Control and Coordination Notes

Introduction

Movement is the characteristic feature of all the living organisms. All living organisms move in response to the stimuli i.e; the change in the environment. These movements are controlled and coordinated by our body’s nervous and endocrine system.

Nervous system in animals

Nervous System: The nervous system is composed of specialized tissues, called nervous tissue. The nerve cell or neuron is the functional unit of the nervous system. It is the nervous system which is mainly responsible for control and coordination in complex animals.

Functions of the nervous system

• Nervous system receives information from the environment.
• To receive the information from the various body.
• To act according to through muscles and glands.

A neuron is the structural and functional unit of the nervous system. 

Neuron: Neuron is a highly specialized cell which is responsible for the transmission of nerve impulses. The neuron consists of the following parts
(i) Cyton or cell body: The cell body or cyton is somewhat star-shaped, with many hair like structures protruding out of the margin. These hair-like structures are called dendrites. Dendrites receive the nerve impulses.

(ii) Axon: This is the tail of the neuron. It ends in several hair-like structures, called axon terminals. The axon terminals relay nerve impulses.
(iii) Myelin sheath: There is an insulator cover around the axon. This is called myelin sheath. The myelin sheath insulates the axon against nerve  impulse from the surroundings.

Types of neuron

• Sensory neuron: These neurons receive signals from a sense organ.
• Motor neuron: These neurons send signals to a muscle or a gland.
• Association or relay neuron: These neurons relay the signals between sensory neuron and motor neuron.

Synapse:The point contact between the terminal branches of axon of one neuron with the dendrite of another neuron is called synapse.

Neuromuscular Junction (NMJ):NMJ is the point where a muscle fibre comes in contact with a motor neuron carrying nerve impulse from the control nervous system.

Transmission of nerve impulse: Nerve impulses travel in the following manner from one neutron to the next :

Chemical released from axon tip of one neuron, cross the synapse or neuromuscular junction to reach the next cell.

Human nervous system

Human Nervous System: The nervous system in humans can be divided into three main parts :

1. Central Nervous System:The central nervous system is composed of the brain and the spinal cord. The brain controls all the functions in the human body. The spinal cord works as the relay channel for signals between the brain and the peripheral nervous system.
2. Peripheral Nervous System:The peripheral nervous system is composed of the cranial nerves and spinal nerves. There are 12 pairs of cranial nerves. The cranial nerves come our of the brain and go to the organs in the head region. There are 31 pairs of spinal nerves. The spinal nerves come out of the spinal cord and go to the organs which are below the head region.
3. Autonomous Nervous System:The autonomous nervous system is composed of a chain of nerve ganglion which runs along the spinal cord. It controls all the involuntary actions in the human body. The autonomous nervous system can be divided into two parts :

• Sympathetic nervous system.
• Parasympathetic nervous system.

Sympathetic Nervous System: This part of the autonomous nervous system heightens the activity of an organ as per the need. For example, during running, there is an increased demand for oxygen by the body. This is fulfilled by an increased breathing rate and increased heart rate. The sympathetic nervous system works to increase the breathing rate the heart rate, in this case.

Parasympathetic Nervous System: This part of the autonomous nervous system slows the down the activity of an organ and thus has a calming effect. During sleep, the breathing rate slows down and so does the heart rate. This is facilitated by the parasympathetic nervous system. It can be said that the parasympathetic nervous system helps in the conservation of energy.

Transmission of impulses

A nerve impulse is transmitted from one neuron to another through junctions called synapses. A synapse is formed by the membranes of a pre-synaptic neuron and a post-synaptic neuron, which may or may not be separated by a gap called synaptic cleft.

• There are two types of synapses, namely electrical synapses and chemical synapses.
• Electric synapse

At electric synapses, the membranes of pre and post-synaptic neurons are in very close proximity .

Transmission of an impulse across electrical synapses is very similar to impulse conduction along a single axon.

Transmission of impulse is always faster than that across a chemical synapse.

• Chemical synapse

At a chemical synapse, the membranes of the pre and post-synaptic neurons are separated by a fluid-filled space called synaptic cleft.

Chemicals called neurotransmitters are involved in the vesicles filled with these synapses.

When an impulse arrives at the axon terminal , it stimulates the movement of the synaptic vesicles towards the membrane where they fuse with the plasma membrane and release their neurotransmitters in the synaptic cleft.

These released neurotransmitter bind to their specific receptors, present on the post-synaptic membrane. This binding opens ion channels present in the membranes, allowing the entry of ions which can generate a new potential in the post-synaptic neuron. the new potential developed may be excitatory or inhibitory.

