nervous system: is the system of communications,the aim of communications is to keep body...

Nervous system: is the system of communications,the aim of communications is to keep body homeostasis, N.S does its functions through a special steps: 1. Detection of the changes 2. Evaluation of the information 3. Responding property Classification of the nervous system: we can classify N.S according to its location or according to its functions.

1. Location of the NS: there are two types: a. central NS.(CNS)which is formed of the brain and the spinal cord. b. perpheral NS. (PNS) or the nerve, they are the axons of two types of neurons: 1. cranial nerves where their cell bodies are present in the brain, they are 12 nerve. 2. spinal nerves: their cell bodies are present in the spinal cord.

Afferent and efferent fibers: afferent: are all the incoming sensory fibers from periphery to the central nervous system. Efferent: are the outcoming motor fibers, carrying the orders from the CNs to the periphery. 2. according to the function: there are two types: a. somatic NS: which controls the skeletal muscles, one type is ordering the muscle movements (efferent), and the other is carrying the sensory impulses (afferent). b. autonomic NS: which is the system of viscera and is formed of two divisions. - Sympathetic system: is the system of fight and flight - Parasympathetic NS. The system of autonomic activity of the viscera

The nervous system is the most highly developed and perhaps the most important of all the system of the body. Not only does it correlate the activities of the other system but also in the brain is situated the site of conciousness, thought, memory, speech and the will to carry out purposeful actions. These factors all contribute to the formation of the personality of the individual. The basic unit of the nervous system is the individual nerve cell, or neuron

. Neurons can be devided into three functional classes: 1. Afferent (sensory)neurons afferent neurons transmit information into the central nervous system from receptors at their peirpheral ending. They are mostly (that is, the cell body and the long peirpheral process of the axon) outside the central nervous system, only the short central process of the axon enters the central nervous system. Afferent neurons have no dendrites.

1. Efferent (motor) neurons efferent neurons transmit information out of the central nervous systemto effector cells, particularly muscles, glands. They are mostly (that is, the cell body, dendrites, and a small segment of the axon) in the central nervous system, most of the axon is outside the central nervous system.

3. Interneurons (connecting neurons) interneurons function as integrators and signal changers. They integrate groups of afferent and efferent neurons into reflex circuits. They lie entirely within the central nervous system, and account fo 99% of all neurons.

Neurons have two characteristics: 1. Excitability ability of the plasma membrane to generate action potential, if a strong enough stimulus affect on it. 2. Conductivity the ability of the neuron to move the action potential from point to the next to it point. Conduction velocities range from about 0.5 m/s for unmyelinated fibers to about 100 m/s for myelinated fibers.

Action potential propagation once generated, one particular action potential does not travel along the membrane. Rather, the local current produced by one action potential serves as the stimulus that depolarizes the adjacent membrane to its threshold potential. The new action potential then produces local currents of its own, which depolarize the region adjacent to it, producing yet another action potential at the next site, and so on to cause action potential a propagation along the length of the membrane. The velocity with which an action potential propagates along a membrane depends upon fiber diameter and whether or not the fiber is myelinated.

The larger the fiber diameter, the faster the action potential propagates. In the myelinated fiber action potentials occur only at the nodes of ranvier where the myelin coating is interrupted and the concentration of sodium channels is high. Thus, action potentials literally jump from one node to the next as they propagate along a myelinated fiber, and for this reason such propagation is called saltatory conduction.

Propagation via saltatory conduction is faster than propagation in nonmyelinated fibers of the same axon diameter. If the fiber continuity is disrupted the action potential will not transmitted. Action potential normally transmitted only in one direction.

synapsis Neurons are connected with each other and from chains of neurons, the axon of one cell extending to the dendrite or body of another cell. The point at which an impulse (action potential) passes from an axon of one neuron to the dendrite or cell body of another is called a synapse

The signal from a presynaptic to a postsynaptic neuron is the neurotransmitter stored in synaptic vesicles in the presynaptic axon terminal. Depolarization within the terminal, which raises the calcium concentration within the terminal, causes the release of neurotransmitter into the synaptic cleft. The neurotransmitter diffuses across the synaptic cleft and binds to receptors on the postsynaptic cell, the activated receptors usually open ion channels. In the synapses the propagation is slower than in the fibers, and may even be delayed in them

