nervous system video

Very good video about nervous system, review for Structure and Function Nervous System. Nervous system video below :

neuron network video

Neuron network in the brain. Neurons are very important member of the nervous system.

Central Nervous System Video

This video summarizes the main parts of the CNS and their major functions. Watch the video from Youtube below:

central peripheral autonomic nervous systems

Central Nervous System which has has the responsibility for issuing nerve impulses and analyzing sensory data, and includes the brain and spinal cord,

Peripheral Nervous System which is responsible for carrying these nerve impulses to and from the body and many structures, including the many craniospinal nerves which branch off the brain and the spinal cord, and the

Autonomic nervous system which is composed of the sympathetic and parasympathetic systems and is responsible for regulating and coordinating the functions of vital organs in the body.

brain healthy and tips

Now you know more about all the cool things you can do your brain. Your brain always takes care of you, so you return the favor! Try either the brain alimentándote well, exercising and getting enough sleep. Protegeles always using a helmet when practicing sports or going by bicycle. Do not drink alcohol or use drugs or smoke snuff - the cells in your brain abhor all these things, because destroy! Take care of your body's head and you will not disappoint - is working harder!

Location of emotions and brain

 With all the other things we do, are you surprised that the brain is responsible for your emotions? Maybe get the toy you wanted for your birthday and you're very happy. Or your friend is sick and you feel sad. Or your little brother you have the messy room and are very angry! Have you ever wondered where they come from those feelings? All come from the brain that controls all the emotions you feel. 

The brain has a small group of cells on each side called the amygdala. The word "amygdala" comes from the Latin word for "nuts" and that is the aspect that has this area. Scientists believe that the tonsils are responsible for emotions. So when you're sad about a friend who moves, your tonsils are working hard. But not everything that makes the amygdala is bad - also makes you feel excited when you win your soccer game. 

It's normal to feel all sorts of emotions, good and bad. Sometimes you can feel a bit sad and ask why. And sometimes you can feel scared, silly or happy. These feelings are part of what makes us human

The hypothalamus

Last but not least, the hypothalamus, which is right in the center of your brain, in the midst of the action. The hypothalamus is like the thermometer of your brain. Know what your body temperature should be (about 98.6 degrees Fahrenheit or 37 degrees Celsius) and transmits messages that tell your body whether to sweat or shiver. Why? Heat and sweat when you have a cold shiver when it is the manner in which your body tries to maintain constant temperature - irrespective of what they're doing or the external temperature. Do you remember the last time you ran and sudaste much? Your hypothalamus was able to realize that your run temperature was rising by so much and sent a message to your skin so that sudara. When you start to sweat, your body began to cool.

The pituitary gland

The pituitary gland is very small - is about the size of a pea! His job is to produce and release hormones in your body. If the clothes of last year I was very young, it is because the pituitary gland has released special hormones that you have made it grow. This gland also plays an important role during puberty. This is the time when the bodies of boys and girls go through major changes as they slowly become men and women - all thanks to hormones released by the pituitary gland. This small gland is involved with many other hormones, such as those that control the amount of sugar and water in the body. And keep your metabolism asset - your metabolism is everything that happens in your body to keep it alive and growing and to give you energy, like breathing, digesting food, and circulating blood

The hippocampus

The hippocampus is an incredibly great, because the use to remember the way to school! The hippocampus is part of the cerebral cortex and is the area of the brain that handles memory. There are different kinds of memory: these are two of the calls short and long term. Try to remember what you have breakfast today - this is an example of the short-term memory. This is information that your brain has just received. Now think of your first day of school or at the birthday party last year. These are examples of events saved on your long-term memory. 

Your hippocampus is the great task of transferring information between memories in the short term and long term. It's hard work, but the hippocampus is always there, making sure you remember the little things, like where you left your yo-yo, and also the big things, like vacations where you went camping for two summers.

The brainstem

The brainstem 

Another part of the brain that is small but powerful is the brainstem that is located below the cerebral cortex and cerebellum ahead. The brainstem connects the rest of the brain to the spinal cord, which covers your neck and back. The brainstem handles all the functions necessary to ensure that your body is alive, such as breathing, digestion of food and blood circulation. 

