2. TOPIC
NERVE IMPULSES & EXTERNAL STIMULI
VISUAL,SOUND & ELECTRICAL SENSORY
ORGANS
Subject
PHYSIOLOGY
By:
ZAHID BHATTI
PARIVISH JOKHIO
SAJJAD ALI
Course # 703
Faculty: Madam Zarina Shafi

3. 3
Ground Rules
 Time allocation: One hour. 50 minutes for
presentation and 10 minutes are for Q/A.
 Questioning and answering are asked at the end of
presentation.
 If you feel any problem or urgency you can leave the
class without any disturbance.
 Turn off your mobile phone.

4. OBJECTIVES
 At the end of this presentation learner will be
able to:
 Define Neuron and function of the parts of a neuron.
 Describe the term Nerve and Nerve Impulses.
 Explain how a Nerve Impulse passes a long a
Neuron(axon).
 Discuss the Resting potential and role of Action
potential in the transmission of a nerve impulse.
 Discuss the External stimuli & visual, sound and
electrical sensory organs.

5. NEURON
 Nerve cell and its fibers
are collectively called as
“Neuron”
 Neurons are the basic
building blocks of the
nervous system.
 These specialized cells
are responsible for
receiving & transmitting
information

6. FUNCTION OF THE PARTS OF A
NEURON
 Dendrite receives
information /message/
impulse from sensory
receptors, then passed
down to the cell body
and to the axon.

7. FUNCTION OF THE PARTS OF A
NEURON
 Axon is the long hair like
fiber ,that extends from
cell body to the terminal
endings.

8. FUNCTION OF THE PARTS OF A
NEURON
 Axon terminal, or
Nerve endings are
responsible for sending
signals to other neurons.
 At the end of terminal
button there is a gap
known as synapse.

9. NEURON
 Axon terminal release a
chemical called
Neurotransmitter,
(Acetylcholine) used to
carry the signal across
the synapse to other
neuron.

10. NERVE
Elongated cord like
bundle of fibers made up
of neurons, forming a
network that transmits
messages in the form of
impulses between the
brain or spinal cord &
the other parts of the
body.

11. NERVE IMPULSE
 Nerve impulse is a wave
of electrical activity that
passes from one end of a
neuron to the other ,due
to ions moving.

12. Explain How a Nerve Impulse
Passes along a neuron(axon)
 The two important ions
in a nerve cell (neuron)
are sodium ions and
Potassium ions.
 The concentration of
Sodium ions is relatively
greater outside, while
the concentration of
potassium is relatively
greater inside a cell.

13. Explain How a Nerve Impulse
Passes along a neuron(axon)
 When neuron is “at rest”
a charge difference is
maintained between the
inside and out side of the
cell .
 The over all result is that
the exterior of the cell
has a net positive charge
and the interior has a net
negative charge.

14. RESTING POTENTIAL
 When neuron is in active
it is said to be at its
resting potential.
 Sodium ions normally
stay outside.
 It remains this way until
a stimulus comes along.
 The difference in charge
B/w the interior &
exterior cell is called
resting potential.

15. ROLE OF ACTION POTENTAL IN THE
TRANSSMISSION OF A NERVE IMPULSE
 when a stimulus/or
impulse disturbs the
plasma membrane on a
dendrite, causing
sodium ion channel to
open.
 Sodium ions flow into
the axon, depolarizing
the membrane.
 Localised electric
currents are generated in
the membrane

16. ROLE OF ACTION POTENTAL IN THE
TRANSSMISSION OF A NERVE IMPULSE

17. ROLE OF ACTION POTENTAL IN THE
TRANSSMISSION OF A NERVE IMPULSE
 The sodium ion channel
close and potassium ion
channel open.
 Potassium ions leave the
axon,repolarizing the
membrane.
 The exiting K+ ions causes
the potential to decline
and the membrane
potential goes back to the
original level

18. ROLE OF ACTION POTENTAL IN THE
TRANSSMISSION OF A NERVE IMPULSE
 In this way local electric
currents cause the nerve
impulse to move along
the axon.
 At the site of first action
potential, potassium
ions diffuse back into the
axon, restoring the
resting potential.
 This is called the
refractory period.

19. ROLE OF ACTION POTENTAL IN THE
TRANSSMISSION OF A NERVE IMPULSE

20. DIAGRAM SHOWING RESTING AND ACTION
POTENTIAL

21. STIMULUS
 Any
action, condition, that
makes an organism to react
or
 Any internal or external
effect on the body is called
stimulus
 An action taken as a result
of a stimulus is called
response
 E.g:- A dog feels hot so it
goes to lay in the shade.

