This ppt will give the understanding about the principle of sensory receptors

1. CHAPTER 4CHAPTER 4
RECEPTOR AND NEURONSRECEPTOR AND NEURONS
By Hermizan Bin HalihanafiahBy Hermizan Bin Halihanafiah
01388189240138818924
hermizanhalihanafiah@gmail.comhermizanhalihanafiah@gmail.com
https://www.slideshare.net/hermizan84https://www.slideshare.net/hermizan84
YOUTUBE/ANATOMI DAN FISIOLOGI KSKB SG BULOHYOUTUBE/ANATOMI DAN FISIOLOGI KSKB SG BULOH

2.  Conscious and subconscious awareness
of changes in the external or internal
environment.
 Perception is the conscious awareness
and interpretation of sensations and is
primarily a function of the cerebral cortex.
 We have no perception of some sensory
information because it never reaches the
cerebral cortex.
 An example: sensory receptor monitor
blood pressure in blood vessels.

3.  Each type of sensations:- touch, pain,
vision or hearing is called sensory
modality.
 A given sensory neuron carries
information for only one sensory modality.
 Sensory modalities grouped into:
1. General senses:-
 Somatic
 Tactile (touch, pressure, vibration)
 Thermal (warm and cold)
 Pain
 Proprioceptive sensations

4.  Somatic sensory modalities allow
perception of both static positions of limbs
and body parts (joint and muscle position
sense) and movements of limbs and head.
 visceral
◦ this sensations provide information about
conditions within internal organs.
2. Special senses
◦ This includes the sensory modalities of smell,
taste, vision, hearing and equilibrium or balance.

5.  It begins in the sensory receptor
(specialized cell or dendrites of a sensory
neuron)
 A given sensory receptor responds
vigorously to one particular kind of stimulus.
 Stimulus is a change in the environment that
can activate certain sensory receptors.
 Sensory receptors respond weakly or not at
all to other stimuli.
 This characteristic of sensory receptors is
known as selectivity.

6. For a sensation to arise, four events typically
should occur:-
1. Stimulation of the sensory receptor.
• Appropriate stimulus must occur within the
sensory receptor`s receptive field (is the body
region where stimulation produces a response)
1. Transduction of the stimulus
• A sensory receptor transduces (converts)
energy in a stimulus into a graded potential.
• Example: odorant molecules, in the air stimulate
olfactory receptors in the nose, which transduce
the molecules` chemical energy into electrical
energy in the form of a graded potential.

7. 3. Generation of nerve impulses
• Once the graded potential in a sensory neuron
reaches threshold, it triggers one or more
nerve impulses and this impulse propagate to
CNS.
• Sensory neurons that conduct impulses from
the PNS into the CNS are called first-order
neurons.
4. Integration of sensory input
• Conscious sensations of perceptions are
integrated in the cerebral cortex.

8. TYPES OF SENSORY RECEPTORS:
1. Sensory receptors at microscopic level
may be classed into:
a. Free nerve ending of first–order neuron
(Unencapsulated nerve endings).
b. Encapsulated nerve endings of first-order
neuron sensory neuron
c. Separate cells that synapse with first-order
sensory neurons.
SENSORY RECEPTORSSENSORY RECEPTORS

9.  Are bare dendrites; they lackAre bare dendrites; they lack
any structural specializationsany structural specializations
that can be seen under a lightthat can be seen under a light
microscopemicroscope
 Dendrites not wrapped inDendrites not wrapped in
connective tissueconnective tissue
 Receptors for pain, thermal,Receptors for pain, thermal,
tickle, itch and some touchtickle, itch and some touch
sensations are free nervesensations are free nerve
endings.endings.

10. • sensory receptors for some special senses:
– Hair cells for hearing & equilibrium in inner ear.
– Gustatory receptor cells in taste buds
– Photoreceptors in the retina of the eye.
b. Separate cellsb. Separate cellsb. Separate cellsb. Separate cells
• Receptors for other somatic and visceral
sensations such as touch, pressure, and vibration.
• Dendrites are wrapped by connective tissues
capsule.
• Different types of capsules enhance the sensitivity
or specificity of the receptor.

