Slides 1 Flashcards
Afferent Pathways motor of sensory
Sensory - signal coming in
Efferent Pathways are motor or sensory
Motor - signal is going out
Hypoperfusion
Too little blood flow (ischemia)
Less that 20ml per 100g per minute
At what point of blood loss does cell death occur
Below 10ml per 100g per minute
What are the two major arteries that supply blood to the brain
- Common carotid arteries
2. Vertebral arteries
Which is the most common place to loose blood in the brain?
Middle cerebral artery
What are the two types of strokes
- Hemerrhagic stroke
2. Ischemic stroke
Hemorrhage stroke
There is a blood leak into the brain
Ischemic stroke
A clot (from brain or peripheri) stops blood supply to an area of the brain
Which type of stroke is most common?
Ischemic stroke, they account for 80% of strokes
What are the 2 types of ischemic strokes?
Thrombotic strokes = blood clot forms in an artery directly leading to the brain
Embolic Stroke = a clot forms somewhere else in the body and travels to the brain
What is the difference between the core and the penumbra areas in an ischemic stroke?
Core area is there blood flow is below 10-25% and necrosis starts
Penumbra area is where there is less than 25-50% blood flow and eventually apoptosis will set in (can recover these regions)
What differentiates neurons from other cells?
- Dendrites
- Axons
What may neurons be classified by?
Shape
Neurotransmitters
Location
Connectivity
What are macrocircuits
They are a group of neurons that project from one region of the brain to another
What are microcircuits?
They are groups of neurons that project within a brain region
What are the 4 main types of neurons?
Sensory
Motor
Principal
Inter
Sensory neuron
Connected to receptors, they carry sensory information to the brain (afferent)
Motor neurons
Responsible for the direct or indirect control of effector organs such as muscles and glands (efferent)
Describe bipolar neurons
They are neurons one axon and one dendrite (that has multiple branches)
Which neuron types are commonly bipolar?
Interneuron/principal neuron
Describe a unipolar neuron
They have one main axon/dendrite and the soma protrudes off pf it
What neurons are typically unipolar?
Sensory neurons
Describe multipolar neurons
A soma that has multiple dendrites coming off of it and one main axon
What neurons are typically multipolar?
Motor neurons
How do interneurons and proncipal neurons differ from one another
Principal neurons are the neurons that connect everything together.
Interneurons exhibit inhibitory control over principal neurons/
Which has greater surface area, the soma or the dendrites?
Dendrites have a much bigger surface area
What gives dendrites such a big surface area?
The dendritic spines increase the size of dendrites surface area
What is a perkinjee cell?
A neuron with a large dendritic tree with a small soma
A principal neuron but it releases GABA
What is the part of the post synaptic terminal that receives the NT from synapse called?
Post synaptic density
What are the 3 types of dendritic spines and what is the difference
- Stubby
- Thin
- Mushroom
- -> They are essentially at different stages of the growth cycle
Thin dendritic spine
It is reaching out probing for an axon to make a connection with
Mushroom dendritic spine
It had a connection with an axon and it is the main excitatory input
Stubby dendritic spine
They do not have a connection yet but they will grow if they sense a possible connection
Axon Collaterals
A branch off the main axon
What significance does diameter size have for axons
Large diameter: less internal resistance so a faster signal flow
–> Also usually myelinated
Small diameter: more internal resistance that causes slower signal flow
Are organelles only in the soma?
No, they can travel up and down the axon on microtubules as needed
Difference between schwann cells and oligodendrocytes
Shwann: - PNS - Can heal - single cell myelinates a single node Oligodendrocyte: - CNS - Cannot heal - single cell can myelinate several nodes and on different axons
What are radial glial cells?
During development, radial glial cells are used as scaffolding for new neurons to travel up into the cortex
What happens to radial glial cells when the scaffolding is no longer needed?
They do not die, rather they turn into other glial cells
Do new neurons even travel back down the radial glial cells?