Human Brain: Human brain is a highly complex organ, which is mainly composed of nervous tissue. The tissues are highly folded to accommodate a large surface area in less space. The brain is covered by a three-layered system of membranes, called meninges. Cerebrospinal fluid is filled between the meninges. The CSF providers cushion the brain against mechanical shocks. Furthermore, protection. The human brain can be divided into three regions, viz. forebrain, midbrain and hindbrain.

Parts of Human Brain :

• Fore-brain
• Mid-brain
• Hind-brain

Forebrain : the forebrain consists of cerebrum, thalamus and hypothalamus.

Cerebrum: The cerebrum is the largest part in the human brains. It is divided into two hemispheres called right and left cerebral hemispheres. These hemispheres are connected with a corpus callosum. The layers of cells which covers the cerebral hemispheres is called cerebral cortex. The cerebral cortex is referred to as grey matter due to its greyish appearance. The cerebral cortex contains motor areas,  sensory areas and large areas that are neither clearly sensory nor motor in action.

Functions of cerebrum

• • The cerebrum controls voluntary motor actions.
  • It is the site of sensory perceptions, like tactile and auditory perceptions.

Hypothalamus : this is also an important part of the brain and it lies at the base of the thalamus. The hypothalamus contains a number of centers which control body temperature, urge for eating and drinking. The inner parts of cerebral hemispheres and a group of associated deep structures like amygdala, hippocampus, etc., form a complex structure called the limbic system. Along with the hypothalamus , this system is involved in the regulation of sexual behavior, expression of emotional reactions (excitement, pleasure, rage and fear) and motivation.

 

Midbrain

The midbrain is located between the thalamus/hypothalamus of the forebrain and pons of the hindbrain. A canal called the cerebral aqueduct passes through the midbrain. Forebrain and Midbrain forms the brainstem.

 

Hindbrain : The hindbrain comprises pons, cerebellum and medulla or medulla oblongata .

• Pons: it consists of fiber tracts that interconnect different regions of the brain. It relays impulses between the lower cerebellum and spinal cord, and higher parts of the brain like the cerebrum and midbrain, also regulates respiration.
• Cerebellum: it has very coiled surface in order to provide the additional space for many more neurons.
• Medulla: Medulla forms the brain stem, along with the pons. It lies at the base of the brain and continues into the spinal cord. The medulla controls various involuntary functions, like hear beat respiration, etc. It controls involuntary actions.
  Example: Blood pressure, salivation, vomiting.
• Spinal cord: Spinal cord controls the reflex actions and conducts massages between different parts of the body and brain.

Reflex actions

Reflex action refers to the simplest form of response in the nervous system, which may be defined as the spontaneous, automatic and mechanical response to a stimulus acting on a specific receptor without conscious effort or thought and requires the involvement of a part of the central nervous system.

The entire process of response to peripheral nervous stimulation , that occurs involuntarily i.e; without conscious effort or thought and requires the involvement of a part of the central nervous system is called reflex action.

The reflex pathway comprises at least one afferent neuron (receptor) and one efferent (effector) neuron appropriately arranged in series .

The afferent neuron receives signal from a sensory organ and transmits the impulse via a dorsal nerve root into the CNS .

The efferent neuron carries signal from CNS to the effector .

Reflex arc

Such a connection is commonly called a reflex arc . . Reflex arcs are formed in this spinal cord itself, although the information input also goes on to reach the brain reflex arcs have evolved in animals because the thinking process of the brain is not fast enough. In fact many animals have very little or none of the complex neuron network needed for thinking. So it is quite likely that reflex arcs have evolved as efficient ways of functioning in the absence of true thought processes. However, even after complex neuron networks have come into existence, reflex arcs continue to be more efficient for quick responses.

• A delicate organ like the brain, which is so important for a variety of activities, needs to be carefully protected. For this, the body is designed so that the brain sits inside a bony box. Inside the box, the brain is contained in a fluid-filled balloon which provides further shock absorption. If you run your hand down the middle of your back, you will feel a hard, bumpy structure. This is the vertebral column or backbone which protects the spinal cord.

ACTION OF NERVOUS TISSUE

• It collects information, sends it around the body, processes information, makes decisions based on information, and conveys decisions to muscles for action.
• In other words, when the action or movement is to be performed, muscle tissue will do the final job.

Movement of muscles

When a nerve impulse reaches the muscle, the muscle fiber must move. The simplest notion of movement at the cellular level is that muscle cells will move by changing their shape so that they shorten.

Shape changing of muscles

Muscle cells have special proteins that change both their shape and their arrangement in the cell in response to nervous electrical impulses. When this happens, new arrangements of these proteins give the muscle cells a shorter form. 

