Fisiologi Kulit dan Somatosensoris

Dr. Dini Sri Damayanti,M.Kes

Kulit

• Terdiri dari 2 lapis :

– Superfisial : epidermis yang terdiri dari jaringan epitel stratified squamous compleks

– Profunda : dermis yang terdiri dari jaringan ikat

Fungsi kulit

• Sebagai pelindung terhadap benturan, kimia, suhu, kuman , sinar matahari,dll

• Sebagai pengatur suhu tubuh• Sebagai tempat ekskresi sisa metabolisme• Mengandung reseptor yang berfungsi sebagai

penerima dan meneruskan rangsangan

Epidermis

• Terdiri dari epitel stratified squamous compleks dengan keratinisasi

• 4 tipe sel yaitu sel keratinosit, sel melanosit, sel Langerhans dan sel Merkel

• Sel keratinosit : penyusun utama dari epidermis, selalu mengalami mitosis,bila mengalami kematian akan terbentuk lapisan tanduk

Lapisan dari epidermis:1. Stratum basale

• lapisan paling dalam berbatasan dengan dermis

• Disebut juga stratum germinativum• Merupakan stem sel dari keratinosit dan aktif

bermitosis• Terdapat sel Merkel yang merupakan sensori

nerve ending• Terdapat sel melanosit yang berfungsi

membentuk pigmen melanin

2. Startum spinosum• Merupakan lapisan yang terdiri dari sel

keratinosit, mitosis lebih sedikit daripada sel basal.

• Terdapat Sel Langerhans yang merupakan sel macrofag yang berperan dalam sistem imun (fagositosis kuman).

3. Stratum granulosum• Mengandung sel keratinosit pipih,

menghasilkan glikolipid yang membuat kulit bersifat waterproof

• Sel sangat tebal sehingga merupakan lapisan pelindung

4. Stratum lucidumdisebut juga zona transisional

5. Stratum corneumTerdiri dari sel-sel kerotinosit yang mati

Dermis

• Terdiri dari jaringan ikat fibroblast, kolagen, elastik dan retikuler

• Mengandug sel-sel macrofag• Banyak terdapat ujung saraf dan pembuluh

darah 5% dari seluruh tubuh

Lapisan dermis

1. Lapisan papilaris- Lapisan superfisial - Terdapat dermal papilaris- Polanya diturunkan secara genetik dan unik untuk tiap individu

2. Lapisan retikuler- Terdiri dari jaringan kolagen dan elastik- Berfungsi sebagai penahan terhadap streching

Hipodermis

• Terdiri dari jaringan lemak• Merupakan depo lemak • Berfungsi segabai insulator

Bentukan yang ada di kulit

1. Folikel rambut• Terdistribusi diseluruh permukaan tubuh

kecuali, tepalak tangan+kaki , putting susu, sebagian dari genetalia eksterna (glan pennis)

• Pigmen rambut dihasilkan oleh melanosit.• Terdapat muskulus erector pili

2. Glandula sebacea• Bermuara di folikel rambut• Menghasilkan sebum• Berfungsi untuk melembabkan kulit, mengurangi

pengeluaran air, dan • membunuh bakteri3. Kelenjar keringat• Berfungsi untuk mengatur suhu tubuh• Terdiri dari 90% air dan garam• Berasal dari filtrasi pembuluh darah• Terdiri dari ekrine dan apokrine• Bermuara di folikel rambut

Kuku

1. Merupakan keratinisasi yang padat2. Warna merah muda pada kuku disebabkan

adanya kapiler darah dibawahnya3. Bagian yang aktif tumbuh disebut matriks kuku

• Stimulus– Internal– External

• Receptors– Sense organs– Transducer

• Afferent pathway• CNS integration

General Properties of Sensory Systems

Type of sensoris system

General sensoris• temperature• pain• touch• pressure• vibration• proprioception

Special sensoris

• smell• sight• taste• hearing

General Properties of Sensory Systems

Figure 10-4: Sensory pathways

Sensoris Receptor

interface between environment and the body

translate stimulus into an AP

receptors distributed throughout the body relatively simple

receptors send info to CNS :• arriving info is called sensation• our awareness of it is perception

• receptors have selective sensivity :

chemicalphysical touchlightheat transfer

Receptor Potential

• Membrane potential of the receptor• A change in the receptor potential is

associated with opening of ion (Na+) channels• Above threshold as the receptor potential

becomes less negative the frequency of AP into the CNS increases

Adaptation

• reduction in sensitivity in the presence of a constant stimulus

Pheriferal : change in receptor activityCentral : inhibition of nuclei in pathway

• adaptation reduces the amount of information reaching the cerebral cortex

about 1% of sensory information coming in reaches our awareness

Adaptation

• Slow-provide continuous information (tonic)-relatively non adapting-respond to sustained stimulus– joint capsul– muscle spindle– Merkel’s discs

• punctate receptive fields

– Ruffini end organ’s (corpusles)• activated by stretching the skin

Adaptation

• Rapid (Fast) or phasic• react strongly when a change is taking place• respond to vibration

– hair receptors 30-40 Hz– Pacinian corpuscles 250 Hz– Meissner’s corpuscles- 30-40 Hz– (Hz represents optimum stimulus rate)

• “Stimulation of a receptor produces action potentials along the axon of a sensory neuron. The frequency or pattern of action potentials contains information about the strength, duration, and variation of the stimulus. Your perception of the nature of that stimulus depends on the path it takes inside the CNS.”

