Central Nervous System: Organization, Brain Structures, and Spinal Reflexes

Comprehensive practice flashcards detailing the anatomical organization, functional divisions, subcortical centers, memory mechanisms, sleep architecture, and spinal reflexes of the human central nervous system.

Afferent Division

The subdivision of the peripheral nervous system that carries information from sensory and visceral stimuli in the periphery toward the central nervous system.

Efferent Division

The subdivision of the peripheral nervous system that transmits regulatory impulses from the central nervous system out to effector organs (muscles and glands).

Somatic Nervous System

The branch of the efferent division made up of motor neurons that supply skeletal muscles under voluntary control.

Autonomic Nervous System

The involuntary branch of the efferent division supplying smooth muscle, cardiac muscle, exocrine glands, and some endocrine glands; subdivided into the sympathetic and parasympathetic nervous systems.

Enteric Nervous System

An extensive nerve network located entirely within the digestive tract that controls digestive organs independently or in conjunction with autonomic inputs.

Astrocytes

Glial cells that physically support neurons in proper spatial alignment, induce blood-brain barrier formation, take up excess $K^+$ and released neurotransmitters (glutamate and GABA), and form neural scar tissue.

Oligodendrocytes

Glial cells responsible for forming myelin sheaths around neuronal axons within the central nervous system.

Microglia

Specialized immune-defense glial cells in the central nervous system that act as phagocytic scavengers and release nerve growth factor.

Ependymal Cells

Glial cells that line the internal fluid-filled cavities (ventricles and central canal) of the brain and spinal cord, contribute to cerebrospinal fluid production, and act as neural stem cells.

Choroid Plexuses

Vascular structures formed by projections of pia mater and ependymal cells dipping into the ventricles that continuously produce cerebrospinal fluid.

Arachnoid Villi

Specialized projections of the arachnoid mater that penetrate into the dural venous sinuses to reabsorb cerebrospinal fluid from the subarachnoid space back into the venous circulation.

Blood-Brain Barrier (BBB)

A physiological barrier formed by brain capillary endothelial cells joined by impermeable tight junctions with no pores, shielding brain tissue from non-lipid-soluble substances in the blood.

Circumventricular Organs (CVOs)

Specialized regions of the brain, including parts of the hypothalamus, where the blood-brain barrier is modified or limited to allow monitoring of systemic blood composition.

Occipital Lobe

The posterior lobe of the cerebral cortex housing the primary visual cortex surrounded by higher-order visual cortex, responsible for visual processing.

Temporal Lobe

The lateral lobe of the cerebral cortex containing the primary auditory cortex and higher-order auditory cortex, responsible for hearing sensation and processing.

Parietal Lobe

The lobe of the cerebral cortex located behind the central sulcus that houses the somatosensory cortex responsible for processing somesthetic sensation and proprioception.

Frontal Lobe

The anterior lobe of the cerebral cortex responsible for voluntary motor control (primary motor cortex), speech formation (Broca's area), and elaboration of thought and planning.

Broca's Area

A motor speech region located in the frontal lobe responsible for speech formation and speaking ability.

Wernicke's Area

A language area situated at the junction of the parietal, temporal, and occipital lobes responsible for speech comprehension and understanding.

Prefrontal Association Cortex

An anterior cortical association region responsible for planning voluntary activity, decision making, predicting consequences, and expressing personality traits.

Parietal-Temporal-Occipital Association Cortex

A cortical association area that pools and integrates somatic, auditory, and visual sensory inputs, playing a key role in language processing.

Limbic Association Cortex

A cortical region located mostly on the inner and bottom surface of the temporal lobe, involved in motivation, emotion, and memory.

Basal Nuclei

Subcortical gray matter masses—including the caudate nucleus, putamen, globus pallidus, and claustrum—that coordinate slow sustained movements, inhibit resting muscle tone, and suppress unwanted movement patterns.

Thalamus

A large diencephalic relay station that filters and directs all incoming synaptic input (except olfactory) to the cerebral cortex, contributes to motor control, and provides crude sensation awareness.

Hypothalamus

A central homeostatic regulating center of the brain controlling body temperature, thirst, urine output, food intake, the autonomic nervous system, endocrine secretion, and the sleep-wake cycle.

Limbic System

A functional ring of interconnected forebrain structures—including the amygdala, hippocampus, and hypothalamus—that controls emotions, basic survival behavioral patterns, and memory formation.

