Dorsal column–medial lemniscus pathway

The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial lemniscus pathway (PCML)) is a sensory pathway of the central nervous system that conveys sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the skin and joints. It transmits information from the body to the primary somatosensory cortex in the postcentral gyrus of the parietal lobe of the brain.[1][2] The pathway receives information from sensory receptors throughout the body, and carries this in nerve tracts in the white matter of the dorsal columns of the spinal cord, to the medulla where it is continued in the medial lemniscus, on to the thalamus and relayed from there through the internal capsule and transmitted to the somatosensory cortex. The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem.

There are three groupings of neurons that are involved in the pathway: first-order neurons, second-order neurons, and third-order neurons. The first-order neurons are sensory neurons located in the dorsal root ganglia, that send their afferent fibers through the two dorsal columns – the gracile fasciculus, or gracile tract, and the cuneate fasciculus or cuneate tract.[3] The first-order axons make contact with second-order neurons at the gracile nucleus and the cuneate nucleus in the lower medulla. The second-order neurons send their axons to the thalamus. The third-order neurons are in the ventral nuclear group in the thalamus and fibres from these ascend to the postcentral gyrus.

Sensory information from the upper half of the body is received at the cervical level of the spinal cord and carried in the cuneate tract, and information from the lower body is received at the lumbar level and carried in the gracile tract. The gracile tract is medial to the more lateral cuneate tract.

The axons of second-order neurons of the gracile and cuneate nuclei are known as the internal arcuate fibers and when they cross over the midline, at the sensory decussation in the medulla, they form the medial lemniscus. All of the axons in the DCML pathway are rapidly conducting, large, myelinated, alpha delta fibers.[2]

Dorsal column-medial lemniscus pathway
Spinal nerve
The formation of the spinal nerve from the dorsal and ventral roots.
Gray759
Originating in peripheral sensory receptors, the dorsal column-medial lemniscus pathway transmits fine touch and conscious proprioceptive information to the brain.
Details
PrecursorNeural tube and crest
SystemSomatosensory system
DecussationMedial lemniscus
ToSensorimotor cortex
FunctionTransmit sensation of fine touch, vibration and proprioception
Identifiers
Latinvia columnae posterioris lemniscique medialis
Acronym(s)DCML, DCML
Anatomical terms of neuroanatomy

Structure

The DCML is made up of the axons of first, second, and third-order neurons, beginning in the dorsal root ganglia. These axons from the first-order neurons form the ascending tracts of the gracile fasciculus and the cuneate fasciculus which synapse on the dorsal column nuclei, the second-order neurons in the gracile nucleus and the cuneate nucleus; axons from these neurons ascend as the internal arcuate fibers; the fibers cross over at the sensory decussation and form the medial lemniscus which connects with thalamus; the axons synapse on neurons in the ventral nuclear group which then send axons to the postcentral gyrus in the parietal lobe. The gracile tract carries sensory information from the lower half of the body entering the spinal cord at the lumbar level. The cuneate tract carries sensory information from the upper half of the body (upper limbs, trunk, and neck) entering the spinal cord at the cervical level.[4]

First-order neurons

Periphery and spinal cord

Pseudounipolar bipolar neurons
The first-order neuron is a pseudounipolar neuron (example here on the left), with a single axon originating from the cell body then splitting into two branches. The body is situated in the dorsal root ganglion, with one axon traveling peripherally to tissue, and one traveling into the dorsal column. On the right is a bipolar neuron.

When an action potential is generated by a mechanoreceptor in the tissue, the action potential will travel along the peripheral axon of the first order neuron. The first order neuron is pseudounipolar in shape with its body in the dorsal root ganglion. The action signal will continue along the central axon of the neuron through the posterior root, into the posterior horn, and up the posterior column of the spinal cord.

Axons from the lower body enter the posterior column below the level of T6 and travel in the midline section of the column called the gracile fasciculus.[5] Axons from the upper body enter at or above T6 and travel up the posterior column on the outside of the gracile fasiculus in a more lateral section called the cuneate fasiculus. These fasciculi are in an area known as the posterior funiculus that lies between the posterolateral and the posterior median sulcus. They are separated by a partition of glial cells which places them on either side of the posterior intermediate sulcus.

