NEURAL CONTORL AND CORDINATION CLASS 11 NOTES

NEURAL CONTORL AND CORDINATION

NEURAL CONTORL AND CORDINATION CLASS 11 NOTES

Coordination is the process through which two or more organs interact and complement the functions of one another.

• For example- When we do physical exercises, the energy demand is increased for maintaining an increased muscular activity.

• In our body, the neural system and the endocrine system jointly coordinate and integrate all the activities of the organs.

NEURAL SYSTEM

• The neural system of all animals is composed of highly specialised cells called neurons.

• The neural organisation is very simple in lower invertebrates.

• For example, in Hydra it is composed of a network of neurons.

• The neural system is better organised in insects and more developed in vertebrates.

HUMAN NEURAL SYSTEM

• The human neural system is divided into two parts:

1.  the central neural system (CNS)

2. the peripheral neural system (PNS)

•The CNS includes the brain and the spinal cord and is the site of information processing and control.

•The PNS comprises of all the nerves of the body associated with the CNS (brain and spinal cord).

•The nerve fibres of the PNS are of two types

1. afferent fibres

2. efferent fibres

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•  The afferent nerve fibres transmit impulses from tissues/organs to the CNS and the efferent fibres transmit regulatory impulses from the CNS to the concerned peripheral tissues/organs.

•  The PNS is divided into two divisions called

1. somatic neural system

2. autonomic neural system.

• The somatic neural system relays impulses from the CNS to skeletal muscles while the autonomic neural system transmits impulses from the CNS to the involuntary organs and smooth muscles of the body.

• The autonomic neural system is further classified into sympathetic neural system and parasympathetic neural system.

NEURAL CONTORL AND CORDINATION CLASS 11 NOTES

NEURON AS STRUCTURAL AND FUNCTIONAL UNIT OF NEURAL SYSTEM

• A neuron is a microscopic structure composed of three major parts

1. cell body

2. dendrites

3. axon

• The cell body contains cytoplasm with typical cell organelles and certain granular bodies called Nissl’s granules.

• Short fibres which branch repeatedly and project out of the cell body also contain Nissl’s granules and are called dendrites.

• The axon is a long fibre, the distal end of which is branched.

• Each branch terminates as a bulb-like structure called synaptic knob which possess synaptic vesicles containing chemicals called

• Based on the number of axon and dendrites, the neurons are divided into three types

1. multipolar

2. bipolar

3. unipolar

• Multipolar neurons contain with one axon and two or more dendrites. For example- neurons of cerebral cortex

• Bipolar neurons are the one which contain one axon and one dendrite. For example- neurons found in the retina of eye.

• Unipolar neurons are the one which contain cell body with one axon only. For example- neurons found in the embryonic stage.

There are two types of axons

1. myelinated

2. Unmyelinated

•The myelinated nerve fibres are enveloped with Schwann cells, which form a myelin sheath around the axon. For example- nerve fibres found in spinal and cranial nerves

•The gaps between two adjacent myelin sheaths are called nodes of Ranvier.

•Unmyelinated nerve fibre is enclosed by a Schwann cell that does not form a myelin sheath around the axon. For example- nerve fibres found in autonomous and the somatic neural systems.

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GENERATION AND CONDUCTION OF NERVE IMPULSE

• Different types of ion channels are present on the neural membrane, which are selectively permeable to different ions.

• When a neuron is not conducting any impulse, i.e., resting, the axonal membrane is comparatively more permeable to potassium ions (K+ ) and nearly impermeable to sodium ions (Na+) and negatively charged proteins present in the axoplasm.

• The axoplasm inside the axon contains high concentration of K+ and negatively charged proteins and low concentration of Na+ .

• The fluid outside the axon contains a low concentration of K+ , a high concentration of Na+ and thus form a concentration gradient.

• The ionic gradients across the resting membrane are maintained by the active transport of ions by the sodium-potassium pump which transports 3 Na+ outwards for 2 K+ into the cell and hence the outer surface of the axonal membrane possesses a positive charge while its inner surface becomes negatively charged and therefore is polarised.

• The electrical potential difference across the resting plasma membrane is called as the resting potential.

