Diencephalon and
telencephalon
Surface structure
• medial surface of the diencephalon
– interthalamic adhesion or massa intermedia
connects two thalami
– bundle of nerve fibers called stria medullaris
thalami
• dorsal surface:
– concealed by fornix, curves over the thalamus
Components
• Diencephalon
– Thalamus, the largest component. Receives sensory
information and involves emotion, memory, sleep
– Subthalamus, ventral to thalamus. reticular formation,
red nucleus, and substantia nigra project fibers into
subthalamus
– Epithalamus, dorsalmedial to thalamus. Includes
pineal body
– Hypothalamus, outgrow into posterior pituitary,
controls endocrine system
Thalamus
• Almost all the nuclei send fibers to the
cortex. However, there is no
interconnection fibers among different
nuclei groups within the thalamus.
Thalamus
• Reticular nucleus
– not connected with the brain stem, unknown function
• Intralaminar nuclei:
– Receive afferent fibers from reticular formation of the
brain stem.
– Also receive collateral fibers from spinothalamic and
trigeminothalamic fibers (main destination is the
ventral posterior nuclei of thalamus), also receives
fibers from cerebellum, and the globus pallidus. There
is extensive connection between intralaminar nuclei
and frontal, parietal lobes. Connection between
reticular formation to cortex through this area involves
alertness and consciousness.
Ventral group of Nuclei
• Medial geniculate body:
• Afferent fibers:
– inferior brachium: fibers from inferior colliculus, which
receive lateral lemniscus. Medial geniculate body
receives fibers from both sides but predominately
from contralateral side. The bilateral distribution is
caused by crossed fiber from ventral cochlear nucleus
and by the commissural fibers between the inferior
colliculi.
• Efferent:
– ipsilateral side of the temporal cortex, conscious
awareness of sound, and the adjacent association
area is responsible for hearing recognition with
previous experience.
Ventral group of Nuclei
• Lateral geniculate body:
– has six layer of neurons (crossed fibers to 1,
4, 6 and uncrossed fibers to 2, 3, 5)
• Afferent fibers:
– fibers from optic nerve. Point to point project
from retina to lateral geniculate body.
• Efferent fibers:
– geniculocalcarine tract: ipsilateral side of the
occipital cortex
Ventral posterior nucleus
• pathway for conscious awareness of somatic sensation, like
pain, temperature info, touch, proprioception
• Afferent fibers:
– all fibers of medial lemniscus, and most of the spinothalamic and
trigeminothalamic tracts
– also fibers from vestibular nuclear complex and fibers from gustatory
nucleus concerning with sensation about position, and taste,
respectively.
– There is a detailed projection of the opposite body on the ventral
posterior nucleus. The lower limb is represented in its dorsolateral
part with upper limb in an intermediate position and the head the
most medial. The importance (not area) of certain body part
determines the area in the ventral posterior nucleus. Same as the
cerebral cortex.
– Ventral posterior nucleus also receives afferent fibers involving taste,
and vestibular information
– The medial region of the nucleus that receives info from head is also
referred as ventral posteromedial division (VPm), the lateral portion
for the rest of the body called ventral posterolateral division (VPl).
• Efferent fibers:
– project to the somesthetic cortex of parietal lobe.
Ventral lateral nucleus
• Includes posterior and anterior divisions.
• Afferent fibers:
– From cerebellum
• Efferent fibers:
– Enter internal capsule and proceed to frontal
lobe
Other nuclei
• Posterior group of nucleus
– Associated with pain reception
• Lateral group of nuclei:
– lateral dorsal nucleus: part of the limbic system
– lateral posterior nucleus: connected with the somatosensory
associate ion area of the parietal lobe
• Medial group of nuclei:
– mediodorsal nucleus: may be related with memory, seen with
Korsakoff's syndrome, and perception of pain
– Afferent fibers are from entorhinal cortex, amygdaloid body and
corpus striatum
– medioventral nucleus: little is known
• Anterior group of nuclei:
– part of the limbic system
Thalamic syndrome
• most often caused by vascular lesion,
usually in ventral posterior region
• Opposite side of the body:
– proprioception and the sensations of touch,
pain, and temperature are affected
contralaterally
– could also involve emotional disturbance
Subthalamus
• sensory fasciculi:
• includes medial lemniscus, spinothalamic tract,
and trigeminothalamic tract
• substantia nigra and red nucleus extend from
midbrain into subthalamus
• Efferent fiber from pallidus pallidus (part of the
basal ganglia, more later) contained in two
bundles, lenticular fasciculus and ansa
lenticularis. Both terminate in the subthalamus.
Fig 11-7
Fig 11-8
Epithalamus
• The epithalamus consists of the hebenular
nuclei and the pineal gland.
