Organization of the Nervous System and other systems

General Design of the Nervous System

• Motor Functions and Effectors
  • Motor functions are activities performed by the nervous system.
  • Muscles and glands are effectors, executing functions based on nerve signals.
• Processing of Information - Integrative Function
  • Attention is selectively drawn to certain sensory information.
  • Important sensory information is channeled to integrative and motor regions for desired responses.
  • This channeling and processing is the integrative function of the nervous system.
• Role of Synapses in Information Processing
  • Synapses are junction points between neurons.
  • They determine the direction of nervous signal spread.
  • Synaptic transmission varies in ease, with control exerted by facilitatory and inhibitory signals.
• Storage of Information - Memory
  • Not all sensory information causes immediate motor response; some is stored.
  • Storage occurs mainly in the cerebral cortex, but also in basal regions and the spinal cord.
  • Memory is the process of information storage, a function of the synapses.
  • Facilitation: Synapses become more capable of transmitting signals with repeated use.
  • Facilitation leads to the brain generating impulses through the same synapse sequences, creating memories of sensations.
  • The mechanisms of long-term synaptic facilitation are still uncertain.

Major Levels of Central Nervous System Function

• The human nervous system has functional capabilities inherited from evolutionary development.
• Three major levels:
  • Spinal cord level
  • Lower brain or subcortical level
  • Higher brain or cortical level

Spinal Cord Level

• The spinal cord is a conduit for signals.
• Organized spinal cord functions:
  • Walking movements
  • Withdrawal reflexes
  • Leg stiffening for gravity support
  • Control of blood vessels, gastrointestinal movements, and urinary excretion

Lower Brain or Subcortical Level

• Feeding reflexes controlled by the medulla, pons, mesencephalon, amygdala, and hypothalamus (e.g., salivation and licking).
• Emotional patterns (e.g. anger, excitement, sexual response, pain, and pleasure) can occur even after cerebral cortex destruction.

Central Nervous System Synapses

• Information transmits as nerve action potentials (nerve impulses).
• Each impulse:
  • May be blocked
  • May be changed into repetitive impulses
  • May be integrated with other impulses
  • These are synaptic functions of neurons.

Types of Synapses – Chemical and Electrical

• Two major types:
  • Chemical
  • Electrical
• Most synapses in the human CNS are chemical.
  • Involve neurotransmitters acting on receptor proteins to excite, inhibit, or modify sensitivity.
• Electrical Synapses
  • Useful for detecting simultaneoussubthreshold depolarizations, increasing sensitivity and synchronous firing.

Physiologic Anatomy of the Synapse

• Ion Channels
  • Located in the postsynaptic neuronal membrane.
  • Two types:
    • Cation channels: Allow passage of sodium, potassium, and/or calcium ions.
    • Anion channels: Allow passage of chloride ions and minute quantities of other anions.
• Ion Selective
  • Channels are selective based on diameter, shape, electrical charges, and chemical bonds.
• Excitatory vs. Inhibitory Transmitters
  • Excitatory transmitter: Opens cation channels, allowing positive sodium ions to enter and excite the neuron.
  • Inhibitory transmitter: Opens anion channels, allowing negative charges to enter and inhibit the neuron.

Second Messenger System

• Required for prolonged changes in neurons (seconds to months).
• Ion channels are unsuitable due to quick closure (milliseconds).
• Prolonged effects are achieved through second messenger systems.
• G Proteins
  • A common second messenger system utilizing G proteins.
  • Inactive G protein complex: Consists of GDP, alpha (α), beta (β), and gamma (γ) components in the cytosol.
  • Activation: Neurotransmitter activates the receptor, causing a conformational change and exposing a binding site for the G protein complex.

Excitatory or Inhibitory Receptors

• Some postsynaptic receptors cause excitation; others cause inhibition.
• This provides an additional dimension to nervous function, allowing restraint and excitation.

Chemical Substances as Synaptic Transmitters

• Over 50 substances function as synaptic transmitters.
• Two groups:
  • Small-molecule, rapidly acting transmitters
  • Neuropeptides (larger, slower acting)
• Gaseous molecules: May act as transmitter modulators.
• Small-molecule transmitters:
  • Involve acute responses (e.g., sensory and motor signals).
• Neuropeptides:
  • Cause prolonged actions (e.g., changes in receptors, ion channels, synapses).

