Brain development & disorders Flashcards
What 3 layers does the embryo form after fertilisation?
Tri-laminar disc
- Ectoderm
- Mesoderm
- Endoderm
What happens to ectoderm shortly after formation?
- Ectoderm thickens to form the neural plate
- Neural plate undergoes differential mitosis to cause the formation of a mid-line groove (NEURAL GROOVE)
- The groove deepens and eventually detaches from the overlying ectoderm to form the NEURAL TUBE
- lateral to the neural plate lie presumptive neural crest cells which run dorsolaterally along the neural groove
What do neural crest cells develop to form?
where do they lie?
- presumptive neural crest cells which run dorsolaterally along the neural groove
- they develop to from a number of cell types including:
1. sensory dorsal root ganglia of the spinal cord and cranial nerves V, VII, IX, X
2. schawn cells
3. pigment cells
4. adrenal medulla
5. In the neck they form much of the bony skull, meninges and dermis
When does the neural tube close?
4th week
What occurs if the neural tube does not close?
- in spinal cord region
- in cephalic region
What can cause this?
- in spinal cord region causes spina bifida
- in cephalic region causes anencephalus (child often has a brain stem to control reflexes like breathing but does not have forebrain or cerebellum -usually still born or live hours/few days)
-Can be caused by fatty induction or environmental teratogens acting on neuroepithelial cells
(a teratogen is anything that may affect the development of a growing featus)
What is spina bifida?
- Failure of dorsal parts of vertebra to fuse
- 4th week
- usually covered by a patch of skin
What is meningiocele?
When the meninges of the spinal cord bulge between vertebrae without any nerve involvement
- Rare
- Symptoms include an abnormal tuft of hair, a birthmark, or protruding spinal cord tissue.
What is myelomeningeocele?
When the spinal cord protrudes through and causes an opening - therefore cells die
(type of spina bifida)
-Rare
-Symptoms include an abnormal tuft of hair, a birthmark, or protruding spinal cord tissue.
What is anencephalus?
When the cephalus tube does not close properly (4th week)
- this means the child does not have forebrain or cerebellum, often they are stillborn or only live a few hours
- four times more likely in females than males
What is cerebral spinal fluid and where can it be found in the body? What is its function?
- Clear liquid containing protein, urea, glucose and salts
- Can be found in ventricles and subarachnoid spaces
- For protection
How many ventricles are there? Name them
- There are 4 ventricles
- lateral (paired)
- III
- IV
What connects ventricles and subarachnoid space?
Cisterns
Where is csf produced? How much?
CSF is produced as a filtrate at the choroid plexus
- and absorbed via arachnid granulations (vilii of the arachnoid through the dura)
- around 120mls in entire csf
What is hydrocephalus?
- Abnormal accumulation of csf in the brain
- Can be communicating (non-obstructive) or non-communicating (obstructive)
- Often due to blocked cerebral aqueduct (connects III ventricle to IV)
- Can cause skull sutures to widen (up to 4 times normal size)
What is the prosencephalon and what develops from it?
- Fore brain
- telencephalon = develops into cerebral hermispheres
- diencephalon = thalamus and hypothalamus
What is the mesencephalon and what develops from it?
- Mid brain
- Colliculi
What is the rhombenphalon and what develops from it?
- Hind brain
- myelencephalon = medulla
- metencephalon = cerebellum and pons
What neural development occurs at 10w?
10 weeks - cerebral expansion and commissures
What neural development occurs at 3m?
3 months - basic structures are established
What neural development occurs at 5m?
5 months - CNS myelination begins (this continues until adolescence)
What neural development occurs at 7m?
7 months - lobed cerebrum formed
What neural development occurs at 9m?
9 months - gyri and sulci are formed
Describe the critical periods of rubella infection during pregnancy
a) 6th week
b) 9th week
c) 5-10th week
d) 2nd trimester
e) after 16 weeks
a) 6th week = eye melformations eg. cataract
b) 9th week = deafness = organ of corti
c) 5-10th week = cardiac malformations
d) 2nd trimester = CNA disorders
e) after 16 weeks = risk is reduced
What causes fetal alcohol syndrome and why?
