CH. 17 Organization and Control of Neural Function

What happens during the depolarization phase of nerve cells?

A rapid change in polarity to one that is positive on the inside and the membrane becomes open to sodium. Depolarization is characterized by a rapid change in polarity of the resting membrane potential, which was negative on the inside and positive on the outside, to one that is positive on the inside and negative on the outside. During the depolarization phase, the membrane suddenly becomes permeable to sodium ions. The rapid inflow of sodium ions produces local electric currents that travel through the adjacent cell membrane, causing the sodium channels in this part of the membrane to open. The resting membrane potential is the undisturbed period of the action potential during which the nerve is not transmitting impulses. A threshold potential represents the membrane potential at which neurons or other excitable tissues are stimulated to fire.

Neuromodulators can produce slower and longer-lasting changes in membrane excitability by acting on postsynaptic receptors. What do neuromodulators do?

Alter the release of or response to neurotransmitters Neuromodulator molecules react with presynaptic or postsynaptic receptors to alter the release of or response to neurotransmitters. The other answers are incorrect.

Following a stroke, injury to nerve cells within the central nervous system needs to be repaired. The health care provider knows that which of the following processes explains how this occurs?

Astrocytes fill up the space to form a glial scar, repairing the area and replacing the CNS cells that cannot regenerate. Astrocytes are the largest and most numerous of neuroglia and are particularly prominent in the gray matter of the CNS. They form a network within the CNS and communicate with neurons to support and modulate their activities. Astrocytes are also the principal cells responsible for repair and scar formation in the brain. The microglia is a small phagocytic cell that is available for cleaning up debris after cellular infection or cell death. The ependymal cell forms the lining of the neural tube cavity, the ventricular system. The oligodendrocytes form the myelin in the CNS. Instead of forming a myelin covering for a single axon, these cells reach out with several processes, each wrapping around and forming a multilayered myelin segment around several different axons.

The parasympathetic nervous system is part of which of the following systems?

Autonomic nervous system The efferent outflow from the autonomic nervous system has two divisions: the sympathetic nervous system and the parasympathetic nervous system.

Which components of the nervous system make up the central nervous system?

Brain and spinal cord The brain and the spinal column make up the central nervous system. The peripheral nervous system lies outside of these two structures.

Which area of the brain is responsible for respiration?

Brain stem The respiratory center is located in the brain stem.

Drugs like diazepam (Valium), a benzodiazepine, exert their action on ion channels. These drugs do not open the GABA-operated ion channel, but they:

Change the effect that GABA has when it binds to the channel at the same time as the drug Amino acids, such as glutamine, glycine, and GABA, serve as neurotransmitters at most CNS synapses. GABA mediates most synaptic inhibition in the CNS. Drugs such as the benzodiazepines (e.g., the tranquilizer diazepam) and the barbiturates exert their action by binding to their own distinct receptor on a GABA-operated ion channel. The drugs by themselves do not open the channel, but they change the effect that GABA has when it binds to the channel at the same time as the drug. Another class of messenger molecules, known as neuromodulators, also may be released from axon terminals. In contrast to neurotransmitters, neuromodulators do not directly activate ion channel receptors but bring about long-term changes that subtly enhance or depress the action of the receptors. Neuromodulators, such as dopamine, serotonin, acetylcholine, histamine, and others, may act at either presynaptic or postsynaptic sites.

A client with a diagnosis of epilepsy has required surgical removal of part of her prefrontal cortex. Which of the following effects should her family and care team anticipate?

Changes in behavior and judgment The prefrontal cortex is thought to be involved in anticipation and prediction of consequences of behavior. It does not contribute directly to balance, sensation, or endocrine function.

Select the function of the occipital lobe.

Color, motion, and depth perception The occipital lobe is associated with the ability to experience color, depth, and motion perception. The temporal lobe is responsible for behavior, and the parietal lobe helps us to determine objects through the sense of feel.

Which of the following characterizes a function of the parasympathetic nervous system (PNS)?

Conservation of energy The functions of the PNS are concerned with conservation of energy, resource replenishment and storage, and maintenance of organ function during periods of minimal activity—the rest-digest response. All other options are functions of the sympathetic nervous system.

The cerebellum, separated from the cerebral hemispheres by the tentorium cerebelli, lies in the posterior fossa of the cranium. What is one of the functions of the cerebellum?

