Nervous System ( 5% ) Flashcards
Visual pathways
- Have P cells that are associated with colour.
- Utilize the primary colours red, yellow and blue.
- Have simple cells which respond to all light stimuli
- Pass through the medial geniculate body.
- Have a temporal path for motion.
Have P cells that are associated with colour.
(aka parvocellular cells, located in the Lateral Geniculate Nucleus. involved in colour transmission)
- Utilise the primary colours red, green, and blue
- Have multiple cell-types, each responding to a different type of stimuli (rods and cones etc)
- Rods respond to lower light intensities (night / scotopic vision) but distinguish higher intensities poorly, hence contribute less to visual acuity. Cones are the opposite
- Pass through the lateral geniculate body
- Have a temporal path for recognition of forms and faces. Output from V1 can go to the parietal lobe (motion) or temporal.
parasympathetic stimulation causes
- sweat secretion
- salivary secretion
- inhibition of peristalsis
- increase in HR
- vasoconstriction of abdominal viscera
salivary secretion
Sympathetic = fight or flight
Parasympathetic = eat and secrete
= rest and digest
= feed and breed
A sense organ for pain is
- Merkel’s disc.
- Kranse end bulb
- Naked nerve endings
- Meissner’s corpuscle
- Encapsulated endings
Naked nerve endings
- Merkel’s disc. - touch (sustained pressure)
- Meissner’s corpuscle - touch (tap, flutter)
- Ruffini endings - touch (skin stretch, vibration)
Pain transmission
- Is by peripheral B fibres.
- Involves cholinergic transmission.
- Is produced by over-stimulation of other receptor types.
- Can be gated by presynaptic inhibition.
- Is via fast C pain fibres.
Can be gated by presynaptic inhibition.
Opioids act on pre- and post-synaptic receptors to inhibit transmission across the synapse in the dorsal horn. Presynaptic decreases calcium influx, inhibiting NT release. Post-synaptic increases K conductance, hyperpolarising the cell. Descending modulatory pathways also act on pre and post-synaptic receptors
- Is by peripheral A delta (thin, myelinated, release glutamate, fast aspect to pain that allows localisation) or C fibres (wide, unmyelinated, glutamate and substance P for slow, dull, intense pain)
- Involves Glutamate and substance P. Descending modulatory pathways use serotonin (nerves from NRM) and catecholamines (nerves from RVM)
- Is produced by specific nociceptors (mechanical, thermal, chemical) that are distinct from other somatosensory receptors
- Is via slow C pain fibres. (all c fibres are slow - unmyelinated)
Co-transmitters released with NA include
- VIP and DA
- ATP and neuropeptide Y
- DA and neuropeptide Y
- Tyrosine and ATP
- ACh and VIP
ATP and neuropeptide Y
The size of the action potential is decreased by
- Decreasing intracellular Ca
- Increasing external Na
- Decreasing the external Na
- Decreasing the internal K
- Increasing the internal K
Decreasing the external Na
Na is involved in magnitude of AP
K is involved in RMP
Ca is involved in degree of neurotransmitter release and muscle contraction
Cl is inhibitory
all of the following ascending sensory pathways are located in the dorsal column except
- pain
- touch
- pressure
- vibration
- proprioception
Pain
Dorsal = light touch, vibration, proprioception, pressure
Ventrolateral spinothalamic = pain, temperature, crude touch
concerning the visual pathway
- macular sparing occurs due to the arrangement of fibres in the optic tract
- Brodmann’s area is located in the temporal lobe.
- The optic tract ends in the medial geniculate body.
- The optic disc lies 3mm medial to and slightly above the posterior pole of the globe
- a pituitary tumour often causes a homonymous hemianopia.
The optic disc lies 3mm medial to and slightly above the posterior pole of the globe
macular sparing occurs because macular representation is seperate from that of the peripheral fields and relatively very large.
