TS Inter 2nd Year Zoology Study Material Chapter 3(b) Neural Control and Coordination

Telangana TSBIE TS Inter 2nd Year Zoology Study Material Lesson 3(b) Neural Control and Coordination Textbook Questions and Answers.

TS Inter 2nd Year Zoology Study Material Lesson 3(b) Neural Control and Coordination

Very Short Answer Type Questions

Question 1.
Name the cranial meninges covering the brain of man.
Answer:
The cranial meninges covering the brain of man are dura mater (outer) arachnoid mater (middle) and pia mater (innermost).

Question 2.
What is corpus callosum? [Mar. ’17 (A.P.); Mar. ’15 (T.S.)]
Answer:
In brain of man the two cerebral hemispheres are internally connected by a transverse, wide and flat bundle of myelinated fibres beneath the cortex called corpus callosum.

Question 3.
What do you know about arbor vitae? [March 2020]
Answer:
In the cerebellum, each hemisphere consists of 3 lobes namely anterior, posterior and floccular lobes. It has a branching tree-like core of white matter called arbor vitae surrounded by a sheath of grey matter.

Question 4.
Why the sympathetic division is called thoraco – lumbar division?
Answer:
In the sympathetic division, pre ganglionic neurons arise from the thoracic and lumbar regions of the spinal cord, hence called “Thoraco – lumbar division”.

Question 5.
Why the parasympathetic division is called craniosacral division?
Answer:
The cell bodies of the preganglionic neurons of the parasympathetic division are located in the brain and in the sacral region of the spinal cord. Hence, the parasympathetic division is also known as the cranio – sacral division.

Question 6.
Distinguish between the absolute and relative refractory periods.
Answer:

1. During the absolute refractory period, even a very strong stimulus cannot initiate a second action potential. This period coincides with the periods of depolarization and repolarization.
2. The relative refractory period is the time during which a second action potential can be initiated by a larger-than-normal stimulus. It coincides with the period of hyper polarization.

Question 7.
What is all -or- none principle?
Answer:
The action potential occurs in response to a threshold stimulus or suprathreshold stimulus but does not occur at sub threshold stimuli. It means the nerve impulse is either conducted totally or not conducted at all and this is called all or non principle.

Question 8.
How do rods and cones of human eye differ from each other chemically and functionally?
Answer:

1. Rods contain a purplish red protein called rhodopsin or visual purple, which contains a derivative of vitamin A and they are important in twilight.
2. Cones contain a visual pigment iodopsin made of a protein called photopsin and they are important in day light and colour vision.

Question 9.
Distinguish between the blind spot and the yellow spot
Answer:

1. The centre of the posterior portion of the retina is called macula lutea or yellow spot.
2. The site of the retina where the optic nerve exits the eye ball is called optic disc or blind spot.

Question 10.
What is organ of Corti? [Mar. 2019, ’17, ’15 (A.P.); May/June ’14]
Answer:
The internal ear consists of 3 parts cochlea, vestibula and semicircular canals. The cochlear epithelium forms a sensory ridge called organ of corti on basilar membrane. The organ of corti contains hair cells that act as “auditory receptors”.

Short Answer Type Questions

Question 1.
Draw a labelled diagram of the T.S. of the spinal cord of man. [May 2017 (A.P.); Mar. 15 (A.P. & T.S.)]
Answer:

Question 2.
Distinguish between somatic and autonomic neural systems.
Answer:
Somatic Neural System (SNS) :
The somatic neural system includes both sensory and motor neurons. The sensory neurons conduct sensory impulses from the different somatic receptors to the CNS. All these sensations normally are consciously perceived. Somatic motor neurons innervate the skeletal muscles and produce voluntary movements. The axon of a single myelinated somatic motor neuron extends from the CNS all the way to the muscle fibres. In the SNS, the effect of a somatic motor neuron always is excitation.

Autonomic Neural System (ANS) :
The ANS usually operates without conscious control. The autonomic neurons are associated with interoceptors (located in the viscera and sense internal stimuli), such as chemoreceptors. These sensory signals are generally not consciously perceived. Autonomic motor neurons regulate the involuntary activities of the cardiac muscle, smooth muscle and glands. The ANS has two divisions : 1. Sympathetic and 2. Parasympathetic divisions.

Question 3.
Give an account of the retina of the human eye.
Answer:
Retina (Nervous tunic) :
This is the third and inner coat of the eye. It consists of a pigmented epithelium (non – visual portion) and a neural portion (visual portion). The pigmented epithelium is a sheet of melanin – containing epithelial cells that lie between the choroid and the neural portion of the retina. The neural portion of the retina has three layers of retinal neurons namely : photoreceptor layer (the layer closest to the choroid coat), bipolar cell layer and ganglion cell layer.

