THE NERVOUS SYSTEM I · The nervous system has two divisions: The central nervous system, which...

NERVOUS SYSTEM

Khaleel Alyahya, PhD, MEdKing Saud UniversityCollege of Medicine @khaleelya

LEARNING OBJECTIVES

At the end of the lecture, students should be able to:

❑ Describe the structure and functions of the nervous system including the brain, spinal cord and nerves.

❑ Describe general classification of the nervous system.

❑ State the meanings of the word elements related to the nervous system.

❑ Apply what they have learned through group and individual exercises.

❑ Build words using the word elements associated with the nervous system.

❑ Recognize, pronounce and effectively use medical terms associated with the nervous system.

❑ Expand abbreviations related to the nervous system.

❑ Describe common pathological conditions associated with the nervous system.

❑ Describe common laboratory tests, diagnostic and surgical procedures associated with the nervous system.

❑ Apply what they have learned by interpreting medical terminology through group and individual

exercises.

RESOURCES

❑ Information, tables and figures of this lecture were taken from the

following books:

▪ “Mastering Medical Terminology”.

o By Sue Walker, Maryann Wood and Jenny Nicol

▪ Essential of Human Anatomy and Physiology

o Elaine Marieb and Suzanne Keller

❑ Additional Recommended Resources:

▪ Mosby’s Dictionary

▪ By Mosby

Prof. Saeed Makarem

❑ The nervous system is arguably the most complex system

in the body.

❑ It facilitates internal communication within the body by

integrating and controlling the various functions of the body.

❑ The nervous system is responsible for sending, receiving

and processing nerve impulses, while the sense organs

detect the various stimuli in the external environment that

humans react to.

❑ Sense organs provide the nervous system with information

about the environment by means of such senses as sight,

hearing, smell, taste and touch.

❑ The activities that keep the body operating, such as

respiration, digestion, heart pumping, movement, all the

senses, and the unique processes that make us human

such as thinking, dreaming, laughing and memory, are not

possible without a properly functioning nervous system.

INTRODUCTION

Khaleel Alyahya, PhD, MEd

Prof. Saeed Makarem

❑ Vision and sight, hearing, smell, taste and touch.

❑ Vision senses are based on receptor cells or groups of

receptor cells called sense organs.

❑ Receptors respond to stimuli in the environment and send

nerve impulses along sensory neurons.

❑ Everything we see, hear, feel, smell or taste requires billions

of nerve impulses to send messages to the brain.

❑ Brain interprets the nerve impulse and, thus, we perceive

the impulse through one of our senses.

❑ The figures illustrate the framework about structure and

function of nervous system and special senses.

SPECIAL SENSES


Prof. Saeed Makarem

❑ The nervous system plays an important role in

coordinating and regulating body functions and

communicating within and between the brain, spinal

cord and all other parts of the body.

❑ Another important function is to interpret stimuli from the

external environment so the body can respond

accordingly.

❑ Working in association with the endocrine system, the

nervous system acts to maintain homeostasis, the

body’s ability to maintain a constant internal state even

in changing external environments.

❑ The nervous system consists of a network of specialized

cells called neurons.

❑ Signals move between the brain and body via these

neural networks.

HOMEOSTASIS


FUNCTIONS

The nervous system has 3 functions:

❑ Sensory Input - collect information

– Sensory receptors monitor changes,

called stimuli, occurring inside and

outside the body.

❑ Integration

– Nervous system processes and

interprets sensory input and decides

whether action is needed.

❑ Motor Output – send feedback

– A response, or effect, activates

muscles or glands.


Prof. Saeed Makarem

❑ The nervous system has two divisions:

▪ The central nervous system, which includes the brain and

spinal cord

▪ The peripheral nervous system, which is composed of nerves

and nerve networks throughout the rest of the body.

❑ Nervous system classifications are based on:

▪ Structures (structural classification).

▪ Activities (functional classification).

ORGANIZATION


Prof. Saeed Makarem

❑ Central Nervous System (CNS)

▪ Organs

• Brain.

• Spinal cord.

▪ Functions:

• Integration; command center.

• Interprets incoming sensory information.

• Issues outgoing instructions.

❑ Peripheral Nervous System (PNS)

▪ Nerves extending from the brain and spinal cord.

