Cells of the nervous system Flashcards
Nearly how many neurons are within the human brain?
~90billion
How many neurons are estimated to be in the neocortex?
~30billion
What type of neurons compromise approximately 25% of the human cortex?
Stellate neurons
How many synapses do stellate neurons contain per neuron?
~10,000
What type of neurons comprise the rest of the 75% of the cortex?
pyramidal neurons
How many synapses do pyramidal neurons contain per neuron?
~18,000
What are the two main classes of cells that are present in the nervous system?
Neurons and Neuroglial cells
What are neurons?
specialized cells for rapid communication through the conduction of nerve impulses and exchanging information with other neurons
What are neuroglia?
non-neuronal cells that perform various important functions
What is the ratio of neuroglia to neurons?
10 to 1
What were glial cells originally thought to do?
originally thought to be supportive, inactive connective tissue
What are the neuroglia of the CNS?
Oligodendrocytes
Astrocytes
Microglial cells
What are oligodendrocytes?
Send out proteoplastic processes that make contact with nearby axons and form myelin sheaths around them
What does myelin consist of?
long sheet of oligodendrocyte plasma membrane that wraps in a spiral fashion around an axon
What is the bare portion at the end of each myelin sheath?
Node of Ranvier
What is the purpose of myelin sheaths?
has certain insulating properties that allow APs to jump from node to node, therefore does not need to be continuous along the entire length of the axon
What is the name for the jumping of node to node during APs?
Saltatory conduction
What are astrocytes?
star-shaped (or stellate) glial cells that contain multiple processes extending form their somas
- Have a wide range of function
What are the functions of astrocytes?
- Produce ECM proteins and adhesion molecules that guide the migration of neurons during development
- Secrete growth factors that regulate the morphology, differentiation, proliferation, and even survival of neurons
- Aid in the formation of the blood-brain barrier by inducing and maintaining the tight junctions in endothelial cells that form the barrier
- Regulate neurotransmitter removal form the synaptic cleft via uptake
- Intracellular signaling and potentially even intercellular signaling through the generation of intracellular Ca waves which can travel to adjacent cells
Which cells detoxify the CNS by sequestering metals and other neuroactive (and potentially harmful) substances?
Astrocytes
Which glial cell mediates astrogliosis and recruitment in response to neural injury or disease in attempt to reduce neural damage, often results in glial scar formation?
Astrocytes
What are microglial cells?
cells with small somas and numerous processes, they mediate the majority of immune reactions within the CNS
- retain the ability to divide
What do microglial cells do? during development?
Phagocytose degenerating cells that are undergoing apoptosis
- During development, they aid in fiber tract development, gliogenesis, and angiogenesis by secreting growth factors
Which glial cell is involved in presenting antigens to T lymphocytes?
microglial cells
Which glial cell becomes reactive and phagocytic during pathological circumstances in the adult CNS?
microglial cells
What are the glial cells of the PNS?
Schwann cells
What do Schwann cells produce?
myelin
What makes Schwann cells different from oligodendrocytes of the CNS?
They only myelinate one axon at a time
What makes the neural triad?
Neurons, Glia and Vasculature
- integral functional and structural components of the CNS
What is the function of Cerebral vasculature in the neural triad?
supports brain development and function both during embyogenesis into adulthood
- Contributes to neurogenesis
- Transports O2 and nutrients into the brain while removing metabolic waste and carbon dioxide
What do endothelial cells of the cerebral vasculature interact with? and what do they form?
Glial cells of the CNS and form the blood-brain barrier (BBB)
What restricts the passage of molecules between the brain and the systemic circulation?
The endothelial cells that interact with glial cells of the CNS which work together forming the BBB
What does the tripartite synapse consist of?
Astrocyte processes that make contact with pre and postsynaptic neurons
How do astrocytes produce signals?
by exhibiting a form of non-electrical hyperexcitability that utilizes Ca
Calcium signaling in astrocytes
Release of Ca from intracellular stores in response to metabotropic r/c activation –> initiates a signal transduction pathway (STP) that prompts the release of stored Ca within the astrocyte
- Slight changes in intracellular [Ca] can lead to Ca-dependent release of NT molecules
What are gliotransmitters
release of NT molecules in response to changes in intracellular Ca (in astrocytes)
- affects the nearby astrocytes and neurons
Do Ca signalling within astrocytes diplay all-or-none features?
No they do not, they increase in intracellular Ca only in a portion of the astrocyte process
- may or may not spread to other parts of the astrocyte
What are the Gliotransmitters?
ATP
Glutamate
D-serine
Target of ATP
glia to glia
Receptor of ATP
metabotropic
Function/ action of ATP
Decreases glial cell calcium levels
GLU target
neurons and glia
GLU r/c
Neuron: Ionotropic (AMPAR’s & NMDAR’s)
Astrocyte: metabotropic
Function/Action of GLU
- Enhances NT release
- Enhances EPSPs
- Modulates glial Ca levels (can increase or decrease)
Target of D-serine
postsynaptic neuron
Receptor of D-serine
Ionotropic (NMDAR’s)
Funcition/Action of D-serine
Enhances EPSPs
