The Nervous System is the:
• Master controller and communicating system in the body
• Every thought, action and emotion reflects its activity.
• It signals the body through electrical impulses that communicate with the body cells.
• Its signaling and responding abilities are highly specific and rapid.
The Nervous System is capable of:
1. Sensory input – gathering information
• To monitor changes occurring inside and outside the body
• Changes = are called stimuli
2. Integration
• N.S. is able to integrate the sensory information, process, interpret and decide if action is needed
3. Motor output
• A response to the integrated stimuli
• The response activates muscles or glands
The NS does not work alone in maintaining homeostasis. It enlists the Endocrine system for regulating and maintain body functions.
• The Neurons (nervous cells) must perform 4 specialized functions
1. Receive information from the internal or external environment
2. Integrate the information received and produce an appropriate output signal (or response)
3. Conduct the signal to its terminal
4. Transmit the signal to another cell (effector)
The Neurons cells have:
• Dendrites – that receive information
• Cell body – that integrates incoming information
• Axon – conducts electrical impulses (signals) to the synaptic terminals
• Synapsis (synaptic terminals) – the site that receives signals and communicates with other cells, tissues, or organs.
The Neurons are nervous cells that transmit messages.
The structure of the neuron has:
• A Cell body – with a nucleus, a large nucleolus
• The Dendrites – conduct impulses toward the cell body (afferent), away from the receptors
• The Axons – conduct impulses away from the cell body (efferent) toward the muscle or endocrine
• Nervous tissue is comprise of 2 types of cells
– Neurons = nerve cells that transmit impulses
– Neuroglia = supporting cells. They act as insulators, adhesive, protectors and nourishers.
Nervous Tissue Supporting Neuroglias include:
1. Astrocytes
• There are an abundant of these star-shaped cells
• They brace themselves onto neurons
• They control the chemical environment of the brain
2. Microglia
• These are Spider-like phagocytes that dispose of debris.
3. Oligodendrocytes
• Produce myelin sheath around nerve fibers in the central nervous system
4. Ependymal cell
- Epithelial-type cells that line the nervous system (brain and spinal cord. They form the Meninges – Dura Mater, Arachnoid Mater and Pia Mater.
5. Satellite cells
• Protect neuron cell bodies
6. Schwann cells
• Form myelin sheath in the peripheral nervous system
How is the Human Nervous System Organized?
The Peripheral Nervous System (PNS) has:
• Sensory (afferent) division - carrying toward a center Nerve fibers that carry information to the central nervousystem
• Somatic sensory - (skin, skeletal muscle)
• Visceral sensory - (visceral organs)
-- AND --
• Motor (efferent) division - Nerve fibers that carry impulses away from the central nervous system (effect) and activate muscles or glands to bring about a response.
The PNS:
The Motor (efferent) has 2 division
1. Somatic nervous system is voluntary (skeletal muscles)
2. Autonomic nervous system = involuntary (smooth and cardiac muscles, glands)
Sensory (afferent) neurons:
Carry impulses from the sensory receptors
Cutaneous (skin) sense organs Proprioceptors – detect stretch or tension
Sensory Motor (efferent) neurons Carry impulses from the central nervous systemnterneurons association neurons)
• Are found in neural pathways in the central nervous system
• They connect sensory and motor neurons
• Are capable of Irritability – ability to respond to stimuli
• Are capable of Conductivity – ability to transmit an impulse
• Are Excitatory & inhibitory potentials
• The plasma membrane at rest is polarized
– Fewer positive ions are inside the cell than outside the cell
Starting a Nerve Impulse
• Depolarization – a stimulus depolarizes the neuron’s membrane
• A depolarized membrane allows sodium (Na+) to flow inside the membrane
• The exchange of ions initiates an action potential in the neuron
The Reflex Arc
• Reflex – is rapid, predictable, and involuntary responses to stimuli
• Reflex arc – directs the route from a sensory neuron, to an interneuron, to an effector
Types of Reflexes and Regulation
• Autonomic reflexes – involves Smooth muscle regulation of the Heart and blood pressure, vessels, Regulation of endocrine glands and the Digestive system regulation. It also involves Somatic reflexes which Activates the skeletal muscles and Voluntary motions.
How do Sensory Receptors Work?
