Bio Exam Notes PDF

CHAPTER 11: HUMAN ORGANIZATION 11.1 Types of Tissues Tissues are composed of similarly specialized cells four major types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Epithelial Tissue Epithelial tissue consists of tightly packed cells that form a continu...

CHAPTER 11: HUMAN ORGANIZATION 11.1 Types of Tissues Tissues are composed of similarly specialized cells four major types: epithelial tissue, connective tissue, muscular tissue, and nervous tissue. Epithelial Tissue Epithelial tissue consists of tightly packed cells that form a continuous layer. Epithelial tissue covers surfaces and lines body cavities. function: protective, carry out secretion, absorption, excretion, and filtration. Junctions between Epithelial Cells The cells of a tissue can function in a coordinated manner when the plasma membranes adjoining cells interact. Three common types of junctions link epithelial cells: tight, gap and adhesion junctions. Connective Tissue Connective tissue binds organs together provides support and protection, fills spaces, produces blood cells, and stores fat. Loose Fibrous and Dense Fibrous Tissues Loose fibrous connective tissue supports epithelium and also many internal organs. Tendons and ligaments are made up of dense fibrous connective tissue, contains many collagen fibers that are packed together. Loose and dense fibrous connective tissues have cells called fibroblasts. Adipose Tissue and Reticular Connective Tissue In adipose tissue, fibroblasts enlarge and store fat. Reticular connective tissue forms the supporting meshwork of lymphoid tissue. Cartilage Cartilage is a specialized form of dense fibrous connective tissue, allow bones to slide against each other in joints. There are three types: hyaline, elastic, and fibrocartilage. Bone Bone is the most rigid connective tissue. extremely hard matrix. Compact bone makes up the shaft of a long bone, the ends of a long bone is spongy bone. Blood Blood not made by cells. The upper, liquid layer of blood is called plasma and makes up about 55% of the volume of whole blood. Red blood cells carry oxygen to tissues; white blood cells fight infection. Platelets are involved in clotting. Muscular Tissue Muscular tissue is made of cells called muscle fibers = actin + myosin There are three types of muscle tissue: skeletal, smooth, and cardiac. Nervous Tissue Nervous tissue contains nerve cells called neurons in the brain and spinal cord. functions: sensory input, integration of data, and motor output. Neuroglia nervous tissue contains neuroglia. function: support and nourish neurons. 11.2 Body Cavities and Body Membranes divided into two main body cavities: the ventral cavity and the dorsal cavity. ventral is divided into the thoracic, abdominal, and pelvic cavities, The dorsal is divided into the cranial cavity and vertebral canal. Body Membranes line cavities and the internal spaces of organs and tubes that open to the outside. different types including mucous membranes, serous membranes, synovial membranes, and the meninges. 11.3 Organ Systems Organ systems work together in the body Integumentary System contains the skin. protective function, synthesizes vitamin D, collects sensory data,helps regulate body temperature. Cardiovascular System heart, the blood, and the vessels that the blood moves through. Blood transports nutrients and oxygen and removes waste molecules, Lymphatic and Immune Systems lymphatic system protects the body from disease by purifying lymph and storing lymphocytes. The immune system consists of all the cells in the body that protect us from disease. Digestive System the mouth, esophagus, stomach, small intestine, and large intestine function: It receives food and digests it into nutrient molecules. Respiratory System lungs and the tubes that take air to and from them. function: moves oxygen and carbon dioxide. Urinary System kidneys, the urinary bladder, and the tubes that carry urine. function: rids the body of metabolic wastes. Nervous System brain, spinal cord, and associated nerves function: allows us to respond to both external and internal stimuli. Musculoskeletal System bones provide a scaffolding that helps hold and protect body parts. The skeleton also helps move the body, stores minerals, and produces blood cells. Endocrine System hormonal glands release hormones Reproductive System different organs in the male and female. function: make a baby 11.4 Integumentary System skin, nails, hair, oil glands, and sweat glands Regions of the Skin The skin has two regions: the epidermis and the dermis. epidermis made of epithelium. dermis = fibrous connective tissue beneath the epidermis. Accessory Organs of the Skin Nails, hair follicles, and glands are structures of epidermal origin Disorders of the Skin The integumentary system is susceptible to a number of diseases. 