Nervous Systems PHYSIOLOGY PHL-226. Your Nervous System is the most complicated and fragile system. It tells all your other systems what to do. The Nervous.

Nervous SystemsPHYSIOLOGY

PHL-226

Your Nervous System is the most complicated and fragile system. It tells all your other systems what to do. The Nervous System carries messages to the brain.

HUMAN NERVOUS SYSTEM

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HUMAN NERVOUS SYSTEM

It is divided into

*central nervous system (CNS)

*peripheral nervous system (PNS)

which is the brain and spinal cord

It consists of cranial and spinal nerves . which connects every organs to the CNS.

HUMAN NERVOUS SYSTEM

cranial nerves-12

pairs

spinal nerves- 31 pairs

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Spinal nerves

They are a part of the peripheral nervous system There are 31 pairs of spinal nerves that

originated from spinal cord. They are named according to the spinal cord

segment from which they originate8 cervical12 thoracic5 lumbar5 sacral1 coccygeal

C1

C1

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Cranial nerves

They are a part of the peripheral nervous system There are 12 pairs of cranial nerves that

originated from the brain it self They are numbered I to XII, Their names reflect

their general distribution or function.

Name and functions of Cranial Nerves

CN Name Function

I Olfactory Sense of smell

II Optic Sense of vision

III Oculomotor Eye movementOpening of eyelid

IV Trochlear Eye movement

V Trigeminal Facial sensation Chewing (Jaw movements)

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Name and functions of Cranial Nerves

VI Abducens Eye movement

VII Facial Facial expression Taste sensation Closing of eye lid

VIII Vestibulocochlear Equilibrium or balance (vestibular)Hearing (cochlear)

IX Glossopharyngeal Taste sensation Swallowing

X Vagus Control most glands and visera

XI Accessory Control neck and shoulder muscles

XII Hypoglossal Tongue movements9

CRANIAL NERVES

Learn them; mneumonic helps, e.g.:“Oh, oh, oh, to touch and feel very good velvet, ah!”

NERVES (CRANIAL OR SPINAL) NERVES (CRANIAL OR SPINAL) may be may be

Sensory (Afferent) Sensory (Afferent) oror Motor (Efferent) Motor (Efferent)

e.g., skin

e.g., muscle

Gray’s Anatomy 38 1999

1-sensory (afferent) nerve

2- motor (efferent) nerve

It transmits commands from CNS to muscles, glands and organs

it sends signals or impulses from senses, skin, muscles, and internal organs to the CNS

The Withdrawal Reflex

cells of The Nervous System

The nervous system is formed of 2 main kinds of cells

–1) Neurons (nerve cells)

–2) Neuroglia ( glia cells)

Neuron (nerve cell)

It is the Basic units of the nervous systemIt is the conducting cell as it transmits electrical impulses from one part of the body to another part

•anatomy later

Neurons structure

Axon of anotherneuron

Axon of anotherneuron

Cell BodyCell BodyDendritesDendrites

AxonAxon

MyelinSheathMyelinSheath

Dendrites of another neuron

Dendrites of another neuron

Specific Parts: The NeuronStructure

Structure of neuron

Cell body •That contains nucleusDendritesMutiple branching hair like extensions that arise from the cell body of a neuron . It receives messages from other neurone and conducts impulses toward the cell bodyAxonSingle long extension of a neuron, ending in branching terminal fibers ( called axon terminals), through which messages are sent to other neurons or to muscles or glands

Neural communication( Synapse)

–It is the site of junction , communication and connection between two neurons (sending and receiving neurons)

Glial cells (neuroglia)