Brodmanns area is a classification of areas in the brain, not an area itself
The optic tract ends in the lateral geniculate body
a pituitary tumour often causes a bitemporal hemianopia (by compressing the nasal nerve fibres in the optic chiasm).
within the sympathetic nervous system
- sweat glands are supplied by β2 receptors.
- activation promotes gluconeogenesis.
- bronchial glandular secretion is inhibited by β2 receptor stimulation
- at the post ganglionic neuron, DA is responsible for the slow excitatory post synaptic potential
- the preganglionic neurons leave the spinal cord in the ventral roots of the thoracolumbar spine
the preganglionic neurons leave the spinal cord in the ventral roots of the thoracolumbar spine
- sweat glands are supplied by alpha 1 receptors.
- activation promotes Glycogenolysis (need to burn fuels)
Need to confirm below
- bronchial glandular secretion is inhibited by β2 receptor stimulation
- at the post ganglionic neuron, DA is responsible for the slow excitatory post synaptic potential
In the visual pathway
- Axons of the ganglion cells pass in the optic nerve and optic tract and end in the medial geniculate body of the hypothalamus.
- Fibres of each temporal hemi-retina decussate in the optic chiasm.
- The primary visual receiving area is Brodmann’s area 17
- The fovea contains no cones.
- 80% of input to the geniculate nucleus comes from the retina, the other input is from brain regions involved in feedback regulation.
The primary visual receiving area is Brodmann’s area 17
- Axons of the ganglion cells pass in the optic nerve and optic tract and end in the lateral geniculate body of the hypothalamus.
- Fibres of each nasal hemi-retina decussate in the optic chiasm (but supply the temoral visual fields)
- The fovea contains no rods - very sensitive to colour and acuity, but poor light perception (in the dark, periphary is more able to pick up dim light sources)
- 10-20% of input to the geniculate nucleus comes from the retina, the other input is from brain regions involved in feedback regulation
Regarding reflexes
- The reaction time for knee jerk is 0.1s
- Jendrassik’s manoeuvre enhances the knee jerk reflex
- Spindles are located in muscle tendons.
- Afferent neurons carry the impulse to the muscle.
- Muscle spindle fibres are innervated by Ib type nerve.
Jendrassik’s manoeuvre enhances the knee jerk reflex
- The reaction time for knee jerk is 0.015-0.03s (15-30ms)
- Spindles are located in Muscle bellies
- Efferent neurons carry the impulse to the muscle
- Muscle spindle fibres are innervated by Ia type nerve. Golgi tendon organs are innervated by 1b
Which of the following is false
- Unilateral transection of the left optic tract causes a right sided homonymous hemianopia
- The fovea contains only cones
- Dark adaption is maximal at around 20 minutes
- Optic nerve fibres from the upper retinal quadrants terminate in the medial half of the lateral geniculate body
- Na channels in rods and cones are open in response to light.
Na channels in rods and cones are Open in absence of light, close in the presence
Photoreceptor cells (rods and cones) produce a stimulus at baseline, in the dark. cGMP-gated Na channels are open in the dark, allowing Na influx into the outer segment. NaKATPase in the inner segment drives this flow. In the light, cGMP breaks down and so the ion channels close, hyperpolarising the cell, and reducing glutamate relase. This reduction in glutamate release is what produces a signal in the bipolar cells.
