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Oooohhhh… aaaahhhh EVOLUTIONARY DEVELOPMENT OF THE NERVOUS SYSTEM These facts prove the evolutionary development of the nervous system… • Cnidarians have a have a nerve net • Cephalization is a trend toward clustering sensory neurons and interneurons at the anterior end. Basically, it is the forming of a head. • Flatworms show cephalization, with a small brain and longitudinal nerve cord. They have the simplest clearly defined central nervous system. • Annelids such as the earthworm and arthropods have a ventral nerve cord. • Vertebrates have a hallow dorsal nerve cord. With cephalization come more complex nervous systems. WHY IS THE NERVOUS SYSTEM IMPORTANT? Nerves send messages to everything from the brain. if there was no nervous system... 1.you're heart wouldn't be told to beat 2. your legs wouldn't be told to walk, and your arms wouldn't be told to move 3. your lungs wouldn't be told to expand and collapse 4. messages wouldn't be able to send messages to the brain, such as tastebuds (no taste) skin, (no feeling,) eyes (no sight), no hearing, and no smelling. The vertebrate nervous system consists of central and peripheral components - the central nervous system (CNS) consists of the brain and spinal cord (nerve bundle that communicates with body) - the peripheral nervous system (PNS) consists of all nerves outside the CNS. PERIPHERAL SYSTEM Sensory system: conveys information from sensory receptors or nerve endings. Motor system: 1. Somatic system: controls the voluntary muscles 2. Autonomic system: Controls involuntary muscles Sympathetic: • Flight or fight response • Increase heart and breathing rate • Liver converts glycogen to glucose • Bronchi of lungs dilate and increase gas exchange • Adrenalin raises glucose levels Parasympathetic: • Rest and digest • Calms the body • Decreases heart/breathing rate • Enhances digestion THE SCHWANN CELL Schwann cells are part of the peripheral nervous system (PNS.) They have two major functions, they produce the myelin sheath which covers the Schwann cell, which helps to repair and regenerate nerves that have been damaged. In addition, they help the nerve impulse to be passed on quicker so that the brain can send a impulse to ones bones and muscles. Functional composition of the PNS. cerebrum corpus callosum thalamus Pineal gland hypothalamus cerebellum pituitary pons spinal cord medulla oblongata CEREBRUM Involved with higher brain functions. Processes sensory information. Initiates motor functions. Integrates information. Frontal lobe. Contains the primary motor cortex. Parietal lobe. Contains the primary somatosensory cortex. Integrative Function of the Association Areas. Much of the cerebrum is given over to association areas. Areas where sensory information is integrated and assessed and motor responses are planned. Lateralization of Brain Function. The left hemisphere. Specializes in language, math, logic operations, and the processing of serial sequences of information, and visual and auditory details. Specializes in detailed activities required for motor control. The right hemisphere. Specializes in pattern recognition, spatial relationships, nonverbal ideation, emotional processing, and the parallel processing of information. FIG. 49-17 Max Hearing words Seeing words Min Speaking words Generating words Language and Speech. Broca’s area. Usually located in the left hemisphere’s frontal lobe Responsible for speech production. Wernicke’s area. Usually located in the right hemisphere’s temporal lobe Responsible for the comprehension of speech. Emotions. In mammals, the limbic system is composed of the hippocampus, olfactory cortex, inner portions of the cortex’s lobes, and parts of the thalamus and hypothalamus. Mediates basic emotions (fear, anger), involved in emotional bonding, establishes emotional memory For example, the amygdala is involved in recognizing the emotional content of facial expression. Memory and Learning. Short-term memory stored in the frontal lobes. The establishment of long-term memory involves the hippocampus. The transfer of information from short-term to long-term memory. Is enhanced by repetition (remember that when you are preparing for an exam). Influenced by emotional states mediated by the amygdala. Influenced by association with previously stored information. Different types of long-term memories are stored in different regions of the brain. Memorization-type memory can be rapid. Primarily involves changes in the strength of existing nerve connections. Learning of skills and procedures is slower. Appears to involves cellular mechanisms similar to those involved in brain growth and development. Human Consciousness. Brain imaging can show neural activity associated with: Conscious perceptual choice Unconscious processing Memory retrieval Working memory. Consciousness appears to be a whole-brain phenomenon. MIDBRAIN Contains ascending and descending tracts to the cerebrum and thalamus. Reflex center for eye muscles. Also involved with processing visual and auditory information (connects head movements with visual and auditory stimuli). MEDULLA OBLONGATA • Composed of nerve tracts to and from the brain (these tracts cross over left to right and right to left) • May be regarded as an extension of the spinal cord • Almost all of the cranial nerves arise from this region MEDULLA