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Questions and Answers
What is an example of an evoked response?
Electrical recordings are the only way to measure the activity of neurons and muscle cells.
False
What are excitable cells?
Cells that can change their membrane potential to transmit information, including neurons and muscle cells.
The resting membrane potential is commonly abbreviated as ______.
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Match the types of stimulation with their corresponding applications:
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Which tool is NOT used in clinical neurophysiology?
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Neurophysiology only examines the central nervous system.
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What occurs during the action potential (AP)?
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What happens to sodium channels during repolarization?
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The duration of an action potential (AP) is the same in all excitable cells.
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What is the role of the Na+/K+-ATPase during the refractory period?
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During the ______ period, the membrane cannot generate a further action potential.
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Match the following types of cells with the duration of their action potentials:
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Which ions are predominantly affected during the action potential process?
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Local anesthetics block calcium channels permanently.
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What is the all-or-none principle in action potentials?
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Refractory periods help determine the maximal ______ rate of action potentials.
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Which component is responsible for stabilizing the membrane of excitable cells?
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Which type of efferent fiber is responsible for innervating the main contractile muscle cells?
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Afferent Ia-fibers carry information about the absolute length of the muscle.
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What is the primary function of Ib-fibers?
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The contractile elements within muscle spindles are called __________.
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Match the following fibers to their functions:
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How do afferent fibers from the tendons protect muscles?
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The elastic center of intrafusal muscle cells helps preserve the sensitivity of the muscle spindle.
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What is the formula for signal-to-noise ratio (SNR)?
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What is the role of α-motoneurons in muscle innervation?
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Electrocerebral silence has a typical SNR of 10:1.
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Afferent fibers from the spindle form the circuit for the __________ reflex.
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What is the typical SNR range for spontaneous activity in EMG?
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Which fibers are part of the muscle spindle that measure the length of the muscle?
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The typical SNR for CMAP in ENG is greater than ______:1.
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Match the following SNR values with their corresponding types:
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What does the evoked response from motor nerve stimulation called?
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The nerve conduction velocity is determined by the diameter of the fibers and their myelination.
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What should be done to ensure that nerve stimulation activates the whole motor pool?
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The ______ latency is observed to measure the time from stimulation to the response onset.
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Match the following conduction velocities with their corresponding fiber classification:
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What factor makes it unreasonable to calculate nerve conduction velocity directly from stimulation to recording?
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Stimulation should occur with submaximal stimuli.
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What is the relationship between the distance between stimulation sites and latency difference?
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Increasing the stimulus strength by 2 mA ensures that the stimulation is ______.
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Which of the following is associated with the slowest conduction velocity?
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What primarily generates the EEG recordings?
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Which frequency band in the EEG is primarily associated with cortical inhibition?
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The ascending reticular activating system (ARAS) primarily regulates which aspects of neural function?
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What does beta activity in the EEG indicate?
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Which statement accurately describes the relationship between frequency bands and synaptic activity in the EEG?
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Which of the following symptoms is NOT a cardinal sign of Parkinson's disease?
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What is the primary target for deep brain stimulation (DBS) in Parkinson's disease?
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What type of recording shows potential input data in the context of DBS?
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Which of the following strategies is NOT aimed at reducing adverse effects during DBS?
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In the context of Parkinson's disease, what physiological change occurs due to the loss of dopaminergic neurons?
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What symptom is associated with the bradykinesia aspect of Parkinson's disease?
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Which of the following best describes the role of the vestibulocerebellum?
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Which of the following is NOT considered an adverse effect of deep brain stimulation?
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What is the primary focus of neurophysiology?
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Which of the following techniques is primarily used for analyzing the electrical activity of single neurons?
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What type of electrical activity does the electromyogram (EMG) primarily measure?
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How is the assessment of heart-rate variability most commonly extracted from ECG recordings?
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What does spontaneous electrical activity in the nervous system refer to?
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Which of the following statements about neurophysiological findings is accurate?
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Which of the following describes the electroencephalogram (EEG)?
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In clinical practice, which measurement is typically excluded from neurophysiology despite its relevance?
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Which physiological characteristic is primarily analyzed using patch clamp techniques?
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What effect does a decrease in the diameter of the motor nerve branches have on action potential propagation velocity?
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In neuromuscular junctions, what is the primary role of the synapse known as the motor end plate?
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Which of the following best defines a motor unit?
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What is the impact of changing the polarity during direct nerve stimulation when recording responses?
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What defines the relationship between the size of motor units and the muscles demonstrating well-graded force development?
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What type of current is typically used to stimulate nerves with bipolar electrodes?
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When recording from a nerve with many fibers, what shape do the recorded responses typically differ from?
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What is a common misconception about the anodal block during nerve stimulation?
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What is the relationship between the distance between stimulation sites and the latency difference?
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What is the purpose of an electrode's cathode placement during nerve stimulation?
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What is the primary characteristic of sensory nerve conduction in carpal tunnel syndrome?
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What treatment is recommended for carpal tunnel syndrome with minor symptoms?
