sensations & perceptions - mans€¦ · sensations & perceptions sensation-is an awareness...

Sensations & PerceptionsSensationSensation - is an awareness of sensory stimuli (external

& internal) in the brainPerception Perception - meaningful interpretation by the brain

(conscious understanding of sensory data)

Receptors• Definition of Sensory Receptors -

- Modified Structures (Free nerve ending or epithelial cells ) that detect changes in external & internal environment & send impulses to the brain.

Types of Receptors1) Receptors for special sense:1) Receptors for special sense:2) Receptors for 2) Receptors for cutanuouscutanuous sensation sensation

((ExtroceptorsExtroceptors) :) :3) Receptors for deep sensation 3) Receptors for deep sensation ((ProprioceptorsProprioceptors))4)Receptors for visceral sensation 4)Receptors for visceral sensation

((visceroceptorsvisceroceptors) :) :--5) Chemo5) Chemo--receptors: respond to changes in the receptors: respond to changes in the

concentration of solutes in Solvents concentration of solutes in Solvents 6)6) OsmoOsmo--receptors:receptors: of hypothalamus which of hypothalamus which

monitors blood osmotic pressuremonitors blood osmotic pressure

Receptors1) Receptors for special sense:Receptors for special sense:• A- Eye → vision → Retina (Rods & Cons).• B- Ear → (Hair cells).

*Hearing → Organ of Corti*Head position & movement→

1-crista ampullaris

2-maculae uterculi & sacculi

• C- Smell → olfactory epithelium. • D- Taste → Taste buds

2) Receptors for Receptors for cutanuouscutanuous sensation sensation ((ExtroceptorsExtroceptors) :) :--• A- Pain (Nocireceptors) → free nerve endings.• B- Temperature (thermoreceptors)

- free nerve endings- Hot sensation Ruffini corpuscles- Cold sensation Krause end bulbs

• C- Touch (Mechanoreceptors) : –Epidermal - Merkel's complex

Dermal - Papillary Layer -Miessner's corpuscles

- Reticular Layer--Free nerve endings (plexus of Bonnet )

-Paccinian corpuscles

-Ruffini corpuscles

-Krause end bulbs

RUFFINI CORPUSCLESite: Deep in dermis and hypodermis(numerous in the sole )

Shape : an Elongated corpuscle.Structure: It has a thin C.T. capsule.

Its Axial core contains Axially arranged collagen fibers whose displacement stimulates the nerve endings. The nerve fiber is Myelinated & penetrates the corpuscle side to give numerous non – myelinatedbranches which end between the collagenous fibers .

Function – Touch_

Sensation

KRAUSE END BULB• Site: Connective tissue of conjunctiva,• tongue and dermis of external genitalia• Shape: Round corpuscle• Structure: It has very poor C.T. capsule. Its nerve

fiber is Myelinated & penetrates the corpuscle side to give numerous non – myelinated branches that end by bulbous terminations.

Function – Touch_

&

Merkel’s ComplexSite:

In the basal cell layer of epidermis.LM:1- Merkel’s cell It is a modified

epidermal cell in the basal layer. This cells is slightly larger than the neighboring cells.

2-A sensory nerve fiber reaches the epidermis, it loses its myelin sheath and neurolemma. The naked nerve penetrates the basement membrane to terminate as a “ terminal disc”around “Merkel’s cell”

Function Touch sensation

MEISSNER 'S CORPUSCLESiteSite: In dermal papillae (numerous in fingers, soles, lips, external

genitalia , nipples and eyelids Shape & SizeShape & Size: an Oval corpuscle wide, with long axis

perpendicular to the surfaceStructureStructure: It has a thick C.T. capsule .

Its Axial core is formed of Transversally arranged modified Schwann cells and some inter – cellular collagenous fibers.

The nerve fiberThe nerve fiber is Myelinated & penetrates the corpuscle base giving 2 – 9 non – myelinated spirally running branches that end between the collagenous fibers.

Function Function light Touch

• The nerve fibers end around the connective tissue sheaths at the bases of the hair follicles, some fibers enter the outer root sheath to end around tactile cells.