Coordinates smooth and accurate movements of the body The cerebellum compares what is actually happening with what is intended to happen. It then transmits the appropriate corrective signals back to the motor system, instructing it to increase or decrease the activity of the participating muscle groups so that smooth and accurate movements can be performed. Answer B describes the trigeminal nerve, which exits the brain stem. Answer C describes the pons. Answer D describes the midbrain.

The nurse is caring for a client who has damage to the facial nerve (CNV II). What complication related to this damage should the nurse closely monitor for?

Corneal scarring from eye dryness Loss of this nerve function or damage to the nerve can result in eye dryness with risk of corneal scarring and blindness. Medial strabismus from loss of eye abduction is due to damage to the abducens nerve (CN VI). Unilateral, severe pain from inflammation of the nerve results from trigemnial nerve damage. Laryngeal obstruction is a result from damage to the vagus nerve (CN X).

Which one of the following meninges provides the major protection for the brain and spinal cord?

Dura mater All surfaces of the spinal cord, brain, and segmental nerves are covered with a delicate connective tissue layer called the pia mater. A second, very delicate, nonvascular, and waterproof layer, called the arachnoid, encloses the entire central nervous system. Immediately outside the arachnoid is a continuous sheath of strong connective tissue, the dura mater, which provides the major protection for the brain and spinal cord. The tentorium cerebelli is the inner layer of the dura that anchors the brain to the skull.

The pathophysiologic effects of spina bifida are due to:

Failure of one or more neural arches to close within the vertebral column of the neural tube The major morphogenic defects of the spinal cord and brain are due to the abnormal formation or closure of the neural tube and surrounding tissues, problems that often result in spina bifida. The health problem is not due to the malformation of the mesoderm, lesions in the dorsal root ganglia, or hypertrophy of the primary vesicles.

A client is having an upper endoscopy to determine the presence of a gastric ulcer. After the procedure is performed, the nurse instructs the client that he cannot have anything to eat or drink until the return of the gag reflex. Which nerve is the nurse testing for return of function?

Glossopharyngeal The glossopharyngeal nerve innervates the stylophargeus muscle, posterior external ear, taste buds of posterior half of tongue, oral pharynx, parotid gland, pharyngeal muscles, and the stylopharyngeus muscle. It affects the function of proprioception, somesthesia, taste, gag reflex, salivary reflex, and assists in swallowing.

Which of the following substances provides the majority of the fuel needs of the neurologic system?

Glucose Glucose is the major fuel source for the nervous system. Unlike muscle cells, neurons have no glycogen stores and must rely on glucose from the blood or the glycogen stores of supporting glial cells to meet their energy needs.

The nurse measures a blood glucose level of 40 mg/dL for a client with diabetes type I. Why would it be important for the nurse to institute an intervention to elevate the glucose level in this client?

Glucose is not stored in the brain and is a major fuel source for brain function. Glucose is the major fuel source for the nervous system but neurons have no provision for storing glucose. Ketones can provide for limited temporary energy requirements. However, these sources are rapidly depleted.

A client has sustained damage to cranial nerve VIII. The nurse recognizes that the client may experience difficulty with:

Hearing Cranial nerve VIII (vestibulocochlear nerve) is associated with hearing. The other options involve different nerves.

A client arrives in the clinic after having a tongue piercing performed and is unable to control the movement of the tongue. The nurse is aware that which nerve may have been damaged from the piercing?

Hypoglossal The general somatic efferent LMNs of the lower segments of the medulla supply the extrinsic and intrinsic muscles of the tongue by means of the hypoglossal nerve (CN XII). Damage to the hypoglossal nerve results in weakness or paralysis of tongue muscles. When the tongue is protruded, it deviates toward the damaged and therefore weaker side because of the greater protrusion strength on the normal side.

A client is unable to stick out his tongue as a result of injury to cranial nerve XII. The nurse recognizes that the client has sustained as damage to which nerve?

Hypoglossal The name of cranial nerve VII is the hypoglossal nerve. It is responsible for the client's ability to stick out his or her tongue without deviation.

Neurotransmitters are small molecules that exert their actions through specific proteins, called receptors, embedded in the postsynaptic membrane. Where are neurotransmitters synthesized?

In the axon terminal Neurotransmitters are synthesized in the cytoplasm of the axon terminal. The other answers are incorrect.

