CORE PAPER IV: ANIMAL PHYSIOLOGY SEMESTER : IV SUBJECT CODE : 18BZO43C UNIT – III EXCRETION, OSMOREGULATION AND MYOLOGY

 EXCRETION – Kidney – Structure and Functions, Mechanism of Urine formation, Kidney Failure.  OSMOREGULATION – Osmoregulation in Mammals.  MUSCLES – Types of muscles, Mechanism of muscle contractions. EXCRETION – Kidney – Structure and Functions, Mechanism of Urine formation, Kidney Failure.

 The kidneys play a role in maintaining the balance of body fluids and regulating blood pressure, among other functions.  The kidneys are at the back of the abdominal cavity, with one sitting on each side of the spine.  The right kidney is generally slightly smaller and lower than the left, to make space for the liver.  Each kidney weighs 125–170 grams (g) in males and 115–155 g in females.  A tough, fibrous renal capsule surrounds each kidney. Beyond that, two layers of fat serve as protection. The adrenal glands lay on top of the kidneys.  Inside the kidneys are a number of pyramid-shaped lobes. Each consists of an outer renal cortex and an inner renal medulla. Nephrons flow between these sections. These are the urine-producing structures of the kidneys.  Blood enters the kidneys through the renal arteries and leaves through the renal veins. The kidneys are relatively small organs but receive 20–25 of the heart’s output.  Each kidney excretes urine through a tube called the ureter that leads to the bladder Kidney – Structure and Functions

Kidney – Structure and Functions

 The main role of the kidneys is maintaining homeostasis. This means they manage fluid levels, electrolyte balance, and other factors that keep the internal environment of the body consistent and comfortable.  They serve a wide range of functions.  Waste excretion - The kidneys remove a number of waste products and get rid of them in the urine. Two major compounds that the kidneys remove are: urea, which results from the breakdown of proteins, uric acid from the breakdown of nucleic acids, Reabsorption of nutrients.

 The kidneys reabsorb nutrients from the blood and transport.

 They also reabsorb other products to help maintain homeostasis.

 Reabsorbed products include: glucose, amino acids, bicarbonate, sodium, water, phosphate, chloride, sodium, magnesium, and potassium ions.

 Osmolality regulation - Osmolality is a measure of the body’s electrolyte-water balance, or the ratio between fluid and minerals in the body. Dehydration is a primary cause of electrolyte imbalance. If osmolality rises in the blood plasma, the hypothalamus in the brain responds by passing a message to the pituitary gland. This, in turn, releases antidiuretic hormone (ADH).

 In response to ADH, the kidney makes a number of changes, including:

• increasing urine concentration

• increasing water reabsorption Kidney – Structure and Functions

 Maintaining pH - In humans, pH level is between 7.38 and 7.42. Below this boundary, the body enters a state of acidemia, and above it, alkalemia.  The kidneys and lungs help keep a stable pH within the human body. The lungs achieve this by moderating the concentration of carbon dioxide.  The kidneys manage the pH through two processes: • Reabsorbing and regenerating bicarbonate from urine: Bicarbonate helps neutralize acids. • Excreting hydrogen ions and fixed acids: Fixed or nonvolatile acids are any acids that do not occur as a result of carbon dioxide. They result from the incomplete metabolism of carbohydrates, fats, and proteins. They include lactic acid, sulfuric acid, and phosphoric acid. Regulating blood pressure The kidneys regulate blood pressure , it work with other functions to increase the kidneys’ absorption of sodium chloride, or salt. This effectively increases the size of the extracellular fluid compartment and raises blood pressure. Anything that alters blood pressure can damage the kidneys over time, including excessive alcohol consumption, smoking, and obesity.

Secretion of active compounds The kidneys release a number of important compounds, including: •Erythropoietin: This controls erythropoiesis, or the production of red blood cells. The liver also produces erythropoietin, but the kidneys are its main producers in adults. •Renin: This helps manage the expansion of arteries and the volume of blood plasma, lymph, and interstitial fluid. Lymph is a fluid that contains white blood cells, which support immune activity, and interstitial fluid is the main component of extracellular fluid. •Calcitriol: This is the hormonally active metabolite of vitamin D. It increases both the amount of calcium that the intestines can absorb and the reabsorption of phosphate in the kidney. MECHANISM OF URINE FORMATION

 The kidneys filter unwanted substances from the blood and produce urine to excrete them. There are three main steps of urine formation: glomerular filtration, reabsorption, and secretion. These processes ensure that only waste and excess water are removed from the body.  There are four basic processes in the formation of urine starting with plasma. • Filtration. • Reabsorption. • Secretion. • Excretion. Regulated reabsorption, in which hormones control the rate of transport of sodium and water depending on systemic conditions, takes place in the distal tubule and collecting duct.