11.  Tactile corpuscle/meissnerTactile corpuscle/meissner
corpusclescorpuscles
◦ fine touch and texturefine touch and texture
◦ are grouped on the skin of the
fingertips, lips, and orifices of the
body and the nipples. Only
stimulated when touched, Meissner
corpuscles tells the brain the shape
and feel of an object in the hand, or
the touch of a kiss. They adjust
constantly to the environment,
which is why the brain eventually
ignores clothing that you are
wearing.
TYPES OF
ENCAPSULAT
ED NERVE
ENDINGS

12.  Lamellated (pacinian)Lamellated (pacinian)
corpusclescorpuscles
 Present in dermis andPresent in dermis and
subcutaneous layer, subsubcutaneous layer, sub
mucosal tissues, joints,mucosal tissues, joints,
periosteumperiosteum
 Deep pressure, tickle and fastDeep pressure, tickle and fast
vibrationvibration
 Detects pressure, telling the
brain when a limb has moved.
After the brain has told a limb,
such as an arm, to move, the
Pacinian corpuscles tells the
brain that that limb has
actually moved into the correct
position.

13.  Ruffini corpusclesRuffini corpuscles
(type II cutaneous(type II cutaneous
mechanoreceptors)mechanoreceptors)
 Found in dermis,Found in dermis,
ligaments and tendons.ligaments and tendons.
 Heavy touch, pressure,Heavy touch, pressure,
joint movements andjoint movements and
stretching.stretching.

14.  Krause`s end bulbKrause`s end bulb
 It is a thermoreceptor (detectIt is a thermoreceptor (detect
cold)cold)
 Thermoreceptors are the
other major group of touch
receptors. There are two
types of thermoreceptors,
the end-bulb of Krause,
which detects cold, and
Ruffini's end organ, which
detects heat.
 The end-bulb of Krause
can be found in the skin,
conjunctiva, lips, and tougue.

15. 2. By location of receptor and origin
stimuli that activate them.
◦ Interoceptors – detect internal stimuli (in blood
vessels, visceral organs)
◦ Proprioceptors – body position, muscle length and
tension, position and movements of joints and
equilibrium (in muscles, tendons, joints and inner
ear)
◦ Exteroceptors – detect external stimuli e.g. taste,
hearing, vision, smell, pain are conveyed by this
(at or near external surface of the body)

16. 3. By modality: type of stimulus detected
◦ Mechanoreceptors
Are sensitive to mechanical stimuli such as
deformation, stretching or bending of the cells.
It provide:
 Sensation of touch
 pressure
 Vibration
 Proprioception
 Hearing and equilibrium
 Monitor stretching of blood vessels
and internal organs
◦ Thermoreceptors
 Detect changes in temperature.

17. – Nociceptors
 respond to painful stimuli resulting from
physical or chemical damage to tissue.
– Photoreceptor
 Detect light that strikes the retina of the
eye.
– Chemoreceptor
 Detect chemicals in mouth (taste), nose
(smell) and body fluids.
– Osmoreceptors
 Detect the osmotic pressure of body
fluids.

18.  Is a characteristic of most sensory receptors.
 In adaption, generator potential or receptor
potential decreases in amplitude during a
maintained, constant stimulus.
 So adaption causes the frequency of nerve
impulses in the first-order neuron to decrease.
 Because of adaption, the perception of a
sensation may fade or disappear even though the
stimulus persists.
 E.g. when first step into a hot shower, the water
may feel very hot, but soon the sensation
decreases to one of comfortable warmth even
though the stimulus does not change.

19.  Receptors vary in how quickly they adapt.
 Rapidly adapting receptors adapt very quickly
 They are specialized for signaling changes in a
stimulus.
 Rapidly adapting receptors: pressure, touch and
smell.
 Slow adapting receptors adapt slowly and continue
to trigger nerve impulses as long as the stimulus
persists.
 Slowly adapting receptors monitor stimuli
associated with pain, body position, and chemical
composition of the blood.

20. otns/vani/kskbsgblh
 Sensory receptors in the skin (cutaneous
sensations), muscles, tendons and joints
and in the inner ear.
 Uneven distribution of receptors.
 Four modalities: tactile, thermal, pain and
proprioceptive.

22.  Include touch, pressure, vibration, itch and tickle.
 Though we perceive differences among these
sensations, they arise by activation of some of the
same types of receptors.
 Some types of encapsulated mechanoreceptors
attached to large-diameter myelinated A fibers and
mediate sensations of touch, pressure and vibration.
 other touch sensations like itch and tickle
sensations are detected by free nerve endings
attached to small-diameter unmyelinated C fibers.

23.  Tactile receptors in the skin or subcutaneous layer are
Meissner corpuscles (corpuscles of touch), hair rootMeissner corpuscles (corpuscles of touch), hair root
plexuses, Merkel discs, Ruffini corpuscles, Pacinianplexuses, Merkel discs, Ruffini corpuscles, Pacinian
corpuscles (lamellated corpuscles), and free nervecorpuscles (lamellated corpuscles), and free nerve
endings.endings.

