Neurobiology (Lecture 20-25) Flashcards
(51 cards)
1
Q
What does the nervous system do?
A
- Sensory system: recieve and interpret information abt the internal and external environments of the body
- Integrating system: making decisions abt information
- Motor system: to organize n carry out action
2
Q
What are the 3 parts of the neuron?
A
- Dendrites
- Soma (cell body)
- Axon
3
Q
What are neurons?
A
Individual cells, which are not continuous to other neurons
4
Q
Dendrites
A
- Increase surface area
- Recieve inputs
5
Q
Axon
A
Carries information
Over distances
6
Q
Myelin
A
Coats axon
Improves conduction
7
Q
Node of Ranvier
A
Break in myelin sheath
8
Q
Terminals
A
- Output region
- Transmitter release
- Synapse w other neurons
9
Q
How should we classify neurons?
A
- Morphology
- Multipolar, unipolar
- Interneurons vs principle neurons
- Interneurons: local circuits
- Principle neurons: extend process over long distances
- Neurotransmitter
- Cholinergic
- Glutamatergic
- GABAergic
10
Q
How do things get to n from axon terminals?
A
- Anterograde transport
- Soma down axon to terminals
- Retrograde transport
- From terminals to soma
- Worn out mitochondria, SER
11
Q
Mechanism of axonal transport
A
- Requires hydrolysis of ATP n microtubules
- Protein shuttles that move in either direction in the microtubule network
- Microtubules are polarized (positive n negative end)
- Molecules “walk”
- This process is catalyzed by ATP (energy-intensive process)
- TAU protein becomes dysfunctional in Alzheimer’s
12
Q
Astrocytes
A
- Making contact w blood vessels
- Associated w synapses
- Correct ionic environment
- Release gliotransmitters (ATP, glumate, D-serine)
- Provide metabolic fuel for neurons
13
Q
Oligodendrocytes
A
- Cells that myelinate axons in the brain and CNS
- Schwann cells myelinate axons in peripheral nervous system
- Oligodendrocytes can myelinate multiple axons
14
Q
Microglial cells
A
- Immune cells of nervous system
- Acts as scavengers
- Clean up cellular debris
15
Q
Describe the structure of vertebrate ganglia
A
- Cell body
- Outside of the ganglia
- Send their axons into the neuropils
- Neuropil: dense regions of nerve fibers devoid of cell bodies
- Axons in tracts
- Run together in nerve trunks [protect axons from damage]
- Ganglion sheath
16
Q
Encephalization quotient
A
- Brain weight/body weight
- Expectation: linear correlation
- Our brain has become folded
- Cell sides and gyri pack more “brain” into skull
17
Q
What are the meninges?
A
- Surround the CNS
- Brain suspended in jacket of cerebrospinal fluid
18
Q
What are the 3 layers of meninges
A
- Dura mater: protects the brain
- Arachnoid mater
- Pia mater: thin membrane that covers actual surface of brain tissue
19
Q
Falx cerebri
A
- Invaginations in the brain b/w the gyri n the longitudinal fissure
- Allows the blood vessels to penetrate the tissue further from the surface of the brain
20
Q
Importance of the ventricular system
A
- Removes waste products
- Supplies brain n spinal cord w nutrients
- Buffers changes in blood pressure n protects the brain
- Supplies brain w fluid during dehydration
- Allows the brain to remain buoyant
21
Q
Composition of CSF
A
- Low levels of protein n glucose
- To protect the brain from glucose fluctuations in the blood
- Ability of astrocytes to regulate glucose uptake into the brain
22
Q
Lumbar puncture
A
- Examine the state of the brain by proxy of what’s happening in the CSF
- Expected: clear colourless fluid
- Blood → subarachnoid hemorrhage
- Yellow CSF → old blood or jaundice
23
Q
CSF n Alzheimer’s Disease
A
Based on the accumulation of proteins in the CSF
24
Q
What is the structure of invertebrate ganglia?
A
- Cell body
- Axons in neuropil
- Ganglion sheath
- Axons in tracts
25
Frontal lobe function
- Executive function
- Judgement
26
Corpus callosum
- White matter tract
- Axons in 1 hemisphere
- Instances when corpus callosum is surgically cut through
- Epilepsy
27
Midbrain
- Visual n auditory information
- Motor control
- Sensation
28
Pons
- Links w cerebellum
- Modifies medulla output
29
Medulla
- Respiration
- Cardiovascular function
30
Cerebellum
- Balance
- Gait
- Fine movement
- Posture
31
Thalamus
- Relay station
- Integrates sensory information
32
Hypothalamus
- Autonomic control
- Homeostasis
- Endocrine control
33
Hyperpolarization
Membrane potential becomes more negative
34
Depolarization
Membrane potential becomes more positive
35
What results in a resting membrane potential?
