Biological Perspective in Neuroscience

Biological Perspective

  • Emphasizes the role of the body in understanding behavior and mental processes.

The Nervous System

  • Fundamental unit: Neuron

    • Definition: An individual nerve cell responsible for transmitting information throughout the body.

Neuroanatomy

  • Components of Neurons:

    • Synapse:

    • Definition: The gap between neurons where neurotransmitters are released and received.

    • Neurotransmitters:

    • Definition: Chemical messengers held in terminal buttons that travel across the synaptic gap to transmit signals between neurons.

    • Cell Body:

    • Definition: The cell's life-support center, containing the nucleus.

    • Dendrites:

    • Definition: Branchlike structures that receive messages from other neurons.

    • Axon:

    • Definition: The long projection of the neuron that passes messages away from the cell body to other neurons, muscles, or glands.

    • Terminal Branches of Axon:

    • Definition: Structures that form junctions with other cells and release neurotransmitters.

    • Neural Impulse:

    • Definition: An electrical signal traveling down the axon of a neuron.

    • Myelin Sheath:

    • Definition: A fatty layer that covers the axon of some neurons, aiding in the speed of neural impulses.

How a Neuron Fires

  • Process: An electrochemical process where:

    • Electrical activity occurs inside the neuron.

    • Chemical reactions occur outside the neuron in the synapse.

  • The firing of a neuron is termed Action Potential.

The All-or-None Response

  • Definition: The principle that a neuron either fires completely or does not fire at all; it cannot fire partially.

    • Metaphor: Similar to a gun, which either fires or does not.

Steps of Action Potential

  1. Resting Potential:

    • State when the neuron is prepared to fire.

  2. Reaching Threshold:

    • Once the neuron reaches a certain level of stimulation, it initiates firing.

  3. Ion Exchange:

    • Sodium ions enter the axon (depolarization), mixing with potassium ions inside.

  4. Electrical Charge Creation:

    • This mixing creates an electrical charge that opens adjacent gates, allowing more sodium ions in and potassium ions out.

  5. Propagation Down the Axon:

    • This process continues down the axon until it reaches the axon terminal.

  6. Neurotransmitter Release:

    • Terminal buttons convert electrical signals back to chemical neurotransmitters and transmit messages across the synapse.

Action Potential Details

  • Neuron stimulation causes a brief change in electrical charge.

  • If stimulation is strong enough:

    • Depolarization occurs, triggering an action potential.

    • Continuation of depolarization results in sequential action potentials down the axon.

Three Phases of Communication within a Neuron

  1. Action Potential:

    • Impulse created when a neuron fires, traveling from dendrites down the axon to axon terminals.

  2. Refractory Period:

    • Brief timespan during which a new action potential cannot be generated as the neuron is recharging.

  3. Resting Potential:

    • The state of readiness for the next action potential, when the neuron is charged but inactive.

Neurotransmitter Effects

  • Excitatory Effect:

    • Definition: A neurotransmitter effect that increases the likelihood of the receiving neuron generating an action potential (firing).

  • Inhibitory Effect:

    • Definition: A neurotransmitter effect that decreases the likelihood of the receiving neuron generating an action potential (firing).

Types of Neurotransmitters

  1. Acetylcholine (ACH):

    • Function: Involved in motor movement and memory.

    • Excess: Can lead to violent muscle contractions, convulsions, death (e.g., black widow spider venom).

    • Deficiency: Can cause paralysis and is linked to Alzheimer’s disease.

  2. Dopamine:

    • Function: Plays a role in motor movement and alertness.

    • Deficiency: Linked to Parkinson’s disease.

    • Excess: Associated with schizophrenia and possible manic phases (e.g., awakenings).

  3. Serotonin:

    • Function: Crucial for mood control.

    • Deficiency: Linked with clinical depression and disorders related to mood.

  4. Endorphins:

    • Function: Involved in pain control.

    • Many addictive drugs interact with endorphin systems (e.g., heroin, morphine).

  5. Epinephrine (Adrenaline):

    • Definition: A hormone released by adrenal glands.

    • Function: Essential for the body’s fight or flight response.

  6. Norepinephrine:

    • Definition: A neurotransmitter involved in the fight or flight response.

    • Deficiency: Can lead to feelings of depression.

  7. GABA (Gamma Amino-Butyric Acid):

    • Function: Associated with hunger and sleep regulation, inhibits central nervous system activity.

    • Alcohol consumption increases GABA levels.

  8. Glutamate:

    • Function: Essential for learning and memory processes.

    • Excitatory neurotransmitter.

    • Imbalance can lead to various health issues, including brain damage or degenerative diseases such as ALS (Lou Gehrig’s disease) and multiple sclerosis (MS).

Importance of Glutamate and GABA Relationship

  • Glutamate acts as an excitatory neurotransmitter, while GABA functions as a calming neurotransmitter.

  • Their balance is crucial for an effective functioning nervous system.

    • High glutamate levels can lead to low GABA levels, causing hyperactivity and anxiety, especially observed in children with autism.

    • It's advised against supplementation of GABA as it can convert back to glutamate.

Substance P

  • Function: Associated with pain signals and inflammatory responses.

  • Location: Present in brain and spinal cord.

Types of Neurons

  1. Efferent (Motor) Neurons:

    • Function: Carry outgoing information from the central nervous system (CNS) to muscles and glands.

