Summary Skin & Sensory System Notes

Sensory Physiology
 Nervous & Endocrine System = control + communication




 Sensory Physiology = how body collects, converts, interprets info from environment.
o Focus = sensory organs + pathways
o Processes = reception, transduction transmission, perception
 Brain  interprets impulses based on their pathway
o Auditory nerve = sound, Optic nerve = sight
 Different sensations ((sound, light, touch, etc.))  depends on distinct neural pathways and synaptic
connections.
 Nerve impulses  carried by sensory neurons to CNS
 Sensory receptors  convert external energy ((light, sound, pressure)) into nerve impulses
o Detect external and internal environment changes
 5 main types of Receptors:
Receptor Type Location Stimuli Detected Function
Mechanoreceptors Skin Mechanical forces Touch
Muscles Pressure Hearing
Ears Balance

Thermoreceptors Skin Temperature changes Thermal regulation
Hypothalamus

Chemoreceptors Tongue Chemical substances Taste
Nose Smell
Blood Vessels Chemical balance

Photoreceptors Eyes Light Vision

Nociceptors Skin Painful stimuli Protection from harm
Organs

o Each type of sensory receptor responds to particular modality of stimulus
o Response by causing production of action potentials in a sensory neuron

,  Impulses are conduction to parts of brain that provide the proper interpretation of sensory
info when that neural pathway is activated


 Type of sensation & reaction  depends on where action potential ends in CNS
 Spinal cord  sensory input triggers simple reflexes ((e.g., withdrawal from pain))
 Brain stem  input triggers complex reflexes ((e.g., heart rate, breathing changes))
 Cerebral cortex  input triggers to conscious perception ((touch, smell, hearing, etc.))
 Perception  conscious awareness & interpretation of sensations ((mainly cortex function))
 Process of Sensation:
1. Stimulation of receptor  sensory receptor detects specific stimulus ((internal/external change))
2. Transduction  receptor converts environmental stimulus energy into graded potential ((electrical
signals)) for nervous system to interpret ((depolarization or hyperpolarization))
3. Generation of action potentials  if graded potential reaches threshold  action potentials fired 
travels to CNS
4. Integration  CNS processes input ((modifies, filters, or passes along)). Conscious perception occurs
in cerebral cortex.



 Mechanoreceptors:
1. Merkel Discs  in basal epidermis  clustered  connect to a single large myelinated fiber
2. Meissner Cells  in basal epidermis  near edges of papillary ridges
3. Pacinian Corpuscles  in dermis  each innervated by one myelinated fiber
4. Ruffini endings  in dermis  each innervated by one myelinated fiber



 Formation of receptor potential in skin  different receptors can be stimulated differently
1. Mechanical deformation of receptor stretches the receptor membrane and opens ion channels.
2. Contact of membrane with the chemical substance opens the ion channels.
3. Membrane temperature change changes the membrane permeability.
4. Electromagnetic radiation contact directly or indirectly changes the membrane properties and ion flow
occurs.


Layers of skin:
o Epidermis  stratified squamous keratinized epithelium // avascular
o Upper cell layers  dead, filled with keratin  form cornified ((protective)) layer
o Underlying layers  living cells support upper layers
o Nourishment  from blood vessels in dermis ((loose connective tissue))
 Epidermis is dynamic  responds to environment
o E.g. abrasions  inc. cell division  thicker cornified layer  callus
 Epidermal infoldings  form sweat glands, sebaceous glands, hair follicles
 Epidermal cell types  keratinocytes, melanocytes, Langerhans cells, Granstein cells
 Hypodermis  loose, fatty connective tissue  anchors skin to muscle or bone

, Collagen Fibers of skin
 Langer’s lines  shows a certain sequence in dermis
o Are in different directions in body parts
o Can be important in operations, vertical sections wounds heals slower than parallel incisions and
may leave scars
 Nails  modified form of epidermis is stratum corneum and contains hard keratin
o It has root and stem parts
o Nail body is keratinized dead cells sit on epithelial layer of skin
o Proximal part is called the lunula ((little moon))
o Root is covered with skin, where new cells are made in the matrix for nail growth
 Hairs  keratin extensions of cells formed in epidermis are found everywhere except in palms, soles,
lips, nipples.
o Have auxiliary ((Supplementary)) and protective duties
o 2 parts: free part and root
o 3 layers: medulla, cortex and chitin
o Pigment in cortex gives color ((in absence of pigment the medulla fills with air and hair is gray))
o There is continuous regeneration ((3-5 yrs of life, 3-4 months of rest))
 With age regeneration decreases
o First hair ((lanugo)) begin in fetal 3rd month
 Eyebrows and hair appear after 5th month  prenatal lanugo hairs fall out  hair +
eyebrows become evident
o Bulge region of hair follicles  contains stem cells
o Keratinocyte stem cells  migrate to germinal matrix  divide  form hair shaft & root sheath
o Skin wounds  stimulate stem cells from follicles to migrate  aid in wound healing
o Melanocyte stem cells ((in bulge))  migrate to germinal matrix  provide hair color
o Hair graying  caused by loss of melanocyte stem cells with age
Sweat Glands
 Merocrine ((eccrine)) glands
o Most common  dense on palms and soles
o Located in dermis  duct opens directly to skin surface
o Secretion  watery/serous, contains salts, ions, ammonia, urea, uric acid, lactic acid
o Sodium reabsorption  active in ducts
 Apocrine glands
o Larger  found in armpits and groin
o Duct opens into hair follicles
o Active from puberty onwards
o Secretion  thick, organic-rich  odor develops with bacterial action
 Nervous control  sweat secretion via sympathetic stimulation, but neurotransmitter = acetylcholine
((Ach))
Sebaceous Glands
 Location  mostly in dermis, btw, hair follicles & piloerector muscle
 Distribution  all over skin except palms & soles, most abundant on face & scalp
 Largest glands  face & wings of the nose
 High density areas  around mouth, forehead, external auditory canal, anus
 Secretion  sebum  oily, prevents drying, partially antibacterial & antifungal