Archive for the ‘Neuroanatomy’ Category

Neuronal Connections in the Cerebellum in Short

January 13, 2013 3 comments

Control of movement is largely determined by incoming (afferent) and outgoing (efferent) neural impulses in the cerebellum.

Motor information input travels from the spinal cord, cerebral cortex and vestibular system via mossy fibers.

Feedback regarding movements returns to the cerebellum via the inferior olivary nucleus in the medulla oblongata. This feedback loop allows the brain to coordinate movement.

All outgoing neural impulses from the cerebellum travel via the deep cerebellar and vestibular nuclei. Proper functioning of the neuronal pathway between mossy fibers, granular cells, parallel fibers, climbing fibers and Purkinje cells are thought to be essential for coordinated muscular movement. Glutamate is a neurotransmitter in the excitatory synapses between climbing fibers and Purkinje cells as well as between granular cells and mossy fibers. Disruptions in this system are thought to be involved in a variety of movement disorders.

Cerebellar connections(click on the picture to view full size)

The Reticular Formation, Limbic System and Basal Ganglia

February 19, 2012 1 comment

The Reticular Formation

It’s a ‘diffuse net’ which is formed by nerve cells and fibers. It extends from the neuroaxis spinal cord through medulla, pons, midbrain, subthalamus, hypothalamus and thalamus (spinal cord is relayed superiorly to the cerebral cortex).

Many afferent and efferent pathways project in and out of the RF from most parts of the CNS. The main pathways through the RF is poorly defined and difficult to trace using silver stains. Reticular formation can be divided into three columns : median, medial and lateral columns.

Functions of the Reticular formation

1.   Control of skeletal muscles:

  • RF modulates muscle tone and reflex activities (via reticulospinal and reticulo bulbar tracts). It is important in controlling muscles of facial expression when associated with emotions.

2.   Control somatic and visceral sensation (influence can be excitatory or inhibitory)

3.   Control of autonomic nervous system

4.   Control of endocrine nervous system (hypothalamus and the pituitary)

5.   Influence on the biological clock (rhythm)

6.   The reticular activating system (arousal and level of consciousness are controlled by the RF)

Clinical note

When a person smiles for a joke, the motor control is provided by the RF on both side of the brain. The fibers from RF is separated from corticobulbar pathway (supply for facial muscles). If a patient suffers a stroke that involves corticobulbar fibers, he or she has facial paralysis on the lower part of the face, but is still able to smile symmetrically.

The Limbic System

 Limbic structures   Functions of the limbic system 
  1. Sub callosal, cingulated and parahippocampal gyri
  2. Hippocampal formation
  3. Amygdaloid nucleus
  4. Mammillary bodies
  5. Anterior thalamic nucleus
1. Influence the emotional behavior:a. Reaction to fear and angerb. Emotions associated with sexual behavior

2. Hippocampus is involved in converting short term memory to long term memory (If the hippocampus is damaged, patient is unable to store long term memory – Anterograde amnesia)

The  Basal Ganglia and their connections

Connections of the Basal Ganglia

Yellow arrow : Pallidofugal fibers

Caudate nucleus and the Putamen: main sites of receiving inputs

Globus pallidus: main site from which output leaves

Afferent and Efferent fibers

Connections of the caudate nucleus and Putamen Connections of the Globus pallidus
Afferent Efferent Afferent Efferent
CS: CorticostriateTS: Thalamostriate

NS: Nigrostriate

BS: Brainstem striatal fibers

SP: Striatopallidalfibers

SN: Striatonigral fibers

SP: Striatopallidalfibers Pallidofugalfibers

Functions of  the Basal Nuclei

Basal Nuclei controls muscular movements by influencing the cerebral cortex (it doesn’t have direct control through descending pathways to the brainstem and spinal cord). It helps to prepare for the movements (enables the trunk and limbs to be placed in appropriate positions before discrete movements of the hands and feet).

