Neurons Are Treated With A Drug That Permanently Stops The Na K Atpase Pumps. What Happens To The Resting Membrane Potential

Spinal cord Dura-arachnoid -Pia-

Sub-arachnoid space -

FIGURE 8-47

The ventricular system of the brain and the distribution of the cerebrospinal fluid, shown in blue. %

total blood supply, which supports its high oxygen utilization. If the blood flow to a region of the brain is reduced to 10 to 25 percent of its normal level, energy stores are depleted, energy-dependent membrane ion pumps fail, membrane ion gradients decrease, the membranes depolarize, and extracellular potassium concentrations increase.

The exchange of substances between blood and extracellular fluid in the central nervous system is different from the more-or-less unrestricted diffusion of nonprotein substances from blood to extracellular fluid in the other organs of the body. A complex group of blood-brain barrier mechanisms closely control both the kinds of substances that enter the extracellular fluid of the brain and the rates at which they enter. These mechanisms minimize the ability of many harmful substances to reach the neurons, but they also reduce the access of the immune system to the brain.

The blood-brain barrier, which comprises the cells that line the smallest blood vessels in the brain, has both anatomical structures, such as tight junctions, and physiological transport systems that handle different classes of substances in different ways. For example, substances that dissolve readily in the lipid components of the plasma membranes enter the brain quickly. Therefore, the extracellular fluid of the brain and spinal cord is a product of, but chemically different from, the blood.

The blood-brain barrier accounts for some drug actions, too, as can be seen from the following scenario: Morphine differs chemically from heroin only in that morphine has two hydroxyl groups whereas heroin has two acetyl groups (—COCH3). This small difference renders heroin more lipid soluble and able to cross the blood-brain barrier more readily than morphine. As soon as heroin enters the brain, however, enzymes remove the acetyl groups from heroin and change it to morphine. The morphine, insoluble in lipid, is then effectively trapped in the brain where it continues to exert its effect. Other drugs that have rapid effects in the central nervous system because of their high lipid solubility are the barbiturates, nicotine, caffeine, and alcohol.

Many substances that do not dissolve readily in lipids, such as glucose and other important substrates of brain metabolism, nonetheless enter the brain quite rapidly by combining with membrane transport proteins in the cells that line the smallest brain blood vessels. Similar transport systems also move substances out of the brain and into the blood, preventing the buildup of molecules that could interfere with brain function.

In addition to its blood supply, the central nervous system is perfused by the cerebrospinal fluid. The cere-brospinal fluid is secreted into the ventricles by epithelial cells that cover the choroid plexuses, which form part of the lining of the four ventricles. A barrier is present here, too, between the blood in the capillaries of the choroid plexuses and the cerebrospinal fluid, and cerebrospinal fluid is a selective secretion. For example, potassium and calcium concentrations are slightly lower in cerebrospinal fluid than in plasma, whereas the sodium and chloride concentrations are slightly higher. The choroid plexuses also trap toxic heavy metals such as lead, thus affording a degree of protection to the brain from these substances.

The cerebrospinal fluid and the extracellular fluid of the brain are, over time, in diffusion equilibrium. Thus, the extracellular environment of the brain and spinal cord neurons is regulated by restrictive, selective barrier mechanisms in the capillaries of the brain and choroid plexuses.

SECTION D SUMMARY

I. Inside the skull and vertebral column, the brain and spinal cord are enclosed in and protected by the meninges.

Central Nervous System: Spinal Cord

I. The spinal cord is divided into two areas: central gray matter, which contains nerve cell bodies and dendrites; and white matter, which surrounds the gray matter and contains myelinated axons organized into ascending or descending tracts.

PART TWO Biological Control Systems

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

PART TWO Biological Control Systems

II. The axons of the afferent and efferent neurons form the spinal nerves.

Central Nervous System: Brain

I. The brain is divided into six regions: cerebrum, diencephalon, midbrain, pons, medulla oblongata, and cerebellum.

II. The midbrain, pons, and medulla oblongata form the brainstem, which contains the reticular formation.

III. The cerebellum plays a role in posture, movement, and some kinds of memory.

IV. The cerebrum, made up of right and left cerebral hemispheres, and the diencephalon together form the forebrain. The cerebral cortex forms the outer shell of the cerebrum and is divided into parietal, frontal, occipital, and temporal lobes.

