Biological Bases Quiz 2 V3

Site of Action

Drugs interact with specific receptors or cellular targets (e.g., neurotransmitters, enzymes) to exert effects.

Excretion Pathways

The routes through which drugs are eliminated from the body.

Primary route

Kidneys, via glomerular filtration, tubular secretion, and reabsorption.

Lipid-soluble drugs

Rapidly absorbed across cell membranes (e.g., brain penetration).

Water-soluble drugs

Require transporters for absorption; excreted more efficiently by kidneys.

Metabolism

The liver is the primary site, using cytochrome P-450 (CYP450) enzymes for Phase I (oxidation, hydrolysis) and Phase II (glucuronidation) reactions.

Dose-Response Curve

Plots drug dose (x-axis) vs. biological response (y-axis).

Efficacy

Maximum effect a drug can produce (e.g., full vs. partial agonists).

Potency

Dose required to produce 50% of maximal effect (ED~50~); higher affinity = lower ED~50~.

Therapeutic Index (TI)

Ratio of toxic dose (TD~50~) to effective dose (ED~50~).

High TI

Wider safety margin (e.g., penicillin).

Low/Narrow TI

Requires careful monitoring (e.g., warfarin).

Drug Affinity

Strength of drug-receptor binding. High affinity = potent effect (e.g., fentanyl vs. morphine).

Agonists

Activate receptors, mimicking endogenous ligands (e.g., morphine at μ-opioid receptors).

Antagonists

Block receptor activation (e.g., naloxone reversing opioid overdose).

Full agonists

Maximal response.

Partial agonists

Submaximal response.

Competitive antagonists

Reversible binding.

Non-competitive antagonists

Irreversible binding.

Clinical Example of Agonists

Dopamine agonists (e.g., levodopa for Parkinson's).

Clinical Example of Antagonists

Antipsychotics (e.g., haloperidol blocking dopamine D2 receptors).

Antipsychotics

Medications like haloperidol that block dopamine D2 receptors.

Affinity

Determines binding strength of a drug to its receptor.

Efficacy

Determines the activation of a receptor by a drug.

Inverse Agonists

Compounds that stabilize receptors in inactive states, such as antihistamines reducing constitutive activity.

Drug Action

Depends on solubility, metabolism, and excretion pathways.

Lipid-soluble drugs

Favor brain penetration and renal excretion dominates elimination.

Dose-response curves

Quantify the efficacy and potency of drugs.

Therapeutic index

Evaluates the safety of a drug.

Agonists

Activate receptors, providing effects like pain relief.

Antagonists

Block receptors, used for reversing overdoses.

Stereotaxic Brain Surgery

A method for precisely targeting brain areas for research or treatment.

Bregma

The anatomical landmark for aligning stereotaxic coordinates in the skull.

Deep brain stimulation

A procedure involving the implantation of electrodes for conditions like Parkinson's.

Neurotransmitter studies

Involves injecting drugs/chemicals into specific brain regions.

Targeted lesions

Created to study effects like hippocampal damage and memory loss.

Stereotaxic atlas

A tool used to map 3D brain coordinates.

fMRI (Functional Magnetic Resonance Imaging)

Detects blood-oxygen-level-dependent (BOLD) signals related to neural activity.

BOLD signals

Reflect changes in blood flow and oxygenation linked to neural activity.

High spatial resolution

fMRI provides spatial resolution of approximately 1-2 mm.

Poor temporal resolution

fMRI has a temporal resolution in seconds, not milliseconds.

EEG (Electroencephalogram)

Measures electrical activity of the brain via scalp electrodes.

High temporal resolution

EEG can detect changes in brain activity in milliseconds.

Low spatial resolution

EEG cannot pinpoint exact sources of electrical activity.

Clinical Use of fMRI

Used for pre-surgical brain mapping and studying disorders like schizophrenia.

Clinical Use of EEG

Diagnosing epilepsy and monitoring coma patients.

PET (Positron Emission Tomography)

A medical imaging technique that tracks radioactive tracers to visualize metabolic and neurochemical activity.

Mechanism

Tracks radioactive tracers (e.g., fluorodeoxyglucose for glucose metabolism).

Strengths

Measures neurotransmitter activity (e.g., dopamine with raclopride) and visualizes metabolic/functional changes (e.g., Alzheimer's hypometabolism).

Limitations

Invasive (radiation exposure) and lower resolution than fMRI.

Clinical Use

Used in oncology for tumor detection and neurodegenerative disease research.

fMRI

Functional Magnetic Resonance Imaging, measures blood flow changes (BOLD) with high spatial and low temporal resolution, used for cognitive tasks and clinical brain mapping.