Functional connections of the Basal Nuclei and how they influence muscle activities

1. Ben Greenstein, Ph.D, Adam Greenstein, BSc (Hons) Mb, ChB Color Atlas of Neuroscience
2. Allan Siegel Ph.D, Hreday N. Sapru Ph.D Essential Neuroscience, 1st Edition
3. Stanley Jacobson, Elliot M. Marcus Neuroanatomy for the Neuroscientist
4. Patrick f. Chinnery Neuroscience for Neurologists
5. Dale Purves Neuroscience, 3rd Edition
6. Suzan Standring Gray’s Anatomy
7. Keith L. Moore, Arthur F. Dalley, Anne M. R. Agur Clinically Oriented Anatomy
8. Frank H. Netter Atlas of Human Anatomy
9. Walter J. Hendelman, M.D., C.M. Atlas of Functional Neuroanatomy
10. Mark F. Bear, Barry W. Connors, Michael A. Paradiso Neuroscience Exploring the Brain
11. Dale Purves et al. Principles of Cognitive Neuroscience
12. Eric R. Kandel et al. Principles of Neural Science

Descending Tracts

February 17, 2012 Leave a comment

Descending tracts have three neurons:

1.   1st order neurons (UMN): cell bodies are in the cerebral cortex and other supra spinal areas

2.   2nd order neurons: short and situated in the anterior grey column of the spinal cord

3.  3rd  order neuron (LMN): situated in the anterior grey column and innervate the skeletal muscles through anterior roots of the spinal nerves

Corticospinal tract: rapid, skilled and voluntary movements

1st order neuron

Axons arise from the pyramidal cells of the cerebral  cortex  (situated  in  the  5th   layer),  2/3 from the pre central gyrus and 1/3 from the post central gyrus:

1. 1/3 of fibers arise from the 1stry motor  cortex (Area 4)

2. 1/3 of fibers arise from the 2ndry motor cortex (Area 6)

3. 1/3 of fibers arise from the parietal lobe

(Area 1, 2 and 3).

Descending fibers converge in the corona radiata and  pass  though  the   posterior  limb  of  the internal capsule; organization of fibers within the internal capsule:

1. close to genu (medial): concerned with the cervical parts of the body

2. away from the genu (lateral): concerned with the lower extremity.

The tract then passes through the middle 3/5 of the basis pedunculi of the midbrain; organization of fibers in the midbrain:

    1. medially: cervical parts of the body
    2. laterally: lower limbs.

When the tract enters the pons, it’s broken into many bundles by the transverse pontocerebellar fibers. In the medulla oblongata, the bundles group together to form the pyramids. At the junction of the MO and the spinal cord, most fibers cross the midline at the decussation of the pyramids and enter the lateral white column of the spinal cord to form the lateral corticospinal tract (LCST). LCST descends length of the spinal cord and terminates in the anterior grey column of all the spinal segments.

The fibers which didn’t cross, descend in the anterior white column of the spinal cord as the anterior corticospinal tract (ACST). Fibers of the ACST eventually cross and terminate in the anterior grey column of the spinal cord segments in the cervical and upper thoracic regions.

2nd order neuron:

It’s an internuncial neuron.

3rd order neuron:

It’s a alpha or gamma motor neuron.

To read more click on this link to the full article: Descending Tracts

Ascending Tracts

February 10, 2012 Leave a comment


They are located in the white matter and conduct afferent information (may or may not reach consciousness). There are two types of information:

  1. Exteroceptive : originates from outside the body (pain, temperature and touch
  2. Proprioceptive : originates from inside the body (from muscles and joints)

Normally there are three neurons in an ascending pathway:

  1. 1st order neuron: cell body is in the posterior root ganglion
  2. 2nd  order neuron: decussates (crosses to the opposite side) and ascends to a higher level of the    CNS
  3. 3rd neuron: located in the thalamus and passes to a sensory region of the cortex

Pain and temperature pathway: lateral spinothalmic tract

1st order neuron

Peripheral process extends to skin or other tissues and ends as free nerve endings (receptors). Cell body is situated in the posterior root ganglion. Central process extends into the posterior grey column and synapses with the 2nd order neuron.

2nd order neuron

The axon crosses obliquely to the opposite side in the anterior grey and white commissures within one spinal segment of the cord. It ascends in the contralateral white column as the lateral spinothalamic tract (LSTT).

As the LSTT ascends through the spinal cord new fibers are added to the anteromedial aspect of the tract (sacral fibers are lateral and cervical fibers are medial). The fibers carrying pain are situated anterior to those conducting temperature.

As the LSTT ascends through the medulla oblongata,  it’s  joined  by  the  anterior spinothalamic tract and the spinotectal tract and forms the spinal lemniscus. Spinal lemniscus ascends through the pons and the mid brain.

Fibers of the LSTT end by synapsing with the 3rd order  neurons  in  the  ventral  posterolateral nucleus  of  the  thalamus  (here  crude  pain  and temperature sensations are appreciated).

