Nerves Flashcards
What makes up 90% of the cental nervous system cells?
Glial cells
What is the function of astrocytes?
Form the blood brain barrier and maintain homeostasis for the neurones.
What is the role of oligodendrocytes?
Form the central nervous system nerves myelin sheath (in the periphery, they’re Schwann cells)
What is the function of microglia?
They act as immune cells for the neural environment
What do ependymal cells produce?
Cerebrospinal fluid
How is a neuronal resting membrane potential maintained?
K+ is pumped into the cell and Na+ is pumped out in a 1:1 ratio. However, K+ leaky channels cause potassium to leave the cell, providing an electrochemical gradient.
When is resting membrane potential equilibrium reached?
When the electrical gradient is equal to and opposite to the chemical concentration potential.
Which equation is used to estimate the resting membrane potential voltage with one ion?
Nernst equation (see nerve cells and connections)
Which equation is used to predict the equilibrium membrane potential generated by multiple ions?
Goldman-Hodgkin-Katz equation (see nerve cells and connections)
What is an IPSP and when does it occur?
Inhibitory postsynaptic potentials occur when graded potentials are hyperpolarising
What is an EPSP and when does it occur?
Excitatory postsynaptic membrane potentials occur when the graded potential is depolarising.
What are Graded potentials?
A potential that is depolarising gradually up to the threshold. The strength of depolarisation directly depends on the strength of the stimulus.
How does the strength of stimulus affect the graded potential?
A stronger signal results in more ion channels opening and thus a larger change in the difference of potential across the membrane.
Why are graded potentials only locally acting?
As the potential has not reached the threshold, the graded potential decreases in current along the axon until it is picked up or faded.
What is graded potential summation?
Summation is when two weak gradient potentials combine and summate to form a single larger potential.
How are graded potentials generated?
Neurotransmitters bind to the postsynaptic membrane and either induce hyper or depolarisation. The amount of neurotransmitter directly influences the strength of potential.
How does the decrementation of graded potentials influence the position of the synapse on the postsynaptic membrane?
As they only act locally, the closer to the cell body, the more likely the potential is to reach threshold in the soma and become an action potential
What is temporal summation?
When two signals on the same postsynaptic membrane integrate and form a single stronger graded potential?
What is spatial summation?
When two signals, that occur at a similar time, from different postsynaptic membranes integrate and form a single stronger graded potential.
What is multi integration?
When excitatory and inhibitory graded potentials integrate and cancel out, or at a slight interval they produce a large non-threshold change in potential.
What is an axo-axonic synapse?
When the postsynaptic membrane is on the axon.
What is an axo-dendritic synapse?
When the postsynaptic membrane occurs at on the dendrite.
What is an axo-somatic synapse?
When the postsynaptic membrane is on the cell soma.
Why does myelination increase conductance velocity?
Increases membrane resistance, thus reducing membrane capacitance and the amount of current lost. Action potentials spread passively from node to node
What is an ionotropic potential?
A fast EPSP, so called because its receptor directly opens ion channels in the synapse.
What is a metabotropic potential?
A slow EPSP, so called because its receptor is only linked to ion channels as a result of g-protein second messengers.
What is self inhibition?
When a neuron activates an interneurone that in inhibits the neurone it was stimulated by. It inhibits itself.
What is a monosynaptic response?
When a sensory neurone directly activates a single motor neurone.
What is a polysynaptic response?
When a series of interneurones lay between the sensory neurone and its motor neurone. These interneurones integrate converging inputs to either activate or inhibit the motor neurone.
What is a muscle spindle?
A stretch receptor activated when a muscle is stretched
What is the muscle spindle reflex?
When the receptor is activated, it send s signal via the CNA to the alpha motor neurone to contract the muscle. This means a muscle can change its contractile strength, but remain at a constant length. This is in response to changing levels of force.
Where do extrafusal fibres lie?
Parallel to the spindle and form the majority of the muscle.
Where do intrafusal fibres lie?
In series with spindles, form a smaller amount of the muscle with ypsilon innervation.
Name a specific example of muscle spindle reflex.
Patellar tendon reflex.
What is a golgi tension receptor organ?
A receptor that activates when a muscle is under so much tension it risks damage.
What is the golgi tendon reflex?
When the muscle is under so much tension it risks damage, the receptor inhibits motorneurones of the muscle via a CNS pathway
Name a specific example of golgi tendon reflex.
Clasp-knife reflex (as in the muscle quickly reduces resistance like a clasp-knife)
What is the flexion & crossed extensor reflex?
When stepping on a painful stimulus, the nociceptors cause the limb in question to recoil (flexion) and extension of the opposite leg, to stop falling over.
How does the flexion cross extensor initiate a response?
The nociceptor pathway inhibits the ipsilateral extensors and activates the ipsilateral flexors; the contralateral limb has its flexors inhibited and extensors activated. A fifth synapse sends the signal to the CNS
Which cortical region is responsible for movement?
The primary motor cortex in the precentral gyrus.
Name the main regions of the basal ganglia?
1) Putamen
2) Caudate
3) Globus Pallidus
4) Substantia nigra
By which pathway do the basal ganglia regions communicate with each other?
Nigrostriatal
Striatonigral
What is destroyed in parkinsons?
80% basal ganglia region pathways.
What are overactive dopamine linked to and in which pathway is this?
Overactive dopamine is linked to schizophrenia and occurs in the nigrostriatal pathway.
Which dopamine precursor is used in the treatment of parkinsonian illnesses?
L-Dopa
What information does the cerebellum receive and what function does it perform?
It receives proprioceptive and vestibular information and is involved in the fine tuning of movements
What functions is the basal ganglia involved with?
It is involved with producing volition for movement and initiating a movement, amongst other things.
Where are locomtory rhytms generated?
Spinal cord.