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Which of the following symptoms is most commonly associated with cubital tunnel syndrome?
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What is a common diagnostic procedure for carpal tunnel syndrome when nerve conduction studies are inconclusive?
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How is muscle atrophy in cubital tunnel syndrome typically evaluated?
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What is a specific finding in nerve conduction tests that indicates Guyon's canal syndrome?
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What is the surgical intervention for carpal tunnel syndrome referred to in the content?
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Which nerve root levels are primarily involved in muscle atrophy associated with cubital tunnel syndrome?
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What distinguishes the symptoms of Guyon's canal syndrome from cubital tunnel syndrome?
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Which treatment strategy is ineffective if carpal tunnel syndrome symptoms are major or refractory to initial therapy?
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Match the components of the basal ganglia pathways with their respective functions:
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Match the types of dopamine receptors with their effects in the striatum:
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Match the phases of cortical stimulation response with their descriptions:
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Match the pathways with their corresponding outcomes:
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Match the anatomical features of the basal ganglia with their specific roles:
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Match the types of evoked responses with their corresponding stimulation methods:
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Match the neurophysiological tools with their applications:
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Match the types of cells with their primary characteristics:
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Match the physiological terms with their definitions:
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Match the types of neurophysiology with their primary focus:
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Match the types of reflex pathways with their characteristics:
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Match the types of ion channels with their roles during action potential:
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Match the definitions with their corresponding physiological processes:
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Match the type of muscle fiber with its primary function:
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Match the type of sensory fiber with its corresponding origin:
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Match the reflex pathway with its associated function:
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Match the component of muscle spindles with its description:
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Match the afferent fiber type with their specific role:
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Match the type of nerve fiber with its conduction velocity:
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Match the following types of refractory periods with their characteristics:
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Match the following cell types with their action potential duration:
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Match the term with its corresponding definition in muscle innervation:
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Match the ion channels with their roles during an action potential:
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Match the type of fiber with the aspect of muscle they innervate:
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Match the sensory fiber type with the information it carries:
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Match the following terms with their definitions related to action potentials:
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Match the following drugs with their effects on ion channels:
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Match the following phases of action potential with their characteristics:
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Match the following cellular activities with their respective ions:
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Match the following anatomical features of neurons with their functions:
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Match the following physiological concepts with their implications in excitable cells:
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Match the EEG frequency bands with their corresponding frequency ranges:
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Match the EEG findings with their descriptions during normal conditions:
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Match the factors affecting normal EEG findings with their descriptions:
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Match the abnormal EEG conditions with their potential causes:
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Match the EEG activity changes with their triggers:
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Match the EEG frequencies with their typical characteristics:
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Match the abnormal EEG patterns with their implications:
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Match the EEG states with their resting conditions:
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Match the EEG findings with their locations in the brain:
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Match the stimulus factors with their effects on EEG activity:
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What are the frequency ranges for the Delta and Beta EEG bands?
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How does lateral inhibition contribute to the localization of a damaging stimulus?
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How does eye opening affect Alpha EEG activity?
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What are potential causes of pathologically slowed EEG activity?
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What role do small interneurons play in the neural circuitry related to pain stimuli?
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Explain how the convergence-divergence circuitry functions in response to sensory input like a pain stimulus.
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What distinguishes the Alpha rhythm in an EEG?
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What does 'electrocerebral silence' indicate in an EEG?
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In the context of clinical neurophysiology, what is a significant challenge in extracellular recordings?
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Why is it important to consider the relationship between stimulus strength and activation of the motor pool?
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What is the consequence of setting recording electrodes too far from excitable cells in neurophysiological studies?
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Describe the significance of time-dependent voltage changes in the context of electrophysiological recording.
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What factors influence the nerve conduction velocity, and how do they relate to fiber diameter?
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What nerve is compressed in meralgia paresthetica?
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What are the roles of the Inner Helmholtz plane (IHP) and Outer Helmholtz plane (OHP) in the electrode-electrolyte interface?
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What are two common symptoms of polyneuropathy?
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What is the primary mechanism behind distal axonopathy?
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Describe the composition and function of mixed nerves.
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What is the significance of pseudounipolar ganglion cells in nerve fiber anatomy?
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What do F-waves signify in neurophysiology?
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What does the H-reflex reflect in the nervous system?
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How do the spinal roots contribute to nerve function?
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Name one inherited cause of polyneuropathy.
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Explain the role of the skin interface in electrode measurements.
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What types of fibers are involved in the spinal nerve structure?
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Which acquired condition is often associated with polyneuropathy?
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Discuss the anatomical locations of somata for afferent somatosensory nerves.
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What is the typical progression pattern of polyneuropathy symptoms?
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What role does assessment with somatosensory evoked potentials play in diagnosing peripheral nerve issues?
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What type of signals do mixed nerves primarily transmit?
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How do efferent motor fibers function in relation to muscle contraction?
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What distinguishes myelinopathy from other types of polyneuropathy?
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Why are vegetative fibers typically not assessed electrophysiologically in mixed nerves?
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What are the main parts of the neuron involved in action potential propagation?
