The cerebellar vermis is located in the medial, cortico-nuclear zone of the cerebellum, which resides in the posterior fossa of the cranium. The primary fissure in the vermis curves ventrolaterally to the superior surface of the cerebellum, dividing it into anterior and posterior lobes. Functionally, the vermis is associated with bodily locomotion; the vermis is included within the spinocerebellum and receives somatic sensory input from the head and proximal body parts via ascending spinal pathways. The cerebellum develops in a rostro-caudal manner, with rostral regions in the midline giving rise to the vermis, caudal regions developing into the cerebellar hemispheres. By 4 months of prenatal development, the vermis becomes foliated, while development of the hemispheres lags by 30–60 days. Postnatally and organization of the cellular components of the cerebellum continues, with completion of the foliation pattern by 7 months of life and final migration and arborization of cerebellar neurons by 20 months.
Inspection of the posterior fossa is a common feature of prenatal ultrasound and is used to determine whether excess fluid or malformations of the cerebellum exist. Anomalies of the cerebellar vermis are diagnosed in this manner and include phenotypes consistent with Dandy-Walker malformation, rhombencephalosynapsis, displaying no vermis with fusion of the cerebellar hemispheres, pontocerebellar hypoplasia, or stunted growth of the cerebellum, neoplasms. In neonates, hypoxic injury to the cerebellum is common, resulting in neuronal loss and gliosis. Symptoms of these disorders range from mild loss of fine motor control to severe mental retardation and death. Karyotyping has shown that most pathologies associated with the vermis are inherited though an autosomal recessive pattern, with most known mutations occurring on the X chromosome; the vermis is intimately associated with all regions of the cerebellar cortex, which can be divided into three functional parts, each having distinct connections with the brain and spinal cord.
These regions are the vestibulocerebellum, responsible for the control of eye movements. The vermis is the median portion of the cerebellum that connects the two hemispheres. Both the vermis and the hemispheres are composed of lobules formed by groups of folia. There are nine lobules of the vermis: lingula, central lobule, clivus, folium of the vermis, pyramid and nodule; these lobules are difficult to observe during human anatomy classes and may vary in size and number of folia. It has been shown that folia of the cerebellum exhibit frequent variations in form and arrangement between individuals; the lingula is the first lobule of the upper portion of the vermis on the superoinferior axis and pertains to the paleocerebellum together with the central lobule, culmen and uvula. It is separated from the central lobule by the pre-central fissure; the central lobule is the second lobule of the upper portion of the vermis on the superoinferior axis. The culmen is the third and largest lobule of the upper portion of the vermis on the superoinferior axis.
It is separated from the declive by the primary fissure and is related with the anterior quadrangular lobule of the hemisphere. The pyramid is the seventh lobule of the vermis on the superoinferior axis, it is separated from the uvula by the pre-pyramidal and secondary fissures, respectively. This lobule is related with the biventral lobule of the hemisphere; the uvula is the second largest lobule, following the culmen. It is separated from the nodule by the posterolateral fissure; the spinocerebellum receives proprioception input from the dorsal columns of the spinal cord and from the trigeminal nerve, as well as from visual and auditory systems. It sends fibers to deep cerebellar nuclei that, in turn, project to both the cerebral cortex and the brain stem, thus providing modulation of descending motor systems; this region comprises the intermediate parts of the cerebellar hemispheres. Sensory information from the periphery and from the primary motor and somatosensory cortex terminate in this region.
Purkinje cells of the vermis project to the fastigial nucleus, controlling the axial and proximal musculature involved in the execution of limb movements. Purkinje cells in the intermediate zone of the spinocerebellum project to the interposed nuclei, which control the distal musculature components of the descending motor pathways needed for limb movement. Both of these nuclei include projections to the motor cortex in the cerebrum; the interposed nucleus is smaller than the dentate nucleus but larger than the fastigial nucleus and functions to modulate muscle stretch reflexes of distal musculature. It is located dorsal to lateral to the fastigial nucleus; the fastigial nucleus is the most medial efferent cerebellar nucleus, targeting the pontine and medullary reticular formation as well as the vestibular nuclei. This region deals with antigravity muscle groups and other synergies involved with standing and walking, it is thought that fastigial nuclei axons are excitatory and project beyond the cerebellum using glutamate and aspartate as neurotransmitters.
