18 - Nervous Tissue Flashcards
What neurones occupy the CNS and PNS?
CNS: neurons and glial cells
PNS: cranial, spinal, autonomic nerves and ganglia
What does white matter consist of and where is it found?
- Myelinated axons
- Peripheral in spinal cord
- Central in brain
What does grey matter consist of and where is it found?
- Neuronal cell bodies, dendrites, axon terminals, non-myelinated axons, neuroglia
- Peripheral in brain
- Central in spinal cord
What are neuroglia and what are the four types?
Cells that support neurons metabolically and supportively in the CNS
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependymal cells
What names are given to grey matter in the brain?
- Cortex (convoluted outer layer of the cerebrum)
- Nuclei (deeply placed collections of cell bodies)
What is myelin made of?
- Lipid rich
- Oligodendrocytes in CNS
- Schwann cells in PNS
- Concentric wrapping of cell around axon
- Multiple cells around one axon
Draw and describe the cross section of a human spinal chord?
- Gray matter is butterfly
- Ventral and dorsal horns
- Grey commisure connects left and right grey matter so can communicate
- Ventral fissure
- Pia mater
- Dorsal roots
What is the ventral fissure?
Groove along the anterior midline of the spinal chord that divides it into two symmetrical halves
a.k.a anterior median fissure
What is the pia mater?
Outer connective tissue layer that contributes to blood brain barrier.
No blood vessels in nervous tissue so pia mater supplies tissue with small blood vessels
How are dendrites made?
Nerve growth factor
What is the basic structure of a neuron?
Main cell body (soma), dendrites and proximal axon in CNS
What is the longest nerve and where does it run to?
Sciatic
- From base of spine to tip of the toes
Where do neurons and their supporting cells originate from?
Neuroectoderm
Cells that line the neural tube elongate and proliferate as neural groove closes. Proliferatre in pseudostratified columunar epithelia and CNS produced from here
What is another word for the cell body?
Perikaryon
What are Nissl bodies?
Aggregations of RER, that are basophilic because of ribosomal RNA.
What are the four types of neurones and where are they found and what are their functions?
- Motor: CNS to PNS. Send signals to effectors
- Sensory neurones: PNS to CNS. Send environmental signals to integrative centre
- Integrative: CNS. Collate information
- Anaaxonic: e.g Retina. Act as relays.
What is the structure of an anaaxonic neuron?
- No axon, many dendrites
- Holds onto signal
- Used for vision
What neurons are found in CNS and what in PNS?
CNS: mainly interneurons but pyramid and purkinje as well. multipolar
PNS: unipolar, bipolar and postsynaptic neurones
What is the difference between a bipolar, pseudounipolar and multipolar neuron?
Pseudounipolar: One process from soma. Dorsal root ganglion
Bi polar: Two processes from soma. Sensory neurones
Multipolar: More than two processes. CNS mainly made of these
What are the main things you see of a neuron when looking down light microscope?
- Nucleolus and soma as they take up stain
- Rarely see axon as two small and doesn’t take up dye
When looking at a neuron down a TEM what do you mainly see?
- Lot of RER
- Lot of euchromatin
- Thin nuclear envelope
- Lots of golgi
- Lots of vesicles and ribosomes
Because cell is generating a lot of proteins
What are anterograde and retrograde vesicles?
Anterograde: being moved away from soma to axon
Reterograde: being moved back towards the soma
How do vesicles get from the soma down the axon?
- When a vesicle is ready to move microtubules are assembled at axon pillock
- Motor protein kinesin moves vesicles and mitochondria anterograde
- Motor protein dynactin moves empty vesicles reterograde
How are neurontransmitteres produced?
Immature vesicle contains only enzyme.
As vesicle travels down axon, using microtubules, neurotransmitter is synthesised
What is the fate of vesicles when they reach the terminal axon?
- Lost to neurolemma
- Recyled by endocytosis when recycling neurotransmitter
What are the different types of synapses?
- Axodendritic or axosomatic: direct to plasma membrane of nerve or cell
- Axodendritic (interneuron): synapse at dendritic spine
- Axoaxonic (enhance or inbit above synapses): synpase at axonic end or hillock
- Dendrodendritic (axoaxonic): synapse between dendrites
What is the changing model of how calcium causes neurotransmitters to bind with plasmalemma?
