The thalamus Flashcards
Thalamus
+Convey sensory input to primary sensory areas of cortex
+gatekeeper preventing or enhancing passage of specific information,
+receive return inputs from the neocortex
+Consists of well- defined nuclei
Some nuclei receive information specific to a sensory modality and project to specific areas while others have more diffuse projections, also connects to frontal lobe and plays a role in memory
The thalamus also receives feedback from the neocortex: input is as large as output
Relay/ Specific Nuclei of the Thalamus
Specific and selective relationship with a particular portion of the neocortex
Anterior
-Surrounded by internal medullary lamina
- Input from mammillary nuclei of hypothalamus & presubiculum of the hippocampal formation
- Related to memory and emotion
- Interconnected with cingulate & frontal cortices
Medial
Mainly consists of Mediodorsal nucleus
- Has three subdivisions which are connected to parts of the frontal cortex
- Input from basal ganglia, amygdala, midbrain
- Related to memory
Ventrolateral
- Ventral anterior and ventral lateral nuclei: Motor control =>carry information from basal ganglia & cerebellum to motor cortex
- Ventral posterior lateral nucleus: Conveys somatosensory information to the neocortex (pathway: medial lemniscus)
Posterior
- Medial geniculate nucleus (posterior part of thalamus): Auditory system, tonotopy, information to the superior temporal gyrus
- Lateral geniculate nucleus (posterior part of thalamus): Visual system, conveys information to the primary visual cortex
Nonspecific nuclei of the Thalamus
Project to several cortical and subcortical regions
- Midline nuclei
- Intralaminar nuclei
- Reticular nucleus
Intralaminar nuclei
- Projections to medial temporal lobe (amygdala, hippocampus) and basal ganglia and receive inputs from spinal cord, brain stem and cerebellum
- Mediate cortical arousal & participate in the integration of sensory submodalities
Reticular nucleus (outer covering of the thalamus)
- Inhibitory neurons using GABA
- Not interconnected with the neocortex but axons terminate on the other nuclei of the thalamus and receives input from these
- ‘Filter’, gating information flow to the neocortex
Basal ganglia
- Receive direct projections from sensory, motor and premotor areas & association cortex parts important for motivation, cognition and emotion
- Output to the thalamus which projects to the cortex
- Dysfunction: Parkinson’s and Huntington’s
Cerebellum
- Receive somatosensory information from primary afferents from spinal cord and corticospinal axons descending from the
neocortex - Error- correcting mechanism: Compare movement commands from cortex with somatic sensory information about what actually happened
Predictive control of movement - Allows motor control systems to adapt motor commands to changing conditions of musculature
- Influence on posture and movement by connecting to brain stem motor nuclei
- Major influence: Connections in ventrolateral nuclei of hypothalamus, which directly connect with motor and premotor cortex
The somatosensory cortex contains several neural maps of the body surface
Area 3: Basic processing of tactile information S1
Brodmann 3b= Sensitive to tactile stimulation of skin surface (Anterior Parietal Cortex= primary somatosensory cortex)
Area 1: Higher- order processing/ more complex
Area 2: Combine tactile information with information concerning limb position, mediating tactile recognition of objects
Unimodal vs Multimodal association modaities
Unimodal: concerned with single modality
Multimodal: Neurons from S1 project to neurons in adjacent areas
+use of somatosensory information to control movement, eye- hand coordination and memories related to touch
o Combination of sensory modalities
o Interconnected with hippocampus important for unified percept and the representation of percept in memory
o Closely linked to Motor cortex (precentral gyrus)
Somatotopic organization
The cortex is organized into columns of cells that have a specialized function: the larger the area of cortex dedicated to a function, the greater the number of columns that are dedicated to it
The somatosensory cortex contains not one but several somatotopic arrays of inputs from the skin several neural maps of the body surface (different maps are for processing of basic or more complex information)
At higher levels in the hierarchy of cortical connections somatosensory info is used in motor control, eye-hand coordination and memory related touch
The processing begins with primary sensory areas, continues in unimodal areas and is completed in multimodal association areas
Processing occurs in serial and parallel pathways
Voluntary movement is mediated by direct connections between the cortex and the spinal cord
primary motor cortex is organized somatotopically like the somatic sensory cortex
Axons of neurons in layer V of the primary motor cortex project through the corticospinal tract to the spinal cord
The axons descend through the subcortical white matter, the internal capsule and the cerebral peduncle in the midbrain
The descending corticospinal tract crosses to the opposite side of the spinal cord – most fibers cross the midline in the medulla
The fibers make monosynaptic connections with motor neurons (individuated finger movements) and form synapses with interneurons in the spinal cord (coordinating larger groups of muscles)
Information is modulated by both sensory information and other motor information
Cerebellum and basal ganglia provide constantly feedback necessary for smoothly executed movements