3rd order neuron

Axons pass through the posterior limb of the internal capsule and corona radiata  to reach the somatosensory  area  in  the  post  central  gyrus  of  the  cerebral  cortex.  From  here  information is transmitted to other regions of the cerebral cortex to be used by motor areas. The role of the cerebral  cortex  is  interpreting  the  quality  of  the  sensory  information  at  the  level  of  the consciousness.

Light (crude) touch and pressure pathway: anterior spinothalamic tract (ASTT)

1st order neuron

It is similar to the pain and temperature pathway.

2nd order neuron

The axon crosses obliquely to the opposite side in the anterior grey and white commissures within several spinal segments. It ascends in the contralateral white column as the anterior spinothalamic tract (ASTT). As the ASTT ascends through the spinal cord new fibers are added to the anteromedial aspect of the tract (sacral fibers are lateral and cervical fibers are medial).

As the ASTT ascends through the medulla oblongata, it’s joined by the lateral spinothalamic tract and the spinotectal tract and forms the spinal lemniscus. Spinal lemniscus ascends through the pons and the midbrain. Fibers of the ASTT end by synapsing with the 3rd order neurons in the ventral posterolateral nucleus of the thalamus (here crude awareness of touch and pressure sensations are appreciated).

3rd order neuron

Axons pass through the posterior limb of the internal capsule and corona radiata to reach the somatosensory area in the post central gyrus of the cerebral cortex. The sensations can be crudely localized. Very little discrimination is possible.

To read more click on this link to the full article: Ascending Tracts (pdf).

Dorsoventral vs. Septotemporal hippocampus

Everybody knows what the hippocampus is for: memory. And…maybe something about anxiety or depression? Yes – over the last 10 years or so many studies have been published showing that the hippocampus has these two roles and that the mnemonic and emotional functions of the hippocampus are associated with its septal (dorsal) and temporal (ventral) ends, respectively. This new knowledge means that we’ve had to reorient our perspective. What we see when we consider the septal hippocampus may not be the same if we only consider its temporal end. My goal here is not to provide a review of the memory vs. emotional functions of the hippocampus (btw this dichotomy is a vast oversimplification). Instead, I’d like to talk about how people have differentiated these two ends of the hippocampus in their analyses. I’m also happy to showcase a bunch of pretty anatomical images that will probably never be published in a traditional journal article.

Some studies showing different functions of septal and temporal hippocampus

  • Some of the best reviews of the topic are by Bannerman et al from 2004 and 2011.
  • A recent and free review article by Fanselow and Dong.
  • Classic Moser papers showing spatial memory is more dependent on dorsal hippocampus and anxiety/fear behavior on ventral hippocampus
  • recent paper suggesting that spatial processing in the septal hippocampus meets the behavioral-control functions of the temporal hippocampus to enable rapid spatial learning

History of neurogenesis quantification. So, back in the day, before I even knew what a neuron was, and before it was well-established that there was functional differentiation along the hippocampal axis, people would pick a few sections from the dorsal hippocampus (it’s much more photogenic, gets all the glory), count new neurons, and make it a density measurement. Then the stereology police arrived (seriously, that’s what they’re called) and pointed out that changes in tissue volume or cell packing could change density measurements without there being any differences in numbers of cells. Stereological analyses also prevent any biases that might arise from creating arbitrary boundaries when examining only part of the hippocampus. And so people started doing stereological counts, which require a systematic quantification throughout the entire hippocampus. My guess is that this probably delayed the appreciation that neurogenesis could vary in magnitude and function along the hippocampal axis. Now that we know that stereology is pointless we can get back to business (this is a joke – please don’t arrest me).

Difficulty of quantifying subregions due to curvature of the hippocampus. One of the reasons the hippocampus is such a popular neurobiological model is its anatomy – the dentate gyrus, CA3 and CA1 subfields are all composed of tightly packed cells that are easy to identify. Thinking of the hippocampus along its long axis, one end projects to the septum and the other abuts the temporal lobe, hence “septotemporal” is technically the most accurate way to refer to the different ends of the hippocamus. The hippocampus is curved in such a way that you can actually cut it along any of the 3 spatial planes (X, Y, Z aka coronal, horizontal, saggital) and hit the hippocampus perpendicular to the septotemporal axis somewhere, giving rise to the classic the trisynaptic circuit. However, because of this same curvature, sectioning the brain in only one of the three planes means that some portion of the hippocampus is not going to be cut perpendicular to the long axis, producing sections in which septotemporal coordinates are hard to define.