22. STIMULUS
 A stimulus may be
tactile :skin
(touch),pain,hot & cold.
 Visual :(light) & colour.
 Auditory (hearing)sound
 Olfactory:(smell)
chemicals in the air.
 Gustatory :tongue
(taste).chemicals in food
& drink

23. HOW TO SENSE (or detect) A
STIMULUS
 RECEPTORS:
Information about your
surrounding is collected
by receptor cells.
 Living objects have
sense organs that detects
forms of energy .
 Human senses include
the senses of touch,
sight. smell, hearing, and
taste.

24. EXTERNAL STIMULI
 A stimulus that comes from
outside an organism. or
 Any external input which
leads to sensation or
reaction is called external
stimuli
 Sensory receptors can
detect changes or receive
information from outside
the body, through sensory
receptors, and convert
these stimulus into
impulses.

25. HOW DO WE RESPOND TO STIMULI
 An action taken as a result
of a stimulus is called
response
 The response to a stimulus
can be
positive, negative, or
ignored as not important.
POSITVE:
 A positive response is
when organism is attracted
to.
E.g:- A person laughs after
hearing a funny joke

26. HOW DO WE RESPOND TO STIMULI
NEGATIVE:
 When you want to avoid
stimulus.
 E.g:-
You make a face after
smelling a bad odor

27. HOW DO WE RESPOND TO STIMULI
IGNORED
 When stimulus is not
important to you
E.g:-
 You pay no attention
when someone is
shouting in front of you
while listening to the
music.

28. EYE (VISUAL ORGAN)
 Vision provides
opportunity for
the brain to perceive
and respond to changes
occurring around the
body.

29. EYE (VISUAL ORGAN)
Components:
 Cornea: where light
enters the eye
 Lens: focuses the light
rays on the retina
 Iris: colored ring of
muscle, constricts or
dilates via amount of light
 Pupil: regulates amount
of light

30. EYE (VISUAL ORGAN)
 Information, or stimuli, in
the form of light enters
the retina
 Where Photoreceptor cells
rods & cones convert light
into Neural Impulses
 The impulse go to the
brain stem via optic nerve
 Cerebral cortex /occipital
lobe perceive the light &
respond.

31. EAR (SOUND ORGAN)
The ear is responsible
for hearing, it consist
of three regions
1)External Ear
2)Middle Ear
3)Inner Ear

32. EAR (SOUND ORGAN)
TRANSMISSION OF SOUNDS
THROUGH THE EAR:
External Ear:
Mostly through Air
(external acoustic Meatus)
Middle Ear:
Through Solid medium-
bone(ossicles)
Inner Ear:
Through fluid medium-
endolymph(cochlea)

33. EAR (SOUND ORGAN)
 In inner Ear, the basilar
membrane of cochlea
contains the corti-receptor
that translate/covert the
vibrations to electric
impulses, the impulses go to
the brain stem via acoustic
nerve (viii).
 Cerebral cortex- interprets
the meaning of the sound
and begins the appropriate
response.

34. TONGUE(SENSORY ORGAN)
 Taste records flavoring of
food and other materials
that pass across
the tongue and through
the mouth.
 Gustatory cells are
located on the surface of
the tongue.

35. TONGUE(SENSORY ORGAN)
35Figure 4.49 The tongue and taste
 Receptor cells found in
taste buds.
Sweet and bitter,
receptors are
called gustducins
Pathway: taste buds >
neural impulse > thalamus
> cortex
 Four primary tastes:
sweet, sour, bitter, and
salty

36. NOSE(SENSORY ORGAN)
 Smell allows the body to
recognize chemical
molecules in the air
through inhalation.
Olfactory receptors =
olfactory cilia
 Pathway: Olfactory cilia ->
neural impulse -> olfactory
nerve -> (brain)

37. SKIN ( SENSORY ORGAN)
 Pain & touch is recorded
by sensory receptors on
the skin.
 Pain receptors are known
as nociceptors.
 Touch receptors are
known as meissner’s
corpuscle.

38. SKIN ( SENSORY ORGAN)
 Pathway: Sensory receptors
> the spinal column >
brainstem > thalamus >
(parietal lobe)
 if it is decided that a
response must be made, a
signal is sent back down to
a muscle, which acts
appropriately according to
the stimulus.

39. REFERENCE:
 Lippincott’s review series medical surgical nursing
fourth edition Ray A. Hargrove-Huttle RN, phD.
 Anatomy & physiology for Nurses (16th edition) by
Evelyn C.Pearce.
 Lynn S. Bickley, Bates’ (8th Edition): Guide to Physical
Examination and History Taking.
 Anne Waugh. Allison Grant (10th Edition): Anatomy
& Physiology in Health & Illness.
 www.ifeet.org/files/eppch_13ed.ppt