Thalamocortical physiology

Question 1

Why can’t the thalamus contribute directly to EEG

Answer 1

Too deep in brain

EEG measure current in column of brain from head surface

Question 2

What is the contribution of thalamus to EEG recording

Answer 2

1) Thalamus projects to cortex (thalamocortial) so EEG measures of cortical activity = thalamic activity

Question 3

EEG recordings at cortical level require ___

Answer 3

simultaneous firing of many cortical cells with parallel orientation

Question 4

what happens with thalamocortical neurons during sleep

Answer 4

fire several times quick during depot in btwn a lull (hyperpol)

–> creates slow (3Hz) delta waves in EEG

Question 5

Thalamic relay neurons project from thalamus and synapse on __

Thalamic relay nuclei inhib by ___, causing ___

Answer 5

excitatory synapse on cortical cells

inhib by reticular cells in thalamus, decr cortical activiyt

Question 6

what channels are in thalamic relay nuclei

How are VG Na and T type calcium channels simil

Answer 6

VG Na, K, T-type Ca2+

both have activation and inactivation gate
inactiv gate opened in hyperpol

Question 7

what is impact on thalamic relay nuclei when you are awake

Answer 7

very little inhib of thalamic relay nuclei by reticular cells

therefore Vm = -55, AP fired from open VG Na+

depol inhib T type Ca2+ channels (closed inactive gate)

Question 8

what is impact on thalamic relay nuclei when you are in slow wave sleep

Answer 8

reticular cells inhib thalamic relay neurons –> Vm = -85 mV

Ca2+ channels activated and Ca2+ enters –> slow AP

then VG Na+ open –> Ca2+ spikes with many fast AP on top of Ca2+ spikes

Question 9

characteristic pattern of slow wave sleep

Answer 9

calcium spikes with 3 Hz = delta wave

Question 10

T-type Ca2+ channels are inactiv by ___

implication?

Answer 10

inactivated by depol (inactiv gates closed)

cannot fire AP unless hyperpol

Question 11

when are t-type Ca2+ channels activated

Answer 11

when thalamic relay neurons inhib by thalamic reticular cells

reticular cells inhib thalamic relay neuron –> hyperpol to -85mV –> Ca2+ spikes

Question 12

how do Ca2+ spikes in thalamic relay neurons at delta freq give rise to slow wave in delta freq in EEG

Answer 12

1) slow Ca2+ spikes in thalamic relay neurons reach terminal, release glut
2) glutamate excite cortical neuron –> fire AP
3) AP in cortical neuron = same freq of relay neuron = slow wave detected

Question 13

absence epilepsy characterized by what symptom

what is appearance on EEG

what is EEg pattern thought to stem from?

Answer 13

sudden staring spells + absence
of activity

brain reg = similar to slow wave sleep = 3 Hz

slow wave abnormal when awake due to defect in T-type Ca2+ channel on thalamic relay nuclei

Question 14

compare t-type ca2+ channel activity in persons awake while in absence epilepsy

Answer 14

normally inactiv by depot (-60 mV) Vm when awake

in absence, channel no longer inhib by depol to -60 mV–> inactiv gate abnormally OPEN at depol –> Ca2+ spikes while awake

Question 15

predisposition for absence seizures in families with ___

Answer 15

t-type ca2+ channel mutations

Question 16

what drugs are used in controlling absence

mechanism

Answer 16

valproic acid
ethosuximide

both inhib t-type ca2+ channel

Question 17

what regulates thalamocortical circuit

Answer 17

ascending brainstem circuits sending axon to thalamus

Question 18

how is regulation of thalamocortical circuit occurring

Answer 18

1) cholinergic neuron
2) noradrenergic neuron
3) serotonergic neuron

Question 19

how is regulation of thalamocortical circuit occurring

describe cholinergic neuron

1) come from
2) when stim

Answer 19

1) come from reticular activating system (circuit btwn brainstem and cortex thru thalamus)
2) stim –> ACh release into thal –> awaken from sleep and disruption to slow waves in EEG

Question 20

how is regulation of thalamocortical circuit occurring

noradrenergic neurons

1) come from
2) when stim

Answer 20

1) come from locus ceruleus (in pons for response to stress and panic)
2) stim during ‘fight or flight’ –> noradrenaline release into thal

Question 21

how is regulation of thalamocortical circuit occurring

serotonergic neurons

1) come from
2) when stim

Answer 21

1) from raphe nucleus

2) stim = release serotonin into thal and involved in sleep/wake cycle

Question 22

when can thalamic relay neurons fire slow spikes

Answer 22

when hyperpol by inhib interneurons/reticular cells from thalamic reticular nuclei

thalamic relay neuron hyperpol to -85 mV –> cause T-type Ca2+ to open –> slow Ca2+ spikes –> slow wave recorded