Which is false
- The alpha rhythm is the dominant rhythm seen on EEG of adults
- Corticospinal and corticobulbar system is the primary pathway for the initiation of skilled voluntary movement
- Basal ganglion is composed of the putamen, globus pallidus and substantia nigra
- Flocculonodular lobe is concerned with equilibrium
- Cold receptors respond from 10-38 degrees Celsius
Basal ganglion is composed of the putamen, globus pallidus and substantia nigra - as well as caudate nucleus and subthalamic nucleus
- The alpha rhythm is the dominant rhythm seen on EEG of adults - when awake, resting, eyes closed, at rest. Not when aroused or focussed (then it is gamma oscillations)
- Corticospinal and corticobulbar system is the primary pathway for the initiation of skilled voluntary movement
- Flocculonodular lobe is concerned with equilibrium
- Cold receptors increase firing from 40-24 degrees Celsius, then reduce to nothing at 10c (so do respond from 10-38 degrees)
Characteristics of the brain, CSF and cerebral circulation include
- CSF volume of 150mL at a lumbar pressure of 0-100 mm CSF
- CSF/plasma protein ratio of 1, glucose of 0.6
- Weight of 1.4 kg suspended in CSF from the dura mater by arachnoid trabeculae
- Susceptibility to convulsions at normal BSLs in diabetics
- Oxygen consumption of 25mL/min ie 10% total body consumption
Susceptibility to convulsions at normal BSLs in diabetics
Regarding the ANS
- Does not have a reflex arc like somatic nervous system.
- Has DA as the main neurotransmitter.
- Has cholinergic division which increases activity of intestinal musculature and increases gastric secretion
- Neurotransmitter NA is metabolized by pseudocholinesterase.
- Is not involved in visceral sensation.
Has cholinergic division which increases activity of intestinal musculature and increases gastric secretion
- Can have a reflex arc like somatic nervous system eg Pupillary reflex
- Has ACh and Na as the main neurotransmitters
- Neurotransmitter NA is metabolized by COMT and MAO
- Carries most visceral sensation.
which is not synthesised in postganglionic sympathetic neurons
- L-dopa
- DA
- NA
- A
- ACh
Adrenaline
In the ANS β agonism results in
- Constriction of the renal vasculature
- Decreased velocity of conduction in the AV node
- Decreased velocity of conduction in the His/Pukinje system
- Decreased ventricular contractility
- Increased insulin and glucagons secetion
Increased insulin and glucagons secetion
- Dilation of the renal vasculature
- Increased velocity of conduction in the AV node
- Increased velocity of conduction in the His/Pukinje system
- Increased ventricular contractility
ie Beta agonism does the opposite of what beta blockers do
The reticular activating system
- Has depressed conduction during anaesthesia
- Is located in the pons
- Is a simple collection of parallel nerve fibres
- Has no input from cranial nerves
- Is electrically isolated from the cortex
Has depressed conduction during anaesthesia
- Is located in medulla and midbrain*
- is a complex polysynaptic network*
- Has converging inputs from sensory and cranial nerves*
- Increases cortical electrical activity*
the most sensitive part of the eye is the
- optic disc
- fovea centralis
- area with maximal rods
Fovea
As it has the highest concentration of cones which all synapse on a single bipolar cell which then go to a single ganglion cell. (Each foveal cell is individually mapped in the visual cortex - I’m pretty sure)
Is thin because it has pushed all its inner cell layer and shit to the side to give greater VA with less stuff blocking the lights path
The optic disk is the optic nerve / blindspot
Rods give light sensitivity but no acuity
regarding CSF
- composition is essentially the same as brain ECF
- CSF production ~ 150mL/d
- Higher concentration of K with respect to plasma
- Higher concentration of protein
No clear answer is correct
- CSF is produced in two steps. First, a transudate forms in the choroid plexus due to hydrostatic pressure. Then active transport of Na, K, and Cl through endothelial cells draws water and CO2 osmotically across the tight junctions.
- Production ~600-700ml/day, about 125ml present at any one time
- CSF has a higher concentration of Na and Cl than plasma, but less K, Ca, glucose, protein
which penetrates the CSF fastest
- H2O, CO2, O2
- CO2, O2, N2O
H2O, CO2, O2
anterolateral dissection of the spinal cord is associated with
- ipsilateral loss of pain
- ipsilateral loss of temperature
- ipsilateral hyperreflexia.
- contralateral vibration loss
- none of the above.
Nick believes c) but had originally been told none of the above
Anterolateral or ventrolateral spinothalamic tract carries pain, temperature, crude touch, tracts to cerebellum
These decussate immediately
Therefore dissection will cause contralateral pain and temperature loss
Will also damage ventral corticospinal tract (direct, has interneurons etc, 20% of fibres), tectospinal, recticulospinal, and vestibulospinal tracts.
