Clinical Case study of chapter 12- Nervous physiology lab. Bad Fish- A Case on Nervous Tissue PDF

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Clinical Case study of chapter 12: Nervous physiology lab. Bad Fish: A Case on Nervous Tissue One evening during a recent trip to Indonesia, Dr. Marshall Westwood sat down to a meal of puffer fish and rice. Within an hour of returning to his hotel room, Dr. Westwood felt numbness in his lips and tongue, which quickly spread to his face and neck. Before he could call the front desk, he began to feel pains in his stomach and throat, which produced feelings of nausea and eventually severe vomiting. Fearing that he had eaten some “bad fish” for dinner, Dr. Westwood called a local hospital to describe his condition. The numbness in his lips and face made it almost impossible for him to communicate, but the hospital staff managed to at least understand the address he gave them and they sent an ambulance. As Dr. Westwood was rushed to the hospital, his breathing became increasingly labored. The patient presented in the ED with diaphoresis, motor dysfunction, paresthesias, nausea, and an ascending paralysis that started in his legs and spread to the upper body, arms, face, and head. The patient was cyanotic and hypoventilating. Within 30 minutes of presenting in the ED, Dr. Westwood developed bradycardia with a BP of 90/50 mmHg. Atropine was administered in response to the bradycardia. Intravenous hydration, gastric lavage, and activated charcoal followed a presumptive diagnosis of tetrodotoxin poisoning that was based on the clinical presentation in the ED. Five hours after treatment, the following vital signs were noted:   

BP 125/79 mmHg HR 78 bpm Oxygen saturation: 97% on room air

After discussing his case with his physician, he learned that he had probably been the victim of puffer fish poisoning. The active toxin in the tissues of this fish is a chemical called tetrodotoxin (TTX). Tetrodotoxin is in a class of chemicals known as neurotoxins because it exerts its effects on neurons. The specific action of tetrodotoxin is that it blocks voltage-gated sodium ion channels.

Short Answer Questions 1. 2. 3. 4. 5.

6.

Which of the following best describes a voltage-gated sodium ion channel? => a protein embedded in the cell membrane of a neuron When a neuron is at rest, the cytoplasmic (inside) side of the cell is ______. => negatively charged relative to the outside of the cell Depolarization of the neuron occurs when ______. => positively charged sodium ions rush into the neuron Which of the following describes why Dr. Westwood experienced paralysis? => The tetrodotoxin prevented the motor neurons from sending signals to skeletal muscle. After recovering, Dr. Westwood decided to learn more about neurotoxins. In conducting his research, he learned about a toxin called batrachotoxin (BTX). BTX also binds to voltage-gated sodium ion channels. Dr. Westwood reviewed experiments with neurons exposed to BTX, which showed that after depolarizing, the membrane potential remained positive for an extended length of time. Repolarization of these neurons was often extremely delayed. Which of the following could help explain this result? => BTX prevents voltage-gated sodium ion channels from inactivating

Define the following phrases and terms associated with the signs and symptoms of Dr. Westwood’s TTX poisoning: - diaphoresis sweating motor dysfunction difficulty moving paresthesias numbness or tingling sensation cyanotic blue or purple coloration of skin hypoventilating Low rate of breathing or volume of breathing bradycardia Low heart rate (< 60bpm) gastric lavage washing out of stomach ("stomach pump") oxygen saturation a measure of how much oxygen the blood is carrying as a percentage of the maximum it could carry .

Diaphoresis refers to excessive sweating for no apparent reason. Often, an underlying medical condition or a natural life event, such as menopause, cause this type of sweating. Motor dysfunction is a complex interaction of brain injury location, developmental plastic adaptation, and multiple physical factors over time such as weakness, dexterity, tone, musculoskeletal issues, and factors inherent to the individual child. Paresthesia is an abnormal sensation such as tingling, tickling, pricking, numbness or burning of a person's skin with no apparent physical cause. Cyanosis refers to bluish discoloration of skin, nail beds, and mucous membranes. Peripheral cyanosis is when there is a bluish discoloration to your hands or feet. It’s usually caused by low oxygen levels in the red blood cells or problems getting oxygenated blood to your body. Hypoventilating or hypoventilation (also known as respiratory depression) occurs when ventilation is inadequate (hypo meaning "below") to perform needed gas exchange. By definition it causes an increased concentration of carbon dioxide (hypercapnia) and respiratory acidosis. Bradycardia is abnormally slow heartbeat. Gastric lavage, also commonly called stomach pumping or gastric irrigation, is the process of cleaning out the contents of the stomach. It has been used for over 200 years as a means of eliminating poisons from the stomach. Oxygen saturation is a term referring to the fraction of oxygen-saturated hemoglobin relative to total hemoglobin (unsaturated + saturated) in the blood. The human body requires and regulates a very precise and specific balance of oxygen in the blood. Normal blood oxygen levels in humans are considered 95-100 percent. 7.