24. TACTILE:TACTILE: TouchTouch
 Sensation of touch generally result from
stimulation of tactile receptors in the skin or
subcutaneous layer.
 Crude touch is the ability to perceive that
something has contacted the skin, eventhough
its exact location, shape, size, or texture cannot
be determined.
 Fine touch provides specific information about a
touch sensation, such as exactly what point on
the body is touched plus the shape, size and
texture of the source of stimulation.

25. TOUCH:TOUCH: Meissner Corpuscles orMeissner Corpuscles or
Corpuscles of TouchCorpuscles of Touch
 Receptors for fine touch located in dermal
papillae of hairless skin.
 Egg-shaped mass of dendrites enclosed by a
capsule of connective tissue.
 Rapidly adapting receptors.
 Found in the dermal papillae of hairless skin
such as in the fingertips, hands, eyelids, tip of
the tongue, lips, nipples, soles, clitoris, and tip
of the penis.

26. TOUCH:TOUCH: Hair Root PlexusesHair Root Plexuses
 Rapidly adapting crude touch receptors
found in the hairy skin.
 Free nerve endings wrapped around hair
follicles.
 Detect movements on the skin surface
that disturb hairs.
 Example: an insect landing on a hair
causes movement of the hair shaft that
stimulates the free nerve endings.

27. TOUCH:TOUCH: Merkel Discs or Tactile DiscsMerkel Discs or Tactile Discs
(Type I cutaneoumechanoreceptors)(Type I cutaneoumechanoreceptors)
 Also known as type I cutaneous
mechanoreceptors function in fine touch.
 Slowly adapting touch receptors.
 Saucer-shaped, flattened free nerve
endings that contact Merkel cells of the
stratum basale.
 Found in the fingertips, hands, lips, and
external genitalia.

28. TOUCH:TOUCH: Ruffini Corpuscles (Type IIRuffini Corpuscles (Type II
cutaneous mechanoreceptors)cutaneous mechanoreceptors)
 Also called as type II cutaneous
mechanoreceptors.
 Elongated, encapsulated receptors.
 Located deep in the dermis and in
ligaments and tendons.
 Found in the hands, and abundant on the
soles.
 They are most sensitive to stretching that
occurs as digits or limbs are moved.

29. TACTILE:TACTILE: Pressure and VibrationPressure and Vibration
 Pressure is a sustained sensation that is felt over
a larger area than touch, occurs with deformation
of deeper tissues.
 Receptors that contribute to sensations of
pressure include corpuscles of touch, type I
mechanoreceptors and lamellated corpuscles.
 Sense of vibration result from rapidly repetitive
sensory signals from tactile receptors.
 Receptors for vibration sensations are corpuscles
of touch and lamellated corpuscles.
 Corpuscles of touch can detect lower frequency
vibrations and lamellated corpuscles detect higher
frequency vibrations.

30. PRESSURE:PRESSURE: Pacinian or LamellatedPacinian or Lamellated
CorpusclesCorpuscles
 Large oval structure composed of a
multilayered connective tissue capsule
that encloses a dendrite.
 Fast adapting receptors.
 Found around joints, tendons, and
muscles; in the periosteum, mammary
glands, external genitalia, pancreas and
urinary bladder.

31. TACTILE:TACTILE: Itch and tickleItch and tickle
 Itch sensations results from stimulation of free
nerve endings by certain chemicals, such as
bradykinin (kinin and potent vasodilator)
 Free nerve ending and lamellated corpuscles
mediate the tickle sensation.

32.  Thermoreceptors are free nerve endings.
 Two distinct thermal sensations:
◦ coldness
◦ warmth
 Both mediated by different receptors
 Cold receptors located in stratum basale
and attached to medium diameter,
myelinated A fibers.
 10˚C - 40˚C activate cold receptors

33.  Warm receptors located in dermis and
attached to small diameter unmyelinated C
fibers.
 Activated by temperature 32˚C – 48˚C
 Both adapt rapidly, generate lower
frequency impulses throughout prolonged
stimulus.
 Temperature below 10˚C and above 48˚C
stimulate pain receptors and not
thermoreceptors.

34.  Protective.
 Sensory receptors are nociceptors.
 These receptors are free nerve endings
and found in every body tissue except
brain.
 Intense thermal, mechanical and chemical
stimuli can activate this.
 Chemical e.g. prostaglandin, kinins,
potassium ions released from injured tissue
stimulate the nociceptors.

