4H Flashcards
Describe the 4 major stages of formation of the neural tube.
1) transformation of the embryonic ectoderm into a thickened neural plate
2) lateral folding of the neural plate along the midline neural groove
3) apposition and fusion of the neural folds, and separation from the overlying ectoderm. Closure begins midway along the craniocaudal axis of the neural tube and extends in both directions
4) closure of the anterior and posterior neuropores, normally occurs during the 4th week.
Explain the importance of folate in the prevention of NTDs
folate is important for DNA and RNA synthesis as it donates carbons in metabolic reactions
NT formation is a period of rapid cell proliferation, therefore requiring a lot of DNA/RNA synthesis
Why can the SLR test elicit pain?
puts tension on the sciatic nerve, irritating the affected spinal nerves
Which spinal nerves are involved in the knee jerk reflex?
L3-L4
Which spinal nerves are involved in the ankle jerk reflex?
S1-S2
Which component of an IVD prolapses?
nucleus pulposus prolapses through the annulus fibrosis
why does a disc tend to prolapse posterolaterally?
the posterior longitudinal ligament attaches firmly to the posterior aspect of the IVD, so that the prolapse is forced to occur to the side of the midline
Which nerves contribute to the sciatic nerve?
L4, L5, S1, S2, S3
Where does the L4 spinal nerve exit from the vertebral canal?
at the intervertebral foramen between the pedicles of L4/L5 vertebrae
Which component of the nervous system is found at the level of L5/s1 IVD?
cauda equina
What is the lowest limit of CSF in the vertebral canal
found as far down as S2 vertebrae where the dural sac (and the lumbar cistern of CSF) terminates
Which nerves are responsible for the maintenance of anal tone and what are their root values?
left and right pudendaal nerves supply the muscle of the external anal sphincter (S2, S3 and S4)
Which nerves supply the detrusor muscle of the bladder? From which spinal nerves do they arise?
S2, S3, S4 = pelvic splanchnic nerves
T10-L2 = hypogastric nerves
30 year old male presents with sudden onset LBP after trying to lift a bag of cement. Pain is radiating to perineum, down the backs of both thighs and towards the calves. Complains that pain in his legs is worse than pain in his back.
Sensation of tingling down the back of the thigh and numbness around the buttocks, genitalia and anus.
Faecal incontinence and no urine passage since the injury (2 hours).
What is the most likely diagnosis?
central prolapse of an IVD
30 year old male presents with sudden onset LBP after trying to lift a bag of cement. Pain is radiating to perineum, down the backs of both thighs and towards the calves. Complains that pain in his legs is worse than pain in his back.
Sensation of tingling down the back of the thigh and numbness around the buttocks, genitalia and anus.
Faecal incontinence and no urine passage since the injury (2 hours).
Difficulty moving ankles and ankle jerk reflexes are diminshed, but knee jerk reflexes seem normal. SLR elicits pain and urinary retention is noticed.
On the basis of the motor signs, which nerve roots are most likely to have been affected?
sacral spinal nerve roots in general.
These roots supply muscles that flex and extend the ankle and these muscles seem weak.
The ankle jerk reflexes on both sides are weak.
anorectal and bladder dysfunction also suggest sacral nerve involvement as these organs are supplied by the sacral nerves
30 year old male presents with sudden onset LBP after trying to lift a bag of cement. Pain is radiating to perineum, down the backs of both thighs and towards the calves. Complains that pain in his legs is worse than pain in his back.
Sensation of tingling down the back of the thigh and numbness around the buttocks, genitalia and anus.
Faecal incontinence and no urine passage since the injury (2 hours).
Difficulty moving ankles and ankle jerk reflexes are diminshed, but knee jerk reflexes seem normal. SLR elicits pain and urinary retention is noticed.
On the basis of the sensory loss, which nerve roots are most likely to have been affected?
numbness on the back of the thigh and perineum are consistent with dysfunction of S2 and S4
What is a hernia?
a hernia occurs when part or all of a structure protrudes though the tissue in which it is normally contained.
what is the differential diagnosis of a groin lump?
inguinal hernia femoral hernia lymphadenopathy femoral aneurysm undescended testical lipoma
On your examination, how would you distinguish a femoral hernia from an inguinal hernia?