-Name some possible consquences
- Mother drinking alcohol during pregnacy
- Alcohol crosses the placenta
- Fetal levels are higher
- Fetus doesn’t clear alcohol well
= can lead to; facial abnormalities irritability - exagerated responses motor and intellectual impairment MICROCEPHALY - (reduction in brain size) loss of cells, loss of fibres, disturbed migration
What does cocaine-abuse during pregnancy lead to?
- neonatal hypoxia
- abortion?
- reduced cognition
- reduced size/development
What is Neonatal Abstinence Syndrome?
- What problems may the baby develop due to drug abuse during pregnancy?
- What are the symptoms of withdrawal in infants?
Neonatal abstinence syndrome (NAS) is a term for a group of problems a baby experiences when withdrawing from exposure to narcotics.
- Poor intrauterine growth
- Premature birth
- Seizures
- Birth defects
Symptoms of withdrawal
=Tremors (trembling), Irritability (excessive crying), Sleep problems, High-pitched crying, Tight muscle tone, Hyperactive reflexes, Seizures, Yawning, stuffy nose, and sneezing, Poor feeding and suck, Vomiting, Diarrhea, Dehydration, Sweating, Fever or unstable temperature
How does myelination affect the speed of conduction? What is the average speed at - 1 to 6 months - 6 to 12 months - 12-24 months
Neonate peripheral nerve ~ 20 - 25m/s
1 – 6m 32 – 50m/s
6 – 12m 33 – 60m/s
12 – 24m 40 – 60m/s
When does a featus develop pain? Why is this important?
-Abortion?
somatosensory input (connections of receptors, sensory neurons, thalamus and cortex etc)
-@28 wks - innervation of dermal skin (subderal at 6-8weeks)
@8 weeks, DRG connection to spinal cord
@23 weeks reflex responses are found in preterm infants
@28 weeks facial response is found in preterm infants
recent imaging studies = 24 WEEKS (abortion limit is 24 weeks)
How are abortions carried out?
Under 22/24 weeks - surgical and medical (prostaglandins induce contractions)
-Over 22 weeks (servere cases)= KCl to heart = feticide rapid
Which sense are well developed at birth?
- Taste and smell
- Hearing (responsive, can locate sounds from 3 days)
- Vision (eyes are open and senistive from 7 months, vision is the LEAST developed at birth)
When does a fetus undergo motor development?
- Writhing from 28-32 weeks
- This increases till birth
Name some postnatal reflexes
- Mororeflex, this is when the baby is in a supine positive and head support is removed. Trunk extension is observed, goes on for 3+ months)
- Stepping - hold baby up with feet on surface, 6 weeks
- Palmar grasp - supports own weight, 3-4 months
- Swimming, 4-6 months (not all babies swim!)
- Babinski reflex, neonates fan toes when sole of foot is stroked, adults curl toes (descending motor tract damage = fan toes)
When do babies begin to reach?
- About 5 months
- Can attain objects around 8-9months
- By 2 years show adult motor patterns
When do babies begin to speak?
