The Human Nervous System

• The human nervous system is composed of the central nervous system and the peripheral nervous system.

Central Nervous System

• Consists of the brain and spinal cord.

Peripheral Nervous System

• Divided into somatic and autonomic systems.
• The somatic nervous system is involved in voluntary behavior.
• The autonomic nervous system controls less voluntary actions, like heart rate.

Neurons

• Neurons are the basic units of the nervous system.
• They receive, integrate, and transmit information.
• Neurons are specialized for communication through electrical impulses and chemical signals.
• There are three phases, reception, integration, and transmission.

Types of Neurons

• Sensory neurons detect signals from the environment and send them to the brain.
• Motor neurons carry messages from the brain to muscles for movement.
• Interneurons process information and connect sensory and motor neurons.

Neuron Structure

• Dendrites detect chemical signals from neighboring neurons.
• The cell body (soma) collects and integrates information received from dendrites.
• The axon transmits electrical impulses.
• Terminal buttons, at the end of each axon, are knoblike structures.
• The synapse is the site of chemical communication between neurons.
• Neurons communicate by sending chemicals into the synapse.
• The synapse is a tiny gap between the terminal buttons of one neuron and the dendrites of another.
• The membrane is the outer surface of a neuron, a fatty barrier that does not dissolve in the watery environment inside and outside the neuron.
• Ion channels are specialized pores on the membrane that allow ions to pass in and out of the cell.
• Ions are electrically charged molecules.

Action Potentials

• Neural communication depends on a neuron’s ability to respond to incoming stimulation.
• The action potential, or neural firing, is the electrical signal that passes along the axon.
• This signal causes the terminal buttons to release chemicals that transmit signals to other neurons.
• When a neuron is resting, the electrical charge inside is slightly more negative than outside, typically -70 millivolts, this is the resting membrane potential.
• The difference in electrical charge occurs because the ratio of negative to positive ions is greater inside the neuron than outside.
• When a neuron has more negative ions inside than outside, it is described as polarized.
• The polarized state creates the electrical energy necessary to power the firing of the neuron.
• Sodium and potassium are two types of ions.
• Sodium channels allow sodium ions, but not potassium ions, to pass through the membrane.
• Potassium channels allow potassium ions, but not sodium ions, to pass through.
• The flow of ions through each channel is controlled by a gating mechanism.
• When a gate is open, ions flow in and out of the neuron through the cell membrane.
• A closed gate prevents their passage.
• Ion flow is also affected by the cell membrane’s selective permeability.
• A neuron receives chemical signals from nearby neurons through its dendrites.
• These chemical signals impact local ion channels, thus influencing the polarization of the neuron.
• Excitatory signals depolarize the cell membrane, increasing the likelihood that the neuron will fire.
• Inhibitory signals hyperpolarize the cell, decreasing the likelihood that the neuron will fire.
• The action potential is an electrical ripple that travels down the axon.
• When a neuron fires, sodium gates in the cell membrane open.
• The open gates allow sodium ions to rush into the neuron, making the inside more positively charged.
• A fraction of a second later, potassium channels open to allow potassium ions to rush out.
• The sodium ion channels then start to close, but potassium ions continue to exit the cell, causing the membrane potential to become negative again.
• The potassium ion channels then close and potassium ions stop exiting the cell.
• At this point, the membrane potential is slightly more negative than the resting potential, and it would require even more excitatory input to trigger another action potential.
• This period is called the relative refractory period.
• The sodium-potassium pump then restores the membrane potential to its resting state.
• Sodium ion channels open in a series.
• Once an ion channel opens and closes, there is a short absolute refractory period in which it cannot open again.
• This is followed by the relative refractory period, in which it takes greater excitation to fire the neuron again.
• The absolute and relative refractory periods prevent ion channels from responding again after they were just active, the action potential always moves in one direction: down the axon.
• The action potential travels down the entire length of the axon.
• The axons of many types of neurons are covered by a myelin sheath.
• A myelin sheath encases and insulates many axons.
• The myelin sheath is made up of glial cells, commonly called glia.
• Between these segments are small gaps of exposed axon called the nodes of Ranvier.
• Because of the insulation provided by the myelin sheath, the action potential does not have to traverse the entire length of the axon and skips.

