health-brain

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Motor system
Motor systems are areas of the brain that are more or less directly involved in producing body movements, that is, in activating muscles. With the exception of the muscles that control the eye, all of the voluntary muscles in the body are directly innervated by motor neurons in the spinal cord, which therefore are the final common path for the movement-generating system.Spinal motor neurons are controlled both by neural circuits intrinsic to the spinal cord, and by inputs that descend from the brain. The intrinsic spinal circuits implement many reflex responses, and also contain pattern generators for rhythmic movements such as walking or swimming. The descending connections from the brain allow for more sophisticated control.

The brain contains a number of areas that project directly to the spinal cord.At the lowest level are motor areas in the medulla and pons. At a higher level are areas in the midbrain, such as the red nucleus, which is responsible for coordinating movements of the arms and legs. At a higher level yet is the primary motor cortex, a strip of tissue located at the posterior edge of the frontal lobe. The primary motor cortex sends projections to the subcortical motor areas, but also sends a massive projection directly to the spinal cord, via the so-called pyramidal tract. This direct corticospinal projection allows for precise voluntary control of the fine details of movements.
Publicat de health victorro la 05:55 0 comentarii
Etichete: legs, Motor, spinal, system
Arousal system
Perhaps the most obvious aspect of the behavior of any animal is the daily cycle between sleeping and waking. Arousal and alertness are also modulated on a finer time scale, though, by an extensive network of brain areas.

A key component of the arousal system is the suprachiasmatic nucleus (SCN), a tiny part of the hypothalamus located directly above the point at which the optic nerves from the two eyes cross. The SCN contains the body's central biological clock. Neurons there show activity levels that rise and fall with a period of about 24 hours, circadian rhythms: these activity fluctuations are driven by rhythmic changes in expression of a set of "clock genes". The SCN continues to keep time even if it is excised from the brain and placed in a dish of warm nutrient solution, but it ordinarily receives input from the optic nerves, through the retinohypothalamic tract (RHT), that allow daily light-dark cycles to calibrate the clock.

The SCN projects to a set of areas in the hypothalamus, brainstem, and midbrain that are involved in implementing sleep-wake cycles. An important component of the system is the so-called reticular formation, a group of neuron-clusters scattered diffusely through the core of the lower brain.Reticular neurons send signals to the thalamus, which in turn sends activity-level-controlling signals to every part of the cortex. Damage to the reticular formation can produce a permanent state of coma.

Sleep involves great changes in brain activity. Until the 1950s it was generally believed that the brain essentially shuts off during sleep,but this is now known to be far from true: activity continues, but the pattern becomes very different. In fact, there are two types of sleep, slow wave sleep (usually non-dreaming) and REM sleep (dreaming), each with its own distinct brain activity pattern. During slow wave sleep, activity in the cortex takes the form of large synchronized waves, where in the waking state it is noisy and desynchronized. Levels of the neurotransmitters norepinephrine and serotonin drop during slow wave sleep, and fall almost to zero during REM sleep; levels of acetylcholine show the reverse pattern.
Publicat de health victorro la 05:54 0 comentarii
Etichete: Arousal, REM, system
Brain energy consumption
Although the brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization.The demands of the brain limit its size in some species, such as bats. The brain mostly utilizes glucose for energy, and deprivation of glucose, as can happen in hypoglycemia, can result in loss of consciousness. The energy consumption of the brain does not vary greatly over time, but active regions of the cortex consume somewhat more energy than inactive regions: this fact forms the basis for the functional brain imaging methods PET and fMRI.
Publicat de health victorro la 05:53 0 comentarii
Etichete: Brain, consumption, energy
Effects of damage and disease
Even though it is protected by the skull and meninges, surrounded by cerebrospinal fluid, and isolated from the bloodstream by the blood-brain barrier, the delicate nature of the brain makes it vulnerable to numerous diseases and several types of damage. Because these problems generally manifest themselves differently in humans than in other species, an overview of brain pathology and how it can be treated is deferred to the Human brain, Brain damage, and Neurology articles.
Publicat de health victorro la 05:53 0 comentarii
Etichete: damage, disease, Effects
Brain and mind
Understanding the relationship between the physical brain and the functional mind is a

challenging problem both philosophically and scientifically. The most straightforward

scientific evidence that there is a strong relationship between the physical brain matter

and the mind is the impact physical alterations to the brain, such as injury and drug use,

have on the mind.

The mind-body problem is one of the central issues in the history of philosophy, which

asks us to consider if the correlation between the physical brain and the mind are

identical, partially distinct, or related in some unknown way. There are three major schools

of thought concerning the answer: dualism, materialism, and idealism. Dualism holds that the

mind exists independently of the brain; materialism holds that mental phenomena are

identical to neuronal phenomena;and idealism holds that only mental substances and

phenomena exist. In addition to the philosophical questions, the relationship between

mind and brain involves a number of scientific questions, including understanding the

relationship between thought and brain activity, the mechanisms by which drugs influence

thought, and the neural correlates of consciousness.

Through most of history many philosophers found it inconceivable that cognition could be

implemented by a physical substance such as brain tissue. Philosophers such as Patricia

Churchland posit that the drug-mind interaction is indicative of an intimate connection

between the brain and the mind, not that the two are the same entity. Even Descartes,

notable for his mechanistic philosophy which found it possible to explain reflexes and other

simple behaviors in mechanistic terms, could not believe that complex thought, language in

particular, could be explained by the physical brain alon.

• Added on: Mar 13th, 2009
• Country: Romania
• Language: English

• Author: rorac2009
• Listed in: Health Medicine
• Tags: arousal system motor system