The Biological Perspective

Overview of the Nervous System

The biological perspective in psychology focuses on the physical and chemical processes underlying behavior, thoughts, and emotions. The nervous system is a complex network of cells that carries information throughout the body, enabling sensation, perception, movement, and cognition.

• Nervous System: Composed of neurons and glial cells, responsible for transmitting and processing information.

• Neurons: Specialized cells that transmit electrical and chemical signals.

• Glial Cells: Support, nourish, and protect neurons.

Structure of a Neuron

Main Components

Neurons are the fundamental units of the nervous system, each with distinct structural parts that enable communication.

• Axon: Long fiber that transmits signals away from the soma to other neurons or muscles.

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

• Soma: The cell body, containing the nucleus and metabolic machinery.

• Axon Terminals: Endings where neurotransmitters are released to communicate with other cells.

Neurotransmitters and Their Functions

Key Neurotransmitters

Neurotransmitters are chemical messengers that transmit signals across synapses. Each has specific effects on behavior and physiology.

• Acetylcholine (ACh): Stimulates skeletal muscle contraction; slows heart muscle contraction. Blocked ACh receptors cause paralysis; excess leads to convulsions. Example: Black widow venom acts as an agonist, causing excessive ACh release.

• Dopamine (DA): Involved in movement, motivation, and reward. Low DA in certain brain areas leads to Parkinson’s disease; excess in other areas may contribute to schizophrenia.

• Serotonin (5-HT): Originates in the lower brain; affects sleep, mood, anxiety, and appetite. Can be excitatory or inhibitory. Low levels are linked to depression.

• Glutamate: Major excitatory neurotransmitter; important for learning, memory, and synaptic plasticity. Excess can cause neuronal damage, associated with stroke and degenerative diseases.

• Gamma-aminobutyric acid (GABA): Main inhibitory neurotransmitter; calms anxiety. Alcohol enhances GABA’s effects (agonist).

• Norepinephrine (NE): Involved in arousal and alertness.

• Endorphins: Endogenous painkillers; inhibit pain signals. Heroin and morphine mimic endorphins, leading to addiction.

Reuptake and Enzymes

After neurotransmitters act, they must be cleared from the synapse for new signals to occur.

• Reuptake: Most neurotransmitters are reabsorbed by the presynaptic neuron for reuse.

• Enzymatic Breakdown: Some, like ACh, are broken down by enzymes for rapid clearance.

• Drug Effects: Some drugs (e.g., cocaine) block reuptake, increasing neurotransmitter activity.

Central Nervous System (CNS)

Structure and Function

The CNS is the control center for processing sensory information, generating thoughts, emotions, and issuing motor commands.

• The Brain: Core of the nervous system; organized into regions for different functions.

• The Spinal Cord: Long bundle of neurons; carries messages between body and brain; responsible for reflexes.

• Neuron Types:

  • Afferent (sensory) neurons: Carry information to the CNS.

  • Efferent (motor) neurons: Carry commands from CNS to muscles.

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

• Spinal Cord Structure: Inner gray matter (cell bodies); outer white matter (myelinated axons).

• Neuroplasticity: The brain’s ability to repair and reorganize after injury.

Peripheral Nervous System (PNS)

Divisions and Functions

The PNS consists of nerves outside the CNS, divided into somatic and autonomic systems.

• Somatic Nervous System: Controls voluntary muscles; includes sensory and motor pathways.

• Autonomic Nervous System: Controls involuntary functions; divided into:

  • Sympathetic Division: Activates during stress (fight or flight).

  • Parasympathetic Division: Restores normal function after stress; responsible for everyday activities.

Endocrine Glands

Hormone-Secreting Organs

Endocrine glands secrete hormones directly into the bloodstream, influencing various bodily functions.

• Pituitary Gland: Master gland; controls other glands; secretes growth and reproductive hormones.

• Pineal Gland: Secretes melatonin; regulates sleep–wake cycle.

• Thyroid Gland: Regulates growth and metabolism via thyroxin.

• Pancreas: Controls blood sugar with insulin and glucagon; imbalance leads to diabetes or hypoglycemia.

• Gonads: Ovaries and testes; regulate sexual behavior and reproduction.

• Adrenal Glands: Located atop kidneys; medulla releases epinephrine/norepinephrine during stress; cortex produces corticoids (steroids) for salt regulation, stress response, and sex hormones. Cortisol releases glucose during stress for energy.

Studying the Brain

Methods of Investigation

Researchers use various techniques to study brain structure and function.

• Lesioning Studies: Examining effects of brain damage.

• Brain Stimulation: Invasive and noninvasive methods to activate brain regions.

• Neuroimaging: Visualizing brain structure and activity.

• Mapping Structure:

  • CT (Computed Tomography): X-ray imaging.

  • MRI (Magnetic Resonance Imaging): Detailed structural imaging.

• Mapping Function:

  • EEG (Electroencephalogram): Measures electrical activity.

  • MEG (Magnetoencephalography): Measures magnetic fields.

  • PET (Positron Emission Tomography): Tracks metabolic activity.

  • fMRI (Functional MRI): Measures changes in blood flow.

Brain Structure

Major Regions and Functions

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

• Forebrain: Includes cortex, basal ganglia, and limbic system.

• Limbic System: Border between upper brain and brain stem; involved in emotions, motivation, memory, and learning.

Limbic System Components

• Thalamus: Relay station for sensory information; abnormal connections can cause dyslexia. Smell bypasses thalamus.

• Hypothalamus: Regulates body temperature, hunger, sleep, sexual activity, and emotions; controls pituitary gland.

• Hippocampus: Forms long-term memories.

• Amygdala: Involved in fear responses and memory of fear; enables rapid reaction to danger.

• Cingulate Cortex: Four regions processing emotional, cognitive, and autonomic information.

Cerebral Cortex and Lobes

• Cerebral Hemispheres: Connected by corpus callosum.

• Occipital Lobes: Visual processing.

• Parietal Lobes: Processing touch, temperature, and body position.

• Temporal Lobes: Auditory processing, language.

• Frontal Lobes: Higher mental functions (planning, personality, memory, decision making, language, emotion); contains motor cortex and mirror neurons.

Midbrain and Hindbrain

• Midbrain: Sensory and motor functions.

• Hindbrain:

  • Medulla: Controls heartbeat, breathing, swallowing.

  • Pons: Connects cerebellum with upper brain; coordinates movement; influences sleep and arousal.

  • Reticular Formation (RF): Alerts to changes in information.

  • Cerebellum: Controls rapid, fine motor movement; coordinates voluntary movements; stores learned skills.

Association Areas of the Cortex

• Broca’s Area: Left frontal lobe; production of speech.

• Wernicke’s Area: Left temporal lobe; understanding meaning of words.

Cerebral Hemispheres

• Split Brain Research: Studies effects of severing corpus callosum.

• Handedness: Preference for using one hand over the other.

Summary Table: Major Neurotransmitters

Additional info:

• Synaptic Plasticity: The ability of the brain to change connections among neurons, crucial for learning and memory.

• Mirror Neurons: Neurons that fire both when an individual acts and when they observe the same action performed by another, important for understanding others' actions.