V414input06.html

INPUT TO THE HUMAN BRAIN, Part 1^*

Introduction to Somesthesia

-- a self-paced audio-tutorial on the neuroanatomy of the general senses^**

Paul Pietsch, PhD,
Professor Emeritus,
School of Optometry
Indiana University

SOUND CONTROL

{90-min tape} Before you mash the tape button Doc, here are a few "suggestions."

First off, the most important part of the lesson uses slides in a carousel you probably don't have. But don't get a case of the uptights!
We've taken those same slides, given them the same numbers as on the tape and put them right here for you. AND we've given you a "slide control panel" -- where the numbers to click match those they guy on the tape will be tell you to go and get.
You won't need the sheep brains you'll hear about. (Go to a French restaurant if that talk makes you hungry.)
Pictures will substitute for the human brain slices the tape also mentions. They're interesting, but optional.
There's a diagram of the Somesthetic System below to compensate for when the tape talks about a drawing in Netter.
And we have some pictures to help you form a 3-D concept of the caudate nucleus.
Also among the pictures is a diagram of the plan of the Trigeminal or Vth cranial nerve. The trigeminal does for the head what spinal nerves do for the rest of the body.
Because you probably don't carry a copy of Truex and Carpenter (T & C) around in your back pack, and thus can't use the atlas referred to on the tape, we've put labels on the slides you'll be working with. If you run across those labels during a preview, don't panic. We'll get to them if they're important. If not, "don't worry about it already," as inhabitants are prone to say on the small island off the east coast of North America known as Manhattan.

SOUND CONTROL {90-min tape}		Before you mash the tape button Doc, here are a few "suggestions." First off, the most important part of the lesson uses slides in a carousel you probably don't have. But don't get a case of the uptights! We've taken those same slides, given them the same numbers as on the tape and put them right here for you. AND we've given you a "slide control panel" -- where the numbers to click match those they guy on the tape will be tell you to go and get. You won't need the sheep brains you'll hear about. (Go to a French restaurant if that talk makes you hungry.) Pictures will substitute for the human brain slices the tape also mentions. They're interesting, but optional. There's a diagram of the Somesthetic System below to compensate for when the tape talks about a drawing in Netter. And we have some pictures to help you form a 3-D concept of the caudate nucleus. Also among the pictures is a diagram of the plan of the Trigeminal or Vth cranial nerve. The trigeminal does for the head what spinal nerves do for the rest of the body. Because you probably don't carry a copy of Truex and Carpenter (T & C) around in your back pack, and thus can't use the atlas referred to on the tape, we've put labels on the slides you'll be working with. If you run across those labels during a preview, don't panic. We'll get to them if they're important. If not, "don't worry about it already," as inhabitants are prone to say on the small island off the east coast of North America known as Manhattan.

Slide Control Panel

They're in descending order here because that's how the man on the tape takes them up.
There is a slide 17 even though you'll hear otherwise -- but still no slide 08.
To get back to "suggestions," click here!

slide 24
slide 23
slide 22
slide 21
slide 20

slide 19
slide 18
slide 17
{17 is there!}
slide 16
slide 15
slide 14

slide 13
slide 12
slide 11
slide 10
slide 09

no slide 08
slide 07
slide 06
slide 05
slide 04
slide 03

SOMESTHETIC PATHWAYSTo get back to "suggestions," click here!

Based on the underlying anatomy, we can think of the the general sensations as falling to into two main categories, with markedly different courses through the spinal cord:

"Dorsal (posterior) Division"

tactile discrimination (smart touch)
deep sensations (from tendons and joints),
proprioception (feedback from sensors in the muscles called muscle spindles)

"Ventral (anterior)-Lateral Division"

pain
temperature
light touch (e. g., itch, tickles, libidinous sensations)

