Download THALAMUS - Wikispaces

THALAMUS
Objectives
• 1. Describe the location of the thalamus
• 2. List the different parts and nuclei of the
thalamus
• 3. List the afferent input to different nuclei of
the thalamus
• 4. List the efferent output from the different
nuclei of the thalamus
Thalamus





Part of the diencephalon (The
other parts are hypothalamus,
subthalamus and
epithalamus)
A midline symmetrical
structure, formed of 2 oval
masses of grey matter
Is the largest nuclear mass
Situated between the cerebral
cortex and brainstem
Together with the
hypothalamus, it forms the
lateral wall of the 3rd ventricle
T
H
3rd ventricle
Thalamus
• Functionally considered as the great sensory gateway
to the cerebral cortex
• It relays received information to the cerebral cortex
from diverse brain regions.
• Axons from every sensory system (except olfaction)
synapse in the thalamus as the last relay site before
the information reaches the cerebral cortex.
• There are some thalamic nuclei that receive input
from cerebellar nuclei, basal ganglia and limbicrelated brain regions.
• Its function includes relaying sensory and motor
signals to the cerebral cortex, along with the
regulation of consciousness, sleep, and alertness.
Relations
 Lateral: Posterior limb of
the internal capsule (IC)
 Medial: Together with
hypothalamus, forms the
lateral wall of the 3rd
ventricle
 Superior: Caudate
nucleus (C) fornix (F) &
lateral ventricle (LV)
 Inferior: Hypothalamus
(H) anteromedially &
Subthalamus (ST)
posterolaterally.
External Features
• Ends : Anterior &
Posterior
• Surfaces : Superior
Inferior
Medial
Lateral
S
M
L
Medial s.: frequently
connected to the thalamus
of the opposite side by the
interthalamic adhesion
(massa intermedia)
I
Thalamus has 2 ends.
*Anterior: Forms a projection called
anterior tubercle which lies just
behind the interventricular foramen.
*Posterior: Forms a projection called
Pulvinar which lies above the
superior colliculus and the lateral &
medial geniculate bodies.
*
*
Interventricular
foramen.
*
*
Pulvinar.
Surfaces
4 Surfaces:
• Superior
• Inferior
• Medial
• Lateral
S
L M
l
Superior Surface
- Bounded laterally by
caudate nucleus,
thalamostriate vein and
a nerve fiber bundle
called stria terminalis
- Lateral part lies in the
floor of the lateral
ventricle & is covered by
ependyma
- Medial part is related
to the choroid plexus of
the 3rd ventricle
stria terminalis caudate nucleus
LV
thalamostriate vein
choroid plexus
ependyma
Lateral Surface
• Related to the
internal capsule
Inferior Surface
• Rests on the
subthalamus &
hypothalamus
Medial Surface
• Stria medullaris thalami
• (a fascicle of nerve fibers)
courses along its
dorsomedial margin
• Below is limited by
hypothalamic sulcus
• Forms the upper part of
the lateral wall of the 3rd
ventricle
• Covered by ependyma
Stria medullaris thalami
Hypothalamic sulcus
Internal Organization
Thalamus is composed of
grey matter, interrupted
by two vertical sheaths of
white matter called
medullary laminae.
• External medullary
lamina:
- Located laterally,
separates reticular
nucleus from the rest of
the thalamic mass
- Contains
thalamocortical &
corticothalamic fibers
• Internal medullary
lamina
 Y- shaped band, divides
thalamus into Anterior,
Medial & Lateral nuclear
groups
 Contains:
 Fibers connecting
thalamic nuclei with
one another
 Neuronal collections
called intralaminar
nuclei
Thalamic Nuclei
• Anterior nuclear group: Anterior nucleus
• Medial nuclear group: Largest nucleus is medial dorsal nucleus
(MD)
• Intralaminar nuclei: Lie within the internal medullary lamina
• Midline nuclei: Lie deep to ependyma of 3rd ventricle
• Lateral Nuclear group
Thalamic Nuclei
Lateral nuclear group is
divided into Dorsal &
Ventral tiers.
 Dorsal tier contains:
 lateral dorsal n. (LD)
 lateral posterior n. (LP)
 pulvinar.
 Ventral tier contains
 ventral anterior (VA)
 ventral lateral (VL)
 ventral posterior (VP)
nuclei, divided into
lateral & medial parts
 medial & lateral
geniculate bodies.