Coordination in Plants

• Plant growth is unique because plants retain the capacity for unlimited growth throughout their life.. the ability of the plants is due to presence of meristems at certain locations in their body.
• The cells of such meristems have the capacity to divide and self perpetuate.
• Primary growth of the plants contribute to the elongation of the plants along their axis.
• Secondary growth contribute to the girth of the plants.

Control and coordination in plants are carried out by hormones. Different plant hormones help to coordinate growth, development and responses to the environment. They are synthesized at places away from where they act and simply diffuse to the area of action.

There are five such hormones as discussed follows :

1. Auxin

This hormone helps in the growth of the plant tissue. These are produced by the apices of roots and shoots. When growing plants detect light, a hormone called auxin, synthesized at the shoot tip, helps the cells to grow longer. When light is coming from one side of the plant, auxin diffuses towards the shady side of the shoot. This concentration of auxin stimulates the cells to grow longer on the side of the shoot which is away from light. Thus, the plant appears to bend towards light.

2. Cytokinin

This hormone helps in cell division process and delays ageing of leaves. These also overcome apical dominance . Cytokinin promote cell division, and it is natural then that they are present in greater concentration in areas of rapid cell division, such as in fruits and seeds. These are examples of plant hormones that help in promoting growth. But plants also need signals to stop growing.

3. Gibberellins

This hormone helps in the growth of stems , initiates seed germination, promotes flowering, cell division and seed growth after germination. gibberellins which, like auxins, help in the growth of the stem

4. Abscisic acid

This hormone inhibits growth and causes wilting of leaves , promotes dormancy of buds and seeds.

5. Ethylene

This hormone is a gaseous hormone which causes the ripening of the fruits.

Plant movements

The movements which are growth related are called tropic movements. These movements occur in response to environmental stimuli and the direction of the response is dependent on the direction of the stimulus.

•  Phototropic movement
• Geotropic movement
• Chemotropic movement
• Hydrotropic movement
• Thigmotropic movement

Phototrophic movement

Movement of plant parts in response to light is known as phototropic movement. E.g., Environmental triggers such as light, or gravity will change the directions that plant parts grow in.

These directional, or tropic, movements can be either towards the stimulus, or away from it. So, in two different kinds of phototropic movement, shoots respond by bending towards light while roots respond by bending away from it.

 

 

Geotropic movement

Movement of plant parts in response to earth’s gravitational force is known as geotropic movement., The root grows towards gravity and shoot grows away from gravity. Plants show tropism in response to other stimuli as well. The roots of a plant always grow downwards while the shoots usually grow upwards and away from the earth. This upward and downward growthof shoots and roots, respectively, in response to the pull of earth or gravity is, obviously, geotropism

 

 

Chemotrophic movement

Movement of plant parts in response to chemical stimuli is known as chemotropic movement. E.g.,  One example of chemotropism is the growth of pollen tubes towards ovules, about which we will learn more when we examine the reproductive processes of living organisms.

 

 

 

 

Hydrotropic movement

 Movement of plant parts in response to water or moisture is known as hydrotropic movement., root movement in search of water is positive hydrotropism.

Thermotropic movement

Movement of plant parts in response to touch is called as thigmotropic movement. E.g., Movement of tendrils around the support is positive thigmotropism. Some plants like the pea plant climb up other plants or fences by means of tendrils. These tendrils are sensitive to touch. When they come in contact with any support, the part of the tendril in contact with the object does not grow as rapidly as the part of the tendril away from the object. This causes the tendril to circle around the object and thus cling to it. More commonly, plants respond to stimuli slowly by growing in a particular direction. Because this growth is directional, it appears as if the plant is moving.

• Plants have neither a nervous system nor muscles. When we touch the leaves of a chhui-mui (the ‘sensitive’ or ‘touch-me-not’ plant of the Mimosa family), they begin to fold up and droop. When a seed germinates, the root goes down, the stem comes up into the air.

COMMUNICATION IN MULTICELLULAR ORGANISMS

PLANTS

Communication in the bodies of multicellular organisms. The movement of the sensitive plant in response to touch is very quick. The movement of sunflowers in response to day or night, on the other hand, is quite slow. Growth-related movement of plants will be even slower. Even in animal bodies, there are carefully controlled directions to growth. Our arms and fingers grow in certain directions, not haphazardly. So controlled movements can be either slow or fast. If fast responses to stimuli are to be made, information transfer must happen very quickly. For this, the medium of transmission must be able to move rapidly.

