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Peripheral Nervous System 1:The Somatic System
Grant’s Atlas 12 2009
Lawrence M. Witmer, PhDProfessor of Anatomy
Dept. of Biomedical SciencesHeritage College of Osteopathic
Medicine, Ohio UniversityAthens, Ohio [email protected]
Taken from and modified……
Dichotomies1. Tissues: neurons vs. glia2. Position: CNS vs. PNS3. Function 1: sensory vs. motor4. Function 2: somatic vs. visceral
Gray’s Anatomy 38 1999
neuron
glial cell
Neurons-a quick review
cellbody
dendrites
axon withmyelin sheath
synapses
Schwanncell
Moore’s COA6 2010
• Dendrites: carry nerve impulses toward cell body• Axon: carries impulses away from cell body• Synapses: site of communication between neurons using chemical neurotransmitters• Myelin & myelin sheath: lipoprotein covering produced by glial cells (e.g., Schwann cells in PNS) that increases axonal conduction velocity• Demyelinating diseases: e.g., Multiple Sclerosis (MS) in CNS or Guillain-
Barré Syndrome in PNS
CNS vs. PNS
Moore’s COA6 2010
Central Nervous System• brain & spinal cord• integration of info passing to & from the periphery
Peripheral Nervous System• 12 cranial nerves• 31 pairs of spinal nerves• Naming convention changes at C7/T1
Collection of nervecell bodies:• CNS: nucleus• PNS: ganglion
Sensory (Afferent) vs. Motor (Efferent)
e.g., skin
e.g., muscle
Gray’s Anatomy 38 1999
sensory (afferent) nerve
motor (efferent) nerve
(pseudo-) unipolar neurons conducting impulsesfrom sensory organs to the CNS
multipolar neurons conducting impulsesfrom the CNS to effector organs (muscles & glands)
Somatic vs. Visceralattribute Somatic System Visceral System
embryological origin of tissue
“body wall:” somatic (parietal) mesoderm (dermatome,
myotome)
“organs:” splanchnic (visceral) mesoderm,
endoderm
examples of adult tissues
dermis of skin, skeletal muscles, connective tissues
glands, cardiac muscle, smooth muscle
perception conscious, voluntary unconscious, involuntary
Langman’s Embryo 9 2004
Sensory/Motor + Somatic/Visceral
Somatic Visceral
Sensory(Afferent)
somatic sensory[General Somatic Afferent (GSA)]
visceral sensory[General Visceral Afferent (GVA)]
Motor(Efferent)
somatic motor[General Somatic Efferent (GSE)]
visceral motor[General Visceral Efferent (GVE)]
SomaticNervousSystem
AutonomicNervousSystem
Structure of the Spinal Cordwhite matter
(axons)
gray matter (cell bodies)• dorsal (posterior) horn• ventral (anterior) horn
meningespia •
arachnoid •dura •
denticulateligament
dorsalrootlets
ventralrootlets
• dura• arachnoid• piameninges
dorsal root(spinal) ganglion
spinal nerve• dorsal primary ramus• ventral primary ramusventral rootMoore’s COA6 2010
subarachnoidspace(CSF)
Structure of Spinal Nerves: Somatic Pathways
dorsal rootdorsal rootganglion
ventral root
spinalnerve
dorsalramus
ventralramus
gray ramuscommunicans
white ramuscommunicans
sympatheticganglion
dorsalhorn
ventralhorn
somaticsensory
nerve(GSA)
somaticmotornerve(GSE)
CNSinter-
neuron
CNSinter-
neuron
Mixed SpinalNerve
Mixed SpinalNerve
Structure of Spinal Nerves: Somatic Pathways
dorsal rootdorsal rootganglion
ventral root
spinalnerve
dorsalramus
gray ramuscommunicans
white ramuscommunicans
sympatheticganglion
dorsalhorn
ventralhorn
somaticsensory
nerve(GSA)
somaticmotornerve(GSE)
CNSinter-
neuron
CNSinter-
neuron
Mixed SpinalNerve
Mixed SpinalNerve
ventralramus
Somatic sensations• touch, pain, temperature,
pressure• proprioception: joints, muscles
Somatic motor activity: innervate skeletal muscles
Somatic Nervous system• Clearly we can see that this aspect of the
peripheral system gathers information from the senses or receptors which are simply organs that detect a change in the internal (bladder full) or external(change in temp/light intensity) and respond in some way.
• The trigger to a “response” is simply called a stimulus.
• The skin responds to many of these stimuli
Skin/ears/eyes• Skin protects us from the outside world as
the receptors are constantly alerting us as to the changes we need to respond to, to protect us.
• The ear groups receptors- sound, and balance
• The eyes clearly enable us to see-msgs are sent via the optic nerve
• See pages 228/229
Autonomic Nervous System• Some activities without you knowing about them-
breathing heartbeat sweating etc.-These are controlled by the autonomic nervous system.
• There are two parts to this system:– The Sympathetic-speeds up body functions to increase
efficiency– Parasympathetic-slows things down-works when you
are at rest-returns the body to normal functioning
These systems are complimentary or opposite to one another in function
Function of the sympathetic Nervous System
Organ EffectEye Dilates pupil
Heart Increases rate and force of contraction
Lungs Dilates bronchioles
Blood Vessels Constricts
Sweat Glands Activates sweat secretion
Digestive tract Inhibits –movement peristalsis
Kidney Increases renin secretion
Pg 230 text book
Functions of the Parasympathetic Nervous System
• Increases blood flow to the digestive tract• Stimulates salivary glands and increases the rate
of digestion• Reduces the diameter of the bronchioles when
there is a reduced need for oxygen• Controls heart beat• Contracts the eye muscles and reduces the
diameter of the pupil
Responding to Stimuli
• Page 231- reflex actions• Read and note• Draw basic diagram using text as a guide• (teacher to draw on white board)
ReferencesAgur, A. M. R. and A. F. Dalley. 2009. Grant’s Atlas of Anatomy, 121th
Edition. Lippincott, Williams & Wilkins, New York.Bannister, L. H. et al. 1999. Gray’s Anatomy, 38th Edition. Churchill
Livingstone, New York.Moore, K. L. , A. F. Dalley, and A. M. R. Agur. 2010. Clinically Oriented
Anatomy, 6th Edition. Lippincott, Williams & Wilkins, New York.Sadler, T. W. 2004. Langman’s Medical Embryology, 9th Edition.
Lippincott, Williams & Wilkins, New York.Stern, J. T., Jr. 1988. Essentials of Gross Anatomy. Davis, Philadelphia.