Neuro Flashcards
when does neurulation beging?
week 3
the neural tube arises from which embryological layer?
ectoderm
First step of neurulation:
Starts around?
The [a] induces differentiation of the [b] along the midline.
This thickening forms the [c]
Day 17
[a] notochord
[b] ectoderm
[c] neural plate
Step 2 of neurulation:
when does it start?
the process of [a] causes a depression to form along the centre - the [b]
day 18
[a] differential mitosis
[b] neural groove
step three of neurulation:
the upper most cells of the neural groove (called what?) differentiate into what?
Neural crest cells:
form: PNS-DRG, Schwann cells, adrenal medulla, meninges, skull, dermis, V/VII/IX/X
NOT ASTROCYTES
when does the nueral tube form?
how?
the neural groove completeley closes around week 4 to form the neural tube.
otherwise neural tube defects
Requires FOLATE
failure of the spinal chord to close in the cephalic region =?
anencephaly
Failure of neural tube to close spinal region?
spina bifida
what are these three types of neural tube defects?
Monogenic causes of neural tube defects have a higher recurrance risk the polygenic.
a sibling of affected child has what chance of being affected?
1/4
when would the brain look like this?
week 4
when would the brain look like this?
week 6
when does eye formation begin?
when do basic brain structures aris?
when does myelination occur?
eye formation = week 3
basic brain structures = 3 months
myelination = 5 months
what are the red cells in this diagram?
what is their role?
Glia Cells
During development, stem cells divide and migrate outwards to various layers of the cortex
Stopped by the red cell – glia – at different levels
what develops into the forebrain?
prosencephalon
what does the diencephalon form?
3rd venrricle, thalamus, hypothalamus
what does the telencephalon form?
cerebral cortex, basal ganglia, lateral ventricles
[?] –> midbrain
[?] —> hindbrain?
mesencephalon –> midbrain
rhomencephalon —> hindbrain
myelencephalon —> [?] + [?]
myelencephalon —> medulla + 4th venrticle
metecephalon —> ?
pons + cerebellum
is micocephaly or macrocephaly more likely to be indicitive of underlying neurological disorder?
microcephaly
- stem cells have not sufficiently divided.
what does this V1 (black water) show?
Periventricular nodular heterotopia
bumpy ventricles
can be associated with epilepsy
how many ml of CSF is there?
around 120ml
what kind of hydocephalus would a tumour or haemorrhage be?
Obstructive (non communicating)
what kind of hydocephalus would increased CSF production be
non-obstructive (communicating)
function of CSF?
cushions brain, helps circulate metabolites (waste products)
what makes up the outer ear?
pinna
external acoustic meatus
tympanic membrane
what makes up the middle ear?
muscles
eustachian tube
ossicles
what makes up the inner ear?
Cochlear
Labyrthinth
Vestibular cochlear nerve
what is the function of the pinna?
Channel sound towards the meautus
Filters out lower frequencies
what is the external acoustic meautus made of?
1/3 cartilage, 2/3 bone
what does the tympanic membrane do?
vibrates in response to sound?
how does the middle ear amplify airborne sound vibrations?
Ratios - force amplifies the sound by amplifying the movement.
TM:Stapes = 14:1
malleolus handle: incus process (lever action) = 1.3:1
total amplification 200x amplification!
What are the muscles of the inner ear?
stapedius
tensor tympani.
what is the function of the muscles of the inner ear?
protect inner ear from acoustic trauma by dampening = involuntary contraction to prevent excess vibration
strapedieus stiffens ossicular chain.
what is the function of the eustachian tube?
equalises pressure.
why does the eustachean tube clog up when ill?
its is formed from respiratory epithelieum which is mucus secreting.
drains into nasopharynx
what are the ossicles?
coonnected by?
malleus
incus
stapes
connected by synovial joints
what is the function of the labrynth?
balance
Innervation of inner ear?
verstibularcochlear nerve.
what, in the ear, detects dynamic changes and what detect static changes?
semi-circular canals detect dynamic changes (affects eyes)
vestibule (utricleand saccule) detect static changes (endolymph and stereocilia)
explain the oculocephalic reflex
head rotates –> endolymph movement bends cupula + ampulla hair cell stereocillia in opposite direction –(CN8)–>medulla nuclei –> both eyes move in opp direction to head
=fixed gaze
cupula + ampula = semicircular canals
how many turns does the cochlea have?
