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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