Part of the role of the brainstem is to control involuntary muscles - those that run automatically, without thinking what. There are involuntary muscles in the heart and stomach, and is the brainstem who tells your heart to pump more blood when you go by bicycle or on your stomach to digest this piece of birthday cake you just eat. (Remember the cortex that controls voluntary muscles. Monitor all the muscles of the body is too big a task for part of the brain!). The brainstem also classifies the millions of messages that the brain and the rest of the body are sent. Uf! It's enough work to be the secretary of the brain!

The cerebellum

The cerebellum 


The next part is the cerebellum. The cerebellum is in the back of the brain, below the crust. It is much smaller than the cerebral cortex, only 1 / 8 of its size. But do not let the small size of the cerebellum fool you - is working hard between racks, controlling the balance, movement and coordination (how your muscles work together). Thanks to the cerebellum can stop you erect, maintain balance and move from side to side. Think of a surfer uploaded to your table on the waves. What is it that more needs to maintain balance? The best table? The suit cooler? None of this - you need your cerebellum!

nervous system

The nervous system controls everything you do, for example, breathing, walking, what you think and what you feel. This system consists of the brain, spinal cord and all the nerves of the body. The brain is the control center and the spinal cord is the main highway that connects with him. Nerves transmit messages to the body and from the brain to interpret and act accordingly.

nerve tissue

Nerve tissue 

Nerve tissue is composed of interconnected neurons. Between the Blutkapillaren glial cells connect with other neurons and glial cells. Through these nerve cells is associated nerve tissue from other tissue types identifiable. Nerve tissue is mainly in the brain, spinal cord and peripheral nerves to find, but also at the gut (→ Enteric Nervous System) and in the retina are net related nerve cells. 

In the living organism has the nerve tissue the color pink to white. In the gray matter outweigh nerve cells. The white matter consists of cable railways, the myelinhaltigen nerve fibers. In the white matter, networking is low.

Nerve tissue leads selectively excitement of receptors on the success of organs. The gray matter processed, the white heads.

nervous system pictures building

Building 
 
Schedule a nerve cell . Basic building block of the nervous system is the nerve tissue. It consists of interconnected nerve cells (neurons), whose cell body as Somata or Perikarya and their survival rates than nerve fibers (axons and dendrites) respectively. 

At higher organisms, the nerve tissue from a network of neurons and glial cells many places to dock. The latter support the activity of nerve cells, without directly to the transmission of stimuli to be involved.

Cephalopods and vertebrates nervous systems

Cephalopods and vertebrates 

Especially highly centralized systems are the nerves of cephalopods and vertebrates. They are a great many functions of the nervous system and muscles of the centrally controlled. It therefore speaks of a central nervous system. This consists of the brain and the spinal cord.

The outside of the central nervous system underlying neural structures to be counted peripheral nervous system. The peripheral nervous system is divided into the somatic nervous system and the vegetative nervous system (including visceral or autonomous nervous system, consisting of sympathetic, and enteric nervous system Parasympathikus) broken. The vegetative nervous system is primarily concerned with controlling the activities of the outside of consciousness expiring body functions.

Arthropod nervous system

Arthropod 
 
Schematic construction of a knitting head of nervous system 

In the arthropod is already in the training of higher processing centers in the form of several nerve knots (ganglia). These ganglia are two nerves like knitting heads together, so we here of a knitting nervous talking head. For most of these animals is particularly great Oberschlundganglion trained. It already assumes the functions of a "brain", especially the processing of sensory stimuli. The ganglia of body segments often control the movements of the leg and wing muscles largely autonomous. The knitting head nerve systems (with the exception of the upper pharyngeal Gang Lions) below the digestive system. Therefore, one speaks also of abdominal Mark.

Evolution

Evolution 

In the course of evolution and with the higher development of individual departments of the animal kingdom is a clear trend towards concentration and associated specialization of parts of the nervous system noted. While in primitive animals, yet some individual neurons fall special functions (eg pacemaker neurons, the clock for elementary body movements of worms pretend), to perform highly complex nervous systems of up to several billions of interconnected neurons in specific tasks. 