No, once they are in place they stay put
Progenitor Cells
Fill in later
Capacitance
The ability to store excess charges
What causes resistance in the membrane?
Ion channels (open vs closed)
What is required to keep the current flowing?
A source of energy
What does a closed system mean?
No energy is lost or grained
How are a capacitor and a battery similar?
They are both able to store energy and then use that energy to drive currents
What does a voltmeter do?
Measuring potential energy difference between two points
what is charge?
The source of the force between objects that can act at a distance
What properties of an atom make it a good conductor?
When its outer electrons have relatively weak bonds to their nuclei
What properties of an atom make a good insulator?
When its outer electrons are tightly bound to their nuclei
What is current?
It is the rate of flow of charge
- Reported as the number of charges per unit time passing through a boundary
What is the standard unit for current?
Ampere (A) = one coulomb per second
Which direction does current usually flow?
From positive to negative == conventional current
How do negative charges flow in relation to positive charges?
In the opposite direction to the electric field
== Opposite to conventional current
3 factors that affect resistance
- Material
- Cross-sectional area
- Temperature
What is the relationship between current and resistance?
Inversely related
More resistance = less current
what is the relationship between current and voltage
They are directly proportional
OHM’s law
The amount of current (I, measures in amps) flowing in a conductor is related to the potential different (V, volts) applied to it
Ohm’s law equation
I = V/R
Does a stronger depolarization result in a higher amplitude action potential (amount of current flowing in)?
No, but it can result in a higher frequency of action potentials but with a fixed amplitude
What tool was used to measure the voltage in the giant axon in the squid?
The Oscilloscope
- filled with salt water
Extracellular recording
Electrode is placed just outside the neuron of interest
–> Looks at how populations of cells work together (in a live animal)
Intracellular recording
Electrode is inserted inside the neuron of interest
–> in vitro (isolated from animal in a dish)
Patch clamp technique
the electrode is closely apposed to the neuron membrane, forming a tight seal with a patch of the membrane
- Isolates that part of the membrane and measures the activity of individual channels
What does the equilibrium potential depend on?
The concentrations of the respective ions (K+, Na+, Cl-) distributed on the inside and outside
The Nernst Equation
Equilibrium potential depends on the relative contribution of the particular ions inside and outside of the neural membrane
Where is the voltage difference the greatest?
Close to the membrane because the positive and negative ions on each side are attracted to each other and will migrate towards the membrane
Why does chloride more back and forth across the axon membrane?
Chloride moves into the axon to move down the concentration gradient, but it also flows back out of the cell because it is attracted to positive sodium ions
Resting membrane potential
-70mV
Particles on the outside of the neuron
Sodium (Na+)
Chloride (Cl-)
Particles on the inside of the membrane
Potassium (K+)
Large protein anions (A-)
Which ions can flow freely?
Chloride and potassium
What is the ratio of potassium ions inside to outside
20:1
Ratio of sodium ions inside to outside
10:1
What makes the inside of the neuron negative?
Large protein anions that cannot move outside of the cell and sodium channels are gated so they keep sodium out
Why don’t chloride ions contribute much to the resting potential?
Because its equilibrium point (concentration gradient = voltage gradient) is the same as the membranes resting potential
Where do graded potentials most often occur?
On the dendrites
where do action potentials most often occur?
On the axon
What are graded potentials?
Small voltage fluctuations across the cell membrane
How do ions flow to create a hyperpolarization?
Influx of chloride
Eflux of potassium
How do ions flow to create a depolarization?
Influx of sodium
Action potential
A large, brief reversal in polarity of an axon
Threshold of excitation voltage
~ -40 to -50mV
What is the cause of absolute refractory during the repolarization of the axon?
During the repolarization the voltage-insensitive sodium gate 2 are closed, so no matter how positively you drive the cell, they will not open
Nerve impulse
Propagation of an action potential on the membrane of an axon
What part of an action potential ensures that the impulse travels in only one direction?
the refractory periods
Conduction between nodes of ranvier
Saltatory conduction
Back propagation
Reverse movement of an action potential from the axon hillock into the dendrites
What is the potential function of back propagation?
