THE NERVOUS SYSTEM

• The nervous system coordinates all body functions, enabling a person to adapt to changes in internal and external environment.

• Stimulus: any change that results in a change in the organism.

– temperature, light, pressure, sound, smell, etc.• Response: any action resulting from a stimulus.

– contraction of muscle cells– secretion by a gland– stimulation of another nerve fiber.

• The nervous system is composed mainly of the nerve cells (neurons) and supporting cells (neuroglia)

• The nervous system coordinates all body functions, enabling a person to adapt to changes in internal and external environment.

• Stimulus: any change that results in a change in the organism.

– temperature, light, pressure, sound, smell, etc.• Response: any action resulting from a stimulus.

– contraction of muscle cells– secretion by a gland– stimulation of another nerve fiber.

• The nervous system is composed mainly of the nerve cells (neurons) and supporting cells (neuroglia)

THE NERVOUS SYSTEM•Function: environment is constantly changing – nervous system detects those changes and helps the organism respond/adapt

• Irritability: ability to respond to a stimulus

THE NERVOUS SYSTEM•Nervous System detects (sensory input), processes (integration), and responds (motor output)

•Peripheral Nervous System detects and responds

•Central Nervous System processes information

NERVOUS SYSTEM

•Central nervous system–brain & spinal cord

•Peripheral nervous system–nerves from senses–nerves to muscles

cerebrumcerebellumspinal cord cervical

nerves

thoracicnerves

lumbarnerves

femoral nerve

sciatic nerve

tibialnerve

THE NEURON (NERVE CELL)• Three types of neurons:

–Sensory – carry impulses from the sense organs (receptors) to the CNS

–Motor – carry impulses from the CNS to the muscles or glands (effectors)

–Interneurons – connect and carry impulses between sensory and motor neurons

• Messages carried by the nervous system are electrical signals = impulses

• Nerve cells that transmit impulses = neurons

THREE COMPONENTS OF NEURONS1. Cell body – largest part; most

metabolic activities take place here; contains nucleus

2. Dendrites – carry impulses from the environment or other neurons toward the cell body

THREE COMPONENTS OF NEURONS3. Axon – long fiber that carries

impulses away from the cell body

• Terminal branches – branching of axon

• Synaptic knobs – ends of axon; contain vesicles with neurotransmitters

FUN FACTS ABOUT NEURONS• Most specialized cell in animals

• Longest cell–blue whale neuron

• 10-30 meters–giraffe axon

• 5 meters–human neuron

• 1-2 meters

Nervous system allows for 1 millisecond response time

THE NEURON• The nervous

system is composed of neurons, which produce and conduct electrochemical impulses and supporting cells, which assist the functions of neurons.

THE NEUROGLIA• The supporting cells• They supply nutrients to the neurons and help maintain the electrical potential

• They also form part of the blood-brain barrier

• They are made up of macroglia, microglia and ependymal cells

THE NEUROGLIA•Oligodendrocytes produce myelin sheath in the CN

•Scwhann cells or lemmocytes produce myelin sheath in the peripheral NS

THE ORGANIZATION OF THE NERVOUS SYSTEM

•The nervous system is divided functionally and structurally into 2 parts•1. Central Nervous System- the Brain and the spinal cord•2. Peripheral Nervous System- the cranial nerves and spinal nerves

THE ORGANIZATION OF THE NERVOUS SYSTEM

•The Peripheral Nervous System is further classified into THREE Functional Divisions•1. The Somatic Nervous System- controls the skeletal muscles•2. The Autonomic Nervous System- controls the visceral organs•3. The Enteric Nervous System- controls the functions of the GIT

THE CENTRAL NERVOUS SYSTEM

Composed of the brain• The brain consists of the gross structures: cerebrum, cerebellum, brainstem and the diencephalon.

• Diencephalon - Thalamus. Hypothalamus and pineal body

• Brainstem- Pons, medulla and Midbrain

THE CEREBRUM• This is the largest part of the brain• Consists of right and left hemisphere

connected by the corpus callosum• Each cerebral hemisphere is composed

of different lobes- frontal, temporal, parietal and occipital

• Embedded in the cerebrum is the BASAL ganglia

THE FRONTAL LOBE OF THE CEREBRUM• Influences the personality of the person

• Also responsible for judgment, abstract reasoning, social behavior, language expression and motor movement.