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How does myelin affect the speed of action potential propagation?
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What is the role of nodes of Ranvier in axonal signaling?
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What initiates the release of neurotransmitters at the synapse?
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Describe the primary method of signal transmission between neurons.
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What factors influence the conduction velocity of nerves?
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What does the term 'saltatory conduction' refer to?
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How does the diameter of an axon affect action potential speed?
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What ensures that two neurons do not connect electrically?
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What is the significance of the action potential's all-or-none principle?
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What does neurophysiology primarily study?
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What historical approach has dominated the field of neurophysiology?
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What is spontaneous electrical activity in neurophysiology exemplified by?
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How does an electromyogram (EMG) relate to neurophysiology?
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Why can knowledge of the nervous system architecture be important in neurophysiology?
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What are voltage-clamp and patch-clamp techniques used for in neurophysiology?
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What role does heart-rate variability play in neurophysiology?
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What characterizes the distinction between EEG and ECG in terms of neurophysiology?
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What are the main types of acute peripheral nerve lesions?
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How does temperature affect motor nerve conduction studies?
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What happens during the regeneration process in neurapraxia?
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What occurs when a neurotransmitter opens sodium channels in the postsynaptic membrane?
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In the context of motor nerve conduction, what is meant by distal motor latency?
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What characterizes chronic peripheral nerve damage compared to acute injuries?
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How does an inhibitory postsynaptic potential (IPSP) affect the postsynaptic neuron?
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What is the significance of the axon hillock in neural signaling?
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Which factors can lead to difficulties in stimulating nerves during conduction studies?
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What are the differences in nerve conduction velocity (NCV) associated with axonotmesis and neurotmesis?
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What is 'divergence' in the context of neural circuitry?
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How does the amplitude of a nerve conduction study change during axonotmesis?
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Describe the process of convergence in neural networks.
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Why is sensory nerve conduction often unsuccessful with skin stimulation?
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How does the convergence-divergence circuitry function in response to a new sensory input?
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What is the main clinical indication for neurotmesis?
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Why do EPSPs and IPSPs last longer than action potentials?
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How many synaptic relays are typically involved in the somatosensory pathway?
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What reflects the dynamic nature of information processing in neural networks?
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What role do subsynaptic membranes play in a neuron?
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What is the role of the striatum in the direct pathway of the basal ganglia?
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Explain how dopaminergic projections from the substantia nigra affect the striatum.
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What are the phases of the triphasic response observed during cortical stimulation?
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Describe the function of the indirect pathway in the basal ganglia.
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What effect does the activation of D1 and D2 receptors in the striatum have on thalamocortical transmission?
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What is the primary function of the basal ganglia in motor control?
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Describe the role of the extrapyramidal system in muscle movement.
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How are the basal ganglia and the thalamus related in the context of neural pathways?
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What processes are modulated by the basal ganglia besides voluntary movement?
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What constitutes the primary role of the N.oculomotorius and N.abducens during intraoperative monitoring?
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Describe the characteristics of muscle spindle afferent fibers.
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What does EMG stand for, and what does it measure in intraoperative monitoring?
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In the context of motor pathways, how does the basal ganglia influence reflex arcs?
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What is the significant role of the cranial nerves monitored during surgery?
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How do the basal ganglia contribute to the stability of movements?
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Which of the following is a cardinal sign of Parkinson's disease?
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Deep brain stimulation (DBS) can only be used when all medication options have been exhausted.
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What is the main neurotransmitter affected in Parkinson's disease?
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In Parkinson's disease, the loss of neurons occurs primarily in the substantia nigra pars __________.
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Match the following symptoms of Parkinson's disease with their descriptions:
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What is the first line of therapy for managing Parkinson's disease?
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Phase amplitude coupling (PAC) is a technique used in DBS optimization to enhance stimulation outcomes.
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List one potential adverse effect of deep brain stimulation (DBS).
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What does neurophysiology primarily study?
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The electrocardiogram (ECG) is typically included in neurophysiological assessments.
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What is a common technique used to record spontaneous electrical activity in the nervous system?
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Neurophysiology examines not only the central but also the ______ and ______ nervous systems.
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Match the following neurophysiological techniques with their primary use:
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Which technique is used to analyze single neurons?
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Spontaneous electrical activity can include measurements from muscle cells.
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The analysis of the electrical activity of ______ has historically dominated neurophysiology.
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What are the electrical measurements typically used in neurophysiology called?
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Which of the following statements is true regarding neurophysiological findings?
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What is one primary function of the basal ganglia?
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The extrapyramidal system consists of only pyramidal tracts.
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What is the role of the basal ganglia in motor control?
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The _______ are a group of subcortical nuclei involved in procedural and habit learning.
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Match the following types of monitoring with their applications:
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Which electrode position corresponds to the front of the brain?
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Midline electrode positions are indicated by even numbers.
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What are the potential differences measured by EEG?
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The __________ electrode position refers to the area of the brain near the ears.
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Which type of montage is described as more sensitive?
