The nervous system is composed of neurons and neuroglia. It detects stimuli through sensory neurons, processes information in the central nervous system, and responds through motor neurons. The central nervous system includes the brain and spinal cord. The brain is made up of the cerebrum, cerebellum, and brainstem. The peripheral nervous system connects the central nervous system to the body and is divided into the somatic, autonomic, and enteric systems. Neurons have a cell body, dendrites, and axon. The nervous system maintains homeostasis through detection of and response to stimuli.

1. THE NERVOUS SYSTEM

2. • 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)

3. 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

4. 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

5. NERVOUS SYSTEM
•Central nervous system
–brain & spinal cord
•Peripheral nervous
system
–nerves from senses
–nerves to muscles
cerebrum
cerebellum
spinal cord cervical
nerves
thoracic
nerves
lumbar
nerves
femoral
nerve
sciatic
nerve
tibial
nerve

7. 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

8. THREE COMPONENTS OF NEURONS
1. 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

9. THREE COMPONENTS OF NEURONS
3. 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

11. 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
Nervous system allows for
1 millisecond response time

12. THE NEURON
• The nervous
system is
composed of
neurons, which
produce and
conduct
electrochemical
impulses and
supporting cells,
which assist the
functions of
neurons.

13. 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

14. THE NEUROGLIA
•Oligodendrocytes produce myelin
sheath in the CN
•Scwhann cells or lemmocytes
produce myelin sheath in the
peripheral NS

17. 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

19. 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

22. 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

24. 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

25. 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.

26. 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.

27. 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

28. THE OCCIPITAL LOBE OF THE CEREBRUM
•This functions
mainly to
interpret
visual stimuli

29. 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

30. 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

31. THE MIDBRAIN
•This connects with the cerebrum
•Contains numerous ascending and
descending tracts and fibers

32. THE PONS
•Connects the cerebellum with the
cerebrum
•Houses the respiratory center and
cardiovascular center
•Exit points for cranial nerves

33. 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

34. 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

35. 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

36. 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

37. 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

38. 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

39. 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

40. 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

42. 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

43. 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.

44. 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

45. 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

46. PARASYMPATHETIC
RESPONSES
The 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

49. 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

50. 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

51. 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.

52. 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.

53. 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.

54. • 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

55. 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).

56. 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.

57. 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

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

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

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

61. 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

62. 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

63. SYNAPSE
Junction between nerve cells
–1st cell releases chemical to trigger
next cell
–where drugs affect nervous system
synapsesynapse

64. NEUROTRANSMITTER ACTION AT SYNAPSE
1. Action potential arrives at axon
terminal of presynaptic neuron
2. Synaptic vesicles rupture, releasing
neurotransmitter into synapse
3. Neurotransmitter diffuses across
synapse & binds to receptor protein
on postsynaptic cell
4. Postsynaptic cell is excited or
inhibited
5. Neurotransmitter in synapse is
deactivated

65. • 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.

66. • 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.

67. • 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.

68. 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.

69. 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

70. 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.

71. • 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.

72. 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.

73. • 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.

74. • 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.

75. 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.

76. REFLEX ARC
A 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)

78. 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)

79. TYPES OF SENSORY
RECEPTORS
•Chemoreceptors – detect chemicals
•Photoreceptors – detect light energy
•Electroreceptors – detect electrical
fields

80. HOW ARE SOUNDS SENSED?
• The ear captures, transmits, and
converts sound into electrical signals
• Ear has three basic parts:
1. Outer ear
2. Middle ear
3. Inner ear

81. HOW ARE SOUNDS SENSED?
•Outer ear: external ear (pinna) and
auditory canal
–Funnels sound
–Sound waves vibrate the tympanic
membrane

82. 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

83. 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)

85. 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

86. 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;

87. 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

88. 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

89. 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

90. 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

92. 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

93. 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

94. 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

96. THANK YOU