1. The Human Nervous System 1- The Autonomic Nervous System (ANS) Physiology -I PHL 215 Prof. Dr/ Gamal Soliman Pharmacy College Pharmacy College 1

2. The human nervous system - Introduction  The human nervous system  The human nervous system is the most important system in the body.  Major divisions of the nervous system :  The nervous system  The nervous system is divided into 2 main sections: I- The Central Nervous System or CNS. brainspinal cord  The CNS consists of the brain and the spinal cord  The CNS is protected by bone and the meninges. cranium vertebrae  The brain is protected within the cranium, while the spinal cord is protected within the vertebrae. II- The Peripheral Nervous System or PNS.  The PNS forms a network of nerves between the CNS and other body organs. cranialspinal nerves ( sensory motor nerves)  It consists of cranial and spinal nerves (OR sensory and motor nerves) which connect the organs to the CNS.  Unlike the CNS, the PNS is not protected by bone or the meninges. NOTE: cranium skull  The bony covering around the brain is called the cranium, which combines with the facial bones to form the skull. 2

3. Nervous Tissue  Nervous tissue is composed of 2 main types of cells: 1] The neurons (nerve cells).  They are responsible for transmitting nerve impulses. 2] The neuroglia (glial cells).  They are responsible for supporting and nourishing the neurons. 1] The neurons (nerve cells):  The neuron represents the basic unit of the nervous system.  The nervous system is consists of more than 10 11 neurons (100 billion neurons). amitotic  The neuron is amitotic (i.e, can not divides). This means that neurons cannot reproduce after damage.  Each neuron is composed of 3 parts: a- The cell body (soma). b- The dendrites. c- The axon (nerve fiber). 3

4. a- The cell body (soma):  It is the main part of the neuron that contains all of the necessary components of the cell. nucleusribosomes mitochondria  It contains the nucleus (which contains DNA), ribosomes (which synthesize proteins) and mitochondria (which produce energy). b- The dendrites :  The dendrites are fine branches surrounding the cell body. toward  They conduct the nerve impulses (action potential) toward the cell body. c- The axon (nerve fiber): axon  The axon is the long extension of the nerve cell. away  It carry the nerve impulse away from the cell body.  There is usually only one axon per neuron. myelin sheath  Some axons are covered with myelin sheath which is formed by the glial cells SO, there are 2 types of axons; mylinated and unmylinated. 4

5. NOTES: myelinated axons  Axons that covered with myelin sheath are called myelinated axons. unmyelinated axons  Axons without myelin sheath are called unmyelinated axons. Functions of the neurons: o The neurons are responsible for receiving, sending and interpreting information from/ to all parts of the body. 5

6. 2] The neuroglia (glial cells):  The neuroglia are the supporting cells of the nervous system.  These cells are non-conductive (don't carry nerve impulses) and undergo mitotic division. Classification:  The neuroglia are classified into CNS glia and PNS glia.  The neuroglia of the CNS:  The number of neuroglial cells in the CNS is about ten times more than that of nerve cells. the microglial cells and the macroglial cells.  The neuroglia of the CNS are of 2 types: the microglial cells and the macroglial cells. A- The microglial cells:  The microglial cells are small cells with few tortuous متعرج processes.  The microglial cells are phagocytic cells SO, they act as the first line of immune defense in the CNS.  They are responsible for phagocytosis of different types of pathogenic microbes and digestion of dead neurons. Functions of microglial cells: 1. Phagocytosis of different types of pathogenic microbes. 2. Digestion of dead neurons. 6

7. B- The macroglial cells are of 3 types : 1- Astrocytes (astroglia):  Astrocytes are the main type of macroglial cells in the CNS.  They have numerous projections that attach neurons to the blood capillaries. Functions of astrocytes: o Some of the processes of astrocytes are attached to the outer surface of the capillaries of brain to acts as Blood-Brain Barrier. o Astrocytes supply neurons with nutrients and oxygen (by transporting certain molecules from the blood to the neuron). o Astrocytes are primary glycogen store in the CNS. 2- Oligodendrocytes:  Oligodendrocytes are smaller than astrocytes and contains less branched processes.  They manufacture the myelin which form myelin sheath around some axons of CNS. Functions: o Oligodendrocytes manufacture the myelin sheath which insulate each neuron from another SO they are responsible for normal transmission of nerve impulses. 7

8. 3- Ependymal cells:  They line the ventricles of the brain and central canal of spinal cord. Functions: o Ependymal cells create and secrete the cerebrospinal fluid (CSF).  The neuroglia of the PNS 1- Schwann cells:  Schwann cells are the main type of the neuroglia of the PNS.  These cells are equivalent to the oligodendrocytes of the CNS.  Schwann cells manufacture the myelin which form myelin sheath around some axons of the PNS. nodes of Ranvier  The sheath is not continuous and the gaps between adjacent Schwann cells are called nodes of Ranvier. Functions: o Schwann cells manufacture the myelin sheath which insulate each neuron from another SO they are responsible for normal transmission of nerve impulses. 2- Satellite glial cells:  Satellite glial cells surround the cell bodies of neurons in the PNS. Functions: o They protect and support the cell bodies of neurons of the PNS. o They supply neurons with nutrients and oxygen (by transporting molecules from the blood to the neuron). 8

9. NOTES:  Myelin  Myelin is a fatty substance that surrounds and insulates the nerve axons to facilitates the conduction of the nerve impulses SO myelinated nerves can conduct impulses quicker than unmyelinated nerves.  Myelin is composed of 70-80% lipids (give white colour to the myelinated axons) and 20-30% protein.  Myelin is produced in the CNS by Oligodendrocytes and in the PNS by Schwann cells.  Clinically, glial cells are important because they are a common source of tumors of the nervous system.  Nodes of Ranvier  Nodes of Ranvier are the unmyelinated gaps between sections of myelin. 9

