iBIOL 1080 W25 - L9

Components of the Control and Communication Network (CCN)

The adult human biological system has a complex Control and Communication Network that plays a crucial role in coordinating functions essential for survival and interaction with the environment.

Main Components

1. Central Nervous System (CNS)

   • Brain: The control center for processing sensory information, regulating mood, and enabling cognitive functions such as thought, memory, and learning. It is divided into multiple regions including the cerebrum, cerebellum, and brainstem.

   • Spinal Cord: It serves as a communication pathway between the brain and the peripheral nervous system, coordinating reflex actions and transmitting sensory information to the brain.

2. Peripheral Nervous System (PNS)

   • Somatic Nervous System: Responsible for voluntary movements and the transmission of sensory information to the CNS from the skin and muscles.

   • Autonomic Nervous System: Regulates involuntary bodily functions, such as heart rate, digestion, and respiratory rate, and is further divided into sympathetic (fight or flight responses) and parasympathetic (rest and digest functions) systems.

3. Endocrine System

   • This system consists of glands that secrete hormones directly into the bloodstream to regulate various physiological processes, including growth, metabolism, and sexual function.

   • Exocrine System with Endocrine-like Activity: Glands that release substances through ducts (e.g., sweat, saliva) sometimes have signaling roles similar to those of hormones.

4. Local Support and Defense System

   • This includes mechanisms that protect the body from local injury and invasion by pathogens, involving local immune responses and tissue repair processes.

5. Maintenance and Support System

   • Structures and interactions that support cellular function and homeostasis in the body, ensuring that environments are favorable for biological processes.

6. Adaptation and Repair System

   • Processes enabling the organism to adapt to environmental changes and repair damaged tissues, crucial for survival.

7. Resident Defense System

   • Involves immune responses that act at the site of infection or injury, activating local immune cells to counteract pathogens.

8. Migrant Defense System

   • Refers to the movement of immune cells throughout the body to respond to threats, providing a robust mechanism against infections and injury.

Nervous System Function

The nervous system regulates and integrates body functions via a complex network of neurons that communicate through electrical impulses and chemical signals.

Overview/Review of the Nervous System

The nervous system integrates and coordinates bodily input and output, depending on key neurotransmitters that play essential roles in neuronal signaling:

• Acetylcholine: Involved in muscle activation and various brain functions.

• Norepinephrine: Affects attention and responding actions in the brain.

• Dopamine: Plays a major role in reward and movement regulation.

• Tryptophan: Precursor to serotonin, influencing mood and sleep.

• GABA: The primary inhibitory neurotransmitter, crucial for reducing neuron excitability, and promoting relaxation.

• Endorphins: Natural painkillers that bring about feelings of pleasure and euphoria.

Major Cell Types in the Adult Human CNS

1. Neurons: The fundamental units of the nervous system responsible for transmitting information.

2. Oligodendrocytes (CNS) and Schwann cells (PNS): Glial cells responsible for the formation of myelin sheath that insulates axons and enhances signal conduction speed.

3. Astrocytes: Star-shaped glial cells important for blood-brain barrier maintenance, nutrient support to neurons, and participating in synapse formation and neurotransmitter uptake.

4. Microglia: Act as immune cells of the CNS, mobile macrophages that clear debris and modulate inflammation.

5. Ependymal Cells: Line the ventricles of the brain and spinal cord, contributing to the production and circulation of cerebrospinal fluid.

Neuron Signal Transmission and Speed

The speed of neuron signals is critical for proper functioning:

• Unmyelinated Neurons: Signal transmission is slower, ranging from 0.5 to 2 m/sec due to the lack of myelin insulation.

• Myelinated Neurons: Much faster at 6 to 120 m/sec, facilitating rapid communication across the nervous system.

Multiple Sclerosis

This condition arises from the destruction of the myelin sheath, an autoimmune response that disrupts communication between neurons and leads to neurological deficits.

Neurotransmitter Specificity and Function

Each presynaptic neuron is designed to release a specific neurotransmitter (e.g., dopamine, serotonin, norepinephrine, acetylcholine) that targets specific receptors on postsynaptic cells, influencing their activity and communication.

Neuron Functions: Excitation and Inhibition

Neurons are built to be either excitatory or inhibitory, with the cell body integrating various inputs. The net effect determines whether an action potential is generated in the postsynaptic neuron, which is a crucial binary event contingent upon achieving a specific threshold.

Neural Network Adaptation in Childhood and Adolescence

Neural remodeling begins around age 10, highlighting:

• The development of new synaptic connections, crucial for learning and adaptation.

• Pruning of unused synapses, refining neural pathways for more efficient communication.

Teenage/Emerging Adult Brain Changes

Significant changes occur during adolescence:

• The growth in brain size reaches about 90% of its adult volume, accompanied by extensive synaptic reorganization.

• Increased sensitivity to dopamine may explain heightened social reward responses, impacting behavior and decision-making.

• Improved myelination further enhances neuronal transmission speeds, aiding rapid information processing essential for learning and social interaction.

Glial Cells and Their Functions

1. Oligodendrocytes (CNS): Support multiple axons by producing myelin sheaths, crucial for effective signal transmission.

2. Schwann Cells (PNS): Produce myelin but are limited to individual axons.

3. Astrocytes: Essential for maintaining the blood-brain barrier, nutrient supply, and involvement in synaptic function.

4. Microglia: Act as the brain’s immune response, protecting and repairing the tissue.

5. Ependymal Cells: Line brain ventricles, forming barriers and regulating cerebrospinal fluid production and circulation.

The Blood-Brain Barrier (BBB)

The BBB is formed by tightly packed capillary endothelial cells, crucial for protecting the brain from potential harmful substances while allowing necessary nutrients to pass:

• Allows the passage of very small lipid-soluble compounds (e.g., essential fatty acids).

• Permits the entry of substances such as caffeine and alcohol, while selectively transporting glucose via GLUT1 transporters (which are not insulin-sensitive).

• It presents challenges for drug delivery targeting the brain, balancing protection against bacteria and toxins with therapeutic access to the brain tissue.