1.0 Introduction to Neurones Flashcards
What is the function of the medulla and pons?
Control regulatory systems for basic function (CVS/resp)
What is the function of the cerebellum?
Planning complex movements
What is the function of the midbrain?
Dorsal surface = tectum<br></br>Contains superior and inferior colliculi <br></br><br></br>Superior colliculi = visual processing<br></br>Inferior colliculi = auditory processing
What is the function of the thalamus?
Closely linked to cerebral cortex (specific areas of cortex are linked to thalamus)
What is the function of the hypothalamus?
Regulator of homeostasis<br></br>Controls endocrine/ANS/behaviour
What is the function of the cerebral cortex?
Largest part of brain<br></br><b>Primary cortical areas</b> = specialised for processing one modality<br></br><br></br><b>Association cortices</b> = receive and associate info of many modalities
What is the function of the basal ganlia?
Group of nuclei under the cortex<br></br>Associated with learned selection and expression of beneficial beavhiour for a given circumstance
What is the function of the amygala?
Assessment and learning of the <b>emotional significance</b> of given sensory info
Function of Soma
Soma = cell body<br></br>It is the metabolic centre of the cell<br></br>Contains nucleus and ER<br></br>Gives rise to dendrites and axons
Function of Dendrites
Receive incoming signals from other nerve cells
Function of Axon Hillock
Specialised part of the soma that connects it to axon. Action potentials are initiated here because it has the lowest threshold potential
Function of Axon
Carries signals to other neurons (can convey singles from 0.1mm to 2m)
For the following ions:<br></br>1) Sodium<br></br>2) Potassium<br></br>3) Chloride<br></br>4) Calcium<br></br><br></br>What is the internal concentration, external conc. , valence, and equilibrium potential?
“<div><img></img></div>”
What is the Nernst potential?
Membrane potential at which there is no net flux of that ion across the membrane<br></br>Depends on <b>chemical</b> and <b>electrical</b> gradients
What is the Nernst equation?
“<div><img></img></div>”
At rest, what ion is the membrane mainly permeable to?
Potassium (K⁺)
What is the Donnan equilibrium?
If a membrane is permeable to both K⁺ and Cl⁻, they will move across until their concentration gradient is balanced by membrane potential.<br></br>Therefore if <b>equilibrium</b> is reached:<br></br>[K⁺]i x [Cl⁻]i = [K⁺]o x [Cl⁻]o
What two secondary active processes are used to extrude Cl⁻:
1) KCC2<br></br>2) NDCBE<br></br>Therefore ECl is usually more negative than membrane potential
What two neurons have increased internal [Cl⁻]?
1) Developing neurones<br></br>2) Adult olfactory receptor neurones<br></br><br></br>Therefore opening of Cl⁻ channels → outward (excitatory) current
3 mechanisms by which calcium is extruded from the cell?
1) ATP-fuelled Ca²⁺ pump<br></br>2) NCX<br></br>3) NCKX
What are the steps for neurotransmitter release?
1) AP reaches nerve terminal<br></br>2) Opening of voltage gated Ca²⁺ channels<br></br>3) ↑ [Ca²⁺]i<br></br>4) Fusion of vesicles with membrane
What proteins are needed for vesicle fusion with plasma membrane?
1) <b>v-SNAREs</b> (synaptobrevin)<br></br>2) <b>t-SNAREs</b> (SNAP-25 and Syntaxin)<br></br>3) Synaptotagmin (Ca²⁺ sensor)
What are the stages for vesicle fusion with plasma membrane?
