Sympathetic Anatomy

Neuroanatomy lecture

1. Neuroanatomy Autonomic Nervous System 1

2. Group Names: Abdullahi Daher Idhere Abdulkani Ibrahim Nour Bushra Abdullahi Issa Hamse Abdullahi Moh’ed Khaled Abdulaziz Hussain

3. Introduction Nervous system is functionally divided into following two components – 1. Somatic nervous system 2. Autonomic nervous system . Somatic nervous system is the part of nervous system that controls voluntary functions of body.

4. Autonomic nervous system is the component of nervous system which controls or regulates involuntary functions of body , i.e. those which cannot be governed as per one’s own desire. Units of these functions are fundamentally following two: Increase rate and force of contraction of involuntary muscles (smooth as well as cardiac muscles). Secretion of exocrine glands .

5. COMPOSITION OF ANS Same as somatic nervous system, autonomic nervous system is made up of following components. Receptors: These are + baroreceptors , + chemoreceptors , + osmoreceptors . + Stretch and pain receptors . Afferent pathway: This are peripheral sensory fibers. Interneurons or connecting neurons: These interconnect afferent autonomic neuron with efferent autonomic neuron.

6. Efferent neurons: There are connector neurons situated in brainstem and spinal cord. Autonomic ganglia: This is the special feature of efferent pathway of autonomic nervous system, by which it differs from somatic nervous system. Postganglionic efferent neurons: These are situated outside central nervous system. Cell bodies of these neurons form autonomic ganglia. Effector organ: either smooth muscle , cardiac muscle or a gland .

7. SUBDIVISION OF ANS Autonomic nervous system is divided into two parts— sympathetic and parasympathetic. Interrelationship : There are many effector organs where one system acts, other does not. For example, arrectores pili muscles => sympathetic exocrine glands => parasympathetic But, there are some organs where both the system produce physiologically antagonistic effects . # Force of contraction of heart muscles is increased by sympathetic, diminished by parasympathetic. # Tracheobronchial tree are stimulated by parasympathetic, but sympathetic causes relaxation (bronchodilatation).

8. Sympathetic Vs Parasymathetic Sympathetic and parasympathetic parts of autonomic nervous system differ from each other as per following criteria – 1. Structural — Anatomical 2. Functional — i) Physiological ii) Pharmacological.

9. I. Structural differences 1. Center: + Sympathetic system: T1 to L2 segments. + parasympathetic system: # Brainstem 3 rd , 7 th , 9 th , 10 th cranial nerve # spinal cord S2, S3 and S4 2. Supraspinal control: + Sympathetic : posterior part of hypothalamus + Parasympathetic : anterior part of hypothalamus

10. 3. Autonomic ganglia : # Sympathetic ganglia ( Sympathetic trunk ) + situated close to central nervous system + postganglionic fibers are longer # Parasympathetic ganglia + situated close to the target organ + postganglionic fibers are shorter

11. II. Physiological difference Sympathetic system gets activated during emergency, stress or anger . Parasympathetic system is concerned with conservation and storage of energy . Sympathetic Heartbeat increases. Pulse rate becomes rapid with rise of blood pressure. Pupils get dilated. Vasodilatation of skeletal muscles due to muscular exercise. Extremities become cold due to peripheral vasoconstriction. Parasympathetic Heart rate settles down. Pulse rate gets slower. Rate of respiration becomes slower with ‘snoring’. Digestion of food gets promoted. Peristaltic movement of intestine is increased

12. III. Pharmacological difference Sympathetic : + Preganglionic secretes acetylcholine + Postganglionic: - Norepinephrine (mostly) - Adrenaline - Acetylcholine Parasympathetic : + Preganglionic: Acetylcholine + Postganglionic: Acetylcholine

13. SYMPATHETIC PART OF ANS Sympathetic system is the greater components of autonomic nervous system and is more widely distributed in the body. Fundamentally sympathetic nervous system regulates following unitary functions – 1. Smooth muscles: Which may be in wall of blood vessels, root of hair follicles ( arrectores pili ) and wall of viscera. 2. Cardiac muscles 3. Exocrine glands: Which are only sweat glands.

