Campaniform sensilla are a class of mechanoreceptors found in insects, which respond to local stress and strain within the animal's cuticle. Campaniform sensilla function as proprioceptors that detect mechanical load as resistance to muscle contraction, [1] [2] similar to mammalian Golgi tendon organs. [3] [4] Sensory feedback from campaniform sensilla is integrated in the control of posture and locomotion. [5] [6]
Each campaniform sensillum consists of a flexible dome, which is embedded in a spongy socket within the cuticle and innervated by the dendrites of a single bipolar sensory neuron (see schematic cross-section). Campaniform sensilla are often oval-shaped with long axes of about 5-10 μm (see SEM).
Campaniform sensilla are distributed across the body surface of many insects. The fruit fly Drosophila melanogaster, for example, has over 680 sensilla. [7] Campaniform sensilla are located in regions where stress is likely to be high, including on the legs, antennae, wings, and halteres. [7] [8] [9] Sensilla may occur alone, but sensilla with similar orientations are often grouped together.
On the legs, groups of campaniform sensilla are located close to the joints on all segments except for the coxa (see leg schematic), with most sensilla located on the proximal trochanter. [10] The number and location of sensilla on the legs varies little across individuals of the same species, [7] and homologous groups of sensilla can be found across species. [10]
Campaniform sensilla typically occur on both sides of the wing (see wing schematic). The exact number and placement varies widely across species, likely mirroring differences in flight behavior. [9] However, across species, most campaniform sensilla are found near the wing base. [9] Computational models predict that this is an optimal location for sensing body rotations during flight, with sensing performance being robust to external perturbations and sensor loss. [11]
In Diptera such as Drosophila, the highest density of campaniform sensilla is found at the base of the modified hind-wings, the halteres (see haltere schematic). [7] [8]
When cuticular deformations compress a campaniform sensillum, the socket edges (collar) indent the cuticular cap. [12] This squeezes the dendritic tip of the sensory neuron and opens its mechanotransduction channels (from the TRP family [13] ), which leads to the generation of action potentials that are transmitted to the ventral nerve cord, the insect analogue to the vertebrate spinal cord.
The activity of campaniform sensilla was first recorded by John William Sutton Pringle in the late 1930s. [14] Pringle also determined that the oval shape of many sensilla makes them directionally selective [15] – they respond best to compression along their short axis. Thus, even neighboring sensilla may have very different sensitivities to strain depending on their orientation in the cuticle. For example, stick insects possess two groups of campaniform sensilla on the dorsal side of their legs' trochanter whose short axes are oriented perpendicularly to one another [1] (see inset in leg schematic). As a result, one group (G3) responds when the leg is bent upwards, whereas the other group (G4) responds when the leg is bent downwards. Round campaniform sensilla can be sensitive in all directions [16] or show directional sensitivity if the cap is asymmetrically coupled with the surrounding collar. [17]
The activity of campaniform sensilla may be slowly-adapting (tonic), signaling the magnitude of cuticular deformation, and/or rapidly adapting (phasic), signaling the rate of cuticular deformation. [1] [18] Based on their responses to white noise stimuli, campaniform sensilla may also be described more generally as signaling two features that approximate the derivative of each other. [19] This suggests that the neural response properties of the sensilla are rather generic, and that functional specialization arises primarily from how the sensilla are embedded in the cuticle. [19] [20] In addition, activity adapts to constant loads and shows hysteresis (history dependence) in response to cyclic loading. [18]
Campaniform sensilla project directly to motor neurons [21] and to various interneurons, which integrate their signals with signals from other proprioceptors. [22] In this way, campaniform sensilla activity can affect the magnitude and timing of muscle contractions. [5]
Campaniform sensilla on the legs are activated during standing and walking. [23] [24] Their sensory feedback is thought to reinforce muscle activity during the stance phase [1] [24] [25] and to contribute to inter-leg coordination, [26] [27] much like sensory feedback from mammalian Golgi tendon organs. [28] [29] Feedback from leg campaniform sensilla is also important for the control of kicking and jumping. [30] [31]
