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Body Logistics > 11.1 - Nervous tissue structure + function > Flashcards

11.1 - Nervous tissue structure + function Flashcards

1
Q

How is the nervous system divided into two main parts?

A

central NS (brain and spinal cord)
peripheral NS (cranial nerves and spinal nerves)

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2
Q

Grey and white matter

A

grey
* peripheral in brain and areas called ‘nuclei’
* Central in spinal cord (H or butterfly shaped)
* Consists of nerve cell bodies, dendrires, axon terminals, non-myelinated axons and neuroglia (support cells)

white
* central in brain
* Peripheral spinal cord
* Consists of myelinated material

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3
Q

Basic structure of a neurone (CNS)

A
  • Has the normal complement of cell organelles
  • Cytoplasmic projections: one axon, many dendrites
  • Distal axon and arborisations (fine branching at end of nerve) are within PNS
  • Main cell body (soma), dendrites and proximal part of the axon are within CNS
  • The myelin surrounding the axon is made up by two different things in CNS vs PNS (different card)
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4
Q

Types of neurones in CNS (locations and functions)

A

motor
CNS → periphery
Has a long axon with arborisations attached to muscle etc, and a cell body with a long axon
Function is to send signals to effector tissues

sensory
Periphery → CNS
Function is to send environmental signals to integrative centre

integrative
Located in the CNS
Function is to collate all information

anaxionic
These have no axon: dendrites can also act as an axon as they release neurotransmitters
Located in the retina (some parts of the CNS)
Function is to act as relays

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5
Q

Which types of nerves are found in/outside the CNS

A

outside CNS = psuedounipolar (unipolar), bipolar and postsynaptic autonomic neuron cell bodies are located outside the CNS

inside CNS
Purkinje and pyramidal cells are restricted to the CNS.The majority of nerves in the CNS are interneurons

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6
Q

Basis of the reflex arc

A

Involves only sensory neuron → interneuron → motor neurone
bypasses the brain and co-ordination centre in order to facilitate a speedy response

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7
Q

What are Nissl bodies and where are they found

A
  • These are aggregates of ribosomes
  • Aka rough endplasmic reticulum
  • Found in cell bodies of neurones
  • Nucleolus in nucleus makes lots of ribosomes/RER
  • The ribosomes are the main thing that will bind to the stain – they stop at the axon hillock (where the axon starts), and therefore the cell body of the nerve is stained darker than the axon
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8
Q

Neurotransmitter synthesis (CNS)

A
  • The Golgi apparatus collect near the axon hillock (where the axon starts)
  • These Golgi apparatus are going to make vesicles
  • Most of the neurotransmitter is made as these vesicles travel down the axon (some are made in the soma body of the nerve)
  • The vesicle membrane has enzymes involved with the synthesis of neurotransmitter
  • The vesicles bind to the microtubule (on a microfilament) via kinesin protein with a mitochondrian attached
  • There are microfilaments and neurofilaments the whole way down the axon
  • The vesicles are moved towards the axon terminal
  • When reached the axon terminal, the microtubule dissolves and the vesicle + mitochondrion are released
  • As the neurotransmitter is released, the vesicle has two fates…
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9
Q

what is the function of the mitochondria in the axon terminal

A

the mitochondrion is the source of the Ca2+ ions for the vesicles to fuse with the plasmalemma

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10
Q

what happens to the vesicle once the neurotransmitter has been released into synaptic cleft

A

☞ recycled through clathrin-coated endocytosis (pinocytosis) and the empty vesicles are brought back from the axon via the same method they were transported down (but bind to dynactin rather than kinesin)
☞ lost to neurolemma → becomes part of synaptic membrane so nerve gets bigger over time

✷ sometimes the neurotransmitter doesn’t bind to a receptor in the synaptic cleft, so it is re-uptaked via pinocytosis back into the synapse, so it can be put back into a vesicle and be recycled → nerve can act very quickly

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11
Q

Retrograde vs Anterograde

A

☞ Anterograde is moving towards the axon terminal (ie neurotransmitter is moved this way)
☞ Retrograde is moving back towards the nucleus (vesicles are brought back to be recycled this way)

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12
Q

Different types of synapse (CNS)

A

axosomatic - synapse delivers neurotransmitter direct to the plasma membrane of nerve or cell
axodentritic - axon terminal synapses with a dendritic spine (ie neurotransmitter delivers directly to a dendrite of a new nerve cell)
axoaxonic - a synapse at the axonic bouton (eg a synapse binds to the side of another synapse, such as an axosomatic one → each synapse could release different neurotransmitters that could enhance or inhibit the other)
dendro-dendritic - dendrite interacts with another dendrite. Eg found at the back of the eye
axo-axoganal - synapse of one axon terminal interacts with the axon of another nerve cell.

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13
Q

Structure of peripheral nerves (PNS)

A

All three types of nerve fibres (sensory, integrative and motor) can be present in peripheral nerves, but each are separated by connective tissue layers

endoneurium
- Loose connective tissue
- Surrounds single nerve cell/axon
- Isolates single nerve cell from the others
perineurium
- Specialised connective tissue with transport proteins
- Controls ion concentration
- Surrounds clusters of axons to form fascicle
epineurium
- Dense irregular connective tissue
- Seperates different types of nerves and fills spaces between fascicles
- Gives nerve strength…very tough to cut
paraneurium
- Specialist connective tissue which allows for flexibility of nerve
- Fascia that separates nerves from surrounding structures (eg nerves, muscles and blood vessels)

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14
Q

What is myelin

A

Myelin is an insulating layer that forms around nerve. It is made up of protein and lipid substances. This myelin sheath and its Nodes of Ranvier allow for quick electrical transmission by saltatory conduction

