Neurology Week 6 Mcq Study Guide Questions

NEUROLOGY WEEK 6 MCQ STUDY GUIDE QUESTIONS 1. Focal seizures: A. They may pass the corpus callosum and thus progress into a generalised seizures and thus can a bilateral involvement. B. In all types of focal seizures there is involvement of the reticular formation and the thalamus. C. The involvement of the thalamus causes auras and Todd’s paralysis, and involvement of the reticular formation causes sensory loss. D. In generalised seizures the non-motor control involves the thalamus and reticular formation. Answer: A 2. Across the basilar membrane there is varying elasticity and stiffness. This determines how strong a vibration needs to be to be able to cause bending of the basilar membrane. Which part of the basilar membrane requires the greatest intensity of vibrations? A. B. C. D. E. Base Middle Apex Midway between the base and middle Midway between the middle and the apex Answer: C 3. Which of the following cocaine administration routes reaches the brain at the highest concentration? A. B. C. D. Smoking IV Snorting All of them reach the brain at equal concentrations. Answer: A 4. Amphetamine’s work by: A. Increasing the release of dopamine from pre-synaptic neurons. B. Inhibiting dopamine re-uptake receptors. C. Lowers the threshold for depolarising the post-synaptic neuron once dopamine is released. D. It works by all three ways. E. A and C Answer: D 5. Which part of the neuron: (1.5 marks) a. Receives incoming information from other neurons, muscles of hormones. (0.5 marks) b. Which part of the neuron sends signals to other neurons or muscles? (0.5 marks) c. What is the role of the soma? (0.5 marks) Answer: a. Dendrites b. Axon terminates. c. Where cell processes take place 6. Compare and contrast movement across myelinated vs. Unmyelinated neurons? Myelinated neurons, unlike unmyelinated neurons, have a myelin sheath which is made out of a fatty layer. In myelinated neurons of the central system the myelin sheath is made out of oligodendrocytes, whereas in the peripheral nervous system the myelin is made out of Schwan cells. The myelin sheath acts as an insulator. This means that in myelinated neuron axons, there is Na+ channels only at the nodes of ravier, rather than the entire length of the axon as seen in the case of unmyelinated neurons. This allows for faster conduction, because when the action potential arrives at neuron, and it meets the threshold and generated at the axon hillocks (have highest concentration of Na+ channels). Once, threshold is reached this will stimulate the opening of Na+ voltage gated channels causing depolarisation. At the same time since the membrane potential in the neuron will be increasing this will stimulate K+ voltage gated channels to open, thus leading to lots of K+ existing, which will decrease the membrane potential thus leading to repolarisation. The signals will be jumping from a node of raviner to a node which is the only site where depolarisation takes place, this is known as salutatory conduction. This is much faster than the conduction taking place at the unmyelinated neurons, because in the unmyelinated neurons depolarisation will be taking place at every single site through the length of the axon, as there is Na+ channels throughout the entire length. 7. Define the following terms and give one example of each. (3 marks) a. Multipolar (1 mark) b. Bipolar (1 mark) c. Unipolar (1 mark) Answer a. 1 axon with many dendrites. This is the most common neuron type. b. 1 axon and 1 dendrite c. 1 axon branches to peripheral and central axon branches 8. Describe the four types of glial cells (4 marks) Answer • • • • Shawn and oligodendrites: myelination of neurons -> faster signal transmission and conduction Microglial: immunity, helps with detecting foreign molecules and stimulates acute inflammation and adaptive immunity Astrocyte: modulate synaptic activity, form blood brain barrier, regulation blood flow and ion transmission Ependymal: make CSF and neurogeneration 9. Describe the process of the neuromuscular junction. When membrane threshold potential is met an action potential is generated at the axon hillocks as that place has a high concentration of Na+ channels. The action potential will travel down the neuron, until it reaches the end of it, where we will have the postsynaptic membrane. Since the membrane potential will be increasing this will lead to the activation of Na+ voltage gated channels. The Na+ channels will open and Na+ will rush in (influx) increasing the membrane potential from -65mV (resting membrane potential) to 30mV. At the same time, the increased membrane potential of 30mV will stimulate the opening of voltage gated K+ channels, leading to an efflux of K+ (K+ existing the cell), decreasing the membrane potential to about -65 mV leading to repolarisation. This is known as the refractory period as the cell can’t be stimulated at that time. The 30mV will also lead to stimulation of Ca+ voltage gated channels allowing Ca2+ to enter the cell (Ca2+ influx). Although, studies are not clear about it, either 2 or 4 Ca2+ will bind onto the Ach vesicles carrying into near the preganglionic membrane. Ca2+ will allow the snare protein of the Ach vesicle to link up with the snare proteins if the membrane. This will allow the vesicle to diffuse with the membrane leading to exocytosis of Ach out of the vesicle and the preganglionic into the synaptic cleft. 