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.
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 : A 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
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
(i) 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 impulse conduction along a single axon.
(ii) 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 plasma 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.
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.
Mid brain : 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 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.
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