Samacheer Class 11 Bio Zoology - Neural Control and Coordination

Slightly below the posterior pole of the eye, the optic nerve and the retinal blood vessels enter the eye. This region is devoid of rods and cones. Hence, this region is called a blind spot.

• The increase in intraocular pressure leads to the disease called Glaucoma.
• Any block in the canal of Schlemm increases the intraocular pressure of aqueous humor and leads to ‘Glaucoma’ where the optic nerve and the retina are compressed due to pressure.

The olfactory nerve carries the sense of smell to the sensory strip present in the cerebrum. The sensory areas are present in the parietal lobe of the cerebrum. The stimuli of smell reaches the mammillary bodies present in the hypothalamus. This produces olfactory reflexes and emotional responses to odour.

The hypothalamus contains a pair of small rounded body called mamillary bodies that are involved in olfactory reflexes and emotional responses to odour
This is also act as centre for appetite thirst and heat regulation.

Cerebrospinal fluid provides buoyancy to the central nervous system.
* It acts as a shock absorber for the brain and spinal cord.
* It nourishes the brain cells by transporting food and oxygen.
* It carries harmful metabolic wastes from the brain to the blood.
* It maintains constant pressure inside the cranial vessels.

The limbic system is a set of components located on both sides of the thalamus present in the inner part of the cerebral hemisphere. It includes the olfactory bulbs, cingulate gyrus, mammillary body, amygdala, hippocampus, and hypothalamus. The limbic system plays a primary role in the regulation of pleasure, pain, anger, fear, sexual feeling, affection, and memory. Hence it is called the emotional brain.

Receptors
Stimulus
Effector organs
Mechano receptors
Pressure and vibration
Mechano receptors are present in the cochlea of the inner ear and the semicircular canal and utriculus
Chemoreceptors
Chemicals
Taste buds in the tongue and nasal epithelium
Thermo receptors
Temperature
Skin
Photoreceptors
Light
Rod and cone cells of the retina in the eye.

Cranial nerves
Nature of nerve
Function
I. Olfactory nerve
Sensory
Sense of smell
II.Optic nerves
Sensory
Sense of sight
III. Oculo motor nerves
Motor
Movement of the eye
IV. Trochlear nerve
Motor
Rotation of the eyeball
V.Trigeminal nerve
Sensory and motor mixed
The functioning of face ball

The structural and functional unit of the nervous system is neurons. They detect, receive, process, and transmit different kinds of stimuli. They are sensory, motor, and autonomic in functions.

The non-nervous special cells called neuroglia from the supporting cells of the nervous tissue.
* Providing nourishment to the neurons
* Repairing the injured tissues
* It helps in dividing and regeneration
* Acting as phagocyte cells to engulf the foreign particles at the time of any injury to the brain.

• They provide nourishment to the surrounding neurons.
• They involve in the memory process.
• They repair the injured tissue due to their dividing and regenerating capacity.
• They engulf the foreign particles at the time of any injury to the brain.

Exteroceptors are located at or near the surface of the body. These are sensitive to external stimuli and receive sensory impulses for hearing, vision, touch, taste, and smell.

• When a very quick response is needed the spinal cord can effect motor initiation as the brain and brings about an effect.
• This rapid action by the spinal cord is called reflex action.

Its cell body is in the brain or spinal card. Its myelinated axon exits the CNS as part of cranial or spinal nerve and end in an autonomic ganglion.

* Scala vestibuli
* Scala tympanii
* Scala media
Separating membranes
Reisner’s membrane. It separates scala vestibuli from scala media
Basilar membrane. It separates scala media from scala tympani.

At one end of each semicircular canal at its lower end has a swollen area called ampulla Each ampulla has sensory hair cells and supporting cells called crista ampullaris. The function is to detect the rotational movement of the head.

• The intensity of sound is measured in decibels. (dB)
• 0-50 dB is the threshold of hearing for normal ear.
• Prolonged exposure to sound with intensities greater than 90dB causes hearing loss.

* The taste bud cells are subjected to huge amounts of friction because of their location and are routinely burned by hot foods.
* These are the most dynamic cells in the body and replaced every seven to ten days.
(3 Marks)
III. Short Answers

* Sensory functions: It receives sensory input from internal and external environment.
Motor functions: It transmits motor commands from the brain to the skeletal and muscular system.
* Autonomic functions: Reflex actions.

• Afferent neurons – That take sensory impulses to the central nervous system from the sensory organs.
• Efferent neurons – That carry motor impulses from CNS to the effector organ.
• Inter neurons – That lie entirely within the CNS between the afferent and efferent neurons.

• Inner to the axolemma the cytoplasm contains the infra cellular fluid with large amounts of potassium and magnesium phosphate with negatively charged proteins and other organic molecules.
• Outside the axolemma contains large amounts of sodium chloride bicarbonates CO 2 and metabolic wastes
• Due to the charged particles present in the inner and outside of the axolemma are responsible for the conduction of nervous impulses.

