302 – LECTURE 3
NEURORADIOLOGY
Intra-cranial Anatomy Imaging
• CT (computerized tomography) and MRI – non-invasive and painless
• CT → trauma while MRI is less effective due to fresh blood not so clear, difficulty getting the pt to stay still and acute needs of a trauma pt
• MRI → tumors, ms etc
• Ultrasound → pediatric only as babies have bone window at ant fontanelle
Sections
• Axial (horizontal or transverse)
• Sagittal (parallel to median plane)
• Coronal (frontal)
Note – CT is axial only while MRI all 3 planes
Meninges
• Dura
• Arachnoid
• Pia
• Spaces where blood, fluid or infection may track → extra-dural, sub-dural or subarachnoid bleeds
2. Extra-dural Hematoma
o aka epidural hematoma
o check for fracture
o middle meningeal art (high pres arterial)
o often caused by a punch in the space betw the eyes and ears where bone is thin
o lens shape (as dura has been ripped from skull)
o tx – drill thru bone to relieve pres and art may need to be clipped
2. Sub-dural Hematoma
o most common
o assoc swelling and contusion of underlying brain with midline shift
o veins between cerebral cortex and dural sinuses (where veins coalesce) – veins can become torn
o 2 types of pts generally – babies or older people (brains are too small for brain vault)
o sheer stress causes slow ooze from veins and gradual accumulation and ↑ pres
o radiologically – always parallel to vault
o tx – drainage – personality often returns
3. Sub-arachnoid Bleed
o sudden massive headache
o also consider party drugs, meningitis or just migraine
o due to berry aneurisms (can be present at birth so can be younger person but usu pt is older)
Ventricular System
• CSF produced in choroid plexus (a vascular proliferation or fringe of the tela choroidea in the 3rd, 4th and lateral ventricles → regulates to some degree intraventricular pres)
• Tela choroidea – portion of the pia mater that covers the roof of the 3rd and 4th ventricles or the medial wall of the lateral ventricle
• Lateral ventricles → 3rd Ventricle → 4th Ventricle
• 4th ventricle – 3 openings –
o median – cistern magna
o lateral – pontine cistern
o absorbed by arachnoid granulations
o many diseases are due to the overproduction (tumors), blockage (bleeding) or reabsorption (meningitis) of CSF
Hydrocephalus
• General term for pressure in ventricles
• Doesn’t indicate the cause of pressure – eg could be a tumor or meningitis etc
Cortical Contusions
• White fluffy patches of blood (fresh blood appears white while water appears black ie ventricles)
• Pinpricks of blood in brain
• Swollen and tight – no gyri/sulci apparent
• Tx – dexamethasone
• Shearing injury and concussion headache
Mass effect – effect of encroachment of a mass
Bulging optic disc – indicates ↑ in intra-cranial pres
BRAINSTEM AND SPINAL CORD
Brainstem Subdivisions
• Midbrain/pons/medulla
• Pars basilaris/tegmentum/roof plate
Pars Basilaris
• Corticospinal pway from motor cortex to the LMNs in spinal cord
• Corticobubar (corticonuclear) pway to the LMNs in the motor cranial nerve nuclei of brainstem
• Corticopontine pway
Tegmentum
• Cranial nerve nuclei
• Other nuclei and pways
• Reticular formation
Roof Plate
• Sup and inf colliculi
Spinal Cord
External Anatomy
• Extends from foramen magnum to lower border L1 (L3 at birth)
• Cervical and lumbar enlargements
• Conus Medullaris
• Segmental arrangement – 31 pairs of spinal nerves incl 8C, 12T, 5L, 5S, 1Co
• Dorsal and ventral roots formed from a series of rootlets
• Cauda equine
• Rship to meninges – pia (filum terminale to co1), arachnoid and dura to S2, denticulate ligaments, subaranoid space extends to lower S2
Internal Anatomy
• Gray v white matter
Organisation of fiber connections
1. Dorsal Root Afferents
• Neurons or dorsal root ganglia convey sensory (afferent) input to spinal cord
• Pseudounipolar neurons – central processes enter (via dorsal root) dorsolateral region of spinal cord – segregated into medial and lateral bundle
• Medial bundle – thick myelinated (fast conduction) conveying discrim touch and pres and propprioception (from encapsulated receptors such as golgi tendon organs, muscle spindles, meissner corpuscles, pacinian corpuscles etc) – divide into short asc and desc collaterals terminating in
Dorsal gray horn (nucleus proprius)
Intermediate gray zone (dorsal nucleus of Clarke)
Ventral gray horn (myotatic reflex)
• A portion (25%) of the medial bundle – gives long asc primary branches which pass in the dorsal faniculus to the cuneate and gracile nuclei of the medulla and form the spinal part of the central pway of discriminative sensation