THE TEMPORAL LOBE OF THE CEREBRUM• This part of the cerebrum controls the hearing, language comprehension, storage and recall of memories

• The LIMBIC system is deeply located in the temporal lobe. This controls the basic drives such as hunger, anger, emotion and sexual drive.

THE PARIETAL LOBE OF THE CEREBRUM

• This is the principal center for the reception and interpretation of Sensation

• This part interprets and integrates the sensory inputs like touch, temperature and pain

• It interprets size, shape, distance and texture

THE OCCIPITAL LOBE OF THE CEREBRUM

• This functions mainly to interpret visual stimuli

THE CEREBELLUM• The second largest brain region• Has also two hemispheres• Functions to maintain muscle tone, coordinate muscle movement, posture and control balance/equilibrium

• If this is damaged, muscle tone decreases and fine motor movements become very clumsy

THE BRAINSTEM

• Lies inferior to the cerebrum• Continuous with the cerebrum and the spinal cord

• It is composed of the midbrain, the pons and the medulla oblongata

• Functions: houses the center for respiration and cardiovascular system

THE MIDBRAIN•This connects with the cerebrum

•Contains numerous ascending and descending tracts and fibers

THE PONS

•Connects the cerebellum with the cerebrum

•Houses the respiratory center and cardiovascular center

•Exit points for cranial nerves

THE MEDULLA OBLONGATA• The most inferior portion of the brainstem

• Serves as the center for autonomic reflexes to maintain homeostasis, regulating respiratory vasomotor and cardiac functions

• Serves as exit of cranial nerves 9,10,11 and 12

THE DIENCEPHALON• The thalamus and the

hypothalamus• The thalamus is the relay

station of all sensory stimuli towards the brain

• The hypothalamus controls body temperature, appetite, water balance, pituitary secretions and sleep-wake cycle

THE SPINAL CORD• The spinal cord carries out two main functions:

It connects a large part of the peripheral nervous system to the brain. Information (nerve impulses) reaching the spinal cord through sensory neurons are transmitted up into the brain.

• A long cylindrical structure extending from the foramen magnum to the L1 in adult, L3/L4 in pedia

• In the cross section of the spinal cord, we find the GRAY matter- contains neurons; and WHITE matter-consists of nerve fibers

• There are 31 pairs of spinal nerves that exit the spinal cord

THE MENINGES• These are 3 connective tissue layers surrounding the brain and spinal cord.

• 1. DURA MATER- the superficial, thickest layer. The area above the dura mater is called epidural space

• 2. ARACHNOID- second layer, thin and wispy.

• 3. PIA MATER- the deepest layer, adhered to the brain and spinal cord substance

THE MENINGES• The space in between the arachnoid and pia mater is called the arachnoid space

• This arachnoid space contains the cerebro-spinal fluid (CSF)

• In this space, blood vessels are also found

THE VENTRICLES• The ventricular system is a set of

communicating cavities within the brain. • These structures are responsible for the

production, transport and removal of cerebrospinal fluid, which bathes the central nervous system.

• These are CSF filled cavities in the brain• The lateral ventricle- found in the cerebrum• The third ventricle- in the center of the thalamus

and hypothalamus• The fourth ventricle- located at the base of the

cerebellum

THE CSF• Cerebrospinal fluid (CSF) is a clear, colorless body

fluid found in the brain and spine. It is produced in the choroid plexuses of the ventricles of the brain. It acts as a cushion or buffer for the brain's cortex, providing basic mechanical and immunological protection to the brain inside the skull.

• This is the fluid found inside the ventricles that bathe the brain and spinal cord

• Function: provides protective cushion around the CNS

• Produced by the choroid plexus in the ventricles• Absorbed by the arachnoid granulations

THE CRANIAL NERVES• Cranial nerves are those nerves which arise from the brain

and brain stem rather than the spinal cord. Nerves arising from the spinal cord are the spinal nerves. There are 12 pairs of cranial nerves and these pairs of nerves passage through foramina in the skull, either individually or in groups.