- Intact cell (semi-permeable) membrane
- Ionic concentration gradients n ionic permeabilities
- Over the long term: metabolic processes
36
Compare the IC n EC ionic concentration gradients
- Higher in IC
- Potassium
- Anions (proteins, phosphate groups)
- Higher in EC
- Sodium
- Chlorine
37
What is the ideal plasma membrane?
Impermeable to Na+ ions thus changing Na+ concentration will not affect resting potential
38
What maintains the balance b/w K+ ions moving out of the cell?
- Concentration gradient of K+ ions to leave the cell
- Favouring efflux of K+ ions to outside the cell
- Inside of the cell is -80mV which counteracts the concentration gradient → keeps K+ inside the cell
39
How does the membrane potential change w EC K+ if membrane is only permeable to K+ ions
As we increase EC K+ ions → membrane becomes depolarized
40
What are the important physiological implications of K+ concentration gradient?
- Epileptic seizure
- Lots of K+ ions that leave the cell -> depolarize adjacent neurons -> cause them to become excitable
- Glial cells attempt to distribute potassium cells from intensively active sites
41
Why is the membrane potential usually less negative than Ek?
- Cell membrane is not completely impermeable to Na+ (Na+ moves in)
- There is K+ leakage (K+ moves out)
- Na+ and K+ movements changes membrane potential
- This positive charge reduces the overall negativity of the resting membrane potential
42
Action potential
- Major mechanism of neuronal communication
- Neurons take in information via dendrites n assimilate this information
- Travels down axon to terminals
- Does not decrement by virtue of myelin sheath
- Trigger transmitter release
43
Action potential depends critically on Na ions. Explain.
If you drop Na conc by 2/3 then overshoot (which is important for action potential propagation) was not achieved (Hodgkin and Katz 1949)
44
Why does Na+ move into cell when channels open?
- Concentration gradient: inward
- Na+ outside cell so chemical driving force
- Electrical gradient: inward
- Draw sodium ions inside the cell
- Driving force = conc gradient + electrical gradient
45
What initially depolarizes neurons to open the voltage-gated Na+ channels?
- Synaptic transmission
- Excitatory postsynaptic potentials (EPSPs)
- Generated by neurotransmitter release at synapses can depolarize the postsynaptic neuron n open voltage-gated Na+ channels
- Generator (receptor) potentials
- Activation of receptors that are permeable to sodium ions
- Sensory neurons: can depolarize membrane by allowing Na+ ions to flow in
- Intrinsic properties
- Pacemaker activity in heart
- Rhythmic depolarizations occur due to intrinsic mechanisms
- Experimental
- Electrical stimulation
46
Why is Na+ channel opening a positive feedback loop?
- Membrane potential of neuron reaches threshold level
- Voltage-gated Na+ channels open
- Na+ ions influx
- Leads to further depolarization
- Opens more channels
47
Action potentials have all “all or nothing” property. Explain.
Once the threshold lvl of depolarization is reached, AP is generated at full magnitude regardless of the strength of the initial stimulus
48
Explain the 2 ways the repolarization of the AP occurs
- Voltage-gated sodium channels start to close
- Deactivate → no more Na+ ions going in
- Activation of K+ channels
- Time lag → allows Na+ channels to open
- Moves K+ out of the cell → makes inside of the cell more negative [losing + ions]
49
What causes hyperpolarization?
- Change in the membrane potential of a neuron where potential becomes more negative than resting membrane potential
- K+ efflux
- Membrane becomes permeable to K+ ions → they move out of the cell → membrane potential becomes more negative
50
What are the key events involved in the repolarization of the membrane after an action potential?
- Around threshold Vm, the membrane becomes much more permeable to Na+ ions
- This leads to depolarisation and further recruitment of VG Na+ channels
- Depolarisation results in VG Na+ channels inactivation (closure)
- After a delay VG K+ channels open
- Both contribute to the repolarisation of the membrane after the action potential
51
Explain the ball n chain method in relation to VG Na+ channel inactivation
- Positively charged activation gate keeps channel closed [repel Na+ ions]
- Depolarization of membrane cause activation gate to swing out of the way
- Allows Na+ ions to enter n cause further depolarization
- Inactivation “ball” rapidly enters the channel to block Na+ influx