• Lateral Bundle – finely myelinated and unmyelinated (slow conduction) conveying pain and temp from non-encapsulated receptors ie free nerve endings – through the dorsolateral tract of lissauer and bifurcate into short asc and desc branches terminating in the substantia gelatinosa (above nucleus proprius)
2. Ventral root afferents
• Axons of 3 types of motorneurons enter the ventral roots
Alpha motor neurons (LMNs) – extrafusal fibers of striate mus
Gamma motor neurons – intrafusal fibers of mus spindles
Intermediolateral motor neurons (visceral) of the autonomic ganglia feeding smooth mus
3. Intrinsic spinal connections
• Ipsilateral and contralateral interconnections exist within the same spinal segment (via intrasegmental interneurons) and with other spinal segments (via intersegmental neurons)
• These intrinsic fibers form the fasciculi proprii (propriospinal or spinospinal tracts) immed adjacent to the spinal gray matter
4. Projections to the brain
• Lateral spinothalmic tract X – from dorsal horn and intermediate gray zone (pain and temp)
• Ventral spinothalamic tract X – from nucleus proprius (light touch)
• Ventral spinocerebellar tract X – from intermediate gray zone (unconscious proprioception)
• Dorsal spinocerebelllar tract – from dorsal nucleus of Clarke (unconscious proprioception)
5. Projections from the brain
• Lateral and anterior corticospinal tracts
• Rubrospinal tract
• Reticulspinal tract
• Vestibulespinal tract
• Note – all of these travel to LMNs either directly or indirectly (via interneurons)
Spinal Reflexes
• Stretch or myotatic reflex (monosynaptic)
• Withdrawal reflex (polysynaptic)
Optic Nerves
CN2 – Optic Nerve
Visual Acuity
• Test pt wearing spectacles if they normally use them
• Refractive errors can be corrected w a pinhole
• Measure visual acuity w snellen chart at 6m or reading chart at 12 inches
• Test each eye separately
• If visual acuity is severely reduced – check if pt can count 3 fingers at 1m, detect hand mvments or differentiate betw light and dark
Visual Fields
• Screening exam
• Test both eyes simultaneously
• Hold both hands out so your fingers are at edges of pts visual fields
• In random order, make small slow mvments of index finger on the R, L or both sides simultaneously in upper and lower quadrants
• Ask pt to point to moving finger
• If pt ignores a stimulus in area, move your hand towards the midline until the pt detects the finger movement
• This test assesses the temporal fields in each eye only but it will detect most homonymous hemianopias, bitemporal hemionopias and visual inattention
• If this test and the visual acuity test are normal (and pt does not have vis sx) – no further testing of visual is usu reqd
If there are vis sx, visual acuity is decr or screening tests of vis field abnormal –
• Check the visual fields in each eye using a 5mm white pin held midway betw you ant pt
• Ask pt to look at your eye, to keep the eye still and to cover the other eye
• Move the pin in along a series of arcs in the upper and lower quadrants on each side to a point about 18 inches in front of the pt
• Use a red pin for testing the visual fields if you suspect compression of the optic n or optic chiasm
• Move the stimulus from the blind area to areas of preserved vis
• Bec it is easier for the pt to detect appearance than disappearance of an object
• Map the size and shape of visual field defect
Optic Fundi (part of eye opposite pupil)
• Usu examined through an undilated pupil
• Darken the room
• Remove pts glasses
• Unless you have astigmatism, remove your glasses
• If possible examine the fundi while pt is sitting – you can stand or sit
• Ask pt to fix on a distant object straight ahead at eye level and avoid looking directly in ophthalmoscope
• To examine pts right eye – use your right eye and hold the oscope w your R hand and stand to the pts R
• Change the lens settings w your index finger
• When examining eye, place your free hand on pts head to help steady yourself, but don’t lean on pt
• Get the oscope as close as possible to your eye
• Keep oscope vertical and if you can, keep both eyes open
• Hold oscope 12-18 in from pt and line up the light beam so that you can see the red light reflex from the retina
• Approach pt keeping the light beam on the retina until your forehead touches your free hand (on the pts forehead) or the knuckle of your oscope hand touches the pts cheek
• Starting at 0 – adujust the lens selector unitl the retinal blood vessels are in focus