• Receptors are cells or clusters of cells that transduce the energy of a specific signal into an electrical signal
• Receptor potential
EXAMPLE: the ear captures, transmits and converts sound into electrical signals
a. The Outer ear captures sound waves
b. Middle ear converts vibrations from sound waves into electrical signals (cochlea)
c. Cochlea is a fluid-filled chamber with 2 membranes (basilar & tectorial) and sensory receptors called hair cells
d. The basilar membrane vibrates in response to sound waves
e. The vibrations causes the hair cells to bend, which generates receptor potentials
f. Larger vibrations bend the hair cells even more, which is perceived as louder sound.
• Loud, prolonged sounds damage hair cells
g. Different parts of the basilar membrane vibrate at different frequencies of sound waves
h. This allows for perception of different pitches
Visual Sensory
• The eye collects, focuses and transduces light waves
• Adjustable lenses allows for distant and nearby focusing.
– Eyeball long – near sightedness
– Eyeball short – farsightedness
• Light strikes the retina’s photoreceptors
• Rods & cones transduce light signals
• Electrical signals are transmitted and processed
• Axons of ganglion cells carry signals to the brain
Rods & Cones
• Rods – dim vision (periphery)
• Cones – color vision (fovea)
Taste that Smell – the Olfactory receptors
• Responsible for sense of smell
• Located at the roof nasal cavity
Olfaction contributes to taste perception. Taste receptors are located in clusters on the tongue
Other Special Senses
• Pain receptors – with Specialized chemical sense
• Echolocation - a type of sonar receptor. Some animals have specialized receptors for navigating and detecting prey. Some birds and fishes use the earth’s magnetic field to navigate long-distance migration
• Electolocation - Some fish use electrolocation for hunting and commuinicating
THE BRAIN
Regions of the Brain
o Cerebral hemispheres
o Diencephalon
o Brain stem
o Cerebellum
Cerebral Hemispheres (Cerebrum)
The surface is made of ridges (gyri) and grooves (sulci)
Lobes of the Cerebrum
- Fissures (deep grooves) divide the cerebrum into lobes
- Surface lobes of the cerebrum
• Frontal lobe
• Parietal lobe
• Occipital lobe
• Temporal lobe
Lobes of the Cerebrum have Specialized Areas of the Cerebrum
- Somatic sensory area – receives impulses from the body’s sensory receptors
- Primary motor area – sends impulses to skeletal muscles
- Broca’s area – involved in our ability to speak
The Specialized Areas of the Cerebrum have cerebral areas that are involved in special senses
• Gustatory area (taste)
• Visual area
• Auditory area
• Olfactory area
The brain has Interpretation areas of the cerebrum for
• Speech/language region
• Language comprehension region
• General interpretation area
The DIENCEPHALON
The Diencephalon Sits on top of the brain stem; it is enclosed by the cerebral heispheres and made of three parts:
• Thalamus
• Hypothalamus
• Epithalamus
Thalamus
- Is the relay station for sensory impulses
- Transfers impulses to the correct part of the cortex for localization and interpretation
Hypothalamus
- Under the thalamus
- Helps regulate body temperature
- Controls water balance
- Regulates metabolism
- An important part of the limbic system (emotions)
- The pituitary gland is attached to the hypothalamus
Epithalamus
- Houses the pineal body (an endocrine gland)
- Includes the choroid plexus – which forms cerebrospinal fluid
The BRAIN STEM
• Attaches to the spinal cord. Parts of the brain stem include:
• The Midbrain, Pons and Medulla oblongata
- The Midbrain – is the Reflex centers for vision and hearing
- The Pons – is the center part of the brain stem which is mostly composed of fiber tracts
- Includes nuclei involved in the control of breathing
- Medulla oblongata - lowest part of the brain stem
- Merges into the spinal cord
- Control center for: Respirations, H.R., B/P swallowing and vomiting
The SPINAL NERVES
- There are 31 pair of spinal nerves at the level of each vertebrae
- Spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal cord
nervous system summarized
The Phosphodiester Bond
Nucleic acids (RNA and DNA):
formed by the condensation of nucleotides, catalyzed by polymerases.
The bond: a phosphodiester bond.
The bond is shown in figure a display of a trinucleotide DNA fragment.
A couple of shorthand notations to designate nucleic acid polymers:
vertical lines represent the sugars
diagonal lines represent the phosphodiester bonds.
More commonly: only indicate the order of bases and the direction of the polymer chain. For instance:
5' - AGTCCGATGCAAGCTCG - 3'
The complementary sequence:
5'-AGTCCGATGCAAGCTCG-3'
3'-TCAGGCTACGTTCGAGC-5'
proposed by James Watson and Francis Crick.