11.5 Homeostasis Homeostasis is the maintenance of a relatively constant internal environment by an organism. Negative Feedback primary homeostatic mechanism that keeps a variable close to set point. two components: a sensor and a control center. Positive Feedback mechanism that brings about an ever greater change in the same direction. The Transport Systems cardiovascular system and lymphatic system both regulate tissue fluid composition. The Maintenance Systems respiratory system adds oxygen to and removes carbon dioxide from the blood The digestive system takes in and digests food, providing nutrient molecules. The liver and kidneys help remove toxins from the blood. The urinary system excretes waste, regulates blood volume, salt balance, and pH. The Support Systems integumentary, skeletal, and muscular systems protect the internal organs. The Control Systems The nervous system and the endocrine system work together to control other body systems so that homeostasis is maintained. Disease abnormality in the body’s normal processes that significantly impairs homeostasis. CHAPTER 19: MUSCULOSKELETAL SYSTEM Overview of Bone and Cartilage bones and muscles make up the musculoskeletal system. Organization of Tissues in the Skeleton bone is classified by its shape enclosed by a tough, fibrous, connective tissue covering called the periosteum. joint is where a long bone contacts another bone -covered by a layer of cartilage. Structure of Bone and Associated Tissues bone, cartilage, and dense fibrous connective tissue. All connective tissues contain cells separated by a matrix that contains fibers. Bone strong because the matrix contains mineral salts, notably calcium phosphate. Compact bone -highly organized and composed of tubular units. spongy bone -unorganized appearance. Bones contain yellow bone marrow, which contains a large amount of fat. The spaces of spongy bone filled with red bone marrow -a tissue that produces all types of blood cells. Cartilage not as strong as bone, but is more flexible because the matrix is gel-like and contains many collagenous and elastic fibers. three types of cartilage: hyaline cartilage, fibrocartilage, and elastic cartilage. Dense Fibrous Connective Tissue Ligaments bind bone to bone tendons connect muscle to bone at joints both of which are dense fibrous connective tissue. Bone Growth and Remodeling Bones are composed of living tissues. Bone Development and Growth The bones of the human skeleton, except those of the skull, first appear during embryonic development as hyaline cartilage. The cartilaginous structures are then gradually replaced by bone -process called endochondral ossification. Remodeling of Bones remodeling: In the adult, bone is continually being broken down and built up again, a process called. 19.2 Bones of the Skeleton functions:supporting the body, protecting soft body parts, producing blood cells, storing minerals and fat, and permitting flexible body movement. Classification of the Bones 206 bones of the skeleton classified as either: - axial (in the midline of the body) -appendicular (the limbs along with their girdles). The Axial Skeleton The axial skeleton consists of the skull, hyoid bone, vertebral column, rib cage, and ossicles. The Skull cranium and the facial bones. The Cranium protects the brain eight bones fitted tightly together. The Facial Bones mandible, the maxillae, the zygomatic bones, and the nasal bones. The Hyoid Bone only bone in the body that does not articulate with another bone It is attached to processes of the temporal bones by muscles and ligaments and to the larynx by a membrane. The Vertebral Column 33 vertebrae normally has four curvatures that provide resilience and strength for an upright posture. Types of Vertebrae The various vertebrae are named according to their location in the vertebral column. Intervertebral Disks Between the vertebrae are intervertebral discs composed of fibrocartilage act as a kind of padding.  The Rib Cage thoracic vertebrae, the ribs and their associated cartilages, and the sternum part of the axial skeleton. The Ribs twelve pairs of ribs -all twelve connect directly to the thoracic vertebrae in the back The upper seven pairs of ribs connect directly to the sternum by costal cartilages. The Sternum The sternum, or breastbone helps protect the heart and lungs. The Appendicular Skeleton consists of the bones within the pectoral and pelvic girdles and their attached limbs. The Pectoral Girdle and Upper Limbs pectoral girdle -consists of a scapula and clavicle (collarbone). upper limb -consists of the humerus in the arm - the radius and ulna in the forearm. - joint between the scapula and the humerus allows the arm to move in almost any direction. The hand has many bones, increasing its flexibility. -The wrist and palms contain carpal and metacarpal bones, - The bones of the digits (fingers) are called phalanges. The Pelvic Girdle and Lower Limb pelvic girdle - consists of two heavy, large coxal bones (hip bones). - Pelvis is a basin composed of the pelvic girdle, sacrum, and coccyx. - The femur (thighbone) is the longest and strongest bone in the body. -kneecap is called the patella - The lower leg is formed from the fibula and the tibia. - Ankles and feet contain tarsal and metatarsal bones, respectively. - The toes are made of phalanges. Joints Bones are joined at the joints classified as fibrous, cartilaginous, or synovial based on their structure and their ability to move. 19.3 Skeletal Muscles Humans have three types of muscle tissue: smooth, cardiac, and skeletal. Skeletal muscle makes up the greatest percentage of muscle tissue in the body. Skeletal Muscles Work in Pairs The contraction of skeletal muscles causes the bones at a joint to move. origin - stationary bone insertion - bone that moves. Most muscles have antagonists that bring about movement in the opposite direction. Major Skeletal Muscles 650 skeletal muscles in the human body. Nomenclature Skeleton muscles are named based on size, shape, location, direction of muscles fibers, number of attachments, and action. 