• When the axolemma reaches the spike potential the sodium voltage – gate closes and potassium – voltage gate opens.
• It checks influx of Na + ions and initiation the efflux of K ions which lowers the number of positive ions within the cell. Thus the potential falls back towards the resting potential.
• The reversal of membrane potential inside the axolemma to negative occurs clue to efflux of K + ions. This is called repolarisation.

• If repolarisation becomes more negative than the resting potential -70 mV to about -90 mV.
• It is called hyper polarisation. During this K + ion, gate is more permeable to K + even after reaching the threshold level as it closes slowly hence called lazy gates.
• The membrane potential return to its original resting state when K + ion channel close completely.
• During hyper polarization the Na + voltage gate remains closed.

The myelinated axon conduction the impulse faster than the non – myelinated axon.
The voltage gated Na + and K + channels are concentrated at the nodes of Ranvier as a result the impulse jumps from node to node. This is called saltatory conduction.

Brain is covered by three cranial meninges.
* The outer thicker layer is duramater which lines the inner surface of the cranial cavity.
* The inner most layer which is adhered to the brain is the piameter.
* The median thin layer is arachnoid mater by a narrow subdural space.
* The piameter is separated from the arachnoid mater by the subarachnoid space.

• It serves as a relay centre for impulses between the spinal and brain and cerebrum.
• Information is sorted and edited.
• It plays a key role in learning and memory.
• It is a co-ordinating centre for sensory and motor signaling.

• The midbrain is located between the diencephalon and the pons.
• The lower portion of the mid-brain consists of a pair of longitudinal bands of nervous tissue called cerebral peduncles.
• This relay impulses back and forth between cerebrum cerebellum pons and medulla.
• The dorsal position of the mid Brain consist of four rounded bodies called corpora quadrigemina which acts as a reflex center for vision and hearing.

• 150ml of cerebro spinal fluid is secreted in an adult.
• 500ml of cerebro spinal fluid is secreted in a day.
• Every 8 hours this fluid is rejuvenated.
• The choroid plexus carries harmful metabolic wastes from the brain to the blood.

1. Exteroceptors: They are located at the surface of the body.
These senses the hearing vision touch taste and smell.
2. Introceptors: They are located in the visceral organs and blood vessels.
They are sensitive to internal stimuli.
3. Prerprioceptors:
They provide information about position and movements of the body.

• The sympathetic and parasympathetic neural system are is mainly involved.
• On seeing his friend out of the happiness his autonomic nervous system is stimulated and he gets tears in his eyes.
• After sometime the parasympathetic stops the secretion of tears.

• Depression is a functional deficiency of serotonin and nor epinephrine.
• This disorder is characterized by a pervasive negative mood, loss of interest an inability to experience pleasure and suicidal tendencies.

Reflex axon.
When a very quick response is needed the spinal cord can effect motor initiation as the brain and brings about an effect it is due to fast action of spinal cord.

Unconditioned reflex
Conditioned reflex
In born reflex for an unconditioned stimulus.
It’s response to a stimulus acquired by learning.
It does not need any past experience or training
Does not naturally exists in animals.
Eg: Blinking of an eye when a dust particle about to fall in it
Eg: Excitement of salivary gland on seeing a food

Exteroceptors
Interoceptors
Located at or near the surface of the body
They are located in the visceral organs and blood vessels.
These receive impulses from hearing vision touch taste and smell.
They are sensitive to internal stimuli.

• The lens is a transparent biconvex structure made up of slender columnar epithelial cells.
• These cells are called as lens fibre.
• These cells are formed of crystaline protein.

Eye is held in its position with the help of six extrinsic muscles. They are
* Superior
* Interior
* Lateral
* Median rectus muscle
* Superior oblique
* Inferior oblique

• Eye lashes and the eye brows
• They help to protect the eyeballs from foreign objects, perspiration and from direct sunrays.
• Sebaceous glands or ciliary glands.
• They secrete a lubricating fluid.
• Lacrymal glands.
• Secrete tears.
• Tears contain salts mucus and lysozyme enzyme to destroy bacteria.

• It supplies nutrients and oxygen to the lens cornea and retinal cells.
• It is produced and drained at same rate.
• It maintains a constant infra ocular pressure of about 16 mmHg.

Any block in the canal of Schlemm increases the intra ocular pressure of aqueous humour and leads to “glaucoma when the optic nerve and the retina are compressed due to pressure.

• Redcones. It contains visual pigment erythropsin which is sensitive to long wavelength close to 560 nm.
• Green cones – It has a pigment chloropsin which is sensitive to medium wavelength of 530 nm.
• Blue cones – It has a pigment which is sensitive to short wavelength of 420 nm.

