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96 Cards in this Set

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General Somatic Afferents (GSA's) of spinal and cranial nerves are classified into what 2 categories?
1. Fine touch and pressure.
2. Pain, temperature and crude touch.
1. FToP
2. PaTeC
What are the critical distinctions between the two General Somatic Afferents (GSA's) classifications that are lost when they are lumped together as GSA's?
1. axonal conduction velocity, 2. axonal diameter
3. their entry to CNS
4. where they synapse and cross CNS midline, where they end up and so on.

These critical distinctions are lost when they are lumped together as GSA's
Describe the synapse of relays of the two functional categories?
They synapse initially at different sites in the CNS, cross the midline at different locations, ascend in different pathways, and finally end in different CNS structures.
Where are the 2 locations of the Peripheral nerves axon
cell bodies?
1. the dorsal root ganglia
(sensory, afferents)

2. the central nervous system (motor, efferents).
1.DruG affects senses
What are 7 characteritics that cause differences in axons of a peripheral nerve?
Axons of the PN do not have a uniform population. They differ in the following characteristics:
1. axon diameter
2. degree of myelination
3. conduction velocity
4. susceptibility to anesthesia and asphyxia
5. site of termination in the central nervous system
6. function
7. physiological characteristics such as spike duration and absolute
refractory period
Axon diameter is :
1. positively correlated with?
2. negatively correlated?
1. positively
correlated with degree of myelination and conduction velocity

2. negatively correlated with susceptibility to anesthesia
Describe a peripheral nerve?
They are different fiber types in a peripheral nerve that differ in characteristics.
There are thousands of axons enclosed by the perinurium called endonurium
They are all myelinated and the axoplasm is in the center
What are the subpopulations of axons within a peripheral nerve?
1. Somatic motor neurons
2. Sympathetic axons
3. Touch
4. Pain, temperature, coarse touch
Compare subpopulations of axons within a peripheral nerve?
1. Somatic motor neurons
Axon diameter 15
Heavily myelinated
Conducts 100 m/sec
Very resistant to anesthesia

2. Sympathetic axons
Axon diameter 1
Conducts 1 m/sec
Susceptible to anesthesia

3. Touch
Axon diameter 8
Moderately myelinated
Conducts 50 m/sec
Resistant to anesthesia

4. Pain, temperature, coarse touch
Pain, temperature, coarse touch
Axon diameter 3
Lightly myelinated
Conducts 15 m/sec
Somewhat resistant to anesthesia
Why are somatic motor neurons Very resistant to anesthesia
They are heavily myelinated and thus conduct very fast via saltatory conduction
Compare Pain fibers and Touch fibers in terms of susceptibility to anesthesia?
Pain fibers are thinly myelinated and susceptible to anesthesia. Touch fibers are more heavily myelinated and less susceptible to anesthesia
How was it showed that there were different populations within the nerves of neurons with different conduction velocities and heights of wave?
They recorded from nerves the compound action potential and they got a series of waves of different spectra - classical physiology. (more functional classification)
What are the 3 ascending pathways?
(The dorsal columns, medial lemniscus and postcentral gyrus)

(The spinothalamic system

(The dorsal and ventral spinocerebellar pathways
1. D = Fine Doctors = DuMP
2. S = PaT's Car
3. J = DoVeS
How do we study the ascending pathways?
Begin in the periphery then go into the CNS. They have several relays or synapses and they cross and terminate in different nuclei and you need to know all their functions
What are the things that we need to know about each pathway?
1. Number of relays
2. Relays: where cell body is, information carried, where first synapse is and what it ends on
3. Know whether that segment is ipislaterally projecting or contralateral (crosses midline)

4. If there are three neurons in the relay, prolly one will cross and others will not as they ascend in the Nervous System.
5. Know effects of lesions of each of the relays
Really SICk Lady
What are some of the segments that the pathway goes through?
1. spinal cord
2. lower medulla
3. open medulla
4. pons
5. inferior colliculus
6. superior colliculus
7. thalamus
8. cerebral cortex.

