Week 5 - Somatosensation Flashcards
Define sensory system
Sensory recpetors
Receive stimuli from external or internal environment
Neural pathways to the brain
Define sensation
If the sensory information reaches the consciousness
Define perception
The understanding of sensations meaning
Define somatic receptors
The receptors in the outer body; skin, skeletal muscle, tendons and joints
Define special senses
Vestibular system, visual system, auditory system, chemical senses (taste,smell)
Define perceptual processing
Understanding and interpreting sensory info
Types of sensory receptors ?
Interceptors → Info. about internal environment
Exteroceptors → Info about ext. environment inc. some special senses e.g. hearing, vision, smell + taste (also touch, pressure, vibration, temp. + pain)
Types of interceptors and examples?
Baroreceptors - blood pressure
Chemoreceptors - Ph and O2 concentration
Types of exteroceptors and examples?
Mechanoreceptors - stretch - Pacinian corpsical, merkel disc, ruffini endings (cutaneous)
Thermoreceptors - heat - Krause end bulbs and ruffini endings detect warmth (cutaneous)
Nociceptors - pain - free nerve endings (cutaneous)
Proprioceptors - knowing where your limbs are in space - muscle spindle and joints (joint capsules tell the brain the position of joint).
Photoreceptors - Golgi tendon organ, retinal ganglion cells, rods and cones
What are free nerve endings?
Can detect pain, touch, itch and temperature
What are encapsulated sensory nerve endings?
These nerve endings are surrounded by a structural specialisation of non-neural tissue, the combination of nerve + it’s encapsulation often being referred to as a 𝗰𝗼𝗿𝗽𝘀𝘂𝗰𝗹𝗲.
What are cutaneous sensory receptors?
Type of sensory receptor found in the skin (dermis or epidermis).
Overview of somatosensory pathways?
Somatosensory pathways relay info. from somatosensory receptors to the primary somatosensory area within the cerebral cortex.
EACH PATHWAY CONSISTS OF 3 NEURONS:
First - order neurone → primary afferent neurone
Second -order neurone → decussates
Third-order neurone → projects to somatosensory cortex
What does the first-order neurone do?
Connects information from receptors → brainstem/ spinal cord
What does the second-order neurone do?
Conducts information from the brainstem and spinal cord to the thalamus.
They always decussate prior to ascending.
What does the third-order neurone do?
Projects to somatosensory cortex on the same side as the thalamus but opposite side to the sensation.
(as this is where perception of the sensation occurs).
What are the main ascending pathways?
spinothalamic
dorsal columns
spinocerebellar
Dorsal columns pathway?
Located at back of spinal cord
2 tracts that convey info regarding proprioception and discriminatory touch:
→ Fasciculus gracilis - lower limbs
→ Fasciculus cuneatus - upper limb
1st order neurone - synapse with medulla at nucleus gracilis/cuneatus (ipsilateral)
2nd order neurone - convey info. from these nuclei to thalamus
3rd order neurone - travel from thalamus to primary sensory cortex (contralateral-becomes conscious)
(deccusates at the medulla)
What are the dorsal columns responsible for?
proprioception and discriminative touch
Spinothalamic tract pathway?
- Peripheral sensory nerves synapse within the dorsal horn with 2nd order neurones from the spinothalamic tract
- Info through spinal cord and brainstem to thalamus
- Thalamus to primary sensory cortex
(pathway decussated immediately- all contralateral)
What is the spinothalamic tract responsible for?
pain, temperature and non-discriminative touch
- able to provide highly organised somatotopical info.→ highly accurate and detailed info regarding sensory stimuli
- sharp prickly pain conducted within this system
Spinocerebellar tract pathway?
- Ascending spinocerebellar fibres (e.g.1a fibre) convey info form muscle spindles, golgi tendons organs and tactile receptors to the cerebellum.
- Info used by cerebellum to control posture and balance (unconscious proprioception)
- Info conveyed from one side of body to same side of cerebellum via posterior/dorsal spinocerebellar tract
- To help coordination of movement, the cerebellum receievs info from opposite side of body via anterior/ventral spinocerebellar tract.
IPSILATERAL
What is spinocerebellar tract responsible for?
Unconscious proprioception
- to control posture and co-ordination of movement
Why does damage to the spinal cord result in brisk reflexes?
Upper motor neurone issue - sensory input does not go to the brain so the reflex is not inhibited by the brain.
Complete spinal cord lesion?
All the way through the spinal cord
No movement at that level onwards
Incomplete spinal cord lesion?
Not all way through spinal cord
Some info can still pass through