Conducting Hearing loss
Neuro sensory
This defect is due to the blockage of ear canal with ear wax
The defect may be in the organ of cortii
Rupture of ear
The auditory nerve
Middle ear infection with fluid accumulation restriction of ossicular movement
In the ascending auditory pathways or auditory cortex

• Melanocytes synthesize melanin.
• It gives colour to skin and protects it from the sun.
• Vitiligo is a condition in which the melanin pigment is lost from the areas of the skin causing white patches.
• The leukoderma appears when melanocytes fails to synthesis melanin pigment.

Taste buds
* Taste buds are subjected to huge amounts of friction because of their location and are routinely burned by hot foods.
* These cells are replaced every 7-10 days.

* These are small light pressure receptors found just beneath the epidermis in the dermal papillae.
* They are numerous in hairless skin areas such as finger tips and soles of the feat.
(5 Marks)
IV. Brief Answers

Neuron is composed of three region.
* Cell body
* Dendrites
* axon.
Cell body:
The cell body is spherical. There is no centriole.
The plasma membrane covering the neuron is called neurilemma and axon is axolemma.
Dendrites:
The repeatedly branched short fibres coming out of the cell bod dendrites which transmit impulses towards the cell body in it’s cytoplasm Nissl’s granules are present.
Axon:
It is a long fibre that arises from a cone shaped area of the cell body. There is no golgi bodies and Nissis granules in its cytoplasm.
The axon of peripheral nerves is surrounded by Schwann’s cells to form myelin sheath. The myelin sheath is not continuous. There are gaps in the myelin sheath between an adjacent Schwann cells called nodes of Ranvier.
Each branch at the distal end of the axon terminates into a knob like structure called synaptic knob which possesses synaptic vesicles filled with transmitters. The axon transmits nerve impulses away from the body to neuro muscular junction. The myelinated nerve cell transmits impulses faster than non – myelinated nerve cells.

1. Multi polar neurons:
They have many processes with one axon and two or more dendrites.
2. Bipolar neurons:
They have two processes with one axon and one dendrites.
These are found in the retina of the eye, inner ear and the olfactory area of the brain.
3. Unipolar neurons:
They have a single short process and one axon.

Ionic channels:
* Leakage channels
* Ligand – gated channels
* Voltage-gated channels.
1. Leakage channels:
*
* These channels are always remain open.
* K + leakage channels are more in number than the Na + leakage channels.
* Sarco lemma has greater permeability to k + icons than Na + icons
* These icons keep moving continuously to maintain the potential continuously to maintain the
* potential difference across the axo lemma.
2. Ligand – gated channels:
These are chemic called gated channels which open or close in response to a chemical stimuli.
* They are located between the pre synaptic membrane of the first axon and post synaptic membrane of the second.
* The neurotransmitter acetylcholine opens ligand channels that allow Na + and Ca ++ ions diffuse inward and K + icon diffuse outward.
Voltage-gated channels:
This channels open in response to a physical stimulus in the form of vibration such as touch and pressure.
* Sodium Voltage gated channels.
* Potassium Voltage gated channels.

