NMH; Lecture 5, 6, 7 and 8 - Thalamus and Hypothalamus, Sensory pathways, Motor pathways: cortical motor function, basal ganglia and cerebellum; and motor pathways: Neuromuscular and spinal c Flashcards
<p>How is the thalamus organised?</p>
<p>Divided in two by the third ventricle, collection of individual nuclei with separate functions -> ispsilateral connection with forebrain, nuclei are interconnected</p>
<p>What is the function of the thalamus?</p>
<p>Relay centre between cerebral cortex and rest of CNS, integrates information and involved in virtually all functional systems</p>
<p>What are the 4 different thalamus nuclei?</p>
<p>Specific, association, intralaminar, reticular</p>
<p>What is the structure of the thalamus?</p>
<p>x</p>
<p>Where does each of the 4 thalamic nuclei connect to in the cortex?</p>
<p>Specific to primary cortical areas; association to association cortex; intralaminar to all cortical areas; reticular not connected to cortex</p>
<p>What are the 6 nuclei in the specific nuclei?</p>
<p>Ventral lateral/anterior, ventral posterolateral/posteromedial and lateral/medial geniculate</p>
<p>Where do the specific nuclei connect to the cortex?</p>
<p>x</p>
<p>What are the functional cortical areas which are coloured in?</p>
<p>x</p>
<p>What are the 5 nuclei in the association nuclei?</p>
<p>Anterior, lateral dorsal, dorsomedial, lateral posterior and pulvinar</p>
<p>Where do the association nuclei connect to the cortex?</p>
<p>How are the thalamic nuclei associated with RAS?</p>
<p>Intralaminar nuclei diffuse cortical projections, reticular nucleus diffuses intrathalamic projection -> both receiving inputs from reticular formation</p>
<p>What is the Reticular Activating System?</p>
<p>What is thalamic syndrome?</p>
<p>Sensation is reduced, exaggerated, altered; pain, emotional disturbance (Dejerine-Roussy Syndrome)</p>
<p>How is the hypothalamus organised?</p>
<p>Divided in two by third ventricle, collection of individual nuclei with separate function, largely ipsilateral connection with forebrain</p>
<p>What are the different hypothalamic nuclei and how are they arranged?</p>
<p>What is the function of the hypothalamus?</p>
<p>Coordinates homeostatic mechanisms via the ANS, ENS and controlling behaviour</p>
<p>What are the associated forebrain structures?</p>
<p>Olfactory system, limbic system</p>
<p>What are the parts of the limbic system?</p>
<p>Hippocampus, amygdala, cingulate cortex, septal nuclei</p>
<p>Which behaviours does the hypothalamus control?</p>
<p>Eating and drinking, expression of emotion, sexual behaviour, circadian rhythm, memory</p>
<p>What are the presenting symptoms of a hypothalamic tumour?</p>
<p>Polydipsia, polyuria, absent menses</p>
<p>What are the later symptoms of a hypothalamic tumour?</p>
<p>Labile emotions, rage, inappropriate sexual behaviour, memory lapses, temperature fluctuation, hyroid, adrenal cortex, gonadal function decreases, hyperphagia</p>
<p>How is thalamic syndrome caused?</p>
<p>Posterior cerebral artery stroke</p>
<p>What structural damage can occur to the hypothalamus?</p>
<p>Craniopharyngioma, other tumours (glioma, meningioma, dermoid, chordoma, hamartoma), sarcoidosis, langerhans cell histiocytosis</p>
<p>What are somatosensory modalities?</p>
<p>Conscious senses other than vision, hearing, balance, taste and smell</p>
<p>What are sensory receptors?</p>
<p>Transducers that convert energy from the env. into the neuronal action potentials -> considered as the nerve ending</p>
<p>What are the kind of sensory stimuli that sensory receptors pick up?</p>
<p>Thermal, mechanical, light and chemical</p>
<p>Which modalities use a mechanoreceptor?</p>
<p>Touch (light touch, pressure and vibration) and proprioception (Joint position, muscle length, muscle tension)</p>
<p>Which modalities use a thermoceptor?</p>
<p>Temperature</p>
<p>Which modalities use a nociceptor?</p>
<p>Pain</p>
<p>How do you form a sense organ with sensory receptors?</p>
<p>Non-neural cells</p>