Urine Formation Waste is excreted from the human body, mainly in the form of urine. Our kidneys play a major role in the process of excretion. Constituents of normal human urine include 95 percent water and 5 percent solid wastes. It is produced in the nephron, which is the structural and functional unit of the kidney. Urine formation in our body is mainly carried out in three phases namely 1.Glomerular filtration 2.Reabsorption 3.Secretion

Mechanism of Urine Formation

The mechanism of urine formation involves the following steps:

Glomerular Filteration Glomerular filtration occurs in the glomerulus where blood is filtered. This process occurs across the three layers- epithelium of Bowman’s capsule, endothelium of glomerular blood vessels, and a membrane between these two layers. Blood is filtered in such a way that all the constituents of the plasma reach the Bowman’s capsule, except proteins. Therefore, this process is known as ultrafiltration

Reabsorption Around 99 percent of the filtrate obtained is reabsorbed by the renal tubules. This is known as reabsorption. This is achieved by active and passive transport.

Secretion The next step in urine formation is the tubular secretion. Here, tubular cells secrete substances like hydrogen ion, potassium ion, etc into the filtrate. By this process, the ionic, acid-base and the balance of other body fluids are maintained. The secreted ions combine with the filtrate and form urine. The urine passes out of the nephron tubule into a collecting duct. Urine The urine produced is 95% water and 5% nitrogenous wastes. Wastes such as urea, ammonia, creatinine are excreted in the urine. Apart from these, the potassium, sodium and calcium ions are also excreted.

KIDNEY FAILURE

 Kidney failure occurs when your kidneys lose the ability to sufficiently filter waste from your blood. Many factors can interfere with your kidney health and function, such as: • toxic exposure to environmental pollutants or certain medications • certain acute and chronic diseases • severe dehydration • kidney trauma • Symptoms • a reduced amount of urine • swelling of your legs, ankles, and feet from retention of fluids caused by the failure of the kidneys to eliminate water waste • unexplained shortness of breath • excessive drowsiness or fatigue • persistent nausea • confusion • pain or pressure in your chest KIDNEY FAILURE

NORMAL ABNORMAL DIALYSIS KIDNEY FAILURE

 Urinalysis  Acute prerenal kidney failure -nsufficient blood flow to the kidneys can cause acute prerenal kidney  Urine volume measurements failure

 Blood samples  Acute intrinsic kidney failure - physical impact or an accident. Causes also include toxin overload and  Imaging ischemia,

 Kidney tissue sample  Chronic prerenal kidney failure - enough blood flowing to the kidneys for an extended period of Kidney failure treatment time, the kidneys begin to shrink and lose the ability  Dialysis to function  Chronic intrinsic kidney failure -long-term damage to  Kidney transplant the kidneys due to intrinsic kidney disease.

 Chronic post-renal kidney failure -A long term blockage of the urinary tract prevents urination. This causes pressure and eventual kidney damage. OSMOREGULATION

 Osmoregulation is the process of regulating body fluids and its compositions.  It maintains the osmotic pressure of the blood and helps in the homeostasis - to consume more water about 2-3 litres, which help in the proper functioning of our kidneys.  Kidneys play a very large role in human osmoregulation by regulating the amount of water reabsorbed from glomerular filtrate in kidney tubules, which is controlled by hormones such as antidiuretic hormone (ADH), aldosterone, and angiotensin II. For example, a decrease in water potential is detected by osmoreceptors in the hypothalamus, which stimulates ADH release from the pituitary gland to increase the permeability of the walls of the collecting ducts in the kidneys. Therefore, a large proportion of water is reabsorbed from fluid in the kidneys to prevent too much water from being excreted.  Waste products of the nitrogen metabolism[edit]  Ammonia is a toxic by-product of protein metabolism and is generally converted to less toxic substances after it is produced then excreted; mammals convert ammonia to urea, whereas birds and reptiles form uric acid to be excreted with other wastes via their cloacas.  Urine Formation and Osmoregulation • Urine is formed in three main steps- glomerular filtration, reabsorption and secretion. • It comprises 95 % water and 5% wastes such as ions of sodium, potassium and calcium, and nitrogenous wastes such as creatinine, urea and ammonia. • Osmoregulation is the process of maintaining homeostasis of the body. • It facilitates diffusion of solutes and water across the semi-permeable membrane thereby maintaining osmotic balance. • The kidney regulates the osmotic pressure of blood through filtration and purification by a process known as osmoregulation. MUSCLES – Types of muscles