Porocytosis
How would you break the neurovascular bundle down?
Neuron –> Fasicle –> Nerve –> Neurovascular Bundle
What is the structure of a peripheral nerve?
Can contain al three types of nerve fibres (sensory, integrative, motor)
- Endoneurium: Covers individual nerve cells. Loose CT
- Perineurium: Surrounds fasicles. Maintains ionic compositon. CT
- Epineurium: Dense irregular CT. Seperates each nerve type
- Paraneurium: Separates nerves from surrounding structures. Covers epineurium and contains blood vessels
How does the peripheral nerve get to the CNS?
- Joins with the spinal nerve and then goes down dorsal or ventral root
Explain the anatomy of this peripheral nerve.
Why do some neurons appear myelinated but they are not?
- Individual axons are engulfed by cytoplasm of schwann cell but not at mesoaxons so still gaps where ion movement can occur
- Slower propogation of action potential
Where is electrical conduction fastest?
- When myelinated as saltatory conduction
- Larger axon diameter
- Large internodal difference (due to larger diameters)
What are A,B and C nerve fibres?
How does myelination occur in the PNS?
- Schwann cells
- Axon sitting in groove surrounded by Schwann cell
- Mesaxon membrane surrounds axon and a sheet like extension then wraps around the axon forming multiple membrane layers
- Cytoplasm extruded between membrane layers, which compacts the membrane (19-20 layers)
How does myelination occur in CNS?
- Same as Schwann cell wrapping but with oligodendrocytes
- Oligodendrocytes wrap round multiple axons
- Still nodes of ranvier
What is the structure and function of oligodendrocytes?
- Insulate axons and support them (myelin sheath)
- 80% lipid, 20% protein
- Wrap around multiple axons
What are the structure and function of astrocytes?
- Star like structure
- Largest glial cell
- Perineural feet that contain gap junctions
- Contribute to blood brain barrier by covering capillaries
- Provide glucose and lactate from blood to neurons
- Biochemical support for endothelial cells of capillary
- Repair and scar brain and spinal cord after injury
- Release glutamate to slow down nerve impulses at nodes od ranvier
- Maintain ion concentration
What is the structure and function of microglial cells?
- Large elongated nucleus
- Smallest and rarest glial cell
- Resident macrophages
How do microglial cells act as macrophages?
- Sense increase in K+ ions causing them to move. increase due to cells damaged
- Phagocytose dead cells or pathogens then act as APC to monocytes as antibodies cannot enter blood-brain barrier
- Also digest protein tangles associated with dementia, so loss of these cells associated with dementia
Where are ependymal cells located?
- Line the spinal canal
- Posterior to ventral median fissure
What is the structure of ependymal cells?
- Look like ciliated simple columnar
- Have cilia and microvilli
- Modified tight junctions
Why are ependymal cells not epithelial?
- No basement membrane
What is the function of ependymal cells?
- Synthesise and secrete CSF
- Cilia move CSF through ventricles to spinal chord and back
- Microvilli absorve CSF to present pathogens to astrocytes and microglial cells
- Tight junctions usually closed but when high CSF pressure they open so CSF can move into nervous tissue of brain. Tight junctions control fluid release to brain
What is a spinal tap?
Removing some CSF from lumbar region of the spine. Gives some indication as to the molecular and cellular contents of the brain as fluid exchange can occur with brain and CSF when tight junctions open
Can nerves regenerate themselves?
- Do not undergo mitosis when mature so cannot regenerate
- If axons still attached to cell body some potential to regenerate proximally
- Satellite cells in perineuriun can repair once
What is multiple sclerosis and why is it caused?
What are two common degenerative changes in peripheral nerves and what do they cause
- Peripheral neuropathy (non-inflammatory)
- Neuritis (inflammatory)
Cause sensory loss and motor weakness
What are ganglia?
In PNS, collection of cell bodies
Where are neuronal cells normally found in the spinal cord?
In ventral horn along with glial cells
- Astrocyte: round and pale
- Oligodendrocytes: round and dark
- Microglia: dark and elongated
