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The Reticular Formation, Limbic System and Basal Ganglia

February 19, 2012 1 comment

The Reticular Formation

It’s a ‘diffuse net’ which is formed by nerve cells and fibers. It extends from the neuroaxis spinal cord through medulla, pons, midbrain, subthalamus, hypothalamus and thalamus (spinal cord is relayed superiorly to the cerebral cortex).

Many afferent and efferent pathways project in and out of the RF from most parts of the CNS. The main pathways through the RF is poorly defined and difficult to trace using silver stains. Reticular formation can be divided into three columns : median, medial and lateral columns.

Functions of the Reticular formation

1.   Control of skeletal muscles:

  • RF modulates muscle tone and reflex activities (via reticulospinal and reticulo bulbar tracts). It is important in controlling muscles of facial expression when associated with emotions.

2.   Control somatic and visceral sensation (influence can be excitatory or inhibitory)

3.   Control of autonomic nervous system

4.   Control of endocrine nervous system (hypothalamus and the pituitary)

5.   Influence on the biological clock (rhythm)

6.   The reticular activating system (arousal and level of consciousness are controlled by the RF)

Clinical note

When a person smiles for a joke, the motor control is provided by the RF on both side of the brain. The fibers from RF is separated from corticobulbar pathway (supply for facial muscles). If a patient suffers a stroke that involves corticobulbar fibers, he or she has facial paralysis on the lower part of the face, but is still able to smile symmetrically.

The Limbic System

 Limbic structures   Functions of the limbic system 
  1. Sub callosal, cingulated and parahippocampal gyri
  2. Hippocampal formation
  3. Amygdaloid nucleus
  4. Mammillary bodies
  5. Anterior thalamic nucleus
1. Influence the emotional behavior:a. Reaction to fear and angerb. Emotions associated with sexual behavior

2. Hippocampus is involved in converting short term memory to long term memory (If the hippocampus is damaged, patient is unable to store long term memory – Anterograde amnesia)

The  Basal Ganglia and their connections

Connections of the Basal Ganglia

Yellow arrow : Pallidofugal fibers

Caudate nucleus and the Putamen: main sites of receiving inputs

Globus pallidus: main site from which output leaves

Afferent and Efferent fibers

Connections of the caudate nucleus and Putamen Connections of the Globus pallidus
Afferent Efferent Afferent Efferent
CS: CorticostriateTS: Thalamostriate

NS: Nigrostriate

BS: Brainstem striatal fibers

SP: Striatopallidalfibers

SN: Striatonigral fibers

SP: Striatopallidalfibers Pallidofugalfibers

Functions of  the Basal Nuclei

Basal Nuclei controls muscular movements by influencing the cerebral cortex (it doesn’t have direct control through descending pathways to the brainstem and spinal cord). It helps to prepare for the movements (enables the trunk and limbs to be placed in appropriate positions before discrete movements of the hands and feet).

Functional connections of the Basal Nuclei and how they influence muscle activities

 
REFERENCES: 
1. Ben Greenstein, Ph.D, Adam Greenstein, BSc (Hons) Mb, ChB Color Atlas of Neuroscience
2. Allan Siegel Ph.D, Hreday N. Sapru Ph.D Essential Neuroscience, 1st Edition
3. Stanley Jacobson, Elliot M. Marcus Neuroanatomy for the Neuroscientist
4. Patrick f. Chinnery Neuroscience for Neurologists
5. Dale Purves Neuroscience, 3rd Edition
6. Suzan Standring Gray’s Anatomy
7. Keith L. Moore, Arthur F. Dalley, Anne M. R. Agur Clinically Oriented Anatomy
8. Frank H. Netter Atlas of Human Anatomy
9. Walter J. Hendelman, M.D., C.M. Atlas of Functional Neuroanatomy
10. Mark F. Bear, Barry W. Connors, Michael A. Paradiso Neuroscience Exploring the Brain
11. Dale Purves et al. Principles of Cognitive Neuroscience
12. Eric R. Kandel et al. Principles of Neural Science

Right And Left Brain

February 17, 2012 1 comment

The brain is divided physically into a left and right half is not a new discovery. The Egyptians knew that the left side of the brain controlled and received sensations from the right side of the body and vice versa.

It is only in the last two dozen years, however, that the true implication of the left/right split has gradually become apparent, through the work of a number of researchers. The most famous are probably Dr.  Roger Sperry and Dr. Robert Ornstein of the California Institute of Technology. Their work has won them a Nobel prize.