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Match the following EEG montages with their characteristics:
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What is the primary disadvantage of bipolar montages?
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The Laplacian montage is primarily used for long-distance signal monitoring.
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What determines how the electrical activity is recorded in EEG?
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The __________ montages typically use an ear as a reference point.
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What is the key factor that leads to a decrease in nerve conduction velocity (NCV) in the case of neurapraxia?
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Axonotmesis is characterized by complete disruption of the entire nerve.
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What is the term for the degeneration that occurs with complete nerve disruption?
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In chronic nerve damage, the repeated degeneration and regeneration of the ______ sheath occurs.
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Match the type of nerve lesion with its characteristic:
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What is a common pitfall that can affect nerve conduction studies?
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Amplitude can be easily assessed due to its consistent variability across stimulation sites.
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What is the typical regeneration rate for axonal repair in case of axonotmesis?
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The ______ is used to measure the time from stimulation to the response onset in nerve conduction studies.
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Which condition does NOT typically involve nerve entrapment syndromes?
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Study Notes
Evoked Responses
- After a stimulus, the evoked response is an approach to analyzing the nervous system.
- It's used to evaluate the connections between neurons. (neural pathways)
Electrical Stimulation
- This involves applying a stimulus to a peripheral nerve.
- It triggers a muscle contraction in the area innervated by the nerve.
- Other than electrical current, techniques like visual, acoustic, mechanical, and magnetic stimulation can also be used to test sensory and motor pathways.
Clinical Neurophysiology
- The application of neurophysiological techniques to human subjects for diagnostic and therapeutic purposes.
- It's used to assess and diagnose diseases of the central, peripheral, and autonomic nervous systems.
- Also used for therapeutic interventions in suitable neurological disorders or functional disturbances.
Cellular Level
- All neurophysiological phenomena are based on the ability of excitable cells to transmit information by changing their membrane potential.
- These include neurons, muscle cells, and some secretory cells.
Action Potential (AP)
- The membrane change associated with signal propagation is called the action potential.
- During repolarization, sodium channels close, and potassium channels open, returning the membrane potential to a negative value.
- The refractory period occurs during which the ion channels are inactivated, and sodium and potassium return to their resting state distributions by the Na+/K+-ATPase (sodium-potassium-pump).
- This period determines the maximum AP repetition rate, limiting the speed of the signal.
Action Potential Properties
- The duration of an AP varies for different excitable cells.
- An AP only triggers when the depolarization threshold is exceeded.
- In physiological conditions, its shape does not differ and is independent of the stimulus current, following the "all or none principle".
Calcium Channels
- Voltage-gated calcium channels have been discovered, influencing cellular activity lasting 100 ms or longer.
- In heart muscles, they're related to the plateau phase of the action potential.
- In some CNS neurons, they contribute to long bursts of sodium spikes.
- They are mediators of cellular activity following the AP in muscle cells.
Neuron Anatomy
- The typical anatomy of a neuron includes:
- Axon
- Dendrites
- Soma (cell body)
Muscle Innervation
- Muscle innervation is complex, involving:
- Two different efferent fibers:
- Aα-fibers from α-motoneurons to the main contractile muscle cells
- Aγ-fibers from γ-motoneurons to the contractile elements of the muscle spindles
- Two afferent sensory fibers from the muscle spindle:
- Ia – fibers carrying information of the velocity of length change
- II – fibers carrying information about the absolute length
- Ib – fibers from receptors in the tendons carry information about the tension
- Two different efferent fibers:
- Afferent fibers establish synaptic contacts directly or via interneurons with the α-motoneurons, crucial for the deep tendon reflexes.
- Afferents from the tendons inhibit the motoneurons, protecting the muscle from damage.
Muscle Spindles
- Contractile elements (intrafusal muscle cells) are located at both ends of the cells. The center is elastic.
- The contraction of the ends compensates for length changes due to the contraction of the outer (extrafusal) muscle cells, preserving receptor sensitivity.
- They are involved in modifying reflex circuits for voluntary movements.
Electroneurography (ENG)
- ENG measures nerve function by stimulating a nerve and recording the electrical response from a muscle.
- There are several peaks in the ENG recording, corresponding to fiber groups of different diameters, myelinisation, and AP propagation velocities.
ENG - Motor Nerve Conduction
- The CMAP (compound muscle action potential) is the evoked response recorded from a muscle.
- The distal motor latency is the time between stimulation and the onset of the response.
- Conduction velocities can be calculated.
- Stimulation should be supramaximal to activate all motor units.
Technical Notes - Signal to Noise Ratio (SNR)
- SNR is the ratio of signal power to noise power.
- Noise can be technical or biological.
- Different neurophysiological recordings have different typical SNRs.
Afferent Pathways
- Descending modulation is primarily inhibitory.
- It travels downwards to spinal levels (spinothalamic tract).
- It's involved in the control of sensitivity in peripheral receptors.