In nervous systems with Zentralganglien the conduction of neurons in Afferenzen (from the sensors to the brain) and Efferenzen (from effectors to the brain, muscles, for example) are divided.

nervous

Nervous 
 
Overview of the human nervous system 

The term nervous system (Systema nervosum lat) is the totality of nerve cells in an organism and describes how they arranged and connected. It is an organ system of higher animals, which has the task to provide information on the environment and the organism record, process and reactions of the organism action to optimal to react to changes. The nervous realized one of the basic properties of life, the irritability (irritability).

Pain sensation

Pain is induced by mechanical damage of tissue cells.
•As a result of damage bradykinin like peptides are released.
•These peptides lead to the stimulation of IV type afferent fibers in the region
Pain sensation is transmitted to the brain by anterolateral pathway.
•The type IV afferents synapse on the neuron in lamina I and IV region of spinal gray matter.
•These second order neuron are inhibited by somatosensoric large afferent fibers.

•That is why the pain sense can be decreased by mechanical stimuli applied from same dermatomal region of pain.

Spinal Cord

•The spinal cord is the part of the central nervous system that is surrounded and protected by vertebral column.
•In cross section, the spinal cord is organized as a butterfly shaped mass of gray matter surrounded by white matter.

•Gray matter of spinal cord are designated as name or romen numeral.
•The neuron cell bodies are organized into three discrete areas of the gray matter: the dorsal horn, the intermediate zone, and the ventral horn

•The CNS is made up not only of the brain, but also the spinal cord.
•The spinal cord is a thick, hollow tube of nerves that runs down the back, through the spine.

•The ventral horn contains the motor neuron bodies for the somatic motor system.
•The white matter contains many sensory tracts ascending to the brain and motor neuron axon descending from the brain

Receptor or Sensory Cell

•There are various type of the receptor cells. They are classified according to their sensitivity to different physical stimuli.
•For example chemical receptors only are stimulated by chemical stimuli.
•Photoreceptors are stimulated by light


•Mechanoreceptor by mechanical stimuli
•Baroreceptor by pressure
•Mechanical receptors are two type: phasic receptor (Paccini corpuscle), tonic mechanoreceptor (Strech receptor on the wall of urinary blood).


•Phasic receptor generate action potential only at the begining of stimuli, but tonic receptor is stimulated continously in the presence of stimuli.
•Photoreceptor found in the retina of eye.
•Baroreceptor found in the wall of blood vessel, they are free nerve ending


•Pain receptor is also free nerve ending and are stimulated chemical mediators relased from damaged cell.
•Chemoreceptors are found in tongue, olfactory nasal region.
•Receptors are localized in certain region of the body. Every receptor can be stimulated by the stimuli applied to region that they are localized.


•Information from around of the body are coded to the central nerveous system by the frequency of action potential.
•Olfactory stimuli is coded by the action potential frequency, since all receptor cell in olfactory region have more than one receptor molecule for different oder stimulant.


Intensity of pressure is also coded by action potential frequency

Anatomy of Vertebrate Nervous Systhem

•Nervous system of animals examined in two region
•Peripheral nervous system; sensory neurons, afferent and efferent nerves and ganglia
•Central Nervous system; Spinal cord and brain


•Somatic afferents and efferents innervate somatic organs that are voluntarily controlled.
•Autonomic afferents and efferents innervate autonomic organs such as heart and digestive channal.
•Cranial nerves innervate usually the muscle and gland of head. They originate from brain stem


•Sensory or receptor cells are stimulated by physical stimuli and localized in various sensory region of the body.
•Environmental information is only recieved by receptor cell or sometimes free afferent nerve endings

Peripheral nervous sytem

•Peripheral nervous sytem comprise peripheral nerves; afferent and efferent, recepors or sensory cell, and autonomic ganglia.
•Afferent nerves carry impulses from sensory cell to the spinal cord or brain.
•Efferent nerves carry impulses from spinal cord or brain to the effector organs (Muscle etc.).

•There are two kind of afferent nerves; somatic, visceral.
•Afferent nerves enter into the cord dorsally, efferent nerves leave the cord ventrally.
•There are two kind of afferent and efferent system.

peripheral nervous system.

Neuron structure

Neurons all have same basic structure, a cell body with a number of dendrites and one long axon

Nerve Tissue and Nerve cells in Animals

•Nervous systhem is composed of various cells having different function.
•Neuron is basic cell type.
•Other cells are; astrocyte, microglial cells, oligodendrocytes, shwann cells, ependimal cells

•Neurons have two extension: long one is called as axon, short one dentrites.
•Neurons can be classified acording to type of extension: Unipolar, bipolar, Multipolar.
•The majority of invertebrates interneurons and motorneurons are unipolar.


