Biopsychology and Neuropsychology (2017-2018)

Nerve Cells and Nerve Impulses

The nervous system consists of two kinds of cells, neurons and glia.

Neurons: receive information and transmit it to other cells

• The adult human brain contains approximately 100 billion neurons
• Santiago Ramón y Cajal: he used newly discovered staining techniques to establish that the nervous system is composed of separate cells, now known as neurons
• Neurons contain the same internal structures as other animal cells
• Neurons have four major parts: a cell body, dendrites, an axon, and presynaptic terminals. Their shapes vary greatly depending on their functions and their connections with other cells.
• A motor neuron, with its soma in the spinal cord, receives excitation through its dendrites and conducts impulses along its axon to a muscle
• A sensory neuron is specialized at one end to be highly sensitive to a particular type of stimulation, such as light, sound, or touch

Glia: the connective tissue of the nervous system, consisting of several different types of cell associated with neurons

• Astrocytes: star-shaped glial cells in the brain and spinal cord
  • By surrounding a synapse between neurons, an astrocyte shields it from chemicals circulating in the surround
  • By taking up ions released by axons and then releasing them back, an astrocyte helps synchronize the activity of the axons, enabling them to send messages in waves
  • Astrocytes guide the formation and elimination of synapses
  • They remove waste material created when neurons die and control the amount of blood flow to each brain area
  • During periods of heightened activity in some brain area, astrocytes dilate the blood vessels to bring more nutrients into that area
• Microglia: cells that act as part of the immune system, removing waste material, viruses, and fungi from the brain
  • They proliferate after brain damage and in most brain diseases
  • Microglia are necessary for the survival of certain neurons early in life
  • They also contribute to learning by removing the weakest synapses
• Oligodendrocytes and Schwann cells: build the myelin sheaths that surround and insulate certain vertebrate axons
  • They supply an axon with nutrients necessary for its functioning
• Radial glia: guide the migration of neurons and their axons and dendrites during embryonic development

Blood–brain barrier: this barrier protects the nervous system from viruses and many dangerous chemicals.

• Because of the barrier many molecules cannot enter the brain
• The barrier consists of an unbroken wall of cells that surround the blood vessels of the brain and spinal cord.
• A few small, uncharged molecules such as water, oxygen, and carbon dioxide cross the barrier freely. So do molecules that dissolve in fats.
• Active transport proteins pump glucose, amino acids, and a few other chemicals into the brain and spinal cord.
• Adult neurons rely heavily on glucose, the only nutrient that crosses the blood–brain barrier in large quantities. They need thiamine (vitamin B1) to use glucose.

References:

Kalat, J. (2016). Biological psychology (12th edition). Boston, MA: Cengage Learning

https://www.google.nl/search?q=glia+definition&oq=glia+definition&aqs=chrome..69i57j0l5.3118j1j7&sourceid=chrome&ie=UTF-8

Picture retrieed from: https://twitter.com/johnpjpinel