Biological Psychology: Organization and Function of the Nervous System

Biological Psychology

Organization of the Nervous System

The nervous system is a complex network of neurons that transmits electrochemical information throughout the body. 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): Composed of all nerves outside the brain and spinal cord; connects the CNS to limbs and organs.

Table: CNS vs. PNS

System	Main Components	Function
CNS	Brain, Spinal Cord	Processes information, controls most functions of the body and mind
PNS	Nerves outside CNS	Connects CNS to limbs and organs

Subdivisions of the Peripheral Nervous System

The PNS is divided into the Somatic Nervous System and the Autonomic Nervous System:

• Somatic Nervous System: Controls voluntary movements by innervating skeletal muscles.

• Autonomic Nervous System: Controls involuntary functions by innervating glands and internal organs.

Table: Somatic vs. Autonomic Nervous System

System	Controls	Innervates
Somatic	Voluntary movement	Skeletal muscles
Autonomic	Involuntary movement	Glands, organs

Subdivisions of the Autonomic Nervous System

The autonomic nervous system is further divided into the Sympathetic Division and the Parasympathetic Division:

• Sympathetic Division: Activated during stress or emergencies ("fight or flight").

• Parasympathetic Division: Activated during rest ("rest and digest").

Table: Sympathetic vs. Parasympathetic Effects

Structure	Sympathetic Effect	Parasympathetic Effect
Cardiac Muscle	Increases heart rate	Decreases heart rate
Bronchioles in Lungs	Expands airways	Constricts airways
Pupil	Dilates pupil	Constricts pupil

Cells of the Nervous System

Neurons vs. Glial Cells

• Neurons: Specialized cells that communicate via electrical and chemical signals.

• Glial Cells: Support, nourish, and protect neurons; maintain homeostasis.

Types of Neurons

• Sensory Neurons: Receive information and convey signals to the CNS.

• Motor Neurons: Carry signals from the CNS to muscles to produce movement.

• Interneurons: Connect sensory and motor neurons within the CNS.

Anatomy of a Neuron

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

• Dendrites: Receive chemical messages from other neurons.

• Axon: Transmits electrical impulses away from the soma.

• Axon Terminals: Release neurotransmitters into the synapse.

The Myelin Sheath

• Many axons are coated in a myelin sheath, a fatty layer produced by glial cells that insulates the axon and speeds up electrical signal transmission.

• Gaps in myelin are called nodes of Ranvier, which facilitate rapid signal conduction.

Communication in the Nervous System

Electrochemical Communication

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

Action Potential

• Neurons start at a resting potential (about -70 mV).

• When the internal voltage reaches a threshold, an action potential is fired.

• Action potentials follow this sequence:

  1. Depolarization: Sodium ions (Na+) rush in, voltage rises.

  2. Repolarization: Potassium ions (K+) exit, voltage drops.

  3. Refractory Period: Neuron cannot fire again until resting potential is restored.

Equation:

$\text{Resting Potential} \approx -70\ \text{mV}$

Chemical Communication – The Synapse

• When an action potential reaches the axon terminal, it triggers the release of neurotransmitters into the synaptic cleft.

• Neurotransmitters bind to receptors on the postsynaptic neuron, altering its voltage and possibly triggering a new action potential.

Table: Major Neurotransmitters and Effects

Neurotransmitter	Known Effects
Glutamate	Major excitatory neurotransmitter in the brain
GABA (Gamma-aminobutyric acid)	Major inhibitory neurotransmitter in the brain
Serotonin	Mood, sleep, appetite
Dopamine	Processing, movement, attention, and cognitive functions
Norepinephrine	Involved in fight or flight response

Introduction to the Brain

Major Divisions of the Brain

• Forebrain: Responsible for complex functions (e.g., cognition, voluntary movement).

• Midbrain: Important for sensory processing and orientation.

• Hindbrain: Controls basic life functions (e.g., breathing, heart rate).

Table: Major Brain Structures and Functions

Structure	Function
Pons	Regulates sleep cycle, arousal, and autonomic functions
Medulla	Controls autonomic functions (e.g., heart rate, breathing)
Reticular Formation	Regulates arousal and alertness
Cerebellum	Coordinates movement and balance

The Cortical Forebrain

• Cerebrum: Largest part of the brain, divided into left and right hemispheres, connected by the corpus callosum.

• Hemispheric Specialization: Each hemisphere controls the opposite side of the body.

• Cerebral Cortex: Outer layer of the cerebrum, responsible for higher cognitive functions.

Lobes of the Cerebral Cortex

• Frontal Lobe: Cognition, thought, voluntary movement, speech

• Parietal Lobe: Sensation (touch, spatial)

• Temporal Lobe: Auditory processing, language comprehension

• Occipital Lobe: Visual processing

Important Regions in the Lobes

• Primary Motor Cortex: Initiates voluntary movements

• Primary Somatosensory Cortex: Processes sensory information

• Broca's Area: Speech production

• Wernicke's Area: Language comprehension

The Subcortical Forebrain

• Basal Ganglia: Involved in movement processing and control

• Thalamus: Relay station for sensory signals

• Limbic System: Includes the hypothalamus (regulation), amygdala (emotion), and hippocampus (memory)

The Endocrine System

• The endocrine system is a network of glands that release hormones into the bloodstream.

• Major glands include the pituitary, thyroid, adrenal glands, pancreas, and gonads (ovaries/testes).

• Hormones travel through the bloodstream and usually have longer-lasting effects than neurotransmitters.

Table: Major Endocrine Glands and Functions

Gland	Function
Pituitary	Controls other glands
Thyroid	Regulates metabolism
Adrenal	Releases hormones for fight or flight response
Pancreas	Regulates blood sugar
Ovaries/Testes	Release sex hormones

Genes and Environment

• Genes: Segments of DNA inherited from parents that code for traits.

• Genotype: Genetic makeup of an individual.

• Phenotype: Observable characteristics resulting from genotype and environment.

• Heritability: Proportion of variation in a trait due to genetic differences (ranges from 0 to 1).

Table: Levels of Genetic Organization

Level	Description
Genes	Biological units of heredity
DNA	Molecule that holds genetic information
Chromosomes	Structures that organize and package DNA

Heritability Studies

• Monozygotic (identical) twins share 100% of genes; dizygotic (fraternal) twins share about 50%.

• Comparing similarities between twins helps estimate genetic and environmental influences.

Key Points to Remember

• Heritability is a population-level concept, not an individual measure.

• Traits can be influenced by both genes and environment.

Additional info: This summary expands on the provided notes with definitions, examples, and tables for clarity and completeness, suitable for exam preparation in a college-level Biological Psychology course.