Spontaneous blinking is an intrinsic motor pattern that maintains the tear film and protects the eye. It involves a stereotyped sequence: rapid contraction of the orbicularis oculi (eyelid‐closing muscle) followed by relaxation and reactivation of the levator palpebrae superioris (eyelid‐opening muscle). Unlike reflex blinks triggered by external stimuli, spontaneous blinks originate in central circuits spanning…
Behaviour
Oxytocin release
Oxytocin is a neuropeptide hormone synthesized in magnocellular neurosecretory cells of the paraventricular and supraoptic nuclei in the hypothalamus [1][2]. It is packaged into neurosecretory vesicles and transported down axons to the posterior pituitary gland, where it is released into the bloodstream [1]. Oxytocin is also released within the brain from dendrites and soma of…
Gamma loop
The gamma loop is a feedback mechanism which allows the nervous system to maintain muscle contraction and proprioception [1]. Gamma motor neurons in the spinal cord excite intrafusal muscle fibers in muscle spindles, causing them to contract [2]. This stretches the central portions of the intrafusal fibers, stimulating the Ia sensory afferents that wrap around…
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…
Itch and scratching
Itch is transmitted to the spinal cord dorsal horn by small diameter C and Aδ fibers responding to pruritogens like histamine [2]. These first order neurons synapse onto second order spinothalamic projection neurons that ascend to the thalamus and cortex to generate the sensation of itch [3][4]. Scratching initiation involves spinal interneurons that form part…
Postural balance and control
Maintaining upright stance requires continuous integration of sensory information and motor output [1]. The size of the base of support influences postural stability, with a larger area (e.g. lying prone) easier to balance over than a small area (e.g. standing) [2]. Postural adjustments involve both reflexive and feedforward control mechanisms [3][4]. Sudden external perturbations elicit…
Control of upright balance
Maintaining upright balance requires continuous integration of sensory information and motor adjustments [1][2]. The three main sensory systems involved are the visual, vestibular, and somatosensory systems [3][4]. Visual input provides information about the environment and body orientation. The vestibular system senses head motion and position via the semicircular canals and otolith organs. Somatosensory receptors, particularly…