• 12 pairs of nerves that exit the brain. Can be classified as : • Sensory• Motor mixed (sensory and motor)• The cranial nerves provide motor and sensory innervation

mainly to the structures within the head and neck. The sensory innervation includes both "general" sensation such as temperature and touch, and "special" innervation such as taste, vision, smell, balance and hearing

THE AUTONOMIC NERVOUS SYSTEM• The part of the peripheral nervous system that innervates

(supply) cardiac muscles, smooth muscles and glands• It also relays visceral sensory information to the central

nervous system and processes it so that alterations can be made in the activity of specific autonomic motor outflows, such as those that control the heart, blood vessels, and other visceral organs.

• It also stimulates the release of certain hormones involved in energy metabolism (e.g., insulin, glucagon, and epinephrine [also called adrenaline]) or cardiovascular functions (e.g., renin and vasopressin). These integrated responses maintain the normal internal environment of the body in an equilibrium state called homeostasis.

• Functionally divided into• Sympathetic Nervous System• Parasympathetic Nervous System

THE SYMPATHETIC SYSTEM• The sympathetic nervous system normally functions to produce localized adjustments (such as sweating as a response to an increase in temperature) and reflex adjustments of the cardiovascular system.• Neurotransmitter agents are Epinephrine and Norepinephrine (coming from the adrenal gland)• ADRENERGIC system - a part of autonomic nervous system that uses epinephrine or norepinephrine as its neurotransmitter• Adrenergic means "working on adrenaline (epinephrine) or noradrenaline (norepinephrine)"

– Epinephrine - hormone that is secreted mainly by the medulla of the adrenal glands and that functions primarily to increase cardiac output and to raise glucose levels in the blood. Epinephrine typically is released during acute stress, and its stimulatory effects fortify and prepare an individual for either “fight or flight” – Norepinephrine - substance that is released predominantly from the ends of sympathetic nerve fibres and that acts to increase the force of skeletal muscle contraction and the rate and force of contraction of the heart. The actions of norepinephrine are vital to the fight-or-flight response, whereby the body prepares to react to or retreat from an acute threat.

SYMPATHETIC RESPONSES• Under conditions of stress, however, the entire sympathetic nervous system is activated, producing an immediate, widespread response called the fight-or-flight response

• This response is characterized by the release of large quantities of epinephrine from the adrenal gland, an increase in heart rate, an increase in cardiac output, skeletal muscle vasodilation, cutaneous and gastrointestinal vasoconstriction, pupillary dilation, bronchial dilation, and pilo erection. The overall effect is to prepare the individual for imminent danger.Sympathetic effects:

– dilates pupil– accelerates heartbeat & respiration– inhibits stomach & intestine activity– relaxes urinary bladder

PARASYMPATHETIC SYSTEM

• The parasympathetic nervous system sometimes called the rest and digest system,

• Neurologically, cholinergic is the abbreviated term referring to acetylcholine. The parasympathetic nervous system, which uses acetylcholine almost exclusively send its messages, and said to be almost entirely cholinergic. Neuromuscular junctions, preganglionic neurons of the sympathetic nervous system, the basal forebrain, and brain stem complexes are also cholinergic

• Neurotransmitter is Acetylcholine

PARASYMPATHETIC RESPONSESThe parasympathetic system conserves

energy as it slows the heart rate, increases intestinal and gland activity, and relaxes sphincter muscles in the gastrointestinal tract.

Parasympathetic effects:• constricts pupil• slows heartbeat & respiration• stimulates stomach & intestine activity• contracts urinary bladder

NERVE PHYSIOLOGY• The nerve cells are excitable cells• Any stimulus will change the membrane potential and cause an action potential to generate impulse transmission or action potential

• The myelin sheath of the nerve cell is responsible for the SALTATORY conduction increases the nerve transmission

FOUR STAGES OF THE MEMBRANE POTENTIAL

1.Resting stage - Polarized stage - this is the normal resting membrane- charges are separated across the plasma membrane, so the membrane has potential. Any time membrane potential is other than 0 millivolts (mV).- the magnitude of the potential is directly proportional to the number of positive and negative charges separated by the membrane and that the sign of the potential (+ or –) always designates whether excess positive or excess negative charges are present, respectively, on the inside of the membrane. - at resting potential, the membrane is polarized at –70 mV in a typical neuron

2. Depolarization stage - the membrane becomes less polarized- the inside becomes less negative than at

resting potential, with the potential moving closer to 0 mV (for example, a change from –70 to -60 mV); fewer charges are separated than at resting potential.

