Sensory system Flashcards
What are the 2 general divisions of sense?
- special sensation
- general sensation
What falls under special sensation?
acoustic, visual, smell and taste
What falls under general sensation?
- Superficial sensation (skin and mucosa): pain, temperature, touch
- Deep sensation (muscles, tendons and joints): vibration, sense, movement sense and position sense 3. Complex sensation (cerebral cortex):
- topognosis (identification of location of stimulus on skin)
- stereognosis (mental perception of depth)
- 2 point discrimination
What is the pathway for the sensation of pain and temperature?
nerve endings in the skin and mucosa –> posterior spinal root ganglion –> spinal cord –> runs up 2-3 spinal segments –> cells in the posterior horn –> crosses through the anterior white commisure to the other side –> lateral spinothalamic tract –> brainstem –> ventroposterior lateral nucleus of the thalamus –> posterior limb of the internal capsule –> postcentral gyrus (parietal lobe)
What is the pathway for touch (tactile) sensation?
skin –> posterior spinal root ganglion –> spinal cord (dividing into 2 routes)
1) Tactile sensation –> posterior white column (fasciculus) –> joins the deep sensation pathway
2) Light touch –> cells in the posterior horn –> crosses through white commisure to the other side –> joins pain and temperature pathway
What is the pathway for deep sensation?
muscles, joints and tendons –> posterior spinal root ganglion –> dorsal root –> posterior spinal cord –> ascending in the ipsilateral fasciculus gracilius and fasciculus cuneatus –> ipsilateral nuclei of fasciculus gracilis and cuneatus (medulla) –> cross in the decussation of the medial lemniscus to the other side –> VPLN of the thalamus –> posterior limb of the internal capsule –> postcentral gyrus
Define: dermatome/ dermatomic area
[how many dermatomes do humans have]
each posterior spinal root comes from one spinal segment which supplies a certain area of skin. The area supplied is known as a dermatome
[31]
Where is segmental cutaneous innervation best seen? Provide locations
Best seen in the thoracic area
T4: nipple
T7: costal arch
T10: umbilicus
T12-L1: groin
Define the following terms which fall under irritative sensory disturbances:
1. Hyperesthesia
2. Hyperpathia
3. Dysesthesia
4. Paraesthesia
5. Pain
-local
-radiating
-spreading
-referred
**caused by irritative lesion in the sensory pathway
1. increased tactile sensibility (small stimuli causes strong sensation)
2. decreased tactile sensibility
3. when a non-painful stimuli causes a painful sensation or when a hot stimuli causes a cold sensation
4. when no stimuli is given, patient may feel an abnormal sensation
5. I pain at the site of the lesion
II. pain is not only at the site of the lesion but follows the distribution of the nerve
III. pain spreads from one nerve branch to another
IV. pain from an internal organ may be spread to a distant dermatomic area
What causes inhibitory symptoms during sensory disturbances and what are the different classifiations?
**inhibitory symptoms are caused by destructive lesions in the sensory pathway
1. hyperesthesia: diminished sensation
2. anaesthesia: loss of sensation
3. complete anaesthesia: complete loss of all sensation
4. dissociated anaesthesia: loss of some forms of sensation (pain and temperature) and preservation of other types of sensation (tactile)
Describe the “distal type” diagnosis of sensory disturbances
symmetric hyperesthesia or anaesthesia of distal extremities in a glove or sock fashion
i.e., polyneuropathy
Describe the “peripheral nerve type” diagnosis of sensory disturbances
sensory disturbance is located in the distribution of the affected peripheral nerve
Describe the “segmental type” diagnosis of sensory disturbance
- Posterior spinal root type: posterior spinal root injury on one side may cause unilateral segmental complete sensory disturbance in its or their distribution, often with radiating pain of the posterior spinal root ganglion
i.e., extramedullary tumour compression - Posterior horn type: a lesion in the posterior spinal horn (syringomyelia) on one side will cause ipsilateral dissociated anaesthesia
- Anterior commisure type: a lesion in the anterior commisure will cause bilateral symmetric segmental dissociated anaesthesia
Describe the “conductive tract type” diagnosis of sensory disturbance
- spinal hemisection (Brown-sequard) syndrome
* ipsilateral deep sensation disturbance and upper motor neuron paralysis below the level of the lesion
*contralateral loss of pain and temperature below level of lesion
*usually caused by extramedullary tumour and haematomyelia - spinal transection lesion
*loss of all sensation below level of lesion
*paraplegia or quadraplegia below level of lesion
*disturbance of bladder and rectum function
*acute transverse myelitis
Describe the “cross type” diagnosis of sensory disturbance
caused by a medullary lesion (Wallenberg syndrome-PICA occlusion)
* loss of pain and sensation on ipsilateral face and contralateral body
* due to damage to ipsilateral nucleus of spinal tact of trigeminal nerve and contralateral spinothalamic tract
* many other structures in medulla is involved
