Dorsal column-medial lemniscal
Large, myelinated fibres
30-110m/s
Discrete types of mechanoreceptive sensation
High degree of spatial orientation of nerve fibres with respect to origin
Anterolateral
Smaller, myelinated fibres
Up to 40m/s
Broad spectrum of sensory modalities
Less spatial orientation
Types of sensory stimulus
Touch sensations requiring a high degree of localisation of stimulus
Touch sensations requiring transmission of fine gradations of intensity
Phasic sensations, such as vibratory sensations
Sensations that signal movement against the skin
Position sensations from the joints
Pressure sensations related to fine degrees of judgement of pressure intensity
Types of sensory stimulus
Pain
Thermal sensations (both warmth and cold)
Crude touch and pressure sensations capable only of crude localising ability on the surface of the body
Tickle and itch sensations
Sexual sensations
Course
Carries signals up to the medulla in the dorsal columns of the spinal cord
Synapse in dorsal column nuclei (the cuneate and gracile nuclei)
Second-order neurons cross immediately to opposite side in medulla
Up through brainstem to thalamus via medial lemniscus
Course
Enter spinal cord via dorsal spinal root nerves
Synapse in dorsal horns of spinal grey matter
Cross to opposite side of cord
Ascend through anterior and lateral white columns of cord
Terminate at all levels of lower brain stem and in thalamus
Medial lemniscal fibres terminate in the thalamic sensory relay area (ventrobasal complex)
From the ventrobasal complex, third-order nerve fibres project mainly to the post-central gyrus of the cerebral cortex (somatic sensory area I)
A distinguishing feature of this system/ pathway
Distinct spatial orientation of nerve fibres from individual parts of body that is maintained through e.g. in the dorsal columns of the spinal cord, the fibres from the lower parts of the body lie toward the centre of the cord, whereas those that enter the cord at progressively higher segmental levels from successive layers laterally
In thalamus, distinct spatial orientation is maintained, with tail end of body represented by the most lateral portions of the ventrobasal complex and the head/ face represented by medial areas of the complex
Because of crossing of the medial lemnisci in the medulla, the left side of the body is represented in the right side of the thalamus and vice versa