Neural Foundations of Behavior: The Biological Perspective

The Nervous System and You

Overview of the Nervous System

The nervous system is a complex network of specialized cells that transmits information throughout the body, enabling rapid communication and coordination of bodily functions.

• Nervous System: An extensive network of cells that carries information to and from all parts of the body.

• Neuroscience: The scientific study of the structure and function of neurons, nerves, and nervous tissue.

• Biological Psychology/Behavioral Neuroscience: A branch of neuroscience focusing on the biological bases of psychological processes, behavior, and learning.

Parts of a Neuron

Structure and Function

Neurons are the basic cells of the nervous system, responsible for receiving and transmitting messages.

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

• Soma (Cell Body): Contains the nucleus and maintains the life of the neuron.

• Axon: A long fiber that transmits messages to other neurons, muscles, or glands.

• Glial Cells: Supportive cells that nourish, protect, and insulate neurons; play roles in development and repair.

• Myelin Sheath: Fatty layer that insulates axons, produced by oligodendrocytes (CNS) and Schwann cells (PNS), increasing the speed of neural transmission.

How a Message is Generated?

Neural Transmission Process

Neurons communicate via electrical and chemical signals, allowing rapid information transfer.

• Resting Potential: The neuron at rest is electrically charged due to ion distribution (mainly sodium and chloride outside, potassium inside).

• Threshold & Stimulus: A stimulus triggers an action potential if it reaches the threshold.

• Action Potential: When threshold is reached, sodium channels open, and the neuron becomes positively charged, transmitting the signal.

• Return to Resting State (Repolarization): Potassium channels open, restoring the negative charge inside the neuron.

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

Equation:

$\text{Action Potential Speed} \approx 2 \text{ to } 270 \text{ mph}$

Synapse & Neurotransmission

Synaptic Gap and Receptor Sites

Neurons communicate across synapses using chemical messengers called neurotransmitters.

• Synaptic Gap: The fluid-filled space between the axon terminal of one neuron and the dendrite or soma of another.

• Receptor Sites: Located on the postsynaptic membrane; accept specific neurotransmitters like a lock and key.

• Excitatory vs. Inhibitory Signals: Excitatory signals increase the likelihood of firing; inhibitory signals decrease it.

Neurotransmission Process

• Action potential travels to axon terminal.

• Neurotransmitters are released into the synaptic vesicles.

• Neurotransmitters cross the synaptic gap.

• Bind to receptor sites on the postsynaptic neuron.

• Neurotransmitters are either reabsorbed (reuptake) or broken down (enzymatic degradation).

Agonists	Antagonists	Reuptake	Enzymatic Degradation
Chemicals that mimic or enhance neurotransmitter effects (e.g., nicotine for ACh, alcohol for GABA).	Chemicals that block or reduce neurotransmitter effects (e.g., curare blocks ACh).	Neurotransmitters taken back into the presynaptic neuron after signaling.	Specific enzymes break down neurotransmitters in the synaptic gap (e.g., acetylcholinesterase for ACh).

Major Neurotransmitters

Neurotransmitter	Function	Neurotransmitter	Function
Acetylcholine (ACh)	Excitatory or inhibitory; controls muscle contractions, memory, attention.	Serotonin (5-HT)	Excitatory or inhibitory; affects sleep, mood, appetite; low levels linked to depression.
Norepinephrine (NE)	Mainly excitatory; involved in arousal, alertness, mood.	Gamma-Aminobutyric Acid (GABA)	Major inhibitory; reduces anxiety, regulates neural activity.
Dopamine (DA)	Excitatory or inhibitory; controls movement, pleasure, learning; implicated in Parkinson's (low) and schizophrenia (high).	Glutamate	Major excitatory; key role in learning, memory, neural plasticity.
Endorphins	Inhibitory; reduce pain, produce euphoria.

Lesioning & Brain Stimulation

Lesioning

Lesioning involves the deliberate destruction of brain tissue using electrical current to study behavioral and functional changes.

• Purpose: To study behavioral/functional changes post-damage.

• Limitation: Human case studies offer insight but have limited generalizability.

• Usage: Common in animal studies; natural lesions studied in humans.

Brain Stimulation

• Electrical Stimulation of the Brain (ESB): Low-intensity current mimics natural signals without damaging neurons.

• Function: Temporarily enhances or disrupts brain activity to study effects.

• Application: Used in both clinical and animal studies.