• Identify the optic disc by approaching the pt about 15 degr temporal to the central vis axis
• If optic disc is not in view, follow the blood vessels backwards until disc is seen
• Next – examine the retinal blood vessels and retina (esp macula) at post pole of eye (it helps to reduce light intensity of light when examining the macula
• Macula – located in centre of retina (temporal to optic n) – fovea at centre
CN3 – OCULOMOTOR
Examine pupils at rest and the papillary light reflexes – look for ptosis – check horizontal and vertical pursuit eye mvments
Prelim Obs
• Examine eyes while pt is sitting and looking straight ahead
• Note if eyes are unligned or ptosis (drooping of the eyelid eg horners syndr)
Pupils
• Examine pupils in moderate lighting
At rest
• First examine the pupils while pt looks straight ahead and fixing on distant object
• Note size, shape and symmetry of pupils
Light reflexes
• Bright narrow light beam (pupil torch)
• Ask pt to fix on distant object (near fixation produces constriction)
• Check the direct response and response of the other pupil (consensual or indirect response)
• Both pupils should react to the light in each eye w equal speed and to same degree
Convergence and Accom
• If light reflex works, so will the near reflex
• If either pupil does not react normally to light, check the near reflexes
• Get the pt to converge by looking at your finger held close to the tip of the pts nose
Eye Mvments
• Ask pt to fix on an object (eg your fingertip) held at least 18 inches in front of pt
• Don’t get the pt to follow an object held much closer, bec it will make the eyes converge
• Move your finger from side to side ina a horizontal arc and then upwards and downwards in the midline
• Ask the pt to follow your finger w their head stationary
• Hold the eyelids up when examining downward gaze
• Ask the pt to report diplopia (double vision)
• Note – if one eye lags behind the other, incomplete range of eye mvements and nystagmus (involve usu rapid mvment of eyeballs (eg side to side) occurring normally w dizziness after body rotation or abnormally following head injury or as a sx of dis)
• If pts reports dipolpia but eye mvments appear to be full, further tests such as the cover test or red glass test will be reqd
CN5 Trigeminal
Test light touch in all three divisions on both side of the face and the corneal reflexes
1. Facial Sensation
• 3 divisions
• Both light touch and pinprick sensation
2. Corneal Reflex
• Earliest sign or CNV lesion may be absent corneal reflex
• Hold lower eyelid down and ask pt to look up and to the opposite side
• Gently stroke lower cornea w a wisp of cotton wool or tis paper
• Do not move the stimulus in front of the pupil and do not touch the eyelashes because these will induce a blink
• Do not stimulate sclera – it is less sensitive than the cornea
3. Muscles of Mastication
• Look for wasting in the temporal fossa
• Ask pt to open mouth widely – normally the jaw opens at the midline
o If there is is unilateral weakness, the jaw deviates towards the side of the weak muscles
o If there is bilateral weakness, the jaw opens in the midline, but the pt may not be able to maintain jaw opening against resistance
• Palpate the masseters while the jaw is clenched
4. Jaw Jerk
• Don’t check the jaw jerk routinely, but may be useful sign
• Eg an absent jaw jerk in pt w UMN signs in arms and legs suggests the lesion is in the cervical spinal cord rather than above the level of the pons
• Ask the pt to let the lower jaw hang open about one inch in a relaxed position
• Place index finger below the lower lip
• Gently tap your finger in a downward direction
• If jaw jerk is present, there is a brisk closure of the jaw
• May be present in normal persons
CN7 – Facial Nerve
Ask pt to smile and wrinkle forehead
Facial Mvment
• Note symmetry, fasciculations and abnormal mvments at rest
• Observe mvment of face while smiling and talking spontaneously
• Observe facial mvment while pt grimaces, tightly closes eyes and wrinkles forehead to command
• Test the strength of facial muscles by asking pt to keep eyes closed or lips sealed as you try to separate them with your fingers
Taste
• Not usu necessary but may help disting betw UMN and LMN weakness
CN8 – Vestibulocochlear Nerve
Test hearing to whispered voice in each ear
Hearing
• Test in quiet room w pt eyes closed
• Ask pt to repeat numbers whispered from a distance of arms length
• Gradually lower voice until whisper inaudible
