The document discusses several components of the basal ganglia and limbic system: 1. The basal ganglia include the corpus striatum, lentiform nucleus, amygdaloid nucleus, and claustrum. The corpus striatum has three parts - the caudate nucleus, putamen, and globus pallidus. 2. The reticular formation is a diffuse network extending from the spinal cord to the cerebrum. It receives sensory input and influences motor activity, sensation, and the autonomic nervous system. 3. The basal ganglia and reticular formation are involved in motor control and planning movements through connections with the cortex and brainstem. Damage can cause disorders like Parkinson's disease

1. Basal Ganglia
Reticular Formation
Limbic System
By
Dr.Faris Al-Haddad
M.B.Ch.B, PhD Anatomy
College of Medicine,
Hawler Medical University
Arbil, Iraq
e-mail: farisurgeon@gmail.com

3. • A collect ion of masses of gray mat t er
sit uat ed wit hin each cerebral
hemisphere. They are t he :
1. Corpus
st riat um : Caudat e, Globus
pallidus and
put amen
2. Amygdaloid nucleus,
3. Claust rum.
• The subt halamic nucleisubt halamic nuclei, t he

6. 1. Caudate Nucleus :
• A large C-shaped mass of gray mat t er
• Closely relat ed t o t he lat eral vent ricle and lies
lat eral t o t he t halamus.
• The lat eral surf ace of t he nucleus is relat ed t o t he
int ernal capsule, which separat es it f rom t he
lent if orm nucleus.
• divided int o a :
A. head,
B. body,
C. t ail.

7. • The head of Caudate Nucleus :
• I s large and rounded
• f orms t he lat eral wall
of ant erior horn of t he
lat eral vent ricle.
• Cont inuous inf eriorly
wit h t he put amen of
t he lent if orm
nucleus
( Bot h Caudat e &

8. • B. The Body Of Caudate Nucleus :
• is long and narrow
• is cont inuous wit h t heis cont inuous wit h t he
headhead in t he region of t he
int ervent ricular f oramen.
• f orms part of t he f loorf loor
of t he body of t he lat eralof t he body of t he lat eral
vent riclevent ricle.

9. C. Tail Of Caudate
Nucleus :
• long and slender
• cont inuous wit h t he
body in t he region of t he
post erior end of t he t halamuspost erior end of t he t halamus.
• I t f ollows t he cont our of t he lat eral vent ricle and cont inues
f orward in t he roof of t he inf erior horn of t he lat eralroof of t he inf erior horn of t he lat eral
vent riclevent ricle.
• I t t erminat es ant eriorly in t he amygdaloid nucleus.amygdaloid nucleus.

10. 2. Lentiform Nucleus :
• I t s a wedge-shaped mass of
gray mat t er
• A base is direct ed lat erally
• A blade is direct ed medially.
• A vert ical whit e mat t er
divides it int o :
* lat eral port ion :
Put amen,
* medial
port ion :
Globus
pallidus.
• I nf eroant eriorly, t he
put amen is cont inuous wit hput amen is cont inuous wit h
t he headt he head of t he caudat e
P
G.P

11. • Lat er ally : a
t hin sheet of
whit e mat t er ,
External
capsule,
separ at es it
f rom a sheet
of gr ay
mat t er, called
Claustrum.
• The
claust rum, in
t ur n,
separ at es t he
ext er nal
capsule f rom
t he
• Medially :
Internal capsule,
separat es it
f r om t he caudat e
nucleus and
t halamus.

12. 3. Amygdaloid Nucleus :
• The amygdaloid nucleus is sit uat ed
in t he t emporal lobe close t o t he uncusin t he t emporal lobe close t o t he uncus.
• is considered t o be part of t he limbic system.
• I t can inf luence t he body' s response t o environment al
changes. I n t he sense of f ear , f or example, it can change
t he heart rat e, blood pressure, skin color, and rat e of
respirat ion.

13. 4. Claustrum :
• The claust rum is a
t hin sheet of graysheet of gray
mat t ermat t er t hat is
separat ed f rom t he
lat eral surf ace of
t he lent if orm
nucleus by t he
ext ernal capsuleext ernal capsule.
• Lat eral t o t he
claust rum is t he
subcort ical whit esubcort ical whit e
mat t er of t he insulamat t er of t he insula.

