CBSE Class 11 Biology || Neural Control and Coordination || Full Chapter || By Shiksha House

0:00 coordination between various organs and systems of the body is crucial to homeostasis or body stability form tissues turn from different organs organs further combine to form different systems each of these organ systems is specialized to perform specific functions and shows interactions and interdependency for example during physical exercise the body demands more energy in the form of increased oxygen and nutrients supply to the muscles the body achieves this by an increased rate of respiration which increases the heartbeat and blood flow to the muscles this is also accompanied by the

0:59 expulsion of wastes through renal excretion and sweating in order to regulate body temperature the activities of all the organs return to normal when physical exercise comes to a stop this is an example of coordination and integration among organs such as the lungs heart kidneys and skin that maintains homeostasis the two systems in our body that maintain homeostasis are the neural system and the endocrine system the neural system provides a network of points to point connections to quick coordination of nerve impulses the endocrine system provides chemical integration to hormones sometimes it acts very quickly while at other times it acts with a leg all animals have a neural system that consists of highly specialized cells

2:06 runs these cells can perceive receive and transmit different kinds of stimuli hence neurons are called the structural and functional units of the neural system neural organization varies from lower invertebrates to vertebrates for example neurons are absent in sponges the neural system of the Hydra comprises a network of neurons example flatworms have a letter type neural system which is composed of nerve rings and nerve cords they are interconnected by transverse

2:52 connectives the neural system of earthworms consists of circumferential nerve ring and a single solid ventral and ganglion ated nerve cord insects have a better organized neural system starfish do not have a brain and it's nerves are readily organized with a connecting ring in the center all vertebrates have a well-developed neural system however the brain is the most complex and advanced in the primates especially in human beings yeah we'll discuss the human neural system in detail

3:40 the human neural system is divided into two parts the central neural system or CNS and the peripheral neural system or pns the brain and the spinal cord from the central neural system the site of information processing and control the peripheral neural system comprises cranial and spinal nerves controls the voluntary functions of the body of peripheral nerves are of two types afferent or sensory no fibers and efferent or motor no fibers current fibers conduct nerve impulses from the sense organs to the central nervous system efferent fibers conduct nerve impulses from the central nervous system to the involuntary organs muscles and glands the peripheral neural system can be further divided into the somatic neural system and the autonomic neurons the function of the somatic neural system is to relay impulses from the

4:58 central neural system to the skeletal muscles the autonomic neurons system controls involuntary functions such as heartbeat menaced Alice's etc this is because the nerve fibers of the autonomic nervous system extend up to the visceral organs and smooth muscles of the body the autonomic new rule system is further classified into the sympathetic neural system and parasympathetic neural system the sympathetic system comprises the neurons of the thoracic and lumbar regions sympathetic system comprises the cranial and sacral neurons let's look at the structure and types of neurons now the neuron is a branched nerve cell and is the longest cell in the body the two main parts of a neuron are the sight on and nerve processes the seitan is also called the soma or cell body it contains granular cytoplasm so-called neuro Pleasant the neuro plasm contains a large spherical nucleus bodies called missiles granules which help in protein synthesis

6:30 number of mitochondria to provide high energy for the conduction of impulses and thread like neural fibers which help in the conduction of impulses processes are of two types gendron's and axons gendron's can be one or more in number they're fine branches are called dendrites impulses towards the cell body an axon is always single it is covered by a plasma membrane called Excel Emma the inner fluid of an axon is known as EXO plasm the distal branched of an axon forms a knob like swelling

7:21 called a synaptic knob the synaptic knob possesses synaptic vesicles which contain chemicals called neurotransmitters on the basis of the number of axons and dendrites divided into three types multipolar bipolar and unipolar multipolar neurons have one axon and two or more dendrites and are found in the cerebral cortex bipolar neurons with one axon and one dendrite are found in the retina of the eye unipolar neurons have a cell body with one axon only and are found in the photoreceptor cells of the retina Suns out of two types myelinated and non myelinated miron a turd at no fibers are enclosed by Schwann cells which form a myelin sheath around the axon the gaps between two adjacent myelin

