Neuroscience Chapter on Action Potentials

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Questions and Answers

What structure do first order neurons synapse with after traveling to the spinal cord?

Laminae II, III, and IV

Anterior white commissure

Substantia gelatinosa (correct)

Dorsal root ganglion

Which tracts do sensory fibers take after crossing the anterior white commissure?

Vestibulospinal tracts

Anterior spinothalamic and lateral spinothalamic tracts (correct)

Dorsal column tracts

Corticospinal tracts

Where do the spinothalamic tracts terminate within the brain?

Motor cortex

Cerebellum

Thalamus and brainstem (correct)

Hippocampus

Which nucleus in the thalamus is associated with pain sensation?

Intralaminar nuclei Signup and view all the answers

What type of sensations do anterolateral fibers primarily carry?

Pain and temperature sensations Signup and view all the answers

What is the threshold range necessary to elicit an action potential?

-40 to -50 Signup and view all the answers

How does the receptor potential change with varying stimulus strength?

It sharply rises at first and then levels off. Signup and view all the answers

What does an increase in receptor potential lead to in terms of action potentials?

An increase in the frequency of action potentials. Signup and view all the answers

What happens to the amplitude of the receptor potential as the stimulus strength increases?

It increases rapidly at first then slows down. Signup and view all the answers

How is sensitivity to weak stimuli accommodated in the sensory system?

Very weak stimuli can be detected without reaching the maximum firing rate. Signup and view all the answers

What effect does very intense stimulation have on action potentials?

It causes additional action potentials to occur. Signup and view all the answers

In the context of sensory experience, what does a broader range of stimulus intensities allow for?

Enhanced discrimination of weak stimuli. Signup and view all the answers

What is the relationship between receptor potential amplitude and stimulus strength?

Amplitude increases with increasing stimulus strength. Signup and view all the answers

What is the primary effect of divergence in neuronal pools?

It amplifies the input, spreading it to more neurons. Signup and view all the answers

How does convergence function within a neuronal circuit?

It combines signals from multiple sources to excite a neuron. Signup and view all the answers

What role does reciprocal inhibition play in motor control?

It helps control opposing muscle groups by exciting one and inhibiting the other. Signup and view all the answers

What is afterdischarge in the context of signal prolongation?

A prolonged output that can last up to several minutes after the initial signal. Signup and view all the answers

What is the significance of reverberatory circuits?

They create a feedback loop, allowing circuits to continuously emit signals. Signup and view all the answers

Which statement about convergence is accurate?

Convergence can unify signals from both single and multiple sources. Signup and view all the answers

What is a key feature of divergence in neuronal signaling?

It allows a stronger signal to propagate in several directions. Signup and view all the answers

Which of the following describes an effect of synaptic afterdischarge?

It allows prolonged output following a single input signal. Signup and view all the answers

What is the primary role of the dorsal column-medial lemniscal system in sensory processing?

Carries fine touch and proprioception signals Signup and view all the answers

How does the anterolateral system process sensory information upon entering the spinal cord?

It crosses to the opposite side before ascending Signup and view all the answers

Which type of sensory information is primarily transmitted by the lateral spinothalamic tract?

Pain and temperature Signup and view all the answers

Where do the signals in the dorsal column-medial lemniscal system cross over to the opposite side?

In the medulla Signup and view all the answers

Which of the following best describes the fibers used in the dorsal column-medial lemniscal system?

Large, myelinated fibers Signup and view all the answers

What type of position sense allows a person to be aware of their body's position in space?

Static position sense Signup and view all the answers

Which mechanoreceptors are NOT involved in the dorsal column-medial lemniscal system?

Free nerve endings Signup and view all the answers

What characteristic differentiates the anterolateral system from the dorsal column-medial lemniscal system in terms of spatial orientation?

The anterolateral system has less spatial orientation. Signup and view all the answers

What is the primary function of nociceptors in the body?

Detect signals of tissue damage or threats of damage Signup and view all the answers

Which type of pain is primarily transmitted through the fast pain pathway?

Sharp, prickling pain Signup and view all the answers

What type of stimuli can activate pain receptors?