14. • substantia nigra of t he midbrain &
subthalamic nuclei of diencephalon :
are f unct ionally closely relat ed t o t he
act ivit ies of t he basal nuclei.
• The neurons of t he subst ant ia nigra are
dopaminergic and inhibit ory and have many
connect ions t o t he corpus st riat um.
• The neurons of t he subt halamic nuclei are
glut aminergic and excit at ory and have many
connect ions t o globus pallidus & subst ant ia
nigra.

15. Connect ions of t he Corpus
St riat um

16. Afferent Fibers
1. Corticostriate Fibers :
The most massive st riat al
af f erent s, f rom somat osensory cort ex
and limbic syst em t o t he corpus
st riat um. I t t hus serves t o modulat e
mot or responses based on limbic
inf ormat ion. I t has glut aminergic
excit at ory ef f ect
2. Thalamostriate Fibers :
Thalamost riat e f ibers are
believed t o be glut amat e excit at ory.

17. 3. Nigrostriate Fibers :
I t has bot h
excit at ory inhibit ory ef f ect on t he
corpus st iat um, but I t is believed t hat
t hese f ibers are more inhibit ory in
f unct ion.
4. Brainstem Striatal Fibers :
I t is t hought t hat
t hese f ibers are inhibit ory in f unct ion.

18. Efferent Fibers
• St riat opallidal Fibers : is
GABAergic
(inhibit ory).
• St riat onigral Fibers : is
glut amat ergic
(excit at ory).

19. Connections of the Globus Pallidus
Afferent Fibers :
• Striatopallidal Fibers : is GABAergic
(inhibit ory).

20. Efferent Fibers:
1. Pallidofugal Fibers :
(A) Ansa lent icularis : pass t o t halamus;
(B) Fasciculus lent icularis :pass t o
subt halamus;
(C) Pallidot egment al f ibers
: pass t o t egment um.
(D) Pallidosubt halamic f ibers : t o
subt halamic.

21. Funct ions of t he Basal Nuclei

22. • The basal nuclei are j oined t oget her and
connect ed wit h many different regions of
t he nervous syst em by a very complex
number of neurons.
• Basically, t he corpus st riat um receives
afferent inf ormat ion f rom most of t he :
Cerebral
cort ex,
Thalamus,
Subt halamus,
Brainst em, including t he Subst ant ia Nigra.
• The inf ormat ion is int egrat ed wit hin t he

23. • This circular pat hway is believed t o f unct ion
as f ollows :
• Writ ing t he let t ers of t he alphabet ,
• Drawing a diagram,
• Passing a f oot ball,
• Using t he vocal cords in t alking and singing,
and
• Using t he eye muscles when looking at an
obj ect
Are a f ew examples where t he basal nuclei
inf luence t he skilled cort ical mot or

24. • Destruction of the primary motor cerebral
cortex prevent s t he individual f rom
perf orming f ine discret e movement s of t hef ine discret e movement s of t he
hands and f eet on t he opposit e side of t hehands and f eet on t he opposit e side of t he
bodybody. However, t he individual is st ill capable
of performinggrosscrudemovementsoftheoppositelimbs.
• If destruction of the corpus striatumt hen
t akes place, paralysis of t he remaining
movement s of t he opposit e side of t he body
occurs.

25. • help prepare for the movements e.g. in
upper limb, by cont rolling t he axial and girdle
movement s of t he body and t he posit ioning
of t he proximal part s of t he limbs bef ore
t he primary mot or part of t he cerebral
cort ex act ivat es discret e movement s in t he
hands and f eet .
• The basal nuclei cont rol muscular movement s
by inf luencing t he cerebral cort ex and have
no direct control through descending
pathways to the brainstem and spinal cord.

26. Clinical Notes

27. Disorders of t he basal nuclei are of t wo
general t ypes :
1. Hyperkinet ic disorders : are t hose in
which t here are excessive and abnormal
movement s.
2. Hypokinet ic disorders : include t hose in
which t here is a lack or slowness of
movement .
3. Parkinson disease : includes bot h t ypes
of mot or dist urbances.

28. • Chorea :
I n chorea, t he pat ient exhibit s involunt ar y, quick,
j er ky, ir regular movement s t hat are nonr epet it ive.
Swif t grimaces and sudden movement s of t he head
or limbs ar e good examples.
• Parkinson Disease :
• Is a progressive disease of unknown cause that commences
between the ages of 45 and 55 years.
• It is associated with neuronal degeneration in substantia nigra
and, to a lesser extent, in the globus pallidus, putamen, and
caudate nucleus.
• The disease affects about 1 million people in the United States.
• The degeneration of the neurons of the substantia nigra that
send their axons to the corpus striatum results in a reduction in
the release of the neurotransmitter dopamine within the corpus
striatum. This leads to hypersensitivity of the dopamine
receptors in the postsynaptic neurons in the striatum.

