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(1) Nervous system is divided into three parts:
(i) Central nervous system (CNS):
(a) In all the vertebrates including man, CNS is dorsal, hollow and non-ganglionated while in invertebrates when present, it is ventral, solid and ganglionated.
(b) CNS is formed of two parts:
Brain – Upper and broader part lying in the head; and
Spinal cord – Lower, long and narrow part running from beginning of neck to trunk.
(ii) Peripheral nervous system (PNS):
(a) It is formed of long, thin, whitish threads called nerves which extend between CNS and body parts (muscles, glands and sense organs).
(b) It controls the voluntary functions of the body.
(c) It has cranial and spinal nerves.
(iii) Autonomic nervous system (ANS):
(a) It is formed of nerve fibres extending upto visceral organs and controls the involuntary functions of visceral organs of body like heart beat, peristalsis etc.
(b) It is again formed of two systems: sympathetic and para-sympathetic nervous system which has opposing functions.
(1) Central nervous system is made up of brain and spinal cord. CNS is covered by 3 meninges and its wall has two type of matter.
(2) Types of matter: CNS of vertebrates is formed of two types of matter –
(a) Grey matter: It is formed of cell-bodies and non-medullated nerve fibres.
(b) White matter: It is formed of only medullated nerve fibres which appear white due to presence of medullary sheath.
It is soft, whitish, large sized and slightly flattened structure present inside cranial cavity of cranium of the skull. In man, it is about 1200-1400 gm in weight and has about 10,000 million neurons. Brain is made up of 3 parts
(1) Fore brain (Prosencephalon)
(i) Olfactory lobe – Rhinencephalon
(ii) Cerebrum – Telencephalon
(iii) Diencephalon – Diencephalon
(2) Mid brain (Mesencephalon)
(i) Optic lobes – Mesencephalon
(3) Hind brain (Rhambencephalon)
(i) Cerebellum – Metencephalon
(ii) Medulla oblongata – Myelencephalon
Location
Function
Premotor area
Frontal lobe
The highest centre for involuntary movements of muscles and ANS.
Motor area
Controls voluntary movements of the muscle
Broca’s area
Motor speech area
Somesthetic area
Parietal lobe
Perception of general sensation like pain, touch and temperature
Auditory area
Temporal lobe
Hearing
Olfactory area
Sense of smell
Wernicke’s area
Understanding speech written and spoken
Gustatory area
Sense of taste
Visual area
Occipital lobe
Sensation of light
Cerebellum
(1) It is the largest part of the brain, forming four-fifths of its weight.
(1) It is the second largest part of the brain, forming one-eighth of its mass.
(2) It covers the rest of the brain.
(2) It covers the medulla oblongata only.
(3) It is a part of the forebrain.
(3) It is a part of the hindbrain.
(4) It consists of 2 cerebral hemispheres each comprising 4 lobes : frontal, occipital, parietal, temporal.
(4) It consists of two cerebellar hemispheres and a median vermis.
(5) It encloses 2 lateral ventricles.
(5) It is solid.
(6) White matter does not form arbor vitae.
(6) White matter form arbor vitae.
(7) It initiates voluntary movements, and is a seat of will, intelligence, memory etc.
(7) It maintains posture and equilibrium.
Divisions
Parts
Cavity
Associated strcutures
(I) Prosencephalon (Forebrain)
(1) Telencephalon
Rhinencephalon
I Ventricle (Rhinocoel)
Olfactory bulbs
Olfactory tracts
Olfactory lobes
Palaeocortex on pallium
Cerebral hemispheres
II or Lateral Ventricles
Corpora striata or basal ganglia
Corpus callosum
Neocortex on pallium
Paraphysis
(2) Diencephalon
Epithalamus (roof)
Habenulae
Pineal apparatus
Parapineal or parietal
Thalamus (sides)
Hypothalamus (floor)
Hypothalamic nuclei
Optic chiasma
Median eminence
Infundibular stalk
Pituitary
Saccus vasculosus
Mamillary bodies
Anterior choroid plexus
(II) Mesencephalon (Midbrain)
–
Crura cerebri (floor)
Iter or cerebral aqueduct
Cerebral peduncles
(III) Rhombencephalon (Hind brain)
(1) Metencephalon
Trapezoid body
Pons
(2) Myelencephalon
Medulla oblongata
IV Ventricle (Metacoel)
Restiform bodies
Pyramids
(1) The reflex actions are involuntary actions because these are not under the conscious control of the brain.