The column reaches the junction between the spinal cord and the medulla oblongata, where lower body axons in the gracile tract connect (synapse) with neurons in the gracile nucleus, and upper body axons in the cuneate tract synapse with neurons in the cuneate nucleus.[6]

First-order neurons secrete substance P in the dorsal horn as a chemical mediator of pain signaling. The dorsal horn of the spinal cord transmits pain and non-noxious signals from the periphery to the spinal cord itself. Adenosine is another local molecule that modulates dorsal horn pain transmission [3]

Spinal cord tracts - English
Tracts of the spinal cord, showing the involved tracts of the Dorsal Column Medial Lemniscus System labeled at right.

Second-order neurons

Brainstem

The neurons in these two nuclei (the dorsal column nuclei) are second-order neurons.[6] Their axons cross over to the other side of the medulla and are now named as the internal arcuate fibers, that form the medial lemniscus on each side. This crossing over is known as the sensory decussation.

At the medulla, the medial lemniscus is orientated perpendicular to the way the fibres travelled in their tracts in the posterior column. For example, in the column, lower limb is medial, upper limb is more lateral. At the medial lemniscus, axons from the leg are more ventral, and axons from the arm are more dorsal. Fibres from the trigeminal nerve (supplying the head) come in dorsal to the arm fibres, and travel up the lemniscus too.

The medial lemniscus rotates 90 degrees at the pons. The secondary axons from neurons giving sensation to the head, stay at around the same place, while the leg axons move outwards.

The axons travel up the rest of the brainstem, and synapse at the thalamus (at the ventral posterolateral nucleus for sensation from the neck, trunk, and extremities, and at the ventral posteromedial nucleus for sensation from the head).

The second-order neuron begins with the dorsal horn of the spinal cord and decussates to the contralateral spinothalamic tract. Second-order neurons are either nociceptive-specific, which exclusively transmit noxious stimuli, or wide dynamic range (WDR) neurons.  WDR neurons are the most prevalent in the dorsal horn and receive signals from A-beta, A-delta, and C fibers.  In the thalamus, the second-order neuron synapses with the third-order neuron that transmits to the corona radiata and internal capsule to the postcentral gyrus.[5]

Third-order neurons

Thalamus to cortex

Axons from the third-order neurons in the ventral posterior nucleus in the thalamus, ascend the posterior limb of the internal capsule. Those originating from the head and the leg swap their relative positions. The axons synapse in the primary somatosensory cortex, with lower body sensation most medial (e.g., the paracentral lobule) and upper body more lateral.

Function

Discriminative sensation is well developed in the fingers of humans and allows the detection of fine textures. It also allows for the ability known as stereognosis, to determine what an unknown object is, using the hands without visual or audio input. This fine sensation is detected by mechanoreceptors called tactile corpuscles that lie in the dermis of the skin close to the epidermis. When these structures are stimulated by slight pressure, an action potential is started. Alternatively, proprioceptive muscle spindles and other skin surface touch receptors such as Merkel cells, bulbous corpuscles, lamellar corpuscles, and hair follicle receptors (peritrichial endings) may involve the first neuron in this pathway.

The sensory neurons in this pathway are pseudounipolar, meaning that they have a single process emanating from the cell body with two distinct branches: one peripheral branch that functions somewhat like a dendrite of a typical neuron by receiving input (although it should not be confused with a true dendrite), and one central branch that functions like a typical axon by carrying information to other neurons (again, both branches are actually part of one axon).

Clinical significance

Damage to the dorsal column-medial lemniscus pathway below the crossing point of its fibers results in loss of vibration and joint sense (proprioception) on the same side of the body as the lesion. Damage above the crossing point result a loss of vibration and joint sense on the opposite side of the body to the lesion. The pathway is tested with Romberg's test.

References

  1. ^ Essentials of Human Physiology by Thomas M. Nosek. Section 8/8ch5/s8ch5_22.
  2. ^ a b O'Sullivan, S. B., & Schmitz, T. J. (2007). Physical Rehabilitation (5th Edition ed.). Philadelphia: F.A. Davis Company.
  3. ^ a b Giuffrida, R; Rustioni, A (1992). "Dorsal root ganglion neurons projecting to the dorsal column nuclei of rats". J. Comp. Neurol. 316: 206–20. doi:10.1002/cne.903160206. PMID 1374085.
  4. ^ Purves, Dale (2011). Neuroscience (5th ed.). Sunderland, Mass.: Sinauer. pp. 198–200. ISBN 9780878936953.
  5. ^ a b Luria, V; Laufer, E (Jul 2, 2007). "Lateral motor column axons execute a ternary trajectory choice between limb and body tissues". Neural development. 2: 13. doi:10.1186/1749-8104-2-13. PMC 1949814. PMID 17605791.
  6. ^ a b Ganong's Review of Medical Physiology. pp. 168–170. ISBN 9780071825108.

