Lecture 21 - Nervous Tissue Structure And Function Flashcards
What are the 2 parts/systems of the Nervous System?
Central Nervous System (CNS)
Peripheral Nervous System (PNS)
What is the CNS comprised of?
The Brain and spinal cord
What are the main type of Neurone found in the Central Nervous System?
Relay neuron
What is the Peripheral Nervous System comprised of?
Cranial Nerves, Spinal Nerves and Peripheral Nerves
What are the 2 types of Neurone found in the Peripheral Nervous System (PNS)?
Sensory Neurons
Motor Neurons
What are the 2 types of matter located in the brain and the spinal cord?
Gray matter
White matter
What is white matter made of and why is it white?
It consists of myelinated axons
Myelination is mainly made up of lipids which are white
How is white matter distributed in the brain?
It is central
How is white matter distributed in the spinal cord (transverse/longitudinal section)?
Peripheral
What is Grey matter made of?
Nerve cell bodies
Dendrites
Non-myelinated axons
Axon terminals
Neuroglia
How is grey matter distributed in the brain?
Peripheral
Also in areas called nuclei
How is grey matter distributed in the spinal cord (transverse/longitudinal section)?
Central Butterfly shape
What is a dendrite?
Extensions of the nerve cell body which receive signals so the nerve cell body can receive inputs
What is a Perikaryon?
The cell body of a neurone
Describe the structure of the grey matter in the spinal cord
Butterfly shape
Prongs/Wings on either side of spinal cord
Posterior prongs called Dorsal Horns (DH)
Anterior prongs called Ventral Horns (VH)
Grey Commissure (GC) is the branch that connects the 2 wings together
What is the role of the white matter?
Contains nerve fibres that form ascending and descending tracts
What is the Pia mater?
The outer connective tissue layer of the brain
Blood vessels are here
What cell is part of and produces the myelin for axons in the CNS?
Oligodendrocytes
What cell is part of and produces the myelin for axons in the PNS?
Schwann cell
What are Nissl bodies?
Granules in the cytoplasm of the Perikaryon (Cell body of neurone) made of aggregations of Rough ENdoplasmic Reticulum (lots of ribosomal RNA)
Basic structure of a neuron
Main cell body (Perikaryon)
Cytoplasmic projections (Dendrites and axon)
Perikaryon, dendrites and proximal part of axon in CNS
Distal axon in PNS
What are the 4 Types of Neuron?
Sensory
Integrative
Motor
(Anaxonic)
What is the function of a sensory neuron?
Sends environmental signals to integrative centre
Periphery towards CNS
What is the function of an integrative neuron?
Collates all information
CNS
What is the function of a motor neurone?
Sends signals to effector tissues
CNS to Periphery
What are the 2 different structures sensory neurones can have?
Bipolar
Psuedounipolar
Describe the structure of a bipolar neuron
Perikaryon (cell body) is inline with the signal/impulse
Has 1 axon and 1 dendrite
Describe the structure of a psuedounipolar neuron
The Perikaryon is not inline with the signal
The Perikaryon use not found in CNS
What is the function of an Anaxonic neurone?
They act as relays
Found in the retina and some parts of the CNS
What is the structure of an Anaxonic neurone
NO AXON
Many DENDRITES
Dendrites releases neurotransmitter
Where are the cell bodies of pseudounipolar, bipolar and postsynaptic autonomic neurones found?
Outside the CNS
Where are Purkinje and pyramidal cells (both integrative neurones) found?
In CNS
What colour do Nissl bodies get stained with Cresyl violet?
PURPLE (stains the Ribosomal RNA)
So nucleolus and Nissl bodies easy to see
What does Anterograde mean?
Moving towards the axon/away from the perikaryon nucleus
What does retrograde mean?
Moving back towards nucleus
What is the axon hillock?
The hill like structure between the main cell body of the neuron and the axon
Where is lots of Golgi apparatus found in neurone?
The axon hillock
Why is there lots of Golgi at the axon hillock?
Enzymes in Golgi vesicles make neurotransmitter which need to travel down the axon
How does neurotransmitter travel down an axon to the synapse?
The microtubule shuttle system
The negative (retrograde) end of the microtubule removed and added onto the positive (anterograde) end
A Kinesin with anterograde vesicle attached and a Kinesin with mitochondria attached walk down the microtubule
What is Kinesin?
Protein associated with the microtubule
What is the role of Kinesin?
It walks the vesicle containing the neurotransmitter (anterograde vesicle) and a mitochondria to the terminal bouton of the axon
What happens to the microtubule once it reaches the terminal bouton?
It dissolves so vesicle with neurotransmitter and mitochondria are deposited at the terminal
How is the empty (retrograde) vesicle transported back to the cell body?
Microtubule with Dynactin associated to it walks along the microtubule as the positive (anterograde) end of the microtubule is removed and added to the negative (retrograde) end
What is dynactin and what is its function?
Protein associated with microtubule which is transported the empty retrograde vesicle back to the perikaryon
Why do the mitochondria which have been transported to the terminal bouton remain there?
They provide the Ca2+ needed for neurotransmitter to fuse with he plasmalemma
What happens to neurotransmitter once its been released from its vesicle into he synaptic cleft?
Binds to postsynaptic neuron receptor
If not bound recycled back into synaptic knob by pinocytosis
What’s are the 4 connective tissue layers found in nerves?
Endoneurium
Perineurium
Epineurium
Paraneurium (fascia separating nerves from surrounding structures
What is the Endoneurium
Loose connective tissue surrounding a single axon
Endoneurium = myelination created by schwann cells
What is perineurium?