NUCLEUS
FUNCTIONS
VPM Relay station for impulses from face, head & taste buds
VPL Relay Station for exteroceptive& proprioceptive from all body EXCEPT head & face
VA Relay station for Striatal impulses (attention & recent memory )
VL (VI) Relay station for cerebellar impulses
MGB Relay station for Auditory impulses
LGB Relay station for Visual(Optic) impulses
NUCLEUS
Anterior
FUNCTIONS
Attention & recent Memory
Medial
dorsal
Associated with mood & emotional balance
Lateral
Dorsal
Integrates Sensory information
Lateral
Posterior
Integrates Sensory information
Pulvinar
Correlates auditory & visual information with sensations
NUCLEUS
FUNCTIONS
Reticular
Forms part of ascending reticular activating system
Intralaminar
(Including
centromedia
n)
Awareness of painful stimuli at thalamic level
Functional Organization
• All the nuclei of the
thalamus except
reticular nucleus,
project to ipsilateral
cerebral cortex
• The whole of the
cerebral cortex
receives input from
the thalamus
• All thalamic nuclei
receive corticofugal
fibers in a basically
reciprocal fashion
• Based on their connection with the
cerebral cortex, the thalamic nuclei are
divided into:
Specific nuclei
Nonspecific nuclei
• Specific nuclei:
• Non-specific Nuclei:
Have well-defined
sensory and motor
functions
Have highly organized
point-to-point connection
with sensory & motor
regions of cerebral cortex
Lie within the ventral
group of the lateral
nuclear group
Receive less functionally
distinct afferent input
Connect with wider area
of cortex, including
associative and limbic
regions
 Include nuclei of the
dorsal tier of lateral
group, and whole of the
anterior and medial
group
Classification of thalamic nuclei according to their
projection
• They could be classified into 3 groups, each group contains 4
nuclei:
A)Simple sensory relay nuclei: receive well defined
sensory impulses, and relay them to functionally distinct
areas of the sensory cortex.
1. Ventral posterolateral nucleus (VPL).
2. Ventral posteromedial nucleus (VPM).
3. Lateral geniculate body (LGB).
4.Medial geniculate body (MGB).
B) Circuit relay nuclei: receive impulses from different areas of
CNS and relay them to specific areas in cerebral cortex. They
include:
1. Lateral ventral nucleus (projects to primary motor cortex).
2. Anterior ventral nucleus (projects to premotor cortex).
3. Anterior nucleus (projects to cingulate gyrus).
4. Part of dorsomedial nucleus.
C) Associative nuclei: receive impulses from other thalamic
nuclei and relay these impulses to the association areas of the
cerebral cortex, They include:
1. Part of dorsomedial nucleus.
2. Pulvinar.
3. Lateral dorsal nucleus.
4. Lateral posterior nucleus.
Functions of Thalamus
• Sensory integration and relay station for all the
sensory pathways except Olfactory
• Recognition of crude pain, temperature & touch
• Influences voluntary movements by receiving
impulses from basal ganglia & cerebellum &
relaying them to motor cortex , influence LMN
• Participates in maintenance of state of
wakefulness & alertness through RAS
• Role in emotions & recent memory
Functional Connections
Lesion: contralateral loss of pain/temp, discrim touch
Globus Pallidus
Substantia Nigra
Mammillary Body
Premotor Cortex
Prefrontal Cortex
Cingulate Gyrus
Anterior
GP
SN
Cerebellum (Dentate)
VA
VL
Primary Motor Cortex (4)
Supplementary Motor Cortex (5_
Cingulate
LD
Sensory Cortex (3,1,2)
DM
Superior Parietal Cortex
(5,7)
Amygdala
Hypothalamus
Olfactory Cortex
Prefrontal Cortex
Spinothalamic and LL/ML
LP
VPL VPM
, Solitary Nucleus
Sensory Cortex
Lesion: contralateral loss of pain/temp, discrim
touch in head; ipsilateral loss of taste
Pulvinar
Lesion: memory loss (Wernicke-Korsakoff)
LGN
MGN
Right Optic Tract
Primary visual Cortex (17)
(lingual gyrus, cuneus)
Lesion: Left Homonymous Hemianopsia
Lesion: Sensory Aphasia
Primary Auditory
Cortex (41,42)
Brachium of Inferior
Association areas of temporal, occipital, parietal lobes
Colliculus
LGN, Superior Colliculus
Thalamic syndrome
• Due to vascular lesion (thrombosis of
thalamogeniculate artery)
• Threshold for pain, touch & temperature
decreased on opposite side of body
• When threshold reached then exaggerated
• Emotional instability, spontaneous laughing &
crying
Thalamic hand
• Opposite hand shows abnormal posture
• Forearm is pronated, wrist flexed,
metacarpophalangeal joints flexed & interphalangeal
joints extended
• Fingers can move actively, but movements are slow
• Due to altered muscle tone in different muscle
groups