IVDD

• when completing CT myelography, contrast must be injected into the vertebral canal. Which compartment will the needle have to enter in order to yield fluid and what is the origin of this fluid?

  Subarachnoid cavity. The fluid is CSF produced by the choroid plexus in the ventricles of the brain.
• suggest potential advantages and disadvantages for atlantooccipital vs caudal lumbar contrast injection

  you choose the site based on which is most appropriate for your lesion. The atlantooccipital placement is at the top of the spinal cord so has the potential to cause lower damage but is easier to access. (can be difficult when an ET tube has been placed). Caudal lumbar is harder to access (especially in fat animals) but is far safer
• describe skeletal muscle histologically

  striated (bands like fish meat) with external nuclei and is multinucleate
• describe smooth muscle histologically

  non-striated and spindle shaped with central nuclei
• describe cardiac muscle histologically

  contains sarcomeres, is striated with intercalated disks. Has 1 or 2 central nuclei and branched fibres
• define an excitable cell

  a cell capable of generating and transmitting an action potential across its membrane
• what are the normal intracellular and extracellular concentrations of sodium and potassium in mammalian cells?

  Na: ICF 14, ECF 142 . K: ICF 140 ECF 4.2
• why is normal resting membrane potential always negative?

  Initiated by leaky K+ channels which leak out. The Na/K pump maintains the negative potential mostly though through the constant pumping of 2 Na in and 3 K out
• briefly explain the shape of an action potential

  A stimulus must reach threshold to initiate an action potential. The cell depolarises as Na+ channels open allowing sodium to rush into the cell. After depolarising, Na+ channels are inactivated and K+ channels open. Potassium ions move out of the cell, initiating repolarisation. A delay in K+ channel closing causes hyperpolarisation, preventing backflow of action potential.
• Lidocaine is a sodium channel blocker. Why is this useful as a local anaesthetic agent?

  Because by blocking the sodium channels, it prevents the initiation of action potentials in the area it is given. Pain signals then don't reach the brain.
• when serum K+ increases, this is hyperkalaemia. Resting membrane potential is less negative and the cell is more excitable and reduced stimulus is required to reach threshold. (profound disturbance may progress to a loss of excitability)
• when serum K+ decreases, this is hypokalaemia. Resting membrane potential is more negative so the cell is less excitable and is therefore hyperpolarised - an increased stimulus is required to reach threshold
• Why do myasthenia gravis not carry through an action potential at the neuromuscular junction?

  No matter how strongly the excitable cell is stimulated, MG patients have little/no capacity to carry the AP as they have insufficient ACh receptors on the other side.
• what are the primary presenting signs for animals with MG

  weakness after exercise, stiffness or lagging in walking
• explain how the Tensilon test (ACh-esterase inhibitor) could confirm a diagnosis of MG?

  muscle strength would increase after administration and remain strong for a short time. This is because ACh isn't broken down and has longer to interact with the available receptors
• How would you classify the type of joint formed by an intervertebral disc?

  Fibrocartilaginous symphysis
• A metaplasia is one cell type being replaced by another.
• Why does the proportion of glycosaminoglycans such as hyaluronic acid and chondroitin within the nucleus pulposus influence its composition and nature?

  GAGs are hydrophilic and bind water to keep the NP gel-like, making it viscous and elastic. GAGs also transport nutrients to the NP to keep it healthy
• How might chondroid metaplasia be associated with the altered composition of the nucleus pulposus in chondrodystrophic dogs?

  There is abnormal cartilage formation and metabolism in the NP, contributing to changes in its composition over time. Chondroid metaplasia can involve transformation from normal NP tissue into cartilage-like tissue
• How does degeneration of the nucleus pulposus influence the biomechanics of the vertebral column of chondrodystrophic dogs?

  There is less shock absorption, less range of motion through the spinal column as there is less compression space. This leads to painful movement.

  The dehydrated NP can eventually swell out and compress the spinal cord
• the major epaxial muscle groups are the longissimus, iliocostalis, transversospinalis. bilateral epaxial flexion causes dorsiflexion. unilateral epaxial flexion causes lateroflexion
• in a hemilaminectomy or corpectomy, which vascular structure within the spinal cord is most likely associated with risk of intraoperative haemorrhage?

  ventral venous sinus as it has no valves so damage will allow for significant haemorrhage. It also covers the entire dorsal area.