bms 236-Developmental Neuro Flashcards
Do reptilian brains have a cerebellum? Prefrontal cortex? Nerves sorted into special sensory modules e.g. vision?
Yes- cerebellum
Yes- sensory modules
Mammalian brains now have a limbic system, this includes..?
Thalamus: integrates sensory information and allow them to be used together. tells signals where to go.
Hypothalamus: regulate the endocrine system and body temp etc.
Hippocampus &amygdala- crude memory
Changes in the human brain?
Larger cortex, e.g. prefrontal cortex allowing for higher level thinking.
Development of the Neocortex
Name where the 4 lobes are? And what for?
Frontal-personality (at front)
Temporal- Deep inside e.g. Hippocampus (side near temples)
Parietal- mathematical (large in einstein- parents must have been so proud)(at top near back (where parents would tap you on the head))
Occipital- visual (opticians) (back of head)
Difference between Brocas area and Wernicke’s?
Brocas- speech making (e.g think of the girl who couldnt speak- brocas aphasia)
Wernicke- grammatical rules (e.g. the man who made no sense)
Brain has plasticity throughout life, what is one area this is very evident in?
Hippocampus- making new memories
What do single celled organisms share with our current nervous system?
Receptive and responsive to environment.
Spontaneous
Light sensitive eyespot
They then respond to this by moving using flagella.
What comes with becoming multicellular?
Specificity
In a sea sponge flow rate of water is regulated by specialised muscle like ….. which respond to stretch receptors.
myocytes
The first neurons probably developed from ……. cells in the ectoderm. These then migrated …
sensorimotor
downwards
Gene expression in a cell is governed by which two things?
Intrinsic factors e.g transcription factors
Extrinsic factors e.g morphogens
How does the neurogenic region arise?
It starts as ectoderm but bmp signalling is inhibited in certain cells and these become neural. This bmp inhibitor is either Chordin or Noggin, and is expressed by the organiser/node on the dorsal side.
The developing blastula secretes bmp which induces ectoderm cells to become epidermal skin cells.
What is the invertebrate homologue of chordin and Bmp?
Chordin: sog
Bmp: dpp
These are on the opposite side, so whereas Chordin is expressed Dorsaly, sog is ventral
What is the spermanns organiser?
Region of mesoderm that induces formation of the neural plate from endoderm. Under the influlence of transcription factors such as Gse the organiser expresses BMP inhibitors
The primary motor cortex projects via the …… tract to the …. The middle level is the ….
Corticospinal tract
Spinal cord
brainstem
what does the primary motor cortex do?
It regulates motor tracts originating in the brain stem
What does the brainstem do in motor control?
It regulates movements, and controls distal limbs (as well as autonomic system)
What does the spinal cord do in motor control?
Reflexes, either monosynaptic or poly, and automated motor movements such as walking
Fun fact: Why can’t babies walk early on?
Their corticospinal tract isn’t fully myelinated.
Hierarchical arrangement of the motor system?
Primary motor cortex to brainstem is via Upper motor
neurons, and brainstem to spinal cord is via Lower motor neurons.
Artificially stimulating the PMC only causes jerks so what two other systems are involved? Where do these project to?
Cerebellum: Mostly PMC (via thalamus), but also directly to brainstem,
Basal Ganglia: PMC (UMNs)
What does the basal ganglia and cerebellum do in terms of motor control?
Receives info from many different areas, projects to the PMC via thalamus. Monitors the commands going down to ensure appropriate for the environment. If not appropriate, send correction signals to motor cortex. Basal ganglia terminates excess movements.
How was the motor cortex found?
1870- electrical stimulus to different areas caused movements on opposite sides of the body.
Where is the motor cortex?
Brodmanns area 4, located in the frontal lobe just before the central sulcus. It is topologically arranged (think man with big hands and lips)
what do Upper motor neurons do?
From cerebral cortex or brainstem. Project to the lower motor neurons via interneurons, for planning, initiating and directing movements
What are the two upper motor neuron pathways?
Direct: UMNs axons from the cerebral cortex Input to LMN
Indirect: UMNs axons from brainstem input to LMNs. Inputs from cerebellum and basal ganglia also join to these.
summary: UMN- Interneurons- LMNS- muscle
:)
change in the muscle tension is detected by?
Golgi tendon organ
Change in muscle length Is detected by?
Spindle
How is tension created within the muscle?
Alpha motor neurons cause the Extrafusal muscles to contract. (if someone is extra they may cause tension within a group)
What do intrafusal skeletal muscles do?
proprioceptors that detect the amount and rate of change of a muscle length. Examples are Ia, II, I or Y.
Which fibres are afferents of the intrafusal and which are efferents? Difference in structure? Function?
