Functional Organisation of CNS Flashcards
Where does a somatosensory neuron make its first synapse?
all the way up through the dorsal column and synapse at the medulla
What are gracile and cuneate nuclei responsible for?
for somatosensation, gracile nucleus is the location for first synapse from the lower body, whereas cuneate is for the upper body
T/F the primary somatosensory neuron decussate at the medulla
False, primary neuron runs ipsilaterally. It’s the secondary neuron that crosses over
The dorsal column is topographically organised. Neurons from the lower body tend to run more ________ while the upper body neurons, like cervical neurons, run more _________. Therefore, gracile nucleus is _______ to cuneate nucleus
medially (medial for lower body)
laterally (lateral for upper body)
Medial, because it receives lower limb neurons
At the point of decussation, the name given to the neurons crossing over is?
internal arcuate fibres
At the point of decussation at the middle region of spinal cord, where are the fibres of cuneate nucleus in relation to fibres of gracile nucleus?
Gracile is ventral to cuneate
Gracile secondary neurons run laterally to cuneate secondary neurons
Where is the second synapse for somatosensation?
At ventral posterolateral nucelus (VPLN) of the thalamus
Where are the neurons from lower reigion in relation to neurons from upper region at the thalamic region?
neurons from lower limb (gracile) are lateral to neurons from upper region (cuneate)
What is the name of the tract where the secondary neurons run within?
medial lemniscus
after synapsing at the thalamus, the tertiary neurons project to which region of the cortex?
Somatosensory cortex (primary, and some secondary), which is posterior to the central sulcus
What is the topographical organisation of the primary somatosensory cortex? What is the significance of that?
Neurons from gracile (lower limb) are located more medially, and neurons from cuneate are located more laterally.
There is a cross over of topographic organisation in the course of tertiary neuron
What are the sub-divisions of primary somatosensory cortex? How are they organised in relation to the central sulcus?
Area 1, 2, 3a, 3b
from central sulcus - 3a -> 3b -> 1 -> 2
makes no sense whatsoever
What is an evidence suggesting that there is a secondary somatosensory cortex?
the representation of body structures are repeated in S2
How many body maps are there in total for sensory cortex?
4 in primary, 2 in posterior parietal cortex. 6 in total
Are slow adapting and fast adpating neurons segregated ?
Yes, there are islands of slow adapting eurons within each topographical map
Which sub-division of S1 receive most input?
3b
What gives rise to “cognitive touch”?
the integration of information from the four-subdivisions of S1 at S2
Area 1 is more for ________, while area 2 is more for _______
area 1 for texture
area 2 for size/shape
what is the function of posterior parietal cortex
it receives and integrates inputs from visual, auditory and somatosensory, and it’s involved in planning movement and working out where you are spatially
Can you reorganise topographic map?
Yes, in an amputated individual, the unused area will get taken up by the nearby areas of neuron
What is an example of normal physiological cortical reorganisation
during lactation, there is increased somatosensory input from breasts
Do PNS nerve injuries recover?
Yes, but it’s never a complete recovery, because there is a lack of specificity with regrowth. The original function can never be restored
What the CNS plasticity respond to? What is the significance?
CNS plasticity responds to the frequency of use, not the pattern of use
If there is peripheral nerve injury, the CNS cannot reorganise to restore the PNS function
“erroneous peripheral nerve regeneration does not produce compensatory central plasticity”
Where are the reflex patterns generated?
in the spinal cord
During development, the growth of spinal cord is ______ than vertebral column, and it stops at the level of _______ , but beyond that, there are bundles of spinal nerves called _______ which give rise to pairs of spinal nerves for the _______
slower
L1/L2
caudal equina
lower limbs
What colour is white matter on histological sections?
black
What colour is fluid on MRI 1) T1 2) T2
On T1, it is dark
On T2, it is bright
Why is there more white matter towards to the upper spinal region?
there are more fibres closer to the head, because spinal roots fan out at each level
Where in the spinal cord does the nociceptive neurons run?
in the anterolateral column
What are proprio-spinal neurons?
neurons that make connection within the spinal cord
What are the two types for pain fibres and what information do they provide?
C fibres - slow, burning pain
A delta fibres - fast, shape pain
Why are lower motor neurons often called the final common pathway
Because they receive inputs and modulations from both local interneurons and upper motor neurons
What is a motor unit
the motor neuron and the muscles fibres that it innervates
What is a motor neuron pool
clusters of motor neurons innervating a group of muscles collectively
Muscles are formed in pairs of _________ , and all muscles except for __________ have proprioceptive _________ that transduce _________ into nerve impulse
functional units
extra-ocular muscles
muscle spindles
muscle stretch
What is the function of gamma motor neurons?