Sperry and Ornstein noted that the left and the rig hemispheres are connected by an incredibly complex  network of up to 300 million nerve fibres called the Corpus callosum. They were also able to show that the two halves of the brain tend to have different functions.

They (and other researchers) indicate that the left brain primarily appears to deal with language and mathematical processes and logical thought, sequences, analysis and what we generally label academic  pursuits. The right brain principally deals with music, and visual impressions, pictures, spatial patterns, and colour recognition. They also ascribe to the right brain the ability to deal with certain kinds of conceptual   thought – intangible ‘ideas’ such as love, loyalty, beauty.

The specialization of the two halves of the brain can result in some bizarre behaviour. Patients who, for medical reasons, have had their Corpus callosum  severed,  have effectively two semi-independent brains: two minds in one head.

If a ball is shown to the left visual field of such a person, i.e. registered to their right brain hemisphere, the speaking half of the brain, which is in the other, (left) brain will claim to have seen nothing. If, however, the patient is asked to feel in a bag of assorted shapes he will correctly pull out a ball. If he is asked what he has done he will say ‘nothing’. The ball has only been seen with the right brain, and felt with the right brain. The speech centre, which is located in the left brain, has registered nothing.

Even more delicate experiments have been performed on surgically split-brained patients. The word SINBAD was projected to such a patient while his eyes were focused on the precise spot between N and B. The first 3 letters went to his right brain, the last three to his left hemisphere. When asked to saywhat he had seen, he replied BAD. When asked to point with his left hand to what he had seen he pointed to the word SIN.

The specialisation of the two brains  has also been demonstrated by measuring the electrical activity of the brain during various activities.

When the brain is relaxed in a state of rest, it tends predominantly to show an alpha brain wave rhythm – i.e. 8-12 Hz waves. Ornstein found that a subject tackling a mathematical problem showed an increase in alpha in the right hemisphere. This indicated that the right side was relaxing whilst the left was active and, therefore, in a beta brain wave pattern. In contrast, when a subject was matching coloured patterns, the left showed alpha (i.e. was resting) and the right showed beta (i.e. was active). More on brain waves can be found here.

The brain scans, show the varying levels of electrical brain activity in a subject listening to music, words and singing. The first activity (music) involved the right brain. The second (listening to words only) involved the  left brain, but singing (words and music together) involved the whole brain.

The left brain is now thought to be the half that specialises in serial, sequential thought, i.e. analysing  information in sequence in a ”logical” step by step approach. The left rationalises. The right brain seems to take in several bits of information ”at a glance” and process them into one overall thought. The right synthesises.

To read more click on this link to the full article: Right and Left Brain

Descending Tracts

February 17, 2012 Leave a comment

Descending tracts have three neurons:

1.   1st order neurons (UMN): cell bodies are in the cerebral cortex and other supra spinal areas

2.   2nd order neurons: short and situated in the anterior grey column of the spinal cord

3.  3rd  order neuron (LMN): situated in the anterior grey column and innervate the skeletal muscles through anterior roots of the spinal nerves

Corticospinal tract: rapid, skilled and voluntary movements

1st order neuron

Axons arise from the pyramidal cells of the cerebral  cortex  (situated  in  the  5th   layer),  2/3 from the pre central gyrus and 1/3 from the post central gyrus:

1. 1/3 of fibers arise from the 1stry motor  cortex (Area 4)

2. 1/3 of fibers arise from the 2ndry motor cortex (Area 6)

3. 1/3 of fibers arise from the parietal lobe

(Area 1, 2 and 3).

Descending fibers converge in the corona radiata and  pass  though  the   posterior  limb  of  the internal capsule; organization of fibers within the internal capsule:

1. close to genu (medial): concerned with the cervical parts of the body

2. away from the genu (lateral): concerned with the lower extremity.

The tract then passes through the middle 3/5 of the basis pedunculi of the midbrain; organization of fibers in the midbrain:

    1. medially: cervical parts of the body
    2. laterally: lower limbs.

When the tract enters the pons, it’s broken into many bundles by the transverse pontocerebellar fibers. In the medulla oblongata, the bundles group together to form the pyramids. At the junction of the MO and the spinal cord, most fibers cross the midline at the decussation of the pyramids and enter the lateral white column of the spinal cord to form the lateral corticospinal tract (LCST). LCST descends length of the spinal cord and terminates in the anterior grey column of all the spinal segments.

