13 - Diencephalon

parts of the diencephalon

epithalamus, subthalamus, thalamus, hypothalamus

nuclei of the dorsal thalamus

afferent and efferent connections

where is the diencephalon located?

mostly hidden from view between the cerebral hemispheres

2% of central nervous system (by weight)

nearly all connections between the cerebral cortex and subcortical structures including the diencephalon travel through the _____.

internal capsule

what part of the diencephalon includes the pineal gland?

epithalamus

what are the borders of the diencephalon?

superior: body of the lateral ventricle

laterally: internal capsule

inferiorly: subarachnoid space

caudally: plane through posterior commissure

rostrally: anterior commissure

hypothalamic sulcus

divides alar plate into superior and inferior portion, differentiates thalamus to hypothalamus

the diencephalon surrounds what ventricle?

3rd ventricle

what does the epithalamus include?

pineal and habenular nuclei

pineal gland is a midline, unpaired structure situated just rostral to the superior colliculi

resembles a pinecone in shape

what is the pineal gland made of? what does it secrete?

connective tissue containing glial cells and pinealocytes, no true neurons

secretes a hormone derived from serotonin - melatonin (during darkness)

what is the pineal gland important for?

regulation of circadian rhythm, sleep wake cycles, involved in seasonal cycles

pineal tumors sx

hydrocephalus in early findings, various deficits in eye movements and pupillary reactions, pineal tumors can cause changes in sexual development

what is the clinical significance of pineal gland?

accrues calcium at about 17 years, opaque in X-rays and shifts in pineal position can indicate expanding masses

where is the habenula?

epithalamus

caudally at the base of the stalk connecting pineal gland to diencephalon is the posterior commissure, rostrally is the habenula

underlying each habenula is habenular nuclei

habenula function and where does it project to?

receives input from basal nuclei and limbic system

project to the reticular formation in the brainstem

how many habenula?

2

(1 pineal gland)

what does the habenula release? what does decreased activity of habenula result in?

biogenic amines from the reticular formation and thought to play a role in assigning reward value to stimuli

habenular nuclei send messages to dopamine and serotonin cells of the brainstem, increase their activity based on how well an individual enjoyed a certain stimulus

lack of activity of the habenula and its projections to the reticular formation may play role in depression

subthalamus nucleus function

receives input from motor areas of cerebral cortex, projects to substantia nigra, reciprocally connected with the globus pallidus, very connected to the basal nuclei

what happens with vascular lesion to subthalamic nucleus?

hemiballismus - involuntary rapdi and forceful movements of contralateral UE

what is prerubral area (Forel’s Field H)?

main length between striatopallidal system and thalamocortical network

connects pathway of basal nuclei and thalamus/cortex

what is the zona incerta? what are its functions?

small mass of gray matter intervening between the subthalamic nucleus and thalamus

involved in sensory-motor programming and cognitive processes related to attention towards important stimuli

primary functions of the subthalamic area?

regulation of movement (basal ganglia)

sensorimotor integration

some cognitive processes

what is the thalamus? how much does it make up diencephalon? boundaries?

pair of large, egg-shaped nuclear masses with a posterior appendage

make up about 80% of diencephalon

extends anteriorly to interventricular foramen, superiorly to the floor of the lateral ventricle, inferiorly to the hypothalamic sulcus, posteriorly overlaps midbrain

what information relays in the thalamus?

all sesnsory pathways (except for olfaction)

many of the anatomical circuits used by cerebellum, basal nuclei, limbic structures

what is the internal medullar lamina?

thin, curved sheet of myelinated fibers in thalamus

divides most of the thalamus into principle cell groups - anterior, medial, lateral, intralaminar nuclear groups

these are midline thalamic nucleus just superior to the hypothalamus sulcus

what is attached to the caudolateral portion of the thalamus?

medial and lateral geniculate bodies

lateral group of thalamic nuclei

composes bulk of thalamus and is further divided into dorsal and ventral tiers

parts of the dorsal tier of lateral nuclei

lateral dorsal nucleus - cingulate gyrus

lateral posterior nucleus - parietal lobe

pulvinar - visual function, eye movements

what is in the ventral tier of the thalamus?

