Primary somatosensory (somesthetic)
cortex (SI)
Somatic sensory association area
Secondary somatic sensory area (SII)
PAIN
 pain is a protective modality
 International Association for the Study of Pain (IASP):
„Pain is an unpleasant sensory and emotional experience
associated with actual or potential tissue damage,
or described in terms of such damage“.
 pain threshold: individual and social influences
Nociceptors/nocisensors
 nocer – to injure or to hurt in Latin
 are activated by noxious mechanical, thermal or chemical
stimuli
 detect signals from damaged tissue or the threat of damage
 free nerve endings found in the skin, muscles, joints, bones
and viscera
Nociceptors
 nociceptors of Aδ fibres (5-40 meters/sec)
 Aδ mechanical nociceptors
 Aδ thermal nociceptors
 nociceptors of C fibres (0.5-2.0 meters/sec)
 C polymodal nociceptors – react to thermal, mechanical
and chemical stimuli
 silent nociceptors (MIA = mechanically insensitive afferents)
- responsive after inflammation and tissue injury
Factors that activate nociceptors
 Peripheral sensitization
 Central sensitization = activity- or use-dependent
neuronal plasticity in the spinal cord
 hyperalgesia - exaggerated or prolonged response
to noxious inputs
 allodynia - pain induced by normally innocuous
inputs
 Aδ fibres – thin myelinated fibres
 sharp, localized pain
 C non-myelinated fibres
 dull, non-localized pain
Nociceptive afferents
Spinoreticular tract
The noxious information from visceral organs and skin
are carried to the CNS in different pathways
Pain pathways from trunk and limbs
PALEOSPINOTHALAMIC
PATHWAY
 tr. spino-reticulo-thalamicus
 diffuse, non-localized pain
 autonomic and reflexive
responses to pain stimuli
 emotional and affective
reactions to pain
 intralaminar nuclei of the
thalamus
 postcentral gyrus,
insula and cingulate gyrus
NEOSPINOTHALAMIC
PATHWAY
 tr. spino-thalamicus lat.
 sharp, localized pain
 ventral posterolateral
(VPL) and posterior
nucleus of the thalamus
 postcentral gyrus
Cortex
Thalamus
Spinal cord
Paleospino-
thalamic
pathway
Neospino-
thalamic
pathway
Pain pathways from head
TRACTUS TRIGEMINO-RETICULO-
THALAMICUS
 diffuse, non-localized pain
TRACTUS TRIGEMINOTHALAMICUS
ANTERIOR
 sharp, localized pain
Cortex
Thalamus
Medulla
The phylogenetically old, paleospinothalamic and trigeminoreticulothalamic,
pathways through the RF are concerned with
the arousal and affective (emotional) aspects of somatic sensory
stimuli.
In contrast, the direct, neospinothalamic and anterior
trigeminothalamic, pathways are analytic, encoding
information about modality, intensity, and location.
Referred pain
MODULATING SYSTEMS
OF NOCICEPTIVE PATHWAYS
 level of modulation of nociceptive pathways
 spinal cord (“gate control theory”)
 RF of brain stem
 periaquaeductal gray matter (PAG)
“Gate control theory”
Stress-induced analgesia
Some necessary components of
proper motor control
 Volition
 Coordination of signals to many muscle groups
 Proprioception
 Postural adjustments
 Sensory feedback
 Compensation for the physical characteristics
of the body and muscles
 Unconscious processing
 Adaptability
Levels of movement regulation
 spinal cord
 brain stem
 cortex
 cerebellum
 basal ganglia
Lower motor neurons – spinal cord
 α motoneurons
 γ motoneurons
 Somatotopic organization
 medial column – axial muscles
 lateral column – limb muscles
 anteriorly – extensors
 posteriorly - flexors
 Motor neurons have highly branched, elaborate
dendritic trees, enabling them to integrate the inputs
from large numbers of other neurons and to calculate
proper outputs.
 The combination of an individual motor neuron and all
of the muscle fibers that it innervates is called
a motor unit.
 size of motor unit
 small motor unit – 1 motoneuron innervates several
muscle fibers (extraocular muscles, muscles of hand)
 large motor unit – 1 motoneuron innervates
500 – 1000 muscle fibers (back muscles)
Lower motor neurons – brain stem
 Somatomotor nuclei
CN III, IV, VI, XII
 Branchiomotor nuclei
CN V, VII, IX, X, XI
Supraspinal system of movement control
 Medial system
 bilateral
 terminates on the interneurons or
the medial column of lower motor neurons
 controls maintenance of balance and postural movements
 Lateral system
 mostly cross the midline and descend contralaterally
 terminates on the interneurons or
the lateral column of lower motor neurons
 controls fine manipulative movements of the hand and
fingers
 The “third” motor system
 aminergic pathways of the brain stem
Medial system
 Subcortical pathways
 Medial and lateral vestibulospinal
tracts - control of balance and
postural movements
 Tectospinal tract (sup. colliculus)
– coordination of movements of
the head and eyes during watching
 Medial (pontine) and lateral
(medullary) reticulospinal tracts
- control of postural movements
 Cortical pathways
 Anterior corticospinal tract
- bilateral, medial column of lower motor neurons
Lateral system
 Subcortical pathways
 Rubrospinal tract
- contralaterally descends to the
lateral column
 Cortical pathways
 Lateral corticospinal tract
Corticospinal and corticonuclear tracts
The third system
 the oldest one
 nuclei of RF – raphespinal and coeruleospinal tracts
 control of involuntary emotional movements
Motor cortex
Planning of movements
Illustrations were copied and lecture was prepared from:
Noback CH.R. et al: The Human Nervous System:
Structure and Function. Humana Press, Totowa, New
Jersey, Sixth ed.
Neuroscience Online, the Open-Access Neuroscience
Electronic Textbook
Department of Neurobiology and Anatomy
University of Texas Medical School at Houston