Neuroanatomy of Peripheral nervous system.pptx

Peripheral nervous system

1. CPM 282 Neuroanatomy Peripheral Nervous S ystem By Pharm F.O DIM 8/10/2023 1

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3. INTRODUCTION : PNS The peripheral nervous system (PNS) consists of all the nerves branching out of the brain and spinal cord (the central nervous system, CNS). If you imagine the CNS as the main highway, then the PNS forms all the connecting secondary roads. These allow electrical impulses to travel to and from the furthest regions, or periphery, of the human body. 8/10/2023 3

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5. The PNS is built almost entirely from nerves. There are two main types; spinal nerves and cranial nerves. Functionally, the PNS can be divided into the Autonomic Nervous System–Sympathetic and Parasympathetic Somatic nervous systems- Sensory and Motor divisions 8/10/2023 5

6. Key facts about the peripheral nervous system Definition A nervous system division composed of all the neural tissue found outside the cranial vault and vertebral canal. Anatomical components Peripheral nerves (spinal nerves, cranial nerves, autonomic nerves) Ganglia Functional components Autonomic nervous system (ANS)  - involuntary part in control of cardiac, smooth and glandular cells. It consists of sympathetic and parasympathetic divisions. Somatic nervous system (SNS)  - voluntary part in control of skeletal muscles and processing of somatic sensation. Function Transmits motor and sensory information between the central nervous system and peripheral body tissues. 8/10/2023 6

7. Peripheral nerves The workhorse of the peripheral nervous system are the peripheral nerves. Each nerve consists of a bundle of many nerve fibers (axons) and their connective tissue coverings. Each nerve fiber is an extension of a neuron whose cell body is held either within the grey matter of the CNS or within ganglia of the PNS.  The comparable structure of the CNS is called a ‘tract’. Peripheral nerves that carry information towards the CNS are called afferent or sensory neurons, while the ones transmitting impulses from the CNS are known as efferent or motor neurons . 8/11/2023 7

8. Afferent neurons transmit a variety of impulses from sensory receptors/sense organs. They carry general sensations like touch, pain, temperature and position in space (proprioception). Some also transmit more special, sensorial information like the special senses of smell, vision, hearing and balance. In contrast, efferent neurons bring general nervous information towards effector organs, like skeletal muscles, visceral organs and glands. They are responsible for initiating voluntary and involuntary motor functions, such as muscle contraction and gland secretion. 8/11/2023 8

9. Nerves can also be classified as ‘cranial’ or ‘spinal’ according to where they exit the CNS. Cranial nerves emerge from the cranium (brain/brainstem) whilst spinal nerves leave the CNS via the spinal cord. There are 12 pairs of cranial nerves and 31 spinal nerve pairs , giving a total of 43 paired nerves forming the basis of the peripheral nervous system. 8/11/2023 9

10. Cranial nerves The first set of peripheral nerves are the twelve cranial nerves:  olfactory (CN I),  optic (CN II),  oculomotor (CN III),  trochlear (CN IV),  trigeminal (CN V1, CN V2, CN V3),  abducens (CN VI),  facial (CN VII),  vestibulocochlear (CN VIII),  glossopharyngeal (CN IX),  vagus  (CN X),  spinal accessory (CN XI), and  hypoglossal (CN XII) nerves. 8/11/2023 10

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12. Cranial nerves are peripheral nerves that mainly innervate anatomical structures of the head and neck. The exception to this is the vagus nerve, which also innervates various thoracic and abdominal organs. Cranial nerves originate from specific nuclei located in the brain. They leave the cranial cavity through foramina and project to their respective target structure. Cranial nerves are divided into three groups according to the type of information carried by their fibers: Sensory Motor Mixed 8/11/2023 12

13. Spinal nerves The second set of peripheral nerves are  spinal nerves , of which there are 31 pairs: eight cervical, twelve thoracic, five lumbar, five sacral, and one coccygeal. Their numbering relates to the  vertebral column  exit level; cervical spinal nerves are numbered according to the vertebra located below, while all the rest according to the vertebra situated above. Each spinal nerve starts as several rootlets that unite to form two main roots. The anterior root carries motor fibers from neurons whose cell bodies are located in the anterior horn of the spinal cord. The posterior root transports sensory fibers from neurons which have their cell bodies in the dorsal root ganglion. In the thoracic and upper lumbar region, the anterior root also carries autonomic fibers from preganglionic sympathetic neurons whose cell bodies are located in the spinal cord’s lateral horn. 8/11/2023 13

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15. The anterior and posterior roots subsequently join to form the spinal nerve proper that carries mixed (sensory, motor, autonomic) fibers. Immediately after the division of the spinal nerve into the two rami, smaller communicating fibers branch out These white and grey rami communicantes establish a connection between spinal nerves and the two sympathetic trunks of the autonomic nervous system that run along the length of the vertebral column. Note: that grey rami communicantes exist at all levels of the spinal cord, whilst white rami are only found at T1-L2 levels. 8/11/2023 15

