Chapter 2: Functional Neuroanatomy

The Nervous System and Behavior

Overview of the nervous system's role in behavior and the body's functions. The nervous system is critical for coordinating actions and responses to environmental stimuli, managing reflexes, and mediating complex processes such as learning and memory.

Cells of the Nervous System

Types of Cells

Neurons and Glia: Two major types of cells in the nervous system. Estimated 86 billion neurons in the adult human brain.

Neurons

Highly organized cells specialized for communication. Their structure enables efficient signal transmission and processing.

Structure of a neuron:

• Cell Body (Soma): Variable shape/size, contains nucleus, responsible for synthesis and metabolism. Houses DNA and the machinery for protein synthesis, integral for the neuron's functional capabilities.

• Dendrites: Thin branches that receive input from other neurons through synapses, essential for integrating signals and determining the neuron's output action potential.

• Axon: Single, thin extension for transmission of signals, can be very long (up to a meter in the case of some peripheral nerves).

• Axon Hillock: Area where axon exits the soma. It integrates inputs from the dendrites and initiates action potentials when a threshold is reached.

• Myelin: Fatty coating around axons that insulates and facilitates rapid conduction of action potentials. Myelination is crucial for speed and efficiency in signal transmission, significantly increasing conduction velocity.

• Nodes of Ranvier: Gaps in myelin, allowing for saltatory conduction where action potentials jump from node to node, enhancing speed.

• Axon Terminals: Release neurotransmitters into synapses to communicate with other neurons.

Neurons vary in shape and size:

• Multipolar Neurons: Have many dendrites, mainly found in the brain and spinal cord.

• Bipolar Neurons: Have one dendrite and one axon, often found in sensory organs (like the retina).

• Unipolar Neurons: Have a single process extending from the cell body, typical in sensory pathways.

• Interneurons: Connect neurons within the same region, critical for reflexes and local signaling.

Membrane Structure

Composed of double lipid layers with protein channels that control the passage of ions and molecules.

• Selective Permeability: Allows certain molecules (O2, CO2) to cross freely, while larger molecules (proteins) and ions (Na+, Cl-) are regulated, maintaining electrochemical gradients critical for neuron function.

Organelles in Neuron Physiology

• Cytoplasm: Medium for chemical reactions, crucial for metabolic activities.

• Nucleus: Encodes and transcribes mRNA which is essential for protein synthesis.

• Ribosomes: Translate mRNA into proteins vital for neuronal function and signaling.

• Endoplasmic Reticulum: Rough ER is involved in protein synthesis, while smooth ER assists in lipid synthesis, both important in maintaining cellular function.

• Golgi Complex: Packages and distributes proteins, key in neurotransmitter vesicle formation.

• Mitochondria: Energetic powerhouse, storing and releasing energy via ATP production, crucial for high energy demands in neurons.

• Microtubules and Filaments: Provide structural support and transport substances within the cell. Important for maintaining shape and facilitating intracellular transport.

Glia

Glial cells provide various functions including insulation, structural support, nutrient transport, and waste removal.

• Ependymal Cells: Line ventricles in the brain, aid in the circulation of cerebrospinal fluid (CSF), contributing to nutrient distribution and waste removal.

• Oligodendrocytes: Form the myelin sheath in the CNS, critical for enhancing signal transmission speeds.

• Astrocytes: Form the blood-CNS barrier, provide trophic support, and maintain extracellular ion balance, regulations crucial for neurotransmission and overall brain health.

• Microglia: Act as the brain's immune defense, removing waste and pathogens, and sculpting synaptic connections, playing an essential role in neuroinflammation.

• Radial Glia: Guide neuron migration during development, critical for proper brain structure formation.

• Satellite Cells: Support peripheral neurons, providing physical support and regulating the microenvironment.

• Schwann Cells: Myelinate axons in the PNS, assisting in nerve regeneration and repair.

Major Systems of the Nervous System

Basic Features

• Central Nervous System (CNS): Includes the brain and spinal cord, responsible for processing information and directing responses.

• Peripheral Nervous System (PNS): Comprises the somatic (voluntary control) and autonomic systems (involuntary control).

Autonomic Nervous System

Regulates involuntary body functions.

• Sympathetic Nervous System (SNS): Responsible for 'fight-or-flight' responses, prepares the body for stressful situations by increasing pulse rate, blood pressure, and bronchodilation.

• Parasympathetic Nervous System (PSNS): Responsible for 'rest-and-digest' responses, conserves energy by decreasing pulse rate and blood pressure while promoting digestion.

• Enteric Nervous System: Governs the function of the gastrointestinal system, often called the "second brain" due to its autonomy and complexity.

The Central Nervous System

Major Divisions

• Forebrain: Responsible for higher cognitive functions, emotions, and sensory processing. Includes the cortex and basal ganglia.

• Midbrain: Plays a role in vision, hearing, and motor control, also involved in arousal and temperature regulation.

• Hindbrain: Controls basic life functions such as breathing and heartbeat and plays a role in coordination and balance.

Detailed Structure of Each Division

Includes notable features such as gyri, sulci, and specific nuclei involved in motor and sensory functions.

Cerebrospinal Fluid (CSF)

CSF provides support, cushioning, and waste transport. It circulates around the brain and spinal cord, acting as a shock absorber.Issues like hydrocephalus can arise when CSF does not properly drain, leading to increased intracranial pressure and potential brain damage.

Brain Functionality

Understanding various brain regions like the thalamus (sensory process), basal ganglia (movement regulation), hypothalamus (hormonal control and homeostasis), and their roles in regulating bodily functions such as movement, emotion, and hormone release is essential for comprehending behavior and physiological responses.

Summary

The nervous system consists of complex networks of neurons and glial cells that serve critical roles in communication, structural support, and maintaining homeostasis through both voluntary and involuntary actions. Understanding its structure and functions is foundational for studying behavior and cognition.