10. Types of neurons of the PNS  Neurons of the PNS are classified in 2 ways: 1- According to the origin of the neuron OR anatomically into: A- Cranial neurons A- Cranial neurons:  The cranial neurons are 12 pairs of neurons originating from the brain. cerebrum brain stem  Only the olfactory nerve (I) and the optic nerve (II) originate from the cerebrum, while the rest emerge from the brain stem.  Ten of the cranial nerves control the sense organs and muscles of the head.  Only the vagus nerve (X) and the accessory nerve (XI) extends beyond head and neck. 10

11. Cranial neurons 11 No.NameFunction IOlfactory nerve smell This is the nerve of smell (olfaction). It transmits the sense of smell to the brain. IIOptic nerve vision This is the nerve of vision. It transmits visual information to the brain. III Oculomotor nerve for looking around It innervates muscles which are responsible for movement of the eyes (for looking around) and the size of eye pupil (responsible for pupillary constriction). IVTrochlear nerve for looking up and down This nerve also innervates muscles which are responsible for movement of the eyes (for looking up and down). VTrigeminal nerve  It is the largest cranial nerve.  It is responsible for the ability to feel the face and inside the mouth. mastication  It innervates muscles which are responsible for mastication (chewing). VIAbducent nerve (for looking laterally) It innervates muscles which are responsible for movement of the eyes (for looking laterally). VII Facial nerve (smile, wink).  It innervates muscles which are responsible for facial expression (smile, wink). taste  It is responsible for the sense of taste. It transmits the taste (gustatory) information from the anterior 2/3 of the tongue to the brain. parotid  It innervates the salivary glands (except parotid) and the lacrimal gland (SO, it is responsible for secretion of saliva and tears).

12. Cranial neurons 12 No.NameFunction VIII Vestibulocochlear nerve hearing balance. It transmits the sense of sound and rotation to the brain SO it is responsible for hearing and balance. IX Glossopharyngeal nerve taste  It is responsible for the sense of taste. It transmits the taste (gustatory) information from the posterior 1/3 of the tongue to the brain. parotidsaliva  It innervates the parotid glands (secretion of saliva) swallowing action).  It innervates pharyngeal muscles (swallowing action). X Vagus nerve gag  It is responsible for the ability to swallow and the gag reflex.  It transmits the taste (gustatory) information from the tongue to the brain.  It innervates most organs with the parasympathetic nerves, SO it control cardiac muscle, smooth muscles and exocrine glands. XI Spinal Accessory nerve It innervates muscles which are responsible for movement of the shoulders and neck. XIIHypoglossal nerveIt moves the tongue for speech and swallowing.

13. 13  Gag reflex (pharyngeal reflex):  It is a reflex contraction of the back of the throat evoked by touching the roof of the mouth, the back of the tongue, the area around the tonsils and the back of the throat.  It prevents the passage of anything to the throat, except during normal swallowing. B- Spinal neurons: o The spinal nerves are 31 pairs of nerves originating from the spinal cord.  Cervical nerves 8  Thoracic nerves 12  Lumbar nerves 5  Sacral nerves 5  Coccygeal nerve 1 NOTE: L 1-2  Adult spinal cord often terminates at the vertebral level of L 1-2.

14. 2- According to the direction of the nerve impulses OR functionally into: A- Sensory neurons(afferent neurons) A- Sensory neurons (afferent neurons) :  They transmit impulses from the sense organs (as skin) to the CNS (i.e. toward the CNS). B- Motor neurons(efferent neurons) B- Motor neurons (efferent neurons) :  They transmit impulses from the CNS to effectors (muscles or glands) to cause an action (i.e. away from the CNS). 14

15. Motor neurons are classified into: a- Autonomic neurons:  They are motor neurons that transmit impulses to cardiac muscle, smooth muscles and exocrine glands. autonomic nervous system involuntary nervous system  They controls the involuntary functions, so called the autonomic nervous system or the involuntary nervous system. b- Somatic neurons:  They are motor neurons that transmits impulses to the skeletal muscles. somatic nervous system or voluntary nervous system  They controls the voluntary functions, so called the somatic nervous system or the voluntary nervous system. 15

16. NOTES:  Cardiac muscle, smooth muscles exocrine glands  Cardiac muscle, smooth muscles and exocrine glands are effector organs for the autonomic nervous system.  Skeletal muscles  Skeletal muscles are the effector organs for the somatic nervous system.  Interneuron  Interneuron is a type of neurons that is found completely within the CNS and transmit signals between motor and sensory neurons. 16

17. Some Terms  Neuron is the nerve cell in either CNS or PNS. It is composed of 3 parts: cell body, dendrites and a single axon. cell bodies  Nucleus is the collection of cell bodies within the CNS. cell bodies  Ganglion is the collection of cell bodies within the PNS.  Tractaxons  Tract is the bundles of axons within the CNS  Nerveaxons  Nerve is the bundles of axons within the PNS, SO there are no cell bodies in the tracts and nerves. neuromuscular junction  Synapse is the gap between two neurons or between a neuron and an effector organ (gland or muscle cell). The synapse between a neuron and skeletal muscle is called a neuromuscular junction. 17

18. 18 Nervous System CNS (Brain + Spinal cord) PNS (Cranial Ns + Spinal Ns) OR Sensory Ns + Motor Ns (Afferent Ns) (Efferent Ns) To Skeletal Ms To Cardiac M, Smooth Ms and Exocrine glands Somatic Nerves Autonomic Nerves OROR Somatic Nervous System (Voluntary Nervous System) Autonomic Nervous System (Involuntary Nervous System)