• Spinal nerves—carry impulses to and from the spinal cord.

• Cranial nerves—carry impulses to and from the brain.

▪ Functions:

• Serve as communication lines among sensory organs, the brain

and spinal cord, and glands or muscles.

STRUCTURAL ORGANIZATION


Prof. Saeed Makarem

❑ Sensory (afferent) division

▪ Nerve fibers that carry information to the central nervous system.

• Somatic sensory (afferent) fibers carry information from the skin,

skeletal muscles, and joints.

• Visceral sensory (afferent) fibers carry information from visceral

organs.

❑ Motor (efferent) division

▪ Nerve fibers that carry impulses away from the central nervous

system organs to effector organs (muscles and glands).

▪ Two subdivisions:

• Somatic nervous system = voluntary.

o Consciously (voluntarily) controls skeletal muscles.

• Autonomic nervous system = involuntary.

o Automatically controls smooth and cardiac muscles and

glands.

o Further divided into the sympathetic and parasympathetic

nervous systems.

FUNCTIONAL ORGANIZATION


COMBINING FORM

PREFIX

SUFFIX

VOCABULARY

❑ Check page 257 from the book “Mastering Medical Terminology” for the complete list of vocabulary.

ABBREVIATION

Prof. Saeed Makarem

❑ It consists of the brain and spinal cord.

❑ These structures serve as the main processing centers

for the rest of the nervous system, controlling the

operations of the body.

❑ All nerve impulses either originate or terminate in the

CNS.

❑ The CNS is responsible for processing sensations and

thoughts using information gathered from sensory

receptors throughout the body.

❑ The CNS also sends messages to the rest of the body

to control movement, actions and responses to the

environment.

❑ The main form of communication in the CNS occurs

through the neurons.

CENTRAL NERVOUS SYSTEM


NERVOUS TISSUE

Prof. Saeed Makarem

❑ Nervous tissue is made up of two principal cell

types:

▪ Neurons.

▪ Supporting cells (called neuroglia, or glial cells, or

glia).

• Resemble neurons.

• Unable to conduct nerve impulses.

• Never lose the ability to divide.

• Support.

• Insulate.

• Protect neurons.

STRUCTURE AND FUNCTIONS


NERVOUS TISSUE

Nervous tissue is organized as:

Grey matter: which contains the cell bodies& the processes of the neurons, theneuroglia and the blood vessels.

White matter: which contains the processesof the neurons (no cell bodies), theneuroglia and the blood vessels.


NEURONS

Prof. Saeed Makarem

❑ Cells specialized to transmit messages (nerve impulses).

❑ Major regions of all neurons:

– Cell body—nucleus and metabolic center of the cell.

– Processes—fibers that extend from the cell body.

❑ Cell body is the metabolic center of the neuron

Nucleus with large nucleolus.

Nissl bodies

▪ Rough endoplasmic reticulum.

Neurofibrils

▪ Intermediate filaments that maintain cell shape.

❑ Processes (fibers)

Dendrites—conduct impulses toward the cell body.

▪ Neurons may have hundreds of dendrites.

Axons—conduct impulses away from the cell body.

▪ Neurons have only one axon arising from the cell body at the

axon hillock.

▪ End in axon terminals, which contain vesicles with

neurotransmitters.

▪ Axon terminals are separated from the next neuron by a gap.

Synaptic cleft—gap between axon terminals and the next neuron.

Synapse—functional junction between nerves where a nerve impulse

is transmitted.

OVERVIEW


Prof. Saeed Makarem

❑ Myelin

White, fatty material covering axons

Protects and insulates fibers

Speeds nerve impulse transmission

❑ Myelin sheaths

Schwann cells—wrap axons in a jelly roll–like fashion (PNS)

to form the myelin sheath

▪ Neurilemma—part of the Schwann cell external to the

myelin sheath

▪ Nodes of Ranvier—gaps in myelin sheath along the

axon

Oligodendrocytes—produce myelin sheaths around axons

of the CNS

▪ Lack a neurilemma

❑ Terminology

Nuclei—clusters of cell bodies in the CNS

Ganglia—collections of cell bodies outside the CNS in the

PNS

Tracts—bundles of nerve fibers in the CNS

Nerves—bundles of nerve fibers in the PNS

White matter—collections of myelinated fibers (tracts)

