Peripheral Nervous System (PNS)

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

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

3. Peripheral Nervous System

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

5. Autonomic Nerve Pathway • Two-neuron chain

6. Sympathetic Nerve Pathway • Sympatheticnerve fibers originate in the thoracicand lumbar regions of the spinal cord • Shortpreganglionic fibers

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. Sympathetic and parasympathetic nervous systems generally exert opposite effectsin 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 Dual innervation of sympathetic and parasympathetic nervous systems

11. Dual innervation of sympathetic and parasympathetic nervous systems

12. Enables precise control over an organ’s activity Advantage of dual autonomic innervation

13. Fight-or-flight response in emergency or stressful situations, such as a physical threat from the outside Sympathetic dominance • 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. Rest-and-digest in quiet, relaxed situations Parasympathetic dominance

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

18. 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). Bind ACh Cholinergic Receptors

19. Found on effector cell membranes • alpha (α): • α1 NE > E • α2 • beta (β) • β1 NE = E • Β2  E > NE Adrenergic Receptors

20. 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) Adrenergic Receptors

21. Agonist 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. Autonomic agonists and antagonists

22. 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 Autonomic agonists and antagonists

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

24. Sympathetic vs. Parasympathetic

25. Somatic Nervous System

26. Somatic Nervous System

27. 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) Somatic Nervous System

28. 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. Motor neurons

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

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

31. 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.) Neuromuscular junction (NMJ)

32. Somatic vs. Autonomic

33. Somatic vs. Autonomic

34. The END