<p>What is the difference between response to a specific stimulus in receptors in a specific sense organ compared to other receptors?</p>
<p>In the specific one they respond to specific stimuli at a much lower threshold than other receptors</p>
<p>What do receptors require to produce a response?</p>
<p>An aqequate or threshold stimulus</p>
<p>What are some examples of mechanoreceptors?</p>
<p>What is vibration detected by?</p>
<p>Rapidly adapting mechanoreceptors -> with each fibre type having different threshold, with receptors generating cycles of AP</p>
<p>What happens if thresholds overlap?</p>
<p>Certain vibrations may fire different fibres simultaneously</p>
<p>What frequency is the body most sensitive to?</p>
<p>250Hz</p>
<p>What is the frequency range for Pacinian corpuscles?</p>
<p>60-400Hz (peak at 250Hz)</p>
<p>What is the frequency range for Meissner's corpuscles?</p>
<p>5-300Hz with peak at 20-50Hz</p>
<p>What is elevation of vibratory threshold a sign of?</p>
<p>Neurodegeneration</p>
<p>What is a tickle?</p>
<p>Relatively mild stimulation of something moving across the skin which may be pleasurable</p>
<p>What causes a tickle?</p>
<p>Areas of the body with naked unmyelinated afferent nerve fibres</p>
<p>What is an itch (pruritis)?</p>
<p>Annoying, relieved by scratching</p>
<p>What causes an itch?</p>
<p>Local mechanical stimulation or chemical agents (histamine, kinins) -> stratching is a stimulation of large nerve fibres overwhelming the spinal transmission (closes the gate)</p>
<p>When does itch occur?</p>
<p>Neuropathy, renal failure, dermatitis</p>
<p>What are temperature gated channels?</p>
<p>Open and closes at different ranges of temperature which detection is most sensitive on face and chest</p>
<p>Which stimuli are detected by TRPV?</p>
<p>Hot temperature and chillies</p>
<p>Which stimuli are detected by TRPM8?</p>
<p>Cold and menthol</p>
<p>Which stimuli are detected by TRPV1?</p>
<p>Hot but also cold -> ice burn</p>
<p>What are nociceptors?</p>
<p>Specialised peripheral cutaneous terminals</p>
<p>What is the function of nociceptors?</p>
<p>Respond to noxious and harmful stimuli with a high threshold required for activation</p>
<p>What do nociceptors activate?</p>
<p>Directly activate ion channel proteins -> Transient Receptor Potential channels, neurotrophin, GPCR</p>
<p>What are some examples of stimuli detected by nociceptors?</p>
<p>Heat -> TRPV1, cold ->TRPM8, pH<7 -> acid sensing ion channels, intense pressure -> K+ channels</p>
<p>What is the commonest cutaneous nociceptor and what is its function?</p>
<p>Polymodal C fibre which responds to pressure, temperature and chemical stimuli</p>
<p>What is the commonest skeletal muscle nociceptor and what is its function?</p>
<p>Chemoreceptor for lactic acid</p>
<p>Which substances can modulate nociception?</p>
<p>Prostaglandin, substance P, histamine, serotonin, CGRP, bradykinin, potassium, ACh -> substances associated with inflammation and explain why its painful</p>
<p>What is the stimulus threshold?</p>
<p>Weakest stimulus detectable; adequate stimulus required to elicit specific response or reflex -> min stimulus detected >50% of time, varying in relation to anatomical location and different in different individuals</p>
<p>How can stimulus intensity be conveyed?</p>
<p>Frequency of AP generated, number of separate receptors activated -> relationship between stimulus intensity and ultimate sensory discrimination may be linear/logarithmic</p>
<p>What is a receptive field?</p>
<p>Area from which stimulus elicits neuronal response and it overlaps -> recruitment of adjacent sensory receptors with increased stimulus intensity -> increased number of A interpreted by brain as increases intensity</p>
<p>What is the function of the synapse?</p>
<p>Allows contact from neurone to muscle or from neurone to neurone -> arrangements can be simple or complex -> contact ratio ranges from 1:1 for muscle to 10^3:1 in CNS</p>
<p>How can the membrane potential of the post synaptic neurone be altered?</p>