The 3D nature of the hippocampus using images from the Allen Brain Explorer:

Figure 1: The dentate gyrus subfield of the hippocampus (i.e. green banana), from its septal pole, extends caudally and laterally and then ventrally. Green axis=dorsoventral, red=rostrocaudal, yellow=mediolateral.

Figure 2: A relatively caudal coronal section with the 3D dentate gyrus shown in the left panel, for comparison. This section contains ventral dentate gyrus (at the bottom, by “temporal”) but, at the top of the section, it also contains a portion of the dentate gyrus that is very dorsal, despite being far from the septal pole.

Figure 3: This section is more caudal than the previous example, yet the dentate granule cells (white patches within the bright green region) do not extend as far in the ventral direction. So, more caudal ≠ more ventral.

Others on the curvature problem:

Schlessinger et al., 1975: Since the dentate gyrus follows the general curvature of the hippocampal formation, it is difficult to apply the usual topographical terms to its various parts. The rostral third or half of the gyrus is more-or-less horizontally disposed within the cerebral hemisphere…At about the junction of its rostral and caudal halves the gyrus is sharply flexed upon itself, and comes to be vertically disposed….Again, because of the flexure of the hippocampal formation, it is inappropriate to refer to the dentate gyrus as having a dorsal (or rostral) and a ventral (or caudal) part. Following Gottlieb and Cowan (’73) we shall refer to the long axis of the gyrus, extending from the temporal pole of the hemisphere to just behind the septal region, as its temporalseptal axis.

Amaral & Witter, 1989: Because of its complex three-dimensional shape, normal sections of the hippocampus, i.e. those oriented perpendicular to the long axis, are obtained for only a small part of its septotemporal extent in standard coronal or horizontal sections. This situation severely complicates the analysis of the connections within the hippocampal formation.

De Hoz et al., 2003: In discussing different regions of the hippocampus, we use the terms “septal” and “temporal” to refer to the rostralmost and the ventralmost poles of the longitudinal axis, respectively, because this terminology allows an even division of this axis into septal and temporal halves. The terms “dorsal” and “ventral” are sometimes used to refer to the same areas; the dorsal hippocampus is, however, more extensive than the ventral.

So how can we divide the hippocampus? Many people work with coronal sections. Can we delineate boundaries between different hippocampal subregions in coronal sections? Banasr et al. has described a reproducible method for separating dorsal from ventral hippocampus using coronal sections. Here, the dorsal regions would contain a fair bit of mid-septotemporal hippocampus but indeed, only the dorsal sections would contain septal hippocampus and only ventral sections would contain temporal hippocampus:

Figure 4: Separating dorsal and ventral hippocampus in coronal sections

Jayatissa et al. has horizontally sectioned the rat brain and then used anatomical coordinates to divide dorsal from ventral. This seems to be a good way to isolate pure, septal hippocampus but dorsal measures would again blur together the septal and mid-septal regions.

What if we wanted to separate the septal and temporal ends of the hippocampus? One method, described in Amaral & Witter, 1989 offers a solution:

We have adopted a strategy first described by Gaarskjaer that obviates this problem. In short…the fixed hippocampal formation is dissected from the brain and gently extended before histological processing. In this way the extended hippocampus can be positioned such that normal sections are obtained from much of the septotemporal extent of the structure.

A similar approach had been used (see here and here). One drawback is that you ruin much of the rest of the brain during the dissection process (insert but-who-cares-about-the-rest-of-the-brain joke here). Here’s a figure from thesis that illustrates the similar-shaped hippocampal slices obtained with this method:

Figure 5: DAPI counterstained sections, evenly spaced across the septotemporal axis. Sampling scheme illustrated at the top. Shaded regions indicate how different septotemporal regions could be binned. S=suprapyramidal blade of the dentate gyrus, I=infrapyramidal blade, DG=dentate gyrus.

Another strategy isn’t too different from the method of Banasr, above. To get at the septal hippocampus you’re just being a bit more selective and only examining portions of the dorsal hippocampus that extend quite far rostrally. For the caudal sections that contain both dorsal and ventral hippocampus the rhinal fissure seems like a good guide – anything falling on the ventral side I’m counting as ventral.

But if you’re lazy…

A fast, revolutionary new method for examining the hippocampus along its full septotemporal axis in a single section! It almost sounds too good to be true. In fact, it is. But it provides some interesting pictures for those of you who have stuck with me this far.