Hormones in animals

 

Hormones are non-nutrient chemicals which act as intercellular messengers and are produced in trace amounts. The hormones are secreted by the organized endocrine glands.

Human endocrine system

The endocrine glands and hormones producing diffused tissues/ cells located in different parts of our body constitute the endocrine system.

The endocrine glands of the body are as follows:

• Pituitary
• Pineal
• Thyroid
• Thymus
• Adrenals
• Gonads(testis and ovaries)

 

Pituitary gland

• It is a pea-sized gland located at the base of the brain.
• It is divided into anterior and posterior pituitary.
• Anterior pituitary releases some important hormones like :
  • Growth hormone(GH)
  • Prolactin releasing hormone(PRL)
  • Thyroid stimulating hormone(TSH)
  • Adrenocorticotropic hormone(ACTH)
  • Luteinizing hormone(LH)
  • Follicle stimulating hormone(FSH)
• Posterior pituitary releases these hormone :
  • Oxytocin
  • Vasopressin
• It is the master gland as it controls the secretions of all the other endocrine glands.
• It also secretes Growth Hormone (GH). Under-secretion of GH causes Dwarfism and over-secretion causes Gigantism in children and ‘Acromegaly’ in adults.

 

 

Thyroid gland

• It is a butterfly-shaped gland located in the throat.
• It secretes two hormones T₃ and T₄ , T₄ is the hormone ‘Thyroxine’ which regulates the metabolism of the body.
• Enlargement of the thyroid gland is the condition known as goiter which occurs due to deficiency of iodine in our diet.

Iodine is necessary for the thyroid gland to make thyroxin hormone. Thyroxin regulates carbohydrate, protein and fat metabolism in the body so as to provide the best balance for growth. Iodine is essential for the synthesis of thyroxin. In case iodine is deficient  in our diet, there is a possibility that we might suffer from goiter. One of the symptoms in this disease is a swollen neck.

Thymus

• Thymus is the lobular structure located between lungs .
• It plays major role in the development of the immune system.
• This hormone degenerates in the old.

 

 

Adrenal gland

• Occurs in pairs above each kidney.
• This gland has two type of tissues : adrenal medulla and adrenal cortex
• Adrenal medulla is in the center and adrenal cortex is in the periphery.
• Adrenal medulla secretes two hormones : adrenaline and nor adrenaline.
• These two hormones are also known as emergency hormones.
• Adrenaline is secreted directly into the blood and carried to different parts of the body. The target organs or the specific tissues on which it acts include the heart. As a result, the heart beats faster, resulting in supply of more oxygen to our muscles. The blood to the digestive system and skin is reduced due to contraction of muscles around small arteries in these organs. This diverts the blood to our skeletal muscles. The breathing rate also increases because of the contractions of the diaphragm and the rib muscles. All these responses together enable the animal body to be ready to deal with the situation. Such animal hormones are part of the endocrine system which constitutes a second way of control and coordination in our body.

• Adrenal cortex secretes different hormones in different layers, that helps in the maintenance of electrolytes, body fluid volume, blood pressure and growth of pubic and axial hair during puberty ,etc.

Pancreas

• Pancreas is a composite gland because it acts as an endocrine and exocrine gland.
• The endocrine part of the pancreas secretes two very important hormones : insulin and glucagon
• Glucagon and insulin plays an important role in maintaining the normal blood glucose levels .
• Glucagon reduces the cellular glucose uptake and insulin works opposite to glucagon.

 

Gonads

Testis and ovaries 

• The testes produce the male hormone testosterone and androgens.
• The ovaries produce the female hormones estrogen and progesterone.
• Testosterone and estrogen help in producing gametes and are responsible for the sexual characteristics of males and females respectively.
• The role of progesterone in female is more in the pregnancy.
• The changes associated with puberty are because of the secretion of testosterone in males and estrogen in females.

Mechanism of hormone action

• Hormones produce their effects on target tissues by binding to specific proteins called hormone receptors located in the target tissues only.
• Hormone receptors that are present on the cell membrane of the target tissues are called membrane-bound receptors.
• Binding of a hormone to its receptor leads to the formation of a hormone receptor complex.
• Each receptor is specific to one hormone only and hence hormone receptors are specific.
• Hormone-receptor complex formation leads to certain biochemical changes in the target tissue.
• Target tissue metabolism and hence physiological functions are regulated by hormones.

Types of hormones:

On the basis of their chemical nature , hormones can be divided into groups :

1. Protein hormone:Insulin, Glucagon, Pituitary hormones
2. Steroidal hormone:Testosterone, Estrogen, progesterone
3. Iodothyronine:Thyroid hormones
4. Amino acid derivative:Adrenaline