ANP 1106 Lecture Notes - Lecture 28: Postcentral Gyrus, Alpha Motor Neuron, Medial Lemniscus
29 Apr 2018
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ANP1106 – Perception
Somesthesia: Proprioceptors
- Proprioception
o Sense associated with posture
o Detected by mechanoreceptors
o Info on changes in muscle length determine joint angle
- 4 types of muscle contractions
o 1) Passive stretch
▪ Imposed stretch
o 2) Passive stretch with infrafusal muscle contraction
▪ Stretch done with activation of gamma motorneurons,
increases sensitivity of spindle afferents
o 3) Extrafusal muscle contraction
▪ Only alpha motor neuron activation
o 4) Extrafusal muscle contraction with intrafusal muscle contraction
▪ Normally happens, activates both alpha and gamma
o To perceive muscle length you need to know both the muscle spindle
afferent activity and gamma motorneuron efferent activity
Somesthesia: Sensory Pathways
- 3 neurons that relay info of stimulus to cerebral cortex for perception
o First order neuron – forwards info to CNS
o Second & third order neurons – form ascending pathway which
conveys info to sensory cortex
- 2 pathways to transmit sensory info to cortex:
o 1) Anterolateral pathway – conveys pain, temp, pressure
o 2) Medial lemniscus pathway – conveys touch, proprioception
o Both pathways end the third order thalamic neuron projecting to
primary somatosensory cortex that lies in postcentral gyrus
Broadmann’s areas ,,
- Sensory fibers coming from internal organs to provide pain when there is
internal organ damage
- Homunculus does not include sensory representation for organs
- Nociceptors join pathways of the homunculus leading to primary
somatosensory cortex (ex. heart joins arm and shoulder which explains the
pain of heart felt in the arm)
Perception Levels
- 1) Receptor level – sensory or first order neuron, transduces stimulus into
electrical activity and forwards info to CNS to synapse with second order
neuron
- 2) Circuit level – second and third order neurons, convey info to primary
sensory cortex
- 3) Perceptual level – cortical neurons, analyze sensory info to provide
perception
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Document Summary
Proprioception: sense associated with posture, detected by mechanoreceptors, info on changes in muscle length determine joint angle. 4 types of muscle contractions: 1) passive stretch. 2 pathways to transmit sensory info to cortex: Sensory fibers coming from internal organs to provide pain when there is internal organ damage. Homunculus does not include sensory representation for organs. Nociceptors join pathways of the homunculus leading to primary somatosensory cortex (ex. heart joins arm and shoulder which explains the pain of heart felt in the arm) Perception levels electrical activity and forwards info to cns to synapse with second order neuron. 1) receptor level sensory or first order neuron, transduces stimulus into. 2) circuit level second and third order neurons, convey info to primary. 3) perceptual level cortical neurons, analyze sensory info to provide sensory cortex perception. Difference between perception and sensation: sensation occurs at unconscious level, perception occurs at conscious level.