16. Somatic nervous system The somatic, voluntary, nervous system is responsible for providing sensory and motor innervation to skin, muscles and sensory organs. In other words, it carries sensations from the body (pain, touch, temperature, proprioception) and innervates skeletal muscles that are under conscious, or voluntary control. In addition, the somatic nervous system is involved in spinal reflexes, an example being the withdrawal reflex. This helps you to instantly pull away your hand when touching a hot object. Both cranial and spinal nerves contribute to the somatic nervous system. Cranial nerves provide voluntary motor control and sensation to the head and face. Spinal nerves supply the trunk and limbs. The posterior rami travel backwards to supply the vertebral column, vertebral muscles and skin of the back whilst the anterior rami supply the limbs and anterior trunk. 8/11/2023 16

17. The majority of anterior rami combine to form nerve plexuses from which many major peripheral nerves stem. The exception to this is the anterior rami of the thoracic region which travel relatively independently from one another without forming plexuses, as the intercostal and  subcostal  nerves of the trunk.  Nervous plexuses, formed by the anterior rami of spinal nerves, are as follows: C1-C4 form the  cervical plexus C5-T1 combine into the  brachial plexus T12-L4 form the  lumbar plexus L4 - S4 combine into the  sacral plexus The lumbar and sacral plexuses can also be combined as one lumbosacral plexus. Each nerve plexus gives out several peripheral nerves, which carry sensory and motor fibers to and from their respective target structures.  8/11/2023 17

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19. Peripheral nerves of the nervous plexuses Cervical plexus Lesser occipital nerve Great auricular nerve Transverse cervical nerve Supraclavicular nerves Phrenic nerve Ansa cervicalis Other smaller branches, for instance the nerves to the  rhomboids  and  serratus anterior muscles Brachial plexus Axillary nerve Musculocutaneous nerve Radial nerve Median nerve Ulnar nerve Other smaller branches such as; dorsal scapular, long thoracic, suprascapular nerve, nerve to  subclavius , lateral & medial pectoral, medial cutaneous of arm &  forearm , superior & inferior subscapular, thoracodorsal Lumbar plexus Iliohypogastric nerve Ilioinguinal nerve Genitofemoral nerve Lateral cutaneous nerve of the thigh Femoral nerve Obturator nerve Sacral plexus Superior gluteal nerve Inferior gluteal nerve Sciatic nerve  ( common fibular  and  tibial  divisions) Posterior cutaneous nerve of the thigh (perforating cutaneous) Pudendal nerve Other smaller branches such as; nerve to  piriformis , nerve to quadratus femoris and  inferior gemellus , nerve to  obturator internus 8/11/2023 19

20. Autonomic nervous system Last but not least, we have reached the autonomic division of the peripheral nervous system (ANS). It is involuntary in nature, meaning that we have no conscious control over it. The ANS is responsible for providing sensory and motor innervation to smooth muscles, blood vessels, glands, and internal organs. As such, it provides a coordinated regulation of visceral and glandular functions, playing a role in maintaining homeostasis. The autonomic nerves are also peripheral in nature, so the general structure of a peripheral nerve discussed earlier still applies. However, there is one caveat; all autonomic nerves synapse with a sympathetic or parasympathetic ganglion. . 8/11/2023 20

21. The portion of the nerve before the ganglion is referred to as preganglionic and carries the impulse towards the cluster of cell bodies. The portion located from the ganglion onwards is called postganglionic and carries the impulse away from the cell bodies The ANS has three major branches: sympathetic, parasympathetic and enteric. The  sympathetic division  prepares the body for dealing with periods of increased physical activity through actions such as regulating blood vessels (often, but not always, vasoconstriction), dilating pupils, increasing heart rate and blood pressure, and decreasing peristalsis. The  parasympathetic division  helps the body to conserve energy, it has ‘rest and digest’, feeding, and breeding functions. This is carried out by actions that slow the  cardiovascular system , stimulates gland secretion and increases peristalsis. 8/11/2023 21

22. The PNS is also involved in sexual arousal and lacrimation (crying). The enteric nervous system (ENS) lies within the walls of the gastrointestinal tract and consists of the myenteric (Auerbach) and submucosal (Meissner) plexuses. They work together to control peristalsis within the digestive system. This system is often described as the second brain because it acts independently while only being influenced by impulses from the ANS. Sympathetic division Sympathetic trunk Truncus sympathicus 1/5 Synonyms: Sympathetic chain, Sympathetic ganglia etc The preganglionic fibers of the sympathetic nerves leave the spinal cord through the T1 to L2 anterior roots, entering the corresponding spinal nerve. The fibers then travel through the white rami communicantes  to paravertebral ganglia of the sympathetic trunks, located on either side of the vertebral column.  8/11/2023 22

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