Chapter 1 A Perspective on Human Genetics

1
Chapter 7 The Peripheral Nervous System
Efferent Division
2
Quiz

• What is a motor end plate?
• What neurotransmitters are used in the ANS?
• What is reciprocal innervation?

3
Outline

• Autonomic nervous system
• Somatic nervous System
• Neuromuscular Junction

4
Outline

• Autonomic nervous system
• Anatomy
• Pre and post fibers, sympathetic ganglia chain,
  collateral ganglia, terminal ganglia
• Neurotransmitters
• Pre Acetylcholine (ach)
• Post adrenaline (epinepherine) noradrenaline
  (norepinepherine)
• Sympathetic and parasympathetic branches
• Dual innervation
• Sympathetic dominance fight or flight
• Parasympathetic dominance rest and digest
• Receptor types
• Cholinergic, muscarinic, nicotinic
• Adrenergic. a1 a2 b1 b2
• CNS control

5
PNS Efferent Division

• Communication link by which CNS controls
  activities of muscles and glands
• Two divisions of PNS
• Autonomic nervous system (ANS)
• Involuntary branch of PNS
• Innervates cardiac muscle, smooth muscle, most
  exocrine glands, some endocrine glands, and
  adipose tissue
• Somatic nervous system
• Subject to voluntary control
• Innervates skeletal muscle

6
Table 7-1, p. 234
7
ANS

• Autonomic nerve pathway
• Extends from CNS to an innervated organ
• Ganglion neuronal cell bodies in the PNS
• Nuclei neuronal cell bodies in the PNS CNS
• Two-neuron chain
• Preganglionic fiber (synapses with cell body of
  second neuron)
• Postganglionic fiber (innervates effector organ)

8
ANS

• Two subdivisions
• Sympathetic nervous system
• Thoracic and lumbar
• Parasympathetic nervous system
• Cervical and sacral

9
Sympathetic system
Brain
ACh
ACh
Effector organs
Parasympathetic system
Terminal ganglion
Cardiac muscle
Preganglionic fiber
Spinal cord
Postganglionic fiber
ACh
NE
Acetylcholine
Sympathetic ganglion chain
Smooth muscle
Norepinephrine
Epinephrine
Craniosacral parasym- pathetic nerves
Thoracolumbar sympathetic nerves
Cell body
Cell body
Adrenal medulla
Blood
Axon
E,NE
ACh
NE
Most exocrine glands and some endocrine glands
Collateral ganglion
ACh
ACh
Terminal ganglion
Fig. 7-2, p. 235
10
ANS

• Most visceral organs innervated by both
  sympathetic and parasympathetic fibers
• In general produce opposite effects in a
  particular organ
• Dual innervation of organs by both branches of
  ANS allows precise control over organs activity

11
ANS

• Sympathetic system dominates in emergency or
  stressful (fight-or-flight) situations
• Promotes responses that prepare body for
  strenuous physical activity
• Parasympathetic system dominates in quiet,
  relaxed (rest-and-digest) situations
• Promotes body-maintenance activities such as
  digestion

12
Eye
Lacrimal gland
Nasal mucosa
Parotid gland
Sympathetic
Parasympathetic
Salivary glands
Trachea
Lung
Cranial nerves
Sympathetic trunk
Heart
Spinal nerves
Liver
Stomach
Splanchino nerves
Spleen
Gall bladder
Sympathetic preganglionic fiber
Adrenal gland
Pancreas
Sympathetic postganglionic fiber
Spinal nerves
Parasympathetic preganglionic fiber
Kidney
Parasympathetic postganglionic fiber
Colon
Small intestine
Rectum
Urinary bladder
Genitalia
Fig. 7-3, p. 237
13
Effects of Autonomic Nervous System on Various
Organs
14
ANS

• Exceptions to general rule of dual reciprocal
  innervation by the two branches of autonomic
  nervous system
• Most arterioles and veins receive only
  sympathetic nerve fibers (arteries and
  capillaries are not innervated)
• Most sweat glands are innervated only by
  sympathetic nerves
• Salivary glands are innervated by both ANS
  divisions but activity is not antagonistic both
  stimulate salivary secretion

15
ANS

• Adrenal medulla is a modified part of sympathetic
  nervous system
• Modified sympathetic ganglion that does not give
  rise to postganglionic fibers
• Stimulation of preganglionic fiber prompts
  secretion of hormones into blood
• About 20 of hormone release is norepinephrine
• About 80 of hormone released is epinephrine
  (adrenaline)
• Broadcast vs. localized

16
Autonomic Neurotransmitters
17
Sympathetic system
Brain
ACh
ACh
Effector organs
Parasympathetic system
Terminal ganglion
Cardiac muscle
Preganglionic fiber
Spinal cord
Postganglionic fiber
ACh
NE
Acetylcholine
Sympathetic ganglion chain
Smooth muscle
Norepinephrine
Epinephrine
Craniosacral parasym- pathetic nerves
Thoracolumbar sympathetic nerves
Cell body
Cell body
Adrenal medulla
Blood
Axon
E,NE
ACh
NE
Most exocrine glands and some endocrine glands
Collateral ganglion
ACh
ACh
Terminal ganglion
Fig. 7-2, p. 235
18
Autonomic Neurotransmitter Receptors