29. • Pat ient s have t he f ollowing charact erist ic
signs and sympt oms:
• Tremor : result of t he alt ernat ing
cont ract ion of agonist s and ant agonist s.
• Rigidity : I f t he t remor is present , t he
muscle resist ance is overcome as a series of
j erks, called cogwheel rigidit y.
• Bradykinesis dif f icult y in init iat ing
(akinesia) and perf orming new movement s.
• Postural disturbances:
The pat ient st ands wit h a
st oop, and his or her arms are f lexed. The
pat ient walks by t aking short st eps and
of t en is unable t o st op. I n f act , he or she

31. • The ret icular f or mat ion, as it s name
would suggest , resembles a net
(ret icular) t hat is made up of nerve
cells and ner ve f ibers.
• The net ext ends up t hr ough t he
axis of t he cent ral nervous syst em
f rom t he spinal cord t o t he
cer ebrum.
• I t is st rat egically placed among
import ant nerve t ract s and nuclei.

32. • I t receives input f rom :
Most of t he sensory syst emsMost of t he sensory syst ems
• I t s out put :
Descend and inf luence nerve cells at
all levels of t he cent ral nervousall levels of t he cent ral nervous
syst emsyst em.
• The exceptionally long dendrites of t he

33. • I t can inf luence :
skelet al muscle act ivit y,
somat ic sensat ion
visceral sensat ions,
aut onomic nervous syst em
endocrine syst ems,

34. General Arrangement :
• The ret icular f ormat ion consist s of a :
(Deeply placed cont inuous net work of nerve
cells and f ibers)
Extend from the :
Spinal cord,
Medulla oblangat a,
Pons,
Midbrain,
Subt halamus,
Hypot halamus,
Thalamus.

35. • The dif f use net work may be divided int o
t hree longit udinal columns:
1. Median coluMn : have int ermediat e-size
neurons,
2. Medial coluMn : have large neurons;
3. lateral coluMn : have small neurons.

37. • Polysynapt ic pat hways exist , and bot h crossed and
uncrossed ascending and descending pat hwaysascending and descending pat hways are
present , involving many neurons in bot h somat ic and
visceral f unct ions.
• Superiorly : impulses are relayed t o cerebral
cort ex; a subst ant ial proj ect ion of f ibers also
leaves t he ret icular f ormat ion t o ent er cerebellum.
• I nf eriorly : t he ret icular f ormat ion is cont inuous
wit h t he int erneurons of t he gray mat t er of t he
spinal cord,

39. 1. Afferent Projections :
• From t he spinal cord :
Spinoret icular t ract s,
Spinot halamic t ract s
Medial lemniscus.
• From t he cranial nerve nuclei :
Vest ibular pat hways
Acoust ic pat hways,
Visual pat hways

40. • Subt halamic,
• Hypot halamic,
• Thalamic nuclei
• Corpus st riat um
• Limbic syst em.
• Ot her import ant af f erent s f rom :
* Primary mot or cort ex of t he
f ront al lobe
* Somest het ic cort ex of t he
pariet al lobe.

41. 2. efferent Projections :
• To neurons in t he mot or nuclei of t he cranialcranial
nervesnerves
brainst em by ret iculobulbar
• To ant erior horn cells of t he spinal cord byant erior horn cells of t he spinal cord by
ret iculo-spinal t ract s.
• To t he sympat het ic out f lowsympat het ic out f low of aut onomic
syst em
• To craniosacral parasympat het ic out f lowparasympat het ic out f low of
t he aut onomic syst em.

42. • Addit ional pat hways ext end :
Corpus st riat um,
Cerebellum,
Red nucleus,
Subst ant ia nigra,
Tect um,
Thalamus,
Subt halamus,
Hypot halamus,
Most cerebral cort ex

43. Funct ion
I t is not sur prising t o f ind t hat t he f unct ions ar e
many.
A f ew of t he more import ant f unct ions ar e
considered here :

44. 1. Cont rol of skelet al muscle :
• By ret iculospinal and ret iculobulbar t ract s,
can modulatemuscletoneandreflexactivity.
• I t can also bring about reciprocalinhibition; f or
example, when t he f lexor muscles cont ract ,
t he ant agonist ic ext ensors relax.