External links

Brainstem

The brainstem (or brain stem) is the posterior part of the brain, continuous with the spinal cord. In the human brain the brainstem includes the midbrain, and the pons and medulla oblongata of the hindbrain. Sometimes the diencephalon, the caudal part of the forebrain, is included.The brainstem provides the main motor and sensory nerve supply to the face and neck via the cranial nerves. Of the thirteen pairs of cranial nerves, ten pairs (or twelve, if the diencephalon is included in the brainstem) come from the brainstem. The brainstem is an extremely important part of the brain as the nerve connections of the motor and sensory systems from the main part of the brain to the rest of the body pass through the brainstem. This includes the corticospinal tract (motor), the dorsal column-medial lemniscus pathway (fine touch, vibration sensation, and proprioception), and the spinothalamic tract (pain, temperature, itch, and crude touch).

The brainstem also plays an important role in the regulation of cardiac and respiratory function. It also regulates the central nervous system, and is pivotal in maintaining consciousness and regulating the sleep cycle. The brainstem has many basic functions including heart rate, breathing, sleeping, and eating.

Brown-Séquard syndrome

Brown-Séquard syndrome (also known as Brown-Séquard's hemiplegia, Brown-Séquard's paralysis, hemiparaplegic syndrome, hemiplegia et hemiparaplegia spinalis, or spinal hemiparaplegia) is caused by damage to one half of the spinal cord, resulting in paralysis and loss of proprioception on the same (or ipsilateral) side as the injury or lesion, and loss of pain and temperature sensation on the opposite (or contralateral) side as the lesion. It is named after physiologist Charles-Édouard Brown-Séquard, who first described the condition in 1850.

Cuneate fasciculus

The cuneate fasciculus, fasciculus cuneatus, cuneate tract, (tract of Burdach, named for Karl Friedrich Burdach) is a tract of nerves in the dorsal column of the spinal cord that primarily transmits information from the upper part of the body (the neck, trunk, and arms). It is part of the dorsal column-medial lemniscus pathway.

DCML

DCML may refer to:

Dorsal column-medial lemniscus pathway

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Dorsal column nuclei

In neuroanatomy, the dorsal column nuclei are a pair of nuclei in the dorsal columns in the brainstem. The name refers collectively to the cuneate nucleus and gracile nucleus, which are present at the junction between the spinal cord and the medulla oblongata. Both nuclei contain second-order neurons of the dorsal column-medial lemniscus pathway, which carries fine touch and proprioceptive information from the body to the brain. Each nucleus has an associated nerve tract, the gracile fasciculus and the cuneate fasciculus.

Gracile fasciculus

The gracile fasciculus (fasciculus gracilis, tract of Goll or gracile tract) is a nerve tract a bundle of nerve fibers) in the dorsal column-medial lemniscus pathway of the spinal cord and carries information from the lower parts of the body. The gracile fasiculus is one of many ascending tracts which carry received sensory information to the brain via the spinal cord. It is also one of the dorsal columns, the other being the cuneate fasciculus.

Human brain

The human brain is the central organ of the human nervous system, and with the spinal cord makes up the central nervous system. The brain consists of the cerebrum, the brainstem and the cerebellum. It controls most of the activities of the body, processing, integrating, and coordinating the information it receives from the sense organs, and making decisions as to the instructions sent to the rest of the body. The brain is contained in, and protected by, the skull bones of the head.

The cerebrum is the largest part of the human brain. It is divided into two cerebral hemispheres. The cerebral cortex is an outer layer of grey matter, covering the core of white matter. The cortex is split into the neocortex and the much smaller allocortex. The neocortex is made up of six neuronal layers, while the allocortex has three or four. Each hemisphere is conventionally divided into four lobes – the frontal, temporal, parietal, and occipital lobes. The frontal lobe is associated with executive functions including self-control, planning, reasoning, and abstract thought, while the occipital lobe is dedicated to vision. Within each lobe, cortical areas are associated with specific functions, such as the sensory, motor and association regions. Although the left and right hemispheres are broadly similar in shape and function, some functions are associated with one side, such as language in the left and visual-spatial ability in the right. The hemispheres are connected by commissural nerve tracts, the largest being the corpus callosum.