Malformations of the posterior fossa have been recognized more during the past few decades as the result of recent advances in technology. Malformations of
The biventer lobule is a region of the cerebellum. It is triangular in shape; the lateral border is separated from the inferior semilunar lobule by the postpyramidal fissure. The base is directed forward, is on a line with the anterior border of the tonsil, is separated from the flocculus by the postnodular fissure; this article incorporates text in the public domain from page 790 of the 20th edition of Gray's Anatomy http://anatomia.wum.edu.pl/atlas/image_08e.htm
Anatomical terms of location
Standard anatomical terms of location deal unambiguously with the anatomy of animals, including humans. All vertebrates have the same basic body plan – they are bilaterally symmetrical in early embryonic stages and bilaterally symmetrical in adulthood; that is, they have mirror-image left and right halves if divided down the middle. For these reasons, the basic directional terms can be considered to be those used in vertebrates. By extension, the same terms are used for many other organisms as well. While these terms are standardized within specific fields of biology, there are unavoidable, sometimes dramatic, differences between some disciplines. For example, differences in terminology remain a problem that, to some extent, still separates the terminology of human anatomy from that used in the study of various other zoological categories. Standardized anatomical and zoological terms of location have been developed based on Latin and Greek words, to enable all biological and medical scientists to delineate and communicate information about animal bodies and their component organs though the meaning of some of the terms is context-sensitive.
The vertebrates and Craniata share a substantial heritage and common structure, so many of the same terms are used for location. To avoid ambiguities this terminology is based on the anatomy of each animal in a standard way. For humans, one type of vertebrate, anatomical terms may differ from other forms of vertebrates. For one reason, this is because humans have a different neuraxis and, unlike animals that rest on four limbs, humans are considered when describing anatomy as being in the standard anatomical position, thus what is on "top" of a human is the head, whereas the "top" of a dog may be its back, the "top" of a flounder could refer to either its left or its right side. For invertebrates, standard application of locational terminology becomes difficult or debatable at best when the differences in morphology are so radical that common concepts are not homologous and do not refer to common concepts. For example, many species are not bilaterally symmetrical. In these species, terminology depends on their type of symmetry.
Because animals can change orientation with respect to their environment, because appendages like limbs and tentacles can change position with respect to the main body, positional descriptive terms need to refer to the animal as in its standard anatomical position. All descriptions are with respect to the organism in its standard anatomical position when the organism in question has appendages in another position; this helps avoid confusion in terminology. In humans, this refers to the body in a standing position with arms at the side and palms facing forward. While the universal vertebrate terminology used in veterinary medicine would work in human medicine, the human terms are thought to be too well established to be worth changing. Many anatomical terms can be combined, either to indicate a position in two axes or to indicate the direction of a movement relative to the body. For example, "anterolateral" indicates a position, both anterior and lateral to the body axis. In radiology, an X-ray image may be said to be "anteroposterior", indicating that the beam of X-rays pass from their source to patient's anterior body wall through the body to exit through posterior body wall.
There is no definite limit to the contexts in which terms may be modified to qualify each other in such combinations. The modifier term is truncated and an "o" or an "i" is added in prefixing it to the qualified term. For example, a view of an animal from an aspect at once dorsal and lateral might be called a "dorsolateral" view. Again, in describing the morphology of an organ or habitus of an animal such as many of the Platyhelminthes, one might speak of it as "dorsiventrally" flattened as opposed to bilaterally flattened animals such as ocean sunfish. Where desirable three or more terms may be agglutinated or concatenated, as in "anteriodorsolateral"; such terms sometimes used to be hyphenated. There is however little basis for any strict rule to interfere with choice of convenience in such usage. Three basic reference planes are used to describe location; the sagittal plane is a plane parallel to the sagittal suture. All other sagittal planes are parallel to it, it is known as a "longitudinal plane".