Afferents: Ia, II, I
Efferents: Y (gamma)
Afferents, wrap around. These give sensory info to CNS as these coils are pulled apart.
Efferents just join to the fibres from the CNS. Gather in the slack to keep tension (make extrafusal muscles contract os spindle shortens)
Ia vs II intrafusal structure? Function?
Ia- largest neuron in body- wrap around the fibres. This relays info as stretches (as coils get further apart)
II- Flower spray ending on fibres. Relays info on final amount of stretch.
Intrafusal vs extrafusal placement around the fibre?
Intrafusal are within the spindle, whereas extrafusal outside.
What is the impact of serotonin and noradrenaline on proprioception?
serotonin increases the AP firing of gamma motor neurons, better at transmitting stretch as more taut
NA decreases.
What is the tendon jerk reflex?
Hit knee- Stretch muscle- Ia intrafusal muscles are fired-causes muscle to stretch and jerk (extrafusal). This happens as is monosynaptic.
Which experiment proved that Sperry’s theory was right over Weiss’s?
If cut optic nerve and remove temoral retina (these axons grow from same place but different target) do the growing optic nerves grow straight to the right target or do they take over temoral retina target then prune back? Straight to correct target.
Also, cut and move chick embryo axon and regrows back to same target.
Sperrys theory vs Weiss?
Sperry: Computational model: Axon outgrowth is specific to the target,
Weiss: Resonance Theory: Axon growth is to everywhere then pruned back.
What is the Labelled pathway hypothesis?
If ablate a target or axon cue, the axon stalls. Early axons (pioneers) make axon scaffolds for later axons to follow.
E.g. subplate neurons project from cortex to thalamus then lateral geniculate nucleus neurons follow. And if ablate subplate early LGN don’t develop here.
Experiment to evidence cues?
Grasshopper if ablate CX1 cue in limb bud, Ti 1 doesn’t cross the limb bud, path changed.
In the limb bud of the grasshopper what guides the Ti 1 axons?
Semaforins, and CX1 cue to cross the limb bud (Semaforins along) also Sema 2 secreted signal.
What is the arrangement of an axon growth cone?
Central part made of microtubules. Then the growing and retreating filopodium is made out of actin in bundles. The following llamellae is crosslinked f actin.
How does the growth cone explore the environment and move?
Actin treadmilling constantly is happening. This is the continuous movement of actin polymerising and breaking down. If the growth cone is attracted to a signal, this treadmilling is slowed, yet the same f Actin subunits are added, so the filapodium grows.
How do growth cones affect the actin treadmilling?
The growth cone receptors sense the growth cue, and a molecule clutch is engaged in the filapodium. This causes the slowing of actin treadmilling.
In addition; an actin myosin tubulin link pulls in the MT central unit into the extending filapodium causing further growth.
what if a filapodium interacts with a repulsion (non- permissive) contact?
The filapodium collapse but leave behind a conection (remembering)
What are semaphorins?
Inhibitory cues. membrane bound or secreted.
What are permissive cues? (contact attractants)
A permissive media is a media that an axon can adhere to and can follow the path of as it is easier to grow on. Blocking this doesn’t change the direction just slows. e.g. optic nerve follows laminin. (only in certain concentration therefore not instructive)
Adhesion growth relationship not simple.
Example of non-permissive cues?
Semaphorin at limb boundary ensure don’t go into until CX1. e.g. K/o Sema3a don’t reach target, or Sema1 antibodes block, cross limb bud too early.
What are Ephrins?
non-permissive. Cause repulsion between cells. Detected by Ephs, they line the rhombomeres so enable compartmentation. Later also keep axons out of certain areas, and also create topographical maps.
Example of Chemoattraction in axons?
Commisural sensory relay neurons are attracted to nectin in the floorplate (also SHH). (bees pick up nectar from the floor next to hedgehogs)
If dissect out and purify can find nectin.
Example of Chemorepulsion in axons?
Roofplate secretes BMP repels from Commisural sensory relay neurons from the roof. e.g. BMP7
Summarise examples of the 4 cues?
Chemoattractants: Nectrin in floorplate and SHH
Chemorepulsions: Semaphorins, Ephrins
Contact attractants: Permissive e.g. laminin optic nerve
Contract repulsions: BMP in roofplate. (CSRN)
How can tell than Nectrin doesn’t work alone?
Experiment:
Some CSRN axons reach floorplate without Nectrin.
K/o of either SMO (receptor for SHH), or Nectrin
How do you create a K/o by cre- recombinase?
Bacteriophage P1 can insert specific DNA sequences in a host genome. These sites are a specific 34 base sequence called LoxP. Two of these can be placed either side of the target gene. Cre Recombinase can bind and cut the host DNA and join to another cut LoxP site.