Small Molecule, Rapidly Acting Transmitters

• Synthesized in the cytosol of the presynaptic terminal.
• Absorbed into transmitter vesicles via active transport.

Recycling of Small-Molecule Types of Vesicles

• Acetylcholine
  • Synthesized from acetyl coenzyme A and choline by choline acetyltransferase.
    Storage and Release
  • Stored in specific vesicles.
  • Released into the synaptic cleft during signal transmission.
• Breakdown and Recycling
  • Split into acetate and choline by cholinesterase.
  • Choline is actively transported back into the presynaptic terminal for reuse.

Characteristics of Some Important Small-Molecule Transmitters

• Acetylcholine
  • Usually excitatory but inhibitory at some parasympathetic nerve endings (e.g., heart inhibition by vagus nerves).
• Dopamine
  • Secreted by neurons from the substantia nigra, terminating in the basal ganglia.
  • Usually inhibitory.
• Glycine
  • Secreted mainly at synapses in the spinal cord.
  • Acts as an inhibitory transmitter.
• Gamma-Aminobutyric Acid (GABA)
  • Secreted by nerve terminals in the spinal cord, cerebellum, basal ganglia, and cortex.
  • Primary inhibitory neurotransmitter in the adult CNS but excitatory during early brain development.
• Glutamate
  • Secreted by presynaptic terminals in sensory pathways and the cerebral cortex.
  • Causes excitation.
• Serotonin
  • Secreted by nuclei originating in the median raphe of the brain stem.
  • Inhibits pain pathways in the spinal cord and helps control mood and sleep in higher regions of the nervous system.
• Nitric Oxide
  • Produced by nerve terminals in areas of the brain responsible for long-term behavior and memory.

Neuropeptides

• Synthesized differently and act slower than small-molecule transmitters.
• Not synthesized in the cytosol of presynaptic terminals.
• Synthesized by ribosomes in the neuronal cell body.
• Enter the endoplasmic reticulum and Golgi apparatus for processing.

Neuropeptide and Small-Molecule Transmitters

• May coexist in the same neurons.
• Their release may be differentially regulated due to different calcium ion sensitivities or spatial segregation of the vesicles on different boutons.

Electrical Events During Neuronal Excitation

• Excitatory Postsynaptic Potential (EPSP)
  • Definition: Positive increase in voltage above normal resting neuronal potential, making it less negative.
  • Mechanism: Rapid influx of positively charged sodium ions neutralizes negativity of resting membrane potential.
  • Example: Increase from −65 to −45 mV.
• Single Presynaptic Terminal Discharge
  • Cannot increase neuronal potential enough to reach threshold (e.g., −45 mV from −65 mV).
  • Requires simultaneous discharge of many terminals (e.g., 40 to 80 for anterior motor neuron).
  • Occurs through summation.

Electrical Events During Neuronal Inhibition

• Inhibitory Postsynaptic Potential (IPSP)
  • Definition: Increase in negativity beyond the normal resting membrane potential level.
  • Inhibition: The neuron inhibits because the membrane potential is more negative than the normal intracellular potential.

Presynaptic Inhibition

• Mechanism
  • Release of an inhibitory substance onto presynaptic nerve fibrils before they terminate on the postsynaptic neuron.
• Inhibitory Transmitter
  • GABA opens anion channels, allowing chloride ions to diffuse into the terminal fibril.
  • Negative charges inhibit synaptic transmission by canceling the excitatory effect of sodium ions.

Spatial Summation

• Definition: Summing simultaneous postsynaptic potentials by activating multiple terminals on widely spaced areas of the neuronal membrane.

Temporal Summation

• Mechanism
  • Each presynaptic terminal firing opens membrane channels for only 1-2 milliseconds.
  • Changed postsynaptic potential lasts up to 15 milliseconds after channels close.
  • Rapid successive opening of the same channels increases postsynaptic potential.
  • Successive discharges from a single presynaptic terminal can summate if they occur rapidly enough.

Facilitation of Neurons

• Summated postsynaptic potential is excitatory but below threshold for firing.
• Membrane potential is closer to the threshold for firing but not yet at the firing level.

