1.1-2.1 Intro Flashcards
What do we know about the NS? : Descartes (3)
”
That we are thinking
Descartes ““I think, therefore I am” (cogito ergo sum
Thought is a private experience and we are aware that we exist.
”
What ELSE do we know about the NS? (3) 1.1
”
- We are embedded actors in an ““externum”” (environment)
- Capacity for action
- Attributes about ourselves (internal state/how we are feeling
All of these are products of operation of the NS
“
Ancient Egyptians view of NS? (3)
Cardio-centric view
- Health of body and mind related to flow of fluid (Like viability of land - River Nile).
- Problems result from too little/too much flow.
- Heart = Mind’s Centre = Centre of flow
Ancient Greece: Hippocrates view of NS?
”
450BC Hippocrates: Brain-centric view
"”from nothing else but the brain comes joy, delights, laughter and sports, and sorrows, griefs despondency and lamentations””
”
Aristotle’s View of NS? (1)
”
300BC. Cardio-centric view, despite growing accepting of brain as seat of the mind
”
Roman Empire? (3) - 200AD Galen and Others
”
200AD Galen: Both cardio-centric and brain-centric. Tripartite view (Brain, Liver, heart) Accepted the classical explanation of humours of the body
- Brain: Intellect
- Liver: Animalistic/Instinctive functions
- Heart: Passion; ““Growing and Living”
Synthesis of a corpus of anatomy found a ‘3rd system’ (Nervous system), supplying tissue and connecting brain and spinal cord. Therefore, while the renaissance reinstated the importance of detailed observation and question, primacy of humours as mechanistic explanation prevailed
”
Reasons for adopting a cardio-centric view of the mind? (6)
- Heart moves, brain sits there
- Simple animals can move and react without brain
- Warmth (= life) emanates from body’s core (heart)
- All known civilisations held heart to be centre of conscious being
- Language contains references to heart as locus of mental experience (e.g., learning by heart)
- Observations that more sophisticated animals have bigger, more convoluted brain can be explained that more heat is generated from heart so more cooling of blood is needed
In NS history, who appreciated the role of the brain (And caveat)
What did others think?
Hippocrates in Ancient Greece then Galan in Ancient Rome appreciated the role of brain but saw its function in terms of 4 humours of the body
Others early views, From ancient Egypt to Aristotle to enlightmenet, ascribed functions to heart
Late Renaissance/Early Modern? (2)
1660AD Descartes
- Mechanical machine: Mechanism of fluid, tubes, and chambers gland
- Inspired by hydraulics
- However, the mind was immaterial, not a mechanical device (Pineal gland). Pineal gland integrates outcomes of physical structures
- Pineal gland controls fluids
Modern Neuroscience view of NS? (2)
What is the implication?
AD 1861 Paul Broca
- Right hemiplegic patient (Damage to right temporal lobe) was unable to produce speech, but can understand language
- Demonstrated localisation of function (Modularity)
Rise of Neurology allowed structured analysis of brain disease
Functions of the NS? (3) 1.3-1.5
- 3 Function of NS 1 - Capacity for Action
- 4 Function of NS 2 - Egocentric External Universe
- 5 Function of NS 3? - Monitor and Control Bodily Functions
1.3 Function of NS 1 - Capacity for Action
Relationship between Genes and NS
Not all complex organisms have a nervous system. An animals’ genome does not inform much about the NS
Arabidopsis thaliana
Complex organism (27,000 genes) but no nervous system. Does not move
Corynactis californica
A “nervous system” comprising a network of nerve cells. Able to move a bit
1..4 Function of NS 2 - Egocentric External Universe
Properties of external/ real world are conscious experiences generated by actions of the nervous system
What do we still not know about NS? (1)
Despite the increasing recognition of the brain as the origin of our mental existence, an understanding of the mind as a function of the brain, i.e., how the mind is generated by the brain, has not emerged. (How the brain produces consciousness)
What are the 3 repugnant ideas of how the NS worked in 1700s? (3)
- Sprits running through hollow nerve fibres, conveying impressions to the brain and activating muscles Descartes’ fluid mechanical model)
- Mini explosions, caused by fermentation from mixing of fluid droplets from the nerve ends and blood, activating muscles (Chemistry): Nerves release some chemical which causes a chemical explosion which activates the next nerve (or muscle)
- Vibrations, light of different energies transferred vibrations to nerves, conveying sensations to the brain (Physics): Nerves vibrate and signal is transmitted from brain to muscles
Evidence against the 3 repugnant ideas of how the NS worked in 1700s? (4)
- Limbs do not increase volume when muscles are activated (Displacement of water does not go up because of increased bulk of muscles, suggesting there is no transfer of fluid)
- Nerves cut underwater did not result in bubbling (No pressure in the system)
- Ligation (Cutting) of nerves didn’t cause accumulation of fluid (No fluid coming out)
- Fluid could not move fast enough to explain NS speed
17th Century: Huge interest in Electricity: Background as to how this was sparked
Relationship between electricity and biology is mainly conferred from electric animals like electric eels - Could see nerves running into those modified muscles that conduct electricity; thus, it was conveying a signal that release stored animal electricity
17th Century and Electricity
Evidences that nerves were related to electricity (2)? Galvani and Aldini
(1780)
- Galvani discovered that electrical stimuli where much more effective in contracting a muscle if they are applied to the muscle’s nerve rather than directly to the muscle, and postulated that nerves contain or conduct “animal electricity”
- Aldini managed to activate facial muscles by stimulating the brain of severed heads (But failed to produce any results by stimulating spinal cord)
Limitations of evidences in the 1700s: Resolution (1) and When do we know about electricity? (1)
Lacked cellular resolution
Only in 1850s, with the detection of tiny currents produced by nerves, could we confirm that nerve signals via. electrical impulses.
