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Coleen Davis
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1 POINTS TO REMEMBER : Dwnladed frm Neural Cntrl and Crdinatin HUMAN NEURAL SYSTEM : The human neural system divided int tw parts The central nervus system (CNS) The peripheral nervus system (PNS) The CNS includes the brain and spinal crd and is the site f infrmatin prcessing and cntrl. The PNS cmprises all nerves f the bdy assciated with CNS. Cranial nerves: nerves arises frm the brain (12 pairs) Spinal nerves: nerves arises frm the spinal crd (33 pairs) The nerve fibres (Cranial and spinal nerves) are f tw types Afferent fibres: transmits impulses frm the tissues t the CNS Efferent fibres: transmits impulses frm the CNS t the tissues. The PNS is divided int tw divisins Smatic neural system. Autnmic neural system. Sympathetic neural system. Parasympathetic neural system. The smatic neural system relays impulses frm the CNS t skeletal muscles. The autnmic neural system transmits impulses frm the CNS t the invluntary rgans and smth muscles f the bdy. NEURON AS STRUCTURAL AND FUNCTUIONAL UNIT OF NERVOUS SYSTEM : A neurn cmpsed f three majr parts Cell bdy Dendrites Axn The cell bdy cntains cytplasm with typical cell rganelles and specific granular bdy called Nissl s granules. Shrt fibres which prfusely branched prjects ut f cell bdy called dendrites. The axn is a lng fibre, branched at the end. Each branch terminates as a bulb-like structure called synaptic knb. Dwnladed frm

2 Dwnladed frm Based n the number f axn and dendrites the neurns are f fllwing types Multiplar: ne axn and several dendrites - fund in cerebral crtex. Biplar: ne axn and ne dendrite - fund in retina f eye. Uniplar: cell bdy with ne axn nly fund in embrynic stage. The axn may be myelinated r nn-myelinated. The myelinated nerve fibres are envelped with Schwann cells, which frm myelin sheath arund the axn. The gaps between tw adjacent myelin sheath are called Ndes f Ranvier. Cranial and spinal nerves are myelinated. Autnmic and smatic neural fibres are nn-myelinated. GENERATIONA ND CONDUCTION OF NERVE IMPULSE : Plarized membrane/resting Ptential : In resting phase when neurn is nt cnducting an impulse, the axnal membrane is called plarized. This is due t difference in cncentratin f ins acrss the axnal membrane. At Rest : Axplasm inside the axn cntains high cnc. f K + and lw cnc. f Na +. The fluid utside the axn cntains lw cnc. f K + and high cnc. f Na +. As a result the uter surface f axnal membrane is psitively charged and inner surface is negatively charged. The electric ptential difference acrss the resting plasma membrane is called resting ptential. Actin Ptential : When a nerve fibre is stimulated, the permeability f membrane t Na + is greatly increased at the pint f stimulus (rapid influx f Na + ) and hence plarity f membrane is reversed and nw membrane is said t be deplarized. The electric ptential difference acrss the plasma membrane at that site is called actin ptential, which in fact termed as nerve impulse. Deplarizatin is very rapid, s that cnductin f nerve impulse alng the entire length f axn ccurs in fractins f secnd. Deplarizatin is fllwed by the increase in permeability f K + t the membrane leads t change in plarizatin i.e. +ve charge utside and ve charge inside. It is called replarizatin. Regain f resting ptential takes place due t actin f Na + /K + ATPase enzyme which transprts three Na+ inside and tw K + inside with expense f ne ATP. It cntinues till the resting ptential becmes -70 mv. Transmissin f impulses thrugh synapse : The functinal junctin between tw neurns is called synapse. A synapse is frmed by the membranes f a pre-synaptic neurn and a pst-synaptic neurn, which may r may nt be separated by a gap called synaptic cleft. There are tw types f synapses: Electrical synapse: pre and pst synaptic membrane with clse prximity withut any synaptic cleft. Chemical synapse: the pre and pst synaptic membrane is separated by a fluid filled synaptic cleft. Dwnladed frm