Serebellum
It's related with muscle motor function. If the serebellum is removed surgically, cordinated muscle contraction is disturbed and maintanence of body posture disappear. The serebellar structure is similar to the cortex cerebri. There are gray matter on the surface but white matter in the inner side. The surface have many small invagination that is called as gyri as like cerebri. Serebellum receives impulses from the perphery by the sipinocerebellar tract and from some nuclei from brain stem and also fibers from motor cortex.
Nervous system animation
Detailed animations about nervouse system and cell singaling, brain signals, central nervous system.
Forebrain
Forebrain is divided into the diencephelon and thelencephelon. the dorsal portion of the diencephelon is the epithalamus, the lateral portion the thalamus and the ventral portion is the hypothalans.
The epithalamus contains a small nucleus that transmits olfactory information to the brain stem, the pineal and parapineal bodies, and the anterior choroid plexus.
In lower vertebrates epithalamus is well developed and importantt for the transmission of impulses from periphery to cerebral cortex, but in mammales most of sensory information is transferred to the cerebral cortex via thalamus.
properties of excitable cell
Rheobase is the lowest current that will initiate an action potential. the chronaxie is the maximum stimulus duration when the current is 2X reheobase. Rheobase and chronaxie define the shape of the strength-duration relationship. A slowly inceasing depolarizing current may not initiate an action potential even though it may rise to an intensity much greater than threshold level. A maintained depolarization causes the threshold to rise towards 0 mV. This called as accomadation.
It is not possible to elicit a second action potential after brief period of first action potential. This period is called as absolute refractory period. in this period all Na channels again can be aplicable for activation, this period is called as relative refractory period.
myelination
first one, in the central nervous system, myelin is formed by the oligodendrocytes. One oligodendrocyte can contribute to the myelin sheath of several axons.
myelination II: in the peripheral nervous system, myelin is formed by Schwann cells. Each Schwann cell associates with only one axon, when forming a myelinated intermode.
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 system included a brain and spinal cord. The peripheral nervous system comprise peripheral nerves extending from spinal cord and peripheral ganglia. nervous
EPSP's and IPSP's
If transmitter opens a cation influx, the resulting depolarization is called an Excitatory Post Synaptic Potential (EPSP). These individual potentials are sub-threshold. If the transmitter opens an anion influx, the resulting hyperpolarization is called an Inhibitory Post synaptic potential (IPSP). All these potentials are additive. ıf some of the synapses are inhibitory in type. The cell produce action potential according to the algebric some of both excitatory and inhibitory synapses. The neurotransmitter GABA causes postsynaptic inhibition because its rceptor gated, postsynaptic membrane channels allow CL-flow.
Repitative stimulation of postsynaptic nerve from single synaptic region can also produce action potential. This kind of summation is called as temporal summation. Sometimes even the cell do not produce action potential, it can be come close to threshold potential , this is called as faciltation. Synaptic depression or fatique occur due to the depletion of synaptic vesicles as a result of repitetive stimulation. Continuous stimulation may led to the decline of postsynaptic potential.
basal ganglia
Basal ganglia is composed of some nuclei in the diencephelon; caudate nucleus, putamen, globus pallidus and substantia nigra. These are neural structure is related with motor function. Basal ganglia receive afferents from motor cortex and send efferents to the thalamus and then to the cortex. Basal ganglia controls the motor impulses conducted from cortex to the spinal cord. The complex fine movements is coordinated by the nasal ganglia. In the failure of the nasal ganglia, spontenous contraction occur in the extremity muscle.
autonomic nervous system
in simple animal autonomic fibers directly originate the segmentally arranged nerve cord and travel to the visceral organ as like peripheral nerves. In higher vertebrate and mammals, there are postganglionic ganglia in the periphery near to the inervated organ. Autonomic nerves innervate involuntary internal organs of the body.
After they emerge from spinal cord, it relays on a ganglia and the postganglionic fibers goes to the organ. When the autonomic nerves of a smooth muscle are cut, the smooth muscle continue to contruct and no athropy seen. But somatic nerve is destroyed, atrophy occur in the innervated organ. Autonomic nervous system is divided into two functional branches: the parasymphatetic branch and symphatetic branch. The preganglionic fibers of the parasymphatetic system exit the central nervous and synapse at the peripheral organs. Nervous system
The preganglionic fibers of symphatetic nerves leave the spinal cord via throracic and lumbar spinal nerves and synaplse on to the ganglia close to the spinal cord or synapse in more peripheral sympathetic ganglia. The symphatetic and parasymphatetic systems have antoganistic actions. In general the symphatetic nervous system preparres the body for response to stressful or dangerous situations; it initiates the fight of flight reactions, elevation of heart rate and increased force of contruction, peripheral vasoconstriction, and sweating.
