Recently in Anatomy Category

Neuroscience podcast 4: autonomic nervous system

Phil & I recorded another neuroscience podcast. Number 4 covers the autonomic nervous system and we talk about the anatomy, the wiring of the neurones, and the neurotransmitters involved.

I might have to listen to that neurotransmitters section a few more times.

MP3: Neuroscience podcast 4 - autonomic nervous system.

iTunes: Neuroscience podcast 4 - autonomic nervous system (enhanced format).

Anatomy & embryology podcast 24

OK, I finally finished the latest podcast in which Rhiannon and I talk about what we think are the important aspects of the anatomy of the lower limb. This is the first part of two, and is 45 minutes long. We talk about the bones of the foot and ankle, the knee, the sciatic nerve, veins, and compartments of the leg. We've got another 5 topics to talk about in episode 25.

Get it from iTunes or from the Medicine page. The iTunes enhanced version has a bunch of images in it.

Learning

Here's a great blog entry about learning for educators and lurners alike:

Donald Clark Plan B: 10 techniques to massively increase retention

There's a lot of really good stuff in there, hopefully stuff we're already trying to do in Swansea. Note number 9: mobile technology. The author talks about drip feeding assessment via those mobile devices that we all have in our pockets. Hopefully some of you have noticed that I've been coincidentally trying to do exactly this using the medium of the moment: Twitter.

Twitter pretty much started with mobile devices (you could use the internet and SMS text messages to post tweets really easily). Can yours follow twitter? If you have a mobile browser on your phone then, yes. Otherwise see this twitter mobile phone FAQ (although that's a little bit retro).

Follow me @samuelwebster and keep your eyes on the twitterwall (which is also linked to from the elearning section of the Swansea Blackboard).

I'll be drip feeding questions that you should be able to answer. You know, the sort of stuff that comes up in exams.

Anatomy: the lumbosacral plexus and the lower limb

On Monday we started looking at the structure of the hip, the muscles there and the nerves involved in motor and sensory innervation. In my station we talked about the lumbosacral plexus. Lots of nerves!

A nerve plexus is merely a lot of separate nerves (it's probably best to think of long, individual nerve cells) coming together into a group and then separating off towards different destinations. Some nerves from different spinal roots run off to those destinations together. It's like cabling in a building. There are no connections between nerves in a plexus.

We said that the lumbar plexus + sacral plexus = lumbosacral plexus. You may read that the coccygeal plexus is involved too, and yes, the coccygeal nerve (the last pair of spinal nerves!) links with sacral nerves.

[Need to review the spinal cord? Check here (missing coccygeal nerve) and here].

The roots of the lumbar plexus are formed by spinal nerves L1-L4. Remember that the posterior rami pass to the back muscles, so the lumbar plexus is formed from anterior rami. The lumbar plexus lies deep to and within the psoas muscles, and the nerves will pass on to the lower limb and the lower part of the abdomen.

The nerves L4 and L5 come together to form the lumbosacral trunk. This links to the sacral plexus, joining the two plexuses and making it easier for us to take them together as the lumbosacral plexus.

The sacral plexus forms from the spinal nerves S1-S5 an lies upon the piriformis muscle. The major nerve from the sacral plexus is the pudendal nerve (S2-S4, main sensory nerve for external genitalia and motor to muscles of continence including the external urethral and anal sphincters and levator ani - these also receive other motor innervation though). The sacral plexus also forms many tiny, short nerves that directly innervate the muscles of the hip that the plexus lies on or near. As such these nerves may be difficult to identify but they exist, for example, the nerve to obturator internus (and gamellus superior) and the nerve to quadratus femoris (and gamellus inferior). Confusing? Sorry.

The nerves of the lumbosacral trunk are combined with the sacral plexus to form the sciatic nerve (L4-S3). This giant nerve running out through the greater sciatic foramen and into the gluteal region descends the length of the posterior lower limb, innervating the posterior compartment of the thigh and all the muscles distal to the knee. It splits into tibial and common fibular (or peroneal) nerves before it reaches the popliteal region behind the knee. This monster nerve, along with the superior gluteal nerve (L4-S1) and inferior gluteal nerve (L5-S2) is the reason why we consider the lumbar and sacral plexuses together. The number of spinal nerves contributing to the sciatic nerve (and the lumbar location of those roots) suggest that it is more likely to suffer impingement than any other nerves. I'm sure that most of you will be aware of sciatica. As the sciatic nerve passes into the gluteal region and is very large you must be aware of its location if you're considering sticking needles into someone's bum.

