Somatosensory System Part 3 SN Flashcards
What is the Ventral Horn and Dorsal Horn referring to?
The grey matter (where cell bodies lie)
Where do large neurons lie?
Ventral Horn
Where do small neurons lie?
Dorsal Horn
In the white matter, what are dorsal columns?
Ascending axons only
In the white matter, what are lateral columns?
Ascending and Descending axons
What are descending axons?
Interneurons and Motor Neurons
In the white matter of ventral columns, what are descending responsible for?
Axial and postural muscles
In the white matter of ventral columns, what are ascending responsible for?
Pain and temperature
What are the fascicles involved in Ascending Axons?
Gracile and Cuneate Fasicles
What do sensory neurons do?
Get information from body surface
What do motor neurons do??
Innervate Skeletal Muscles
What do Sacral Levels contain?
Few axons, less white matter
What do Cervical Levels Contain?
Many axons, more white matter
Where are descending axons mostly found in?
Cervical Level
What are Larger Ventral Horns?
Spinal Levels that innervate arms and legs
What do Larger Ventral Horns have more of?
Motor Neurons
What does more motor neurons mean?
They have to innervate more muscle cells
What do larger dorsal horns reflect?
A greater density of sensory receptors which can send more fibres to spinal cord.
Where do ascending axons and somatotropin distribution start?
Sacral Regions
What happens in sacral regions?
Axons move into pathways more medial in dorsal columns
What happens in sacral to cervical regions?
Progressive Merging of axons medial to lateral
What happens in Gracile Fascicle?
- Medial Clustered Neurons….motor fibres from lower extremities
- Terminates in gracile nucleus (cluster of neurons in spinal cord)
What happens in the Cuneate Fascicle?
- Lateral Clustered Neurons
- Terminates in Cuneate Nucleus
What is the Medial Lemniscus?
- Long Fibre Bundles from Medulla Oblongata
- Synapses onto thalamic relay nuclei (VP nucleus)
- Arranged somatotopically
What is the Thalamus?
- Conveys sensory input to sensory axons of cerebral cortex and transmit and modulates inputs (motor information)
What is the Thalamus made up of?
50 distinct nuclei
Where do output axons travel through in the Thalamus?
The internal capsule
What are the 4 major groups of the thalamus?
Anterior, Medial, Ventral, Posterior
What is the Anterior Part of the Thalamus responsible for?
- Major inputs from hypothalamus and hippocampus
- involved with Memory and Emotion
- Connection with Frontal Cortex
What is the Medial Part of the Thalamus responsible for?
- 3 Sub-Divisions
- Connections to Frontal Cortex, Memory
- Inputs from Basal Ganglia, amygdala
What is the Ventral Part of the Thalamus responsible for?
- Motor Control, relays information from Basal Ganglia and Cerebellum
- Conveys to Somatosensory
What is the Posterior Part of the Thalamus responsible for?
- Auditory Nuclei, conveys to temporal lobe
- Input from Retina, conveys to visual cortex (occipital lobe)
What are Relay Nuclei?
Neuron clusters that terminate onto specific regions of cortex.
What is the Reticular Nucleus?
- The outer covering of thalamus, sheet-like neurons
What does the thalamic relay nuclei release?
Glutamate (excitatory)
What does Thalamic Nuclei (Outgoing) send?
Collaterals to Reticular Nucleus
What is the function of the Reticular Nucleus?
Modulates activity of thalamic nuclei and monitors the thalamocorticol stream of information
What does somatosensory information consist of?
- Primary Somatosensory Cortex (S1)
- Broadmann’s Area (3b)
- Area of Cortex devoted to body parts, not mass
What is the Primary Somatosensory Cortex?
Anterior Parietal Cortex
What are the 4 complete maps of skin in the Primary Somatosensory Cortex?
3a, 3b, 1 and 2
What does Area 2 mediate?
Tactile information is combined with limb position which mediates tactile recognition of objects
How does the Primary Somatosensory Cortex project to other areas of cortex?
- Motor Control
- Eye-Hand Coordination
- Memory Related to Touch
What is voluntary movement?
Primary motor cortex that is somatotopically organized
What does voluntary movement project through?
Corticospinal tracts to ventral horn of spinal cord through internal capsule (apart of the mid brain)
What are Direct Connections in Voluntary Movement?
Ventral Motor Neurons that are monosynaptic
What are Indirect Connections in Voluntary Movement?
Through Interneurons, coordinates large muscle groups
How is voluntary movement modulated by?
Sensory Information and Other Motor Region (cerebellum, basal ganglia, pre-motor)
What are the inputs of the cerebellum?
Somatosensory primary afferent and corticospinal axons
What are Error Correcting Mechanisms?
- Predictive Control of Movements
- Outgoing Commands adjusted based on information based on information about the reflections of prior movements
What are posture and movements in relation to the cerebellum?
- Connections to brain stem nuclei
- Direct modulation of spinal motor circuits
- Major influence through thalamic connections