Inguinal hernia: neck of an inguinal hernia lies above and medial to the pubic tubercle, above inguinal ligament
Femoral hernia: lies below and lateral to pubic tubercle, below inguinal ligament
What does it mean if a hernia is reducible?
contents can be returned to the abdominal cavity when the patient lies down or when pressure is applied
List three complications of an irriducible hernia
obstruction - loop of bowel becomes oedematous
strangulation - blood supply of the piece of bowel becomes compromised
peritonitis - due to sepsis spreading from the compromised bowel
How do you distinguish between direct and indirect hernias on clinical examination?
if possible, reduce the hernia and press over the deep ring. ask the patient to cough. a protrusion medial to the deep ring suggests a direct hernia
Which artery can be used as a landmark for the deep inguinal ring?
femoral artery. Palpable midway between ASIS and pubic symphysis (midinguinal point)
What is the relationship of the femoral artery to the femoral nerve and vein?
femoral nerve lies lateral to the artery, vein lies medial to the artery
What is the position of the deep inguinal ring?
lies above the inguinal ligament midway between ASIS and the pubic tubercle
What is the position of the deep inguinal ring in relation to the femoral artery?
lies immediately lateral and 2cm superior to femoral artery
What structure passes through the deep inguinal ring in males that makes it easily identifiable?
spermatic cord
Name two structures in the inguinal canal that a surgeon would take particular care to avoid damaging
ilioinguinal nerve
spermatic cord
Name 4 structures that lie within the spermatic cord
ductus deferens pampiniform plexus testicular artery lymphatic vessels autonomic nerves
artery of the ductus deferens
genital branch of the genitofemoral nerve
A hernial sac lies medial to the inferior epigastric vessels. What kind of hernia is it?
direct hernia because it has passed directly through the posterior wall of the inguinal canal
What is the conjoint tendon and where does it lie in relation to the inguinal canal
conjoint tendon (inguinal falx) is the common aponeurosis of the transversus abdominis and internal oblique muscles. Lies in the posterior wall of the inguinal canal
Which muscle is the principal flexor of the hip?
psoas major
Which muscle are the principal flexors of the knee
biceps femoris, semitendinous and semimembranous muscles
What is motor neuron disease?
degenerative neurological disease
Which CNS component is affected in MND?
neurons in the motor cortex, cranial nerve nuclei and corticospinal tracts
clinical manifestations are primarily in skeletal muscles rather than smooth/cardiac
often no involvement of the extraocular muscles - very late feature of the disease
In which pathways from the motor cortex do most motor impulses descend?
lateral and anterior corticospinal tracts and the corticobulbar tracts
what is a motor unit?
a single lower motor neuron and all the muscle fibres it stimulates
What do fasciculations indicate?
lower motor neuron injury
Fasciculations are small involuntary contractions of a motor unit. Can only be seen if the muscle is relaxed
List the six muscles responsible for moving the eyeball and the nerve supply of each
1) superior rectus - CN III
2) inferior rectus - CN III
3) medial rectus - CN III
4) lateral rectus - CN VI
5) superior oblique - CN IV
6) inferior oblique - CN III
Which muscle moves the eyelid and what is its nerve supply
levator palpebrae superioris - CN III
What is a PEG tube?
percutaneous endoscopic gastrostomy tube
allows nutrient solution to be passed directly into the stomach alleviating the need to chew or swallow food
What is the innervation of the muscles of mastication?
mandibular branch of the trigeminal nerve
Which muscle is responsible for raising the eyebrows?
occipitofrontalis muscle
Which muscle is responsible for closing the eyes tightly?
orbicularis oculi
Which muscle is used with blowing out the cheek?
orbicularis oris (relies upon the pursing of the lips to create an airtight seal)
What are the sensory and autonomic functions of the facial nerve?
sensory - anterior 2/3 of the tongue (taste) = chorda tympani
autonomic - innervation of submandibular and sublingual salivary glands, lacrimal glands (saliva and tears)
Which CN innervates the parotid gland?
glossopharyngeal nerve
Which CN is responsible for shrugging of the shoulders?
