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Spinal cord #cord #compression


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spinal cord

cord

any long, cylindrical, flexible structure; called also chord. chorda. and funiculus .

spermatic cord the structure extending from the abdominal inguinal ring to the testis, comprising the pampiniform plexus, nerves, ductus deferens, testicular artery, and other vessels.

tethered cord a congenital anomaly resulting from defective closure of the neural tube; the conus medullaris is abnormally low and tethered by a short, thickened filum terminale, fibrous bands, intradural lipoma, or some other intradural abnormality. Surgical correction in infancy or early childhood is necessary to prevent progressive neurological deficit in the lower limb and bladder dysfunction.

spinal

1. pertaining to a spine.

2. pertaining to the vertebral column.

spinal cord that part of the central nervous system lodged in the spinal canal, extending from the foramen magnum to the upper part of the lumbar region. It is composed of an inner core of gray substance in which nerve cells predominate and an outer layer of white substance in which myelinated nerve fibers predominate. Called also medulla spinalis. (See Plates and see accompanying figures.)

Gross anatomy of the spinal cord. From Applegate, 2000.

Cross section of the spinal cord. From Applegate, 2000.

spi nal cord

the elongated cylindric portion of the cerebrospinal axis, or central nervous system, which is contained in the spinal or vertebral canal.

spinal cord

The thick, whitish cord of nerve tissue that extends from the medulla oblongata down through the spinal column and from which the spinal nerves branch off to various parts of the body.

spinal cord

a long, nearly cylindric structure lodged in the vertebral canal and extending from the foramen magnum at the base of the skull to the upper part of the lumbar region. A major component of the central nervous system, the adult cord is approximately 1 cm in diameter, with an average length of 42 to 45 cm and a weight of 30 g. The cord is an extension of the medulla oblongata of the brain that extends at the level of the first or second lumbar vertebra. The cord conducts sensory and motor impulses to and from the brain and controls many reflexes. Thirty-one pairs of spinal nerves originate from the cord: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. It has an inner core of gray material consisting mainly of nerve cell bodies. The cord is enclosed by three protective membranes (meninges): the dura mater, arachnoid, and pia mater. Also called chorda spinalis, medulla spinalis. See also segments of spinal cord, spinal nerves.

Cross section of the spinal cord

spi nal cord

( sp ‘n l k rd ) [TA]

The elongated cylindric portion of the cerebrospinal axis, or central nervous system, which is contained in the spinal or vertebral canal.
Synonym(s): medulla spinalis.

spinal cord

SPINAL CORD: Cross-section with nerve roots on left side and examples of tracts on right side

Part of the central nervous system, the spinal cord is an ovoid column of nerve tissue 40 to 50 cm long that extends from the medulla to the second lumbar vertebra; it is within the spinal (vertebral) canal, protected by bone, and directly enclosed in the meninges. The center of the cord is gray matter in the shape of the letter H; it consists of the cell bodies and dendrites of neurons. The ventral (anterior) horns of the gray matter contain cell bodies of somatic motor neurons; the dorsal (posterior) horns contain cell bodies of interneurons. The white matter is arranged in tracts around the gray matter. It consists of myelinated axons that transmit impulses to and from the brain, or between levels of gray matter in the spinal cord, or that will leave the cord as part of peripheral nerves. The spinal cord is the pathway for sensory impulses to the brain and motor impulses from the brain; it also mediates stretch reflexes and the defecation and urination reflexes. Thirty-one pairs of spinal nerves emerge from the spinal cord and innervate the trunk and limbs. See: illustration

spinal cord

The downward continuation of the BRAINSTEM that lies within a canal in the spine (VERTEBRAL COLUMN ). The cord is a cylinder of nerve tissue about 45 cm long containing bundles of nerve fibre tracts running up and down, to and from the brain. These tracts form SYNAPSES with the 62 spinal nerves that emerge in pairs from either side of the cord, between adjacent vertebrae, and carry nerve impulses to and from all parts of the trunk and the limbs.

spinal cord

a cable-like nervous structure in vertebrates, enclosed in the backbone and extending the full length of the body behind the head. Pairs of spinal nerves leave the cord in each segment of the body The cord forms part of the CENTRAL NERVOUS SYSTEM and contains many NERVE CELLS and bundles of fibres, many associated with simple REFLEX ARCS. others with the brain. Coordination of movement of various parts of the body is brought about in the spinal cord.

Spinal cord

Elongated nerve bundles that lie in the vertebral canal and from which the spinal nerves emerge.

Section of the spinal cord.