  2. Interneurons:

    • Function: Internally communicate and intervene between sensory inputs and motor outputs.

  3. Afferent (Sensory) Neurons:

    • Function: Carry incoming sensory information to the CNS.

A Neural Chain

  1. Skin Receptors:

    • Detect heat and generate nerve impulses.

  2. Sensory Information:

    • Sensory nerves carry information to the spinal cord.

  3. Interneurons:

    • Process sensory information in the brain and spinal cord.

  4. Motor Neurons:

    • Carry commands to withdraw limbs based on processed information.

Overview of the Nervous System

  • Peripheral Nervous System (PNS): All nerves outside of the brain and spinal cord.

    • Subdivisions:

    • Autonomic Nervous System: Controls involuntary body actions.

    • Somatic Nervous System: Controls voluntary movements of skeletal muscles.

  • Central Nervous System (CNS): Comprises the brain and spinal cord.

  • Autonomic Nervous System Divisions:

    • Sympathetic: Activates fight or flight response, increases heart rate, dilates pupils.

    • Parasympathetic: Calms the body post-stress, slowing down heart rate and enhancing digestion.

Reflexes and Neural Pathway Development

  • Sensory neurons typically transmit information to the brain; however, reflexes may occur directly through the spinal cord for fast responses.

  • Multiple Sclerosis:

    • Affects myelin in CNS, leading to various symptoms like muscle weakness, vision changes, and memory issues.

  • Myasthenia Gravis:

    • Affects communication between nerves and muscles, causing muscle weakness that worsens with activity.

Brain Study Techniques

  1. Accidents:

    • Important historical cases like Phineas Gage reveal brain function.

  2. Lesions:

    • Studying changes in the brain through cuts or tumors.

  3. Less Invasive Techniques:

    • EEG: Measures brain waves.

    • CAT Scan: Provides brain x-ray images.

    • MRI: Uses magnetic fields for detailed brain structure images.

    • PET Scan: Monitors brain activity via radioactive glucose.

  4. Functional MRI (fMRI):

    • Shows blood flow related to brain function.

The Brain's Structure and Functions

  • Brain Composition: Neurons and glial cells; glial cells support and nourish neurons.

  • Divisions of the Brain:

    • Hindbrain, Midbrain, Forebrain: Main divisions in brain anatomy.

  • Key Structures:

    • Medulla Oblongata: Controls basic functions such as heart rate and breathing.

    • Cerebellum: Coordinates fine motor activities and maintains balance.

    • Thalamus: Acts as a sensory control hub, processing incoming signals.

    • Limbic System: Controls emotional responses and includes the hypothalamus, amygdala, and hippocampus.

    • Cerebral Cortex: The outer layer responsible for higher brain functions; divided into lobes (frontal, parietal, temporal, occipital).

    • Frontal Lobe: Involved in reasoning, planning, and motor functions.

    • Temporal Lobe: Critical for processing sound and language comprehension.

    • Occipital Lobe: Handles visual data.

    • Parietal Lobe: Involved in sensory processing (touch).

Brain Lateralization and Split-Brain Patients

  • The two hemispheres of the brain are involved in different functions; each hemisphere controls the opposite side of the body, a phenomenon known as contralateral control.

  • Corpus Callosum: Connects both hemispheres; understanding split-brain patients informs us about functional lateralization.

Brain Plasticity

  • Definition: The brain's ability to adapt and form new connections post-injury; high levels of plasticity are seen in younger brains.

The Endocrine System

  • A network of glands that release hormones throughout the body, controlling slower responses than the nervous system.

    • Regulated by the hypothalamus, includes glands such as:

    • Pituitary: Regulates growth and other hormonal functions (anterior and posterior lobes).

    • Adrenal Glands: Trigger fight or flight responses.

    • Thyroid: Manages metabolism.

    • Gonads (Ovaries & Testes): Produce sex hormones.

Hormonal Regulation of Weight

  1. Leptin:

    • Hormone related to fat storage; regulates long-term satiety.

    • Leptin resistance can lead to overeating despite adequate body fat.

  2. Ghrelin:

    • Hormone secreted by the stomach that signals hunger.

    • Levels rise when hungry and decrease post-meal; imbalances affect obesity.

  3. Melatonin:

    • Regulates sleep-wake cycles; its secretion is influenced by light.

  4. Oxytocin:

    • Stimulates childbirth and influences social bonding and reproductive behaviors.

Nature vs. Nurture

  • Important consideration in understanding human behavior and the impact of genetic versus environmental factors.

    • Genes: Biological blueprint containing our DNA, located in chromosomes.

  • Human Genome Project: Initiative to map out all human genes, revealing approximately 20,500 genes present in human DNA.

Impact of Environment on Behavior

  • Behavior Genetics: Studies the influence of genetics and surroundings on behaviors.

  • Twin Studies: Show similarities in behavior even when raised in different environments, emphasizing genetic influences.

  • Heritability: The measurement of how much variation in traits can be attributed to genetics.

  • Recognizing prenatal influences and the significant role parents play in shaping beliefs (but not personality).

  • The disparity in brain development in impoverished versus enriched environments emphasizes the need for stimulation for cognitive development.

  • Peer Influence and Cultural Factors: Strong environmental influences on behavior, values, and actions, shaped by cultural norms and practices.