We didn't talk about the parasympathetic nerves arising within the pelvis, so we'll pick those up in other, pelvic-related weeks. The pudendal nerve also takes a very interesting route to reach its destination outside the pelvis, which we'll also discuss in other sessions.

So, the lumbosacral plexus is formed from the anterior rami of spinal nerves L1-S5. The most important nerves to watch out for are probably those mentioned above, the lumbosacral trunk is the link, and the sciatic nerve (and gluteal nerves) is the main reason for the link. Make sure you can link these plexuses and nerves into your understanding of the abdomen, pelvis and lower limb.

46 days post-fracture

Messy, huh?

Anatomy: the orbit & superior orbital fissure

On Monday we went through the bones of the orbit, what the superior orbital fissure (and inferior orbital fissure and optic canal) were, and what went through it (and them).

To review the bones of the orbit look at these images. Hover over the bones to be reminded of their names. We also noted that the palatine bones just about reach up to the orbit, but you can't see this on the images.

The superior orbital fissure is the slit in the posterior wall of the orbit. It passes through to the middle cranial fossa within the cranial cavity. The inferior orbital fissure is the slit in the floor of the orbit passing to the infratemporal fossa.

The superior orbital fissure is the main route for stuff to get from the brain to the orbit then. Everything in the orbit (muscles, glands, mucosa, skin, etc) will need to receive nerve fibres from cranial nerves passing through the superior orbital fissure. The optic nerve and the retina are the exceptions to this.

With regards to blood supply though, the ophthalmic artery passes through the optic canal with the optic nerve. It is a branch from the internal carotid artery and sends arterial branches out and around the orbit. The ophthalmic veins (there are superior and inferior opthalmic veins) do pass through the orbital fissures. Maybe a little counterintuitively the superior ophthalmic vein drains blood from the orbit back into the cranial cavity by passing through the superior orbital fissure. (The venous blood passes to the cavernous sinus on the other side and eventually leaves the cranial cavity through the internal jugular vein). This gives a route by which infection or drugs can pass intracranially from superficial structures, and will no doubt be mentioned a number of times in your studies. The inferior opthalmic vein connects to the pterygoid venous plexus of the face by sending branches through the inferior orbital fissure.

So what nerves pass through the superior orbital fissure? In essence, cranial nerves III, IV, V and VI. Easy, eh? Well, there's a little more detail to it that you need to know.

CN III
Also known as the oculomotor nerve, this sends fibres to almost all of the muscles in the orbit (both extra-ocular and intra-ocular, i.e. the muscles of the lense and the constrictor muscle of the iris). It divides into superior and inferior branches before it emerges from the superior orbital fissure.

CN IV
Also known as the trochlear nerve (trochlea comes from the Greek word for "pulley", and this is the nerve to a muscle that has a pulley) this is another motor nerve with the singular task of innervating the superior oblique muscle.

CN V
Here things get a little more complicated. Cranial nerve V is the trigeminal nerve, which divides into 3 branches within the cranial cavity: V₁ (ophthalmic nerve), V₂ (maxillary nerve) and V₃ (mandibular nerve). These are the sensory nerves of the face (although you'll remember that the mandibular nerve also sends some motor fibres to the muscles of mastication) and we're interested in the ophthalmic nerve when we look at the orbit. Just before the ophthalmic nerve enters the superior orbital fissure it divides into 3 smaller nerves:
- frontal branch
- lacrimal branch
- nasociliary branch

So that's a little inconvenient and tricky to remember. Note that some of these branches are rather interesting in function and in the other nerve fibres that they pick up that are not from the trigeminal nerve, but I won't talk about that here.

CN VI
Last of all we have the abducent nerve (or abducens, whichever you prefer). The name of this nerve comes from its ability to abduct the eye, as it sends motor fibres to the lateral rectus muscle.

That's about it for structures passing through the superior orbital fissure. Make sure that you can link all this up with what you learnt about the other parts of the orbit and the eye, and what you will learn about the functions of those structures.

Podcast episode 23

A new podcast is up on iTunes and the medicine page of my blog. Rhi and I finish talking about our list of things med students really should know about the anatomy of the pelvis. We include the vas deferens and the urethra, the os, the organs of the female pelvis and their ligaments, and sensory innervation from external genitalia.

