vacancy news

लिंग निर्धारण

एकलिंगी जीवों में नर तथा मादा जनन अंग अलग - अलग जन्तुओं में होते हैं । नर तथा मादा में लिंग भेद होता है । 

एकलिंगी जीवों के लिंग भेद प्रक्रिया के भेद में मैक्लंग ने लिंग निर्धारण का गुणसूत्रवाद दिया । इसके अनुसार लिंग का निर्धारण गुणसूत्रों पर निर्भर करता है तथा इसकी वंशागति मेण्डेल के नियमों के अनुसार होती है ।

लिंग गुणसूत्र का निर्धारण सिद्धान्त सी. ई. मैक्लंग ने सन् 1902 में दिया था । इसके अनुसार प्राणियों में दो प्रकार के गुणसूत्र पाये जाते हैं -

(1) समजात गुणसूत्र 

(2) लैंगिक गुणसूत्र या एलोसोम 

सभी जीवों में गुणसूत्रों की संख्या निश्चित होती है , जिसे  2 X से प्रदर्शित करते हैं । इनमें से दो गुणसूत्र लैंगिक गुणसूत्र होते हैं । 

लैंगिक गुणसूत्र दो प्रकार के होते हैं - X तथा Y । कुछ जन्तुओं में एक लिंग में दोनो लैंगिक गुणसूत्र समान होते हैं तथा दूसरे लिंग में लिंग गुणसूत्र असमान होते हैं। 

लिंग निर्धारण की XY विधि :- इस विधि में मादा के दोनों लैंगिक गुणसूत्र XX होते हैं तथा नर नर में एक लैंगिक गुणसूत्र X तथा दूसरा Y होता है। मादा में जब अण्डजनन होता है , तब सभी अण्डाणुओं में एक अगुणित सैट दैहिक गुणसूत्र का तथा एक X लैंगिक गुणसूत्र होता है (A + X) । इस प्रकार सारे अण्डाणु समान होते हैं । अत: मादा को समयुग्मकी कहते हैं । इसके विपरीत नर में शुक्राणुजनन के समय कुछ शुक्राणुओं में एक सैट दैहिक गुणसूत्रों का तथा Y गुणसूत्र (A + X or A + Y) होते हैं । इस प्रकार दो प्रकार के शुक्राणुओं का निर्माण होता है । लगभग 50% शुक्राणु A + X तथा 50%  A + Y गुणसूत्रों वाले होते हैं । अत: नर को विषमयुग्मजी कहते हैं । 

निषेचन के समय यदि A + Y शुक्राणु का समेकन अण्डाणु के साथ होता है , तब नर संतान पैदा होती है । यदि अण्डाणु के समेकन A + X शुक्राणु के साथ होता है , तथा मादा सन्तान पैदा होती है । यह केवल संयोग है कि कौन से शुक्राणु का समेकन अण्डाणु के साथ हो । इसी के आधार पर सन्तान लिंग निर्धारण होता है । 

लिंग निर्धारण की यह विधि मनुष्य में पायी जाती है । स्त्रियों की गुणसूत्र संख्या 44 + XX होती है । पुरुषों की गुणसूत्र संख्या 44 + XY होती है । इस प्रकार इस विधि के अनुसार सन्तानों में लिंग निर्धारण के लिए पिता उत्तरदायी है ।     

ARTERIES VS VEINS

Comparison Chart

BASIS FOR COMPARISON	ARTERIES	VEINS
Role	The artery carries oxygenated blood away from the heart.	Veins carry deoxygenated blood towards the heart.
Colour	Red in colour, as they carry oxygenated blood.	Blue in colour, as they carry deoxygenated blood.
Location	Arteries located deep within the body.	Veins are present close to the skin, in the body.
Kind of blood	Oxygenated blood, except pulmonary artery. As pulmonary artery carries deoxygenated blood.	Deoxygenated blood except for pulmonary veins. As pulmonary veins carry oxygenated blood.
Lumen	Narrow lumen.	Broad lumen.
Wall	Thick walled, which is more elastic.	Thin walled and are less elastic.
Tunica	Externa tunica is less strong and less developed.	Here externa tunica is more strong and more developed.
	Media tunica is more muscular and thick.	Media tunica are less muscular and relatively thin.
Types	Pulmonary and Systemic artery.	Superficial veins, deep veins, pulmonary veins and systemic veins.
Muscles tissues layer	Thick layer that supports the high pressure of blood.	It has the thin layer.
Blood pressure	More.	Less.
Blood volume	Low, which is around 30%.	High, which is around 65%.
Pulse	Detectable in the artery.	Undetectable in veins.
Valves	No valves.	Valves present.
Disease	The main disease affecting the arteries is Atherosclerosis.	The main disease affecting the veins is Deep vein thrombosis.
Side effect	If the blood flow stops, it will collapse.	As it has the thick muscular layer, it would remain open even if the flow of blood stopped.