Simultaneous Summation of Inhibitory and Excitatory Postsynaptic Potentials

• IPSP decreases membrane potential, while EPSP increases it.
• These effects can nullify each other.
• Inhibitory signal reduces postsynaptic potential below the threshold for excitation, turning off neuron activity.
• Facilitation by Diffuse Signals
  • Diffuse signals facilitate large groups of neurons.
  • Neurons respond quickly to signals from other sources.

Fatigue of Synaptic Transmission

• Rapid, repetitive stimulation of excitatory synapses reduces firing rate over time.
• Protective Mechanism: Protects against overexcitation
  • Excess excitability is reduced.
  • Example: Termination of epileptic seizures.

Effect of Acidosis or Alkalosis on Synaptic Transmission

• pH Sensitivity
  • Neurons are highly responsive to changes in pH of interstitial fluids.
• Alkalosis
  • Increases neuronal excitability.
  • Arterial blood pH rise (e.g., 7.4 to 7.8-8.0) can cause cerebral epileptic seizures.
  • Short hyperventilation can trigger attacks by elevating pH.
• Acidosis
  • Depresses neuronal activity.
  • pH fall (e.g., from 7.4 to below 7.0) usually leads to a comatose state.
  • Severe diabetic or uremic acidosis can cause coma.

Effect of Hypoxia on Synaptic Transmission

• Oxygen Dependence
  • Neuronal excitability depends on adequate oxygen supply.
  • Cessation of oxygen for a few seconds can cause complete inexcitability.
• Interruption of Brain Blood Flow
  • Temporary interruption leads to unconsciousness within 3-7 seconds.

Effect of Drugs on Synaptic Transmission

• Excitability Enhancers
  • Caffeine, theophylline, and theobromine (coffee, tea, cocoa) increase excitability by reducing the excitation threshold.
• Strychnine
  • Increases excitability by inhibiting inhibitory transmitter substances, especially glycine in the spinal cord.
  • Excitatory transmitters overwhelm neurons, causing rapid, repetitive discharge and tonic muscle spasms.
• Anesthetics
  • Increase the neuronal membrane threshold for excitation.
  • Decrease synaptic transmission.
  • Lipid solubility may alter neuronal membrane characteristics, reducing responsiveness to excitatory agents.

Synaptic Delay

• Definition: Minimal time for all events to take place (~0.5 millisecond).
• Measurement
  • Measured delay between input and output volley of impulses.
  • Used to estimate the number of series neurons in a circuit.

Physiological Anatomy of Skeletal Muscle

• Innervation
  • Each muscle fiber, except for 2%, is innervated by a single nerve end in the middle region.

Myofibrils

• Sarcomere: Portion of myofibril (or entire muscle fiber) between two Z lines.
  • Normal, fully stretched state: Sarcomere length is approximately 2 micrometers.
  • Actin filaments overlap myosin filaments and each other.
  • This size creates the greatest contraction force.
• Titin Molecules
  • Filamentous structure holding myosin and actin together.
  • Molecular weight: Up to 3,000,000.
  • One of the largest and most flexible protein molecules in the body.
  • Provides a framework for the actin and myosin contractile machine in the sarcomere.
  • Plays a mold role in the formation of contractile parts of the sarcomere, particularly myosin.

Molecular Mechanism of Muscle Contraction

• Myosin Filament
  • Cross-bridges: Arms and heads extending outward.
  • Hinges: Bendable points at the head-filament separation and where two heads meet the arm.
  • Hinged arms allow head movement away from or towards the myosin filament body.
  • Hinged heads participate in the actual contraction event.
• Actin Filament
  • Complex of actin, tropomyosin, and troponin.
  • Backbone: Double-helix F-actin protein molecule.

Tension Development and Filament Overlap

• Overlapping
  • Determines tension developed by contracting muscle fiber. Figure shows the effect of sarcomere length and the amount of myosin-actin filament overlap on the active tension developed by a contracting muscle fiber.

Isometric vs. Isotonic Contractions

• Isometric Contraction: Muscle does not shorten during contraction.
• Isotonic Contraction: Muscle shortens, but tension remains constant.

Isometric Twitch Characteristics

• Ocular Muscle: Duration of isometric contraction less than 1/50 second.
• Gastrocnemius Muscle: Duration of contraction about 1/15 second.
• Soleus Muscle: Duration of contraction about 1/5 second.

