Podcast
Questions and Answers
Which of the following accurately describes the roles of the three main categories of neurons in responding to a painful stimulus, such as stepping on a tack?
Which of the following accurately describes the roles of the three main categories of neurons in responding to a painful stimulus, such as stepping on a tack?
- Sensory neurons transmit the signal to the brain, which then sends a signal back through interneurons to motor neurons, causing muscle contraction.
- Sensory neurons detect the pain and directly signal motor neurons, which then cause muscles to contract, while interneurons modulate the intensity of the sensation in the brain.
- Sensory neurons detect the pain and transmit the signal to interneurons in the spinal cord, which then relay the signal to motor neurons to stimulate muscle contraction. (correct)
- Interneurons in the skin detect the pain and stimulate sensory neurons, which then activate motor neurons to cause muscle contraction and transmit pain signals to the brain.
If a drug selectively blocked the function of interneurons in the spinal cord, which of the following responses to a painful stimulus would be most directly affected?
If a drug selectively blocked the function of interneurons in the spinal cord, which of the following responses to a painful stimulus would be most directly affected?
- The ability to initially detect the painful stimulus.
- The strength of the muscle contraction in response to the stimulus.
- The speed at which the brain perceives the pain.
- The reflex action of withdrawing from the stimulus. (correct)
How would severing the axon of a motor neuron affect its function?
How would severing the axon of a motor neuron affect its function?
- The neuron would transform into an interneuron.
- The neuron would no longer be able to transmit signals to muscle cells or glands. (correct)
- The neuron would no longer be able to receive signals from other neurons.
- The neuron would begin to fire action potentials spontaneously.
What is the primary role of dendrites in a neuron?
What is the primary role of dendrites in a neuron?
How does the myelin sheath contribute to the function of a neuron?
How does the myelin sheath contribute to the function of a neuron?
What distinguishes a motor neuron from a sensory neuron in terms of its primary function?
What distinguishes a motor neuron from a sensory neuron in terms of its primary function?
Which part of the neuron is primarily responsible for transmitting signals away from the cell body to other neurons or target cells?
Which part of the neuron is primarily responsible for transmitting signals away from the cell body to other neurons or target cells?
If a researcher is studying the transmission of a neural impulse from one neuron to another, which specific area should they focus on?
If a researcher is studying the transmission of a neural impulse from one neuron to another, which specific area should they focus on?
If a neurotoxin specifically targets and destroys myelin sheaths, what is the most likely consequence for nerve signal transmission?
If a neurotoxin specifically targets and destroys myelin sheaths, what is the most likely consequence for nerve signal transmission?
What proportion of neurons are interneurons?
What proportion of neurons are interneurons?
What is the primary role of the sodium-potassium pump in maintaining a neuron's resting potential?
What is the primary role of the sodium-potassium pump in maintaining a neuron's resting potential?
Which of the following factors contributes most significantly to the negative charge inside a neuron at rest?
Which of the following factors contributes most significantly to the negative charge inside a neuron at rest?
Why is the term 'resting potential' somewhat misleading when describing a neuron's state?
Why is the term 'resting potential' somewhat misleading when describing a neuron's state?
How do leakage channels contribute to the resting membrane potential of a neuron?
How do leakage channels contribute to the resting membrane potential of a neuron?
Which of the following best describes the balance of forces that determine a neuron's resting potential?
Which of the following best describes the balance of forces that determine a neuron's resting potential?
If the sodium-potassium pump were to suddenly stop functioning, what would be the most immediate effect on the neuron's membrane potential?
If the sodium-potassium pump were to suddenly stop functioning, what would be the most immediate effect on the neuron's membrane potential?
Which event triggers an action potential in a neuron?
Which event triggers an action potential in a neuron?
Based on the reaction time experiment described, what is the primary factor limiting the speed of your reaction?
Based on the reaction time experiment described, what is the primary factor limiting the speed of your reaction?
How does the concentration gradient of potassium ($K^+$) across the neuron membrane contribute to the resting potential?
How does the concentration gradient of potassium ($K^+$) across the neuron membrane contribute to the resting potential?
What would be the effect on the neuron's resting membrane potential if the permeability of the membrane to $Na^+$ ions significantly increased?
What would be the effect on the neuron's resting membrane potential if the permeability of the membrane to $Na^+$ ions significantly increased?
Which of the following is the MOST accurate description of how the nervous system maintains homeostasis?
