Cells and Neuroanatomy: Key Concepts
Overview of the Nervous System's Role
The nervous system is comprehensive, extending into every part of the body.
It coordinates all bodily functions, encompassing both automatic processes (e.g., heart rate) and highly sophisticated responses (e.g., complex emotions, elaborate behavioral actions).
Neurons: The Fundamental Units of Information Processing
The nervous system requires an immensely complicated computational system due to the vast amount of information processing it performs.
It contains nearly 80-90 billion neurons.
Neurons exhibit wide variations in shape and size, which directly reflects their specialized functions.
Despite their diversity, neurons can be generally categorized by their layout, size, and function.
Functionally, neurons share four basic elements:
Input Zone: Consists of dendrites, which can be elaborately branched and contain dendritic spines. This is where neurons receive signals.
Integration Zone: Composed of the cell body (soma) and the axon hillock. This is where incoming signals are integrated to determine if an action potential will be generated.
Conduction Zone: The axon, which serves to transmit the electrical signal. It may split into branches called axon collaterals.
Output Zone: Made up of the axon terminals. This is where the neuron transmits signals to other cells.
Glial Cells: Support and Active Participation
Glial cells perform critical functions within the nervous system, extending beyond mere support.
Key functions include:
Myelination: Forming myelin sheaths around axons, which insulates them and speeds up signal conduction.
Nutrient Exchange: Facilitating the exchange of nutrients and other vital substances with neurons.
Debris Removal: Clearing cellular debris, contributing to the maintenance of a healthy neural environment.
Recent research highlights additional active roles for glial cells:
Significant participants in pain perception.
Involvement in neuronal remodeling, indicating their role in structural and functional plasticity.
Contribution to the onset and progression of cognitive impairments observed in neurodegenerative diseases, such as Alzheimer’s disease.
Synaptic Transmission: How Neurons Communicate
Information is transmitted between neurons, or from neurons to target cells (muscles or glands), via specialized junctions called synapses.
In most neurons, the axon terminals contain specialized structures known as “boutons.”
Upon the arrival of an electrical impulse along the axon, these boutons release molecules of neurotransmitter.
The neurotransmitter then diffuses across a microscopic gap called the synaptic cleft.
It subsequently binds to specific receptor proteins on the postsynaptic cell.
This binding event alters the electrical properties of the postsynaptic cell, causing either excitation or inhibition, thereby transmitting the signal.
Divisions of the Nervous System
The nervous system is broadly divided into two main components:
Central Nervous System (CNS): Comprises the brain and the spinal cord.
Peripheral Nervous System (PNS): Consists of the somatic nervous system and the autonomic nervous system.
Somatic Nervous System: Responsible for connecting muscles and sensory systems with the central nervous system, mediating voluntary movements and sensory perception.
Autonomic Nervous System: Connects the internal organs to the central nervous system, regulating involuntary bodily functions.
Further subdivided into two antagonistic divisions:
Sympathetic Nervous System: Generally prepares body systems for