The plane is perpendicular to the ground. The median plane or midsagittal plane is in the midline of the body, divides the body into left and right portions; this passes through the head, spinal cord, and, in many animals, the tail. The term "median plane" can refer to the midsagittal plane of other structures, such as a digit; the frontal plane or coronal plane divides the body into ventral portions. For post-embryonic humans a coronal plane is vertical and a transverse plane is horizontal, but for embryos and quadrupeds a coronal plane is horizontal and a transverse plane is vertical. A longitudinal plane is any plane perpendicular to the transverse plane; the coronal plane and the sagittal plane are examples of longitudinal planes. A transverse plane known as a cross-section, divides the body into cranial and caudal portions. In human anatomy: A transverse plane is an X-Z plane, parallel to the ground, which s
Purkinje cells, or Purkinje neurons, are a class of GABAergic neurons located in the cerebellum. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839; these cells are some of the largest neurons in the human brain, with an intricately elaborate dendritic arbor, characterized by a large number of dendritic spines. Purkinje cells are found within the Purkinje layer in the cerebellum. Purkinje cells are aligned like dominos stacked one in front of the other, their large dendritic arbors form nearly two-dimensional layers through which parallel fibers from the deeper-layers pass. These parallel fibers make weaker excitatory synapses to spines in the Purkinje cell dendrite, whereas climbing fibers originating from the inferior olivary nucleus in the medulla provide powerful excitatory input to the proximal dendrites and cell soma. Parallel fibers pass orthogonally through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers forming a Granule-cell-Purkinje-cell synapse with a single Purkinje cell.
Each Purkinje cell receives 500 climbing fiber synapses, all originating from a single climbing fiber. Both basket and stellate cells provide inhibitory input to the Purkinje cell, with basket cells synapsing on the Purkinje cell axon initial segment and stellate cells onto the dendrites. Purkinje cells send inhibitory projections to the deep cerebellar nuclei, constitute the sole output of all motor coordination in the cerebellar cortex; the Purkinje layer of the cerebellum, which contains the cell bodies of the Purkinje cells and Bergmann glia, express a large number of unique genes. Purkinje-specific gene markers were proposed by comparing the transcriptome of Purkinje-deficient mice with that of wild-type mice. One illustrative example is the Purkinje cell protein 4 in knockout mice, which exhibit impaired locomotor learning and markedly altered synaptic plasticity in Purkinje neurons. PCP4 accelerates both the association and dissociation of calcium with calmodulin in the cytoplasm of Purkinje cells, its absence impairs the physiology of these neurons.
There is evidence in mice and humans that bone marrow cells either fuse with or generate cerebellar Purkinje cells, it is possible that bone marrow cells, either by direct generation or by cell fusion, could play a role in repair of central nervous system damage. Further evidence points yet towards the possibility of a common stem cell ancestor among Purkinje neurons, B-lymphocytes and aldosterone-producing cells of the human adrenal cortex. Purkinje cells show two distinct forms of electrophysiological activity: Simple spikes occur at rates of 17 – 150 Hz, either spontaneously or when Purkinje cells are activated synaptically by the parallel fibers, the axons of the granule cells. Complex spikes are slow, 1–3 Hz spikes, characterized by an initial prolonged large-amplitude spike, followed by a high-frequency burst of smaller-amplitude action potentials, they are caused by climbing fiber activation and can involve the generation of calcium-mediated action potentials in the dendrites. Following complex spike activity, simple spikes can be suppressed by the powerful complex spike input.