45. • The ret icular f ormat ion, assist ed by t he
vest ibular apparat us of t he inner ear and t he
vest ibular spinal t ract plays an import ant
role in maint aining :
(Toneoftheantigravitymuscleswhenstanding ). E.g. :
Erect or Spinae
Glut eus Maximus
Hip Flexors
Quadriceps
Hamst rings
Gast rocnemius
Soleus
Tibialis Ant erior

46. • The so-called respirat ory cent ers of t he
brainst em ( by neurophysiologist s ) as
beinginthecontroloftherespiratorymuscles, are now considered
part of t he ret icular f ormat ion.
2. Controlling the muscles of facial
expression
when associatedwithemotion. For example, when a
person smiles or laughs in response t o a
j oke,

47. 3.Control of somatic and visceral sensations.
• The ret icular f ormat ion can inf luence allinf luence all
ascending pat hwaysascending pat hways t hat pass t o supraspinal
levels.
• The inf luence may be f acilit at ive or
inhibit ory. I n part icular, t he ret icular
f ormat ion may have a key role in t he “gat ing
mechanism” forthecontrolofpainperception.

48. 4.Control of the autonomic nervous system.
Highercontroloftheautonomicnervoussystem, f rom t he
cerebral cort ex, hypot halamus, and ot her
subcort ical nuclei, canbeexertedbythe:
reticulobulbartract
reticulospinaltract
which descend t o t he sympat het ic out f low
and t he parasympat het ic craniosacral
out f low.

49. 5. Control of the endocrine nervous system.
• Eit her direct ly or indirect ly t hrough t het hrough t he
hypot halamic nuclei,hypot halamic nuclei, t he ret icular f ormat ion
can inf luence t he synt hesis releasing or
inhibit ing f act ors

50. 6 .Arousal and the level of consciousness.
• Mult iple ascending pat hways carryingascending pat hways carrying
sensory inf ormat ion t o higher cent erssensory inf ormat ion t o higher cent ers are
channeled t hrough t he ret icular f ormat ion,
• which, in t urn, proj ect s t his inf ormat ion t oproj ect s t his inf ormat ion t o
dif f erent part s of t he cerebral cort exdif f erent part s of t he cerebral cort ex,
causing a sleeping person t o awaken.

51. • I n f act , it is now believed t hat t he st at e of
conscious-ness is dependent on t he
cont inuous proj ect ion of sensory inf ormat ion
t o t he cort ex f rom t he ret icular f ormat ion.
• IncomingpainsensationsIncomingpainsensations st r ongly increase t he act ivit y
of t he ret icular f ormat ion, which, in t urn,
great ly excit es t he cerebral cort ex.

52. Clinical notes
Loss of Consciousness :
• I n experiment al animals, damagetoreticularformation,
which spares t he ascending sensory
pat hways, causes persistentunconsciousness.
• Pat hologic lesionsofthereticularformationin humans can
result in lossofconsciousness and even coma.
• I t has been suggest ed t hat lossofconsciousnessthatoccursin
epilepsy may be due t o inhibit ion of t he act ivit y
of t he ret icular f ormat ion in t he upper part
of t he diencephalon.

54. • The t erm limbic lobe ref ers t o t he
st ruct ures t hat f orm a limbus (ring or
border) around t he brain st em.
• Now it is recognized, t hat t he limbic
syst em is involved wit h many ot her
st ruct ures beyond t he border zone in
t he cont rol of emotion, behavior, and
drive; it also appears t o be import ant t o
memory.

55. Anat omically, t he limbic st ruct ures
include :
1. Subcallosal gyrus,
2. Cingulat e gyrus,
3. Parahippocampal gyrus,
4. Hippocampal f ormat ion,
5. Amygdaloid nucleus,
6. Mammillary bodies,
7. Ant erior t halamic nucleus.

56. Connecting pathways of limbic
system:
• Alveus,
• Fimbria,
• Fornix,
• Mammillot halamic t ract ,
• St ria t erminalis.