These pathways cross through these regions
SLOPIS Taste Crappy
What is unique at at each level of medulla and pons?
The shapes look different! Therefore look for landmarks on each level to ID what they are when you don’t have the overall scheme in front of you
1. fasiculus gracilis
2. fasiculus cuneatus
1. fasiculus gracilis: either of a pair of nerve tracts of the posterior funiculus of the spinal cord that carry fibers from the lower parts of the body and they are more medial. It terminates in the Nucleus Gracilis of the medulla.

2. fasiculus cuneatus:either of a pair of nerve tracts of the posterior funiculus of the spinal cord that are situated on opposite sides of the posterior median septum lateral to the fasiulus graciis and carry nerve fibers from the upper part of the body. It terminates in the more rostral Nucleus Cuneatus of the medulla.

More laterally is fasiculus cuneatus
Describe the First -order relay in the fine touch system (Dorsal column - medial leminscus pathway)?
The originating cell bodies are in the dorsal root ganglion at all levels. Distal process went out to skin in pacinian corpuscle perhaps. So the impulse went from the skin so the skin stimulus to dorsal root ganglion .
Describe the First -order relay from its origination in the dorsal root ganglion to where it terminates?
The skin stimulus goes to the dorsal root ganglion and enters the spinal cord (does not synapse) and turns into dorsal column (Fasciculus Gracilis or Fasciculus Cuneatus) and makes a right angle turn to ascend and it ends at the Nucleus Gracilis or Nucleus Cuneatus on the same side
What will happen if there is any damage to dorsal root ganglion or the nerve or in the CNS ?
It will produce a fine touch pressure deficit that will be ipsilateral to the lesion site because there was no crossing whatsoever
Describe the second order relay of the DCMLS?
The neurons are located in the nucleus gracile and nucleus cuneatus of the caudal medulla. They give rise axons, internal arcuate fibers (IAF) that decussate and form a compact bundle, the medial leminiscus (ML). The medial leminiscus (ML) ascends through the contralateral brainstem to terminate in the ventral posterolateral (VPL) nucleus of the thalamus.
What will happen if there is Damage to second order cells’ axons (medial lemniscus)?
It results in contralateral deficit in fine touch, pressire on the body. You cannot see the lesion so you test the patient for deficits. If it is a second order relay it is always in reference to site of the lesion. Deficit here will be on the site opposite the lesion. Deficit is alwys in reference to site of lesion cos you are given lesion on the exam and you have to say what the effect on the body is– look at the wording very carefully
What is the area of the open medulla and what is right above it?
4th ventricle area is the level of the open medulla
Cerebellar peduncles are right above it and they close to form the cerebral aqueduct of sylvius
What is located in the Closed medulla ?
1. crossing of pyramids
2. crossing of dorsal column nuclei
3. crossing of axons
What is the Ascending axons?
They are touch axons that are purely sensory and ascend without a synapse
Describe the orientation of the ascending axon?
Septum in dorsal part– medial = Fasciculus Gracilis and lateral = Fasiculus Cuneatus. Axons enter medial to dorsal horn and are fast conducting
Describe the entire pathway from top to bottom?
Cerebral cortex to internal capsule to thalamus to substantia nigra to pons attached to cerebellum to medulla to spinal cord
