kolbintro6e_lectureslides_ch05_UPLOAD

Introduction to Neurons

• Overview of neuronal communication and adaptation

Key Concepts

• Neurons communicate via chemical messages.

• Different varieties of neurotransmitters and their receptors.

• Understanding neurotransmitter systems and their relation to behavior.

• Importance of synaptic adaptations in learning and memory.

A Chemical Message

Experimentation Background

• Initial studies on neuronal communication were aimed at understanding the control of heart rate.

• Heart rates increase during excitement or exercise and decrease when at rest, indicating a chemical relay of messages.

• Excitatory chemicals speed up heart rate; inhibitory chemicals slow it down.

Otto Loewi's Discovery (1921)

• Groundbreaking experiment using frog hearts.

• Role of vagus nerve and neurotransmitter acetylcholine (ACh) in heart rate modulation.

  • Acetylcholine is the first neurotransmitter identified in both the peripheral and central nervous systems.

  • It activates skeletal muscles and can have excitatory or inhibitory effects on internal organs.

Neurotransmitter Function

• A neurotransmitter is a chemical released by a neuron to exert excitatory or inhibitory effects on a target cell.

• Outside the CNS, neurotransmitters can circulate in the bloodstream as hormones, which act slower than neurotransmitters.

Structure of Synapses

Visual Anatomy (Electron Microscope)

• Components of a chemical synapse:

  • Presynaptic neuron: sends neurotransmitters.

  • Postsynaptic neuron: receives neurotransmitters.

  • Synaptic cleft: gap separating the presynaptic terminal from the postsynaptic membrane.

  • Synaptic vesicles: contain neurotransmitters for release.

Functionality of Synapses

• Presynaptic membrane: where neurotransmitter release occurs.

• Postsynaptic membrane: receives signals, generating excitatory postsynaptic potentials (EPSPs) or inhibitory postsynaptic potentials (IPSPs).

• Tripartite synapse: includes surrounding astrocytes contributing to synaptic function.

Neurotransmission Process (Five Steps)

1. Synthesis: Neurotransmitter formation from precursor chemicals.

2. Storage: Packaging in vesicles at the axon terminal.

3. Release: Triggered by action potential, ions facilitate release into the synaptic cleft.

4. Receptor Binding: Neurotransmitter activates receptors on postsynaptic membrane.

5. Inactivation: Mechanisms for neurotransmitter removal after action.

Adaptation and Learning

Neuroplasticity

• Capacity of the nervous system to change and adapt, essential for learning and memory.

• Hebb's theory: Synaptic efficiency improves when cells are activated together.

• Example: Eric Kandel's synaptic basis of learning using Aplysia.

Types of Learning Responses

• Habituation: Decreased response to repeated stimuli.

• Sensitization: Increased response to new or intense stimuli.

• Both forms of learning lead to synaptic changes, impacting neurotransmitter release and synapse structure.

Neurotransmitter Classes

• Small-molecule transmitters: Quick-acting neurotransmitters synthesized from nutrients.

• Peptide neurotransmitters: Synthesized from mRNA, slower acting, and involved in hormonal responses.

• Lipid neurotransmitters: Examples include endocannabinoids.

• Gaseous neurotransmitters: Such as nitric oxide, synthesized as needed.

Receptors and Their Functions

Receptor Types

• Ionotropic receptors: Fast acting, allow direct ion flow to change cell voltage.

• Metabotropic receptors: Longer-lasting effects, tied to G-protein signaling.

Neurotransmitter Systems and Behavior

• Different neurotransmitters may coincide within the same synapse.

• Systems like cholinergic and dopaminergic are crucial for various physiological activities and behavioral responses.

Conclusion

• The communication between neurons is a complex system crucial for almost all body functions and behaviors. Understanding these processes is key to comprehending brain function and behavior modulation.