Neurology Week 1 Saq Study Guide Questions

NEUROLOGY WEEK 1 SAQ STUDY GUIDE QUESTIONS 1. Ben is a 33-year-old male with a spinal cord injury. (7.5 marks) a. What is the main difference between the grey and white matter of the spinal cord? (1 mark) b. What is the name of the condition where there are sympathetic and parasympathetic system disturbances? (0.5 marks) c. Explain what happens in the condition in part (b). (5 marks) d. Upon further examinations and investigations, it is discovered that Ben’s injury is at C6. How would this affect his respiratory system? (2 marks) Answer: a. The grey matter part of the spinal cord contains unmyelinated neurons. Meaning the lack myelin sheath and have a slower conduction. The white matter of the spinal cord contains myelinated neurons, meaning they have a myelin sheath and have a faster conduction velocity compared to the neurons within the grey matter of the spinal cord. b. Autonomic Dysreflexia c. Autonomic Dysreflexia (AD) is a condition where there is a spinal injury at or above T6. In this condition signals from the brain cannot get to below the injury and signals from below the injury cannot get to the brain. When the gut will try to send signal to the brain, this won’t be possible as it is below T6. This will lead to the stimulation of the sympathetic nervous system below the level of injury. This will cause vasoconstriction of blood vessels. This will increase blood pressure and have major effects on the overall blood pressure of the body, as the blood vessels of the gut (splanchnic blood vessels), hold about 1/3 of our blood. As a result, AD patients will have hypertension. The increased blood pressure will be detected by carotid baroreceptors leading to a decreased heart rate in attempt to try to counteract the hypertension. This means that below the level of injury we have an uncontrolled sympathetic system, as any parasympathetic signals from the brain cannot get below the site of injury. In contrast, above the site of injury we will have an uncontrolled parasympathetic system activity, where there will be vasodilation causing flushing and increasing blood blow causing erythema and warmness as the blood that comes from the core to the periphery is warm. d. Since Ben’s injury is at C6, this means he has autonomic dysreflexia as the injury is above T6. At C6 and above he is going to have an uncontrolled and unopposed parasympathetic system, this means that since the sympathetic system will not be acting and the parasympathetic is the only one that is able to act, there is going to relaxation of blood vessels within the bronchus, which decreases the space for O2 and there is going to be decreased bronchodilation, thus also reducing oxygen intake. This means that there is going to be a reduced respiratory rate. 2. Describe the course of the branch of the fascial nerve that takes pain and temperature sensations from the soft palate. (2 marks) Answer: 1. Pain and temperature sensations from the soft palate are carried by the general visceral afferents. 2. These fibres will then go onto the synapse at the geniculate nucleus and then enter through the internal acoustic foramen. 3. These then go the CN V nucleus and the NTS nucleus. 3. List three functions of the superior olivary nucleus. (1.5 marks) Answer: 1. Timing of sound detection. 2. Location of sound detection. 3. Determination of sound intensity. 4. Describe the response to loud noises. (3 marks) • • • • • • Lound sounds have high amplitude. The high amplitude activates the olivocochlear bundle, which are cholinergic neurons meaning they will release Ach. These will bind on muscarinic receptors causing hyperpolarisation via stimulating the exist of K+ ions. These will also trigger a cascade inhibiting pristine molecules to be inhibited and thus they will not contract and change shape. This will inhibit the basilar membrane to bow down and inhibit hair cells from focusing on loud sounds. These will act as a protective mechanism against damage from loud sounds. 5. Describe the accommodation reflex with respect to: a. Light flashing into eye. (4 marks) b. Not flashing light into the eye. (4 marks) c. Explain what myopia is and how it can be corrected (2 marks) d. Explain what hyperopia is and how it can be corrected (2 marks) Answer: a. When light is flashed this will activate the SNS and the following happens: 1. Preganglionic SNS fibres synapse at the superior cervical ganglion with the postganglionic SNS fibres which then wrap around the carotid artery forming the carotid plexus. These will give rise to the long ciliary nerve. 