Which of the following is the MOST accurate description of how the nervous system maintains homeostasis?
What distinguishes the central nervous system (CNS) from the peripheral nervous system (PNS)?
What distinguishes the central nervous system (CNS) from the peripheral nervous system (PNS)?
In the context of the nervous system, what role do neuroglia play?
In the context of the nervous system, what role do neuroglia play?
If a trauma damages the communication lines of the nervous system, which of the following is LEAST likely to be directly affected?
If a trauma damages the communication lines of the nervous system, which of the following is LEAST likely to be directly affected?
How do the nervous and endocrine systems differ in their methods of communication and the speed of their effects?
How do the nervous and endocrine systems differ in their methods of communication and the speed of their effects?
Based on the description of the nervous system's function, which scenario BEST exemplifies the integration of sensory input and motor response?
Based on the description of the nervous system's function, which scenario BEST exemplifies the integration of sensory input and motor response?
In the lynx and hare example, what aspect of nervous system function does the lynx's nose detecting the hare represent?
In the lynx and hare example, what aspect of nervous system function does the lynx's nose detecting the hare represent?
The text mentions that nervous systems have increased in complexity through the evolution of animals. Which capability is LEAST directly associated with this increasing complexity?
The text mentions that nervous systems have increased in complexity through the evolution of animals. Which capability is LEAST directly associated with this increasing complexity?
What is the main function of the myelin sheath in neural impulse transmission?
What is the main function of the myelin sheath in neural impulse transmission?
Why is the nervous system considered a rapid communication network?
Why is the nervous system considered a rapid communication network?
Which of the scenarios is primarily governed by the nervous system's role in maintaining optimal internal conditions?
Which of the scenarios is primarily governed by the nervous system's role in maintaining optimal internal conditions?
How does the diameter of an axon affect the speed of neural impulse transmission?
How does the diameter of an axon affect the speed of neural impulse transmission?
What is the significance of the gaps in the myelin sheath (nodes of Ranvier)?
What is the significance of the gaps in the myelin sheath (nodes of Ranvier)?
In a synapse, what role do neurotransmitters play?
In a synapse, what role do neurotransmitters play?
Which of the following is a component of a synapse?
Which of the following is a component of a synapse?
What is contained within the vesicles located in the axon terminal?
What is contained within the vesicles located in the axon terminal?
What distinguishes neural pathways with unmyelinated axons from those with myelinated axons?
What distinguishes neural pathways with unmyelinated axons from those with myelinated axons?
Receptor proteins on the receiving cell bind to what?
Receptor proteins on the receiving cell bind to what?
How does the myelin sheath contribute to the efficiency of neural communication?
How does the myelin sheath contribute to the efficiency of neural communication?
What would happen if the myelin sheath were completely continuous, with no gaps?
What would happen if the myelin sheath were completely continuous, with no gaps?
Amphetamine drugs mimic the effects of norepinephrine by:
Amphetamine drugs mimic the effects of norepinephrine by:
Nicotine's addictive properties are primarily due to its ability to:
Nicotine's addictive properties are primarily due to its ability to:
Poisonous nerve gases and some insecticides are deadly because they:
Poisonous nerve gases and some insecticides are deadly because they:
Selective serotonin reuptake inhibitors (SSRIs) alleviate depression by:
Selective serotonin reuptake inhibitors (SSRIs) alleviate depression by:
Opiate drugs such as morphine and codeine act as painkillers by:
Opiate drugs such as morphine and codeine act as painkillers by:
How do amphetamines lead to a feeling of euphoria?
How do amphetamines lead to a feeling of euphoria?
Which of the following best describes the function of cranial nerves?
Which of the following best describes the function of cranial nerves?
How does nicotine impact dopamine levels in the brain?
How does nicotine impact dopamine levels in the brain?
What physiological process do nerve gases and some insecticides disrupt, leading to their toxic effects?
What physiological process do nerve gases and some insecticides disrupt, leading to their toxic effects?
What is the primary function of the peripheral nervous system (PNS)?
What is the primary function of the peripheral nervous system (PNS)?
What is the primary event that initiates an action potential?
What is the primary event that initiates an action potential?
During the repolarization phase of an action potential, which of the following events primarily contributes to the restoration of the negative membrane potential?
During the repolarization phase of an action potential, which of the following events primarily contributes to the restoration of the negative membrane potential?
How does the sodium-potassium pump contribute to the action potential?