2 Ach will bind on each available nicotinic receptors on the surface of the postganglionic membrane, which will cause the nicotinic receptors to open and allow Na+ from the synaptic cleft to rush into the postganglionic. If high enough amounts of Na+ to increase membrane potential enter, it will generate an action potential. 10. Provide a definition of a motor neuron (0.5 marks) Answer: A motor neuron refers to a single neuron that innervates a group of skeletal muscles. 11. Compare and contrast nerves and hormones (3 marks) Answer: Nerves • • Localised effect Rapid onset • • Brief effects Very specific on what to act on Hormones • • • • Distant effects Slow onset Longer lasting effects Can act on multiple things. 12. Describe the factors that can affect the magnitude of effect of the action of the nerve. Answer • • • • Post-synaptic receptor availability: the receptors are blocked from things such as antibodies from B cells, then neurotransmitters such as Ach cannot bind on postsynaptic receptors like nicotinic receptors. Post synaptic receptor excitability. Amount of neurotransmitter released. Period of availability in synaptic left. The longer it is there the long it is available, for example the time Ach needs to be broken down. 13. Compare and contrast neurogenic shock and spinal cord injury (6 marks) Answer: A neurogenic shock involves the entire nervous system, whereas a spinal cord injury only involves the spinal cord. A neurogenic shock typically occurs at or above T6. This leads to loss of the sympathetic nervous system, where there will be an unopposed vagal activity on organs such as the heart. This means that it is common for neurogenic shock patients to present with symptoms such as bradycardia and hypotension. This is because the diminishing of sympathetic activity, means that there is very little if any catecholamines (epinephrine and norepinephrine) which are essential for increasing heart rate and for causing vasoconstriction. Their absence means that there is reduced heart rate and vasoconstriction, consequently leading to the low blood pressure (hypotension), which are further reduced because of the unopposed vagus nerve. On the other hand, a spinal shock it only affects the spine, where the area that is affected causes bleeding and inflammation, thus damaging tissue as well as the release of vasoconstriction mediators which aim to reduce the blood loss, however, this will mean that the spinal cord will be getting less blood thus the spinal hypoxia and ischemia. This will result in paralysis where there will be loss of sensation blow the level of injury. If the spinal cord injury happens to be incomplete there will only be loss of temperature and pain sensation, but sensation of light touch, vibration and motion will remain as usual. But it is complete spinal injury then there will be loss of all sensations as well as motor loss. Answer: B 14. a. Explain the difference between upper and lower motor neurons. (2 marks) b. Discuss the muscle fibres that lower motor neurons act upon? (2 marks) c. Explain the different types of lower motor neurons. Comment on their speeds. (4 marks) Answer: a. Upper motor neurons origin from the brain. Their main function is to innervate lower motor neurons. Lower motor neurons, originate from the spinal cord. Once, they are innervated by the upper motor neurons, the lower motor neurons innervate muscle fibres. b. There are two types of muscle fibres that are acted upon by the lower motor neuron: - Intrafusal fibres: these form the muscle spindle and are located deep within the extrafusal fibres. - Extrafusal fibres: these form the majority of muscle fibre and control contractile functions. c. There are three types of lower motor neurons: - Alpha: also known as skeletomotor neurons. It is responsible for innervating skeletal muscles. - Gamma: also known as fusimotor neurons innervates muscle spindles - Beta: can innervate both extrafusal and intrafusal fibres - Alpha has the fastest condition velocity as they also have the largest diameter. The second fastest and with the second largest diameter is gamma lower motor neurons, followed by beta lower motor neurons. 