8:39 sheaths are called the nodes of ranvier these fibers are found in cranial and spinal nerves unmyelinated nerve fiber is enclosed by a Schwann cell that does not form a myelin sheath around the axon nodes of ranvier are absent found in the autonomic and somatic neural systems on the basis of the functions of neurons they can be divided into three types sensory motor and Association neurons sensory or afferent neurons are found in the sense organs they receive impulses

9:27 from receptors and direct them towards the central nervous system motor or efferent neurons are found in the central nervous system for example the ventral horn of the spinal cord they carry impulses from the central nervous system to organs such as the muscles and glands the Association neurons which are also called inter neurons or mixed neurons are found in the central nervous system for example the dorsal Horn of the spinal cord they interlink the axon of a sensory neuron with the dendron of a motor neuron the nerve impulse is the sum of mechanical chemical and electrical disturbances created by a stimulus in a neuron

10:24 the conduction of the nerve impulse can be divided into two main phases resting membrane potential and action membrane potential neurons are excitable cells they may be stimulated by physical chemical or electrical stimuli the nerve fiber or axe is covered by a neural axonal or plasma membrane the neural membrane has sodium and potassium ion channels called voltage-gated or regulated channels these channels open or close according to the electric potential across the membrane the ion channels of the resting membrane are differentially permeable to ions at different rates it is more permeable two potassium ions most impermeable to sodium ions and totally impermeable to the negatively charged proteins of the egg so plasm therefore the eggs are plasm inside the axon

11:50 contains a high concentration of potassium ions negatively charged proteins and a low concentration of sodium ions on the contrary the extracellular fluid outside the axon contains a low concentration of potassium and a high concentration of sodium this differential permeability is maintained by a sodium potassium pump present inside the membrane potassium pump transports three sodium ions outside the cell for every two potassium ions that enter the cell this electrical potential difference across the membrane in an unacceptable is called resting potential and the neuron is called a polarized nerve fiber

12:47 when a stimulus is applied to a site c/e membrane the sodium ion channels open and the membrane at the site becomes freely permeable to sodium ions this leads to a rapid influx of sodium ions that reverses the polarity of the site that is the outer surface of the membrane becomes negatively charged and the inner surface becomes positively charged this reversal of polarity across the two sides of the membrane is called depolarization the electrical potential difference across the plasma membrane at site a is called the action potential

13:37 action potential travels as a wave of depolarization along the length of the nerve fiber in a particular direction and is called the nerve impulse at site B the axon membrane has a positive charge on the outer surface and a negative charge on the inner surface as a result the current flows on the inner surface from site a to site B service a current flows from site B to site a to complete the circuit of current flow this reverses the polarity at the site and an action potential is generated at site B thus the impulse generated at site a arrives at site B the sequence repeats along the length of the axon for the impulse to be conducted

14:44 and the peak of action potential the permeability of the membrane to sodium ions decreases while it becomes more permeable to potassium ions this is because sodium channels start closing and potassium channels start opening however this part of the membrane regains its original polarity within milliseconds and this phenomenon is called repolarization a repolarized nerve fiber undergoes a refractory period of a few milliseconds during which the original ionic distribution is restored by a sodium potassium pump which actively transports sodium ions outward and potassium ions inward this returns the membrane to its resting potential and the neuron is ready to receive another stimulus a junction helps transmit the nerve impulse from one neuron to another junctions are called synapses

16:01 a synapse is formed by the membranes of a presynaptic neuron and a postsynaptic neuron which may or may not be separated by a gap called the synaptic cleft there are two types of synapses on the basis of the nature of transfer of information these are chemical synapses and electrical synapses chemical synapses are common in the human system and consists of a presynaptic neuron synaptic cleft and synaptic neuron a presynaptic neuron ends with a synaptic knob a synaptic knob has a large number of mitochondria and many synaptic vesicles