 Muscle is a soft tissue found in most animals. Muscle cells contain protein filaments of actin and myosin that slide past one another, producing a contraction that changes both the length and the shape of the cell. Muscles function to produce force and motion.  The three main types of muscle include: • Skeletal muscle • Smooth muscle • Cardiac muscle  Skeletal Muscle  Skeletal muscle, attached to bones, is responsible for skeletal movements. The peripheral portion of the central nervous system (CNS) controls the skeletal muscles. Thus, these muscles are under conscious, or voluntary, control. The basic unit is the muscle fiber with many nuclei. These muscle fibers are striated (having transverse streaks) and each acts independently of neighboring muscle fibers.  Smooth Muscle  Smooth muscle, found in the walls of the hollow internal organs such as blood vessels, the gastrointestinal tract, bladder, and uterus, is under control of the autonomic nervous system. Smooth muscle cannot be controlled consciously and thus acts involuntarily. The non- striated (smooth) muscle cell is spindle-shaped and has one central nucleus. Smooth muscle contracts slowly and rhythmically.  Cardiac Muscle  Cardiac muscle, found in the walls of the heart, is also under control of the autonomic nervous system. The cardiac muscle cell has one central nucleus, like smooth muscle, but it also is striated, like skeletal muscle. The cardiac muscle cell is rectangular in shape. The contraction of cardiac muscle is involuntary, strong, and rhythmical. TYPES OF MUSCLES Mechanism of muscle contractions

 A muscle contraction is an increase in the tension or a decrease in the length of a muscle. A muscle contraction is isometric if muscle tension changes, but muscle length remains the same. It is isotonic if muscle length changes, but muscle tension remains the same.

 Muscle contraction occurs when the thin actin and thick myosin filaments slide past each other. It is generally assumed that this process is driven by cross-bridges which extend from the myosin filaments and cyclically interact with the actin filaments as ATP is hydrolysed.

 Four types of muscular contraction

 Isometric: A muscular contraction in which the length of the muscle does not change.

 isotonic: A muscular contraction in which the length of the muscle changes.

 eccentric: An isotonic contraction where the muscle lengthens.

 concentric: An isotonic contraction where the muscle shortens.

 skeletal muscle contractions are neurogenic as they require synaptic input from motor neurons to produce muscle contractions. A single motor neuron is able to innervate multiple muscle fibers, thereby causing the fibers to contract at the same time. Once innervated, the protein filaments within each skeletal muscle fiber slide past each other to produce a contraction, which is explained by the sliding filament theory. The contraction produced can be described as a twitch, summation, or tetanus, depending on the frequency of action potentials. In skeletal muscles, muscle tension is at its greatest when the muscle is stretched to an intermediate length as described by the length- tension relationship.

 Unlike skeletal muscle, the contractions of smooth and cardiac muscles are myogenic (meaning that they are initiated by the smooth or heart muscle cells themselves instead of being stimulated by an outside event such as nerve stimulation), although they can be modulated by stimuli from the autonomic nervous system. The mechanisms of contraction in these muscle tissues are similar to those in skeletal muscle tissues.

Mechanism of muscle contractions CORE PAPER IV: ANIMAL PHYSIOLOGY

SEMESTER : IV SUBJECT CODE : 18BZO43C

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 UNIT – IV NERVOUS SYSTEM AND RECEPTORS

• NERVOUS TISSUE – Neuron – Structure, Types of neurons, Nerve impulse. • SYNAPSE – Synaptic transmission, Neurotransmitters. • RECEPTORS – Photoreceptor – Mammalian Eye – Physiology of vision. • PHONORECEPTORS – Mammalian Ear and Phonoreception in Bat.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 NERVOUS TISSUE – NEURON – STRUCTURE, TYPES OF NEURONS, NERVE IMPULSE.

• The nervous system is the part of an animal's body that coordinates its behavior and transmits signals between different body areas. In vertebrates it consists of two main parts, called the central nervous system (CNS) and the peripheral nervous system (PNS). The CNS contains the brain and spinal cord. • The nervous system comprises the central nervous system, consisting of the brain and spinal cord, and the peripheral nervous system, consisting of the cranial, spinal, and peripheral nerves, together with their motor and sensory endings. • The four main functions of the nervous system are: • Control of body's internal environment to maintain 'homeostasis' An example of this is the regulation of body temperature. ... • Programming of spinal cord reflexes. An example of this is the stretch reflex. ... • Memory and learning. ... • Voluntary control of movement.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 NEURON – STRUCTURE, TYPES OF NEURONS, NERVE IMPULSE.

