Somatosensory Systems Flashcards
the hierarchal control of sensory function
Sensory information from the muscles and sensors travels to the cranial and spinal nerves, then the brainstem, subcortex, and lastly the cortex
This is bottom up processing
basic function of the somatosensory system
carry information about pain, touch, temperature, and proprioception from the body to
the brain.
Somatosensory information from the head and neck is carried along cranial nerves
Somatosensory functions, particularly proprioception, are crucial inputs for the motor systems. For example, if you are gesturing to show a friend exactly how big the fish was that you caught compared to your brother’s fish, your motor system needs to know where your arms are to begin with (e.g., by your side) to move your hands close together to show how small your brother’s fish was
sensory homunculus
- a map along the cerebral cortex of where each part of the body is processed
*illustrates the amount of representation each part of the body has in the sensory cortex, the human homunculus emphasizes the hand and face. We gather most of our senses to make perceptions.
Phantom Limb
*On the pst central gyrus, the lower face is represented next to the hand
*When the hand is removed that cortical area is deprived of an input
*The sensory input normally destined for the face cortex now activates the vacated territory
*when the Lower face is touched, the somatosensory cortex interprets it as touch to the hand
Spinal Cord segment identification (screenshots)
grey matter, white matter, dorsal and ventral roots.
Dermatomes
*A peripheral region innervated by sensory fibers from single nerve root
*the dermatomes for the different spinal levels form a map over the surface of the body
Dorsal Column / Medial Lemniscus Pathway: general somatosensory tract pathway
*Carries information about proprioception, vibration sense, and fine touch from the periphery
- enters the posterior/dorsal horn of the spinal cord with no modification of the signal in the spinal cord (no synapse)
- Fibers ascend to the brainstem, where they synapse
- Postsynaptic fibers cross the midline and ascend to the contralateral thalamus
- Fibres synapse in the thalamus and postsynaptic fibres reach the sensory cortex
Dorsal Column / Medial Lemniscus Pathway: landmarks related to first, second, and third order neurons:
First order: Pseudounipolar; Dendrites: Mechanoreceptors and proprioceptors in the PNS/dorsal root ganglion; Axon: through dorsal root to dorsal column(gracilis/lower body & cuneatus/upper body); Synapse: Ipsilateral medulla. nucleus gracilis (lower body) or nucleus cuneatus (upper body)
Second Order: Multipolar; Dendrites: Nucleus cuneatus or gracilis; Axon: crosses over and extends through medial lemniscus; Synapse: Contralateral thalamus, ventroposterolateral nucleus
Third Order: Multipolar; Dendrites: thalamus, ventroposterolateral nucleus; Axon: extends through corona radiata; Synapse: Contralateral post central gyrus, primary somatosensory area
Dorsal Column / Medial Lemniscus Pathway: type of somatosensory information they transmit:
descriptive touch, vibration, proprioception
Dorsal Column / Medial Lemniscus Pathway: manifestations of pathway specific damage:
*Sensation; tingling, numbness, feeling of tight band-like sensation around trunk or limbs, dulled sensation on fingertips
Anterolateral System (Spinothalamic Tract): general somatosensory tract pathway
*Carries information about pain and temp from the periphery; technically there are 3 (spinothalamic, spinoreticular, spinomesencephalic)
- Enters the posterior(dorsal) horn of the spinal cord
- Information is modified directly into the spinal cord in the posterior horn (synapses!)
- Fibres corse the midline in the spinal cord and ascend to the contralateral thalamus
- Fibres synapse in the thalamus and post synaptic fibers reach the sensory cortex
Anterolateral System (Spinothalamic Tract): landmarks related to first, second, and third order neurons:
First order: Pseudounipolar; Dendrites: pain and temp receptors in the PNS/dorsal toor ganglion; Axon: through dorsal root to dorsal horn; Synapse: ipsilateral dorsal horn
Second order: Multipolar; dendrites: dorsal horn; Axon: crosses over and extends superiorly through the anterior or lateral white matter; Synapse: contralateral thalamus, ventropoterolateral nucleus
Third order: Multipolar; Dendrites: Thalamus, ventroposterolateral nucleus; Axon: extends through corona radiata; Synapse: Contralateral post central gyrus, primary somatosensory area
Anterolateral System (Spinothalamic Tract): type of somatosensory information they transmit:
Pain and temperature
Anterolateral System (Spinothalamic Tract): manifestations of pathway specific damage:
*Pain: sharp or burning/searing pain
Spinothalamic Tract
mediates discriminative aspects of pain and temperature, such as location and intensity of stimulus