How can you create tissue specific recombination?
cross Cre- recombination mouse (under tissue specific promoter: Wnt 1 for Cre) and a mouse with floxed (LoxP either side of target gene) gene in germ line in all tissues.
Result: in all tissue bar target, floxed genes but no cre, in target tissue, target gene been spliced out and cre expressed.
What is an example of axons reprogramming their response to cues?
CSRN- after crossing the midline lose responsiveness to nectin.
Experiment: Put an ectopic floor plate (Nectin) after crossed the midline and the axon does not respond to it, but sees it as inhibitory. WHY DOESN’T STAY IN THE MIDLINE.
Why after crossing the midline do CSRN see the floorplate as inhibitory?
Semaphorins and Slits (inhibitory proteins) in floorplate and ventral SC guide axons. After cross the midline levels of the receptor for Slits increases so see it as inhibitory.
What is the receptor for inhibitory Slit?
Robo- Roundabout (because K/O of keeps going round in midline- no inhibition by Slit)
Robo levels are high in axons that …..
do not cross the midline.
What prevents Robo reaching the cell surface?
Comm- Commisureless (because K/O doesn’t cross the midline and commissure) so doesn’t reach Slit inhibition.
Vertebrate homologue Robo1 expressed before and after crossing and doesn’t commissure.
Rig1 expressed before crossing, block Robo1 until after crossed (K/O Rig1 doesn’t reach floorplate)
Comm expression in axons?
Expressed before crossing the midline, after cross switched off (so more robo, so respond to inhibitory slits)
How can follower axons follow an axon scaffold?
Cell adhesion molecules (CAMs) e.g. Fas II (can cause aggregation)
Fas II K/o?
Overexpression?
In flies, defasculated axons not in fascicles.
Overexpression: ‘bypass’ phenotype, fail to defasculate from scaffold so miss target.
Rods are active( depolarise) in …. light, whereas cones are active in ….. light
whereas in the opposite they hyperpolarise.
Rods active in dim
Cones active in bright (cones bright orange colour)
After the photoreceptor depolarises, what’s next in the trasduction?
Bipolar cells
- On bipolar cells are on in the light
- Off bipolar cells are off in the light
e. g. in rods depolarisation (active in dim light) inhibits on biplolar cells, activate off.
e. g. in cones depolarisation (bright light) depolarises on bipolar cells
How does the transduction from light to releasing glutamate (or not) happen in rods?
Normally the sodium channels are open, causing depolarisation which releases glutamate.
Rhodopsin light-transducin GDP to GTP, activates PDE.
This converts cGMP to GMP which closes the sodium channels, hyperpolarising so not releasing gluatmate.
What dictates that the off bipolar cells …… with glutamate, and on …… with glutamate?
off depolarise with glutamate as they have excitatory ionotophic receptors
on hyperpolarise with glutamate as they have inhibitory metabotrophic receptors
The bipolar cells inhibit ….. cells
ganglion cells
and amacrine cells
What is a receptive field?
an area in the retina which when illuminated activates a visual neuron.
can have on and off centre receptive fields what does this mean?
On centre receptive field more AP’s fires when lit in the middle, but not when the surround is lit. When all is lit together these contradict, and no more AP’s are fired.
why when the surround and the centre are lit do they contradict?
Because of the horizontal cells feeding back.
And many photopreceptors converge onto one bipolar cell, so if some are activated and some arent they cancel each other out. One hyperpolarised v one depolarised.
What are the layers called in the eye?
photoreceptor to bipolar and horizontal in the outer plexiform layer, then ganglion and amacrine in the inner plexiform layer.
What is unique about photoreceptor synapses?
They can release vesicles of NT constantly, just the release rate goes up or down (graded potential). They are ribbon synapses- always vesicles in the active zone.
What areas of the brain recieves visual info, completing the most processing?
LGN- Lateral Geniculate nucleus in thalamus pre-processes before sent to the visual cortex.
Cortext also feeds back to here.
What are the two visual pathways from the primary visual cortex?
Ventral- ‘What’ object is- temporal (get temporal headache after venting about what is wrong)
Dorsal- ‘Where’ spatial location- parietal (Go through the door with parents to get where you want)
Function of:
Pupil, lens, fovea
Pupil dictates amount of light through to retina
Lens focuses the image on fovea
Fovea part of retina with the highest acuity (cones mostly)
In off bipolar cells if stimulate the centre of rods receptive field what happens?
Rods hyperpolarise, off bipolar cell hyperpolarises
In off bipolar cells if stimulate the surround of rods receptive field what happens?