Purkinje cells show spontaneous electrophysiological activity in the form of trains of spikes both sodium-dependent and calcium-dependent. This was shown by Rodolfo Llinas. P-type calcium channels were named after Purkinje cells, where they were encountered, which are crucial in cerebellar function. We now know that activation of the Purkinje cell by climbing fibers can shift its activity from a quiet state to a spontaneously active state and vice versa, serving as a kind of toggle switch; these findings have been challenged by a study suggesting that such toggling by climbing-fiber inputs occurs predominantly in anaesthetized animals and that Purkinje cells in awake behaving animals, in general, operate continuously in the upstate. But this latter study has itself been challenged and Purkinje cell toggling has since been observed in awake cats. A computational model of the Purkinje cell has shown intracellular calcium computations to be responsible for toggling. Findings have suggested that Purkinje cell dendrites release endocannabinoids that can transiently downregulate both excitatory and inhibitory synapses.
The intrinsic activity mode of Purkinje cells is controlled by the sodium-potassium pump. This suggests that the pump might not be a homeostatic, "housekeeping" molecule for ionic gradients. Instead, it could be a computation element in the brain. Indeed, a mutation in the Na + - K + pump. Furthermore, using the poison ouabain to block Na+-K+ pumps in the cerebellum of a live mouse induces ataxia and dystonia. Numerical modeling of experimental data suggests that, in vivo, the Na+-K+ pump produces long quiescent punctuations to Purkinje neuron firing. Alcohol inhibits Na+-K+ pumps in the cerebellum and this is how it corrupts cerebellar computation and body co-ordination. In humans, Purkinje cells can be harmed by a variety causes: toxic exposure, e.g. to alcohol or lithium. Gluten ataxia is an autoimmune disease triggere
Sense of balance
The sense of balance or equilibrioception is one of the physiological senses related to balance. It helps prevent animals from falling over when standing or moving. Balance is the result of a number of body systems working together: the eyes and the body's sense of where it is in space ideally need to be intact; the vestibular system, the region of the inner ear where three semicircular canals converge, works with the visual system to keep objects in focus when the head is moving. This is called the vestibulo-ocular reflex; the balance system works with the skeletal systems to maintain orientation or balance. Visual signals sent to the brain about the body's position in relation to its surroundings are processed by the brain and compared to information from the vestibular and skeletal systems. In the vestibular system, equilibrioception is determined by the level of a fluid called endolymph in the labyrinth, a complex set of tubing in the inner ear; when the sense of balance is interrupted it causes dizziness and nausea.
Balance can be upset by Ménière's disease, superior canal dehiscence syndrome, an inner ear infection, by a bad common cold affecting the head or a number of other medical conditions including but not limited to vertigo. It can be temporarily disturbed by quick or prolonged acceleration, for example riding on a merry-go-round. Blows can affect equilibrioreception those to the side of the head or directly to the ear. Most astronauts find that their sense of balance is impaired when in orbit because they are in a constant state of weightlessness; this causes. This overview explains acceleration as its processes are interconnected with balance. There are five sensory organs innervated by the vestibular nerve; each semicircular canal is a thin tube that doubles in thickness at a point called osseous ampullae. At their center-base each contains an ampullary cupula; the cupula is a gelatin bulb connected to stereocilia, affected by the relative movement of the endolymph it is bathed in. Since the cupula is part of the bony labyrinth it rotates along with actual head movement unable to cause stimulation by itself.
Endolymph follows the rotation of the canal, due to inertia its movement lags behind that of the bony labyrinth. The delayed movement of the endolymph bends and activates the cupula, signalling to the body that it has moved in space. After any extended rotation the endolymph catches up to the canal and the cupula returns to its upright position and resets; when extended rotation ceases, endolymph continues, which bends and activates the cupula once again to signal a change in movement. Pilots doing long banked turns begin to feel upright. Stereocilia bend causing chemical reactions in the crita ampullaris; the HSCC handles head rotations about a vertical axis, SSCC handles head movement about a lateral axis, PSCC handles head rotation about a rostral-caudal axis. E.g. HSCC: looking side to side. SCC sends adaptive signals, unlike the otolith organs. A shift in the otolithic membrane that stimulates the cilia is considered the state of the body until the cilia are once again stimulated. E.g. lying down stimulates cilia and standing up stimulates cilia, for the time spent lying the signal that you are lying remains active though the membrane resets.
