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Midterm

HMB200H1 Study Guide - Midterm Guide: Squid Giant Axon, Alpha Beta Gamma, Trigeminal Nerve


Department
Human Biology
Course Code
HMB200H1
Professor
John Yeomans
Study Guide
Midterm

Page:
of 9
HMB200
Lecture 3
Cognitive Neuroscience – trying to understand what is going on in the brain when thinking
o EEG – temporal changes
Found internal brain waves
Alpha waves
Beta / gamma waves – occurs during thinking (intensely)
Also changing during sleep – from alpha to beta to gamma to delta waves
During dream sleep – switch to beta / gamma
Discovered that hippocampus was important for conscious and declarative memories
Declarative memories Cannot be made when medial temporal lobe is missing
o CAT Scans – using x-rays
X-rays aimed from 6 different angles – allows you to see different densities like
ventricles and tumours
o PET – injecting radioactive chemicals
Emit gamma rays in two directions and when detected, you can calculate the
concentration of these chemicals – DA, O
2
, 5HT, etc.
o fMRI
Looking for oxygenation of Hemoglobin and views brain oxygen levels in 3 dimensions –
these measures allow you to see changes using a subtractive method of multiple images
Neurons and Proteins
o Within the axons there are pumps and voltage gated channels that give neurons their firing
properties – on the post synaptic side, there are a lot of receptors that initiate gene transcription
and other actions
o Lets start with some of the proteins:
These have to be made via gene transcription… we know this – these single proteins
can then come together with other proteins to make more complex structures like
channels, receptors, etc. (BCH210)
Lipophilic part of the protein interact with the membrane and the hydrophilic part
interacts with the ECF or cytosol
Voltage gated channels contain a domain that is positively charged and is attracted to
the cytosolic leaflet (closed) – when membrane is depolarized, the channel opens
Finding mRNA in Brain
In situ hybridization in which you create a labelled complementary strand to the
target mRNA – then wash the brain slice to view these new double stranded
mRNA in cells that express that protein
Immunocytochemistry makes labelled antibodies that target specific protein to
see where the proteins actually stick to on the brain / neurons (terminals, etc.)
Gap junctions are located on the synapses which causes electrical synapses via the
exchange of ions from presynaptic to postsynaptic neurons – they account for most of
the electrical impulse in an AP – no synaptic delay where as chemical has ½ms delay –
made of 12 connexons (6 on pre and 6 on postsynaptic neuron) – make tight junctions
Lecture 4
Neurotransmitters (NT) include
o Monoamines
Glutamate – excitatory
Glycine – inhibitory in spinal cord
GABA – made from glutamate via GAD and is inhibitory in brain
In order to determine whether a neuron is inhibitory, you look for GAD
o Acetylcholine (ACh)
Excitatory in muscles / Inhibitory in heart
Fast nicotinic receptors / Slow muscarinic receptors
First NT discovered – acts on peripheral nerves going to the gut, salivary glands,
ganglion of ANS, spinal cord and brain – maps of these NT discovered via label of
enzymes (Choline Acetyltransferase) – important for forebrain arousal
find more resources at oneclass.com
find more resources at oneclass.com
Labelled CH1 – CH8
o Norepinephrine (NE) and Epinephrine (E) and Dopamine (DA)
Are excitatory that act on the heart and PNS – These are synthesized from tyrosine
which is converted into L-Dopa – this is a treatment for Parkinson’s Disease, individuals
that do not have dopaminergic neurons, by administering L-Dopa supplements which will
increase amounts of DA in the remaining functioning neurons – They have two important
parts, two binding sites: the catechol ring and amine end
NE neurons form a long chain going down on the brainstem (A1 – A7) – the biggest is
A6 the locus coeruleus – they are a small group of a few thousand neurons that have
projections through the entire cortex
DA neurons (A8 – A17)
o Serotonin (5HT) – indolamine
The amine NT Serotonin, also called 5-Hydroxytryptamine is derived from Tryptophan.
These neurons are relatively few in numbers. However, play an important in the brain
systems that regulate mood, emotional behaviour and sleep – synthesis is a two step
process where tryptophan is converted into an intermediate and then to 5HT – range
from B1 – B9
o Other NT and Intercellular Messengers
Polypeptides
Chopping up proteins like enkephalin and hormones – has its own receptor with
slower effects – known as modulators – found as 2
nd
messengers
ATP and Purines
Released along with transmitter and can have transmitter based release effects
Nitric Oxide – retrograde transmitter that can go forward or backwards and have 2
nd
messenger effects
Endocannabinoids – they are very odd in their actions, lipophilic and can be retrograde
Growth Factors – called neurotrophins
Receptors