• A neuron is a cell that transmits nerve impulses. It consists of the following parts, The cell body (soma or perikaryon) contains the nucleus and other cell organelles. • There are clusters of rough endoplasmic reticulum that are called Nissl bodies or are sometimes referred to as chromatophilic substances. • The dendrite is typically a short, abundantly branched, slender process (extension) of the cell body that receives stimuli. • The axon is typically a long, slender process of the cell body that sends nerve impulses. It emerges from the cell body at the cone‐shaped axon hillock. Nerve impulses arise in the trigger zone, generally located in the initial segment, an area just outside the axon hillock. The cytoplasm of the axon, the axoplasm, is surrounded by its plasma membrane, the axolemma. A few axons branch along their lengths to form axon collaterals, and these branches may return to merge with the main axon. At its end, each axon or axon collateral usually forms numerous branches ( telodendria), with most branches terminating in bulb‐shaped structures called synaptic knobs (synaptic end bulbs, also called terminal boutons). The synaptic knobs contain neurotransmitters, chemicals that transmit nerve impulses to a muscle or another neuron. Neurons can be classified by function or by structure. Functionally, they fall into three groups: • Sensory neurons ( afferent neurons) transmit sensory impulses from the skin and other sensory organs or from various places within the body toward the central nervous system (CNS), which consists of the brain and spinal cord. • Motor neurons ( efferent neurons) transmit nerve impulses from the CNS toward effectors, target cells that produce some kind of response. Effectors include muscles, sweat glands, and many other organs.

• AssociationDR.P.S.neurons SUJATHA,( DEPT.interneurons OF ZOOLOGY,) are GAC, locatedCBE-18 in the CNS and transmit impulses from sensory neurons to motor neurons. More than 90 percent of the neurons of the body are association neurons. DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 TYPES OF NEURONS - SENSORY NEURONS, MOTOR NEURONS, AND INTERNEURONS.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 A unipolar neuron is a neuron in which only one process, called a neurite, extends from the cell body. The neurite then branches to form dendritic and axonal processes. Most neurons in the central nervous systems of invertebrates, including insects, are unipolar.

A bipolar neuron, or bipolar cell, is a type of neuron that has two extensions (one axon and one dendrite). Many bipolar cells are specialized sensory neurons for the transmission of sense. As such, they are part of the sensory pathways for smell, sight, taste, hearing, touch, balance and proprioception.

A multipolar neuron is a type of neuron that possesses a single axon and many dendrites (and dendritic branches), allowing for the integration of a great deal of information from other neurons. These processes are projections from the neuron cell body.

A pseudounipolar neuron is a type of neuron which has one extension from its cell body. This type of neuron contains an axon that has split into two branches; one branch travels to the peripheral nervous system and the other to the central nervous system.

•A nerve fiber is an axon. A nerve is a bundle of nerve fibers in the peripheral nervous system (PNS). Most nerves contain both sensory and motor fibers. Cell bodies are usually grouped into separate bundles called ganglia. •A peripheral nerve consists of three layers:

•The epineuriumDR.P.S. SUJATHA,is DEPT.the OFouter ZOOLOGY, layer GAC, that CBE-18 surrounds the entire nerve. The perineurium surrounds bundles of axons. Bundles of axons are called fascicles. There could be 10 or more fascicles per nerve. Surrounding each individual axon is the endoneurium. A nerve tract is a bundle of nerve fibers in the CNS. Anatomy of a neuron Neurons, like other cells, have a cell body (called the soma). The nucleus of the neuron is found in the soma. Neurons need to produce a lot of proteins, and most neuronal proteins are synthesized in the soma as well. Various processes (appendages or protrusions) extend from the cell body. These include many short, branching processes, known as dendrites, and a separate process that is typically longer than the dendrites, known as the axon. Dendrites The first two neuronal functions, receiving and processing incoming information, generally take place in the dendrites and cell body. Incoming signals can be either excitatory – which means they tend to make the neuron fire (generate an electrical impulse) – or inhibitory – which means that they tend to keep the neuron from firing. Most neurons receive many input signals throughout their dendritic trees. A single neuron may have more than one set of dendrites, and may receive many thousands of input signals. Whether or not a neuron is excited into firing an impulse depends on the sum of all of the excitatory and inhibitory signals it receives. If the neuron does end up firing, the nerve impulse, or action potential, is conducted down the axon. Axons Axons differ from dendrites in several ways. •The dendrites tend to taper and are often covered with little bumps called spines. In contrast, the axon tends to stay the same diameter for most of its length and doesn't have spines. •The axon arises from the cell body at a specialized area called the axon hillock. •Finally, many axons are covered with a special insulating substance called myelin, which helps them convey the nerve impulse rapidly. Myelin is never found on dendrites. Towards its end, the axon splits up into many branches and develops bulbous swellings known as axon terminals (or nerve terminalsDR.P.S.). These SUJATHA,axon DEPT. OFterminals ZOOLOGY, GAC,make CBE-18connections on target cells. Synapses Neuron-to-neuron connections are made onto the dendrites and cell bodies of other neurons. These connections, known as synapses, are the sites at which information is carried from the first neuron, the presynaptic neuron, to the target neuron (the postsynaptic neuron). The synaptic connections between neurons and skeletal muscle cells are generally called neuromuscular junctions, and the connections between neurons and smooth muscle cells or glands are known as neuroeffector junctions. At most synapses and junctions, information is transmitted in the form of chemical messengers called neurotransmitters. When an action potential travels down an axon and reaches the axon terminal, it triggers the release of neurotransmitter from the presynaptic cell. Neurotransmitter molecules cross the synapse and bind to membrane receptors on the postsynaptic cell, conveying an excitatory or inhibitory signal. Thus, the third basic neuronal function – communicating information to target cells – is carried out by the axon and the axon terminals. Just as a single neuron may receive inputs from many presynaptic neurons, it may also make synaptic connections on numerous postsynaptic neurons via different axon terminals. Neurons form networks A single neuron can’t do very much by itself, and nervous system function depends on groups of neurons that work together. Individual neurons connect to other neurons to stimulate or inhibit their activity, forming circuits that can process incoming information and carry out a response. Neuronal circuits can be very simple, and composed of only a few neurons, or they can involve more complex neuronal networks.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 TRANSMISSION OF NERVE IMPULSES