CN XI - spinal accessory
What is amaurosis fugaux?
transient loss of vision in one eye
common painless symptom and implies transient retinal ischaemia
associated with emboli or stenosis of ipsilateral ICA
What is a transient ischaemic attack?
episode where there is a temporary loss of brain function due to vascular insufficiency
usually lasts about 30 minutes with a complete recovery within 24 hours
What symptoms are typical of a transient ischaemic attack in the anterior (internal carotid) circulation?
dysphasia
one-sided motor weakness in the upper and/or lower limb
hemisensory deficit
visual disturbance
What symptoms are typical of a transient ischaemic attack in the posterior (vertebral artery) circulation?
diplopia
ataxia
amnesia
vertigo
what is xanthelasma and what is its clinical significance?
adipose deposit at the eyelids
associated with hyperlipidaemia or hypercholesterolaemia
Describe the mechanism of action of aspirin
antiplatelet drug
inhibits thromboxane A2 in platelets and prostacyclin in endothelial cell walls
Describe the mechanism of action of statins
lipid modulating drugs
inhibit HMG-CoA reductase, an enzyme involved in cholesterol biosynthesis
results in decreased plasma cholesterol and increased LDL receptors
Describe the mechanism of action of thiazide diuretics
inhibit sodium reabsorption in the PCT, reducing water reabsorption and thereby BP
What arteries arise from the ICA at the cranial cavity?
anterior cerebral artery
middle cerebral artery
posterior communicating arteru
opthalmic artery
In neuroanatomy, what is meant by the term somatotopic localisation?
concept that certain regions of the nervous system mediate neurological function in certain parts of the body
61 year old man has two episodes:
1) vision in left eye went foggy for about two minutes
2) vision ‘went funny’ again and became weak down his right side (right hand and lower limb). Visual disturbance affected right side of field of vision in both eyes
What is the most likely diagnosis of the first episode?
amaurosis fugax - transient loss of vision in one eye
suggests ischaemia of left retina or left optic nerve
61 year old man has two episodes:
1) vision in left eye went foggy for about two minutes
2) vision ‘went funny’ again and became weak down his right side (right hand and lower limb). Visual disturbance affected right side of field of vision in both eyes
What is the most likely diagnosis of the second episode?
Ischaemia in the left internal capsule
ischaemia in the cerebral hemisphere.
visual and motor pathways both decussate, therefore the problem must be in the left hemisphere
the motor and visual pathways run close together in the region of the internal capsule
What will cause left hemiplegia (weakness of face, upper limb and lower limb)
infarction of the right internal capsule
what motor loss is associated with occlusion of the anterior cerebral artery?
lower limb region
what motor loss is associated with occlusion of the middle cerebral artery?
upper limb/head and neck
Which cells are responsible for myelin production?
CNS - oligodendrocytes
PNS - schwann cells
Give 3 ways in which a LMN differs from a sensory neuron
Motor neuron:
- all myelinated
- transmission from CNS to muscle fibres
- multipolar
- cell body in ventral grey horn
Sensory neuron:
- some myelinated
- transmission to CNS from surroundings
- unipolar
- cell body in DRG
patient’s right pupil constricts further when light is shone into left eye than when light is shone into right eye directly. what is the name of this phenomenon?
relative afferent pupillary defect (RAPD)
Describe the steps of a normal pupillary light reflex
Light shone into the eye activates retinal ganglion cells. This triggers an action potential in the optic nerve, which carries the impulse to the pretectal nucleus of the midbrain, where it synapses. The impulse is passed to the Edinger-Westphal (parasympathetic) nucleus of CN III.
Oculomotor parasympathetic nerve fibres synapse in the ciliary ganglion. ciliary ganglion. Ciliary ganglion neurons innervate the constrictor muscle of the iris, causing pupillary constriction
Name the ridges on the surface of the cerebellum
folia
Name the principal nucleus that lies within the cerebellar hemisphere
dentate nucleus
Name the bundles that connect the cerebellum to the midbrain, pons and medulla
midbrain - superior peduncle
pons - middle peduncle
medulla - inferior peduncle
Give 6 signs of cerebellar dysfunction
1) ataxia
2) dysdiadochokinesis
3) nystagmus
4) intention tremor
5) scanning speech
6) past pointing
7) hypotonia
Remember: DANISH Pastry D = dysdiadochokinesis A = ataxia N = nystagmus I = intention tremor S = scanning speech H = hypotonia P = past pointing
What are the clinical features of an UMN lesion?
hyperreflexia hypertonia (spastic paralysis) Clonus weakness (decreased power) positive babinski
Through which opening in the base of the skull is the spinal cord continuous with the brainstem?
foramen magnum
At what vertebral level does the spinal cord end?
L1/L2
Loss of vibration sensation below the level of the umbilicus indicates spinal cord compression at what level?
