Nervous tissue fibres synapses receptors effectors Dr Zita

Nervous tissue: fibres, synapses receptors, effectors Dr. Zita Puskár EDI 30/11/1018

Axons Myelinated (enclosed within special sheet) Unmyelinated

Myelinated axon

Myelin sheath in the CNS The myelin sheat is formed by the processes of oligodendrocyte. One oligodendrocyte myelinate parts of several axons.

Composition of myelin MBP: Myelin basic protein PLP: Proteolipid protein 40% water, 70 -85% lipid és 15 -30% protein

Myelination in the periphery internodium Axons are sheated by Schwann cells.

http: //www. youtube. com/watch? v=DJe 3_3 Xs. BOg

A portion along the axon sheated by the Schwann cell is the internodal segment. Unmyelinated part of the axon between two internodal segments is the node of Ranvier. The node of Ranvier is covered by basement membrane produced by the two neighbouring Schwann cells. Schmidt-Lantermann clefts: nexus, punctum adherens → diffúsion path, maintenance

Unmyelinated axons PNS CNS Peripheral Nervous System (PNS) Central Nervous System(CNS) More than one axon is engulfed by Schwann cells Free axons. Only astrocyte endfeets are attached to them. They are not sheated at all.

Excitable membranes

Functions of the myelin sheath: saltatoric conduction

http: //www. youtube. com/watch? v=DJe 3_3 Xs. BOg

Functions of the myelin sheath: regeneration

Nerve fibers Nerve fiber: Axon (neurit) + glial sheath (if exists) Boundles of nerve fibers form tracts in the CNS

Boundles of nerve fibers form the peripheral nerve in the periphery Fascicles Sensory and motor fibers are mixed generally in the peripheral nerve

Connective tissue sheaths of the peripheral nerve Endoneurium: loose connective tissue with reticular fibres around each fibre Perineurium: myofilament containing, flat, epithelial like cells among circularly arranged connective tissue fibres around each fascicles (1 -10 layers). The cells attached to each other by tight junctions and form diffusion barrier. Blood vessels are located in this layer. Epineurium: connective tissue sheath containing long, wavy collagen fibres around the nerve. It contains larger blood vessels. Paraneurium*: loose connective tissue.

Peripheral nerve fibers Conduction velocity and diameter A fibers B fibers C fibers 1 -20 µm Ø 1 -3 µm Ø 0, 5 -1 µm Ø 70 -120 m/s 3 -60 m/s 0, 5 -2 m/s M S, N Pr N, Po M: motor, S: Sensory, Pr: preganglionic N: nociceptor, Po: postganglionic

Sclerosis Multiplex

Interneuronal communication: synapsis Classification: (1) pre-and postsynaptic elements : axo-axonic, axo-dendritic, axosomatic, dendro-dendritic , (2) modalities of the transmission (electronical, chemical), (3) postsynaptic effect (excitatory, inhibitory), (4) morphology: simple, composed

Axo-dendritic, axo-somatic, axo-axonic, dendro-dendritic szinapses

Electrical and chemical synapses bidirectional

Electrical synapses Connexon-6 connexin Synaptic cleft: 2 nm Exchange of ions, small molecules Bidirectional connection Sensory cortex, cerebellar cortex, retina, bulbus olfactorius

Chemical syanpses Composition: presynaptic element (axon terminal) • vesicles containing neurotransmitter, • presynaptic membrane, Synaptic cleft: 20 nm synaptic cleft Unidirectional connection Postsynaptic element (soma, dendrite) Postsynaptic membrane specialization with receptors

Inhibitory or excitatory synapses

Simple or composed synapses Simple glomerulus (composed) thalamus, spinal cord

http: //www. youtube. com/watch? v=90 cj 4 NX 87 Yk

Classification of sensation Special General/Somatic Special sense organ No special sense organs Vision, hearing, balance, sense of smell or touch, thermal, pain (nociception), taste movement mozgás Somatic sensation receptor location function exteroceptor skin touch, pressure, vibration, heat -cold, pain proprioceptor muscle, joint, tendon, deep tissues, vessels posture, movement (kinesthesia), deep pressure interoceptor internal organs (viscera) homeostasis, organ functions Exteroceptor: information from the outside world Proprioceptor: information about the skeleto-muscular system, deep tissues Interoceptor: information about the state of the internal organs Sherrington (1906)

Sensation - Perception - Response Central Nervous System somatosensory afferents viscerosensory afferents receptor visceromotor efferents somatomotor efferents effector stimulus skin, muscle tendon (outside world) viscera glands, smooth muscles striated muscles

Receptor molecules light ions small molecules proteins Receptors – special protein complexes Location: cell membrane, cytoplasm, nucleus Activation: binding of specific molekules (ligands) or direct energy (heat) Consequences: ion movement and/or activation of second messanger systems resulting in specific cell response. stimulus → receptor activation (transduction) → (nerve)impulse

Receptor cell Secondary sensory epithelium Primary sensory epithelium Olfactory epithelium Hair cells Taste bud

Sensory receptors

Free nerve ending Thin myelinated (Aδ) or unmyelinated (C) afferent nerve endings containing complex receptor molecules. It can be thermo-, cold receptor or nociceptor (responds to damaging or potentially damaging stimuli)

Nociceptors Polimodal nociceptor Stimuli: mechanical, heat, chemical Mechano-cold nociceptor Stimuli: mechanical, cold Insensitive to mechanical stimuli Michael S. Gold & Gerald F Gebhart (2010) Nature Medicine, 16: 1248 -1257

Mechanoreceptors of the skin Merkel Meissner Vater-Pacini Ruffini

Tactile (Merkel) Cell Mechanoreceptor cells that are activated by (light) pressure. They are located in the str. basale of the epithelium containing keratin and few melanosome. Basolateral surface of the cells contact the terminal discs of sensory fibers (Aβ).

Tactile (Meissner) - Corpuscle Mechanoreceptor that is activated by light pressure (touch). It is an ellipsoid shape structure enclosed by a connective tissue capsule (40 x 100 μm). MC is located in the dermal papillae. It consists of 5 -10 of flattened layers of cells, each with an elongated nucleus. The (Aβ) nerve ending loosing its myelin sheath is coiled among these cells.

Ruffini Corpuscle Ruffini’s present to Sherringtonnak Oxford University It is encapsulated cilindrical structure. The RC is a tension (mechano) receptor. The structure is very similar to the Golgi tendon.

Vater-Pacini corpuscle It is an encapsulated mechanoreceptor that is activated by course or sustained touch and vibration. It consists of connective tissue capsule with elastic fibres, outer lamellar and inner cylindrical structure. Lamellae: perineural cells (50 -60 layers) and gel. Inner cylinder: unmyelinated nerve ending surrounded by circularly arranged Schwann cell layers and fluid. Location: dermis, joints, tendons

Vater-Pacini corpuscle

Krause - corpuscle Encapsulated mechanoreceptor. It is activated by tension. (Location: lips, tongue and genitals (erogen zone).

Muscle spindle (stretch receptor) Detects changes in the length of the muscle → regulation of the contraction of the muscle (stretch reflex)

Muscle spindle

Golgi tendon organ Detects the changes in muscle tension

Smooth muscle Glands Effectors Striated muscle

Nociception

Somatosensory system

Irodalom: Röhlich Pál: Szövettan. Budapest, 2006 Eric R. Kandel, James H Schwartz and Thomas M Jessel: Principle of neural science, New York, 2000 Anthony L. Mescher: Junqueira’s Basic Histology, New York, 2010 Michael Ross and Lynn J. Romrell: Histology, Baltimore, 1989