The health care provider is performing a spinal tap on a client with suspected infection. The provider would perform the procedure at:

L3 or L4 A pocket of CSF, the dural cisterna spinalis, extends from approximately L2 to S2. Because this area contains an abundant supply of CSF and the spinal cord does not extend this far, the area often is used for sampling the CSF. A procedure called a spinal tap, or puncture, can be done by inserting a special needle into the dural sac at L3 or L4. The spinal roots, which are covered with pia mater, are in little danger of trauma from the needle used for this purpose.

The region of the brain involved in emotional experience and control of emotional behavior is the:

Limbic system The limbic region of the brain is involved in emotional experience and in the control of emotion-related behavior. Stimulation of specific areas in this system can lead to feelings of dread, high anxiety, or exquisite pleasure. It also can result in violent behaviors, including attack, defense, or explosive and emotional speech. The occipital lobe plays an important role in the meaningfulness of visual experience, including experiences of color, motion, depth perception, pattern, form, and location in space. The parietal lobe is necessary for perceiving the meaningfulness of integrated sensory information from various sensory systems, especially the perception of "where" the stimulus is in space and in relation to body parts. Axons of the olfactory nerve, or cranial nerve I, terminate in the most primitive portion of the cerebrum—the olfactory bulb, where initial processing of olfactory information occurs.

Which of the following is the primary component of white matter?

Myelinated fibers Myelin has a high lipid content, which gives it a whitish color, and the name "white matter" is given to the masses of myelinated fibers in the spinal cord and brain. The other options are not myelinated.

During embryonic development, which of the following structures develops into the central nervous system (CNS)?

Neural tube During embryonic development, the neural tube develops into the CNS, whereas the notochord becomes the foundation around which the vertebral column ultimately develops. As the neural tube closes, ectoderm cells called neural crest cells, migrate away from the dorsal surface of the neural tube to become progenitors of the neurons and supporting cells of the parasympathetic nervous system. The surface ectoderm separates from the neural tube and fuses over the top to become the outer layer of skin.

Which of the following chemicals does blood-brain and CSF-brain barrier control with easy entrance?

Oxygen Two barriers, the blood-brain barrier and the cerebrospinal fluid (CSF)-brain barrier, provide the means for maintaining the stable chemical environment of the brain. Only water, carbon dioxide, and oxygen enter the brain with relative ease. Large molecules such as proteins are largely excluded from crossing the blood-brain barrier. In the brain, ammonia is converted to glutamine by astrocytes. Potassium has controlled entrance into the brain; the result of slight fluctuations of potassium concentration in the brain would be uncontrolled neural activity because ions such as potassium influence the threshold for neural firing.

Spinal nerves that form complex nerve networks are called which of the following?

Plexuses Spinal nerves do not go directly to skin and muscle fibers; instead, they form complicated nerve networks called plexuses. A plexus is a site of intermixing nerve branches. After emerging from the vertebral column, the spinal nerve divides into two branches, or rami. The choroid plexus produces cerebrospinal fluit in the lateral, third and fourth ventricles. Reticular formation is the location of many important reflex circuits of the spinal cord and brain stem.

Which parts of the brain make up the brain stem?

Pons and medulla oblongata The brain stem consists of the pons and the medulla.

What is the role of a neuromodulator when it acts on a postsynaptic receptor?

Produces slower and longer-lasting changes in membrane excitability The neuromodulators react with presynaptic or postsynaptic receptors to alter the release of or response to neurotransmitters. With postsynaptic receptors, they produce slower and longer-lasting changes in membrane excitability.

Muscle spindles and Golgi tendon organs are two types of sensory receptors that provide information to the central nervous system (CNS). This information is relayed to the thalamus ans sensory cortex and is experienced as which of the following?

Proprioception Specialized sensory nerve terminals in the skeletal muscles (muscle spindles) and tendons (Golgi tendon organs) relay information about muscle stretch and joint tension to the CNS. This information is relayed to the thalamus and sensory cortex and is experienced as proprioception, the sense of body movement and position. The other functions are not mediated by these receptors.

Neurotransmitters exert their actions through specific proteins that are known as:

Receptors Neurotransmitters exert their actions through specific proteins that are known as called receptors, embedded in the postsynaptic membrane.

A client's primary care provider has prescribed a β-adrenergic receptor blocker. Which of the following therapeutic effects do the client and care provider likely seek?

Reduction in heart rate and blood pressure β1-adrenergic receptors are located primarily in the heart, the blood vessels of skeletal muscle, and the bronchioles. As such, drugs that block these receptors can bring about a reduction in heart rate, stroke volume, and blood pressure.

Which types of cells are supporting cells of the peripheral nervous system?