1) Vesicle <b>docks</b> at presynaptic active zone<br></br>2) Vesicle is <b>primed</b> by close association between v-SNAREs and t-SNAREs<br></br>3) Vesicles <b>fuse</b> with plasma membrane in <b>Ca²⁺ dependent manner</b>
3 criteria needed for a substance to be considered a neurotransmitter
1) Present at pre-synaptic terminal<br></br>2) Released during stimulation<br></br>3) Must have same effect when exogenously applied
- Direct mechanism of action
- Ionic channels
- Rapid
- Can allow Ca²⁺ influx
Metabotropic
- Indirect mechanisms
- Uses 2nd messengers
- Effect is usually via α-subunit bound to GTP
- Can also be due to βγ (usually acting on K⁺ channels)
- Results in amplification
GABA
Glycine
NA
Dopamine
Serotonin
Histamine
Adenosine
CO
Causes depolarisation
Permeable to Ca²⁺ + Na⁺
At -ve potentials channel is blocked by Mg²⁺
When depolarised, membrane is relieved and Na⁺ + Ca²⁺ can pass
Causes depolarisation
Permeable to Na⁺ + K⁺
Impermeable to divalent ions
Gαs coupled → activation of adenylyl cyclase → ↑cAMP
Causes depolarisation
Permeable to Na⁺ + K⁺
Causes hyperpolarisation
Permeable to Cl⁻
Causes hyperpolarisation
Permeable to Cl⁻ + K⁺
2) Lamellae in Pacinian corpuscules (allow rapid adaptation)
Reversal potential = 0mV
Opening of channel → membrane potential is drawn closer to reversal potential and depolarizing the cell
Glycine
↑ Cl⁻ conduction → hyperpolarisation
Reversal potential = -80mV
GABA
↑ Cl⁻ + K⁺ conductance → hyperpolarisation
Excitatory
Found on spine and shaft
Round vesicles
Type II
Inhibitory
Flat vesicles
Found on soma
Larger space constant favours spatial summation
Larger time constant favours temporal summation
Allows control as inhibitory and excitatory inputs can be collated together and APs only fire is threshold is reached.
↑ space constant favours spatial summation
Allows APs to initiate in situations of high frequency stimulation of the receptor (successive excitatory post-synaptic potentials take membrane potential to threshold)
↑ time constant favours temporal summation
Much less excitatory current is available than would be expected (↓ inhibitory current is needed to dissipate excitation)
This is why excitatory inputs are further away on dendrites compared to inhibitory inputs on soma
This offers powerful control over synaptic transmitter release
Inhibitory signal must occur at same time as action potential
Cl⁻ + K⁺ channel opening → ↓ AP → ↓ Ca²⁺ influx → ↓ neurotransmitter release → preventing neuron from generating EPSP
Inactivated with depolarisation
Function = spaces spikes in spike train (it leads to a graded change in frequency that is dependent on the initial depolarising current*
Ik - takes membrane potential back to resting levels
A current - keeps membrane potential at resting levels by opposing depolarising current. But a greater depolarisation → quicker inactivation of the A current → more frequent spikes
Transient
Threshold = -65mV
Inactivates with moderate speed (20-50ms)
Function = Rhythmic burst firing
L
Long lasting
Threshold = -20mV
Inactivates with very slow speed (>500ms)
Function = Synaptic transmission + dendritic Ca²⁺ spikes
N
Neither
Threshold = -20mV
Inactivates with moderate speed (50-80ms)
Function = synaptic transmission + dendritic Ca²⁺ spikes
P
Purkinje
Threshold = -50mV
Function = dendritic Ca²⁺ spikes
Can be important for excitation as one EPSP may not be enough to reach threshold
Some neurons are excited but not enough to reach threshold. These are called the subliminal fringe (Neurons within the motor neuron pool that are stimulated, but not sufficiently to reach firing threshold)
Overlap of 2x subliminal fringes → summation in a supra-linear manner
(e.g. inhibition of extensor muscles when flexors are stumulated)
Example = Renshaw cell of spinal cord (stabilises motor neuron firing)
1) Inhibition of extensors
2) Stimulation of flexors
Above two responses → withdraw limb from harm
1) Stimulation of contralateral extensors
2) Inhibition of contralateral flexors
Above two responses → provides support
Due to ↑ Ca²⁺ within the terminal → ↑ transmitter release
Due to depletion of vesicle pool
This is due to actions of Ca²⁺ on vesicle priming (can persist for several minutes after stimulation)
However, exposure to the pheremones of the mated male does not terminate pregnancy
Mechanism:
1) A specific mitral cell is activated by the odour of the familiar male, and releases glutamate in response
2) Glutamate stimulates adjacent granule and peri-glomerular cells, and granules cells promote reciprical inhibition of the stimulating mitral cell with GABA
3) During mating, noradrenaline acts on adrenergic receptors on both the granule cell and mitral cell to reduce GABA release, such that the specific mitral cells responding to the mated male odour is strongly activated
4) Following this strong activation, inhibition of the synapses stimulated by the male odour is strongly enhanced, which prevents pregnancy block
