What are the developmental milestones in development?
- By 3 weeks there is eye formation
- 10 weeks = cerebral expansion + commissures
- 3 months = basic structures established
- 5 months = myelination has begun
- 7 months = lobes cerebrum has formed
- 9 months = gyri + sulci formed
What are some critical periods in development?
- Abnormalities to CNS are dependent on time of infection
- 6th week = eye malformations occur, e.g. cataracts
- 9th week = deafness can occur, e.g. malformation of the organ of Corti
- 5th to 10th week = cardiac malformation occurs
- In general, CNS disorders occur in the 2nd trimester
- Risk of disorders falls after 16 weeks due to the fact that most of the structures of the CNS have developed by this time
How can increases in neural activity be detected by a lumbar puncture?
- Increases in neural activity results in the increase in the release of neurotransmitters + their associated breakdown products, this can be detected in the CSF by lumbar puncture
What do more neurally active regions require?
- More neurally active regions require more O2 + thus more blood, this is the basis of modern imaging techniques as they detect haemodynamic changes
What does an EEG give an indication of?
- EEG gives an indication of regional brain activity underlying electrodes
- Sensitive to activity in the temporal regions but less sensitive to those in the spatial regions
- EEG is good at detecting signs of epilepsy
What are the two types of muscle fibres?
- Slow twitch
- Fast twitch, 2a = glycolytic and oxidative (intermediate), 2b = glycolytic (white)
What is a motor unit?
- A motor unit is made up of a motor neuron + skeletal muscle fibres innervated by that motor neuron's axonal terminals
- Groups of motor units often work together to coordinate the contractions of a single muscle
- Loss of innervation causes fibre atrophy
What are mitochondrial cytopathies?
- Mitochondrial cytopathies = heterogenous group of multisystem disorders which preferentially affect the muscle + nervous systems
- They are either caused by mutations in the maternally inherited mitochondrial genome, or by nuclear DNA mutations
What are dystrophies?
- Dystrophies are genetically determined, destructive + mainly progressive disorders of muscle
- Many types, defects of proteins that confer stability to the sarcolemma are one group of causes
Membrane stain of dystrophin.
What are the 3 layers of the eye? What do they contain?
- Fibrous (outer) layer = cornea + sclera
- Vascular (middle) layer = iris, ciliary body and choroid
- Inner layer (retina)
What is the humour called in the anterior and posterior chamber? How about the rest of the eye?
- Anterior and posterior chamber = aqueous humour (thin, transparent fluid, 99.9% water)
- Rest of the eye = vitreous humour (clear gel)
What is the fibrous layer comprised of? What do these do?
- Made up of cornea + sclera
- Sclera = tough fibrous outer coat, made of collagen, 85% of layer
- Cornea = made of collagen, part of fibrous layer over pupil + iris so transparent
What is the vascular layer comprised of? What do these do?
- Vascular layer comprised of choroid, ciliary body (ciliary muscle + ciliary processes) and iris
- Iris = coloured part of the eye. Controls the size of the pupil through dilator and sphincter papillae muscles
- Ciliary body (ciliary muscle + ciliary processes) = controls size of lens and forms aqueous humour
- Choroid = connective tissue + blood vessels, blood supply to outer third of retina
When the ciliary muscles contract, what happens?
Ciliary muscle contracts, suspensory ligaments relax, this relaxes tension on lens + lens becomes more rounded
What do the sphincter papillae and dilator papillae do? What are these innervated by?
- Sphincter papillae = constricts the pupil = PARASYMPATHETIC (oculomotor CN)
- Dilator papillae = dilates the pupil = SYMPATHETIC
What is in the inner layer?
- Two parts: optic part (light sensitive) + nonvisual part (covers internal surface of ciliary body and iris)
- There are many layers to the retina
What are the layers of the retina? What is found within them?
- Pigmented layer
- Neural layer:
- Photoreceptors. RODS = function in dim light + are insensitive to colour. CONES = respond to bright light and sensitive to colour
- Bipolar cells
- Ganglion cells = synapse in the lateral geniculate body
What are the layers through which a photon must travel through the eye?
- Tear film (3 layers: anterior lipid, middle aqueous and posterior mucous)
- Cornea (transmission + refraction)
- Aqueous humour
- Vitreous humour
- Ganglion cell
- Amacrine cell
- Bipolar cell
- Horizontal cell
- Pigmented epithelium (absorption of excess photons)
What are the two main different cell types in the CNS?
- Glial cells (provide support + protection for neurons = glue)
What are some different types of glial cells?
Picture of a neuron.
What are neurons used for? Where do they mainly develop?
- Specialised for intercellular electrical signalling via synapses
- Dendrites receives inputs (dendritic spines), transmit to cell body (soma)
- Action potentials propagate along axon
- Mainly develop during brain development
Neurons communicate via synapses. What are the two types?
- Chemical (majority)
- Electrical (less abundant, enable synchronised electrical activity)
What are oligodendrocytes?
- Myelinating cells of the CNS
- Myelin insulates axon segments, allows rapid conduction
- Myelin sheath interrupted by nodes of Ranvier = saltatory conduction
How are oligodendrocytes different from Schwann cells?
- Schwann cells = PNS, oligodendrocytes = CNS
What are microglia?
- Resident immune cells of CNS
- Upon activation, become amoeboid + mobile
What are astrocytes? What are the 3 types?
- Most numerous cells in the CNS
- 3 types = radial glia, Bergmann glia + Müller cells
What are the two forms of astrocytes?
- Fibrous = white matter, contact blood vessels, pia + nodes of Ranvier
- Protoplasmic = grey matter, contact blood vessels + pia
What are the functions of astrocytes?
- Contribute to blood-brain barrier
- Structural - define brain micro-architecture
- Envelop synapses