Somatic Nervous System

The Somatic Nervous System

Chapter Objectives

  • Components of the Somatic Nervous System: Understand the structure and function of the somatic nervous system (SNS) as a key part of the peripheral nervous system (PNS).

  • Sensory Systems: Identify modalities and submodalities.

  • General vs. Special Senses: Distinguish between these two types of senses.

  • Central Nervous System Regions: Learn how CNS regions contribute to somatic functions.

  • Stimulus-Response Motor Pathway: Explain this pathway in the context of sensory perception and motor response.

14.1 Sensory Perception

  • Sensory Receptors: Specialized cells which respond to environmental stimuli and transmit information via sensory neurons to the brain:

    • Classified based on:

    • Structure: e.g., dendrites embedded in tissues, encapsulated receptors for enhanced sensitivity.

    • Location of Stimulus:

      • Exteroceptors: Detect external stimuli (e.g., skin receptors).

      • Interoceptors: Respond to internal stimuli from organs (e.g., blood pressure).

      • Proprioceptors: Monitor body position and movement near muscles.

    • Function:

      • Chemoreceptors: Respond to chemicals (taste/smell).

      • Nociceptors: Detect pain.

      • Mechanoreceptors: Respond to physical changes (pressure, vibration).

      • Thermoreceptors: Sensitive to temperature changes.

14.2 Sensory Modalities

Gustation (Taste)

  • Taste Sensations: Six basic tastes - sweet, salty, sour, bitter, umami, and fats/lipids.

  • Taste Buds: Located in papillae, consist of chemoreceptors that require dissolved substances for detection.

Olfaction (Smell)

  • The sense of smell is vital for identifying airborne chemicals.

Audition (Hearing)

  • Anatomy of the Ear: Includes auricle, ear canal, malleus, incus, stapes (ossicles), cochlea, and more.

  • Auditory Pathway: Sound waves cause vibration of the tympanic membrane, which is amplified across ossicles and sets standing waves in cochlear fluid.

Vision

  • Photoreceptors in the Eye: Rods (dim light) and cones (bright light and color detection).

  • Structures of the Eye: Consists of three layers: fibrous tunic, vascular tunic, and neural tunic.

  • Visual Pathway: Images processed through optic nerves and optic tracts, reaching the correct visual cortex for interpretation.

14.3 Motor Responses

  • Basic Processing Stream: Involves the motor cortex, basal ganglia, extrapyramidal system, and spinal cord.

  • Descending Pathways:

    • Corticospinal Tract: Controls voluntary skeletal muscle movement; originates in the primary motor cortex and extends to the spinal cord.

    • Corticobulbar Tract: Involved in controlling facial and neck muscles.

  • Reflex Arc: A rapid, automatic response involving:

    • Five components: receptor cell, sensory neuron, interneurons, motor neuron, and effector cell.

    • Classification: Based on development, nature of response, and processing site. Includes innate, acquired, somatic, and visceral reflexes.

Key Terms

  • Somatic Nervous System: Involved in voluntary control of body movements via skeletal muscles.

  • Sensory Receptors: Cells that receive and process environmental stimuli.

  • Reflex: Automatic response to specific stimuli involving a pathway through the nervous system.