The Neuron and its Function

• Neurons are cells in the nervous system that communicate with each other to perform information-processing tasks.

Components of a Neuron

• The cell body coordinates information-processing tasks and keeps the cell alive, involving protein synthesis, energy production, and metabolism, and contains the nucleus with DNA.
• Dendrites receive information from other neurons and relay it to the cell body.
• The axon carries information to other cells.
• The myelin sheath is an insulating layer of fatty material that prevents electrical current from leaking out and is supported by glial cells.
• Nodes of Ranvier are breakpoints on the axon.

Types of Neurons by Function

• Sensory neurons receive information from the external world and convey it to the brain from the spinal cord.
• Motor neurons carry signals from the spinal cord to the muscles to produce movement.
• Interneurons connect sensory neurons, motor neurons, and other interneurons, carrying information within the nervous system and working together to perform simple tasks like identifying sensory signals and recognizing faces.

Electrochemical Actions of Neurons

• Resting Potential (-70mV): The difference in electric charge between the inside and outside of a neuron's membrane.
• Inside the neuron: potassium ions and protein ions are present.
• Outside the neuron: sodium neurons are present.
• Action potential: An electric signal is conducted along the length of the axon to a synapse, reached when the electric shock reaches a threshold ("all or none" principle).

Action Potential Propagation

• When the electrical charge reaches the threshold, sodium channels open, and Na+ rushes into the cell.
• Na+ spreads into the cell, increasing the electrical charge in neighboring areas, causing adjacent cell membranes to open and let in more Na+ (domino effect).
• Saltatory conduction: Electrical current jumps from node to node, speeding up the flow of information down the axon.
• Refractory period: The time following an action potential during which a new action potential cannot be initiated.
• To restore electrical balance, Na+ channels close, K+ channels open, K+ ions rush into the cell causing the membrane to change to a negative state.
• Ion pumps (Na+/K+ pump) push Na+ out and K+ into the cell to reach the resting potential.

Synaptic Transmission

• Synaptic transmission involves the sending and receiving of chemical neurotransmitters.
• The action potential travels down the axon, stimulating the release of neurotransmitters from vesicles.
• Terminal buttons, knob-like structures branching out from an axon, are filled with vesicles containing neurotransmitters, which transmit information across the synapse to the dendrites of a receiving neuron.
• Neurotransmitters are released into the synapse and bind to receptor sites on postsynaptic neurons to initiate a new action potential.
  • Receptors are parts of the cell membrane that receive the neurotransmitter and either initiate or prevent a new electric signal.
• After a chemical message is relayed, neurotransmitters left in the synapse undergo:
  • Reuptake: NT absorbed by terminal buttons.
  • Enzyme deactivation: Destroyed by enzymes
  • Diffusion: NT drifts out of synapse.

Types of Neurotransmitters

• Acetylcholine: involved in voluntary motor control and linked to Alzheimer's disease.
• Dopamine: regulates motor behavior, motivation, pleasure, and arousal, and is linked to schizophrenia and Parkinson's disease.
• Glutamate: a major excitatory neurotransmitter that enhances the transmission of information between neurons.
• Gamma-aminobutyric acid: primary inhibitory neurotransmitter is linked to seizures.
• Norepinephrine: affects vigilance and heightened awareness of dangers.
• Serotonin: regulates sleep, wakefulness, eating, and aggressive behavior, and is linked to depression.
• Endorphins: act within pain pathways and emotion centers of the brain.

Drugs that Mimic Neurotransmitters

• Agonists: Drugs that increase the action of a neurotransmitter, acting as a neurotransmitter when binding to a receptor.
• Antagonist: A drug that prevents a neurotransmitter from acting or lessens its effect.
• L-dopa: Made from dopamine and used to treat Parkinson's disease, elevates concentration in the brain and spurs surviving neurons to produce more dopamine, acting as an agonist.
• Amphetamine: Stimulates the release of norepinephrine and dopamine and is an agonist that creates an excess of neurotransmitters flooding a synapse.
• Cocaine: Prevents the reuptake of neurotransmitters, also acting as an agonist, and affects norepinephrine and dopamine control mood to increase feelings of euphoria, wakefulness, and energy and increase heart rate.
• Opioids: agonists for endorphins that create feelings of calmness and euphoria, but antagonists for decrease of neurotransmitters involved with pain.
• Naloxone: a drug that bloding agonists heroin and preventing their effects on neurons, binds to opioid receptors, and used to treat opioid excess in the body in emergency.
• Prozac: An agonist blocks the reuptake of serotonin, treating depression by blocking reuptake, allowing more serotonin to remain in the synapse longer and produces greater activation of serotonin receptors.
• Propanolol: A beta blocker obstructing receptor sites in the heart for norepinephrine to decrease heart rate; beta blockers can reduce agitation, racing heart, and nervousness.