Photoreceptor layer consists of two types of photoreceptor cells called rods and cones. Rods contain a purplish – red protein called the rhodopsin or visual purple, which contains a derivative of vitamin – A and they are important in twilight (scotopic vision – the vision of the eye under low light conditions).

Cones contain a visual pigment (iodopsin, made of a protein called photopsin) and they are important in daylight (photopic) vision and colour vision. There are three types of cones, each having different sensitivity and they provide ‘optimal response’ to red, green and blue colours.

The centre of the posterior portion of the retina is called the macula lutea or yellow spot. A small depression present in the centre of the yellow spot is called fovea centralis, and it contains only cones. Fobea is responsible for sharp, central vision, which is useful while walking, reading, driving etc. The axons of the ganglion cells extend posteriorly and exit the eye ball as the optic nerve. The site of the retina where the optic nerve exits the eye ball is called optic disc or blind spot which is devoid of photoreceptor cells (no image is formed at that spot).

Question 4.
Give an account of Synaptic transmission. [March 2018 (A.P.)]
Answer:
The functional junction formed between two neurons is called synapse. In a chemical synapse, the presynaptic neuron synthesizes the neurotransmitter and stores in the synaptic vesicles of synaptic terminals.

When an action potential reaches a synaptic terminal, it depolarizes the membrane. By this voltage gated calcium channels open. The rise is the Ca²⁺ concentration leads to the release of neurotransmitters by exocytosis. The neuro transmitter diffuses across the synaptic cleft.

The postsynaptic membrane has ligandgated in channels. Binding of the neurotransmitter to a receptor of the channel opens the channel and allows specific ions to diffuse across the postsynaptic membrane. It results in a postsynoptic membrane potential. Excitatory neurotransmitters depolarize the postsynaptic membrane while inhibitory neurotransmitters cause hyperpolarization of post synaptic membrane.

Acetylcholine is the most common neurotransmitter. It may be excitatory or inhibitory. Gama aminobutyric acid (GABA) and glycine are the inhibitory neurotransmitters.

Question 5.
List out the differences between sympathetic and parasympathestic neural systems in man.
Answer:
Differences between Sympathetic and Parasympathetic neural systems.

Long Answer Type Questions

Question 1.
Give a brief account of the structure and functions of the brain of man.
Answer:
Brain (‘the living super computer’) :
It is the site of information processing and control. It is protected in the cranial cavity and covered by three connective tissue membranes called ‘cranial meninges’ namely, dura mater, arachnoid mater and pia matter. Dura mater is the outer most, thick, double layered membrane which lines the inner surface of the cranial cavity. Arachnoid mater is a thin, webby middle membrane covering the brain. It is separated from the dura mater by a narrow subdural space. Pia matter is a thin, innermost meninx which closely adheres to the brain. Pia mater is separated from the arachnoid membrane by the subarachnoid space. The brain can be divided into three major parts called
i) Forebrain, ii) Midbrain and iii) Hindbrain.

I) Forebrain (Prosencephalon) The forebrain consists of i) Olfactory bulb, ii) Cerebrum and iii) Diencephalon.
i) Olfactory Bulb :
Olfactory bulbs receive impulses pertaining to smell from the olfactory epithelium.

ii) Cerebrum :
Cerebrum forms the major part of the brain and is longitudinally divided into the left and the right cerebral hemispheres by a deep cleft called ‘longitudinal fissure’. The two hemispheres are internally connected by a transverse, wide and flat bundle of myelinated fibres beneath the cortex, called ‘corpus callosum’ (colossal commissure).lt brings ‘coordination’ between the right and left sides of the cerebral hemispheres. The surface of the cerebrum is composed of grey matter and is called ‘cerebral cortex’. The neuronal cell bodies are concentrated int he cerebral cortex.

The surrace of the cerebral cortex shows many convolutions or folds and grooves. The folds are called gyri (singular: gyrus), the deepest and shallower grooves between the folds are called fissures and sulci, respectively. Gyri and sulci increase the surface area of the cerebral cortex (which is an indication of the higher level of evolution of the human being).