Otolithic organs have a thick, heavy gelatin membrane that, due to inertia, lags behind and continues ahead past the macula it overlays and activating the contained cilia. Utricle responds to linear accelerations and head-tilts in the horizontal plane, whereas saccule responds to linear accelerations and head-tilts in the vertical plane. Otolithic organs update the brain on the head-location. Kinocilium are positioned in the center of the bundle. If stereocilia go towards kinocilium depolarization occurs causing more neurotransmitter, more vestibular nerve firings as compared to when stereocilia tilt away from kinocilium. First order vestibular nuclei project to IVN, MVN, SVN; the inferior cerebellar peduncle is the largest center. It is the area of integration between proprioceptive, vestibular inputs to aid in unconscious maintenance of balance and posture. Inferior olive nucleus aids in complex motor tasks by encoding coordinating timing sensory info. Cerebellar vermis has three main parts: vestibulocerebellum, spinocerebellum [integrates visual, auditory and balance info to act out body and limb movements.
Trigeminal and dorsal column proprioceptive input, thalamus, reticular formation and vestibular nuclei out
Anterior inferior cerebellar artery
The anterior inferior cerebellar artery is one of three pairs of arteries that supplies blood to the cerebellum. It arises from the basilar artery on each side at the level of the junction between the medulla oblongata and the pons in the brainstem, it has a variable course, passing backward to be distributed to the anterior part of the undersurface of the cerebellum, anastomosing with both the posterior inferior cerebellar branch of the vertebral artery and the superior cerebellar artery. It gives off the internal auditory or labyrinthine artery in most cases; the amount of tissue supplied by the AICA is variable, depending upon whether the PICA is more or less dominant, but includes the anteroinferior surface of the cerebellum, the flocculus, middle cerebellar peduncle and inferolateral portion of the pons. Occlusion of AICA is considered rare, but results in a lateral pontine syndrome known as AICA syndrome; the symptoms include sudden onset of vertigo and vomiting, dysarthria, falling to the side of the lesion, a variety of ipsilateral features including hemiataxia, loss of all modalities of sensation of the face, facial paralysis, hearing loss and tinnitus.
Vertigo may sometimes present as an isolated symptom several weeks or months before acute ischemia and cerebral infarction occurs with the meaning of transient ischemia of the inner ear or the vestibular nerve. There is loss of pain and temperature sensation from the contralateral limbs and trunk, which can lead to diagnostic confusion with lateral medullary syndrome, which gives rise to "crossed" neurological signs but does not cause cochlear symptoms, severe facial palsy or multimodal facial sensory loss; this article incorporates text in the public domain from page 580 of the 20th edition of Gray's Anatomy Anatomy photo:28:09-0224 at the SUNY Downstate Medical Center http://neuroangio.org/anatomy-and-variants/aica/ "Anatomy diagram: 13048.000-1". Roche Lexicon - illustrated navigator. Elsevier. Archived from the original on 2014-01-01
The vestibulo-ocular reflex is a reflex, where activation of the vestibular system causes eye movement. This reflex functions to stabilize images on the retinas during head movement by producing eye movements in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the eyes move to the left, vice versa. Since slight head movement is present all the time, VOR is necessary for stabilizing vision: patients whose VOR is impaired find it difficult to read using print, because they cannot stabilize the eyes during small head tremors, because damage to the VOR can cause vestibular nystagmus; the VOR does not depend on visual input. It can be elicited by caloric stimulation of the inner ear, works in total darkness or when the eyes are closed. However, in the presence of light, the fixation reflex is added to the movement. In other animals, the organs that coordinate balance and motor coordination do not operate independently from the organs that control the eyes.
