Physiology Flashcards
What is the principal functional unit of the nervous system?
Neurons
How many neurone does the human system have?
10 to the (11-12) neurons
Which non-neuronal cell forms the blood brain barrier and also produces neutrophins?
Astroglia cells
What is the purpose of oligodendrogliocytes?
To produce myelin sheaths
Which cells in the non - neuronal cell is phagocytic in nature?
Microglial cells
What is the purpose of ependymal cells?
- They line the fluid- filled ventricles of the brain in the choriod plexus where the help to produce cerebral spinal fluid.
- They help to direct cell migration during development of the brain.
Which cells contains a glial fibrillary acidic protein (GFAP) that is used as a marker in brain cancers such as astrocytoma or glioblastoma?
Astrocytes
Functions of Astrocytes? ( most abundant)
- Help in recycling neurotransmitters(glutamate, GABA and serotonin)
- They buffer the extracellular potassium concentration .
- Respond to injury (gliosis)
- Help to make up the BBB
Damage to which cells causes multiple sclerosis(MS) or leukodystrophies?
Oligodendrogliocytes
Which glial cell is responsible for myelination in the PNS ?
Schwann cells ( One Schwann cell myelinate one neuron)
Abbreviation COPS
Cns- Oligodendrogliocytes Pns- Schwann cells
What is anterograde transport?
Movement of proteins from soma to terminal ends ( A=ST)
What is retrograde transport?
Movement of proteins from terminal ends to soma (R= TS)
Describe a grade 1 nerve injury
Applied pressure ( resting head on hand)
can result in hypoxia
LEAST HARMFUL ( regeneration starts quickly)
What grade is the most severe type of nerve injury?
Grade 5 ( Completer severance of the nerve)
What are the changes that occur in the nerve cell body at a grade 5 nerve injury?
1.Chromatolysis occurs within 24 hrs ( last about 15-20 days)
2.Neurofibrils and Golgi apparatus starts to disappear/disintegrate
3.Cell body swells assumes a spherical shape
4. Nucleus is the pushed to one side of neurone.
What is Wallerian degeneration?
Wallerian degeneration is an active process of retrograde degeneration of the distal end of an axon that is a result of a nerve lesion.
What are the changes that occur within the nerve fibre when it is damaged?
1.Myelin sheath breaks down
2. Macrophages appear
3.Schwann cells divide mitotically forming cords of cells lying within the endoneurial tubes
4.Macrophages from the endoneurium invade the degenerating myelin sheath and axis cylinder and remove debris. As debris is removed, Schwann cell cytoplasm fills the endoneurial tubes. The process takes - 3 months.
What are the processes that occur at the site of injury?
a. Schwann cells elongate and send processes outward to the injured site. This is known as Regenerative Sprouting.
b. Neurofibrils from the proximal end begin to grow and are guided by the Schwann cells into the old cylinder, in which they grow and eventually form the new axon.
c. Schwann cells then spin new myelin sheaths around the cylinder and gradually the entire neurone is regenerated.
What are functions of the sodium- potassium ATPases pumps?
- Pump 3 Na outside the cell and 2 K inside the cell.
- They generate a small negative charge inside the cell at rest.
- They generate concentration gradients for ions to move.
Which is the cell more permeable towards?
Potassium
Which direction does the chemical gradient of sodium moves?
Inwards
What is the value for a resting membrane potential for a nerve?
-70 mV
What is equilibrium potential?
Membrane potential at which the tendency to move against the electrical or concentration gradient is exactly balanced
What is the equilibrium potential for Chloride?
-70 mV ( equilibrium potential = resting membrane potential)
What is the equilibrium potential for sodium?
+61 mV
What is the equilibrium for potassium?
-94.1 mV
What are the assumptions of Nernst Potential?
1.Membrane is selectively and totally permeable to each ion.
2.Each ion is in electrochemical equilibrium across the membrane.
3.Diffusing ion is isolated from all other ions.
What is Hyperkalemia?
This is an INCREASE in the potassium levels in ones plasma concentration It can result in tachycardia ( Heart beats faster ie. >100 bpm)
What is Hypokalaemia?
This is a DECREASE in the potassium levels in ones plasma concentration.
