Intracellular Signaling Pathways in Neurons
Signal Transduction Inside Neurons
Second Messengers and Enzymes
Neurons use intracellular signaling cascades to convert external events into durable changes. Calcium, cyclic nucleotides, kinases, phosphatases, and small G proteins all participate in these processes.
Major Signaling Elements
Balancing Act
Neuronal signaling often depends on the balance between kinase and phosphatase activity, not simply on whether a pathway is 'on' or 'off'.
What is a common function of protein kinases in neurons?
Kinases regulate protein function by phosphorylation.
Correct answer: They add phosphate groups to proteins
Which second messenger is most directly associated with activation of PKA?
cAMP activates protein kinase A in many signaling pathways.
Correct answer: cAMP
Signal Integration
Multiple inputs often converge on the same signaling hub. For example, calcium and cyclic nucleotide pathways can interact to regulate transcription factors, ion channel properties, and cytoskeletal remodeling.
Signal Duration
Fast signaling
- Milliseconds to seconds
- Often involves ion flux and phosphorylation
Slow signaling
- Minutes to hours or longer
- Often involves transcription and translation
How an Intracellular Cascade Works
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1
Step 1: A receptor or channel is activated.
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2
Step 2: Second messengers are generated or released.
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3
Step 3: Kinases and phosphatases modify target proteins.
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4
Step 4: Cellular properties change.
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5
Step 5: Repeated signaling may alter gene expression.
Which molecule is a classic second messenger in neurons?
cAMP is a classic second messenger in many neuronal pathways.
Correct answer: cAMP
What is one consequence of increased intracellular calcium in neurons?
Calcium can activate kinases, phosphatases, and transcriptional programs.
Correct answer: Activation of signaling cascades