Degree of damage would determine if lateral corticospinal tract was damaged, but this should give ipsilateral UMN lesion, ie involve hyperreflexia.
Dorsal column carries light touch, vibration, proprioception
These decussate in medulla
Even if cut in the question, would provide ipsilateral vibration loss
The sensation for cold
- Is relayed by the thalamus
- Is transmitted by the dorsal columns. Anterolateral spinothalamic tract
- Is an uncrossed sensory modality
- Is mediated by substance P fibres
- Is mediated by A α fibres
Is relayed by the thalamus
Is transmitted by the anterolateral spinothalamic tract
Decussates immediately
Is mediated by A delta and C fibres
(warm is just C)
Substance P is involved in dull aching pain
1 Regarding muscle spindles:
- a) are composed of extrafusal fibres
- b) receive δ efferents
- c) all subtypes send afferents via “flower spray” ended 1a nerves
- d) nuclear chain fibres show dynamic response
- e) afferent discharge decreased with muscle stretch
b) Receive delta efferents
Are composed of intrafusal fibres (extrafusal is all the other muscle cells in the muscle)
Afferent discharge is increased with muscle stretch
2 Regarding the dorsal column:
- a) carries ipsilateral pain and temperature
- b) ascends to the nuclei gracillis and cuneate
- c) receives efferents from contralateral stimuli
- d) sacral efferents lie laterally
- e) runs anteriorly in the cord
b) ascends to the nuclei gracillis and cuneate
Dorsal column carries ipsilateral touch, proprioception, vibration, and thus receives efferent from ipsilateral stimuli. Arranged anatomically, so the sacral nerves are most medial, and cervical most lateral
As its name suggests, it runs dorsally.
Anterolateral spinothalamic carries contralateral pain and temperature
3 Temperature sensation:
- a) respond to compartitive temp gradient ??? skin
- b) cold receptors predominate
- c) warm receptors respond 30° - 100°
- d) afferents carried via the dorsal column
- e) warm and cold afferents carried via Adelta fibre
Cold receptors predominate (4-10x as many as warm)
Afferents carried in anterolateral spinothalamic columns (along with pain)
Warm receptors respond via C fibres from 30-46 degrees (after which nociceptors take over)
(Cold receptors are carried via C and Adelta fibres, fire increasing from 40-24 degrees, then reduce to 10c)
4 Regarding visual receptors:
- a) rods predominate in the fovea
- b) rhodopsin is the primary pigment of rods
- c) lie anterior (superficial) to their neural pathway
- d) colour blindness is an autosomal recessive gene
- e) supplied by retinal vessels
Rhodopsin is the primary pigment of rods
(made up of retinal [Vit. A aldehyde] and opsin)
Rods and cones get their nutrient supply from the choroid plexus
Lie behind their neural pathway (ie the light mist pass through the bipolar cells and nerve fibres before it gets to the photoreceptors)
Colour blindness is autosomal dominant
Cones predominate in the fovea
5 Regarding sound and hearing:
- a) high pitched sounds are detected at the apex of the cochlear
- b) Hair cells are bathed in endolymph
- c) detected by hair cells found within the tectorium membrane
- d) 95% of afferent neurones → outer hair cells
- e) ???????
Apparently the answer is ‘e) ??????’
I’m sure it is b). Gangongs is confusing, but seems to imply hair cells are bathed in endolymph, which is high in K+, and this helps to generate the K+ influx needed to generate a potential. Could be both, I don’t know.
High pitched sounds are detected at the base, low pitch sounds at the apex
There are 20,000 outer hair cells, 3500 inner hair cells. 90-95% afferent neurons supply inner hair cells. On the other hand, most efferent nerves supply the outer hair cells.
Tectorial membrane has the tips of outer hair cells embedded in it.
