Sensory tracts

Question 1

Types of mechano receptors

Answer 1

• Meissner’s Corpuscles: detect light touch
• Pacinian corpuscles: sense deep pressure and vibration (e.g. power tool)
• Merkel cell: detect fine shape and texture
  Ruffini endings: detect stretch and sustained pressure

Question 2

Thermo recepto

Answer 2

detect temp changes in environment and body
Free nerve endings in skin and hypothalamus

Question 3

Cold receptors

Answer 3

sensitive to 10-40 CC, connect to A Delta fibres

Question 4

Warm receptors

Answer 4

sensitive to 30-50 C, connect to C fibres

Question 5

Extreme temp receptors

Answer 5

Detected by nociceptors (<10 or >50)

Question 6

Nociceptors and their axon connection

Answer 6

specialized receptors that detect pain caused by tissue damage
Free nerve endings connected to A delta fibers (sharp pain) or C fibres (dull pain)

Question 7

Types of nociceptors

Answer 7

• Mechanical: Activated by sharp or intense opressure
  ○ Thermal: extreme heat
  ○ Chemical: triggered by harmful substance like toxins or inflammatory mediators
  Polymodal: respond to a combination of stimuli

Question 8

Proprioceptors

Answer 8

Provide info about body position
- Muscle spindles: detect change in muscle length and muscle stretch
- Golgi tendon organ: monitor tension in tendons, preventing overloading
- Joint receptros: sense joint position and angles
In muscles, tendons and joint capsule

Question 9

Phasic skin receptors

Answer 9

Rapidly adapting receptors
○ Respond to changes or the beginning/end of a stimulus
○ Detect movement or changes
○ Stop responding after short period of time
○ Meissners’. Corpuscle or Pacinin corpuscle

Question 10

Tonic skin receptors

Answer 10

Slowly adapting
○ Continue to fire as long as stimulus is present
○ Merkel or ruffini ends
Important for postural control or sustained grip activities

Question 11

Axon Alpha A

Answer 11

• Largest diameter
  Highly myelinated

Question 12

Axon A beta

Answer 12

• Highly myelinated
  
  • Touch and pressure
    Very precise

Question 13

Axona A gamma

Answer 13

muscle spindle support
- Moderately myelinated
Maintains muscle tone

Question 14

Axon A Delta

Answer 14

• Lightly myelinated
  
  • Sharp, localized pain and cold temp
    The alarm system

Question 15

Axon B fibres

Answer 15

Lightly myelinated
Preganglionic autonomic system - control smooth muscles

Question 16

Axon C fibres

Answer 16

Slow but steady
- Non-myelinated, very slow
- Dull pain, warm temp and postganglionic autonomic system

Question 17

PCML tract

Answer 17

• Transmits fine touch, vibration and proprioception from body to the brain
  
  • Enables precise sensory perception, critical for balance and movement
    Helps in precise movement and spatial awareness

Question 18

Damage to PCML

Answer 18

Numbness, loss of vibration, loss of balance (proprioception)

Question 19

PCML tract pathway

Answer 19

1. Sensory fibres detect fine touch and proprioception
2. Travels via dorsal collumn (gracillis for below C6 and cuneatus for C6 and above)
3. Synapses and crosses at medulla
4. Ascends through medial lemniscus through thalamus
5. Ends in primary sensory cortex

Question 20

Spinothalamic tract

Answer 20

• Transmits pain, temperature and crude touch signals to the brain
  
  • Critical for detecting harmful stimuli and triggering protective reflexes
    Serves as the body’s alarm system for detecting harmful stimuli

Question 21

Damage to STT

Answer 21

Numbness
Loss of temp
Loss of pain

Question 22

STT pathway

Answer 22

1. Nociceptors and thermoreceptors in skin and viscera
2. synpase in dorsal horn
3. axons go up and down a few segments
4. crosse at anterior commisure in spinal cord
5. ascend contralaterally in anterolateral system
6. ascends to thalamus
7. ends in primary sensory cortex

Question 23

Spinocerebellar tract

Answer 23

• Transmits proprioceptive information to the cerebellum for balance and coordination
  
  • Fine tunes motor movements and ensures smooth coordination
  • Essential for unconscious proprioception
  • Originates in muscle spindles and GTO
    Travels ipsilaterally in the anterior and posterior spinocerebellar tracts

Question 24

Damage to SCT

Answer 24

Loss of muscle coordination and proprioception (ataxia)
Loss of balance

Question 25

SCT pathway

Answer 25

1. Sensory receptors in GTO, muscle spindles 2. Synpase in dorsal horn 3. Travel ipsilaterally 4. End in cerebellum for proccesing and coordination

Question 26

Somatopic organization of sensory tracts

Answer 26

○ All have cervical closer to grey matter and the spread from there ○ PCML: lower limb travels medial (gracilis) and upper limb travel lateral (cuneatus) ○ STT: lower limbs are lateral, upper limbs are medial ○ Clinical significance In an incomplete lesion, the spinal tract more lateral may still be intact while the closer tracts may be damaged

Question 27

Arterial supply to sensory tracts

Answer 27

Anterior spinal artery - Supplies the anterior 2/3 of spinal cord - Formed by branches of vertebral arteries Posterior spinal arteries - Supply the posterior one third of the spinal cord - Arise from vertebral or posterior inferior cerebellar arteries Segmental arteries Reinforce blood supply along the cord

Question 28

Venous drainage of spinal cord

Answer 28

- Anterior and posterior spinal veins collect venous blood from the cord - Internal vertebral venous plexus is located in epidural space ○ Connects with external venous system

Question 29

Anterior spinal artery syndrome

Answer 29

Motor paralysis and loss of pain/temp sensation ○ Discriminative touch and proprioception remains intact This is because we have the 2 posterior arteries that take care of supplying these tracts

Question 30

Posterior spinal artery syndrome

Answer 30

affects fine touch and proprioception ○ Motor control and pain/temp remain intact This is because anterior arteries supply this