Cells of the Nervous System Flashcards
Where are the myelinated axons located in the spinal cord?
White matter
Where are the cell bodies of neurons in the spinal cord?
Grey matter
Where does the PNS form from?
The neural crest
Where does the CNS form from?
The neural tube
What are the two types of astrocyte?
Protoplasmic astrocytes
Fibrous astrocytes
What are protoplasmic astrocytes and where are they found?
Short branching processes found in gray matter.
What are fibrous astrocytes and where are they found?
Long unbranched processes found in white matter.
What are the functions of astrocytes?
- Support neurons
- Support and stimulate formation of the blood brain barrier
- In the embryo astrocytes secrete chemical signals that stimulate growth and connections in neurons.
- Maintenance of the chemical environment needed for the generation of nerve impulses.
- Role in learning and memory by influencing the formation of neural synapses.
What do oligodendrocytes do?
Responsible for forming and maintaining the myelin sheath around CNS axons.
What do microglial cells do?
Function as phagocytes, phagocytozing microbes and damaged nervous tissue.
Where are ependymal cells located?
Ependymal cells line the ventricles of the brain and the central canal of the spinal cord.
What is the function of ependymal cells?
Monitor and assist in the circulation of CSF. Ependymal cells also form the blood cerebro-spinal fluid barrier.
What type of cells are ependymal cells?
Columnar with microvilli and cilia
What are the two types of glial cells in the PNS?
Schwann cells and satellite cells
Where are schwann cells found?
Encircling PNS axons
Where are oligodendrocytes found?
Encircling CNS axons
What is the function of schwann cells?
Myelinate axons speeding up nerve transmission and participate in axon regeneration.
Where are satellite cells found?
Surrounding the cell bodies of PNS neurons
What do satellite cells do?
Provide structural support and regulate exchange of material between neuronal cell bodies and interstitial fluid.
Where are bipolar neurons found?
Found in the retina of the eye, the inner ear and the olfactory area.
What do unipolar neurons usually function as?
Sensory receptors that detect touch, pressure, pain and thermal stimuli.
What type of neurons are sensory neurons?
Unipolar neurons
What type of neurons are motor neurons?
Multipolar neurons
What type of neurons are interneurons?
Multipolar neurons
What do interneurons do?
Connect sensory and motor neurons to one another.
Which type of neuron is the most abundant in the CNS?
Multipolar neurons
Where in the CNS are oligodendrocytes located?
White matter
What can diffuse across the blood brain barrier?
Lipid soluble substances such as O2, CO2, steroid hormones, alcohol, nicotine and water can diffuse acorss the lipid bilayer.
What is the outer nucleated cytoplasmic sheath of the schwann cell called?
Neurolemma
What are the gaps between the myelin sheaths?
Nodes of Ranvier
How would you describe the cross sectional histology of the cerebellar cortex?
Stripes
What is the specialised somatosensory receptor of the skin?
Merkel cell
What does the Meissner receptor detect?
Touch - movement
Where are Meissner receptors?
Skin
What does the pacinian corpuscle detect?
Touch - vibration
Where are pacinian corpuscle receptors?
Skin
What do Ruffini corpuscles detect?
Touch - stretch
What do hair follicles detect?
Touch - movement
What do Merkels receptors detect?
Touch - pressure
What do free nerve endings detect?
Pain, touch and temperature
What is Nissl substance used for?
Nissl substance stains the endoplasmic reticulum of cells
What is the soma of a neuron?
Cell body
What is the axon hillock?
The axon hillock is the region in a neuron between the cell body and axon.
What is the function of the axon hillock?
The axon hillock is where impulses are propagated in the neuron from.
What is the name of the conduction method myelin sheath enables?
Saltatory conduction
What are the specialised intracellular transport structures in neurons?
Neurofilaments
Explain the transport of ions in the sodium potassium pump of a neuron.
3Na+ out of the cell
2K+ into the cell
What is the Na+/K+ pump of a neuron said to be electrogenic?
It results in the net loss of one positively charged ion.
What is the process of an action potential of a neuron?
- Stimulus causes the target cell to depolarize toward the threshold potential.
- If the threshold of excitation is reached, all Voltage Gated Na+ channels open and the membrane depolarizes, there is Na+ influx by diffusion.
- At the peak action potential, Voltage Gated K+ channels open and K+ begins to leave the cell by diffusion, at the same time, Na+ channels close and the membrane potential becomes increasingly negative again.
- The membrane becomes hyperpolarized as K+ ions continue to leave the cell. The hyperpolarized membrane is in a refractory period and cannot fire.
- The membrane potential is restored, K+ channels close and the Na+/K+ transporter restores the resting
potential.
What happens when the threshold of excitation is reached in a neuron?
