Introduction to Neuroscience: Anatomy, Physiology, and Neurochemistry

Course Introduction and Resources

• The course covers the biological bases of psychological processes including emotion, behavior, thought, and perception.
• Learning resources and communication:
  • The primary website for supplemental information is BrainFacts.org. It is designed for the general public and is factually correct without being overly technical.
  • The relevant textbook chapter for this module is titled 'The Biology of Behaviour'.
  • Exam questions are based exclusively on lecture material rather than the textbook alone.
  • Lectures one through three focus on Anatomy, Physiology, and Neurochemistry of the Nervous System.
  • Lecture four covers the methods used to study the brain.
  • Lectures five and six address specific topics: Motivation, Feeling, Reward, Sleep, Wakefulness, Language, Learning, and Memory.

The Philosophy of Behavioral Neuroscience

• Behavioral neuroscience is the study of how psychological processes are instantiated in the brain.
• The fundamental perspective of this field is that all psychological processes—including every thought, feeling, and behavior—depend entirely on the brain.
• While philosophical or religious beliefs may suggest the mind and brain are separate entities, the neuroscientific approach operates on the belief that all mental life originates from brain activity.

Terminology and Anatomical Directions

• Neuroscience terminology can be intimidating due to the use of Latin names and specialized jargon established in the late 19th and early 20th centuries.
• Many terms refer to multiple things, potentially causing confusion:
  • Nucleus (Cellular): Refers to the structure inside a single cell body where intracellular processes and genetic machinery reside.
  • Nucleus (Neuroanatomical): Refers to a collection or cluster of neurons within the brain, such as the nucleus of the amygdala.
• Standard directional terms in neuroscience:
  • Dorsal: Refers to the top of the brain.
  • Ventral: Refers to the bottom of the brain.
  • Medial: Refers to the middle or midline of the brain.
  • Lateral: Refers to the side of the brain.

Rationale for Studying Neuroscience in Psychology

• Understanding Mechanisms: Neuroscience helps distinguish between seemingly similar psychological processes. For example, voluntary goal-directed actions and automatic habits are controlled by different neural circuits. A behavior might begin as a goal-directed action requiring high attention and transition into a habit once it becomes automatic after repetition (e.g., walking a common route to university).
• Establishing Causality: Studying the brain allows researchers to move beyond correlation. In studies of obsessive-compulsive disorder (OCD), substance use disorder, and Parkinson’s disease, neuroinflammation is observed in the striatum alongside impaired decision-making. By inducing neuroinflammation in the striatum of rats, researchers confirmed that this inflammation actually causes changes in decision-making capabilities, rather than being a mere epiphenomenon.
• Informing Psychological Theory: Identifying distinct neural circuits for different types of action selection informs and refines psychological theories.
• Hardware and Software Analogy: The brain is viewed as the 'hardware' and psychology as the 'software'. Neither is fully functional or useful without the other; together, they allow for processing, feeling, and action.

Divisions of the Nervous System

• The nervous system is divided into two primary sections:
  • Central Nervous System (CNS): Consists of the brain, brain stem, and spinal cord.
  • Peripheral Nervous System (PNS): Includes all parts of the nervous system outside the CNS. It serves as the interface between the CNS and the rest of the body.
• Functions of the PNS:
  • Executes motor signals from the CNS (e.g., walking to get water when thirsty).
  • Transmits sensory inputs to the CNS (e.g., tactile sensations, pain, photoreceptors in the eyes, and auditory receptors in the ears).

The Autonomic Nervous System (ANS)

• The ANS is a subdivision of the PNS that modulates involuntary bodily processes.
• It manages the "Four F's": Feeding, Fight, Flight, and Sexual Arousal.
• The ANS consists of two branches with opposing effects:
  • Sympathetic Nervous System: Engaged during high arousal, excitement, exercise, or embarrassment (the "Four E's"). It prepares the body for action (Fight or Flight) by increasing heart rate, widening airways for oxygen intake, and breaking down fuel reserves. It diverts blood away from the skin and viscera toward the heart, lungs, and skeletal muscles.
  • Parasympathetic Nervous System: Involved in rest, energy conservation, and the "Three Ds": Digestion, Defecation, and Diuresis. It decreases heart rate, narrows airways, and increases blood flow to the digestive and urinary systems.