Recently, a lot of rats has been irradiated to eliminate adult neurogenesis. Before coming to any conclusions about the behavioral data it was needed to know whether neurogenesis was completely blocked AND whether it was blocked throughout the entire dentate gyrus. Due to laziness to cut hundreds of sections for each rat, the hippocampus was extracted but instead of sectioning perpendicular to its septotemporal axis, it was sectioned parallel to, or along, its septotemporal axis by flattening and freezing it on a microtome stage. With this approach the entire dentate gyrus could be cut in about 30 sections and sections that had the entire septotemporal length of the dentate gyrus became present. Then they were stained for NeuN and DCX to visualize neurons and immature neurons, respectively. I think every other section was stained; one example is shown below.

Figure 6: Hippocampal sections stained for NeuN and DCX. The dentate gyrus can be identified as the layer of tightly-packed orange cells on the left, that are bordered by green DCX+ cells. Sections were cut from the side of the infrapyramidal blade towards the suprapyramidal blade (direction of cutting = section 1→9). Images were taken with a 20x objective and subsequently stitched together.

Is it really necessary to divide septotemporally? I guess it depends. Many studies that have focussed more on dorsal vs. ventral have made significant findings. If the anatomical method is well-described and reproducible, what more could you ask for? It’s possible, however, that combining different septotemporal regions into the same analysis could obscure a result. For example, when the activation of new neurons was examined after water maze training, it was found a steadily-increasing amount of activation as going from septal to temporal (see Figure 7). Had the 2 septal quartiles been pooled together and the 2 temporal quartiles pooled together, the observed difference would have been much smaller than when comparing the septalmost quartile with the temporalmost quartile.

Figure 7: The density of ‘activated’ new neurons (i.e. PSA-NCAM+ and Fos+) increased from septal to temporal. Note the mid-septal and mid-temporal regions were similar. Also note that I used D and V nomenclature, for ‘dorsal’ and ‘ventral’, despite repeatedly emphasizing in this post that ’septal’ and ‘temporal’ is more accurate.


and now…

Pretty pictures from these sections!


Just a nice example of some DCX dendrites.

DCX labeling outside of the dentate gyrus. I think this was in the subiculum but who can say for sure with these weird sections.

Septotemporal sample #1

Septotemporal sample #2

Septotemporal sample #3

Septotemporal sample #4




Special thanks and credit to and to Sarah Ferrante for sectioning, staining and imaging the tissue.

Artificial nerve grafts made from spider silk

Every year, hundreds of thousands of people suffer from paralyzed limbs as a result of peripheral nerve injury. Recently, implantation of artificial nerve grafts has become the method of choice for repairing damaged peripheral nerves. Grafts can lead to some degree of functional recovery when a short segment of nerve is damaged. But they are of little use when it comes to regenerating nerves over distances greater than a few millimeters, and such injuries therefore often lead to permanent paralysis.


Now though, surgeons from Germany have made what could be a significant advance in nerve tissue engineering. They have developed artificial nerve grafts made from hollowed-out pig veins filled with spider silk fibres and, in a series of animal experiments, showed that the grafts can enhance the regeneration of peripheral nerves over distances of up to 6cm. Their findings have just been published in the open access journal PLoS One.

Peripheral nerves have a greater regenerative capacity than those in the central nervous system, but regenerating them properly is challenging. The individual nerve fibres must not only regrow into the damaged area, but also find their proper targets. Furthermore, the regenerated nerve will not function properly unless it is populated by Schwann cells, which produce myelin. This fatty tissue is essential for full recovery, as it wraps itself around the nerve fibres at regular intervals (a process called myelination), facilitating the conductance of nervous impulses along their length.

Conventionally, damaged peripheral nerves are treated either by suturing or by implantation of nerve grafts. The two ends of a severed nerve can be surgically re-attached to each other, as long as the nerve is not stretched in the process. This is not possible for gaps longer than about 5mm, in which case a short length of nerve from elsewhere in the patient’s body can be grafted into the damaged area. But this often causes causes pain in the donor area, and it can be difficult to find a nerve segment that has the same diameter as the damaged nerve. Nerves can be obtained from another person, but they can be rejected by the recipient’s immune system, so drugs that suppress the immune response are usually administered.