NEURAL CONTROL AND COORDINATION

CHAPTER

NEURAL CONTROL AND COORDINATION

1.    Action potential: A sudden change in the electrical charges in the plasma membrane of a nerve fibre.

2.    Aqueous humour: The thin watery fluid that occupy space between lens and cornea in eye.

3.    Blind spot: A spot on retina which is free from rods and cones and lack the ability for vision.

4.    Cerebrospinal fluid: An alkaline fluid present in between inner two layer of meninges and also in the cavities (ventricles) found Inside brain and spinal cord.

5.    Cerebellum: A part of hind brain that controls the balance and posture of the body.

6.    Cochlea: A spirally coiled part of internal ear which is responsible for hearing.

7.    Corpus callosum: A curved thick bundle of nerve fibres that joins two cerebral hemisphere.

8.    Depolarisation: A condition when polarity of the plasma membrane of nerve fibre is reversed.

9.    Endolymph: The fluid filled within membranous labyrinth.

10.  Ecustachian tube: A tube which connect ear cavity with the pharynx.

11.  Fovea: An area of highest vision on the retina which contain only cones.

12.  Meninges: Three sheets of covering of connective tissue wrapping the brain and spinal cord.

13.  Grey Matter: This shows many convolutions which increase the amount of vital nerve tissue.

14.  Medulla oblongata: Posterior most part of the brain which is continuous with spinal cord and control respiration, heart rate, swallowing, vomiting.

15.  Pons: Thick bundles of fibres on the ventral side of brain below cerebellum.

16.  Foramen magnum: A big aperture in the skull posteriorly through which spinal cord emerges out.

17.  Spinal cord: A tubular structure connected with medulla oblongata of brain and situated in the neural canal of the vertebral column, covered by meninges.

18.  White matter: It lies inner to the grey matter in the brain and outer the grey matter in the spinal cord. This white matter is made of medullated (myelinated) axons of millions of nerve cells (neurons).

19.  Ventricles: The hollow spaces found in side the brain and spinal cord. These ventricles are filled with cerebro spinal fluid.

20.  Synaptic cleft: A narrow fluid filled space which separates two membranes of the two neurons at the synapse.

21.  Synaptic vesicles: These are membrane bound vesicles in the axoplasm of the axon terminal and these store neurotransmitters substances like acetylcholine, norepinephrine.

22.  Neurotransmitter: These are chemicals stored in synaptic vesicles, diffuse to reach the membrane of next neuron for its stimulation.

23.  Synapse: A physiological junction between axon of one neuron and dendrite of next neuron.

CNS − Central Neural system PNS − Peripheral Neural system ANS − Autonomic Neural system

Neural Sytem

Central neural Sytem

Peripheral neural System

Brain

Spinal cord

Cranial nerve

Spinal nerve

12 pairs

31 pairs

Nerve fibres of PNS

Afferent fibres

Efferent fibres

Transmit impulse from

Transmit impulse

Tissue/organ to CNS

from CNS to

Peripheral tissue/organ

Division of PNS

Somatic neural System

Autonomic neural system

Relays impulse from CNS

Transmit impulse

to Skeletal muscle

from CNS to involuntary

Organ and smooth muscles

 Cell body (cyton) = Cytoplasm with nucleus,

			Cell organelles and Nissle’s granules
Parts of	Dendrites	=	Short fibres which branch rapidly
Neuron
			And project out of cell
	Axon	=	Single, long fibre, branched at distal end
	Multi polar	=	One axon and two or more dendrites
			Found is cerebral cortex
Axon	Bipolar	=	One axon and one dendrite
			Found in retina of eye
	Unipolar	=	Cell body with axon only
			Found usually in the embryonic stage

Conduction of nerve impulse along axon

Polarized membrane/Resting Potential

In resting phase when neuron is not conducting an impulse, the axonal membrane is called polarized. This is due to difference in concentration of ions across the axonal membrane.

