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Cells of the nervous system - Coggle Diagram
Cells of the nervous system
2 kinds of cells
neurons
receive and transmit information to other cells
adult human brain: 86 billion neurons
glia
a
cell
membrane
: the surface of the cell --> only important chemicals can cross
water, oxygen, sodium, potassium, calcium, chloride, etc. can cross
nucleus
: the structure that contains the chromosomes
mitochondrion
: performs metabolic activities, providing the energy that the cell uses for activity
ribosomes
: sythesize new protein molecules - protein provide building material for the cell and facilitate chemical reactions
some ribosomes flloat freely within the cell, but others are attached to the
endoplasmatic reticulum
endopl. ret.: network of thin tubes - transport newly synthesized proteins to other locations
neurons
motor neuron
its soma is in the spinal cord, it receives excitation through its dendrites and conducts impulses along its axon to a muscle
sensory neuron
specialised at one end to be highly sensitive to a particular type of stimulation, such as light, sound or touch; the sensory neuron conducts information from the skin to the spinal cord
the cell's soma is located on a little stalk off the main trunk
parts of neurons
dendrites
their surface is lined with specialized synaptic receptors, at which the dendrite receives information from other neurons
the greater the surface area of a dendrite, the more information it can receive
branching fibers that get narrower near their ends
soma
(cell body): contains the nucleus, robisomes and mitochondria - most metabolic work occurs here
axon
: thin fiber: conveys an impulse toward other neurons, an organ or a muscle
can be more than a meter in length (e.g.: axons from spinal cord to feet)
vertebrate axons: many are covered with an insulating material -
myelin sheath
, with interruptions known as nodes of Ranvier
a neuron can have only one axon but the axon may have branches - the end of each branch has a swelling, called a
presynaptic terminal
they can be: afferent, efferent and intrinsic
afferent: brings info into a structure - sensory neurons
efferent neurons carries info away from a structure - motor neurons
intrinsic neuron/interneuron: if a cell's dendrites and axons are entirely contained within a single structure - e.g.: an intrinsic neuron of the thalamus has its axon and its denrites within the thalamus
vary enormously in size, shape and function
glia
the term glia is derived from a greek word meaning glue
neurons outnumber glia in a lot of brain areas, especially the cerebellum; but overall the numbers are almost equal
several types
astrocytes
- important for generating rhythms such as breathing
microglia
- tiny cells, part of the immune system, removing viruses and fungi from the brain; they proliferate after brain damage, removing dead or damaged neurons; contribute to learning and memory by removing weak synapses
oligodendrocytes
(in the brain) +
Schwann cells
(in the periphery of the body) - building myelin sheaths around axons
radial glia
- guide the migration of nerions and their axons and dendrites during embryonic development
The blood-brain barrier
like any other organ, the brain needs to receive nutrients from the blood - but many chemicals cannot cross from the blood to the brain - this excluding mechanism is called the blood-brain barrier
why we neeed it: a virus infected cell can be replaced easily, if its for example a skin cell or a blood cell, but the vertebrate brain
does not replace damaged neurons
- BBB minimizes the risk of irreparable damage
but it also blocks out useful chemicals such as amino acids, th ebuilding blocks for proteins (thats why it can only be found in the brain and not in the rest of the body
molecules crossing
molecules that dissolve in the fats of the membrane cross easily too -
vitamins A and D
, + drugs that affect the brain
(how fast a drug takes effect depends largely on how readily it dissolves in fats and therefore crosses the blood-brain barrier)
water
crosses through special protein channels in the wall of the endothelial cells
oxygen + carbon dioxide
- small, uncharged molecules, so they don't need special mechanism to cross
for certain chemicals, the brain uses active transport (a protein-mediated process) -
glucose (the brain's main fuel), amino acids, purines, choline, vitamins, iron
a disadvantage: treating brain cancer - nearly all the drugs used for chemotherapy dail to cross the BBB
nourishment of neurons
glucose (the only nurtient that crosses the BBB in large quantities) - neurons depend almost entirely on this sugar
the human brain uses about 20 % of the body's oxygen and 25 % of its glucose
to use glucose, the body needs vitamin B1,
thiamine
prolonged thiamine deficiency (common in chromic alcoholism) leads to death of neurons + a condition called
Korsakoff's syndrome
, marked by severe memory impairments