Basal Ganglia
- Responsible for a variety of motor functions including initiation and termination of movements, stabilization of movements, and stabilizing muscles at rest
- Involved in several diseases, including Parkinson's Disease
Parkinson's Disease
- Characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta
- May result in hyperactivity of the SNret and inhibition of thalamocortical projections, inhibiting movement initiation
- Displays four cardinal signs:
- Akinesia/Bradykinesia
- Difficulty with starting and stopping movements
- Impaired facial expressions
- Micrography
- Parkinsonian gait
- Tremor
- Rigidity
- Postural instability
- Akinesia/Bradykinesia
- Other symptoms include neuropsychiatric and vegetative disturbances
Parkinson's Disease Therapy
- First-line treatment involves medications such as L-Dopa and dopamine agonists
- In case of drug resistance, deep brain stimulation (DBS) is an alternative treatment method
Deep Brain Stimulation (DBS) in Parkinson's Disease
- Uses electrodes implanted in the subthalamic nucleus (STN)
- Records neurophysiological biomarkers via extracellular microelectrodes or implanted DBS electrodes
- Recording involves:
- Extracellular recordings of a circumscribed neuron population which are then processed via:
- High-pass filter to assess neuronal firing and action potentials of local neurons (output)
- Low-pass filter to assess local field potential
- Represents pre- and postsynaptic potentials (input)
- Often transferred in the frequency domain and labeled according to EEG frequency bands
- Extracellular recordings of a circumscribed neuron population which are then processed via:
DBS Optimization
- The optimal DBS location can be determined by analyzing neuron firing patterns
- Microelectrodes record from a limited number of neurons compared to DBS electrodes
- DBS optimization involves analyzing local field potentials (LFPs), which show a peak in the lower beta frequency band
- Modern DBS systems with multiple electrodes can record LFPs for closed-loop stimulation (aDBS)
DBS Effect on LFPs
- DBS can change LFPs and alter neuron firing patterns
- Phase-amplitude coupling (PAC) describes the interplay between oscillations in different frequency bands
DBS Segmented Stimulation
- Stimulates specific brain regions at different times in a controlled manner
- Used to reduce side effects and improve treatment efficacy
DBS Adverse Effects
- Includes infections, hemorrhage, speech arrest, apathy, hallucinations, hypersexuality, cognitive dysfunction, depression, and euphoria
- Strategies to avoid adverse effects include single-shot antibiotics, electrophysiologically optimized placement of DBS electrodes, closed-loop stimulation, and directional stimulation
Cerebellum
- Plays a significant role in coordinating movements and maintaining balance
- Divided into three main regions:
- Vestibulocerebellum: Responsible for posture, equilibrium, and muscle tone
- Spinocerebellum: Responsible for error correction, adjusting posture, and smooth movement coordination
- Cerebrocerebellum: Responsible for planning, programming, and coordination of complex movements, as well as timing and sequencing of movements
Evoked Responses and Neurophysiology
- Evoked responses are used to analyze the nervous system, especially to assess neural pathways.
- Stimuli like electrical, visual, acoustic, mechanical, and magnetic stimulation are used to assess sensory and motor pathways.
Electrical and Mechanical Recordings
- Electrical recordings are not the only way to measure neuron and muscle cell activity.
- Mechanical transducers can be used to assess muscle contractions, like in bladder or rectal pressure measurements.
- Neurophysiology uses tools from chemistry, physics, and other fields to examine brain activity.
Clinical Neurophysiology
- Clinical neurophysiology applies neurophysiological techniques to humans for diagnostic and therapeutic purposes.
Cellular Level and Excitable Cells
- Neurons, muscle cells, and some secretory cells are excitable cells.
- These cells transmit information through changes in their membrane potential.
- The baseline membrane potential is called resting (membrane) potential (RMP).
- The membrane change associated with signal propagation is called action potential (AP).
Action Potential (AP)
- AP is made up of four phases: depolarization, repolarization, refractory period, and return to resting state.
- The duration of an AP varies across excitable cells, lasting 1 ms in nerve cells, 10 ms in muscle cells, and up to 500 ms in heart muscle cells.
- AP triggers when the depolarization threshold is exceeded.
- The shape of the AP is cell-specific and independent of the stimulus current, following the all-or-none principle.
- Ion channels and the Na+/K+ - ATPase can be affected by drugs used for clinical purposes.
Calcium and AP
- Extracellular Ca++ is essential for membrane stability in excitable cells.
- Several voltage-gated Ca++ - channels result in Ca++ - based activity.
- Ca++ activity is related to the plateau phase of the action potential in heart muscles and slow calcium spikes in CNS neurons.
Neuron Anatomy
- Neurons are comprised of a soma (cell body), dendrites (receiving signals), and an axon (transmitting signals).
Muscle Innervation
- Muscle innervation involves two types of efferent fibers: Aα-fibers and Aγ-fibers.
- Aα-fibers from α-motoneurons innervate the main contractile muscle cells.
- Aγ-fibers from γ-motoneurons innervate the contractile elements of muscle spindles.
- Muscle spindles also contain two types of afferent sensory fibers: Ia – fibers and II – fibers.
- Ia – fibers carry information about the velocity of length change.
- II – fibers carry information about the absolute length.