•Astrocytes provide connection between capillaries and neurons.
•Oligodendrocyte make myelin sheeth
•Microglia are phagocytic, motile cells that engulf and destroy cellular debris and microbes.

•Glial Cells are three type: Astrocyte, oligodentrocyte, microglia.


•In the peripheral nervous system, myelin is formed by Schwann cells.
•Each Schwann cell associates with only one axon, when forming a myelinated internode.

Vertebrate Nervous System

•The organization of the vertebrate nervous system is different from invertebrates.
•Vertebrates have a well-organized hollow dorsal nervous system.
•The central nervous sytem inclued a brain and spinal cord.
•The peripheral nervous sytem comprise peripheral nerves extending from spinal cord and peripheral ganglia

Nervous System Generally Informations

Nervous sytem of human body; tasting, smelling, seeing, hearing, thinking, dreaming, breathing, heart beating, moving, running, sleeping, laughing, singing, remembering, feeling pain or pleasure, painting, writing all of these activites are depend on nervous system of our body.

you couldn't do any of these things without your central and peripheral nervous system.

so what is the nervous system?

answer : composed of your brain, your spinal cord, and an enormous network of nerves.

it's the control center for your entire body.

The brain uses information it receives from your nerves to coordinate all of your action,reaction

RESPONSE OF NERVE TISSUE TO INJURY

ØA. Damage to the Cell Body: Because mature neurons cannot divide, dead neurons cannot be replaced. Neurons not connected with otherfunctioning neurons or end organs are useless, and mechanisms have evolved to dispose of them. Thus, if a neuron makes synaptic contact with Only one other neuron and the latter is destroyed, the former undergoes autolysis, a process termed transneuronal degeneration. Most neurons, however, have multiple connections.
ØB. Damage to the Axon: Regeneration can occur in axons injured or severed Far enough from the soma to spare the cell. Such injuries are followed by partial degeneration and then regeneration. Nervous system
Ø1. Degeneration. A crushed or severed axon degenerates both distal and proximal to the injury. Distal to the site Of injury, both the axon and myelin sheath undergo complete degeneration connection with the soma has been lost. During this Wallerian, descendent, or secondary degeneration, whichusually lakes about 2-3 days, nearby Schwann cells proliferate, phagocytose degenerated tissue, and invade the remaining endoneurial channel. Proximal to the site of injury, degeneration of the axon and myelin sheath is similar but incomplete. This retrograde, ascendent, orprimary degeneration proceeds for about 2 internodes before the injured axon is sealed. The cell body also changes in response to injury. The perikaryon enlarges; chromatolysis, or dispersion of Nissl substance, occurs; and the nucleus moves to an eccentric position. Proximal degeneration and cell body changes fake about 2 weeks. 2. Regeneration. This begins in the third week after the injury. As the perikaryon gears up for increased protein synthesis, the Nissl bodies 'eappear. The axon's proximal stump gives off a profusion of smaller processes called neurites; one of these encounters and grows into the endoneurial channel, while the others degenerate. In the channel, the neurite grows 3-4 mm/d, guided and then myelinated by the Schwann cells. Growth is maintained by orthograde axoplasmic transport of material synthesized in the soma. When the tip of the neurite reaches its termination, it connects with its end organ or another neuron in the chain. If the cut ends of a severed nerve are matched by by fascicle size and arrangement and sutured together by their epineurial sheaths within 34 weeks after injury, sensory and motor innervation can often be restored. If the gap between the cut ends is too wide, the neurites may fail to find endoneurial sheaths to grow into and may grow out in a potentially painful disorganized swelling called a neuroma. Target organs deprived of innervation often atrophy.