Synaptic effectiveness are influenced by presynaptic and postsynaptic events, drugs, and diseases. Neurotransmitters are chemical substances, released from axon terminals of presynaptic. At most synapses, the signal is transmitted from one neuron to another by neurotransmitters. These chemical messengers diffuse across an extracellular gab to the cell opposite the terminal. Neurotransmitters bind to receptors on the plasma membrane of the postsynaptic cell. The result of the binding of neurotransmitter to receptor is the causing of the action potential

Neurotransmitter binding to the receptor is a transient event, and the ion channels in the postsynaptic membrane return to their resting state when the neurotransmitter is no longer bound. Unbound neurotransmitters are removed from the synaptic cleft when they enzymatically transformed into ineffective substances.

Control systems In order to synchronize the functions of the trillion of cells of the human body, two control systems exist. One, the endocrine system, a collection of blood- borne messengers, that works slowly, and for long term. The other is the nervous system, which is a rapid and short term control system. Together they regulate many internal functions and organize and control the activities we know as human behavior.

Parts of nervous system The various structures of the nervous system are intemately interconnected, but for convenience they are divided into: 1. Central nervous system (CNS) 2. Peripheral nervous system 3. Autonomic nervous system

Central nervous system central nervous system composed of the brain and spinal cord. Inside the skull and vertebral column, the brain and spinal cord are enclosed in and protected by the meninges. Spinal cord Spinal cord is divided into two areas: central gray matter, which contains nerve cell bodies and dendrites, and white matter, which surrounds the gray matters and contains myelinated axons organized into ascending (sensory) or descending (motor)tracts. The axons of the afferent and efferent neurons from the spinal nerves

Function of the spinal cord The main functions of the spinal cord are: 1. The spinal cord communicates through nerve fibers, its nervous pathways, with various parts of the brain and through spinal nerves with organs. The spinal cord contains two kinds of nervous pathway: ascending (sensory) and descending (motor). The spinal nerve also contain two types of nerve fiber sensory and motor. Nerve impulses are transmitted to spinal cord from the periphery, from organs, along sensory fibers of the spinal nerves, then conducted along the ascending nervous pathways to brain.

Nerve impulses are transmitted from the brain to the spinal cord along the descending pathways and thence along motor fibers of the spinal nerves to the periphery, the organs. These impulses alter the state of various organs

2. Reflex activity the spinal cord contains the reflex centers of various functions. Reflex is an involuntary, unpremeditated, unlearned built in response to astimulus. Examples of such reflexes include pulling ones hand away from a hot object or shutting ones eyes as an object rapidly approaches the face. The pathway mediating a reflex is known as the reflex arc.

A stimulus is a detectable change in the internal or external environment, such as a change in temperature, or blood pressure. A receptor detects the environmental change. A stimulus acts upon a receptor to produce a signal that is relayed to an integrating center. The pathway traveled by the signal between the receptor and the integrating center is known as the afferent pathway (the general term afferent means to carry to in this case, to carry to integrating center).

An integrating center often receives signals from many receptors, some of which may be responding to quite different types of stimuli. Thus, the output of an integrating center reflects the net effect of the total afferent input, that is, it represents an integration of numerous bits of information. The output of an integrating center is sent to the last component of the system, a device whose change in activity constitutes the overall response of the system.

This component is known as an effectors. The information going from an integrating center to an effector is like a command directing the effector to alter its activity. The pathway along which this information travels is known as the efferent pathway (the general term efferent means to carry away from , in this case, away from the integrating center).

Characteristics of reflexes: 1. Many reflexes are protective in character. 2. Reflexes are designed to obtain the quickest possible motor response 3. Some reflexes are concerned with automatic control of functions which do not require the supervision of consciousness. 4. Reflexes are specific: each stimulus has its own response. 5. Most reflexes are subject to alteration by learning.