What happens if there is an increase of the equilibrium potential of Potassium?
The membrane potential (Vm) decreases ( remember the homework!!)
What is Goldman’s Equation ?
The Goldman Equation relates the membrane potential, V, to the concentration gradient of, and membrane permeability to K+, Na+, and Cl- ions. It is derived by working out the membrane potential at which the fluxes of positive and negative ions balance perfectly, so that the net current flow will be zero, and the system will be in equilibrium.
V = RT Ln PK+ [K+]0 + P Na+ [Na+]0 + PCl-[Cl-]i
zF PK+ [K+]i + P Na+ [Na+ ]i + PCl-[Cl-]o
Which cells can undergo action potentials?
Neurons and Muscle cells
Values for depolarisation?
-70 mV to -55mV and to +35mv
Values for hyperpolarisation?
-70mV to -90mV
What is the threshold potential value?
-55mV
Does decreasing the external Na+ concentration have an effect on the resting membrane potential?
NO!
It has an effect on the ACTION POTENTIAL. Resting membrane potential uses leaky channels and the membrane is more permeable to K+ than NA+
Which sodium voltage gate is opened on the inside at rest?
The inactivated gate!!
At depolarisation, which sodium voltage gate is opened?
The activated gate!! ( on the outside)
True or False?
If there is an increase in K+ extracellular concentration , the resting membrane potential will reach closer to threshold potential which may elicit an action potential?
True!!
Remember hw( Using Goldman’s law when calculating an increase in K+ there was a decrease in the equilibrium potential ans = -56mV and Threshold potential is (-55mV)
What is the normal body potassium level?
3.5 - 5.0 mEq/L
What is the All or none law?
A minimum current of threshold intensity generates the full-fledged Action Potential.
Once initiated, the Action Potential does not change in size or form if the current strength is increased above the threshold intensity.
When does NA+ channel activation start?
After 7- 15 mV of depolarisation
What results in after hyper-polarisation?
Na+/ K+ ATPase pump returns the Resting Membrane Potential ( –70mV)
How can one treat Hyperkalemia?
- Enforce a low potassium diet
- IV administration of Calcium to protect the heart and muscles
- Administration of sodium bicarbonate to promote excretion of K+.
At what value are the activation gates for Calcium opened?
+35mV
Where is acetyl choline produced?
In the Synaptic bulb/ Terminal Ends
NOT in the cell body/soma.
What are the two types of Astrocytes?
Fibrous Astrocytes and Protoplasmic Astrocytes
True or False?
Protoplasmic Astrocytes are found in Gray matter?
TRUE!
Where are Fibrous Astrocytes found?
In White matter. FAW ( Fibrous Astrocytes - White Matter)
At what value is the firing level?
-55mV
What is the point at which re-stimulation can occur?
The after- depolarisation
How long does after hyper-polarisation lasts for?
40 ms
What is the Absolute Refractory Period?
This period starts from the Firing level until about 1/3 of repolarization is completed. During the Absolute refractory period NO stimulus , no matter how strong, will excite the nerve/ elicit an action potential.
What is the relative refractory period?
This period starts from the 1/3 depolarisation state , reached from the absolute refractory period, to after-depolarisation ( resting level). A stronger stimulus WILL cause excitation within the nerve.
What is Orthodromic conduction?
This is the normal conduction , in which action potential moves toward the distal ends
What is Antidromic conduction?
This is the conductions towards the soma , the action potential is dissipated in the soma.
Where are voltage gated Na+ channels highly concentrated at?
Nodes of Ranvier - 2,000 - 12,000
Initial segment - 350-500
What is the saltatory conduction?
It is a rapid process that allows myelinated axons to conduct up to 50 times faster than the fastest unmyelinated fibers by “jumping” from one node to the next.
True or False?
In a Hyperkalemic state , the resting membrane potential of skeletal muscle moves from a normal value of -90mV to a value of -60mV which inactivates Na+ channels and prevents action potential generation
TRUE!!
What are large axons normally associated with?
Proprioceptive sensation, somatic motor function, conscious touch and pressure.
What are small axons normally associated with?
Pain, temperature regulations and autonomic functions
Which nerve fibres are described as slow and gives off pain, temperature and other receptors?
