Sensory and Motor Key Words

Sensory pathways [5]

1. dorsal columns (gracile-cuneate tracts)

2. spino-cervico-thalamic

3. spino-reticular

4. spino-cerebellar

Somatosensory cortex

• regular somatatotropic organisation

• disproporitonate arrangement

• inverted image - lower body, higher up in parietal cortex

• caudal to cruciate sulcus

  • sulcus = groove

  • gyrus = raised fold

Dorsal columns ROLE

• gracile hindlimb

• cuneate forelimb

• Touch

• Pressure

• Kinesthesia

Spino-cervico-thalamic ROLE

Mainly touch and pressure

(very minor role in superficial pain - not really in pain unit as not bilateral)

Spino-thalamic ROLE

• Pain/Nociception

  • superficial, fast ‘pinprick pain’

  • pain unit with spinoreticular

• Temp - skin + viscera

Spino-reticular ROLE

Wake-fullness

Slow, delayed, ‘true’ pain - (other than pinprick)

• part of pain unit

• superficial to deep tissues

• all intensities (itch→agony)

• persistent pain leads to nausa and lower blood pressure

Spino-cerebellar role

UNCONSIOUS proprioception

• cerebral cortex does conscious proprioception

• coordinates and finetunes motor activity

• interacts with pyramidal system for movement

Medial lemniscal system

• in medulla oblongata

• concentrated + heavily myelinated neurones

• where most decussation of fibres tales place

• mainly part of bilateral contralateral relay - except for spinothalamic = multi-relay

• relays sensory info via thalamus

• then reaches somatosensory cortex in cerebrum (parietal lobe)

Which three pathways go through the medial lemniscal system [3]

1) Dorsal columns

2) Spinocervicothalamic tracts

3) Spinothalamic tracts

Dorsal column pathway

3 neurones

[sensory, medial lemniscus, thalamus]

1. sensory neurone [dorsal root ganglion] (psudounipolar)

2. travels up spinal cord

3. synapse in nucleus gracilis of medulla

4. contralateral decussation of neurone in medial lemniscus

5. synapse at the thalamus

6. fibre travels to somatosensory cortex

Dorsal columns - brain lesion

Contralateral

lesion in left brain → no sensation in right

Spino-cervico-thalamic pathway

4 neurones

[sensory, RELAY, medial lemniscus, thalamus]

1. sensory neurone [dorsal root ganglion] (psudounipolar)

2. synapses AT spinal cord

3. synapse in C1/C2 lateral cervical nucleus

4. contralateral decussation of neurone in medial lemniscus

5. synapse at the thalamus

6. neurone travels to somatosensory cortex

Spino-thalamic pathway

Multineurone pathway

• humans → 3 relay, so 6 in total

• [sensory, RELAYS, medial lemniscus, thalamus]

1. sensory neurone [dorsal root ganglion] (psudounipolar)

2. BILATERAL synapse at spinal cord

3. Multiple RELAYS

4. Medial lemniscus neurones

5. Thalami

6. Somatosensory cortex

Spino-reticular pathway

Multirelay

• [sensory, ascending reticular formation (multiple relays), thalamus]

1. sensory neurone [dorsal root ganglion] (psudounipolar)

2. BILATERAL synapse at spinal cord

3. up ascending reticular formation

4. thalami

5. somatosensory cortex

Spino-cerebellar

2 neurones (sensory + relay)

1. sensory neurone [dorsal root ganglion] (psudounipolar)

2. ipsilateral synapse in spinal cord

3. PARTIAL decussation to contralateral side

   • (fibre splits in 2)

4. PARTIAL decussation back to ipsilateral side

5. neurone continues to palaeo-cerebrum/VERMIS (proprioception)

Bilateral relays lesions

• spinoreticular

• spinothalamic

• cannot tell location of lesion

• if cannot feel deep pain/complete loss of pain

  • spinoreticular damaged

  • deep and robust fibres

  • so severe damage to the body

Spinocerebellar - main exception LESION

ATAXIA on the ipsilateral side