Brain Bee Prep

Competition Flashcards

Total Neuron and Glial Cell Population in the Human Brain

Approximately $86\text{ billion}$ neurons and roughly an equal number ($1:1$ ratio, $\sim 86\text{ billion}$) of non-neuronal glial cells.

Corpus Callosum

The thick white-matter tract spanning the longitudinal fissure that connects the left and right cerebral hemispheres to enable bilateral communication.

Frontal Lobe (Primary Functions)

The anterior cortical region responsible for motor planning, executive decision-making, working memory, impulse regulation, and speech production (Broca's area).

Parietal Lobe (Primary Functions)

The cortical region posterior to the central sulcus that houses the primary somatosensory cortex and integrates spatial, sensory, and bodily orientation data.

Temporal Lobe (Primary Functions)

The ventrolateral cortical region that houses the primary auditory cortex, structures for language comprehension (Wernicke's area), and medial structures for memory (hippocampus) and emotion (amygdala).

Occipital Lobe (Primary Functions)

The posterior cortical region dedicated to decoding and processing visual stimuli, including the primary visual cortex (V1 / striate cortex).

Thalamus

The major diencephalic relay station that filters and directs incoming sensory signals to their respective primary cortices, bypassing only olfaction (smell).

Hypothalamus

The ventral diencephalic structure regulating the autonomic nervous system and endocrine output via the pituitary gland (controlling body temperature, circadian rhythms, hunger, thirst, and hormone release).

Basal Ganglia

A set of interconnected subcortical nuclei (including the caudate, putamen, and globus pallidus) that coordinates voluntary motor control, habit learning, and movement initiation.

Cerebellum (Function & Lesion Deficit)

The hindbrain structure coordinating fine motor timing, posture, and motor learning; damage causes ataxia, dysmetria, and an irregular gait.

Medulla Oblongata

The caudal brainstem structure housing essential autonomic reflex centers that maintain heart rate, vascular tone, and respiration.

Pyramidal Cells

The predominant excitatory projection neurons in the mammalian cerebral cortex, accounting for roughly $80\%$ of cortical neurons and utilizing glutamate.

Astrocytes

Star-shaped glial cells that maintain the blood-brain barrier, regulate extracellular potassium, clear excess synaptic glutamate, and provide metabolic support to neurons.

Oligodendrocytes vs. Schwann Cells

Oligodendrocytes produce myelin sheaths around multiple axons in the CNS; Schwann cells produce myelin around a single axon segment in the PNS.

Microglia

The resident immune defense cells and phagocytes of the CNS that clear cellular debris, pathogens, and prune redundant synapses.

Ependymal Cells

Specialized ciliated glial cells that line the ventricles of the brain and central canal of the spinal cord, assisting in the production and circulation of cerebrospinal fluid (CSF).

Resting Membrane Potential (Value & Maintenance)

Typically around $-70\,\text{mV}$; established by passive $\text{K}^+$ leak channels and actively maintained by the $\text{Na}^+/\text{K}^+$ ATPase pump (pumping $3\,\text{Na}^+$ out for every $2\,\text{K}^+$ in).

Action Potential Phases & Ion Movements

Depolarization is caused by rapid influx of $\text{Na}^+$ through voltage-gated $\text{Na}^+$ channels; repolarization is driven by outward flux of $\text{K}^+$ through voltage-gated $\text{K}^+$ channels.

Synaptic Vesicle Exocytosis Trigger

Depolarization of the presynaptic terminal opens voltage-gated calcium ($\text{Ca}^{2+}$) channels; the resulting influx of $\text{Ca}^{2+}$ binds to synaptotagmin to trigger SNARE-mediated vesicle fusion.

Kinesin vs. Dynein

Kinesin mediates anterograde axonal transport (from soma toward synaptic terminal); dynein mediates retrograde axonal transport (from terminal back toward soma).

Glutamate Receptors (AMPA vs. NMDA)

AMPA mediates fast EPSPs permeable to $\text{Na}^+$ and $\text{K}^+$; NMDA is permeable to $\text{Ca}^{2+}$ and $\text{Na}^+$, possesses a voltage-dependent $\text{Mg}^{2+}$ block at resting potential, and is critical for long-term potentiation (LTP).

GABA_A Receptor Mechanism

An ionotropic receptor that, upon GABA binding, opens integral chloride ($\text{Cl}^-$) channels; inward $\text{Cl}^-$ flux hyperpolarizes the membrane, driving an inhibitory postsynaptic potential (IPSP).

Ionotropic vs. Metabotropic Receptors

Ionotropic receptors are ligand-gated ion channels that produce immediate, millisecond-scale potential changes; metabotropic receptors are G-protein coupled receptors (GPCRs) that modulate downstream second-messenger cascades (e.g., cAMP, IP3) over longer durations.

