Week 5 - Somatosensation

Question 1

Define sensory system

Answer 1

Sensory recpetors
Receive stimuli from external or internal environment
Neural pathways to the brain

Question 2

Define sensation

Answer 2

If the sensory information reaches the consciousness

Question 3

Define perception

Answer 3

The understanding of sensations meaning

Question 4

Define somatic receptors

Answer 4

The receptors in the outer body; skin, skeletal muscle, tendons and joints

Question 5

Define special senses

Answer 5

Vestibular system, visual system, auditory system, chemical senses (taste,smell)

Question 6

Define perceptual processing

Answer 6

Understanding and interpreting sensory info

Question 7

Types of sensory receptors ?

Answer 7

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)

Question 8

Types of interceptors and examples?

Answer 8

Baroreceptors - blood pressure

Chemoreceptors - Ph and O2 concentration

Question 9

Types of exteroceptors and examples?

Answer 9

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

Question 10

What are free nerve endings?

Answer 10

Can detect pain, touch, itch and temperature

Question 11

What are encapsulated sensory nerve endings?

Answer 11

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.

Question 12

What are cutaneous sensory receptors?

Answer 12

Type of sensory receptor found in the skin (dermis or epidermis).

Question 13

Overview of somatosensory pathways?

Answer 13

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

Question 14

What does the first-order neurone do?

Answer 14

Connects information from receptors → brainstem/ spinal cord

Question 15

What does the second-order neurone do?

Answer 15

Conducts information from the brainstem and spinal cord to the thalamus.
They always decussate prior to ascending.

Question 16

What does the third-order neurone do?

Answer 16

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).

Question 17

What are the main ascending pathways?

Answer 17

spinothalamic
dorsal columns
spinocerebellar

Question 18

Dorsal columns pathway?

Answer 18

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)

Question 19

What are the dorsal columns responsible for?

Answer 19

proprioception and discriminative touch

Question 20

Spinothalamic tract pathway?

Answer 20

• 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)

Question 21

What is the spinothalamic tract responsible for?

Answer 21

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

Question 22

Spinocerebellar tract pathway?

Answer 22

• 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

Question 23

What is spinocerebellar tract responsible for?

Answer 23

Unconscious proprioception
- to control posture and co-ordination of movement

Question 24

Why does damage to the spinal cord result in brisk reflexes?

Answer 24

Upper motor neurone issue - sensory input does not go to the brain so the reflex is not inhibited by the brain.

Question 25

Complete spinal cord lesion?

Answer 25

All the way through the spinal cord

No movement at that level onwards

Question 26

Incomplete spinal cord lesion?

Answer 26

Not all way through spinal cord

Some info can still pass through