- this term also refers to the inside even becoming positive as it does during an action potential (a major type of electrical signal) when the membrane

potential reverses itself (for example, becoming +30 mV)3. Repolarization stage.

- The membrane returns to resting potential after having been depolarized.

4. Hyperpolarization Stage.- The membrane becomes more polarized;

the inside becomes more negative than at resting potential, with the potential moving even farther from 0 mV (for instance, a change from –70 to –80 mV); more charges are separated than at resting potential.

Electrical signals are produced by changes in ion movement across the plasma membrane

- Changes in membrane potential are brought about by changes in ion movement across the membrane. For example, if the net inward flow of positively charged ions increases compared to the resting state (such as more Na+ moves in), the membrane depolarizes (becomes less negative inside). By contrast, if the net outward flow of positively charged ions increases compared to the resting state (such as more K+ moves out), the membrane hyperpolarizes (becomes more negative inside).

- Changes in ion movement are brought about by changes in membrane permeability in response to triggering events.

- A triggering event triggers a change in membrane potential by altering membrane permeability and consequently altering ion flow across the membrane. These ion movements redistribute charge across the membrane, causing membrane potential to fluctuate.

• Because the water-soluble ions responsible for carrying charge cannot penetrate the plasma membrane’s lipid bilayer,

• Therefore these charges can cross the membrane only through channels specific for them or by carrier-mediated transport.

• Membrane channels may be either leak channels or gated channels.

• Leak channels, which are open all the time, permit unregulated leakage of their specific ion across the membrane through the channels. Gated channels, in contrast, have gates that can be open or closed, permitting ion passage through the channels when open and preventing ion passage through the channels when closed

FOUR KINDS OF GATED CHANNELS • (1) voltage-gated channels open or close in

response to changes in membrane potential, • (2) chemically gated channels change shape in

response to binding of a specifi c extracellular chemical messenger to a surface membrane receptor,

• (3) mechanically gated channels respond to stretching or other mechanical deformation, and

• (4) thermally gated channels respond to local changes in temperature (heat or cold).

TWO BASIC FORMS OF ELECTRICAL SIGNALS• Graded potentials are local changes in membrane

potential that occur in varying grades or degrees of magnitude or strength. For example, membrane potential could change from –70 to –60 mV (a 10-mV graded potential) or from –70 to –50 mV (a 20-mV graded potential)

• Action potentials are brief, rapid, large (100 mV) changes in membrane potential during which the potential actually reverses so that the inside of the excitable cell transiently becomes more positive than the outside.

MYELIN

• Is composed of 80% lipid and 20% protein

• Used for insulation and to help speed up the nerve impulse

• Wraps around the axon of some neurons

MYELIN•Gaps in myelin sheath cells called Nodes of Ranvier – allow impulses to move more quickly down neurons

MYELIN• In Saltatory Conduction, only the Nodes of Ranvier depolarize and therefore conduct an impulse faster

Myelin is a fatty substance that wraps around nerve fibers and serves to increase the speed of electrical communication between neurons. 

THE SYNAPSE• SYNAPSE: the space between the axon of one neuron and the dendrite of another

• Axon terminals have vesicles containing chemicals: NEUROTRANSMITTERS

• These chemicals are secreted from the axon of one neuron stimulates receptor sites on the effector or the dendrite of the next neuron

SYNAPSE• Neurons have specialized projections called dendrites and axons.

Dendrites bring information to the cell body and axons take information away from the cell body.

• Information from one neuron flows to another neuron across a synapse. The synapse contains a small gap separating neurons. The synapse consists of:

• 1.a presynaptic ending that contains neurotransmitters, mitochondria and other cell organelles

• 2.a postsynaptic ending that contains receptor sites for neurotransmitters

• 3.a synaptic cleft or space between the presynaptic and postsynaptic endings

SYNAPSEJunction between nerve cells

–1st cell releases chemical to trigger next cell

–where drugs affect nervous system

synapsesynapse

NEUROTRANSMITTER ACTION AT SYNAPSE1. Action potential arrives at axon terminal of

presynaptic neuron2. Synaptic vesicles rupture, releasing

neurotransmitter into synapse3. Neurotransmitter diffuses across synapse

& binds to receptor protein on postsynaptic cell

4. Postsynaptic cell is excited or inhibited5. Neurotransmitter in synapse is deactivated

• Neurotransmitters are the chemicals which allow the transmission of signals from one neuron to the next across synapses.