• A nerve impulse is the way nerve cells (neurons) communicate with one another. Nerve impulses are mostly electrical signals along the dendrites to produce a nerve impulse or action potential. • The action potential is the result of ions moving in and out of the cell. The transmission of a nerve impulse along a neuron from one end to the other occurs as a result of electrical changes across the membrane of the neuron. • The membrane of an unstimulated neuron is polarized—that is, there is a difference in electrical charge between the outside and inside of the membrane. The inside is negative with respect to the outside. Polarization is established by maintaining an excess of sodium ions (Na +) on the outside and an excess of potassium ions (K +) on the inside. A certain amount of Na + and K + is always leaking across the membrane through leakage channels, but Na +/K + pumps in the membrane actively restore the ions to the appropriate side. • The main contribution to the resting membrane potential (a polarized nerve) is the difference in permeability of the resting membrane to potassium ions versus sodium ions. The resting membrane is much more permeable to potassium ions than to sodium ions resulting in slightly more net potassium ion diffusion (from the inside of the neuron to the outside) than sodium ion diffusion (from the outside of the neuron to the inside) causing the slight difference in polarity right along the membrane of the axon. • Other ions, such as large, negatively charged proteins and nucleic acids, reside within the cell. It is these large, negatively charged ions that contribute to the overall negative charge on the inside of the cell membrane as compared to the outside.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 TRANSMISSION OF NERVE IMPULSES

• The following events characterize the transmission of a nerve impulse • Resting potential. The resting potential describes the unstimulated, polarized state of a neuron (at about –70 millivolts).

1. Graded potential. A graded potential is a change in the resting potential of the plasma membrane in the response to a stimulus. A graded potential occurs when the stimulus causes Na + or K + gated channels to open.

• If Na + channels open, positive sodium ions enter, and the membrane depolarizes (becomes more positive).

• If the stimulus opens K + channels, then positive potassium ions exit across the membrane and the membrane hyperpolarizes (becomes more negative).

• A graded potential is a local event that does not travel far from its origin. Graded potentials occur in cell bodies and dendrites.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 • Light, heat, mechanical pressure, and chemicals, such as neurotransmitters, are examples of stimuli that may generate a graded potential (depending upon the neuron) 1.Action potential. Unlike a graded potential, an action potential is capable of traveling long distances. If a depolarizing graded potential is sufficiently large, Na + channels in the trigger zone open. In response, Na + on the outside of the membrane becomes depolarized (as in a graded potential). If the stimulus is strong enough—that is, if it is above a certain threshold level—additional Na + gates open, increasing the flow of Na + even more, causing an action potential, or complete depolarization (from –70 to about +30 millivolts). This in turn stimulates neighboring Na + gates, farther down the axon, to open. In this manner, the action potential travels down the length of the axon as opened Na + gates stimulate neighboring Na + gates to open. The action potential is an all‐or‐nothing event: When the stimulus fails to produce depolarization that exceeds the threshold value, no action potential results, but when threshold potential is exceeded, complete depolarization occurs. 2.Repolarization. In response to the inflow of Na +, K + channels open, this time allowing K + on the inside to rush out of the cell. The movement of K + out of the cell causes repolarization by restoring the original membrane polarization. Unlike the resting potential, however, in repolarization the K + are on the outside and the Na + are on the inside. Soon after the K + gates open, the Na + gates close. 3.Hyperpolarization. By the time the K + channels close, more K + have moved out of the cell than is actually necessary to establish the original polarized potential. Thus, the membrane becomes hyperpolarized (about –80 millivolts). 4.Refractory period. With the passage of the action potential, the cell membrane is in an unusual state of affairs. The membrane is polarized, but the Na + and K + are on the wrong sides of the membrane. During this refractory period, the axon will not respond to a new stimulus. To reestablish the original distribution of these ions, the Na + and K + are returned to their resting potential location by Na +/K + pumps in the cell membrane. Once these ions areDR.P.S.completely SUJATHA, DEPT.returned OF ZOOLOGY,to GAC,their CBEresting-18 potential location, the neuron is ready for another stimuli. RECEPTORS – PHOTORECEPTOR – MAMMALIAN EYE – PHYSIOLOGY OF VISION. • The human eye is a sense organ that reacts to light and allows vision. Rod and cone cells in the retina are photoreceptive cells which are able to detect visible light and convey this information to the brain. • Physiological events of vision consists of following; 1.Refraction of light entering the eye 2.Focusing of image on the retina by accommodation of lens 3.Convergence of image 4.Photo-chemical activity in retina and conversion into neural impulse 5.Processing in brain and perception

