Nervous system. The main regulation mechanism of organism's functions

Transcription

1 Nervous system The main regulation mechanism of organism's functions

2 Questions Neuron The reflex arc The nervous centers Properties of the nervous centers The general principles of coordination Inhibition in the CNS Spinal cord 2

3 Classification according to a structure and function: 3

4 Nervous system Grey matter White matter Neuron bodies Processes of nervous cells 4

5 Neuron is structural and a functional unit of nervous system 5

6 Classification of neurons: 6

7 Classification of neurons by function neurons Sensory (afferent) neurons transmit impulses from skin and other sensory organs or from various places of the body to the CNS Contact (intercalary, association) neurons provide communication between neurons. Motor (efferent) neurons transmit impulses from the CNS to effectors (muscles or glands) 7

8 Functions of the nervous system Perception of external and internal stimuli, the organization of corresponding adaptive reactions. The nervous system provides the behavior organization. Nervous system integrates and monitors the countless actions occurring simultaneously throughout the entire human body. NS is a material basis of mental activity. There are speech, thinking, consciousness. 8

9 Reflex - the basic form nervous activity. The answer of an organism to a boring of receptors with the assistance of a CNS. A reflex arc is the neural pathway that mediates a reflex action. Reflex arch Simple Monosynaptic Complex Polysynaptic (with contact neurons) 9

10 Reflex arch consists of 5 main parts 10

11 1. The receptor perceives a irritation, transforms energy of a irritation into energy of nervous impulse. The receptor exteroreceptors interoreceptors proprioreceptors senses by which we perceive the outside world (receptors of a skin, eye, ear, nasal cavity, etc.) senses, by which we perceive the pain and movement of internal organs (receptors of vessels, internal organs) react to change of body parts position in space (receptors of muscles, ligaments, tendons) 11

12 2.An afferent a nervous way - processes of receptor neurons which transfer the information to the nervous center. 3.The reflex (nervous) center (is located in the CNS) - group of neurons, which transfer nervous impulses from afferent to efferent nervous way 4.An efferent a nervous way transfer the information to an effektor. 5. An effektor organ, which can answer the impulses. The impulse causes changes of its activity. 12

13 The nervous centers The nervous center is: Anatomic definition: the anatomic clump of the neurons are located in certain department of a CNS. Physiological definition: functional association of the several (anatomic) centers are located at different levels of a CNS, which provide difficult reflex acts (digestion, breathing, etc.)

14 Properties of the nervous centers depend on mechanisms of conduction of excitation in synapses 1. One-sited conduction of excitation. It is transferring of impulse from receptor neuron to effector. It is caused by presence of synaptic transfer of excitation where it is possible only in one site (from presynaptic to a postsynaptic membrane). 2. The delay of conduction of excitation it is caused by presence of a considerable quantity of synapses, mediator releasing, diffusion through synaptic cleft. Excitation of a postsynaptic membrane demands time it is called synaptic delay" 3. Summation of excitation (subliminal stimulus are summated): summation in time - numerous irritation of receptor by subliminal stimulus causes a reflex. spatial summation - irritation of receptors of reflex zones by subliminal stimulus at the same time. 14

15 4. Transformation of rhythm excitation capacity of nervous center exchange rhythm of impulses, that transfer from afferent ways; 5. Afteraction of excitation circulation of impulses on chains of nervous center; 6. Fatigue of nervous center efficiency decreasing, this is due to disorder of synaptic transmission, attrition of mediator`s pull and depression of receptors sensitivity to a mediator (adaptation); 7. The tonus of the nervous centers is supported by an afteraction of excitation by afferent impulses, humoral influences 8. Plasticity of the nervous centers ability to change characteristic function for them (dysfunction of brain's parts are provided by other centers) 15

16 The general principles of coordination Function of organism Coordination - interaction of nervous processes in the CNS, referred on association (integration) of organs` functions and systems. 1. Morphological principles depend on features of a structure of nervous system 2. Functional principles depend on functions of nervous system 16

17 Morphological principles Divergence principle neurons are capable to form numerous synaptic communications with other neurons from which there is a redistribution of impulses. 17

18 Morphological principles Convergence principle concentration of excitation from different neurons to one. 18

19 Morphological principles Principle of the general final way - afferent fibers converge on the same intercalary efferent neurons. Feedback principle control of accuracy of impellent reflexes. 19

20 Functional principles 1.Irradiation of excitation (diffusion) long strong excitation causes excitation of many nervous centers. 2.Concentration of excitation. 3.Induction excitation of the certain nervous center leads to opposite process inhibition of the center bound to it. 20

21 Dominant principle separated strong excited center inhibits all other centers. 21

22 Inhibition in CNS Is active nervous process, form of the response to a influence which is manifested by inhibition or excitation decreasing Inhibition types According to connection with inhibitory neurons As consequence of excitation presynaptic postsynaptic The return pessimal 22

23 Presynaptic inhibition Development of a slow and long depolarization of the presynaptic termination of excitable neuron is inhibited by neurotransmitter blockade of carrying out of excitation 23

24 Postsynaptic inhibition Postsynaptic membrane is inhibited by neurotransmitter 24

25 The return inhibition - Oppression of activity of neuron by a return collateral of an axon. Pessimal inhibition - A high frequency of a stimulation of the neuron causes an inhibition after excitation 25

26 Value of inhibition The organism adaptation to environment Remission of the CNS of processing of the insignificant information; Coordination of motor reactions; Protection of the nervous centers from fatigue and attrition 26

27 Structure of spinal cord 27

28 Spinal cord The spinal cord is the most important structure between the body and the brain. The spinal cord extends from the foramen magnum where it is continuous with the medulla to the level of the first or second lumbar vertebrae. It is a vital link between the brain and the body, and from the body to the brain. The spinal cord is 40 to 50 cm long and 1 cm to 1.5 cm in diameter. Two consecutive rows of nerve roots emerge on each of its sides. These nerve roots join distally to form 31 pairs of spinal nerves. These nerves are divided into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal nerve. The spinal nerve contains motor and sensory nerve fibers to and from all parts of the body. The spinal cord is a cylindrical structure of nervous tissue composed of white and gray matter. The gray matter contains the nerve cell bodies and all of the many thousands of connections between nerves. The white matter is more like a freeway composed of nerve axon fibers traveling long distances from the spine to the brain. The ventral root carries motor axon fibers from cells in the gray matter out to the muscles. Incoming sensory signals pass through a connection - or synapse in the dorsal root ganglion, and then follow the dorsal root into the grey matter. 28

29 Segment and covers of spinal cord 29

30 Spinal cord covers The cord is sheathed in the same three connective tissue meninges as is the brain: the pia (vasculosa), arachnoid (serosa) and dura (fibrosa). The dura is the tough outer sheath, the arachnoid lies beneath it, and the pia closely adheres to the surface of the cord, blood vessels are located in there Cerebrospinal fluid (CSF) is located between it and pia mater (vascular). 30

31 Spinal cord Grey matter is White matter is Contact neurons Body and dendrites of motor (efferent) neurons Axons of neurons, which form: descending (motor) tracts ascending (sensory) 31 tracts

32 Functions of spinal cord Reflex function participation in impellent reactions Conduction transfering of nervous impulses Reflexes of muscles of antagonists: reduction flexor oppression of a tonus of extensors Rhythmic reflexes: alternate action flexor and extensors of extremities (walking, run) Tonic reflexes maintenance of position of a body in space (a long strain of muscles) Vegetative reflexes regulation of work of an internal, vessels, muscles Connection of different departments of spinal cord; Connection of brain with other department of CNS; Поєднання receptors with виконавчими organs. 32