• Simple receptors• Complex neural• Special senses• Chemoreceptors• Mechanoreceptors• Thermoreceptors• Photoreceptors

Sensory Receptor Types

Sensory Receptor Types

Figure 10-1: Sensory receptors

• Receptor– Threshold– Action potential

• Sensory neurons– Primary – medulla – Secondary – thalamus– Tertiary – cortex

• Integration– Receptive field– Multiple levels

Somatic Pathways

Somatic Pathways

Figure 10-9: Sensory pathways cross the body’s midline

• Location– Lateral inhibition– Receptive field

• Intensity• Duration• Tonic receptors• Phasic receptors• Adaptation

Sensory Modality

Sensory Modality

Figure 10-3: Two-point discrimination

Sensory Modality

Figure 10-6: Lateral inhibition

Type sensoris receptor based on nature stimulus

• Nociceptors : pain

• Thermoreceptors : heat flow

• Mechanoreceptors : physical distortion

• Chemoreceptors : chemical consentration

Nocireseptor

• common in:– skin– joint capsules– coverings of bones– around blood vessel walls

•free nerve endings

•large receptive fields

• sensitive to:–extreme temperature –mechanical damage–dissolved chemicals

• (like those release by damaged cells)

• two fiber types convey info• type A

– fast pain (cut, etc.,)– easy to localize

• type C– slow pain (“burning, aching”)– difficult to localize

• tonic receptorsno significant peripheral adaptation as long as the stimulus is present, it will hurt

• but central adaptation can occur (perception of pain may decrease)

• sensory neurons bringing in pain info use glutamate and/or substance P as their neurotransmitter

• these nts can cause facilitation (?)pain may be disproportional (feels worse than it should)

• pain can be reduced by endorphins and enkephalins (inhibit activity in pathway)

Pain vs. Nociception

• Nociception-reception of signals in CNS evoked by stimulation of specialized sensory receptors (nociceptors) that provide information about tissue damage from external or internal sources– Activated by mechanical, thermal, chemical

• Pain-perception of adversive or unpleasant sensation that originates from a specific region of the body– Sensations of pain

• Pricking, burning, aching stinging soreness

Sensitization of Nociceptors

• Potassium from damaged cells-activation• Serotonin from platelets- activation• Bradykinin from plasma kininogen-activate• Histamine from mast cells-activation• Prostaglandins & leukotriens from arachidonic

acid-damaged cells-sensitize• Substance P from the 1o afferent-sensitize

Nociceptive pathways

• Spinothalamic-major – neo- fast (A delta)– paleo- slow (C fibers)

• Spinoreticular• Spinomesencephalic• Spinocervical (mostly tactile)• Dorsal columns- (mostly tactile)

Pain and Itching

Figure 10-12: The gate control theory of pain modulation

Thermoreceptor

free nerve endings in the dermis, skeletal muscle, hypothalamus and liver

warm receptors or cold receptors

phasic receptors active when temperature is changing, quickly adapting to stable temperature

detect transfer of heatheat loss from skin :coolheat gain to skin : warm

Mechanoreceptor

• contain mechanically regulated ion channels

3 type of mechanoreceptor:•Tactil receptor :touch, pressure, vibration•Baroreceptor : pressure changes(gut, genitourinary)•Propioreceptor : position of joints/muscles

Touch (pressure)

Figure 10-11: Touch-pressure receptors

Mechanoreceptors in the Skin

• Rapidly adapting cutaneous– Meissner’s corpuscles in glabrous (non hairy) skin-

(more superficial)• signals edges

– Hair follicle receptors in hairy skin – Pacinian corpuscles in subcutaneous tissue

(deeper)

Mechanoreceptors in the Skin

• Slowly adapting cutaneous– Merkel’s discs have punctate receptive fields

(superficial)• senses curvature of an object’s surface

– Ruffini end organs activated by stretching the skin (deep)

• even at some distance away from receptor

Baroreceptor

• free nerve endings in the walls of organs that stretch–e.g., blood vessels

when pressure changes they expand or contract

Proprioreceptor

1. Type of proprioreceptor:• Muscle spinde: stretch reflex• Golgi tendon organ : monitor tendon

tension• Receptor in joints capsule : free nerve endings in joints2. no adaptation3. continuously send info to CNS4. most processed at subconscious level

Somatosensory Cortex

• Two major pathways– Dorsal column-medial lemniscal system

• Most aspects of touch, proprioception

– Anterolateral system• Sensations of pain (nociception) and temperature• Sexual sensations, tickle and itch• Crude touch and pressure• Conduction velocity 1/3 – ½ that of dorsal columns

Somatosensory Cortex (SSC)• Inputs to SSC are organized into columns by

submodality– cortical neurons defined by receptive field &

modality– most nerve cells are responsive to only one

modality e.g. superficial tactile, deep pressure, temperature, nociception

• some columns activated by rapidly adapting Messiner’s, others by slowly adapting Merkel’s, still others by Paccinian corp.

Somatosensory cortex• Brodman area 3, 1, 2 (dominate input)

– 3a-from muscle stretch receptors (spindles)– 3b-from cutaneous receptors– 2-from deep pressure receptors– 1-rapidly adapting cutaneous receptors

• These 4 areas are extensively interconnected (serial & parallel processing)

• Each of the 4 regions contains a complete map of the body surface “homonculus”

Other Somatosensory Cortical Areas• Posterior parietal cortex (BM 5 & 7)

– BM 5 integrates tactile information from mechanoreceptors in skin with proprioceptive inputs from underlying muscles & joints

– BM 7 receives visual, tactile, proprioceptive inputs • intergrates stereognostic and visual information

– Projects to motor areas of frontal lobe– sensory initiation & guidance of movement

Secondary SSC (S-II)

• Secondary somatic sensory cortex (S-II)– located in superior bank of the lateral fissure– projections from S-1 are required for function of

S-II– projects to the insular cortex, which innervates

regions of temporal lobe believed to be important in tactile memory

Somatomotor area