6 Regarding noradrenergic stimulation:
- a) miosis occurs
- b) increases blood flow to the skin
- c) increases thresholds in the reticular formation
- d) causes erection in males
- e) elevates free fatty acid levels
Answer listed as D) but this is wrong. I think it is e) elevates FFA levels.
Norad = sympathetic
B3 → lipolysis + A1/B2 → glycogenolysis (likely increases FFA)
- Mydriasis* occurs (pupil dilation; cholinergics cause miosis)
- Sympathetic ACh* release causes increased blood flow to skin/skeletal muscles (along with sweat glands are the two sympathetic ACh uses)
Parasympathetic causes erection, sympathetic causes ejaculation
Clarify if RAS activation or deactivation causes sleep
7 Regarding cholinergic stimulation:
- a) causes amylase secretion from salivary glands
- b) decreases secretion from pancreatic acini cells
- c) relaxes the gallbladder
- d) has no effect on renal arterioles
- e) relaxes bronchial smooth muscle
d) has no effect on renal arterioles
Parasympathetic has no effect on any arteriole or vein (or skin for that matter)
Causes contraction of the GB
Constricts bronchial smooth muscle
Causes a profuse watery salivary secretion, whereas a1 or B (sympathetic) causes a thick, viscous secretion with amylase
Increases panceatic acini cell secretion (digestion), but has no effect on Islet cells (insulin - this is mediated by a2 and B2)
The emotional component to pain is due to activation of:
- a) post central gyrus
- b) sylvian fissure
- c) hippocampus
- d) cingulated cortex
- e) calcavine fissure
a) post central gyrus
The chemical agent that initiates impulses in pain fibres is:
- a) ATP
- b) substanceP
- c) Ca2+
- d) H+
- e) K+
b) substance P
Along with glutamate
Regarding thermoceptors:
- a) there are more warm receptors than cold receptors
- b) cold receptors respond to 10-38°C
- c) afferents for cold receptors are C fibres only
- d) afferents found in the ventral spinothalamic tract
- e) respond to the temperature gradient across the skin
b) cold receptors respond to 10-38°C
- ~40→ 10c, increase firing then they decrease towards 10*
- 4-10x as many cold as warm*
- Warm respond 25→45*
Afferents for cold are C and Adelta (warm is C only)
Afferents are in the Lateral spinothalamic tract (crude touch and pressure are ventral)
Regarding body temperature:
- a) humans are poikilothermic
- b) oral temperature is usually higher than rectal temperature
- c) it is usually lowest at 6am
- d) children have more precise temperature regulation
- e) emotion has no effect on core temperature
- c) it is usually lowest at 6am (and highest in the evenings)
- Poikilothermic = cold blooded. Humans are homeothermic
- Oral temp ~0.5c lower than rectal
- Temp control is less precise in children, they often run 0.5c hotter than adults.
- Rises slightly during emotional excitement (likely due to unconscious tensing of muscles)
Regarding the hypothalamus:
- a) it has neural connections with the anterior pituitary gland
- b) it integrates the vomiting reflex
- c) the anterior hypothalamus responds to cold
- d) it controls circadian rhythms via the supraoptic nuclei
- e) it has osmoreceptors in the anterior hypothalamus to stimulate thirst and vasopressin release
Answer given as b) vomiting reflex, but this is in the Medulla
Unsure if C or E
Anterior hypothalamus does have temperature receptors, but the posterior hypothalamus is involved in systemic response to cold, anterior to heat.
Regarding osmoreceptors:
Osmoreceptors in the anterior hypothalamus stimulate thirst, and vasopressin is released from the posterior pituitary in response to osmoreceptors which may or may not be the same as those involved in thirst. Also notes multiple other locations it can be secreted from. (This answer could also be correct)
It has neural connections with the posterior pituitary, but only a portal blood supply to the anterior
Circadian rhythm seems to be controlled by the pineal gland and thalamus
26 When a visual stimulus falls on a given point in the retina for a long time:
- a) the image becomes more clearly focused
- b) there is adaptation in the visual cortex
- c) the discharge rate in the bipolar cells increases
- d) the pupils constrict
- e) the image fades and disappears
They think A) image becomes more focussed.