Motor Unit

• Definition - All muscle fibers innervated by a single nerve fiber.
• Small Muscles
  • React rapidly and require exact control.
  • More nerve fibers for fewer muscle fibers.
  • Example: Laryngeal muscles with 2–3 muscle fibers per motor unit.
• Large Muscles
  • Do not require fine control.
  • Several hundred muscle fibers in a motor unit.
  • Example: Soleus muscle.

Muscle Contractions - Force Summation

• Two Mechanisms:
  • Multiple Fiber Summation: Increasing the number of motor units contracting simultaneously.
  • Frequency Summation: Increasing the frequency of contraction, leading to tetanization.

Frequency Summation and Tetanization

• Twitch Contractions
  • Individual twitches occur one after another at low stimulation frequency.
• Frequency Increase
  • Each new contraction occurs before the preceding one is over.
• Resulting Contraction Strength
  • Second contraction is added partially to the first, increasing the total strength with increasing frequency.
• Tetanization
  • Successive contractions become so rapid that they fuse together.
  • Muscle contraction appears smooth and continuous.

Staircase Effect (Treppe)

• Definition - Increase in Initial Contraction Strength
  • When a muscle begins contracting after a long rest period, its initial strength may be as little as one-half its strength 10 to 50 muscle twitches later.
• Plateau
  • Strength of contraction increases to a plateau.

Remodeling of Muscle

• Muscle Hypertrophy
  • Increase in total muscle mass.
  • Results from an increase in the number of actin and myosin filaments in each muscle fiber.
  • Causes enlargement of individual muscle fibers (fiber hypertrophy).
  • Occurs to a greater extent when the muscle is loaded during contraction.
• Hyperplasia of Muscle Fibers
  • Rare increase in the actual number of muscle fibers (only by a few percent).
  • Occurs under extreme muscle force generation.
  • Mechanism: Linear splitting of previously enlarged fibers.

Poliomyelitis Recovery

• Mechanism of Muscle Recovery
  • When some nerve fibers to a muscle are destroyed, as happens in poliomyelitis, the remaining nerve fibers branch off to form new axons.
• Macromotor Units
  • Resulting large motor units containing as many as five times the normal number of muscle fibers for each motoneuron coming from the spinal cord.

Rigor Mortis

• Postmortem Muscle State
  • Several hours after death, all body muscles enter a state of contracture known as rigor mortis.
• Mechanism
  • Loss of all ATP prevents separation of cross-bridges from actin filaments during relaxation.
• Resolution
  • Muscles remain in rigor until muscle proteins deteriorate about 15-25 hours later via autolysis caused by lysosome enzymes.

Muscular Dystrophy

• Genetic Basis
  • Affects only males.
  • Transmitted as an X-linked recessive trait.
• Dystrophin Mutation
  • Caused by mutation of the gene that encodes dystrophin, linking actins to proteins in the muscle cell membrane.
• Function of Dystrophin
  • Forms an interface between intracellular contractile apparatus and extracellular connective matrix.
• Effects of Dystrophin Deficiency
  • Muscle cell membrane destabilization and activation of pathophysiological processes.
  • Altered intracellular calcium handling and impaired membrane repair after injury.

Types of Muscular Dystrophy

• Duchenne Muscular Dystrophy (DMD)
  • Symptoms: Muscle weakness beginning in early childhood and rapid progression.
  • Patients usually need wheelchairs by age 12 and often die of respiratory failure before age 30.
• Becker Muscular Dystrophy (BMD)
  • Milder form caused by mutations of gene for dystrophin, with later onset & longer survival.
• Prevalence
  • DMD and BMD affect 1 of every 5,600 to 7,700 males between ages 5-24 years.
• Treatment
  • No effective treatment exists, but genetic basis characterization provides potential for future gene therapy.

Neuromuscular Junction

• Branching and Stimulation
  • Each nerve fiber branches to stimulate 3-several hundred skeletal muscle fibers.
  • Each nerve ending forms neuromuscular junction with the muscle fiber at its midpoint.
• Motor End Plate
  • A complex of branching nerve terminals that invaginate into the muscle fiber's surface but lie outside the plasma membrane.