Short-Term Memory

A memory storage mechanism with immediate acquisition, limited capacity, and short duration (seconds to hours) that involves transient synaptic modifications such as altering neurotransmitter release.

Long-Term Memory

A stable memory storage system of very large capacity and long duration (days to years) that involves permanent structural and functional alterations between neurons, such as the formation of new synapses and protein synthesis.

Memory Consolidation

The process by which short-term memory traces are gradually converted into permanent, structurally encoded long-term memory stores, enhanced by rehearsal or practice.

Long-Term Potentiation (LTP)

A prolonged strengthening of synaptic transmission resulting from high-frequency activity, mediated by glutamate binding to AMPA and NMDA receptors, magnesium removal, calcium influx, and retrograde nitric oxide release.

Memantine (Namenda)

A non-competitive NMDA receptor channel blocker used to prevent glutamate-induced calcium overload and neuronal excitotoxicity.

Functional Divisions of the Cerebellum

Three functionally distinct cerebellar regions: green indicates the vestibulocerebellum (balance and eye movements), purple indicates the spinocerebellum (muscle tone and skilled movement coordination), and blue indicates the cerebrocerebellum (planning voluntary movements and procedural memories).

Vestibulocerebellum

The functional division of the cerebellum critical for the maintenance of balance, equilibrium, and the control of eye movements (including prevention of nystagmus).

Spinocerebellum

The functional division of the cerebellum that coordinates skilled voluntary muscle movements, regulates resting muscle tone, and processes proprioceptive feedback about body position.

Cerebrocerebellum

The functional division of the cerebellum that interacts with the motor cortex to plan and initiate voluntary activities and store procedural memories.

Medulla Oblongata

The lowest brain stem component housing vital centers for cardiovascular and respiratory regulation, swallowing and salivation reflexes, and the chemoreceptor trigger zone (CTZ).

Pons

The middle section of the brain stem containing respiratory centers, cardiovascular control circuits, and pathways involved in analgesia.

Reticular Activating System (RAS)

A diffuse network of ascending neurons originating in the brain stem reticular formation that projects to the thalamus and widely alerts, activates, and arouses the cerebral cortex.

Vagus Nerve (Cranial Nerve X)

A major mixed cranial nerve originating in the brain stem that provides extensive parasympathetic motor innervation to thoracic and abdominal organs and carries sensory signals from them.

Slow-Wave Sleep

Sleep characterized by slow waves on an EEG, preserved muscle tone, minor drops in heart rate and blood pressure, rare dreaming, and comprising $80\%$ of sleeping time across four distinct stages.

Paradoxical Sleep (REM Sleep)

A sleep state comprising $20\%$ of sleep characterized by rapid eye movements, an EEG pattern resembling an alert awake person, abrupt skeletal muscle inhibition (atonia), irregular vitals, and vivid dreaming.

Dorsal Horn

The posterior gray matter column of the spinal cord containing the cell bodies of interneurons on which afferent sensory neurons terminate.

Lateral Horn

The thoracic and lumbar spinal gray matter projection containing the cell bodies of autonomic efferent preganglionic nerve fibers.

Ventral Horn

The anterior gray matter column of the spinal cord containing the cell bodies of somatic efferent motor neurons supplying skeletal muscles.

Dorsal Columns

Ascending spinal cord tracts that transmit conscious proprioception (muscle sense regarding body position) along with crossed touch, pressure, and vibration sensations to the brain.

Lateral Corticospinal Tract

A prominent descending white matter motor tract that crosses in the brain stem to transmit conscious voluntary motor commands to skeletal muscles.

Dorsal Spinocerebellar Tract

An uncrossed ascending white matter tract carrying unconscious muscle proprioceptive signals to the cerebellum to help regulate posture and muscle tone.

Reflex Arc

The anatomical pathway mediating a reflex action, consisting of a sensory receptor, an afferent pathway, an integrating center (CNS), an efferent pathway, and an effector organ.

Withdrawal Reflex

A polysynaptic protective spinal reflex where painful stimulation activates afferent pathways to stimulate ipsilateral flexor muscles (and inhibit extensor muscles), pulling the injured limb away from harm.

Crossed Extensor Reflex

A contralateral spinal reflex initiated during a withdrawal reflex where extensor muscles of the opposite limb contract and flexors relax, enabling the opposite extremity to support body weight.

Patellar Tendon Reflex

A monosynaptic stretch reflex triggered by tapping the patellar tendon, which stretches muscle spindles in the quadriceps femoris and directly activates alpha motor neurons to extend the knee.