CITy SuPports CriMeS
Describe the third order relay
The cells are located in the VPL of the thalamus. They project via the dorsal limb of the internal capsule and on the more medial side of the somatosensory cortex, postcentral gyrus.
TIP; T= Third, I = Internal capsule, P = postcentral gyrus
Compare :
1. Relay one
2. Relay two
3. Relay three
1. Relay one = uncrossed
2. Relay two = crossed
3. Relay three = uncrossed, a deficit in fine touch pressure that is contralateral
What will happen if there is destruction of the postcentral gyrus of the somatosensory cortex due to a blood vessel blockage of Anterior cerebral artery (ACA)?
You will affect things on the medial surface of the brain, if it is motor cortex, it will be a motor deficit like wiggling your toes but if it is on the post central gyrus, it will be a sensory deficit to the toes or foot
What is the role of the Anterior cerebral artery (ACA)?
It goes over the corpus callosum and cingulate gyrus and feeds a particular area of the cortex and the rest for the cortex is the Middle cerebral artery .
How are the pathways organized ?
They are somatotopically organized by dermatome. Each one like S5 provides touch for the associated dermatome ex: S5 provides touch for a paritcular dermatome (bottom of buttocks)
All the sensory sytems except for taste and smell have what type of organization when they enter the brain?
topographical organization that is a diagnostic clue
. Can test dermatome by dermatome to see where the cut off is
If there is a Lesion at T6 what happens?
Everything below the lesion site is affected but the upper part of the body is intact.
What could happen if you damage the spinal cord at the C2 or C3 level?
You will severe all the ascending pathways, therefore, you will not feel anything below the C2 or C3 level. Say this person fell of a horse and broke their back, at the T6 level, or T12 level, you will be fine at the upper body but not below the site of the lesion. spinal cord break = most terrible of CNS injuries
What does breathing depend on?
descending pathways from the medulla and they will be destroyed if there is a lesion at the C3 level and diving accidents and car accidents can cause this too.
What happens when neurons enter the spinal cord and ascend from caudal to more rostral levels?
The axons pack on laterally because the median space is already taken esp. since the fasiculus gracilis enters the spinal cord first from T6 to S5 levels and ascends so it is more medial. So, this leaves organization of DC so that S5s are in the midline, then S4, S3, and so on more laterally. Most lateral of FG would contain the T6 axons (those that entered at that level)
What happens when fasiculus cuneatus enters the spinal cord?
Fasiculus Cuneatus is a continuation of the somatotopic organization. They pack on laterally also so there is a somatotopic organization to columns that is dermatomal. With more caudal ones more medial and more rostral ones more lateral
Note the stains used
Lesion at FG axon = fine touch/ pressure axon with ipsilateral deficit
Differentiate btw the type of staines used for:
1. cell bodies
2. axons
1. cell bodies = Nissl stains
2. axons - Mylein stains
1. CNS
2. AMS
What are pyramids?
They are either of the 2 large bundles of motor fibers from the cerebral cortex that reach the medulla oblongata and are continuous with the corticospinal tract of the spinal cord
Just b4 the level of the spinal cord, the pyramidal tracts cross at the lower level of the medulla.

