The substantia nigra (Latin for "black substance", Soemering) or locus niger is a heterogeneous portion of the midbrain, separating the pes (foot) from the tegmentum (covering), and a major element of the basal ganglia system. It consists of two strongly contrasted ensembles, the pars compacta and adjacent dopaminergic groups, and another ensemble made up of the pars reticulata and the pars lateralis. The latter two, along with the pallidal nuclei, are elements of the core of the basal ganglia. Although intricate and interconnected, the two ensembles must imperatively be distinguished.
The substantia nigra compacta and surrounding is responsible for dopamine production in the brain, and therefore plays a vital role in reward and addiction.
Trophoblasts (from Greek threphein: to feed) are cells forming the outer layer of a blastocyst, which provide nutrients to the embryo and develop into a large part of the placenta. They are formed during the first stage of pregnancy and are the first cells to differentiate from the fertilized egg.
In physics, a potential may refer to the scalar potential or to the vector potential. In either case, it is a field defined in space, from which many important physical properties may be derived. Leading examples are the gravitational potential and the electric potential, from which the motion of gravitating or electrically charged bodies may be obtained.
Many entities in physics may be described as vector fields, but it is often easier to work with the corresponding potentials as proxies for the fields themselves. For instance, some force fields exert forces on a body equal to the product of the field and some invariant scalar property of the body, such as the mass or charge. As a body moves through such a force field, it rises and falls in the field's potential, gaining and losing energy through mechanical work. This exchange of energy allows the interaction to be analyzed in terms of simple laws of conservation of energy, without resorting to kinematics, which can be computationally difficult.
The spinocerebellar tract is a set of axonal fibers originating in the spinal cord and terminating in the ipsilateral cerebellum. This tract conveys information to the cerebellum about limb and joint position (proprioception).
Alternating hemiplegia is a rare condition where a child has episodes of weakness affecting one side of the body. This weakness can affect all the muscles on the affected side, not just those in the limbs. After an episode, the weakness improves, but will recur during the next episode. Alternating hemiplegia is a variable condition that affects children to differing degrees and in a variety of ways. This can make it a difficult condition to diagnose and manage but much expertise has been gained in recent years.
Alternating hemiplegia is a condition which has transient weakness of either, or sometimes both, sides of the body. The attacks may alternate or sometimes overlap, that is the second side is affected before the first recovers. Attacks start in the first year of life and are often accompanied by unusual irregular eye movements. The attacks last from less than an hour which is unusual to sometimes several days. When the attacks are prolonged the manifestations are not apparent during sleep or for the first fifteen to twenty minutes on waking when they then return. This is a very characteristic finding and when there are bilateral attacks this may allow feeding and drinking to occur in that short clear period after waking. The episodes of hemiplegia are not epileptic in nature but epileptic seizures may co-exist and require separate anti-epileptic drug treatment.
The cause is not known. Affected children usually have significant learning disabilities and motor organisational problems, including unsteadiness. There is a tendency for these problems to increase with repeated episodes.
Treatment is with flunarizine (a calcium channel blocker). Other drugs have not been found to be consistently helpful.
Serotonergic means "related to the neurotransmitter serotonin". A synapse is serotonergic if it uses serotonin as its neurotransmitter. A substance is serotonergic if it is capable of producing, altering, or releasing serotonin.
A serotonergic, or serotonergic agent, is any chemical which functions to enhance the effects mediated by serotonin in the central nervous system, and they include the following classes of chemicals:
Serotonin precursors (such as tryptophan and 5-HTP)
Cofactors required in the body's production of serotonin
Selective serotonin reuptake inhibitor - A common class of serotonergic antidepressants
Noradrenergic and specific serotonergic antidepressant - Another class of serotonergic antidepressants
serotonergic psychedelics - The serotonergic hallucinogenic drugs
In the brain, the subarachnoid space (subarachnoid cavity) is the interval between the arachnoid mater and pia mater.
It is occupied by a spongy tissue consisting of trabeculæ (delicate connective tissue filaments that extend from the arachnoid mater and blend into the pia mater) and intercommunicating channels in which the cerebrospinal fluid is contained.
This cavity is small on the surface of the hemispheres of the brain. On the summit of each gyrus the pia mater and the arachnoid are in close contact, but in the sulci between the gyri, triangular spaces are left, in which the subarachnoid trabecular tissue is found. Whilst the pia mater closely follows the surface of the brain and dips into the sulci, the arachnoid bridges across them from gyrus to gyrus.
Discuss the mechanism of electroencephalography and its clinical value
In neurophysiology, an evoked potential (or "evoked response") is an electrical potential recorded from a human or animal following presentation of a stimulus, as distinct from spontaneous potentials as detected by electroencephalograms or electromyograms. Evoked potential amplitudes tend to be low, ranging from less than a microvolt to several microvolts, compared to tens of microvolts for EEG, millivolts for EMG, and often close to a volt for EKG. To resolve these low-amplitude potentials against the background of ongoing EEG, EKG, EMG and other biological signals and ambient noise, signal averaging is usually required. The signal is time-locked to the stimulus and most of the noise occurs randomly, allowing the noise to be averaged out with averaging of repeated responses.
Signals can be recorded from cerebral cortex, brain stem, spinal cord and peripheral nerves. Usually the term "evoked potential" is reserved for responses involving either recording from, or stimulation of, central nervous system structures. Thus evoked CMAP (compound motor action potentials) or SNAP (sensory nerve action potentials) as used in NCV (nerve conduction studies) are generally not thought of as evoked potentials, though they do meet the above definition.
Referred painis a phenomenon used to describe pain perceived at a site adjacent to or at a distance from the site of an injury's origin. One of the best examples of this is during ischaemia brought on by an angina pectoris, or heart attack. Even though the heart is directly affected the pain is often felt in the neck, shoulders and back rather than the chest.
X-ray technique that involves injection of radiopaque substance for examining the structural architecture of blood vessels.
State of profound unconsciousness in which the patient does not respond to respond to sensory stimuli. It is usually seen in patients with TBI and with cerebral toxicity.
X-ray brain-imaging technique that provides cross-sectional images of the live brain and body in different planes.
Neuropsychological testing tool that involves simultaneous presentation of auditory stimuli to both ears. It is used for evaluating cerebral dominance.
Genetic expression mode in which a dysfunctional allele possessed by on parent dominates the second allele from the other parent. Each offspring has a 50% probability of inheriting this dysfunctional gene and the disorder.
Technique that records normal and abnormal electrical activity from the brain. Also used to evaluate seizure disorders.
Visual record of muscle electrical activity during rest and spontaneous and/or voluntary movements. It is used to determine causes of muscular weakness, paralysis, and involuntary twitching.
Imaging technique that uses magnetic activity of the tissue to create clear images of the living brain and body.
Genetic mode of inheritance in which both parents transmit the same affected alleles. It results in 25% probability of this dysfunctional gene transmission from both parents and the child being affected with the condition.
Unresponsiveness from which a patient can be aroused transiently with strong and repeated stimulation.
Genetic inheritance mode where diseases or traits are transmitted by a gene or genes on the X (sex) chromosome.