35.  Pain may persist even after the stimulus is
removed – pain mediating chemicals linger
and little adaptation
 Pain caused by distension (stretching),
prolonged muscle contraction, muscle
spasm or ischaemia.
 Two types of pain: fast and slow.
 Fast pain: acute, sharp or pricking pain.
 Perceived within 0.1 second as nerve
impulses propagate along medium-
diameter myelinated A fibers.
 E.g. pain from needle puncture or knife cut
 Not felt in deeper tissues of the body.

36.  Slow pain: chronic, burning, aching or
throbbing pain.
 Perception begins a second or more after
stimulus.
 Gradually increases in intensity over a
period of several seconds or minutes.
 Impulses conducted along small diameter
unmyelinated C fibers.
 Occur both in skin and deeper tissues or
internal organs.
 E.g. toothache.

37.  Superficial somatic pain – receptors in skin
 Deep somatic pain – receptors in skeletal
muscle, joints, tendons and fascia
 Visceral pain – nociceptors in visceral
organs
 Diffuse stimulation of visceral nociceptors
can cause severe pain.

38.  Fast pain very precisely localized to
stimulated area.
 Somatic slow pain also well localized but
more diffuse.
 Visceral slow pain, affected area is where the
pain is felt.
 However in many instances of visceral pain,
is felt in or just deep to the skin that overlies
the stimulated organ or in a surface area far
from the stimulated organ. This is called
referred pain.

40.  Allow us to know where our head and limbs
are located and how they are moving even if
we are not looking at them - we can walk,
type or dress without using our eyes.
 Weight discrimination and determine the
muscular effort necessary to perform a task.
 Receptors are called proprioceptors.
 Slow adaptation.
 proprioceptors embedded in muscles and
tendons tell us the degree of muscle
contraction, the amount of tension on
tendons and the positions of joints.

41.  Hair cells of the inner ear monitor the
orientation of the head relative to the
ground and head position during
movements.
 Types of proprioceptors:-
◦ Muscle spindle within skeletal muscle
◦ Tendon organs within tendon
◦ Joint kinesthetic receptors within synovial joint
capsules.

42.  Measure muscle stretching (length of skeletal
muscle) and participate in stretch reflex.
 Consists of intrafusal muscle fibers- specialized
muscle fibers with sensory nerve endings and
motor neurons called gamma motor neurons.
 Extrafusal muscle fibers- surrounding muscle
fibers supplied by alpha motor neurons.
 Is interspersed among most skeletal muscle
fibers and aligned parallel to them.

43.  Are plentiful in muscle that produce finely
controlled movements such as fingers or
eyes.
 Muscles involved in coarser but more
forceful movements like quadriceps femoris
and hamstring muscles have fewer muscle
spindle.
 Tiny muscles of middle ear lack spindles.

44.  Located at the junction of a tendon and a
muscle.
 Consists of a thin capsule of connective
tissue that encloses a few tendon fascicles.
 Protect tendons and their associated muscles
from damage due to excessive tension.
 By sending information to CNS about
changes in muscle tension.
 Tendon reflex decreases muscle tension by
causing muscle relaxation.

45.  Found within or around the articular
capsules of synovial joints.
 Free nerve endings and Ruffini corpuscles
in the capsules of joints respond to
pressure.
 Pacinian corpuscles outside the articular
capsules respond to acceleration and
deceleration of joints during movement.

46.  Possess electrical excitability
◦ Ability to respond to a stimulus and convert it
into an action potential.
◦ Also able to conduct electrical signals.
*stimulus*:
Is any change in the environment that is
strong enough to initiate an action
potential.

47. Cell bodyCell body
 nucleus surrounded by cytoplasm
◦ Contains typical cellular organelles:-
lysosomes, mitochondria, golgi complex.
 Free ribosomes and endoplasmic
reticulum termed nissl bodies
◦ Ribosomes are sites of protein synthesis.

48. Nerve fibersNerve fibers
 is a general term for any neuronal process or
extension that emerges from the cell body of a
neuron.
 Most neurons have two kinds of processes:-
◦ Multiple and
single axon

49. DendritesDendrites
 receiving or input
portions of a neuron.
 Usually short, tapering,
and highly branched.
 In many neurons the
dendrites form a tree-
shaped array of
processes extending
from the cell body.
 Their cytoplasm
contains Nissl bodies,
mitochondria, and other
organelles.

50. AxonAxon
 propagates nerve impulses toward
another neuron, a muscle fiber, or
a gland cell.
 It is a long thin, cylindrical
projection that often joins the cell
body at a cone – shape elevation
called a axon hillock.
 The part of the axon closest to the
axon hillock is the initial segment.
 In most neurons, the nerve
impulses arise at the junction of
the axon hillock and the initial
segment, an area called the
trigger zone.