<p>Can be made less negative called excitatory post synaptic potential; can be made more negative called inhibitory post synaptic potential (closer to threshold for firing) -> graded effects for summation (EPSPs and IPSPs can also summate)</p>
<p>What does the degree of summation determine?</p>
<p>How readily a neuron can reach threshold to produce an AP</p>
<p>What is a neuromuscular junction?</p>
<p>Specialised synapse between the motor neuron and the motor end plate, the muscle fibre cell membrane</p>
<p>How is the NMJ activated?</p>
<p>When an AP arrives at the NM, Ca infux causes ACh release and binds to receptors on motor end plate, causing ion channels to open - Na influx causes AP in muscle fibre</p>
<p>What are mEPP?</p>
<p>At rest, individual vesicles release ACh at very ow rate causing minature end-plate potentials</p>
<p>What are alpha motor neurones?</p>
<p>Lower motor neurones of the brainstem and the spinal cord</p>
<p>What is the function of alpha motor neurones?</p>
<p>Innervate the extrafusal muscle fibres of the skeletal muscle - activation causes muscle contraction; motor neurone pool contains all alpha motor neurones innervating a single muscle</p>
<p>What is the motor unit?</p>
<p>Single motor neurone together with all the muscle fibres that it innervates -> smallest functional unit with which to produce force -> on average each otor neurone supplies about 600 muscle fibres - stimulation of one motor unit causes contraction of all muscle fibres in that unit</p>
<p>What are the 3 types of motor units?</p>
<p>Slow (S, type I), Fast/fatigue resistant (FR, type IIA) and Fast//fatigueable (FF, type IIB)</p>
<p>What are the characteristics of a slow type I motor unit (cell bodies, dendrites, axons and conduction velocity)?</p>
<p>Smallest diameter cell bodies with small dendritic trees, thinnest axons and slowest conduction velocity</p>
<p>What are the characteristics of a FR type IIA motor unit (cell bodies, dendrites, axons and conduction velocity)?</p>
<p>Larger diameter cell bodies, larger dendritic trees, thicker axons, faster conduction velocity</p>
<p>What are the characteristics of a FF type IIB motor unit (cell bodies, dendrites, axons and conduction velocity)?</p>
<p>Larger diameter cell bodies, larger dendritic trees, thicker axons, faster conduction velocity</p>
<p>How can the 3 motor unit types be classified?</p>
<p>By amount of tension generated, speed of contraction and fatiguability of the motor unit</p>
<p>What are the 2 mechanisms by which the brain regulates force that a single muscle can produce?</p>
<p>Recruitment and rate coding</p>
<p>What is recruitment (regulation of muscle force)?</p>
<p>Motor units aren't randomly recruited -> governed by the size principle, where smaller units are recruited first (slow twitch units) and as more force is required, more units are recruited allowing fine control under which low force levels are required</p>
<p>What is rate coding (regulation of muscle force)?</p>
<p>Motor unit can fire at a range of frequencies and slow units fire at lower frequencies -> as firing rate increases, force produced by unit increases; summation occurs when units fire at frequency too fast to allow muscle to relax between arriving action potentials</p>
<p>What are neurotrophic factors?</p>
<p>Type of growth factor, preventing neuronal death; promotes growth of neurones after injury</p>
<p>What is the effect of neurotrophic factors?</p>
<p>Motor unit and fibre characteristics are dependent on innervating nerve -> if fast twitch muscle and slow muscle are cross innervated, soleus becomes fast and FDL become slow -> motor neurone has some effect on properties of muscle fibres which it innervates</p>
<p>How can the fibre types of the motor units change and which types change under which conditions?</p>