Neurotransmitters

• Neurotransmitters are chemicals made in the axon or cell body and stored in vesicles.
• Vesicles are small, fluid-filled sacs inside each terminal button of the presynaptic neuron.
• Different neurotransmitters influence emotion, thought, or behavior, depending on the type of receptor and the location within the brain.
• After an action potential travels to the terminal button, it causes the vesicles to attach to the presynaptic membrane and release their neurotransmitters into the synapse.
• These neurotransmitters then travel across the synapse and bind to receptors on the dendrites of the postsynaptic neuron.
• Receptors are specialized protein molecules on the postsynaptic membrane that specifically respond to the chemical structure of the neurotransmitter available in the synapse.
• Each receptor on the postsynaptic neuron can be influenced by only one type of neurotransmitter.
• The binding of a neurotransmitter with a receptor can cause ion channels to open or close, producing an excitatory or an inhibitory signal in the postsynaptic neuron.

Reuptake, Enzyme Deactivation, and Autoreception

• Once a neurotransmitter is released into the synapse, it exerts an effect until its influence is terminated.
• The three major events that terminate the neurotransmitter’s influence in the synapse are reuptake, enzyme deactivation, and autoreception.
• Reuptake occurs when the neurotransmitter is taken back into the presynaptic terminal buttons.
• An action potential prompts terminal buttons to release the neurotransmitter into the synapse and then take it back for recycling.
• Enzyme deactivation occurs when an enzyme destroys the neurotransmitter in the synapse.
• Different enzymes break down different neurotransmitters.
• Neurotransmitters can also bind with receptors on the presynaptic neuron.
• This process is called autoreception.
• Autoreceptors monitor how much neurotransmitter has been released into the synapse.
• When an excess is detected, the autoreceptors signal the presynaptic neuron to stop releasing the neurotransmitter.

Agonists and Antagonists

• Agonists are drugs and toxins that enhance the actions of neurotransmitters.
• Antagonists are drugs and toxins that inhibit the actions of neurotransmitters.
• Examples of how an agonist enhances the action of a neurotransmitter include
  • Introducing a substance that helps produce the neurotransmitter, thus increasing the amount of neurotransmitter made and released by the presynaptic neuron.
  • Blocking the receptors on the presynaptic cell that trigger the reuptake of the neurotransmitter, thus keeping it in the synapse longer.
  • Mimicking the action of the neurotransmitter on the postsynaptic cell, thus activating the receptor or increasing the neurotransmitter impact.
• Similarly, an antagonist could impair the action of a neurotransmitter in a number of ways, including
  • Introducing a substance that reduces the amount of neurotransmitter made and released into the synapse.
  • Introducing a substance that facilitates the destruction or breaking down of the neurotransmitter, thus reducing the time it is in the synapse.
  • Blocking the postsynaptic receptors, thus preventing the neurotransmitter from activating them.

Broca's Area

• Broca found a large area of damage in a section of the front left side of a patient's brain.
• This observation led him to conclude that this particular region was important for speech.
• This left frontal region, crucial for the production of language, became known as Broca’s area.

Brain Monitoring Techniques

• Electroencephalography (EEG) is a technique for measuring electrical activity in the brain.
• Positron emission tomography (PET) is a method of brain imaging that assesses metabolic activity by using a radioactive substance injected into the bloodstream.
• Magnetic resonance imaging (MRI) is a method of brain imaging that uses a powerful magnetic field to produce high-quality images of the brain.
• Functional magnetic resonance imaging (fMRI) is an imaging technique used to examine changes in the activity of the working human brain by measuring changes in the blood’s oxygen levels.
• Transcranial magnetic stimulation (TMS) is the use of strong magnets to briefly interrupt normal brain activity as a way to study brain regions.