Gray matter—mostly unmyelinated fibers and cell bodies

INTRODUCTION


NucleusA group of neurons

within the CNS

Ganglion A group of neurons outside

the CNS

Tract A group of nerve fibers (axons)

within the CNS

Nerve A group of nerve fibers

(axons) outside the CNS


Prof. Saeed Makarem

❑ Sensory (afferent) neurons

Carry impulses from the sensory receptors to the

CNS

Receptors include:

• Cutaneous sense organs in skin

• Proprioceptors in muscles and tendons

❑ Motor (efferent) neurons

Carry impulses from the central nervous system to

viscera and/or muscles and glands

❑ Interneurons (association neurons)

Cell bodies located in the CNS

Connect sensory and motor neurons

FUNCTIONAL CLASSIFICATION


Prof. Saeed Makarem

❑ Electrical conditions of a resting neuron’s membrane

▪ The plasma membrane at rest is inactive (polarized).

▪ Fewer positive ions are inside the neuron’s plasma

membrane than outside.

• K+ is the major positive ion inside the cell.

• Na+ is the major positive ion outside the cell.

▪ As long as the inside of the membrane is more

negative (fewer positive ions) than the outside, the cell

remains inactive.

❑ Action potential initiation and generation

▪ A stimulus changes the permeability of the neuron’s

membrane to sodium ions.

▪ Sodium channels now open, and sodium (Na+)

diffuses into the neuron.

▪ The inward rush of sodium ions changes the polarity at

that site and is called depolarization.

PHYSIOLOGY


Prof. Saeed Makarem

1) Stimulus starts the rapid change in voltage or action

potential. In patch-clamp mode, sufficient current must

be administered to the cell in order to raise the voltage

above the threshold voltage to start membrane

depolarization.

2) Depolarization is caused by a rapid rise in membrane

potential opening of sodium channels in the cellular

membrane, resulting in a large influx of sodium ions.

3) Membrane Repolarization results from rapid sodium

channel inactivation as well as a large efflux of

potassium ions resulting from activated potassium

channels.

4) Hyperpolarization is a lowered membrane potential

caused by the efflux of potassium ions and closing of

the potassium channels.

5) Resting state is when membrane potential returns to

the resting voltage that occurred before the stimulus

occurred.

ACTION POTENTIAL


Prof. Saeed Makarem

❑ Neurons have two major functional properties:

▪ Irritability, the ability to respond to a stimulus and convert

it into a nerve impulse.

▪ Conductivity, the ability to transmit the impulse to other

neurons, muscles, or glands.

❑ A nerve impulse is the way nerve cells (neurons)

communicate with one another.

❑ Nerve impulses are mostly electrical signals along

the dendrites to produce a nerve impulse or action

potential.

❑ The action potential is the result of ions moving in and out

of the cell.

❑ Specifically, it involves potassium (K+) and sodium (Na+)

ions.

❑ The ions are moved in and out of the cell by potassium

channels, sodium channels and the sodium-potassium

pump.

PHYSIOLOGY: NERVE IMPULSES


Prof. Saeed Makarem

(1) Resting membrane is polarized.

▪ In the resting state, the external face of the membrane

is slightly positive; its internal face is slightly negative.

The chief extracellular ion is sodium (Na+), whereas

the chief intracellular ion is potassium (K+).

▪ The membrane is relatively impermeable to both ions.

(2) Stimulus initiates local depolarization.

▪ A stimulus changes the permeability of a local "patch"

of the membrane, and sodium ions diffuse rapidly into

the cell.

▪ This changes the polarity of the membrane (the inside

becomes more positive; the outside becomes more

negative) at that site.

(3) Depolarization and generation of an action potential.

▪ If the stimulus is strong enough, depolarization causes

membrane polarity to be completely reversed, and an

action potential is initiated.



Prof. Saeed Makarem

(4) Propagation of the action potential.

▪ Depolarization of the first membrane patch causes

permeability changes in the adjacent membrane,

and the events described in step 2 are repeated.

▪ Thus, the action potential propagates rapidly along

the entire length of the membrane.