Specialised connective tissue which contains transport proteins to control the ionic concentration of a fascicle
Surrounds clusters of axons to form a FASCICLE
What is Epineurium?
Dense Irregular connective tissue
Contains all the fascicles
What is the Paraneurium?
Dense regular connective tissue
Spiral connective tissue which surrounds multiple nerves.
Fascia that separates nerves from surrounding structures
What does damage to the myelin in the CNS cause?
Multiple Sclerosis
What does damage to myelin in the PNS cause?
Gillian Barre syndrome
How does an axon of the PNS become myelinated by a Schwann cell?
Axon surrounded/engulfed by a Schwann cell
Mesaxon membranes surround embedded axon
1 mesaxon membrane successively wraps axon in concentric circles stimulated by Neuregulin 1 (NRG1)
Cytoplasm of Schwann cell squeezed out , this compaction forms the finished myelin
What is Neuregulin 1?
An epidermal growth factor
What does Neuregulin 1 do?
Stimulates a mesaxon of the Schwann cell to wrap around the embedded axon in successive concentric circles about 20 times
What does a mutation in the Neuregulin-1 gene (NRG-1) cause?
Schizophrenia
How does an Oligodendrocyte myelinate a nerve in the CNS?
Produces MULTIPLE cytoplasmic processes that wrap around MULTIPLE axons
What is the key difference in the myelination process of a Schwann cell (PNS) and Oligodendrocyte (CNS)?
The cell body of the Oligodendrocyte sits outside of the neuron
The cell body of a Schwann cell wraps itself around the neuron
How do Myelinated peripheral never appear with Toluidine blue stain?
Thick continuous blue layer (indicates the myelination)
Toluidine stains fat blue
How do unmyelinated peripheral nerves appear with Toluidine stain?
2 separate blue layers
Inner layer is membrane of nerve/axon
Outer layer is membrane of Schwann cell
The Schwann cell is not contiguous
What are the gaps between 2 schwann cells called?
Nodes of Ranvier
What is the small amount of cytoplasm that can be found at the nodes of Ranvier called?
Schmidt Lanterman Clefts
Do myelinated or unmyelinated nerves transmit nervous impulses the fastest?
Myelinated
Saltatory conduction can occur
What is saltatory conduction?
When the electrical impulse jumps from 1 node of Ranvier to the next since the myelination insulates the axon so depolarisation can only happen at these regions
Why is the conduction of an electrical impulse in an unmyelinated axon slower than a myelinated one?
Depolarisation has to continuously progress all the way down the axon which is slower than jumping between nodes of Ranvier in a myelinated axon
How does diameter of an axon affect the speed it conducts nervous impulses?
Larger the diameter the faster the speed of impulse transmission
Why do axons with larger diameters conduct electrical impulses faster?
Less resistance to flow of ions
The gaps between Nodes of Ranvier are larger in myelinated axons
Describe the structure of an unmyelinated nerve
The axons are engulfed by the cytoplasm of the schwann cell
There are gaps between the axons
What are the support cells of the CNS called?
Neuroglial cells (Glia)
What are the 4 types of Neuroglial cells in the CNS
Oligodendrocytes
Astrocytes
Microglial cells
Ependymal cells
Role of Oligodendrocytes
Myelinate/insulate axons in the CNS
Describe the structure of an Astrocyte
Star like structure
Have feet which attach to blood vessels (peri vascular feet) in the brain and feet which attach to nerves (perineural feet)
What is the role of an Astrocyte?
Contributes to blood brain barrier
Transports nutrients (lactate) from blood to nerve cells
Release Glutamate near to Nodes of Ranvier regulating/stimulating nervous impulses
What is the strucutre of a Microglial cell?
Large cell with FLAT ELONGATED NUCLEUS
What is the role of Microglial cells?
They are macrophages which reside in the CNS
They have immune function
Remove damaged nerve cells
Digest protein tangles associated with senile DEMENTIA and ALZHEIMERS
Where are Ependymal cells located in the CNS?
They are located in the spinal canal which is at the centre of the Grey Comissure which is Posterior to the Ventral Median Fissure
What type of tissue are Ependymal cells derived from?
neural tissue and neural crest
What structures do Ependymal cells have on their Apical surface?
Cilia
Microvilli
What is the function of Ependymal cells?
Produce and secrete Cerbrospinal Fluid (CSF)
Cilia moves CSF through ventricles to spinal cord
Microvilli absorb CSF for removal of PATHOGENS
CSF also protects brain and spinal cord from sudden impacts
What is the importance of the modified tight junctions of Ependymal cells?
Control release of CSF into brain
What is Multiple Sclerosis (MS)?
Autoimmune degradation of the myelin sheath
Patchy loss, some parts of axon also destroyed
Is remmiting and relapsing
MS affects which part of the nervous system?
CNS
Degrades myelin in CNS
What are the Symptoms of MS?
Fatigue
Vision problems (Diplopia)
Slurred speech (Dysarthria)
Mobility issues
Dysphagia (Difficulty eating and swallowing)
Numbness and tingling
What is Guillian Barré syndrome?
Demyelination of motor neurones
Affects the PNS
What type of symptoms does Guillain Barré syndrome cause?
Produces bilateral symptoms affecting both sides of body
Numbness
Pins and needles
Weakness
Pain
Balance and coordination
Why can Guillain Barré syndrome be deadly?
May affect Neurons leading to intercostal muscles and diaphragm leading to breathing issues
Why are symptoms produced from MS and GBS?
Speed of conduction of impulses down axons are affected