Acetylcholine (ACh)

• Synthesis and Storage
  • Synthesized in the nerve terminal's cytoplasm but rapidly absorbed into ~300,000 synaptic vesicles.
• Acetylcholinesterase
  • Enzyme present in large quantities in the synaptic space.
  • Destroys acetylcholine a few milliseconds after its release.

Secretion of Acetylcholine

• Release from Terminals
  • Nerve impulse releases about 125 vesicles of acetylcholine from the terminals into the synaptic space.
• Voltage-Gated Calcium Channels
  • Protein particles penetrate the neural membrane, acting as voltage-gated calcium channels.
  • Action potential opens these channels, allowing calcium ions to diffuse into the nerve terminal.

Acetylcholine and Ion Channels

• Receptor Composition
  • Fetal acetylcholine receptor complex: Two alpha proteins and one each of beta, delta, and gamma proteins.
  • Adult: Epsilon protein substitutes for the gamma protein.
• Sodium Ion Flow
  • More sodium ions flow through acetylcholine-gated channels than other ions because there are high concentrations of sodium ions in the extracellular fluid and potassium ions in the intracellular fluid.

End Plate Potential

• Curare
  • Blocks acetylcholine gating action on acetylcholine channels by competing for receptor sites.
  • Weakens end plate potential.
• Botulinum Toxin
  • Decreases acetylcholine release by nerve terminals.
  • Weakens end plate potential.

Safety Factor for Neuromuscular Transmission

• High Safety Factor
  • Each impulse causes about three times more end plate potential than needed to stimulate the muscle fiber.
• Fatigue
  • Stimulation at rates over 100 times per second for several minutes may diminish acetylcholine vesicles, causing impulses to fail.
  • Also, causes fatigue of synapses in the central nervous system when the synapses are overexcited.
  • Measurable fatigue rarely occurs under normal conditions.

Acetylcholine Formation and Release

• Vesicle Availability
  • Sufficient for only a few thousand nerve-to-muscle impulses.
• Re-formation
  • New vesicles need to be re-formed rapidly for continued neuromuscular junction function.
• Coated Pits
  • Appear in the terminal nerve membrane seconds after each action potential, from contractile proteins (clathrin).

Stimulation of Neuromuscular Junction

• Drugs
  • Neostigmine, physostigmine, and diisopropyl fluorophosphate. Inactivate acetylcholinesterase preventing acetylcholine hydrolysis.
• Neostigmine and Physostigmine
  • Combine with acetylcholinesterase to inactivate it for several hours, after which they are displaced, and the esterase becomes active again.
• Diisopropyl Fluorophosphate
  • Nerve gas poison that inactivates acetylcholinesterase for weeks, making it lethal.

Excitation-Contraction Coupling

• Calcium Ions
  • Sarcoplasmic reticulum contains excess calcium ions at high concentration.
  • Many ions are released when an action potential occurs in the adjacent T tubule.
• Dihydropyridine and Ryanodine Receptors
  • Action potential in T tubule sensed by dihydropyridine receptors.
  • Linked to calcium release channels (ryanodine receptor channels) in sarcoplasmic reticular cisternae.
• Calcium Pump (SERCA)
  • Concentrates calcium ions approximately 10,000 fold inside the tubules.

Types of Smooth Muscle

• Two Major Types
  • Multi-Unit Smooth Muscle
  • Unitary (Single-Unit) Smooth Muscle

Multi-Unit Smooth Muscle

• Composition
  • Composed of discrete, separate, smooth muscle fibers.
• Function
  • Each fiber operates independently of the others.
  • Often innervated by a single nerve ending, like skeletal muscle fibers.

Urinary Smooth Muscle

• Definition
  • A mass of hundreds to thousands of smooth muscle fibers that contract together as a single unit.
• Arrangement
  • Fibers arranged in sheets or bundles.
  • Cell membranes are adherent, allowing force transmission between fibers.

Chemical Basis

• Actin and Myosin Filaments
  • Present with chemical characteristics similar to skeletal muscle.
• Troponin Complex
  • Absent, so control mechanism is different.