C fibres
Which type of nerve fibres are ONLY found in the Autonomic nervous system?
B fibres (preganglionic)
True of false? A alpha fibres are the fastest and the most responsive nerve fibres.
TRUE!!
True of False? C fibres are all myelinated
FALSE!! All C fibres are UNMYELINATED. A & B fibres are all myelinated.
Which nerve fibres give off a sharp, prickly pain
A delta fibres
Which nerve fibres originate from the Golgi tendon organ?
A alpha Ib
Where does A alpha Ia originate from?
Muscle spindle, annulo-spiral ending
Which never fibres are the most susceptible to local anaesthetics?
C fibres ( Nociceptive fibres)
True or false? B fibres are the most susceptible to Hypoxia
TRUE!!
Which of the following is most susceptible to Pressure?
1.A fibres
2.B fibres
3.C fibres
A fibres
How does axonal Transport occur?
Along microtubules by dynein and kinesin
How does local anesthesia works ( lidocaine,bupivacine)?
They block the conduction of action potentials by blocking voltage -gated Na+ channels on the nerve cell. This causes a gradual increase in the threshold for electrical excitability of the nerve, a reduction in the rate of rise of the action potential, and a slowing of axonal conduction velocity.
What is the only naturally occurring local anesthetic?
Cocaine ( Erythroxylan coca)
What is the purpose of Neutrophins?
They are necessary for the growth and survival of neurons
Describe the nature of Nerve Growth Factor(NGF)?
It has 2 alpha subunits (trypsin like activity)
2 beta subunits
2 gamma subunits (serine protease activity)
How is NGF transported?
Retrograde Transport ( terminal ends to soma)
What is the function of Neurotrophin 3 (NT-3)?
NT-3 is important for proprioceptor neurons that innervate the muscle spindle and mechanoreceptors in the skin.
What is the function of Neurotrophin 4/5(NT -4/5)?
NT-4/5 is important for neurons that innervate the hair follicle
What is the function of brain -derived neurotrophic factor(BDNF)?
They can depolarise neurons.
What is Multiple Sclerosis (MS)?
In MS, antibodies and white blood cells in the immune system attack myelin, causing inflammation and injury to the sheath and eventually the nerves that it surrounds. Loss of myelin leads to leakage of K+ through voltage-gated channels, hyperpolarization, and failure to conduct action potentials.
What are the receptors for NGF?
Tyrosin Kinase A and p75
How wide is the synaptic cleft?
20-40 nm
What is the motor end plate?
Specialized portion of the sarcolemma of the muscle fibre innervated by a single motor nerve ending
What happens as the motor neuronal axon approaches the sarcolemma of the muscle fibre?
It loses its myelin sheath and divides into a number of terminal buttons.
The terminal ending fits into a depression of the muscle membrane which is thrown into folds called?
Palisades
Describe the nature of cholinergic transmission?
It is Ca2+ dependent
What is the name of the protein that Ca2+ binds to in the ANS ?
Calmodulin
What is the name of the enzyme that phosphorylates the Synapsin 1 molecule?
Ca 2+ calmodulin kinase
What are the functions of Synaptotagmin?
- Calcium sensor of release of the neurotransmitter.
- Allows for vesicle fusion proteins to bind during exocytosis.
- Involved in docking, binding and endocytosis f the synaptic vesicles.
What protein is inactivated by Tetanus toxin& Botulinum toxins?
Synaptobrevin
What is the time for the synaptic delay?
0.5 ms
True or False? Acetylcholine seeks out receptors that have high affinity for it, namely nicotinic receptors ONLY found in skeletal muscles.
TRUE!!
Which sub unit of the nicotinic receptor does Acetylcholine bind to?
Alpha subunit
What coats the vesicle facilitating the endocytosis?
Clathrin
What are the roles of the poisonous toxins( Clostridium tetani and Clostridium botulinum ?
These neurotoxins act by preventing the release of neurotransmitters in the CNS and at the neuromuscular junction. The tetanus toxins block the release of GABA and Glycine in which the activity of motor neurons is markedly increased. It causes a spastic paralysis.
Botox A, B and E are toxic to humans. They cleave SNAP-25 blocking the realise of Ach resulting in flaccid paralysis.