Compare Somatic and Autonomic Nervous Systems

SNS: Functional Organization

• controlled/percieved consciously

• motor + sensory

  • motor = initiation from CNS → somatic motor neuron → somatic effector (skm)

    • voluntary involve cerebrum

    • reflexive involve brainstem/spinal cord

  • sensory = detection of stimuli by sensory receptors of special senses (vision, hearing, equilibrium, smell, taste) tactile receptors of skin and mucous membranes, proprioceptors

ANS: Functional Organization

• not conscious, motor only (autonomic motor or visceral motor system)

• signals from CNS to hear, smooth muscle, glands

• responds to visceral sensory inputs (from blood vessels)

  • sensory neurons not not part of ANS

• functions to maintain homeostasis

• hypothalamus in control

  • divided into sympathetic and parasympathetic

SNS: Lower Motor Neuron

• single cell from CNS to skm fibers

  • cell body in brainstem/spinal cord, exits to skm

  • myelinated + fat = fast propagation of signals

  • releases ACh from synaptic knob to excite

ANS: Lower Motor Neuron

• 2 neurons from CNS to cardia, smooth + glands

• First is preganglionic:

  • cell body in brainstem/sc

  • thin, myelinated axon to autonomic ganglion in peripheral nervous system

  • release ACh from synaptic knob to excite second motor neuron

• Second is ganglionic (postganglionic) neuron

  • cell body in autonomic ganglion

  • very thin, unmyelinated axon projects to cardiac muscle, smooth muscle, or glands

  • releases ACh or NC from synaptic knob to excite or inhibit

Advantages ANS has with 2 neurons

• neural convergence: many preganglionic synapsing on 1 ganglionic

• neural divergence: 1 preganglionic synapsing on many ganglionic

CNS control of ANS

• ANS regulated by parts brain/sc

• Hypothalamus: nuclei controlling both divisions

  • emotional ANS processes (fight-or-flight)

  • influenced by areas of cortex, thalamus, limbic system

• Brainstem: nuclei mediate visceral reflexes

  • maintain blood pressure, heart rate, respiration

• Spinal cord: some ANS reflexes

  • defecation and urination controlled by PNS