Links:

- Subscribe in iTunes

- Download the MP3: Episode 23: 10 things you should know about the anatomy of the pelvis (part 2).

Spiral fracture of the distal shaft of the fifth metatarsal bone of my left foot

After a very brief assessment in fracture clinic this morning (and all that was needed) I had a load bearing cast wrapped around my leg, ankle and foot to replace the weekend's temporary backslap plaster cast.

The verdict: 6 weeks in a cast, no load bearing for 2 weeks, expect 8-12 weeks before walking with little pain. That rather dulls the 2010 racing season for me.

It is what it is and there's no point crying about it. I'll sit down and look at the year I had planned. I'll probably add a half-marathon to the end of the year (Cardiff maybe) to extend it and try to get under 80 minutes, and remember my long term goals. Races up to July will have new goals of "finish the race" and "learn". Training to that point and from July to October is unplannable at this stage. I'll get into the gym & work on the rest of my body, although walking on crutches is already helping that. I think I may be able to come up with some lightweight elastic band exercises but I can't exercise my left calf muscles at all, and I have to be careful of damaging the cast.

It is what it is.

X-ray

Well, there it is.

Broken

Oh dear. I broke my foot this morning. I foolishly left too much crap in the hall downstairs, and when I ran downstairs to answer the door I was looking at the stuff instead of where I was placing my feet. I missed the bottom step, landed heavily and inverted my left foot. I couldn't walk it off and a rather nice haematoma had appeared by the time I took my sock off a little later, so I spent the afternoon in A&E/X-ray/fracture clinic. I have a spiral fracture of the shaft of my 5th metatarsal.

I've got plaster on for the weekend & will get reassessed on Monday. I'll probably get a walking cast put on then.

Bugger. I guess I'll level all my World of Warcraft characters to level 80 then.

Week 121: Skull, the temporal region

This week we made it all the way up to the head. To look at the anatomy of the head, we need to start by looking at the bones. Different stations looked at different parts of the skull and teeth, and I spoke about the temporal region.

The temporal region (or as laymen may call it, your "temples") lies superior to the zygomatic arch and within the edges of the temporalis muscle. You may see curves on the skull around the edge of the temporal fossa that correspond to the attachment of the flat temporalis muscle. There is a depression here in which a few superficial structures lie, and this is the temporal fossa.

The bones here are the parietal bone, the temporal bone (it has squamous - flattened - and petrous - lumpy/rocky - parts) and the sphenoid bone. Use the skull bone images here to see these. Note also the frontal bone and the zygomatic bone. Spend some time in the lab with a coloured skull and a detailed skull (the numbered ones are best) to be clear on the shapes of these bones.

We talked about the nature of sutures linking the bones of the skull, which are fixed in the adult and contribute to the aim of the skull to protect the brain. There are some sutures that you should be able to name and you can also see these in the skull images (here). Note also the bregma (where the coronal suture meets the sagittal suture) and the lambda (where the sagittal suture meets the lambdoid suture).

These points correspond to where the anterior and posterior fontanelles were at birth. The bones of the skull are able to slide over one another to some extent to aid passage through the birth canal, and this is known as moulding. The bones are not fixed by sutures at this time, but are linked by softer membrane-like connective tissues. After birth the anterior fontanelle is known as the soft spot and can be an important diagnostic indicator. The fontanelles also allow the bones of the skull to grow.

Back to the temporal region: the sutures linking the parietal, frontal, sphenoid, and temporal (squamous) bones join here to form an H-shaped group of sutures known as the pterion. This potential weakness in the skull is made weaker by a thinning of the bones here (you can often see this on real skulls in the lab, but not on plastic skulls). To make matters even worse, the middle meningeal artery runs inside the skull, deep to the pterion. A fracture here is likely to tear the middle meningeal artery, causing blood to pool between the bone and the dura mater, pressing on the brain. This is an extradural haemorrhage and can be fatal (and in fact, dural venous sinuses may also be involved).