Small-Molecule vs. Neuropeptide Neurotransmitter Synthesis

Small-molecule transmitters (ACh, dopamine, GABA) are synthesized and packaged directly in axon terminals; neuropeptides are synthesized as precursor proteins in the soma's rough ER and transported down the axon.

Endocannabinoids

Retrograde lipid-derived messengers (e.g., anandamide, 2-AG) synthesized on-demand postsynaptically that travel backward across the synaptic cleft to bind presynaptic CB1 receptors and inhibit further neurotransmitter release.

Alpha vs. Delta EEG Waves

Alpha waves ($8-13\,\text{Hz}$) typify awake, relaxed states with closed eyes; Delta waves ($< 3.5\,\text{Hz}$) are high-amplitude slow waves characteristic of deep Stage 3 (N3) slow-wave sleep.

Feedback Inhibition

A microcircuit motif where an active excitatory principal neuron stimulates an inhibitory local interneuron, which in turn synapses back onto the originating cell to suppress its firing.

Anterior Commissure

A distinct transverse tract of white matter connecting the middle and inferior temporal gyri across hemispheres, operating alongside the corpus callosum.

Cortical Columns

Vertical repeating modules spanning all six cortical layers that process specific sensory inputs or computational features as unified microcircuits.

Tay-Sachs Disease (Pathophysiology)

An autosomal recessive lysosomal storage disease caused by mutations in the HEXA gene (beta-hexosaminidase A), resulting in toxic buildup of GM2 gangliosides in neurons.

Cortical Area Devoted to Vision

Approximately $30\%$ of the human cerebral cortex is involved in processing visual information.

Total Photoreceptor Count & Proportion of Rods

Each human eye contains approximately $125\text{ million}$ photoreceptors, with rods comprising about $95\%$ of the total population.

Fovea (Photoreceptor Distribution)

The central specialized pit of the retina containing an exclusively high density of red and green cones, lacking rods and blue cones.

Macula

The central area of the retina surrounding the fovea responsible for high-acuity central vision; macular degeneration is a leading cause of blindness in adults older than $55$.

Retinal Center-Surround Antagonism

The receptive field organization of bipolar and ganglion cells that accentuates edges and optimizes contrast perception by contrasting a center receptive field against an opposing ring.

Physiological Blind Spot

The region of the retina where ganglion cell axons converge to form the optic nerve and exit the eye, creating a visual field gap due to the complete absence of photoreceptors.

Optic Chiasm (Axon Decussation Pattern)

The visual crossing where axons originating from the nasal retinas cross (decussate) to the contralateral hemisphere, while temporal retinal fibers stay uncrossed on the ipsilateral side.

Lateral Geniculate Nucleus (LGN)

The specialized sensory relay nucleus within the thalamus that receives input from retinal ganglion cells and projects directly to the primary visual cortex (V1).

Middle Layer of Primary Visual Cortex (Layer IV)

The specific cortical layer in V1 that receives direct thalamic projections from the LGN, preserving the precise retinotopic map of the visual field.

Dorsal vs. Ventral Visual Streams

The dorsal stream ("where/how" pathway) extends into the parietal lobe to process motion and spatial location; the ventral stream ("what" pathway) projects into the temporal lobe to decode shape, color, and object identity.

Strabismus & Critical Period for Vision

A condition where misaligned eyes prevent binocular image fusion; if left uncorrected before approximately age $8$, functional vision in the suppressed eye is permanently lost (amblyopia).

Auditory Ossicles (Sequence of Transmission)

Sound vibrations pass sequentially from the tympanic membrane through the malleus (hammer), incus (anvil), and stapes (stirrup) onto the oval window.

Tonotopic Organization of the Basilar Membrane

High-frequency sound vibrations are detected near the narrow, stiff base close to the oval window; low-frequency sound waves travel to the wider, more flexible apex.

Auditory Hair Cell Transduction

Sound vibrations deflect hair cell stereocilia against the overlying tectorial membrane, physically opening mechanically gated potassium ($\text{K}^+$) channels to depolarize the cell.

Wernicke's Aphasia

A receptive language deficit caused by damage to Wernicke's area in the left temporal lobe, characterized by fluent but meaningless speech and severely impaired language comprehension.

Adult Olfactory Neurogenesis

Olfactory receptor neurons are specialized bipolar sensory cells that are continuously replaced throughout adulthood via stem cell differentiation in the olfactory epithelium.

Olfactory Projection Pathway

The sensory modality that bypasses the thalamus; olfactory receptor axons project directly through the cribriform plate to the olfactory bulb, which synapses straight onto the primary olfactory cortex and limbic structures.

Olfactory Sniff Identification Speed

Human behavioral testing demonstrates that the brain can identify an odor within as little as $110\,\text{ms}$ after an initial sniff.