Figure 1: Efferent nerve pathways from the brainstem and spinal cord. Shown on the right: somatic, to skeletal muscles. Shown on the left: autonomic. B brain stem, C cervical, T thoracic, L lumbar, S sacral segments of the spinal cord. (Red shaded regions are those with no autonomic outflow.)

spinal cord

the part of the central nervous system that extends, in continuity with the brain, from the base of the skull down the vertebral (spinal) canal as far as the top of the second lumbar vertebra. Surrounded by the membranous tube of the meninges (in continuity with the coverings of the brain) and bathed within this by cerebrospinal fluid . Consists of nerve cells (grey matter) and nerve tracts (white matter). Anterior (efferent) and posterior (afferent) spinal nerve roots leave and enter through the intervertebral foramina, linking it to the peripheral nervous system. See also vertebral column ; Figure 1.

spi nal cord

( sp ‘n l k rd ) [TA]

The elongated cylindric portion of the cerebrospinal axis, or central nervous system, which is contained in the spinal or vertebral canal.
Synonym(s): medulla spinalis.

spinal cord

that part of the central nervous system lodged in the spinal canal, extending from the foramen magnum to a point in the lumbar or sacral vertebrae, depending on the species.

spinal cord abscess

spinal cord atrophy

diminution in mass of the entire cord, is usually the hallmark of undernutrition or old age, or both.

spinal cord compression

may be gradual due to space-occupying lesion of vertebral canal, such as abscess, callus of a fracture, or a tumor, or acute due to fracture dislocation or thrombosis. In general, clinical signs include paresis or paralysis, but depending on the level of the spinal cord involved and the type of lesion present there may also be urinary incontinence, loss of sensation, Horner’s syndrome, and in acute lesions, spinal shock.

spinal cord degeneration

spinal cord hemorrhage

spinal cord hypoplasia

usually segmental, especially in the lumbar area.

spinal cord local ischemia

caused by embolus of a spinal artery; has the same effect as traumatic injury (see below).

spinal cord tracts

more or less distinct bundles of fibers within the white matter of the spinal cord. There are three funiculi on each side of the cord dorsal, lateral and ventral; subdivisions within the funiculi include eleven major tracts gracile and cuneate fasciculi, lateral and ventral corticospinal tracts, rubrospinal tract, dorsal and ventral spinocerebellar tracts, lateral and ventral spinothalamic tracts, elementary apparatus fibers, ventral corticospinal tract, vestibulospinal tract.

spinal cord traumatic injury

fracture or dislocation of one or more vertebrae; causes a syndrome of acute flaccid paralysis in the area supplied with nerves from the injured segment and spastic paralysis in the parts supplied by the cord segments caudal to the injury.

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Using Avro in MapReduce jobs with Hadoop, Pig, Hive – Michael G #hadoop-streaming, #avro #hadoop #pig #hive #mapreduce #streaming #snappy #compression #codec #data #serialization #format #tutorial #howto


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Using Avro in MapReduce Jobs With Hadoop, Pig, Hive

Apache Avro is a very popular data serialization format in the Hadoop technology stack. In this article I show code examples of MapReduce jobs in Java, Hadoop Streaming, Pig and Hive that read and/or write data in Avro format. We will use a small, Twitter-like data set as input for our example MapReduce jobs.

The latest version of this article and the corresponding code examples are available at avro-hadoop-starter on GitHub.

Requirements

The examples require the following software versions:

  • Gradle 1.3+ (only for the Java examples)
  • Java JDK 7 (only for the Java examples)
    • It is easy to switch to JDK 6. Mostly you will need to change the sourceCompatibility and targetCompatibility parameters in build.gradle from 1.7 to 1.6. But since there are a couple of JDK 7 related gotchas (e.g. problems with its new bytecode verifier) that the Java example code solves I decided to stick with JDK 7 as the default.
  • Hadoop 2.x with MRv1 (not MRv2/YARN)
    • Tested with Cloudera CDH 4.3
  • Pig 0.11
    • Tested with Pig 0.11.0-cdh4.3.0
  • Hive 0.10
    • Tested with Hive 0.10.0-cdh4.3.0
  • Avro 1.7.4

Prerequisites

First you must clone my avro-hadoop-starter repository on GitHub.

Example data

Examples

TweetCount

TweetCount implements a MapReduce job that counts the number of tweets created by Twitter users.

TweetCountTest

TweetCountTest is very similar to TweetCount. It uses twitter.avro as its input and runs a unit test on it with the same MapReduce job as TweetCount. The unit test includes comparing the actual MapReduce output (in Snappy-compressed Avro format) with expected output. TweetCountTest extends ClusterMapReduceTestCase (MRv1), which means that the corresponding MapReduce job is launched in-memory via MiniMRCluster .

MiniMRCluster and Hadoop MRv2

The MiniMRCluster that is used by ClusterMapReduceTestCase in MRv1 is deprecated in Hadoop MRv2. When using MRv2 you should switch to MiniMRClientClusterFactory. which provides a wrapper interface called MiniMRClientCluster around the MiniMRYarnCluster (MRv2):

MiniMRClientClusterFactory: A MiniMRCluster factory. In MR2, it provides a wrapper MiniMRClientCluster interface around the MiniMRYarnCluster. While in MR1, it provides such wrapper around MiniMRCluster. This factory should be used in tests to provide an easy migration of tests across MR1 and MR2.