15. Discuss the process of the Dorsal column medial lemniscal pathway (5 marks) Answer The dorsal column lemnisci pathway is responsible for conveying tactile information from the body. It all begins with a tactile stimulus. This is carried by the peripheral neurons to the dorsal ganglion, where the peripheral nerve synapses with the first order neuron. Through the dorsal root, this information is carried to the spinal cord. If the information is coming from the lower limb, then the spinal region that the signal is carried to is within the lumbar spine, where upon entry via the first order neuron via the dorsal root, it goes though the fasciculus gracilis. But if the information is coming from the upper limb, then the info goes through a similar pathway, but in the cervical region of the spine and goes through the fasciculus cutaneous region of the spinal cord. From there, the information undergoes the ipsilateral dorsal column and ascend to the medulla, where it synapses at the dorsal nuclei (nucleus gracilis if from lower limb, nucleus cutaneous if from upper limb), where it will synapse with second order neurons. The signal will then cross to the contralateral side of the medulla, where it also goes though the decussation of medial lemniscus within the medulla, ascend through the pons and mid brain via passing though the medial lemniscus, and then ascend to the thymus, there the second order neurons will synapse with the third order neuron. The third order neurons will then carry the signal from the thymus to the relevant part of the somatosensory cortex. 16. Describe the process of the spinothalamic tract (5 marks) Answer: The spinothalamic tract conveys information about crude touch, pain, and temperature to the body. It involves the use of nociceptive neurons, which are slow as they are unmyelinated and have a narrow diameter. Peripheral neurons will carry information from a crude touch, pain or a temperature stimulus, synapse with the first order neurons at the dorsal ganglia and enter the spinal cord through the dorsal root. The signal may ascend or descend 1 or 2 vertebras. Then, it will synapse with the second order neuron ipsilaterally at the nucleus proprious. From there the signal will cross over to the contralateral side of the spinal cord. If it is carrying information about pain or temperature, it will go through the tract of the same spinal vertebra where the synapse with the second order neuron took place. If it is carrying information about crude touch, instead it will go through the anterior spinothalamic tract. The signal will then ascend to the medulla oblongata, then ascend to the thalamus where it will synapse with a third order neuron, which will then transmit this, to the relevant region of the somatosensory cortex. 17. Describe the corticospinal tract (4 marks) Answer: The corticospinal tract, carries descending information from the brain to the relevant muscle/s. When there has been a stimulus, of which a signal is generated and ascended to the brain, and requires the corticospinal tract to innervate muscles, layer V pyramidal axons of the corticospinal tract will transmit descending signals to the pyramidal decussation within the medulla obolngata via an internal capsule. The signal/info will then cross to the contralateral side of the medulla. The signal will continue to descend via the lateral column spine until it reaches the relevant region of the spinal cord. It will then synapse with the appropriate lower motor neurons, and then innervate the required muscle fibres. Important note: before the lower motor neuron (which originate from the spine), it was the upper motor neurons that where in action, they originate from the brain and innervate the lower motor neuron as explained above. Anika: Mention first synapse of a corticospinal neurone is located in the ventral horn (merci x oxo) 18. What is the main difference between the corticospinal and corticobulbar tracts? (1 mark) Answer: • • The corticospinal tract terminates in the spinal cord. The corticobulbar tract terminates in the brainstem. 19. Describe the different sympathetic nervous system pathways (5 marks) Answer: There are three different sympathetic innervation pathways: • Pathway 1: Synapse at a sympathetic ganglion at the same level The visceral sensory fibre enters the spinal column via the dorsal root of the spinal cord, goes through the dorsal root ganglion, enters the spinal cord where it synapses with at the integration centre with the preganglionic nerve fibre, exists the spinal cord via ventral root, then ramus -> white rami communicant enters the sympathetic ganglion where it will synapse with the post sympathetic neuron, exit via the grey rami communicant -> ventral ramus -> travel to target organ/tissue • Pathway 2: Synapse at a sympathetic ganglion at a different level - Same as above but instead, after existing the spinal cord via the ventral root, it will ascend or descend to a ganglion at a different level and synapse there with the postganglionic nerve fibre. • Pathway 3: Splanchnic pathway - The visceral sensory fibre enters the spinal column via the dorsal root of the spinal cord, goes through the dorsal root ganglion, enters the spinal cord where it synapses with at the integration centre with the preganglionic nerve fibre, travels through a long nerve known as the splanchnic nerve, where it will either synapse with a postganglionic nerve fibre close to the target tissue/organ or at the target tissue/organ. A. the grey and white matter of the spinal cord from T1 to L2/L3 20. In the sympathetic nervous system, where is the postganglionic cell body located and where does to it terminate? (1 mark) Answer: • • Location: sympathetic ganglion Termination: organ or tissue supplied