They are non conducting cells that cover some axons forming mylein sheath . The nerve fibers that are covered by mylein sheath are called myleinated nerve fibers Mylein sheath formed of lipid that give a white colour to the myelinated nerve axon They insulate, support and protect nerve cells

anatomy later

The brain and spinal cord are protected by :-

1- The bony skull for the brain and vertebrae for the spinal cord

Protection of the Brain

2- Meninges

3- Cerebrospinal Fluid

4-Blood-Brain Barrier

The brain and spinal cord are covered by a tissue known as the

meninges The meninges is made up of 3 layers: 1. Dura Mater – Which is the outer most layer

under the bony skull. It is strongly adherent to the

base of the skull It is a tough layer, as it is formed of strong

connective tissue thus called tough mother

Meninges

3. Pia Mater – It is the innermost layer covering the brain loosely, and passing over sulci which . It is formed of a delicate membrane thus called delicate mother.

2. Arachnoid Layer – It is the middle layer .it is a‘spider’ web like structure filled with cerebrospinal fluid ( CSF ).

Subdural space Potential space between dura and

arachnoid mater.

Meningeal Spaces

Epidural spacePotential space superior to dura.

Subarachnoid spaceFilled with CSFContains the blood vessels

supplying brain.

.

Functions of the Meninges

1- protects the central nervous system and cerebral blood vessels .

2- It contain CSF .

.1- Cerebrospinal fluid (CSF) is a clear, colorless, bodily fluid that occupies the subarachnoid space and the ventricular system of the brain and spinal cord

2- CSF is produced in the choroid plexus. It circulates from the lateral ventricles to the foramen of Monro , third ventricle, aqueduct of Sylvius, fourth ventricle, foramen of Magendie, and the subarachnoid space over the brain and the spinal cord .

3- in adult the total volume of CSF is a bout 150 mL.

CSF

1- Protection of the brain :- CSF protects the brain tissue from different type of trauma . 2- nourishes the brain :- CSF carries nutrient from the blood to the brain 3- chemical stability :- it removes waste products from the brain

Functions of the CSF

Blood brain barrier (BBB)

Sensation : is a state of awareness of a stimulus.

Sensation requires:-

1)A stimulus : Any changes in the environment, either internal or external , e.g. body temp, pH, light, sound, pressure ….. etc.

2)Receptor : which receive stimulus

3)Conduction of nerve impulse to the CNS

4)Translation at different regionS of the brain

A: Free nerve endings (pain, temperature)

B: Pacinian corpuscle (pressure)

C: Meissner’s corpuscle (touch)

D: Muscle spindle (stretch of muscle )

E: Merkel discs (light touch) D: Ruffini’s corpsucles (deep

pressure and stretch)

A

B C

D

E

F

Carries pain, temperature, touch and pressure signals1st neuron enters spinal cord through dorsal root2nd neuron crosses over in spinal cord; ascends to thalamus3rd neuron projects from thalamus to somatosensory cortex

Spinothalamic PathwayPrimary somatosensory cortex

Thalamus

Medulla 1st neurone enters spinal cord through dorsal root

Spinothalamic tract 2 nd neurone decussates

the spinal cord and ascend to the thalamus

1st 2nd

3rd 3rd neurone arise from thalamus to somatosensory area of the cortex

Cones and Rods mediate different kinds of vision

◦Cones – photopic (day time) vision High sensitive to color in a good lighting

◦Rods – scotopic (night time) visionHigh-sensitivite to low-acuity vision in dim light

NB:Rods and cones present in the retina of the eye

Cone and Rod Cone and Rod are receptor are receptor for Visionfor Vision

Figure 6.5

Olfactory epithelium in the nose acts as a receptor for smell sensation

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Cochlea

Vestibulocochlear nerve sends impulses to the auditory cortex of the temporal lobe of brain and interpreted as sound

Auditory ( hearing ) receptor : The special receptor for hearing is the hair cells in the organ of corti which is present inside the cochlea in the inner air

Equilibrium: is the ability to detect head position and movement ( or acceleration)Utricle and saccule contain sensory or receptor cells for linear-acceleration Crista ampularis contain sensory cells for rotational- acceleration