Human Nervous system
BIOLOGY
15. Human Body - Nervous system
Nervous system
The functions of our body are controlled and coordinated by two systems namely the nervous and endocrine system. The nervous system consists of animals within the animal organisms that are concerned with the reception of stimuli, the transmission of nerve impulses, or the activation of muscle mechanisms. A nerve tissue composed primarily of cells called neurons. A neuron consists ofdendrites, a cell body and an axon. The dendrites generate nerve impulses in response to stimulation from a sense receptor or from another neuron and carry impulses toward the cell body, which contains the cell’s nucleus. The axon carries an impulse
transmitted to it by the cell body to another neuron or to an effector muscle or gland. There are three types of neuron sensory, motor and association. A synapse is the junction between two neuron.
In mammals these neuron comprise 2 types of nervous system i.e.Central nervous system and peripheral nervous system. The brain and spinal cord make up the central nervous system (CNS).
The Central Nervous System (CNS) is composed of the brain and spinal cord.
Composition of the brain
The average adult human brain weighs 1.3 to 1.4 kg (approximately 3 pounds). The brain contains about 100 billion nerve cells (neurons) and trillons of "support cells" called glia. The brain consists of gray matter (40%) and white matter (60%) contained within the skull. The brain has three main parts: the cerebrum, the cerebellum, and the brain stem (medulla). Cerebrospinal fluid (CSF) surrounds the brain. Although the brain is only 2% of the bodys weight, it uses 20% of the oxygen supply and gets 20% of the blood flow.
Brain contained in the skull called cranium. The brain appears as three distinct but connected parts: the cerebrum, cerebellum and the brain stem a central core that gradually becomes the spinal chord.
Brain contained in the skull called cranium. The brain appears as three distinct but connected parts: the cerebrum, cerebellum and the brain stem a central core that gradually becomes the spinal chord.
(i) cerebrum The cerebrum is the largest part of brain and makes up 85% of the brains weight. This is the thinking part of the brain.The cerebrum is made up of two halves, with one on either side of the head. The right half of the cerebrum controls the left side of your body, and the left half controls the right side. These two hemisphere is jointed by a nerve fibres known as corpus callosum. The surface of each cerebral hemisphere shows many convolutions called Gyri separated by sulci(depressions). Each cerebral hemisphere is divided into
a) frontal lobe : It has motor area ( controls voluntary movements of the muscles), pre motor area ( involuntary movement and automatic nervous system) and association area (association between various sensation and movements)
a) frontal lobe : It has motor area ( controls voluntary movements of the muscles), pre motor area ( involuntary movement and automatic nervous system) and association area (association between various sensation and movements)
b) parietal : It has somaesthetic area or general sensory area is the seat for general sensation like pain, touch and temperature.
c) temporal lobe :The temporal lobes are anterior to the occipital lobes and lateral to the Fissure of Sylvius. Temporal lobes are associated with emotional responses, hearing, memory and speech.
d) occipital lobes : It has a visual area ( visual sensation) and auditory area ( hearing)
(ii) Hypothalmus : The hypothalamus is composed of scattered masses of grey matter in white matter at the base of the brain. Although it is the size of only a pea (about 1/300 of the total brain weight), the hypothalamus is responsible for some very important functions. It is responsible for regulation of temperature, hunger, thirst and emotional reactions. The hypothalamus also controls the pituitary.
Hind Brain
a) Cerebellum: The cerebellum is at the back of the brain, below the cerebrum. It is smaller than the cerebrum at only 1/8 of its size. It controls our balance, movement, and coordination (how your muscles work together). Because of our cerebellum, we can stand upright, keep your balance, and move around.
a) Cerebellum: The cerebellum is at the back of the brain, below the cerebrum. It is smaller than the cerebrum at only 1/8 of its size. It controls our balance, movement, and coordination (how your muscles work together). Because of our cerebellum, we can stand upright, keep your balance, and move around.
b) Brainstem : The brain stem is a general term for the area of the brain between the thalamus and spinal cord. Structures within the brain stem include the medulla, pons, tectum, reticular formation and tegmentum. Some of these areas are responsible for the most basic functions of life such as breathing, heart rate and blood pressure.
Spinal Cord: spinal cord is about 43 cm long in adult women and 45 cm long in adult men and weighs about 35-40 grams. The vertebral column, the collection of bones (back bone) that houses the spinal cord, is about 70 cm long. Therefore, the spinal cord is much shorter than the vertebral column. It is covered by the same meninges as the brain and its main function is conduct impulses to and from the brain and acts as a reflex centre.
Mid Brain
It contains many groups of nerve cells scatterd in white matter such as the superior and inferior colliculi and red nucleus. They are involved in controlling the muscle tone and modify some motor activities initiated by the cortex.
It contains many groups of nerve cells scatterd in white matter such as the superior and inferior colliculi and red nucleus. They are involved in controlling the muscle tone and modify some motor activities initiated by the cortex.
Peripheral nervous system
The nerves that connect the CNS to the rest of the body are called the peripheral nervous system.
