The PNS and CNS are composed of
Neurons and Support cells
Ganglia (groups of neuron cell bodies), nerves, nerve endings, receptors on neurons or on peripheral targets (skeletal muscle, smooth muscle, etc)
Peripheral Nervous System (PNS)
What are two examples of PNS support cells?
Satellite cells and Schwann cells
Nuclei (groups of neuron cell bodies) or cortices (sheets of neuronal cell bodies), nerves, nerve endings, receptors on neurons (or on glia)
Central Nervous System
What are four support cells of the CNS?
Oligodendrocytesm Astrocytes, Ependymal Cells, and Microglia
The first evidence of a nervous system is detected during the
3rd week in development
The ectoderm in the dorsal midline thickens to form the
Neural Plate
The neural plate gives rise to the
CNS
Develops from the region lateral to the neural plate and gives rise to the PNS
Neural Crest
Develops into the brain and spinal cord (CNS)
Neural tube
The neural tube initially consists of an
Epithelium with cilia
Give rise to neurons and glia of the CNS
Epithelium
Provide guidance to migrating neurons and growth factor support
Glial cells
It is important to note that neurons stop dividing when they
Differentiate
Can not regenerate if injured by environmental toxins, stroke, or unknown factors leading to degenerative diseases
Neurons
Functions to receive, integrate, conduct, and transmit information
Neuron
Neurons vary tremendously in appearance and in
Transmitter content
The dendritic and somal membrane serves and integrating function by
Summing excitatory and inhibitory information that reaches neuron
In a neuron, information is received at contact points called
Synapses
Has the highest concentration of voltage sensitive ion channels and the lowest threshold for firing action potentials
Initial axonal segment
Presynaptic neurons communicate signals with post synaptic neurons via
Synapses
Synthesizes proteins and contains the Nissl Bodies (ribosomes and RER)
Neuronal cell body (soma)
The cell body provides protein to support the
Axon
The axon is entirely dependent on the cell body for essential materials such as
Proteins
The axon lacks
Nissl bodies
The extensions of the cell body and contain most of the organelles of the cell body
Dendrites
Cytoskeletal elements are found throughout the neuron including in the
Axon
Contains cytoskeletal elements but no Nissl bodies
Axon
Axonal transport can occur in which two directions?
Anterograde and Retrograde
From cell body to the axon terminal
Anterograde
From axon terminal to the cell body
Retrograde
Associated with anterograde AND retrograde transport
Fast axonal transport
Moves such constituents as synaptic vesicles, endosomes, and mitochondria
Fast axonal transport
Anterograde transport can also be slow and transport things such as elements of the cytoskeleton and proteins such as
Clathrin
Can also be slow
Anterograde transport
Fast transport in the anterograde or retrograde direction is associated with
Microtubules
The “motor” for anterograde transport and in some rare cases, for retrograde transport
Kinesin
The “motor” for retrograde transport
Dynein
Although it has been most studied in axons, transport also occurs in
Dendrites
Play a support function and help regulate axonal growth
Intermediate filaments and microfilaments
Associated with synaptic vesicle release
Microfilaments
Spacially discrete membrane specializations which function to mediate communications between neurons and target cells
Synapses
What are the two types of synapses?
Electrichal and chemical
Relatively rare in humans and correspond to gap junctions
-seen exclusively during development
Electrical synapses
In electrical synapses, small pores allow ions and molecules like ATP or small signalling molecules to pass from
One cell to the next
Made up of a presynaptic element, a synaptic cleft, and a post synaptic element
Chemical Synapse
Utilizes neurotransmitter molecules
Chemical synapses
The area in the presynaptic neuron where there is an accumulation of neurotransmitter-filled vesicles
Active zone
Neurotransmitters are released from vesicles in the presynaptic neuron into the synaptic cleft by way of
Exocytosis
Vesicles collect in active zones and release their contents when
Action potentials invade the terminal
Vesicle release from the presynaptic neuron into the synaptic cleft requires
Ca2+ influx
Binds neurotransmitter vesicles to actin filaments and other components of the cytoskeleton
Synapsin I
Synapsin I is phosphorylated by a
Ca2+/calmodulin dependent kinase
What happens when synapsin I is phosphorylated by Ca+2 / calmodulin dependent protein kinase?
