Neural control

 

Points To Remember

Coordination : Process through which two or more organs interact and complement the functions of one another surrounding the brain.

Action potential : A sudden change in the electrical charges in the plasma

membrane of a nerve fibre.

Aqueous humour : The thin watery fluid that occupy space between lens

and cornea in eye.

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

Cerebrospinal fluid : An alkaline fluid present in between inner two layer

of meninges, surrounding the brain and spinal cord.

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

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

Corpus callosum : A curved thick bundle of nerve fibres that joins two

cerebral hemisphere.

Depolarisation : A condition when polarity of the plasma membrane of

nerve fibre is reversed.

Endolymph : The fluid filled within membranous labyrinth. Ecustachian tube : A tube which connect ear cavity with the pharynx. Fovea : An area of highest vision on the ratina which contain only cones.

Meninges : Three sheets of covering of connective tissue wrapping the brain.

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

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

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

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

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

Synaptic cleft : A narrow fluid filled space which separates two membranes

of the two neurons at the synapse.

Synaptic vesicles : These are membrane bound vesicles in the axoplasm of the axon terminal and these store neurotransmitter.

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

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 System

Central neural System    Peripheral neural System

Brain	Spinal cord	Cranial nerve	Spinal nerve
		12 pairs	31 pairs

Nerve fibres of PNS

Afferent fibres Tansmit impulse    Efferent fibres Transmit impulse

from Tissue/organ to CNS        from CNS to Peripherel tissue/organ Division of PNS

Somatic neural System    Automatic neural system Transmit

Relays impulse from CNS    impulse from CNS to involuntary to Skeletal muscle    Organ and smooth muslces

Cell body = Cytoplasm with nucleus, cell organelles and Nissl’s granules

Parts of Neuron    Dendrites = Short fibres which branch rapidly and project

out of cell

Axon =    Single, long fibre, branched at distal endit (Refer fig. 21.1, page 317, NCERT - Biology, Class-XI)

Multipolar = : One axon and two or more dentrites

: Found in cerebral Cortex

Neuron    Bipolar =    : One axon and one dendrite

: Found in ratina of eye Unipolar =    : Cell body with axon only

: Found usually in the embryonic stage

Conduction of nerve impulse along axon

Polarised membrane/Resting Potential

In resting phase when neuron is not conducting an impulse, the axonal membrane is called polarised. 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+.

    The fluid outside the axon contain low conc. of K+ and high conc. of Na+.

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 depolarised. The electric potential difference across the plasma membrane at that site is called action potential, which infact termed as nerve impulse.

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

Transmission of Impulses at Synapse

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

2. At chemical synapses : Here the membrane of pre and post-syneptic neuron are separated by fluid filled space called synaptic cleft. Neurotransmitter are involved here.

When an impulse arrives at the axon terminal, it stimulates the movement of the synaptic vesicles towards membrane and they fuse with the plsama membrane and release their neurotransmitter in the syneptic cleft. These chemicals bind to specific receptors, present on the post-syneptic membrane. Their binding opens ion channels and allow the entry of ion which generate new potential in post synaptic neuron.

Human brain : Human brain is the major portion of central neural system.

Which is well protected by the skull.

The brain is surrounded by three cranial meninges—

1. Duramater—outer alyer

2. Arachnoid—middle layer

3. Piamter—Inner layer-remain incontact with brain

Parts of Brain

Fore brain	Mid brain	Hind brain
Cerebrum Thalamus Hypothalamus		Cerebellum Pons Medulla oblongata

Functions of pars 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.

Midbrain : Responsible to coordinate visual reflexes and auditory reflexes.

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

Pons : Relays impulses between medulla oblongata and cerebral hemisphere and between the hemisphere of cerebrum and cerebellum. It also heps to regulate breathing.

Medulla oblongata : Centre that control heart beat, breathing, swallowing, salivation, sneezing, vomitting and coughing.

Reflex action : It is spontaneous, autonomic and mechanical response to

a stimulus that occurs at the level of spinal cord, without involvement of brain.

Reflex arc : The flow of nerve along the specific during reflex action. It

consist of—

1. A receptor

2. An Afferent neuron (sensory neuron)

3. An inter neuron

4. An efferent neuron (motor neuron)

5. An effector organ

Sensory neuron

Stimulus    Receptor

(REFLEX - ARC)        Inter neuron of spinal cord Response    Effector organ

motor neuron

Organ of Sight-Eye

Layer    Component    Function

1. External layer    Sclera    Protects and maintain shape of the

eye ball

Cornea    Outermost transparent portion of eye which allows light to enter

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. Sends the image to brain through optical nerves.

(Refer-Fig. 21.6, Page 323 NCERT-Biology, Class XI)

Organ of Hearing–Ear

Portion of the ear   Component    Function

1. External ear    Pinna    Collect sound waves

External    Direct sound waves towards ear drum,

auditory canal    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 equalising the pressure

on either side of ear drum.

3. Internal ear    Cochlea    Hearing organ.

Vestebular    Balancing of body.

apparatus

(Refer Fig. 21.7, page 325-NCERT-Biology, Class XI)