16:57 each synaptic vesicle contains neurotransmitter chemical molecules such as acetylcholine the synaptic cleft is a fluid-filled gap between the axon terminal and the dendron of another neuron so there is no protoplasmic continuity between neurons when an impulse or action potential arrives at the axon terminal it stimulates the movement of the synaptic vesicles towards the presynaptic membrane synaptic vesicles fuse with the plasma membrane and release their neurotransmitters into the synaptic cleft the neurotransmitters thus released bind to their specific chemo receptors present on the postsynaptic membrane of the dendron

17:57 this binding opens sodium ion channels that allow the entry of ions to generate a new potential in the postsynaptic neuron this may lead to the development of an excitatory new potential or an inhibitory new potential Electrical synapses are the less common of the two types they were first found in crayfish later in sedan turrets analogies arthropods and fish the membranes of pre and postsynaptic neurons of electrical synapses are in very close proximity

18:50 this allows the direct flow of electric current from one neuron to another synaptic vesicles are absent and only a few mitochondria are present impulse transmitter electrical synapse is faster than that across a chemical synapse the brain and spinal cord are collectively known as the central neural system however it does not include muscles and nerves which arise from the spinal cord and innovates the body the brain is the central information processing organ of our body and it acts as the command and control system it controls voluntary movement as well as the involuntary movement of organs such as the lungs heart kidneys stomach vessels

19:54 it also controls the processes of vision hearing speech memory intelligence emotions and thought the brain lies inside a bony case the skull and is well protected by three layers of tree Niall meninges these are the outer dura mater middle arachnoid and inner diameter the space between the arachnoid and Pia mater is filled with cerebral spinal fluid which acts as a shock absorber and prevents the brain tissue from rubbing against other parts the brain can be divided into three main parts forebrain midbrain and hindbrain

20:56 the largest part of the brain it is made up of the cerebrum illumise and hypothalamus a deep cleft divides the cerebrum longitudinally into two hugs the left and right cerebral hemispheres a thick band of nerve fibers called the corpus callosum connects the two hemispheres and facilitates communication between them the cerebral hemispheres are covered with a layer of cells known as the cerebral cortex it has prominent folds with ridges and depressions called gyri and sulci respectively the neuron cell bodies concentrated in the cerebral hemispheres lend a gray color to the region

21:52 therefore the cerebral cortex is called gray matter it contains motor areas sensory areas and association areas Association areas are responsible for complex functions such as inter sensory associations memory and communication due to the presence of myelinated axons the inner part of the cerebral Hemisphere appears white and is thus called white matter the thalamus is located between the cerebral cortex and midbrain and acts as a major coordinating Center for sensory and motor signaling

22:42 the hypothalamus is situated at the base of the thalamus and it contains the centers that control body temperature the circadian rhythms and the urge to eat and drink several groups of neurosecretory cells are also present in the hypothalamus which secrete hormones that control the pituitary which in turn controls the secretions of other endocrine glands the collection of structures within the forebrain including the amygdala and hippocampus is known as the limbic system the limbic system along with the hypothalamus Subal for the regulation of sexual behavior long-term memory olfaction pression of emotional reactions such as excitement pleasure rage fear and motivation the midbrain is located between the thalamus hypothalamus of the forebrain and ones of the hind brain the cerebral aqueduct containing cerebrospinal fluid passes through the midbrain and connects the third ventricle to the fourth ventricle of the brain it is also called the aqueduct of sylvius

24:10 the dorsal portion of the midbrain consists of four lobes called corpora quadrigemina it contains reflex centers for vision and hearing the midbrain and hindbrain form the brainstem it acts as a relay station for auditory and visual information that is every impulse conducted between brain and spinal cord passes through the brainstem the hindbrain is formed of the puns cerebellum and medulla oblongata the pons consists of fiber tracts that interconnect the cerebral cortex and medulla to the cerebellum of the brain the convoluted surface of the cerebellum provides a lot of space to accommodate the maximum number of neurons this part of the brain is responsible for coordinated body movement or balance of the body the medulla oblongata acts as a link between the brain and spinal cord the centers in the medulla oblongata control involuntary activities such as respiration blood pressure cardiovascular reflexes and gastric secretions we react instantly when we come in

