1. Peripheral Nervous System (PNS)
بسم الله الرحمن الرحيم
Peripheral Nervous System (PNS)
Dr. Othman Al-Shboul
Department of Physiology

2. Peripheral Nervous System (PNS)
Composed of:
Autonomic nervous system
Somatic Nervous System

3. Peripheral Nervous System

4. Autonomic Nervous System (ANS)
Composed of:
Sympathetic Nervous System
Parasympathetic Nervous System

5. Autonomic Nerve Pathway
Two-neuron chain

6. Sympathetic Nerve Pathway
Sympathetic nerve fibers originate in the thoracic and lumbar regions of the spinal cord
Short preganglionic fibers
sympathetic preganglionic fibers are very short, synapsing with
cell bodies of postganglionic neurons within ganglia that lie
in a sympathetic ganglion chain (also called the sympathetic
trunk) located along either side of the spinal cord. Long postganglionic
fibers originating in the ganglion chain end on the
effector organs. Some preganglionic fibers pass through the
ganglion chain without synapsing. Instead, they end later in
sympathetic collateral ganglia about halfway between the CNS
and the innervated organs, with postganglionic fibers traveling
the rest of the distance

7. Parasympathetic Nerve Pathway
Parasympathetic preganglionic fibers arise from the cranial (brain) and sacral (lower spinal cord) areas of the CNS
Long preganglionic fibers

8. Neurotransmitters of the ANS
All preganglionic fibers release Ach
Sympathetic postganglionic fibers release NE/E mainly
Parasympathetic postganglionic fibers release Ach

9. Postganglionic nerve terminals

10. Dual innervation of sympathetic and parasympathetic nervous systems
Sympathetic and parasympathetic nervous systems generally exert opposite effects in a particular organ
Both systems increase the activity of some organs and reduce the activity of others.
Usually both systems are partially active; sympathetic or parasympathetic tone or tonic activity, but activity of one division can dominate the other

11. Dual innervation of sympathetic and parasympathetic nervous systems

12. Advantage of dual autonomic innervation
Enables precise control over an organ’s activity
like having both an accelerator
and a brake to control the speed of a car. If an animal suddenly
darts across the road as you are driving, you could eventually
stop if you just took your foot off the accelerator, but
you might stop too slowly to avoid hitting the animal. If you
simultaneously apply the brake as you lift up on the accelerator,
however, you can come to a more rapid, controlled stop.

13. Sympathetic dominance
Fight-or-flight response
in emergency or stressful situations, such as a physical threat from the outside
Heart: beats more rapidly and more forcefully,
Blood pressure is elevated by generalized constriction of the blood vessels,
Respiratory airways open wide to permit maximal air flow,
Glycogen (stored sugar) and fat stores are broken down to release extra fuel into the blood,
Blood vessels supplying skeletal muscles dilate (open more widely).
Providing increased flow of oxygenated, nutrient-rich blood to the skeletal muscles in anticipation of strenuous physical activity.
The pupils dilate and the eyes adjust for far vision, letting the person visually assess the entire threatening scene.
Sweating is promoted in anticipation of excess heat production by the physical exertion.
Inhibition of digestive and urinary activities; not essential in meeting the threat

14. Parasympathetic dominance
Rest-and-digest
in quiet, relaxed situations

15. The Adrenal Medulla Cortex Medulla Medulla secretes:
Epinephrine (mainly) & Norepinephrine

16. The Adrenal Medulla Part of the sympathetic nervous system
Receives preganglionic fibers
Does not have postganglionic fibers
Instead, releases E & NE into the blood

17. Receptor types for autonomic neurotransmitters
Specific neurotransmitter action results from specificity of receptors
2 types of receptors in ANS:
Cholinergic
Adrenergic

18. Cholinergic Receptors
Nicotinic receptors:
found on the postganglionic cell bodies in all autonomic ganglia
Bind ACh
Muscarinic receptors:
found on effector cell membranes (smooth muscle, cardiac muscle, and glands).

19. Adrenergic Receptors Found on effector cell membranes alpha (α):
α NE > E α2
beta (β)
β1 NE = E
Β2  E > NE

20. Adrenergic Receptors α1  Excitatory; e.g., arteriolar constriction
α2  Inhibitory; e.g., GI smooth muscle
β1  Excitatory; e.g., increased rate and force of cardiac contraction
β2  Inhibitory; e.g., arteriolar & bronchiolar (dilation)

21. Autonomic agonists and antagonists
Binds with a neurotransmitter’s receptor and elicits an effect that mimics that of the neurotransmitter.
Antagonist
Binds with a neurotransmitter’s receptor and blocks the neurotransmitter’s response.

22. Autonomic agonists and antagonists
Atropine
Blocks the effect of acetylcholine at muscarinic receptors but does not affect nicotinic receptors
Suppresses salivary and bronchial secretions before surgery, to reduce the risk of a patient inhaling these secretions into the lungs

23. Autonomic agonists and antagonists
Salbutamol
Selectively activates β 2 adrenergic receptors at low doses
Dilate the bronchioles in the treatment of asthma without undesirably stimulating the heart

24. Sympathetic vs. Parasympathetic

25. Somatic Nervous System

26. Somatic Nervous System

27. Somatic Nervous System
Composed of the axons of the motor neurons which innervate skeletal muscles
Motor neurons:
The cell bodies are within the spinal cord. (except motor neurons supplying muscles in the head, they are in the brain stem)
Release acetylcholine (ACh)
Can only stimulate skeletal muscles (no inhibition)
Inhibition
of skeletal muscle activity can be accomplished only within
the CNS through inhibitory synaptic input to the dendrites
and cell bodies of the motor neurons supplying that particular
muscle.

28. Motor neurons
The dendrites and cell bodies are influenced by many converging presynaptic inputs, both excitatory (EPSP) and inhibitory (IPSP).
The level of activity in a motor neuron and its subsequent output to the skeletal muscle fibers it innervates depend on the relative balance of EPSPs and IPSPs
Motor neurons are considered the final common pathway, because the only way any other parts of the nervous system can influence skeletal muscle activity is by acting on these motor neurons.

29. Somatic Nervous System
The somatic system is under voluntary control
However, much of the skeletal muscle activity involving posture, balance, and stereotypical movements is subconsciously controlled

30. Neuromuscular junction (NMJ)
Axon of motor neuron
Synaptic vesicles
Axon of motor neuron
Terminal button
Neuromuscular junction
motor end plate

31. Neuromuscular junction (NMJ)
Nerve and muscle cells do not actually come into direct contact at a neuromuscular junction
The space, or cleft, between these two structures is too large to permit electrical transmission of an impulse between them
The chemical messenger is acetylcholine (ACh.)

32. Somatic vs. Autonomic

33. Somatic vs. Autonomic

34. The END