Rock your clinical exam!

What sensation is probably the most important to test and why?

Rewind double feature! Part 2

(for part 1, click here)

In conjunction with the latest PODcast talking about efferent copy, we thought it appropriate to talk about the cerebellum here. In this capsule we talk about the efferent pathways

Enjoy! and have a nice weekend (not that we are telling you what to do…)

Ivo and Shawn

Just when you thought it was safe to watch a Neuromechanics Weekly episode, Dr Ivo throws a curveball. Check out the interesting clinical asides about myelopathy (pressure on the spinal cord causing ataxic gait) and the importance of which modality to check 1st, when doing an exam.

Keep these things in mind the next time you are evaluating someone’s gait.

In this Neuromechanics weekly, Dr Waerlop Introduces the cerebellum and talks about its importance clinically, since it contains more than 1/2 of the neurons in the brain! It’s anatomy and inputs from the periphery are discussed. The take home message is the cerebellum is the key to understanding and directing movement, since it receives feedback from most ascending and descending pathways.

And now, some light reading for a Saturday….

Review of knee proprioception and the relation to extremity function after an anterior cruciate ligament rupture.

J Orthop Sports Phys Ther. 2001 Oct;31(10):567-7

http://www.ncbi.nlm.nih.gov/pubmed/11665744

What the Gait Guys say about this article:

Aren’t you glad you have mechanoreceptors?

As we have discussed in other posts, proprioception is subserved by cutaneous receptors in the skin (pacinian corpuscles, Ruffini endings, etc.), joint mechanoreceptors (types I,II,III and IV) and muscle spindles (nuclear bag and nuclear chain fibers) . It is both conscious and unconscious and travels in two  main pathways in the nervous system.

Conscious proprioception (awareness of where a joint or body part is in space or action) arises from the peripheral mechanoreceptors in the skin and joints and travels in the dorsal column system (an ascending spinal cord information highway) to ultimately end in the thalamus of the brain, where the information is relayed to the cerebral cortex.

Unconscious proprioception arises from joint mechanoreceptors and muscle spindles and travels in the spino-cerebellar pathways to end in the midline vermis and flocculonodular lobes of the cerebellum.

Conscious proprioceptive information is relayed to other areas of the cortex and the cerebellum. Unconscious proprioceptive information is relayed from the cerebellum to the red nucleus to the thalamus and back to the cortex, to get integrated with the conscious proprioceptive information. This information is then sent down the spinal cord to effect a response in the periphery. As you can see, there is a constant feed back loop between the proprioceptors, the cerebellum and the cerebral cortex. This is what allow us to be balanced and coordinated in our movements and actions.

The ACL is blessed with type I, II and IV mechanoreceptors (Knee Surgery, Sports Traumatology, Arthroscopy Volume 9, Number 6)   We remember that type I mechanoreceptors exist in the periphery of a joint capsule (or in this case, the periphery of the ACL) and are largely tonic in function (ie: they fire all the time) and type II are located deeper in the joint (or deeper in the ACL) and are largely phasic (ie they fire with movement). Type IV mechanoreceptors are largely pain receptors and anyone who has injured his knee can tell you all about them.

The article does a great job reviewing the importance of proprioception and how it relates to knee function and concludes A higher physiological sensitivity to detecting a passive joint motion closer to full extension has been found both experimentally and clinically, which may protect the joint due to the close proximity to the limit of joint motion. Proprioception has been found to have a relation to subjective knee function, and patients with symptomatic ACL deficiency seem to have larger deficits than asymptomatic individuals.”  Bottom line, never quit on the rehab and training of an ACL deficient knee until the absolute best outcome has unequivocally been achieved with certainty that no further improvement can be achieved…… absolute certainty.  Too many stop shy of certainty, and your brain will know it.  And it will show it in small gait, running and athletic skills.

Yup, this is some heavy stuff, but hey…you’re reading it, right?  If we didn’t explain it in detail you might not believe that WE are The Gait Guys ……. more than just foot and shoe guys. After all, there is a brain attached to the other end calling the shots.

Sorting it out so you don’t have to…We remain…The Gait Guys

Ah yes, the Ia and type II afferents.

One of our favorites! Acting as a sentinel from the muscle spindle, concentrated in the antigravity and extensor musculature, Ia and type II afferents live in the belly of the muscle and send information regarding length and rate of change of length to the CNS via the spino cerebellar and inferior olivary pathways. In more simpler terms, think of muscle spindles as small computer chips embedded in the muscle and using la and type II afferents the team act as volume controls helping to set the tone of the muscle and it responsiveness to stretch. If they are active, they make a muscle more sensitive to stretch.

So what does that mean? Muscle spindles turn up the volume or sensitivity of the muscles response to stretch. Remember when we stretch a muscle, it’s response is to contract. Think about when a doctor tests your reflexes. What makes them more or less reactive? You guessed it, the muscle spindle; which is a reflection of what is going on in the higher centers of the brain. The muscle spindles level of excitation is based on the sum total of all information acting on the gamma motor neuron (ie the neuron going to the muscle spindle) in the spinal cord. That includes all the afferent (ie. sensory) information coming in (things like pain can make it more or less active) as well as information descending from higher centers (like the brain, brainstem and cerebellum) which will again influence it at the spinal cord level.

So we found this cool study that looks at spindles and supports their actions:

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http://www.ncbi.nlm.nih.gov/pubmed/19451207

J Physiol. 2009 Jul 1;587(Pt 13):3375-82. Epub 2009 May 18.

Mechanical and neural stretch responses of the human soleus muscle at different walking speeds.

Cronin NJ, Ishikawa M, Grey MJ, af Klint R, Komi PV, Avela J, Sinkjaer T, Voigt M.

At increased speeds of walking, the muscles themselves (particularly the soleus in this study) become stiffer due to changes in spindle responsiveness. The decline in amplitude and velocity of stretch of the soleus muscle fasicles with increasing walking speeds was NOT accompanied by a change in muscle spindle amplitude, as was hypothesized.

Clinically, this means that the spindles were STILL RESPONSIVE to stretch, even though the characteristics of the muscle changed with greater speeds of action. This may be one of the reasons you may injure yourself when moving or running quickly; the muscle becomes stiffer and the spindle action remains constant (the volume is UP).

Thankfully, we have another system that can intervene (sometimes) when the system is overloaded, and take the stress of the muscle. This is due to the golgi tendon organ; but that is a post for another day…

Geeking out and exploring the subtleties of the neurology as it relates to the system, we remain…The Gait Guys

Welcome to Neuromechanics Weeekly. This week Dr Waerlop discusses the afferent sensory pathways and brings us from the receptor to the higher centers. Hold on tight!