May play a role in plastic changes in the neuron that underlie learning
Neuroepithelial cells can proliferate and generate what 2 things, and then differentiate into what?
Neuroblasts
Immature neurons
» Then differentiate into radial glia
Most, but not all, astrocytes have what features in common?
Star-like
GFAP marker
Make contact with brain capillaries
Where are protoplasmic astrocytes located?
In the grey matter
What is the main function of protoplasmic astrocytes?
Their end-feet called perivascular end feet make contact with blood vessels as well as multiple contacts with neurons
Which astrocytes make up the blood brain barrier?
Protoplasmic astrocytes
Other than blood vessels and neurons, where to protoplasmic astrocytes make contact?
The pia matter
= subpial end-feet
Where are fibrous astrocytes located?
In the white matter
What are the main points of contact for fibrous astrocytes?
At the nodes of Ranvier
Also blood vessels (perivascular) and pia matter (sub-pial)
What is the purpose of fibrous astrocytes as the perinodes?
It cleans up the imbalance of ions in at the nodes of ranvier
> prevents ions from leaking in and out of axon
What are the 5 main roles of an astrocyte?
- Control extracellular K+ homeostasis
- Remove excess glutamate (protoplasmic)
- Control local blood flow and provide neurons with metabolic support
- Control synaptogensis and synaptic maintenance
- (not main) Supply glutamate to main glutamatergic neurotransmission
How to oligodendrocytes and schwann cells form the myelin around axons?
By enwrapping their membrane several times around the axon
What role do schwann cells play with smaller axons if not providing myelin?
Encloses them to hold axons together
>keeps them in place
Are there oligodendrocytes that do not myelinate?
Yes
> do not know exact function
Where are non-myelinating oligodendrocytes found?
In the grey matter
What is the internodal region of an axon?
The area not covered by myelin –> node of ranvier
Is the internode (Node of Ranvier) empty?
No, fibrous astrocytes are there
How are microglia distributed through the CNS?
Relatively evenly
In what way to microglia combat pathogens?
Through phagocytosis
What functions to microglia have? (4)
- Regulating cell death
- Synapse pruning
- Neurogenesis
- Neuronal surveillance
What are the 2 phenotypes of microglia and what are their roles?
M1 - reactive»_space; will activate astrocytes to let t-cells in from the periphery to help with immune response
> Kill cells
M2 - repair cells, restrict BBB permeability
How can M1 microglial response be bad?
When M1 cells are triggered, they activate astrocytes to increase BBB permeability to let helper T-cells in to help with the immune response.
These T-cells can sometimes see oligodendrocytes as bas and attack them, destroying the myelin
What is the blood brain barrier?
A highly selective semipermeable membrane barrier that separates the circulating blood from the brain and extracellular fluid in the CNS
What molecules are allowed to pass through the BBB?
Water Some gasses Lipid soluble molecules Glucose Amino acids
Cytoarchitectonics
One of the ways to parse the brain by staining it to reveal how neurons are “stacked” into layers
Area 41 and 42
Temporal lobe - hearing
Area 44 and 44
Broca’s area for language
Area 1,2,3
Somatosentory
Area 17 and 18
Primary visual areas
What part of the brain to the common carotid arteries innervate?
Front and top
What part of the brain do the vertebral arteries innervate?
Middle and side
Does a principle cell synapse more with an interneuron than an interneuron synapses with a principle neuron, or vise versa?
Vis versa, an interneuron synapses more with a principle neuron than a principle neuron synapses with an interneuron
Glial cells interaction with the BBB (5)
- Tight junctions
- Structural support
- Influence cell function
- Channels for glucose and amino acids
- Movement of sodium
Voltage
The measure of specific potential energy between two locations
