1. Receptors and effector nerve endings
Idegvégződés, fájdalom, propriocepció, receptor, reflex
Receptors and effector nerve endings
Dr. Csáki Ágnes

2. Axon myelinated non-myelinated
Myelin is a fatty white substance that surrounds the axon of some nerve cells,
forming an electrically insulating layer.
It is essential for the proper functioning of the nervous system. This arrangement permits
saltatory conduction of action potentials with repropagation at the nodes of Ranvier
In this way, myelination greatly increases speed of conduction and saves energy

3. Myelin sheath in the CNS
Myelin sheath in the PNS
Myelin sheath is formed by the processes of the oligodendrocyte.
A single oligodendrocyte can extend its processes to 50 axons, wrapping approximately 1 μm of myelin sheath around each axon.
Myelin sheath is formed by the Schwann cell
A well-developed Schwann cell is shaped like a rolled-up sheet of paper.

4. Myelinating Schwann cells wrap around axons of neurons to form the myelin sheath.
inner and outer mesaxon

5. The sheath is not continuous
The sheath is not continuous. Individual myelinating Schwann cells cover about 100 micrometres of an axon - internodium.The gaps between adjacent Schwann cells - nodes of Ranvier
The basal lamina of the cells is continuous
Only a small volume of residual cytoplasm allows communication between the inner and outer layers. This is seen as the Schmidt-Lantermann incisure.

6. Non myelinated axons PNS CNS Many axons in the same cell, no rotation
No covering around the axons
(pinkish structures)

7. Nerve fiber Axon (neurit) + glial covering (if exists)
Bundle of fibers in CNS: tract or pathway
Bundle of fibers in PNS: nerve(nervus)
Usually mixed: contains both sensory and motor fibers

8. Peripheral nerve
Peripheral nerves have multiple layers of connective tissue surrounding axons.
endoneurium surrounding individual axons: fine reticular fibers of conn tissue
perineurium binding fibers into fascicles: epitheloid cells in 5-10 layers, collagen
epineurium binding the fascicles into a nerve: dense irr. conn. tissue.

9. Classifying II. Sensory fibers according to their conduction velocity
Ia. Annulospiral ending in the muscle spindle,
Nuclear bag receptor
Ib. Flower-spray ending in the muscle spindle
Nuclear chain receptor
II. Mechanoreceptors (Golgi tendon receptor)
III. Mechanoreceptors
IV. Nociceptive receptors
The thicker the fiber the more the conduction velocity
(A the largest and fastest axons, C the smallest and slowest)
I. Classifying axons according to their thickness
A fibers B fibers C fibers
1-20 µm Ø µm Ø ,5-1 µm Ø
m/s m/s 0,5-2 m/s
   
M S M S Pr (M) P(S), Po(M)
M: motor, S: sensory, Pr: preganglionic P: pain Po: postganglionic

10. Stimuli –sensation– response
CNS
somatosensor
afferens
viscerosensor
afferens
visceromotor
efferens
somatomotor
efferens
receptor
effector
stimuli
Skin, muscle,
tendon
viscera
Gland,
smooth muscle
Striated muscle

11. Stimuli –sensation– response Functional categories
receptor
CNS
effector
afferent
efferent
Afferent or Sensory :input, from the external environment or from the body
Efferent or Motor :output, toward the goal organ
Somatosensor: from the skin, muscle, tendon, etc
Somatomotor: to striated sceletal muscle
Viscerosensor : from internal organs, vessels
Visceromotor :
General Visceromotor : to smooth muscle of internal organs, vessels, glands
Special Visceromotor or Branchialmotor : to striated muscles derived from branchial arches!! : larynx, pharynx etc