The red and blue lines represent MEDIAL LEMINISCUS
What level of the CNS is this and what does the red and blue lines represent?
What is inferior olive?
A large grey nucleus on that forms the interior of the olive on each side of the medulla oblongata.
Discuss how dermatomes are arranged and what is unique about the organization of the pons?
Each dermatome maintains relationship to adjecent dermatome and in the pons, the Medial Leminiscus does a 90degree rotation but it is still somatotopically organized
What are the key identification features of the open medulla?
1. inferor olive
2. top dark peduncles
3. fourth ventricle on top
5. pyramids at the bottom
First DIP
How do we know that we are at the pons instead of medulla?
There is
1. cerebelar cortex at the top
2. the shape is different
Note sagging belly of the pons at the bottom of the pic
3. You have a hole called the cerebral acqueduct
2. VPL
3. 3rd ventricle
4. second order relays terminate here on cells that will be third order (thalamus)
3. What else is seen here?
4. Why is this level important?
2. contralateral deficit
2. lesions in this or on top of it will cause what?
2. medial leminiscus
3. cerebral peduncles
2, white outline?
3. What else is seen here?
2. cerebral acqueduct
3. Medial Leminiscus that is changing orientation
2. What is the hole here called?
3. What is outlined white?
The spinothalamic system and Spinothalamic tract is a part of the system.
Here there are the peripheral A delta and C fibers coming and the second order relay goes up to the thalamus
What are the pain and temperature afferents
nerve cell bodies of the trigemina (CNV) ganglion with divisions– V1, V2 and V3
Where does the pain/temperature for face comes in from?
They come in at the pontine level and descend ipsilaterally at spinal nucleus of CNV and synapse then 2nd relay crosses and ascends
Where does pain/ temp for the rest of body come in from?
They come in at all levels and there are no distinctions
Describe the first order neurons of the spinothalamic tract?
They are found in the dorsal root ganglia at all levels and they project axons to the second order neurons in the dorsal horn, where they also synapse with the 2nd order neuron.
In terms of synapse, compare fine touch/ pressure to pain/temperature?
pain/temperature DO synapse in the dorsal gray matter but the fine touch/ pressure does not!
Describe the 2nd order relay of pain/temp?
They are found in the dorsal horn and they give rise to axons that decussate in the ventral white commissure and ascend in the ventrolateral funiculus and then go laterally
What is termination end point for first order axons in pain pathways?
Spinal nucleus of 5 (lateral pink)
Describe Blood vessels going in to the brain at the pons?
They are small and sensitive to High BP and rupture
What happens to the pain pathway as it ascends to the VPL thalamus ?
It ascends without a synapse of some axons and with others .
As it ascends it sends off collaterals into the reticular formation and the axons of the cells scattered in there go diffusely to the entire brain. It is the reticular activating system.
What do Pain fibers activate ?
It activates the reticular activating system (sting or wound,etc you need to wake up cos is tissue damaging and threat to your body) which wakes up the brain
Branches may be called the spinal reticulars and they are branches off the brain pathway
Spinal nuc of 5 gets second relay info from?
nerves (pain) which descned then cross
Where is the Chief sensory nucleus and what is its significance?
It is in the pons, where the trigeminal input comes in
The touch/pressure system was in the dorsal nucleus of the spinal cord and also in the head for the Chief sensory nucleus of 5
Compare the termination point for:
1. Pain pathway head:
2. Touch for head:
1. Pain pathway head: terminates in spinal nucleus of 5
2. Touch for head: terminates in chief sensory in the pons
Pain pathway is lateral to what?
Medial leminiscus
Where does the 2nd relay end?
It projects to the reticular formation and terminates contralaterally in the VPL .
What does recording from cells in post-central gyrus show?
10% respond to pain/temp and the rest is a mystery.
Pain due to cancer for example is not eliminated with removal of contra post-C gyrus
There are many thalamic nuclei which get pain information
It is a mystery as to the final site of the pain pathway
Where is Substantia gelatinasa ?
layer II of dorsal spinal cord
What are the two types of pain?
1. sharp
2. protopathic (deep, hurting and lasting pain). Latter comes from 2 or 3 to 5 of dorsal horn.
The dorsal and ventral spinocerebellar pathways
Touch for face terminates where?
in the medulla (Chief sensory nucleus). Then goes up to VPM. It then terminates just superior to sylvian fissure. Therefore, cerebral cortex is somatotopically organized with lumbar at top, going downwards to V1, V2, V3
All lines of communication are dedicated
What provides inputs coming in sensitive to joint position rel. to space, stretch, etc?
T1 to L4)
Describe the dorsal spinocerebellar pathway?
It transmits unconscious propioceptive information to the cerebellum and it is involved in fine coordination of posture and movement of individual muscles of the lower extremeity.
Where does the dorsal spinocerebellar pathway receive input from?
1. Muscle spindles
2. Golgi Tendon Organs (GTO)
3. Pressure receptors
Differentiate btw 1A and 1B?
1. IA from muscle spindle to Clarke’s nuc.

