Psychology Lecture: Brain Structure, Neurons, and Neurotransmitters

• Upcoming Examination Timeline:

  • Next Wednesday: Review session covering Chapter 4 material.

  • Exam Date: Scheduled for one week from next Wednesday.

  • Scope of Coverage: Chapters 1, 2, and 4.

  • Pacing Notice: The exam is scheduled about two to three weeks earlier than typical introductory psychology classes.

  • Assessment Strategy and Short-Answer Format:

  • The exam focuses on short-answer writing.

  • It requires deep understanding and recall, not just recognition, leading to clear explanations of neurobiological processes.

• Short Answer Item 1: Neural Structure and Function

Basic Anatomy of the Neuron

• Definition of a Neuron: A specialized cell in the brain or nerves that communicates through electrical and chemical signals.

• Three Main Structural Parts:

  • Soma: The cell body that keeps the neuron alive and decides when it will send signals.

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

  • Axon: A long projection that sends electrical signals away from the soma to other neurons, muscles, or glands.

Neural Impulse Dynamics and Quantitative Metrics

• Neural Impulse: The signal transmission method used by neurons. A neural impulse indicates that the brain is active.

• Neurobiology Statistics:

  • Total Neurons: About $3 imes 10^9$ to $5 imes 10^9$ neurons in the human body.

  • Axonal Network Length: Roughly $3 imes 10^8$ miles of axons throughout the body.

  • Impulse Speed: Neural impulses travel at speeds up to $200$ mph.

  • Battery Analogy:

  • Resting Charge: A neuron works like a battery, with a negative charge inside and a positive charge outside.

  • Action Potential: When stimulated, the neuron's charge changes from negative to positive.

  • Wave Propagation: This change creates a wave of electrical activity that moves down the axon and can be measured using neuroimaging techniques.

Synaptic Architecture

• Separation: Neurons do not touch; there are tiny gaps separating them.

• Interconnectivity: Each neuron connects to about $1{,}500$ other neurons in complex networks.

• Synapse: The small gap between the end of one neuron and the start of another where signals are transmitted using chemicals called neurotransmitters.

- Synaptic Communication: The process of sending information across the synapse with neurotransmitters.

Neurotransmitters and Behavioral Pharmacology

Excitatory vs. Inhibitory Functional Dynamics

• Excitatory Neurotransmitters: Increase the chances of the receiving neuron firing, promoting brain activity.

• Inhibitory Neurotransmitters: Decrease the chances of firing, signaling the neuron to slow down or stop.

• Need for Inhibitory Control: Without inhibitory signals, neurons would become hyperactive and not stop firing.

Specific Neurotransmitters and Clinical Pathology

Acetylcholine (ACh)

• Role: Can be excitatory or inhibitory, depending on where it acts.

• Muscle Function: Triggers muscle contractions.

• Memory Function: Important for long-term memory formation.

• Memory Trace: Changes in the brain that represent stored memories.

• Alzheimer's Disease: Leads to reduced ACh production, affecting memory.

• Clinical Details:

  • Loss of ACh makes new memory formation difficult.

  • Older memories may fade in the reverse order.

  • Behavioral changes may include confusion and loss of inhibition.

Serotonin

• Role: Regulates mood, appetite, and sleep.

• Mood Relation: Higher levels of serotonin correlate with better moods, while lower levels can lead to depression.

• Natural Increase: Can be improved through good sleep, nutrition, exercise, and socializing.

• SSRIs: Medications that increase serotonin activity in the brain to improve mood without widely affecting other brain functions.

Dopamine

• Role: Helps control movement and processes feelings of pleasure and reward.

• Parkinson's Disease: Involves the death of dopamine-producing neurons, leading to tremors and loss of motor control.

• Natural Rewards: Dopamine levels rise during enjoyable activities.

• Cocaine: A drug that disrupts the natural dopamine system and can drastically deplete dopamine over time, leading to long recovery periods.

• Anhedonia: A condition where an individual can’t feel pleasure due to dopamine loss.

Endorphins and Hormonal Modulation

• Endorphins: Natural pain-relieving chemicals in the body.

• Working Mechanism: Block pain signals temporarily during injury rather than fixing the injury itself.

• Adrenaline Connection: Works with adrenaline to help during emergencies.

- Placebo Effect: Expectations of relief can lead to actual endorphin release, reducing symptoms.

Autonomic Nervous System Dynamics

Sympathetic Nervous System Activation

• Role: Prepares the body for emergencies by activating the “fight or flight” response.

• Body Changes: Slows digestion, inhibits salivation, affects bladder function, and speeds up heart and breathing rates.

• Behavior Responses:

  • Fight: Attack the threat.

  • Flight: Quickly escape.

  • Freeze: Involuntary stillness, common in trauma survivors.

Parasympathetic Nervous System Recovery

• Role: Calms the body after a threat passes, returning to a state of balance.

• Body Restoration: Restores digestion and slows the heart rate.

• Breathing Technique: Deep belly breathing (diaphragmatic breathing) to promote calming by slowing the heart and relaxing muscles.

Short Answer Item 2: Architecture of the Brain (Stovall's Three Supercomputers Framework)

Conceptual Overview

• The adult human brain weighs about $2.5$ lbs and operates as three connected systems.

Supercomputer 1: The Brain Stem

• Location: At the base of the brain.

• Function: Controls essential life functions.

• Key Structure: The Medulla regulates heartbeat and breathing.

• Neuroplasticity: The brain's ability to adapt and recover from injuries is stronger in young children.

Supercomputer 2: The Cerebellum

• Location: At the back of the brain.

• Function: Manages movement, balance, and coordination.

Supercomputer 3: The Cerebral Cortex

• Overview: The outer layer of the brain, divided into two hemispheres.

• Four Lobes:

  • Frontal Lobe: Located in the front, responsible for decision-making and personality.

  • Parietal Lobe: Located at the top, processes touch sensations and spatial orientation.

  • Occipital Lobe: At the back, involved in processing visual information.

  • Temporal Lobe: Above the ears, responsible for hearing and language understanding.

Cerebrum

• Overview: The largest part of the brain, divided into two hemispheres (right and left).

• Functions:

  • Higher Cognitive Functions: Involved in reasoning, decision-making, problem-solving, and complex thought processes.

  • Emotional Regulation: Plays a role in emotions and social interactions.

  • Memory Formation: Critical for the processing and storage of memories.

  • Language Function: Responsible for language comprehension and production in certain areas (primarily the left hemisphere for right-handed individuals).

• Cerebral Cortex: The outer layer of the cerebrum, divided into four lobes (frontal, parietal, occipital, and temporal) that each have specific functions related to sensation, perception, and integration of information.

• Connectivity: Interconnected with various brain regions, allowing for the integration of sensory data and coordination of motor responses.

• Neuroplasticity: The ability of the cerebrum to reorganize itself by forming new connections and pathways, especially across different experiences and learning.

The endocrine system is a collection of glands situated throughout the body that regulate various functions by releasing hormones into the bloodstream. These glands coordinate important physiological processes, including metabolism, growth, and mood regulation. The major glands of the endocrine system include the pituitary, thyroid, and adrenal glands, among others. Figure 2.21 outlines their locations and functions, emphasizing their role as the body's "pumping stations" for hormones that affect organ function and overall health.