3 Cnductin f impulse in chemical synapse : Dwnladed frm The axn terminals cntains vesicles filled with chemicals calledneurtransmitters. When the actin ptential arrives at the axn terminals, it stimulates the mvement f synaptic vesicles twards the membrane. Synaptic vesicle fused with the pre-synaptic membrane and releases the neurtransmitter int the synaptic cleft. The neurtransmitter binds with the receptrs lcated n the pst-synaptic membrane. Activatin f receptrs n pst-synaptic membrane makes it permeable t Na+ and generates actin ptential as it dne by stimulus. The new ptential develped may be either excitatry r inhibitry depends n the nature f the neurtransmitter. CENTRAL NERVOUS SYSTEM : Brain is the central cntrl and cmmand system in neural crdinatin. The human brain is well prtected by the skull. Inside the skull the brain is cvered by cranial meninges. Meninges cnsists f fllwing layers Outer layer dura mater. Middle layer thin arachnid. Inner layer pia mater remain clse cntact with the brain. The human brain is divided int three majr parts Fre brain. Cerebrum. Thalamus. Hypthalamus. Mid brain. Hind brain. Pns. Cerebellum Medulla blngata. Fre brain : Cerebrum is the majr part f the fre brain. Deep median fissure divides the cerebrum int tw equal cerebral hemisphere. The hemispheres are cnnected by tract f nerve fibres called crpus callsum. The thin layers f cells cvers the cerebral hemispheres called cerebral crtex and are thrwn int prminent flds. The cerebral crtex is referred as the grey matter. The cerebral crtex differentiated int Mtr areas sends infrmatin t the bdy Sensry areas receives infrmatin frm the bdy Assciatin area-neither sensry nr mtr (c-rdinates the infrmatin) Dwnladed frm

4 Dwnladed frm Interir f the brain is called white matter due t myelin sheath f tract f nerve fibres. The cerebrum is wraps arund a structure called thalamus, which is a majr crdinating centre fr sensry and mtr signaling. At the base f the thalamus is the hypthalamus. The hypthalamus have fllwing functins Cntrl bdy temperature. Urge fr eating and drinking. Neursensry cells secrete different hrmnes. The inner part f the cerebral hemispheres and a grup f assciated deep structures like amygdala, hippcampusetc. frms cmplex structure called the limbic lbe r limbic system. Alng with the hypthalamus it is invlved in the regulatin f sexual behaviur, expressin f emtinal reactins (excitement, pleasure, rage and fear) and mtivatin. Mid brain: The mid brain is lcated between the thalamus and pns f the hind brain. A canal called cerebral aqueduct passes thrugh the mid brain. The drsal part f the mid brain cnsists f fur swelling called crpra quadrigemina. Hind brain: Cmprises pns, cerebellum and medulla blngata. Pns cnsists f fibre tracts that intercnnect different regins f the brain. Cerebellum has very cnvluted surface in rder t prvide the additinal space fr many mre neurn. Medulla f the brain is cntinued as spinal crd. Medulla cntains centers which cntrl respiratin, cardivascular reflexes and gastric secretin. REFLEX ACTION AND REFLEX ARC : Sudden spntaneus, invluntary reactin t a stimulus withut invlvement f brain is called reflex actin. Sme examples f such actins are Sudden withdrawal f the bdy part which cmes in cntact with bjects that are extremely ht, cld, pinted. Reflex arc: sensry rgan sensry neurn spinal crd mtr neurn effectr rgan. SENSORY RECEPTION AND PROCESSING : Eye : Eye is the sensry rgan f visin. Our paired eyes are lcated in sckets f the skull called rbit. Eye cnsists f three layer Sclera: tunica fibrsa. External layer cmpsed f dense cnnective tissue. It is the nly cmplete layer f the eye. The anterir prtin f this layer is transparent and called crnea. Dwnladed frm

5 Dwnladed frm Chrid: tunica vascularis. It is the middle layer f the eye. It is well vascularized and lks bluish clr. Psterir tw third parts is thin. Anterir part is thick and frm ciliary bdy. The ciliary bdy itself cntinues frward t frm a pigmented and paque structure called iris (the visible clured prtin f the eye). Iris cntains a central aperture called pupil. The diameter f pupil is regulated by the muscle f iris. Retina r tunica nervsa. It is the innermst layer f the eye. It cnsists f three layer f cells frm inside t utside Ganglin cells Biplar cells Phtreceptr cells. There are tw types f phtreceptr cells namely rds and cnes. Cnes cntain phtpigment called idpsin. Cnes respnsible fr daylight (phtpic) visin and clr visin. Rds cntain phtpigment called rhdpsin r visual purple, which cntain a derivative f Vitamin-A. Rds respnsible fr twilight (sctpic) visin. The ptic nerves leave the eye and the retinal bld vessel enters it at a pint where rds and cnes are absent hence called blind spt. At the psterir ple f the eye lateral t blind spt there is a yellwish pigmented spt called macula lutea. Macula lutea with highly cncentrated cnes, where the visin is sharpest ( high reslutin visin) In the centre f macula lutea there is a central pit called fvea centralis, a tightly packed array f specializedphtsensr-receptr cells. It prevents the entry f high intensity light by clsing the eye by reflex actin. The lens cmpsed f crystalline prtein, is suspended behind the pupil by a suspensry ligament attached t the ciliary bdy. The lens and suspensry ligament divide the cavity f the eye ball int tw chambers. Chamber in frnt f lens called aqueus chamber filled with aqueus humr. Chamber behind the lens is called vitreus chamber filled with transparent gel called vitreus humr. Mechanism f visin : The light rays in visible spectrum fcused n the retina thrugh the crnea and lens generate ptentials (impulses) in rds and cnes. Phtsensitive pigments cmpsed f psin (a prtein) and retinal (an aldehyde f vitamin-a). Light induces dissciatin f the retinal frm psin resulting changes in structure f psin. This causes change in membrane permeability. As a result, ptential differences are generated in the phtreceptr cells. This prduces a signal that generates actin ptential in the ganglin cells thrugh biplar cells. Dwnladed frm