2.5
how many compartments does the cochlea have?
3 compartments: scala vestibuli, scala media, and scala tympani
how many openings does the cochlea have?
2 openings: round window and oval window (andhelicotrema?)
what are the two ionic fluids of the cochlea?
endolymph (K+) and perilymph (Na+)
ionic gradients maintained by pumps
explain how pressure moves along the cochlea
scala vestibulli —> heliocotrema —> scala tympani —> round window
this moves the BASILAR MEMBRANE
how does the basilar membrane respond to different frequencies?
the outer end / base is stiff and narrow = high frequencies
inner end / apex is broad and floppy = low frequencies
tonotopt
what allows the cochlea to detect intensity/loudness of sound?
number of nerves responding and firing in cochlear
what is the organ of corti?
3 rows of outer hair cells
1 row of inner hair cells
movement of basilar membrane —> inner hair cells —[transducing cells]–>auditory nerve activation
what is responsible for fine tuning of sound?
the outer hair cells
- pull the tympanic membran down either side of the best nerve for that frequence/pitch
how does the brian localise sound?
the brainstem and coincidence detectors
-intraneural time difference
what are the steps of the auditory pathway?
ECOLIMA
what can cause hearing loss in the outer/middle ear?
conductive issues - no mechanical transmission to oval window
what can cause hearing loss in the inner ear?
sensorineural issues - cochlear not working
Neurons are specialised for [a]
Inputs via [b]
Action potentials propogate along the [c]
electrical signalling
dendrites
axons
there are two types of neuronal communications. explain how both work.
Chemical = majority; via neuro transmitters
Electrical = via direct flow of ions = breathing, hormone secretion
how can you tell which neuron is post synaptic and which is pre synaptic?
This is a chemical synapse.
* vesicles in the presynaptic axon
* mitochondira in presynaptic axon
* electron dense material in post synaptic dentrite (proteins)
outline how chemical synaptic transmission happens
- axon potential depolarises synaptic terminal membrane
- opening of voltage-gated calcium channels leads to calcium influx
- clacium influx triggers neurotransmitters
what kind of synapse is this? How can you tell?
this is an electrical synapse.
differs from structure of chemical synapse in that there are no synapse vesicles, and electron dense material can be seen on both sides.
NO SYNAPTIC CLEFT (ONLY CHEMICAL) - INSTEAD IT HAS GAP JUNCTIONS
what is neural plasticity and what does it allow for?
- changes in neuroal/synaptic structure and function in response to neural activity.
- allows for learning/memory
relevent to diseases like alzheimers - decreased spine density postmortem
neurons can differ from eacchother in 4 ways:
- size
- morpology
- neurotransmitter content
- electrical properties
what are Betz cells - describe their morphology
betz cells = upper motor neuron cells
large, long, pyramidal, excitory,
vulnerable in MND
describe the morphology of medium spiny neurons
striated, small, inhiibitory
vulnerable in huntingtons
what are glia cells?
non-neuronal cells (i.e. not nerves) of the brain and nervous system.
what are oligodendrocytes?
myelinating cells of CNS
unique to vertebrates
what does myelin do?
insulate axon segments, enabling rapid nerve conduction
metabolic support for axons
difference in myelination in CNS and PNS?
In the central nervous system (CNS), oligodendrocytes myelinate multiple axons; in the peripheral nervous system (PNS), Schwann cells (SCs) myelinate a single axon.
why does the myelin sheath appear white?
70% lipids
30% protein
what are the immune cells of the CNS?
Microglia
when would the microglia look like these different forms?
Ramified when body is “helathy” - exploring environment
Unramified when encounters pathogen - mobile and phagocytic
what cells in the CNS are responsible for pruning of spines, phagocytosis and immune surveillance?
microglia
x6 purposes
what type of cell is this? what is its purpose?