The potential difference during electrical stimulation? (Image)
Define Resting; Passive Response; AP
Resting: -65mV
Passive Response: Hyperpolarisation/Depolarisation (Not threshold)
AP: All or Nothing (Intensity reflected in frequency, not amplitude)
How is the resting membrane potential established
Potassium dominates the ionic flux at rest.
At electrochemical equilibrium, there is an exact balance between two opposing forces:
- Concentration gradient that causes K+ to move from A to B, taking along the positive charges
- Opposing electrical gradient that increasingly tends to stop K+ from moving across the membrane (K+ repels one another)
Properties of Ion Transporters:
- What kind of proteins are they?
- Energy and Concentration Gradient
- Importance
- Usually multimeric proteins in plasma membrane of the neuron
- Actively move ions against concentration gradient (Uses ATP). Called electrogenic pump
- Important for thousands of AP and maintaining the potential difference (e.g., if the difference starts to decline) does not have a role in the setting up the initial potential difference.
How do we know ion transporters are only important in maintaining MP difference? Experiment that inhibits ion transporters
- When ouabain, an ATPase inhibitor is applied, stimulating still gave muscle twitch. However, after a number of rapid stimulations, there was a decline in the twitch response
- The decline was because ion transporters were not able to maintain the -65 RMP; RMP slowly increased, and the gap between the peak and the bottom decreased
- This suggests we only need ATPase to maintain the RMP, and the cell can actually passively move to RMP without their intervention
What are ion channels? (3)
- Concentration gradient (And Energy)
- Properties (Permeability and Direction)
- Importance
- Allows ions to diffuse down concentration gradient (No ATP)
- Some:
- Selective permeability to certain ions such as only allowing Na+ or K+
- Non-selective (e.g., non-selective cation channels)
- Rectifying: Only allows one direction of transport
- This selective permeability is the key to how resting membrane potential sets up (initial setup)
What happens if a channel is non-selective? (1)
If channel is non-selective, both positive and negative ion will diffuse, leading to net zero movements.
What is the key to generating and modulating action potentials? What does myelination do?
- Electrical impulse travels along the neuron as a result of voltage-gated Na+ and K+ ion channels opening and activating adjacent voltage-gated Na+ and K+ ion channels
- Myelination increases conduction velocity, where the electrical impulse jumps from node to node
End of 19th Century: What was the main contribution of microscopy
By the end of the 19th Century, Neuron doctrine had prevailed: Neurons were made of discrete cells and not a reticular network (vs Reticular theory)
Unanswered question before Microscopy
We know that nerve tissues are excitable and generate electrical impulses; however, the nature of the nerve cells themselves and their interrelationship was unclear: Are nerves a continuous connection or discrete elements signalling to one another?
Researchers involved in microscopy/cell theory: Schwann, Leeuwenhoeks, and Robert Hooke
Proponents of Cell Theory, though it was thought to inapplicable to the NS
Who was the first to suggest that NS, like other tissues, were composed of discrete cells
Purkinje
Golgi (1840s)
Silver staining of single nerve cells in tissue showed neurons were cells in the nervous system.
Cajal (End of 19th Century) (2)
Further refined silver staining technique
Discovered growth cones and dynamic morphology of growing neurons - Raising the question of whether the same plasticity occurred in adult brains