Anterolateral System

GSA - general somatic afferent; somatosensation

includes 4 tracts, only 1 ends in the cortex

* Modalities transmitted by ALS * 

Nociception (pain)

Thermoreception (temperature)

Crude Touch

where the Spinothalamic Tract projects to

primary somato sensory cortex via the thalamus

Broadmann's Area 3,1,2

modality of Spinothalamic tract

concious perception - goes to the cortex

Where do axons come from in the Spinothalamic Tract

anterolateral tract

axons come from somatic structures (not visceral)

Where does the Spinoreticular Tract project to?

It projects to the Reticular Formation, which runs from the midbrain to the medulla

Important functions of the Spinoreticular Tract

Important in autonomic function, pain pathways, and as an alerting system for the brain

Function of the Reticular Formation

important in alerting the cortex, focusing attention, and some autonomic functions

where the spinoreticular tract projects to 

Spinomesencephalic Tract

is a subset of the spinotectal tract (consists of info from the superior colliculi - the "visual grasp" reflex to orient body, ears, eyes to a stim)

projects to the midbrain - not conscious

has some fibers for pain modulation via the periaquiductal grey

Spinohypothalamic Tract projects to ... 

the hypothalamus 

Spinohypothalamic tract is responsible for ... 

autonomic responses to stimuli (in the hypothalamus) - not conscious

Anterolateral System

areas connected to the Limbic System include ... 

Hypothalamus and Reticular Formation - generate complex emotional behaviors and emotional responses to pain

we are hardwired to have emotional responses to pain 

Axons in the Anterolateral System 

small - medium sized, lightly or un-myleinated

A beta

A delta

C 

A beta fibers 

carry information related to touch and temperature (non-noxious)

skin mechanoreceptors - have some myelination

A-delta fibers

carry information for pain and temperature; have very little mylein 

C fibers

carry information for pain, temperature, and itch; have no mylein (naked) and smallest in diameter; slowest

Which ALS tract(s) has controlateral projection?

 only

Spinothalamic tract

Which ALS tract(s) has bilateral projection?

Spinoreticular tract

Spinomesencephalic tract

Spinohypothalamic tract

Visceral Afferents

GVA (general visceral afferents)

Most is unconscious - drives reflexes

some conscious - when excessive or painful

consist of small, C-fibers

Receptors of GVA's

mostly nociceptors

stretch/pressure receptors

What tract(s) are GVA's apparent in?

Mostly in Spinoreticular, Spinomesencephalic, Spinohypothalamic - the non-conscious tracts

Posterolateral Tract

part of the primary afferent ascends +/or descends to superior and inferior spinal cord segments to contribute to the system - synapses onto the 2nd order/interneuron

Somatotopy of Spinothalamic tract

is very good

Parts of the Spinothalamic tract

1. Receptor (touch receptor, thermo receptor, nociceptor - naked nerve ending)
2. Primary Afferent w/ cell body in a ganglion (Posterior Root Ganglion)
3. Synapses onto 2nd order neuron in the Posterior Horn at the Pre-Thalamic Nucleus
4. Decussates at the Anterior White Commissure
5. Ascends the cord
6. Synapes onto the 3rd order neuron at the VPL (Thalamic Relay Nucleus)
7. Passes through the Posterior Limb of the Interal Capsule
8. Enters the Primary Somatosensory cortex