Mechanical, chemical, and thermal Signup and view all the answers

Which neurotransmitter is primarily associated with the neospinothalamic tract?

Glutamate Signup and view all the answers

What is hyperalgesia?

Unusually severe pain in normal situations Signup and view all the answers

How does the paleospinothalamic tract primarily transmit pain?

Using mainly C fibers and some A-delta fibers Signup and view all the answers

What is the role of prostaglandins in pain perception?

They enhance the sensitivity of pain endings Signup and view all the answers

At what temperature does an average person begin to perceive pain from heat?

45º C Signup and view all the answers

What characterizes the slow-chronic pain transmitted through the paleospinothalamic tract?

It contributes to emotional and autonomic aspects of pain. Signup and view all the answers

Which layer in the spinal cord do pain fibers in the neospinothalamic tract predominantly terminate?

Lamina I (lamina marginalis) Signup and view all the answers

Study Notes

Action Potentials and Stimuli

Threshold for eliciting an action potential is between -40 to -50 mV.
Stronger stimuli increase the receptor potential sharply at first, then the response levels off despite continued stimulus.
Amplitude reflects the strength of the receptor potential, which increases with stimulus strength.
Frequency of action potentials rises with receptor potential increase; more intense stimuli lead to more rapid neuron firing.
The system detects very weak stimuli without reaching maximum firing rates until stimuli are very strong.
Higher receptor potentials correlate with increased action potential frequency, encoding various stimulus intensities.

Divergence and Convergence

Divergence spreads weak signals from a neuronal pool to excite more nerve fibers, allowing amplification of input.
Multiple tracts can transmit divergent signals in different directions.
Convergence allows signals from multiple sources to unite, facilitating information summation for CNS processing.

Reciprocal Inhibition Circuits

Excitatory signals in one direction can trigger inhibitory signals in another, helping to control opposing muscle groups (e.g., biceps and triceps).

Signal Prolongation

Afterdischarge refers to prolonged output lasting milliseconds to minutes post-signal.
Synaptic afterdischarge allows sustained output from a single input through repetitive signals.
Reverberatory circuits provide feedback, enabling continuous signal emission with varying complexity.

Sensory Pathways

Sensory information from the body primarily enters the spinal cord via dorsal roots of spinal nerves.
Two main sensory pathways:
- Dorsal Column-Medial Lemniscal System: Carries mechanoreceptive sensations with large myelinated fibers, crossing in the medulla.
- Anterolateral System: Senses crude touch, pain, and temperature, using smaller myelinated fibers.

Dorsal Column-Medial Lemniscal System

Transmits fine touch, proprioception, vibration, pressure.
Proprioception involves position sense with two types: static and kinesthesia.
Mechanoreceptors: Meissner’s corpuscles, Merkel’s discs, Ruffini endings, Pacinian corpuscles.

Anterolateral System

Crosses to the opposite side upon entering the spinal cord then ascends.
Comprises two tracts: Anterior Spinothalamic Tract (crude touch) and Lateral Spinothalamic Tract (pain and temperature).
Conduction slower with poor spatial localization.

Pain Perception

Acute pain serves protective functions: withdrawal, avoidance, facilitating healing.
Pain receptors (nociceptors) are free nerve endings, responsive to mechanical, chemical, and thermal stimuli.
Common pain-related chemicals include bradykinin, serotonin, histamine, and prostaglandins.
Hyperalgesia refers to enhanced pain response in normal pain situations.

Pain Pathways

Pain signals travel via two pathways:
- Neospinothalamic tract (fast, sharp, direct) utilizes A-Delta fibers for acute pain, terminating in the thalamus.
- Paleospinothalamic tract (slow, chronic, indirect) primarily uses C fibers, conveys emotional aspects of pain, terminating in the thalamus and influencing autonomic responses.

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Description

Explore the mechanisms behind action potentials in neurons and how receptor potentials respond to varying stimulus strengths. This quiz covers key concepts such as threshold levels and frequency of action potentials. Test your understanding of neurophysiology through thought-provoking questions.