o The ability for the NT to have a second binding site gives them selectivity
o Classes of Receptors
Muscarinic
Muscarine is found in mushrooms
1 3 5 are excitatory; 2 4 are inhibitory (M2 inhibits the heart)metabotropic
Nicotinic
Fast and mimicked by the poison nicotine and is found on muscles – ionotropic
o Glutamate have AMPA / Kainate – fast; NMDA are calcium channels for mem.; metabotropic
o GABA A-ionotropic (20 genes); GABA B-metabotropic (few genes)
o Two type of Receptors
Ionotropic are essentially ion channels that bind a NT and allows for ion flow – ligand
gated – made of 5TM proteins
Metabotropic are GPCR that opens channels, an indirect effect – binding causes the
alpha, beta and gamma subunits in the G protein where either one of the subunits opens
a complementary ion channel – made of 7TM proteins – can activate 2
nd
messengers
o NE and cAMP
The beta receptor is an excitatory receptor and that is because it is associated with an
excitatory G protein (G
S
or G
O
) – There is also, in the heart, an inhibitory receptor alpha-
2 receptor which has a slower inhibitory effect
The release of the alpha subunit of G protein causes activation of adenylyl cyclase
creating cAMP (for excitatory)
o Rhodopsin and cGMP
Excited by photons in light, creating hyperpolarization of the cell – closes an open
channel so this GPCR activates cGMP hyperpolarizing the cell
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Lecture 5
Fast Reflexes – Speed and Timing in CNS
o Nervous systems evolved because they are faster then hormonal systems – you get fast
muscular reactions / actions
o Voltage-gated Na
+
channels produce AP
o Axons – fast (myelinated A) and slow (C) – myelinated with Schwann cells – A neurons are
separated into subtypes (alpha beta gamma and delta in order of speed)
o Receptors – fast, GPCR and hormonal
o Circuits – number of synapses and processing at each synapse
o Fast systems with large neurons are the easiest to study – reflexes with giant neurons
o Fast and slow receptors (Transmitter gated, GPCR, Tyrosine Kinase, Steroid and Hormones)
o Squid Jet Reflex
The squid giant axon is actually made of multiple cells – axons are graded by the
distance they have to travel – larger axons have a greater distance to travel and thinner
for short neurons – therefore axon diameter is proportional to distance / length
Muscles surround the mantle (body cavity) which contains water that is squeezed out to
allow for the squid to escape – neurons are very specially made so that muscles are
activated at the same time, so that water is squeezed out controllably
Axons from head activate stellate ganglia together, due to axo-axonal synapse in
cerebral ganglion – command neurons in head that command two sides simultaneously
– basically the response is initiated in the cerebral ganglion; the neurons in the cerebral
ganglion synapse on the giant squid axons in the stellate ganglia – it is the site of the
giant neurons in the squid axons which project the graded neurons down the length of
the body
o Mauthner Cell Reflex in Fish
Largest vertebrate neurons found in fish and tadpoles – inputs from V (Trigeminal) and
VIII (Vestibular) nerves (mechanoreceptors) directly to M cell dendrites; One AP elicits
tail flick response to escape threats – fast escape, startle like response
Mauther cell is found in the hindbrain and on each side of the medulla – causes twitching
on opposite sides of the body the fish / tadpole to flick tail sideways and escape predator
o Startle Reflex in Mammals
Giant neurons in Pontine Reticular Formation (PnC) – Startle reflex is a bilateral
response triggered by the Pontine Reticular Neurons (approx. 60 on each side of brain)
Send their axons down the Reticulospinal Tract to activate motor neurons on the spinal
cord – responds to input from Cranial Nerves V (Trigeminal - Tactile) and VIII
(Vestibulocochlear – Equilibrium-Acoustical) – Fast against concussive blows to head
Startle reflex circuits
Trigeminal Nerve (V) Trigeminal N. PnC Reticulospinal Tract
Vestibulocochlear Nerve (VIII) Cochlear N. PnC Reticulospinal Tract
Vestibulocochlear Nerve (VIII) Vestibular N. Vestibulospinal Tract
Vestibulocochlear Nerve (VIII) Vestibular N. PnC Reticulospinal Tract
Acoustic startle triggered by loud, sudden noise activates most muscles at short latency
– clap or snap – found in all mammals – tactile and vestibular stimuli also elicit startle
Hindbrain Organization – fast mechanoreceptors and axons – large neurons in primary
sensory nuclei (trigeminal, cochlear, vestibular) – direct connection to PnC
Transmitters – excitation via glutamate and AMPA – inhibition via ACh, GABA
and glycine – Mutations in glycine alpha 1 leads to hyperstartle syndrome
Amygdala controls these startle neurons – it learns the fear and changes in the
amygdala and fear circuits results in the descending pathway that activates fear
in the Pons
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find more resources at oneclass.com