In contrast, the parasymphatetic nervous system controls general bodily functions such as digestion. The neurotransmitter of postganglionic parasymphatetic synapse is acetylcholine, so the postsynaptyic receptors of these synapses are cholinergic.. http://nervous-system-info.blogspot.com/
The neurotransmitter of the symphatetic postganglionic synapse is usually norepinephrine, so there are adrenergic. The symphatetic neurotransmitter is epinephrine rather than norepinephrine rather than norepnephrine in some vertebrates. The neurotransmitter at the preganglionic synapse of both the parasymphatetic and symphatetic branches is acetylcholine.http://nervous-system-info.blogspot.com/
chemical synapses
The sequence of events during chemical synaptic transmission is :
1- the presynaptic action potential depolarizes the presynaptic membrane. 2- Ca+ permeability increase through the presynaptic membrane.
3-the elevated intracellular Ca+ concentration causes the release of neurotransmitter from synaptic vesicles in to synaptic cleft.
4- Neurotransmitter molecules diffuse across the synaptic cleft to the postsynaptic membrane and they reversibly bind to the specific receptors on the postsynaptic membrane.
Ca is very important in neurotransmitter release . The neuromucular junction is a typical chemical synapse. In this case two acetylcoline molecule are required to open the sodium channel. Postsynaptic membrane include acetycholine esterase to remove ACh.
In each postsynaptic end, a small depolarization is generated. That is called as end plate potential (EPP) or postsynaptic endplate potential.
These mini EPPs reflect the spontaneous release of one, or a few synaptic vesicles. Single EPPs does not generate in chemical synapsis . This ranges from 0.5 msec to 2.0 msec or even more.
electrical synapses
Electronic conduction is provided by gap junction between two neuronal membrane. these gap junctions are composed of numerous connections that allow direct movement of ions and small molecules. The direct electrical coupling of neurons is often observed when there is a requirement for the closesyncronization of effector organs. Examples are the cells of lobster heart, the electronic organ of mormyrid fish. the sound production muscle of toadfish and the escape response of some invertebrates.
http://nervous-system-info.blogspot.com/
There is no time delay, or latency in transmission of electrical depolarization in electrical synapses. The normal direction of synaptic transmission is from the presynaptic membrane to the postsynaptic membrane. Some electrical synapsis are inhibitory.
Synaptic Transmission
Action potentials are transmitted from one cell to another. There are two different mechanism for transfer of electrical from one cell to another .
1) electrical synapsis
2)chemical synapses
in electrical synapses, the action potential jumps electrotonically from the presynaptic cell membrane to the postsynaptic cell membrane. In the chemical synapsis, neurotransmitter released from one cell provide transmission of impulses.
What Happens To The Nervous System Under Stress?
The nervous system is the messenger between the brain and the other parts of the body. It is a labyrinth of connections that ensure that every signal transmitted by the brain triggers the necessary response in the body. Needless to say, it is an indispensable part of the body mechanism yet one of the most neglected ones. The nervous system remains active even when the rest of the body is in the resting state. It is also the main center for triggering the fight or flight response and the involuntary responses that keep us safe from potentially harmful stimuli.
When the nervous system is neglected i.e. by lack of proper sleep, stress and other factors, the repercussions are slowly but surely felt. The severity might vary from mood swings, poor hand eye co-ordination, fatigue to even depression and Alzheimer’s disease. The nervous system can also be affected adversely by improper food and sleeping patterns, lack of exercise, excessive exposure to stimulants such as coffee, certain medication and neglecting the need for relaxing activity. When the nervous system is not in ship shape, it can lead to the impairment of daily life and significantly increase the risk of occurrence of other medical conditions.
On the other hand, when the nervous system is performing to its full potential it fortifies the immune system, the ability to focus and multitask increases, the capacity to perform complicated tasks is enhanced and the risk of depression is significantly lowered. It also contributes towards a positive frame of mind and improving resistance towards stress. As the nervous system affects the body, the vice versa also holds true. Proper nutrition, rest and regular exercise release beneficial hormones such as endorphins into the system and help balance the several regulatory mechanisms of the body. A healthy body is truly run by a healthy nervous system.
Nervous System general
do you want to explore the nervous system ? this is general nervous system video.. there is a biochemical communications network of the human body, Revealing visuals are supported by informative features in which a neurologist discusses the chemistry of a nerve impulse.
The Nervous System video
The Nervous System video Animation from youtube . very great animation how nervous system works?
