IM

receptors

Upcoming Test Information

  • Test Date: Tuesday, the 25th

  • Test Type: Test One

  • Resources Available:

    • Prep materials on Canvas

    • Practice questions

    • Podcasts available for review

Action Potential

  • Movement along the Axon: Action potentials can travel via two methods.

  • Myelin:

    • Myelin is a fatty substance that insulates the axon.

    • No voltage-gated channels in the myelin segments.

  • Nodes of Ranvier:

    • The gaps in the myelin sheath are called nodes.

    • Action potential jumps from node to node (saltatory conduction) for faster transmission.

    • Distance between nodes optimized to reach threshold potential (about -55mV).

Action Potential Dynamics

  • The influx of sodium ions at nodes initiates the action potential.

  • Action potentials occur via:

    • Graded potentials being subthreshold (less frequent) or superthreshold (more frequent).

    • Stronger stimuli generate more frequent action potentials.

Electrical to Chemical Communication

  • Neurons Interaction:

    • When neurons communicate, action potentials reach synaptic bulbs, releasing neurotransmitters.

  • Synaptic Transfer:

    • Action potential opens voltage-gated calcium channels.

    • Calcium ions enter the presynaptic neuron, triggering neurotransmitter release through exocytosis.

  • Presynaptic vs. Postsynaptic cells:

    • Presynaptic neurons release neurotransmitters.

    • Postsynaptic neurons have receptors that respond to these neurotransmitters.

Key Concepts in Neurotransmitter Function

  • Neurotransmitter Types:

    • Excitatory Neurotransmitters enable action potentials, while Inhibitory Neurotransmitters prevent them.

    • Example: Acetylcholine released at synapses is excitatory, binding to cholinergic receptors.

  • Receptor Types:

    • Cholinergic receptors can be nicotinic (excitatory) or muscarinic (varying effects).

Inhibitory Mechanisms

  • Acetylcholinesterase: Enzyme that breaks down acetylcholine in the synaptic cleft to prevent continuous stimulation.

Summary of Action Potentials' Characteristics

  • Differences between graded potentials and action potentials:

    • Action potentials are all-or-nothing responses, while graded potentials vary in strength.

    • Action potentials travel long distances; graded potentials are limited to local effects.

Action Potential and Signal Coding

  • The frequency of action potentials encodes the strength of a stimulus.

  • Different types of ion channels contribute to excitatory or inhibitory postsynaptic potentials (EPSP or IPSP).

Closing Remarks

  • Understanding the intricate details of action potentials, neurotransmitter function, and synaptic transmission is crucial for comprehending neural communication.