The document discusses nerve impulses, external stimuli, and sensory organs. It defines key terms like neuron, nerve, nerve impulse, and stimulus. It explains how nerve impulses are transmitted along neurons through the interaction of sodium and potassium ions, causing changes in the resting potential and the generation of action potentials. The document also describes several sensory organs - the eye, ear, tongue, nose, and skin - and how they detect various external stimuli like light, sound, taste, smell, pain and touch through specialized receptor cells.

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