(2) The spinal cord and brain stem are responsible for most of the reflex movements.
(3) A few examples of the reflex actions are withdrawal of hand or leg if pricked by a pin, secretion of saliva as soon as one thinks of delicious food or mere its sight causes salivation, if the body part is touched with acid or hot object it is automatically, without thinking and planning is withdrawn, cycling, motor driving etc.
(4) Component of reflex action: The whole of the reflex are includes six parts –
(a) Receptor organs: Receptors are windows of the body or guards of the body. These are situated on all, important organs, for example – eyes, nose, ear, tongue, integument etc. These perceive the stimuli from outside the body.
(b) Sensory neurons: These are also termed afferent neurons. These carry the stimuli from receptors to spinal cord. These neurons are situated in the ganglion on the dorsal side of spinal cord.
(c) Nerve centre: Spinal cord is termed as nerve centre. Synaptic connections are formed in it.
(d) Association neurons: These are also called intermediate neurons or interstitial neurons. These are found in spinal cord. They transfer the impulses from sensory neurons to motor neurons.
(e) Motor neurons: These are situated in the ventral horn of spinal cord. These carry the impulses to effector organs.
(f) Effector organs: These are the organs, which react and behave in response to various stimuli, for example – muscles and glands.
(5) Type of reflexes: The reflexes are of following types –
(a) Monosynaptic reflex
(b) Polysynaptic Spinal Reflex
(c) Polysynaptic Spinal/Brain Reflexes
(d) Unconditioned or Simple reflex
(e) Conditioned or Acquired reflex
S.No.
Name
Nature
Origin
Distribution
(1)
Olfactory Nerves
Sensory
Olfactory lobe
Sensory epithelium of olfactory sacs
Receive stimuli from the sensory epithelium of olfactory sac and carry them to olfactory lobes
(2)
Optic nerves
Optic lobes
Retina in Eyes
Stimulus of light is carried to optic lobes
(3)
Occulomotor nerves
Motor
Crura cerebri
Eye ball muscles, except superior oblique muscle
Carry the impulses from crura cerebri to the eye muscles
(4)
Trochlear nerves
From in between the optic lobes and cerebellum
Superior oblique muscle of eye ball
Carry the impulses from the brain to superior oblique muscles of the eye
(5)
Trigeminal nerves
Mixed
From the gassarion galglia situated on the lateral side of medulla oblongata
—
(i)
Ophthalmic nerve
,,
Skin of lips
(ii)
Maxillary
Upper lip, skin of nose, lower eye lid.
Carry the stimuli from these organs to brain
(iii)
Mandibular nerve
Lower lip and skin of jaw
(6)
Abducens nerves
Medulla
Eye muscles
Carry the impulses from the brain (medulla) to eye muscles
(7)
Facial nerves
Behind trigeminal nerve, from geniculate ganglion
Palatinus
In the roof of mouth cavity
Carry the impulses from roof of mouth cavity
Hyoman dibular
Muscles of low jaw, muscles of neck and pinna (external ear)
Carry the impulses from brain muslces of lower jaws, neck and pinna.
Chordotympani
In salivary glands and taste buds
Receives the stimuli from the taste buds and carry the stimulus to salivary gland.
(8)
Auditory nerves
Vestibular nerve
Utriculus, sacculus, semicircular canals and Cochlea.
Receives impulses from the internal ear and carry to brain.
Cochlear nerve
Cochlea
(9)
Glossopharyngeal nerve
Taste buds present in tongue and muslces of oesphagus
Carry sound impulses to brain, to muscles of oesophagus and carry the taste impulse of tongue to the brain
(10)
Vagus nerve
After arising from medulla, 9th and 10th cranial nerves unite to form vagus nerve but become separate and divide into branches
Superior laryngeal nerve
Glottis
Carry the impulse to muscle of glottis
Recurrent laryngeal nerve
Cardiac nerve
Heart Muscles
From brain to heart muscles
(iv)
Pneumogastric
In the abdominal cavity, in stomach and lungs.
Carry impulse from these organs to brain and from brain to muscles of these organs.
(v)
Depresser nerve
Diaphragm
Carry the impulse to diaphragm
(11)
Spinal accessory
Muscles of neck and shoulders
From brain to muscles of neck and shoulder
(12)
Hypoglossal nerve
Muscles of tongue and neck
From brain to their muscles
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