The cerebrum is connected by the brainstem to the spinal cord. The brainstem consists of the midbrain, the pons, and the medulla oblongata. The cerebellum is connected to the brainstem by pairs of tracts. Within the cerebrum is the ventricular system, consisting of four interconnected ventricles in which cerebrospinal fluid is produced and circulated. Underneath the cerebral cortex are several important structures, including the thalamus, the epithalamus, the pineal gland, the hypothalamus, the pituitary gland, and the subthalamus; the limbic structures, including the amygdala and the hippocampus; the claustrum, the various nuclei of the basal ganglia; the basal forebrain structures, and the three circumventricular organs. The cells of the brain include neurons and supportive glial cells. There are more than 86 billion neurons in the brain, and a more or less equal number of other cells. Brain activity is made possible by the interconnections of neurons and their release of neurotransmitters in response to nerve impulses. Neurons connect to form neural pathways, neural circuits, and elaborate network systems. The whole circuitry is driven by the process of neurotransmission.

The brain is protected by the skull, suspended in cerebrospinal fluid, and isolated from the bloodstream by the blood–brain barrier. However, the brain is still susceptible to damage, disease, and infection. Damage can be caused by trauma, or a loss of blood supply known as a stroke. The brain is susceptible to degenerative disorders, such as Parkinson's disease, dementias including Alzheimer's disease, and multiple sclerosis. Psychiatric conditions, including schizophrenia and clinical depression, are thought to be associated with brain dysfunctions. The brain can also be the site of tumours, both benign and malignant; these mostly originate from other sites in the body.

The study of the anatomy of the brain is neuroanatomy, while the study of its function is neuroscience. A number of techniques are used to study the brain. Specimens from other animals, which may be examined microscopically, have traditionally provided much information. Medical imaging technologies such as functional neuroimaging, and electroencephalography (EEG) recordings are important in studying the brain. The medical history of people with brain injury has provided insight into the function of each part of the brain.

In culture, the philosophy of mind has for centuries attempted to address the question of the nature of consciousness and the mind-body problem. The pseudoscience of phrenology attempted to localise personality attributes to regions of the cortex in the 19th century. In science fiction, brain transplants are imagined in tales such as the 1942 Donovan's Brain.

List of regions in the human brain

The human brain anatomical regions are ordered following standard neuroanatomy hierarchies. Functional, connective, and developmental regions are listed in parentheses where appropriate.

Medial lemniscus

The medial lemniscus, also known as Reil's band or Reil's ribbon, is a large ascending bundle of heavily myelinated axons that decussate in the brainstem, specifically in the medulla oblongata. The medial lemniscus is formed by the crossings of the internal arcuate fibers. The internal arcuate fibers are composed of axons of nucleus gracilis and nucleus cuneatus. The axons of the nucleus gracilis and nucleus cuneatus in the medial lemniscus have cell bodies that lie contralaterally.

The medial lemniscus is part of the dorsal column–medial lemniscus pathway, which ascends from the skin to the thalamus, which is important for somatosensation from the skin and joints, therefore, lesion of the medial lemnisci causes an impairment of vibratory and touch-pressure sense.

Neural pathway

A neural pathway is the connection formed by axons that project from neurons to make synapses onto neurons in another location, to enable a signal to be sent from one region of the nervous system to another. Neurons are connected by a single axon, or by a bundle of axons known as a nerve tract, or fasciculus. Shorter neural pathways are found within grey matter in the brain, whereas longer projections, made up of myelinated axons, constitute white matter.

In the hippocampus there are neural pathways involved in its circuitry including the perforant pathway, that provides a connectional route from the entorhinal cortex to all fields of the hippocampal formation, including the dentate gyrus, all CA fields (including CA1), and the subiculum.

Descending motor pathways of the pyramidal tracts travel from the cerebral cortex to the brainstem or lower spinal cord. Ascending sensory tracts in the dorsal column–medial lemniscus pathway (DCML) carry information from the periphery to the cortex of the brain.