Neurotransmitters in the PNS and CNS

• The brain and the body use the same chemical messengers, though their roles differ by location:
  • Acetylcholine: In the brain, it is associated with attention and flexible responding. In the PNS, it is required for every muscle movement.
  • Noradrenaline: Primarily associated with sympathetic nervous system arousal (the "adrenaline rush").
• Clinical Implications: Because the same neurotransmitters are used throughout the body, drugs designed to target the brain often have peripheral side effects. For example, anticholinergic drugs used for Alzheimer’s disease can cause dry mouth because they affect acetylcholine receptors in the periphery.

The Enteric Nervous System

• Often called the "second brain," this system consists of approximately $0.5$ billion neurons located in the walls of the gastrointestinal tract.
• It controls digestive activity, including peristalsis (intestinal contractions) and the secretion of enzymes.
• It senses the chemical and physical conditions of the gut.
• Interaction with the ANS:
  • The sympathetic nervous system inhibits the enteric system.
  • The parasympathetic nervous system amplifies the enteric system.
• The enteric system can function independently of the brain if necessary, though it normally communicates with it.
• It utilizes neurotransmitters like dopamine and serotonin:
  • Dopamine: Associated with reward in the brain but digestion and hormone function in the body. (Note: The concept of a "dopamine fast" is considered biological nonsense as it would impair basic digestion).
  • Serotonin: Associated with mood and antidepressants in the brain but aids digestion in the periphery.

Brain Energy Consumption and the 10% Myth

• The idea that humans only use $10\%$ of their brain is a myth; humans use all of their brain, though not all at the same time.
• Evolutionary and biological evidence against the myth:
  • The brain accounts for only $2\%$ of body mass but consumes $20\%$ of the blood supply and $25\%$ of the body's oxygen.
  • The high energy cost makes it unlikely that we would evolve to use only a small fraction of the organ.
  • Large human brain size (and heads) makes childbirth significantly more dangerous for humans than other species; this risk would not be evolutionarily justified if the brain were largely unused.

Protective Systems of the Brain

• The brain is delicate and lacks pain receptors inside the tissue (though the surrounding skull and tissue do have them).
• Adults generally do not create new brain cells (with minor exceptions), meaning the cells we are born with must last a lifetime to preserve memory and knowledge.
• Mechanical Protection:
  • Bone: The thick skull protects the brain, and the spinal column protects the spinal cord.
  • The Meninges: Three layers of protective tissue:
    1. Dura Mater: The "hard mother"; a thick, rigid outer layer.
    2. Arachnoid Mater: A web-like middle layer. It includes the subarachnoid space filled with Cerebrospinal Fluid (CSF), which acts as a cushion and houses blood vessels.
    3. Pia Mater: The "delicate mother"; a thin, flexible layer that follows the exact folds and contours of the brain's surface.
• Chemical Protection (The Blood-Brain Barrier):
  • The brain has high energy demands and requires constant blood flow, making it vulnerable to toxins in the blood.
  • Capillaries in the brain have walls made of endothelial cells with very small pores.
  • These small pores restrict the entry of large molecules and chemicals into the CNS while allowing necessary information and smaller molecules to pass. This barrier also makes it difficult to develop drugs that effectively reach the brain.

The Spinal Cord and Reflexes

• The spinal cord is a cable of neural fibers that serves as the interface between the brain and the PNS.
• It facilitates motor actions from the brain and sensory input from the body.
• Spinal Reflexes: Some motor responses are triggered directly by the spinal cord without requiring initial brain involvement for the sake of speed.
  • Hot Surface Reflex: Pulling a hand away from something hot happens before the brain processes the pain.
  • Patellar (Knee-jerk) Reflex: Used constantly during walking to maintain stability. If you trip or step on an uneven surface, the reflex acts quickly to prevent a fall.
  • While the reflex occurs independently, the information is sent back to the brain immediately afterward for processing and learning.

Questions & Discussion

• Question: How much of our psychological processes depend on the brain?
• Response: In behavioral neuroscience, the belief is that $100\%$ of psychological processes depend on the brain.
• Question: Re-affirming the usage of the brain; is it true we only use $10\%$?
• Response: No, the answer is zero percent truth to that. We use all of it, as evidenced by the extreme energy and oxygen consumption of the organ.
• Question: Regarding the high arousal state, if you're not aware of why you're aroused, does it still function as a fight or flight response?
• Response: Yes, the sympathetic nervous system functions based on factors in the environment telling you you're aroused, even if you aren't consciously aware of the specific reason. This can contribute to the addictive nature of certain states or substances, especially when reward pathways are also activated.