The transmission of impulse involves two main phases; Resting membrane potential and Action membrane potential. Resting membrane Potential: The electrical potential difference across the plasma membrane of a resting neuron is called the resting potential during which the interior of the cell is negative due to greater efflux of K + outside the cell than Na + influx into the cell.
When the axon is not conducting any impulses i.e. in resting condition, the axon membrane is more permeable to K + and less permeable to Na + ions, whereas it remains impermeable to negatively charge protein ions. The axoplasm contains high concentration of K + and negatively charged proteins and low concentration of Na + ions.
In contrast, fluid outside the axon (ECF) contains a low concentration of K+ and a high concentration of Na+, and this forms a concentration gradient. This ionic gradient across the resting membrane is maintained by ATP driven Sodium-Potassium pump, which exchanges 3Na+ outwards for 2K+ into the cells.
In this state, the cell membrane is said to be polarized. In neurons, the resting membrane potential ranges from -40 mV to -90 mV, and its normal value is -70 mV. The minus sign indicates that the inside of the cell is negative with respect to the outside.
Action membrane potential:
An action potential occurs when a neuron sends information down an axon, away from the cell body. It includes the following phases, depolarization, repolarization, and hyperpolarization.
Depolarization – Reversal of polarity:
When a nerve fibre is stimulated, sodium voltage-gated opens and makes the axolemma permeable to Na+ ions; meanwhile the potassium voltage-gated closes. As a result, the rate of flow of Na + ions into the axoplasm exceeds the rate of flow of K + ions to the outside fluid [ECF]. Therefore, the axolemma becomes positively charged inside and negatively charged outside.
This reversal of electrical charge is called Depolarization. During depolarization, when enough Na + ions enter the cell, the action potential reaches a certain level, called threshold potential [-55 mV], The particular stimulus which is able to bring the membrane potential to the threshold is called threshold stimulus.
The action potential occurs in response to a threshold stimulus but does not occur at subthreshold stimuli. This is called the all or none principle. Due to the rapid influx of Na + ions, the membrane potential shoots rapidly up to + 45 mV which is called the Spike potential.
Repolarisation [Falling Phase]: When the membrane reaches the spike potential, the sodium voltage-gated closes, and the potassium voltage-gated opens. It checks influx of Na + ions and initiates the efflux of K + ions which lowers the number of positive ions within the cell.’Thus,.the potential falls back towards the resting potential. The reversal of membrane potential inside the axolemma to negative occurs due to the efflux of K+ ions. This is called Repolarisation.
Hyperpolarization:
If repolarization becomes more negative than the resting potential -70 mV to about -90 mV, it is called Hyperpolarization. During this, K + ion gates are more permeable to K+ even after reaching the threshold level as it closes slowly; hence called Lazy gates. The membrane potential returns to its original resting state when K + ion channels close completely. During hyperpolarization, the Na + voltage gate remains closed.
Conduction Speed of a nerve impulse: The conduction speed of a nerve impulse depends on the diameter of axon. The greater the axon’s diameter, the faster is the conduction.. The myelinated axon conducts the impulse faster than the non-myelinated axon.
The voltage-gated Na + and K + channels are concentrated at the nodes of Ranvier. As a result, the impulse jumps node to node, rather than traveling the entire length of the nerve fibre. This mechanism of conduction is called Saltatory Conduction. Nerve impulses travel at the speed of 1-300 m/s.

a) An action potential occurs when a neuron sends information down an axon away from the cell body.
b) When a nerve fibre is stimulated sodium voltage gate opens and makes the axo lemma permeable to Na ++ and the potassium voltage gate closes and potassium is getting out of the axo lemma. The concentration reduces
* The axo lemma becomes positively charged inside and negatively charged outside.
* This reversal of electrical charge is called depolarisation potential reaches level called threshold potential (-55mV)
* The stimulus which bring this threshold potential is called threshold stimulus.
* The action potential occur in response to a threshold stimulus but does not occur at subthreshold stimuli. This is called all or none principle.
* Due to the rapid influx of Na + ions the membrane potential shoots rapidly up to +45mV which is called the spike potential.

• The junction between two neurons is called a synapses through which a nerve impulse is transmitted,
• The first neuron involved in the synapse forms the pre synaptic neuron and the second neuron is the post – synaptic neuron
• A small gap between the two neuron is synaptic cleft.
• The axon terminals contain synaptic vesicles filled with neurotransmitters.
• When an impulse arrives at the axon terminals it depolorizes the pre – synaptic membrane opening the voltage gated calcium channels.
• Influx of calcium ions stimulates the synaptic vesicles toward the pre – synaptic membrane and fuse with it.
• In the neurilemma the vesicles release their neurotransmitters into the synaptic cleft by exocytosis.
• The released neurotransmitters bind to their specific receptors.
• The entry of the ions can generate a new potential in the post synaptic neuron.
• This excitatory post – synaptic potential causes depolarisation and in inhibitory post – synaptic potential causes hyperpolarisation.

* The brain is located in the cranial cavity and it is covered by three cranial membranes.
* The outer layer — durameter the inner most layer piameter and the median thin layer arachnoid. The brain is divided into three major regions. Fore brain, Mid-brain, Hind
* It comprises of cerebrum and diencephalon.
* Tire cerebral cortex is composed of grey and unmyelinated nerve cells.
* The medulla is composed of white mater.
* The surface of the cerebrum shows many convolutions and grooves. The folds are called gyri and the shallow groove is sulci.
There are eight lobes in cerebrum.
A pair of frontals, parietals temporals and occipital lobes.
The longitudinal fissure divides the cerebrum longitudinally into two hemispheres The hemispheres are connected by a tract of nerve fibres called corpus callosum.
Cerebral cortex has three functional areas
Sensory areas:
It occurs in the parietal temporal and occipital lobes of the cortex.
Motor areas:
This controls voluntary muscular movement which lies in the posterior part of the frontal iobes.
Association area:
It lies in between cortex and diencephalan This involves in memory communication learning and reasoning.

