SENSORY PATHWAYS AND THE SOMATIC NERVOUS SYSTEM

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SENSORY PATHWAYS AND THE SOMATIC NERVOUS SYSTEM

• Chapter 15

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SENSORY RECEPTION

• Sensation
• Perception
• General Senses
• Special Senses

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STIMULI DETECTION

• Receptor specificity
• Receptive Field
• Stimuli are varied but message is electrical
• Receptors generate receptor potentials
• Sensory neurons generate action potentials

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INTERPRETATION

• Labeled lines
• Sensory coding
• Tonic receptors
• Phasic receptors

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ADAPTATION

• Reduction in sensitivity to a constant stimulus
• Fast-adapting receptors
• Slow-adapting receptors
• Peripheral adaptation
• Central adaptation
• Reticular activating system focuses our attention

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SENSORY RECEPTORS

• Classified by nature of the stimulus
• Nociceptors
• Thermoreceptors
• Chemoreceptors
• Mechanoreceptors

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MECHANORECEPTORS

• Tactile receptors
• Baroreceptors
• Proprioceptors

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TACTILE RECEPTORS

• Fine touch and pressure receptors
• Crude touch and pressure receptors
• Complexity
• Free nerve endings
• Root hair plexus
• Tactile discs
• Tactile corpuscles
• Lamellated corpuscles
• Ruffini corpuscles

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BARORECEPTORS PROPRIOCEPTORS

• Baroreceptors
• Free nerve endings in walls of organs
• Rapidly adapting
• Proprioceptors
• Joint positioning, tendon tension, muscle tone
• Muscle spindles
• Golgi tendon organs
• Free nerve endings in joint capsules

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PATHWAYS
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SENSORY PATHWAYS

• Remember the components of a reflex arc
• First order neurons
• Second order neurons
• Third order neurons

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SOMATIC SENSORY PATHWAYS

• Spinothalamic pathway
• Posterior column pathway
• Spinocerebellar
• Phantom limb pain
• Referred pain

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VISCERAL SENSORY PATHWAYS

• First order neurons follow autonomic motor fibers
• Cranial nerves V, VII, IX, X, synapse in
  solitary nucleus of medulla oblongata
• Spinal nerves in thoracic and lumbar synapse in
  dorsal root ganglion
• First order neurons use spinothalamic pathway to
  solitary nucleus

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SOMATIC NERVOUS SYSTEM

• Motor commands
• Skeletal muscle control
• Upper motor neuron
• Lower motor neuron
• Three main pathways Corticospinal, Medial
  Lateral pathways
• Pathways regulated by basal nuclei and cerebellum

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CORTICOSPINAL PATHWAY

• Pyramidal system
• Direct and indirect pathways
• Three pairs of descending tracts, each using
  cerebral peduncles
• Corticobulbar tracts
• Lateral corticospinal tracts
• Anterior corticospinal tracts

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MEDIAL PATHWAY

• Medial Pathway
• Gross or coarse movements
• Located within vestibular nuclei, corpora
  quadrigemina
• Three main tracts Vestibulospinal, Tectospinal
  Reticulospinal tracts
• Lateral pathways regulate upper limb muscle tone
  and precise movement

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BASAL NUCLEI

• Coordination and Control of muscle contractions
• Walking or running
• No direct control over lower motor neurons
• Respond to substantial nigra and cerebral cortex

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CEREBELLUM

• Utilizes information from Proprioceptors, eyes,
  ears and all motor pathways
• Develops movement based on sensory information
  and previous experience
• Excitatory and inhibitory
• Coarse and precise movements