25:39 contact with an extremely hot or cold object something poisonous etc this quick immediate involuntary response to an external stimulus that occurs without any conscious effort or thought is called reflex action such a reaction requires the involvement of only a part of the central neural system mostly the spinal cord the path through which the reflex action is conducted is also called the reflex arc the reflex arc consists of a receptor sensory or afferent neuron an interneuron or association neuron motor or efferent neurons and an effector organ

26:36 the afferent neuron receives a nerve in from sensory organs such as the skin and transmits it through the dorsal nerve root or sensory nerve into the spinal cord in the spinal cord sensory neuron is connected to the association neuron transmits the stimulus to the effector neuron the efferent neuron then passes the stimulus to effector organs such as the muscles through the ventral nerve cord reflex arc saves time by bypassing impulse transmission to the brain and thus helps us avoid painful experiences I is the organ of sight it helps detect changes in the environment and dispatches signals to the central neural system human beings have a pair of spherical eyes located in eye sockets or orbits of the skull the eyes are directed forward and adapted for binocular vision these are protected by the eyebrows eyelids and lacrimal glands

27:52 secrete an aqueous solution that lubricates the eyes and helps rotate the eyeballs freely the wall of the human eye is composed of three layers external layer or sclera is made of a dense connective tissue the anterior portion of the sclera is the cornea the middle layer or choroid is bluish in color and contains many blood vessels the choroid layer is thin over the posterior 2/3 of the eyeball and thick in the anterior region where it forms the ciliary body the ciliary body continues to form the iris visible colored portion of the eye the eyeball contains a transparent crystalline lens held in place by the ligaments of the ciliary body in front of the lens the iris surrounds and which are called the pupil the muscle fibers of the iris regulate the diameter of the pupil the inner layer is the retina which contains three layers of cells the innermost layer is called ganglion cells

29:17 the middle layer is called bipolar cells and the outermost layer is called photoreceptor cells photoreceptor cells are of two types rods and cones cells contain photopigments the cones are responsible for color vision and daylight vision known as photo pick vision the rods are responsible for Twilight vision which is also known as score topic vision a purple pigment called Road option is present in the rods which contains a derivative of vitamin A dim light however the rods do not play any role in color vision a violet pigment called rhodopsin is present in the cones [Music] sensitive to bright daylight or photopic vision cones are of three types and contain different photo pigments and respond to red green and blue light radiations other colors are detected by simultaneous stimulation of more than one type of bones

30:43 equal stimulation of all the three cones produces a sensation of white light the Coons are insensitive to dim light so a person cannot see colors at night the retina contains two spots known as the blind spot and the fovea the blind spot is the reason on the posterior pole of the eye where the optic nerve leaves the eye and retinal blood vessel enters the organ for the receptor cells are absent in this region and therefore no image forms in the blind spot the posterior end of the eyeball lateral to the blind spot has a yellowish pigmented spot called the macula lutea with a central pit called the fovea the density of cones in this region it's the best visual acuity

31:51 you the equus chamber lies between the cornea and lens it is filled with a thin watery fluid enak was human that provides nutrition to the lens and Konya the vitreous chamber is larger than the Equus chamber and lies between the lens and retina filled with a transparent gel called vitreous humor that gives shape to the eye supports the retina and lens light rays and maintains intraocular pressure inside the eye the human eye works like a camera the cornea Aquos humor lens and vitreous humor

32:46 all actor small lenses and reflect light rays to focus on the retina the iris acts as a diaphragm and regulates the amount of light entering the eye maximum refraction is done by the cornea and the lens brings final adjustment light radiations stimulate the photoreceptors on the retina and form a small and inverted image but the object image is perceived in the right manner due to the interpretation of nerve impulses by the brain light rays in the visible wavelength focus on the retina to generate impulses in the rods and cones the photopigments of the photoreceptors in the human eye are composed of opsin and retinal light dissociates retinol from opsin which results in changing the structure of option the structural change in opsin changes membrane permeability which in turn results in potential differences in the photoreceptor cells this results in the generation of action potential in the ganglion cells through the bipolar cells