They adjust the length of muscle spindles so spindles are always in the optimal position to detect muscle length
Why are the sensory apparatus for muscle spindles also called interfusal fibres?
because the apparatus has its own fibrous sheath
T/F muscle spindles start off as normal muscles
True, but sensory neurons come in to differentiate muscles into spindles
What is the function of golgi tendon
respond to amount of force placed on the muscles
Golgi tendons are described to be in ______ with muscle fibres, while muscle spindles are in ______ with muscle fibres
series
parallel
Why is “knee jerk” a monosynaptic reflex?
there is only one central synapse - sensory neuron picks up the stretch signal and directly feeds it back to the motor neuron for the same muscle
What is the function of reflex system?
reflex maintains joint position and posture
The sensory neuron excites the motor neuron from the same muscle, but what else does it need to do?
synapse on an inhibitory interneuron to inhibit/relax the antagonist muscle
Describe the golgi tendon feedback circuit
golgi tendon regulates force
too much force -> need to drop the load
sensory neuron synapse to two separate interneurons - inhibitory to primary muscle (relax primary)
excitatory to antagonist muscle (contraction)
Is golgi feedback circuit monosynaptic?
No, it synapses onto an interneuron first
When we step on something sharp, what happens to
1) ipsilateral flexor?
2) ipsilateral extensor?
3) contralateral flexor?
4) contralateral extensor?
1) contracts
2) relaxes
3) relaxes
4) contracts
Ipsilateral muscle groups do the opposite of contralateral ones
Why are priospinal neurons short in the lateral region?
Lateral region is more for distal structures like digits. They are more fine movements rather than posture control, so the local interneuron circuits don’t need to be long
T/F the pattern for reflex tends to change with different starting positions
False, the pattern is the same as long as the stimulus is applied at the same spot. This is because the purpose of reflex is the same even with different starting positions
Most interneurons in the spinal cord are _______ , same as the _______ motor neuron
inhibitory
upper
What is the clinical presentation of upper motor neuron damage
UMN damage = lifted inhibition on LMN
Increase reflex, tone, and muscle excitability
Is Myasthenia Gravis a motor neuron disease
Yes, although there is nothing wrong with the motor neuron
What are the two sets of SNS ganglion?
prevertebral and paravertebral ganglion
Which part of the ANS nerve is myelinated?
the preganglionic neuron is lightly myelinated
postganglionic neuron is not myelinated
What are some non-classical transmitters?
ATP, nitric oxide, neuropeptides
What is co-transmission?
multiple transmitters being released with one AP
T/F There is one neurotransmitter release site per axon
False, there are multiple release sites
Why are some receptors expressed remotely from the synapse? What is the name of this kind of receptor?
Don’t know why, but they can be used as exogenous drug targets
They are called extra-junctional receptors
Where are the SNS neurons located in the spinal cord?
in the intermediaolateral nucleus
What is it important to have ganglions?
the ganglions are essential for integrating and coordinating information before reaching organs
What does 1) paravertebral ganglia 2) prevertebral ganglia control?
1) para - constriction of vasculature
2) pre - control smooth muscle
T/F SNS ganglia communicates to a single neuron
false, the ganglia works in a divergence and convergence fashion, receiving many signals and sending out many signals
What is the function of adrenaline?
it is activated along with the SNS system to double the effect by having circulating adrenaline, activating receptors all throughout the body
What are the four PNS ganglion in the cranial region?
Edinger-Westphal nucleus
Salivatory nuclei
Dorsal motor nucleus of vagus
nucleus ambiguus
What is the name of the sacral collection of PNS ganglions? In what way are they different to the cranial ganglions?
inferior hypogastric plexus
They have long post-ganglionic neurons
they are mixed with the sympathetic neurons
There is little integration, more like a relay station
Do PNS provide circulating factors?
no, the action is more local
Do SNS and PNS always work antagonistically?
No, they are not antagonists of each other in functions like
1) salivary secretion
2) tear secretion
What are some examples of antagonism of SNS and PNS at cellular level?
control of heart rate and force of contraction
control of airway
what are some examples of functional antagonism via different cells?
control of pupil
control of bladder (SNS controls the base, PNS controls the body of the bladder)
What are some examples of different but not opposite actions
SNS serous salivary secretion, PNS mucous salivary secretion
SNS for constriction of abdominal vasculature and lipolysis
PNS for tear secretion at the lacrimal gland
What is the only correct way of identifying SNS and PNS neurons?
based on the anatomy/location of the preganglionic neurons
What is the term describing ANS reflexes involving the brain?
supraspinal reflex
What are some sensory inputs to trigger ANS reflex?
chemical signal
distensible organ stretch
What are some possible consequences of ANS dysfunction when the spinal cord is severed
bladder, bowel, sexual dysfunction
CV dysregulation
thermal dysregulation
What is the main function of nucleus of solitary tract of the medulla?
it’s a major integrative centre for ANS function
What are the two possible pathways when signal reaches the nucleus of solitary tract?
1) trigger immediate feedback to control local reflexes
2) provide information to higher centres to drive complex response involving other components like emotion/endocrin
What is the most important higher centre for autonomic output?
paraventricular nucleus of the hypothalamus
ANS provides complex changes around the body. Therefore, what do drugs need to do in order to modulate these complex functions?
Drugs need to target the autonomic centres in the CNS in order to relief the complex connections involving pain, emotion and their relevant physiological changes
