8/17/2019 Neuroscience Essay - Basal Ganglia
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Neuroscience essay title:
1. Describe the functional organization of the basal ganglia and
state how this isaltered in Parkinson's disease.
Essay:
Parkinson’s disease (PD is a neurodegenerati!e "o!e"ent disorder
characterised byhy#okinesia$ tre"or and rigidity. %&ecting
about 1$ #eo#le in the )* alone$ thischronic disorder has !ariable
"otor and non+"otor sy"#to"s. ,he aetiology of thisco"#le- disorder
is not co"#letely co"#rehended. owe!er$ scientists ha!e
#ro#osed"any theories surrounding the degeneration of do#a"inergic
neurons in the basalganglia. /t is crucial to understand the
function of the basal ganglia to gain an insight intohow its
dysfunction could contribute to so"e of the sy"#to"s e-#erienced in
PD.
,he basal ganglia are a cluster of brain cells found at
the base of the forebrain consistingofthe substantia nigra$
caudate$ #uta"en$ globus #allidus and subthala"us. ,he caudateand
#uta"en are anato"ically se#arated by the internal ca#sule$ but are
functionallygrou#ed together as the 0striatu". ,he #uta"en and
globus #allidus are anato"icallygrou#ed as the 0lentifor" nucleus.
owe!er$ they are distinct functionally.
,he co"#le- basal ganglia circuit runs in two #athways:
direct and indirect. ,he direct#athway$ as the na"e suggests$ is a
"ore straightforward circuit$ while the indirect#athway takes a
long+winded route through the subthala"ic nucleus.
,o co""ence the direct #athway$ an e-citatory signal
arri!es fro" the "otor corte- tothe striatu". ,he striatu" then
#ro2ects inhibitory neurons to the internal #art of globus#allidus
(3Pi. 3Pi in turn sends inhibitory signals to the thala"us. ,he
thala"us #ro2ectse-citatory neurons back to the "otor corte-. ,he
e-citatory and inhibitory signals aretrans"itted by gluta"ate and
3%4% res#ecti!ely. /n this co"bination of e-citatory and
inhibitory signalling$ the double 0inhibitory signals between
the striatu"$ 3Pi andthala"us$ result in a 5nal e-citatory
trans"ission fro" the thala"us to the "otor corte-. ,herefore$
the direct #athway has a P67/,/8E "odulation of "o!e"ent on the
"otorcorte-9 if the direct #athway is sti"ulated$ "otor acti!ity is
increased.
6n the other hand$ the indirect #athway achie!es the o##osite
e&ect in the following"anner. %fter an e-citatory signal
reaches the striatu" fro" the "otor corte-$ thestriatu" sends
inhibitory signals to the e-ternal #art of 3lobus #allidus (3Pe.
3Pe sendsinhibitory signals to the subthala"ic nucleus (7,N. 7,N
then #ro2ects e-citatory 5bres to3Pi. ,he circuit then follows the
sa"e route as the direct #athway fro" the 3Pi$ to thethala"us$ back
to the "otor corte-. owe!er$ in this #athway$ the 5nal e&ect is
adecrease in "otor acti!ity due to the #ositi!e signal that
aug"ents the negati!e e&ect inthe 7,N.
,wo neurotrans"itters engage in these #athways to inuence
these "odulations further:Do#a"ine and %cetylcholine.
Do#a"ine$ a "onoa"ine neurotrans"itter$ #artici#ates in the
"esoli"bic$ "esocorticaland nigostriatal #athways in the ;N7. /t is
its #artici#ation in the nigostriatal #athwaythat inuences "o!e"ent
control. Do#a"ine is #roduced by the cells of the P% 3+#rotein
cou#led rece#tor$ and when bound to do#a"ine$ it #otentiates
thee&ects of the D/
8/17/2019 Neuroscience Essay - Basal Ganglia
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%ll these "echanis"s reiterate the i"#ortance of the basal
ganglia in "ediating"o!e"ent control in the brain. )nderstanding
the role of these "echanis"s could bead!antageous in disco!ering
thera#ies to "ani#ulate these #athways. ,his could#otential delay
or e!en re!erse the degenerati!e #athways in the basal
ganglia.y#okinesia could be e-#lained using the loss of
do#a"inergic neurons$ but there areother "otor and non+"otor
sy"#to"s whose "echanis"s are still being disco!ered. %
!ery recent #ublication has shown #ro"ising e!idence where
consistent and #rogressi!e"icrogra#hia$ another PD sy"#to" could be
attributed to a dysfunction in the basal
ganglia "otor circuit ((Wu et al., 2015). ,his shows a #ro"ising
#otential towards research
and thera#eutics of this "ulti+faced disorder.