Campaniform sensilla on the wings and halteres are activated as these structures oscillate back and forth during flight, with the phase of activation depending on the placement of the sensilla. [9] [32] The campaniform sensilla on the wing encode the wing's aerodynamic and inertial forces, whereas sensilla on the base of the haltere are thought to encode Coriolis forces induced by body rotation during flight, allowing the structure to function as a gyroscope. [33] Feedback from wing and haltere campaniform sensilla is thought to mediate compensatory reflexes to maintain equilibrium during flight. [34] [35]
To better understand the function of campaniform sensilla, computational models that mimic their response properties are being developed for use in simulations and robotics. [36] [37] On robotic legs, the models can filter input from engineered strain sensors "campaniform-sensilla-style" in real time. [38] One advantage of this bio-inspired filtering is that it enables adaptation to load over time (see above), which makes strain sensors essentially self-calibrating to different loads carried by the robot. [38]
Halteres are a pair of small club-shaped organs on the body of two orders of flying insects that provide information about body rotations during flight. Insects of the large order Diptera (flies) have halteres which evolved from a pair of ancestral hindwings, while males of the much smaller order Strepsiptera (stylops) have halteres which evolved from a pair of ancestral forewings.
In biology, a reflex, or reflex action, is an involuntary, unplanned sequence or action and nearly instantaneous response to a stimulus.
A mechanoreceptor, also called mechanoceptor, is a sensory receptor that responds to mechanical pressure or distortion. Mechanoreceptors are innervated by sensory neurons that convert mechanical pressure into electrical signals that, in animals, are sent to the central nervous system.
Range fractionation is a term used in biology to describe the way by which a group of sensory neurons are able to encode varying magnitudes of a stimulus. Sense organs are usually composed of many sensory receptors measuring the same property. These sensory receptors show a limited degree of precision due to an upper limit in firing rate. If the receptors are endowed with distinct transfer functions in such a way that the points of highest sensitivity are scattered along the axis of the quality being measured, the precision of the sense organ as a whole can be increased.
The brown-banded cockroach is a species of small cockroach, measuring about 10 to 14 mm long and the most well-known in the genus Supella. It is tan to light brown and has two light-colored bands across the wings and abdomen, which may sometimes appear to be broken or irregular but are quite noticeable. The bands may be partly obscured by the wings. The male has wings that cover the abdomen, while the female has wings that do not cover the abdomen completely. The male appears more slender than the female, the female appears wider.
Octopamine (molecular formula C8H11NO2; also known as OA, and also norsynephrine, para-octopamine and others) is an organic chemical closely related to norepinephrine, and synthesized biologically by a homologous pathway. Octopamine is often considered the major "fight-or-flight" neurohormone of invertebrates. Its name is derived from the fact that it was first identified in the salivary glands of the octopus.
Johnston's organ is a collection of sensory cells found in the pedicel of the antennae in the class Insecta. Johnston's organ detects motion in the flagellum. It consists of scolopidia arrayed in a bowl shape, each of which contains a mechanosensory chordotonal neuron. The number of scolopidia varies between species. In homopterans, the Johnston's organs contain 25 - 79 scolopidia. The presence of Johnston's organ is a defining characteristic which separates the class Insecta from the other hexapods belonging to the group Entognatha. Johnston's organ was named after the physician Christopher Johnston, father of the physician and Assyriologist Christopher Johnston.
The antennal lobe is the primary olfactory brain area in insects. The antennal lobe is a sphere-shaped deutocerebral neuropil in the brain that receives input from the olfactory sensory neurons in the antennae and mouthparts. Functionally, it shares some similarities with the olfactory bulb in vertebrates. The anatomy and physiology function of the insect brain can be studied by dissecting open the insect brain and imaging or carrying out in vivo electrophysiological recordings from it.
