps from one node of Ranvier to the next. (B) Signup and view all the answers

What is the primary function of the sodium-potassium pump in maintaining the resting membrane potential?

It maintains the concentration gradients for sodium and potassium across the cell membrane. (B) Signup and view all the answers

Why does hypopolarization make the membrane potential closer to threshold?

Because it makes the inside of the cell more positive. (C) Signup and view all the answers

Which of the following correctly describes the difference between graded potentials and action potentials?

Graded potentials are localized and decremental, while action potentials propagate without decrement. (A) Signup and view all the answers

Which of the following factors does NOT influence the magnitude of a graded potential?

The presence or absence of myelin. (D) Signup and view all the answers

What is the primary role of myelination in nerve fibers?

To increase the speed of action potential propagation. (D) Signup and view all the answers

What is the difference between the absolute refractory period and the relative refractory period?

During the absolute refractory period, the cell is unable to generate another action potential, while during the relative refractory period, the cell is able to generate another action potential, but it requires a stronger stimulus. (A) Signup and view all the answers

Which of the following statements is TRUE regarding the equilibrium potential for potassium?

The equilibrium potential for potassium is primarily determined by the concentration gradient for potassium. (D) Signup and view all the answers

Which of the following is NOT a characteristic of action potentials?

Action potentials are graded in amplitude and duration. (B) Signup and view all the answers

What is the primary role of the axon hillock in a neuron?

To integrate the signals from other neurons and initiate action potentials. (B) Signup and view all the answers

How does the concentration gradient for sodium affect the membrane potential?

The concentration gradient for sodium moves sodium ions inward, making the inside of the cell more positive. (B) Signup and view all the answers

What is the relationship between the strength of a stimulus and the frequency of action potentials?

A stronger stimulus will result in a higher frequency of action potentials. (D) Signup and view all the answers

Which condition is associated with hypersecretion of aldosterone due to an adrenal tumor?

Conn’s syndrome (A) Signup and view all the answers

What triggers the release of cortisol in the body?

ACTH (D) Signup and view all the answers

What role does cortisol play in the body’s response to stress?

Increases blood glucose and fatty acids (C) Signup and view all the answers

Which mechanism is NOT associated with the actions of aldosterone?

Inhibition of water retention (D) Signup and view all the answers

What primary deficiency is seen in Addison’s disease?

All corticosteroids (B) Signup and view all the answers

What is a common cause of hypersecretion of cortisol leading to Cushing’s syndrome?

Adrenal tumors (D) Signup and view all the answers

Which condition is characterized by hyperpigmentation due to excessive ACTH secretion?

Addison’s disease (B) Signup and view all the answers

How is thyroid hormone predominantly secreted into circulation from follicular cells?

Phagocytosis of colloid (A) Signup and view all the answers

What is the primary action of DHEA in females?

Enhancing pubertal growth spurt (A) Signup and view all the answers

What triggers the release of thyroid hormones from the thyroid gland?

Thyroid-stimulating hormone (TSH) (C) Signup and view all the answers

In which condition is excessive secretion of GH most likely to result in dwarfism?

Laron dwarfism (C) Signup and view all the answers

Which of the following is an effect of thyroid hormones on the cardiovascular system?

Increased force of contraction (B) Signup and view all the answers

Hypersecretion of which hormone is primarily responsible for the symptoms of hyperthyroidism?

Triiodothyronine (T3) (C) Signup and view all the answers

What causes the condition known as myxedema?

Primary hypothyroidism (D) Signup and view all the answers

Which hormone has a significant role in stimulating the secretion of insulin-like growth factor 1 (IGF-1)?

Growth hormone (A) Signup and view all the answers

Which factor causes a goiter in hypothyroidism due to the failure of the thyroid gland?

Increased TSH secretion (B) Signup and view all the answers

What is the primary action of IGF-1 in bone growth?

Stimulating proliferation of epiphyseal cartilage (D) Signup and view all the answers

During which developmental phase is GH most critical for growth?

Postnatal growth spurts (C) Signup and view all the answers

What is the primary neurotransmitter released by adrenergic postganglionic fibers?

Norepinephrine (D) Signup and view all the answers

Which neurotransmitter is primarily involved in the activation of nicotinic receptors?

Acetylcholine (D) Signup and view all the answers

Which of the following is a role of the sympathetic nervous system?

Increasing heart rate (B) Signup and view all the answers

Where does the cell body of the first neuron in an autonomic nerve pathway reside?

In the central nervous system (D) Signup and view all the answers

What effect does binding of norepinephrine to alpha-1 receptors typically have?

Contraction of peripheral vascular smooth muscle (B) Signup and view all the answers

Which hormone is primarily stored and secreted by the adrenal medulla?

Epinephrine (B) Signup and view all the answers

In which signaling type does a hormone bind to a receptor on its own cell to exert its effects?

