L15 Sensory Pathways

Question 1

What structure protects the spinal cord?

Answer 1

The vertebral column

Question 2

What structures are covered by the dura?

Answer 2

• Spinal cord
• Dorsal roots
• Dorsal root ganglia

Question 3

What is a dermatome?

Answer 3

A region of skin supplied by an individual spinal nerve (DRG neuron), DRG neurons do not innervate the face or upper scalp.

Question 4

What is referred pain?

Answer 4

Pain percieved at alternative site to the stimulus/origin of pain.
Can be used to diagnose visceral problems.
E.g. spinal nerve carrying axons to dermatome but also carrying to internal organ, damage to internal organ may be then percieved as pain in the skin

Question 5

Name the sensory end organs of low threshold mechanoreceptors.

Answer 5

Low threshold mechanoreceptors innervate many end organs in the skin:

• Hair follicle ending
• Merkel’s endings (dense on finger pads)
• Meissner’s ending (brief touch)
• Pacinian corpuscle (vibration)
• Ruffini ending (shear stress)

Question 6

What is the name of the sensory ending of nociceptive neurons?

Answer 6

Naked endings: pain temperature and itch

Question 7

What is the dorsal column pathway?

Answer 7

Tract carrying info on discriminative touch (touch provided by low threshold mechanoreceptors) and conscious proprioception

Question 8

Describe the route of the dorsal column pathway.

Answer 8

• Central axons exit dorsal horn and branch
• Axons project into medulla and make synaptic connection with dorsal column nuclei
• Neurons of dorsal column nuclei project axon which crosses midline and travels in fibre tract up to the thalamus
• Synapses with ventral posterior thalamic nulcei (somatically mapped = precise pain location, discrimative touch)

Question 9

What is two point discrimination?

Answer 9

The ability to distinguish between two points of sensory contact on the skin.
This ability varies for different regions of the body and depends on the density of sensory innervation.

Question 10

Where is two point discrimination more sensitive, and where is it weaker?

Answer 10

• Sensitive: lip (6mm), index finger (2.5mm)

- Weak: forearm (38mm), calf (47mm)

Question 11

What is the spinocerebellar pathway?

Answer 11

Tract for non-conscious proprioception (ability to know where our limbs are in space).

Question 12

Describe the route of the spinocerebellar pathway.

Answer 12

• Proprioceptive neuron from DRG, 1 branch contacts motor neuron in ventral horn, 1 branch contacts synaptic neuron in the nucleus of Clarke
• Neurons from nucleus of Clarke travel up to the medulla
• Neurons from lateral cuneate nucleus in the medulla travel to the cerebellum

Question 13

What are the trigeminal sensory/motor pathways?

Answer 13

Pathways which emerge from the trigeminal nuclei to provide sensory innervation to the face and motor innervation to the muscles of mastication and facial expression.
Recieve info from trigeminal ganglia.

Question 14

What are the 3 trigeminal nuclei?

Answer 14

• Mesencephalic nucleus
• Main/pontine nucleis
• Spinal nucleus

Question 15

Describe the mesencephalic nucleus.

Answer 15

Found at the top of the spinal cord.

Cell bodies of trigeminal proprioceptors innervating muscles of mastication and facial expression.

Question 16

Describe the main/pontine nucleus.

Answer 16

Found in the pons.

Recieves input from trigeminal ganlgion neurons that detect discriminative touch sensation.

Question 17

Describe the spinal nucleus.

Answer 17

Found in the medulla.
Recieves input from trigeminal ganglion neurons detecting pain, temperature, itch and simple touch.
Somatic sensory input from cranial nerves VII, IX, X.

Question 18

Describe face mapping.

Answer 18

The face is mapped into 5 concentric dermatomes.

Each dermatome innervated by the 3 branches of the trigeminal nerve: opthalmic, maxillary, mandibular.

Question 19

Which cranial nerves provide somatic sensory innervation to the external ear and auditory canal?

Answer 19

• Cranial nerves VII, IX and X
• VII assocaited somatic sensory neurons are in geniculate ganglion
• IX assocaited somatic senosry neurons are in petrosal ganglion
• X associated somatic sensory neurons are in nodose ganglion

Question 20

Which spinal nerves provide somatic sensory innervation to the lower scalp, lower edges of the jaw and neck?

Answer 20

• Spinal nerves, C2, C3 and C4

Question 21

Does the brain have sensory innervation?

Answer 21

No, brain parenchyma receives no sensory innervation.

Question 22

What neurons innervate the dura?

Answer 22

Trigeminal ganglion neurons

Question 23

What neurons innervate the oral and nasal cavity and teeth?

Answer 23

Trigeminal nerve branches

Question 24

Which neurons innervate the spinal dura?

Answer 24

C2, C3 DRG