Cells of the nervous system Flashcards
What are the 2 main cells of the nervous system?
- Neurones
- Glia
What are glia?
Supporting cells found around neurones
What does the Nissl stain do?
- Distinguishes between neurones and glia by highlighting the endoplasmic reticulum and free ribosomes in the cell bodies of neurones
- Allows visualisation of variation in size density, distribution of neurones
Which part of cells does the Nissl stain highlight?
Nucleic acids (rRNA in nucleolus etc.)
What is the soma?
Cell body of neurones
Which organelle is particularly abundant in cell bodies of neurones?
Mitochondria
What does the Golgi stain do?
- Highlights a random small percentage of neurones in the sample
- Shows dendrites
What is the Golgi stain made of?
Silver chromate
What are the 4 major compartments of the neuron?
- Cell body
- Dendrites
- Axons
- Presynaptic terminal
What is the perikaryon?
Another name for the cell body/soma of neurones
What are neurites?
- A process coming off a neuron
- Dendrite or axon
What are the 3 main elements of the cytoskeleton of neurones?
- Microtubules
- Microfilaments
- Neurofilaments
What are microtubules?
- Run longitudinally down neurites
- Made of hollow tubes of tubulin
What are microfilaments?
- Polymers of actin
- Randomly orientated and associated with the membrane
What are microfilaments made of?
Actin
What are microtubules made of?
Tubulin
What are neurofilaments made of?
Long protein molecules which have been wound together
What are the 4 areas of the axon?
- Axon hillock
- Axon initial segment
- Axon collaterals
- Axon terminal/terminal bouton
What are axon collaterals?
Side branches of axons
What is absent in the axon that is in the cell bodies?
- Rough ER
- Free ribosomes
What is immunohistochemistry?
- Method to identify the locations of specific proteins
- Specific primary antibodies which bind to the protein of interest
- Fluorescent secondary antibodies which bind to the primary antibody
What are the specialisations of the presynaptic terminals?
- No microtubules
- Many mitochondria
- Synaptic vesicles
What are boutons en passent?
A presynaptic terminal in the middle of an axon
What is axoplasmic transport?
Transport of molecules up and down axons
Which protein does anterograde transport down the axon?
Kinesin
Which protein does retrograde transport down the axon?
Dynein
How do kinesin and dynein transport molecules along axons?
“Walk” along the microtubules
What is the function of dendrites?
Receive information from other neurones
What are dendritic spines?
Small protrusions of the dendrite membrane
What is the function of dendritic spines? (3)
- Isolate chemical reactions
- Axons can synapse onto them
- Very plastic depending on activity of the dendrite
What are the classifications of neurons based on number of neurites? (4)
- Unipolar
- Pseudounipolar
- Bipolar
- Multipolar
What is a unipolar neuron?
One neurite coming off its cell body
What is a pseudounipolar neuron?
- One neurite coming off the cell body which splits into two
- Peripheral process is partly axon
What is a bipolar neuron?
- 2 neurites coming off the soma
- One side is dendritic, other is axon
What is a multipolar neuron?
- Multiple neurites coming off the soma
- One axon and multiple branching dendritic portions
What is a ganglion?
Group of neuronal cell bodies found in the periphery
What kind of neurons are dorsal root ganglion neurons? (2)
- Sensory neurons
- Pseudounipolar neurons
What classification are dorsal root ganglion neurons?
Pseudounipolar
What is an example of a pseudounipolar neuron?
Dorsal root ganglion neuron
How are dorsal root ganglion neurons arranged?
- Cell body sits in the dorsal root ganglion
- One side projects to the periphery and dendritic portion picks up signals
- Other side projects into the dorsal horn of the spinal cord
What does the acronym DAVE mean?
Dorsal Afferent Ventral Efferent
(Afferent neurons enter the spinal cord dorsally carrying signals from the body to the brain, efferent neurons exit the spinal cord ventrally carrying signals from the brain to the body)
What are the features of pseudounipolar neurons? (3)
- Process projecting into the periphery is part axon
- Small dendritic portion for receiving synaptic input
- Reliable relay of information due to not much integration
What is an example of a bipolar neuron?