How does the sodium-potassium pump contribute to the action potential?
What prevents the neural impulse from spreading backward along the axon during the action potential?
What prevents the neural impulse from spreading backward along the axon during the action potential?
What is the approximate duration of an action potential, from the initial influx of $Na+$ to the restoration of the resting potential?
What is the approximate duration of an action potential, from the initial influx of $Na+$ to the restoration of the resting potential?
How does the influx of $Na+$ ions affect the membrane potential during an action potential?
How does the influx of $Na+$ ions affect the membrane potential during an action potential?
Which of the following analogies best describes the propagation of a neural impulse along an axon?
Which of the following analogies best describes the propagation of a neural impulse along an axon?
What happens to the $Na+$ channels near the peak of the action potential?
What happens to the $Na+$ channels near the peak of the action potential?
What is the role of the threshold potential in initiating an action potential?
What is the role of the threshold potential in initiating an action potential?
How does local influx of $Na+$ contribute to the propagation of the action potential along the axon?
How does local influx of $Na+$ contribute to the propagation of the action potential along the axon?
Which of the following scenarios best illustrates the concept of 'present value' in financial decision-making?
Which of the following scenarios best illustrates the concept of 'present value' in financial decision-making?
An investor is considering two projects: Project A, which requires an initial investment of $50,000 and is expected to return $15,000 per year for 5 years, and Project B, which requires an initial investment of $75,000 and is expected to return $20,000 per year for 5 years. Assuming a discount rate of 8%, which project has a higher net present value (NPV)?
An investor is considering two projects: Project A, which requires an initial investment of $50,000 and is expected to return $15,000 per year for 5 years, and Project B, which requires an initial investment of $75,000 and is expected to return $20,000 per year for 5 years. Assuming a discount rate of 8%, which project has a higher net present value (NPV)?
A company is evaluating whether to invest in new equipment that costs $200,000. The equipment is expected to generate additional cash flows of $60,000 per year for the next four years. The company's cost of capital is 10%. What is the discounted payback period for this investment?
A company is evaluating whether to invest in new equipment that costs $200,000. The equipment is expected to generate additional cash flows of $60,000 per year for the next four years. The company's cost of capital is 10%. What is the discounted payback period for this investment?
A project has the following cash flows: Initial Investment = $100,000, Year 1 = $30,000, Year 2 = $40,000, Year 3 = $50,000, and Year 4 = $20,000. If the discount rate is 10%, what is the profitability index (PI) of the project?
A project has the following cash flows: Initial Investment = $100,000, Year 1 = $30,000, Year 2 = $40,000, Year 3 = $50,000, and Year 4 = $20,000. If the discount rate is 10%, what is the profitability index (PI) of the project?
A firm is deciding between two mutually exclusive projects. Project X has an IRR of 15%, while Project Y has an IRR of 20%. The firm's cost of capital is 12%. Which project should the firm choose, and why?
A firm is deciding between two mutually exclusive projects. Project X has an IRR of 15%, while Project Y has an IRR of 20%. The firm's cost of capital is 12%. Which project should the firm choose, and why?
Which of the following accurately describes the sequence of events at a synapse?
Which of the following accurately describes the sequence of events at a synapse?
What primarily determines whether a neurotransmitter's effect on a receiving cell is excitatory or inhibitory?
What primarily determines whether a neurotransmitter's effect on a receiving cell is excitatory or inhibitory?
Which of the following is NOT a typical fate of a neurotransmitter after it has been released into the synaptic cleft?
Which of the following is NOT a typical fate of a neurotransmitter after it has been released into the synaptic cleft?
A patient is experiencing tremors, muscle rigidity, and slowed movements. According to the information, which neurotransmitter imbalance is MOST likely associated with these symptoms?
A patient is experiencing tremors, muscle rigidity, and slowed movements. According to the information, which neurotransmitter imbalance is MOST likely associated with these symptoms?
How does the influx of chlorine ions (Cl-) into a receiving cell typically affect the likelihood of an action potential?
How does the influx of chlorine ions (Cl-) into a receiving cell typically affect the likelihood of an action potential?
In the context of neurotransmission, what is the role of the synaptic cleft?
In the context of neurotransmission, what is the role of the synaptic cleft?
Which of the following conditions is associated with a deficiency in acetylcholine?
Which of the following conditions is associated with a deficiency in acetylcholine?
What is the primary function of synaptic vesicles within the sending neuron?
