Chapter 26 Lecture Outline See PowerPoint Image Slides for all figures and tables pre-inserted into PowerPoint without notes.
Coordination in Multicellular Animals • Maintaining a constant internal environment is crucial for large multicellular organisms. • Accomplished by monitoring and modifying the functioning of various systems • Called homeostasis • Homeostasis maintains oxygen levels, blood pressure, heart rate, body temperature, fluid levels, pH, etc. • Homeostasis is maintained by the nervous, endocrine and immune systems. • Example: Running up a hill
Negative Feedback Control • A common homeostatic mechanism • Occurs when an increase in the stimulus results in a decrease in response • Functions to maintain a set point • Example: Thermostat
Positive Feedback Regulation • When an increase in stimulus results in an increase in response • Does not result in homeostasis, but plays an important role in homeostasis • Childbirth
Nervous System Function • Important in making adjustments over a short time period • Transmission of information is very fast in the nervous system.
The Structure of the Nervous System • Consists of a network of cells that carry information from one part of the body to another • Made up of specialized cells called neurons • Cell body or soma-contains the nucleus • Dendrites-receive information and carry it to the cell body • Axons-carry information away from the cell body
Central Nervous System • Brain and spinal cord • Protected by skull and vertebrae • Receives input from sensory organs • Interprets and integrates information • Generates responses
Peripheral Nervous System • Located outside the skull and vertebral column • Consists of bundles of axons and dendrites called nerves • Somatic nervous system • Nerves that control the skeletal muscles • Autonomic nervous system • Nerves that control the involuntary muscles, the heart and glands
Types of Neurons • Motor neurons • Carry messages from the central nervous system to muscles and glands • Usually have one long axon that runs from the spinal cord to the muscle or gland • Sensory neurons • Carry input from sense organs to the central nervous system • Have long dendrites that carry input from the sense organ to the brain or spinal cord
The Nature of Nerve Impulses • Information is transmitted through neurons in the form of nerve impulses. • Also known as action potentials • Involve a sequence of chemical events at the cell membrane of the neuron
Neurons have an Unequal Distribution of Ions Inside and Outside of the Cell • Active transport pumps sodium out and potassium in • More sodium is pumped out than potassium pumped in • As a result • Sodium is concentrated outside the cell. • Potassium is concentrated inside the cell.
Neurons have an Unequal Distribution of Ions Inside and Outside of the Cell • This unequal distribution of charge generates a voltage across the neuronal cell membrane. • Voltage is a measure of the electrical charge difference that exists between two points. • The inside of the cell is more negative than the outside. • At rest, the membrane voltage of a neuron is about -70mV. • The voltage across the membrane makes it polarized.
Generation of a Nerve Impulse • When a neuron is stimulated by an input … • The cell membrane becomes more permeable to sodium. • Sodium ions enter the cell down their concentration gradient. • The inside of the cell becomes more positive. • The cell is depolarized. • The depolarization spreads down the axon.
Generation of a Nerve Impulse • Depolarization of any one segment of membrane is brief. • Membrane becomes repolarized when potassium flows out of the cell • Repolarization is followed by the pumping of sodium out of and potassium into the cell. • This re-establishes the original concentration gradients. • This brings the cell back to its resting membrane potential.
Activities at the Synapse • The synapse is the small space between the axon of one neuron and the dendrite of another neuron. • Neurons communicate with one another through the activities at the synapse. • When the nerve impulse in one neuron reaches the synapse, chemicals are released from the end of the axon. • Called neurotransmitters • Diffuse across the synapse and bind to receptor sites on the dendrite of the other neuron • This can cause depolarization and generate a nerve impulse in the second neuron.
Neurotransmitters • Made in the cell body and transported to the end of the axon to be stored until released. • Acetylcholine was the first neurotransmitter identified. • Bind to receptors and stimulate them as long as they are bound • Enzymes in the synapse destroy neurotransmitters, allowing the second cell to return to resting state. • Acetylcholinesterase is the enzyme that breaks down acetylcholine. • Many drugs interfere with neurotransmission at the synapse.
Direction of Information Flow • Information in the nervous system only travels in one direction… • From the axon of one cell to the dendrite of another in a synapse • From the dendrites to the cell body of one neuron • From the cell body through the axon to the synapse
The Organization of the Central Nervous System • The brain consists of several different regions that have specific functions. • The functions of the brain can be divided into three major levels. • Automatic activities • Basic decision making and emotions • Thinking and reasoning
The Organization of the Central Nervous System • Spinal cord • Collection of neurons and nerve fibers surrounded by the vertebrae • Conveys information to and from the brain • Medulla oblongata • The base of the brain where the spinal cord enters the brain • Controls fundamental life support activities such as • Blood pressure • Breathing • Heart rate • Fibers from the spinal cord cross sides in the medulla • Right side of body is controlled by left side of brain and vice versa
The Organization of the Central Nervous System • Cerebellum • Large bulge at the base of the brain • Connected to the medulla oblongata • Receives information from sensory organs that involve balance • Inner ear, eyes, pressure sensors in muscles and tendons • Regulates muscle activity to establish balance and coordination
The Organization of the Central Nervous System • Pons • The region of the brain that is anterior to the medulla oblongata • Controls many sensory and motor functions of the head and face • Thalamus • Located between the pons and the cerebrum • Relays information between the cerebrum and the lower centers of the brain • Spinal cord, medulla, pons • Important in awareness • Involved in sleep and arousal
The Organization of the Central Nervous System • Hypothalamus • Involved in sleep and arousal • Important in emotions • Fear, anger, pleasure, hunger, sexual responses, pain • Regulates body temperature, blood pressure and blood volume • Connected to and controls the pituitary gland • Controls the release of hormones
The Organization of the Central Nervous System • Cerebrum • The thinking part of the brain. • Comprised of two hemispheres • Controls memory, language, movement • Responsible for the integration of sensory input • The major site of association and cognition.