The forebrain comprises the following regions: Cerebrum and Diencephalon. The cerebrum is the ‘seat of intelligence’ and forms the major part of the brain. The cerebrum consists of an outer cortex, inner medulla and basal nuclei.
The superficial region of the cerebrum is called the cerebral cortex, which looks grey due to the presence of unmyelinated nerve cells. Cerebral cortex – consists of the neuronal cell body, dendrites, associated glial and blood vessels.
The surface of the cerebrum shows many convolutions (folds) and grooves. The folds are called gyri, the shallow grooves between the gyri are called sulci and deep grooves are called fissures. These sulci and gyri increase the surface area of the cerebral cortex. Several sulci divide the cerebrum into eight lobes; a pair of frontals, parietals, temporals and occipital lobes.
A median longitudinal fissure divides the cerebrum longitudinally into two cerebral hemispheres. A transverse fissure separates the cerebral hemispheres from the cerebellum.
The hemispheres are connected by a tract of nerve fibres called corpus callosum. Cerebral cortex has three functional areas namely sensory areas occur in the parietal, temporal and occipital lobes of the cortex. They receive and interpret the sensory impulses.
Motor area of the cortex which controls voluntary muscular movements lies in the posterior part of the frontal lobes. The areas other than sensory and motor areas are called Association areas that deal with integrative functions such as memory, communications, learning and reasoning. Inner to the cortex is medulla which is white in colour and acts as a nerve tract between the cortex and the diencephalon.
Diencephalon consists largely of following three paired structures. The epithalamus forms the roof of the diencephalon and it is a non-nervous tissue. The anterior part of the epithalamus is vascular and folded to form the choroid plexus. Just behind the choroid plexus, the epithalamus forms a short stalk that ends in a rounded body called pineal body which secretes the hormone, melatonin which regulates the sleep and wake cycle.
Thalamus is composed of grey matter which serves as a relay centre for impulses between the spinal cord, brain stem and cerebrum. Within the thalamus, information is sorted and edited and plays a key role in learning and memory. It is a major coordinating centre for sensory and motor signaling.
Hypothalamus forms the floor of the diencephalon. The downward extension of the hypothalamus, the infundibulum connects the hypothalamus with the pituitary gland. The hypothalamus contains a pair of small rounded body called mammillary bodies that are involved in olfactory reflexes and emotional responses to odour.
Hypothalamus maintains homeostasis and has many centres which control the body temperature, urge for eating and drinking. It also contains a group of neurosecretory cells which secrete the hypothalamic hormones. Hypothalamus also acts as the satiety centre.
Limbic system: The inner part of the cerebral hemisphere constitutes the limbic system. The main components of limbic system are olfactory bulbs, cingulate gyrus, mammillary body, amygdala, hippocampus and hypothalamus.
The limbic system is called the ‘emotional brain’ because it plays a primary role in the regulation of pleasure, pain, anger, fear, sexual feeling and affection. The hippocampus and amygdala also play a role in memory. Brain stem is the part of the brain between the spinal cord and the diencephalon. It consists of mid-brain, pons varolii and medulla oblongata.

Epithalamus:
* It is a non – nervous tissue.
* The anterior part of epithalamus is vascular and folded to form the anterior choroid plexus.
* The epithalamus forms a short stalk which ends in a rounded body called pineal body.
* This secretes the hormone melotonin which regulates sleep and wake cycle.
Thalamus:
* It is formed of grey matter
* It serves as a relay centre for impulses between the spinal cord brain stem and cerebrum.
* It plays a key role in learning and memory.
* It is a major co-ordinating centre for sensory and motor signalling.
Hypothalamus:
* It forms the floor of the diencephalon.
* It has a pair of small rounded body called mammillary bodies
* It involves in olfactory reflexes and emotional responses to odour.
* It maintains homeostasis.
* It controls the body temperature.
* Urge for eating and drinking.
* It also contains a group of neuro secretory cells which secrete the hypothalamic hormones.
* It also acts as the satiety centre.

Rhombencephalon forms the hindbrain. It comprises of cerebellum, pons varolii and medulla oblongata. The cerebellum is the second largest part of the brain. It consists of two cerebellar hemispheres and a central worm-shaped part, the vermis. The cerebellum controls and coordinates muscular movements and body equilibrium. Any damage to the cerebellum often results in uncoordinated voluntary muscle movements.
Pons varoli lies in front of the cerebellum between the midbrain and the medulla oblongata. The nerve fibres in the pons varolii form a bridge between the two cerebellar hemispheres and connect the medulla oblongata with the other region of the brain. The respiratory nuclei found in the pons cooperate with the medulla to control respiration.
Medulla oblongata forms the posterior-most part of the brain. It connects the spinal cord with various parts of the brain. It receives and integrates signals from spinal cord and sends it to the cerebellum and thalamus. Medulla contains vital centres that control cardiovascular reflexes, respiration and gastric secretions.