Retinal bipolar cells
Between rods/cones and retinal ganglion cells
What are the features of bipolar neurons? (2)
- Small area for receiving synaptic input
- Reliable relay of information
What are the features of multipolar neurons? (2)
- Large area for receiving synaptic input
- High levels of convergence
Which class of neurons is the most common in the brain?
Multipolar neurons
What is an example of a multipolar neuron?
Purkinje cell
What are the classifications of neurons based on dendritic geometry? (2)
- Pyramidal
- Stellate
What are the features of pyramidal neurons? (2)
- Pyramid shaped soma
- Apical and basal dendritic tress
Where are pyramidal neurons found in the brain? (2)
- Neocortex
- Hippocampus
What are the features of stellate neurons? (1)
Star shaped dendritic arbour
Where are stellate neurons found in the brain?
Neocortex
Are sensory neurons afferent or efferent?
Afferent
Are motor neurons afferent or efferent?
Efferent
How are motor neurons arranged?
Project from the ventral horn into the periphery
What part of the nervous system contains interneurons?
CNS
What is the largest class of neurons?
Interneurons
What are the 2 classes of interneurons?
- Relay/projection neurons
- Local interneurons
What do relay/projection neurons do?
Connect brain regions
What do local interneurons do?
- Process information in local circuits
- Short axons
What is the main difference between neurons and glia?
Glia can proliferate throughout life but neurons don’t regenerate
What are the glial cells in the CNS? (3)
- Astrocytes
- Oligodendrocytes
- Microglia
What are the glial cells in the PNS? (3)
- Satellite cells
- Schwann cells
- Macrophages
What are the glial cells in the ENS? (1)
Enteric glia
Which glial cells in the CNS have a homeostatic function?
Astrocytes
Which glial cells in the PNS have a homeostatic function?
Satellite cells
Which glial cells in the ENS have a homeostatic function?
Enteric glia
Which glial cells have a homeostatic function? (3)
- Astrocytes
- Satellite cells
- Enteric glia
Which glial cells in the CNS are myelinating?
Oligodendrocytes
Which glial cells in the PNS are myelinating?
Schwann cells
Which glial cells are myelinating? (2)
- Oligodendrocytes
- Schwann cells
What are astrocytes?
Glial cells in the CNS with homeostatic functions
What are satellite cells?
Glial cells in the PNS with homeostatic functions
What are enteric glia?
Glial cells in the ENS with homeostatic functions
What are oligodendrocytes?
Glial cells in the CNS that are myelinating
What are Schwann cells?
Glial cells in the PNS that are myelinating and phagocytic
Which glial cells in the CNS are phagocytic?
Microglia
Which glial cells in the PNS are phagocytic?
Schwann cells and macrophages
Which glial cells are phagocytic? (3)
- Microglia
- Macrophages
- Schwann cells
What are microglia?
Glial cells in the CNS that are phagocytic
What are macrophages?
Glial cells in the PNS that are phagocytic
What are ependymal cells?
Astrocytes which line the ventricles and central canal (CSF)
What are the features of astrocytes? (3)
- Store glycogen to supply energy in the form of lactate to the neurons
- Endfeet around capillaries take up glucose and keep vasculature separate from neurons
- Modifies synapses
What do astrocytes do at synapses?
- Terminates neurotransmitter activity
- Can recycle neurotransmitter back into presynaptic terminal
What is a tripartite synapse?
Synapse involving 3 different cells
What proportion of the CNS glial cells are microglia?
15%
Which glial cells are involved in synaptic pruning?
Microglia
How can microglia have detrimental effects?
Can play a role in neurodegenerative diseases
What is the main difference between oligodendrocytes and Schwann cells?
Oligodendrocytes can have many processes from one cell body to myelin sheath whereas Schwann cells only provides one myelin segment to a single axon
How do myelin sheaths form?
- A process from a cell wraps around the axon many times
- Cytoplasm is squeezed out by compaction
What is the function of myelin?
Insulating and creates nodes of Ranvier so action potentials can jump down the axon (saltatory conduction)
What is a difference between CNS and PNS axons?
PNS axons can regenerate after injury but CNS axons can’t
How are myelin sheaths maintained?
Stay connected to the Schwann cell/oligodendrocyte for nourishment