6 Dwnladed frm These actin ptentials transmitted by ptic nerves t the visual crtex area f brain where the neural impulses are analyzed and the image frmed n the retina is recgnized. THE EAR : The ear perfrms tw sensry functin, hearing and maintenance f bdy balance. Anatmically, the ear can be divided int three majr sectin Outer ear r external ear. Middle ear. Internal ear r inner ear External ear : Outer ear cnsists f the pinna and external auditry meatus (canal). Pinna cllects the vibratin in the air which prduces sund. Auditry meatus extends upt the tympanic membrane (the ear drum). Tympanic membrane is made f cnnective tissue cvered with skin. Middle ear : Middle ear cntains three ear ssicles called Malleus (hammer),incus (anvil) and stapes (stirrup). The Malleus is attached t the tympanic membrane and the stapes is attached t the val windw f the cchlea. The ear ssicles amplify the sund waves cmes frm the tympanic membrane. A Eustachian tube cnnects the middle ear cavity with the pharynx. Eustachian tube helps in equalizing the pressures n either sides f the ear drum. Internal ear : The fluid filled internal ear is called labyrinth cnsists f tw parts, the bny and membranus labyrinth. The bny labyrinth is a series f channels, inside these channels lies the membranus labyrinth, which is surrunded by a fluid called perilymph. The membranus labyrinth is filled by a fluid called endlymph. The labyrinth cnsists f tw prtins The ciled prtin called cchlea. The cmplex abve the cchlea called vestibular apparatus. Cchlea: The ciled prtin f the labyrinth is called cchlea. The membrane cnstituting cchlea are The reissner s membrane The basilar membrane. Reissner s and basilar membrane divide the surrunding perilymph int an upper scala vestibuli and lwer scala tympani. The space within cchlea called scala media is filled with endlymph. At the base f the cchlea, the scala vestibule ends at the val windw (fenestra valis), while scala tympani terminate at the rund windw (fenestra rtundus) which pens int the middle ear. Dwnladed frm

7 Dwnladed frm The rgan f crti is a structure lcated n the basilar membrane which cntains hair cells that act as auditry receptrs. The basal end f hair cells is in clse cntact with the afferent nerve fibres. Hair cells cntain stere cilia prjected frm the apical part f each hair cell. Hair cells cvered by a thin elastic membrane called tectrial membrane. Vestibular apparatus: Vestibular apparatus lcated abve the cchlea. Vestibular apparatus cnsists f Three semi-circular canals Otlith rgan cnsisting saccule and utricle. Each semicircular canal lies in a different plane at right angles t each ther. Membranus semi-circular canals are suspended in the perilymph f bny canal. The base f canals is swllen and is called ampulla, which cntain a prjecting ridge called crista ampullaris with hair cells. The saccule and utricle cntain a prjecting ridge called macula. Crista and macula are the specific receptrs f the vestibular apparatus respnsible fr maintenance f balance f the bdy and psture. Mechanism f hearing: The external ear receives sund waves and directs them t the ear drum. Sund waves are amplified by the ear ssicles and send it t the val windw in the middle ear. The vibratin f the val windw creates waves in the perilymph f scala vestibuli. The waves in perilymph induce a ripple in the basilar membrane. Mvements f the basilar membrane bend the hair cells, pressing them against the tectrial membrane. As a result nerve impulses are generated in the assciated afferent neurn. These impulses are transprted t the auditry crtex f the brain where the impulses are analysed and the sund is recgnized. Dwnladed frm

Topic 11: Senses. Sensory Receptors

Topic 11: Senses. Sensory Receptors Tpic 11: Senses Sensry Receptrs Part f the nervus system that detects a stimulus A sensry receptr culd be: Types f Sensry Receptrs: Chemreceptrs: detects chemicals ( ) Phtreceptrs: detects light (fund