Schwann cells The Schwann cells play an important role in supporting the peripheral nervous system. The other cells support the central nervous system.

Neurons communicate with each other through which of the following structures?

Synapses Neurons communicate with each other through structures known as synapses. Cell bodies and dendrites are covered in synapses. Neural crest cells migrate aways from the forming neural tube and are progenitors to the parasympathetic nervous system.

Which of the following messages is most likely to be carried by general somatic afferent (GSA) neurons?

The sensation of cold when touching ice General somatic afferent (GSA) neurons innervate the skin and other somatic structures, responding to stimuli such as those that produce pressure or pain. Initiation of motion is the control of efferent neurons, whereas information about the position of a joint is undercarried by the special somatic afferent (SSA) fibers.

On which of the following do chemical synapses rely to provide communication between neurons?

Transmitter molecules Electrical and chemical synapses permit communication between neurons. Chemical synapses rely on chemical transmitter molecules, released from the presynaptic neuron, that cross the synaptic cleft and then interact with receptors on the postsynaptic neuron. Electrical synapses consist of gap junctions between adjacent cells that allow action potentials to move rapidly from one cell to another. Satellite cells secrete a basement membrane that protects the cell body from the diffusion of large molecules.

Which of the following nerves exits the pons and conveys the modalities of pain, temperature, touch, and proprioception to the superficial and deep regions of the face?

Trigeminal nerve The trigeminal nerve, which has both sensory and motor subdivisions, exits the brain stem latterally on the forward surface of the pons. The trigeminal nerve is the main sensory nerve conveying the modalities of pain, temperature, touch, and proprioception to the superficial and deep regions of the face. The abducen nerve arises from the pons to innervate the lateral rectus muscle of the eye. The facial nerve arises from the junction of the pons and medulla and innervates the nasopharynx and taste buds of the palate. The spinal accessory nerve arises from the upper cervical spinal segments and innervates the sternocleidomastoid muscle.

The arachnoid membrane is the middle layer of the three meninges.

True

Dopamine is an intermediate compound made during the synthesis of norepinephrine. It is the principal inhibitory transmitter of the internuncial neurons in the sympathetic ganglia. What other action does it have?

Vasodilates renal and coronary blood vessels when given intravenously Dopamine, which is an intermediate compound in the synthesis of norepinephrine, also acts as a neurotransmitter. It is the principal inhibitory transmitter of internuncial neurons in the sympathetic ganglia. It also has vasodilator effects on renal, splanchnic, and coronary blood vessels when given intravenously and is sometimes used in the treatment of shock.

Ion channels in nervous system cells generate action potentials in the cells. What are the ion channels guarded by?

Voltage-dependent gates These membrane channels are guarded by voltage-dependent gates that open and close with changes in the membrane potential. The other answers are incorrect.

Which of the following processes is most likely to occur as a result of a spinal reflex?

Withdrawal of a hand from a hot stove element A reflex is a highly predictable relationship between a stimulus and an elicited motor response. The withdrawal reflex is stimulated by a painful (nociceptive) stimulus and quickly moves the body part away from the offending stimulus, usually by flexing a limb part. Peristalsis, oculomotor function, and pain are not mediated by spinal reflexes.

Which of the following types of reflex is stimulated by a nociceptive stimulus?

Withdrawal reflex The withdrawal reflex is stimulated by a damaging (nociceptive) stimulus. The myotatic, or stretch reflex, controls muscle tone and helps maintain posture. The carotid sinus baroreflex assists adjustment of the cardiovascular system at the level of the brain stem.

Which of the following are the main neurotransmitters of the autonomic nervous system (ANS)? Select all that apply.

• Acetylcholine • Epinephrine • Norepinephrine The main neurotransmitters of the ANS are acetylcholine and the catecholamines epinephrine and norepinephrine. Monoamine oxidase is found in the nerve endings to degrade catecholamines. Tyrosine is an amino acid that is a precursor to catecholamines.

A client has sustained damage to cranial nerve VIII. The nurse recognizes that the client may experience difficulty with:

• Depolarization • Hyperpolarization • Repolarization The ion gate is open or closed during the polarization stage of action potential when the threshold potential is met. The other stages allow movements in and out of sodium and potassium.

Which structures are part of the brain stem? Select all that apply.

• Medulla oblongata • Pons • Midbrain The term brain stem is often used to include the medulla, pons, and midbrain. The cerebellum is not part of the brain stem.