Neuroscience and Behavior: Structure and Function of Neurons

Neurons and Their Role in Behavior

Introduction

Neurons are the fundamental units of the nervous system, responsible for transmitting information throughout the body. Understanding their structure and function is essential for comprehending how the brain and nervous system influence behavior.

Structure of a Neuron

Neurons are specialized nerve cells that serve as the basic building blocks of the nervous system. Each neuron consists of several key components:

• Dendrites: Branch-like fibers that receive electrical messages (impulses) from other neurons.

• Cell Body (Soma): Contains the nucleus and is responsible for maintaining the life of the cell.

• Axon: A long, slender projection that carries messages away from the cell body to other neurons, muscles, or glands.

• Myelin Sheath: A protective coating of fat and protein that wraps around the axon, increasing the speed and efficiency of electrical signal transmission.

• Terminal Buttons: Small structures at the end of the axon that release neurotransmitters into the synapse.

Example: The myelin sheath acts like insulation on an electrical wire, allowing signals to travel rapidly and efficiently.

Where Neurons Connect: The Synapse

Neurons communicate with each other at junctions called synapses. The synapse is the small gap between the axon terminal of the sending neuron and the dendrites of the receiving neuron. Communication across the synapse occurs via chemical messengers called neurotransmitters.

• Synapse: The space where the axon of one neuron communicates with the dendrites of another neuron using chemical signals.

Example: When you touch a hot surface, sensory neurons transmit signals to the spinal cord, which then relays the message to motor neurons to withdraw your hand.

How Neurons Fire

Neurons transmit information through electrical impulses known as action potentials. The process of firing follows specific principles:

• All-or-None Law: A neuron either fires completely or not at all; the strength of the stimulus does not affect the strength of the action potential.

• Resting State: The neuron is inactive, with a negative charge inside relative to the outside.

• Action Potential: A brief electrical charge that travels down the axon when the neuron is activated.

• Mirror Neurons: Specialized neurons that fire both when an individual performs an action and when they observe the same action performed by another.

Equation:

$V_{m} = V_{rest} + ext{Action Potential}$

Example: Mirror neurons are thought to play a role in empathy and learning by imitation.

Neurotransmitters: Chemical Messengers

Neurotransmitters are chemicals released by neurons to transmit signals across the synapse to other neurons. They can have excitatory or inhibitory effects:

• Excitatory Neurotransmitters: Increase the likelihood that the receiving neuron will fire.

• Inhibitory Neurotransmitters: Decrease the likelihood that the receiving neuron will fire.

Example: Glutamate is a major excitatory neurotransmitter, while GABA is a major inhibitory neurotransmitter.

Major Neurotransmitters and Their Functions

Neurotransmitter	Main Functions	Example/Application
Acetylcholine (ACh)	Muscle movement, memory, cognitive functions	Deficiency linked to Alzheimer's disease
Dopamine (DA)	Movement, attention, learning	Imbalance associated with Parkinson's disease and schizophrenia
Serotonin	Sleeping, eating, mood, pain	Low levels linked to depression
Endorphins	Pain suppression, pleasure, appetites	Released during exercise, producing 'runner's high'

The Nervous and Endocrine Systems

Introduction

The nervous and endocrine systems are two major communication networks in the body, coordinating behavior and physiological processes through electrical and chemical signals.

The Nervous System

• Central Nervous System (CNS): Consists of the brain and spinal cord; responsible for processing and responding to sensory information.

• Peripheral Nervous System (PNS): All parts of the nervous system outside the CNS; connects the CNS to limbs and organs.

• Reflex: An automatic, involuntary response to a stimulus, often mediated by the spinal cord.

Divisions of the Peripheral Nervous System:

• Somatic Division: Controls voluntary movements and communication with sense organs.

• Autonomic Division: Regulates involuntary bodily functions (e.g., heart rate, digestion).

  • Sympathetic Division: Prepares the body for stressful or emergency situations ('fight or flight').

  • Parasympathetic Division: Restores the body to a state of calm ('rest and digest').

The Endocrine System

The endocrine system is a chemical communication network that uses hormones to regulate various bodily functions.

• Hormones: Chemical messengers secreted into the bloodstream by glands.

• Pituitary Gland: Often called the 'master gland,' it regulates other endocrine glands and many body functions.

Example: Adrenaline (epinephrine) is released by the adrenal glands during stress, increasing heart rate and energy.

The Brain: Structure and Function

Introduction

The brain is the central organ of the nervous system, responsible for processing information, regulating bodily functions, and enabling complex behaviors.

Studying the Brain

• Electroencephalogram (EEG): Measures electrical activity in the brain.

• Positron Emission Tomography (PET): Visualizes brain activity by detecting radioactive tracers.

• Functional Magnetic Resonance Imaging (fMRI): Maps brain activity by measuring changes in blood flow.

• Transcranial Magnetic Stimulation (TMS): Uses magnetic fields to stimulate nerve cells in the brain.

The Central Core: The "Old" Brain

The central core of the brain controls basic life functions and includes several key structures:

• Medulla: Regulates breathing and heartbeat.

• Pons: Integrates movement between the right and left sides of the body; regulates sleep.

• Cerebellum: Controls bodily balance and coordination.

• Reticular Formation: Activates other parts of the brain to produce arousal.

• Thalamus: Acts as a relay station for sensory information.

• Hypothalamus: Maintains homeostasis by regulating survival-related functions (e.g., hunger, thirst, temperature).

The Limbic System

The limbic system is involved in emotion, learning, memory, pleasure, and self-preservation. Major components include:

• Amygdala: Processes emotions such as fear and aggression.

• Hippocampus: Essential for forming new memories.

Example: Damage to the hippocampus can result in difficulty forming new memories.

The Cerebral Cortex

The cerebral cortex is responsible for higher-order information processing and is divided into four lobes:

• Frontal Lobes: Involved in reasoning, planning, movement, and problem-solving.

• Parietal Lobes: Process sensory information related to touch, temperature, and pain.

• Temporal Lobes: Involved in hearing, language, and memory.

• Occipital Lobes: Responsible for visual processing.

Functional Areas:

• Motor Area: Controls voluntary movements.

• Sensory Area: Processes sensory input.

• Association Areas: Integrate information from different sensory modalities and are involved in complex cognitive processes.

Neuroplasticity and the Brain

Neuroplasticity refers to the brain's ability to change and adapt throughout life. This includes the formation of new neurons (neurogenesis), new connections between neurons, and the reorganization of information-processing areas.

• Example: After a brain injury, other parts of the brain may take over functions previously managed by the damaged area.

Specialized Hemispheres

The brain is divided into left and right hemispheres, each controlling motion and sensation on the opposite side of the body. Some functions are more dominant in one hemisphere:

• Left Hemisphere: Typically dominant for language, logic, and analytical tasks.

• Right Hemisphere: Typically dominant for spatial abilities, creativity, and holistic processing.

Example: Damage to the left hemisphere may impair speech, while damage to the right hemisphere may affect spatial awareness.