• Tissues innervated by autonomic nervous system
  have one or more of several different receptor
  types for postganglionic chemical messengers
• Alter tissue/cell response instead of chemical
  message
• Alter the distribution (localized varicosity,
  broadcast adrenal medulla)
• Cholinergic receptors bind to ACh
• Nicotinic receptors found on postganglionic
  cell bodies of all autonomic ganglia
• nicotine
• Muscarinic receptors found on effector cell
  membranes
• Mushroom poison
• Andrenergic receptors bind to norepinephrine
  and epinephrine
• Alpha (a) receptors
• Beta (ß) receptors

19
Autonomic Agonists and Antagonists

• Agonists
• Bind to same receptor as neurotransmitter
• Elicit an effect that mimics that of
  neurotransmitter
• Antagonists
• Bind with receptor
• Block neurotransmitters response

20
Regions of CNS Involved in Control of Autonomic
Activities

• Can be influenced by prefrontal association
  complex through its involvement with emotional
  expression characteristic of individuals
  personality
• Hypothalamus plays important role in integrating
  autonomic, somatic, and endocrine responses that
  automatically accompany various emotional and
  behavioral states
• Medulla within brain stem is region directly
  responsible for autonomic output
• Some autonomic reflexes, such as urination,
  defecation, and erection, are integrated at
  spinal cord level

21
Distinguishing Characteristics of Sympathetic and
Parasympathetic Nervous Systems
22
Outline

• Somatic nervous system
• Anatomy
• Motor neurons
• Continuous to effector
• Voluntary
• Final common pathway
• ALS Amyotropic lateral sclerosis, death of
  motor neurons

23
Somatic Nervous System

• Consists of axons of motor neurons of motor
  neurons that originate in spinal cord or brain
  stem and end on skeletal muscle
• Motor neuron releases neurotransmitter, Ach,
  which stimulates muscle contraction
• Motor neurons are final common pathway by which
  various regions of CNS exert control over
  skeletal muscle activity
• These areas of CNS include spinal cord, motor
  regions of cortex, basal nuclei, cerebellum, and
  brain stem

24
Comparison of Somatic and Autonomic Nervous System
25
Spinal cord
Acetylcholine
Norepinephrine
Sympathetic preganglionic fiber
Epinephrine
Adrenal medulla
Sympathetic postganglionic fiber
Blood
Target organs
Fig. 7-4, p. 239
26
Outline

• Neuromuscular junction
• Anatomy
• Muscle fiber, terminal button
• motor end plate
• Ach release
• Presynaptic vesicular
• Postsynaptic intracellular
• Ach activation of end plate potentials
• Activation of nicotinic receptors
• Inflow of sodium and potassium
• Ap propagated along the muscle fiber
• Ach breakdown
• AChe

27
Neuromuscular Junction

• Axon terminal of motor neuron forms neuromuscular
  junction with a single muscle cell
• Signals are passed between nerve terminal and
  muscle fiber by means of neurotransmitter ACh
• Released ACh binds to receptor sites on motor end
  plate of muscle cell membrane
• Binding triggers opening of specific channels in
  motor end plate
• Ion movements depolarize motor end plate,
  producing end-plate potential
• Local current flow between depolarized end plate
  and adjacent muscle cell membrane brings adjacent
  areas to threshold
• Action potential is initiated and propagated
  throughout muscle fiber

28
Neuromuscular Junction

• Acetylcholinesterase
• Inactivates ACh
• Ends end-plate potential and the action potential
  and resultant contraction
• Neuromuscular junction is vulnerable to chemical
  agents and diseases
• Black widow spider venom causes explosive release
  of ACh
• Botulism toxin blocks release of ACh
• Curare blocks action of ACh at receptor sites
• Organophosphates prevent inactivation of ACh
• Myasthenia gravis inactivates ACh receptor sites

29
Axon of motor neuron
Action potential propagation in motor neuron
Myelin sheath
Axon terminal
Terminal button
Voltage-gated calcium channel
Vesicle of acetylcholine
Acetylcholine receptor site
Action potential propagation in muscle fiber
Acetycholinesterase
Plasma membrane of muscle fiber
Voltage-gated Na channel
Chemically gated cation channel
Motor end plate
Contractile elements within muscle fiber
Fig. 7-6, p. 245
30
Neuromuscular conditions and compounds

• ALS
• Lou Gehrigs Disease
• death of motor neurons
• Black widow venom
• Explosive release of Ach
• Paralysis of the diaphram
• Botulinum toxin
• Inhibits Ach release
• Curare
• Ach receptor blocker (chloinergic)
• Organophosphates
• Ache inhibition
• Mysanthia Gravis
• Autoimmune, body attacks Ach receptors
• Rigor mortis

31
(No Transcript)