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Revision Notes on Neural Control and Coordination  

Parts of nervous system

(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.

          

Central nervous system:

(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.

Brain (Encephalon):

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

Important areas in the human brain

Area

Location

Function

Premotor area

Frontal lobe

The highest centre for involuntary movements of muscles and ANS.

Motor area

Frontal lobe

Controls voluntary movements of the muscle

Broca’s area

Frontal lobe

Motor speech area

Somesthetic area

Parietal lobe

Perception of general sensation like pain, touch and temperature

Auditory area

Temporal lobe

Hearing

Olfactory area

Temporal lobe

Sense of smell

Wernicke’s area

Temporal lobe

Understanding speech written and spoken

Gustatory area

Parietal lobe

Sense of taste

Visual area

Occipital lobe

Sensation of light

Differences between Cerebrum and Cerebellum

Cerebrum

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.

Subdivisions, parts and associated structures of a vertebrate brain

Divisions

Subdivisions

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

Cerebellum

 

Trapezoid body

Pons

(2) Myelencephalon

Medulla oblongata

IV Ventricle (Metacoel)

Restiform bodies

Pyramids

Reflex action

                                   

(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

Cranial nerves of mammal at a glance

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S.No.

Name

Nature

Origin

Distribution

Function

(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

Sensory

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

Motor

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

Sensory

,,

Skin of lips

 

(ii)

Maxillary

Sensory

,,

Upper lip, skin of nose, lower eye lid.

Carry the stimuli from these organs to brain

(iii)

Mandibular nerve

Mixed

,,

Lower lip and skin of jaw

Carry the stimuli from these organs to brain

(6)

Abducens nerves

Motor

Medulla

Eye muscles

Carry the impulses from the brain (medulla) to eye muscles

(7)

Facial nerves

Mixed

Behind trigeminal nerve, from geniculate ganglion

(i)

Palatinus

Sensory

In the roof of mouth cavity

Carry the impulses from roof of mouth cavity

(ii)

Hyoman dibular

Motor

Muscles of low jaw, muscles of neck and pinna (external ear)

Carry the impulses from brain muslces of lower jaws, neck and pinna.

(iii)

Chordotympani

Mixed

In salivary glands and taste buds

Receives the stimuli from the taste buds and carry the stimulus to salivary gland.

(8)

Auditory nerves

Sensory