Transcript thalamus
THALAMUS Epithalamus Habenular Nuclei: Thought to be involved in emotional and visceral responses to odors. Projects to septal nuclei (in thalamus): Via stria medullaris thalami. Projects to interpeduncular nucleus: Via habenulointerpeduncular tract. Epithalamus Pineal Body Secretes melatonin (hormone): Regulates circadian rhythms. Activity is modulated by light-dark cycle: Via sympathetic inputs activated by hypothalamic suprachiasmatic nucleus. Calcification accrues with maturity. Lesions associated with precocious puberty. Thalamus Is a large egg- shaped mass of gray Matter that forms the major part of the diencephalon. Separated from hypothalamus via: Hypothalamic sulcus (groove) Other landmarks: Optic recess Infundibular recess Pineal recess It has a narrow and rounded anterior end which forms the posterior boundary of the Interventricular foramen. The posterior end is expanded and forms the pulvinar which overhangs the inferior colliculus. The inferior surface is continuous with the tegmentum of the midbrain. It is covered on its superior surface by a thin layer of white matter, called the Stratum Zonale and on its lateral surface by another layer, the external medullary lamina. Thalamus Commissures: Habenular : Above the pineal recess. Posterior: Below the pineal recess. Thalamus Functions: Relays all sensory information except smell to the cerebral cortex. Provides crude awareness of sensation. Plays a role in arousal and alertness. Plays a role in complex reflex movements. Thalamus Anterior Nucleus Concerned with certain emotions, attention and memory. Afferents: Mamillothalamic tract from the mamillary bodies Efferents: Cingulate gyrus Connections of the ventral group In the ventral group there is the a. ventral anterior b. ventrolateral c. ventral posterior nuclei. Ventral anterior nucleus Afferents: Globus pallidus , cerebellum Efferents: 4,6 ( pre- and primary motor cortex) Ventrolateral Nucleus Afferents: Cerebellum ( dentate nucleus), Globus pallidus Efferents: 4,6 ( pre- and primary motor cortex) Ventral posterior nuclei: General sensations and taste. It is divided into : a. Ventral posteromedial nucleus b. Ventral posterolateral nucleus Ventral Posteromedial Nucleus Afferents: Trigeminothalamic tract, Solitariothalamic tract. Efferents: Primary Somatosensory cortex (3, 1, 2) Ventral Posterolateral Nucleus Afferents: Medial Lemniscus , Spinal lemniscus Efferents: 3,1,2 Connections of the Lateral Group Three nuclei are found here: a. Lateral Dorsal b. Lateral Posterior c. Pulvinar Their functions are not cleary understood. Lateral Dorsal Nucleus Afferents : Superior colliculus Efferents: Cingulate gyrus Lateral Posterior Nucleus Afferents: Superior colliculus Efferents: Superior parietal lobule (5, 7) Pulvinar Afferents: Superior Colliculus Efferents: Extrastriate visual cortex (18, 19) Connections of the medial group This contains a large Dorsomedial nucleus and several smaller nuclei Afferents: Prefrontal cortex Efferents: Prefrontal cortex It controls emotional states. Damage results in decreased anxiety, tension and aggression. Others Medial geniculate body: Afferents: Inferior brachium from the inferior colliculus Efferents: Projects to primary auditory cortex in temporal lobe. Areas 41, 42 ( Heschl's gyri or Heschl's convolutions ). Lateral geniculate body: Afferents: Visual from the optic tract Projects to primary visual cortex in occipital cortex ( Area 17). Thalamic reticular neurons Modifies neuronal activity in the thalamus. May be involved in: Regulating sleep-wakefulness cycle and levels of awareness. They include: a. Intralaminar b. Midline Intralaminar and midlineNuclei Afferents: Brain- stem reticular formation, spinothalamic tracts Efferents: Pain information is sent to the cingulate gyrus Thalamic Pain May occur as the patient is recovering from a thalamic infarct. The pain is spontaneous , often excessive and occurs on the opposite side of the body. This sensation can be aroused by light touch or cold and may fail to respond to powerful analgesic drugs. Abnormal involuntary movts Choreoathetosis with ataxia may follow vascular lesions of the thalamus. Could be due to involvement of the neighboring caudate and lentiform nuclei Thalamic Hand The wrist is pronated and flexed, the metacarpophalangeal joints are flexed, and the interphalangeal joints are extended. The fingers can be actively moved though the movements are slow. Due to altered muscle tone in different muscle groups.