The two systems part company in the spinal cord but reunite in the upper brainstem in a final common pathway, the medical lemniscus.
The medial lemniscus terminates in the thalamus. Axons from the thalamus pass though the internal capsule and white matter of the parietal lobe to relay the somesthetic signals to the postcentral gyrus, -- the primary sensory cortex.
The neuronal cell bodies of both sets occupy the dorsal (posterior) root ganglia (in the head, the trigeminal nerve's ganglion -- semilunar g. -- serves the same purpose). The neurons of the sensory ganglia are so-called bipolar cells, with one fiber attached to the sense organ in the periphery and the other entering the spinal cord (or brainstem up in the head).
Upon penetrating the spinal cord, the incoming fibers give off branches for local (or spinal or bulbar) reflexes.
The main trunk of the fibers serving the dorsal division enter and form the bulik of the dorsal part of the spinal cord (the dorsal funiculus); uncrossed, these fibers proceed virtually straight up the spinal cord to the medulla before synapsing in the nucleus gracilis or nucleus cuneatus). [The tracts formed by these fibers are called the fasciculus (or tractus) gracilis and cuneatus. Gracilis serves the lower and cuneatus the parts of the body.]
Axons from the cuneate and gracile nuclei arc ventrally in the medulla, as the internal arcuate fibers; they cross to the opposite side of the brainstem as the decussation of the medial lemniscus.
The medial lemniscus proceeds up to and terminates in the thalamus. Fibers from cells in the thalamus pass through the internal capsule, into the white matter of the parietal lobe and terminte in the cortex of the postcentral gyrus.
Senstions of the somesthetic system's ventral division travel on fibers that synapse soon after entering the spinal cord -- on cells of the dorsal gray horn. Fibers of dorsal horn cells cross to the other side of the cord (in the anterior commissure) and form tracts in the ventral (anterior) and ventro-lateral portions of the of the cord: the spino-thalamic tracts. The spinothalamic tracts join the medial lemniscus in the midbrain and thereafter follow the same overall pathway as the somesthetic system in general. (See also discussion relative to the trigeminal nerve).

LATERAL DISSECTION OF THE INTERNAL CAPSULE

Here, the side of the cerebrum and lenticular nucleus have been dissected away to expose the lateral aspect of the internal capsule:

anterior limb -- AL
genu --G
posterior limb -- PL
the untagged arrow points toward what shows of the brain stem
The thalamus lies on the other side of the posterior limb of the internal capsule (PL). Somesthetic pathways from the thalamus reach the postcenral gyrus (partially dissected away here) via the internal capsule. Back to narrative on somesthetic pathways!

CAUDATE NUCLEUSTo get back to "suggestions," click here!

Parasagittal Section:

Head of the caudate nucleus
genu of the internal capsule
lateral ventricle (body)
lenticular nucleus (note connection to caudate n.)

T, thalamus (arrow on pulvinar)
O, occipital lobe
Scroll the window into the next row and note overall shape of the caudate nucleus ---

The tail of the caudate nucleus follows the Lateral Ventricle down into the temporal lobe and goes all the way forward to the amygdala.
The amygdala, remember, is one of the basal nuclei, too, Doc!

To get back to "suggestions," click here!

Slide 03: plane of sectioning:

Looks almost like spinal cord, doesn't it, Doc?
click for slide control

Slide 04:
plane of sectioning:

Note the nucleus gracilis. The large, unlabeled arrowhead marks the boundry between the nucleus gracilis and the fasciculus/nucleus cuneatus; the pink material scattered through the cuneate tract formation marks the beginnings of the cuneate nucleus. Gracilis mediates sensations from the lower and cuneatus from the upper the body.
The spinal tract and nucleus of the trigeminal nerve (V) are tagged.
Note also the crossing or decussation of the pyramids.
click for slide control

Slide 05:

The gracile and cuneate fasciculi [or tracti], collectively the dorsal funiculus of the spinal cord and lower medulla), terminate here in their respective nuclei. Those nuclei stain pinkish, while the fasciculi stain dark blue; the mixture of pink and blue indicates that a given nucleus and its corresponding tract extends vertically through the equivalence of several sections.
The nerve fibers in those two tract formations belong to neurons of the dorsal root ganglia; they convey the following sensory information: a) discriminating and 2-point touch; b) deep sensations (from receptors in tendons); and c) proprioception (feedback signals from muscles).
plane of sectioning:

Also take note of the spinal (or descending) nucleus and tract of the trigeminal (Vth cranial nerve); the spinal nucleus of V (pink) lies medial to the spinal tract of V. Fibers of the spinal tract of V synapse in the spinal nucleus of V. Axons from the spinal nucleus of V fibers cross to the opposite side, turn up and, baring experimental techniques, become indistinguishable from the rest of the medial lemniscus. Note though, some authors do refer to trigeminal lemnisci.
click for slide control

Slide 06:
plane of sectioning:

The internal arcuate fibers, tagged here but barely visible in the photograph, are the axons of cells in the cuneate and gracile nuclei (better seen in lower sections); those fibers arc ventrally, cross to the other of the medulla, as decussation of the medial lemniscius, then turn upwards, towards the thalamus.
click for slide control

Slide 07:

Here again the medial lemniscus and the MLF touch and create the impression (false) that they're an intergral part of the same formation. Recall that at higher levels the medial lemnsicus twists laterally to line up with the thalamus, where it will terminate. The MLF, because it is a fairly straight tract formation, lies in about the same relative position in all cross sections through the medulla and midbrain. plane of sectioning:

D is the dentate nucleus of the cerebellum; 4 marks the fourth ventricle. Note choroid plexus in the fourth ventricle. Recall that cerebrospinal fluid is produce by choroid plexus.
The section contains part of the auditory (acoustic) nerve; i.e., cranial nerve VIII.
The small but conspicuous solitary tract can be seen here; the small pink mass just lateral to it is the solitary nucleus. The latter tract and nucleus convey taste sensations carried by the facial (VII) glossopharyngeal (IX) and vagus (X) cranial nerves.
click for slide control

Slide 09: (No 8)
plane of sectioning:

First take note of the medial lemniscus. Notice how it seems almost continuous (above) with the MLF, the medial longitudinal fasciculus.
Note also the inferior olive, lateral to the pyramid (pyr). The section also shows two of the three pairs of cerebellar peduncles, here the middle (mid.) and inferior sets. The inferior cerebellar peduncle is also know as the restiform body.
The nodulus, suspended into the 4th ventricle here, is a part of the cerebellum's vermis.
click for slide control

Slide 10:

The dentate nucleus belongs to the cerebellum. plane of sectioning:
The facial colliculus is a bump in the floor of the 4th ventricle that provides a surface marker for fibers of the facial nerve (VII); those fibers swoop dorsally from the nucleus of VII and form a genu (or bend) around the abducens nucleus (VI); the arrow on the left points to fibers of the abducens nerve, en route to exit just below the pons (as seen in the last section). The fibers of VII, after making the bend around the abducens nucleus, leave this plane of sectioning, loop ventrally and exit at the inferior-lateral edge of the pons.
Note the location of the medial lemniscus.
click for slide control

Slide 11:
plane of sectioning:

The pyramids (output pathways) emerge because the section is below the pons (note plane of sectioning). Note the abducens nerve (sixth cranial nerve) on your right.
click for slide control

Slide 12:
plane of sectioning:

click for slide control

Slide 13:
plane of sectioning:

Note the mesencephalic tract and nucleus of the trigeminal (V). For a closer view of the latter, click here.
click for slide control

Slide 14:
plane of sectioning:

Note the roots of the trigeminal nerve. Other tags as before.
click for slide control

Slide 15:
plane of sectioning:

First, note the medial lemniscus. Again, the MLF is the medial longitudinal fasciculus.
The decussation of the trochlear nerve, mentioned in the previous caption, is conspicuous (and tagged) in the anterior medullary velum (not labeled).
The cerebellum's midline vermis is tagged, as are the laterally situated cerebellar hemispheres. The cerebellar peduncles represent conduits to bring information into and out of the cerebellum. That feedback information forms a dynamic link between input and output.
Other labels as in previous captions.
click for slide control

Slide 16:

First, take note of the medial lemniscus. You can see the lateral lemniscus just above (dorsal) to it, here. (The lateral lemniscus is on its way into the inferior colliculus.) This section just nicked the lower ends of the two inferior colliculi (or auditory tectum). The MLF is still the medial longitudinal fasciculus. Note again the sup. (superior) cerebellar peduncle.
Note too the trochlear nerve (IVth cranial nerve); the big arrow points to trochlear fibers destined to exit just below the inferior colliculi. The latter fibers arose at a higher level (slide 18), then passed down (to the level in slide 15) where they crossed (or decussated). Do you see those two little dark dots at the end of the little arrow? Those dark dots are trochlear fibers in the anterior medullary velum descending toward their decussation; after decussating, they loop into the anterior medullary velum to execute their cross to the side opposite their origin. The big deal is that the trochlear nerve innervates a muscle, the superior oblique of the eye, on the contralateral side of the body.
plane of sectioning:

Note here the 4th ventricle. The latter space is directly in line with the cerebral aqueduct (iter). A ventricle, qua ventricle, must have some choroid plexus in it; that's also true of the lateral and third ventricles-- but not the cerebral aqueduct! (That's why the cerebral aqueduct is given a name but not a ventricle number. )
Note the mid. (middle) cerebellar peduncle. Also known as the brachium pontis, (can you guess why?), the middle cerebellar peduncle links the pons to the cerebellum. The superior cerebellar peduncle is also tagged in this section.
Again the pyramids (output pathways) can be seen passing vertically through the pons.
click for slide control