Taste Bud Population & Cranial Nerves

Humans possess roughly $5{,}000$ to $10{,}000$ taste buds; gustatory signals are carried to the brainstem via Cranial Nerves VII (Facial), IX (Glossopharyngeal), and X (Vagus).

A-Beta Fibers

Thick, heavily myelinated peripheral sensory nerve fibers that transmit non-painful touch, vibration, and pressure stimuli at high conduction velocities.

Two-Point Discrimination

A clinical test measuring spatial tactile acuity by finding the smallest distance at which two separate cutaneous pressure points are felt individually, reflecting receptive field size and cortical magnification.

Nociceptors

Specialized high-threshold peripheral sensory nerve endings that fire in response to noxious mechanical, thermal, or chemical stimuli capable of causing tissue injury.

A-Delta vs. C Fibers (Pain Transmission)

Myelinated A-delta fibers conduct fast, sharp, localized "first pain"; unmyelinated C fibers slowly transmit diffuse, dull, aching "second pain."

Allodynia vs. Hyperalgesia

Allodynia is the perception of pain produced by a normally innocuous stimulus (e.g., light touch on sunburned skin); hyperalgesia is an exaggerated, heightened pain response to an already noxious stimulus.

Periaqueductal Gray (PAG)

The midbrain region surrounding the cerebral aqueduct that serves as a primary hub for descending endogenous pain modulation, densely populated with endorphin and opioid receptors.

Endogenous Pain Modulation by Cannabinoids

Cannabinoids attenuate the emotional suffering and distress associated with chronic pain primarily by dampening hyperactive neural circuits within the limbic system.

Motor Unit

An individual alpha motor neuron and all the specific skeletal muscle fibers it innervates; represents the basic functional unit of neuromuscular control.

Neuromuscular Junction Neurotransmitter & Receptor

Acetylcholine (ACh), which binds to ionotropic nicotinic acetylcholine receptors on the motor end plate to drive rapid depolarization and muscle contraction.

Muscle Spindles

Intrafusal mechanoreceptors arranged in parallel with skeletal muscle fibers that detect changes in muscle length and rate of stretch.

Golgi Tendon Organs (GTOs)

Sensory receptors located in series at junction points between muscles and tendons that measure muscle tension and contraction force to prevent overload.

Monosynaptic Stretch Reflex Mechanism

Rapid muscle stretch activates group $\text{Ia}$ sensory afferents that synapse directly onto alpha motor neurons in the spinal cord, causing immediate contraction of the stretched agonist muscle (e.g., knee-jerk patellar reflex).

Reciprocal Inhibition

A spinal reflex circuit wherein sensory $\text{Ia}$ afferents stimulate inhibitory interneurons that simultaneously relax the antagonistic muscle while the agonist muscle contracts.

Flexor Withdrawal Reflex

A polysynaptic protective reflex where a painful cutaneous stimulus excites ipsilateral flexor motor neurons to rapidly pull a threatened limb away.

Crossed Extensor Reflex

A contralateral spinal pathway where interneurons cross the midline to excite extensor muscles in the opposite limb, maintaining postural stability when one leg withdraws from pain.

Primary Motor Cortex (M1) Organization

Located in the precentral gyrus of the frontal lobe (Brodmann area $4$) and arranged as a somatotopic motor homunculus, with outsized representation given to hands, fingers, and lips.

Supplementary Motor Area (SMA) vs. Premotor Cortex

The SMA plans internally initiated, complex sequences of voluntary movements, whereas the premotor cortex coordinates motor actions guided by external sensory cues.

Basal Ganglia (Core Nuclei)

Subcortical structures comprising the striatum (caudate nucleus and putamen), globus pallidus (internal and external segments), subthalamic nucleus (STN), and substantia nigra (pars compacta and pars reticulata).

Basal Ganglia Direct Pathway ("Go" Pathway)

Striatal medium spiny neurons directly inhibit the GPi and substantia nigra pars reticulata, releasing the motor thalamus from tonic inhibition and facilitating movement.

Basal Ganglia Indirect Pathway ("Stop" Pathway)

Striatal neurons inhibit the GPe, disinhibiting the subthalamic nucleus; the STN then excites the GPi/SNr to increase inhibitory output onto the thalamus, suppressing unintended movement.

Striatal Dopamine Actions ($D_1$ vs. $D_2$ Receptors)

Dopamine released from the substantia nigra pars compacta binds $D_1$ receptors to excite the direct pathway and $D_2$ receptors to inhibit the indirect pathway, promoting movement initiation.

Parkinson's Disease (Pathology & Classic Triad)

Progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta; clinically presents with bradykinesia, resting tremor, and cogwheel rigidity.

