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.

Factors Affecting Neuron Function

Several factors influence the functioning of neurons in the nervous system. Key among these are:

1. Na-K pump $Active transport$: This protein actively moves sodium and potassium ions across the cell membrane, maintaining the resting potential.
2. Ion channels $Passive transport$: These channel proteins allow specific ions to move across the membrane based on concentration gradients.
3. Negatively charged proteins and associated anions: These contribute to the overall charge distribution across the neuron membrane.

The brain's functional areas play crucial roles in various processes:

• Motor areas control movement
• Sensory areas process incoming sensory information
• Association areas integrate information and are involved in higher cognitive functions

Highlight: The balance of ions across the neuron membrane is critical for proper nervous system function and signal transmission.

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.

Nervous System Components

The central nervous system $CNS$ consists of the brain and spinal cord, which are protected by several layers:

1. Dura mater: The outermost tough protective layer
2. Arachnoid mater: The middle layer
3. Pia mater: The innermost layer, closely adhering to the brain and spinal cord

The brain contains fluid-filled cavities called ventricles:

1. Two lateral ventricles
2. Third ventricle
3. Cerebral aqueduct
4. Fourth ventricle

Cerebrospinal fluid $CSF$ is produced by the choroid plexus and circulates through these ventricles, providing cushioning and nutrients.

Definition: Choroid plexus - A network of blood vessels and cells in the ventricles that produces cerebrospinal fluid.

Highlight: The central nervous system is well-protected by meninges and bathed in cerebrospinal fluid, which provides both physical and chemical protection.

Brain Structure and Development

The brain develops from the neural tube, which forms five primary vesicles:

1. Telencephalon $forms the cerebrum$
2. Diencephalon $forms the thalamus and hypothalamus$
3. Mesencephalon $forms the midbrain$
4. Metencephalon $forms the pons and cerebellum$
5. Myelencephalon $forms the medulla oblongata$

The cerebrum, the largest part of the brain, consists of gray matter $cortex$ and white matter. It is divided into several lobes, each with specific functions:

• Frontal lobe: Motor control, planning, reasoning
• Parietal lobe: Sensory processing
• Temporal lobe: Auditory processing, memory
• Occipital lobe: Visual processing

Example: The Broca's area in the frontal lobe is responsible for speech production, while Wernicke's area in the temporal lobe is involved in language comprehension.

Highlight: Understanding the nervous system anatomy and physiology is crucial for comprehending how different brain regions contribute to various functions.

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.

Page 8: Cerebellar Functions

This final page focuses on the cerebellum's role in motor control and balance.

Definition: The cerebellum is responsible for coordinating voluntary movements and maintaining balance.

Highlight: The cerebellum's function is essential for activities requiring precise motor control.

Example: Activities like skiing require constant cerebellar input for maintaining balance and coordination.

Nervous System Overview

The nervous system is a vital component of the body's regulatory mechanisms, working in tandem with the endocrine system to maintain homeostasis. While the endocrine system provides slow-speed coordination, the nervous system offers high-speed coordination, allowing for rapid responses to stimuli.

The basic structural and functional unit of the nervous system is the neuron. Neurons consist of several key parts:

1. Cyton $cell body or pericaryon$: The main regulating part
2. Dendrites: Processes that receive signals
3. Axon: The main functional part for transmitting signals

Supporting the neurons are neuroglia cells, which provide essential functions such as packaging, protection, support, and nutrition to the neurons.

Vocabulary: Homeostasis - The tendency of the body to maintain a stable internal environment.

Highlight: The nervous system's ability to provide high-speed coordination is crucial for rapid responses to environmental changes and internal stimuli.