T10
spinocerebellar tract
ascending tract
conveys proprioceptive information from muscle and joint receptors to the cerebellum
How do you routinely measure systolic and diastolic BP using a stethoscope?
take arm measurements using a sphymomanometer. Place the inflatable cuff around the arm and inflate until pressure is greater than that expected. slowly deflate the cuff with the stethoscope over the brachial artery. systolic BP is when korotkoff sounds are first heard, diastolic is when the sounds become muffled
What do you do with BP results?
record them reading in the notes and arrange for two repeat measurements at separate times. Give lifestyle advice if required.
What is the calculation for determining MAP?
MAP = diastolic + 1/3(systolic-diastolic)
MAP is a time-weighted average of arterial BP over the whole of the cardiac cycle
How is BMI calculated?
BMI = weight (kg)/height (m)^2
What are the BMI categories?
<18.5kg/m2 = underweight 18.5-24.9 = healthy weight 25-29.9 = overweight >30 = obese
Explain the physiological mechanism by which postural hypotension occurs
whenba person stands up quickly, there is a sudden fall in venous return to the heart from veins of the lower limbs. This leads to a fall in stroke volume, cardiac output and therefore decreases BP
What are two specific areas of the brain associated with speech, and what language problems can result from damage to these areas?
Brocas area - coordinates speech production. damage gives expressive aphasia
Wernicke’s area - centre for comprehension of speech. Damage gives receptive aphasia
Both supplied by the middle cerebral artery. Usually found in the dominant hemisphere (left in most)
Patient with trouble comprehending spoken and written language, producing coherent speech, paralysis on right side in upper limb and face.
Blockage of which artery most likely explains these symptoms?
Left middle cerebral artery
Which artery supplies the region of the motor cortex that controls the lower limb?
anterior cerebral artery
How can AF lead to stroke?
AF is a complication of hypertension.
AF means blood is not pumped effectively through the atria and can clot, leading to an embolism, which can lodge in the brain
What could be the underlying problem in a patient who wakes up one morning with:
o Right-sided weakness (hemiparesis) affecting most of the body, but sparing the leg
o aphasia
a stroke (cerebrovascular accident) affecting the left middle cerebral artery
Supplies motor cortex as well as broca’s/wernicke’s areas
Movement in the leg was spared because the area of the motor cortex controlling the leg is supplied by
the anterior cerebral artery
Multiple sclerosis
Inflammatory disease affecting white matter; caused by discrete lesions affecting myelin that surrounds many CNS axons.
– seen as plaques in white matter of brain and spinal cord
pattern of symptoms/signs cannot be explained by one focal lesion
In MS, lesions occur in several different regions of CNS white matter
may have: o partial loss of vision o double vision (altered eye movements) o sensory changes (e.g. numbness) o motor symptoms (e.g. weakness, ataxia)
Alar plate
forms dorsal horn
Basal plate
forms ventral horn
Spina bifida
failure of closure of the neural tube
occulta
meningocoele
myelomeningocoele
What is the relationship between spinal nerves and the meninges
As spinal nerves and their roots pass laterally, they are surrounded by tubular sleeves of dura mater, which
merge with and become part of the epineurium
Blood Supply of the Spinal Cord
The vertebral arteries are the main source of blood to the spinal cord. Branches from the vertebral arteries directly supply the spinal cord itself:
1) one anterior spinal artery
2) two posterior spinal arteries
3) anterior and posterior radicular (segmental) arteries – small vessels which enter via the nerve roots. The largest anterior segmental medullary artery is the artery of Adamkiewicz. It arises from the inferior intercostal or upper lumbar arteries, and supplies the inferior 2/3 of the spinal cord.
Venous drainage of the Spinal Cord
three anterior and three posterior spinal veins.
valveless, and form an anastamosing network along the surface of the spinal cord. They also receive venous blood from the radicular veins.
In epidural space
Lidocaine mechanism
local anaesthetic
Block voltage-gated sodium channel
Sodium cannot enter the neuron and threshold is not reached, and impulses cannot be
transmitted
Propagation of the action potential
Generated in the axon hillock
When the sodium channels are opened, sodium ions rush in; once inside they cause nearby regions of the
neuron to become depolarized by moving laterally through the axon.
This, in turn, causes the opening of more voltage-gated sodium channels in those regions.
i.e. the currents flowing inwards at a point on the axon during anaction potentialspread out along the axon,
and depolarize the adjacent sections of its membrane