Conditioned
Unconditioned
1. Not through learning
Acquired by learning
2. In born reflex
It is not an in born reflex
3. It does not need any past experience
Experience makes it a part of the behaviour
4. Eg: Blinking of an eye when a dust fall in to it.
Eg: Secretion of salivary gland on seeing the food

Cranial nerves
Nature of nerve
Function
I Olfactory nerve
Sensory
Sense of smell
II Optic nerve
Sensory
Sense of sight
III Oculomotor nerve
Motor
Movement of the eye
IV Trochlear nerve
Motor
Rotation of the eye ball
V Trigeminal nerve
Sensory and motor (mixed)
Functioning of facial parts
VI Abducens nerve
Motor
Rotation of the eye ball
VII Facial nerve
Mixed
Functioning of facial parts
VIII Auditory/ Vestibulocochlear nerve
Sensory
Maintains the equilibrium of the body/ Auditory function
IX Glossopharyngeal nerve
Mixed
Taste and touch
X Vagus
Mixed
Regulation of the visceral organs
XI Spinal accessory
Motor
Muscular movement of pharynx, larynx, neck and shoulder
XII Hypoglossal
Motor
Speech and swallowing

Sympathetic nervous system
Para sympathetic nervous system
1. It dialates pupil
It constricts pupil of the eye
2. It inhibits the secretion of saliva
It stimulates saliva secretion
3. It increases the heart beat
It reduces the heart beat
4. It dialates bronches
It constricts the bronchus
5. It inhibits digestion
It stimulates digestion
6. It increases the glucose release
It stimulates bile release
7. Stimulates epinephrine and nor epinephrine release
It reduces the epinephrine and nor epinephrine release
8. Inhibits peristalsis and secretion
Stimulates peristalsis and secretion
9. Reflexes bladder
Contracts bladder

• There are two indentations the posterior median sulcus and the anterior median fissure.
• In the spinal cord the grey matter forms an inner butterfly-shaped region surrounded by the outer white matter.
• The grey matter consists of dendrites inter neurons and guai cells.
• White matter consists of bundles of nerve fibres.
• Each half of the grey matter is divided into a
• Dorsal horn – Cell bodies of inter neurons.
• Ventral horn – Efferent motor neurons supplying the skeletal muscle.
• Lateral horn – Nerves supply to heart smooth muscles exocrine glands. Originate from the cell bodies.
• Ascending tract – This carry sensory impulses to the brain.
• Descending tract – This carry motor impulses to brain.

Sensory receptor – It is a sensory structure that responds to specific stimulus.
Sensory neuron – This neuron takes the sensory impulse to the grey (afferent) matter of the
spinal cord through the dorsal root of the spinal cord.
Inter neuron – It may serve to transmit the impulses from the sensory neuron to the motor neuron.
Motor neuron – It transmits impulse from CNS to the effector organ
Effector neuron – It may be a muscle or gland which responds to the impulse received.
* Lacrymal glands located in the upper lateral region of each orbit secrete tears.
* Tears are secreted at the rate of 1 ml/day.
* Tears contain salt mucus and lysozyme enzyme to destroy bacteria.
* The protective mucus membrane present in the outer surface of the eye ball.
* The eye has two compartments anterior and posterior compartments filled with aqueous humour and vitreous humour respectively.
* The eye ball is consists of three layers sclera, vascular choroid and sensory retina.
Sclera:
* It consists of anterior cornea and the posterior sclera.
* Cornea is composed of stratified squamous epithelium. Sclera forms the white of the eye and protects the eyeball.
* At the junction of the sclera and the cornea is a channel called canal of schlemm which continuously drains out the excess of aqueous humour.
Choroid layer:
It is highly vascularised pigmented layer.

Sympathetic Neural System (SNS)
Parasympathetic Neural System (PNS)
SNS originates in the thoracic and lumbar region of the spinal cord.
PNS originates in the cranial region of the brain and the sacral region of the spinal cord.
Sympathetic ganglia are linked up to form a chain.
Its ganglia remain isolated
Preganglionic fibres are short and the postganglionic fibres are long.
Preganglionic fibres are long and the postganglionic fibres are short.
Noradrenaline is produced at the terminal ends of the postganglionic fibres at the effector organs. Hence the system is adrenergic.
Acetylcholine is produced at the terminal ends of the postganglionic fibres at the effector organs. Hence the system is cholinergic.
Active during stressful conditions preparing the body to face them.
Active during relaxing times restoring normal activity after a stress.
The overall effect is excitatory and stimulating.
The overall effect is inhibitory.
It is considered as the flight or fight system.
It is considered as “The rest and Digest System” or “The Feed and Breed System”.

