14. Nervous Tissue Flashcards
What are the two divisions of the nervous system?
• Central nervous system (CNS)
- Brain and spinal cord
• Peripheral nervous system (PNS)
- Cranial nerves and spinal nerves and some of the peripheral nerves
Where is the grey matter in the brain and spinal cord?
- Peripheral in brain and in areas called ‘nuclei’
* Central in spinal cord (H- or butterfly-shaped)
What does the grey matter consist of?
Consists of: • Nerve cell bodies • Dendrites • Axon terminals • Non-myelinated axons • Neuroglia (support cells)
Where is the white matter found in the brain and spinal cord?
- Central in brain
* Peripheral in spinal cord
What des white matter consist of?
Consists of:
• Myelinated material
• axons
• no cell bodies
What is the grey matter roughly in the form of in the spinal cord?
A butterfly
What are the anterior and posterior prongs of the grey matter in spinal cord referred to as?
The anterior = ventral
horns
posterior = dorsal horns
In the grey matter in spinal cord, what connects the dorsal and ventral horns?
grey commissure
What is the direction of the ascending and descending neurones in the white matter?
- Ascending neurone - from periphery to brain
* Descending neurone - from rain to periphery
Where do the neurones from ventral and dorsal horns come out of?
Neurones in the dorsal horn come out through the dorsal root.
Neurones in the ventral horn come out through the ventral root.
What is the pia mater?
The outer connective tissue layer of the spinal cord
What is the ventral fissure?
a groove along the anterior midline of the spinal cord that incompletely divides it into symmetrical halves
Describe the location of the structures of a neurone
• The main cell body (soma), dendrites, and proximal part of
the axon are within the CNS
• Distal axon and arborisations are within PNS
In the CNS what produces the myelin?
In the CNS, the myelin for the axon is produced by, and is
part of, an oligodendrocyte
In the PNS what produces the myelin?
in the PNS, the myelin is produced by, and is part of, a Schwann cell
What are the 4 types of neurones?
- Motor
- Sensory
- Integrative
- Anaxonic
What is the location of motor neurones?
CNS to periphery
What is the function of motor neurones?
to send signals to effector tissues
What is the location of sensory neurones?
Periphery towards CNS
What is the function of sensory neurones?
to send environmental signals to integrative centre
Which motor neurones act on a secondary neurone?
Presynaptic autonomic neurone
Which motor neurone act on smooth muscle in blood vessels and in the gut?
Post-synaptic autonomic neurone
In sensory neurones, when the nerve body is sitting to one side, what is the neurone called?
pseudounipolar neuron
In sensory neurones, when the nerve body is sitting in the middle, what is the neurone called?
Bipolar neurone
What is the location of integrative neurones?
CNS
What is the function of integrative neurones?
To Collate all information
What are the 3 types of integrative neurone?
- Pyramidal cell
- Interneurones
- Purkinje cell
What is the location of anaxonic neurones?
Retina and some parts of CNS
What is the function of anaxonic neurones?
To act as relays
How are anaxonic neurones specifically different from the other neurones?
They don’t have any axons,
Which neuron cell bodies are located outside the CNS?
pseudounipolar (unipolar), bipolar, and
postsynaptic autonomic neuron cell bodies
Which cell bodies are restricted to the CNS?
Purkinje and pyramidal cells
Which type of neurones is the majority in the CNS?
Interneurones
Describe multipolar neurones(purkinje and pyramidal cell)
- one axon and multiple
- most common
- most neurones in the CNS
Describe the bipolar neurones
- one axon and one dendrite
- found in olfactory cells, retina, inner ear
Describe unipolar neurones
- Single process leading away form the soma
- sensory from skin and organs to spinal cord
Describe anaxonic neurones
- many dendrites but no axon
- help in visual processes
What are nissl bodies?
A Nissl body is a large granular body found in neurons. These granules are of rough endoplasmic reticulum (RER) with rosettes of free ribosomes, and are the site of protein synthesis.
Which organelles are abundant in neurones?
RER
Free Ribosomes
Folding apparatus
Describe axonal transport
- Empty vesicles are transported to the axon by intracellular neurofilaments
- When they reach the axon hillock, they assemble which allows them to move along a transport system in the axon
- The transport system starts with a neurofilament sitting on a microfilament
- As it forms , a new structure comes in called a microtubule which is made up of different subunits - the subunits come together and bring in a protein called kinesin which can bind empty vesicles and mitochondria and transport them along this transport system in a process called anterograde from the axon hillock to the end of the axon - proximal end of axon to distal.
- Retrograde movement of material - empty vesicle that have not been used or have been reprocessed at the synapse are brought back to the body . They use dynein which only bring back empty vesicles not mitochondria
What are the 5 different types of synapses?
- Axodendritic
- axosomatic
- Axoaxonic
- Dendrodendritic
- Axo-axonal
What are axodendritic synapses?