•• Function Function light Touch

3) Receptors for deep sensationReceptors for deep sensation• A- Proprioceptors

-Tactile localization -Tactile discrimination- stereognosis,- deep pressure -vibration

• B- Kinesthesia ( motion sensation) - Paccinian corpuscle - muscle spindles - Tendon spindles - joint receptors.

Site:Site: 1 ) deep in dermis & hypodermis ( numerous in fingers , external genitalia and breast )

• 2 ) sites subjected to pressure e.g. inter – muscular septa , joint capsules, inter – osseous membranes , wall of urinary bladder and mesentery.

Shape : Shape : Oval corpuscle.Structure:Structure: A thin C.T. capsule separated from the corpuscle

by a sub – capsular space. Its Axial core is formed of 20 – 80 concentric layers of

flat modified Schwann cells joined together by desmosomesand separated by inter – cellular spaces containing collagenous fibers and tissue fluid , thus , in L . S .it exhibits an ONION like appearance.

The nerve fiberThe nerve fiber is Myelinated & penetrates the corpuscle at one pole to become non myelinated, then runs to the nearby of the opposite pole to terminate by an expanded terminal .

PACCINIAN CORPUSCLEPACCINIAN CORPUSCLE

PACCINIAN CORPUSCLEPACCINIAN CORPUSCLEFunction• A- Proprioceptors

-Tactile localization -Tactile discrimination- stereognosis,- deep pressure -vibration

B- Kinesthesia ( motion sensation)C- Deep touch

MUSCLE SPINDLE• Site:• 1) between the striated muscle fibers

specially near their insertion .• 2) numerous in small muscles doing fine

work e.g. Hand muscles.• Size:- 3– 5 m .m × 0.2 m.m.• Shape:- fusiform.• Structure:-• 1) Capsule:- stretchable connective

tissue .• 2) Intrafusal muscle fibres :-• (2 – 12) in number.• -Nuclear bag and Nuclear chain fibers

bathed in tissue fluid. • Each fiber is formed of a non - contractile

central part and contractile two poles.

MUSCLE SPINDLE

contains a chain of nuclei

contains a bag of nuclei

not expandedexpandedCentral Part

NumerousFewerNo

Thinner shorterThicker & longerSize

Nuclear chain fibers

Nuclear bag fibers

MUSCLE SPINDLE• 3) Innervations:-• Afferents:1ry (annulo – spiral ) ending → thick myelinated

fiber end around the central part.2 ry ( flower spray) ending → thin myelinated

fibers end around the sides of the 1ry afferents.

*The bags have only 1ry endings while the chains have 1ry & 2ry endings.

• Efferent:- fibers (fine fibers from anterior horn) supply the contractile poles of the intrafusal muscle fibers → more stretch and more firing of AFFERENT fibers.

•• Function:Function:-- a stretch receptor for kinesthesia a stretch receptor for kinesthesia and reflex control of muscle tone, and reflex control of muscle tone, movement and posturemovement and posture..

annulo – spiral ) ending

flower spray) ending

Efferent - fibers

• They differ from the muscle spindle in:• 1) No efferent fibers.• 2) Contain collagenous intrafusal fibers

enclosing the terminal ramifications of the afferent nerve. When the tendon becomes tense → compression of nerve fibers between the intrafusal collagenous fibers → impulse firing.

• They help in kinesthesia i.e. perception of movement & position of various parts of the body.

• Site: in the joint capsule and synovialmembrane.

• Type: - Ruffini and- pacinian corpuscles

4)4)Receptors for visceral sensation Receptors for visceral sensation ((visceroceptorsvisceroceptors) :) :--

toto transmit autonomic sensation transmit autonomic sensation from the stomach, U. bladder, from the stomach, U. bladder, ……. . etc etc ……Via the autonomic nervous Via the autonomic nervous system to the system to the C.N.S. C.N.S.

Q.1• In the following diagram of the Skin, identify

the structures labelled by the letters A-E?

Q. 2• What are the kinds of sensation which

affected by Diabetes Mellitus?