<p>Type IIA/IIB change following training; type I/II in cases of severe deconditioning/spinal cord injury; microgravity during spaceflight results in shift from slow to fast muscle fibres; ageing is associated with loss of TI/II fibres but also preferential loss of tII fibres which results in larger proportion of tI fuibres in aged muscle (evidence from slower contraction times)</p>
<p>How are the motor tracts in the spinal cord organised?</p>
<p>What is a reflex?</p>
<p>Automatic and often inborn response to stimulus that involves a nerve impulse passing inward from receptor to nerve centre and then outward to effector without reaching level of consciousness; involuntary coordinated pattern of muscle contraction and relaxation elicited by peripheral stimuli</p>
<p>What are the components of a reflex arc?</p>
<p>Sensory receptor, sensory neuron, integrating centre, motor neurone, effector</p>
<p>What is the monosynaptic reflex (stretch)?</p>
<p>What is the Hoffman Reflex?</p>
<p>What is the flexion withdrawal polysynaptic reflex?</p>
<p>What is the flexion withdrawal and crossed extensor?</p>
<p>?What is the Jendrassik manoeuvre?</p>
<p>? Influencing reflexes by e.g. clenching teeth or making fist when patellar tendon is being tapped</p>
<p>What kind of regulation can the higher centres of CNS exert upon stretch reflex?</p>
<p>Inhibitory and excitatory regulation; with inhibitory control dominating in normal conditions, and decerebration revealing excitatory control from supraspinal areas -> rigidity and spasticity can result from brain damage giving overactive/tonic stretch reflex</p>
<p>How do higher centres influence reflexes - and which higher centres/pathways are involved?</p>
<p>1) Activating alpha motor neurons
2) Activating inhibitory interneurons
3) Activating propriospinal neurons
4) Activating gamma motor neurons
5) Activating terminals of afferent fibres;
Cortex (corticospinal), red nucleus (rubrospinal), vestibular nuclei (vestibulospinal), tectum (tectospinal)</p>
<p>What is the function of the corticospinal, rubrospinal, vestibulospinal, tectospinal control of reflexes?</p>
<p>Corticospinal - Fine control of limb movement, body adjustments; rubrospinal - Automatic movements of arm in response to posture/balance changes; vestibulospinal - Altering posture to maintain balance; tectospinal - head movements in response to visual information</p>
<p>What is the gamma reflex loop?</p>
<p>If the knee is extended and the muscle goes slack; the spindle is shortened to maintain its sensitivity</p>
<p>What is hyperreflexia?</p>
<p>Loss of descending inhibition after the reflex -> can be due to a stroke</p>
<p>What is clonus hyperreflexia?</p>
<p>x</p>
<p>What is the Babinski sign (hyperreflexia)?</p>
<p>x</p>
<p>What is hyporeflexia?</p>
<p>Below normal/absent reflexes; mostly associated with lower motor neuron diseases</p>
<p>What is functional segregation?</p>
<p>The motor system is organised in a number of different areas that control different aspects of movement</p>
<p>What is hierarchical organisation?</p>
<p>High order areas of hierarchy are involved in more complex tasks (programme and decide movements, coordinate muscle activity); lower areas of hierarchy perform lower level tasks (execution of movement)</p>
<p>What is the motor system hierarchy?</p>
<p>What are the three different areas of the frontal lobe anterior to the central sulcus?</p>
<p>Primary motor cortex (M1/Broadmann's area 4), Premotor cortex (Broadmann's area 6), Supplementary motor area (Broadmann's area 6)</p>
<p>Where is the primary motor cortex/Broadmann's area 4 located?</p>
<p>Frontal lobe on precentral gyrus, anterior to central sulcus</p>
<p>What is the function of the primary motor cortex?</p>
<p>Controls fine, discrete, precise voluntary movements -> provides the descending signals to execute movements</p>
<p>What kind of motor control does the primary motor cortex control?</p>
<p>Contralateral motor control</p>
<p>Where is the premotor cortex located?</p>
<p>Frontal lobe, anterior to PMC</p>
<p>What are the parts of the association cortex?</p>
