Anatomy And Physiology

Anatomy Physiology



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The brain is part of the central nervous system which includes in addition to the brain the spinal cord.  The brain is divided into several anatomic structures.  These are the cerebrum and the diencephalon and the cerebellum in addition to the brainstem.  Another division of the brain anatomically is the anterior part or supratentorium and the posterior part or posterior fossa. 

The anterior part of the brain is supplied with blood from the carotid artery, while the posterior part of the brain is supplied with blood from the vertebral and basilar arteries. 

The cortex of the cerebrum supplies the voluntary muscles of the body with motor and sensory innervation.  The anterior part of the cortex supplies muscles of the face and extremeties with motor innervation while the posterior part of the cerebral cortex supplies the muscles with sensory innervation. 

The left side of the cortex supplies innervation to the right side of the body while the right side of the cortex supplies the left side of the body with innervation. 

Upper motor neurons are neurons in the cortex and which supply motor innervation to facial muscles in addition to muscles of the extremeties.  Lower motor neurons are neurons in the spinal cord and which innervate the skeletal muscles with motor innervation. 

Lack of reflexes in muscles of the extremeties is an indication to damage of lower motor neurons in the spinal cord while hyperreflexia is an indication to upper motor neurons damage in the brain.  The hyperreflexia occurs due to the lack of the usual inhibition on neurons activity by the upper motor neurons.

The basal ganglia is part of the brain and which is specific for coordination of muscles activity of the exteremeties.  It does so along with the cerebellum.  The basal ganglia nuclei usually secrete the neurotransmitter dopamine.  Dopamine is an inhibitory neurotransmitter which functions by inhibiting muscular activity. 

A damage to the basal ganglia as occurs in parkinson disease or in wilson dsease can lead to overactivity of of muscles tremor due to the lack of usual inhibition by the dopamine secreting cells.  Another cause to this phenomenon is administration of drugs that antagonize the action of dopamine such as the antipsychotic drug zyprexa.

The cerebellum like the basal ganglia has a function related to coordination of muscular movement.  A damage to the cerebellum can cause as a result movement incoordination or ataxia. 

The brainstem is another part of the posterior brain and is divided into three structures.  These are the medulla oblongata and the pons and the midbrain.  The brainstem has important functions that are related to maintaining important physiological functions such as breathing and heartbeat rythme control. 

Two endocrine glands are very important for the proper functioning of the body are located at the base of the brain.  These are the pituitary gland and the hypothalamus.  The pituitary gland is located immediately below the hypothalamus and is controlled by hormones that are secreted by the hypothalamus. 

The pituitary gland despite its small size controlls all endocrine glands in the body by secreting hormones that stimulate these glands.  All hormones that are secreted by the pituitary gland are regulated by a postitive feedback loop from hormones in the hypothalamus except of hormone which is called prolactin and which is controlled by a negative feedback from a hormone from the hypothalamus and which is called dopamine.

The brain contains empty spaces within its structure that houses fluid that is called cerebrospinal fluid.  This empty space is divided into four chambers which are called ventricles.  These ventricles are divided into two lateral rooms and one that is called the third ventricle and another that is called the fourth ventricle. 

These ventricles communicate with each other through opennings that are called foramina.  The cerebrospinal fluid is produced by the choroid plexus that lines the epithelium of the ventricles.  The rate of production of the cerebrospinal fluid and its reabsorption into the superior sagittal sinus is kept constant so that a constant intracranial pressure is maintained.  

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