19.4 Mechanism of Muscle Fiber Contraction Skeletal muscle tissue has alternating light and dark bands due to the arrangement of myofilaments in the muscle fiber. Muscle Fiber a cell containing the usual cellular components Myofibrils and Sarcomeres Myofibrils -cylindrical in shape - run the length of the muscle fiber. The striations of skeletal muscle fibers are formed by the placement of myofilaments within units of myofibrils and sarcomeres. sarcomere contains two types of protein myofilaments:myosin and actin. Myofilaments Thick Filament composed several hundred molecules of myosin -shaped like a golf club. Thin Filaments consists of two intertwining strands of action. Sliding Filament Model When a sarcomere shortens, the actin filaments slide past the myosin filaments and approach one another This movement is called the sliding filament model of muscle contraction. Skeletal Muscle Contraction Muscle fibers are stimulated to contract by motor neurons whose axons are in nerves Sarcomere contraction causes myofibril contraction -results in the contraction of a muscle fiber and, eventually, a whole muscle. The Molecular Mechanism of Contraction Two other proteins, tropomyosin and troponin, are associated with actin filaments. When calcium ions are released from the sarcoplasmic reticulum, they combine with troponin, this causes the tropomyosin threads to shift their position, revealing ATP binding sites. Energy for Muscle Contraction ATP produced previous to strenuous exercise lasts a few seconds then muscles acquire new ATP in three different ways. Creatine Phosphate Breakdown Creatine phosphate is a high-energy compound built up when a muscle is resting, It can regenerate ATP. Fermentation Fermentation supplies ATP without consuming oxygen. glucose is broken down to lactate, the accumulation of which makes the cytoplasm of muscle fibers are more acidic. Cellular Respiration provides most of a muscle’s ATP. Oxygen Debt Oxygen debt is obvious when a person continues to breathe heavily after exercising. Whole Muscle Contraction In the Laboratory A muscle fiber contracts completely or not at all, whereas a whole muscle shows degrees of contraction. A myogram is a visual pattern representing the mechanical force of a signal contraction (muscle twitch) in an isolated muscle. It is customarily divided into three stages: the latent period, the contraction period, and the relaxation period. Maximal sustained Contraction is called tetanus. In the Body In the body, nerves cause muscles to contract. A nerve fiber along with all the muscle fibers it innervates is called a motor unit. A motor unit obeys the all-or-none law. Even when muscles appear to be at rest, they exhibit muscle tone, in which some of their fibers are always contracting.  Athletics and Muscle Contraction Athletes and the general public are interested in staying fit by exercising. Exercise and Size of Muscles Muscles that are not used or that are used for only very weak contractions decrease in size, or atrophy. Slow-Twitch and Fast-Twitch Muscle Fibers Slow-twitch fibers have a steadier tug and more endurance, and tend to be aerobic. Fast-twitch fibers tend to be anaerobic and seem designed for strength. Disorders of the Musculoskeletal System Disorders of the Skeleton and Joints Bones are susceptible to being broken, or fractured, the most common cause of which is trauma Osteoporosis is a condition in which bone loses mass and mineral content. many different types of arthritis (inflammation of the joints) Rheumatoid arthritis is considered an autoimmune disease -body’s immune system attacks the joints as as well as other tissues. Disorders of the Muscles Muscle cramps and twitches do not usually rise to the level of a disorder. Fibromyalgia is a disorder that causes chronic pain in the muscles and ligaments. Muscular dystrophy refers to a group of genetic diseases that affect the muscles. CHAPTER 17: NERVOUS SYSTEM 17.1 Nervous Tissue helps coordinate and regulate the functioning of the body’s other systems. divided into the central nervous system (CNS) - brain and spinal cord, and the peripheral nervous system (PNS) - consists of nerves that carry messages to the CNS from the CNS to the muscles and glands. The nervous system contains two types of cells: neurons and neuroglia. Types of Neurons and Neuron Structure There are three classes of neurons sensory neurons take messages to the CNS interneurons are in the CNS and can receive input motor neurons take messages away from the CNS. Most neurons have three parts: a cell body, dendrites, and an axon. Myelin Sheath axons are covered by a protective myelin sheath. -plays an important role in nerve regeneration in the PNS - gives nerve fibers a white appearance. 