Neuron Structure and Types

Neurons, the fundamental units of the nervous system, have distinct structural components that enable their function. The cell body, or cyton, contains important cellular structures:

1. Nissl's granules (tigroid body): Involved in protein synthesis
2. Neurofibrils: Aid in internal conduction

The axon, a key component for signal transmission, can be either myelinated or non-myelinated. Myelinated axons in the central nervous system are covered by oligodendrocytes, while those in the peripheral nervous system are wrapped by Schwann cells.

Neurons can be classified based on their function:

1. Sensory neurons (receptors)
2. Motor neurons (effectors)
3. Interneurons (interconnecting)

Definition: Myelin sheath - A fatty insulating layer around some axons that speeds up signal transmission.

Example: The thyroxine hormone, along with vitamin B12, plays a crucial role in the multiplication and division of neurons during embryonic development.

Action Potential Generation

The action potential is a key process in nervous system physiology, involving several stages:

1. Polarization (Resting State): The neuron maintains a resting membrane potential of about -70mV.

2. Depolarization: A stimulus causes sodium channels to open, allowing sodium ions to flow into the cell. This raises the membrane potential to the threshold level (about -55mV).

3. Rising Phase: If the threshold is reached, more voltage-gated sodium channels open, causing a rapid influx of sodium ions. The membrane potential quickly rises to about +30 to +45mV.

4. Repolarization: Potassium channels open, and potassium ions flow out of the cell. Simultaneously, sodium channels close. This causes the membrane potential to return towards the resting level.

5. Hyperpolarization: The membrane potential briefly becomes more negative than the resting state due to the continued outflow of potassium ions.

Vocabulary: Threshold potential - The minimum membrane potential that triggers an action potential.

Highlight: The 7 steps of action potential involve polarization, depolarization, rising phase, peak, falling phase, repolarization, and hyperpolarization.

Limbic System and Hypothalamus

The limbic system is a group of interconnected structures involved in emotion, behavior, and memory. Key components include:

1. Amygdala: Processes emotions, particularly fear and aggression
2. Hippocampus: Crucial for forming new memories and spatial navigation

The hypothalamus is a small but vital structure that serves as a link between the nervous system and the endocrine system. Its functions include:

1. Regulating behavior and emotions
2. Controlling the endocrine system through the pituitary gland
3. Thermoregulation
4. Autonomic nervous system control
5. Maintaining the body's biological clock

The olfactory system, responsible for the sense of smell, consists of:

1. Olfactory bulbs: Receive input from olfactory receptors in the nose
2. Olfactory tract: Transmits information to other brain areas
3. Olfactory cortex: Processes and interprets smell information

Vocabulary: Olfactory - Relating to the sense of smell.

Highlight: The hypothalamus plays a crucial role in maintaining homeostasis by integrating nervous system function with endocrine system control.