At Rest: • Axoplasm inside the axon contain high conc. of K⁺ and low conc. of Na⁺ etc., resulting in the gross electrical charge ‘Negative’.

•    The fluid outside the axon contain low conc. of K⁺ and high conc. of Na⁺ etc., resulting in the gross electrical charge ‘Positive’.

As a result the outer surface of axonal membrane is positively charged and inner surface is negatively charged. The electric potential difference across the resting plasma membrane is called resting potential.

Action Potential: When a nerve fibre is stimulated, the permeability of membrane to Na⁺ is greatly increased at the point of stimulus (rapid influx of Na⁺) and hence polarity of membrane is reversed and now membrane is said to be depolarized. The electric potential difference across the plasma membrane at that site is called action potential, which infact termed as nerve impulse.

Depolarization is very rapid, so that conduction of nerve impulse along the entire length of axon occurs in fractions of second.

(i)   At electrical synapses: Here the membrane of pre and post-synaptic neuron are in very close proximity. Electric current can flow directly from one neuron into other across these synapses, like impulse conduction along a single axon.

(ii)   At chemical synapses: Here the membrane of pre and post-synaptic neuron are separated by fluid filled space called synaptic cleft. Neurotransmitter are involved here. When an impulse arrives at the axon terminal, it stimulates themovement of the synaptic vesicles towards membrane and they fuse with the plasma membrane and release their neurotransmitter in the synaptic cleft. These chemicals bind to specific receptors, present on the post-synaptic membrane. Their binding opens up ion channels and allow the entry of ion which generate new potential in post synaptic neuron.

Parts of Brain

Fore brain

(a) Cerebrum

(b) Thalamus

(c) Hypothalamus

Mid brain

Hind brain

(a) Cerebellum

(b) Pons

(c) Medulla oblongata

Functions of parts of brain:

Cerebrum: Centre of intelligence, memory and imagination, reasoning, judgement, expression of will power.

Thalamus: Acts as relay centre to receive and transmit general sensation of pain, touch and temperature.

Hypothalamus: Centre for regulation of body temperature, urge for eating and drinking (Homeostasis).

Mid brain: Responsible for coordinating visual reflexes and auditory reflexes -- corpora quadrigemine.

Cerebellum: Maintains posture and equilibrium of the body as well as coordinates and regulates voluntary movement.

Pons varoli: Relays impulses between medulla oblongata and cerebral hemisphere and between the hemisphere of cerebrum and cerebellum. Medulla oblongata: Centre that control heart beat, breathing, swallowing, salivation, sneezing, vomiting and coughing gives rise to cranial nerves (12 pairs).

Organ of Sight − Eye

Layer		Component		Function
1. External layer		Sclera		Protects and maintain shape of the
				eye ball.
		Cornea		Absorb O2 from the air, helps to
				focus light rays.
2. Middle layer		Choroid		Absorb light and prevent light
				from being reflected within the eye
				ball.
		Ciliary body		Holds lens, regulate shape of the
				lens.
		Iris		Control amount of light entering.
3. Inner layer		Retina		Vision in dim light, colour vision,
				vision in bright light.
		Organ of Hearing − Ear
Portion of the ear	Component			Function
1. External ear	Pinna		Collect sound waves.
	External auditory		Direct sound waves towards ear
	canal		drum, ear wax prevents the entry
			of foreign bodies.
2. Middle ear	Tympanic		Acts as resonator that reproduces
	membrane		the vibration of sound.
	Ear ossicles		Transmit sound waves to internal
			ear.
	Eustachian tube		Helps in equalizing the pressure of
			either side of ear drum.

3. Internal ear	Cochlea	Hearing.
	Vestibular	Balancing of body.
	apparatus