Lateral inhibition (inhibition of nearby neural units if one is activated) helps sharpen the edges of an object (or any sensation). It is not clear that this occurs only if the stimulus is there for a long time or any time. I can’t find anything else in Ganongs to point me further.
Regarding the vomiting reflex, which is INCORRECT?
- a) it is integrated by the medulla
- b) breath is held in expiration
- c) the glottis closes
- d) it involves salivation
- e) there are afferents from vestibular nuclei
b) breath is held in mid-inspiration
Starts with salivation and nausea, reverse peristalsis moves small intestine contents → stomach, glottis closes, breath held. Abdominal muscles contract and sphincters loosen.
Integrated by the medulla.
Motion/vertigo → labyrinth→ cerebellum→ vomiting centre (also pain, sights, anticipation, pharyngeal stimuatlion, gastric irritants, drugs acting on vomiting centre itself eg opioids or chemotherapy)
Herring bodies are:
- a) nuclei of the hypothalamus
- b) secretory granules in the posterior pituitary
- c) circumventricular organs
- d) neurons connecting vestibular nuclei with the vomiting centre
- e) vesicles containing ACTH, TSH, GH, FSH, CH and PRL
b) secretory granules in the posterior pituitary
Herring bodies or neurosecretory bodies are structures found in the posterior pituitary. They represent the terminal end of the axons from the hypothalamus, and hormones are temporarily stored in these locations. They are neurosecretory terminals.
(they thought c); most answers they give in this section are wrong)
15 The neurotransmitter secreted by primary afferent fibres for severe pain is:
- a) glutamate
- b) acetylcholine
- c) substance P
- d) opioid peptides
- e) noradrenaline
Answer given is d) opioid receptors but this is clearly wrong (endogenous opioids modulate pain response - are not involved in the primary afferent).
I would guess the answer is A (but C partially correct too)
Acute pain is transmitted by Adelta fibres and uses glutamate as its transmitter for speed. Substance P is used in C fibres (along with glutamate) to transmit deep, visceral pain (which Ganongs notes can be severe).
Regarding rods and cones:
- a) Na+ channels are closed in the dark
- b) light striking the outer segments results in a depolarising receptor potential
- c) the receptor potentials are all-or-nothing
- d) rhodopsin is a serpentine receptor
- e) acetylcholine is released from the synaptic terminal
b) Light striking the outer segment causes a depolarising receptor potential (as in towards the outside of the eye, cf inner which are closer to the inside; remember the backwards arrangement of neurons in the eye)
Na channels are open in the dark, inhibited by light.
Rods and cones give varying degrees of EPSP/IPSP - not all or nothing
Rhodopsin is a photosensitive pigment in rods
Synaptic transmitter is Glutamate (not ACh)
17 The visual cortex is situated at the:
- a) parieto-occipital sulcus
- b) cuneus
- c) calcarine fissure
- d) lateral geniculate body
- e) angulargyrus
Primary visual cortex (aka Brodmanns area 17) is located in the occipital lobe around the calcarine fissure (C is the answer)
Lateral geniculate body in the thalamus is the end of the ganglion cells/optic nerve/optic tract. Tract between LGB and PVC is called the geniculocalcarine tract
(as an aside, the answer given here was d) - whoever wrote this section is a dipshit, most answers are wrong)
18 In the visual pathway:
- a) the lateral geniculate bodies are made up of t layers
- b) fibres for reflex pupillary constriction leave the optic nerve at the optic chiasm
- c) pituitary tumours can cause homonymous hemianopia
- d) macular sparing may or may not occur with lesions in the geniculocalcanine tract
- e) binasal visual field fibres decussate at the opticchiasm
D) macular sparing may occur - the macular fibres separate from the peripheral fibres in the LGB and run a seperate tract, and are located in a seperate area on the visual cortex. The macula also occupies relatively much more of the neurons and primary visual cortex, thus an injury must cover a very large area to knock it all out.
