(2) Sensory Pathways

Afferent pathway

carry information from the body to the brain

1st order neuron

detects the stimulus and enters CNS from the sensory receptor to the spinal cord or brainstem

2nd order neuron

sensory information crosses to the opposite side, starting in the spinal cord or medulla to the thalamus

3rd order neuron

sends sensation to the correct brain region for conscious perception, from thalamus to primary sensory cortex

Three major sensation groups

1. somatic

2. visceral

3. special

Somatic senses

body and skin

• touch

• pressure

• pain

• temperature

Visceral senses

internal organs

• pressure

• volume

• internal discomfort/pain

Special senses

use cranial nerves instead of spinal sensory pathways

• vision

• hearing

• taste

• smell

• balance

Three major sensory pathways

1. dorsal column-medial lemniscus pathway

2. spinothalamic tract

3. spinocerebellar pathway

Dorsal Column-Medial Lemniscus Pathway

carries high-resolution sensory information:

• fine touch

• 2 point discrimination

• vibration

• conscious proprioception

• pressure

Where does dorsal column-medial lemniscus pathway cross?

in the medulla

Where does dorsal column-medial lemniscus pathway end?

sensory cortex

Spinothalamic tract (anterolateral system)

carries protective sensations

• pain

• temperature

• crude touch

• pressure

Where does the spinothalamic tract cross?

immediately at spinal cord entry level

Where does the spinothalamic tract end?

sensory cortex

Spinocerebellar pathway

• carries unconscious proprioception (coordination/balance)

• helps coordinate ongoing movements

Where does the spinocerebellar tract end?

cerebellum

Where is sensory loss if damage occurs to a tract before crossing?

on the same side

Where is sensory loss if damage occurs to a tract after crossing?

on the opposite side

Somatosensory homunculus (primary sensory cortex)

a map of the body on the brain located in postcentral gyrus (parietal lobe); shows which parts of the body have greater sensory representation

Body parts with high sensitivity

• lips

• face

• hands

• tongue

Body parts with less sensitivity

• back

• trunk

• legs