Neuroscience: Neurons and Potentials

• Neuroscience connects the brain with behavior
• Neuro is the study of the brain, which directs behaviors

Neuron Components

• Neurons are key parts of the nervous system
• Dendrites receive signals from other neurons, triggering a go/no-go response
• The cell body produces transmitter molecules and is semipermeable
• Axons are insulated by myelin, speeding up nerve message conduction
• Axon terminal buttons release transmitters
• Bundles of nerves consist of clustered axons

Graded Potentials

• Nerve membrane stimulation can open ion channels
• Influx of Na+ (sodium) depolarizes the membrane, shifting it from -70 mV to -60 mV
• Efflux of K+ (potassium) hyperpolarizes the membrane, shifting it from -70 mV to -90 mV
• Depolarization reduces polarization
• Hyperpolarization increases polarization
• The refractory period influences the rate of neuronal firing

Action Potential

• Graded potentials travel from dendrites to the axon hillock
• Action potentials (AP) occur if summed activity at the axon hillock exceeds the membrane potential threshold
• During an action potential, Na+ ions enter the cell, raising the membrane potential to +40mV and causing a spike
• K+ channel opening restores the membrane potential to -70mV
• Action potentials travel along the axon to the terminals

Post-Firing Events

• Post firing events include being pushed out (binded), or vacuumed up (reuptake)
• Enzymes deactivate neurotransmitters by taking them out as waste.

Major Neurotransmitters

• Acetylcholine (Ach) is responsible for motor movement, memory, sleep and dreaming
• Alzheimer's disease is related to acetylcholine disfunction
• Endogenous acetylcholine is manufactured inside the body
• Exogenous acetylcholine is manufactured outside the body, pretending to be a neurotransmitter
• Nicotine acts like acetylcholine
• Protagonist neurotransmitters mimic/enhance the effects of natural neurotransmitters
• Antagonist neurotransmitters block receptor sites, inhibiting neurotransmitter effects
• Epinephrine dilates blood vessels, and is part of the adrenaline package for fight or flight responses
• Norepinephrine regulates arousal, learning, and dreaming, and its levels relate to mania and depression
• Serotonin regulates emotional states and is important for self-control and basic life functions
• Dopamine is linked to reward and feeling good, and relates to anticipating desired things
• Too much dopamine can trigger schizophrenia
• Too little dopamine can trigger Parkinson's disease
• GABA (gamma-aminobutyric acid) is the most important neurotransmitter
• GABA is an amino acid
• Alcohol acts like GABA
• Low GABA levels correlate with anxiety
• Glutamate is an amino acid that enhances long-term potentiation, memory, and learning
• Too much glutamate can overstimulate neurons, causing headaches or seizures

Overview of the Nervous System

• Soma refers to body senses

Autonomic Nervous System (ANS)

• Contains sympathetic and parasympathetic divisions
• The sympathetic division is responsible for the emergency system and fight or flight response
• The parasympathetic division is responsible for vegetative functions such as digestion
• The two systems often oppose each other, such as in heart rate control
• The two systems can act in concert as in sexual reflexes

Midline Brain Structures

• The medulla controls heart rate and respiration
• The cerebellum coordinates smooth movements, balance, and posture
• The pons is involved in sleep regulation

Limbic System Functions

• The septal area drives pleasure and relief
• The amygdala contributes to learning and fear recognition; more sensitive amygdalae relate to anxiety
• The hippocampus is involved in memory

Cerebral Cortex Functions

• The cerebral cortex provides flexible movement control
• The cerebral cortex allows subtle sensory pattern discrimination
• The cerebral cortex enables symbolic thinking
• Symbolic thought is the base for language and human thought

Frontal Lobe and Personality

• Frontal lobes govern movement, attention, planning, memory, and personality
• The case of Phineas Gage reveals the frontal lobe's role in personality
• Gage suffered frontal lobe damage from a dynamite tamping rod accident
• Prior to the damage, Gage was a railroad supervisor
• Post-damage, Gage became childish, irreverent, impulsive, and struggled to plan

Cerebral Lateralization

• Cortex and sub-cortex structures show functional specialization
• Hemispheric Specialization describes how the left brain dominates language, logic, and complex motor actions
• The right brain dominates non-linguistic functions like recognizing faces, places, and sounds
• Hemispheric specializations are evident from brain-damage and split-brain studies

Split-Brain Studies

• Information from a visual field typically travels to the opposite visual cortex
• The corpus callosum integrates two hemispheres
• Cutting the corpus callosum can limit information to one hemisphere
• With a cut corpus callosum, language relies on information reaching the left hemisphere

The Endocrine System

• Glands secrete hormones into the bloodstream, regulating bodily functions
• The hypothalamus connects to the pituitary gland (master gland)
• Adrenal glands control fight-or-flight responses
• Gonads regulate secondary sex characteristics

Endocrine System Function

• Endocrine glands release hormones into the bloodstream
• Hormones exert effects across diffuse bodily sites
• Hormones bind to receptors
• Hormones exert organizational effects (permanent structure/function changes)
• Hormones exert activational effects
• Reduced testosterone diminishes sexual behavior