NEURAL CONTORL AND CORDINATION CLASS 11 NOTES

Mechanisms of generation of nerve impulse and its conduction along an axon

• When a stimulus is applied at a site on the polarised membrane, the membrane at the site A becomes freely permeable to Na+, which leads to a rapid influx of Na+ followed by the reversal of the polarity at that site, and the membrane is depolarised.
• The electric potential difference across the plasma membrane is called action potential.
• Depolarisation is followed by the increase in permeability of K+ to the membrane leading to change in polarization and the process is called repolarisation, and the membrane is repolarised.
• During depolarisation, the outer surface of the membrane becomes negatively charged and the inner side becomes positively charged.
• During repolarisation, outside of membrane becomes positively charged and inside becomes negative.
• Regain of resting potential takes place dueto action of NA+/K+ ATPase enzyme, which transports three Na+ inside and two K+ with expense of one ATP.

Neural Control and Coordination Class 11 Notes NCERT

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TRANSMISSION OF IMPULSE

• A nerve impulse is transmitted from one neuron to another through junctions called synapses.
• A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft.
• There are two types of synapses, namely,

1. electrical synapses
2. chemical synapses.

• At electrical synapses, the membranes of pre- and post-synaptic neurons are in very close proximity and electrical current can flow directly from one neuron into the other across these synapses.
• Impulse transmission across an electrical synapse is always faster than that across a chemical synapse.
• At a chemical synapse, the membranes of the pre- and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft.
• Chemicals called neurotransmitters are involved in the transmission of impulses at synapses.
• The axon terminals contain vesicles filled with these neurotransmitters.
• When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft.

The released neurotransmitters bind to their specific receptors, present on the post-synaptic membrane , which opens ion channels allowing the entry of ions which can generate a new potential in the post-synaptic neuron.

CENTRAL NERVOUS SYSTEM

• The brain is the central information processing organ of our body, and acts as the ‘command and control system’.
• It controls the voluntary movements, balance of the body, thermoregulation, and the brain also processes vision, hearing, speech etc.
• The human brain is well protected by the skull.Inside the skull, the brain is covered by cranial meninges consisting of an

1. outer layer called dura mater
2. a very thin middle layer called arachnoid
3. and an inner layer called pia mater.

The brain can be divided into three major parts:

1. forebrain
2. midbrain
3. hindbrain

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REFLEX ACTION

The entire process of response to a peripheral nervous stimulation, that occurs involuntarily, requires the involvment of a part of the central nervous system is called a reflex action.

1. The reflex pathway comprises
2. Receptor
3. Afferent neurons
4. Central nervous system
5. Motor neurons
6. Effector

• Receptor is a structure that receives stimuli.
• The afferent neuron receives signal from a sensory organ and transmits the impulse via a dorsal nerve root into the CNS.
• Central nervous system is the region which initiates response for stimuli.
• The efferent neuron carries signals from CNS to the effector.
• Effector is a muscle or gland that receives motor impulse and exhibits pressure.

SENSORY RECEPTION AND PROCESSING

• The sensory organs detect all types of changes in the environment and send appropriate signals to the CNS, where all the inputs are processed and analysed.
• Signals are then sent to different parts/ centres of the brain and this is how changes in the environment can be sensed.

Examples of sensory organ- eye, ear, nose, skin, tongue.

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THE EYE

• Our paired eyes are located in sockets of the skull called Parts of eye
• The adult human eye ball is nearly a spherical structure.
• The wall of the eye ball is composed of three layers
• external layer is composed of a dense connective tissue and is called the sclera
• anterior portion of this layer is called the cornea
• middle layer is choroid, which contains many blood vessels and looks bluish in colour.
• The choroid layer is thin over the posterior two-thirds of the eye ball, but it becomes thick in the anterior part to form the ciliary body.
• The ciliary body itself continues forward to form a pigmented and opaque structure called the iris which is the visible coloured portion of the eye.
• The eye ball contains a transparent crystalline lens which is held in place by ligaments attached to the ciliary body.
• In front of the lens, the aperture surrounded by the iris is called the pupil.
• The diameter of the pupil is regulated by the muscle fibres of iris.
• The inner layer is the retina and it contains three layers of cells, from inside to outside

1. ganglion cells
2. bipolar cells
3. photoreceptor cells.