9-18 months = 1st word 18-24 months = 2 words 2-3.5 years = simple conversation, why stage (terrible threes) 3.5 - 8 = increase in complexity 8yr+ = adult
What are the main structures of the basal ganglia
Caudate nucleus
Putamen
Glocus pallidus
Substantia nigra, subthalamic nucelus (caudal)
What circuits is the basal ganglia involved in
- Motor (what to do, fine tuning)
- Limbic
- Oculomotor
Describe the affect of the basal ganglia (and DA) in PD and HD
- Huntingtons
- increased DA production (due to decreased GABA which inhibits DA and therefore increased movement)
- increased movements (overshotting)
- decreased muscle tone - Parkinson’s
- Decreased DA (less DA from substantia nigra)
- decreased movements
- increased muscle tone
Describe symptoms of PD and drug treatment
- Brady/akinesia
- smaller writing
- walking deterioration
- problems doing up buttons etc - Tremor
- resting
- maybe one side - Rigidity
- pain
- problems turning
Drug treatment
- increase DA
- electrical stimulation of subthalamic nucleus
Describe symptoms of HD and drug treatment
- Chorea (jerky movements) - limbic
- Dementia and personality change (prefrontal
- balance (cerebellum)
Autosomal dominant (increased CAG repeats = earlier onset)
drug treatment - dopamine receptor blockers
What are the main symptoms of depression
Sustained feelings of sadness interfering with ability to function at work, school or home
Characterized by:
– Loss of interest/ pleasure in doing things
– Decreased energy
– Feelings of guilt or low self-worth
– Disturbed sleep or appetite
– Poor concentration
What is the impact of depression of health?
– quality of life – employment – personal finances – activities of daily living Increased risk of mortality, CHD, stroke, colorectal cancer, back pain, irritable bowel syndrome and multiple sclerosis -more likely to be non-compliant
- If you have a physical illness:
e. g. hypertension, asthma, arthritis and rheumatism, back pain, diabetes, heart disease and chronic bronchitis – you are more likely to develop depression - two or more recent adverse life events:
you are six times more likely to experience mental illness compared to those with no physical illness
What neurological diseases have instantaneous onset?
“Electrical” events Epilepsies Myoclonic jerks Neuralgic pain Vascular events Subarachnoid haemorrhage Intracerebral haemorrhage
How can CNS and PNS affect movement?
- CNS Disorders affecting Movement
Brain
Brain Stem
Spinal Cord
2. PNS Disorders affecting Movement Root Peripheral Nerve NMJ Muscle
What are symptoms of UMN lesion?
Upper motor neuron:
No atrophy or fasciculations
Increased, spastic tone
Pyramidal pattern of weakness
Increased deep tendon reflexes
PNS - mononeuropathy (damage to a nerve outside of CNS)
Individual nerve deficits in isolation
Upper limb nerves mostly affected at compression points
Median nerve entrapment at the wrist most common ( Carpal Tunnel Syndrome)
Ulnar nerve at elbow common
Radial nerve in axilla common
Common peroneal nerve in leg most common
PNS - polyneuropathy (generation of nerves outside of CNS, spreads from PNS to CNS)
Sometimes just shortened to “neuropathy” Usually chronic and slowly progressive Usually starts in the legs and longer nerves Usually eventually becomes of a glove and stocking variety Can be asymmetrical Rarely can affect arms more than legs Occasionally can be acute or sub-acute (common causes, HIV, leprosy, diabetes)
Peripheral Nerve Disorders: Radiculopathy or Root Lesion
Damage to the nerve root
Usually within the exit foraminae of vertebra
Lumbar root lesions more common than cervical root lesions
Disc disease and degenerative disease of the lumbar and cervical spine most common
May be acute, sub-acute or chronic and painful
Signs are confined to the matching dermatome and myotome
Radiculopathy: Clinical Features
Pain
Loss or impaired sensation in specific dermatomes
Weakness and wasting in specific myotomes
Absent or reduced reflexes at appropriate levels
What are myopathies?
Myopathies are muscle disorders Most commonly have fixed weakness Most commonly weakness is in proximal muscles (neck,shoulder and pelvic girdles) Muscle weakness can be distal Rarely muscle weakness can be dynamic Rarely focal muscle weakness can occur
What are the symptoms of myopathies?
Stairs, chairs and hair
Wasting is common
Facial weakness occurs in some e.g. Facioscapulohumeral dystophy
Neck weakness can occur
Contractures can occur
Scoliosis is often a feature esp. in Duchenne
Eye movement disorders are rare
(common causes -Steroid myopathy Statin myopathy Metabolic and endocrine myopathies Myotonic dystrophy)