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 MAMMALIAN EYE

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 1. Tear Layer The Tear Layer (The Lacrimal System) is the first layer of the eye that light strikes. It is clear, moist, and salty. Its purpose is to keep the eye smooth and moist. 2. Cornea The Cornea is the second structure that light strikes. It is the clear, transparent front part of the eye that covers the iris, pupil and anterior chamber and provides most of an eye’s optical power. 3. Anterior Chamber The Anterior Chamber is filled with Aqueous Humor. Aqueous Humour is a clear, watery fluid that fills the space between the back surface of the cornea and the front surface of the vitreous, bathing the lens . 4. Iris The iris is the pigmented tissue lying behind the cornea that gives color to the eye and controls the amount of light entering the eye by varying the size of the papillary opening. It functions like a camera. 5. Lens The lens is the natural lens of the eye (chrystaline lens). Transparent, biconvex intraocular tissue that helps bring rays of light to focus on the retina 6. Vitreous Humour (Chamber) Vitreous Humour (Chamber) is the transparent, colorless gelatinous mass that fills rear two-thirds of the eyeball, between the lens and the retina. 7. Retina The retina is the light sensitive nerve tissue in the eye that converts images from the eye’s optical system into electrical impulses that are sent along the optic nerve to the brain, to interpret as vision. 8. Choroid The vascular (major blood vessel), central layer of the eye lying between the retina and sclera. Its 9. Sclera The sclera is the opaque, fibrous, tough, protective outer layer of the eye (“white of the eye”) that is directly continuous with the cornea in front and with the sheath covering the optic nerve behind. The sclera provides protection and form. 10. Optic Nerve The Optic Nerve is the largest sensory nerve of the eye. It carries impulses for sight from the retina to the brain. 11. Extraocular Muscles •There are six extraocular muscles in each eye •:Rectus Muscles. There are four Rectus muscles that are responsible for straight movements: Superior (upward), Inferior (lower), Lateral (toward the outside, or away from the nose), and Medial (toward the inside, or toward the nose). •Oblique Muscles. There are two Oblique muscles that are responsible for angled movements. The superior oblique muscles control angled movements upward toward the DR.P.S.right orSUJATHA, left. Inferior DEPT. OF oblique ZOOLOGY, muscles GAC, controlCBE-18 angled movements downward toward the right or left. Focus on distant object: Ciliary muscles relaxes——ciliary body return to its normal resting state—–tension on suspensory

RODS AND CONES

• The photosensitive cells are, in the human and in most vertebrate retinas, of two kinds, called rods and cones, the rods being usually much thinner than the cones but both being built up on the same plan.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 Refraction of light entering the eye: •Light wave travels parallel to each other but they bend when passes from one medium to another. This phenomenon is called refraction. •Before light reach retina it passes through cornea, aqueous humor, lens vitrous humor, so refraction takes place in every medium before it falls on retina. •In normal eye, light wave focused on retina. •However in myopic eye (short sightedness) light focused in front of retina. So this defect can be treated by using cancave lens. •In case of far sightedness light focused behind retina, so no image is formed. This defect can be treated by using convex lens. Accommodation of lens to focus image: •Accommodation is a reflex process to bring light rays from object into perfect focus on retina by adjusting the lens. •When an object lying less than 6 meter away is viewed, image formed behind retina. But due to accommodation of lens image formed in retina and we can see the object. •For accommodation to view closer object, ciliary muscle contract and lens become thick which causes focus on closer object. •Similarly, when distant object is viewed, ciliary muscles relaxes, so the tension of ligament become greater which pull lens and lens become thinner, due to which image forms on retina. •The normal eye is able to accommodate light from object about 25 cm to infinity. DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 PHYSIOLOGY OF VISION

Focus on nearer object: Ciliary muscle contract——-ciliary body pull forward and inward ——— tension on suspensory ligament of lens reduced ——lens become thicker and round due to its elasticity ——possible to focus near object

• Focus on distant object:

Ciliary muscles relaxes – ciliary body return to its normal resting state – tension on suspensory – Ligament of Lens increases – Lens become thinner and flat – Possible to focus distant object.