• All nervous tissue outside the central nervous system is the peripheral neural system.
• It includes nerves ganglia enteric plexuses and sensory receptors.
• Ganglia are Sinai masses of nervous tissue.
• The neurons of these plexuses help in regulating the digestive system.
• The specialised structure that helps to respond to changes in the environment are called sensory receptor.
• This triggers nerve impulses along the afferent fibres to CNS.
• PNS comprises 12 pairs of cranial nerves and 31 pairs of the spinal nerve.
• The neural retina layer consists of cones and rods.
• The yellow flat spot at the centre of the posterior region of the retina is called macula lutea.
• A small depression present in the centre of the

The autonomic neural system is auto-functioning and self-governed. It is a part of the peripheral neural system that innervates smooth muscles, glands, and cardiac muscle. This system controls and coordinates the involuntary activities of various organs. ANS controlling centre is in the hypothalamus.
An autonomic neural system comprises the following components:
* A preganglionic neuron whose cell body is in the brain or spinal cord; its myelinated axon exits the CNS as part of cranial or spinal nerve and ends in an autonomic ganglion.
* Autonomic ganglion consists of an axon of preganglionic neurons and cell bodies of the postganglionic neurons.
* Postganglionic neuron conveys nerve impulses from autonomic ganglia to visceral effector organs.
* The autonomic neural system consists of the Sympathetic neural system and the Parasympathetic neural system.

• When light enters the eye it gets refracted by the cornea, aqueous humor and lens and it is focused on the retina and excites the rod and cone cells.
• The rods and cones contain the retinal a derivative of vitamin A and the photo pigment opsin.
• Light induces dissociation of retinal from opsin and causes the structural changes in opsin.
• This generates an action potential in the photo receptor cells.
• It is transmitted by the optic nerves to the visual cortex of the brain via the optic nerves for the perception of vision.

Myopia
* The affected person cannot see distant objects.
* As the eyeball is elongated or thickened lens the image of distant object is formed in front of the yellow spot.
* This error can be corrected using a concave lens.
Hypermetropia
* Affected person cannot see the nearby objects.
* This is due to a shortened eyeball and thin lens. So the image of closest object is converged behind the retina.
* This defect can be corrected by using convex lens.
Presbyopia
* Due to aging, the lens loses elasticity and the power of accommodation.
* Convex lenses are used to correct this defect.
Astigmatism
* It is due to the rough curvature of the cornea or lens.
* Cylindrical glasses are used to correct this error.

Anatomically the ear is divided into three regions external ear middle ear and inner ear.
External ear:
* It consists of pinna external auditory meatus and ear drum.
* The pinna collects the sound waves.
* The external auditory meatus extends up to the tympanic membrane.
* The tympanic membrane is covered with skin outside and with mucus membrane inside.
Middle ear:
* It is an air-filled cavity in the temporal bone.
* The middle ear contains three ossicles malleus incus and stapes.
* The malleus is attached to the tympanic membrane and its head articulates with the incus.
* The stapes is attached to the oval window in the inner ear.
* The Eustachian tube connects the middle ear cavity with the pharynx
Inner ear:-
* It is the fluid-filled cavity consisting of two parts the bony labyrinth and the membranous labyrinths.
* The bony labyrinth consists of three areas, cochlea, vestibule, and semicircular canals.
a Cochlea is a coiled portion consists of 3 chambers namely.
* Scala vestibule
* Scala media
* Scala tympanii.
Scala vestibule and scala tympani are filled with peri lymph.
The scala media is filled with endo lymph.

• Organ of corti is a sensory ridge located on the top of the basilar membrane.
• Basilar membrane contains numerous hair cells that are arranged in four rows.
• Protruding from the apical part of each hair cell is hair like structures known as stereocilia.
• On the organ of cortii a stiff gel membrane called tectorial membrane is situated.
• During the conduction of sound wave sterocilia makes contact with tectorial membrane.

Myopia (nearsightedness): The affected person can see the nearby objects but not the distant objects. This condition may result due to an elongated eyeball or thickened lens; so that the image of a distant object is formed in front of the yellow spot. This error can be corrected using a concave lens that diverges the entering light rays and focuses them on the retina.
Hypermetropia (long-sightedness): the affected person can see only the distant objects clearly but not the objects nearby. This condition results due to a shortened eyeball and thin lens; so the image of the closest object is converged behind the retina. This defect can be overcome by using a convex lens that converges the entering light rays on the retina.
Presbyopia:
Due to aging, the lens loses elasticity and the power of accommodation. Convex lenses are used to correct this defect. Astigmatism is due to the rough (irregular) curvature of the cornea or lens. Cylindrical glasses are used to correct this error.
Cataract:
Due to the changes in the nature of the protein, the lens becomes opaque. It can be corrected by surgical procedures.

Rods
Cones
1. Helps in seeing in dim light
Colour perception in bright light
2. Contains Rhodopsin pigment
Contains photopsin
3. The protein retinol and vitamins aldehyde combine to form scotoptin called Rhodopsin
The protein opsin and retinol combine to form photopsin.
4. There are 120 million rods are seen on the retina
6-7 million cone cells are seen on the retina
5. Rods are seen richly over the surface of the foveal region.
Cones are richly present on the foveal region.

