Cells, synapses, and Neurotransmitters

During hight activity the Na+ - K+ ATPase can be outspace, so that

K+ builds up in the Extracellualr fluid (ECF)

Ependymal cells

Ependymal cells are a type of glial cell and are also CSF producing cells.The ependymal cells are cuboidal epithelial cells that line the CSF-filled ventricles in the brain and the central canal of the spinal cord. They contribute to the formation of CSF. The ependymal cells are ciliated.

Types of astrocytes

Fibrous and protoplasmic astrocytes

What are glial cell?

Glial cells are supportive cell in the central nervous system. Unlike neurons, glial cells do not conduct electrical impulses. The glial cells surround neurons and provide support for and insulation between them. Glial cells are the most abundant cell types in the central nervous system. Types of glial cells include oligodendrocytes, astrocytes, ependymal cells, Schwann cells, microglia, and satellite cells.

Axosecretory connections

In Axosecretory connections the axon dumps its transmitter into the blood.

In PNS, what form the myelin sheath?

In PNS, Schawnn cells form myelin.

Electrical synapses

In an electrical synapse, the presynaptic and postsynaptic cell membranes are connected by special channels called gap junctions that are capable of passing electric current, causing voltage changes in the presynaptic cell to induce voltage changes in the postsynaptic cell. The main advantage of an electrical synapse is the rapid transfer of signals from one cell to the next

Astrocytes take up what ion released from the neuron during repolarisation after the action potential.

K+

There are 2 types of vesicles

1) Small clear vesicles, or small synaptic vesicles (SSV's) 2) Large dense core vesicles, or LDCV's.

Synaptic Vesicles (SSV's)

1. Synthesized in cell body, enzymes required for transport of transmitter is added to the membrane via ER to Golgi. 2. Slowly transported along axon through a specialized set of microtubules to the terminal. 3. In the terminal, the specialized transporters will store classical, small molecule transmitters such as dopamine, glutamate and acetylcholine.

It interacts with the capillaries within the CNs to form tight junctions, which make up the blood brain barrier.

Astrocytes

Large Dense Core Vesicles (LDCV's)

Packaging of precursor proteins that are synthesized in the rough ER, moved to Golgi, with processing from prepropeptides to propeptides. Transport down microtubules along axon during which time, further cleavage, glycosylation and bonds are formed, until delivery to the terminal as the peptide. Requires more calcium, longer duration of stimulations to release peptides like NPY.

Synaptobrevin, also called VAMP, or

or vesicle associated membrane protein.

The cell receiving the messsage is the

post-synaptic cell

The cell sending the message is the

pre-synaptic cell

Sometimes axoaxonal synapses occur clse to the point at which an axon makes another axoaxonal connection. These are called

pre-synaptic connections

Synaptic proteins

v-SNARE and t-SNARE

Astrocytes perform a number of functions

Astrocytes are star shaped glial cells that perform a variety of functions in the CNS. Astrocytes provide physical support to neurons and clean up debris within the brain. They also provide neurons with some of the chemicals needed for proper functioning and help control the chemical composition of fluid surrounding neurons. Finally, astrocytes play a role in providing nourishment to neurons.

What helps shut off neurotransmission by taking up released neurotransmitters such as GABA and glutamate.

Astrocytes help shut off neurotransmission by taking up released neurotransmitters such as GABA and glutamate.

Where the axon has access to ions in the ECF?

At the node of Ranvier

Axoextracellular synapses

Axoextracellular synapses have no post-synaptic membrane, the axon dumps its transmitter into the extracellular fluid

Regenerative currents flow across the

Axolemma, only at the nodes.

Location of synapses

Axosomatic Axodendritic Axoaxonic dentrodentritic etc

The two types of vesicles are synthesized differently, store different transmitters and require different stimulation conditions for their release. What does both of them require?

Both vesicle types require calcium.

By speeding up the reaction, astrocytes help regulate what?

By speeding up the reaction, astrocytes help regulate the pH of the intertistial fluid.

Connection synapse are unidirectional or bidirectional?

Connection synapse are bidirectional

Vesicle Fusion Machinery

Docking/tethering Priming (ATP-dept) Fusing (Ca-dept) Recycling

Microglial cells

Like astrocytes, microglia digest parts of dead neurons. The originate in the blood and enter the brain during inflammation; They have phagocytotic activity

Neurotransmitter in SSV are Acetocholine, glutamate, GABA and ATP. What are the transmitters for LDVVs?

Neurotransmitter for LDCVs are Amines and peptides

General mechanism of neurotransmission

Neurotransmitters are formed in a presynaptic neuron and stored in small membrane-bound sacks, called vesicles , inside this neuron. When this neuron is activated, these intracellular vesicles fuse with the cell membrane and release their contents into the synapse, a process called exocytosis. Once the neurotransmitter is in the synapse, several events may occur. It may (1) diffuse across the synapse and bind to a receptor on the postsynaptic membrane, (2) diffuse back to the presynaptic neuron and bind to a presynaptic receptor causing modulation of neurotransmitter release, (3) be chemically altered by an enzyme in the synapse, or (4) be transported into a nearby cell. For the chemical message to be passed to another cell, however, the neurotransmitter must bind to its protein receptor on the postsynaptic side. The binding of a neurotransmitter to its receptor is a key event in the action of all neurotransmitters.