What is the primary function of synaptic vesicles within the sending neuron?
Which of the following neurotransmitter imbalances is implicated in schizophrenia?
Which of the following neurotransmitter imbalances is implicated in schizophrenia?
If a drug mimics a neurotransmitter, binds to its receptor, and elicits the same response as that neurotransmitter, that drug is acting as an:
If a drug mimics a neurotransmitter, binds to its receptor, and elicits the same response as that neurotransmitter, that drug is acting as an:
Which of the following is the primary function of the spinal cord?
Which of the following is the primary function of the spinal cord?
What distinguishes the somatic nervous system from the autonomic nervous system?
What distinguishes the somatic nervous system from the autonomic nervous system?
In a dangerous situation, such as narrowly avoiding a car accident, which part of the nervous system is primarily activated?
In a dangerous situation, such as narrowly avoiding a car accident, which part of the nervous system is primarily activated?
What is generally the effect of the parasympathetic nervous system on the body?
What is generally the effect of the parasympathetic nervous system on the body?
Which of the following best describes the relationship between the sensory and motor pathways in the peripheral nervous system?
Which of the following best describes the relationship between the sensory and motor pathways in the peripheral nervous system?
A person is diagnosed with damage to the somatic motor neurons. Which function would most likely be impaired?
A person is diagnosed with damage to the somatic motor neurons. Which function would most likely be impaired?
How does the nervous system contribute to maintaining homeostasis in the body?
How does the nervous system contribute to maintaining homeostasis in the body?
What is the primary role of nerves in the nervous system?
What is the primary role of nerves in the nervous system?
In Guillain-Barré syndrome, the immune system attacks the peripheral nervous system. What is a potential life-threatening consequence of this?
In Guillain-Barré syndrome, the immune system attacks the peripheral nervous system. What is a potential life-threatening consequence of this?
What is the main difference between autonomic motor neurons and somatic motor neurons?
What is the main difference between autonomic motor neurons and somatic motor neurons?
A patient is experiencing facial paralysis on one side of their face with sudden onset. Which condition is most likely the cause?
A patient is experiencing facial paralysis on one side of their face with sudden onset. Which condition is most likely the cause?
When the sympathetic nervous system is activated, which of the following physiological responses would NOT be expected?
When the sympathetic nervous system is activated, which of the following physiological responses would NOT be expected?
Which division of the nervous system is responsible for slowing the heart rate and promoting digestion after a stressful event?
Which division of the nervous system is responsible for slowing the heart rate and promoting digestion after a stressful event?
A doctor tells a patient that their reflexes are not working correctly. Which part of the nervous system is likely affected?
A doctor tells a patient that their reflexes are not working correctly. Which part of the nervous system is likely affected?
What tissue type is responsible for making up the brain, spinal cord and nerves?
What tissue type is responsible for making up the brain, spinal cord and nerves?
Which of the following accurately describes the functional organization of a nervous system in coordinating a response to a stimulus, such as a lynx catching a hare?
Which of the following accurately describes the functional organization of a nervous system in coordinating a response to a stimulus, such as a lynx catching a hare?
How does the structure of a neuron directly facilitate its function in transmitting electrical and chemical signals throughout the nervous system?
How does the structure of a neuron directly facilitate its function in transmitting electrical and chemical signals throughout the nervous system?
Imagine a neuron with a damaged myelin sheath. What is the MOST likely consequence of this damage on nerve impulse transmission?
Imagine a neuron with a damaged myelin sheath. What is the MOST likely consequence of this damage on nerve impulse transmission?
Which of the following BEST describes the roles of sensory, motor, and interneurons in the nervous system?
Which of the following BEST describes the roles of sensory, motor, and interneurons in the nervous system?
If a scientist is studying neurons that respond to changes in pressure on the skin, which type of neuron are they MOST likely studying?
If a scientist is studying neurons that respond to changes in pressure on the skin, which type of neuron are they MOST likely studying?
A neurobiologist is investigating a new drug that enhances the function of synapses. Which part of the neuron is the primary target of this drug?
A neurobiologist is investigating a new drug that enhances the function of synapses. Which part of the neuron is the primary target of this drug?
How might an injury to the spinal cord affect the function of sensory and motor neurons?
How might an injury to the spinal cord affect the function of sensory and motor neurons?
Which of the following analogies BEST describes the relationship between dendrites, the cell body, and the axon of a neuron?