HISTOPHYSIOLOGY OF NERVE TISSUE

ØA. Axoplasmlc(Axonal) Transport: Movement of metabolic products through the axoplasm Can be fast (up to 400 mm/d) or slow (eg, 1 mm/d), and it involves neurotubules and neurofilaments. Anterograde or Orthograde axoplasmic transport moves newly synthesized products and synaptic vesicles toward the axon's terminal arborization and can be fast or slow. Retrograde axoplasmic transport, the return of worn materials to the perikaryon for degradation or reutilization, is usually relatively fast.
ØB. Signal Generation and Transmission: The basic function of nerve tissue is to generate and transmit signals, in the form of nerve impulses or action potentials, from one part of the body to another. The arrangement of neurons in chains and circuits allows integration of simple on-off Signals into complex information. The microscopic structure of nerve tissue (axon diameter, presence or absence of myelin, etc) exploits physicochemical phenomena to regulate the rate and sequence of signal transmission.


Ø1. Resting membrane potential.
Ø2. Firing and propagation of action potentials.
Ø3. Refractory period.
Ø4. Direction of signal transmission.
Ø5. Saltatory conduction.
Ø6. Blocking signal transmission,

SYNAPSES (CHEMICAL)

Synapses are specialized junctions by which a stimulus is transmitted from a neuron to its target cell. Artificially stimulated axons can propagate a wave of depolarization in either direction, but the signal can travel in only one direction across a synapse, which functions as a unidirectional signal valve. Synapses are named according to the structures they connect, eg, axodendritic, axosomatic, axoaxonic, and dendrodendritic synapses. The 3 major structural components of each synapse are the pre and postsynaptic membranes and the synaptic cleft that separates them.
A. Presynaptic Membrane: This is the part of the terminal bouton membrane closest to the target cell. It consists of an electron-dense thickening into which insert many short intermediate filaments, as in a hemidesmosome. On stimulation, neurosecretory vesicles in the bouton fuse with the presynaptic membrane and exocytose their neurotransmitters into the synaptic cleft. Neurosecretory vesicles are present only in the presynaptic component of the junction. The vesicle membrane added to the presynaptic membrane is recycled by endocytosis of the mem brane lateral to the synaptic cleft. Intact vesicles do not cross the synaptic cleft.
B. Synaptic Cleft (Synaptic Gap): This is a fluid-filled space, generally 20 nm wide, between the pre- and postsynaptic membranes. It is shielded from the rest of the extracellular space by supporting cell processes and basal lamina material that binds the pre- and postsynaptic mem branes together. Some clefts are traversed by dense filaments that link the membranes and perhaps guide neurotransmitters across the gap.
C. Postsynaptic Membrane: This is a thickening of the plasma membrane of the next neuron or target cell leg, muscle). It resembles the presynaptic membrane but also contains receptors for neurotransmitters. When enough receptors are occupied, hydrophilic channels open, resulting in depolarization of the postsynaptic membrane. Neurotransmitter leg, acetylcholine) remaining in the cleft after stimulation of the postsynaptic neuron (or other target cell) is degraded by enzyme leg, acetylcholinesterase) in the cleft. Degradation products are endocytosed by coated pits in the membrane of the bouton, lateral to the presynaptic thickening. Removal of excess transmitter allows the postsynaptic membrane to reestablish its resting spotential and prevents continuous firing of the postsynaptic neuron in response to a single stimulus.

Supporting Cells of the PNS:

1. Schwann cells are the supporting cells of the peripheral nerves. One Schwann cell may envelop segments of several unmyelinated axons or provide a segment of a single myelinated axon with its myelin sheath. Each myelinated axon segment is surrounded by multiple layers of a Schwann cell process with most of its cytoplasm squeezed out; the remaining multilayered Schwann cell plasma membrane, called myelin, consists mainly of phospholipid. The gaps between the myelin sheath Se8ments are the nodes of Ranvier. Ovoid or flattened Schwann cell nuclei lie peripheral to the axon they support. They are usually more euchromatic than the nuclei of the fibrocytes scattered among the axons.
2. Satellite cells are specialized Schwann cells in craniospinal and autonomic ganglia, where they form a one-cell-thick covering over the cell bodies of the neurons (ganglion cells). Their nuclei are spheric with mottled chromatin. In sections, the nuclei typically appear as a "string of pearls" surrounding the much larger ganglion cell bodies.