(5) Repolarization.

▪ Potassium ions diffuse out of the cell as the

membrane permeability changes again, restoring

the negative charge on the inside of the membrane

and the positive charge on the outside surface.

▪ Repolarization occurs in the same direction as

depolarization.

(6) Initial ionic conditions restored.

▪ The ionic conditions of the resting state are restored

later by the activity of the sodium-potassium pump.

Three sodium ions are ejected for every two

potassium ions carried back into the cell.



❑ Reflexes are rapid, predictable, and involuntary

responses to stimuli.

❑ Reflexes occur over neural pathways called reflex

arcs.

❑ Two types of reflexes:

▪ Somatic reflexes.

▪ Autonomic reflexes.

❑ Somatic reflexes:

▪ Reflexes that stimulate the skeletal muscles.

▪ Involuntary, although skeletal muscle is normally

under voluntary control.

▪ Example: pulling your hand away from a hot object.

❑ Autonomic reflexes:

▪ Regulate the activity of smooth muscles, the heart,

and glands.

▪ Example: regulation of smooth muscles, heart and

blood pressure, glands, digestive system.

REFLEXES


❑ Five elements of a reflex arc:

▪ Sensory receptor—reacts to a stimulus.

▪ Sensory neuron—carries message to the integration

center.

▪ Integration center (CNS)—processes information and

directs motor output.

▪ Motor neuron—carries message to an effector.

▪ Effector organ—is the muscle or gland to be

stimulated.

❑ Two-neuron reflex arcs:

▪ Simplest type.

▪ Example: patellar (knee-jerk) reflex.

❑ Three-neuron reflex arcs:

▪ Consists of five elements: receptor, sensory neuron,

interneuron, motor neuron, and effector.

▪ Example: flexor (withdrawal) reflex.

ELEMENTS OF REFLEXES


SUPPORTING CELLS

Prof. Saeed Makarem

❑ CNS glial cells: astrocytes

– Abundant, star-shaped cells.

– Brace and anchor neurons to blood capillaries.

– Determine permeability and exchanges between blood capillaries

and neurons.

– Protect neurons from harmful substances in blood.

– Control the chemical environment of the brain.

❑ CNS glial cells: microglia

– Spiderlike phagocytes.

– Monitor health of nearby neurons.

– Dispose of debris.

❑ CNS glial cells: ependymal cells

– Line cavities of the brain and spinal cord.

– Cilia assist with circulation of cerebrospinal fluid.

❑ CNS glial cells: oligodendrocytes

– Wrap around nerve fibers in the central nervous system.

– Produce myelin sheaths.

❑ PNS glial cells

– Schwann cells.

• Form myelin sheath around nerve fibers in the PNS.

– Satellite cells.

• Protect and cushion neuron cell bodies.

OVERVIEW


CENTRAL NERVOUS SYSTEM

❑ Large mass of nervous tissue located in the cranial cavity.

❑ Has four major regions.

Cerebrum

Cerebellum

Brainstem: Midbrain, Pons & Medulla oblongata

Diencephalon

Thalamus, Hypothalamus, Subthalamus & Epithalamus

BRAIN


Prof. Saeed Makarem

❑ Cerebral hemispheres are paired (left and right)

superior parts of the brain

▪ Include more than half of the brain mass.

▪ The surface is made of ridges (gyri) and grooves (sulci).

▪ Fissures are deeper grooves.

▪ Lobes are named for the cranial bones that lie over them.

▪ Frontal, Parietal, Temporal and Occipital lobes.

❑ Three main regions of cerebral hemisphere

▪ Cortex is superficial gray matter.

▪ White matter.

▪ Basal nuclei are deep pockets of gray matter.

❑ Cerebral cortex

▪ Primary somatic sensory area

▪ Located in parietal lobe posterior to central sulcus.

▪ Receives impulses from the body’s sensory receptors.

▪ Pain, temperature, light touch (except for special senses).

▪ Left side of the primary somatic sensory area receives

impulses from right side (and vice versa).

