The Human Nervous System The Human Nervous System 1- The Autonomic Nervous System 1- The Autonomic Nervous System (ANS)(ANS)

Physiology -IPhysiology -IPHL 215PHL 215

Prof. Dr/ Gamal SolimanProf. Dr/ Gamal Soliman

Pharmacy CollegePharmacy College

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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 systemMajor divisions of the nervous system : : The nervous system The nervous system is divided into 2 main sections:

I- The Central Nervous System or CNS. The CNS consists of the brainbrain and the spinal cordspinal cord The CNS is protected by bone and the meninges. The brain is protected within the craniumcranium, while the spinal cord is

protected within the vertebraevertebrae.

II- The Peripheral Nervous System or PNS. The PNS forms a network of nerves between the CNS and other body

organs. It consists of cranialcranial and spinal nerves (spinal nerves (OR sensory sensory and motor nerves) motor nerves)

which connect the organs to the CNS. Unlike the CNS, the PNS is not protected by bone or the meninges.

NOTE: The bony covering around the brain is called the craniumcranium, which

combines with the facial bones to form the skullskull.

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Nervous Tissue

Nervous tissue is composed of 2 main types of cells:

1] The neurons (nerve cells).1] The neurons (nerve cells). They are responsible for transmitting nerve impulses.

2] The neuroglia (glial cells).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 1011 neurons (100

billion neurons). The neuron is amitoticamitotic (i.e, can not divides). This means that

neurons cannot reproduce after damage.

Each neuron is composed of 3 parts: Each neuron is composed of 3 parts:

a- The cell body (soma).

b- The dendrites.

c- The axon (nerve fiber).

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a- The cell body (soma): a- The cell body (soma): It is the main part of the neuron that contains all of the

necessary components of the cell. It contains the nucleusnucleus (which contains DNA), ribosomesribosomes

(which synthesize proteins) and mitochondriamitochondria (which produce energy).

b- The dendritesb- The dendrites : : The dendrites are fine branches surrounding the cell

body. They conduct the nerve impulses (action potential)

towardtoward the cell body.

c- The axon (nerve fiber):c- The axon (nerve fiber): The axonaxon is the long extension of the nerve cell. It carry the nerve impulse awayaway from the cell body. There is usually only one axon per neuron. Some axons are covered with myelin sheath myelin sheath which is

formed by the glial cells SO, there are 2 types of axons; mylinated and unmylinated.

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NOTES:Axons that covered with myelin sheath are called myelinated axonsmyelinated axons. Axons without myelin sheath are called unmyelinated axonsunmyelinated axons.

Functions of the neurons:oThe neurons are responsible for receiving, sending and interpreting information from/ to all parts of the body.

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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 neuroglia of the CNS are of 2 types: the microglial cells and the the microglial cells and the

macroglial cells.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

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:oSome 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).oAstrocytes 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: oOligodendrocytes manufacture the myelin sheath which insulate each neuron from another SO they are responsible for normal transmission of nerve impulses.

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3- Ependymal cells: They line the ventricles of the brain and central canal of spinal cord.

Functions: oEpendymal 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. The sheath is not continuous and the gaps between adjacent Schwann cells are called nodes of Ranviernodes of Ranvier.

Functions:oSchwann 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:oThey 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

NOTES:MyelinMyelin 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.

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Types of neurons of the PNS

Neurons of the PNS are classified in 2 Neurons of the PNS are classified in 2 ways:ways:

1- According to the origin of the neuron OR anatomically into:

A- Cranial neuronsA- Cranial neurons: The cranial neurons are 12 pairs of neurons

originating from the brain. Only the olfactory nerve (I) and the optic

nerve (II) originate from the cerebrumcerebrum, while the rest emerge from the brain stembrain 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.

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Cranial neuronsCranial neurons

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No.No. NameName FunctionFunction

II Olfactory nerve This is the nerve of smellsmell (olfaction). It transmits the sense of smell to the brain.

IIII Optic nerve This is the nerve of visionvision. It transmits visual information to the brain.

IIIIIIOculomotor Oculomotor

nervenerveIt innervates muscles which are responsible for movement of the eyes (for looking for looking

aroundaround) and the size of eye pupil (responsible for pupillary constriction).