All voltage gated Na+ channels open
In what state is a neuron in when it’s membrane is hyperpolarized?
Refractory period
What do metabotropic receptors do?
Indirectly depolarise cells by activating the ionotropic receptors.
What type of receptor are metabotropic receptors?
G-protein coupled receptors
How do metabtropic receptors activate ionotropic receptors?
They use GTP and alpha subunits to activate intermediates opening the ionotropic receptor channel.
What type of neurotransmitter is Nitric oxide?
Excitatory
What type of neurotransmitter are dopamine and serotonin?
Inhibitory
What type of neurotransmitter are acetylcholine and norepinephrine?
Both excitatory and inhibitory
Dopamine, serotonin, epinephrine and norepinephrine are what type of amine?
Monoamines
Where do action potentials start in a neuron and then propagate to dendrites from?
The axon hillock
How do electrical synapses work?
Electrical synapses conduct directly through the plasma membranes of adjacent neurons through gap junctions.
How are the cytosol of the two cells connected in electrical synapses?
Each gap junction contains tubular connexons, which connect the cytosol of the two cells directly and the action potential spreads from cell to cell.
Where are gap junctions of electrical synapses located in the body?
Visceral smooth muscle
Cardiac muscle
Embryo
What are the two advantages of electrical synapses over chemical synapses?
Faster communication
Synchronization - can contract muscle fibres in unison.
Where are synaptic clefts found and what are they?
The spaces between the neurons found in chemical synapses.
Explain how chemical synapses transmit signals.
- Impulse arrives at the synaptic bulb of a pre-synaptic neuron.
- The depolarizing phase of the impulse open voltage gated Ca2+ channels, in the membrane of the synaptic bulb.
- Ca2+ ions flow through the open channels down their concentration gradient.
- Increased concentration of Ca2+ ions in the pre-synaptic neuron triggers exocytosis of synaptic vesicles.
- As the vesicle membrane merges with the plasma membrane, neurotransmitter molecules in the vesicle are released into the synaptic cleft.
- Neurotransmitters diffuse across the synaptic cleft and bind to receptors on the post-synaptic membrane.
- The binding of the neurotransmitter to their ligand-gated channel receptors opens the channels, allowing ions to flow across the membrane.
- This changes the voltage across the membrane. This change in membrane voltage is the postsynaptic potential. This potential could be depolarization (excitatory) or hyperpolarization (inhibitory).
- Depolarization triggers another action potential once it reaches it’s threshold.
What does the opening of Na+ channels in the post synaptic neuron cause?
Depolarization
What does the opening of K+ channels in the post synaptic neuron cause?
Hyperpolarization
What does the opening of Cl- channels in the post synaptic neuron cause?
Hyperpolarization
What property of direction do chemical synapses have?
They are uni-directional.
What enzyme breaks down acetylcholine in the synaptic cleft?
Acetylcholinesterase
What is the threshold to trigger an action potential in a normal cell?
-55mV
What is spatial summation?
Multiple pre-synaptic neurons at different locations stimulate one neuron at the same time causing it to reach it’s action potential.
What is temporal summation?
Occurs when one pre-synaptic neuron fires many times in quick succession, causing the post-synaptic neuron to reach it threshold potential.
What is long term potentiation?
A process in which synaptic connections between neurons become stronger with frequent activation.
What is long term potentiation thought to result in?
The formation of long term memories and learning.
What are the neurotransmitters and receptors involved in long term potentiation?
Gluatmate neurotransmitters
NDMA receptors
What are the neurons that stimulate skeletal muscle fibres?
Somatic motor neurons
What is the neurotransmitter released at the neuromuscular junction?
Acetylcholine
Explain how acetylcholine release occurs.
Arrival of the nerve impulse at the synaptic bulb causes Ca2+ channels to open in the bulb.
Ca2+ then diffuses into the synaptic bulb.
The increase in Ca2+ concentration causes vesicles containing Ach to fuse with the pre-synaptic membrane and release Ach into the synaptic cleft.
What does activation of the Ach receptors cause?
Opening of the Na+ channels in the post-synaptic neuron.
How the production of the muscle action potential cause muscle contraction?
The muscle action potential propogates along the sarcolemma into the system of T tubules.
This causes the sarcoplasmic reticulum to release it’s stored calcium into the sarcoplasm, the muscle fibre therefore contracts.
What are merkel cells?
Mechanoreceptors on the skin that detect light touch.
How is the axon hillock adapted to it’s function.
Tight junctions preventing lateral diffusion.
Has many high density voltage gated ion channels to aid generation of the action potential.
What is a neurolemma?
The outer nucleated cytoplasmic sheath of the schwann cell.
Which region of the brain has a stripey appearance in it’s histology?
Cerebral cortex
