Neurons, Hormones, and the Brain

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The Nervous System

  • The nervous system comprises the central nervous system and the peripheral nervous system.
  • The central nervous system consists of the brain and the spinal cord. The spinal cord connects the brain to the rest of the body.
  • The peripheral nervous system consists of the somatic nervous system and the autonomic nervous system. The somatic nervous system affects voluntary muscles and organs. The autonomic nervous system affects the heart, blood vessels, glands, and smooth or involuntary muscles.
  • The autonomic nervous system contains the sympathetic nervous system, which prepares the body for emergency action, and the parasympathetic nervous system, which helps the body conserve energy and relax.

Neurons: Cells of the Nervous System

  • Glial cells support neuron function.
  • Neurons, the other type of cell in the nervous system, receive, integrate, and pass along information.
  • A neuron contains the soma, dendrites, axon, and myelin sheath.
  • Terminal buttons at the ends of axons release neurotransmitters or chemicals that cross over to neighboring neurons.
  • The space between neurons is the synapse.
  • The resting potential of a neuron is the stable negative charge inside the neuron when it is inactive.
  • The action potential is a temporary change in electric charge inside a neuron.
  • Neural impulses conform to the all-or-none law, which means that neurons fire to generate an action potential only if stimulation reaches a minimum threshold.
  • In neural communication, receptor sites on postsynaptic cells can be excitatory or inhibitory.


  • Neurotransmitters are chemicals that enable neurons to communicate with each other.
  • Major neurotransmitters include acetylcholine, dopamine, serotonin, endorphins, norepinephrine, GABA, and glutamate.
  • Agonists are chemicals that mimic the action of neurotransmitters.
  • Antagonists are chemicals that block the action of neurotransmitters.

Studying the Brain

  • Researchers use lesioning and electric stimulation of the brain to study animals.
  • To study human brains, researchers use electroencephalographs, computerized tomography, magnetic resonance imaging, and positron emission tomography. Researchers also study the impact of brain injuries and diseases.

Structure and Functions of the Brain

  • The brain consists of the hindbrain, midbrain, and forebrain. Each section of the brain contains subsections, which control different functions.
  • The hindbrain contains the medulla, the pons, and the cerebellum.
  • The midbrain contains a dopamine-releasing system and helps us to locate events in space.
  • The forebrain is the largest part of the brain and includes the thalamus, the hypothalamus, the limbic system, and the cerebrum.
  • Lateralization refers to how the right and left sides of the brain specialize in different functions. The left hemisphere processes verbal skills, while the right side processes nonverbal tasks.
  • The left side of the brain affects the functioning of the right side of the body. Conversely, the right side of the brain affects the functioning of the left side of the body.

The Endocrine System

  • The endocrine system, which consists of glands that release hormones, also helps communication within the body.
  • Hormones are chemicals that regulate body functions.
  • The pituitary gland is the master gland of the endocrine system.
  • Major hormones include thyroxine, insulin, melatonin, adrenal hormones, androgens, estrogens, and progesterone.

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