Cerebral cortex has three functioinal areas called a) sensory areas, that receive and interpret the sensory impulses b) motor areas. Which control voluntary muscular movements c) association areas, which are neither clearly sensory nor motor in function and they deal with more complex ‘integrative functions’ such as memory and communications. The cerebral medulla consists of mostly myelinated axons (white matter). Each cerebral hemisphere of the cerebrum is divided into four lobes namely frotnal, parietal, temporal and occipital lobes.

iii) Diencephalon (Thalamencephalon) :
The main parts of the diencephalon are the epithalamus, thalamus and hypothalamus.

i) Epithalamus :
It is the roof of the diencephalon. It is a non – nervous part which is fused with the pia mater to form the anterior choroid plexus. Just behind the anterior choroid plexus, the epithelium of the epithalamus forms a pineal stalk, which ends in a rounded structure called pineal body.

ii) Thalamus :
It lies superior to the mid brain. It is the major coordinating centre for sensory and motor signalling.

iii) Hypothalamus (the thermostat of the body):
It lies at the base of the thalamus. The hypothalamus forms a funnel – shaped downward extension called ‘infundibulum’, connecting the hypothalamus with the pituitary gland. It also contains several groups of neurosecretory cells, which secrete hormones called hypothalamic hormones. Hypothalamus controls and integrates the activities of the autonomous nervous system (ANS) and it has osmoregulatory, thermoregulatory, thirst, feeding (hunger) and satiety centres.

I) Limbic system :
The inner parts of the cerebral hemispheres and a group of associated deep structures like amygdala or amygdale, hippocampus etc., form the limbic system. The limbic system along with hypothalamus is involved in the regulation of sexual behaviour and expression of emotional reactions.

II) Midbrain (Mesencephalon) :
The midbrain is located between the thalamus / hypothalamus of the forebrain and the pons Varolii of the hindbrain. The ventral portion of the mid brain consists of a pair of longitudinal bands of nervous tissue called cerebral peduncles or crura cerebri (sing: crus cerebrum) (which connect the cerebral hemispheres with the pons). The dorsal portion of the midbrain consists of four rounded lobes called copora quadrigemina (Four optic lobes). The two larger anterior optic lobes are called superior colliculi and the smaller x posterior lobes are called inferior colliculi. The superior colliculi and the inferior colliculi are concerned with visual and auditory functions, respectively.

III) Hindbrain (Rhombencephalon) :
The hind brain comprises cerebellum, pons Varolii and medulla oblongata.

Cerebellum (‘the little brain’) :
It is the second largest part of the brain. It consists of two cerebellar hemispheres and a central vermis. Each cerebellar hemisphere consists of three lobes namely anterior, posterior and floccular lobes. It has a branching tree – like core of white mater called arbor vitae (the tree of life) ” surrounded by a sheath of grey matter (cerebellar cortex).

Pons Varolii :
It lies front of the cerebellum below the mid brain and above the medulla oblongata. It consists of nerve fibres which form a bridge between the two cerebellar hemispheres. It is a relay station between the cerebellum, spinal > cord and the rest of the brain. Pons has the pneumotaxic centre (involved in the control of the respiratory muscles as it regulates the amount of air a person can take in, each time).

Medulla oblongata :
It is the posterior most part of the brain. It extends from the pons Varolii above and continuous with the spinal cord below. It has a very . thin, vascular folded structure called posterior choroid plexus. Medulla includes cardiovascular and respiratory centers, the centers for swallowing, vomiting, coughing, sneezing and hiccupping. The midbrain, pons and the medulla oblongata . are together referred to as the’brain stem’ .The medulla oblongata passes out of the cranium through the foramen magnum and joins the spinal cord.

Human brain consists of four ventricles. The first and second ventricles (lateral ventricles or paracoels) are present in the right and left cerebral hemispheres respectively. The third ventricle (diocoel) occurs in the diencephalon. The two paracoels are connected to the median diocoel individually by the two ‘foramina of Monro’ (interventricular foramina). The fourth ventricle (myelocoel) is present in the medulla. The myelocoel and the diocoel are connected by a narrow canal called iter or aqueduct of Sylvius/cerebral aqueduct. The metacoel is continuous with the central canal of the spinal cord.

The ventricles of the brain, and the subarachnoid space are filled with Cerebro – spinal fluid (CSF). CSF is an alkaline, colourless fluid which is filtered from the choroid plexuses into the ventricles of the brain.