Huntington's Disease (Primary Striatal Loss)

Selective degradation of GABAergic medium spiny neurons projecting along the indirect pathway within the caudate and putamen, causing uncontrollable choreic movements.

Cerebellum (Primary Role in Motor Control)

Acts as a comparator, integrating intended motor commands from the cortex with actual sensory feedback from the periphery to calculate real-time error corrections, timing, and smooth coordination.

Purkinje Cells

Giant, planar neurons with expansive dendritic trees that serve as the sole output of the cerebellar cortex, releasing inhibitory GABA onto deep cerebellar nuclei.

Climbing Fibers vs. Mossy Fibers

Climbing fibers originate exclusively in the inferior olive and form powerful synapses directly on Purkinje cells; mossy fibers originate from widespread pontine and spinal nuclei to excite granule cells.

Cerebellar Ataxia

A coordination disorder resulting from cerebellar damage, marked by clumsy, uncoordinated voluntary movements, dysmetria (overshooting/undershooting targets), and an unsteady, wide-based gait.

Pyramidal (Corticospinal) Decussation

The anatomical crossing of approximately $85\%$ to $90\%$ of descending corticospinal tract axons in the caudal medulla, which causes each cerebral hemisphere to control contralateral body movements.

Central Pattern Generators (CPGs)

Local autonomous neural circuits in the spinal cord and brainstem capable of generating rhythmic, repetitive motor outputs (such as locomotion and breathing) without continuous cortical input or sensory cues.

Upper Motor Neuron (UMN) vs. Lower Motor Neuron (LMN) Lesions

UMN damage produces spastic paralysis, hyperreflexia, and a positive Babinski sign; LMN damage produces flaccid paralysis, severe muscle atrophy, fasciculations, and hyporeflexia.

Amyotrophic Lateral Sclerosis (ALS)

A progressive, fatal neurodegenerative disease marked by the simultaneous death of upper motor neurons in the cortex and lower motor neurons in the brainstem and spinal cord.

Patient H.M. (Henry Molaison)

A landmark patient whose bilateral medial temporal lobectomy (removing sections of his temporal lobes including most of both hippocampi) abated severe seizures but caused permanent anterograde amnesia while leaving intellect, personality, perception, working memory, and motor skill learning intact.

Anterograde Amnesia vs. Retrograde Amnesia

Anterograde amnesia is the inability to convert new short-term experiences into long-term conscious memories; retrograde amnesia is the loss of memories acquired prior to the injury or neurological trauma.

Declarative Memory (Explicit Memory)

Conscious, voluntary recollection of facts, data, and events that can be consciously recalled and described; subdivided into semantic memory and episodic memory.

Semantic Memory

A category of declarative memory that stores culturally shared concepts, ideas, word definitions, and general world facts without personal chronological context.

Episodic Memory

A category of declarative memory representing unique personal autobiographical experiences tied to specific sights, sounds, time, space, and emotions.

Role of the Parahippocampal Region in Declarative Memory

Aids the hippocampus in encoding the "what" of episodic memories, rather than the "where" or "when".

Working Memory

A temporary form of declarative/short-term memory coordinated by the prefrontal cortex (PFC) that maintains and manipulates small sums of information "online" for immediate use before rapid decay occurs.

Prefrontal Cortex (PFC) Activity during Working Memory

PFC neurons fire in bursts/spurts to keep representations active and coordinated across multiple posterior cortical networks while a person concentrates on holding information in mind.

Place Cells

Specialized pyramidal neurons in the hippocampus that selectively increase their firing rates when an individual or animal traverses a specific, familiar spatial location in an environment.

Grid Cells

Spatial coordinate neurons located in the entorhinal cortex that fire at periodic intervals to track an organism's position in space when environmental landmarks or external cues are absent.

Nondeclarative Memory (Implicit / Procedural Memory)

Memory stored and retrieved without conscious effort, supporting learned motor skills, habits, and emotional conditioning (e.g., speech articulation, riding a bicycle, mirror-tracing).

Core Brain Regions for Motor Skill Learning

The basal ganglia (the "habit center"), the prefrontal cortex, and the cerebellum.

Synaptic Plasticity

The ability of synapses to physically and chemically remodel themselves by altering synaptic number, shape, neurotransmitter release, or postsynaptic receptor abundance in response to experience.

Aplysia californica (Sea Slug Model)

A foundational invertebrate model organism studied by neuroscientists to uncover the fundamental chemical and structural synaptic changes underlying simple learning and memory due to its small, easily observable nervous system.

Long-Term Potentiation (LTP)

A persistent, activity-dependent increase in synaptic strength following repetitive stimulation, studied extensively in the hippocampus as the cellular mechanism underlying memory consolidation.

Long-Term Depression (LTD)

An activity-dependent, persistent decrease in synaptic transmission efficacy that weakens less active or inappropriate synaptic connections.