58. 1. Hippocampal Formation :
• I t is named hippocampus because in coronal sect ion
it resembles :
A SEA HORSE
• Consist s of t he :
hippocampus,
dent at e gyrus,
parahippocampal gyrus

59. A. Hippocampus :
is a
curved elevat ion of gray
mat t er, ext ends t hroughout
t he ent ire lengt h of t he f loor
of t he inf erior horn of t he
lat eral vent ricle.
• I t s ant erior end is expanded
t o f orm t he pes hippocampus.
• The hippocampus t erminat es
post eriorly beneat h t he
splenium of t he corpus

60. B. Dentate gyrus :
is a narrow, not ched
band of gray mat t er t hat lies
bet ween t he f imbria
of t he
hippocampus and t he
parahippocampal gyrus.
• Ant eriorly, t he dent at e gyrus
is cont inued int o t he uncus.
• Post eriorly, t he gyrus
accompanies t he f imbria
almost t o t he splenium of t he
corpus callosum and becomes
cont inuous wit h t he indusiumgriseum.

61. • The indusium griseum : is a t hin, vest igial
layer of gray mat t er t hat covers t he
superior surf ace of t he corpus callosum.
C. The parahippocampal gyrus : lies bet ween
t he hippocampal f issure and t he collat eral
sulcus and is cont inuous wit h t he
hippocampus along t he medial edge of t he
t emporal lobe.

62. 2. Amygdaloid Nucleus :
• The amygdaloid nucleus is so named because
it resembles an almond.
• I t is sit uat ed anteriosuperiortothetipof t he inf erior
horn of t he lat eral vent ricle.
• I t is fusedwiththetipofthetailofthecaudate nucleus, which has
passed ant eriorly in t he roof of t he inf erior
horn of t he lat eral vent ricle.
• Thestriaterminalisemergesfromitsposterioraspect.

63. Connect ing Pat hways of t he Limbic
Syst em:
• Alveus,
• Fimbria,
• Fornix,
• Mammillot halamic t ract ,
• St ria t erminalis.

64. • The convex vent ricular
surf ace of hippocampus is
covered wit h ependyma,
beneat h which lies a t hin
layer of whit e mat t er
called
• Alveus :
consist s of nerve f ibers
t hat have originat ed in t he
hippocampus, and t hese
converge medially t o f orm
a bundle called t he f imbria
• Fimbria :
in t urn, becomes

65. • The crus
f rom each side
curves post eriorly and
superiorly beneat h t he
splenium of t he corpus
callosum and around t he
post erior surf ace of t he
t halamus.
• The t wo crura now
converge t o f orm t he
body of t he f ornix,
which is applied closely
t o t he undersurf ace of
t he corpus callosum.

66. • As t he t wo crura come
t oget her, t hey are
connect ed by t ransverse
f ibers called commissure
of t he f ornix. These
f ibers decussat e and j oin
t he hippocampi of t he
t wo sides.
• Ant eriorly, t he body of
t he f ornix is connect ed
t o t he undersurf ace of
t he corpus callosum by
t he sept um
pellucidum.

67. • The body of t he
f ornix split s
ant eriorly int o t wo
ant erior columns of
t he f ornix,
• Then, each column
disappears int o t he
lat eral wall of t he
t hird vent ricle t o
reach t he

69. Af f erent Connect ions

70. Afferent Connections of the Hippocampus :
From :
Cingulat e gyrus
Sept al nuclei
One hippocampus t o t he
opposit e
hippocampus (in t he
commissure
of t he f ornix).
I ndusium griseum

71. Efferent Connections of the Hippocampus:
To : Mammillary body,
Ant erior nuclei of t he
t halamus,
Tegment um of t he
midbrain.
Sept al nuclei,
Lat eral preopt ic area,
Ant erior part of t he
hypot halamus*
Habenular nuclei.

72. Funct ions of t he Limbic
Syst em

73. • The limbic syst em, via t he hypot halamus
cont rols t he out f low of t he aut onomic
nervous syst em, so it cont rol s t he
endocri ne s ys t em, is :
able t o inf luence many aspect s of emotionalbehavior.
These include part icularly t he react ions of fear
andangerand t he emot ions associat ed wit h sexual
behavior.

74. • There is also evidence t hat t he hippocampus
is concerned wit h :
(convert ing recent memory t o long-t erm
memory) .
• A lesion of hippocampus result s in individual
being unable t o st ore long-t erm memory.
• Memory of remot e past event s bef ore t he
lesion developed is unaf f ect ed. This
condit ion is called ant erograde amnesia.
• I t is int erest ing t o not e t hat inj ury t o
amygdaloid nucleus & hippocampus produces a
great er memory loss t han inj ury t o eit her
one of t hese st ruct ures alone.

75. • There is no evidence t hat t he limbic syst em
has an olf act ory f unct ion.