FUNCTIONAL ANATOMY OF THE BRAIN


Prof. Saeed Makarem

❑ Cerebral areas involved in special senses

▪ Visual area (occipital lobe)

▪ Auditory area (temporal lobe)

▪ Olfactory area (temporal lobe)

▪ Primary motor area

• Located anterior to the central sulcus in the frontal lobe

• Allows us to consciously move skeletal muscles

• Motor neurons form pyramidal (corticospinal) tract, which descends to spinal

cord.

▪ Broca’s area (motor speech area)

• Speech Production

• Involved in our ability to speak

• Usually in left hemisphere

▪ Other specialized areas

• Anterior association area (frontal lobe)

• Posterior association area (posterior cortex)

• Speech area (Wernicke’s area) (for comprehension of written and spoken

language)

❑ Cerebral white matter

▪ Composed of fiber tracts deep to the gray matter

• Corpus callosum connects hemispheres

• Tracts, such as the corpus callosum, are known as commissures

• Association fiber tracts connect areas within a hemisphere

• Projection fiber tracts connect the cerebrum with lower CNS centers

❑ Basal nuclei▪ Islands of gray matter buried deep within the white matter of the cerebrum.

▪ Regulate voluntary motor activities by modifying instructions sent to skeletal

muscles by the primary motor cortex.

FUNCTIONAL ANATOMY OF THE BRAIN


BASAL NUCLEI


Prof. Saeed Makarem

❑ Sits on top of the brain stem.

❑ Enclosed by the cerebral hemispheres.

❑ Made of three structures:▪ Thalamus

▪ Hypothalamus

▪ Epithalamus

❑ Thalamus▪ Encloses the third ventricle

▪ Relay station for sensory impulses passing upward to the cerebral cortex

▪ Transfers impulses to the correct part of the cortex for localization and

interpretation

❑ Hypothalamus▪ Makes up the floor of the diencephalon

▪ Important autonomic nervous system center

• Regulates body temperature

• Regulates water balance

• Regulates metabolism

▪ Houses the limbic center for emotions

▪ Regulates the nearby pituitary gland

▪ Houses mammillary bodies for olfaction (smell)

❑ Epithalamus▪ Forms the roof of the third ventricle

▪ Houses the pineal body (an endocrine gland)

▪ Includes the choroid plexus—forms cerebrospinal fluid

DIENCEPHALON


Prof. Saeed Makarem

❑ Attaches to the spinal cord

❑ Parts of the brain stem:

▪ Midbrain

▪ Pons

▪ Medulla oblongata

❑ Midbrain

▪ Extends from the mammillary bodies to the pons inferiorly

▪ Cerebral aqueduct (tiny canal) connects the third and fourth ventricles

▪ Two bulging fiber tracts, cerebral peduncles, convey ascending and descending impulses

▪ Four rounded protrusions, corpora quadrigemina, are visual and auditory reflex centers

❑ Pons

▪ The rounded structure protruding just below the midbrain

▪ Mostly composed of fiber tracts

▪ Includes nuclei involved in the control of breathing

❑ Medulla Oblongata

▪ The most inferior part of the brain stem that merges into the spinal cord

▪ Includes important fiber tracts

▪ Contains important centers that control:

• Heart rate and Blood pressure

• Breathing, Swallowing and Vomiting

▪ Fourth ventricle lies posterior to pons and medulla

❑ Reticular Formation

▪ Diffuse mass of gray matter along the brain stem

▪ Involved in motor control of visceral organs

• Reticular activating system (RAS)

• Plays a role in awake/sleep cycles and consciousness

• Filter for incoming sensory information

BRAIN STEM


Prof. Saeed Makarem

❑ Two hemispheres with convoluted surfaces.

❑ Outer cortex of gray matter and inner region of white

matter.

❑ Control balance.

❑ Provides precise timing for skeletal muscle activity and

coordination of body movements.

CEREBELLUM


Prof. Saeed Makarem

❑ Meninges

▪ Dura mater

• Outermost leathery layer

• Double-layered external covering

o Periosteum—attached to inner surface of the skull

o Meningeal layer—outer covering of the brain

• Folds inward in several areas

o Falx cerebri

o Tentorium cerebelli

▪ Arachnoid layer

• Middle layer

• Weblike extensions span the subarachnoid space to

attach it to the pia mater

• Subarachnoid space is filled with cerebrospinal fluid

• Arachnoid granulations protrude through the dura

mater and absorb cerebrospinal fluid into venous

blood

▪ Pia mater

• Internal layer

• Clings to the surface of the brain and spinal cord

PROTECTION OF CNS


Prof. Saeed Makarem

❑ Cerebrospinal fluid

▪ Similar to blood plasma in composition.