17.2 Transmission of Nerve Impulses The nervous system uses the nerve impulse to convey information The nature of a nerve impulse can be characterized by voltage changes. Resting Potential When the axon is not conducting an impulse, the inside of the axon is negatively charged compared to the outside, giving it a resting potential of -70 mV difference across the membrane. This charge difference is due to the ion distribution on either side of the membrane, which is a result of the action of the sodium-potassium pump that actively transports sodium out of and potassium into the axon. Action Potential a rapid change in polarity across an axonal membrane as the nerve impulse occurs. all-or-none phenomenon. Sodium Gates Open When the action potential begins, the gates of the sodium channels open and sodium flows into the axon. The membrane potential changes from –70 mV to +40 mV. Potassium Gates Open Second, the gates of the potassium channels open, and potassium flows to outside the axon. This repolarizes the axon as the inside resumes a negative charge. Conduction of an Action Potential The action potential travels down an axon toward its terminals. It travels faster in myelinated than unmyelinated axons. Transmission Across a Synapse Every axon branches into many fine endings, each tipped by an axon terminal. Each terminal lies very close to either the dendrite or cell body of another neuron. This region is called a synapse, The two neurons are separated by the synaptic cleft. Communication between the two neurons is carried out by molecules called neurotransmitters, which are stored in synaptic vesicles in the axon terminals and released when nerve impulses reach the axon terminal. Synaptic Integration A single neuron may receive many excitatory and inhibitory signals, which have a depolarizing or hyperpolarizing effect, respectively. Integration is the summing up of excitatory and inhibitory signals by a neuron. Neurotransmitters 25 different neurotransmitters have been identified. Once a neurotransmitter has been released into a synaptic cleft and has initiated a response, it is removed from the cleft. 17.3 The Central Nervous System spinal cord and the brain where sensory information is received and motor control is initiated. The Spinal Cord extends from the base of the brain through a large opening in the skull and into the vertebral canal. Structure of the Spinal Cord The spinal nerves project from the cord between the vertebrae. Fluid-filled intervertebral disks cushion and separate the vertebrae. A cross section of the spinal cord shows a central canal, gray matter, and white matter. Functions of the Spinal Cord The spinal cord provides a means of communication between the brain and the peripheral nerves that leave the cord. The spinal cord is also the center for thousands of reflex arcs, which allow the nerves and muscles to respond very quickly. The Brain The four major parts of the brain are the cerebrum, the diencephalon, the cerebellum, and the brain stem. The Cerebrum  The cerebrum is the largest portion of the brain. It is the last center to receive sensory input and carry out integration before commanding voluntary motor responses. It communicates with and coordinates the activities of the other parts of the brain. The Cerebral Hemispheres The cerebrum is divided by a deep groove, called the longitudinal fissure, into the left and right cerebral hemispheres. The two halves communicate via the corpus callosum, an extensive bridge of nerve tracts. Shallow grooves divide each hemisphere into lobes: frontal, parietal, occipital and temporal lobes. The cerebral cortex is a thin, highly convoluted outer layer of gray matter that covers the cerebral hemispheres, it accounts for sensation, voluntary movement, and all the thought processes associated with consciousness. Primary Motor and Sensory Areas of the Cortex The primary motor area is located in the frontal lobe, voluntary commands to skeletal muscles begin here. The primary somatosensory area is located in the parietal lobe and is where sensory information from the skin and skeletal muscles arrive. Association Areas Association areas are places where integration occurs and memories are stored. Processing Centers Processing centers of the cortex receive information from the other association areas and perform higher-level analytical functions. Central White Matter Most of the rest of the cerebrum beneath the cerebral cortex is composed of white matter. Tracts within the cerebrum take information between the different sensory, motor, and association areas. Basal Nuclei Masses of gray matter located deep within the white matter are called basal nuclei, they integrate motor commands, ensuring that proper muscle groups are activated or inhibited. The Diencephalon The hypothalamus and the thalamus are in the diencephalon. The hypothalamus is an integrating center that helps maintain homeostasis by regulating hunger, sleep, thirst, body temperature, and water balance. The thalamus integrates sensory input from the visual, auditory, taste, and somatosensory systems. The pineal gland is located in the diencephalon and secretes a hormone that maintains our normal sleep-wake cycle. The Cerebellum The cerebellum receives sensory input from the joints, muscles, and other sensory pathways about the present position of body parts. It also receives motor output from the cerebral cortex about where these parts should be located. The cerebellum maintains balance and posture by integrating this information.  