Which of the following analogies BEST describes the relationship between dendrites, the cell body, and the axon of a neuron?
If a researcher discovers a new type of neuron that has multiple dendrites and a very short axon, what type of function would you predict this neuron to have?
If a researcher discovers a new type of neuron that has multiple dendrites and a very short axon, what type of function would you predict this neuron to have?
How does the presence of a myelin sheath around an axon affect the energy consumption of a neuron during the transmission of a nerve impulse?
How does the presence of a myelin sheath around an axon affect the energy consumption of a neuron during the transmission of a nerve impulse?
Flashcards
Membrane potential
Membrane potential
The difference in electrical charge between the inside and outside of a neuron.
Resting potential
Resting potential
The membrane potential of a neuron when it's not conducting a signal; inside is negative.
Sodium-potassium pump
Sodium-potassium pump
Maintains resting potential by pumping 3 $Na^+$ out and 2 $K^+$ in, using ATP.
$K^+$ leakage channels
$K^+$ leakage channels
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Action potential
Action potential
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[$K^+$] inside neuron
[$K^+$] inside neuron
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[$Na^+$] outside neuron
[$Na^+$] outside neuron
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Neuron charge at rest
Neuron charge at rest
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$K^+$ equilibrium
$K^+$ equilibrium
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Resting potential generation
Resting potential generation
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Nervous System
Nervous System
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Neurons
Neurons
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Neuroglia
Neuroglia
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Central Nervous System (CNS)
Central Nervous System (CNS)
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Peripheral Nervous System (PNS)
Peripheral Nervous System (PNS)
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Sensory Input
Sensory Input
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Sensory Integration
Sensory Integration
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Motor Response
Motor Response
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Homeostasis
Homeostasis
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Nervous system speed
Nervous system speed
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Threshold Potential
Threshold Potential
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Sodium Channels
Sodium Channels
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Potassium Channels
Potassium Channels
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Influx of Na+
Influx of Na+
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Efflux of K+
Efflux of K+
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Restoration of Resting Potential
Restoration of Resting Potential
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Neural Impulse Transmission
Neural Impulse Transmission
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Nervous System Function
Nervous System Function
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Neuron Cell Body
Neuron Cell Body
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Dendrites
Dendrites
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Axon
Axon
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Synapse
Synapse
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Myelin Sheath
Myelin Sheath
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Sensory Neuron
Sensory Neuron
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Interneurons
Interneurons
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Motor Neuron
Motor Neuron
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Neural Impulse
Neural Impulse
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Cell Body (Neuron)
Cell Body (Neuron)
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Neural Impulse Speed Factors
Neural Impulse Speed Factors
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Nodes of Ranvier
Nodes of Ranvier
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Neurotransmitter
Neurotransmitter
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Synapse Components
Synapse Components
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Vesicles
Vesicles
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Receptor Proteins
Receptor Proteins
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Norepinephrine & Euphoria
Norepinephrine & Euphoria
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Nicotine's Mechanism
Nicotine's Mechanism
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Nerve Gases/Insecticides Effect
Nerve Gases/Insecticides Effect
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SSRIs Mechanism
SSRIs Mechanism
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Opiate Drugs & Endorphins
Opiate Drugs & Endorphins
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Peripheral Nervous System
Peripheral Nervous System
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Cranial Nerves
Cranial Nerves
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Spinal Nerves
Spinal Nerves
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Neurotransmitters & Depression
Neurotransmitters & Depression
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Endorphins Function
Endorphins Function
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What is a synapse?
What is a synapse?
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What is an action potential's role at the synapse?
What is an action potential's role at the synapse?
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What are synaptic vesicles?
What are synaptic vesicles?
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What are neurotransmitters?
What are neurotransmitters?
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What is the synaptic cleft?
What is the synaptic cleft?
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What is reuptake?
What is reuptake?
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What is acetylcholine?
What is acetylcholine?
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What is dopamine?
What is dopamine?
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What is GABA?
What is GABA?
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How are neurotransmitters removed from the synaptic cleft?
How are neurotransmitters removed from the synaptic cleft?