Pallesthesia

Pallesthesia (\ˌpal-es-ˈthē-zh(ē-)ə\), or vibratory sensation, is the ability to perceive vibration. This sensation, often conducted through skin and bone, is usually generated by mechanoreceptors such as Pacinian corpuscles, Merkel disk receptors, and tactile corpuscles. All of these receptors stimulate an action potential in afferent nerves (sensory neurons) found in various layers of the skin and body. The afferent neuron travels to the spinal column and then to the brain where the information is processed. Damage to the peripheral nervous system or central nervous system can result in a decline or loss of pallesthesia.

A diminished sense of vibration is known as pallhypesthesia. To determine whether a patient has diminished or absent pallesthesia, testing can be conducted using a tuning fork at 128 Hz by placing it on the skin overlying a bone. This works because bones are good resonators of vibrations.

Proprioception

Proprioception ( PROH-pree-o-SEP-shən), is the sense of the relative position of one's own parts of the body and strength of effort being employed in movement. It is sometimes described as the "sixth sense".In humans, it is provided by proprioceptors in skeletal striated muscles (muscle spindles) and tendons (Golgi tendon organ) and the fibrous membrane in joint capsules. It is distinguished from exteroception, by which one perceives the outside world, and interoception, by which one perceives pain, hunger, etc., and the movement of internal organs.

The brain integrates information from proprioception and from the vestibular system into its overall sense of body position, movement, and acceleration. The word kinesthesia or kinæsthesia (kinesthetic sense) strictly means movement sense, but has been used inconsistently to refer either to proprioception alone or to the brain's integration of proprioceptive and vestibular inputs.

Proprioception has also been described in other animals such as vertebrates, and in some invertebrates such as arthropods. More recently proprioception has also been described in flowering land plants (angiosperms).

Pseudounipolar neuron

A pseudounipolar neuron (pseudo – false, uni – one) is a kind of sensory neuron in the peripheral nervous system. This neuron contains an axon that has split into two branches; one branch runs to the periphery and the other to the spinal cord.

Somatosensory system

The somatosensory system is a part of the sensory nervous system. The somatosensory system is a complex system of sensory neurons and pathways that responds to changes at the surface or inside the body. The axons (as afferent nerve fibers) of sensory neurons connect with, or respond to, various receptor cells. These sensory receptor cells are activated by different stimuli such as heat and nociception, giving a functional name to the responding sensory neuron, such as a thermoreceptor which carries information about temperature changes. Other types include mechanoreceptors, chemoreceptors, and nociceptors which send signals along a sensory nerve to the spinal cord where they may be processed by other sensory neurons and then relayed to the brain for further processing. Sensory receptors are found all over the body including the skin, epithelial tissues, muscles, bones and joints, internal organs, and the cardiovascular system.

Somatic senses are sometimes referred to as somesthetic senses, with the understanding that somesthesis includes the sense of touch, proprioception (sense of position and movement), and (depending on usage) haptic perception.The mapping of the body surfaces in the brain is called somatotopy. In the cortex, it is also referred to as the cortical homunculus. This brain-surface ("cortical") map is not immutable, however. Dramatic shifts can occur in response to stroke or injury.

Spinothalamic tract

The spinothalamic tract (also known as anterolateral systemm or the ventrolateral system) is a sensory pathway from the skin to the thalamus. From the ventral posterolateral nucleus in the thalamus, sensory information is relayed upward to the somatosensory cortex of the postcentral gyrus.

The spinothalamic tract consists of two adjacent pathways: anterior and lateral. The anterior spinothalamic tract carries information about crude touch. The lateral spinothalamic tract conveys pain and temperature.

In the spinal cord, the spinothalamic tract has somatotopic organization. This is the segmental organization of its cervical, thoracic, lumbar, and sacral components, which is arranged from most medial to most lateral respectively.

The pathway crosses over (decussates) at the level of the spinal cord, rather than in the brainstem like the dorsal column-medial lemniscus pathway and lateral corticospinal tract.

Stereognosis

Stereognosis (also known as haptic perception or tactile gnosis) is the ability to perceive and recognize the form of an object in the absence of visual and auditory information, by using tactile information to provide cues from texture, size, spatial properties, and temperature, etc. In humans, this sense, along with tactile spatial acuity, vibration perception, texture discrimination and proprioception, is mediated by the dorsal column-medial lemniscus pathway of the central nervous system. Stereognosis tests determine whether or not the parietal lobe of the brain is intact. Typically, these tests involved having the patient identify common objects (e.g. keys, comb, safety pins) placed in their hand without any visual cues.