Slide 17:
plane of sectioning:

This slide became available after the tape was in the can. The section is through the lower part of the tectum, inferior colliculus (aka the auditory tectum). Note the location of the medial lemniscus. There is a lateral lemniscus. While the medial lemniscus belongs to the somesthetic system, the lateral lemniscus is major conduit of the auditory system.
Note the pyramidal tracts, or pyramids (also called the cortico-spinal and cortico-bulbar tracts). The pyramids are output (motor) pathways.
Check out the sup. (superior) cerebellar peduncle in the tegmentum (aka, the the brachium conjunctivum); the cerebellum is served by three pairs of peduncles (big tract formations): inferior, middle and the superior, tagged here.
MLF, as before, is the medial longitudinal fasciculus.
click for slide control

Slide 18:

click for slide control
In a cross section through the midbrain (or mesencephalon) what lies above the cerebral aqueduct is the tectum (superior and inferior colliculi) and below, the midbrain tegmentum. Notice the MLF, medial longitudinal fasciculus and the medial lemniscus.

Slide 19:

click for slide control
The large upper arrow points to a superior colliculus. MLF is the medial longitudinal fasciculus; a recess of the interpeduncular fossa curls upwards at the upper border of the pons and here gives the false appearence of being a hole. Note especially the medial lemniscus and the heart-shaped oculomotor nuclear complex. The pineal body seeming floats above the tectum; it's delicate stalk, is not in this plane.

Slide 20: -- click for slide control
plane of sectioning:

LGB, lateral geniculate body (nucleus); P, pulvinar (of thalamus) on reader's left; Nuc. III, oculomotor (or 3rd cranial nerve) nuclear complex; centr. gray is a cylinder of central gray matter surrounding the cerebral aqueduct or iter (not labeled); post com., the posterior commissure is a bridge over the central gray matter used in pupillary reflexes; pre-text., the pretectal area(or nuclei), for which this plane of sectioning is named; br. sup. col., brachium of the superior colliculus, a branch of the optic tract with input for internal eye reflexes; (on the left side the latter appears as a dark triangle, apex skewed left, while on the reader's right the fibers in question appear as a dark tuft squeezing between the pulvinar and the medial geniculate body (nucleus),m; the apparent difference in the two sides is because the section is slightly (but fortuitously) cockeyed;sub. nigra, substantia nigra; F, interpeduncular fossa; U, uncus (contains the amygdala); the splenium of the corpus callosum lies at 12 o'clock. [This section is just anterior to the tectum (superior colliculi); thus the term "pre-tectal" area.]

Slide 21:
plane of sectioning:

CC, corpus callosum (body), LV, lateral ventricle; T, thalamus; 3, third ventrticle; IR, infundibular recess of third ventricle; m mammilliary body (nucleus); M-T, mammillo-thalamic tract. The arrow point just visible at 6 o'clock points to the infundibulum of hypothalamus.
Notice, among other things, how the uncus (of the temporal lobe) presses the optic tract against the internal capsule
click for slide control panel

Slide 22:
plane of sectioning:
cp, choroid plexus; 3, third ventricle
click for slide control

Slide 23:
plane of sectioning:
click for slide control
CN, head of caudate nucleus; LN, lenticular nucleus (putamen); other abbreviations as in legend for Slide 24.

Slide 24:
plane of sectioning:

click for slide control
IC, internal capsule (anterior limb) N, head of the caudate nucleus; black C, cingulate gyrus; white F, (above and below) longitudinal fissure; s.p.'s, septi pellucida; X, cavity of septum pellucidum; 1 & 2, lateral ventricles; since the plane is through the genu (knee or bend) of the corpus callosum, we see parts of the structure in the upper and lower parts of the section.

PLAN OF THE TRIGEMINAL NERVE (Cranial Nerve V)To get back to "suggestions," click here!

The mesencephalic tract and nucleus of V (ascending) seem to handle proprioception (feedback from muscles).
The trigeminal nerve does have a motor (output) component -- the motor nucleus of the trigeminal, which serves head muscles and lies close to the mesencephalic nucleus of V. Incidentally, motor fibers of the trigeminal nerve are found only the mandibular division (3).
The "main" (or principal) sensory nucleus of V, some authors tell us, handles touch.
The spinal tract and nucleus of V (descending) takes care of pain and temperature.
What about the central connections for somesthesia from the head?
Axons from the trigeminal nuclei eventually cross (decussate) to the other side. In the conventional wisdom, somesthesia from the head travels upstairs via so-called trigeminal lemnisci. But the fibers of the latter are indistinguishable from medial lemniscus. Also, the textbooks show trigeminal lemnisci ending on a piece thalamus called the arcuate nucleus. But one can say the same thing about signals from the elbow versus the little toe.
Ergo, why sweat the small stuff? (Anatomy's bad enough anyway, eh Doc?)

