Nervous System: CNS and PNS

Nervous System Overview

• It is the command center regulating body systems and enabling environmental interaction.
• Neurons transmit signals throughout the body.
• Signals travel among the brain, skin, organs, glands, and muscles for movement, sensation, and information processing, relaying data to the brain.

Central Nervous System (CNS)

• The brain resides within the skull.
• It provides conscious awareness and drives psychological processes.
• The cerebral cortex, an outer layer, supports higher thought, language, and consciousness and divides into lobes.
• The spinal cord is located within the vertebrae.
• It transfers messages between the brain and the body.
• It mediates simple reflex actions in response to stimuli.
• The connection between the brain and spinal cord is essential for message transmission, enabling bodily responses.

Peripheral Nervous System (PNS)

• Nerves and ganglia send signals.
• The Somatic Nervous System controls voluntary movements like walking with communication between the CNS, muscles, and the external world.
• Sensory pathways carry information to the spinal cord and brain.
• Motor pathways allow the brain to control movement.
• The Autonomic Nervous System controls involuntary movements like breathing and digestion.

Autonomic Nervous System Divisions

• The Parasympathetic Division manages homeostasis and the body's functions during rest, often termed "rest & digest" and constricts pupils whilst also stimulating salivation.
• It constricts airways, slows heartbeat, stimulates stomach activity, inhibits glucose release, stimulates the gallbladder & intestines whilst also contracting the bladder.
• The Sympathetic Division manages responses to perceived threats or "fight & flight" responses.
• It dilates pupils, inhibits salivation, relaxes airways, and increases heartbeat.
• It also inhibits stomach and intestinal activities as well as gallbladder function, stimulates glucose release, secretes epinephrine and norepinephrine and relaxes the bladder.

Brain Structure: Lobes

• The cerebral cortex houses hemispheres.
• The Frontal Lobe is responsible for higher thought, reasoning, and voluntary movement directly behind the forehead.
• It facilitates movement, language creation, creativity, high cognition, and executive functions.
• Judgment and decision-making improve in an individuals twenties.
• Damage can impair language, speech, movement (paralysis), higher cognition, and personality.
• It works with the limbic system for emotions and impulse control.
• The Temporal Lobe processes auditory stimuli and language.
• Located in the temple area, it stores memory, language, emotion, and visual input.
• It also receives stimuli from senses.
• Damage can cause difficulty in understanding speech, memorizing information, comprehending language, recognizing faces, emotional deregulation, and vision changes.
• The Parietal Lobe processes touch and spatial surroundings in the top middle of the brain.
• It is responsible for coordination, learning new movements, converting sensory input into useful information, and processing surroundings.
• Damage can limit sensory and spatial processing but can help the occipital with visual processing
• The Occipital Lobe processes and interprets visual information at the back of the brain.
• It supports spatial awareness, distance/depth perception, recognition, and long-term memory
• It converts eye input into useful information and works in conjunction with the parietal lobe.
• Damage can cause visual impairment, blindness, and navigational difficulties due to impaired depth and distance perception

Limbic System

• The limbic system is located in the midbrain and controls emotional and motivational responses.
• The Amygdala creates memories and processes emotions, primarily fear and anxiety, as well as supporting emotional learning and social behavior in the middle temporal lobe on both sides.
• Damage can increase emotions or confusion, anxiety, depression, and autism.
• Loss can cause people to be fearless.
• The Hippocampus handles learning and memory on both sides beside the temples.
• Functions of the hippocampus include learning, memory formation, spatial navigation, and verbal memory.
• Loss can cause a lack of explicit memories and loss in emotions.
• The Hypothalamus regulates bodily systems.
• It regulates body temperature, blood pressure, hunger, thirst, satiety, mood, and sleep and maintains homeostasis.
• Damage can cause abnormal autonomic functions, emotional and behavioral changes, and uncontrolled appetite or thirst.
• The Pituitary Gland releases hormones that regulate growth, metabolism, reproductive development and also regulates hormones.
• Loss can cause hormone dysfunction, changes in body composition, mood swings, and increased stress.

Old Brain

• The old brain keeps individuals alive.
• The Medulla controls automatic functions.
• The Pons coordinate autonomic functions.
• The Thalamus sends messages to different parts of the brain and manages sensory information, memory, focus, attention, consciousness, and wakefulness.
• Loss can cause negative effects to the senses, vision problems, motor issues, chronic pain, and comas.
• The Brain Stem is the core of the brain.
• Connects to the spine.
• The Reticular Formation (RAS) manages alertness and sleepiness.
• The Cerebellum coordinates balance and movement, records surroundings, coordinates eye movement/timing, and adjusts motor commands for speech, language, mood, and precision/smoothness of movement.
• Loss can cause issues in coordination, posture, balance, language, and social interaction, which may require others to compensate.
• The Olfactory Bulb processes smell information and sends sensory information to other areas.
• Loss can cause anosmia, changes in eating habits, eating disorders, and depression.
• The Somatosensory System is also a key brain structure.