Types of Brain Stimulation

Invasive Brain Stimulation	Noninvasive Brain Stimulation
Deep Brain Stimulation (DBS): Electrodes implanted in deep brain areas; used for Parkinson's, depression, OCD. Optogenetics: Neurons genetically modified to respond to light; used in animal research.	Transcranial Magnetic Stimulation (TMS): Magnetic fields stimulate brain regions; used for depression, learning, and cognitive enhancement. Transcranial Direct Current Stimulation (tDCS): Weak electrical current passed between scalp electrodes; used for mood, learning, and rehabilitation.

Neuroimaging Techniques

Structural and Functional Mapping

Neuroimaging allows visualization of brain structure and function, aiding diagnosis and research.

Technique	Type	How it Works	Advantages	Limitations
CT Scan	Structural	X-rays create cross-sectional images ('slices') of the brain.	Good for detecting skull fractures; preferred if MRI unavailable.	Lower detail compared to MRI.
MRI	Structural	Uses magnetic field to align hydrogen atoms; produces detailed images.	High spatial resolution; detects tumors, strokes.	Expensive; not suitable for patients with metal implants.
fMRI	Functional	Measures oxygen level changes in blood; maps brain activity.	Tracks brain function during cognitive tasks.	Requires subject cooperation; expensive.
EEG	Functional	Electrodes on scalp record electrical activity; detects brain waves.	Excellent temporal resolution; useful for sleep studies.	Poor spatial resolution.
PET	Functional	Radioactive tracer injected; detects metabolic activity.	Shows active brain regions during tasks.	Exposure to radioactivity; lower spatial resolution than MRI.

Brain Structures

Major Divisions and Functions

The brain is divided into the hindbrain, midbrain, and forebrain, each with specialized structures and functions.

• Cerebral Cortex: Complex thought processes.

• Corpus Callosum: Connects left and right hemispheres.

• Thalamus: Relays sensory information.

• Basal Ganglia: Movement regulation.

• Amygdala: Fear, threat, emotional responses.

• Cerebellum: Balance, coordination.

• Hippocampus: Memory formation.

• Medulla: Heartbeat, breathing.

• Reticular Formation: Arousal, attention.

• Pituitary Gland: Hormone regulation.

Brain Structures: Hindbrain & Limbic System

Hindbrain	Limbic System
Medulla: Controls vital life functions; damage is life-threatening. Pons: Bridge between cerebellum and cortex; regulates sleep, dreaming, arousal. Cerebellum: Balance, coordination, voluntary movement.	Thalamus: Sensory relay station. Hypothalamus: Regulates hunger, thirst, sleep, body temperature. Hippocampus: Memory formation. Amygdala: Fear, emotional responses.

Cerebral Hemispheres

Lobes and Functions

The cerebral cortex is divided into lobes, each with specialized functions.

• Frontal Lobe: Planning, decision-making, voluntary movement.

• Parietal Lobe: Sensory information processing.

• Temporal Lobe: Auditory processing, memory.

• Occipital Lobe: Visual processing.

Information Transmission: Contralateral (opposite side) and ipsilateral (same side) organization; most sensory and motor signals cross to the opposite side of the brain.

Association Areas of Cortex

Broca's Area and Wernicke's Area

Association areas integrate sensory input with memory, knowledge, and meaning.

• Broca's Area: Located in the left frontal lobe; involved in speech production. Damage leads to Broca's aphasia (impaired speech).

• Wernicke's Area: Located in the left temporal lobe; involved in language comprehension. Damage leads to Wernicke's aphasia (fluent but nonsensical speech).

Cerebral Hemispheres: Split-Brain Research & Specialization

Split-Brain Research

Research by Roger Sperry and Michael Gazzaniga involved cutting the corpus callosum to study hemisphere specialization in patients with severe epilepsy.

• Stopped communication between hemispheres, allowing study of separate functions.

• Left visual field processed by right hemisphere; right hemisphere cannot produce speech but can draw or recognize objects.

Hemisphere Specialization

• Left Hemisphere: Language, logical analysis, sequential processing.

• Right Hemisphere: Spatial abilities, face recognition, holistic processing, emotional expression.

• Both hemispheres have strengths; dominance varies slightly among individuals.

• Left brain = Structuralist (breaks things into parts); Right brain = Gestaltist (sees the whole picture).

Sample Questions & Answers

Review Questions

• Q1: What structure is severed in split-brain surgery to reduce epileptic seizures? Answer: Corpus Callosum

• Q2: In split-brain patients, if an object is shown to the left visual field, which is true? Answer: The object can be drawn with the left hand but not named.

• Q3: Which is primarily associated with the left hemisphere? Answer: Language and logical analysis.

• Q4: Which best describes the right hemisphere's processing style? Answer: It processes information holistically and all at once.

• Q5: Correct pairing of hemisphere and function? Answer: Left Hemisphere - Sequential Processing.