LGB is made up of 6 layers (1-2=magnocellular, 3-6=parvocellular). Don’t know where the fuck T came from.
Reflex pupillary constriction is a reflex arc - afferents come from the optic nerve (II), efferents come from the Occulomotor nerve (III)
Pituitary tumours can cause a bitemporal hemianopia. Lesions in optic tract cause a homonymous hemianopia
Bitemporal visual fields decussate at the optic chiasm (received by the nasal regions of the retina though)
19 When a normal innervated skeletal muscle is stretched, the initial response is contraction, but with increasing stretch, the muscle suddenly relaxes because:
- a) with strong stretch, the efferent discharge is decreased
- b) with strong stretch, the discharge from the annulospiral endings of afferent nerve fibres is inhibited
- c) with strong stretch, there is decreased activity in the afferent nerve fibres from the Golgi tendon organs
- d) with strong stretch, there is increased activity in the afferent nerve fibres from the Golgi tendon organs
- e) because of reciprocal innervation, there is increased discharge in the afferent nerve fibres from the antagonists to the stretched muscle
d) with strong stretch, there is increased activity in the afferent nerve fibres from the Golgi tendon organs
* Inverse Stretch reflex:* Golgi tendon organs mediate contraction strength of a muscle, much as muscle spindles mediate muscle length. Have an inhibitory response on muscle contraction. They are in series with muscle (unlike spindles which are in parallel); the muscle takes up most passive stretch as it is more elastic, but if it is stretched too much, they will fire and relaxation occurs.
20 With regard to spinal tracts, which is INCORRECT?
- a) lateral corticospinal fibres decussate in the pyramids of the medulla
- b) ventral corticospinal fibres decussate at the level of synapse in spinal cord
- c) dorsal column fibres synapse in gracile and cuneate nuclei with decussating
- d) lateral spinothalamic tract carries pain and temperature fibres
- e) ventral spinothalamic tract decussates at the medial lemniscus
e) ventral spinothalamic tract decussates at the medial lemniscus
* Both spinothalmaic tracts decussate in the spinal cord in the anterior white commissure.*
* Lateral spinothalamic carries pain and temp*
* Ventral spinothalamic carries crude touch and pressure*
Dorsal column fibres synapse in gracile and cuneate nuclei of medulla, before decussating and ascending the medial lemniscus
In a polysynaptic reflex, which of the following happen when the strength of the adequate stimulus is increased?
- a) the amplitude of the motor response is increased
- b) the motor response spreads to include other muscles and even other limbs
- c) there is increased inhibition of stretch reflexes
- d) the duration of the motor response increases
- e) all of the above are true
They thought A, I reckon E) all of the above.
The withdrawal reflex is an example of a polysynaptic reflex. Weak noxious stimuli produce a weak flexion response (eg lifting a foot). Stronger stimuli produce a larger response (lift the foot higher), more prolonged response, stretch reflex is inhibited (eg the knee is flexed in withdrawal - the extension of the patellar reflex is inhibited), and can also spread to other muscle groups as part of the crossed extensor response which ensures you don’t fall over when this happens.
22 A tumour causing external compression to the anterior cervical spinal cord would be expected to:
- a) impair pressure and pain sensation mostly from sacral and lumbar areas
- b) impair fine touch and vibration mostly from sacral and lumbar areas
- c) impair pain only from cervical areas
- d) impair vibration sense only from cervical areas
- e) impair joint position from sacral areas only
They thought D, I think:
- c) impair pain only from cervical areas
The spinothalamic tracts decussate in the anterior white commissure and so would be vulnerable at the level they decussate - ie cervical spinothalamic tracts.
Pain and pressure - lateral spinothalamic tract
Fine touch, vibration, proprioception - dorsal columns
None of these fibres run anteriorly (crude touch and pressure in the ventral spinothalamic tract is the only sensory column that could be affected (Motorwise the ventral corticospinal runs anteriorly [carries 20% of motor efferents]; also the tectospinal, vestibulospinal, and various other specialised motor tracts).