The fibers which didn’t cross, descend in the anterior white column of the spinal cord as the anterior corticospinal tract (ACST). Fibers of the ACST eventually cross and terminate in the anterior grey column of the spinal cord segments in the cervical and upper thoracic regions.

2nd order neuron:

It’s an internuncial neuron.

3rd order neuron:

It’s a alpha or gamma motor neuron.

To read more click on this link to the full article: Descending Tracts

Clinical Syndromes, Laboratory Diagnosis and Treatment of Orthomyxoviruses

February 12, 2012 3 comments

Clinical Syndromes

Depending on the degree of immunity to the infecting strain of virus and other factors, infection may range from asymptomatic to severe. Patients with underlying cardiorespiratory disease, people with immune deficiency (even that associated with pregnancy), the elderly, and smokers are more prone to have a severe case.

After an incubation period of 1 to 4 days, the “flu syndrome” begins with a brief prodrome of malaise and headache lasting a few hours. The prodrome is followed by the abrupt onset of fever, chills, severe myalgias, loss of appetite, weakness and fatigue, sore throat, and usually a nonproductive cough. The fever persists for 3 to 8 days, and unless a complication occurs, recovery is complete within 7 to 10 days. Influenza in young children (under 3 years) resembles other severe respiratory tract infections, causing bronchiolitis, croup, otitis media, vomiting, and abdominal pain, accompanied rarely by febrile convulsions (Table 1). Complications of influenza include bacterial pneumonia, myositis, and Reye syndrome. The central nervous system can also be involved. Influenza B disease is similar to influenza A disease.

Influenza may directly cause pneumonia, but it more commonly promotes a secondary bacterial superinfection that leads to bronchitis or pneumonia. The tissue damage caused by progressive influenza virus infection of alveoli can be extensive, leading to hypoxia and bilateral pneumonia. Secondary bacterial infection usually involves Streptococcus pneumoniae, Haemophilus influenzae, or Staphylococcus aureus. In these infections, sputum usually is produced and becomes purulent.

Although the infection generally is limited to the lung, some strains of influenza can spread to other sites in certain people. For example, myositis (inflammation of muscle) may occur in children. Encephalopathy, although rare, may accompany an acute influenza illness and can be fatal. Postinfluenza encephalitis occurs 2 to 3 weeks after recovery from influenza. It is associated with evidence of inflammation but is rarely fatal.

Reye syndrome is an acute encephalitis that affects children and occurs after a variety of acute febrile viral infections, including varicella and influenza B and A diseases. Children given salicylates (aspirin) are at increased risk for this syndrome. In addition to encephalopathy, hepatic dysfunction is present. The mortality rate may be as high as 40%.

Laboratory Diagnosis

The diagnosis of influenza is usually based on the characteristic symptoms, the season, and the presence of the virus in the community. Laboratory methods that distinguish influenza from other respiratory viruses and identify its type and strain confirm the diagnosis (Table 2).

Influenza viruses are obtained from respiratory secretions. The virus is generally isolated in primary monkey kidney cell cultures or the Madin-Darby canine kidney cell line. Nonspecific cytopathologic effects are often difficult to distinguish but may be noted within as few as 2 days (average, 4 days). Before the cytopathologic effects develop, the addition of guinea pig erythrocytes may reveal hemadsorption (the adherence of these erythrocytes to HA-expressing infected cells). The addition of influenza virus-containing media to erythrocytes promotes the formation of a gel-like aggregate due to hemagglutination. Hemagglutination and hemadsorption are not specific to influenza viruses, however; parainfluenza and other viruses also exhibit these properties.

More rapid techniques detect and identify the influenza genome or antigens of the virus. Rapid antigen assays (less than 30 min) can detect and distinguish influenza A and B. Reverse transcriptase polymerase chain reaction (RT-PCR) using generic influenza primers can be used to detect and distinguish influenza A and B, and more specific primers can be used to distinguish the different strains, such as H5N1. Enzyme immunoassay or immunofluorescence can be used to detect viral antigen in exfoliated cells, respiratory secretions, or cell culture and are more sensitive assays. Immunofluorescence or inhibition of hemadsorption or hemagglutination (hemagglutination inhibition [HI]) with specific antibody can also detect and distinguish different influenza strains. Laboratory studies are primarily used for epidemiologic purposes.