<p>Posterior parietal cortex - ensures movements are targeted accurately to objects in external space; Prefrontal cortex - involved in selection of appropriate movements for a particular course of action</p>
<p>What is clonus?</p>
<p>Abnormal oscillatory muscle contraction</p>
<p>What is Babinski's sign?</p>
<p>What are the upper motor neuron signs in MND?</p>
<p>Increased muscle tone (spasticity of limbs and tongue), brisk limbs and jaw reflexes, Babinski's sign, loss of dexterity, dysarthria, dysphagia</p>
<p>What is the function of the side loops in the motor hierarchy?</p>
<p>Help the cortical areas involved movement control to regulate the motor behaviour (PMC to execute movements, PC+SMA to plan movements, association cortex for selection and accuracy of movements)</p>
<p>What is the anatomy of the basal ganglia?</p>
<p>Striatum (caudate and putamen), Globus pallidus externa (GPe) and globus pallidus interna (GPi), Substantia nigra pars compacta (SNc) andpars reticulata (SNr), Subthalamic nucleus (STN)</p>
<p>What is the function of the basal ganglia?</p>
<p>Elaborating associated movements, moderating and coordinating movement (suppressing unwanted movements), performing movements in order</p>
<p>What is Parkinson's disease?</p>
<p>Neuronal degeneration of substantia nigra pars compacta -> 80% DA cells</p>
<p>How does the basal ganglia circuit work in hyperkinetic disorders?</p>
<p>Degeneration of GABAergic neurons in the striatum; disruption of the fine balance between inhibition and excitation; motor cortex gets excessive excitatory input; motor cortex continuously sends involuntary commands for movements and movements sequences to the muscles</p>
<p>What are the main signs of Huntington's disease?</p>
<p>Choreic movements (rapid jerky involuntary movements of the body, with hands and face affected first; then legs and rest of body); speech impairment; difficulty swallowing; unsteady gait; and later on cognitive decline and dementia</p>
<p>What are the main NT in the cerebellum?</p>
<p>Glutamate (+) and GABA (-)</p>
<p>What is the function of the vestibulocerebellum?</p>
<p>Regulation of gait, posture and equilibrium; coordination of head movements with eye movements</p>
<p>What is the function of spinocerebellum?</p>
<p>Coordination of speech, adjustment of muscle tone, coordination of limb movements</p>
<p>What is the involvement of cortical neurones in pain pathways?</p>
<p>In perception and interpretation of pain</p>
<p>How does touch and proprioception ascend the spinal cord?</p>
<p>Dorsal column (Lemniscal system), decussation (crossing) in brainstem, somatotopy throughout pathway, lateral inhibition in dorsal column nuclei</p>
<p>How does pain and temperature ascend the spinal cord?</p>
<p>Spinothalamic tract, decussation in spinal cord via interneurones, somatotopy throughout pathway; consider in spinal cord injury; Brown-Sequard syndrome: hemisection of spinal cord</p>
<p>How are the sensory pathways somatotopically organised?</p>
<p>Dorsal horns of spinal cord -> Rexed Laminae I-VII -> lamina II is substantia genlatinosa -> large myelinated Abeta(Aalpha) [mechanical stimuli LIII-VI], small myelinated Adelta [cold and fast pain nociception LI-LII], small unmyelinated C-fibres [pain and temp LI-II], projection neurones from LI which are parabrachial area/periaqueductal grey, interneurones connect between different laminae, wiide dynamic range neurones project from LV to thalamus via spinothalamic tract</p>
<p>What are the regions of the cerebral cortex?</p>
<p>What is the cortical homunculus?</p>
<p>What are the dermatomes?</p>
<p>What is referred pain?</p>
<p>Occurs at sites of body wall whose innervation enters spinal cord at same level as organ's -> sharper, better localised than visceral pain</p>
<p>What is peripheral and central sensitisation?</p>
<p>How do you diagnose and assess neuropathic pain?</p>
<p>What is the clinical pathway for high strength capsaicin patch therapy?</p>
<p>Must have peripheral NP (allodynia/hyperalgesia)</p>