A fish, for instance, moves its eyes by reflex. Humans have semicircular canals, neck muscle "stretch" receptors, the utricle. Though the semicircular canals cause most of the reflexes which are responsive to acceleration, the maintaining of balance is mediated by the stretch of neck muscles and the pull of gravity on the utricle of the inner ear; the VOR has both translational aspects. When the head rotates about any axis distant visual images are stabilized by rotating the eyes about the same axis, but in the opposite direction; when the head translates, for example during walking, the visual fixation point is maintained by rotating gaze direction in the opposite direction, by an amount that depends on distance. The VOR is driven by signals from the vestibular apparatus in the inner ear; the semicircular canals detect head rotation and drive the rotational VOR, whereas the otoliths detect head translation and drive the translational VOR. The main "direct path" neural circuit for the horizontal rotational VOR is simple.
It starts in the vestibular system, where semicircular canals get activated by head rotation and send their impulses via the vestibular nerve through the vestibular ganglion and end in the vestibular nuclei in the brainstem. From these nuclei, fibers cross to the contralateral cranial nerve VI nucleus. There they synapse with 2 additional pathways. One pathway projects directly to the lateral rectus of the eye via the abducens nerve. Another nerve tract projects from the abducens nucleus by the medial longitudinal fasciculus to the contralateral oculomotor nucleus, which contains motorneurons that drive eye muscle activity activating the medial rectus muscle of the eye through the oculomotor nerve. Another pathway directly projects from the vestibular nucleus through the ascending tract of Dieters to the ipsilateral medial rectus motoneuron. In addition there are inhibitory vestibular pathways to the ipsilateral abducens nucleus; however no direct vestibular neuron to medial rectus motoneuron pathway exists.
Similar pathways exist for the vertical and torsional components of the VOR. In addition to these direct pathways, which drive the velocity of eye rotation, there is an indirect pathway that builds up the position signal needed to prevent the eye from rolling back to center when the head stops moving; this pathway is important when the head is moving because here position signals dominate over velocity signals. David A. Robinson discovered that the eye muscles require this dual velocity-position drive, proposed that it must arise in the brain by mathematically integrating the velocity signal and sending the resulting position signal to the motoneurons. Robinson was correct: the'neural integrator' for horizontal eye position was found in the nucleus prepositus hypoglossi in the medulla, the neural integrator for vertical and torsional eye positions was found in the interstitial nucleus of Cajal in the midbrain; the same neural integrators generate eye position for other conjugate eye movements such as saccades and smooth pursuit.
For instance, if the head is turned clockwise as seen from above excitatory impulses are sent from the semicircular canal on the right side via the vestibular nerve through Scarpa's ganglion and end in the right vestibular nuclei in the brainstem. From this nuclei excitatory fibres cross to the left abducens nucleus. There they stimulate the lateral rectus of the left eye via the abducens nerve. In addition, by the medial longitudinal fasciculus and oculomotor nuclei, they activate the medial rectus muscles on the right eye; as a result, both eyes will turn counter-clockwise. Furthermore, some neurons from the right vestibular nucleus directly stimulate the right medial rectus motoneurons, inhibits the right abducens nucleus; the vestibulo-ocular reflex needs to be fast: for clear vision, head movement must be compensated immediately. To achieve clear vision, signals from the semicircular canals are sent as directly as possible to the eye muscles: the connection involves only three neurons, is correspondingly called the three neuron arc.
Using these direct connections, eye movements lag the head movements by less than 10 ms, thus the vestibulo-ocular reflex is one of the fastest reflexes in the human body. During head-free pursuit of moving targets, the VOR is counterproductive to the goal of reducing retinal offset. Research indicates that th