The nerves that connect the CNS to the rest of the body are called the peripheral nervous system.
a) spinal nerves are those nerves emerge from the spinal cord . There are 31 pairs of spinal nerves all of them are mixed nerves consisting of sensory and motor neurons .
b) cranial nerves are those nerves that emerge from the brain. There are twelve pairs of them. Some are sensory, some are motor and some are mixed nerves.
c) autonomic nervous system : This is organised into two distinct regions along the central nervous system forming the sympathetic and parasympathetic system. These two systems act opposite to each other in their action in their muscles and glands they control. It controls the rate and force of the heart beat, the contraction of involuntary muscles and the size of pupils of eye.
Our sensory organs - Eye
Eye is the light sensitive organ of vision. The function of the eye is to translate the electromagnetic vibrations of light into patterns of nerve impulses that are transmitted to the brain. The eye sits in a little hollow area (the eye socket) in the skull and protected by the eyelid. The eyelid helps keep the eye clean and moist. Tear is a clear, salty liquid that is produced by Lacrimal glands in the eyes. The eyelid also has great reflexes, which are automatic body responses that protect the eye.
Let us see various parts of our eye and how it functions.
The white part of the eyeball is called the sclera made of tough material covers the eye ball. The part of the sclera in front of the colored part of the eye is called the cornea which is transparent allows light to pass through it. Behind the cornea are the iris and the pupil. The iris is the colorful part of the eye. When you see people with brown or blue eyes, it really means that the colour of iris. The iris has muscles attached to it that change its shape. This allows the iris to control how much light goes through the pupil. The pupil is the black circle in the center of the iris and it changes size as the amount of light changes (the more light, the smaller the hole). Between the iris and cornea is the anterior chamber. This chamber is filled with a special transparent fluid that gives the eye oxygen, protein, and glucose (a type of sugar in the body) to keep it healthy. Retina is a sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve. Lens, a crystalline structure located just behind the iris - it focuses light onto the retina whose shape is adjusted by the ciliary body. The biggest part of the eye sits behind the lens and is called the vitreous body. The vitreous body forms two thirds of the eyes volume and gives the eye its shape. It is filled with a clear, jelly-like material called the vitreous humor.
The retina uses special cells called rods and cones to process light. Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods cannot tell the difference between colors, but they are super-sensitive, allowing us to see when it is very dark.
Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. The retina has three types of cones - red, green, and blue - to help you see different ranges of color. Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.
There are 2 types of eyes found in animals: single (found in Humans ) and compound eyes. Compound eyes are only found in arthropods such as insects and crustaceans.
Let us see various parts of our eye and how it functions.
The white part of the eyeball is called the sclera made of tough material covers the eye ball. The part of the sclera in front of the colored part of the eye is called the cornea which is transparent allows light to pass through it. Behind the cornea are the iris and the pupil. The iris is the colorful part of the eye. When you see people with brown or blue eyes, it really means that the colour of iris. The iris has muscles attached to it that change its shape. This allows the iris to control how much light goes through the pupil. The pupil is the black circle in the center of the iris and it changes size as the amount of light changes (the more light, the smaller the hole). Between the iris and cornea is the anterior chamber. This chamber is filled with a special transparent fluid that gives the eye oxygen, protein, and glucose (a type of sugar in the body) to keep it healthy. Retina is a sensory tissue that lines the back of the eye. It contains millions of photoreceptors (rods and cones) that convert light rays into electrical impulses that are relayed to the brain via the optic nerve. Lens, a crystalline structure located just behind the iris - it focuses light onto the retina whose shape is adjusted by the ciliary body. The biggest part of the eye sits behind the lens and is called the vitreous body. The vitreous body forms two thirds of the eyes volume and gives the eye its shape. It is filled with a clear, jelly-like material called the vitreous humor.
The retina uses special cells called rods and cones to process light. Rods see in black, white, and shades of gray and tell us the form or shape that something has. Rods cannot tell the difference between colors, but they are super-sensitive, allowing us to see when it is very dark.
Cones sense color and they need more light than rods to work well. Cones are most helpful in normal or bright light. The retina has three types of cones - red, green, and blue - to help you see different ranges of color. Together, these cones can sense combinations of light waves that enable our eyes to see millions of colors.
There are 2 types of eyes found in animals: single (found in Humans ) and compound eyes. Compound eyes are only found in arthropods such as insects and crustaceans.
Diseases and disorders of eye
1) Myopia (nearsightedness or short sightedness) is a refractive defect where the person affected usually can see nearby objects clearly but distant objects appear blurred. The eye is slightly elongated front to back,causing images to be focused in front of the retina rather than directly on it. This defect can be corrected by wearing a biconcave or diverging lenses.
1) Myopia (nearsightedness or short sightedness) is a refractive defect where the person affected usually can see nearby objects clearly but distant objects appear blurred. The eye is slightly elongated front to back,causing images to be focused in front of the retina rather than directly on it. This defect can be corrected by wearing a biconcave or diverging lenses.
2) Hypermetropia is also known and long-sightedness, and it is a defect of vision caused by an impefection in the eye, causing inablility to focus on near objects and in extreme cases causing a sufferer to be unable to focus on objects at any distance. It is corrected by a using glasses with lenses of positive curvature ("magnifying glasses").