The rod photoreceptor depolarises, and the surround cells hyperpolarise. This gets fed to the horizontal cells which hyperpolarise. This has an inhibitory affect on the photoreceptors in the centre so they depolarise. So bipolar cell depolarises
What if it’s an on centre receptive field in cones? If light in centre? Light surround?
Light in centre: depolarises
Light in surround: hyperpolarises
What if the whole receptive field is lit?
the amount of depolarisation=the amount of hyperpolarisation by horizontal or amacrine cells on the bipolar or ganglion cell, therefore cancel each other out.
What are the two types of ganglion cell? How common?
Parvocellular (80%) and Magnocellular (10%)
What are the two shapes of the dendritic fields and body for the two types of ganglion cells?
Parvocellular have a miget dendritic field with more dense body, whereas magnocellular have a parasol shape with lots of dendrites.
What do the shapes of the two types of ganglion cells mean for function?
Parvocellular shorter dendritic field- higher acuity and detail, lower sensitivity to light.
Magnocellular- less high acuity, but high sensitivity to light
Different spiking patterns for the two ganglion cell types? Function?
Parvocellular- ‘sustained’ spike for quite a while. Making conduction velocity slower.
Magnocellular- ‘Transient’ burst spiking- good for tranferring information (less high acuity) quickly.
Primary function of two types of ganglion cells then (summary):
Parvocellular: Midget, high acuity, low light, sustained spiking, slower velocity = FORM AND COLOUR (ventral)
Magnocellular: Parasol, low acuity, high sesnitivity to light, short spiking, high speed= MOTION DETECTION (dorsal stream)
How do the photoreceptors adapt to contrast?
Depression- If high temporal contrast initial high spiking but reduces sensitivity over time as adapts
Facilitation- If low contrast or recovering from depression.
During the day we mostly use ….. photoreceptors? Why?
Cones. These fire at bright light, whereas the rods saturate.
Cone cells have differet spectral sensitivities why?
Depending on optimum wavelength there are three opsins, red, green, blue so can see in colour depending on amount that fire where etc.
If damage dorsal stream?
Trouble processing motion
How does direction motion relate to spiking?
If in the preferred direction there is lots of spiking, whereas little if in the null direction.
Excitatory info if in the right direction, but inhibitory if in the other. Depolarisation not sufficient to spike as inhibitory greater than excitatory.
What are the three types of cell found in the V1?
Simple, complex and hypercomplex
Ablation of ….. leads to disappearance of the orientating reflex
Optic tectum or superior colliculus in lower vertebrates.
What did the Hubel and wiesel experiment find?
The three types of cells in the V1, also that in the cat V1 cortex everytime light was shone neurons fired, but some also fired when the light stopped shining. (inhibitory surround cells) but if cover whole receptive field none fired.
When would the simple cells fire? not?
They fire more when there is light shone on the centre, but stop firing if outside field. Don’t fire if all over field and surround, and don’t fire if the orientation of the light has changed unfavourably.
Why would the simple cells fire in some but not in other orientations?
Depends on orientation, as the Lateral geniculate nucleus neurons often line up in a line converging to the simple cell, so when all of these experience light in this orientation all fire, whereas if only some do, may also have surround inhibition which overrides and cancels out the excitation.
Structure of the Lateral Geniculate Cortex?
In thalamus. Relay centre.
6 layers, with layers alternating input from each eye.
2 of these, so contralateral to layers 1,4,6
ipsilateral 2,3,5.
1-2= magnocellular project
3-6= Parvocellular
What are retinotopic maps?
Neighbouring photoreceptors feed into neighbouring parts of the brain so image stays in tact.
Why are receptive fields of the LGN similar to ganglion receptive fields?
Because 1:1 connection to LGN projection neurons.
sequence of the ventral stream?
Vent= What
Parvocellular ganglion cells-LGN parvo-V1-V2-V4- IT neurons shows form (inferior temporal)
Sequence of the Dorsal stream?
Dosal=motion
Magnocelluar ganglion cels- LGN magno- V1-V2-V3- Parietal (some feeds to v4 for colour processing) to detect movement
How does object recognition largely work?
if see an object, certain neurons in brain fire for that object, so if encounter again and the same neurons fire we recognise it as the same as before e.g. one specific cell- Jennifer aniston cell.
What is the hierarchical sequence of object recognition?
(V1)Detection of edges- (V2,V4) detection of combination of edges and contours- (temporal)detection of key shapes e.g. face- detection from one point of view e.g. front- particular person or car- categorization e.g a human, animal
(increases complexity along the ventral stream and increase in receptive field size)
Other names for the dorsal and ventral streams?
Temporal= Ventral (get a temper as you vent) Parietal= Dorsal (walk through door with parents)