▪ Formed continually by the choroid plexuses.

• Choroid plexuses—capillaries in the ventricles of the brain.

▪ CSF forms a watery cushion to protect the brain and spinal

cord.

▪ Circulated in the arachnoid space, ventricles, and central canal

of the spinal cord.

❑ Cerebrospinal fluid circulation

▪ CSF is produced by the choroid plexus of each ventricle.

▪ CSF flows through the ventricles and into the subarachnoid

space via the median and lateral apertures. Some CSF flows

through the central canal of the spinal cord.

▪ CSF flows through the subarachnoid space.

▪ CSF is absorbed into the dural venous sinuses via the

arachnoid villi.

❑ Blood-brain barrier

▪ Includes the least permeable capillaries of the body.

▪ Allows water, glucose, and amino acids to pass through the

capillary walls.

▪ Excludes many potentially harmful substances from entering

the brain, such as wastes.

▪ Useless as a barrier against some substances.

PROTECTION OF CNS


❑ Traumatic brain injuries

▪ Concussion

• Slight brain injury.

• Typically little permanent brain damage occurs.

▪ Contusion

• Marked nervous tissue destruction occurs.

• Coma may occur.

▪ Death may occur after head blows due to:

• Intracranial hemorrhage.

• Cerebral edema.

❑ Cerebrovascular accident (CVA), or stroke

▪ Results when blood circulation to a brain area is blocked and

brain tissue dies.

▪ Loss of some functions or death may result.

• Hemiplegia—one-sided paralysis.

• Aphasia—damage to speech center in left hemisphere.

❑ Transient ischemic attack (TIA)

▪ Temporary brain ischemia (restriction of blood flow).

▪ Numbness, temporary paralysis, impaired speech.

BRAIN DYSFUNCTIONS


Prof. Saeed Makarem

❑ Extends from the foramen magnum of the skull to the first or

second lumbar vertebra

❑ Cauda equina is a collection of spinal nerves at the inferior

end

❑ Provides a two-way conduction pathway to and from the brain

❑ 31 pairs of spinal nerves arise from the spinal cord

❑ Gray matter of the spinal cord and spinal roots

▪ Internal gray matter is mostly cell bodies

▪ Dorsal (posterior) horns house interneurons

• Receive information from sensory neurons in the dorsal root; cell

bodies housed in dorsal root ganglion

▪ Anterior (ventral) horns house motor neurons of the somatic

(voluntary) nervous system

• Send information out ventral root

▪ Gray matter surrounds the central canal, which is filled with

cerebrospinal fluid

❑ White matter of the spinal cord

▪ Composed of myelinated fiber tracts

▪ Three regions: dorsal, lateral, ventral columns

▪ Sensory (afferent) tracts conduct impulses toward brain

▪ Motor (efferent) tracts carry impulses from brain to skeletal

muscles

SPINAL CORD


PERIPHERAL NERVOUS SYSTEM

Prof. Saeed Makarem

❑ PNS consists of nerves and ganglia outside the CNS.

❑ Nerves are bundles of neurons found outside the CNS.

❑ Endoneurium is a connective tissue sheath that

surrounds each fiber.

❑ Perineurium wraps groups of fibers bound into a fascicle.

❑ Epineurium binds groups of fascicles.

❑ Mixed nerves.

▪ Contain both sensory and motor fibers.

❑ Sensory (afferent) nerves.

▪ Carry impulses toward the CNS.

❑ Motor (efferent) nerves.

▪ Carry impulses away from the CNS.

STRUCTURE OF THE NERVE


Prof. Saeed Makarem

❑ 12 pairs of nerves serve mostly the head and neck.

❑ 4 pairs are mixed:• trigeminal n. (5th).

• facial n. (7th).

• glossopharyngeal n. (9th).

• vagus n. (10th).

❑ 5 pairs are motor:• occulomotor n. (3rd).

• trochlear n. (4th).