In CNS, what form the myelin sheath?

Oligodendrocytes

Protoplasmic astrocytes

Protoplasmic astrocytes have fewer filaments and are found in the gray matter .

Specific cell types found in the cerebellum are

Purkinje cells

According to their function neurons can be categorized into

Sensory, interneurons, and efferent neurons

Astrocytes

Star-shaped cells that provide physical and nutritional support for neurons.. They help form blood-brain barriers, take up ions and neurotransmitters.

Support cells

Support cells comprise the major part of the nervous system, outnumbering the neurons 10 to 1.

Integration of signals on the input side makes use of

Temporal and spatial summation

Glial cells functions

The Glial cells provide support and protection for neurons. They are thus known as the "supporting cells" of the nervous system. The four main functions of glial cells are: to surround neurons and hold them in place, to supply nutrients and oxygen to neurons, to insulate one neuron from another, and to destroy and remove the carcasses of dead neurons (clean up).

What are the neurons?

The Neurons are the "functional" units of the nervous system. These cells receive inputs, make a "decision" based on these inputs, and transmit "information" on to other cells. They are characterize by their ability to produce action potentials in response to inputs.

Within the ventricles of the brain, a population of modified ependymal cells and capillaries together form a system called

The choroid plexus, which produces the CSF.

What is the function of the active zone in the chemical synapses?

The function of the active zone is to ensure that neurotransmitters can be reliably released in a specific location of a neuron and only released when the neuron fires an action potential.

The main purpose of a myelin layer

The main purpose of a myelin layer (or sheath) is to increase the speed at which impulses propagate along the myelinated fiber. Along unmyelinated fibers, impulses move continuously as waves, but, in myelinated fibers, they hop or "propagate by saltation." Myelin decreases capacitance across the cell membrane, and increases electrical resistance. Thus, myelination helps prevent the electrical current from leaving the axon. It has been suggested that myelin permits larger body size by maintaining agile communication between distant body parts.

What is the nervous tissue is comprised of?

The nervous tissue is comprised of neurons and supporting cells

Oligodendrocytes

The principle function of oligodendrocytes is to provide support to axons and to produce the Myelin sheath, which insulates axons. Provide the insulation (myelin) to neurons in the central nervous system.

Glial cells locations

There 4 major types of glial cells in the CNS and another type in the PNS. There are collectively called neuroglia, which means nerve glue.

Different types of synapses

There are two fundamentally different types of synapses: Chemical and electrical synapses

Fibrous astrocytes

They have many filaments in their cytoplasm and they are found in bundles of axons of myelinated fibers in the white matter of the brain.

Basic functions of neurons

They produce and conduct messages via action potentials (fast!).

Node of Ranvier separates the cell process of one oligodendroglia from the next. True or false.

True

True or false. Electrical synapses form when a connexin hexamer on one cell membrane joins up with a second connexin hexamer on the other cell membrane.

True. . Electrical synapses form when a connexin hexamer on one cell membrane joins up with a second connexin hexamer on the other cell membrane.

True or false. Neurons differ in their size and shape

True. Neurons differ in their size and shape

True or false. The brain and our behavior has a cellular basis

True. The brain and our behavior has a cellular basis. The nervous system behavior derives from cell behavior.

True or false Within the ventricles of the brain, a population of modified ependymal cells and capillaries together form a system called the choroid plexus, which produces the CSF.

True. Within the ventricles of the brain, a population of modified ependymal cells and capillaries together form a system called the choroid plexus, which produces the CSF.

List the 4 different types of glial cells

Types of glial cells include oligodendrocytes, astrocytes, ependymal cells, and microglia cells.

Typically, transmission across chemical synapses is unidirectional or bidirectional?

Unidirectional because the vesicles containing neurotransmitter must be present on the pre-synaptic side.

According to their processes neurons can be categorized into

Unipolar(pseudo), bipolar, or multipolar.

The connexin hexamer forms a pore that allow low molecular weight materiasl such as ions, Na, K, Ca and signaling moleculs such as

cAMP and cGMP to pass from one cell to another.

Astrocytes contain the enzyme called .

carbonic anhydrase. This enzyme speeds up the equilibrium between CO2 and carbonic acid.

Unipolar cells

dorsal root and peripheral ganglion

The lower motor neurons in the ventral horn of the spinal cord are

efferent neurons

Purkinje cells and pyramidal cells are

interneurons

Removal of the excess K+ helps

keep the resting membrane potentials at the proper level so that neuronal activity can continue

Specific cell types found in the cerebral cortex are

pyramidal cells

Cell forms junctions with with other neurons called

synapses

The three SNARE proteins are

synaptobrevin, syntaxin and SNAP-25