The Brain Stem The brainstem contains the midbrain, the pons, and the medulla oblongata. The midbrain relays messages between the cerebrum and the spinal cord or cerebellum. The pons contains bundles of axons traveling between the cerebellum and the rest of the CNS. The medulla oblongata regulates vital functions like heartbeat, breathing, and blood pressure. Electroencephalograms The electrical activity of the brain can be recorded in the form of an electroencephalogram (EEG). 17.4 The Limbic System and Higher Mental Functions Emotions and higher mental functions are associated with the limbic system in the brain. The limbic system blends primitive emotions and higher mental functions into a united whole. Anatomy of the Limbic System The limbic system is a complex network of tracts and nuclei that incorporates portions of the cerebral lobes, the basal nuclei, and the diencephalon. The hippocampus communicates with the prefrontal area of the brain, which is involved in learning and memory. The amygdala allows us to respond to and display anger, avoidance, defensiveness, and fear; it prompts release of adrenaline and other hormones. Higher Mental Functions The human cerebrum is responsible for higher mental functions such as memory and learning, as as well as language and speech. Memory and Learning Memory is the ability to hold a thought in mind or to recall events from the past. Learning takes place when we retain and utilize past memories. Types of Memory Short-term memories are stored in the prefrontal area. Long-term memory is typically a mixture of semantic and episodic memory. Skill memory is another type of memory involved in performing motor activities. Long-Term Memory Storage and Retrieval Our long-term memories are stored in bits and pieces throughout the sensory association areas of the cerebral cortex. The hippocampus serves as a bridge between the sensory association areas and the prefrontal area. Long-term potentiation is an enhanced response at synapses within the hippocampus. Language and Speech Language is dependent upon semantic memory and involves the motor speech (Broca’s) area and sensory speech (Wernicke’s) area. The left and right hemispheres have different functions in relation to language and speech; recent studies suggest that the hemispheres process the same information differently. 17.5 The Peripheral Nervous System The peripheral nervous system (PNS) is composed of nerves, which are bundles of axons, and ganglia, which contain collections of cell bodies. Somatic System The PNS is subdivided into the somatic system and the autonomic system. The somatic system serves the skin, skeletal muscles, and tendons. Some actions in the somatic system are due to reflex actions, which are automatic responses to a stimulus. The Reflex Arc Reflexes are programmed, built-in circuits that allow for protection and survival. They require no conscious thought. Nerve impulses travel from the sensory neuron to the spinal cord and back to the motor neuron. Autonomic System The autonomic system regulates the activity of cardiac and smooth muscle and glands. The system is composed of the sympathetic and parasympathetic divisions. These divisions function automatically and usually in an involuntary manner; they innervate all internal organs, and utilize two motor neurons that synapse at a ganglion. Sympathetic Division The sympathetic division is especially important during emergency situations when a “fight or flight” response is required. Parasympathetic Division The parasympathetic division is sometimes called the housekeeper division because it promotes all the internal responses we associate with “rest and digest.” 17.6 Drug Abuse Most illicit drugs affect the action of a particular neurotransmitter at synapses in the brain. Stimulants are drugs that increase the likelihood of neuron excitation, while depressants decrease it. Some Specific Drugs of Abuse Nicotine Nicotine causes a release of epinephrine, increasing blood sugar levels and causing an initial feeling of stimulation. It induces both physiological and psychological dependence. Alcohol (Ethanol) Ethanol influences the action of GABA, an inhibitory neurotransmitter. As it is metabolized, it disrupts the normal workings of the liver and may eventually damage it. Marijuana Marijuana is rich in tetrahydrocannabinol (THC), which binds a receptor for a neurotransmitter in the brain that is important for short-term memory processing. Cocaine and Crack Cocaine is sold in powder form and as crack, a more potent extract. It prevents the synaptic uptake of dopamine, causing the user to experience a rush sensation and a state of arousal that lasts for several minutes afterward. Cocaine causes extreme physical dependence.  