10 sensory tracts

4 (or 5) somatic sensory modalities

Touch, pressure, proprioception, pain, temperature

Quantitative sensations

Touch, pressure (vibration), proprioception

Qualitative sensations

Pain, temperature

Is balance a somatic sensory modality?

No (special sense)

Ascending spinal tracts are

Sensory afferents

Dorsal root carries

Sensory (afferent) axons

Dorsal root ganglion contains

Cell bodies of 1st-order sensory neurons

Ventral root carries

Motor (efferent) axons

Spinal nerve carries

Both sensory and motor fibres

Dermatome

Area of skin supplied by one spinal level

Spinal epidural space is filled with

Adipose tissue and blood vessels

Pathways using a 3-neuron system

Sensory pathways (e.g. spinothalamic, DCML)

1st-order sensory neuron

Receptor → DRG → spinal cord

2nd-order sensory neuron

Ascending tract (decussates) → thalamus

3rd-order sensory neuron

Thalamus → internal capsule → postcentral gyrus

Extra structure where sensory (but not motor) pathways synapse

Thalamus

Internal capsule

Projection fibres between thalamus and basal nuclei; sensory + motor; becomes corona radiata

Does the 3rd-order neuron decussate at the thalamus?

No

Spinothalamic tract carries

Pain and temperature

Spinothalamic receptors

Free nerve endings

Spinothalamic 1st synapse

Dorsal horn grey matter of the spinal cord

Spinothalamic decussation

Spinal cord

Spinothalamic ascends on which side?

Contralateral (opposite the stimulus)

Spinothalamic 2nd synapse

Thalamus

Spinothalamic extra terminations

Temporal lobe (memory/emotion), reticular formation (pain modulation, alertness)

Spinothalamic fibres cut before decussating → deficit side

Ipsilateral

DCML stands for

Dorsal column - medial lemniscus

DCML carries

Touch, pressure, vibration, proprioception

DCML ascends in the spinal cord on which side?

Ipsilateral (same side)

Gracile fasciculus carries

Info from the legs (below T6); sensory, not motor

Cuneate fasciculus carries

Info from the arms (above T6)

Spinal level separating gracile and cuneate input

T6

Left cuneate fasciculus carries

Proprioception (and touch) from the left upper limb

DCML 1st synapse

Medulla (nucleus gracilis / nucleus cuneatus)

Leg fibres in DCML synapse in

Nucleus gracilis

DCML decussation

Medulla

After decussating, DCML fibres become the

Medial lemniscus

DCML 2nd synapse

Thalamus

Spinal pathway for touch

DCML

Proprioception to the cerebellum travels via

Spinocerebellar tract (ipsilateral, inferior cerebellar peduncle)

Spinocerebellar receptors

Muscle spindles and tendon organs

Left dorsal column lesion →

Loss of touch/pressure/vibration on the LEFT below the lesion

Right spinal cord hemisection at T8 →

Right loss of proprioception/touch; left loss of pain/temp, below T8

Left spinal cord hemisection at T12 →

Left leg loses touch/pressure/proprioception; right leg loses pain/temperature

Left pain/temp loss + right touch loss → lesion site

Right spinal cord

Right medial lemniscus (medulla) lesion →

Left touch and proprioception lost

Can't feel vibration in toes but pain intact → tract

DCML

Lesion above the medulla → sensory loss side

Opposite (contralateral) for everything

Interoceptors

Autonomic sensory receptors inside organs

Visceral vs somatic pain quality

Visceral = dull, poorly localized; somatic = sharp, well localized

Mechanism of referred pain

Visceral and somatic fibres converge on the same 2nd-order neurons in the dorsal horn; brain can't tell the source

Gallbladder pain felt in the right shoulder is

Referred pain

Why appendicitis pain moves to the RLQ

Somatic fibres in the abdominal wall become involved

Dermatome levels by plexus

Brachial C5-T1; intercostals T1-T12; lumbar L2-L5; sacral S1-S4

Dorsal vs ventral rami

Branches of the spinal nerve to the back vs. front of the body

Spinothalamic collaterals go to

Medullary and pontine reticular formation and periaqueductal grey (pain modulation, alertness)

Spinocerebellar tract enters the cerebellum via

Inferior cerebellar peduncle

Do autonomic sensory fibres travel with motor fibres?

Yes - they follow autonomic motor fibres to the spinal cord, then join the spinothalamic pathway