Diencephalon Diencephalon Diencephalon has Diencephalon has four major four major divisions divisions Epithalamus: Epithalamus: – a. Pineal gland a. Pineal gland

(=epiphysis cerebri) (=epiphysis cerebri) – b. Habenula nuclei:b. Habenula nuclei:

SubthalamusSubthalamusHypothalamus: Hypothalamus: The thalamus: The thalamus:

ThalamusThalamusGreek word thalamos, meaning an inner room or storeroom of a Greek or Roman houseIts nuclei are conventionally Its nuclei are conventionally divided into groups based on their divided into groups based on their anatomical locationsanatomical locations internal medullary laminainternal medullary lamina– This is a curved thin sheet of This is a curved thin sheet of

myelinated fibers. It divides most myelinated fibers. It divides most nuclei into medial and lateral nuclei into medial and lateral groupings groupings

– Rostrally, the lamina bifurcates to Rostrally, the lamina bifurcates to enclose the anterior nucleus, enclose the anterior nucleus, which may be divided into smaller which may be divided into smaller groupings (However, all of these groupings (However, all of these subdivisions of the anterior subdivisions of the anterior nuclear complex have similar nuclear complex have similar connections). connections).

Thalamus cont..Thalamus cont..1.Lateral Grouping1.Lateral Grouping: : This is the bulk of the This is the bulk of the thalamus. This thalamus. This collection of nuclei is collection of nuclei is divided into a divided into a dorsal dorsal tiertier and a and a ventral ventral tiertier..– a. Dorsal tier: Pulvinar, a. Dorsal tier: Pulvinar,

lateral posterior, and lateral posterior, and lateral dorsal nuclei.lateral dorsal nuclei.

– b. Ventral tier: ventral b. Ventral tier: ventral anterior, ventral lateral, anterior, ventral lateral, ventral posterior medial ventral posterior medial (VPM), ventroposterior (VPM), ventroposterior lateral nuclei (VPL). lateral nuclei (VPL).

2. 2. Medial GroupMedial Group: : There is only one There is only one nucleus, the dorsal nucleus, the dorsal medial nucleus,medial nucleus,3.3. Medial and Medial and laterallateral geniculate geniculate bodiesbodies: : – The nuclei are caudal The nuclei are caudal

extensions of the extensions of the thalamus and receive thalamus and receive auditory and visual auditory and visual inputs, respectivelyinputs, respectively(Metathalamus) (Metathalamus)

Intralaminar nuclei: Intralaminar nuclei: The largest is the The largest is the centromedian nucleus centromedian nucleus

Thalamus ConnectionsThalamus Connections

Thalamus Functional SubdivisionsThalamus Functional Subdivisions

1. Specific relay: 1. Specific relay:

These nuclei receive incoming sensory or These nuclei receive incoming sensory or motor information on its way to the cortex.motor information on its way to the cortex.– a. Medial geniculate: auditiona. Medial geniculate: audition– b. Lateral geniculate: vision b. Lateral geniculate: vision – c. VPM/VPL: somatosensory c. VPM/VPL: somatosensory – d. VA/VL motor: cerebellum, basal ganglia to d. VA/VL motor: cerebellum, basal ganglia to

cortex (motor and premotor cortices). VL cortex (motor and premotor cortices). VL thalamectomy for Parkinson's disease helps thalamectomy for Parkinson's disease helps reduce rigidity, but not tremor. This suggests reduce rigidity, but not tremor. This suggests that the VL is involved in the control of muscle that the VL is involved in the control of muscle tone. tone.

Thalamus Functional SubdivisionsThalamus Functional Subdivisions

2. Association: 2. Association: – a. Pulvinar/Lateral Posterior Complexa. Pulvinar/Lateral Posterior Complex– b. Lateral Dorsal (LD):b. Lateral Dorsal (LD):– c. Dorsal medial (DM):c. Dorsal medial (DM):

3. Nonspecific nuclei: 3. Nonspecific nuclei: – a. Part of VA: a. Part of VA: – b. Intralaminar:b. Intralaminar:

– i. Centromedian nucleus: i. Centromedian nucleus: – aa . Reticular Nucleus. Reticular Nucleus

Thalamic syndromesThalamic syndromesTumors and especially vascular lesions Tumors and especially vascular lesions related to the middle and posterior related to the middle and posterior cerebral arteries may involve thalamus cerebral arteries may involve thalamus to some extent.to some extent. A typical condition is known as A typical condition is known as thalamic pain syndrome, which is thalamic pain syndrome, which is caused by destruction of the sensory caused by destruction of the sensory relay nuclei in the posterior half of the relay nuclei in the posterior half of the thalamus.thalamus. It is most often caused by occlusion of It is most often caused by occlusion of the thalamogeniculate branches of the the thalamogeniculate branches of the posterior cerebral artery. posterior cerebral artery.

In addition to injury of the internal capsule In addition to injury of the internal capsule with transitory hemiparesis and with transitory hemiparesis and homonymous hemianopsia, there is homonymous hemianopsia, there is usually impairment of superficial sensation usually impairment of superficial sensation of the opposite side of the body. of the opposite side of the body. Position sense may be affected more Position sense may be affected more frequently than other sensory systems. An frequently than other sensory systems. An agonizing concomitant of this syndrome is agonizing concomitant of this syndrome is a burning or knife-like pain, which usually a burning or knife-like pain, which usually appears after several weeks or months appears after several weeks or months when other sensory functions are when other sensory functions are beginning to return.beginning to return.

Clinical Case Clinical Case A 45 year old woman started month earlier A 45 year old woman started month earlier with sudden weakness and numbness down the with sudden weakness and numbness down the whole of the left side. There was a family whole of the left side. There was a family history of diabetes and high blood pressure. history of diabetes and high blood pressure. When examined locally she was weak and When examined locally she was weak and numb on the left side with chorea of the left numb on the left side with chorea of the left arm. arm. Over the next month her weakness and sensory Over the next month her weakness and sensory loss improved but she developed an unpleasant loss improved but she developed an unpleasant burning sensation on the left side, which burning sensation on the left side, which persisted. persisted. She also experienced two episodes of transient She also experienced two episodes of transient dizziness on head movements.dizziness on head movements.