The Nervous System

1
The Nervous System
2
Spinal Cord

• Continuation of the medulla oblongata
• Extends from foramen magnum to L2
• Below L2 is the cauda equina (a collection of
  spinal nerves)
  
• Enlargements occur in the cervical and lumbar
  regions (nerve flow to and from extremities)

Figure 7.18
3
Spinal Cord Anatomy

• Exterior white mater nerve tracts traveling up
  and down the spinal cord
  
• Gray matter dorsal, ventral and lateral horns
  neuron cell bodies

Figure 7.19
4
Spinal Cord Anatomy

• Dorsal root
• Contains sensory axons into spinal cord
• Dorsal root ganglion contains neuron cell bodies
  of sensory neurons
  
• Ventral root
• Contains motor axons leaving spinal cord
• Roots connect to form spinal nerve.

5
Peripheral Nervous System

• Nerves and ganglia outside the central nervous
  system
  
• Nerve bundle of neuron fibers (axons)
• Neuron fibers are bundled by connective tissue
• Endoneurium surrounds nerve fiber
• Perineurium surrounds fascicle
• Epierurium surrounds entire nerve

6
Structure of a Nerve

• Endoneurium surrounds each fiber
• Groups of fibers are bound into fascicles by
  perineurium
  
• Fascicles are bound together by epineurium into
  the whole nerve

Figure 7.20
7
Classification of Nerves

• Mixed nerves both sensory and motor fibers
• Afferent (sensory) nerves carry impulses toward
  the CNS
  
• Efferent (motor) nerves carry impulses away
  from the CNS

8
Cranial Nerves

• 12 pairs of nerves that mostly serve the head and
  neck
  
• Numbered in order, front to back
• Most are mixed nerves, but three are sensory
  only
  
• Cranial nerves extend out from the brain, mostly
  the brain stem

9
Distribution of Cranial Nerves
Figure 7.21
10
Cranial Nerves

• I Olfactory nerve sensory for smell
• II Optic nerve sensory for vision
• III Oculomotor nerve motor fibers to eye
  muscles
  
• IV Trochlear motor fiber to eye muscles
• V Trigeminal nerve sensory for the face motor
  fibers to chewing muscles
  
• VI Abducens nerve motor fibers to eye muscles

11
Cranial Nerves

• VII Facial nerve sensory for taste motor
  fibers to the face
  
• VIII Vestibulocochlear nerve sensory for
  balance and hearing
  
• IX Glossopharyngeal nerve sensory for taste
  motor fibers to the pharynx
  
• X Vagus nerves sensory and motor fibers for
  pharynx, larynx. Autonomic to thoracic and
  abdominal organs
  
• XI Accessory nerve motor fibers to neck and
  upper back
  
• XII Hypoglossal nerve motor fibers to tongue

12
Spinal Nerves

• There is a pair of spinal nerves at the level of
  each vertebrae for a total of 31 pairs
  
• 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, 1
  coccygeal
  
• Spinal nerves are named for the region from which
  they arise
  
• Spinal nerves are formed by the combination of
  the ventral and dorsal roots of the spinal cord

13
Spinal Nerves
Figure 7.22a
14
Anatomy of Spinal Nerves

• Spinal nerves divide soon after leaving the
  spinal cord
  
• Dorsal rami serve the skin and muscles of the
  posterior trunk
  
• Ventral rami form a complex of networks called
  plexuses

Figure 7.22b
15
Plexuses

• Cervical plexus C1-C5
• Important nerve phrenic to diaphragn
• Brachial plexus C5-T1
• Nerves to shoulder, arm, hand, fingers
• Lumbar plexus L1-L4
• Nerves to buttocks, thighs and legs
• Sacral plexus L4-S4
• Important nerve sciatic to posterior thigh and
  leg

16
Examples of Nerve Distribution
Figure 7.23
17
Autonomic Nervous System

• Motor subdivision of the PNS that autonomically
  controls heart, smooth muscles and glands.
  
• Divided into two divisions
• Sympathetic division
• Parasympathetic division

18
Differences Between Somatic and Autonomic Nervous
Systems

• Somatic nervous system
• One motor neuron extends to skeletal muscle
• Always uses neurotransmitter acetylcholine
• Autonomic nervous system
• 2 neuron sequence to reach smooth muscle, cardiac
  muscle and glands.
  
• Uses neurotransmitters, acetylcholine,
  epinephrine and norepinephrine

19
Comparison of Somatic and Autonomic Nervous
Systems
Figure 7.24
20
Anatomy of the Sympathetic Division

• Originates from the spinal cord at the T1 through
  L2
  
• Ganglia are in the sympathetic chain ganglia
  (near the spinal cord)
  
• Short pre-ganglionic neuron and long
  postganglionic neuron transmit impulse from CNS
  to the effector organ
  
• Norepinephrine and epinephrine are
  neurotransmitters to the effector organs

21
Sympathetic Pathways
Figure 7.26
22
Anatomy of the Parasympathetic Division

• Originates from the brain stem and S1 through S4
• Terminal ganglia are at the effector organs
• Always uses acetylcholine as a neurotransmitter

23
Anatomy of the Autonomic Nervous System
Figure 7.25
24
Autonomic Functioning

• Sympathetic nervous system prepares the body for
  activity
  
• Remember as the E division exercise,
  excitement, emergency, and embarrassment
  
• Heart beats faster, breath faster, more blood to
  muscles, airways dilate, perspire
  
• Less blood to digestive system

25
Autonomic Functioning

• Parasympathetic housekeeping activites
• Conserves energy
• Maintains daily necessary body functions
• Remember as the D division - digestion,
  defecation, and diuresis
  
• Heart beats slower, slower respiratory rate, more
  blood to digestive organs