Autocrine signaling (C) Signup and view all the answers

Which receptor is primarily responsible for the inhibitory effects of norepinephrine in the digestive tract?

Alpha-2 (A) Signup and view all the answers

What type of chemical messenger primarily utilizes intracellular receptors to exert effects?

Lipid-soluble hormones (B) Signup and view all the answers

What is the primary action of receptors after being activated by lipophilic hormones?

Modulate gene expression (C) Signup and view all the answers

Which of the following chemicals primarily binds to muscarinic receptors?

Acetylcholine (C) Signup and view all the answers

Which structure is responsible for the synthesis of hormones in the posterior pituitary?

Hypothalamus (D) Signup and view all the answers

What is the function of JAK/STAT signaling in response to extracellular messengers?

Gene expression regulation (B) Signup and view all the answers

What is a characteristic of the adrenal cortex?

Secretes mineralocorticoids, glucocorticoids, and sex hormones (D) Signup and view all the answers

Study Notes

Excitable Cells

Ligand-gated channels bind neurotransmitters and ions, changing conformation in response to their presence.
Voltage-gated channels alter conformation in response to changes in membrane potential.
Ion distribution: sodium (Na+) is highly concentrated outside cells, potassium (K+) inside, and intracellular proteins have a negative charge.
Intracellular fluid (ICF) is more negative than extracellular fluid (ECF).
Cell membrane permeability to K+ is higher than Na+.
Two forces influence ions: concentration and electrical gradient.

Membrane Potential

Separation of opposite charges across a membrane, with the membrane itself being neutral.
Only excitable cells (muscle and nerve) generate action potentials using membrane potentials.
Resting membrane potential (RMP) is the membrane potential of non-excitable and excitable cells at rest, approximately -70mV, electrically neutral.
Equilibrium potential is the membrane potential where the electrical and concentration gradients for an ion are balanced, with no net movement.
Nernst equation calculates equilibrium potential for a specific ion.

Autonomic Nervous System I

Peripheral nervous system (PNS) lies outside brain and spinal cord.
Afferent division conveys signals from body receptors to the central nervous system (CNS).
Efferent division carries signals from CNS to muscles and glands, split into somatic and autonomic nervous systems.
Autonomic nervous system is further divided into sympathetic and parasympathetic.
Sympathetic pathways use primarily norepinephrine (adrenergic).
Parasympathetic pathways utilize acetylcholine (cholinergic)
Sympathetic pathways originate in thoracic and lumbar regions, with short preganglionic and long postganglionic fibers.
Parasympathetic pathways arise from cranial and sacral regions, have long preganglionic and short postganglionic fibers.

Autonomic Nervous System II

Cholinergic receptors bind acetylcholine.
Nicotinic receptors are present on postganglionic cell bodies in all autonomic ganglia.
Muscarinic receptors are present on effector cell membranes.
Muscarinic M1 stimulates the brain and stomach, M2 lowers heart rate, and M3 stimulates glands (salivary, lacrimal, sweat, digestive).
Adrenergic receptors bind norepinephrine and epinephrine.

Endocrinology

Intercellular communication includes paracrines/autocrines, neurotransmitters, neurohormones, and hormones.
Intracrine signaling occurs within a cell.
Autocrine signaling involves a cell responding to its own secreted hormone.
Paracrine signaling targets nearby cells.
Endocrine signaling uses the bloodstream to reach distant target cells.
Hormone classification: peptide (water-soluble) or lipid (hydrophobic).
Peptide hormones are synthesized in rough ER and packaged in Golgi vesicles, while lipid hormones originate from cholesterol in mitochondria.
Water-soluble hormones bind extracellular receptors, triggering intracellular signaling cascades.
Lipid-soluble hormones diffuse through membranes and bind intracellular receptors, altering gene expression.

Endocrinology - Systems

Hypothalamus-pituitary axes involve the hypothalamus and pituitary glands to regulate other endocrine glands controlling metabolic and reproductive processes.
Hypothalamic-hypophyseal portal system is a unique vascular arrangement that allows blood to flow directly to the anterior pituitary from the hypothalamus, facilitating the direct modulation of hormone secretion.
Thyroid gland synthesizes and secretes the thyroid hormones, regulating metabolic rate; and also secretes calcitonin.
Adrenal glands regulate stress responses. The adrenal medulla produces epinephrine and norepinephrine (catecholamines), while the adrenal cortex produces steroid hormones (e.g., cortisol, aldosterone).
Renin-angiotensin-aldosterone system (RAAS) regulates blood pressure and electrolyte balance involving the kidneys, blood vessels, and adrenal glands.
Adrenal androgens (e.g., DHEA) are involved in secondary sexual characteristics, growth and development.

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Description

Test your understanding of excitable cells and the principles of membrane potential. This quiz covers ligand-gated and voltage-gated channels, ion distribution, and the factors affecting membrane potential. Perfect for students studying physiology or cellular biology.