The human milk letdown reflex, a critical neuroendocrine mechanism for neonatal survival, is initiated by the suckling stimulus at the nipple and areola, which are densely innervated cutaneous regions (1, 2, 3). This tactile stimulation activates a complex neural pathway culminating in the pulsatile release of oxytocin from the posterior pituitary gland, leading to the…
Reflexes
Atrial reflex
The atrial reflex, also known as the Bainbridge reflex, is an important neural mechanism which helps maintain cardiovascular homeostasis, providing several key benefits to the body [1]. This reflex is mediated by stretch receptors in the atria which detect changes in blood volume. These receptors send signals via vagal afferent nerves to the nucleus tractus…
Optokinetic nystagmus or optokinetic reflex
Optokinetic nystagmus (OKN) is an involuntary eye movement which occurs when visually tracking a moving object across the visual field. It serves to stabilize images on the retina by keeping the object centered on the fovea, allowing for clear vision [1][3]. OKN has two phases – a slow tracking phase in the direction of motion,…
Laughter
Laughter is a complex vocal expression of positive emotion which is ubiquitous in human behavior. It serves several social functions like diffusing tension and strengthening bonds. Laughter is also pleasurable and activates ancient brain circuits related to reward and social affiliation [1][2][6]. Neuroimaging studies show that humorous stimuli engage key nodes of the brain’s mesolimbic…
Snout reflex
The snout reflex is a primitive reflex observed in infants that facilitates rooting and suckling behaviors [1]. When the infant’s cheek is stroked or tapped near the mouth, it responds by turning its head in that direction and opening its mouth, appearing to search for the stimulus [2]. This reflex emerges as early as the…
Landau reflex
The Landau reflex is a primitive reflex observed in infants that facilitates crawling movements [1]. When the infant is held in a vertical position with their feet touching a flat surface, a reflexive stepping motion occurs as the infant places one foot in front of the other [2]. This reflex emerges around 8-10 months of…
Oculocardiac reflex
The oculocardiac reflex is a brainstem reflex that causes a decrease in heart rate during traction on the extraocular muscles (1). This reflex protects the retina from potential damage during eye movement by coordinating the actions of the oculomotor and vagus nerves (2). When the eye is moved by applying pressure on the globe, this…
Optical blink reflex
The optical blink reflex (sometimes called the “dazzle reflex”) is a rapid protective closure of the eyelids triggered by sudden visual stimuli (e.g. bright light or an approaching object) and is mediated by a subcortical brainstem circuit. In humans, this reflex begins with retinal photoreceptors (rods and cones) and retinal ganglion cells (RGCs) detecting the stimulus. These…
Blink reflex
The blink reflex protects the eye from potential damage when foreign objects make contact with the cornea or conjunctiva (1). This reflexive blinking is accomplished through a reflex arc between the trigeminal nerve (CN V) and facial nerve (CN VII) (2). When the cornea or conjunctiva are stimulated, sensory information is transmitted via the ophthalmic…
Reflex tear secretion
Reflex tear secretion is a fundamental protective mechanism of the ocular surface, triggered by a variety of stimuli that engage a complex neurocircuitry to elicit a rapid and graded lacrimal gland response. This process is distinct from basal and emotional tearing, relying on a well-defined reflex arc involving sensory afferents, central processing units within the…