The temporal fossa has a few superficial structures of interest passing through it. The pulse you feel in your "temples" is the pulse of the superficial temporal artery, a branch from the end of the external carotid artery. The superficial temporal vein, draining a similar area of the scalp, is nearby. The superficial nerve here is the auriculotemporal nerve. This nerve carries sensory information from this area, and is a branch of the mandibular nerve, which itself is a branch of the trigeminal nerve, also known as cranial nerve V (CN V). I have a feeling we will be meeting this nerve again in the future when we start adding more detail to our head and neck anatomy and look at the infratemporal fossa. For example, this nerve also carries parasympathetic nerve fibres from CN IX to the parotid gland (that tell it to secrete saliva).

Fun, eh? The anatomy of the head and neck can be very detailed, delicate and intricate. It's a fascinating region anatomically, and by building up your knowledge bit by bit over the next 18 months or so you should develop a solid understanding of what's going on in there.

Elearning: skull bones

We're looking at some head and neck anatomy on Monday, and some stations will be looking at the bones of the skull. I have an elearning thingy here to help you with bones, sutures and foramina of the head:

www.dontbeasalmon.net/elearning/skull

Week 114: anatomy of the bladder

This week we pretty much finished off looking at the renal system by looking at the bladder (we only have the male urethra yet to study).

We used visiblebody.com to get an idea of where the bladder is (and that it is anterior within the pelvis, right up against the pubis bones) and the shape of the bladder. Textbooks sometimes describe the bladder as an upside-down pyramid, which kind of fits. Visiblebody.com shows the shape quite well, which is something that's difficult to get from an image or a prosection. Some of the plastic models in the lab are quite good, and most of the torsos have them.

Remembering that the bladder is the most anterior viscera in the pelvis is helpful. When looking at prosections, particularly of female pelvises, it can get a little confusing. Remembering that the bladder is anterior makes it easy to locate and identify (male: bladder-rectum, female: bladder-vagina-rectum).

The bladder receives urine from the two ureters that enter its posterior wall (also known as the base). The ureters don't have real sphincters to prevent backflow from the bladder, but they do pass through the detrusor muscle of the bladder at an angle that gives a physiological sphincter.

The bladder is lined with a specialised epithelium called transistional epithelium or urothelium that allows for the stretch of the bladder as it fills and is not too fussed about constantly being in contact with urine. This urothelium lines a layer of detrusor muscle that contracts to squeeze and empty the bladder (so, along with the peristaltic contractions of the ureters this means that you should be able to urinate upside-down, or in space - this isn't a gravity-fed system). When the detrusor muscle contracts it also squeezes and closes off the ureters.

The trigone of the bladder describes a triangular area of the bladder seen as a smooth patch internally, between the ureters and the urethra. Here the urothelium is tightly adherent to the detrusor muscle. Elsewhere the inside of the bladder appears folded, much like the rugae that we saw in the stomach.

The urothelium and the rugae allow the bladder to stretch to hold maybe 500ml of urine or more. By this point your parasympathetic nervous system may well have triggered the detrusor muscle to squeeze and the internal sphincter muscle to open to try to empty the bladder. Luckily you still have control over the external sphincter (and your levator ani muscle group) so hopefully you can hold on until you find somewhere appropriate to relieve yourself. Before your bladder fills to maximum capacity your micturition control centre in your frontal lobe will hopefully give you a level of control over where and when you choose to empty your bladder (and you can read more about nervous control in this eMedicine article: Neurogenic bladder.

The neck of the bladder is its most fixed part, and we saw in the prosections how mobile the bladder is. It is supported and surrounded by the muscles of the pelvic floor, the obturator internus muscles, the visera of the pelvis, the peritoneum, and the overlying small bowel. In the female pelvis the neck of the bladder is attached to the pubis bones by the pubovesical ligament, and in the male pelvis by the puboprostatic ligament (and as the name implies, the prostate gland directly inferior to the bladder is also fixed in place by this).

You may wish to review the blood supply of the pelvis as a whole (particularly the branches of the anterior trunk of the internal iliac artery) to better understand the arteries that supply the bladder in both male and female pelvises but I won't go into that here. Maybe take a look at this diagram on Instant Anatomy.

Simbryo - embryology animation

I mentioned Simbryo in one of my recent lectures. If you want to find out more go to the official website at simbryo.stanford.edu.

If you have, or are planning to buy, a copy of the Langman's Medical Embryology textbook I believe that you get a copy of Simbryo with it.

Week 110 - anatomy of the elbow (well, movements & muscles)

On Monday I spent most of the morning flexing my guns and poking my cubital fossa. Our aims were to look at the movements of the elbow joint, the muscles involved, and the important structures passing through this region, with particular regard to the cubital fossa. That video makes me feel a little bit ill. And I'm an anatomist.

