Hormones and Endocrine Glands

• Distinction between hormones:

  • Hormones are chemical messengers in the body.

• Posterior Pituitary:

  • Function: Modifies and secretes hormones made by the hypothalamus.

  • Importance: Only endocrine gland that modifies and secretes these hormones.

• Anterior Pituitary:

  • Function: Produces its own hormones.

  • Definition: Tropic hormones; affect other endocrine glands by stimulating hormone production.

Neurons and Neurobiology

• Concepts of Neuronal Structure:

  • Basic hierarchy of complexity:

  • Order: Neurons → Nerves → Ganglia → Brains.

  • Additional order can emphasize complexity: Neurons → Nerves → Ganglia → Brains.

  • Components of nerve cells:

  • Dendrites: Function to receive signals.

  • Axons: Function to pass on signals.

• Directionality of Nerve Signals:

  • Dendrites receive input (where the signal comes in).

  • Axons transmit output (where the signal goes out).

  • Importance of distinguishing between dendrites and axons in diagrams and real life.

Anatomy and Physiology of Neurons

• Types of Neurons:

  • Interneurons: Characterized by shorter axons, found in the brain and ganglia.

  • Notable for their lack of long axons compared to other neuron types.

• Cell Body Responsibilities:

  • Contains nucleus, mitochondria, and organelles like lysosomes.

• Resting Potential:

  • The major cation involved is potassium ($K^+$).

  • Concentrations:

  • High potassium inside cells.

  • High sodium ($Na^+$) outside cells.

• Action Potential:

  • Described as a sequence of electrical events that regenerate a nerve impulse.

  • Key sequence of ion movements:

    1. Sodium channels open → influx of $Na^+$, causing depolarization.

    2. Sodium channels close, potassium channels open → efflux of $K^+$, causing repolarization.

  • Diagram explanation from depolarization to repolarization:

  • Membrane potential moves from negative to positive during depolarization and back to negative during repolarization.

Sodium-Potassium Pump

• Functionality:

  • Establishes the resting potential of approximately -70 mV via active transport.

  • Pumps $3Na^+$ out of the cell for every $2K^+$ pumped in.

  • Essential for maintaining gradients that lead to action potentials.

Myelination and Signal Propagation

• Schwann Cells and Myelin Sheath:

  • Function: Provide insulation around axons, increasing the speed of nerve impulse transmission (up to tenfold).

  • Structure: Nodes of Ranvier allow for the flow of ions, facilitating rapid signal conduction through saltatory conduction.

Neurotransmission Dynamics

• Process of Neurotransmitter Release:

  • Neurotransmitters are released into the synapse via fusion of vesicles with the presynaptic membrane.

  • Fast process, taking place within milliseconds during synaptic transmission.

• Synapse Description:

  • Defined as the gap where neurotransmitters diffuse from one neuron to another.

• Neurotransmitter Actions:

  • Bind to receptors on the postsynaptic cell, initiating signals for communication or action potential generation.

  • After binding, neurotransmitters are typically reabsorbed or broken down by enzymes to reset the synapse for future impulses.

Excitatory and Inhibitory Signals

• EPSP (Excitatory Postsynaptic Potential):

  • Functions to bring neurons closer to threshold for action potential generation.

  • Can arise from strong excitatory inputs or summation of smaller signals in rapid succession.

• Subthreshold Responses:

  • Describe how weak neurotransmitter signals must occur closely together to effectively elicit a response.

Dynamic Nature of Neurons

• Neural Plasticity:

  • Neurons can increase their response to repeated stimuli by modifying the number of receptors and enhancing synaptic strength (learning mechanism).

  • Neurons may lose responsiveness if stimuli are not repeated frequently, demonstrating plasticity and adaptation.

Types of Neurotransmitters

• General overview:

  • There are over 100 different known neurotransmitters, with significant ones including acetylcholine, dopamine, and serotonin.

• Specialization of Neurons:

  • Each neuron typically uses a specific neurotransmitter type and does not change.

• Opioid Receptors:

  • Natural binding: Endorphins are the body's naturally occurring opioids that activate these receptors.

  • Classification: Opiates are natural, while opioids are a broader category that includes both natural and synthetic compounds.

Summary of Neurotransmitter Mechanisms

• Communication via neurotransmitters is similar across different signaling pathways, indicating a unified mechanism of cellular communication.

• Role of neurotransmitters in action potential initiation and neural communication.

• Importance of knowing neurotransmitter types in understanding both physiological and psychological effects of various drugs.

Conclusion

• Contact between neurons is crucial for communication; the mechanisms developed from various cellular adaptations show a sophisticated understanding of neural function. Further learning and exploration in the field can yield insights into treatments for neurological disorders and enhance our grasp of brain functions.