3) Presbyopia is a condition that occurs with growing age and results in the inability of the human eye to focus on objects in varying distances. Presbyopia cannot be cured, but the loss of focusing ability can be compensated by wearing glasses with varying power, so-called multifocal lenses or progressive addition lenses.
4) Astigmatism is a refractive defect of the eye characterized by an aspherical cornea in which one axis of corneal steepness is greater than the perpendicular axis. Astigmatism causes difficulties in seeing fine detail, and can be often corrected by glasses with a cylindrical lens or by toric contact lenses.
5) Arc eye is a painful condition sometimes experienced by welders who have failed to use adequate eye protection. It can also occur due to light reflected from snow (known as snow blindness), water or sand. The intense ultraviolet light emitted by the arc causes a superficial and painful keratitis.
6) A cataract is any opacity which develops in the crystalline lens of the eye or in its envelope. Cataracts form for a variety of reasons, including ultraviolet exposure, secondary effects of diseases such as diabetes, or simply due to advanced age; they are usually a result of denaturation of lens proteins.
7) Conjunctivitis is an inflammation of the conjunctiva (the outermost layer of the eye that covers the sclera), often due to infection. There are three common varieties of conjunctivitis, viral, allergic, and bacterial. Viral and bacterial conjunctivitis are contagious.
8) Blindness caused by cloudiness or scarring of the cornea can sometimes be cured by surgical removal of the affected portion of the corneal tissue. Only corneal tissue is taken from deceased persons for eye grafts.
9) Glaucoma is an eye disease that is defined as a characteristic optic neuropathy, or disease of the optic nerve. The most common cause of glaucoma is increased intraocular pressure. Both laser and conventional surgeries are performed to treat glaucoma.
Our sensory organs - Nose
Nose is the smell receptors or olfactory organs. Nose has two holes called Nostrils. The nostrils and nasal passage is separated by septum made of cartilage. There is a space in the middle of our face called nasal cavity which connect to the back of the throat which in turn connects trachea. When we inhale air, membrane warms and moistens it. mucous traps dust, gems and other particles. Cilia are the name given to small hairs in your nose. An olfactory epithelium is situated on the roof of mouth has very small receptors which are sensitive to odour molecules. odour stimulate different receptor and olfactory nerve sends message to brain and it interprets different smells.
Ear
An ear is an organ of hearing and balance. Human ear consists of of three sections: the outer, middle, and inner ear. The outer and middle ears function only for hearing, while the inner ear also serves the functions of balance and orientation. In the outer hear, the visible part is called the pinna, or auricle, and functions to collect and focus sound waves. From the pinna, the sound pressure waves p (Pascal) moves into the ear canal, a simple tube running to the middle ear.The middle ear includes the eardrum (tympanum or tympanic membrane) and the ossicles, three tiny bones of the middle ear. i.e. malleus, incus, and stapes(smallest bone in human body). Mammals are unique in having three ear bones. These bones form the linkage between the tympanic membrane and the oval window that leads to the inner ear. The tympanum turns vibrations of air in the ear canal into vibrations of the ossicles. The ossicles in turn transmit the vibrations through the membrane of the oval window into the fluid of the inner ear. The inner ear comprises both the organ of hearing (the cochlea) and the labyrinth or vestibular apparatus, the organ of balance located in the inner ear that consists of three semicircular canals and the vestibule. The eustachian tube helps keep the eardrum intact by equalizing the pressure between the middle and outer ear. For example, if a person travels from sea level to a mountaintop, where air pressure is lower, the eardrums may cause pain because the air pressure in the middle ear becomes greater than the air pressure in the outer ear.
Non-mammalian hearing organs Spiders have hairs on their legs which are used for detecting sound.; Reptilian ears only have one bone - the malleus.
Non-mammalian hearing organs Spiders have hairs on their legs which are used for detecting sound.; Reptilian ears only have one bone - the malleus.
Skin
Skin is the biggest organ in our body. It covers and protects our body. The skin is made up three layers. The outermost is epidermis. It consists mostly of dead skin cells. It has a substance called melanin which gives the skin its colour. Dermis is situated below the epidermis. It contains blood vessels, nerve endings, oil glands (sebaceous), and sweat glands. The nerve endings help us to sense touch by communicating to brain. The third and bottom layer is called the subcutaneous layer. It is made mostly of fat and helps your body stay warm, absorb shocks, here we find hair follicles.
Tongue
Tongue is primary organ of taste, plays an important role in chewing and swallowing of food. The tongue is covered with dozens of pimple-like projections called papillae. These grip and move food when you chew. Around the sides of the papillae are about 10,000 microscopic taste buds. Different parts of the tongue are sensitive to different flavours: sweet, salt, sour and bitter.
Tongue is primary organ of taste, plays an important role in chewing and swallowing of food. The tongue is covered with dozens of pimple-like projections called papillae. These grip and move food when you chew. Around the sides of the papillae are about 10,000 microscopic taste buds. Different parts of the tongue are sensitive to different flavours: sweet, salt, sour and bitter.
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