Anatomically, the brain is composed of four subdivisions: cerebrum, diencephalon, brainstem, and cerebellum. The cerebrum and diencephalons together constitute the forebrain. The brainstem consists four interconnected cavities, the cerebral ventricles, which are filled with circulating cerebrospinal fluid. Brainstem brainstem is composed midbrain, pons, and medulla oblongata. The brain

Function of the midbrain : 1. Regulation of the cerebrospinal fluid circulation. 2. The gray matter forms the nuclei of third and fourth cranial nerves. 3. Joins the cerebral hemispheres above to the pons below. Function of the pons: 1. It acts a bridge between the two lobes of the cerebellum. 2. Nerve fibers pass up and down between the midbrain above and the medulla oblongata below. 3. The gray matter forms the nuclei of the 5 th,6 th,and 7 th cranial nerves.

Function of medulla oblongata: 1. Connects the brain with the spinal cord. 2. Contains fibers passing from spinal cord, forebrain, and cerebellum. 3. It contains also collection of gray matter known as vital centers. The most important of these are: a. the respiratory center which controls the rate and depth of respiration. b. the vasomotor center which controls the caliber of the blood vessels.

c. the cardiac center which influences the rate of the heart. d. special centers such as the swallowing, vomiting centers, centers for the movement of the stomach and the secretion of saliva and gastric juice. 4. The gray matter forms the nuclei of 9 th, 10 th, 11 th.12 th, cranial nerves.

cerebellum Function of the cerebellum 1. Coordinates movements, including those for posture and balance. 2. participates in some forms of learning. 3. it helps to maintain balance and equilibrium.

cerebrum The cerebrum consists of the right and left cerebral hemispheres. Functions of the cerebral hemispheres: 1. Contain the cerebral cortex, which participates in perception, the generation of skilled movements, reasoning, learning, and memory. 2. Contain subcortical nuclei, which participata in coordination of skeletal-muscle activity. 3. Contain interconnecting fiber pathways

Diencephalon (between brain) Diencephalon contains two major parts: the thalamus and hypothalamus. Functions of thalamus 1. Is a synaptic relay station for sensory pathways on their way to the cerebral cortex. 2. Participates in control of skeletal-muscle coordination 3. Plays a key role in awareness.

Function of hypothalamus: 1. Regulates the anterior pituitary gland. 2. Regulates water balance. 3. Participates in regulation of autonomic nervous system. 4. Regulates eating and drinking behavior. 5. Regulates reproductive system. 6. Reinforces certain behaviors. 7. Generates and regulates circadian rhythms. 8. Regulates body temperature. 9. Participates in generation of emotional behavior.

The physiology of the brain The brain is the control center of the whole human body. Physiologically it may be divided into the higher centers which are the seat of consciousness, mind, memory and will; and the lower centers which control many important unconscious acts. The higher centers are situated in the cerebral hemispheres while the lower ones are found in the cerebellum and brainstem as well as in the basal ganglia of the cerebrum.

The following mechanisms enable the brain to exercise this power of control: 1. It receive sensory or afferent impulses from all parts of the body, through the sensory pathway. 2. It is able to send out motor or afferent impulse from all parts of the body, through the motor pathway, which has two tracts: pyramidal(corticospinal) tract, which may be two kinds : straight or crossed, and extrapyramidal tract.

3. There is a complicated system of connection between all parts of the brain with each other. Projection fibers transmits the impulse from the brainstem to the cerebral cortex. Association fibers which are situated in the cerebral cortex transmits the impulse from one area to another within the same hemisphere. Commissural fibers transmit the impulse from one hemisphere to another one (from right to the left for example)

Functional regions All areas of the cortex are interconnected and the activity of each depends on the state of the entire cortex. however, the different regions differ in function and structure. These areas are: 1. The motor cortex area the motor cortex area is located in the frontal lobe from the cell of this area, voluntary motor impulses arises and are transmitted to the various groups of muscles in the body are represented in this area. The right cerebral hemisphere controls the left side of the body and vice versa

nervous system: is the system of communications,the aim of communications is to keep body...

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