Notes on Neural Control and Coordination

Parts of nervous system

(1) Nervous system is divided into three parts:

(i) Central nervous system (CNS):

  1. In all the vertebrates including man, CNS is dorsal, hollow and non-ganglionated while in invertebrates when present, it is ventral, solid and ganglionated.
  2. 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):

  1. It is formed of long, thin, whitish threads called nerves which extend between CNS and body parts (muscles, glands and sense organs).
  2. It controls the voluntary functions of the body.
  3. It has cranial and spinal nerves.

(iii) Autonomic nervous system (ANS):

  1. 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.
  2. It is again formed of two systems: sympathetic and para-sympathetic nervous system which has opposing functions.
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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 –

  • Grey matter: It is formed of cell-bodies and non-medullated nerve fibres.
  • 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)

  1. Olfactory lobe – Rhinencephalon
  2. Cerebrum – Telencephalon
  3. Diencephalon – Diencephalon

(2) Mid brain (Mesencephalon)

Optic lobes – Mesencephalon

(3) Hind brain (Rhambencephalon)

  1. Cerebellum – Metencephalon                  
  2. Medulla oblongata – Myelencephalon

Important areas in the human brain

AreaLocationFunction
Premotor areaFrontal lobeThe highest centre for involuntary movements of muscles and ANS.
Motor areaFrontal lobeControls voluntary movements of the muscle
Broca’s areaFrontal lobeMotor speech area
Somesthetic areaParietal lobePerception of general sensation like pain, touch and temperature
Auditory areaTemporal lobeHearing
Olfactory areaTemporal lobeSense of smell
Wernicke’s areaTemporal lobeUnderstanding speech written and spoken
Gustatory areaParietal lobeSense of taste
Visual areaOccipital lobeSensation of light

Differences between Cerebrum and Cerebellum

CerebrumCerebellum
(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

DivisionsSubdivisionsPartsCavityAssociated strcutures
  (I) Prosencephalon (Forebrain) (1) TelencephalonRhinencephalonI Ventricle (Rhinocoel)Olfactory bulbsOlfactory tractsOlfactory lobesPalaeocortex on pallium
Cerebral hemispheresII or Lateral Ventricles Corpora striata or basal gangliaCorpus callosumNeocortex on palliumParaphysis
(2) DiencephalonEpithalamus (roof) HabenulaePineal apparatusParapineal or parietal
Thalamus (sides)  
Hypothalamus (floor) Hypothalamic nucleiOptic chiasmaMedian eminenceInfundibular stalkPituitarySaccus vasculosusMamillary bodiesAnterior choroid plexus
(II) Mesencephalon (Midbrain)Crura cerebri (floor)Iter or cerebral aqueductCerebral peduncles
(III) Rhombencephalon (Hind brain)(1) MetencephalonCerebellum Trapezoid bodyPons
(2) MyelencephalonMedulla oblongataIV Ventricle (Metacoel)Restiform bodiesPyramids

Reflex action

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(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 –

  1. 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.
  2. 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.
  3. Nerve centre: Spinal cord is termed as nerve centre. Synaptic connections are formed in it.
  4. 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.
  5. Motor neurons: These are situated in the ventral horn of spinal cord. These carry the impulses to effector organs.
  6. 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 –

  1. Monosynaptic reflex                                              
  2. Polysynaptic Spinal Reflex
  3. Polysynaptic Spinal/Brain Reflexes     
  4. Unconditioned or Simple reflex
  5. Conditioned or Acquired reflex

Cranial nerves of mammal at a glance

S.No.NameNatureOriginDistributionFunction
(1)Olfactory NervesSensoryOlfactory lobeSensory epithelium of olfactory sacsReceive stimuli from the sensory epithelium of olfactory sac and carry them to olfactory lobes
(2)Optic nervesSensoryOptic lobesRetina in EyesStimulus of light is carried to optic lobes
(3)Occulomotor nervesMotorCrura cerebriEye ball muscles, except superior oblique muscleCarry the impulses from crura cerebri to the eye muscles
(4)Trochlear nervesMotorFrom in between the optic lobes and cerebellumSuperior oblique muscle of eye ballCarry the impulses from the brain to superior oblique muscles of the eye
(5)Trigeminal nervesMixedFrom the gassarion galglia situated on the lateral side of medulla oblongata
(i)Ophthalmic nerveSensory,,Skin of lips 
(ii)MaxillarySensory,,Upper lip, skin of nose, lower eye lid.Carry the stimuli from these organs to brain
(iii)Mandibular nerveMixed,,Lower lip and skin of jawCarry the stimuli from these organs to brain
(6)Abducens nervesMotorMedullaEye musclesCarry the impulses from the brain (medulla) to eye muscles
(7)Facial nervesMixedBehind trigeminal nerve, from geniculate ganglion
(i)PalatinusSensoryIn the roof of mouth cavityCarry the impulses from roof of mouth cavity
(ii)Hyoman dibularMotorMuscles of low jaw, muscles of neck and pinna (external ear)Carry the impulses from brain muslces of lower jaws, neck and pinna.
(iii)ChordotympaniMixedIn salivary glands and taste budsReceives the stimuli from the taste buds and carry the stimulus to salivary gland.
(8)Auditory nervesSensoryMedulla
(i)Vestibular nerve,,,,Utriculus, sacculus, semicircular canals and Cochlea.Receives impulses from the internal ear and carry to brain.
(ii)Cochlear nerve,,,,Cochlea
(9)Glossopharyngeal nerveMixed,,Taste buds present in tongue and muslces of oesphagusCarry sound impulses to brain, to muscles of oesophagus and carry the taste impulse of tongue to the brain
(10)Vagus nerveMixedAfter arising from medulla, 9th and 10th cranial nerves unite to form vagus nerve but become separate and divide into branches
(i)Superior laryngeal nerveMotorGlottisCarry the impulse to muscle of glottis
(ii)Recurrent laryngeal nerveMotorGlottis,,
(iii)Cardiac nerveMotorHeart MusclesFrom brain to heart muscles
(iv)PneumogastricMotorIn the abdominal cavity, in stomach and lungs.Carry impulse from these organs to brain and from brain to muscles of these organs.
(v)Depresser nerveMotorDiaphragmCarry the impulse to diaphragm
(11)Spinal accessoryMotorMedullaMuscles of neck and shouldersFrom brain to muscles of neck and shoulder
(12)Hypoglossal nerveMotor,,Muscles of tongue and neckFrom brain to their muscles

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