Class notes
Somatic and autonomic reflex
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Descriptions of sensory and motor input and output from the nervous system, the classification of reflexes including important reflexes used daily
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Somatic and autonomicreflex
Friday, 5 November 2021 9:31 AM
Somatic and autonomic nervous system
- Nucleus / nuclei
○ A group of nerve cell bodies in CNS
- Ganglion / ganglia
○ A group of nerve cell bodies in PNS
- Fibre
○ A bundle of nerve axons
- Functional divisions
○ All skeletal muscles controlled by somatic motor fibres
§ Only one motor neuron innervates the skeletal
muscle
○ Smooth muscle, cardiac muscle and gland cells innervated
by sympathetic and parasympathetic fibres of ANS
§ Goes through two neurons and forms a synapse
- Organization
○ Somatic NS
§ Upper motor neurons in the primary motor cortex
§ Synapses with Somatic motor nuclei of brain stem or
spinal cord
□ Sends motor signal to skeletal muscle
§ Only one axon and neuron to control the skeletal
muscle
○ Autonomic NS
§ Have two neurons that synapse at autonomic ganglia
before reaching visceral effectors
□ Smooth muscle / glands / cardiac muscle /
adipocytes
- The sectional organization of the spinal cord
○ Somatic
§ Posterior gray horn (sensory) and anterior gray horn
(motor)
○ Autonomic
§ Lateral gray horn
○ Sensory fibres on dorsal side / motor fibres on ventral side
○ Grey matter
§ The cell bodies of neurons in the gray matter of the
spinal cord are organized into functional groups
, ○
§ Lateral gray horn
○ Sensory fibres on dorsal side / motor fibres on ventral side
○ Grey matter
§ The cell bodies of neurons in the gray matter of the
spinal cord are organized into functional groups
called nuclei
○ White matter
§ Nerve fibres that are myelinated so gives white
colour
- Sensory information to the NS
○ A spinal nerve collects sensory information from peripheral
structures and delivers it to sensory nuclei in the spinal
cord
1. The sympathetic nerve carries sensory information from
the visceral organs
i. From interoceptors of visceral organs
2. The ventral ramus carries sensory information from the
ventrolateral body surface, structures in the body wall and
the limbs
i. Somatic sensation
1) From exteroceptors, proprioceptors of body
wall and limbs
ii. Visceral sensation
1) From interoceptors of body wall and limbs
3. The dorsal ramus carries sensory information from the skin
and skeletal muscles of the back
i. From interoceptors of back for visceral
ii. From exteroceptors, proprioceptors of back
4. The dorsal root of each spinal nerve carries sensory
information to the spinal cord
- Motor commands from the NS
○ A spinal nerve distributes motor commands that originate
in motor nuclei of the spinal cord
1. The ventral root of each spinal nerve contains the axons of
somatic motor and visceral motor neurons
2. The spinal nerve forms just lateral to the intervertebral
foramen where the dorsal and ventral roots unite
3. The dorsal ramus contains somatic and visceral motor
fibres that innervate the skin and skeletal muscles of the
back
i. Somatic motor commands to the skeletal muscles of
the back
ii. Visceral motor commands through postganglionic
fibres to smooth muscles, glands of the back
4. The axons in the relatively large ventral ramus supply the
ventrolateral body surface in the body wall and the limbs
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