V. The diencephalon contains the thalamus and hypothalamus.

VI. The limbic system is a set of deep forebrain structures associated with learning and emotions.

Peripheral Nervous System

I. The peripheral nervous system consists of 43 paired nerves—12 pairs of cranial nerves and 31 pairs of spinal nerves. Most nerves contain axons of both afferent and efferent neurons.

II. The efferent division of the peripheral nervous system is divided into somatic and autonomic parts. The somatic fibers innervate skeletal-muscle cells and release the neurotransmitter acetylcholine.

III. The autonomic nervous system innervates cardiac and smooth muscle, glands, and gastrointestinal-tract neurons. Each autonomic pathway consists of a preganglionic neuron with its cell body in the CNS and a postganglionic neuron with its cell body in an autonomic ganglion outside the CNS.

a. The autonomic nervous system is divided into sympathetic and parasympathetic components. The preganglionic neurons in both sympathetic and parasympathetic divisions release acetylcholine; the postganglionic parasympathetic neurons release mainly acetylcholine; and the postganglionic sympathetics release mainly norepinephrine.

b. The receptors that respond to acetylcholine are classified as nicotinic and muscarinic, and those that respond to norepinephrine or epinephrine as alpha- and beta-adrenergic types.

c. The adrenal medulla is a hormone-secreting part of the sympathetic nervous system and secretes mainly epinephrine.

d. Many effector organs innervated by the autonomic nervous system receive dual innervation.

Blood Supply, Blood-Brain Barrier Phenomena, and Cerebrospinal Fluid

I. Brain tissue depends on a continuous supply of glucose and oxygen for metabolism.

II. The brain ventricles and the space within the meninges are filled with cerebrospinal fluid, which is formed in the ventricles.

III. The chemical composition of the extracellular fluid of the CNS is closely regulated by the blood-brain barrier.

SECTION D KEY TERMS

pathway tract commissure long neural pathway multineuronal pathway multisynaptic pathway ganglia nuclei gray matter white matter dorsal root dorsal root ganglia ventral root spinal nerve cerebrum diencephalon brainstem cerebellum forebrain midbrain pons medulla oblongata cerebral ventricle reticular formation cranial nerve cerebral hemisphere cerebral cortex subcortical nuclei corpus callosum frontal lobe parietal lobe occipital lobe temporal lobe basal ganglia thalamus hypothalamus limbic system efferent division of the peripheral nervous system afferent division of the peripheral nervous system somatic nervous system autonomic nervous system motor neuron enteric nervous system autonomic ganglion preganglionic fiber postganglionic fiber sympathetic division of the autonomic nervous system parasympathetic division of the autonomic nervous system sympathetic trunk adrenal medulla dual innervation fight-or-flight response meninges cerebrospinal fluid (CSF) blood-brain barrier choroid plexuses

SECTION D REVIEW QUESTIONS

Make an organizational chart showing the central nervous system, peripheral nervous system, brain, spinal cord, spinal nerves, cranial nerves, forebrain, brainstem, cerebrum, diencephalon, midbrain, pons, medulla oblongata, and cerebellum.

Draw a cross section of the spinal cord showing the gray and white matter, dorsal and ventral roots, dorsal root ganglion, and spinal nerve. Indicate the general location of pathways.

List two functions of the thalamus.

List the functions of the hypothalamus.

Make a peripheral nervous system chart indicating the relationships among afferent and efferent divisions, somatic and autonomic nervous systems, and sympathetic and parasympathetic divisions.

Contrast the somatic and autonomic divisions of the efferent nervous system; mention at least three characteristics of each.

Vander et al.: Human Physiology: The Mechanism of Body Function, Eighth Edition

Neural Control Mechanisms CHAPTER EIGHT

Neural Control Mechanisms CHAPTER EIGHT

Name the neurotransmitter released at each synapse or neuroeffector junction in the somatic and autonomic systems.

