Biological Psychology: Nervous System, Neurons, and Brain Structure

Hierarchy of the Nervous System

Overview of Nervous System Organization

The nervous system is a complex network responsible for transmitting signals throughout the body, enabling sensation, movement, and cognition. It is divided into two main parts: the central nervous system (CNS) and the peripheral nervous system (PNS).

• Central Nervous System (CNS): Composed of the brain and spinal cord; responsible for processing and integrating information.

• Peripheral Nervous System (PNS): Consists of nerves outside the CNS; connects the CNS to limbs and organs.

Divisions of the Nervous System

Nervous System	Central Nervous System	Peripheral Nervous System
	Brain, Spinal Cord	Somatic Division (voluntary muscle activation), Autonomic Division (involuntary functions)
	Forebrain, Midbrain, Hindbrain	Sympathetic Division (activates), Parasympathetic Division (inhibits)

Neurons: Structure and Function

Basic Structure of a Neuron

Neurons are the fundamental units of the nervous system, specialized for communication. They transmit electrical and chemical signals.

• Dendrites: Receive incoming signals from other neurons.

• Cell Body (Soma): Contains the nucleus and integrates signals.

• Axon: Conducts electrical impulses away from the cell body.

• Myelin Sheath: Insulates the axon, speeding up signal transmission.

• Axon Terminals: Release neurotransmitters to communicate with other neurons or muscles.

Direction of Impulse

• Signals travel from dendrites → cell body → axon → axon terminals → synapse.

Axon Conduction & Synaptic Transmission

Neurons communicate via electrical impulses (action potentials) and chemical signals (neurotransmitters).

• Resting Potential: The neuron at rest has a negative charge inside relative to outside, typically -70mV.

• Action Potential: A rapid change in charge (+40mV) occurs when the neuron is stimulated, allowing the signal to travel down the axon.

Stages of Action Potential

1. Resting state: Inside is negatively charged.

2. Depolarization: Positive ions enter, charge becomes positive.

3. Repolarization: Positive ions exit, returning to negative charge.

4. Return to resting state.

Ion Channels and Transporters

• Open ion channels permit ions to enter/leave the axon.

• Closed ion channels prevent ion movement.

• Ion transporters actively pump ions in/out to maintain resting potential.

Synaptic Transmission

At the synapse, electrical signals are converted to chemical signals via neurotransmitters.

• Neurotransmitters: Chemical messengers (e.g., acetylcholine, serotonin) released from axon terminals into the synaptic cleft.

• Receptor Sites: Located on the postsynaptic neuron; activation can be excitatory or inhibitory.

Effects of Drugs and Toxins

Substance	Effect
Black widow spider venom	Causes excess acetylcholine release
Botulinum toxin	Prevents acetylcholine release
Nicotine	Stimulates acetylcholine receptors
Curare	Blocks acetylcholine receptors

Reuptake Mechanism

• Neurotransmitters are reabsorbed by the presynaptic neuron (reuptake).

• Drugs like cocaine and amphetamine prevent reuptake, prolonging neurotransmitter effects.

The Brain: Structures and Lobes

Major Brain Regions

The brain is divided into several regions, each with specialized functions.

• Forebrain: Includes the cerebral cortex, basal ganglia, limbic system, corpus callosum, thalamus, hypothalamus.

• Midbrain: Contains structures involved in vision, hearing, and motor control.

• Hindbrain: Includes the cerebellum, pons, medulla, reticular formation.

Lobes of the Cerebrum

Lobe	Main Functions
Frontal	Planning, decision-making, motor control
Parietal	Sensory processing, spatial awareness
Temporal	Auditory processing, memory
Occipital	Visual processing

Motor, Sensory, Visual, and Auditory Cortices

• Motor Cortex: Controls voluntary movements.

• Somatosensory Cortex: Processes touch and body sensations.

• Visual Cortex: Processes visual information.

• Auditory Cortex: Processes sound.

Homunculus Representation

• Shows the amount of cortex devoted to different body parts for motor and sensory functions.

Brain Scans

Techniques for Studying Brain Structure and Function

• Positron Emission Tomography (PET): Measures cell activity using radioactive glucose.

• Computerized Axial Tomography (CAT): Uses X-rays to measure brain structure.

• Magnetic Resonance Imaging (MRI): Measures brain structure by realigning hydrogen atoms with magnets.

Split Brain Research and Lateralization

Hemispheric Specialization

The brain's two hemispheres have specialized functions, connected by the corpus callosum.

• Left Hemisphere: Language, logic, analytical tasks.

• Right Hemisphere: Spatial abilities, creativity, holistic processing.

Split-Brain Studies

• Severing the corpus callosum (e.g., in epilepsy treatment) reveals distinct functions of each hemisphere.

• Patients may process information differently depending on which hemisphere receives input.

Autonomic Nervous System and Phobic Reactions

Sympathetic vs. Parasympathetic Systems

The autonomic nervous system regulates involuntary bodily functions and is divided into two branches:

• Sympathetic: Activates 'fight or flight' responses (increased heart rate, breathing).

• Parasympathetic: Promotes 'rest and digest' (slows heart rate, stimulates digestion).

Phobic Reactions

• Most phobias trigger the sympathetic system (alarm reaction).

• Blood-trauma phobias may trigger the parasympathetic system (fainting, slow heart rate).

Endogenous Morphine: Endorphins

The Body's Natural Painkillers

• Endorphins: Neurotransmitters that block pain by occupying pain receptor sites.

• Activities like running, injury, or sunbathing can increase endorphin release ('runner's high').

• External morphine use inhibits endorphin return, increasing pain sensitivity.

Additional info:

• Descartes' hydraulic model is a historical concept, not current scientific understanding.

• Homunculus diagrams illustrate cortical representation of body parts.