VA - motor related

VL - motor-related

VP - includes VPL and VPM which are somatosensory info

parts and functions of the geniculate nuclei?

lateral geniculate nucleus - afferents from retina via optic tract and projects to the primary visual cortex

medial geniculate nucleus - afferent auditory input via brachium of inferior colliculus and projects to the primary auditory cortex

where are the geniculate nuclei located?

posterior to the ventral tier nuclei and inferior to the pulvinar, protrude posteriorly alongside the midbrain

functions of the thalamus

specific or relay nuclei - subcortical structures → cerebral cortex

process, integrate and relays information realted to sensory, motor and limbic system

anterior nucleus

limbic system - cingulate gyrus

dorsomedial nucleus

orbitofrontal cortex

frontal cortex mostly

lateral dorsal nucleus

input to limbic cortical

pulvinar

eye movements, visual function

ventral anterior, ventral lateral

motor

ventral posterior (VPL, VPM)

somatosensory, information from sensory contralateral side of body (VPL), medial lemniscus, spinal trigeminal fibers (VPL), principal trigeminal fibers (VPM)

the somatosensory is organized somatotopically and by function

what is the motor relay nuclei pathway?

cerebellum → VL → M1, M2, SMA

basal nuclei → globus pallidus → VA → prefrontal cortex, frontal eye field

basal nuclei → globus pallidus → VL → SMA, premotor area

limbic relay

hippocampus connects to mammillary bodies

mammillothalamic tract to the anterior nucleus

connections to the cingulate gyrus

internal capsule radiates up to:

thalamocortical

corticothalamic

cortex → subcortical

pathway of cortex to thalamus

corona radiata → internal capsule

cortex associated with parts of thalamus

anterior and posterior limb of internal capsule

anterior - contains the fibers interconnecting the anterior nucleus and the cingulate gyrus, most of those interconnecting the dorsomedial nucleus and prefrontal cortex

posterior - contains fibers interconnecting VA and VL with motor areas of the cortex. contains corticospinal and corticobulbar fibers and the somatosensory fibers projecting from VPL/VPM to the postcentral gyrus

what is internal capsule genu?

transition zone between the anterior and posterior limb and contains some corticobulbar fibers to CN motor nuclei

hypothalamus role

controlling internal environment

modulates ANS, receptors sense and respond to temperature, osmolality, hormones, produces releasing factors to regulate hormone production, releases neurohormones into circulation includes satiety center

hypothalamus parts

3 sections

lateral hypothalamic area - cardiorespiratory function and regulation of food and water intake

medial zone - “meat and potatoes” of hypothalamus

periventricular zone - includes neurons that border ependymal surfaces of the third ventricle

chiastmatic region of medial zone

chiasmatic region - preoptic, supraoptive, paraventricular, anterior and suprachiasmatic nuclei

regulate hormone release, circadian rhythm, body temperature and heat loss mechanisms

tuberal region of medial zone

dorsomedial, ventromedial and arcuate nuclei

• ventromedial - satiety center

• arcuate - hormonal regulation

mammillary region

posterior nucleus and mammillary nuclei

projects tot eh anterior thalamic nuclei via mammillothalamic tract

neurons of posterior nucleus involved in elevation of blood pressure, pupillary dilation, shivering or body heat conservation

mammillary nuclei are involved in control of reflexes associated with feeding and memory formation

blood supply to the thalamus

posteromedial branches of the posterior cerebral artery and posterior communicating artery

including thalamogeniculate and thalamoperforating artery

thalamogeniculate a supplies

ventral and posterolateral and posteromedial part of thalamus

thalamoperforating a supplies

anterior portion of thalamus and choroid plexus

symptoms of a loss of blood flow to the thalamus and internal capsule

contralateral hemiparesis combined with hemianesthesia

branches of posterior cerebral artery - thalamic pain syndrome and “Pusher syndrome”

thalamic pain syndrome

affects 25% of patients that suffer a stroke to the thalamus region

most commonly implicated artery is the thalamogeniculate artery

sx: contralateral sensory loss, astereognosis, progresses to burning, scalding, usually vauge, allodynia (pain from touch), delayed gradual onset of pain sx

Pusher syndrome

often damage to right side of brain

while sitting or standing pushes away from not injured side until they fall towards hemiparetic side - no proprioception on that side, thinks leaning over is upright