Cerebral Cortex

• The cerebral cortex is the outer layer of the cerebral hemispheres and gives the brain its distinctive wrinkled appearance.
• The corpus callosum, a massive bridge of millions of myelinated axons (white matter), connects the hemispheres and allows information to flow between them.

Lobes of the Brain

• The occipital lobes are at the back of the head and are devoted almost exclusively to vision, including the primary visual cortex.
• The parietal lobes are devoted partially to touch.
• The left hemisphere receives touch information from the right side of the body, and the right hemisphere receives touch information from the left side of the body.
• In each parietal lobe, this information is directed to the primary somatosensory cortex.
• The temporal lobes hold the primary auditory cortex, which is the brain region responsible for hearing.
• At the intersection of the temporal and occipital lobes is the fusiform face area.
• The frontal lobes are essential for planning and movement.
• In the back part of the frontal lobes, along the central fissure, is the primary motor cortex.
• The prefrontal cortex consists of the rest of the frontal lobes.
• The prefrontal cortex is responsible for directing and maintaining attention, keeping ideas in mind while distractions bombard people from the outside world, and developing and acting on plans.

Somatic Nervous System

• Transmits sensory signals to the CNS via nerves.
• Specialized receptors in the skin, muscles, and joints send sensory information to the spinal cord, which relays it to the brain.

Autonomic Nervous System

• Regulates the body’s internal environment by stimulating glands and by maintaining internal organs.
• Consists of the sympathetic division and the parasympathetic division.
• The sympathetic division prepares the body for action.
• The parasympathetic division returns the body to its resting state.

Plasticity

• A property of the brain that allows it to change as a result of experience or injury.
• Plasticity has critical periods, during which particular experiences must occur for development to proceed normally.

Genes

• A dominant gene from either parent is expressed whenever it is present.
• A recessive gene is expressed only when it is matched with a similar gene from the other parent.
• The genotype is an organism’s genetic makeup.
• The phenotype is that organism’s observable physical characteristics and is always changing.

Reputake

• The process whereby a neurotransmitter is taken back into the presynaptic terminal buttons, thereby stopping its activity.

Brain Hemispheres

• The brain is divided into two hemispheres
  • Left Hemisphere (Logical & Analytical)
  • Right Hemisphere (Creative & Intuitive)
• Connected by the corpus callosum, which allows them to communicate.
• Each hemisphere controls the opposite side of the body

Left Hemisphere - The "Logical" Side

• Functions:
• Language & Speech (Broca’s & Wernicke’s areas)
• Logical Thinking & Reasoning
• Math & Problem-Solving
• Analyzing Details
• Sequential Processing (Step-by-Step Thinking)

Right Hemisphere - The Creative Side

• Functions:
• Creativity & Imagination
• Art & Music Skills
• Emotional Recognition
• Spatial Awareness & Visual Perception
• Big-Picture Thinking

Parts of the Brains

• Ventral cortex refers to areas of the brain located on the underside (ventral side) of the cerebral cortex.
• Is involved in several important functions, particularly related to vision, emotion, and decision-making.
• The primary somatosensory cortex is the part of the brain that helps you feel things like touch, temperature, pain, and body position.
• The association cortex is the part of the brain responsible for complex thinking, problem-solving, and integrating sensory and motor information.
• The prefrontal cortex helps with decision-making, planning, problem-solving, and self-control. Is what makes us think before we act!
• Broca’s area is a small portion of the left frontal region of the brain, crucial for the production of language.
• The prefrontal cortex is often used informally to describe the prefrontal cortex, especially in discussions about how brain injuries affect personality and behavior.
• The thalamus is the gateway to the brain and receives almost all incoming sensory information.
• The amygdala is a brain structure that serves a vital role in learning to associate things with emotional responses and in processing emotional information.
• The frontal lobe is important for movement and higher-level psychological processes associated with the prefrontal cortex.
• The hippocampus is associated with the formation of memories.
• The basal ganglia are important for the planning and production of movement.
• The brain stem houses structures that control functions associated with survival, such as heart rate, breathing, swallowing, vomiting, urination, and orgasm. The cerebellum is essential for coordinated movement and balance.
• The insula is important for taste, pain, perception of bodily states, and empathy.