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Nervous System Tissues
Nervous System Tissues
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Brain Function
Brain Function
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Spinal Cord Function
Spinal Cord Function
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Nerve Function
Nerve Function
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Sensory Pathways
Sensory Pathways
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Motor Pathways
Motor Pathways
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Somatic Nervous System
Somatic Nervous System
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Autonomic Nervous System
Autonomic Nervous System
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Sympathetic Nervous System
Sympathetic Nervous System
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Parasympathetic Nervous System
Parasympathetic Nervous System
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Guillain-Barré Syndrome
Guillain-Barré Syndrome
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Bell's Palsy
Bell's Palsy
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Study Notes
The Nervous System
- The nervous system, along with the endocrine system, facilitates communication within the body.
- A major difference between the nervous and endocrine systems is the speed at which they act and electrochemical impulses of the nervous system travel rapidly offering virtually instantaneous effects.
- The nervous system regulates other organ systems.
- Sensory organs like ears, eyes, and nose receive sensory input.
- The central nervous system integrates this sensory input and sends signals for appropriate motor responses.
- Nervous tissue contains interconnected neurons and neuroglia.
- Neurons communicate with each other, muscles, and glands.
- Neuroglia are cells that provide support, aid neuron growth, and maintain homeostasis in the fluid surrounding neurons.
- Vertebrate's nervous systems consist of the central nervous system and the peripheral nervous system.
- The central nervous system contains the brain (inside the skull) and spinal cord.
- The main function of the central nervous system is to integrate sensory information and coordinate the body's response.
- The peripheral nervous system carries messages between the central nervous system and the rest of the body.
Neurons as Functional Units
- Neurons communicate using electrical and chemical signals.
- Neurons' function is rapid communication with each other or with muscles and glands.
Neuron Structure
- A typical neuron contains a cell body, dendrites, and an axon.
- The enlarged, rounded cell body contains the nucleus, mitochondria (for ATP), ribosomes (for protein manufacture), and other organelles.
- Dendrites are branched extensions that transmit information toward the cell body.
- Dendrite quantity ranges from one to thousands and each can receive input from many other neurons.
- The axon, aka the nerve fiber, conducts nerve impulses away from the cell body.
- Typically the axon is a single long extension that has tiny extensions at its tip.
- Each tiny terminal extension communicates with another cell at a junction called a synapse.
- Axons in many neurons have a myelin sheath that speeds nerve impulse conduction.
- Neurons are divided into three classes based on function.
- Sensory neurons bring information to the central nervous system from the rest of the body like light, pressure, sound waves, heat, touch, pain, and chemicals with the dendrites, cell body, and most of the axon residing in the peripheral nervous and the axon's endings existing in the central nervous system.
- About 90% of all neurons are interneurons, connecting one neuron to another within the spinal cord and brain with their role to receive information from sensory neurons, process, and generate messages that the motor neurons carry to muscles and glands.
- A motor neuron carries messages from the central nervous system to a muscle or gland cell with the cell body and dendrites residing in the central nervous system, but its axon extends into the peripheral nervous system to stimulate muscle cells and glands into secreting products.
Action Potentials
- Neurons transmit messages through action potentials like a wave of charged particles (ions) propagating along an axon.
- A neuron at rest has a negative charge due to membrane potential.
- Membrane potential refers to the difference in electrical charge between the inside and outside of the neuron.
- Resting potential is the membrane potential of a neuron that is not conducting a neural impulse.
- At rest, the inside of a neuron carries a negative electrical charge versus the outside.
- A neuron maintains an unequal distribution of ions across its membrane that helps maintain its gradient.
- Potassium (K+) concentration is higher inside the cell.
- Sodium (Na+) concentration is higher outside the cell.
- The sodium-potassium pump maintains this gradient by pumping three of Na+ out for every two of K+ entering for every cycle, which consumes 1 ATP.
- Membrane proteins called "leakage channels" allow some K+ to diffuse following its concentration gradient, contributing to outside being positively charged while negatively charged proteins trapped inside the cell attract K+, resulting in charge interactions and resting potential.
- Maintaining the resting potential consumes a lot of energy, with the nervous system devoting about three-quarters of its total energy budget to maintaining the ion gradients that are key to quickly responding to a stimulus.
- Changes may trigger a neuron to "fire", meaning that action potentials begin.
- An action potential is a brief reversal in membrane potential that propagates like a wave along the membrane of the axon.
- A neuron's resting potential keeps it primed to send messages and if a stimulus arrives, a small amount of Na+ leaks into the cell via sodium channels that open and immediately close, usually near the dendrites or cell body.
- If the cell's threshold potential is reached, an action potential starts leading more sodium channels to open and Na+ pours into the cell.