14. EFFERENT COMPONENT Sympathetic part of autonomic nervous system is made up of following efferent components— Spinal center: This is the collection of nerve cells in the intermediolateral column if spinal cord extending from T1–L2 (may be L3) segments. These cells are called connector neurons . Effector neuron: These neurons are situated outside central nervous system (spinal cord) which receive synaptic connection from axons of connector neuron.

15. Effector organs: Effector organs which receive axon terminal of effector neuron, are i . Cardiac muscle fibers ii. Smooth muscle fibers iii. Sweat glands. Supraspinal center: Nuclei of posterior half of hypothalamus which influence spinal center through hypothalamospinal tract.

16. Types of outflow from Sympathetic ganglia Lateral branches. Medial branches. Sympathetic trunk. Above T1: + Superior cervical ganglion (C1- C4) + Middle cervical ganglion (C5 - C6) + Inferior cervical ganglion (C7 – C8) Below L2: + lower lumbar ( L3 – L5 ) + sacral ( S1 – S5 ) + one coccygeal

17. Detailed Efferent Outflow Distribution of branches from whole sympathetic trunk needs to be studied in following three components. Branches from thoracic sympathetic ganglia . Branches from cervical sympathetic ganglia . Branches from lumbosacral sympathetic ganglia .

18. Branches from Thoracic Sympathetic Ganglia Thoracic part of sympathetic chain is continuous above with its cervical part and below with its lumbosacral part. The thoracic part of the trunk contains 12 ganglia numbered as 1st (T1)–12th (T12) thoracic ganglia. Sometimes, they may be 11 in number, when 1st ganglion fuses with inferior cervical ganglion to form cervicothoracic ganglion . It is called stellate ganglion .

19. Branches: Lateral branches: lateral branches of all the 12 thoracic ganglia are gray rami which join the respective thoracic spinal nerve. Medial branches: medial splanchnic branches of 12 pair of thoracic ganglia have the duty to supply branches to thoracic viscera, and to upper abdominal viscera. That is why medial branches of thoracic sympathetic ganglia are classified into following two groups: 1. Medial branches from T1–T5 ganglia to thoracic viscera . 2. Medial branches from T5–T12 ganglia to upper abdominal viscera .

20. Medial branches from T1–T5 ganglia: Before reaching the target organs these branches of sympathetic ganglia form plexuses with parasympathetic fibers of vagus (10th cranial) nerve close to the viscera. The plexuses are following— Cardiac plexus Pulmonary plexus Esophageal plexus Aortic plexus

21. Medial branches from T5–T12 ganglia: Nerves formed by medial branches from T5–T12 ganglia are following: These three nerves are commonly termed as thoracic splanchnic nerve . Greater splanchnic nerve: T5 – T9 ganglia. Lesser splanchnic nerve: T10 and T11 ganglia. Least (Lowest) splanchnic nerve: T12 ganglia

22. Cervical Part of Sympathetic Trunk Cervical part of sympathetic trunks are situated on either side of cervical part of vertebral column, behind the carotid sheath and in front of prevertebral layer. The trunk presents three cervical ganglia — Superior, middle and inferior. preganglionic fibers arise from T1 – T4, and postganglionic emerges in two forms: + Lateral + Medial

23. 1. Superior cervical ganglion: Lateral : 4 gray communicantis joins C1-C4 Medial : Internal carotid nerve Branches of external carotid artery Pharyngeal branch Cardiac branch

24. 2. Medial cervical ganglion: Lateral: 2 gray rami communicantis joins C5-C6 Medial: Tracheal and esophageal plexus Thyroid branch Cardiac branch

25. 3. Inferior cervical ganglion: Lateral: 2 lateral branches forming inferior cervical ganglion Medial: Ansa subclavia Vertebral nerve Cardiac branch