To read more click on this link to the full article: Clinical Syndromes, Laboratory Diagnosis and Treatment of Orthomyxoviruses

Notre Dame researchers report fundamental malaria discovery

February 11, 2012 1 comment

A team of researchers led by Kasturi Haldar and Souvik Bhattacharjee of the University of Notre Dame’s Center for Rare and Neglected Diseases has made a fundamental discovery in understanding how malaria parasites cause deadly disease.

The researchers show how parasites target proteins to the surface of the red blood cell that enables sticking to and blocking blood vessels. Strategies that prevent this host-targeting process will block disease.

The research findings appear in the Jan. 20 edition of the journal Cell, the leading journal in the life sciences. The study was supported by the National Institutes of Health.

Malaria is a blood disease that kills nearly 1-3 million people each year. It is caused by a parasite that infects red cells in the blood. Once inside the cell, the parasite exports proteins beyond its own plasma membrane border into the blood cell. These proteins function as adhesins that help the infected red blood cells stick to the walls of blood vessels in the brain and cause cerebral malaria, a deadly form of the disease that kills over half a million children each year.

In all cells, proteins are made in a specialized cell compartment called the endoplasmic reticulum (ER) from where they are delivered to other parts of the cell. Haldar and Bhattacharjee and collaborators Robert Stahelin at the Indiana University School of Medicine – South Bend (who also is an adjunct faculty member in Notre Dame’s Department of Chemistry and Biochemistry), and David and Kaye Speicher at the University of Pennsylvania’s Wistar Institute discovered that for host-targeted malaria proteins the very first step is binding to the lipid phosphatidylinositol 3-phosphate, PI(3)P, in the ER.

This was surprising for two reasons. Previous studies suggested an enzyme called Plasmepsin V that released the proteins into the ER was also the export mechanism. However, Haldar, Bhattacharjee and colleagues discovered that binding to PI(3)P lipid which occurs first is the gate keeper to control export and that export can occur without Plasmepsin V action. Further, in higher eukaryotic cells (such as in humans), the lipid PI(3)P is not usually found within the ER membrane but rather is exposed to the cellular cytoplasm.

Haldar and Bhattacharjee are experts in malaria parasite biology and pathogenesis. Stahelin is an expert in PI(3)P lipid biology, and David and Kaye Speicher are experts in proteomics and a method called mass spectrometry.

Story Source:

The above story is reprinted (with editorial adaptations by MedicalXpress staff) from materials provided by University of Notre Dame (news : web)

Ascending Tracts

February 10, 2012 Leave a comment

Introduction

They are located in the white matter and conduct afferent information (may or may not reach consciousness). There are two types of information:

  1. Exteroceptive : originates from outside the body (pain, temperature and touch
  2. Proprioceptive : originates from inside the body (from muscles and joints)

Normally there are three neurons in an ascending pathway:

  1. 1st order neuron: cell body is in the posterior root ganglion
  2. 2nd  order neuron: decussates (crosses to the opposite side) and ascends to a higher level of the    CNS
  3. 3rd neuron: located in the thalamus and passes to a sensory region of the cortex

Pain and temperature pathway: lateral spinothalmic tract

1st order neuron

Peripheral process extends to skin or other tissues and ends as free nerve endings (receptors). Cell body is situated in the posterior root ganglion. Central process extends into the posterior grey column and synapses with the 2nd order neuron.

2nd order neuron

The axon crosses obliquely to the opposite side in the anterior grey and white commissures within one spinal segment of the cord. It ascends in the contralateral white column as the lateral spinothalamic tract (LSTT).

As the LSTT ascends through the spinal cord new fibers are added to the anteromedial aspect of the tract (sacral fibers are lateral and cervical fibers are medial). The fibers carrying pain are situated anterior to those conducting temperature.

As the LSTT ascends through the medulla oblongata,  it’s  joined  by  the  anterior spinothalamic tract and the spinotectal tract and forms the spinal lemniscus. Spinal lemniscus ascends through the pons and the mid brain.

Fibers of the LSTT end by synapsing with the 3rd order  neurons  in  the  ventral  posterolateral nucleus  of  the  thalamus  (here  crude  pain  and temperature sensations are appreciated).

3rd order neuron

Axons pass through the posterior limb of the internal capsule and corona radiata  to reach the somatosensory  area  in  the  post  central  gyrus  of  the  cerebral  cortex.  From  here  information is transmitted to other regions of the cerebral cortex to be used by motor areas. The role of the cerebral  cortex  is  interpreting  the  quality  of  the  sensory  information  at  the  level  of  the consciousness.