Convergence of image:

Human eye have binocular vision – two eye – Perceive single image. In binocular vision, two eye ball turns slightly inward to focus a close object so that both image falls on retina at same time, This phenomenon is called convergence.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 •Photochemical activity in Rods •Each eye contains 125 million rods which are located in neuro-retina. •Rods contains light sensitive pigment-rhodopsin. •Rhodopsin is a molecule formed by combination of a protein scotopsin and a light sensitive small molecule retinal (retinene). •Retinene (retinal) is a carotenoid molecule and is derivative of vitamin A (retinol). •Retinal exists in two isomeric form- cis and trans according to light condition. •The extra cellular fluids surrounding rod cells contains high concentration of Na+ ion and low concentration of K+ ions while concentration of Na+ is low and K+ is high inside rod cells. The concentration is maintained by Na-K pump. •In resting phase, K+ tends to move outside the rod cells creating slightly –ve charge inside. •When light is falls on rod cell, it is absorbed by rhodopsin and it breaks into scotopsin and 11 cis- retinal. The process is known as bleaching. •11 cis-retinal absorb photon of light and change into all trans-retinal which inturn activates scotopsin into enzyme. •This reaction produces large amount of transducin which activates another enzyme phosphodiesterase. •Phosphodiesterase hydrolyses cGMP which causes to cease the flow of Na+ ion inside rod cell. This causes increased negative charge inside cell creating hyperpolarized state. •Hyperpolarized rod cells transmit the neural signal to bipolar cell.

•BipolarDR.P.S. SUJATHA, cell, DEPT. amacrine OF ZOOLOGY, cell GAC, and CBE-18 ganglion cell process the neural signal and generate action potential to transmit to brain via optic nerve. Photochemical activity in cones: •Each eye contains 7 million cone cells. •The neural activity in cone cell is similar to that of rod cell but there are three different types of cone cells and each cone cell contains different photo-pigment and are sensitive to red, green and blue. •Like rod, cone cell contains iodopsin as photo-pigment which is composed of 11 cis-retinal and photopsin. •The perception of color depends upon which cone are stimulated. •The final perceived color is combination of all three types of cone cell stimulated depending upon the level of stimulation. •The proper mix of all three color produce the perception of white and absence of all color produce perception of black.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 PHONORECEPTORS – MAMMALIAN EAR AND PHONORECEPTION IN BAT.

• The ear is the organ of hearing and, in mammals, balance. In mammals, the ear is usually described as having three parts—the outer ear, the middle ear and the inner ear. The outer ear consists of the pinna and the ear canal. Since the outer ear is the only visible portion of the ear in most animals, the word "ear" often refers to the external part alone.[1] The middle ear includes the tympanic cavity and the three ossicles. The inner ear sits in the bony labyrinth, and contains structures which are key to several senses: the semicircular canals, which enable balance and eye tracking when moving; the utricle and saccule, which enable balance when stationary; and the cochlea, which enables hearing. The ears of vertebrates are placed somewhat symmetrically on either side of the head, an arrangement that aids sound localisation.

• The ear develops from the first pharyngeal pouch and six small swellings that develop in the early embryo called otic placodes, which are derived from ectoderm. •

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 The external ear consists of pinna, external auditory meatus and ear drum. The pinna is flap of elastic cartilage covered by skin. It collects the sound waves. The external auditory meatus is a curved tube that extends up to the tympanic membrane [the ear drum]. The tympanic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside. There are very fine hairs and wax producing sebaceous glands called ceruminous glands in the external auditory meatus. The combination of hair and the ear wax [cerumen] helps in preventing dust and foreign particles from entering the ear. The middle ear is a small air-filled cavity in the temporal bone. It is separated from the external ear by the eardrum and from the internal ear by a thin bony partition; the bony partition contains two small membrane covered openings called the oval window and the round window. • The middle ear contains three ossicles: malleus [hammer bone], incus [anvil bone] and stapes [stirrup bone] which are attached to one another. The malleus is attached to the tympanic membrane and its head articulates with the incus which is the intermediate bone lying between the malleus and stapes. The stapes is attached to the oval window in the inner ear. The ear ossicles transmit sound waves to the inner ear. A tube called Eustachian tube connects the middle ear cavity with the pharynx. This tube helps in equalizing the pressure of air on either sides of the ear drum. Inner ear 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. The cochlea is a coiled portion consisting of 3 chambers namely: scala vestibuli and scala tympani- these two are filled with perilymph; and the scala media is filled with endolymph. At the base of the cochlea, the scala vestibule ends at the ‘oval window’ whereas the scala tympani ends at the ‘round window’ of the middle ear. The chambers scala vestibuli and scala media are separated by a membrane called Reisner’s membrane whereas the scala media and scala tympani are separated by a membrane called Basilar membrane.