12. Sensors, somato- and viscero, generally
( not in sensory organs like eye, ear etc) Sensory neurons are somewhat unique, having an axon that extends to the periphery and another axon that extends into the central nervous system via the dorsal root.The cell body of this neuron is located in the dorsal root ganglion or one of the sensory ganglia of sensory cranial nerves. Both the peripheral and the central axon attach to the soma at the same point, and these sensory neurons are called "pseudounipolar" neurons.
Receptive membrane: stimulus causes receptor potential (Transduction)
Regenerative membrane: action potencial (Transformation)
Spinale ggl
Spinal nerve
Afferent fiber
Receptor nerve ending

13. Categories of sensation and receptors
Special
Special organs
vision, hearing, balance, smell, taste
General
Light touch, pressure temperature, pain, sense of body and limb movement
General sensation
situation
function
exteroceptor
skin
tactile, pressure, vibration, heat, pain
proprioceptor
Muscle, joint, tendon, deep tissues
Set up (pozition), movement(kinesthesia)
deep pressure
interoceptor
Internal organs(viscera)
homeostasis, function of int organs
Exteroceptor: information from the external enviroment
Proprioceptor: skeleto-muscular information (under the skin)
Interoceptor: about the internal organs Sherrington (1906)

14. Classifications of receptors
Morphology : encapsulated, nonencapsulated
Stimulus
-touch
-pressure
-vibration
-strech
-pain
-temperature
III. Position
-Exteroceptor (skin)
-Proprioceptors
(in muscles, tendons are special for the sensation of the proper motion of the body)
-Interoceptor/Visceroceptor (internal organs, vessels)
may destroy the tissue: Noxious stimuli

15. HEAT (Temperature), PAIN, TOUCH, VIBRATION, PRESSURE
Exteroceptors
provide information about the external enviroment:
HEAT (Temperature), PAIN, TOUCH, VIBRATION, PRESSURE
mechanoreceptor thermoreceptor nociceptor
mechanoreceptors
Receptors specialized to sense mechanical forces
threshold
The level of membrane potential at which an action potential is generated – low or high
conduction velocity
The speed at which an action potential  is propagated along an axon. – fast or slow
adaptation
The phenomenon of sensory receptor adjustment to different levels of stimulation;
critical for allowing sensory systems to operate over a wide dynamic range. – fast or slow
(„it remembers quickly or slowly”)

16. Mechanoreceptors
Four major types of encapsulated mechanoreceptors are specialized to provide information to the CNS about touch, pressure, vibration, and cutaneous tension:
Meissner's corpuscles,
Pacinian corpuscles,
Merkel's disks, and
Ruffini's corpuscles
These receptors are referred to collectively as low-threshold (or high-sensitivity)
mechanoreceptors because even weak mechanical stimulation of the skin
induces them to produce action potentials.
All low-threshold mechanoreceptors are innervated by
relatively large myelinated axons (type Aβ)
ensuring the rapid central transmission (fast velocity) of tactile information.

17. Meissner’s-corpuscle
In the dermal papilla
mechanoreceptor (fine touch)
Sensitive to changing of the pressure,
rapidly adapting action potentials
follow minimal skin depression.
Meissner's corpuscles are the most
common mechanoreceptor of “glabrous”
(smooth, hairless) skin (the fingertips, for instance),
and their afferent fibers account for
about 40% of the sensory innervation of the human hand.
These corpuscles are particularly efficient
in transducing information about the
relatively low-frequency vibrations (30–50 Hz)
that occur when textured objects are moved across the skin.
Non-myelinated axon endings
Schwann-cell lamelle
Perineural capsule
Keilförmigen Schwann-Zell lamellen
One or more thick,
myelinated fiber (II type)

18. Pacinian corpuscle Non myelinated rapidly adapting axon in the center
Schwann-cell layers (inner tube)
Perineural cells in layers (50 layers ): lamellae form onion-like capsule
Viscous fluid between the lamellae
It occurs in the deeper layers of the skin,
in the peritoneum, mesenterium pleura and internal organs,
in fascias, periosteum and periarticular connective tissue.
Responds to mechanical distorsion especially vibration at high frequencies (250–350 Hz)
provide information primarily about the dynamic qualities of mechanical stimuli.
thick, II type myelinated fibre