SUPPORTING CELLS

A. Supporting Cells of the CNS: There are about 10 neuroglial cells per neuron in the CNS. Glial cells are generally smaller than neurons. Their processes, although abundant and exten sive, are indistinguishable without special stains. Identification is usually based on nuclear morphology. The major supporting cells in the CNS are the macroglia, including astrocytes and oligodendrocytes, the microglia, and the ependymal cells. 
1. Astrocytes are the largest glial cells. Their nuclei, also the largest, are irregular, spheric, and pale-staining with a prominent nucleolus. Their branching cytoplasmic processes often have, at their tips, expanded pediclcs, or vascular end-feet. These surround capillaries of the pia mater and are important components of the blood-brain barrier . Proteplasmic astro cytes (messy cells) are more common in gray matter. They have ample granular cytoplasm and short, thick, highly branched processes. Fibrens astrecytes are more common in white matter. Silver stains show their cytoplasm to be full of fibrous material. Their long, thin processes are less branched than those of protoplasmic astrocytes. 2. Oligedendroglia or oligodendrocytes, the most numerous glial cells, are found in both gray and white matter. Their spheric nuclei fall between those of astrocytes and microglia in terms of size and staining intensity. Like the Schwann cells of the PNS, oligodendrocytes form myelin and occur in long rows as required to myelinate entire axons. Unlike a Schwann cell, each may have several cell processes and may provide myelin for segments of several axons. Unmyelinated axons of the CNS are not sheathed. 3. Microglia, the smallest and rarest of the glia, are found in both gray and white matter. Their nuclei are small and elongate (often bean-shaped), and their chromatin is so condensed that they often appear black in H&E-stained sections. Their processes are shorter than those of astrocytes and are covered with thorny branches. Microglial cells may derive from mes enchyme, or they may be glioblasts (immature oligodendrocytes) of neuroepithelial origin. Some microglia may be components of the mononuclear phagocyte system and have phago cytic capabilities. When neural injury is unaccompanied by vascular injury, phagocytic cells in the lesioned area appear to derive from macroglia. 4. Ependymal cells derive from ciliated neuroepithelial cells of the internal lining of the neural tube. In adults, they retain their epithelial nature and some cilia, and they line the remnants of the neural tube (ventricles and aqueducts of the brain and the central canal of the spinal cord). The lining resembles a simple columnar epithelium, but epcndymal cells have basal cell processes that extend deep into the gray matter. The ependymal lining is con tinuous with the cuboidal epithelium of the choroid plexus.

Neurons

ØA. Cell Body: The cell body (soma, perikaryon) is the synthetic and trophic center of the neuron. It can receive signals from axons of other neurons through synaptic contacts on its plasma membrane and relay them to its axon. The abundant free and RER-associated polyribosomes appear as clumps of basophilic material collectively called Nissl bodies.
ØB. Dendrites: These extensions of the soma are specialized to increase the surface available for incoming signals.
ØC. Axon: Each neuron has one axon, a complex cell process that carries impulses away from the soma. An axon is divisible into several regions. The axon billock, the part of the soma leading into the axon, differs from the rest of the perikaryon in that it lacks Nissl bodies.
ØD. Classification of Neurons

properties of nervous system - 2

H. Blood-Brain Barrier: Nerve tissue of the CNS receives oxygen and nutrients from capillaries in the pia mater. These capillaries are relatively impermeable because (1) their endothelial cells lack fenestrations and are joined at their borders by tight junctions, and (2) they are partly surrounded by the cytoplasmic processes of neuroglia called astrocytes. These features contribute to a structural and functional barrier that protects CNS neurons from many extraneous influences and prevents certain antibiotics and chemotherapeutic agents from reaching the CNS.

Properties of nervous system

E. Embryonic Development of Nerve Tissue: All neurons and supporting cells derive from embryonic ectoderm.

F. Aging and Repair: Mature neurons are incapable of mitosis and are often used as examples of terminally differentiated cells. Neurons of the elderly may contain abundant lipofuscin pigment. The inability of neurons to divide makes repair of injured nerve tissue more difficult than for most other tissues. Neuron cell bodies lost through injury or surgery cannot be replaced, but if an axon is severed or crushed and the cell body remains intact, regeneration of the injured axon is possible. Supporting cells, unlike neurons, can divide if stimulated by injury.