23 Which of the following need to be intact for normal stereognosis:
- a) dorsal columns
- b) parietal lobe
- c) pressure pathways
- d) all of the above
- e) noneoftheabove
Stereognosis is the ability to perceive the form and nature of an object without looking at it (eg keys or a nice hat). This requires intact touch and pressure sensation, and thus an intact dorsal column.
Answer is all of the above, as it needs a dorsal column and pressure pathway, as well as an intact primary sensory cortex.
Tactile agnosia is the absence of this, and can be due to damage to dorsal column, cerebral cortex, or primary sensory cortex.
24 Bitemporal hemianopia is most likely to be caused by a lesion at the:
- a) optic nerve
- b) optic chiasm
- c) optic tract
- d) optic radiation
- e) visual cortex
Optic chasm
25 Regarding temperature regulation, which is NOT true?
- a) the anterior hypothalamus contains temperature sensitive cells
- b) shivering is activated by the posterior hypothalamus
- c) the anterior hypothalamus controls mechanisms activated by heat
- d) horripilation acts to increase heat production
- e) fever is produced by the action of cytokines on the hypothalmus
e) fever is produced by the action of cytokines on the hypothalamus.
Bacterial toxins → make macrocytes, monophages, and Kupffer cells to produce cytokines that act as endogenous pyrogens
Eg IL-1B, IL-6, TNF-a, IFN
However these cytokines are too large to cross the BBB, so act indirectly on the hypothalamus via OVLT.
Anterior hypothalamus itself has temp sensitive cells, along with inputs (primarily cold receptors) from skin, spinal cord, deep tissue, and extra thalamic portions of the brain.
Responses to cold are mediated by the posterior hypothalamus, responses to heat by the anterior hypothalamus.
27 Which of the following affect visual activity?
- a) cataracts
- b) vitamin A deficiency
- c) astigmatism
- d) contrast between stimulus and background
- e) all of the above
e) all of the above
28 The ‘tympanic reflex’:
- a) is activated by foreign bodies in the external auditory canal
- b) results in vertigo
- c) is activated by high-pitched sounds only
- d) results in the decreased transmission of sound
- e) noneoftheabove
d) results in the decreased transmission of sound
Tympanic reflex = contraction of tensor tympani and stapedius, which causes reduced sound transmission to prevent strong sound waves excessively stimulating the auditory receptors.
29 If one leg is immersed in ice water, the subject’s immediate response(s) include:
- a) generalised vasoconstriction
- b) increased secretion of adrenaline
- c) shivering
- d) all of the above
- e) noneoftheabove
They think ‘?’
Cold causes shivering and catecholamine release, and localised cutaneous vasoconstriction.
‘Generalised vasoconstriction’ seems to be wrong
Shivering and adrenaline release can occur in cold, but unsure if these happen ‘immediately’, or if just the one leg is placed in water. If generalised vasoconstriction does not occur, I don’t know which of the other two, if either, occurs first or immediately.
30 Regarding pain transmission, which is NOT true?
- a) ‘fast pain’ fibres are Aδ fibres
- b) ‘slow pain’ fibres are C fibres
- c) substance P is the central transmitter
- d) all impulses pass through the central horn
- e) pain sensation results from over-stimulation of other sensory modalities
e) pain sensation results from stimulation of specific nociceptors (generally naked nerve endings)
31 Which is NOT a part of the basal ganglia?
- a) caudate nucleus
- b) cuneate nucleus
- c) substantia nigra
- d) putamen
- e) globus pallidum
b) → the old cunt eater nucleus.
But seriously the answer is B.
Basal ganglia are the caudate nucleus, putamen, substantia nigra, globus pallidum, and subthalamic nucleus
Caudate nucleus + putamen = striatum
Globus palladus + putamen = lenticular nucleus