Consciousness vs Attention

• Consciousness consists of one’s moment-by-moment personal, subjective experiences.
• Attention involves being able to focus selectively on some things and not others.
• Consciousness is limited meaning that we often miss things
• Change blindness is missing large changes because you are focusing on something else.

Attention

• Endogenous attention is directed voluntarily.
• Exogenous attention is directed involuntarily by a stimulus.

Priming

• Priming occurs when the response to a stimulus is influenced or facilitated by recent experience with that stimulus or a related stimulus.
• Subliminal perception occurs when stimuli are processed by sensory systems, but do not reach consciousness, due to the short durations or subtlety.
• In meditation, a person focuses attention on an external object, an internal event, or a sense of awareness to create a state of altered consciousness.

Types of Awareness

• Consciousness is the subjective experience of the world.
• Controlled processing is the type of consciousness needed to perform slow, deliberate, and intentional tasks.
• Subliminal perception is processing sensory information without conscious awareness.
• Change blindness is the failure to notice large changes in one’s environment.
• Automatic processing is the type of consciousness needed to perform quick, automatic behaviors or habits.

Altered States of Consciousness

• Flow state is a focused, active engagement of the consciousness in an enjoyable activity.
• Concentrative meditation is a type of meditation where you focus on one thing, like your breath or an image.
• Religious activity is brought about by religious ceremonies, directs attention away from one’s self and allows a person to focus on spiritual awareness.
• Escapist activities avoid problems and disengage with life.
• Hypnosis is a social interaction in which one person is in a suggestible, altered state of consciousness.
• Mindfulness meditation is a state of free-flowing thoughts.

Characteristics of Flow

• A person typically loses track of time.
• Something is being done for its own sake rather than as a means to an end.

Mindfulness vs Dissociation

Mindfulness is the intentional focus on the present moment with full awareness and acceptance, without judgment.

• Increased Awareness
• Present-Focused
• Controlled Attention
• Relaxation & Emotional Regulation

Dissociation: Detachment from Reality

• Decreased Awareness
• Sense of Unreality
• Memory Gaps
• Automatic Behavior

Brain Research on Meditation

• Those who practice meditation may also have other lifestyle differences that affect brain aging.

Pain Hypnosis

• The use of hypnosis for pain reduction is called hypnotic analgesia.
• Brain studies indicate that after hypnosis the sensory-processing part of the brain responds to pain stimuli just as strongly, but the emotion-processing part responds less strongly.
• This supports the dissociation theory of hypnosis.

Sleep Structure

• Changes in light register in the suprachiasmatic nucleus of the hypothalamus.
• This region signals the pineal gland when the time for sleep or the time for wakefulness has come.
• Circadian Rhythms- “Biological patterns that occur at regular intervals as a function of time of day.”

Dream Theory

• REM dreams are caused by the activation of emotional and visual centers without the activation of the logic areas of the brain.
• During non-REM sleep, there is a general deactivation of many brain regions.
• Manifest content is a dream the way the dreamer remembers it.

The Activation Synthesis Theory

• States that dreams are the result of the mind making sense of random neural firings that occur during sleep by synthesizing them with memories.

Freud’s Interpretation of Dreams Theory

• States that dreams are a tool to access the unconscious.
• All dream content is symbolic of unconscious conflicts.
• Latent content is what a dream symbolizes.

Understanding Hypnosis

• Hypnosis is a social interaction during which a person, responding to suggestions, experiences changes in memory, perception, and/or voluntary action.
• During a hypnotic induction, the hypnotist makes a series of suggestions to at least one person.
• As the listener falls more deeply into the hypnotic state, the hypnotist makes more suggestions.
• If everything goes according to plan, the listener follows all the suggestions without hesitation.

