Lesson 6
What type of somatosensory information is there?
What are the 3 main functions of somatosensory info?
- somatosensation: sensory information from the skin and musculoskeletal systems
1. exteroception: sense of direct interactions with the external world and its impact on the body
2. proprioception: sense of one's own body, involving sensations from muscles, joints, and tendons
3. interoception: sense of the functions and state of internal body organs
What are the general tactile system functions?
-Discriminative touch/ tactile perception
- detection and perception of objects and materials that contact skin
- contributes to development of body schema of praxis
- associated with fine motor coordination
- social/ affective touch
- light, caressing touch
- emotional bonding: contact and comfort
- emotion and arousal regulation
What are the infant social emotional development in humans?
- being held and the comfort it provides is important developmentally
- early caregiver neglect may change the way the brain is wired
What is proprioception?
- perception of:
- joint and body movements
- position of the body (body segments) in space
- provides a continuous flow of sensation from the muscles, joints and tendons
- detection of joint position and movement (including rate and timing of movements)
- spatial orientation of the body/ body parts
- amount of force our muscles are exerting
Why is tactile/ touch important?
-physical safely
-connection with the social world
- exploration of the environment
- development of body scheme and motor skills
- influence on state regulation (arousal and activation)
ex: squeezes and tight hugs
Why is proprioception important?
-physical safely
-development of motor skills/ motor learning
- refinement of movement
- timing of movement
- influence on state regulation (arousal and activation)
ex: big, heavy movements
What are the somatosensory receptors?
-touch: mechanoreceptors (respond to mechanical deformation of receptor)
- Body part position and movement: proprioceptors (responds to length of muscle, tension of joints and tendons, etc)
- Temperature: thermoreceptors (responds to heat or cooling)
- Chemicals: chemoreceptors (responds to substances released by cells)
- Pain: nocioceptors -subset of all above- (sensitive to stimuli that damage or can damage)
* information from all of these may reach awareness but much of the information is used to make automatic adjustments
What is the function of the somatosensory receptor?
What are the adaptations?
-transduction of stimulus into an electrical signal
Adaptations
- slow adapting/ tonic: receptor continues to fire during entire presentation of the stimulus (ex: weight lifting)
- fast adapting/ phasic: receptors adapts quickly to stimulus and stops responding
- phasic receptors ( wearing a watch all day)
what is receptor density?
- number of receptors within a given area of body surface
What is receptive field?
area of skin innervated by a single afferent neuron
- large: borders are difficult to define; often cover a large area
- small: borders are sharply defined; small area
* distal regions tend to have greater density of receptors than proximal regions and smaller receptive fields
What are proprioceptors?
- body part position (stationary and movement)
- mechanoreceptors: joints, muscles
- muscle spindle
- Golgi tendon organ
What are the types of sensory pathways?
-Conscious relay pathway: info about location and type of stimulation to cortex (fine details)
- Divergent pathways: transmit info to many areas of the brainstem and cerebrum
- unconscious pathways: brings unconscious proprioceptive and other movement related information to the cerebellum (influencing poster)
what are the 3 primary components of somatosensory pathways?
- receptors
- sensory pathways
- brain centers
What is the primary afferent fiber?
- first order neurons are pseudounipolar
- not receiving any info from other neurons
- cell body: dorsal root ganglia (distal/ peripheral and proximal/ central branches
- dorsal root( sensory)= afferent sensory root that enters the SC (dorsal horn)
- dorsal horn: grey matter
- dorsal column: white matter
What are dermatomes?
-loss sensation
- the area of skin innervated by axons from cell bodies in a single dorsal root
- these are overlapping (potential for preservation of function)
What is the DCML?
-dorsal column medial lemniscal tract
Functions
- discriminative touch: localization of touch and the ability to discriminate between two closely spaced points touching skin (details)
- vibration
- Conscious proprioception/ kinesthesia: the awareness of movements and relative position of body parts
receptors: mechanoreceptors and proprioceptors
three neuron projection system (high fidelity= great accuracy)
What is the 1st order neuron?
- DCML
-conveys info from the receptor to the medulla
- cell bodies located in dorsal root ganglia (diameter of 1st order neuron=big)
-ipsilateral projection into dorsal root and then into the dorsal column (organization of SC: fascicles cuneatus- axons from upper limbs; fascicles gracilis: axons from lower limbs)
-synapse at dorsal column nuclei of medulla
- nucleus cuneatus
- nucleus gracilis
What is the 2nd order neuron?
- DCML
-conveys info from the medulla to thalamus
- cell bodies located in the nucleus gracilis or cuneatus
- decussation occurs at the level of medusa (crosses over)
- ascend as the medial lemniscus
- project to VPL (ventral posterolateral nucleus) of the thalamus
what is the 3rd order neuron?
- DCML
What is the primary somatosensory Cortex (S1)
- conveys info from thalamus to the cortex
- Cell bodies located in VPL of thalamus
- Projects through internal capsule to primary somatosensory cortex
Primary Somatosensory Cortex (S1)
- somatotpic representation: Homunculus
- somatosensory association areas
What are the unconscious relay tracts to the cerebellum?
- spinocerebellar tracts
- information from proprioceptors transmitted to the cerebellum
- critical for unconscious adjustments to movement and posture
What is the anterolateral system?
- named for fiber tract in the ventral (anterior) aspect of the spinal cord
- several parallel tracts ascend in the anterolateral spinal cord
- function: carries info about pain, temperature, crude/coarse touch
What are the pathways of the anterolateral system? *spinothalamic tract
- Spinomesencephalic tract
- involved in turning the eyes and head toward the source of noxious input (break hand, eyes target area)
-Spinoreticular tract
- involved in pain stimuli commanding attention and interfering with sleep ( can't stop paying attention to pain)
- spinolimbic (spinohypothalamic) tract
-involved in emotions, personality, movement, etc (sends to limbic system- emotional)
1. discriminative (fast) pain
2. Discriminative temperature
3. Crude/ coarse (non specific touch)
- Receptors: nocioceptors and thermoreceptors
- three neuron projection system
What is the 1st order neuron?
STT
- conveys info from receptor to dorsal horn
- cell bodies located in dorsal root ganglion
- can join tract of Lissauer (goes up or down 102 levels)
- synapses in the ipsilateral dorsal horn
Where is the 2nd order neuron?
-STT
-conveys info from dorsal horn to thalamus
- cell bodies located in the ipsilateral dorsal horn
- decussates to contralateral spinal cord
- ascends in the anterolateral white matter tract area to VPL of the thalamus