Endocrine System • The Endocrine system • A collection of glands that communicate with one another and with body tissues through the release of hormones. • Hormones • Chemical signals released by one organ that are transported to another organ where it triggers a change in activity • Glands • Organs that make and release specific chemicals • Endocrine glands • Lack ducts • Secrete hormones in to the circulatory system • Exocrine glands • Have ducts • Release their products into the digestive tract or onto the skin • Digestive glands, sweat glands
Endocrine System Function • Hormones released by endocrine glands travel throughout the entire body. • However, they only bind to and affect target cells that have receptors. • Target cells respond by • Releasing products that have been previously made • Making new molecules or increasing metabolic activity • Dividing and growing
Some Examples of Hormone Action • Epinephrine and norepinephrine • Released by the adrenal medulla during emergency situations • Acts quickly • Increases heart rate, blood pressure and breathing rate • Shunts blood to muscles • Antidiuretic hormone • Released from posterior pituitary in response to dehydration • Acts more slowly • Targets kidney cells • Increases the re-absorption of water
Some Examples of Hormone Action • Insulin • Works rapidly • Produced and released from the pancreas • Stimulates cells to take in glucose • Is released in response to high glucose levels in the blood • Would occur after a high carbohydrate meal • Diabetes is a lack of insulin • Cells don’t take in glucose • Growth-stimulating hormone • Works over a period of several years during childhood • Produced by the anterior pituitary • Stimulates growth
Integration of Nervous System and Endocrine System Function • The pituitary gland links the endocrine system to the nervous system. • Located at the base of the brain • Divided into two parts • Anterior pituitary • An endocrine gland • Produces hormones that trigger other glands to release their hormones • Receives commands from the chemicals released from the hypothalamus • Posterior pituitary • Part of the brain • Holds the axons from cells in the hypothalamus • Releases specific hormones into the bloodstream
Integration of Nervous System and Endocrine System Function • Example: In songbirds, the length of day causes hormonal changes that prepare the animals for reproduction. • Length of day is sensed by the pineal body in the brain. • The pineal gland controls the release of chemicals from the hypothalamus. • The chemicals released by the hypothalamus trigger the pituitary to release hormones into the bloodstream. • These pituitary hormones stimulate the reproductive organs to secrete reproductive hormones. • These reproductive hormones trigger courtship and mating rituals in birds.
Sensory Input • The nervous and endocrine systems respond to sensory input. • This input comes from sense organs. • Some sense organs detect external stimuli. • Vision, hearing, touch • Other sense organs detect internal stimuli. • Pain and pressure • The sense organs detect changes; the brain is responsible for perception.
Chemical Detection • All neurons have chemical receptors on their surface. • When chemicals bind to these receptors, the activity of the cell changes. • Usually results in depolarization and the generation of a nerve impulse. • Other types of cells have chemical receptors as well. • The aorta can sense and respond to changes in hydrogen ions, carbon dioxide and oxygen in the blood.
Taste • Taste buds are sensory cells located on the tongue. • They have chemical receptors that respond to classes of molecules. • These classes correspond with the five kinds of taste we experience. • Sweet, sour, salt, bitter and umami (meaty)
Taste • Sour and salty sensation results from ions entering taste buds and causing a depolarization. • Sour sensing taste buds respond to hydrogen ions. • Salty sensing taste buds respond to sodium chloride. • Sweet, bitter and umami sensations result from molecules binding to receptors on taste buds. • Sweet receptors are stimulated by sugars, artificial sweeteners, etc. • Umami receptors are stimulated by glutamate.
Smell • The sensory receptors in the nose are more versatile than taste buds. • They can sense thousands of different molecules at low concentrations. • Found in the olfactory epithelium • Very sensitive • Fatigue quickly
Vision • The sensory cells in the eyes respond to changes in the flow of light energy. • Light-sensing cells are found in the retina. • At the back of the eye • The other parts of the eye are designed to focus light onto the retina • Light-sensing cells are called rods and cones. • Rods are very sensitive and can detect dim light but not color. • Cones are less sensitive, but can detect different wavelengths of light (color). • This is why we cannot see color at night.
Vision • The fovea centralis is a region in the retina with many cones and no rods. • This area gives us the most focused and detailed vision. • Rods and cones sense light because they contain pigment molecules. • Rhodopsin is the pigment in rods. • When light hits rhodopsin, it changes shape and causes the rod to depolarize. • This generates a nerve impulse that is sent to the brain. • Different types of cones have different pigments that respond to specific wavelengths of light.
Hearing and Balance • One set of sensory cells in the ear responds to changes in sound waves. • These sensory cells are found in the cochlea. • Sound is produced by the vibration of molecules. • Volume is a measure of the intensity of the vibration. • Pitch is determined by the frequency of the vibration. • The other set of sensory cells in the ear responds to movements of the head. • These cells are found in the fluid-filled semi-circular canals. • They sense the position of the head with respect to the force of gravity. • Helps maintain balance