Heroin Heroin binds to receptors meant for endorphins, natural neurotransmitters that kill pain and produce a feeling of tranquility. “Club” Drugs Ecstasy, Rohypnol, and ketamine are drugs that are abused by teens and young adults who attend night-long dances called raves or trances. Methamphetamine “Meth” or “crank” is a powerful CNS stimulant, the most immediate effect of which is an initial “rush” of euphoria. “Bath Salts” “Bath salts” are synthetic powders that contain synthetic amphetamine-like chemicals and inhibit the reuptake of several neurotransmitters, producing a euphoric sensation. 17.7 Disorders of the Nervous System A myriad of abnormal conditions can affect the nervous system. Disorders of the Brain Alzheimer disease is the most common cause of dementia, an impairment of brain function that interferes with a patient’s ability to carry on daily activities. Parkinson disease is characterized by a gradual loss of motor control. Multiple sclerosis is the most common neurological disease that afflicts young adults; it is an autoimmune disease in which the patient’s own white blood cells attack the myelin of the nervous system. A stroke results in disruption of the blood supply to the brain. Meningitis is an infection of the meninges that surround the brain and spinal cord. Several brain diseases are caused by prions, infectious agents that are believed to be composed of only protein. Examples are kuru, Creutzfeldt-Jakob disease, fatal familial insomnia and mad cow disease. Disorders of the Spinal Cord Spinal cord injuries may result from trauma. Because little or no nerve regeneration is possible In the CNS, any resulting disability is usually permanent. The location and extent of the damage produce a variety of effects. Amyotrophic lateral sclerosis is a rare, but devastating condition that affects the motor nerve cells of the spinal cord. Disorders of the Peripheral Nerves Guillain-Barré syndrome is an inflammatory disease that causes demyelination of peripheral nerve axons. Myasthenia gravis is an autoimmune disorder in which antibodies are formed that react against the acetylcholine receptor at the neuromuscular junction of the skeletal muscles, preventing muscle stimulation. CHAPTER 18: SENSES LECTURE OUTLINE 18.1 Sensory Receptors and Sensations Sensory receptors are specialized cells that detect certain types of stimuli. Interoceptors receive stimuli from inside the body, while exteroceptors detect stimuli from outside the body. Types of Sensory Receptors Sensory receptors can be classified into four categories: chemoreceptors, photoreceptors, mechanoreceptors, and thermoreceptors, which respond to chemical substances, light energy, mechanical forces, and changes in temperature, respectively. How Sensation Occurs Sensory receptors respond to environmental stimuli by generating nerve impulses. Detection occurs when environmental changes stimulate sensory receptors. Sensation occurs when nerve impulses arrive at the cerebral cortex of the brain. Perception occurs when the brain interprets the meaning of stimuli. 18.2 Somatic Senses Those senses whose receptors are associated with the skin, muscles, joints, and viscera are considered the somatic senses. They can be categorized into three types: proprioceptors, cutaneous receptors, and pain receptors. Proprioceptors Proprioceptors are mechanoreceptors involved in reflex actions that maintain muscle tone, and thereby the body’s equilibrium and posture. Cutaneous Receptors The epidermis and dermis of the skin contain cutaneous receptors that make the skin sensitive to touch, pressure, pain, and temperature. Pain Receptors The skin and many internal organs and tissues have pain receptors that are sensitive to chemicals released by damaged cells. 18.3 Senses of Taste and Smell Taste and smell are called chemical senses because their receptors are sensitive to molecules in the food we eat and the air we breathe. Sense of Taste The sensory receptors for the sense of taste, the taste cells, are found in taste buds located primarily on the tongue. Different taste cells can detect at least the five primary types of taste: salty, sour, bitter, sweet, and umami (savory).  How the Brain Receives Taste Information The brain appears to survey the overall pattern of incoming sensory impulses and to take a “weighted average” of their taste messages as the perceived taste. Sense of Smell Approximately 80-90% of what we perceive as “taste” is actually due to the sense of smell, which is dependent on olfactory cells located within olfactory epithelium. Olfactory cells are modified neurons. How the Brain Receives Odor Information An odor contains many odor molecules, which activate a characteristic combination of receptor proteins. The olfactory bulbs have direct connections to the limbic system and its centers for emotions and memory. 