• Mask hearing in the opposite ear by rubbing your thumb and index finger together near the other ear
Otoscopy
• If hearing ↓ check ear canal and ear drum
Tuning Fork Tests
• If hearing ↓ determine if hearing loss is sensorineural or conductive by using a 258Hz tuning fork – may not be reliable if hearing loss if severe
o Rinne’s Test
Tympanic membrane and osicles act as an amplifier for sound
Normally the tuning fork is held better when held close to ear than when the base is applied to the mastoid process (air v bone conduction)
• If sensioneural hearing loss, air conduction is still better than bone conduction
• In conductive hearing loss, bone conduction is better than air conduction
o Webers test
Place base tuning fork in middle of pts forehead
Ask if heard better in one ear than the other or in the centre of the head
Normally heard equally in both ears
Unilateral sensoneural deafness is heard better by the normal ear
Unilateral conductive deafness – tuning fork held better in abnormal ear
Unhelpful test if there is bilateral deafness or if conductive and sensioneural hearing loss in same ear
Vestibular Function
• Not normally part of routine nervous sys exam but may be impt in assessing balance and gait
CN 9 and 10 – Glossopharyngeal and Hypoglossal
Examined together – note quality of pts voice, cough or inspiratory stridor, ask pt to swallow
Palate
• Observe soft palate at rest and during phonation (pt saying ah)
• If unilateral weakness – the paralysed side does not move and the midline of the palate is pulled toward the normal side
• If bilateral weakness, elevation of palate is symmetrically reduced
Sensation
• Gently touch the pharyngeal wall or post 1/3 of tongue w a wooden spatula
• Ask pt if it feels the same on R and L
• This should provoke contraction of pharynx w or w/o gagging
• Check each side
• In many normal people – pharyngeal contraction and gagging can not be elicited on either side but unilateral absence of gag reflex is always abnormal
Swallowing
• Ask pt to swallow saliva
• If this is normal ask pt to drink small sips of water
• Note if pt coughs or if voice sounds moist after swallowing
CN11 – Accessory Nerve
Observe SMC and trapezius at rest – note wasting, fasciculations or abnormal sustain contraction (dystonia or torticollis), observe and palpate the muscles during contraction
SMC
• Ask pt to turn head to one side then try to bring the head back to midline against resistance
• SMC helps turn the head to the opposite side
• Other neck muscles also having impt turning head role and the strength of head turning may be normal when there is wasting and weakness of SMC
• In pts w a unilateral cerebral hemisphere lesion causing a contralateral hemiparesis, head turning towards the hemiparetic side is weak (ie SMC ipsilateral to lesion is weak)
Trapezius
• Stand behind pt
• Ask pt to shrug shoulders
• Compare strength of both sides
CN12 – Hypoglossal Nerve
Examine the tongue at rest and then ask pt to protrude the tongue
• Observe tongue at rest in the floor of mouth – note wasting or fasciculations
• Ask pt to protrude tongue – if there is unilateral weakness, the tongue can not be protruded
• Deviation of tongue is difficult to assess if there unilateral facial weakness – to overcome this, hold the corner of mouth back in its normal position
• Strength in the tongue can also be tested by having the pt push it into each check against your finger
• To test rapid alternating mvments, ask pt to protrude tongue and then move it rapidly from side to side or repeat lalala rapidly
LIMBIC SYSTEM AND MONOAMINERGIC PATHWAYS
Objective
• To outline the overall org and chemical anatomy of the major regions and connections of the brain which are involved w emotions and beh (the limbic sys)
• Limbic Sys – limbic lobe, prefrontal lobe and monoaminergic pathways
Refer to Diagrams in Lecture Handout
Limbic Lobe
• Lies on medial side of the brain and forms a boundary (limbus) betw cerebral cortex and thalamus
• Original limbic lobe – consists of cingulate gyrus, parahippocampal gyrus, hippocampus and amygdala – ring of cortex
• Limbic lobe – major role in emotions and the circuit (Papez’s Circuit) linking the limbic lobe and hypothalamus/thalamus also has a major role in emotion – stream of feeling
• Limbic = emotion, behaviour, mood control
Papez’s Circuit – 5 Neuron Pway
• 1. Cingulate gyrus → 2. parahippocampal gyrus → 3. hippocampus (4. fornix) → hypothalamus (5. mamillary body) → thalamus → cingulate gyrus → ….