• abducent n. (6th).

• accessory n. (11th).

• hypoglossal n. (12th).

❑ 3 pairs are sensory:• olfactory n. (1st).

• optic n. (2nd).

• vestibulocochlear n. (8th).

❑ Only the pair of vagus nerves extends to thoracic

and abdominal cavities.

CRANIAL NERVES


Prof. Saeed Makarem

i. Oh – Olfactory

ii. Oh – Optic

iii. Oh – Oculomotor

iv. To – Trochlear

v. Touch – Trigeminal

vi. And – Abducens

vii. Feel – Facial

viii. Very – Vestibulocochlear

ix. Green – Glossopharyngeal

x. Vegetables – Vagus

xi. A – Accessory

xii. H – Hypoglossal

CRANIAL NERVES MNEMONIC DEVICE


Prof. Saeed Makarem

❑ 31 pairs.

❑ Formed by the combination of the ventral and dorsal

roots of the spinal cord.

❑ Named for the region of the spinal cord from which they

arise.

❑ Spinal nerves divide soon after leaving the spinal cord.

into a dorsal ramus and a ventral ramus.▪ Ramus—branch of a spinal nerve; contains both motor and sensory

fibers.

▪ Dorsal rami—serve the skin and muscles of the posterior trunk.

▪ Ventral rami (T1–T12) —form the intercostal nerves that supply

muscles and skin of the ribs and trunk.

▪ Ventral rami (except T1–T12)—form a complex of networks (plexus)

for the anterior.

❑ Plexus—networks of nerves serving motor and sensory

needs of the limbs.

❑ Form from ventral rami of spinal nerves in the cervical,

lumbar, and sacral regions.

❑ Four plexuses:▪ Cervical.

▪ Brachial.

▪ Lumbar.

▪ Sacral.

SPINAL NERVES


AUTONOMIC NERVOUS SYSTEM

Prof. Saeed Makarem

❑ Motor subdivision of the PNS▪ Consists only of motor nerves.

▪ Controls the body automatically (and is also known as the

involuntary nervous system).

▪ Regulates cardiac and smooth muscles and glands.

❑ Somatic and Autonomic Nervous Systems Compared

▪ Somatic nervous system

• Motor neuron cell bodies originate inside the CNS

• Axons extends to skeletal muscles that are served

▪ Autonomic nervous system

• Chain of two motor neurons

o Preganglionic neuron is in the brain or spinal cord

o Postganglionic neuron extends to the organ

• Has two arms

o Sympathetic division

o Parasympathetic division

INTRODUCTION


Prof. Saeed Makarem

❑ Body organs served by the autonomic nervous system

receive fibers from both divisions.▪ Exceptions: blood vessels, structures of the skin, some glands, and the

adrenal medulla.

▪ These exceptions receive only sympathetic fibers.

❑ When body divisions serve the same organ, they cause

antagonistic effects due to different neurotransmitters.▪ Parasympathetic (cholinergic) fibers release acetylcholine.

▪ Sympathetic postganglionic (adrenergic) fibers release norepinephrine.

▪ Preganglionic axons of both divisions release acetylcholine.

❑ Sympathetic—“fight or flight” division▪ Response to unusual stimulus when emotionally or physically stressed or

threatened.

▪ Takes over to increase activities.

▪ Remember as the “E” division.

• Exercise

• Excitement

• Emergency

• Embarrassment

❑ Parasympathetic—“housekeeping” activates.▪ “Rest-and-digest” system.

▪ Conserves energy.

▪ Maintains daily necessary body functions.

▪ Remember as the “D” division.

• Digestion

• Defecation

• Diuresis

FUNCTIONS


PATHOLOGY & DISEASES

Check page 263-267 from the book

“Mastering Medical Terminology”

for the complete list of pathology

and diseases

ALZHEIMER’S DISEASE

❑ Alzheimer’s disease (dementia) also known asAlzheimer’s dementia, is an irreversible, progressivebrain disorder of deteriorating mental capacity.

❑ It is characterized by confusion, memory loss, othercognitive defects and eventually even the inability tocarry out the simplest tasks or activities of daily living.

❑ The Alzheimer’s brain is characterized by the deposit ofamyloid plaques and atrophy.