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15
Q

What is the myelin made from in CNS/PNS axon

A
  • In the CNS, the myelin for the axon is produced by, and is part of an oligodendrocyte
  • In the PNS, the myelin is produced by, and is a part of, a Schwann cell
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16
Q

Damage to myelin in CNS + PNS is a cause of…(two separate)

A
  • Damage to myelin in CNS is cause of multiple sclerosis
  • Damage to myelin in PNS is a cause of Guillain-Barre syndrome
17
Q

How does myelination take place – Schwann cell in PNS

A
  • Axon sits in a groove of Schwann cell
  • Schwann cell wants to move around axon
  • Stimulated by Nrg1 binding to axon membrane (neuroregulin)
  • A sheet-like extension of mesaxon membrane (part of Schwann cell) wraps successively around axon
  • This forms multiple layers
  • Cytoplasm is pushed out from between the plasma membranes between layers, forming compacted myelin
    Note: an unmyelinated axon still has a Schwann cell around it, but the schwann cell doesn’t fully wrap around the axon – there is a gap.
18
Q

What mutation causes schizophrenia

A
  • A mutation in Nrg1 (neuroregulin 1)
  • Nrg1 is responsible for stimulating Schwann cell wrapping around axon
  • Therefore Nrg1 stimulates neurone myelination
19
Q

What is an oligodendrocyte

A
  • Oligodendrocyte does the same thing as a Schwann cell but in the CNS
  • However, oligodendrocyte only wraps part of its cytoplasm around the axon, not the whole cell. Therefore the cell body is left outside the axon
  • Many cytoplasmic processes from the oligodendrocyte cell body allow the oligodendrocyte to wrap multiple axons simultaneously
  • Oligodendrocytes line up next to the length of several axons
20
Q

Nerves histology – things to note

A

in cross section
- Unmyelinated neurones will have two layers visible – one is plasma membrane, and the other is the Schwann cell (but this will have a gap in it)
- Myelinated neurones will have thick line around the outside of each nerve – this is the myelin sheath
other points
- Nodes of ranvier present, will find cytoplasm here

21
Q

Electrical transmission in nerves

A
  • Saltatory conduction (and therefore electrical transmission) is faster in myelinated nerves due to the presence of nodes of ranvier
  • Conduction is faster in larger diameter axons (less ions lost)
  • Internodal distance (distance between nodes of ranvier) are larger in larger diameter axons
22
Q

Difference between A, B + C fibres (need to know after sem 2)

A
  • size A thickest, B medium, C thinnest
  • speed A fastest, B intermediate, C slowest
  • location A in CNS, B in viscera, C in PNS
  • function A motor, B + C sensory
  • myelination A+B myelinated, C unmyelinated
  • internodal distance A largest, B smallest, C n/a
23
Q

Unmyelinated nerve cells

A
  • Schwann cell sits in the middle of several axons
  • Schwann cell doesn’t completely wrap around axons, leaving gap
  • Gap is between two mesaxons
  • This gap allows material to flow along the nerve
  • Unmyelinated nerves have slower electrical transmission
24
Q

Support cells in the CNS – details on separate cards

A
  • Aka Glia
  • oligodendrocytes (just like Schwann cells). These are extremely small but sit in a line along an axon
  • astrocytes control flow of nutrients in CNS, impact on numerous nerve cells and contribute to the blood-brain barrier (star shaped, bigger). More on next card
  • microglial cells act as a resident macrophage. More on following cards
  • ependymal cells synthesise + secrete CSF
25
Q

Astrocytes

A
  • Star like + much larger than ogliodendrocytes
  • Have perineural feet ☞ provide biochemical support for endothelial cells (surround blood vessels in brain) + transport of nutrients (and lactate) from blood to nerve cells
  • Regulate nerve impulses by releasing glutamate (stimulator of nerves) near to the nerve of Ranvier
  • Calcium regulation
  • Contribute to the blood-brain barrier
26
Q

Microglial cells

A
  • Large cell with elongated nuclei
  • Found throughout the CNS
  • Have few cytoplasmic extensions (processes) from cell body, in comparison to most other nerve cells
  • resident macrophage ☞ immune function, removing damaged nerve cells + sense increased K+ ions
  • K+ is very dangerous in the brain so microglial cells can introduce the astrocytes to remove the K+ from the brain
  • Microglial cells thought to digest protein tangles associated with senile dementia + alzheimer’s → microglial protect against development of alzheimers
27
Q

Ependymal cell

A
  • Neural tissue derived from neural crest
  • Neuroectoderm cell, so look like columnar epithelial cells (line the spinal canal and brain ventricles)
  • Has cilia on surface and microvilli on surface
  • Has modified and very tight junction at apical surface → controls fluid levels released to brain and spinal cord → prevents swelling
  • Synthesise and secrete CSF in ventricles
  • Cilia move through ventricles to spinal cord
  • Microvilli absorb CSF for removal of pathogens eg if infection in spinal cord (present pathogens to microglial cells + astrocytes so that pathogens can be destroyed)
28
Q

Multiple sclerosis + it’s symptoms

A
  • 4 types of this
  • Degenerative disease
  • Caused by autoimmune degradation of myelin, probably against EBV
    symptoms caused by autoimmune degradation of myelin, so doesn’t conduct electricity as well as it should
  • Fatigue
  • Diplopia – vision problems
  • Dysarthria – slurred speech
  • Paraesthesia – numbness + tingling
  • Mobility issues eg muscle spasms
  • Urinary retention
  • Constipation
29
Q

What is the most common type of multiple sclerosis

A
  • There are 4 types
  • Remitting and relapsing disease is most common
  • This means that the symptoms come + go
  • This is degenerative – general degradation down pathway to death

Body Logistics (11 decks)

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