Astrocyte
- blood-brain barrier contribution
- structural: brain’s micro architecture
- envelop synampses = buffer excess K+, glutamate etc = homeostasis @ synapse
- metabolic support = glutamate-glutamine shuttle
- neurvasuclar coupling = changes in blood flow in repsonse to neural activity
- proliferate in disease = glyosis/astrocytosis
which cell in the CNS maintains homeostasis at the synapse?
astrocytes
- buffer excess K+/glutamate
what are the most numerous cells in the CNS?
astrocytes
which cells are the neural stem cells?
radial glia (specialised astrocyte)
which cells are iimportant for cerebellum structure?
bergmann glia
what do müller cells do?
scaffold for other cells in retina
MND spinal cord shows pathological changes in which cells?
Motor Neurons
Mircoglia
Astrocytes
MND sypotoms are su
MND symptoms are due to a loss of what cells?
Motor Neurons
Acute symptoms in MS refelct dysfunction of what cells?
Neurons
primary pathology due to oligodendrocytes
pathology of CNS lesions in MS involve what cells?
neurons, oligodendrocytes, T cells
what feauturs of the blood brain barrier make it more difficult to penetrate (4)?
why can this be an issue?
- endothelial tight junctions
- unfenestrated basement membrane
- astrocyte feet envelop
- pericytes = contractile
can be an issue for drug delivery - neuro drugs therefore need to me small and hydrophobic
how is CSF resorbed?
by the arachnoid granulations
what cells produce CSF?
ependymal cells:
- epethelial like
- ciliate = flow of CNS
- allows solute exchange between nervous tissue and CFS
what is the main site of CSF production?
Choroid plexus
-formed from modifies ependymal cells
- projections in ventricles
- highly vasuclarised
- gap junction for blood-CSF barrier
what are the three connective tissues of the skeletal muscle?
epimysium
perimusium
endomysium
what is the function of the basement membrane?
tensile strength, regeneration, development
How many nerves is each skeletal muscle fibre innervated by?
Each individual muscle fiber in a muscle is innervated by one, and only one, motor neuron (make sure you understand the difference between a muscle and a muscle fiber). A single motor neuron, however, can innervate many muscle fibers.
At the synapse, rapid transmissions of depolarises impulses is facilitated by what neurotransmitter?
Acetyl Choline - binds post synaptic AChR(eceptor)
what do muscle spindles do?
important to mediate stretch reflections and propioception (muscle position)
what do Golgi tendon organs measure?
tension
what are type 1 muscle fibres?
slow twitch - oxidative , fatigue resistant
long distance running muscles
what are type 2a muscle fibres?
Fast Twitch : intermediate types - glycolytic AND oxidative
power, lactic
what are type 2B muscle fibres?
fast twitch - glycolytic (white)
power, lactic
Do neurons innervate different types of fibres, or the same type of fibres?
same type.
what has happened here?
- Loss of innervation has caused a cell to atrophy
- Adjacent motor units are induced to sprout in order to re-innervate that muscle
- Motor unit therefore larger
- Fibres will shift its type to fit the adjacent neurons type
What is a sarcomere?
basic unit of contraction
-repeating arrangement of thick (myosin) and thin (actin) filaments
or intermediate filaments = cell type specific
what is linked to the actin that is important for calcium regulation?
troponin/tropomyosin complex
what is required for the myosin and actin to slide over eachother?
ATP
binding of ATP allows release and hydolysis of ADP which allows movement of myosin head (rowing) ADP released during power stroke
what initiates the sliding of the actin and myosin?
increase in intracellular caclium
calcium increase mediated by troponin and tropomyosin
ATP is the immediate source of energy for muscle fibres.
what can be used as a short term energy store?
Creatine Phosphate
what is creatine phosphare replenished by?
CK Creatine Kinase
CK is released on muscle fibre damage - clinical meausre
mitochondrial cytopathies general affect the [?] but not always
muscle - (some tissue affected some not - heteroplasmy)
which protein is essential for muscle cell membrane stability during contraction?
Dystrophin - inside the sarcolemma
if pathology = distrophy = many types, progressive
what are the two types of dystophin related dystrophy?
