Neuroscience Terms Starting With F
Neuroscience Glossary: F
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Fight or Flight Response
/ fyt or flyt ree-SPONS / · Old English feohtan + fleon + Latin responsio
Fight or Flight Response is the rapid physiological reaction to perceived threat, triggered by the sympathetic nervous system and adrenal hormones to prepare the body for vigorous physical action.
Described by Walter Cannon in 1915, the fight-or-flight response begins in the amygdala, which sends alarm signals to the hypothalamus, activating the sympathetic nervous system and triggering adrenaline release from the adrenal medulla. Within seconds, heart rate increases, pupils dilate, bronchioles widen for greater oxygen intake, blood is diverted from digestion to skeletal muscles, and glucose is released from the liver. The response evolved for acute physical threats but is also triggered by psychological stressors, contributing to chronic stress-related health problems including hypertension and immune suppression when activation becomes prolonged.
Cortisol, released more slowly from the adrenal cortex over minutes to hours, sustains the metabolic changes initiated by adrenaline and helps restore homeostasis once the threat passes.
The fight-or-flight response can be activated by merely imagining a threatening scenario. The brain's threat-detection circuitry responds to symbolic and anticipated threats as well as physically present ones, which is why vivid mental rehearsal of a feared event can produce measurable increases in heart rate and skin conductance.
The fight-or-flight response does not always produce fighting or fleeing. Freezing, orienting, scanning, and other defensive behaviors can also occur during acute stress, depending on the nature and proximity of the perceived threat.
Adrenaline released during the fight-or-flight response enhances memory consolidation of emotionally significant events by activating beta-adrenergic receptors in the amygdala. In human studies, beta-blockers given within several hours of trauma can weaken later physiological fear responses, showing that stress hormones shape memory persistence during a narrow post-event window.
Forebrain
/ FOR-brayn / · From Old English fore, meaning front or before, plus brain, from Proto-Germanic braginam.
Forebrain is the largest and most anterior division of the vertebrate brain, comprising the cerebrum, thalamus, hypothalamus, and limbic system, and governing higher cognitive, sensory, and regulatory functions.
The forebrain represents approximately 85 percent of total brain mass in adult humans and governs higher cognitive functions including reasoning, emotion, and sensory processing. During embryonic development, it arises from the prosencephalon, the most anterior of three primary brain vesicles that appear around the third week of gestation. Within the forebrain, the cerebral cortex alone contains roughly 16 billion neurons organized into six distinct layers, each with characteristic cell types and long-range connectivity.
Dramatic expansion of forebrain tissue during primate evolution, particularly in the prefrontal areas, underlies the executive function and complex social behavior that distinguish humans from other mammals. Extensive reciprocal connections between the forebrain and lower brainstem structures coordinate voluntary motor responses with autonomic and homeostatic regulation.
The human forebrain continues developing well into the mid-twenties, with the prefrontal cortex being among the last regions to fully mature. This extended developmental timeline explains why adolescents often exhibit impulsive behavior and difficulty with long-term planning.
The forebrain and cerebrum are not identical structures. The forebrain includes several components beyond the cerebrum, such as the thalamus, hypothalamus, and epithalamus, each with distinct functions in sensory relay, hormone regulation, and circadian timing.
In bottlenose dolphins (Tursiops truncatus), the forebrain shows exceptional development of auditory processing regions related to echolocation. Some auditory cortical fields are proportionally enlarged by several-fold compared with visual fields, reflecting the animal's dependence on sonar for navigation and prey detection.
Free Nerve Ending
/ FREE NURV EN-ding / · Free from Latin liber, meaning unbound; nerve from Latin nervus, meaning sinew; ending from Old English endung, meaning conclusion.
Free Nerve Ending is an unencapsulated sensory receptor consisting of bare axon terminals found throughout the skin and internal tissues, detecting pain, temperature, itch, and crude touch by responding to mechanical, thermal, or chemical stimuli.
Free nerve endings represent the most abundant type of sensory receptor in the human body, with particularly high densities in the skin, cornea, and dental pulp. Unlike encapsulated receptors such as Meissner’s corpuscles, these receptors lack specialized accessory structures and arise from thinly myelinated A-delta fibers, which signal sharp fast pain, and unmyelinated C fibers, which signal slow burning pain. The cornea contains approximately 7,000 free nerve endings per square millimeter, making it one of the most densely innervated tissues in the body.
These receptors respond to mechanical deformation, extreme temperatures ranging from below 15 degrees Celsius to above 45 degrees Celsius, and chemical irritants released during tissue damage, including bradykinin and prostaglandins. Transient receptor potential channels such as TRPV1 detect both capsaicin and noxious heat, explaining why chili peppers produce a burning sensation indistinguishable from thermal injury.
Free nerve endings can become sensitized after injury, lowering their activation threshold so that normally innocuous stimuli like light touch feel painful. This phenomenon, called allodynia, affects millions of people with chronic pain conditions including fibromyalgia and postherpetic neuralgia.
Free nerve endings only detect pain. These receptors also sense temperature changes, itch, and certain forms of pleasurable touch, with C-tactile afferents responding preferentially to gentle stroking at velocities of 1 to 10 centimeters per second.
The star-nosed mole (Condylura cristata) concentrates more than 25,000 minute sensory receptors, including free nerve endings, across the 22 fleshy appendages of its nasal star. Each appendage is roughly 1 millimeter wide, yet this North American mammal processes tactile information fast enough to identify and consume prey items in under 230 milliseconds.
Frontal Lobe
/ FRUN-tul lohb / · Latin frontalis (of the forehead) + Greek lobos
Frontal Lobe is the anterior region of each cerebral hemisphere, governing voluntary movement, executive function, decision-making, working memory, language production, and the regulation of social behavior and personality.
The frontal lobe contains the primary motor cortex in the precentral gyrus, which controls voluntary movement through a precise topographic map of the body, the premotor cortex coordinating complex motor sequences, and the prefrontal cortex supporting planning, working memory, and decision-making. Broca’s area, located in the left inferior frontal gyrus in most right-handed individuals, is dedicated to speech production, and damage there produces Broca’s aphasia, in which patients understand language but cannot produce fluent speech. Phineas Gage, a railroad worker who survived an iron tamping rod passing through his prefrontal cortex in 1848, exhibited dramatic personality changes and impulsive decision-making, providing early evidence that frontal cortex damage alters judgment and social behavior.
The prefrontal cortex is proportionally larger in humans than in any other primate and shows protracted development into the mid-twenties, explaining adolescent difficulty with impulse control and future planning.
The prefrontal cortex, the region directly behind the forehead, is not fully mature until around age 25. Adolescents show greater risk-taking and weaker impulse control than adults partly because the long-range white matter connections linking the prefrontal cortex to subcortical structures are still being myelinated during this period.
The frontal lobe is not only involved in rational thought. It also drives emotional processing, social judgment, and moral reasoning, with damage producing dramatic personality changes alongside cognitive deficits, as documented in patients with frontotemporal dementia.
Patients with damage to the right orbitofrontal cortex, a ventral region of the frontal lobe, show impaired decision-making on the Iowa Gambling Task even when their general intelligence remains intact. In studies by Antonio Damasio and colleagues in the 1990s, such patients continued choosing high-reward but ultimately losing card decks, failing to learn from negative feedback across hundreds of trials.