As mentioned in the case description, tetrodotoxin is a molecule that blocks voltage-gated sodium ion channels. What is a voltage-gated sodium ion channel and what is its function? - A voltage-gated sodium ion channel is a protein embedded in the membrane of a cell. These channels have gates that open in response to changes in membrane voltage. Its function is to allow sodium ions to cross the cell membrane. (NOTE Chemically gated channels are similar, but open in response to the binding of another molecule (chemical messenger) to their surface.)

A voltage gated sodium channel is protein located in the cell membrane that allows sodium to pass into the cell when it reaches a certain voltage. 8.

When nerve cells are at rest, there is an unequal amount of positive and negative charges on either side of a nerve cell membrane. This charge difference creates an electrical potential. Describe how the resting membrane potential (resting potential) is generated. - At rest, positively charged sodium ions are at a higher concentration outside the cell, while positively charged potassium ions are at a higher concentration inside the cell. Sodium and potassium ions diffuse across the membrane while the cell is at rest. The rate at which this movement happens is dependent upon the permeability of the membrane to these two important ions. At rest, the electrical potential is negative, because positively charged potassium ions "leak" down their electrochemical gradient at a greater rate. This "drain" of positive charge from inside the cell causes the interior to become negative.

The resting membrane potential is generated by the Na+K+ ATPase pump which pumps three sodium out and two potassium in for each ATP that is used. 9.

What is happening to the electrical potential of a neuron when it generates an action potential? What is the function of the action potential in neurons? - During an action potential, there is a brief reversal in membrane potential as the interior of the cell becomes positive (depolarization) and then returns to negative resting potential (repolarization). The action potential is the electrical signal generated by neurons that is used in long distance communication.

When a neuron generates an action potential, there is a domino-like opening of sodium channels along the length of the axon. Axon potentials are the way that a neuron encodes the intensity of the signal it wants to send. 10.

Describe the role of sodium ions and sodium channels in generating an action potential. - The opening of voltage-gated sodium ion channel gates leads to the rapid diffusion of sodium ions into the cell (down their electrochemical gradient). As these positively charged ions enter the cell, the membrane potential becomes positive for a brief period (depolarization). At the peak of the action potential, the sodium ion channels inactivate. The sodium ions cause depolarization of the nerve cell membrane and the sodium channels open up allowing the sodium to influx into the cell.

11.

What would happen to a neuron if it was exposed to tetrodotoxin? Be specific regarding its effect on the ability of a neuron to communicate. - When TTX binds to the sodium ion channels, it effectively prevents sodium ions from entering the channel. This would prevent the cell from depolarizing and block the cell from generating an action potential. Since the action potential is the signal that neurons use in cell-to-cell communication, the ability of a neuron to communicate would be inhibited.

Tetrodotoxin blocks the opening of voltage gated sodium channels which would prevent an action potential from occurring. 12.

Paralysis is a term used to describe the loss of muscle function. If tetrodotoxin’s effect is on neurons, why did Dr. Westwood experience paralysis? - Muscles contract after receiving signals from motor neurons. Since TTX prevents the generation of action potentials in these neurons, the ability of a motor neuron to generate this signal will be inhibited. The result would be the emergence of paralysis in the affected areas. Sodium ions also contribute to the action potential generated in muscle cells, so TTX inhibits muscle activity directly.

In order for a muscle cell to contract, it must receive action potentials so that neurotransmitter release (ACh) into the neuromuscular junction will occur. 13.

Now that you have addressed some of the basic biology of this case, explain why Dr. Westwood experienced numbness after eating the pufferfish meal. - TTX inhibits neurons that transmit sensory information to the brain. Since TTX prevents the generation of action potentials in sensory nerves, the ability of the neurons to transmit sensory information will be inhibited. This loss of sensory information would be experienced as "numbness."

Dr. Westwood experienced numbness after eating the puffer fish meal because we have neurons that receive and send impulses and the poison blocked the conduction of nerve impulses which caused him to have paresthesia....