Theories of Hypnosis

• According to the sociocognitive theory of hypnosis, hypnotized people behave as they expect hypnotized people to behave, even if those expectations are faulty.
• The neo-dissociation theory of hypnosis acknowledges the importance of social context to hypnosis, but it views the hypnotic state as an altered state.
• According to this theory, hypnosis is a trancelike state in which conscious awareness is separated, or dissociated, from other aspects of consciousness.
• A post-hypnotic suggestion is a command or idea given during hypnosis that affects a person's thoughts, feelings, or behaviors after they wake up from the hypnotic state.

Dream Hypothesis

• According to Hobson, dreams begin with random neuron firings, which the brain attempts to interpret.
• Later, Hobson identified the limbic system as responsible for dreams’ emotional content, and the deactivation of the prefrontal cortex as responsible for dreams’ chaotic character.
• Critics argue that dreams generally make more sense than Hobson’s hypothesis would suggest.

Stages of Sleep

• Beta ( REM, awake) brain stem, amygdala, motor cortex, visual association areas
• What happens in REM:
  • Muscles are paralyzed
  • The brain produces beta waves
  • People’s eyes dart around
  • There is high activity in the occipital lobe
• Alpha (falling asleep)
• Theta (stage 1)
• Theta, sleep spindle, and K-complex
• Delta (stages 3 and 4) * The brain produces delta waves, the brain is in slow-wave sleep, and the mind remains alert to environmental signs of danger*

Sleep consolidation

• Sleep with dreams is better than sleep without dreams for consolidating information.
• A person’s sleep patterns may change in response to a need to consolidate more information.

Sleeping Brain

• Multiple brain regions are involved in producing and maintaining circadian rhythms and sleep.
• Information about light detected by the eyes is sent to a small region of the hypothalamus called the suprachiasmatic nucleus.
• This region then sends signals to a tiny structure called the pineal gland.
• The pineal gland then secretes melatonin, a hormone that travels through the bloodstream and affects various receptors in the body, including the brain.
• Bright light suppresses the production of melatonin, whereas darkness triggers its release.
• Facilitation of Learning Neural connections made during the day, which serve as the basis of learning, are strengthened during sleep ”

Need to Sleep

• Research suggests sleep is adaptive for three functions: restoration, avoiding danger at certain times of the day, and facilitation of learning.
• Restorative Theory, sleep allows the body, including the brain, to rest and repair itself.
• After people engage in vigorous physical activity, such as running a marathon, they generally sleep longer than usual.
• Circadian rhythm theory proposes that sleep has evolved to keep animals quiet and inactive during times of the day when there is the greatest danger, usually when it is dark.

Sleep Disorders

• REM behavior disorder: most often seen in elderly males, associated with neurological deficit.
• Somnambulism: usually occurs at night, occurs during slow-sleep wave, most seen often in young children.
• Insomnia is a sleep disorder in which people’s mental health and ability to function in daily life are compromised by difficulty both falling asleep and staying asleep.
• Obstructive sleep apnea. People with this disorder stop breathing for short periods during sleep because their throat closes.
• Narcolepsy is “excessive sleepiness that lasts from several seconds to minutes occurs during normal waking hours.”

Drugs

• Psychoactive drugs cause changes in mood, awareness, thoughts, feelings, or behavior.
• These drugs change the brain’s neurochemistry by activating neurotransmitter systems by imitating the brain’s natural neurotransmitters.
  • Stimulants increase behavioral and mental activity.
  • Depressants reduce behavioral and mental activity by depressing the central nervous system.
  • Opioids, sometimes called narcotics, include heroin, morphine, and codeine.
  • These drugs, derived from the opium poppy, bind with a special type of receptor in the brain.
  • Hallucinogens, sometimes called psychedelics, produce alterations in cognition, mood, and perception by changing how users experience the world around them.

LSD Drug

• Lysergic acid diethylamide, or LSD, is a hallucinogen made from fungus that grows on rye and related grains.
• It is usually taken orally and produces a “trip” that lasts roughly 12 hours.