Ch 3

Neuron Functions and Classification

  • Reception, Integration, and Transmission

    • Neurons have three primary functions:

    • Reception: Neurons detect information from the environment.

    • Integration: Neurons integrate and process the received information.

    • Transmission: Neurons transmit signals to other neurons or muscles.

  • Components of Neurons

    • Sensory Neurons:

    • Detect information from the physical environment and relay it to the brain.

    • Example: Feeling a burn on the skin activates sensory neurons that send signals to the brain to initiate a reaction (e.g., withdrawing the hand).

    • Motor Neurons:

    • Responsible for carrying commands from the brain to muscles, resulting in physical actions such as retraction from a hot surface.

Structure of Neurons

  • Dendrites:

    • Branch-like extensions that receive incoming signals from other neurons.

  • Cell Body (Soma):

    • Integrates information received by dendrites and processes it within the neuron.

  • Axon:

    • The part of the neuron where electrical signals (action potentials) travel to transmit information to other neurons or muscles.

  • Myelin Sheath:

    • Insulating layer around the axon that speeds up the transmission of electrical signals.

    • Damage to the myelin sheath can slow down reactions and decrease awareness to stimuli.

  • Axon Terminals:

    • Release neurotransmitters, which transmit signals to other neurons.

Neuronal Communication

  • Action Potential:

    • An electrical impulse that travels down the axon, adhering to the all-or-nothing principle: the neuron either fires or it does not.

  • Resting Membrane Potential:

    • The electrical charge difference across the neuronal membrane when the neuron is not active, influenced by ion distribution inside and outside the neuron.

  • Polarization:

    • A state where the inside of the neuron has a higher concentration of negative ions compared to the outside, establishing resting potential.

Neurotransmitters

  • Definition:

    • Chemical messengers that influence behavior and mood by binding to receptors on the receiving neurons.

  • Key Types of Neurotransmitters:

    • Dopamine: Associated with reward, motivation, and movement.

    • Norepinephrine: Involved in mood regulation; increased levels are targeted by medications for anxiety and depression.

    • Serotonin: Plays a crucial role in mood regulation, sleep, appetite, and impulse control.

    • Acetylcholine: Facilitates muscle action and is involved in cognition.

    • GABA (gamma-aminobutyric acid): An inhibitory neurotransmitter; reduces neuronal excitability.

    • Glutamate: An excitatory neurotransmitter; plays a role in learning and memory.

    • Endorphins: Involved in pain reduction and create feelings of pleasure or euphoria.

Impact of Drugs on Neurotransmitters

  • SSRIs (Selective Serotonin Reuptake Inhibitors):

    • Increase serotonin availability, utilized in treating depression.

  • Stimulants:

    • Increase the activity of dopamine and norepinephrine in the brain.

Brain Structure Overview

  • Study of the Brain:

    • Various methods exist for studying brain structure and function, including:

    • Lesion Studies: Analyze effects of damage in specific brain areas.

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

    • CT (Computed Tomography): Provides a structural view of the brain.

    • MRI (Magnetic Resonance Imaging): Structural imaging to assess brain anatomy.

    • PET (Positron Emission Tomography): Offers functional imaging, providing insight into brain activity.

    • fMRI (Functional Magnetic Resonance Imaging): Measures brain activity by detecting changes associated with blood flow.

  • Brain Stem:

    • Controls basic survival functions like breathing and heart rate.

    • Composed of:

    • Medulla Oblongata: Regulates heart rate and breathing.

    • Pons: Involved in sleep, dreaming, and coordination of body movements.

    • Midbrain: Functions in vision, hearing, pain regulation, and sleep.

  • Cerebellum:

    • Coordinates movement and balance; plays a role in learning and processing.

  • Limbic System:

    • Amygdala: Central to processing emotions, especially fear.

    • Hypothalamus: Regulates hormones and drives related to survival (e.g., hunger, thirst).

    • Hippocampus: Crucial for memory formation; linked to conditions like Alzheimer's and dementia.

Neurological Conditions and Recovery

  • Understanding neurotransmitter roles and brain areas is key to diagnosing and treating neurological disorders.

  • Research indicates the possibility of brain repair and recovery even after severe injuries, previously thought to be nonreversible.

  • Continuous cognitive engagement is encouraged, especially for older adults, as it can help delay the onset of cognitive decline related to dementia and Alzheimer's.