18.4 Sense of Vision Vision requires the work of the eyes and the brain. Anatomy and Physiology of the Eye The eye has three layers: the sclera, the choroid, and the retina. The retina contains photoreceptors called rod cells and cone cells. Function of the Lens The lens, assisted by the cornea and the humors, focuses images on the retina. Visual Pathway to the Brain The pathway for vision begins once light has been focused on the photoreceptors in the retina. Function of Photoreceptors Rods are very sensitive to light, and are therefore suited to night vision. The cones allow us to detect the fine detail and the color of an object. Function of the Retina The retina has three layers of neurons: the choroid contains the rod and cone cells, the middle layer contains bipolar cells, and the innermost layer contains ganglion cells. The rod and cone cells are sensitive to light. They synapse with bipolar cells, which in turn synapse with ganglion cells whose axons become the optic nerve. Blind Spot There are no rods and cones where the optic nerve exits the retina. This is your blind spot. From the Retina to the Visual Cortex The axons of ganglion cells in the retina assemble to form the optic nerves that carry nerve impulses from the eyes to the optic chiasma. The optic tracts synapse with neurons in nuclei within the thalamus, which then take nerve impulses to the visual area within the occipital lobe. The primary visual areas parcels out information regarding color, form, motion, and possibly other attributes to different portions of the adjoining visual association area. 18.5 Sense of Hearing The ear functions in hearing as well as balance (equilibrium). The sensory receptors for both of these are mechanoreceptors located in the inner ear that are sensitive to mechanical stimulation. Anatomy of the Ear The outer ear collects and funnels sound into the auditory canal. The middle ear transmits sound from the tympanic membrane to the oval window. The inner ear is filled with fluid. The The cochlea of the inner ear functions in hearing. Auditory Pathway to the Brain Hearing requires the ear, the cochlear nerve, and the auditory cortex of the brain. Through the Auditory Canal and Middle Ear The process of hearing begins when sound waves enter the auditory canal. The tympanic membrane passes these vibrations through the malleus, incus, and stapes to the oval window, causing it to vibrate. The pressure is passed to the fluid within the cochlea. From the Cochlea to the Auditory Cortex The cochlear canal contains the organ of Corti, the sense organ for hearing. It consists of little hair cells and a gelatinous material called the tectorial membrane. When the hair cells embedded in the tectorial membrane bend, the nerve impulses begin in the cochlear nerve and travel to the brain. When they reach the auditory cortex in the temporal lobe, they are interpreted as a sound. 18.6 Sense of Equilibrium Mechanoreceptors in the inner ear detect rotation and/or angular movement of the head (rotational equilibrium), and movement of the head in the vertical or horizontal planes (gravitational equilibrium). Rotational Equilibrium Pathway Rotational equilibrium involves the three semicircular canals, which are arranged so that there is one in each dimension of space. Gravitational Equilibrium Pathway Gravitational equilibrium depends on the utricle and the saccule, two membranous sacs located in the vestibule. The utricle is especially sensitive to horizontal movements and the bending of the head, while the saccule responds best to vertical movements. 18.7 Disorders that Affect the Senses Disorders of Taste and Smell Disorders that affect taste and smell may not sound very serious, but these senses contribute substantially to our enjoyment of life. Unpleasant smells and tastes can warn us about dangers. Disorders of the Eye Color blindness and problems with visual focus are two common abnormalities of the eye. More serious disorders can result in blindness. Color Blindness  Complete color blindness is extremely rare. In most instances, a particular type of cone is lacking or deficient in number. Visual Focus The majority of people can see what is designated as a size 20 letter 20 feet away, and so are said to have 20/20 vision. Persons who can see close objects but cannot see the letter from this distance are said to be nearsighted. Persons who can see the letter but cannot see close objects well are farsighted. Astigmatism results when the cornea or lens is uneven resulting in a fuzzy image. Common Causes of Blindness The most frequent causes of blindness in adults are retinal disorders, glaucoma, and cataracts, in that order. Disorders of Hearing and Equilibrium Hearing loss can develop gradually or suddenly and has many potential causes. Disorders of equilibrium often manifest as vertigo, the feeling that a person or the environment is moving when no motion is occurring. Study Information - Chapter 20 ENDOCRINE SYSTEM Overview of the Endocrine System The endocrine system consists of glands and tissues that secrete hormones. Hormones are chemicals that affect the behavior of other glands or tissues. Endocrine glands have no ducts, they secrete their hormones into tissue fluid. o Hormones and Homeostasis o Like the nervous system, the endocrine system is involved in homeostasis. Hormones secreted by the endocrine system must reach their target organs via the blood, resulting in a slower, but often a more prolonged response than the nervous system. The production of hormones is controlled by negative feedback and by the action