13: Somatic Senses

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The somatic nervous system (SNS) is the part of the peripheral nervous system responsible for our conscious perception of the environment through general and special senses as well as for our voluntary motor responses to that perception by means of skeletal muscles. In this chapter, you will look at the peripheral sensory structures that receive input from environmental stimuli and trace their afferent pathways into the CNS.

13.1: Introduction to the Somatic Senses
The somatic nervous system includes all the afferent, sensory receptors from the skin, skeletal muscles, joints and special senses which are responsible for our conscious perception of the environment. It also includes the efferent, motor division which reaches the skeletal muscles and is responsible for our voluntary motor response.
13.2: Sensory Modalities and General Senses
Sensory receptors can be classified based on cell type, location or type of stimuli. The general sense of somatosensation (touch) contains receptors spread throughout the body.
13.3: Hearing and Balance
Hearing, balance and vision belong to the special senses. Both hearing and balance depend on hair cells within the inner ear. The cochlea is responsible for hearing. The vestibule detects linear acceleration of the head. The semicircular canals sense the rotation of the head. Vision rely on photoreceptor cells within the retina of the eye that detect light and colors. The eyes are protected by the bones of the orbits, the eyelids, the tarsal glands, and the lacrimal apparatus.
13.4: Vision
Sensory information conveyed through spinal nerves will project to the opposite side of the brain. The cranial nerves are connected to the same side of the brain from which the sensory information originates, except for the optic nerve. Sensory input to the brain enters through pathways that travel through either the spinal cord (for somatosensory input from the body) or the brainstem (for everything else, except the visual and olfactory systems) to reach the diencephalon and thalamus.
13.5: Taste and Smell
The prefrontal cortex, secondary motor cortices and primary motor cortex plan, coordinate and execute movement of skeletal muscles. Axons project through the corticobulbar and corticospinal tracts to synapse on lower motor neurons in the brainstem and ventral horn of the spinal cord, respectively. The extrapyramidal system includes projections from the brainstem and higher centers that influence movement. Somatic reflexes include the withdrawal reflex and stretch reflex.
13.6: Anatomical Atlas - Somatic Senses
A compendium of anatomical images: slides, models, and/or cadavers.
13.7: Practice Practical - Somatic Senses
Practical examinations in anatomy ask you to identify structures that you have viewed in the laboratory. For each question you will see an image of a slide, model, specimen, etc. and will be asked to give the name or another piece of information about indicated item(s).