The Biology of Mind: Neural Systems, Brain Structures, and Behavior Genetics
The Biology of Mind: Neural and Hormonal Systems, Brain Structures, and Behavior Genetics
Introduction to Biological Psychology
Searching for the Biology of "Self": Biological psychologists investigate the intricate connections between the body, mind, and behavior to understand where our identity resides—is it the heart, the brain, or the whole body?
Overview of Mind's Building Blocks:
Neurons: The fundamental components and their communication mechanisms, primarily involving neurotransmitters.
Nervous System: Various parts of the nervous system and their functions in building the mind.
Endocrine System: A slower-communicating system that uses hormones as chemical messengers.
Tools for Brain Examination: Techniques for studying brain activity.
Brain Structures: Examination of both primitive and advanced brain regions.
Neural and Hormonal Systems: Communication and Structure
Hand-Withdrawal Reflex:
An involuntary response where sensory neurons from skin receptors transmit information to the spinal cord.
Interneurons in the spinal cord bypass the brain, communicating directly with motor neurons.
Motor neurons then instruct muscles to contract, causing withdrawal from a harmful stimulus (e.g., a candle flame).
This reflex occurs before the information reaches the brain, demonstrating that pain is experienced after the action.
Neurons: Building Blocks of the Nervous System
Definition: Neurons are nerve cells, billions of which are present throughout the body.
Neural Networks: Neurons interconnect to form complex webs, which are modified with experience. The principle "Neurons that fire together, wire together" highlights this plasticity.
Neuronal Communication: Action Potential
Action Potential: A neural impulse that propagates along an axon, similar to a wave.
It involves rapid ion exchanges moving in and out of the axon membrane.
Process of Communication:
A neuron receives signals from other neurons, some excitatory ("Fire!") and some inhibitory ("Don't fire!").
Threshold: An action potential is triggered when the excitatory signals sufficiently outweigh inhibitory signals to reach a specific threshold.
"All-or-None" Response: Once the threshold is met, the neuron fires completely or not at all; increasing stimulation beyond the threshold does not affect the intensity or speed of the action potential.
The action potential travels down the axon, from the cell body to the terminal branches.
The signal is transmitted to another cell, but it must cross a gap, known as the synapse.
The Synapse
Definition: Also called the "synaptic junction" or "synaptic gap," it is the specialized junction between the axon tip of a sending neuron and the dendrite or cell body of a receiving neuron.
Neurotransmitters
Definition: Chemicals responsible for transmitting signals across the synaptic gap.
Mechanism: When an action potential reaches the axon terminal, it stimulates the release of neurotransmitter molecules.
Binding: These molecules traverse the synaptic gap and bind to specific receptor sites on the receiving neuron.
Effect: This binding allows electrically charged atoms to enter the receiving neuron, exciting or inhibiting a new action potential.
Reuptake: After neurotransmitters stimulate the receptors, excess molecules are reabsorbed back into the sending neuron to be recycled, a process critical for regulating their activity.
Roles of Different Neurotransmitters
Serotonin:
Function: Affects mood, hunger, sleep, and arousal.
Imbalance: Undersupply is linked to depression; many antidepressant drugs increase serotonin levels.
Dopamine:
Function: Influences movement, learning, attention, and emotion.
Imbalance: Oversupply is linked to schizophrenia; undersupply is associated with tremors and decreased mobility in Parkinson’s disease and ADHD.
Acetylcholine (ACh):
Function: Enables muscle action, learning, and memory.
Imbalance: ACh-producing neurons deteriorate as Alzheimer’s disease progresses, leading to cognitive decline.
Norepinephrine:
Function: Helps control alertness and arousal.
Imbalance: Undersupply can depress mood and cause attention problems similar to those seen in ADHD.
GABA (gamma-aminobutyric acid):
Function: A major inhibitory neurotransmitter.
Imbalance: Undersupply is linked to seizures, tremors, and insomnia.
Glutamate:
Function: A major excitatory neurotransmitter, crucial for memory.
Imbalance: Oversupply can overstimulate the brain, leading to migraines or seizures (e.g., some people avoid MSG due to this effect).
Endorphins:
Function: Body’s natural painkillers; they diminish sensitivity to pain and elevate mood.
Imbalance: Undersupply can lead to depression, anxiety, moodiness, aches and pains, addiction readiness, and trouble sleeping. Oversupply due to opiate drug use can suppress the body’s natural endorphin production.
The Nervous System: Divisions and Functions
Central Nervous System (CNS):
Comprises the brain and spinal cord.
Acts as the body's primary decision-maker.
Peripheral Nervous System (PNS):
Gathers information from the body and sensory receptors.
Transmits CNS decisions to various parts of the body.
Types of Neurons
Sensory Neurons (Afferent): Carry incoming messages from the body’s tissues and sensory receptors to the CNS for processing.
Motor Neurons (Efferent): Carry outgoing instructions from the CNS to the body’s tissues and muscles.
Interneurons: Found within the brain and spinal cord, they process information between sensory input and motor output.
Divisions of the Peripheral Nervous System
Somatic Nervous System:
Controls voluntary movements of skeletal muscles.
Enables conscious control over body movements.
Autonomic Nervous System (ANS):
Controls self-regulated actions of internal organs and glands.
Operates largely unconsciously.
Sympathetic Nervous System (Arousing):
Prepares the body for stress or action ("fight-or-flight").
Dilates pupils, accelerates heartbeat, inhibits digestion, stimulates glucose release from the liver, stimulates secretion of epinephrine and norepinephrine (adrenaline).
Parasympathetic Nervous System (Calming):
Returns the body to a relaxed state ("rest and digest").
Contracts pupils, slows heartbeat, stimulates digestion, stimulates gallbladder, contracts bladder, allows blood flow to sex organs.
Interneurons in the Spine (Reflex Actions):
Some decisions are made without brain involvement.
Spinal interneurons can trigger reflex actions (e.g., hand-withdrawal from fire, knee-jerk response).
The brain is informed about the reflex after it has occurred.