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What are the two main cell types in the brain?
- Glial cells or glia
- "Nerve cells"
- "Thinking" cells of the brain
- Receive, process, and transmit information by manipulating the flow of charge across their membranes.
- Note the parallels:
- -Receive = sensory
- -process = integrative
- -transmit = motor
- Each neuron does, in miniature, what the entire nervous system does as an organ
Glial cells or glia
- outnumber neurons
- Maintain the structural and chemical environment of the brain so that neurons can do their job.
- Major role in support and nutrition of the brain
- Do not manipulate information
- Astrocytes - borders and chemical balance
- Oligodendrocytes - insulation
- Microglia - immune defense
- Ependymal cell - make fluid
True or False
Einstein's brain had the same number of neurons as you and I, but more glial cells than normal.
A "Typical" Neuron
- Neurons gather information at dendrites
- they process info in the dendritic tree and cell body
- they transmit info. using their axon and axon terminals.
- a multipolar neuron has an extensively branched tree surrounding its cells body
- Dendrites are where a neuron receives info.
- also used in the initial stages of info. processing
- Function follows form - the shape of the dendritic tree tells us what the neuron does.
True or false
In a dendrite, information coming into fine, faraway branches has less of an effect on the output of a neuron than information coming into thicker, nearer branches.
Soma or cell body
- The metabolic center of a neuron, which includes its nucleus
- it also aids in the processing of information
- The output of a neuron travels through its axon.
- if info. must travel a long distance, the axon is myelinated: covered with an insulated sheath
- The axon ends in one or more axon terminals (or terminal knobs or terminal boutons)
These are the sites where information is sent to the next neuron in line, or to muscle or glands
_________ must process information in many different ways, in many different locations.
True or False
Each type of information processing demands a different shaped neuron.
- For example, if the dendrites are where the neuron picks up info, then there is a huge dendritic tree.
- i.e. one type of neuron in the cerebellum, called a Purkinje cell, has a large and elaborate dentritic tree
- collect a lot of information from a lot of cells over a wide area.
- Example of a multipolar neuron
- Also an example of a multipolar neuron
- a type of cell in the motor areas of cortex
- This cell might collect info over as area of the same size as the purkinje cells, but from a much smaller number of cells,
- so its dendritic tree doesn't need as may branches
What are the three types of neurons?
- Multypolar neurons
- Bipolar neurons
- Unipolar neurons
- neurons that have a dendritic tree and axonal branches that look like mirror images of each other.
- Formed in places where info is relayed - pass information from on cell to another.
- also called pseudo-unipolar neurons
- move the cell body of to the side, so the information can bypass the cell body and not be processed or transformed
- Sensory cell: pick up info. about the environment, pass it along to the CNS
- Picks up information over a large area
- lots of processing
What are the four types of glial cells in the CNS?
- Ependymal cells
Astrocytes (also called astroglia )
- Form the boarders of the CNS
- they cooperate with the blood vessels of the blood-brain barrier (BBB), which keeps certain substances out of the CNS
- The end feet of astrocytes make up the pia mater- one of the coverings on the outside of the brain.
- they also wall off groups of neurons and act as sponges to soak up potentially harmful ions and wast products.
Blood-Brain Barrier (BBB)
- permits only lipid-soluble substances, certain amino acids, and glucose to pass.
- this helps protect the brain from chemical or microbiological damage
- But also makes it hard for the body to mount a defense against something that curcumvents the BBB
Oligodendrocytes (also called oligodendro-glia)
- Form myelin sheaths - which insulate nerve axons that must send information over long distances
- Cannot regrow if cut or damaged
Nodes of Ranvier
Gaps in in the myelin sheath, every few hundred micrometers.
- The brains equivalent to monocytes- When activated turn into macrophages, a type of cell that swallows and digests invaders and waste products
- The brain is termed an "immunologically privileged site", so no immune cells can pass the BBB. Only the microglia are allowed to carry out immune functions in the brain.
- Along with astrocytes, make up a single layer of border cells lining the ventricles.
- Ependymal cells have cilia that continuously "row" CSF through the ventricular system
Open spaces in the brain that are filled with cerebrolspinal fluid (CSF)- which bathes, floats, and cushions the brain.
Cerebrolspinal fluid (CSF)
- bathes, floats, and cushions the brain.
- circulates continuously, being made by a specific tissue in special locations, traveling through the chambers of the brain, spinal cord, and finally being absorbed into veins at another location.
What are the Glial cell types in the PNS?
- Satelite cells
- Schwann cells
- in the PNS perform the same basic function as astrocytes in the CNS
- Maintenance of a favorable chemical environment and mechanical/structural support
- Found mostly in ganglia- collection of nerve cells in the PNS
- Found in the PNS in place of the oligodendrocytes of the CNS
- they can regenerate (regrow) if cut or damaged
- Example: if your cut nerves in your finger the finger may be numb for several weeks but eventually the nerves will regrow.
What is the difference between nerves and tracts?
- They are both bundles of axons all traveling together
- the only difference is that nerves are in the PNS and tracts are in the CNS
True or False
both nerves and tracts may be myelinated or unmyelinated.
How are nerves usually named?
By location or funciton
example: vagus nerve
How are tracts usually named?
- by appearance or location- fasciculus gracilis, part of posterior column
- or by where they start and where they end up (corticospinal tract).