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Title: CENTRAL NERVOUS SYSTEM
Description: CNS notes for intermediate students and NEET aspirants
Description: CNS notes for intermediate students and NEET aspirants
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INTERMEDIATE BIOLOGY
NERVOUS SYSTEM
-Neural (Nervous) system is a system that controls and coordinates the body activities, conducts
and integrates the
information and responds to stimuli
...
- It is made up of specialized cells known as neurons
...
• DENDRON
-Short fibres projecting from the cyton
...
• AXON
-A long fibre which transmit impulses away from the cell body
...
-Each axonite ends as a bulb-like structure called synaptic knob
...
-No Dendron
...
• BIPOLAR
-One axon and one dendron
...
• MULTIPOLAR
-One axon and 2 or more dendrons
...
-Found in the CNS & PNS
...
-Found in spinal & cranial nerves
...
-Gaps b/w 2 adjacent myelin sheaths are called nodes of Ranvier
...
-The gray coloured area without myelin
sheath is called gray matter
...
#IMPULSE TRANSMISSION
-Impulse transmission is electrochemical
...
MAINTANENCE OF RESTING MEMBRANE POTENTIAL
- Neural membrane contains various selectively permeable
ion channels
...
-Also, the membrane is impermeable to
negatively charged proteins in axoplasm
...
- The fluid outside the axon contains low concentration of K+ and high concentration of Na+
...
- The ionic gradients are maintained by the active transport of ions by the Na-K pump
...
-As a result, the outer surface becomes positively charged and inner surface becomes
negatively charged (i
...
- The electrical potential difference across the resting plasma membrane is called as the resting
potential
...
ACTION POTENTIAL
- When a stimulus is applied, the membrane at the site A becomes permeable to Na+
...
It is called depolarization
...
3
...
As a result, a
current flows on the inner surface from site A to site B
...
-Hence, the polarity is reversed and action potential is generated at site B
...
e
...
- The sequence is repeated along the axon and the impulse is conducted
...
-It is quickly followed by a rise in permeability to K+
...
- Thus the fibre becomes ready for further stimulation
...
- It is 2 types: Electrical & Chemical
...
ELECTRICAL SYNAPSES
- In this, the membranes of pre- and post-synaptic neurons are in close proximity
...
- Impulse transmission is faster than in chemical synapse
...
2
...
- The presynaptic regions have swellings called Synaptic knob (buttons)
...
-1Impulse reaches at axon terminal → synaptic vesicles bind on
plasma membrane → release of neurotransmitter → It diffuses across synaptic cleft → combine
with receptors on the post synaptic membrane → opening of ion channels allowing
entry of ions → generates action potential
...
NERVOUS SYSTEM
#It has 2 parts:
• Central neural system (CNS): Brain & spinal cord
...
CENTRAL NEURAL SYSTEM (CNS)
A
...
- It has 3-layered connective tissue membranes called cranial meninges
...
- The subarachnoid space (space between pia mater and arachnoid mater) is filled with
cerebrospinal fluid (CSF)
...
- Brain has 3 divisions: Forebrain, Midbrain & Hindbrain
...
FOREBRAIN
-Also k/aProsencephalon
-It is the anterior part
-Consists of cerebrum & diencephalon
...
-It has 2 cerebral hemispheres held together by a tract of nerve fibres (Corpus callosum)
...
- It has convulsions & depressions and is formed of gray matter
...
- Inner part of cerebrum is formed of white matter
...
• Sensory (Somaesthetic) area:
Controls the functioning
of sense organs
...
-Responsible for intersensory associations,memory and communication
...
-It is a coordinating centre (relay station) for sensory and motor impulses
...
It
a
...
b
...
c
...
d
...
- The inner parts of cerebral hemispheres and a group of associated deep structures like
amygdala, hippocampus, hypothalamus, etc
...
-It regulates sexual behavior, motivations,
emotions (excitement, pleasure, rage, fear etc)
...
MIDBRAIN
-Also k/a Mesencephalon
- It is located between thalamus/hypothalamus and Pons
...
-Mid brain consists of 4 round lobes called Corpora quadrigemina
...
c
...
-Midbrain & hindbrain form the Brain stem
...
-It co-ordinates muscular activities and body equilibrium
...
- It co-ordinates the activities of eye and ear and regulates respiration
...
