rdNR in RA- is MOTOR NR. ( in ventral horn of sp. cord).

Embryonic origins:A) for NRs of C NS (brain and sp. cord) – are neuroblasts of MANTLE zone of NEURAL TUBE. B) for NRs of P NS (of ganglia) – are neuroblasts of NEURAL CREST.

Crest also give rise to: Satellite cells of ganglia and – to Schwan cells of nerves.

GLIAL cells (supporting cells) of C entral N ervous S ystem (CNS):

1) PROTOPLASMIC astrocytes. It locate in GRAY matter of C NS.

2) FIBROUS astrocytes. It locate in WHITE matter of C NS. Struct.: both types have many cytoplasmic processes. Funct.: a) support high concentration of K+ ions between neurons; b) form blood-brain barrier; c) form cellular SCAR in damaged areas of CNS

3) OLIGODENDROCYTES. Occur in both gray and white matter. Funct.: participate in FORMATION of nerve FIBREs. In MYELINATED nerve FIBRES these cells produce MYELIN SHEATH. Injury of those cs is accompanied by DEmyelination disease.

4) EPENDYMAL cells. It line wall of brain VENTRICLES and CENTRAL CANAL of sp. cord. It are cuboidal cells with apical CILIA. Funct.: it participate in secretion and movement of CEREBROSPINAL fluid.

5) MICROGLIAL cells. It originate from MONOCYTes and are macrophages of nervous tissue. Funct.: phagocytosis of damaged neurons.

GLIAL cells (supporting cells) of P eripheral N ervous S ystem (P NS).

P NS includes: a) ganglia and b) spinal and cranial nerves.

1. SCHWAN cells. It locate in peripheral nerves. Funct.: participate in FORMATION of nerve FIBREs. In MYELINATED nerve FIBRES these cells produce MYELIN SHEATH. Injury of those cs is accompanied by DEmyelination disease.

2. Satellite cells. It locate in all GANGLIA, surrounding perikaryones of neurons.

NERVOUS TISSUE. part 2. NERVE FIBRES. NERVE ENDINGS.

NERVE FIBRES(= NF s).

There are 2 types of NFs: 1) MYELINATED NFs (= M NFs) and 2) UN myelinated NFs.(= U NFs).

BOTH types of NFs form peripheral NERVE and white matter of C NS..

Structure of M NF on the cross section (from centre to periphery):

1. One AXON of neuron is in the centre;
2. MYELIN SHEATH (=MS) surrounds axon;
3. NEURILEMMA surrounds myelin sheath.

MS – is spirally wrapped plasma membrane of SCHWANN cell (in peripheral NERVE) or of OLIGODENDROCYTE (in brain and spinal cord). Chemically MS is composed of phospholipids. Neurilemma – is cytoplasm with nucleus of SCHWANN cell (in P NS) or of OLIGODENDROCYTE. It means: nerve fibre is formed by 2 cell types:

1. NEURON gives 1 AXON for fibre,

2. SCHWANN cell or OLIGODENDROCYTE give myelin sheath and neurilemma.

Structure of M NF on the longitudinal section

1. AXON of neuron is in the centre. Plasma membrane of axon is AXOLEMMA.Funct.:it conducts nerve impulse,
2. INTERNODAL segment s. Segment corresponds ONE SCHWANN cell (in P NS) or OLIGODENDROCYTE(in C NS). Segment contains MYELIN sheath.,
3. Nodes of RANVIER. Node corresponds junction BETWEEN adjacent Schwann cs or olygodendrocytes. Node does NOT contain myelin sheath.

Structure of U NF on the cross section (from centre to periphery):

1. Several UN myelinated AXON s of several neurons are in cytoplasm of Schwann cell or olygodendrocyte;
2. NEURILEMMA surrounds several axons,
3. Double-membrane mesaxons binds each axon with Schwann cell plasma membrane.

SYNAPSES. (= SP s).

SP s – are specialized junctions between 2 neurons (interneuronal SPs) or between neuron and muscle fibre (myo-neural junction). In SP nerve impulse is presented by chemical messengers named NEUROTRANSMITTERS (= NT s).

SP is composed of: 1) PREsynaptic membrane, 2) Synaptic CLEFT, 3) POSTsynaptic membrane.

Presynaptic membr. is formed by axonic terminal of previous neuron. It contains synaptic vesicles with NT s. Examples of NT s: a) ACETYLCHOLINE, b) NORADRENALINE (or norepinephrine). Group of SPs, containing acetylcholine - are CHOLINERGIC SPs. Group of SPs, containing noradrenaline - are ADRENERGIC SPs. Post synaptic membr. contains RECEPTORs molecules, recognizing NTs. This membr. may be formed by 3 components of following neuron: a) by perikaryon. Type of so SP – is axo- somatic SP; b) by dendrite of next neuron. Type of so SP- is axo- dendritic SP; c) by axon of second neuron. Type of so SP – is axo- axonic SP. (a,b,c – are morphologic types of interneuronal SPs).

SP between axon terminal and muscle fibre – is myo-neural junction. It belongs to group of MOTOR nerveendings:a) pre synaptic membr. is formed by axonic terminal of neuron, BUT b) post synaptic membr. is formed by muscle fibre SARCOLEMMA (contains receprors to NTs). Functioning of NTs in synaptic cleft provide CONTRACTION of muscle fibre.

N ERVE E NDINGS. (= NEs). Includes 3 groups:

1. MOTOR NEs - it is myo-neural junction. It provides contraction of muscle fibre.
2. SECRETORY NEs – it is SP between axon and exo-/endocrine GLAND. It provides secretion of secretory product.
3. SENSORY NEs (or receptors). It are formed by DENDRITE terminal. Group of sensory NEs, perceiving touch, stretch, pressure – are MECHANORECEPTORS. Such as:a) MERKELs disks: unmyelinated dendrite terminal is surrounded by Merkel cells. Disks locate in skin. Funct.: to perceive discriminatory touch. b) MEISSNERs corpuscles: three unmyelinated dendrite terminals are surrounded by Schwann cells and connective tissue CAPSULE. Corpuscles locate in skin dermis. Funct.: for tactile discriminaton. c) PACINIAN corpuscles: one unmyelinated dendrite terminal is surrounded by Schwann cells+ by fibroblasts +by connective tissue CAPSULE. It locate in skin dermis and joints. Funct.: to perceive pressure, touch and vibration.

Составитель – доцент В.В. Бондаренко.

Дата добавления: 2015-10-31