Organization of Nervous System

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Organization of Nervous System
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Neurotransmitter

• Chemical made by neurons, or nerve cells. Neurons
  send out neurotransmitters as chemical signals to
  activate or inhibit the function of neighboring
  cells.
• Within the central nervous system, which consists
  of the brain and the spinal cord,
  neurotransmitters pass from neuron to neuron. In
  the peripheral nervous system, which is made up
  of the nerves that run from the central nervous
  system to the rest of the body, the chemical
  signals pass between a neuron and an adjacent
  muscle or gland cell.

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Types of Neurotransmitters

• Nine chemical compounds that belong to three
  chemical families.
• Amines Acetylcholine, norepinephrine, dopamine
  and serotonin.
• Amino Acids Glycine, glutamic and aspartic
  acids, seratonin and gamma-amino butyric acid
  (GABA).
• Peptides Compounds that contain at least 2, and
  sometimes as many as 100 amino acids.

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Amines and Amino Acids

• Amines
• Acetylcholine Most widely used in the body.
• Dopamine involved in muscle movement and
  controls secretion of prolaction (triggers milk
  production in nursing mothers).
• Amino Acids Glutamic acid and GABA are the most
  abundant neurotransmitters within the central
  nervous system, and especially in the cerebral
  cortex, which is largely responsible for such
  higher brain functions as thought and
  interpreting sensations.

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Chemical Transmission of Signals

• When the electrical signal reaches the tip of an
  axon, it stimulates small presynaptic vesicles in
  the cell. These vesicles contain chemicals called
  neurotransmitters, which are released into the
  microscopic space between neurons (the synaptic
  cleft). The neurotransmitters attach to
  specialized receptors on the surface of the
  adjacent neuron.
• This stimulus causes the adjacent cell to
  depolarize and propagate an action potential of
  its own. The duration of a stimulus from a
  neurotransmitter is limited by the breakdown of
  the chemicals in the synaptic cleft and the
  reuptake by the neuron that produced them.

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How Neurotransmission Works
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Hormones

• Hormones from the endocrine organs are secreted
  directly into the bloodstream, where special
  proteins usually bind to them, helping to keep
  the hormones intact as they travel throughout the
  body.
• The proteins also act as a reservoir, allowing
  only a small fraction of the hormone circulating
  in the blood to affect the target tissue.
• Specialized proteins in the target tissue, called
  receptors, bind with the hormones in the
  bloodstream, inducing chemical changes in
  response to the bodys needs.
• Typically, only minute concentrations of a
  hormone are needed to achieve the desired effect.

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Hormone Regulation

• Too much or too little hormone can be harmful to
  the body, so hormone levels are regulated by a
  feedback mechanism.
• Feedback works something like a household
  thermostat.
• When the heat in a house falls, the thermostat
  responds by switching the furnace on, and when
  the temperature is too warm, the thermostat
  switches the furnace off.
• Usually, the change that a hormone produces also
  serves to regulate that hormone's secretion.

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Endocrine System

• Hypothalamus
• Pituitary Gland
• Thyroid
• Parathyroid
• Adrenal Glands
• Pineal Body
• Pancreas
• Ovary/Testis

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Hypothalamus and Pituitary
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Hypothalamus

• Found deep within the brain, directly controls
  the pituitary gland. It is sometimes described as
  the coordinator of the endocrine system.
• When information reaching the brain indicates
  that changes are needed somewhere in the body,
  nerve cells in the hypothalamus secrete body
  chemicals that either stimulate or suppress
  hormone secretions from the pituitary gland.
• Acting as liaison between the brain and the
  pituitary gland, the hypothalamus is the primary
  link between the endocrine and nervous systems.

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Pituitary Gland

• Often described as the bodys master gland, the
  pituitary secretes several hormones that regulate
  the function of the other endocrine glands.
• Contains two lobes that have different functions
  Anterior and Posterior

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Anterior and Posterior Lobes

• Regulates the activity of the thyroid and adrenal
  glands as well as the reproductive glands.
• Regulates the body's growth and stimulates milk
  production in women who are breast-feeding.
• Hormones secreted by the anterior lobe include
  adrenocorticotropic hormone (ACTH), thyrotropic
  hormone (TSH), luteinizing hormone (LH),
  follicle-stimulating hormone (FSH), growth
  hormone (GH), and prolactin.
• Also secretes endorphins, chemicals that act on
  the nervous system to reduce sensitivity to pain.

• Contains the nerve endings (axons) from the
  hypothalamus, which stimulate or suppress hormone
  production.
• Secretes antidiuretic hormones (ADH), which
  control water balance in the body, and oxytocin,
  which controls muscle contractions in the uterus.

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Thyroid and Parathyroid

• Secretes hormones in response to stimulation by
  TSH from the pituitary gland.
• Secretes thyroxine and three-iodothyronine that
  regulate growth and metabolism and play a role in
  brain development during childhood.

• Four small glands located at the four corners of
  the thyroid gland.
• Secretes parathyroid hormone to regulate the
  level of calcium in the blood.

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Adrenal Gland

• Produces a variety of hormones called
  corticosteroid.
• These regulate salt and water balance in the
  body, prepare the body for stress, regulate
  metabolism, interact with the immune system and
  influence sexual function.
• The inner part, the adrenal medulla, produces
  catecholamines, such as epinephrine, also called
  adrenaline, which increase the blood pressure and
  heart rate during times of stress.

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Pineal Body

• Located in the middle of the brain.
• Secretes melatonin, a hormone that may help
  regulate the wake-sleep cycle.