chapter 48 biology 1201

Course Review Schedule

  • Cumulative Review:

    • Date: Next Monday

    • Focus: Why cumulative review before Thanksgiving break? Students are familiar with the information.

  • Next Wednesday Class:

    • Time: Class after 12:30 (after break starts).

  • Learning Status After Next Monday:

    • No more learning sessions after next Monday during study week.

    • Two classes during study week: Monday and Wednesday.

    • Extra credit opportunities will be provided for participation in class; attendance is mandatory for extra credit.

Chapter Status Updates

  • Chapter Completion:

    • All content of Chapter 50 will be finished before the upcoming deadlines.

  • Learning Time Rates:

    • Updated as of last week (not necessarily last Friday).

  • Quizzes Due:

    • Due at 9 AM on December 1 (Week 13). No points assigned during study week.

Ion Channels

  • Types of Ion Channels:

    • Gated Ion Channels:

    • Voltage Gated - Responds to changes in membrane voltage.

    • Ligand Gated - Responds to neurotransmitter binding (e.g., epinephrine).

    • Functionality:

    • Ligand gated channels open in response to a signal from outside the cell, triggering an action potential.

    • Voltage gated channels activate upon detecting voltage changes across the membrane.

Membrane Potential Overview

  • Membrane Potential Graph:

    • Y-axis: Membrane potential.

    • X-axis: Time.

  • Key Values:

    • Resting potential is around -75 mV (negative number is crucial).

    • Threshold: Necessary for action potentials.

Key Processes in Action Potentials

  • Hyperpolarization vs. Depolarization:

    • Hyperpolarization:

    • Membrane potential becomes more negative.

    • Potassium channels typically lead to hyperpolarization (increases negativity).

    • Depolarization:

    • Membrane potential becomes less negative (moving closer to threshold).

    • Sodium channels lead to depolarization.

  • Changes in Membrane Potential:

    • Graded responses for depolarization and hyperpolarization.

    • Action potentials are not graded; they reach the same height every time regardless of stimulus strength.

Mechanism of Action Potentials

  • Action Potential Phases:

    • Resting Phase: Closed sodium and potassium channels.

    • Depolarization Phase: Sodium channels open; membrane reaches threshold.

    • Rising Phase: Rapid depolarization to the peak.

    • Falling Phase: Sodium channels close; potassium channels open.

    • Undershoot Phase: Membrane potential decreases past resting level before stabilizing back to resting potential.

    • Sodium-Potassium Pump: Reestablishes resting state post-action potential.

Conclusion of Signal Transmission

  • Propagation of Action Potential:

    • Depolarization at one part of the membrane triggers adjacent areas due to local changes in ion concentrations.

    • Refractory Period: Prevents backward signaling and ensures unidirectionality of action potentials.

Myelination of Axons

  • Myelin Sheaths:

    • Function: Insulation and speed enhancement for signals traveling along axons (like coating for internet cables).

    • Nodes of Ranvier: Areas between myelin sheaths where action potentials can jump (saltatory conduction).

    • Supporting Cells:

    • CNS: Oligodendrocytes.

    • PNS: Schwann cells.

Synaptic Transmission

  • Synapses: Junctions between neurons.

    • Chemical Synapses: Use neurotransmitters to relay signals.

    • Components:

    • Presynaptic cell (sending signal).

    • Postsynaptic cell (receiving signal).

    • Synaptic cleft (space between the two).

Neurotransmitter Functions

  • Types of Neurotransmitters:

    • Acetylcholine: Common neurotransmitter in multiple organisms.

    • Amino Acids, Biogenic Amines, Neuropeptides: Broad categories of neurotransmitters.

    • Nitric Oxide: Unique signaling molecule (promotes vasodilation).

Specific Examples of Neurotransmitters

  • Glutamate: Major excitatory neurotransmitter in the brain (associated with umami flavor).

  • GABA: Inhibitory neurotransmitter, regulates anxiety (affected by substances like alcohol).

  • Dopamine & Serotonin: Associated with mood regulation and feelings of pleasure.

  • Endorphins: Pain and perception regulation, involved in the body's response during physical exertion.

Signal Summation Types

  • Excitatory and Inhibitory Postsynaptic Potentials (EPSPs & IPSPs):

    • EPSPs make it more likely to reach action potential threshold.

    • IPSPs make it less likely to reach action potential threshold.

    • Summation Types:

    • Temporal Summation: Two excitatory signals close in time from the same synapse.

    • Spatial Summation: Simultaneous excitatory signals from multiple synapses.

Termination of the Signal

  • Signal Termination Mechanisms:

    • Stopping neurotransmitter release and decreasing concentration in the synaptic cleft.

    • Possible methods:

    • Diffusion away.

    • Reuptake by presynaptic neuron.

Metabotropic Effects and Signaling Pathways

  • G-Protein Coupled Receptors (GPCRs): Involved in metabotropic signaling pathways that can lead to changes in ion concentrations.

    • Common Second Messengers: cAMP (cyclic AMP) and calcium ions.

    • Adenylyl Cyclase Enzyme: Converts ATP to cAMP; regulated by glucose.

  • Epinephrine Cascade: Triggers various physiological responses related to "fight or flight".

Summary of Required Knowledge for Exams

  • Differentiate between ionotropic and metabotropic effects.

  • Identify neurotransmitter classes and specific examples (Acetylcholine and Nitric Oxide).

  • Understand structure of amino acids.

  • Summarize differences between spatial and temporal summation to understand action potential generation.