51. A fibers
 Large diameter axon (5-20 µm) (larger
surface area)
 Myelinated
 Propagate impulses faster (12- 130 m/sec)
 Sensory neurons associated with touch,
pressure, position of joints, some thermal
sensations.
 Motor neurons conduct impulses to
skeletal muscles.

52. B fibers
 diameter of axon  2-3 µm
 Myelinated
 Propagate impulses at the speed of 15
m/sec
 sensory nerve impulse from viscera to
brain and spinal cord.
 Also constitute all axons of autonomic
motor neurons that extend from the brain
and spinal cord to ANS relay stations
called autonomic ganglia.

53. C fibers
 smallest diameter axon (0.5 – 1.5 µm)
 Unmyelinated
 Propagate impulses at the speed of 0.5–
2m/sec)
 Conduct sensory impulses for pain, touch,
pressure, heat and cold from the skin and
pain from viscera.
 Autonomic motor fiber that extend from
autonomic ganglia to the heart, smooth
muscle and glands are also C fibers.
 E.g. motor functions of B and C fibers are
constricting and dilating the pupils,
increasing and decreasing heart rate, and
contracting and relaxing the urinary
bladder.

54.  Axon terminals
(telodendria)
 Synaptic end bulbs
◦ Contain tiny
membrane-enclosed
sacs called synaptic
vesicles that store
chemical
neurotransmitters.
otns/vani/kskbsgblh

55.  Multilayered lipid and protein covering.
 Called myelin sheath.
 Sheath electrically insulates the axon
of a neuron and increases the speed of
nerve impulse conduction.
 Axon without myelin sheath is called
unmyelinated.
 Only 2 types of neuroglia produce
myelin sheath: Schwan cells (in PNS)
and oligodendrocytes (in CNS).

56.  Schwann cells begins to form myelin sheath
around axon during fetal development.
 Eventually multiple layers of glial plasma
membrane surround the axon, with the
Schwan cell`s cytoplasm and nucleus
forming the outermost layer.
 Inner portion, consist of up to 100 layers of
Schwan cell membrane, is the myelin
sheath.
 The out nucleated cytoplasmic layer of the
schwann cell, which encloses the myelin
sheath, is the neurolemma (sheath of
schwann).

57.  A neurolemma is found only around axons
in the PNS.
 When an axon is injured, the neurolemma
aids regeneration by forming a
regeneration tube that guides and
stimulates regrowth of the axon.
 Gaps in the myelin sheath is called nodes
of Ranvier which appear at intervals along
the axon.
 Each Schwann cell wraps one axon
segment between two nodes.

58.  Myelination begins during fetal
development, but proceeds, most rapidly
in infancy.

59.  Schwann cells hold small nerve fibers in
grooves on their surface with only one
membrane wrapping.

60.  Oligodendrocytes myelinate parts of several
axons.
 Each oligodendrocytes puts forth about 15
broad, flat processes that spiral around CNS
axons, forming a myelin sheath.
 A neurolemma is not present, however nodes of
Ranvier are present in small number.
 The axons in the CNS display little growth after
injury. (this is thought to be due, in part, to the
absence of a neurolemma, and in part to an
inhibitory influence exerted by the
oligodendrocytes on axon regrowth.

61.  White matterWhite matter
◦ Composed of myelinated axons.
◦ Whitish color of myelin give white matter its
name.
 Gray matterGray matter
◦ Consists of neuronal cell bodies, dendrites,
unmyelinated axons, axon terminals and
neuroglia.
◦ It appears grayish, rather than white because of
the Nissl bodies impart a gray color and there is
little or no myelin in these area.
◦ Blood vessels are present in both white and gray
matter.

62. Spinal cord
 White matter surrounds an inner core of gray matter
– shaped like a butterfly of the letter H.

63. Brain
 white
matter is
the inner
core in
cerebrum
and
cerebellum

64.  insulating layer around a nerve fiber:
◦ Oligodendrocytes in CNS and Schwann cells
in PNS
◦ Formed from wrappings of plasma membrane
◦ All myelination completed by late
adolescence.
 In PNS, hundreds of layers wrap axon.
◦ The outermost coil is Schwann cell
(neurilemma)
◦ Covered by basal lamina and endoneurium.

65.  In CNS – no neurilemma or endoneurium.
 Oligodendrocytes myelinate several
fibers
◦ Myelination spirals inward with new layers
pushed under the old ones.
 Gaps between myelin segments = nodes
of Ranvier.
 Initial segment (area 1st
Schwann cell)
and axon hillock form trigger zone where
signals begins.