- Ib – fibers from receptors in the tendons carry information about tension.
Muscle Spindles
- The contractile elements within the muscle spindles (intrafusal muscle cells) are located at both ends of the cells.
- The center of the cells is elastic.
- The contraction of the ends compensates for length changes due to contraction of the outer (extrafusal) muscle cells.
- This ensures the sensitivity of the receptor and modifies the reflex circuit during voluntary movement.
Electroencephalography (EEG)
- The brain displays permanent electrical activity.
- EEG records this activity on the scalp as rhythmic activity within distinct frequency bands: Gamma, Beta, Alpha, Theta, and Delta.
Normal EEG Findings
- Normal EEG varies depending on individual factors, normal variants, region of origin, external stimuli, attention level, age, and sleep stage.
- Alpha-EEG is very regular, with individual-specific frequency.
- It's accentuated over the occipital and temporal lobes.
- Side differences in amplitude of less than 50% are normal.
- Alpha-EEG is often modulated in the form of a spindle.
- It's blocked by eye opening and restored after eye closing.
Beta-EEG
- Beta-activity is present in all channels with alpha-activity seen after eye closing.
- It indicates drowsiness, sleep, strain, and drug-induced states.
Abnormal EEG Findings
- Pathologically slowed EEG is dominated by Theta- and/or Delta-activity.
- It's associated with elevated intracranial pressure, impaired consciousness, and specific sleep stages.
- Alpha-coma is a unique condition where alpha-activity is present despite impaired consciousness.
- Burst-suppression EEG contains alternating periods of high-amplitude bursts and suppression of activity.
- Electrocerebral silence is a complete absence of EEG activity.
- Focal abnormalities are circumscribed slowing or epileptic activity.
- They can indicate tumors, small bleedings, infarctions, etc.
Basal Ganglia
- The basal ganglia regulate voluntary movement, learning, and cognition.
- It receives input from the cortex and projects to the thalamus.
- The basal ganglia consist of the striatum, globus pallidus, subthalamic nucleus, and substantia nigra.
- There are two pathways: direct and indirect.
- The direct pathway facilitates thalamocortical projections, while the indirect pathway inhibits them.
- The substantia nigra pars compacta provides dopaminergic projections to the striatum.
- D1 receptors in the striatum cause excitation, while D2 receptors cause inhibition.
- These dopaminergic projections modulate the balance between the direct and indirect pathways.
Cortical Stimulation and Basal Ganglia
- Cortical stimulation yields a triphasic response in the basal ganglia output nuclei (SNret/GPi).
- The initial response is increased activity, inhibiting thalamocortical projections.
- This is followed by decreased activity, leading to disinhibition and movement release.
- The final phase shows increased activity again, inhibiting thalamocortical projections and stopping movement release.
Neural Networks
- A pain stimulus activates a convergence-divergence circuitry, amplifying the signal for a rapid response.
- Lateral inhibition: Interneurons in each relay level create inhibitory connections, refining the localization of the stimulus by enhancing contrast.
- Lateral inhibition limits impulse propagation to the afferences from the damaged site.
Electrophysiological Recording
- Extracellular recording measures voltage changes related to the activity of excitable cells.
- The potential difference between two electrodes is amplified and converted to a signal for display.
- Extracellular recordings have a lower signal-to-noise ratio and complex relationship between the extracellular field and cellular processes.
Action Potential (AP) Propagation
- APs propagate along the axon membrane, allowing signal transmission.
- Propagation occurs due to local transmembrane currents that depolarize the membrane, triggering APs in adjacent segments.
- AP propagation can occur in both directions but is much slower than the current in electric cables.
Myelination & Conduction Velocity
- Myelin sheaths accelerate AP propagation by increasing membrane resistance and reducing capacitance.
- Myelin is made up of Schwann cells in the peripheral nervous system and oligodendrocytes in the central nervous system.
- Factors affecting conduction velocity: axon diameter, temperature, length of the inter-node distance.
Neuron Anatomy
- The axon typically branches, establishing contact with other neurons or muscle cells at the terminals.
- Electrical connections between neurons are uncommon.
Synapses
- The usual signal transfer between neurons occurs chemically at synapses.
- Axon terminals contain vesicles filled with neurotransmitters.
- AP arrival at the presynaptic axon triggers the release of neurotransmitters, opening Ca++ channels.
- Released neurotransmitters bind to receptors on the post-synaptic membrane, influencing ion channel activity.
Electrode-Electrolyte Reaction
- An electrode-electrolyte interface forms between an electrode and an electrolyte solution.
- The interface is characterized by the formation of an Inner Helmholtz Plane (IHP) and an Outer Helmholtz Plane (OHP).
Electroneurography (ENG)
- Most nerves are mixed, containing motor and sensory fibers.
- Motor fibers are axons of motoneurons, conveying commands to voluntary muscles.
- Sensory fibers transmit information from sensory receptors to the CNS.
- Somatosensory neuron cell bodies reside in spinal ganglia.
- Mixed nerves also contain vegetative fibers, but are not usually assessed electrophysiologically.