• They are also found at the axon endings of motor neurons, where they stimulate the muscle fibers.

• They and their close relatives are produced by some glands such as the pituitary and the adrenal glands.

• They are chemicals that communicate information throughout our brain and body. 

• The brain uses neurotransmitters to tell your heart to beat, your lungs to breathe, and your stomach to digest. 

• They can also affect mood, sleep, concentration, weight, and can cause adverse symptoms when they are out of balance.

• Neurotransmitter levels can be depleted many ways.

• Stress, poor diet, neurotoxins, genetic predisposition, drug (prescription and recreational), alcohol and caffeine usage can cause these levels to be out of optimal range.

TYPES OF NEUROTRANSMITTERS• Two kinds of neurotransmitters – INHIBITORY and

EXCITATORY.  • Excitatory neurotransmitters are not necessarily

exciting – they are what stimulate the brain. 

• Inhibitory - calm the brain and help create balance are called .  – balance mood and are easily depleted when the

excitatory neurotransmitters are overactive. 

Small molecule neurotransmitters

Type Neurotransmitter Postsynaptic effect

Acetylcholine Excitatory

Amino acids Gamma aminobutyric acidGABA Inhibitory

Glycine Inhibitory

Glutamate Excitatory

Aspartate Excitatory

Biogenic amines Dopamine Inhibitory

Noradrenaline Excitatory

Serotonin Inhibitory

Histamine Excitatory

ACETYLCHOLINE• Acetylcholine was the first neurotransmitter

to be discovered.• It is responsible for much of the stimulation

of muscles, including the muscles of the gastro-intestinal system. 

• It is also found in sensory neurons and in the autonomic nervous system, and has a part in scheduling REM (dream) sleep.

• There is a link between acetylcholine and Alzheimer's disease:  There is something on the order of a 90% loss of acetylcholine in the brains of people suffering from Alzheimer's, which is a major cause of senility.

• Outside the brain, acetylcholine is the main neurotransmitter in the parasympathetic nervous system – the system that controls functions such as heart rate, digestion, secretion of saliva and bladder function.

• The plant poisons curare cause paralysis by blocking the acetylcholine receptor sites of muscle cells. 

• The well-known poison botulin works by preventing the vesicles in the axon ending from releasing acetylcholine, causing paralysis. 

SEROTONIN • SEROTONIN is an inhibitory neurotransmitter –

which means that it does not stimulate the brain. • Adequate amounts of serotonin are necessary for

a stable mood and to balance any excessive excitatory (stimulating) neurotransmitter firing in the brain. 

• If you use stimulant medications or caffeine in your daily regimen – it can cause a depletion of serotonin over time. 

• Low serotonin levels leads to an increased appetite for carbohydrates (starchy foods) and trouble sleeping, which are also associated with depression and other emotional disorders.  It has also been tied to migraines, irritable bowel syndrome, and fibromyalgia.

• Low serotonin levels are also associated with decreased immune system function.

• In addition to mood control, serotonin has been linked with a wide variety of functions, including the regulation of sleep, pain perception, body temperature, blood pressure and hormonal activity

• Largest amount of serotonin is found in the intestinal mucosa.

• Although the CNS contains less than 2% of the total serotonin in the body, serotonin plays a very important role in a range of brain functions. It is synthesized from the amino acid tryptophan.

• Gamma amino butyric acid(GABA) is the major inhibitory neurotransmitter that is often referred to as “nature’s VALIUM-like substance”.  When GABA is out of range (high or low excretion values), it is likely that an excitatory neurotransmitter is firing too often in the brain.  GABA will be sent out to attempt to balance this stimulating over-firing.

• People with too little GABA tend to suffer from anxiety disorders, and drugs like Valium work by enhancing the effects of GABA.  Lots of other drugs influence GABA receptors, including alcohol and barbiturates.  If GABA is lacking in certain parts of the brain, epilepsy results.