EEG

Electroencephalography, measures electrical activity with high temporal and low spatial resolution, used for epilepsy monitoring and sleep studies.

Clinical Connections

Links between case studies and research, illustrating how EEG and PET help diagnose conditions like visual agnosia.

Sensory Transduction

The conversion of external stimuli (e.g., light, sound, touch) into action potentials via specialized receptors.

Vision

Photons activate photoreceptors (rods/cones) in the retina, triggering a biochemical cascade that generates neural signals.

Audition

Hair cells in the cochlea convert sound vibrations into electrical signals.

Clinical Relevance

Damage to transduction mechanisms causes disorders like blindness (retinal degeneration) or deafness (hair cell loss).

Lens

Adjusts curvature (accommodation) to focus light onto the retina.

Myopia/Hyperopia

Lens shape abnormalities cause nearsightedness (myopia) and farsightedness (hyperopia).

Retina

The light-sensitive layer at the back of the eye that contains photoreceptors.

Rods

120 million cells in the retina; sensitive to low light (scotopic vision) and absent in the fovea.

Cones

6 million cells in the retina; detect color (photopic vision) and fine detail, concentrated in the fovea.

Macular degeneration

A condition that impairs cones in the retina, affecting vision.

Retinal Processing

Horizontal and amacrine cells integrate signals before transmission to the optic nerve.

Horizontal cells

Cells in the retina that integrate signals from photoreceptors.

Amacrine cells

Cells in the retina that integrate signals before they are sent to the optic nerve.

Optic nerve

The nerve that transmits visual information from the retina to the brain.

Neurotransmitter activity

The release and action of chemical messengers in the brain, such as dopamine.

Alzheimer's hypometabolism

A condition characterized by reduced metabolic activity in the brain associated with Alzheimer's disease.

Lateral Geniculate Nucleus (LGN)

Relays visual information from the retina to the primary visual cortex (V1) while filtering irrelevant data.

Parvocellular

Processes color, fine details, and static form.

Magnocellular

Detects motion, spatial patterns.

Striate Cortex (V1)

Located in the occipital lobe; processes orientation, edges, and spatial frequency.

Cortical blindness

Damage to V1 causes this condition, exemplified by blindsight.

Extrastriate Cortex (V2-V5)

Integrates V1 outputs for complex perception.

Dorsal ("Where") Pathway

Route: V1 → MT/V5 (middle temporal area) → parietal lobe; Function: Spatial awareness, motion detection.

Akinetopsia

Motion blindness resulting from damage to MT.

Ventral ("What") Pathway

Route: V1 → V4 → fusiform face area (FFA) → temporal lobe; Function: Object/face recognition, color processing.

Prosopagnosia

Face blindness due to damage in the fusiform face area (FFA).

Motion Perception

MT/V5 is the key area for detecting direction/speed of movement.

Depth Cues

Various signals used to perceive depth in vision.

Binocular Disparity

Differing retinal images that contribute to 3D perception.

Motion Parallax

Nearby objects move faster than distant ones.

Perspective

Parallel lines converge with distance.

Clinical Case

Sacks' The Man Who Mistook His Wife for a Hat describes patients with impaired depth perception due to parietal lobe lesions.

Transduction

The initial process of converting light into neural signals in photoreceptors.

Dorsal Stream

Guides spatial navigation.

Ventral Stream

Enables object recognition.

Specialized cortical areas

Regions like MT/V5 are critical for motion and depth perception.

Modular organization of visual processing

Disorders like prosopagnosia or akinetopsia illustrate this concept.

Acquired Prosopagnosia

Results from brain damage to the right occipitotemporal cortex, often due to stroke, traumatic brain injury, or neurodegenerative diseases.

Developmental Prosopagnosia

A congenital form (present from birth) linked to genetic factors or atypical development of the FFA.

Fusiform Gyrus (FFA)

Integrates facial features into a cohesive whole; damage here disrupts holistic face processing, forcing reliance on piecemeal feature analysis.

Functional MRI Studies

Show reduced FFA activation in prosopagnosics, impairing their ability to distinguish faces from objects.

Symptoms of Prosopagnosia

Inability to recognize family, friends, or oneself in mirrors.

Compensatory Strategies

Identifying people by voice, gait, or clothing.

Preserved Abilities

Recognizing facial expressions and emotions under optimal conditions.

Visual Agnosia

Dr. P exhibited impaired object and face recognition despite intact vision.

Neurological Basis of Dr. P's Condition

Likely damage to the right fusiform gyrus, disrupting holistic visual processing.