Contrast the sympathetic and parasympathetic components of the autonomic nervous system; mention at least four characteristics of each. Explain how the adrenal medulla can affect receptors on various effector organs despite the fact that its cells have no axons.

The chemical composition of the CNS extracellular fluid is different from that of blood. Explain how this difference is achieved.

CHAPTER 8 CLINICAL TERMS

local anesthetic agonist antagonist tetanus toxin

Alzheimer's disease analgesic hydrocephalus stroke

CHAPTER 8 THOUGHT QUESTIONS

(Answers are given in Appendix A)

1. Neurons are treated with a drug that instantly and permanently stops the Na,K-ATPase pumps. Assume for this question that the pumps are not electrogenic. What happens to the resting membrane potential immediately and over time?

2. Extracellular potassium concentration in a person is increased with no change in intracellular potassium concentration. What happens to the resting potential and the action potential?

3. A person has received a severe blow to the head but appears to be all right. Over the next weeks, however, he develops loss of appetite, thirst, and sexual capacity, but no loss in sensory or motor function. What part of the brain do you think may have been damaged?

4. A person is taking a drug that causes, among other things, dryness of the mouth and speeding of the heart rate but no impairment of the ability to use the skeletal muscles. What type of receptor does this drug probably block? (Table 8-12 will help you answer this.)

5. Some cells are treated with a drug that blocks chloride channels, and the membrane potential of these cells becomes slightly depolarized (less negative). From these facts, predict whether the plasma membrane of these cells actively transports chloride and, if so, in what direction.

6. If the enzyme acetylcholinesterase were blocked with a drug, what malfunctions would occur?

7. The compound tetraethylammonium (TEA) blocks the voltage-gated changes in potassium permeability that occur during an action potential. After administration of TEA, what changes would you expect in the action potential? In the afterhyperpolarization?

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Responses

  • stephan
    What type of receptor does this drug probably block?
    7 years ago
  • OLO
    What happens to membrane potential if na k pump stops?
    7 years ago
  • pauliina
    How would you expect the action potential to change if you treated a neuron with tea?
    6 years ago
  • Joona Halvari
    How would you expect the action potential to change if you treated a neuron with tetraethylammonium?
    7 years ago
  • jasper aitken
    What happens to membrane potential if na/k atpase is blocked?
    7 years ago
  • teppo
    What happens when you block na/k atpase intracellular concentration?
    7 years ago
  • Aisha
    What happens to an action potential when extracellular potassium concentrations are increased?
    7 years ago
  • charlotte
    What happens to resting membrane potential when Sodium potassium ATPase stops?
    7 years ago
  • bonnie
    What happens neuron when na k stop?
    7 years ago
  • LOTHO
    When katpase pump stop what will happen?
    7 years ago
  • BARBARA
    What happens when sodium potassium atpase stops working due to a drug?
    6 years ago
  • jessika
    What if na/k atpase pump stops resting potential?
    6 years ago
  • NOORA
    What happens to resting membrane potential when na/k atpase pumps are permanently stopped?
    6 years ago
  • Arabella
    What happenes if you stop the K Na ATPase pump in nueron?
    6 years ago
  • consuelo
    What will happen if the na/k atpase pump stops permanently?
    6 years ago
  • JUHANA
    What will happen to membrane potential of na k pump stops?
    6 years ago
  • darren
    What happens to resting membrane potential when na/k atpase pump permanently stops?
    6 years ago
  • furuta
    What happens if neurons are treated with a drug to stop atp pump?
    6 years ago
  • billy fouche
    What happens to membrane potential if sodium potassium atpase pump stops?
    6 years ago
  • Sebhat
    What happens when atpase pumps stop?
    6 years ago
  • Mayme
    What happens to neurons when na/k atpase fails?
    6 years ago
  • Monica
    How are brain neurons treated?
    6 years ago
  • Monica
    What happens over time to the membrane potential if the sodium atpase pump fails?
    5 years ago

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