Meralgia Paresthetica
- Compression of the lateral femoral cutaneous nerve under the inguinal ligament.
- Causes pain and numbness on the lateral aspect of the thigh.
- No reliable sensory nerve conduction test for diagnosis.
Polyneuropathy
- Damage or disease affecting peripheral nerves bilaterally.
- Symptoms include weakness, numbness, burning pain.
- Often begins in hands and feet, progressing to arms, legs, and potentially the autonomic nervous system.
- Can be acute or chronic.
- Causes include diabetes, alcoholism, vitamin B12 deficiency, and various genetic conditions.
Polyneuropathy Classification
- Distal axonopathy: Interrupted function of peripheral nerves due to metabolic or toxic disturbances.
- Myelinopathy: Loss of myelin.
- Neuronopathy: Issues with peripheral nervous system neuron cell bodies.
F-waves & H-reflex
- F-waves are evoked by supramaximal electrical stimuli applied to the distal portion of a nerve.
- The impulse travels orthodromically (towards muscle) and antidromically (towards the cell body).
- The orthodromic impulse elicits a direct motor response (M).
- The antidromic impulse reaching the spinal cord cell bodies generates a second AP (F-response) due to persistent dendritic depolarization.
H-reflex
- Reflects the monosynaptic reflex circuit of spinal stretch reflexes.
Electroencephalography (EEG) Frequency Bands
- The brain exhibits continuous electrical activity, recorded as rhythmic activity within distinct frequency bands.
- Gamma: > 31 Hz
- Beta: 13-30 Hz
- Alpha: 8-12 Hz
- Theta: 4-7 Hz
- Delta: < 4 Hz
Normal EEG Findings
- The EEG varies based on individual factors, normal variants, recording location, stimuli, attention level, sleep stage, and age.
- Alpha EEG is regular, individual-specific, accentuated over occipital and temporal lobes, and blocked by eye opening.
- Beta EEG is dominant when the individual is awake, alert, or stressed.
- Theta and Delta activity are characteristic of sleep stages.
Abnormal EEG Findings
- Pathologically Slowed EEG: Dominated by Theta and/or Delta activity, indicating potential issues such as elevated intracranial pressure or impaired consciousness.
- Burst-Suppression EEG: Alternating periods of electrical activity and suppression, commonly associated with severe brain injury or coma.
- Electrocerebral Silence: Absence of electrical activity, considered a sign of brain death.
- Focal Abnormalities: Localized slowing or epileptic activity, indicating possible underlying pathology.
Neurophysiology Definition
- Neurophysiology is a branch of biology focusing on the functionality of the nervous system
- Neurophysiology studies the central, peripheral, and autonomous nervous systems
- Analyzing the activity of neurons is a key element of historical neurophysiology
- The understanding of the nervous system architecture is essential to interpret neurophysiological findings.
Postsynaptic Potentials
- Neurotransmitters can open sodium channels, causing depolarization (EPSP)
- Neurotransmitters can also open potassium channels, causing hyperpolarization (IPSP)
- EPSPs and IPSPs last longer than action potentials and can add or subtract
Neural Network Example
- Sensory pathways typically have three synaptic relays from the periphery to primary sensory cortex neurons.
- Presynaptic axons establish excitatory synaptic connections with many postsynaptic neurons (divergence).
- Postsynaptic neurons recieve input from many excitatory presynaptic axons (convergence).
- This convergence-divergence circuitry acts like an amplifier, enabling a quick response to potentially harmful stimuli.
Electromyography (EMG) Motor Nerve Conduction
- Potential difficulties with stimulation include thick subcutaneous tissue and deep, intramuscular nerve courses.
- Stimulation can be irraditated to neighboring nerves, especially at the wrist.
- Temperature variations in the extremities are a consideration.
EMG Motor Nerve Conduction Assessment
- The assessment involves analysis of distal motor latency, amplitude, and velocity.
- Side differences and differences between stimulation sites are noted.
- Absolute amplitude values are difficult to assess due to variability.
EMG Motor Nerve Conduction Age
- The values of motor nerve conduction change with age.
Peripheral Nerve Lesion Types
-
Acute Injuries
- Neurapraxia: Segmental degeneration of the myelin sheath
- Axonotmesis: Disruption of axons with intact connective tissue sheaths; partial block, amplitude decreases initially
- Neurotmesis: Complete disruption of the entire nerve; total block, neuroma/retrograde degeneration with neuron loss
-
Chronic Injuries (Entrapment Syndromes)
- Repetitive regeneration of the myelin sheath
- Axonal damage due to reduced blood perfusion
Intraoperative Monitoring
- Intraoperative monitoring is used to assess nerve function during surgery.
- The recording equipment can measure electrical activity.
- Nerve function can be monitored during procedures on the skull base, as well as other areas.
Motor Pathways: Extrapyramidal System
- It's defined as all nuclei/tracts not part of the pyramidal system.
- Polysynaptic corticospinal projections.
- The system includes the cerebellum and basal ganglia.