19. (Vater-)Pacinian-corpuscle
The largest receptor, about 1 mm in diameter
thick, myelinated fibre II type

20. Merkel’s-disk Epidermis, str. Basale Slowly adapting mechanoreceptor
Fingertip: /cm2
Merkel cells are anchored to the keratinocytes by desmosomes,
enlarges into a saucer-shaped ending that is closely applied to the cell containing vesicles that apparently release peptides that modulate the nerve terminal.
Selective stimulation of these receptors in humans produces a sensation of light pressure.
Merkel's disks play a major role in the static discrimination of shapes, edges, and rough textures.

21. Dermal papilla

22. Ruffini corpuscle
Ruffini’s gift to Sherrington
Oxfordi Egyetem tulajdona
Slowly adapting receptor in the deeper layers of the skin
elongated structure with collagen fibers
sensitive to the cutaneous stretching produced by digit or limb movements

23. Nonencapsulated: Free nerve endings
Most abundant type of sensory endings:
The non-encapsulated endings include free nerve endings, which are simply the peripheral end of the sensory axon. These mostly respond to noxious (pain) and thermal stimuli.
Situation
-Epidermis, dermis
-Wall of vessels
-Gut tube
-Dura mater
-cornea
Thin myelinated (III type) or
non-myelinated (IV type),
slow conducting
Receptive membrane field
Schwann cell

24. Free nerve ending in the skin
Str. Granulosum
Lamina Basalis

25. Location of the exteroceptors in the skin

26. Proprioceptors Muscle spindle Golgi tendon organ
Proprioception: information about the location and proper motion of the body
Muscle spindle
Golgi tendon organ

27. Muscle spindle
Spindle shape structure in the perimysium of striated muscle :5-10 intrafusal fibers covered by conn tissue capsule. Sensory and motor afferents end on the intrafusal muscle fibers
Nuclear chain fiberr- nuclei in the center in a row
Nuclear bag fiber: many nuclei in the central dilation.
Anulospiral nerve ending: the central portion of the muscle spindle is clear and is wrapped by an Ia sensory nerve ending. This ending is activated by stretch of the muscle spindle or by contraction of the the muscle fibers
Flower spray ending:: II. afferent, near the ends of the intrafusal fibers activated by the tenses of the muscle fibers
γ motneurons make synapses at the ends of the intrafusal muscle fibers which are contractile; regulate the sensitivity of the intrafusal fibers

28. Proprioceptor: Muscle spindle
Intrafusal fiber
Nuclear bag fibers
Nuclear chain fibers
Aɣ nerve
ending
Anulospiral
nerve ending
Ia type IA II
„flower -spray” nerve ending
II type Aγ
Aɣ nerve
ending Aα
Aα nerve ending
Extrafusal (working) fibers

29. Cross section of muscle spindle (HE)

30. Muscle spindles stimulate reflexively a muscle contraction to prevent overstretching
and muscle fiber damage, this is known as the stretch or myotatic reflex
While stretching the muscle spindle,
an impulse is immediately sent to the spinal cord and a response to contract
the muscle is received, for protecting it from being pulled forcefully or beyond a normal range.
It is a very quick impulse, because the impulse only has to go to the spinal cord and back

31. Contraction of extarfusal fibers
-among the working fibers in paralel position, strech receptor
-control of muscle tone and fine, skilled movement
Contraction of extarfusal fibers

32. Golgi tendon organ
At the tendon-muscle junction (one after the other position)
Senses the tightness of muscle fibers
Respons to the tension
Thick, myelinated fibre type IB type
Protects again the too much tension
(stops the motoneuron in the spinal cord)
Die afferenten nervenfasern erreichen die Körperchen an deren Langsseite

