Principles of Neuroscience

[ferrsal]

Does anyone know what lectures will be covered in the mid semester test?
Also, thought I'd create this topic for any further queries/discussions regarding this subject 

[MelonBar]

They'll prob let us know later but I'd guess weeks 1-5.

[ferrsal]

In lecture 14, im a bit confused about slide 14. Is the diagram shown the corticobulbar tract? Why is the reticulospinal tract shown there?

 Does this mean that the primary motor cortex is connected to the descending projections from the brainstem to spinal cord (e.g. reticulospinal tract, colliculospinal tract). I thought the brainstem and cortex axons were separate 

Thanks in advance if anyone can help me out

[nino quincampoix]

Re Lecture 14 slide 14. I take it that the diagram to which you are referring is the one concerning motor and non-motor loops of the basal ganglia.

In the above case, the four sections of the diagram just refer to different functions of the basal ganglia. In most instances, the basal ganglia are thought to modulate voluntary movement, hence the motor loops. The following is from Purves: the pre-frontal loop may regulate the initiation and termination of cognitive processes such as planning, working memory, and attention. Likewise, the limbic loop may regulate emotional and motivated behaviour, as well as the transitions from one mood state to another.

Either way, these loops, be they motor or non-motor, all relate back to some form of motor associated modulation.


If, however, you are referring to Lecture 13 slide 14, then I'll presume you you are talking about the indirect pathway from the motor cortex to the spinal cord.

The reticulospinal tract starts in the reticular formation in the pons and medulla (activation and suppression of movement).

In relation to the feed-forward mechanism mentioned in the lecture (pulling on the bar, but gastrocnemius EMG activity measured before biceps EMG activity):

• It is anticipated that posture will somehow change (i.e., pulling on the bar).
• Pre-frontal and motor cortex neurons "activate" the reticular formation (note that only some neurons from these cortices are activated in this way; this is important because most motor neurons do not run in the corticobulbar tract - most run in the corticospinal tract instead).
• Via the reticulospinal tract the relevant parts of the spinal cord become "activated" and their associated motor neurons also become "activated."

From Purves (may be of more clarity): Neurons in the motor cortex that supply the lateral part of the ventral horn to initiate movements of the distal limbs also terminate on neurons in the reticular formation to mediate postural adjustments that support the movement. The reticulospinal pathway terminates in the more medial parts of the ventral horn, where lower motor neurons that innervate axial and proximal muscles are located. Thus, the motor cortex can influence the activity of spinal cord neurons via both direct and indirect routes.

So, to answer your question, yes the brainstem nuclei and motor cortex are largely separate, especially for most voluntary motor control, but in some instances, such as the feed-forward mechanism described above, the corticobulbar does link the motor cortex to the spinal cord via the brainstem.


Lastly, hopefully what I've written makes sense - let me know if it doesn't. And I hope my lecturing numbering is right, otherwise...

[ferrsal]

Omg thanks so much for always helping me out and the clear explanations! One more question, given that the corticobulbar sometimes links the motor cortex to the spinal cord via the reticulospinal tract, is this also true regarding the vestibulospinal and colliculospinal tracts?

[nino quincampoix]

While it was not explicitly discussed in the lecture, nor in the lecture notes, I found the following in Purves, but it is a little ambiguous in that it won't give you the exact answer you're looking for.

The reticular formation and the vestibular nuclei (upper motor neurons in the brainstem) are responsible for postural regulation:

• Reticular formation is important for feed-forward control of posture.
• Vestibular nuclei that project to the spinal cord are important for feedback postural mechanisms.

Brainstem pathways can independently organise gross motor control. Direct projections from the motor cortex to local circuit neurons in the brainstem and spinal cord are important for movements of the face and the distal parts of the limbs.


As for the colliculospinal tract (dorsal midbrain):

Superior colliculus upper motor neurons (not sure if all do this or just some) innervate circuits in the reticular formation that supply medial parts of the cervical spinal cord. Functionally, this pathway helps control axial musculature in the neck (generation of orienting movements of the head).

In the lecture, Peter spoke of "hearing a sound and orienting towards its location." So, my best guess would be that there would have to be some sort of higher input, but whether it would be higher motor input is not clear from what I have read.

[ferrsal]

Awesome, thanks so much again!

[nino quincampoix]

No problem

[MelonBar]

To people who did the subject in recent years, were there diagrams or graphs on the mid semester test?

[Sinner]

I'm assuming that you PoNs guys have done your midsem at this point? If so, how many marks was it out of?

In the NEUR30002 fraternity here the first midsem was out of 32 marks (originally 34) and the upcoming 2nd one out of 37; both are worth 25%, not far from your 30%, which is the most insane midsem mark allocation/assessment I've seen in these 3 years. Even just considering this first one, people who barely pass will be holding onto the potential for a final H1 grade by the skin of their teeth.

Luckily I did well here, but I'm not sure if I would be so lucky for next round and there are also people who are unhappy with their scores this time around.

I was talking to an alumni friend who did NEUR30002 a couple of years ago and she was surprised, so it seems like this was a fairly recent development.

[ferrsal]

It's actually the NEUR30002 mid sem results that we just got! Our PoNs mid sem is this tuesday. But yeah, massive weighting that can really make or break your chances of doing well.

[MelonBar]

On the plus side for neurophysiology.. if you do well on the mid sems you can really lower that bar for an h1... potentially a 60 something % on the exam will put you over the line if you did well enough on the msts. This set up really favours people who work consistently and rips people who don't... and why don't they just break up the 30% principles mid sem like in neurophysiology?

anywho, lecture 5.3.. if dopamine is so pro-movement , why does it inhibit the cortex in the indirect pathway? I suppose the indirect path is meant to contrast the selected movement so i guess that doesn't stand here??

[nino quincampoix]

Slide 12 of lecture 5.3 sums up why there are inhibitory and excitatory outputs of the substantia nigra pars compacta.

Direct pathway: excitatory dopaminergic (D1) output effectively selects desired movements.

Indirect pathway: inhibitory dopaminergic (D2) output effectively deselects/dampens unwanted movements.

Together, there is a level of contrast sensitivity.

Also, note that different dopaminergic receptors are in play here [from NEUR30002 Lecture 4.3: Dopamine recetpors are GPCR. D1 family: excitatory (D1, D5); D2 family: inhibitory (D2, D3, D4)].

[ferrsal]

Does anyone know the difference between "range" and "sensitivity and dynamic range" in those tables that were featured in the somatosensory and hearing lectures? Even with his explanations and google, they seem like the exact same thing to me

[nino quincampoix]

It's more or less the same thing. Take EM radiation for example: our eyes can perceive 400-700 nm (i.e., range), which could be perceived from a single photon or from a ray of sunlight (i.e., dynamic range and sensitivity).