34:02 the action potential or impulses are transmitted to the visual area of the cerebral by the optic nerve these nerve impulses are analyzed in the visual area and help to recognize the image formed the air is an important organ that not only assists in hearing but also helps the body maintain balance it can be divided into three sections the outer ear the middle here and the inner ear the outer and middle ear structures persist only in hearing while the inner ear also helps to maintain the body's equilibrium the outer air comprises a funnel-like structure called the pillar and an s-shaped tube called the external auditory meatus

35:10 very fine hairs and wax secreting sebaceous glands are present on the skin of the pillar and the meters which prevent dust and small insects from entering the air the pinna is responsible for collecting vibrations in the air and directing sound into the meatus the meters further extends into the middle here the middle air consists of an air-filled space called the tympanic cavity that separates the outer and inner ears the tympanic cavity is bound externally by the tympanic membrane also known as the eardrum and internally by an auditory capsule the tympanic membrane is composed of connective tissue that is covered with skin on the outside and a mucous membrane on the inside

36:13 the auditory capsule on the other hand has to membrane-bound apertures called the oval window and the round window the middle ear also has three small moveable bones or ossicles called the malleus incus and stapes on the floor of the tympanic cavity these ossicles are attached to one another in a chain like fashion they increase the efficiency of transmission of sound waves to the inner ear air pressure also needs to be maintained on both sides of the air drum for normal hearing

37:00 this is done by the eustachian tube which connects the tympanic cavity to the pharynx the inner air consists of a complex system of intercommunicating chambers and tubes called a labyrinth the labyrinth consists of two functional parts the cochlea which is responsible for hearing and the vestibular apparatus which is responsible for balance the labyrinth is of two types Lonnie and membranous the bony labyrinth is a series of channels filled with a fluid called

37:45 perilymph while the membranous labyrinth lies within the bony labyrinth and is filled with endolymph the cochlea is the coiled portion of the bony labyrinth and is also known as the auditory section of the inner ear the cochlear intern has two membranes namely listeners membrane and the basilar membrane Rizla's membrane and the basilar membrane divide the bony labyrinth into an upper section called the scalar vestibule I and a law section called the scaler tympani which are both filled with perilymph coming to the membranous labyrinth the space between the scaler vestibuli and scaler tympani is called the scaler media and is filled with endolymph the fluids in the labyrinth cushioned the soft structures and conduct waves from the middle ear to the organ of Corti the organ of Corti

39:06 located in the scalar media is the actual receptor of sound it is composed of hair cells that act as auditory receptors above the row of hair cells lies a thin elastic membrane called the tectorial membrane each hair cell has cilia on an apical part which are in contact with the tectorial membrane whose basal end is in contact with afferent nerve fibers the inner air also contains a complex system called the vestibular apparatus that helps maintain the body's balance it is located above the cochlear and consists of three semicircular canals and the auto lift organ which consists of the saccule and utricle each semicircular canal is c-shaped lies at right angles to the other two

40:15 and is suspended in the perilymph the swollen base of these canals is called the ampulla contains a sensory spot called the crista and pilaris the saccule and utricle also contain a sensory spot called the macula both Krista and macula contain hair cells that act as receptors of the vestibular apparatus and are responsible for maintaining the body's balance and posture now we'll see how the ears enable us to perceive sounds the external air receives sound waves and elects them to the air drum the eardrum vibrates in response to sound waves and transmits them through the air ossicles the malleus incus and stapes to the oval window

41:26 the ossicles intern amplify the sound and pass the vibrations through the oval window to the fluid of the cochlea this generates waves in the lymph that induces a ripple in the basilar membrane the vibrations of the basilar membrane then bend the hair cells pressing them against the tectorial membrane the hairs move back and forth against the tectorial membrane which stimulates the hair cells or receptor cells as a result the hair cells generate nerve impulses mitad along afferent nerve fibers and auditory nerves to the auditory cortex of the brain

42:25 the brain then interprets these nerve impulses and sound is recognized in this manner the air forms an important part of the auditory system and also helps us maintain our balance