We talked about the major movements of flexion and extension of the elbow joint, which you all were aware of, and mentioned pronation and supination of the forearm. I didn't talk about the bones or the articulating surfaces in much detail as my clinical colleagues had pinched all the skeletons, and I'm sure they did a far better job of talking about the osteology than I would have done. Focusing on flexion and extension we identified the three main muscles involved: biceps brachii, brachialis and triceps brachii.

The biceps brachii muscle has 2 heads. The short head arises from the coracoid process of the scapula and the long head arises from the supraglenoid tubercle (lumpy bit above the glenoid cavity of the shoulder joint). The long head must pass through the shoulder joint, change direction and then run through the bicipital groove (or intertubercular sulcus) in the humerus. Have a brief look at the humerus and scapula in the anatomy lab to be clear on where these bony bits are.

The fibres of the biceps brachii muscle come together distally to insert into the radial tuberosity (another lumpy bit, on the radius). This means that not only is the biceps muscle a flexor of the elbow joint, but it can also powerfully supinate the forearm when the elbow joint is already flexed. Try this out next time you're turning a screw or a bolt - feel biceps contract as you supinate the forearm and tighten the bolt. This also explains the different biceps flexing poses that bodybuilders may use to show off biceps (i.e. it's bigger when the forearm is supine - get posing in front of the mirror to check this).

The other thing we talked about with regards to biceps was that you can palpate not only the tendon inserting into the radius but also a weird, flat tendon medially. This is the bicipital aponeurosis (see me poking mine in the photo to the right), and connects the biceps to the deep fascia of the forearm. Clever, eh?

Don't forget that as biceps brachii also crosses the shoulder joint it is also able to flex the glenohumeral (shoulder) joint, although it's not great at this.

Deep to biceps we found the brachialis muscle arising from the humerus and passing across the elbow joint to insert into the tuberosity of the ulna. This muscle is flattened, and is the most powerful flexor of the elbow joint. The musculocutaneous nerve runs between brachialis and biceps brachii, innervating both muscles.

To extend the elbow joint we use one muscle: triceps brachii. By it's name this must be a muscle of the brachium (upper arm) with 3 heads. The long head comes from the infraglenoid tubercle on the scapula (on the other side to the long head of biceps brachii), the medial head comes from the posterior surface of the humerus and the lateral head also comes from the posterior surface of the humerus, but a little more laterally. There's a groove between the medial and lateral heads, and in this groove we find the radial nerve. This is the nerve of the posterior compartment of the arm and it is innervating the triceps muscle.

All of the muscle fibres of triceps come together to insert in the bony, sticky outy bit of the elbow (very sticky outy in my case, as some of you noticed): the olecranon. The olecranon is part of the ulna, so contraction of the triceps muscle pulls the olecranon and extends the elbow.

The next bit to look at was the cubital fossa. We had to find the brachioradialis and pronator teres muscles to find the lateral and medial borders, and add an imaginary line between the epicondyles of the humerus to add the proximal boundary. Brachioradialis is pretty easy to find on the lateral edge of the anterior supinated forearm, running from the humerus to the radius as the name implies. It is also innervated by the radial nerve, and when we lifted the brachioradialis muscle at the border of the cubital fossa we found the radial nerve twisting around the humerus to get to the anterior side.

Pronator teres was a little trickier to find, but it was clearly running diagonally across the proximal part of the forearm. Structures within the cubital fossa looked as though they would be protected by the biciptial aponeurosis.

What did we find in there? We saw the median nerve running (medially) alongside the brachial artery within the fossa itself (i.e. superficially to brachialis but deep to the fascia and skin) and noted that the median cubital vein, from which blood is commonly taken, was a superficial structure here. You remembered, of course, that this was where you listened to the brachial pulse when taking someones's blood pressure.

After chatting about funny bones, we realised that we could now find all the major neurovascular structures of the upper limb at the elbow. The ulnar nerve is where we bang it (that made more sense during the discussion), the radial nerve is deep to brachioradialis, the median nerve is on the medial side of the cubital fossa with the brachial artery, and the musculocutaneous nerve peters out from between the biceps brachii and brachialis muscles as a cutaneous nerve, having done it's "musculo" job.

Not bad for 25 minutes work.