- The system modulates spinal reflex arcs, usually with inhibitory effects.
Basal Ganglia
- A group of subcortical nuclei in the forebrain and midbrain.
- Numerous functions including:
- Control of voluntary movements.
- Procedural learning, habit learning, and conditional learning.
- Eye movements.
- Cognition and emotions.
Basal Ganglia Functions
- Involved in initiation, termination, and stabilization of movements.
- Help stabilize muscles at rest.
Basal Ganglia Connectivity
- Inputs from the cortex to the basal ganglia are received by the striatum.
- Output to the thalamus via the globus pallidus interna and substantia nigra pars reticularis.
- Direct pathway: Striatum –> SNret/GPi –> Thalamus (facilitation of thalamocortical projections)
- Indirect pathway: Striatum –> GPe –> STN –> SNret/GPi –> Thalamus (inhibition of thalamocortical projections)
Basal Ganglia: Substantia Nigra Pars Compacta
- Dopaminergic projections to the striatum.
- D1 receptors in the striatum lead to excitation.
- D2 receptors in the striatum lead to inhibition.
- The different pathways, D1 and D2, facilitate thalamocortical impulse transmission.
Cortical Stimulation: Effects on Basal Ganglia
- Cortical stimulation produces a triphasic response in the basal ganglia output nuclei.
- An initial delay followed by increased activity, inhibiting thalamocortical projections.
- Decreased activity happens next, leading to disinhibition and movement release.
- Finally, increased activity resumes, inhibiting thalamocortical projections and stopping movement release.
Basal Ganglia
- Part of the extrapyramidal system
- Located at the base of the forebrain and the top of the midbrain
- Associated with a variety of functions including:
- Control of voluntary movements
- Procedural learning
- Habit learning
- Conditional learning
- Eye movements
- Cognition
- Emotion
- Initiation and termination of movements
- Stabilization of movements
- Stabilizing muscles at rest
Basal Ganglia Diseases
- Parkinson's disease
- Loss of dopaminergic neurons in the substantia nigra pars compacta
- Cortical activation leads to hyperactivity of SNret and an inhibition of thalamocortical projections required for movement initiation
- Cardinal signs:
- Akinesia/Bradykinesia
- Start/Stop disturbances
- Impaired facial expressions
- Micrography
- Parkinsonian gait
- Tremor
- Rigidity
- Postural instability
- Akinesia/Bradykinesia
- Other Symptoms
- Neuropsychiatric
- Vegetative
Parkinson's Disease Therapy
- First line: drugs (L-Dopa, Dopamine agonists…)
- In case of drug resistance: Deep brain stimulation (DBS)
DBS for Parkinson's Disease
- Neurophysiological Biomarkers
- Recorded via:
- Extracellular microelectrodes (or the inserted DBS electrodes)
- Extracellular recording of a circumscribed neuron population -> raw data
- High-pass filter -> neuronal firing:
- Action potentials of local neurons (Output?)
- Recorded via:
DBS for Parkinson's Disease
- Targeting the optimal DBS location by analyzing neuronal firing
- Microelectrodes record only from a limited number of neurons around the tip when compared to DBS electrodes
DBS Optimization with Neuronal Firing
- Neurophysiological Biomarkers
- Recorded via:
- Extracellular microelectrodes (or the inserted DBS electrodes)
- Extracellular recording of a circumscribed neuron population -> raw data
- Low-pass filter -> local field potential:
- Pre- and postsynaptic potentials (Input?)
- Often transferred in the frequency domain and labeled according to the EEG frequency bands
- Recorded via:
DBS Optimization with Local Field Potentials
- E0 is the common electrode showing a peak in the lower beta frequency band and is chosen for DBS
- In modern systems with more electrodes, the channels not in use for stimulation may be used to record local field potentials, which are evaluated for an adaptation of DBS (aDBS – closed loop stimulation)
DBS Effect upon Local Field Potentials
- PAC – phase amplitude coupling
DBS for Parkinson's Disease - Segmented Stimulation
- DBS can be segmented to stimulate specific areas at different times
DBS for Parkinson's Disease - Adverse Effects
- Infections
- Hemorrhage
- Speech arrest
- Apathy
- Hallucinations
- Hypersexuality
- Cognitive dysfunction
- Depression
- Euphoria
Strategies to Avoid DBS Adverse Effects
- Single shot antibiotics
- Electrophysiologically optimized placement of the DBS electrodes
- Closed loop stimulation
- Electrode optimization (directional stimulation)
Cerebellum
- Vestibulocerebellum
- Maintenance of posture and equilibrium
- Maintenance of muscle tone
- Spinocerebellum
- Error correction, adjusts posture
- Smoothness and coordination of movements
- Cerebrocerebellum
- Planning and programming
- Coordination of complex movements
- Sequence and precision of movements
- Timing of movements
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Description
This quiz explores the concepts of evoked responses, electrical stimulation, and the clinical applications of neurophysiology. Learn about how these techniques help analyze and diagnose conditions related to the nervous system. Delve into the cellular mechanisms that facilitate nerve communication.