Further readings on Java

  • Package Documentation for org.apache.avro.mapred – Run Hadoop MapReduce jobs over Avro data, with map and reduce functions written in Java. This document provides detailed information on how you should use the Avro Java API to implement MapReduce jobs that read and/or write data in Avro format.
  • Java MapReduce and Avro – Cloudera CDH4 documentation

Hadoop Streaming

Preliminaries

Important: The examples below assume you have access to a running Hadoop cluster.

How Streaming sees data when reading via AvroAsTextInputFormat

When using AvroAsTextInputFormat as the input format your streaming code will receive the data in JSON format, one record (“datum” in Avro parlance) per line. Note that Avro will also add a trailing TAB ( \t ) at the end of each line.

Here is the basic data flow from your input data in binary Avro format to our streaming mapper:

Examples

Prerequisites

The example commands below use the Hadoop Streaming jar for MRv1 shipped with Cloudera CDH4:

If you are not using Cloudera CDH4 or are using a new version of CDH4 just replace the jar file with the one included in your Hadoop installation.

The Avro jar files are straight from the Avro project :

Reading Avro, writing plain-text

The following command reads Avro data from the relative HDFS directory examples/input/ (which normally resolves to /user/ your-unix-username /examples/input/ ). It writes the deserialized version of each data record (see section How Streaming sees data when reading via AvroAsTextInputFormat above) as is to the output HDFS directory streaming/output/. For this simple demonstration we are using the IdentityMapper as a naive map step implementation – it outputs its input data unmodified (equivalently we coud use the Unix tool cat. here). We do not need to run a reduce phase here, which is why we disable the reduce step via the option -D mapred.reduce.tasks=0 (see Specifying Map-Only Jobs in the Hadoop Streaming documentation).

Custom Avro output schema

This looks not to be supported by stock Avro at the moment. A related JIRA ticket AVRO-1067. created in April 2012, is still unresolved as of July 2013.

For a workaround take a look at the section Avro output for Hadoop Streaming at avro-utils. a third-party library for Avro.

Enabling compression of Avro output data (Snappy or Deflate)

If you want to enable compression for the Avro output data, you must add the following parameters to the streaming job:

Be aware that if you enable compression with mapred.output.compress but are NOT specifying an Avro output format (such as AvroTextOutputFormat) your cluster’s configured default compression codec will determine the final format of the output data. For instance, if mapred.output.compression.codec is set to com.hadoop.compression.lzo.LzopCodec then the job’s output files would be compressed with LZO (e.g. you would see part-00000.lzo output files instead of uncompressed part-00000 files).

See also Compression and Avro in the CDH4 documentation.

Further readings on Hadoop Streaming

Preliminaries

Important: The examples below assume you have access to a running Hadoop cluster.

Examples

In this section we demonstrate how to create a Hive table backed by Avro data, followed by running a few simple Hive queries against that data.

Defining a Hive table backed by Avro data

Using avro.schema.url to point to remote a Avro schema file

The following CREATE TABLE statement creates an external Hive table named tweets for storing Twitter messages in a very basic data structure that consists of username, content of the message and a timestamp.

Where to go from here

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Spinal Cord Compression – Neurologic Disorders – Merck Manuals Professional Edition #cord #compression


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Spinal Cord Compression

Acute compression develops within minutes to hours. It is often due to trauma (eg, vertebral crush fracture with displacement of fracture fragments, acute disk herniation. metastatic tumor, severe bone or ligamentous injury causing hematoma, vertebral subluxation or dislocation). It is occasionally due to abscess and rarely due to spontaneous epidural hematoma. Acute compression may follow subacute and chronic compression, especially if the cause is abscess or tumor.

Subacute compression develops over days to weeks. It is usually caused by a metastatic extramedullary tumor, a subdural or an epidural abscess or hematoma, or a cervical or, rarely, thoracic herniated disk.

Chronic compression develops over months to years. It is commonly caused by bony protrusions into the cervical, thoracic, or lumbar spinal canal (eg, due to osteophytes or spondylosis, especially when the spinal canal is narrow, as occurs in spinal stenosis ). Compression can be aggravated by a herniated disk and hypertrophy of the ligamentum flavum. Less common causes include arteriovenous malformations and slow-growing extramedullary tumors.

Lesions that compress the spinal cord may also compress nerve roots or, rarely, occlude the spinal cord’s blood supply, causing spinal cord infarction .

Symptoms and Signs

Acute or advanced spinal cord compression causes segmental deficits, paraparesis or quadriparesis, hyporeflexia (when acute) followed by hyperreflexia, extensor plantar responses, loss of sphincter tone (with bowel and bladder dysfunction), and sensory deficits. Subacute or chronic compression may begin with local back pain, often radiating down the distribution of a nerve root (radicular pain), and sometimes hyperreflexia and loss of sensation. Sensory loss may begin in the sacral segments. Complete loss of function may follow suddenly and unpredictably, possibly resulting from secondary spinal cord infarction.

Spinal percussion tenderness is prominent if the cause is metastatic carcinoma, abscess, or hematoma.

Intramedullary lesions tend to cause poorly localized burning pain rather than radicular pain and to spare sensation in sacral dermatomes. These lesions usually result in spastic paresis.

Diagnosis

Also of Interest

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