Vesicles released from actin and move to active zone
Docking and fusion of vesicles with presynaptic membrane appears to be associated with multiple proteins including
VAMPs and t-SNAREs
Calcium sensing proteins such as synaptotagmins are thought to regulate the
Docking and fusing process
What are the four fates of neurotransmitters in the synaptic cleft that have not bound to the postsynaptic neuron?
- ) degraded by enzymes
- ) taken back up by pre-synaptic terminal
- ) taken up by glia
- ) diffuse away
After transmitter release, exocytotic vesicles remain associated with the plasma membrane and are
Recycled
After endocytosis, coated vesicles pinch off from the presynaptic membrane, the coat is lost, and the vesicles fuse with the
Early endosome
In some cases vesicles may be refilled with transmitter without going through the
Early endosome pathway
Can not be used indefinitely. Some is retrogradely transported and degraded by lysosomes in the cell body
Vesicle membrane
Neurotransmitter is synthesized and stored in vesicles. Then an action potential invades the presynaptic neuron and causes
Depolarization of presynaptic terminal resulting in Ca2+ influx
Causes vesicles to fuse with presynaptic membrane
Ca2+ influx
Causes excitatory or inhibitory postsynaptic potential that changes the excitability of the post synaptic cell
Postsynaptic Current
Some diseases and chemicals with which we may come into contact can affect aspects of
Synaptic transmission
Results in impaired vesicle recycling
Congenital myasthenic syndromes
Attacks presynaptic Ca2+ channels
LEM
Affect SNARE proteins involved in vesicle fusion
Botulinum and tetanus
We focused on synapses that are between an axon and a dendrite. There are also
Axo-somatic, axo-axonic, and dendro-dendritic synapses
There are synapses with a cleft of 400nm and no recognizable densities in the
ANS
A highly polarized cell
Neuron
In most cases, each region of a neuron is specialized to contribute to the neuron’s function of
Receiving, integrating, and transmitting information
Generally the regions of the neuron that receive synaptic signals are
-synaptic signals can be found on other parts of the neuron
Dendrites
If the neuron is cut off from its source of trophic substances or if an axon is cut off from the cell body it is in danger of
Dying
In the PNS, groups of neuronal cell bodies are called
Ganglia
In the CNS, groups of neuronal cell bodies are called
Nuclei
Provide structural support for migrating neurons and also provide growth factors
Glial cells
The cell body (soma) can also be referred to as the
Trophic locus of the cell
Increase surface area of dendritic branches
-are extended in an active cell and retracted in an inactive cell
Dendritic Spines
What are the three main types of dendritic spine presynaptic membranes?
- ) Ion channels
- ) G-protein linked receptors
- ) Kinase receptors
Affect polarity of membrane
Ion channels
The cell body (trophic locus) of a neuron has an extensive
RER and ribosomes (Nissl bodies)
Nissl bodies extend into
Dendrites
Organneles move through the axon on microtubules, but in order to reach the terminal, they are transferred to
Actin filaments
Gap junctions that are typically only present during development
Electrical synapses
Invaginations in the post synaptic membrane across from vesiccles
Junctional folds
Phosphorylates synapsin I and allows docked vesicles to move from the actin filament to the presynaptic membrane
Ca2+/calmodulin dependent kinase
Produced by target cells and released from postsynaptic membranes where they are taken up in vesicles at pre-synaptic membranes
Growth factors
Growth factors are taken up in vesicles called signaling endosomes, which exhibit which type of transport?
Retrograde transport
If a lesion causes the cell body to lose it’s growth factors it undergoes
-Nissl bodies move to periphery and disintegrate
Chromatolysis