Light (crude) touch and pressure pathway: anterior spinothalamic tract (ASTT)

1st order neuron

It is similar to the pain and temperature pathway.

2nd order neuron

The axon crosses obliquely to the opposite side in the anterior grey and white commissures within several spinal segments. It ascends in the contralateral white column as the anterior spinothalamic tract (ASTT). As the ASTT ascends through the spinal cord new fibers are added to the anteromedial aspect of the tract (sacral fibers are lateral and cervical fibers are medial).

As the ASTT ascends through the medulla oblongata, it’s joined by the lateral spinothalamic tract and the spinotectal tract and forms the spinal lemniscus. Spinal lemniscus ascends through the pons and the midbrain. Fibers of the ASTT end by synapsing with the 3rd order neurons in the ventral posterolateral nucleus of the thalamus (here crude awareness of touch and pressure sensations are appreciated).

3rd order neuron

Axons pass through the posterior limb of the internal capsule and corona radiata to reach the somatosensory area in the post central gyrus of the cerebral cortex. The sensations can be crudely localized. Very little discrimination is possible.

To read more click on this link to the full article: Ascending Tracts (pdf).

Brain Waves

February 10, 2012 3 comments

Introduction Brain waves

The brain generates tiny electrical pulses as The brain produces four main waves with thoughts traverse the labyrinth of the mind. The specific frequencies:

physical conduits of these thoughts are the millions of nerve cells or neurons in the brain. Just as radio signals, in order to make a comprehensible message, are beamed out on radio waves, a band of signals within a defined frequency, so the brain’s activity also occurs in waves. Brain waves can be measured on an electro-encephalograph machine (which is normally abbreviated to EEG Machine). By attaching sensitive electrodes to the scalp, it is possible to measure accurately the type of brain wave that a subject is producing. These waves are usually expressed in the number of cycles per second (CPS) or with their frequency (Hz).

1. Beta level brain waves – range 12-16 Hz (also 13-25 Hz)

2. Alpha level brain waves – range 8-12 Hz 3. Theta level brain waves – range 4-7 Hz
4. Delta level brain waves – range 0.5-3 Hz

The following chart relates each type of brain wave to its principal function. We must remember however, that when we speak of someone being ‘in alpha’ we mean that this is their characteristic and predominant brain wave. Other brain waves will also be present, but in smaller quantities than usual.

Brain activities

The linking of left and right brain activities is important in producing a shift from learning to accelerated learning. Yet our society is very ‘beta orientated’. We are busy thinking about the problem in hand, but don’t leave ourselves sufficiently open to other influences, which would help us memorize faster and make the sort of less expected connections that we call creative thinking.

Beta brain

In beta you don’t see the wood for concentrating on the trees. But learn to relax, increase the proportion of the alpha and ideally theta brain waves, and you have created the conditions where you may begin to see the whole picture.

Alpha brain

‘Alpha’ is a natural and receptive state of mind, that we can all attain through the techniques of relaxation. They principally involve simple and pleasant relaxation exercises and listening to certain types of music.

Theta brain

The theta brain wave pattern is especially interesting. It occurs spontaneously to most of us in the twilight state between being fully awake and falling asleep. Arthur Koestler called it ‘reverie’. This drowsy stage is associated with fleeting semi-hallucinatory images. Thousands of artistic and literary inspirations and scientific inventions have been credited to this state, a sort of freeform thinking that puts you in touch with your subconscious.

Brain waves interpretation

Many psychologists would agree it is a reasonable hypothesis that, when left/right brain symbiosis takes place, conscious and subconscious are also united. The proportion of theta brain waves becomes much higher than normal. This is the moment when logical left brain activity declines. The left brain, which normally acts as a filter or censor to the subconscious, drops its guard, and allows the more intuitive, emotional and creative depths of the right brain to become increasingly influential.

If the hypothesis is true, then do women, popularly characterised as more intuitive, reach a walking theta state more often than men; and can this be associated with the fact that their left/right brain link, the Corpus callosum, is larger and richer in connective capabilities than men’s? We do not yet know, but it is a fascinating area for future research.

At the University of Colorado Medical Centre and at the Biofeedback Centre in Denver, Dr. Thomas Budzyski has found that, when people were trained to achieve and maintain theta brain waves using biofeedback techniques, they did indeed learn much faster. Moreover, many emotional and attitudinal problems were solved at the same time.

To read more click on this link to the full article: Brain Waves (pdf).