33. Interoceptors including internal nociceptors, chemoreceptors, and mechanoreceptors, inform the CNS about the internal state of the body.
The carotid body, a specialized chemoreceptor for detecting carbon dioxide (in a hypoxic state) or to a lesser extent low blood pH resulting in increased respiration, is associated with afferent axons of CN IX that project to the caudal nucleus solitarius in the medulla.
The carotid sinus, a thin-walled region of the carotid artery, contains encapsulated and bare nerve endings that act as stretch receptors. These stretch receptors respond to increased arterial pressure as baroreceptors, send primary afferents to the caudal nucleus solitarius via CN IX, and elicit reflex bradycardia and decrease in blood pressure.

34. All of these are specialized synapses
Effectors
Neuromuscular ending
Neuroglandular ending
Neurohormonal ending
All of these are specialized synapses

35. Neuromuscular efferents
In Smooth muscle:
Bouton “en passant”
In striated muscle: motor end plate
or neuromuscular junction

36. Motor end-plate
A neuromuscular junction is the synapse of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potential across the muscle's surface, ultimately causing the muscle to contract.
This myoneural junction includes a complex infolding of the muscle membrane („subneural apparat”), the ridges of which contain nicotinic acetylcholine receptors. There is also a matrix in the synaptic cleft containing cetylcholinesterase,
involved in termination of action of the neurotransmitter.
Enzime histochemistry
Acetiycholine esterase

37. One motor neuron has connections with many muscle fibers through collateral branches of the axon. This is called the "motor unit" and can vary from a handful of muscle fibers per motor neuron in muscles of very fine control (such as eye muscles) up to several thousands (as in the gluteal muscles).

38. Neuroeffector Junctions
Autonomic postganglionic axons form neuroeffector junctions with (A) cardiac muscle, smooth muscle, (B) secretory glands or (C) metabolic cells such as hepatocytes, fat cells, and cells of the immune system.
These nerve endings terminate as neuroeffector junctions, releasing neurotransmitter into interstitial spaces. This permits a widespread diffusion of the neurotransmitter as a paracrine secretion, initiating postsynaptic responses on cells with appropriate receptors (including many types of cells of the immune system).
Not all smooth muscle cells
are innervated by neuroeffector junctions;
they are coupled by gap junctions and
can contract together when the
innervated smooth muscle cell
contracts

39. Nerve fibers group function diameter( μm) Conducting velocity(m/s)
Aα IA IB
Motor end plate efferent (extrafusal) muscle spindle afferent (primer) tendon organ afferent
12-20 myelinated
70-120
II II
Mechanoreseptor afferents in the skin muscle spindle afferent (secunder)
6-12 myelinated
30-70
Aγ III
Muscle spindle efferent mechano and theroreceptor afferents in the skin
2-5 myelinated
12-30
B III
Preganglionic sympathetic efferent deep mechaoreceptor afferent in the muscle
3 myelinated
C IV
Postganglyonic sympatietic efferent pain and thermo afferent
1 non-myelinated
0,5-2

40. Position of the fibers in the dorsal horn
thick fibers enter the horn medially
thin fibers enter more laterally

41. Introduction to the reflexes
A reflex is an involuntary, stereotyped response brought about by a sensory stimulus
CNS
afferent neuron
Efferent neuron
REFLEX arc
Receptor
Effektor
Althought the qualitative nature of the response is constant
it may vary in a quantitative sense due to supraspinal influences (in delay, duration, extent)

42. Thanks for your attention!
Crossman, A. R. Neuroanatomy, illustrated colour text, 2010, Elsevier
Barr, M.L., Kiernan, J.A. The Human Nervous System. An Anatomical Viewpoint. Philadelphia, 1993.
Burt, A.M., Textbook of Neuroanatomy W.B. Saunders Company
Kahle, W., Leonhardt, H., Platzer, W. Color Atlas/Text of Human Anatomy, Vol. 3. Nervous System and Sensory Organs. Stuttgart, New York, 1993.