Axon connecting directly to the dendrite of another neurone
Or
Axon terminal synapses connecting with a dendritic spine. Axon bouton change shape to envelope the spine
What are axosomatic neurone?
Axons connecting directly to cell body of another neurone
What is the advantage of axodendritic synapses with a dendrite spine?
More neurotransmitter can get across the synapse more quickly because there is a larger surface area
What are axoaxonic synapses?
When axon bouton of one neurone meets the axon bouton of another neurone that is interacting with a dendrite. The axoaxonic synapse may enhance or inhibit the
axodendritic (or axosomatic) synapse
What are dendro-dendritic synapses?
Synapses between nerves that don’t have axons
What are axo-axonal synapses
Axon connecting to another axon at the axon hillock. impinging dendritic/axonal synapse usually inhibits
other inputs
Which types of nerve fibres are present in peripheral nerves?
All 3 types of nerve fibres (sensory, integrative and motor) can
be present in peripheral nerves
What separates each nerve fibre?
Each are separated by connective tissue layers
In the peripheral nerves, what is the Endoneurium?
• Loose connective tissue • Surrounds single nerve cells
In the peripheral nerves, what is the Perineurium?
- Specialised connective tissue – transport proteins • Maintains ionic composition
- Surrounds clusters of axons (each fascicle)
In the peripheral nerves, what is the Epineurium?
- Dense irregular connective tissue
* Separates different types of nerves and fills spaces between fascicles
In the peripheral nerves, what is the Paraneurium?
Fascia that separates nerves from surrounding structures
How do axons get myelinated?
- The axon sitting in a groove is surrounded by a Schwann cell
- The mesaxon membrane initiates myelination by
surrounding the embedded axon - A sheet-like extension of the mesaxon membrane then wraps
successively around the axon, forming multiple membrane
layers - Cytoplasm is extruded from between the two apposing
plasma membranes of the Schwann cell, which then become
compacted to form myelin (19-20 rounds)
What is an oligodendrocyte?
• The oligodendrocyte does the same thing as a
Schwann cell, but in the CNS
• Cytoplasmic processes from the oligodendrocyte cell
body form flattened cytoplasmic sheaths that wrap
around each of the axons
• The relationship of cytoplasm and myelin is
essentially the same as that of Schwann cells
Three-d
What is the difference between a Schwann cell and oligodendrocyte?
Difference: oligodendrocyte wraps around more than one axon
simultaneously
What are the 4 support cells in the CNS?
- Oligodendrocytes
- Astrocytes
- Microglial cells
- Ependymal cells
What is the structure of astrocytes?
Star-like structure
What is the function of astrocytes?
• Have ‘perineural feet’ that contain gap
junctions
- biochemical support for endothelial cells
- transport of nutrients (lactate) from blood to
nerve cells
• Regulate nerve impulses by releasing
glutamate (near to Node of Ranvier)
• Contribute to the blood-brain barrier
• Many other [conjectured functions] e.g.
calcium regulation?
What are microglial cells?
- Large cells with elongated nucleus and relatively few processes emanating from the cell body
- Found throughout the CNS
What is the function of microglial cells?
• Resident macrophage – Immune function – Remove damaged nerve cells – Sense increased K+ ions • NB. Also thought to digest protein tangles that are associated with senile dementia and Alzheimer’s disease
What are ependymal cells?
> Ependymal cells line the spinal canal
Just posterior to ventral median fissure
Ependymal cells are of derived from the neural crest and are neural tissue
They look like columnar epithelial cells lining of the spinal canal and ventricles of the brain
They are joined by a junctional complex (JC) that separates the lumen of the canal from the lateral intercellular space
The apical surface has both cilia (C) and microvilli (M)
What are the functions of ependymal cells?
• Synthesise and secrete CSF in the ventricles (choroid plexus)
• Cilia move cerebrospinal fluid (CSF) through the ventricles to the spinal
cord
• Microvilli absorb CSF for removal of pathogens
- Present pathogens to microglial cells and astrocytes
• Modified tight junctions between epithelial cells control fluid release into brain
- Molecular and cellular contents of brain can be monitored – ‘spinal tap’
What causes multiple sclerosis?
Caused by autoimmune degradation of myelin
What type of disease is multiple sclerosis?
- Remitting and relapsing disease
* Degenerative
What are the symptoms of multiple sclerosis?
Fatigue Vision problems (diplopia) Slurred speech (dysarthria) Numbness and tingling sensations (paraesthesia) Mobility issues (muscle spasms) Urinary retention Constipation
Symptoms caused by loss of conduction velocity
What are the 2 divisions of the peripheral nervous system?
- Somatic
2. Autonomic
What are the 3 divisions of the autonomic nervous system?
