Biological Foundations of Behavior: The Nervous System, Brain, and Genetics

The Nervous System

Characteristics of the Nervous System

The nervous system is a complex, highly organized network that enables organisms to sense, process, and respond to internal and external stimuli. It is essential for behavior, cognition, and bodily regulation.

• Complexity: The nervous system contains billions of nerve cells (neurons) and trillions of connections, allowing for intricate processing and integration of information.

• Integration: The system coordinates information from various sources, integrating sensory input and motor output for coherent responses.

• Adaptability: The nervous system can change in response to experience, a property known as plasticity. This allows learning, memory, and recovery from injury.

Example: When learning to drive, the nervous system adapts to new sensory and motor demands, improving performance over time.

Pathways in the Nervous System

• Afferent (Sensory) Pathways: Carry information from sensory receptors to the brain and spinal cord.

• Efferent (Motor) Pathways: Transmit commands from the brain and spinal cord to muscles and glands.

Divisions of the Nervous System

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

• Peripheral Nervous System (PNS): Connects the CNS to the rest of the body; includes the somatic (voluntary control) and autonomic (involuntary control) systems.

• Autonomic Nervous System: Subdivided into the sympathetic (arouses the body) and parasympathetic (calms the body) systems.

Neurons

Structure and Function

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

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

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

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

• Myelin Sheath: Fatty layer that insulates the axon, speeding up signal transmission.

Types of Neurons

• Sensory Neurons: Carry information from sensory receptors to the CNS.

• Motor Neurons: Transmit commands from the CNS to muscles and glands.

• Interneurons: Connect neurons within the CNS, facilitating communication between sensory and motor neurons.

Specialized Cell Structure

• Glial Cells: Support, nourish, and protect neurons. Types include astrocytes, oligodendrocytes, and Schwann cells.

The Neural Impulse

Action Potential

An action potential is a brief electrical charge that travels down the axon, enabling communication between neurons.

• Resting Potential: The neuron’s membrane potential when not transmitting a signal (typically -70 mV).

• Depolarization: Sodium ions enter the neuron, making the inside more positive and triggering the action potential.

• Repolarization: Potassium ions exit, restoring the negative charge inside the neuron.

Equation:

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

Synapses and Neurotransmitters

Neurons communicate at synapses, where neurotransmitters are released from the axon terminal of one neuron and bind to receptors on another.

• Synaptic Transmission: The process by which neurotransmitters cross the synaptic gap to transmit signals.

• Neurotransmitters: Chemical messengers such as dopamine, serotonin, acetylcholine, and norepinephrine.

Structures of the Brain and Their Functions

How Researchers Study the Brain

• Brain Lesioning: Studying the effects of brain damage to understand function.

• Electrical Recording (EEG): Measures electrical activity in the brain.

• Brain Imaging: Techniques such as MRI and PET scans provide detailed images of brain structure and function.

Major Brain Structures

• Hindbrain: Includes the medulla, pons, and cerebellum; controls vital functions and coordination.

• Midbrain: Relays information between the hindbrain and forebrain; involved in arousal and movement.

• Forebrain: Includes the thalamus, hypothalamus, limbic system, and cerebral cortex; responsible for higher-order functions.

The Cerebral Cortex

• Lobes: The cortex is divided into frontal, parietal, occipital, and temporal lobes, each with specialized functions.

• Somatosensory Cortex: Processes sensory information from the body.

• Motor Cortex: Controls voluntary movements.

• Association Cortex: Integrates information for complex functions such as thinking and decision-making.

The Cerebral Hemispheres and Split-Brain Research

• Left Hemisphere: Typically dominant for language, logic, and analytical tasks.

• Right Hemisphere: Specializes in spatial, creative, and holistic processing.

• Split-Brain Research: Studies of patients with severed corpus callosum reveal functional specialization of hemispheres.

The Endocrine System

The endocrine system is a network of glands that secrete hormones, regulating processes such as growth, metabolism, and mood.

• Pituitary Gland: The "master gland" that controls other endocrine glands.

• Adrenal Glands: Produce hormones involved in stress response.

• Thyroid Gland: Regulates metabolism.

Brain Damage, Plasticity, and Repair

Plasticity

The brain’s ability to change and adapt in response to experience or injury is known as plasticity. This includes the formation of new connections and, in some cases, the generation of new neurons (neurogenesis).

• Example: After a stroke, undamaged brain areas may take over functions lost due to injury.

Brain Tissue Implants

Experimental procedures involve implanting healthy tissue to restore lost brain function, though this is still largely in the research phase.

Genetics and Behavior

Chromosomes, Genes, and DNA

• Chromosomes: Structures in the cell nucleus that contain DNA.

• Genes: Segments of DNA that code for proteins and influence traits.

• DNA: The molecule that carries genetic information.

The Study of Genetics

• Behavioral Genetics: Examines the influence of genetics and environment on behavior.

• Molecular Genetics: Studies the structure and function of genes at a molecular level.

• Selective Breeding: Used to study genetic influences by breeding animals for specific traits.

Genes and the Environment

Behavior is influenced by the interaction of genetic predispositions and environmental factors. This is known as gene-environment interaction.

Psychology’s Biological Foundations and Health and Wellness

Biological processes, including those in the nervous and endocrine systems, play a crucial role in health, wellness, and psychological functioning. Understanding these foundations helps explain the links between biology, behavior, and mental health.

Division	Main Function	Key Structures
Central Nervous System (CNS)	Processing and integration	Brain, Spinal Cord
Peripheral Nervous System (PNS)	Communication between CNS and body	Nerves, Ganglia
Somatic Nervous System	Voluntary control of muscles	Motor and Sensory Nerves
Autonomic Nervous System	Involuntary control of organs	Sympathetic and Parasympathetic Divisions

Additional info: Some explanations and examples have been expanded for clarity and completeness, based on standard academic knowledge in biological psychology.