Chordotonal organs are stretch receptor organs found only in insects and crustaceans. They are located at most joints and are made up of clusters of scolopidia that either directly or indirectly connect two joints and sense their movements relative to one another. They can have both extero- and proprioceptive functions, for example sensing auditory stimuli or leg movement. The word was coined by Vitus Graber in 1882, though he interpreted them as being stretched between two points like a string, sensing vibrations through resonance.
Odorant-binding proteins (OBPs) are small soluble proteins secreted by auxiliary cells surrounding olfactory receptor neurons, including the nasal mucus of many vertebrate species and in the sensillar lymph of chemosensory sensilla of insects. OBPs are characterized by a specific protein domain that comprises six α-helices joined by three disulfide bonds. Although the function of the OBPs as a whole is not well established, it is believed that they act as odorant transporters, delivering the odorant molecules to olfactory receptors in the cell membrane of sensory neurons.
A sensillum is an arthropod sensory organ protruding from the cuticle of exoskeleton, or sometimes lying within or beneath it. Sensilla appear as small hairs or pegs over an individual's body. Inside each sensillum there are two to four sensory neurons. These neurons, or receptors, gather information about environment the arthropod is in:
Planar cell polarity (PCP) is the protein-mediated signaling that coordinates the orientation of cells in a layer of epithelial tissue. In vertebrates, examples of mature PCP oriented tissue are the stereo-cilia bundles in the inner ear, motile cilia of the epithelium, and cell motility in epidermal wound healing. Additionally, PCP is known to be crucial to major developmental time points including coordinating convergent extension during gastrulation and coordinating cell behavior for neural tube closure. Cells orient themselves and their neighbors by establishing asymmetric expression of PCP components on opposing cell members within cells to establish and maintain the directionality of the cells. Some of these PCP components are transmembrane proteins which can proliferate the orientation signal to the surrounding cells.
Proprioception is the sense of self-movement, force, and body position.
TRPN is a member of the transient receptor potential channel family of ion channels, which is a diverse group of proteins thought to be involved in mechanoreception. The TRPN gene was given the name no mechanoreceptor potential C (nompC) when it was first discovered in fruit flies, hence the N in TRPN. Since its discovery in fruit flies, TRPN homologs have been discovered and characterized in worms, frogs, and zebrafish.
The subgenual organ is an organ in insects that is involved in the perception of sound. The name refers to the location of the organ just below the knee in the tibia of all legs in most insects.
Hair-plates are a type of proprioceptor found in the folds of insect joints. They consist of a cluster of hairs, in which each hair is innervated by a single mechanosensory neuron. Functionally, hair-plates operate as "limit-detectors" by signaling the extreme ranges of motion of a joint.
Reinhard F. Stocker is a Swiss biologist. He pioneered the analysis of the sense of smell and taste in higher animals, using the fly Drosophila melanogaster as a study case. He provided a detailed account of the anatomy and development of the olfactory system, in particular across metamorphosis, for which he received the Théodore-Ott-Prize of the Swiss Academy of Medical Sciences in 2007, and pioneered the use of larval Drosophila for the brain and behavioural sciences.
The femoral chordotonal organ is a group of mechanosensory neurons found in an insect leg that detects the movements and the position of the femur/tibia joint. It is thought to function as a proprioceptor that is critical for precise control of leg position by sending the information regarding the femur/tibia joint to the motor circuits in the ventral nerve cord and the brain
A descending neuron is a neuron that conveys signals from the brain to neural circuits in the spinal cord (vertebrates) or ventral nerve cord (invertebrates). As the sole conduits of information between the brain and the body, descending neurons play a key role in behavior. Their activity can initiate, maintain, modulate, and terminate behaviors such as locomotion. Because the number of descending neurons is several orders of magnitude smaller than the number of neurons in either the brain or spinal cord/ventral nerve cord, this class of cells represents a critical bottleneck in the flow of information from sensory systems to motor circuits.