- Duchenne
- deletion: disruption in reading frame (almost no normal dystrophin produced)
- more severe - Becker’s
- in frame deletion (some normal dystrophin produced)
- less severe
Outline the steps of axonal neurotransmission
1.Neurotransmitters activate receptors on dendrites / soma
2. Receptors open ion channels
3. Ions cross plasma membrane, changing the membrane potential
4. The potential changes spread through the cell
5. If the potential changes felt at the axon hillock are positive (+mV), and large enough, an action potential is triggered (ie action potential must meet threshold to be “felt” at axon hillock)
What is the resting voltage inside a neuron?
What keeps it this way?
-70mV
maintined by semipermiable membrane: diffusion, electrostatic pressure and sodium-potassium pump
Large A-‘s stay inside - can’t leave
K+ want into the negative inside
Na+ also wants in (ellectrostatic and diffusion), but harder to cross membrane, and pump pushes back out
Cl- wants out the negative area, can move readily
What do excitory neurotransmitters do to the cell membrane?
Depolarise the cell membrane.
↳causes Excitory Post Synaptic Response
↳increases probibility of reaching action potential threshold
what two factors can work together to generate an action potential?
temporal and spatial summation
What do inhibitory neurtransmitters do to the cell membrane?
hyperpolarise the cell membrane
↳ Inhibitory Post Synaptic Potential (IPSP)
↳ decreases probablity of action potential being elicited
Label the steps of the Action Potential generation
Explain how the action potential is self perpetuating in axonal neurotransmission
voltage changes control ion channels
ion channels control voltage changes
how does myelin speed up propogation of action potentials?
Saltatory Conduction
- decremental (jumping)conduction between nodes of ranvier - boosted each time
- most CNS neurons
during which period can another cation potential not be generated?
during the Absolute refratory period
prvevent backwards flow of action potential
during which period can an action potential be generated if there is a stronger than normal stimulus?
relative refractory period
Outline Neuromuscular Transmission (Synaptic Neurotransmission, no axonal)
- Acetylcholine release
- Acetylcholine’s action
- Increasing endplate potential
- Reaching the threshold for endplate action potential
- Acetylcholine is destroyed
Nerve impulse or action potential
↓
Opening of voltage-gated calcium channels
↓
Influx of calcium ions inside the cell increases
↓
Opening/rupture of vesicle and release of acetylcholine
↓
Acetylcholine comes to the synaptic cleft
↓
Acetylcholine binds with nicotinic receptors to form the acetylcholine-receptor complex
↓
Opening of ligand-gated sodium channels
↓
Influx of sodium ions inside the cell increases
↓
Development of endplate potential
↓
Generate muscle action potential
↓
Muscle contraction takes place
Outline: “1. Acetylcholine release” stage of neuromuscluar transmission
- Acetylcholine release
- Action potential opens voltage gated calcium channels . Ca2+ enters and move the presynaptic vesicles containing ACh to the presynaptic membrane which bursts the vesicles open. ACh released and diffuses through membrane and enters synaptic cleft through exocitosis
Outline “2. Acetylcholine’s action” step in neuromuscular transmission
- Acteylcholine’s action
- at the synaptic cleft Ach interacts with nicotinic recpetors in the post synamptic membrane to form AchR complex which opens sodium channels. Na+ enters. this leads to 3.
Outline “3. Increasing end plate potential”
- Increasing end plate potential
– due to sodium ions entering
Outline “4. Reaching the threshold for endplayte action potential” of neuromuscular transmission
- Reaching the threshold for endplate potential
- small amount of Ach released from axon terminal, but not enough to reach the threshold required for muscle to develop action potential. more vesicles with more Ach arriving eventually produces an endplate postenial which results in an action potential in the muscle
Outline “5. Acetylcholine is destroyed” step of neuromusculatr transmission
- Acetylcholine is destroyed
– Acetylcholinesterase enzyme quickly destroys the acetylcholine released into the synaptic cleft. This stops the muscle fibre from being excited repeatedly and enables the muscle to relax.