2. The log ciliary nerve will release catecholamines that will: a) Contraction of the radial muscles which will contract outward and increase the size of the pupil hole to allow more light to come in. b) Relaxation of the ciliary muscle and thus tighten the zonules and thus pull on the lens so that they become flat. This causes the refracted rays to go the fovea to help with far vision. b. When in dimmer environments: 1. The pre-ganglionic PSNS fibres from the Edinger west fall nucleus, of which after passing the optic chiasma will synapse with the post-ganglionic PSNS fibres, which are known as the short ciliary nerve. This will release Ach on muscarinic receptors causing the following effect: a) On the ciliary muscle it will cause increase Ca2+ release causing them to contract which makes the zonules lose so that the lens budges, decrease focal length and thus help with near vision. b) In will also increase Ca2+ release in the sphincter pupil muscle causing them to contract and squeeze so that the pupil becomes small and diverge light away from coming into the retina and fovea. c. Myopia is near slightness where a person will have difficulty seeing far away. This is because light rays when enter are focused on a certain point that cause the image to form in front of the retina. This can be corrected via the use of concave lens, because it causes the light rays to spread out and form the image on the retina. d. Hyperopia refers to long-slightness, where a person will have trouble with close up vision. This is because the rays enter and form an image behind the retina. To correct this, convex lens should be given so that they rays enter closer together and the image thus forms at the retina. 6. Explain the stretch reflex. Answer: • • • • • • When a hammer taps the tendon there will be stretching of the nuclear bag and nuclear chain fibres. The stretch will be picked by the type I fibres found on the nuclear and chain fibres, and the type II fibres, which are located only the nuclear chain fibres. When there is stretching this stimulates the mechanically gated Na+ ion channels located on the terminals of the myelinated I am fibres. They will cause an influx of Na+ ions which will increase the resting membrane potential causing stimulation of voltage gated Na+ ion channels causing even more Na+ influx. This will further increase the resting membrane potential carrying to the threshold potential to cause an action potential. Moreover, gamma motor neurons become activated from the stretch, and cause contraction of the ends of the muscle and the tendons and thus lengthen the fibre length. The sensory neuron carries the signal into the spinal cord. From there the following happens: - At the ventral grey horn with alpha motor neurons, which then send signals through their fibres to cause contraction of the quadriceps. (Extrafusal fibres). At the ventral grey horn, the sensory neuron synapses with inter neurons then with an alpha motor neuron which sends signals down its axons to inhibit the hamstrings. This process is known as reciprocal inhibition. At the same time the gamma motor neurons will follow the same pathway, but instead of targeting the skeletal muscles, but will instead targe the muscle spindles to cause their contraction (intrafusal fibres). This is so that we remain aware of out proprioception. 7. Describe the of lacrimation pathway. (3 marks) Answer: • • • From the temporal side of the eye, the lacrimal glands secrete lubrication fluid into the lateral commissure via the lacrimal ducts. The lubrication fluid will then flow downwards and diagonally to the medial commissure. From there the lubrication fluid will flow through the lacrimal puncta (holes) into the lacrimal canaliculi and then to the lacrimal sac and then via the nasal lacrimal duct into the nose. 8. The blood brain barrier is important for controlling what goes to the brain. a. Describe the component of the blood brain barrier (3 marks) b. Explain what kind of things can pass by. (1.5 marks) c. Why we do not want proteins passing through. (1 mark) Answer: a. • Endothelial layer: - Cells - Tight junctions to control permeability. • Basal lamina - Protein connective tissues. • Astrocyte foot processes: - These make growth factors that cause the endothelium to make tight junctions to decrease permeability. b. • Things that can pass: - Lipid soluble. - Respiratory gases. - Cl-, Na+ and H2O but via transporters. c. Because proteins can stimulate and inhibit neurons and thus alter brain activities.