• Organ of corti - The organ of corti (figure.10.19) is a sensory ridge located on the top of the Basilar membrane and it contains numerous hair cells that are arranged in four rows along the length of the basilar membrane. Protruding from the apical part of each hair cell is hair like structures known as stereocilia. During the conduction of sound wave, stereocilia makes a contact with the stiff gel membrane called tectorial membrane, a roof like structure overhanging the organ of corti throughout its length.

• Mechanism of hearing - • Sound waves entering the external auditory meatus fall on the tympanic membrane. This causes the ear drum to vibrate, and these vibrations are transmitted to the oval window through the three auditory ossicles. Since the tympanic membrane is 17-20 times larger than the oval window, the pressure exerted on the oval window is about 20 times more than that on the tympanic membrane. • This increased pressure generates pressure waves in the fluid of perilymph. This pressure causes the round window to alternately bulge outward and inward meanwhile the basilar membrane along with the organ of Corti move up and down. These movements of the hair alternately open and close the mechanically gated ion channels in the base of hair cells and the action potential is propagated to the brain as sound sensation through cochlear nerve.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 Organ of Equilibrium Balance is part of a sense called proprioception, which is the ability to sense the position, orientation and movement of the body. The organ of balance is known as the vestibular system which is located in the inner ear next to the cochlea. The vestibular system is composed of a series of fluid filled sacs and tubules.These sacs and tubules contain endolymph and are kept in the surrounding perilymph (Figure-10.20). These two fluids, perilymph and endolymph, respond to the mechanical forces, during changes occurring in body position and acceleration The utricle and saccule are two membranous sacs, found nearest the cochlea and contain equilibrium receptor regions called maculae that are involved in detecting the linear movement of the head. The maculae contain the hair cells that act as mechanorecptors. These hair cells are embeded in a gelatinous otolithic membrane that contains small calcareous particles called otoliths. This membrane adds weight to the top of the hair cells and increase the inertia.

The canals that lie posterior and lateral to the vestibule are semicircular canals; they are anterior, posterior and lateral canals oriented at right angles to each other. At one end of each semicircular canal, at its lower end has a swollen area called ampulla. Each ampulla has a sensory area known as crista ampullaris which is formed of sensory hair cells and supporting cells. The function of these canals is to detect rotational movement of the head.

DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 DR.P.S. SUJATHA, DEPT. OF ZOOLOGY, GAC, CBE-18 PHONORECEPTION IN BAT.

• Echolocation--the active use of sonar (SOund Navigation And Ranging) along with special morphological (physical features) and physiological adaptations--allows bats to "see" with sound. Most bats produce echolocation sounds by contracting their larynx (voice box). A few species, though, click their tongues. These sounds are generally emitted through the mouth, but Horseshoe bats (Rhinolophidae) and Old World leaf-nosed bats (Hipposideridae) emit their echolocation calls through their nostrils: there they have basal fleshy horseshoe or leaf-like structures that are well-adapted to function as megaphones.

• Echolocation calls are usually ultrasonic--ranging in frequency from 20 to 200 kilohertz (kHz), whereas human hearing normally tops out at around 20 kHz. Even so, we can hear echolocation clicks from some bats, such as the Spotted bat (Euderma maculatum). These noises resemble the sounds made by hitting two round pebbles together. In general, echolocation calls are characterized by their frequency; their intensity in decibels (dB); and their duration in milliseconds (ms).

• In terms of pitch, bats produce echolocation calls with both constant frequencies (CF calls) and varying frequencies that are frequently modulated (FM calls). Most bats produce a complicated sequence of calls, combining CF and FM components. Although low frequency sound travels further than high-frequency sound, calls at higher frequencies give the bats more detailed information--such as size, range, position, speed and direction of a prey's flight. Thus, these sounds are used more often.

• In terms of loudness, bats emit calls as low as 50 dB and as high as 120 dB, which is louder than a smoke detector 10 centimetersDR.P.S. SUJATHA,from your DEPT. OF ear. ZOOLOGY, That's GAC, not CBE just-18 loud, but damaging to human hearing. The Little brown bat (Myotis lucifugus) can emit such an intense sound. The good news is that because this call has an ultrasonic frequency, we are unable to hear it. •