Patients with Myasthenia Gravis have variable weakness.
How can administering Acetyl Cholinesterase inhibitors improve muscle function?
Myasthenia Gravis is an autoimmune desease which attack the Ach receptors. = Not enough receptors to meet threshold to activate excitation.
Inhibit the breakdown of Acetylcholine (with Acetyl Cholinesterase inhibitors) so you will have more ACh for the receptors that are left (?)
Name thee fast neurotransmitters
Acetylcholine (ACh) - Excitory in skeletal muscle, inhibitory in heart
Glutamate (GLU) - excitory
Gamma-aminobutyric acid (GABA) - inhibitory
short term effects
name three neuromodulators
Dopamine (DA)
Noradrenalin (NA) (norepenephrine)
Serotonin (5HT) (5-hydroxytryptamine)
slower timescale
How do local anaesthetics work?
procain and lignocaine
Na+ channels blockers
Blocks progress of action potential
particularly well absorbed through mucous membranes, so can act on muscle too.
what can affect Ach?
Cigarettes (nicotine - agonist)
Poison arrows (curare - antagonist)
Spider toxins (black widow - release)
Nerve gas (WW-I – blocks break-down)
What can affect Noradrenaline?
Transmitter in peripheral (heart) and central nervous systems
Antidepressant drugs
Stimulants
what can affect dopamine?
Important transmitter in basal ganglia
Antipsychotic drugs
Stimulants
Anti-Parkinson drugs
what can affect serotonin (5-HT)?
Diverging projections in the brain – innervating many structures
Antidepressant drugs
Hallucinogens
Ecstasy
Hallucinogenic drugs include LSD, Magic Mushrooms, Ketamine
They mimic serotonin, and can activate numerous different serotonin receptor subtypes
But the hallucinogenic effect itself appears to be specifically related to the way they target the serotonin ‘2a’ receptor (5-HT2a
What can affect GABA (Gamma-aminobutyric Acid)
Main inhibitory transmitter
Anti-anxiety drugs
Anticonvulsant drugs
Anaesthetics
what are the main excitory and inhibitory neurotransmitters?
Glutamate - excitory
GABA - inhibitory
Each Schwann cell is responsible for [how many] segment[s] of myelin
Each Schwann cell is responsible for one segment of myelin
In the CNS 1 oligodendroctye myelinates =
In the PNS, 1 Schwann cell myelinates =
In the CNS 1 oligodendroctye myelinates = multiple axons
In the PNS, 1 Schwann cell myelinates = one axon
1 Schwan cell to how many unmyelinated axons?
1 schwann cell to multiple unmyelinated axons
At the nodes on ranvier, there are lots of [?]
ion channels
myelination allows [?] conduction
myelination allows solitary conduction which means jumping conduction.
more rapid conduction
Peripheral neuropathies can occur in which 3 ways?
- damage to motor/sesory neurons
- damage to axons
- demyelination
what happens when you cut/damage and axon
Distal fragmentation of axon
- myelin breaks down into globules (phagocytose by Schwann cell)
Proximal axon will try to regenerate/sprout
-multiple small axons which will grow along the oclumns of proliferating schwann cells - 1 remains
-regenerated axons will remyelinate
why does a remyelinated axon (after damage) conduct more slowly than the original axon.
tend to have shorter and thinner myelin sheaths and
MS is a demyelinating disorder of CNS.
This is distinct from PNS.
In PNS demyelination tends to be [?] because one schwann cell myelinates one segment
segmental
difference in remyelination between axon cutting and myelination disorders?
axonal = shorter regenerated myelin sgements
demyelination = thinner regenerated myelin segments
both slow conduction
Each spinal nerve is formed by the combination of nerve fibers from the dorsal and ventral roots of the spinal cord.
The dorsal roots carry what axons, while the ventral roots carry what axons.
Dorsal = afferent sensory axons (affected by the world)
- plus a “copy” to the brain so it knows whats going on
Ventral = Efferent Motor axons (effect on the world)
Ventral roots are Anterior or Posterior?
Dorsal Roots are Anterior or Posterior?
Ventral = Anterior
Dorsal = Posterior