Question 2.
Explain the transmission of nerve impulse through a nerve fibre with the help of suitable diagrams.
Answer:
Generation and Conduction of Nerve Impulse :
Nerve cells exhibit a special property called electrical excitability. The signal that travels along the length of a nerve fiber and ends in the release of neurotransmitters is called a nerve impulse. Neurons can respond to external and internal stimuli and conduct nerve impulses (action potentials) because in a neuron a membrane potential is established across the neuronal membrane. It means there is an ‘unequal distribution of ions’ (charged atoms) on the two sides of a nerve cell membrane with the cell’s interior more negative with respect to that of the exterior. Ions keep moving in and out of an axon through several ‘ion channels’. The axolemma of a neuron has the following three different types of ion channels.

1) Leakage channels :
They are K⁺ and Na⁺ leakage channels. K⁺ leakage channels are more than those of Na⁺ leakage channels. Hence axolemma has greater permeability to K⁺ ions than Na⁺ ions.

2) Ligand – gated channels :
They are located in the post synaptic membrane (dendrites and cells bodies) and open or close in response to chemical stimuli.

3) Voltage gated channels :
These channels open in response to a change in membrane potential. There are sodium voltage gated and potassium voltage gated channels across the axolemma. Sodium voltage gated channels are of two types. They are sodium activation and inactivation voltage gated channels. For K⁺ only potassium activation voltage gated channel is present.

Resting membrane potential :
The resting membrane potential exists because of a small buildup of negative ions in the axoplasm along the inside of the membrane and an equal buildup of positive ions in the extra cellular fluid along the outer surface of the membrane. Such a separation of positive and negative electrical charges is a form of potential energy. In neurons, the resting membrane potential ranges from -40 to -99 mV. A typical value is -70 mV. The minus sign indicates that the inside of the cell is negative relative to the outside.

At resting phase, the axolemma is polarized. The membrane potential can change from its resting value when the membrane’s permeability to particular ions changes. If the inner side becomes less negative, it is said to be depolarized. If the inner side becomes more negative, it is said to be hyperpolarized. During the resting phase the activation gates of sodium are closed, the inactivation gates of sodium are open and the activation gates of potassium are closed.

Sodium – potassium pump :
Sodium and potassium ions diffuse inwards and outwards, respectively, down their concentration gradients through leakage channels. Such a movement of ions, if unchecked, would eventually disturb the resting membrane potential. These flows of ions are offset by sodium – potassium pumps (Na⁺/ K⁺ ATPases) present in the axonal walls. These pumps expel three Na+ ions for each two K⁺ ions imported. As these pumps remove more positive charges from the axoplasm than they bring into it, they contribute to the negativity of the resting membrane potential i.e., -70 mv.

Depolarization (Rising phase) :
When a nerve fibre is stimulated, the plasma membrane becomes more permeable to Na⁺ ions than to K⁺ ions as the activation and inactivation voltage gates of sodium open and activation voltage gates of potassium close. As a result the rate of flow of Na⁺ into the axoplasm exceeds the rate of flow of K⁺ to the ECF. Hence, the axolemma is positively charged inside and negatively charged outside. This reversal of electrical charge is called “depolarization”.

Outer face of the point which is adjacent to the site of depolarization remains positively charged. The electrical potential difference between these two areas is called “action potential”. An action potential occurs in the membrane of the axon of a neuron when depolarization reaches a certain level called ‘threshold potential’ (-55 mV). The particular stimulus which is able to bring the membrane potential to threshold is called ‘threshold stimulus’. The action potential occurs in response to a threshold stimulus or suprathreshold stimulus but does not occur at subthreshold stimuli. It means the nerve impulse is either conducted totally or not conducted at all and this is called ‘all – or – none principle’. Due to the rapid influx of Na⁺ ions, the membrane potential shoots rapidly up to +45mV (spike potential).

Repolarization (Falling phase) :
As the wave of depolarization passes away from its site of origin to the adjacent point, the activation gates of sodium remain open, inactivation gates of sodium close and activation gates of potassium open at the site of origin of depolarization. As a result the influx of Na⁺ ions into the axoplasm from the ECF is checked and ‘efflux’ of K⁺ ions occurs, which leads to the returning of axolemma to the resting state (exit of potassium ions causes a reversal of membrane potential to negative inside). This is called ‘repolarization’.

Hyperpolarization (Undershoot) :
The repolarization typically goes more negative than the resting potential to about – 90 mV. This is called ‘hyperpolarization’. This occurs because of the increased K⁺ permeability that exists while voltage – gated K⁺ channels are open (however they close rather slowly as K voltage gates are said to be ‘lazy’ gates), activation and inactivation gates of Na⁺ channels remain closed. The membrane potential returns to its original resting state as the K⁺ channels close completely. As the voltage falls below the – 70mV level of the resting state, it is called ‘undershoot’.