Smooth vs Skeletal

• Actin and Myosin Interaction
  • Interact similarly.
• Activation and Energy Source
  • Activated by calcium ions.
  • ATP is degraded to ADP for energy.
• Primary Differences
  • Physical organization, excitation-contraction coupling, calcium control, contraction duration, and energy requirements.

Comparison - Contractile Unit

• Similar to skeletal muscle, but without the regularity of its structure.
• Dense bodies serve the same role as Z disks in skeletal muscle.

Latch Mechanism

• Sustained Contraction
  • Amount of continuing excitation needed to maintain full contraction force can be reduced.
• Energy Consumption
  • Energy consumed is often minuscule even as little as 1/300 of the energy required for comparable sustained skeletal muscle contraction.

Stress-Relaxation of Smooth Muscle

• Characteristics
  • Ability to return to nearly the original force of contraction seconds or minutes after elongation or shortening.
• Sudden Increase in Fluid Volume
  • Causes immediate large increase in pressure.
• Ureters as example
  • During the next 15-60 seconds, despite continued stretch of the bladder wall, the pressure returns almost exactly back to the original level.
• Importance
  • Allows a hollow organ to maintain the same pressure despite sustained changes in volume.

Calcium Importance

• Initiating Stimulus
  • Increase in intracellular calcium ions.
  • Caused by nerve stimulation, hormonal stimulation, fiber stretch, or chemical environment changes.
• Absence of Troponin
  • No troponin; contraction activated by a different mechanism.

Regulation of Contraction

• Calcium-Calmodulin Activation
  • Smooth muscle cells contain calmodulin.
  • Calmodulin activates myosin cross-bridges.

Nervous and Hormonal Control

• Multiple Stimuli
  • Smooth muscle can be stimulated by nervous signals, hormonal stimulation, muscle stretch and through several other means.
• Many Receptor Proteins
  • Smooth muscle membrane contains many types of receptors to initiate or inhibit the contractile process.

Neuromuscular Junctions

• Diffuse Junctions
  • Autonomic nerve fibers form diffuse junctions instead of direct contact with muscle fibers.
• Transmitter Diffusion
  • Transmitter substance is secreted into the matrix coating of the smooth muscle.

Factors Causing Smooth Muscle Contraction

• Non-nervous and Nonaction Potential Stimulating Factors
  • Local tissue chemical factors
  • Various hormones.
• Local Tissue Chemical Factors
  • Lack of oxygen in local tissues causes smooth muscle relaxation, therefore vasodilation.
  • Excess in carbon dioxide causes vasodilation.
  • Increased hydrogen ion concentration causes vasodilation.
  • Adenosine, lactic acid, increased potassium ions, nitric oxide, increased body temperature and decreased blood pressure all vasodilation.
• Hormone Effects
  • Circulating hormones affecting the process: norepinephrine, epinephrine, angiotensin II, endothelin, vasopressin, oxytocin, serotonin, and histamine.

Cardiac Muscle

• Types
  • Atrial muscle
  • Ventricular muscle
  • Specialized excitatory and conductive muscle fibers.
  • Excitation and conductive fibers contract feebly, exhibiting automatic rhythmical electrical discharge and conduction of action potentials.

Syncytium

• Intercalated Discs
  • Cell membranes separate individual cardiac muscle cells.
• Two Syncytiums
  • Atrial
  • Ventricular
  • The presence of intercalated discs and functional syncytium helps the heart to be more resistant to damage and continue function normally.

Action Potential Plateau

• Channel Types
  • Voltage-activated fast sodium channels.
  • L-type calcium channels (slow calcium channels, calcium-sodium channels).

Refractory Period

• Cardiac muscle refractory to restimulation during action potential, ensuring rhythmic contractions.

Excitation-Contraction Coupling

• Mechanism
  • Action potential spreads along the membranes of the transverse (T) tubules.
• Calcium Release
  • T tubule action potentials cause release of calcium ions into the muscle sarcoplasm from the sarcoplasmic reticulum.
• Reaction
  • Calcium ions diffuse into the myofibrils.
  • Promote the sliding of actin and myosin filaments along one another, which produces the muscle contraction.
• Additional Calcium Source
  • Voltage-dependent calcium channels in the membrane of the T tubule open during the action potential.
  • Sarcoplasmic Reticulum Calcium ATPase transports Ca+ from the cytosol into the lumen of the sarcoplasmic reticulum.

