Nervous tissue Flashcards
Is nervous tissue excitable ?
Yes
Why are nervous tissue considered excitable ?
The exhibit electrical excitability - the ability to respond to certain stimuli by producing electrical signals (action potentials).
Why can action potentials propagate along the plasma membrane of a neuron or muscle fiber ?
They can travel through specific voltage gated ion channels.
What happens after a action forms in a neutron ?
The neuron releases chemicals called neurotransmitters - which allow neutrons to communicate with other neurons, muscle fibers or glands.
What happens when an action potential occurs in a muscle fiber ?
The muscle fiber contracts, resulting in activities such as movements of limbs, propulsion of food through the small intestine and movement of blood out of the heart and into the blood vessels of the heart.
What are the two main classes of cells that make up the nervous tissue ?
Neuron and neuroglia
What do neurons do ?
Propagate information via electrochemical impulses - action potential - which are biochemically linked to the release of chemical signals.
What do neuroglia do ?
Support neutrons and modulating their information propagation.
What are the three main parts of neurons ?
- The cell body
Two kinds of cell processes - dendrites and axon
What does the cell body contain ?
Most of the cytoplasm, the organelles and the nucleus.
Dendrites (structure)
Branch of the cell body and appear as thin extensions
Dendrites (functions)
Major receiving and input portion of a neuron.
Axon (structure)
Single, thin and cylindrical process. Can have myelin insulating layer around it.
Axon (function)
Output portion of a neuron, conducting nerve impulses towards another neuron or other type of tissue.
Synapse
Gap between nerve cells or between nerve cell and target (muscle or gland example).
Across which the impulse is transmitted by chemical compounds such as neurotransmitters.
Multipolar neuron
Several dendrites and axon with the cell body.
Unipolar neuron
Single process extending out of the cell body that divides into the functional dendrite and functional axon.
Bipolar neuron
Single dendrite and axon with cell body.
Astrocyte
- Type of glia
- Abundant in CNS
- Distinctive star shape
- regulate ion concentration in intercellular space
- uptake of breakdown of some neurotransmitters
- forms the blood brain barrier
Microglia
- protects nervous system from infection, not nervous tissue
- related to macrophages
Oligodendrocytes
- Produce myelin
- In CNS
What are the cell membranes referred to as ?
Processes
Axon hillock
Where the axon emerges from the cell body.
Axoplasm
Within the axon hillock, the cytoplasm changes to a solution of limited components.
What is the beginning of the axon called, it occurs after the axon hillock narrows ?
The initial segment.
What is the trigger zone ?
It is a combination of the axon hillock and the initial segment. It is where action potentials are generated.
What are the gaps called on the axon, where is it wrapped with myelin ?
Each gap is called the node of Ranvier. Important in how electrical signals travel down the axon.
Axon segment
The length of the axon between each gap that is wrapped in the axon terminal.
Axon terminal
At the end of the axon. It usually has several branches extending towards the target cell. Each with ends in enlargement - synaptic end bulb.
Synaptic end bulb
Makes the connection with the target cell at the synapse.
How are processes broken down ?
One is the axon and the rest are dendrites.
Unipolar
Only has one process emerging from the cell. Humans have pseudo unipolar cell. Axon that emerges from the cell body, it splits so that the axon can extend long distances. One end is the dendrites and the other is the axons that form synaptic connections with a target.
What type of neuron is unipolar neurons exclusively ?
Sensory neurons
What two unique characteristics due unipolar neurons have ?
- Their dendrites are receiving sensory information, sometimes directly from the stimulus itself.
- Cell bodies of unipolar neurons are always found in the ganglia (clusters of nerve cell bodies in the periphery).
Why is the cell body in the ganglion for unipolar cells?
Sensory reception is a peripheral function (dendrites in the periphery) so the cell body is in the periphery - though closer to CNS in a ganglion and into CNS.
Bipolar cells
Have two processes which extend in opposite directions from the cell body. One is the axon and one is the dendrite. Not very common.
Where are bipolar cells mainly found ?
In the olfactory epithelium (smell) and parts of the retina.
Multipolar
Have one axon and two or more dendrites.
Glia cells in the CNS
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal cell
Glial cells in the PNS
- Satellite cells
- Schwann cell
Function of Astrocyte and satellite cells
Support
Function of oligodendrocytes and Schwann cell
Insulation and myelination
Function of microglia
Immune surveillance and phagocytosis
Function of ependymal cell
Creating CSH - cerebrospinal fluid
Astrocyte
- CNS
- Star shaped
- Many processes extending from cell body
- Processes extend to interact with neurons, blood vessels or connective tissue
- support
- maintaining concentration of chemicals in the extracellular space
- removing excess signaling molecules
- reacting to tissue damage
- contributing to BBB
Oligodendrocytes
- CNS
- few branches that extend from cell body
- each one reaches out and surrounds an axon to insulate it with myelin
Microglia
- Smaller than most glial cells
- CNS
- function related to what macrophages do in the rest of the body
- phagocytosis
Ependymal cell
- filters blood to make cerebrospinal fluid (CSF) which circulates in the CNS
- Ependymal cells line each ventricle
- appear similar to epithelial cells
- single layer of cells with little intracellular space and tight junctions between adjacent cells
- have cilia on their apical surface and help move the CSF to ventricular space
Choroid plexus
Specialized structure in the ventricles where ependymal cells come in contact with blood vessels and filter and absorb components of the blood to produce cerebrospinal fluid.
Satellite cells
- PNS
- Found in sensory and autonomic ganglia
- Surround the cell bodies of neurons
- Support
- Similar tasks to astrocytes but don’t establish BBB
Schwann Cell
- Insulates axons with myelin in the periphery
- Differ from oligodendrocytes in that a Schwann cell wraps around a portion of only one axon segment and no other
- nucleus and cytoplasm of schwann cells are on the edge of the myelin sheath.
Myelin
Lipid rich sheath that facilitates the transmission of electrical signals along the axon. Phospholipids. Also has proteins.
Cytoplasm in myelin
Wrapped around with little to no cytoplasm.
Schwann has cytoplasm, bulges at one side.
Oligodendrocytes - rest of the cell is separate from myelin sheath.
