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 45701witmerL@ohio.edu

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

Diagrams

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

overview

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.