An alternative approach, which has emerged in the past ten years or so, is the use of artificial nerve grafts made from silicon or synthetic polymers such as polyethylene. These form scaffolds which bridge the gap in the damaged nerve and serve as conduits through which the nerve fibres can regrow. Artificial grafts can lead to some degree of functional recovery, but they can become toxic with time, or they can constrict the nerve.

These problems can potentially be overcome by using nerve grafts made from biodegradable materials. Five years ago, Peter Vogt and his colleagues in the Department of Plastic, Hand and Reconstructive Surgery at Hannover Medical School reported that Schwann cells readily ensheath spider silk fibres when grown on them, and that nerve grafts made of de-cellularized veins filled with spider silk can be maintained in culture for periods of up to a week. More recently, they showed that spider silk vein grafts can be used to regenerate 20mm gap in the sciatic nerve of rats, either alone or when supplemented with Schwann cells.

In the new study, Vogt’s group dissected 6cm lengths from the small veins in pigs’ legs, washed them and stripped away most of the endothelial cells from their inner walls. They then harvested dragline silk from the golden silk spider Nephila clavipes and pulled the silk through the de-cellularized veins, until it filled about one quarter of their diameter. Using adult sheep, the researchers removed a 6cm length of the tibial nerve in the leg. In one group of animals, the gap was bridged with the spider silk constructs; in another, the section of nerve that had been removed was replaced in reverse orientation.

Defects in the animals’ gait became apparent immediately after the surgery – the hind limb was partially paralyzed and flexed abnormally. But within three weeks there was a significant improvement, with both groups of animals being able to stand properly. By four months, the animals could stand upright on both hind limbs, the hind limbs moved in co-ordination with one another during walking, and there was no obvious difference in strength between the operated and unoperated limbs.

Ten months after surgery, the sheep were killed and their regenerated nerves examined under the microscope. In both groups of animals, the severed nerve fibres had regrown into the nerve grafts to bridge the 6cm gap; Schwann cells had migrated into the grafts and wrapped themselves around the entire length of the regenerated nerves; and the sodium channels required for generating nerve impulses were distributed irregularly along the fibres. This shows that myelination had occurred properly, with the formation of Nodes of Ranvier, the regular gaps in the myelin sheath at which the sodium channels normally cluster. No trace of residual spider silk was detected in the experimental animals, and there was no sign of inflammation at the repair site, indicating that the silk fibres were absorbed subtly without adverse effects.

These findings could have important applications in reconstructive nerve surgery. This is the first time that a large animal model has been used to study nerve regeneration, and the study is the first in which a defect longer than 2cm in length has been successfully repaired. The spider silk constructs enhanced nerve regeneration at least as effectively as the sheeps’ own nerves, and would be advantageous in the clinic, because transplanting large lengths of a patient’s own nerves is unfeasible.

More work will be needed before the technique can be applied to humans. Meanwhile, the regeneration reported here could be further enhanced in a number of ways. The spider silk constructs could, for example, be loaded with substances such as Nerve Growth Factor, or they could be grafted together with Schwann cells, to speed up nerve regrowth. But ultimately, engineering fully functional peripheral nerves will probably require a combination of advanced microsurgery, transplantation of both cells and tissues, advances in materials science and, possibly, gene transfer for the effective delivery of growth factors.



Radtke, C. et al. (2011). Spider Silk Constructs Enhance Axonal Regeneration and Remyelination in Long Nerve Defects in Sheep. PLoS ONE, 6 (2) DOI: 10.1371/journal.pone.0016990.

Blood supply of the spinal cord

August 12, 2010 1 comment

Arterial supply : Supplied by 3 small arteries + feeder arteries

Segmental spinal arteries

ASA and PSA arteries are reinforced by segmental arteries, which enter the vertebral canal through the inter vertebral foramina. These arteries are branches of arteries outside the vertebral column (deep cervical, intercostal and lumbar arteries). Segmental arteries give rise to anterior and posterior radicular arteries.

Feeder arteries

Enter the vertebral arteries and anastomose with the ASA & PSA. The most important feeder artery is the Great anterior medullar artery (GAM) of Adamkiewicz. It arises from the aorta at lower thoracic or upper lumbar vertebral levels. This artery is unilateral. It lies in the left side of most people. It represents the major source of blood to the lower 2/3 of the spinal cord.

Veins of the spinal cord

Drain mainly into the veins of the brain and the venous sinuses via 6 tortuous longitudinal channels. Finally, they drain into the internal vertebral venous plexus.