Sound Definitions and Ranges

• Continuous Rapid Movements
  • Vibrations traveling through air or water.
• Properties
  • Amplitude, wavelength, period, and frequency.
• Frequencies
  • Infrasound: Less than 20 Hz.
  • Ultrasound: More than 20 kHz.

Ultrasound Production

• Transducers
  • Convert electrical current to ultrasound waves.
  • Convert ultrasound waves to sinusoidal electric current.
  • Convert magnetic field into stress waves.
• Types
  • Piezoelectric transducers
  • Magnetostrictive transducers.

Piezoelectric Transducers

• Material
  • Ferroelectric materials
• Ferroelectricity
  • Ability to have a spontaneous electric polarization.
  • Polarization can be reversed by applying an external electric field.

Doppler Method Measurement

• Moving Reflector
  • Using the Doppler frequency shift of waves to measure the reflector's velocity.
• Doppler Effect
  • Change in frequency of a wave in relation to an observer who is moving relative to the wave source.

Pulse-Reverb Methods

• Reflection Strength
  • Higher from tissues with high elasticity.
• Tissue Density Variation
  • While soft tissues (adipose, kidney, liver, brain) densities aren't very disparate, tissues high in elastic traits from high in collagen content reflect more ultrasound. Thus, the pulse amplitude reflected from these tissues is high.

B-Scan

• Production
  • Produces a cross-sectional view of eye and orbit.
• Usage
  • Used to see inside the eye when media is hazy (cataract or corneal opacity).

Visible Light Imaging (Endoscopy)

• Methods
  • Examination by inspection, palpation, percussion, and auscultation.
• Total Reflection
  • If the angle of incidence of light is greater than the boundary angle, all light is reflected and returned to the original environment.

Laparoscopic Surgery

• Intervention
  • Second, third, or fourth entrance channels can be opened outside the body.
• Technique
  • Modern surgical approach called minimally invasive surgery, bandaid surgery, or keyhole surgery.

Medical Applications

• ARTHROSCOPY
• HYSTEROSCOPY/UTEROSCOPY/PELVISCOPY/AMNIOSCOPY/FETOSCOPY
• SYNOSCOPY/NASOPHARYNGOSCOPY
• GASTRODUODENOSCOPY/ESOPHAGOSCOPY
• COLONOSCOPY
• CYSTOSCOPY
• URETEROSCOPY/NEPHROSCOPY
• BRONCHOSCOPY
• THORACOSCOPY
• LARINGO-TRACHEOSCOPY

Ionizing Radiation

• Form of energy removing electrons from atoms and molecules in materials like air, water, and living tissue.

Natural Sources

• Radon:Natural radioactive gas found in rock formations, posing health risks and is the second leading cause of lung cancer in the United States.

Manmade Sources

• Medical Diagnostic Exams
  • Patients can track number and type of medical diagnostic exams received regularly.
• Non-Ionizing Diagnostic Exams
  • Endoscope, Magnetic Resonance Imaging (MRIs) and Ultrasound (US) technology are examples of diagnostic exams that do not involve exposure to ionizing radiation.

Radioactive Isotopes

• Release of Radiation
  • Atoms expel energy from the nucleus, altering its composition to reach a more stable state, known as radioactive decay.

Measuring Radiation Dose

• Alarming Dosimeters
  • Used by first responders and safety officers to monitor dose in real time.
• Specialized Instruments
  • Used by hospitals and laboratories to measure dose.

Computerized Tomography (CT)

• Shadow Image
  • Obtained from the attenuated areas on the body in a single plane of radiography (x-ray).
• Anatomical Structures Arrangement
  • Stacked on top of each other, forming a flat radiographic image.

Magnetic Resonance Imaging (MRI)

• Definition
  • Non-invasive, multi-slice imaging technique for superficial and deep anatomical structures.
• Use
  • Often used for disease detection, diagnosis, and treatment monitoring.
• Mechanism
  • Excites and detects changes in the direction of the rotational axis of protons found in the water of living tissues.
• Functional MRI (fMRI)
  • Observes brain structures and determines which areas activate (consume more oxygen) during cognitive tasks.
  • Advances the understanding of brain organization and offers a potential new standard for assessing neurological status and neurosurgical risk.