❑ Alzheimer’s disease is the most common cause ofdementia among older people.


PARKINSON’S DISEASE

❑ Parkinson’s disease is a slowly progressive,degenerative neurologic disorder.

❑ Nerve cells in the brain deteriorate causing a deficiencyof the neurotransmitter dopamine.

❑ Parkinson’s disease is characterized by:

▪ Rhythmic fine tremors or trembling in the hands,arms, legs, jaw and face.

▪ Stiffness of the limbs and joints.

▪ Bradykinesia.

▪ Impaired balance and coordination.

❑ It causes weakness and stiffness of the muscles andinterferes with speech, walking and daily tasks.

❑ There is no cure for Parkinson’s disease, thereforetreatment is aimed at improving the symptoms.


EPILEPSY

❑ Epilepsy is an episodic neurological disorder characterizedby recurrent, transient abnormal electrical activity in thebrain.

❑ The normal pattern of neuronal activity becomes disturbed,causing a period of confusion, sensory disturbances, astaring spell, convulsions, muscle spasms and/or loss ofconsciousness.

❑ Epilepsy has many possible causes, including illness, animbalance of neurotransmitters, brain injury and abnormalbrain development.

❑ In many cases, the cause is unknown.

❑ Epilepsy is classified by the type of seizure; partial orfocal and generalised.

❑ In partial seizures, there is no loss of consciousness ratherthe patient may appear to be daydreaming with only mildsymptoms.

❑ Generalised seizures include a loss of consciousnesswith possible musclespasm.

❑ Epilepsy can usually be controlled by anticonvulsantmedications.


MENINGITIS

❑ Meningitis is an inflammation in the meninges.

❑ Most cases are due to a bacterial or viral infection.

❑ Meningitis usually has a sudden onset and is characterizedby a severe headache, neck stiffness, irritability, fever,nausea, vomiting and delirium.

❑ A particular type of meningitis, meningococcal meningitis,is characterized by a rapidly spreading rash.

❑ Meningitis can be life threatening because of theproximity to the brain and spinal cord; therefore thecondition is classified as a medical emergency.

❑ A lumbar puncture is performed to diagnose the condition.

❑ Treatment is with specific antibiotics.


PARALYSIS

❑ Paralysis is loss of the ability to move one or moremuscles.

❑ It may be associated with loss of feeling and otherbodily functions.

❑ Paralysis may be partial or complete, andtemporary or permanent.

❑ It is not usually caused by problems with themuscles, but by problems with the spinal cord ornerves that control muscles.

❑ A person with paralysis will usually have someform of nerve damage.

❑ Most paralysis results from cerebrovascularaccidents and spinal cord injuries.

❑ Other causes of paralysis include Bell’s palsy,multiple sclerosis, and Guillain-Barré syndrome.


TESTS & PROCEDURES

Check page 268-269 from the book

“Mastering Medical Terminology”

for the complete list of tests and

procedures.

CEREBRAL ANGIOGRAPHY

❑ Cerebral angiography is a procedure whichuses radio-opaque contrast to record x-rayimages of the blood vessels in the brain toidentify conditions such as aneurysms,occlusion and haemorrhage in the brain.


CEREBROSPINAL FLUID ANALYSIS

❑ Cerebrospinal fluid (CSF) analysis is a testthat is undertaken to diagnose a range ofdiseases and conditions affecting the CNS.

❑ Conditions include infectious diseases such asmeningitis and encephalitis, haemorrhagingfrom the brain and tumours within the CNS.


LUMBAR PUNCTURE

❑ A. The patient lies on one side, curled forward toopen the interspinous spaces of the lumbar region.The spine of vertebra L4 is identified in theintercristal (supracristal) plane at the level of the topsof the iliac crests.

❑ B. Under aseptic conditions, a lumbar punctureneedle is introduced obliquely above the spine ofvertebra L4, parallel to the plane of the spine. Theneedle is passed through the interspinous ligament.A slight give is perceived when the needle piercesthe dura–arachnoid mater and enters thesubarachnoid space.

❑ C. Transverse section showing the cauda equinafloating in the subarachnoid space. The anteriorand posterior roots of spinal nerve L3 are comingtogether as they leave the lumbar cistern.


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