- Sympathetic
- Parasympathetic
- Enteric
What is the enteric nervous system?
Intrinsic nervous system in the gut
What is the sympathetic nervous system involved in?
Mediates flight or fight.
All parts of he body activated
What is the parasympathetic nervous system involved in?
Involved in rest and digest
More localised
Approximately how many segments are there in the spinal cord?
31
In the spinal cord, what are the 2 roots that are connected to all the segment?
Dorsal root
Ventral root
Which root is purely sensory?
Dorsal root
Which root is purely motor?
Ventral
What does both the roots connect to ?
Spinal nerve
Is the spinal nerve sensory or motor?
Both
Why does myelin look white?
Because it is made from lipid and water
What is a ganglion?
A collection of cell bodies in the peripheral nervous system
What type system is the autonomic nervous system?
A motor system
What is the difference in autonomic and somatic nervous system considering the motor neurones?
In somatic nervous system, there is one motor neurone between the CNS and target organ whereas the autonomic nervous system has a chain
of two neurones between the CNS and the target organ
In the autonomic nervous system, where is the synapse between the two motor neurones found?
In an autonomic ganglion
In autonomic nervous system, where is the preganglionic cell body found?
In the CNS
In the autonomic nervous system, where is the post-ganglionic cell body of the motor neurone found?
In the peripheral nervous system
In the autonomic nervous system, describe the length of the preganglionic and postganglionic axons in the sympathetic system
Preganglionic axon is short and the post ganglion is axon is long
In the autonomic nervous system, describe the length of the preganglionic and postganglionic axons in the parasympathetic system
Preganglionic axon is long and post ganglion is axon is short
What is the major target for the sympathetic nervous system?
Vascular smooth muscle - regulate blood flow to various tissues
What is the major target for the parasympathetic system?
Glands
What is the sympathetic chain?
Long chain of ganglia on either side of the spinal cord where the post-ganglion is cell bodies are found in the sympathetic system
Where is the sympathetic output from the CNS?
The spinal cord
Where is the parasympathetic output from the CNS?
From the brain stem and the lower part of the spinal cord
For the parasympathetic system, what does the nerves from the brain stem deal with?
Head and kneck structures
For the parasympathetic system, what does the nerves from the lower part of the spinal cord deal with?
The genitourinary structures
Where are autonomic preganglionic neurone cell bodies found in the CNS?
Sympathetic – Lateral horn in T1-L2 cord
segments
Parasympathetic – S2-S4 cord segments and brainstem
If the sympathetic nervous system needs to supply the dermatomes(skin) at the T1-L2 level, what happens?
The signal synapses at the level of entry - Postganglionics get to their targets
through the T1-L2 spinal nerves
If the sympathetic nervous system needs to supply the dermatomes(skin) above T1 level (need and neck )what happens?
Signal Ascend the chain then synapse - Postganglionics get to their targets along
the walls of blood vessels
If the sympathetic nervous system needs to supply the dermatomes(skin) below L2 level (lower limbs)what happens?
Signal Descend the chain then synapse. Postganglionics
get to their targets through the spinal
nerves at levels L3 and below
How does the sympathetic system supply the abdominal viscera?
Sympathetic preganglionics can also traverse the chain then synapse in a pre- aortic ganglion (to supply abdominal viscera). Postganglionics get to their targets along blood vessels
What are splanchnic nerves?
Specialist nerves supplying preganglionic input to the gut
Can sensory fibres be sound in the sympathetic system?
Yes, Sensory fibres also travel along
sympathetics destined for the abdomen
and relay pain from viscera back to the
CNS
Where do parasympathetic preganglionic neurones typically synapse?
Parasympathetic preganglionic neurones typically synapse in ganglia that sit close to their target organs (often in the wall of the target)
What is the major source of parasympathetic preganglionic input to the thoracic and abdominal viscera?
The major source of parasympathetic preganglionic input to the thoracic and abdominal viscera is the vagus nerve
What are the 4 4 species parasympathetic ganglia for the head?
- Ciliary glanglion
- Pterygopalatine ganglion
- Submandibular ganglion
- Optic ganglion
What is the ciliary ganglion involved in?
The ciliary ganglion receives parasympathetic
preganglionics from the oculomotor nerve and distributes
parasympathetic postganglionics to the eye
What is the pterygopalatine ganglion involved in?
The pterygopalatine ganglion receives parasympathetic
preganglionics from the facial nerve and distributes
parasympathetic postganglionics to the lacrimal gland
What is the submandibular ganglion involved in?
The submandibular ganglion receives parasympathetic
preganglionics from the facial nerve and distributes
parasympathetic postganglionics to the submandibular
and sublingual salivary glands
What is the optic ganglion involved in?
The otic ganglion receives parasympathetic
preganglionics from the glossopharyngeal nerve and
distributes parasympathetic postganglionics to the
parotid gland