Speaking of the stuff of Trivial Pursuits, there are a couple of minor exceptions to the trigeminal as the mediator of somesthesia from the head:

the facial nerve (cranial nerve VII) innervates the skin on the inner side of that little gizmo guarding the ear hole (the gizmo's name is the tragus);
the vagus nerve (X) takes care of skin on the rear (posterior) wall of the ear hole (external auditory meatus). But (and you'll like this, Doc), the pathways in the brain stem for both these exceptions are the same as those of the trigeminal nerve. In other words, there's nothing extra to learn.
The exceptions to the trigeminal have significance in evolution. We had ancestors who had gills were our earhole now lie; the gills homologus to our ear holes are innervated by cranial nerves VII and X.

Finally, spinal nerves (C2) innervate the back of the head (occipital region).

Mesencephalic tract and nuc. of V (arrow)

back to slide 13

Electronic Reserve collection of the Indiana University School of Optometry Library

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Slide 03:	plane of sectioning: Looks almost like spinal cord, doesn't it, Doc? click for slide control
Slide 04:	plane of sectioning: Note the nucleus gracilis. The large, unlabeled arrowhead marks the boundry between the nucleus gracilis and the fasciculus/nucleus cuneatus; the pink material scattered through the cuneate tract formation marks the beginnings of the cuneate nucleus. Gracilis mediates sensations from the lower and cuneatus from the upper the body. The spinal tract and nucleus of the trigeminal nerve (V) are tagged. Note also the crossing or decussation of the pyramids. click for slide control
Slide 05: The gracile and cuneate fasciculi [or tracti], collectively the dorsal funiculus of the spinal cord and lower medulla), terminate here in their respective nuclei. Those nuclei stain pinkish, while the fasciculi stain dark blue; the mixture of pink and blue indicates that a given nucleus and its corresponding tract extends vertically through the equivalence of several sections. The nerve fibers in those two tract formations belong to neurons of the dorsal root ganglia; they convey the following sensory information: a) discriminating and 2-point touch; b) deep sensations (from receptors in tendons); and c) proprioception (feedback signals from muscles).	plane of sectioning: Also take note of the spinal (or descending) nucleus and tract of the trigeminal (Vth cranial nerve); the spinal nucleus of V (pink) lies medial to the spinal tract of V. Fibers of the spinal tract of V synapse in the spinal nucleus of V. Axons from the spinal nucleus of V fibers cross to the opposite side, turn up and, baring experimental techniques, become indistinguishable from the rest of the medial lemniscus. Note though, some authors do refer to trigeminal lemnisci. click for slide control
Slide 06:	plane of sectioning: The internal arcuate fibers, tagged here but barely visible in the photograph, are the axons of cells in the cuneate and gracile nuclei (better seen in lower sections); those fibers arc ventrally, cross to the other of the medulla, as decussation of the medial lemniscius, then turn upwards, towards the thalamus. click for slide control
Slide 07: Here again the medial lemniscus and the MLF touch and create the impression (false) that they're an intergral part of the same formation. Recall that at higher levels the medial lemnsicus twists laterally to line up with the thalamus, where it will terminate. The MLF, because it is a fairly straight tract formation, lies in about the same relative position in all cross sections through the medulla and midbrain.	plane of sectioning: D is the dentate nucleus of the cerebellum; 4 marks the fourth ventricle. Note choroid plexus in the fourth ventricle. Recall that cerebrospinal fluid is produce by choroid plexus. The section contains part of the auditory (acoustic) nerve; i.e., cranial nerve VIII. The small but conspicuous solitary tract can be seen here; the small pink mass just lateral to it is the solitary nucleus. The latter tract and nucleus convey taste sensations carried by the facial (VII) glossopharyngeal (IX) and vagus (X) cranial nerves. click for slide control
Slide 09: (No 8)	plane of sectioning: First take note of the medial lemniscus. Notice how it seems almost continuous (above) with the MLF, the medial longitudinal fasciculus. Note also the inferior olive, lateral to the pyramid (pyr). The section also shows two of the three pairs of cerebellar peduncles, here the middle (mid.) and inferior sets. The inferior cerebellar peduncle is also know as the restiform body. The nodulus, suspended into the 4th ventricle here, is a part of the cerebellum's vermis. click for slide control
Slide 10: The dentate nucleus belongs to the cerebellum.	plane of sectioning: The facial colliculus is a bump in the floor of the 4th ventricle that provides a surface marker for fibers of the facial nerve (VII); those fibers swoop dorsally from the nucleus of VII and form a genu (or bend) around the abducens nucleus (VI); the arrow on the left points to fibers of the abducens nerve, en route to exit just below the pons (as seen in the last section). The fibers of VII, after making the bend around the abducens nucleus, leave this plane of sectioning, loop ventrally and exit at the inferior-lateral edge of the pons. Note the location of the medial lemniscus. click for slide control
Slide 11:	plane of sectioning: The pyramids (output pathways) emerge because the section is below the pons (note plane of sectioning). Note the abducens nerve (sixth cranial nerve) on your right. click for slide control
Slide 12:	plane of sectioning: click for slide control
Slide 13:	plane of sectioning: Note the mesencephalic tract and nucleus of the trigeminal (V). For a closer view of the latter, click here. click for slide control
Slide 14:	plane of sectioning: Note the roots of the trigeminal nerve. Other tags as before. click for slide control
Slide 15:	plane of sectioning: First, note the medial lemniscus. Again, the MLF is the medial longitudinal fasciculus. The decussation of the trochlear nerve, mentioned in the previous caption, is conspicuous (and tagged) in the anterior medullary velum (not labeled). The cerebellum's midline vermis is tagged, as are the laterally situated cerebellar hemispheres. The cerebellar peduncles represent conduits to bring information into and out of the cerebellum. That feedback information forms a dynamic link between input and output. Other labels as in previous captions. click for slide control