Stereognosis is a higher cerebral associative cortical function.Astereognosis is the failure to identify or recognize objects by palpation in the absence of visual or auditory information, even though tactile, proprioceptive, and thermal sensations may be unaffected. It may be caused by disease of the sensory cortex or posterior columns. People suffering from Alzheimer's disease show a reduction in stereognosis. Astereognosis can be caused by damage to the posterior association areas of the parietal, temporal, or occipital lobes, or the postcentral gyrus of either hemisphere. For other types of dementia, stereognosis does not appear to decline.

Mechanism of neural pathway

The dorsal column medial lemniscus pathway is responsible for relaying sensory information regarding proprioception, vibration, and fine touch. First order neurons carry sensory information from proprioceptive and tactile receptors to the medulla oblongata where they synapse in either the medullary gracilus or cunate nuclei. Information carried from regions above spinal level T6 synapse at the cunate nuclei, while information carried from T6 and below synapse at the gracilus nuclei. At this point, second order neurons decussate and relay information through the contralateral medial lemniscus to the thalamus. At the thalamus, second order neurons synapse with third order neurons, which continue through the internal capsule to the primary sensory cortex of the post central gyrus where the tract terminates. Stereognosis determines whether or not this tract is properly functioning.An individual who cannot properly identify an object using stereognosis, could suffer from lesions in nerve roots, peripheral nerves, the spinal cord, thalamus, or primary sensory cortex. Because the dorsal column medial lemniscus pathway travels through and relays information to these areas, a lack of proper sensation indicates a problem with this neural sensory tract. Administered tests and recognition of pattern sensory loss can identify lesions in particular nerves or areas.

Stroke

A stroke is a medical condition in which poor blood flow to the brain results in cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both result in parts of the brain not functioning properly. Signs and symptoms of a stroke may include an inability to move or feel on one side of the body, problems understanding or speaking, dizziness, or loss of vision to one side. Signs and symptoms often appear soon after the stroke has occurred. If symptoms last less than one or two hours it is known as a transient ischemic attack (TIA) or mini-stroke. A hemorrhagic stroke may also be associated with a severe headache. The symptoms of a stroke can be permanent. Long-term complications may include pneumonia or loss of bladder control.The main risk factor for stroke is high blood pressure. Other risk factors include tobacco smoking, obesity, high blood cholesterol, diabetes mellitus, a previous TIA, and atrial fibrillation. An ischemic stroke is typically caused by blockage of a blood vessel, though there are also less common causes. A hemorrhagic stroke is caused by either bleeding directly into the brain or into the space between the brain's membranes. Bleeding may occur due to a ruptured brain aneurysm. Diagnosis is typically based on a physical exam and supported by medical imaging such as a CT scan or MRI scan. A CT scan can rule out bleeding, but may not necessarily rule out ischemia, which early on typically does not show up on a CT scan. Other tests such as an electrocardiogram (ECG) and blood tests are done to determine risk factors and rule out other possible causes. Low blood sugar may cause similar symptoms.Prevention includes decreasing risk factors, as well as possibly aspirin, statins, surgery to open up the arteries to the brain in those with problematic narrowing, and warfarin in those with atrial fibrillation. A stroke or TIA often requires emergency care. An ischemic stroke, if detected within three to four and half hours, may be treatable with a medication that can break down the clot. Aspirin should be used. Some hemorrhagic strokes benefit from surgery. Treatment to try to recover lost function is called stroke rehabilitation and ideally takes place in a stroke unit; however, these are not available in much of the world.In 2013 approximately 6.9 million people had an ischemic stroke and 3.4 million people had a hemorrhagic stroke. In 2015 there were about 42.4 million people who had previously had a stroke and were still alive. Between 1990 and 2010 the number of strokes which occurred each year decreased by approximately 10% in the developed world and increased by 10% in the developing world. In 2015, stroke was the second most frequent cause of death after coronary artery disease, accounting for 6.3 million deaths (11% of the total). About 3.0 million deaths resulted from ischemic stroke while 3.3 million deaths resulted from hemorrhagic stroke. About half of people who have had a stroke live less than one year. Overall, two thirds of strokes occurred in those over 65 years old.

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