• The link between emotion (limbic sys) and hypothalamus (control of Autonomic functions) thus effects of stress affect the hypothalamus and pituitary gland and hormonal control
Stedmans – Papez Circuit
• A long circuitous conduction chain in the mammalian forebrain, leading from the hippocampus by way of the fornix to the mammillary body and thence returning to the hippocampus by way of the anterior thalamic nuclei, cingulate gyrus and parahippocampal gyrus
Plate 106A
Definitions
• Limbic Lobe – originally defined by Broca – the nearly closed ring of brain structures surrounding the hilus or margin of the cerebral hemisphere – composed of fornicate gyrus (cingulate gyrus and parahippocampal gyrus), hippocampus and amygdala
• Limbic System – collective term denoting a heterogeneous array of brain structures at or near the edge (limbus) of the medial wall of the cerebral hemisphere – in partic the hippocampus, amygdala ad fornicate gyrus – the term is often used to include the interconnections of these structures as well as their connections with the septal area, the hippocampus and a medial zone of mesencephalic tegmentum – by way of the later connections, the limbic sysexerts inpt influene on the endocrine and autonomic motor sys’s – its functions also appear to affect motivational and mood states
Prefrontal Lobe
• Def – prefrontal lobe consists of the region of the frontal lobe ant to the motor cortex
• Together with the limbic lobe, the prefrontal lobe also plays a major role in emo, mot and beh, state of mind, personality etc
Input to prefrontal lobe – Afferent connections from –
• All secondary sensory cortices (multisensory)
• Limbic cortex
• ANS
Output from prefrontal lobe – efferent connections to –
• Secondary sensory cortex areas
• Limbic lobe
• ANS
• Basal Ganglia
• Basal ganglia incorporate our emos/beh into mvment → mood and mvment
• Diseases of the basal ganglia therefore result in d/os of mood and mvment
• Prefrontal lobe and basal ganglia should therefore be included in the extended LIMBIC SYS
Monoaminergic Pways
Three Monoaminergic Systems – Dopamine, Serotonin and Nor-Adr
• Modulate the activity of the limbic lobe, prefrontal lobe and basal ganglia (extended limbic sys)
• Play a major role in the control and expression of emo, beh, motiv, state of mind etc
• Many of the drugs which are used in the tx of mood and emoal d/os act via the receptors for DA, 5HT and nor-adr
Monoamine (monamine) – containing only one amine grp
Organisation of monoaminergic pways – Refer to lecture diagrams
1. Dopamine System
• Dopamine cell grps (A8,A9 and A10) are found mainly in the midbrain (substantia nigra)
• Major projections to the striatum (basal ganglia), prefrontal lobe, limbic lobe and hypothalamus
2. Serotonin System
• Similar to dopamine sys but wider
• Serotonin cell grps are found in the midline nuclei (raphe nucle) of brainstem (midbrain, pons, medulla)
• Major projections to striatum (basal ganglia) prefrontal lobe, limbic lobe, hypothalamus AND cerebellum, spinal cord
3. Nor-adr System
• Nor-adrenergic cells found mainly in the locus coeruleus of the pons
• Highly branched projections to almost all regions of the brain and spinal cord
• Synaptic and non-synaptic (neuromodulatory) modes of transmission
• These cells send diffuse projections ie 2 branches from the same axon to completely different locations eg one branch to cingulate gyrus and another branch to the spinal cord!
Synaptic Transmission
• Fast transmission – Glutamate, GABA, Acetyl Choline
o One neuron – one axon – release of synaptic vesicles into synapse with one receptor
• Cf – Monoamine Branching axons
o Modulate other n cells – sets excitability of fast conduction neurons – either excitatory or inhibitory
o They affect n cells bec they are diffuse in ECF (hundreds of cells sit in ECF)
o Current thinking – monoamines secrete nor-adr, DA and Serotonin into ECF surrounding adjacent dendrites
o Monoamine – slow neurotransmission (neurohumeral)
• Two types of neurotransmission – synaptic and non-synaptic (neuromodulatory transmission)
• Mood controlling drugs – slow neurotransmission via diffusion
• GABAa Receptor – 5 subunits
o Cl- channel in the middle (crossing cell membr)
o These 5 subunits are from a possible 19 diff subunits
o Hence need to know the config of subunits to know the function of receptors
o Hence when talking about receptors for drugs → GABA can be excitatory at one site but inhibitory at another!