It controls respiration, cardiovascular reflexes, gastric secretions, peristalsis etc
...
B
...
- It is also protected by meninges
...
- Outer white matter and inner gray matter
...
Conduction of impulses to and from the brain
...
Centre of spinal reflexes
...
Nerve fibres of PNS are 2 types:
• AFFERENT(SENSORY)FIBRES
Carry impulses from sense organs to CNS
...
#PNS has 2 divisions
...
• AUTONOMIC NURAL SYSTEM(ANS): -Transmits impulses from CNS to involuntary organs &
smooth muscles
...
-Sympathetic system prepares body to cope with emergencies, stresses &
dangers
...
-Parasympathetic
system returns
the body to a resting state after stressful situations and slows down heartbeat, dilates arteries,
lowers BP etc
...
- It includes nerves, fibres, ganglia & plexus by which impulses travel
from CNS to the viscera and from viscera to CNS
...
E
...
¨ Withdrawal of the hand when it touches a hot object
...
- These are the organs that detect the changes in the environment and convey the information
to the CNS
...
EYE
- Two eyes are located in sockets of the skull called orbits
...
- Eyeball has three layers: Sclera, Choroid & Retina
...
- Anterior transparent portion of sclera is called cornea
...
Contains many blood vessels
...
- Ciliary body continues forward to form a visible pigmented
and opaque portion of the eye called the iris
...
The diameter of the pupil is regulated by the muscle
fibres of iris
...
- The eyeball contains a transparent crystalline lens
...
¨ Closing of the eyelids when light falls on them
...
¨ If a child sees or smells a food unknown to him, he does
not salivate
- But if he sees or smells that food every time before tasting it, he salivates (conditioned reflex)
...
It consists of
§ A receptor organ:
It receives the stimulus
...
§ Intermediate (connector) neuron:
It connects sensory and
motor neurons
...
§ An effector organ (muscle/gland):
It responds to impulse
...
It contains 3 layers of cells – from inner to outer
– ganglion cells, bipolar cells & photoreceptor cells
...
They contain photosensitive proteins (photopigments)
...
CONE CELLS
• Function: Daylight (photopic) vision & colour vision
...
• The sensations of different colours are produced by
combinations of these cones and their photopigments
...
ROD CELLS
• Function: Twilight (scotopic) vision
...
It contains a derivative of Vitamin A
...
Here, photoreceptor cells are absent
...
- Lateral to the blind spot, there is a yellowish pigmented spot called macula lutea with a central
pit (fovea)
...
- It is the point of greatest visual acuity (resolution)
...
+-It contains aqueous humor (thin watery fluid)
...
- It contains vitreous humor (a transparent gel)
...
- It has 3 divisions: External ear, middle ear & inner ear
...
- At the opening of ear canal, hairs are seen
...
-They secrete wax (cerumen)
...
- Ear canal ends in tympanic membrane (Tympanum or ear drum)
...
MIDDLE EAR
- Consists of tympanic cavity and ear ossicles
...
- An auditory tube (Eustachian canal) connects middle ear to the pharynx
...
- Ear ossicles include 3 small bones namely Malleus, Incus
and stapes
...
- Stapes is the smallest bone of the body
...
Inner ear
- It consists of bony labyrinth & membranous labyrinth
...
- The membranous labyrinth consists of cochlea and Vestibular apparatus
...
- Scala vestibula & scala media are separated by Reissner’s membrane
...
- S
...
tympani are filled with perilymph and scala media is filled with endolymph
...
-It consists of row of sensory hair cells
...
VESTIBULAR APPARATUS
- It consists of 3 semicircular canals and otolith organ
...
-One end of each canal has a bulging called ampulla
...
-Long cilia of cells of crista are grouped together in a
bundle (cupula)
...
- Utricle & Saccule have a projecting ridge called macula
...
- They are responsible equilibrium & posture of body
...
- It contains mucus-coated receptors (olfactory receptors) made up of olfactory epithelium
...
- It contains 3 kinds of cells
...
-These are extensions of the brain’s limbic system
...
- 4 primary tastes are sweet, salt, sour and bitter
...
SKIN
(Cutaneous receptors)
- Largest sense organ
Title: CENTRAL NERVOUS SYSTEM
Description: CNS notes for intermediate students and NEET aspirants
Description: CNS notes for intermediate students and NEET aspirants