mnsr 25 Flashcards
input of the nervous system is provided by
sensory receptors
( these are nerve endings that converts stimuli from external and internal environment into afferent nerve impulses which passes into CNS )
general senses include
pain, pressure, light touch, tempreture, limb position all to maintain heamostasis
Five functional sensory receptors
( there’s is NO satisfactory system of classification of both functional and morphological )
1- mechanoreceptors - detects mechanical stimulation
2- thermoreceptors - defects changes in temp ( Krause’s end bulbs and corpuscle )
3- nocirepteors ( pain) - all free nerve endings for pinching tearing and burning
4- photoreceptors - rods and cones of the retina
5- chemoreceptors - taste and smells
mechanoreceptor consist of
- free nerve ending
- tactical hair cells
- complicated encapsulated end organ
( the may be found in many parts of the body as skin, muscles, gut, hair cells in ear )
the naked nerve ending are the
end of the dendrites of sensory neurons in tissues that detect pain temp and light touch
encapsulated receptors consist of
nerve endings surrounded by one or more layers of skin
pacinian corpuscle : mechanoreceptor
- pressure transmitted to the naked nerve needing causes the Na+ ion channels to open and causes depolarisation of the nerve fibre
- small onion pierced w a thin wire
- largest of the encapsulated nerve ending ( 1-2 mm )
-found in subdermal skin layers, abdominal mesenteries, external gentelia, tendons, ligaments, joints - response for rapid movement and good detection for vibration
- consists of central non-myelinated tip of never fibre surrounded by 30 concentric layers of connective tissue and there will be movement of fluid
- fast adapting and responds to vibrations
- hairy and glabrous skin
ruffini’s end: mehcnaorecpetor
- loosely incapsulated nerve ending
- size intermediate between pacini and and Krause end bulbs
- in loose connective tissue, the myelinated nerve fiber loose their sheath and break into branches w terminal knobs
- found in dermis and deeper organs as joints
- thought it had tactical function intermediate between meisneers light touch and pacinian deep pressure but it was later found: thermoreceptor
- slow adapting
- allows rotation of joints
- allows stretching
- hairy and glabrous skin
meissenrs corpuscle: mechanoreceptor
- common encapsulated sensory receptor
- smaller than pacinian corpuscle
- oval receptor consist of loose stacks of lamella and 2 or 3 spiralling dendritic ends of nerve fiber surround by thin cellular capsule
- concentrated in the dermal papilla ( fingertips , lips , palms , soles of the feet, sensitive areas of the skin )
- detects light touch
- allows the body to recognise the exact point has been touched
- fast adapting repsonds indentation, glabrous skin
merkles discs: mechanocrecptors
- found in the epidermis near stratum Basale
- aka: expanded tip tactile receptors found in smooth but less frequently in hairy skin
- detects light touches sensation
- consist of small cup shaped cells and naked nerve ending .
- expanded discs at the base of merkels cells are connected via non myelinated fibres to a large myelinated nerve fiber
- merkles cells cytoplasm contains vesicles similar to synapses but no neruotransmitter seen yet.
- slow adapting, responds pressure, glabrous skin
sense of position with no adaptation is
proprioreceptor.
responds continuously to tension and movement in strained muscles and in tendons
proprioreceptor
The two main types in proprioreceptor is
muscle spindle and Golgi tendon organ
1- muscle spindle: specialised muscle fibres surrounded by sensory nerve endings enclosed w connective tissue sheath. emits sensory nerve impulses contioniyisly and more active than any other sensory receptor.
The stretching of the muscles increases the rate of firing = muscle tone Detects muscle length
2- Golgi tendon organ: lies within the muscle tendon and attached to muscle fibres. composed of connective tissue fibres surrounded by dendrite and encased in capsule resembles ruffini ending. Detects tension. Provides the nervous system w instants info on degree of tension. Forms 2 receptors that are subconious level and no sensory perception . Allows cns to exactly control and coordinate the skeletal muscle contraction
chemoreceptors are sensed by small organs called
taste buds of the tongue.
- about 3000 located in tiny elevation of the tongue: lingual papilla
- taste buds are composed of 50 modified epithelial cells arranged around taste pores
- each taste bud is innervated by 50 non myelinated nerve fibers with innervate both type of cells. has closer relationship w gustatory cells
taste buds are stimulated by
chemicals in the food we eat and are bathed w saliva
taste buds are found in
roof of our oral cavity, the pharynx and larynx but in smaller number. Two types of cells are described in taste buds
the four primary sensation of taste are
sour , sweet, salty, bitter
taste buds detect
chemicals dissolved in our saliva
sugar molecule activate a signal transduction process involving
G protein
gustatory cells and darker sustencular cells have
long microvilli
( guastory cells and darker sustencular cells w third basal cells now recognised )
microvilli or taste hairs protrude into
pores and are taste receptors
the plasma membrane of the taste hair contains
cluster of proteins
the stimulation of the receptor stimulates
the dendrites of the sensory nerve wrapped around the receptor cell and impulses from taste buds and transmitted to the brain.
the function of zinc
stimulates division of the cells in the taste buds
although gustatory cells are thought to be taste receptors sustencular cells
serve receptor function
the process of the stimaltion include:
1- chemical interact w receptor
2- involves G protein and adenylyl cyclase which increases cyclic amount level
3- activating of protein kinase which phsophorelates and closes k+ ion channels
4- decrease k ion permeability sets up depolarisation which generates action potential
—- is a patch of receptor cells in the roof of the nasal cavity that detects —-
1- olfactory epithelium
2- odour
—- lies in the upper part of the nostrils where its folded over the —-
1- olfactory membrane ( which contains 100 million olfactory receptors cells )
2- turbinal bone
the olfactory cells are
culumonar epithelium of the mucus membrane and there are three types of cells
1- olfactory cells
2- sustencular cells
3- basal epithelial cells
olfactory receptors are true —- whose cell body is located in the —- of the mucosa
bipolar and middle stratum
the axons of the sensory neruons pass through
20 small holes on each side of the cribifrom plate of ethmoid bone and enter the olfactory bulb in the brain
a single —- process extends from —- to the free surface where it terminates a small swelling ——
dentrictic, soma, olfactory knob ( has cilia or olfactory hair )
each cell gives rise to non-mylnated axon and join to pass through the bone to reach olfactory bulb of the forebrain
the role of sustnecular cells in olfactory process
is poorly understood but they contain microvilli which is responsible for mechanical and physiological support
the — are chemoreceptors are reacts to —- by stimulating —–
cilia, odour , olfactory cells
process:
cyclic amp opens gated channels , opening of the Na+ ion channels causing depolarisation.
humans can detect
seven main classes of odour ( camphor, musk, floral, peppermint, ethereal, pungent, putrid )
1000 genes for 1000 types of olfactory receptors
we can distingush 10,000 different senses
olfactory receptors respond to small amount of substances ( example: threshold for olfactory perception of iodine the synthetic of violet is 1 part of 30 billion )
—- is a feature of sensory receptors and olyfatory receptors as they —–
adaptation , they adapt rapidly
50% in first second or so after situmaltion and they will be orderless after a few minutes