2. IB from Golgi tendon organ

They both tell you how limbs are position in space
What 2 places do IA and IB go to?
1. Clarke’s nuc
2. spinal border cells, L3-L5
Describe the first order relay of the dorsal spinocerebellar tract?
They are found in the dorsal root ganglia from C8 to S3 and they provide the afferent limb for muscle stretch reflexes (e.g patellar reflex).
They project via the medial root entry zone to synapse in the clarke's nucleus.
Describe the second order neurons of dorsal spinocerebellar tract?
They are found in clarke's nucleus (C8 -L3) and they give rise to axons that ascend in the lateral funiculus and reach the cerebellum via the inferior cerebellar peduncle. • The Fibres in the tract project ipsilaterally to the vermis of the cerebellum through the inferior cerebellar peduncle.
Describe the ventral Spinocerebellar Tract ?
It transmits unconscious proprioreceptive info to the cerebellum and it is concerned with coordinated movement and posture of the entire lower extremity.
Describe the first order relay of the ventral Spinocerebellar Tract ?
They are found in the dorsal root ganglion from L1 to S2 , providing afferent limb for miuscle reflexes. They synapse on spinal border cells.
Describe the second order relay of the ventral Spinocerebellar Tract ?
The are spinal border cells found in the ventral horns (L1-S2). They give rise to axons that enter the cerebellum via the superior cerebella peduncle and terminate contralaterally as mossy fibers in the cortex of the rostral cerebellar vermis.
What is the main difference btw:
1.dorsal spinocerebellar tract

2. ventral spinocerebellar tract
1. 1.dorsal spinocerebellar tract is an uncrossed tract so it ascends ipsilaterally.

2. ventral spinocerebellar tract is a crossed tract so it ascends contralaterally.
Describe the location of the inferior cerebellar peduncles?
They are large fiber pathways at level of open medulla with 4th ventricle and overlying cerebellum , and they connect the medulla to the cerebellum.
Describe the location of the superior cerebellar peduncle?
They are above the pons, flanking the cereberal aqueduct and they connect the cerebellum with the pons.
Middle cerebellar peduncles are huge black things flanking the pons
Describe collateral neurons?
They are from the ventral spinocerebellar tract and they ascend contralaterally to pons where they enter contralaterally into the superior peduncle and then they re-cross and end up on the cerebellar cortex ipsilateral to where the original cell bodies were.
Inferior cerebellar peduncle
What is circled in white?
Superior cerebellar peduncle
What is highlighted in white?
What happens if there is a lesion for the dorsal spinocerebellar pathway?
There will be problem touching nose with eyes closed.
Where does Touch for face terminate?
It terminates in the medulla (Chief sensory nucleus). Then goes up to VPM. It then terminates just superior to sylvian fissure. Therefore, cerebral cortex is somatotopically organized with lumbar at top, going downwards to V1, V2, V3
All lines of communication are dedicated
1. Relation of Pons to the medulla
2. Location of Chief sensory nucleus?

3. Location of pain fibers?
4. Role of chief sensory nucleus of the pons?
5. Location of Trigeminal input?
1. Pons is more rostral than the medulla

2. Chief sensory nucleus is in the medulla

3. Pain fibers is in spinal nucleus of 5

4. There is a chief sensory nucleus of the pons which is getting input from trigeminal nerve for fine touch and pressure

5. Trigeminal input comes in at the pontine level and descends
1. Termination of cell bodies and dorsal root ganglia in the pain pathway?

2. The role of postcentral gyrus in the pain pathway?
1. Cell bodies and dorsal root ganglia of pain pathway terminate in dorsal horn and ascend to VPL then descend to spinal nucleus of 5 and the axons cross over and ascend to VPM

2. Limited amount of pain gets up to post central gyrus
So if you wipe out post-central gyrus, there will be dilution but not absence of pain
Describe the organization of the postcentral gyrus?
The organization is somatotopic, but more specifically dermatomal.
Postcentral gyrus goes into lateral fissure and there is also internal touch (pharynx, ex) and they are represented most ventrally in the brain
Touch is therefore represented throughout the brain
Why is there a distortion of the shape of the human body based on the sensory represenation of the contralateral surface of the body?
Because every neuron coming in demands EQUAL CORTICAL SPACE. Where there is dense innervation for the lips for ex, each of the neurons demand equal space and so the lips get more cortex. With less innervation in the foot, each gets same amount of cortical space and there is less total cortical space for the foot