Endocrine System

• The endocrine system works with the nervous system to maintain homeostasis.
• The peripheral nervous system collects information on the body's state.
• Problems in the CNS trigger a signal to the endocrine glands, which produce hormones to restore homeostasis.
• This system is slower but more widespread than the nervous system.
• Glands are organs that produce hormones. Major glands: pituitary (master hormone controller) and gonads: female(ovaries)estrogen, male(testes)testosterone and androgen

Hormones Defined

• They are chemical messages affecting cells with appropriate receptors in the bloodstream
• Some neurotransmitters are also hormones.
• Thyroxine, made by the thyroid, affects cells in the heart and body, increasing metabolic/growth rates.
• Hypothalamus triggers the sympathetic nervous system, causing ANS activation, adrenaline production, and physiological changes such as increased heart rate, dilated pupils, and decreased salivation.
• The parasympathetic system restores balance after the threat passes.

Survival Mechanisms

• The above physiological changes evolve as a survival mechanism in life-threatening situations for quick escape or confrontation.
• Heart rate: Increases oxygen/glucose delivery for energy.
• Breathing: Becomes rapid.
• Muscles Tense
• Non-essential processes stop to conserve energy. Digestion pauses. Pupils dilate to increase awareness.

Neurons

• Neurons are the special structures (dendrites and axons) which make up the brain, communicating messages and processing information.
• Dendrites receive chemical messages from axon terminals of other cells.
• When enough chemical messengers accumulate, the neuron transmits messages - stores information (DNA).
• The Soma, or cell body, holds everything together.
• The Myelin Sheath helps messages travel quickly and smoothly.
• Impulses from dendrites travel down the Axon to the Axon Terminals, which release neurotransmitters into the Synapse to continue the signal.
• A synapse is a gap where messages transition from one cell to the next without physical contact.
• Inside cells, messages travel via electrochemical gradients and neurotransmitters.

Neurotransmitters

• Neurotransmitters are chemicals stored at axon terminals that are released when prompted, stimulate receptors on dendrites within a synapse, and are then reabsorbed and reused.
• Acetylcholine facilitates voluntary muscle movement.
• Endorphins regulate pleasure, pain, and mood, are released during pleasurable activities (exercise, massage, eating) and relieve pain and stress.
• Dopamine affects mood and emotional behavior, gives feelings of pleasure, satisfaction, and motivation.
• Serotonin impacts mood, emotion, sleep, digestion, wound healing, and bone health; low levels can cause depression.
• Norepinephrine regulates arousal, attention, cognitive function, and stress reactions.
• GABA has a calming effect, slowing down the brain by blocking specific signals in the CNS.
• Glutamate is an excitatory neurotransmitter important for memory, cognition, and mood regulation.

Brain Anatomy

• Gyrus/gyri (ridges) and sulcus/sulci (grooves) increase surface area, form divisions between lobes/hemispheres, and allow more information storage.
• Glial cells support, nourish, insulate, and help transmit signals within the nervous system, and also help to keep neurons together.

Aspects of the Brain

• The localisation of the brain states in 19th century, scientists thought the brain worked holistically.
• Broca and Wernicke's research supported the concept of localization, emphasizing each part's unique function and control.
• Neuroplasticity is the brain's ability to learn and reorganize which occurs through changes in neuron areas/connections.
• Functions can be reassigned from damaged to healthy areas.
• Phrenology is an early biospsychology from Franz Gall (18th century), associates head shapes with character traits.
• The Right and Left Hemispheres have specific responsibilities.
• Right hemisphere controls the body's left side, and vice versa (contralateral), the outer layer is made of cerebral cortex.
• The left hemisphere focuses on reasoning and logic and the right hemisphere is for language and creativity.

Brain Hemispheres

• The Corpus Callosum is a thick nerve fiber bundle connecting hemispheres, enabling communication and prevents split brain.

Specific Brain Areas

• The Motor Cortex controls voluntary movement.
• The damage can cause loss of control over fine movements and is logically ordered, with the arm next to the hand.
• The Somatosensory Cortex processes sensory information and is adaptable.
• The Auditory Cortex analyzes speech and processes sound; damage correlates with hearing loss.
• The Visual Cortex receives and processes input from the eyes and sends this information contralaterally.
• Broca’s Area handles speech production resulting in Broca's aphasia can cause broken speech.
• Wernicke’s Area handles language comprehension and Damage can cause the production of nonsense words (neologisms)

Types of Brain Scans

• fMRI shows active brain parts by tracking blood flow.
• PET scans show organ/tissue function via injected radioactive material.
• CT scans provide detailed imaging through X-rays.
• EEG diagnoses epilepsy/brain injuries using scalp sensors.
• DTI maps brain pathways by tracking water movement.