* The skin senses this skin is the largest sense organ.
* All over the skin sensory receptors of pressure heat cold and pain.
* Following are the sensory receptors of the skin.
Tactile Merkel disc
* It is a light touch receptor lying in the deeper layer of the epidermis.
* Hair follicle receptors. These are light-touch receptors lying around the hair follicles.
Meissner’s corpuscles
* These are small light pressure receptors found just beneath the epidermis in the dermal papillae.
* They are numerous in hair less skin areas such as finger tips and soles of the feet.
Pacinian corpuscles
* These are the large egg-shaped receptors found scattered in the dermis.
* It detects different textures temperature hardness and pain.
Ruffini endings
This lie in the dermis responds to continuous pressure Krause end bulbs are thermo receptors that sense temperature.

• Deafness may be temporary or permanent
• Conductive deafness
• Possible causes
• The blockage of the ear canal with ear wax.
• Rupture of the ear drum.
• Middle ear infection with fluid accumulation,
• Restriction of ossicular movement.
• Sensory-neural deafness
• The defect may be in the organ of cortii or the auditory nerve or in the ascending auditory pathways or auditory cortex.

• Sound waves entering the external auditory meatus fall on the tympanic membrane and get vibrated.
• These vibrations are transmitted to the oval window through the three ear ossicles.
• Since the tympani membrane is 17-20 times larger than the oval windows. This pressure exerted on the oval window is about 20 times more than that on the tympanic membrane.
• This pressure causes the round window to alternately bulge outward and inward meanwhile the basilar membrane along with the organ of Corti moves up and down.
• These movements of hair alternately open and close the mechanically gated ion channel causes action potential.
• This is propagated to the brain as a sound sensation through the cochlear nerve.

Skin is the sensory organ of touch and is also the largest sense organ. This sensation conies from millions of microscopic sensory receptors located all over the skin and associated with the general sensations of contact, pressure, heat, cold and pain. Some parts of the body, such as the fingertips have a large number of these receptors, making them more sensitive. Some of the sensory receptors present in the skin are:
* Tactile Merkel disc is a light touch receptor lying in the deeper layer of the epidermis.
* Hair follicle receptors are light-touch receptors lying around the hair follicles.
* Meissner’s corpuscles are small light pressure receptors found just beneath the epidermis in the dermal papillae. They are numerous in hairless skin areas such as fingertips and soles of the feet.
* Pacinian corpuscles are the large egg-shaped receptors found scattered deep in the dermis and monitoring vibration due to pressure. It allows detecting different textures, temperatures, hardness, and pain.
* Ruffini endings which lie in the dermis respond to continuous pressure.
* Krause end bulbs are thermoreceptors that sense temperature.

• Taste buds are flask-shaped. There are two major types.
• Gustatory epithelial cells or taste cells.
• Basal epithelial cells or repairing cells.
• Long micro villi called gustatory hairs project from the tip of the gustatory cells and extends through a taste pore to the surface of the epithelium.
• Gustatory hairs are tire sensitive portion of the gustatory cells and they have sensory dendrites which send the signal to the brain.
• The basal cells that act as stem cells divide and differentiate into new gustatory cells.

* The sense of taste is considered to be the most pleasurable of all senses.
* The tongue is provided with many small projections called papillae.
* Taste buds are located mainly on the papillae.
* Taste buds are flask-shaped.
There are two major types.
* Gustatory epithelial cells or taste cells.
* Basal epithelial cells or repairing cells.
* Long microvilli called gustatory hairs project from the tip of the gustatory cells and extend through a taste pore to the surface of the epithelium.
* Gustatory hairs are the sensitive portion of the gustatory cells and they have sensory dendrites which send the signal to the brain.
* The basal cells that act as stem cells divide and differentiate into new gustatory cells.

The smell receptors are excited by air-borne chemicals that dissolve in fluids. The yellow coloured patches of olfactory epithelium form the olfactory organs that are located on the roof of the nasal cavity.
The olfactory epithelium is covered by a thin coat of mucus layer below and olfactory glands bounded connective tissues, above. It contains three types of cells: supporting cells, Basal cells and millions of pin-shaped olfactory receptor cells (which are unusual bipolar cells).
The olfactory glands and the supporting cells secrete the mucus. The unmyelinated axons of the olfactory receptor cells are gathered to form the filaments of the olfactory nerve [cranial nerve-I] which synapses with cells of the olfactory bulb.
The impulse, through the olfactory nerves, is transmitted to the frontal lobe of the brain for identification of smell and the limbic system for the emotional responses to odour.
Part-II.
11th Bio Zoology Guide Neural Control and Coordination Additional Important Questions and Answers
I. Choose The Correct Answer