HISTAMINE• Amino acid Histidine is the precursor of an important

neurotransmitter histamine.• Histamine is present in venom and other stinging

secretions.• Histamine is a biogenic amine involved in local

immune responses. • Regulate physiological function in the gut • Act as a neurotransmitter. • Triggers the inflammatory response.

REFLEX ARCA reflex arc is a neural pathway that controls an action reflex. In higher animals, most sensory neurons do not pass directly into the brain, but synapse in the spinal cord.

This characteristic allows reflex actions to occur relatively quickly by activating spinal motor neurons without the delay of routing signals through the brain, although the brain will receive sensory input while the reflex action occurs. There are two types of reflex arcs: autonomic reflex arc (affecting inner organs) and somatic reflex arc (affecting muscles)

TYPES OF SENSORY RECEPTORS• Thermoreceptors – detect heat and cold• Pain receptors (nocioceptors) – detect

chemicals released from injured cells• Mechanoreceptors – detect mechanical

energy (touch, pressure, vibration)

TYPES OF SENSORY RECEPTORS• Chemoreceptors – detect chemicals

• Photoreceptors – detect light energy

• Electroreceptors – detect electrical fields

HOW ARE SOUNDS SENSED?• The ear captures, transmits, and

converts sound into electrical signals

• Ear has three basic parts:1. Outer ear2. Middle ear3. Inner ear

HOW ARE SOUNDS SENSED?

•Outer ear: external ear (pinna) and auditory canal –Funnels sound–Sound waves vibrate the tympanic membrane

HOW ARE SOUNDS SENSED?• Middle ear–Tympanic membrane (ear drum)–Three tiny bones: malleus (hammer), incus (anvil), stapes (stirrup); transfer vibrations to the oval window on the cochlea

–Eustachian tube – equalize pressure; connects middle ear to pharynx

HOW ARE SOUNDS SENSED?• Inner ear: cochlea–converts vibrations into electrical signals

–As the oval window vibrates, it sets the cochlear fluid in motion

–Moving fluid brushes over hairs–Bending of hairs is sensed by mechanoreceptors and sends the signal to the brain (auditory nerve)

FISH “HEARING” – LATERAL LINES• Contains mechanoreceptors that function similarly to mammalian inner ear

• Gives info about direction and velocity of water flowing over fish’s body

HOW IS LIGHT SENSED?• Light waves travel at a speed of 186,000 miles per second. Light is reflected into the eyes by objects within the field of vision.

• In order to achieve clear vision, light reflected from objects within the visual field is focused in to the retina of both eyes.

• The processes involved in producing a clear image are refraction of the light rays and accommodation of the eyes.

• The eye is made up of three layers– Fibrous layer- sclerae and cornea– Uvea- choroid and iris and ciliary bodies– Nervous coat- retina

• Sclera – tough, white layer• Conjunctiva – external cover of sclera; keeps eye moist;

conjuctivitis (pink eye)

HOW IS LIGHT SENSED?• Cornea – transparent covering in front of eye

• Choroid – thin, pigmented layer lining interior surface of the sclera; prevents light rays from scattering and distorting the image

• Iris - regulates size of pupil/amount of light into eye

HOW IS LIGHT SENSED?• Lens focuses light on retina

• Retina – Contains photoreceptors (Except at the optic disk where the optic nerve attaches)–Rods: Black and White–Cones: Color

• Optic nerve takes electric signals from eye to brain

HOW ARE SCENTS SENSED?• Insects smell through their legs and antennae

Male silkworm moth Bombyx mori

Sensory hairs on antennae detect pheromones released by female

HOW ARE SCENTS SENSED?•Olfactory nerves are stimulated when chemicals touch them

•Different chemicals create different responses in the olfactory nerves; hence we detect different smells

HOW ARE TASTES SENSED?• Taste buds on tongue act just like the olfactory nerves–Different chemicals stimulate the nerves in the taste buds differently; hence we detect different tastes

• Four “primary” tastes are bitter, sour, salty, and sweet

THE GUSTATORY APPARATUS

•The receptor for taste are cells in the tongue group together called the taste buds

•They are numerous in the vallate and fungiform papillae

THE GUSTATORY APPARATUS

Basic taste modalities• Sweet- tip of the tongue• Salty- over the dorsum of the tongue

• Sour- sides of the tongue• Bitter- back of the tongue

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