Neurons and Nerve Cells

• Nerve cells are called neurons

Types of Neurons

• Sensory neurons detect environmental changes and body functioning
• Motor neurons control movement and hormone production
• Interneurons connect neurons with each other

Parts of a Neuron

• Soma (cell body)

• Dendrites receive signals

• Axon transmits signals

• Myelin sheath insulates the axon

• Terminal buttons release neurotransmitters

• Neurotransmitters leave terminal buttons and travel through synapses between cells

• Neurotransmitters "dock" at dendrites

• Myelination involves glial cells

• Nerves are bundles of many axons

• Neurons use both electrical and chemical signals to communicate

• Electrical signals are like a light switch

• Neurons contain ions (mostly sodium) that store electricity

• A signal travels down the axon when a neuron is momentarily switched on

• This triggers the release of neurotransmitters into the synapse

• Resting potential leads to action potential leads to firing and then refractory period

• Neurotransmitters travel across the synapse and trigger dendrites of other cells

• Different neurotransmitters carry different messages

• Different neurotransmitters trigger different spots on neighboring cells

• Psychopharmaceuticals mimic neurotransmitters and change received signals

• Agonists enhance signal strength and antagonists block signals

• The process starts over when the transmitter cell reuptakes its messenger chemicals, or the body breaks them down and discards them

Nervous System

• The central nervous system and peripheral nervous system
• The peripheral system feeds and responds to the central system
• The peripheral nervous system receives signals from body parts
• The body and senses are part of the somatic nervous system
• Information travels to the central nervous system before action
• The autonomic nervous system controls automatic functions
• Sympathetic functions are reactionary, fight-or-flight
• Parasympathetic functions are for daily life and returning to normal (homeostasis)
• The central nervous system (brain, spinal column) processes signals received from nerves
• The central nervous system generates signals that activate other systems
• The spinal cord is an extension of the brain running down and inside the spine
• Spinal reflexes inform the brain after the reflex occurs

Parts of the Brain

• The hindbrain is the body's life support system
• The medulla (brainstem) controls breathing and heartbeat
• Pons is responsible for PNS communication, and being awake/asleep
• Cerebellum handles motor coordination, balance, and voluntary movement
• The midbrain handles attention and focus (physical and psychological)
• The forebrain is the most complex and coordinates multiple in- and out-put systems
• The limbic system includes the thalamus, hypothalamus, amygdala, and hippocampus
• The thalamus sorts and redirects information from the senses
• The hypothalamus reacts to sensory information and regulates homeostasis
• The amygdala is for emotional response and sense-making
• The hippocampus handles memory formation and learning

Higher Order Thought

• The cerebral cortex is the outermost layer of the cerebral hemispheres
• The cerebral cortex makes up 80% of brain mass in humans
• The higher-order functions include thought, language, communication, decision-making, problem-solving, voluntary movement, and motivation
• Lateralization means certain functions occur typically in one hemisphere
• The left hemisphere handles logic, problem-solving, and language
• The right hemisphere handles nonverbal, spatial, interpretation, and creativity appreciation
• The corpus callosum joins the two hemispheres and helps with intercommunication
• Different lobes do different tasks
• The occipital lobes (back of head) house the visual cortex
• The parietal lobes (side, back of head) house skin receptors (somatosensory cortex)
• The temporal lobes (side, front of head) house the auditory complex & language
• The frontal lobes (forehead) include self-awareness, social awareness, memory, and decisions, and include the motor cortex and mirror neurons

Studying the Brain

• Structures in the brain can be imaged through CT scans (narrow x-rays from multiple angles) and MRI (magnets and radio wave bursts)
• Electrical brain activity can be recorded through EEG
• PET scans use radioactive substances to show which parts of the brain are most active
• FMRI takes multiple images rapidly for a non-invasive activity picture
• Brain activity can be manipulated by lesioning (intentional damage), electrical recording (implanted track devices), and electrical stimulation
• Neurochemical levels can be manipulated using modern pharmacotherapy
• Psychoactive chemicals can change how the brain works

Hormones & the Endocrine System

• The endocrine system is made up of glands that produce hormones
• Hormones and neurotransmitters are similar chemically but different functionally
• Hormones travel long distances by blood
• Hormones have a generalized and slow impact
• Neurotransmitters travel short distances by synapse
• Neurotransmitters have a local and fast impact
• Some hormones, such as (nor)epinephrine, function in the brain and body
• Hormones affect growth, sexual maturation, reaction to the environment, digestion, body functions, and the sleep cycle
• The hypothalamus triggers the pituitary gland, which triggers others

Genetics, Epigenetics, & Environment

• Humans have 23 chromosomes with 20,000-25,000 genes
• Genes determine how cells and tissues form prenatally and function
• Chromosomes are made of two strands of DNA
• Half of our DNA comes from our mother, half from our father
• Some traits come from one gene, some from many, some are dominant or recessive
• Twin studies help determine if something is genetic, environmental, or both
• Evolution states individuals best suited to the environment survive to reproduce
• The environment includes the people and experiences in your life (nutrition, diseases, chemicals, history)
• The environment and genetics are bidirectional
• Epigenetics is when a gene's expression is impacted by the environment
• This influence is a chemical interaction

Prenatal Development

• In prenatal development, the germinal period can take 30min-12hrs to reach the ovary, and can survive 48-72hrs
• Contraception prevents the sperm & ovum from interacting
• Miscarriages occur early in pregnancy with early cell replication or implantation occurs
• The embryo stage lasts from 2 weeks to 2 months, while the major features of the body form
• The neural tube (which becomes the brain & spinal column) needs enough folic acid
• The fetus stage lasts from 9 weeks to (38)40 weeks when body systems fully develop

Teratogens and Epigenetics

• Epigenetics states we have lots of genes, many dormant until triggered
• Environmental influences are able to turn genes on or off, or up or down
• Epigenetic tags can pass down from one generation to the next
• A teratogen is any substance that negatively impacts pregnancy
• This can include exposures even months or years before fertilization
• Can impact the ova, sperm formation, cellular replication, and organogenesis
• Psychoactive substances, malnutrition, disease, STIs, and environmental toxins can all be teratogens
• The germinal period is most vulnerable to genetic concerns, but least vulnerable to teratogens