G. Meninges: The brain and spinal cord are separated from the bony compartments that house them (skull and vertebral canal) by 3 connective tissue layers termed the meninges. The outer layer, or dura mater, is dense connective tissue bound tightly to the periosteum of the surround ing bone. The middle layer, or arachnoid, has 2 components: (1) a layer of loose connective tissue in contact with the dura mater, and (2) many connective tissue trabeculae (strands) that attach the arachnoid to the underlying pia mater. The spaces between the arachnoid trabeculae contain cerebrospinal fluid. Projections of the arachnoid into sinuses in the dura are called arachnoid villi. The innermost layer, or pia mater, is a thin, richly vascularized layer of loose connective tissue that is firmly attached to the surface of the brain or spinal cord but separated from the neurons by neuroglial cells processes. Ramified, cuboidal epithelium-covered projections of the pia matter into the ventricles of the brain are collectively termed the choroid plexus; they produce the cerebrospinal fluid by selective ultrafiltration of the blood plasma.

Subsystems of the Nervous System

ØD. Subsystems of the Nervous System: The nervous system is divisible into 2 overlapping pairs of subsystems:

Ø1. The central and peripheral nervous systems are defined mainly by location. The central nervous system (CNS) includes the brain and spinal cord. The peripheral nervous system (PNS) includes all other nerve tissue. 2. The autonomic and somatic nervous systems are defined according to function, but have distinctive anatomic features as well.

Each has CNS and PNS components. The autonomic nervous system controls involuntary visceral functions leg, glandular secretions, smooth muscle contraction) and has both motor and sensory pathways, although some authors exclude visceral sensory pathways from the ANS. Each motor pathway consists of 2 neurons that synapse in a peripheral autonomic ganglion. The cell body of the first (preganglionic) neuron is in the CNS; the cell body of the second (postganglionic) neuron is in the autonomic ganglion. The cell bodies of the sensory neurons are located in craniospinal ganglia and have processes that extend peripherally.

The ANS is subdivided into the sympathetic and parasympathetic nervous systems. When they innervate the same end organ, sympathetic and parasympathetic nerves usually have opposing effects. The somatic nervous system includes all nerve tissue except the ANS. It controls somatosensory perception leg, touch, heat, cold) and somatomotor (voluntary) functions (eg, skeletal muscle contraction). Acetylcholine is the most common somatic neurotransmitter.

GENERAL FEATURES OF NERVE TISSUE & THE NERVOUS SYSTEM 2

ØB. Impulse Conduction: Within a neuron, signals (impulses) are propagated as a wave of depolarization along the plasma membrane of the dendrites, soma, and axon. Depolarization involves channels (ionophores) in the membrane, which allow ions (e.g, Na+, K-) to enter or exit the cell. In unmyelinated axons, depolarization is continuous. In myelinated axons, depolarization occurs only at nodes of Ranvier, jumping from node to node (saltatory conduction). Impulse conduction is thus faster in myelinated axons.


ØC. Synapses: Signals pass from neuron to target cell by specialized connections called synapses. The target may be another neuron or a cell in the end organ leg, gland or muscle) it supplies. At chemical synapses, the signal is transmitted by exocytosis of neurotransmitters, chemicals such as acetylcholine that cross the narrow gap (synaptic cleft) between the cells to initiate depolarization of the target cell. At the less common electrical synapses, the signal is transmitted by ions flowing through a gap junction-like complex.

GENERAL FEATURES OF NERVE TISSUE & THE NERVOUS SYSTEM

ØA. Two Classes of Cells: Nerve tissue consists of the neurons that transmit impulses and the supporting cells that surround them. It contains little extracellular material.

Ø1. Neurons. These cells are highly specialized to carry out nerve tissue functions. Neurons receive, integrate, and transmit electrochemical messages. Each has a cell body, also called the soma ("body") or perikaryon ("around the nucleus"), comprising the nucleus and the surrounding cytoplasm and plasma membrane. Each neuron has a variable number of dendrites, cytoplasmic processes that collect incoming messages and carry them toward the soma, and a single axon, a cytoplasmic process that transmits messages to the target cell. Axons of most neurons have a myelin sheath formed by supporting cells and interrupted by gaps called nodes of Ranvier. Myelinated axon segments between the gaps are called internodes. 2. Supporting cells. These cells are called neuroglia ("nerve glue") or glial cells. Their functions include structural and nutritional support of neurons, electrical insulation, and enhancement of impulse conduction velocity along axons.