1.17 Nervous tissues Flashcards
Characteristics of nervous tissue.
- Exists as either part of the central nervous system (CNS; brain and spinal cord- what sits inside the cranium and spinal canal) or peripheral nervous system (PNS; nerves, sensory receptors, ganglia- everything else that’s not in cranium and spinal canal).
- Cells of nervous tissue are characterised by having many cellular
processes (cytoplasmic extensions). - Depending upon where you’re looking – CNS or PNS – Nervous Tissue can have different characteristics.
What are the cells within the nervous system and where are they found? Briefly talk about their functions.
- Neurons (N)
- main functional cells - Glial cells (supporting)
- oligodendrocytes (O)
long cytoplasmic processes form wrappings around neuron’s axons
- astrocytes (CNS)
abundant, wrap around blood vessels, contact with axons of neurons - microglia (CNS)
macrophages of CNS (damage/ bacteria thru blood brain barrier, responsible for gobbling them up/ microorganisms - ependymal cells (CNS)
line various cavities- produce cerebral spinal fluid (base surfaces) - Schwann cells (PNS)
neurolemmocyte (membranous cell of peripheral nervous system) - satellite cells (PNS)
found in ganglia(clusters of nerve cell bodies found throughout the body) (part of peripheral ns- specifically found there)
Neurons characteristics (function, structure, etc)
- Cells (neurons) are widely scattered with only limited contact at the extremities.
(Connective tissues are widely placed with ECM, minimal contact with each other. Neurons are similar in that they have supporting cells made up of cellular material) - Neurons have the ability to transmit a signal (action potential) along a cell by reversing the polarity (depolarisation) of the cell membrane (excitable cells).
- Have highly specialised contact points (synapses) that exist between cells which enable the signal to be transmitted from cell to cell. - action potential travels on neuron, jumps from synapses to another cell
- Glials also have them
CNS cells diagram fill in
photos
Fill out the multipolar neuron diagram and describe each of its parts.
(Photos)
- Cell body: soma= body
~ main part of cytoplasm of neuron
- Dendrite: cytoplasmic projections (projections are called dendritic spines
~ increase SA
~ lots of neurons will make synapses upon dendrites of this cell - Axon hillock is important: stimulatory or inherently, neuron determines whether it is gonna allow an action potential to occur
~ summation occurs here and determines whether or not it’s gonna conduct an action potential, will occur from here if yes - Axolemma wall= have lots of voltage-gated ion channels (when it reaches a certain voltage, ion channels open up, allowing it to conduct an action potential
- Schwann cells wrap around axon many many times
~ form insulated regions, where voltage doesn’t intervene where it is wrapped- myelin sheath= region where Schwann cell wraps)- encapsulates it like insulating wire outside of conducting wires- leaves little spaces called nodes of Ranvier - accumulated ion channels in nodes(action potential jumps from node to node, increasing speed of conduction (moves faster myelinated than myelinated (if not indeed to open all the ion channels down the way)
- axon terminal, branching points: the end of those are where synapses are formed (ends are sometimes referred to as axon boutons
What are the types of neuron? Explain
- Multipolar neuron
- carries out motor function: bring about main functioning of skeletal muscles, glands, etc) - Unipolar neuron
- dendrites receiving information (e.g. heat/cold/pressure), action potential in synapses to another neuron to bring about a reflex (reflex arcs) - located in skin, internal organs
- detects stretch
- PNS
- In sensory receptors, we find unipolar neurons
(the rest of them that aren’t associated with special senses) - Bipolar neurons:
- two different types of processes, associated with special senses (retinal cells, olfactory cells, taste cells in tongue)
- dendrites exposed to external environment or close to to detect various things (e.g. light, taste molecules)
- in the PNS, runs back to cns, also type of sensury
How do neurons pass messages to other cells? (diagram available)
- Neurons pass messages to other cells at synapses. These are special contact points between a neuron’s axon terminal (pre-synaptic
neuron) and another cell (post-synaptic cell; e.g., a dendrite of another neuron or a skeletal muscle cell). - They allow communication.