Slide 17:	plane of sectioning: This slide became available after the tape was in the can. The section is through the lower part of the tectum, inferior colliculus (aka the auditory tectum). Note the location of the medial lemniscus. There is a lateral lemniscus. While the medial lemniscus belongs to the somesthetic system, the lateral lemniscus is major conduit of the auditory system. Note the pyramidal tracts, or pyramids (also called the cortico-spinal and cortico-bulbar tracts). The pyramids are output (motor) pathways. Check out the sup. (superior) cerebellar peduncle in the tegmentum (aka, the the brachium conjunctivum); the cerebellum is served by three pairs of peduncles (big tract formations): inferior, middle and the superior, tagged here. MLF, as before, is the medial longitudinal fasciculus. click for slide control
Slide 18:	click for slide control In a cross section through the midbrain (or mesencephalon) what lies above the cerebral aqueduct is the tectum (superior and inferior colliculi) and below, the midbrain tegmentum. Notice the MLF, medial longitudinal fasciculus and the medial lemniscus.
Slide 19:	click for slide control The large upper arrow points to a superior colliculus. MLF is the medial longitudinal fasciculus; a recess of the interpeduncular fossa curls upwards at the upper border of the pons and here gives the false appearence of being a hole. Note especially the medial lemniscus and the heart-shaped oculomotor nuclear complex. The pineal body seeming floats above the tectum; it's delicate stalk, is not in this plane.

Slide 21:	plane of sectioning: CC, corpus callosum (body), LV, lateral ventricle; T, thalamus; 3, third ventrticle; IR, infundibular recess of third ventricle; m mammilliary body (nucleus); M-T, mammillo-thalamic tract. The arrow point just visible at 6 o'clock points to the infundibulum of hypothalamus. Notice, among other things, how the uncus (of the temporal lobe) presses the optic tract against the internal capsule click for slide control panel
Slide 22:	plane of sectioning: cp, choroid plexus; 3, third ventricle click for slide control
Slide 23: plane of sectioning:	click for slide control CN, head of caudate nucleus; LN, lenticular nucleus (putamen); other abbreviations as in legend for Slide 24.
Slide 24:	plane of sectioning: click for slide control IC, internal capsule (anterior limb) N, head of the caudate nucleus; black C, cingulate gyrus; white F, (above and below) longitudinal fissure; s.p.'s, septi pellucida; X, cavity of septum pellucidum; 1 & 2, lateral ventricles; since the plane is through the genu (knee or bend) of the corpus callosum, we see parts of the structure in the upper and lower parts of the section.

Introduction to Somesthesia

-- a self-paced audio-tutorial on the neuroanatomy of the general senses**

-- a self-paced audio-tutorial on the neuroanatomy of the general senses^**