From the Guidelines
The structure that senses head acceleration is the vestibular system, specifically the cristae of the three semicircular canals. The vestibular system, as defined by 1, is the sensory system within the inner ear that provides fundamental input to the brain regarding balance and spatial orientation. The cristae are sensory structures located within the ampullae of the semicircular canals in the inner ear, and each crista contains hair cells that are embedded in a gelatinous structure called the cupula. When the head accelerates or rotates, the movement of endolymph fluid in the semicircular canals causes the cupula to bend, which in turn stimulates the hair cells. These hair cells then transmit signals to the brain via the vestibular nerve, providing information about the head's rotational acceleration in three dimensions.
Key points to consider:
- The vestibular system is responsible for sensing head acceleration and maintaining balance and spatial orientation during head movements.
- The cristae of the three semicircular canals are the specific structures within the vestibular system that sense rotational acceleration.
- The maculae of the utricle and saccule, also part of the vestibular system, primarily sense linear acceleration and head position relative to gravity, rather than rotational acceleration, as noted in 1.
- Proprioception involves sensing the position and movement of body parts but is not specifically responsible for detecting head acceleration.
It's worth noting that the evidence from 1 and 1 provides a comprehensive understanding of the vestibular system and its role in sensing head acceleration, and is consistent with the definition of the vestibular system/apparatus provided in 1. However, the most recent and highest quality study, 1, is prioritized in making this recommendation.
From the Research
Structure Sensing Head Acceleration
The structure that senses head acceleration is the otolith organs, which include the utricle and saccule, as part of the vestibular system 2, 3, 4, 5, 6.
Key Components
- The utricle and saccule are gravity receptor organs that rely on a high-density otoconial membrane to detect linear acceleration and the position of the cranium relative to Earth's gravitational vector 2.
- The linear vestibular evoked potential (VsEP) is an effective non-invasive functional test for otoconial gravity receptors, and can be used to independently test utricular and saccular function 2.
- The utricular macula and saccular macula are sensory epithelia that contain hair cells which detect linear acceleration and head tilt relative to gravity 3, 4, 5.
Functionality
- The utricle and saccule detect linear acceleration and head orientation with respect to gravity, providing the vestibular reflex pathways with the sensory codes of inertial acceleration of self-motion and head orientation 5.
- The linear vestibuloocular reflex and the angular vestibuloocular reflex can support each other dynamically whenever they are co-activated without a change in the spatial response characteristics 6.
Morphology
- The morphology of the utricular otolith organ in the toadfish, Opsanus tau, has been described, including the sensory epithelium, neural innervation, and synaptic organization 5.
- The membranous membrana limitans (ML) provides support for the utricular macula and acts as a structural boundary between the superior and inferior portions of the vestibular labyrinth 3.