- do that via electrical or chemical transmission of neurotransmitters
1. Action potential comes down along neuron to the synapses, opening voltage-gated ion channels
2. This causes calcium ions to flood the system, causing exocytosis of synaptic vesicles containing neurotransmitters
3. They then bind to ligand-gated ion channels (name of receptors)
4. Once enough of these ligand bind, it opens up ion channels, allowing for sodium and things to enter the cell, which conducts action potential down to the other neuro or the skeletal muscle cell etc.
Where are neuronal cell bodies found?
Neuronal cell bodies (soma) exist only:
* in the CNS (brain, spinal cord)
or
* in accumulations of neuronal cell bodies in
the PNS called ganglia. Nerve cell bodies are
NOT found in peripheral nerves!
- cell bodies for bipolar are found in the epithelia
What are the two types of glial cells that are responsible for the myelination of axons?
- oligodendrocytes for CNS an Schwann cells for PNS
Explain the role of oligodendrocytes and how it carries out its process, provide an example.
- carries out cytoplasmic process, wraps around axon for many times
Saltatory conduction or continuous conduction occurs:
- Myelin, then, acts as an insulator –an action potential “jumps” from one node to the next – this speeds up the conduction of the signal- This is called saltatory conduction.
- Axons that are not myelinated (unmyelinated axons) tend to be smaller in diameter and the action potential travels down the entire length. This is called continuous conduction. It is slower.
- e.g. find in neuron which are autonomic nervous system, e.g. power sympathetic nervous system, most of the times want myelinated if want quick reflex, or else small intestine (no need rapid conduction)- unmyelinated
(- Voltage-gated ion channels are concentrated on the axon cell membrane (axolemma) at the spaces between the myelin sheaths in spaces called Nodes of Ranvier (or “myelin sheath gaps”).
- A myelinated axon, therefore, consists of myelin sheaths (internodes) and nodes of Ranvier. )
How to know that it is oligodendrocytes forming myelin sheaths in the CNS? (How’s it different from Schwann cells?)
- know its CNS if many cytoplasmic processes with no space in between
- looks like octopus (big long arms wrapping around the axon
- can myelinate multiple different axons at once
- or same axon multiple times
- long cytoplasmic processes that wrap around axons.
How to know that it is Schwann cells forming myelin sheaths in the PNS? (How’s it different from oligodendrocytes?)
- In the PNS, Schwann cells can only myelinate one part of one axon(one internode).
- Compared with oligodendrocytes, Schwann cells are always intimately associated with their axons.
- One axon may have up to 10K Schwann cells (depending upon its length).
- schwann wraps around further and further and firm sheath
other types of glial cells(not oligodendrocytes or schwann) (list them and provide a rough explanation)
Astrocytes:
- (star cells)
– have many cellular processes that
mechanically and physiologically support neurons, blood vessels (form blood-brain barrier- tight junctions between endothelial cells between blood vessels preventing leakage of stuff into CNS (prevents damage), etc.. in the CNS
- form scar tissue when damage occurs- (multiply to form scar tissue that prevent reformation of neurons (research looks for how to regrow neuron instead of scar tissue instead)
- Microglia:
– small support cells
– resident macrophages of the CNS (innate immunological function- non-specific) - Ependymal cells
– line the brain’s ventricle and the spinal cords central canal; help produce and monitor cerebrospinal fluid (fluid that bathes central nervous system (moist and nutrition - Satellite cells
– a support cell type found exclusively within ganglia (accumulations of neuronal cell bodies in the PNS) that
surround neuronal cell bodies (like satellites orbiting a planet)
What is myelin?
- Myelin is a wrapping of the axon by cell membrane (therefore, phospholipid-rich) from either an oligodendrocyte or a Schwann cell.
What is the ganglia?
accumulaton of nerve cell bodies