• Habenular neuclei
– Afferent fibers are received through the stria
medularis thalami
– Efferent fibers known as habenulointerpeduncular
fasciculus terminate in the interpeduncular nuclei in
the roof of the interpeduncular fossa. The
interpeduncular nuclei influence neurons in the
hypothalamus and preganglionic autonomic neurons
via relays in reticular formation.
Fig 11-9
Fig 11-7
Pineal gland
• influenced by light, regulate time and day
night changes and onset of puberty in
human
Hypothalamus
• The hypothalamus can be divided into
medial and lateral zones
Medial Zone
• contains suprachiasmatic, tuberal, and mamillary regions.
• Within suprachiasmatic region, it contains supraoptic,
paraventricular, suprachiasmatic and anterior nuclei
– Supraoptic: large cells, above the optic chiasm
– Paraventricular nucleus: large cells
– Both supraoptic and paraventricular nuclei secrete hormones
(ADH and Oxytoxin), form the hypothalamo-hypophysial tract
– Suprachiasmatic neurons are releasing action potential
spontaneously at rugular rhythm and pattern. Axons from retina
leave the optic chisma and termiate into this area and regulate the
light-dark cycle.
– Anterior nucleus: some neurons in this area are twice as many in
males as in females (one possible reason is females experience
neuronal death after 4 yr. old)
• Tuberal region contains ventromedial, dorsomedial, and
infundibular nuclei
• Mamillary region contains mamillary body and the
posterior nucleus.
Lateral Zone
large nerve cells sparsely located and
collectively constitute the lateral nucleus of
the hypothalamus.
• Lateral zone includes the lateral tuberal
nucleus
• Fibers of hypothalamus
– hypothalamus served as the main integrator
of the autonomic and endocrine systems
Afferent fibers
• Ascending afferents: convey information of visceral origin
• Most of the ascending fibers originate from nuclei of
reticular formation
• Medial forebrain bundle originates from septal area, with
fibers originate from intermediate and lateral olfactory
areas, conducts information related to basic emotional
drives and the sense of smell, smaller in humans
• Fibers from amygdaloid body also involve smell and
emotional drives by stria terminalis (arise from
amygdaloid body and ends in the preoptic area, anterior
nucleus, and the septal area).
• Fornix:
• originates from hippocampal formation (hippocampus)
and parahippocampal gyrusends in the hypothalamus
Efferent fibers
• Originate from hypothalamus (paraventricular nucleus), starts as
periventricular fibers underneath the third ventricle and continue into
the dorsal longitudinal fasciculus in the periaqueductal gray matter
of the midbrain. Some terminate into dorsal nucleus of vagus nerve
and other may end in the intermediolateral cell column and sacral
autonomic nucleus (via spinal cord). Thus the influence from
hypothalamus to the preganglionic fibers of sympathetic and
parasympathetic nervous system.
• Hypothalamus also influence cells in motor nuclei of trigeminal,
facial nerves, nucleus of ambiguus and the hypoglossal nucleus to
regulate muscles used in feeding and drinking. Motor neurons in
spinal cord is also affected by hypothalamus thus in shivering
response.
• Fibers originate from mamillary body
• mamillothalamic fasciculus: project to anterior nuclei of the thalamus
• collateral branches of the fibers of the mamillothalamic fasciculus
are also called mamillotegmental fasciculus, end in nuclei of the
reticular formation of the midbrain and pons.
Functional aspect of hypothalamus
• Stimulation of anterior hypothalamus( preoptic area and
anterior nucleus)
• slowing heart rate, vasodilation, lowering blood pressure,
salivation, increased peristalsis in the gastrointestinal
gract, contraction of urinary bladder, sweating. Action of
parasypathtic system.
• Stimulation of posterior and lateral nuclei:
• sympathetic activation: cardia accelaeration, elevation of
blood pressure, cessation of peristalsis, dalation off pupil,
hyperglycemia.
• Hypothalamus is also responsible for regulating
temperature control, Neurons in anterior hypothalamus are
sensitive to temperature changes. If temperature is high,
heat loss mechanism will be activated including cutaneous
vasodilation, sweating. Lesion of anterior hypothalamus =
= > hyperthemia.
Functional aspect of hypothalamus
• Cells in posterior hypothalamus are responsible for
lowering blood temperature, triggering heat conservation
response, including coetaneous vasoconstriction, and
shivering. Lesion in posterior hypothalamus impairs
temperature regulation, causes hypothemia.
• Hypothalamus is also responsible for regulation food
intake and water intake. Hunger or feeding center is
located in the lateral zone and satiety center in the
region of ventromedial nucleus. Lesion of ventromedial
nucleus results excessive food intake and obesity.
• Hypothalamus and pituitary
• Hypothalamus constitute the posterior part of pituitary.
Secrete ADH and Oxytoxin.