- The axon's membrane then has a positive charge at its interior side, this reversal of polarity only lasts for a moment.
- Near the moment when the action potential peaks, sodium channels close, preventing Na+ from entering to then see delayed K+ channels open for K+ to begin diffusing out of the cell, making the inside of the axon negative relative to outside.
- The sodium-potassium pump works to restore resting potential with the entire process taking only 1 to 5 milliseconds to complete from the initial influx of Na+.
- Action potentials appear to "jump" between the gaps to speed impulse transmission along the axon.
Neurotransmitters
- A neuron conducting action potentials must convey the impulse to muscles and glands.
- An action potential causes the release of a neurotransmitter for a sending cell to transmit a chemical signal that travels to a "receiving" cell across a tiny space.
- A synapse is a specialized junction where a neuron's axon communicates with another cell that has three components: the neuron sending the message, the cell receiving the message, and the synaptic cleft.
- Neurotransmitters diffuse across the synaptic cleft and attach to ion channel proteins on the membrane of the receiving cell.
The Myelin Sheath
- The greater the diameter of an axon, the faster it conducts an impulse.
- Myelin prevents ion flow across the membrane and acts as insulation to prevent the spread of action potentials.
- Ions can move across the membrane at the gaps in the sheath and the incoming Na+ entering the axon diffuses to the next gap to trigger an action potential to "jump".
- The neural impulse moves up to 100 times faster in a myelinated axon and sensory messages travel from toe to spine in about one third the speed of sound.
Disorders Associated with Neurotransmitter Imbalances
- Alzheimer's disease: deficient acetylcholine leads to memory loss, depression, disorientation, dementia, hallucinations, and death.
- Epilepsy: excess GABA, norepinephrine, and dopamine leads to seizures and loss of consciousness.
- Huntington's disease: deficient GABA causes uncontrollable movements, dementia, behavioral and personality changes, and death.
- Parkinson's disease: deficient dopamine exhibits tremors of hands, slowed movements, and muscle rigidity.
- Schizophrenia: deficient GABA and excess dopamine causes inappropriate emotional responses and hallucinations.
Drugs and Neurotransmitters
- Amphetamine drugs cause alertness and mood by binding to norepinephrine receptors and blocking reuptake of norepinephrine.
- Nicotine crosses the blood-brain barrier and reaches the brain within seconds of inhaling to attach to acetylcholine receptor proteins to release dopamine, which provides pleasurable feelings of avoiding withdrawals.
- Drugs that increase the amount of serotonin in a synapse appear to reduce depression as selective serotonin reuptake inhibitors(SSRIs) block the reuptake of serotonin to accumulate serotonin.
- Humans produce several types of endorphins whose molecules influence mood and perception of pain; Opiate drugs such as morphine, heroin, codeine, and opium are potent painkillers that bind endorphin receptors to elevate mood as well.
Peripheral Nervous System
- Neurons of the brain and spinal cord interact constantly with nerves and axons encased in connective tissue.
- Cranial nerves emerge directly from the brain carry sensory information to the central nervous system.
- Spinal nerves emerge from the spinal cord and control functions from the neck down.
- The peripheral nervous system is divided into sensory and motor divisions.
- Sensory pathways carry signals to the central nervous system from sensory receptors.
- Motor pathways convey information from the central nervous system to glands and muscles.
- The motor pathways of the peripheral nervous system include the somatic (voluntary) and autonomic (involuntary) nervous systems.
- The somatic nervous system carries signals from the brain to voluntary skeletal muscle.
- The autonomic nervous system transmits impulses to smooth and cardiac muscle as well as glands and internal organs without awareness.
- The autonomic nervous system is divided into the sympathetic and parasympathetic nervous systems.
- The sympathetic nervous system dominates in times of stress including emergencies and prepares the body for "fight or flight" by increasing heart rate and breathing.
- The parasympathetic nervous system returns body systems to normal during relaxed times for "rest and repose" to slow heart rate and resume digestion.
- The autonomic nervous system remains always active to maintain homeostasis through the balance of the sympathetic and parasympathetic system.
- Guillain-Barré syndrome causes the immune system to attack and destroy peripheral nervous system nerves and can be life-threatening if it causes paralysis, breathing difficulty, or heart problems.
- Bell's palsy is another peripheral nervous system disorder and damages a cranial nerve controlling the muscles on one side of the face which strikes quickly and resolves or remains permanent.
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