IVIV Trochlear nerveThis nerve also innervates muscles which are responsible for movement of the eyes (for looking up and downfor looking up and down).

VV Trigeminal nerve It is the largest cranial nerve. It is responsible for the ability to feel the face and inside the mouth. It innervates muscles which are responsible for mastication mastication (chewing).

VIVI Abducent nerve It innervates muscles which are responsible for movement of the eyes (for looking (for looking laterally)laterally).

VIIVII Facial nerveFacial nerve

It innervates muscles which are responsible for facial expression (smile, wink).(smile, wink). It is responsible for the sense of tastetaste. It transmits the taste (gustatory)

information from the anterior 2/3 of the tongue to the brain. It innervates the salivary glands (except parotidparotid) and the lacrimal gland (SO, it

is responsible for secretion of saliva and tears).

Cranial neuronsCranial neurons

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No.No. NameName FunctionFunction

VIIIVIIIVestibulocochlear nerve

It transmits the sense of sound and rotation to the brain SO it is responsible for hearing hearing and balance.balance.

IXIX Glossopharyngeal Glossopharyngeal

nervenerve

It is responsible for the sense of tastetaste. It transmits the taste (gustatory) information from the posterior 1/3 of the tongue to the brain.

It innervates the parotidparotid glands (secretion of salivasaliva) It innervates pharyngeal muscles (swallowing action).swallowing action).

XX Vagus nerveVagus nerve It is responsible for the ability to swallow and the gaggag 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.

XIXISpinal Accessory nerve

It innervates muscles which are responsible for movement of the shoulders and neck.

XIIXII Hypoglossal nerve It moves the tongue for speech and swallowing.

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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: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: Adult spinal cord often terminates at the vertebral

level of L 1-2L 1-2.

2- According to the direction of the nerve impulses OR functionally into:2- According to the direction of the nerve impulses OR functionally into:

A- Sensory neuronsA- Sensory neurons (afferent neurons) (afferent neurons) : They transmit impulses from the sense organs (as skin) to the CNS (i.e. toward the CNS).

B- Motor neuronsB- Motor neurons (efferent neurons) (efferent neurons) : They transmit impulses from the CNS to effectors (muscles or glands) to cause an action (i.e. away from the CNS).

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Motor neurons are classified into:Motor neurons are classified into:

a- Autonomic neurons: a- Autonomic neurons: They are motor neurons that transmit impulses to cardiac muscle, smooth muscles and

exocrine glands. They controls the involuntary functions, so called the autonomic nervous systemautonomic nervous system or the

involuntary nervous systeminvoluntary nervous system.

b- Somatic neurons: b- Somatic neurons: They are motor neurons that transmits impulses to the skeletal muscles. They controls the voluntary functions, so called the somatic nervous system or somatic nervous system or the

voluntary nervous systemvoluntary nervous system.

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NOTES:Cardiac muscle, smooth muscles Cardiac muscle, smooth muscles and exocrine glands 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.

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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.

Nucleus is the collection of cell bodies cell bodies within the CNS. Ganglion is the collection of cell bodies cell bodies within the PNS. TractTract is the bundles of axonsaxons within the CNS NerveNerve is the bundles of axonsaxons within the PNS, SO there are no cell

bodies in the tracts and nerves. 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 junctionneuromuscular junction.

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Nervous SystemNervous System

CNSCNS(Brain + Spinal cord)(Brain + Spinal cord)

PNSPNS(Cranial Ns + Spinal Ns)(Cranial Ns + Spinal Ns)

ORORSensory Ns + Motor Ns Sensory Ns + Motor Ns

(Afferent Ns) (Efferent Ns)(Afferent Ns) (Efferent Ns)

To Skeletal MsTo Skeletal Ms To Cardiac M, Smooth Ms and Exocrine To Cardiac M, Smooth Ms and Exocrine glandsglands

Somatic NervesSomatic Nerves Autonomic NervesAutonomic Nerves

OROR OROR

Somatic Nervous SystemSomatic Nervous System(Voluntary Nervous System)(Voluntary Nervous System)

Autonomic Nervous System Autonomic Nervous System (Involuntary Nervous System)(Involuntary Nervous System)