Organization of the Nervous System

• Central Nervous System: Composed of the brain and spinal cord, receives sensory information from the world, processes and coordinates information, and sends commands to skeletal and muscular systems.
  • Spinal cord: Processes sensory information and relays commands to the body.
• Peripheral Nervous System: Connects the central nervous system to the body's organs and muscles.
  • Somatic nervous system: Nerves that convey information between skeletal muscle and CNS, allowing conscious control to perceive, think, and coordinate conscious behaviors.
  • Autonomic nervous system: Nerves that carry involuntary and automatic commands controlling blood vessels, organs, and glands.
    • Sympathetic nervous system: Prepares the body for action in challenging or threatening situations (fight or flight), causing pupil dilation, increased heart rate, increased respiration, activation of sweat glands, and suppression of the immune system, pain, injury, and digestive system.
    • Parasympathetic nervous system: Helps the body return to a normal resting state (rest and digest), constricting pupils, decreasing heart rate and respiration, increasing blood flow to the digestive system, and decreasing activity in sweat glands.

Reflex Arc

• Spinal reflexes: Simple pathways in the nervous system that rapidly generate muscle contractions.
• Reflex Arc: A neural pathway that controls reflex actions.
  • PNS sends a signal from sensory neurons through the brain and spinal cord.
  • The brain sends commands for voluntary movement through the spinal cord to motor neurons.
  • Axons from motor neurons branch to effector muscles for reflex.
• The spinal cord regulates breathing, responses to pain, movement in muscles, and motor movement.
• Brain: Higher processes

Brain Structure

• The Hindbrain: Responsible for essential life-sustaining functions, including motor coordination, alertness, and body processes.
  • Medulla: Controls heart rate, circulation, and respiration.
  • Reticular formation: Regulates sleep, wakefulness, and arousal.
  • Cerebellum: Coordinates motor movements and balance and contributes to cognitive and social functions.
  • Pons: A bridge for relaying information between the cerebellum and other brain areas.
• Midbrain: Involved in sensory processing and movement coordination.
  • Tectum: Orients organisms to environmental stimuli.
  • Tegmentum: Influences movement and arousal, mood, and motivation.
• Forebrain: Responsible for complex cognitive, emotional, and sensory functions.
  • Cerebral cortex: Outer layer of the brain responsible for higher-level processing.
  • Subcortical structures
    • Thalamus: Sensory relay.
    • Hypothalamus: Regulation of basic drives.
    • Limbic system: Emotion and memory.
      • Hippocampus: Memories and integrating memories into knowledge to be soted
      • Amygdala: Involved in emotional processes and the formation of emotional memories.
    • Basal ganglia: Plays a role in movement and reward processing.
• Endocrine system: A network of glands that produce and secrete hormones into the bloodstreams, influencing metabolism, growth, and sexual development.
  • Pituitary gland: Regulates hormone levels and homeostasis within the body to regulate other glands. Functions of the Cerebral Cortex
• Sensory processing
• Movement
• Higher cognitive functions

Organization of the Cerebral Cortex

• Right hemisphere: Controls movement and processes sensory input from the left side of the body.
• Left hemisphere: Controls the right side of the body.
• Corpus callosum: The structure through which two hemispheres communicate.
• Divided into four lobes:
  • Occipital lobe: Processes visual information, including detecting edges, color, and motion (primary visual cortex).
  • Parietal lobe: Processes touch, spatial awareness, and body position.
    • Somatosensory cortex: Maps sensory input from different body parts.
  • Temporal lobe: Processes hearing and language (primary auditory cortex), recognizes objects, and interprets the meaning of sounds and visual stimuli.
  • Frontal lobe: Involved in movement, decision-making, problem-solving, and planning.
    • Motor cortex: Controls voluntary movement.
• Organization within specific lobes includes primary processing areas for basic sensory input like vision, touch, and hearing, and association areas that integrate and interpret sensory information, allowing for complex thought and perception.

Brain Plasticity

• Changes in sensory input can lead to the brain reallocating sensory processing areas.
  • Example: Phantom limb syndrome, where cortical areas once dedicated to a lost limb respond to input from adjacent body parts.
• Learning and experience: Repeated use of particular skills leads to cortical reorganization.
  • Example: Musicians and quilters develop enlarged cortical representations of their hands due to practice.
• Physical exercise: Cardiovascular exercise promotes neurogenesis (the formation of new neurons) and increases synaptic connections in the hippocampus, improving cognitive function.
• Cultural influences shape how the brain processes information.
• Recovery from brain injury: When one area of the brain is damaged, other areas can take over function.
• Enhanced skills and abilities: Intensive practice leads to increased brain efficiency in related tasks.
  • Example: Musicians exhibit more remarkable motor cortex plasticity, allowing for faster and more precise finger movements.
• Phantom limb sensations: After amputation, brain regions responsible for the lost limb get reassigned, leading to sensations in the missing limb when nearby body parts are touched.
• Cognitive and memory benefits: Exercise can boost memory, problem-solving skills, and mental performance.
• Rehabilitation potential: Understanding plasticity helps in treating spinal cord injuries and neurological disorders by designing targeted therapies to stimulate brain reorganization.