There are two types of photoreceptor cells

1. rods

Neural control and Coordination Class 11 Notes for NEET

• Photoreceptor cells contain the light-sensitive proteins called the photopigments.
• The daylight vision and colour vision are functions of cones and the twilight vision is the function of the rods.
• The rods contain a purplish-red protein called the rhodopsin or visual purple, which contains a derivative of Vitamin A.
• In the human eye, there are three types of cones which possess their own characteristic photopigments that respond to red, green and blue lights.
• The optic nerves leave the eye and the retinal blood vessels enter it at a point medial to and slightly above the posterior pole of the eye ball.
• Photoreceptor cells are not present the medial region and hence it is called the blind spot.
• At the posterior pole of the eye lateral to the blind spot, there is a yellowish pigmented spot called macula lutea with a central pit called the fovea, is a thinned-out portion of the retina where only the cones are densely packed.
• The space between the cornea and the lens is called the aqueous chamber and contains a thin watery fluid called aqueous humor.
• The space between the lens and the retina is called the vitreous chamber and is filled with a transparent gel called vitreous humor.

Mechanism of vision

• The light rays in visible wavelength focussed on the retina through the cornea and lens generate potentials in rods and cones.
• The photosensitive compounds (photopigments) in the human eyes is composed of

1. opsin
2. oretinal

• Light induces dissociation of the retinal from opsin resulting in changes in the structure of the opsin, which causes membrane permeability changes and that is why potential differences are generated in the photoreceptor cells, which produces a signal that generates action potentials in the ganglion cells through the bipolar cells.
• The action potentials are transmitted by the optic nerves to the visual cortex area of the brain, where the neural impulses are analysed and the image formed on the retina is recognised.

THE EAR

• The ears perform two sensory functions

1. hearing
2. maintenance of body balance

NEURAL CONTORL AND CORDINATION CLASS 11 NOTES

Parts of ear

• The ear can be divided into three major sections called the

1. outer ear
2. the middle ear
3. the inner ear

The outer ear consists of

1. pinna
2. external auditory meatus (canal).

• The external auditory meatus leads inwards and extends up to the tympanic membrane (the ear drum).
• The middle ear contains three ossicles called

1. malleus
2. incus
3. ostapes

• The malleus is attached to the tympanic membrane and the stapes is attached to the oval window of the cochlea.
• An Eustachian tube connects the middle ear cavity with the pharynx, and the tube helps in equalising the pressures on either sides of the ear drum.
• The fluid-filled inner ear called labyrinth consists of two parts

1. the bony
2. othe membranous labyrinths.

• The bony labyrinth is a series of channels and inside these channels lies the membranous labyrinth, which is surrounded by a fluid called perilymph.
• The membranous labyrinth is filled with a fluid called endolymph.
• The coiled portion of the labyrinth is called cochlea.
• The membranes constituting cochlea, the reissner’s and basilar, divide the surounding perilymph filled bony labyrinth into an upper scala vestibuli and a lower scala tympani.
• The space within cochlea called scala media is filled with endolymph.
• At the base of the cochlea, the scala vestibuli ends at the oval window, while the scala tympani terminates at the round window which opens to the middle ear.
• The organ of corti is a structure located on the basilar membrane which contains hair cells that act as auditory receptors.
• The hair cells are present in rows on the internal side of the organ of corti and above the rows of the hair cells is a thin elastic membrane called tectorial membrane.
• The inner ear also contains a complex system called vestibular apparatus, located above the cochlea.
• The vestibular apparatus is composed of three semi-circular canals and the otolith organ consisting of the saccule and utricle.
• The base of canals is swollen and is called ampulla, which contains a projecting ridge called crista ampullaris, which has hair cells.
• The saccule and utricle contain a projecting ridge called macula.

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Mechanism of hearing

• The external ear receives sound waves and directs them to the ear drum..
• The ear drum vibrates in response to the sound waves and these vibrations are transmitted through the ear ossicles (malleus, incus and stapes) to the oval window, and the vibrations are passed through the oval window on to the fluid of the cochlea, where they generate waves in the lymphs.
• The waves in the lymphs induce a ripple in the basilar membrane and these movements of the basilar membrane bend the hair cells, pressing them against the tectorial membrane, due to this, nerve impulses are generated in the associated afferent neurons.
• The impulses are transmitted by the afferent fibres via auditory nerves to the auditory cortex of the brain, where the impulses are analysed and the sound is recognised.

NEURAL CONTORL AND CORDINATION CLASS 11 NOTES