of antagonistic hormones. o The Action of Hormones o Hormones are a type of chemical signal used to communicate between cells, body parts, or individuals. Hormones fall into two basic chemical classes. ▪ Peptide hormones ▪ Peptide hormones are either peptides, proteins, glycoproteins, or modified amino acids. ▪ Steroid hormones ▪ Steroid hormones always have the same complex of four carbon rings, but with different side chains. o Pheromones o Chemical signals that act between individuals of the same species are called pheromones. Hypothalamus and Pituitary Gland The hypothalamus helps regulate the internal environment through the autonomic system, where it modulates heartbeat, blood pressure, hunger and appetite, body temperature, and water balance, and through the glandular secretions of the pituitary gland. Posterior Pituitary Neurons in the hypothalamus produce the hormones antidiuretic hormone (ADH) and oxytocin that pass through axons into the posterior pituitary where they are stored. ADH is released when blood is too concentrated and it causes water to be reabsorbed in the kidneys. Oxytocin causes uterine contraction during childbirth and milk letdown when a baby is nursing, its release from the pituitary is controlled by a positive feedback. Anterior Pituitary The hypothalamus controls the anterior pituitary by producing hypothalamic-releasing and hypothalamic-inhibiting hormones. These stimulate the anterior pituitary to secrete hormones such as thyroid-stimulating hormone, adrenocorticotropic hormone, gonadotropic hormones, prolactin, melanocyte-stimulating hormone, and growth hormone. Thyroid and Parathyroid Glands The thyroid gland is located in the neck. The parathyroid glands are embedded in the posterior surface of the thyroid gland. Thyroid Gland The thyroid gland produces hormones that increase the metabolic rate and control the blood calcium levels. Parathyroid Gland Parathyroid hormone causes the blood phosphate level to decrease and the blood calcium level to increase. Adrenal Glands The adrenal glands sit atop the kidneys. Adrenal Medulla The adrenal medulla produces epinephrine and norepinephrine, which provide a short-term response to stress. Adrenal Cortex The hormones produced by the adrenal cortex provide a longer-term response to stress. These include the mineralocorticoids and the glucocorticoids. Glucocorticoids Cortisol is a glucocorticoid. Cortisol raises the blood glucose level and counteracts the inflammatory response that leads to the pain and swelling of joints. Mineralocorticoids Aldosterone is the most important of the mineralocorticoids. It targets the kidney where it helps regulate blood volume and blood pressure. Pancreas The pancreas has two types of tissue, exocrine tissue produces and secretes digestive juices by way of ducts to the small intestine. The pancreatic islets are composed of endocrine cells that produce and secrete insulin and glucagon that help regulate the blood glucose level, as well as somatostatin, a growth hormone inhibitor. Other Endocrine Glands The gonads are endocrine glands that are the testes in males and the ovaries in females. Testes and Ovaries The testes produce sperm and androgens (e.g., testosterone), which are the male sex hormones. The ovaries produce eggs, as well as estrogen and progesterone, the female sex hormones. The hypothalamus and the pituitary gland control the hormonal secretions of the gonads. Secretion of both the male and female sex hormones at the time of puberty results in the development of secondary sex characteristics. Thymus The thymus secretes thymosins, which aid in the differentiation of T lymphocytes. Pineal Gland The pineal gland produces melatonin that is involved in our daily sleep-wake cycle. Hormones from Other Tissues Some organs that are usually not considered endocrine glands can secrete hormones. Leptin Leptin is a protein hormone produced by adipose tissue and it signals satiety. Growth Factors A number of different types of organs and cells produce growth factors, which stimulate cell division and mitosis. Prostaglandins Prostaglandins are potent chemical signals that act locally, quite close to where they were produced. Disorders of the Endocrine System An increase or decrease in the product of most hormones can cause significant disease. Disorders of the Pituitary Gland Disorders of the pituitary gland can have dramatic effects on the body. These disorders include diabetes insipidus, pituitary dwarfism, gigantism, acromegaly, and Cushing syndrome and are associated with too much or too little antidiuretic hormone, growth hormone or adrenocorticotropic hormone. Disorders of the Thyroid, Parathyroid, and Adrenal Glands  If the thyroid gland does not produce enough thyroid hormones, hypothyroidism occurs. A lack iodine in the diet may result in a simple goiter. Hyperthyroidism results from the oversecretion of thyroid hormones. Adrenal gland insufficiency is called Addison disease. Diabetes Mellitus Diabetes mellitus is a condition that affects the ability to regulate glucose metabolism. People with diabetes either do not produce enough insulin (type 1) or cannot properly use the insulin they produce (type 2).