OBLONGATA Contains control centers for many subconscious activities • Respiratory rate • Heart rate • Arteriole constriction • Swallowing • Hiccupping • Coughing • Sneezing CEREBELLUM Controls and coordinates muscular activity. Important in equilibrium, posture and movement. THE NEURON The neuron consists of a cell body, which contains the nucleus and other organelles, and two types of cytoplasmic extensions called dendrites and axons. Dendrites are sensory; they receive incoming messages from other cells and carry electrical signal to the cell body. Axons transmit an impulse from the cell body outward to another cell. 3 types of neurons: Sensory neurons: receive an initial stimulus from a sense organ Motor neuron: stimulates effectors (muscles or glands) Interneuron/association neuron: resides within the spinal cord and brain, receives sensory stimuli, and transfers the information directly to a motor neuron or to the brain for processing. SYNAPSE • Each branched end of an exon transmits information to another cell at a junction called a synapse. • The part of each axon branch that forms this specialized junction is a synaptic terminal. • Chemical messengers called neurotransmitters pass information from the transmitting neuron to the receiving cell. With the signaling of influx of Calcium ions into the neuron. The neurotransmitters will match up with another ion channel, and change it’s shape so it can take in ions. Now, sodium can flow in into the next neuron • The transmitting neuron is the presynaptic cell • The neuron, muscle, or gland cell that receives the signal is the postsynaptic cell THE REFLEX ARC The simplest nerve response. It is inborn, automatic, and protective. i.e the knee-jerk reflex: consists of only 2 neurons: sensory and motor. A stimulus, a tap from a hammer, is felt in the sensory neuron of the kneecap, which sends an impulse to the motor neuron, which directs the thigh muscle to contract. Complex reflex consists of 3 neurons: sensory, motor and interneuron a sensory neuron transmits an impulse to the interneuron in the spinal cord, which sends one impulse to the brain for processing and also one to the motor neuron to effect change immediately (jerk hand away from hot iron). 1. The reflex is initiated artificially by tapping the tendon connected to the quadriceps muscle. 2. Sensors detect a sudden stretch in the quadriceps 3. Sensory neurons convey the information to the spinal cord. 4. In response to signals, motor neurons convey signals to the quadriceps, causing it to contract and jerking the lower leg forward. 5. Sensory also communicate with interneurons in the spinal cord. 6. The interneurons inhibit motor neurons that lead to the hamstring muscle. This inhibition prevents contraction of the hamstring which would resist the action of the quadriceps. RESTING POTENTIAL All living cells have a membrane potential: a difference in electrical charge between the cytoplasm (negative ions) and extracellular fluid (positive ions). This potential should be between -50mV and -100mV. A neuron in its unstimulated/polarized state (resting potential) has a membrane potential -70mV. The sodiumpotassium pump maintains the polarization by actively pumping ions that leak across the membrane. In order nerve to fire, a stimulus must be strong enough to overcome resting potential. The larger the membrane potential, the stronger the stimulus must be to cause the nerve to fire. GATED CHANNELS Neurons have gated-ion channels that open or close in response to a stimulus and play an essential role in transmission of electrical impulses. Allow one kind of ion, i.e. sodium or potassium, to flow through. If stimulus triggers sodium ion-gated channel to open: sodium flow into cytoplasm -> decrease in polarization (-60mV); membrane becomes depolarized-> easier for nerve to fire. Potassium ion-gated channel: membrane potential increases, membrane becomes hyperpolarized (-75mV), harder for neuron to fire. ACTION POTENTIAL - generated only in the axon of a neuron - when axon is stimulated sufficiently to overcome resting potential, permeability of the region suddenly changes and impulse can pass - sodium channels open and sodium flood into the cell - in response, potassium channels open and potassium floods out of the cell - rapid movement of ions (wave of depolarization) reverses the polarity of the membrane -> action potential - the sodium-potassium pump restores the membrane to its original polarized condition by pumping sodium and potassium ions back to original position -> Period of repolarization called refractory period, neuron cannot respond to another stimulus. THE INTERDEPENDENCE The nervous and muscular systems work together and are very unique systems that could not function without each other. The muscular system gets messages from the nervous system, telling it what to do, how to do it, and exactly when to perform the action. Without the nervous system, the muscular system would not be able to move us, because it would have nothing to tell it what to do. And without the muscular system, we wouldn't be able to move even if we did have the nervous system. Also, the skeletal system, female reproductive system, male reproductive system, endocrine system. Your conscious mind relays a command to your central nervous system, which translates it into electrical impulses. When the muscles are ready, a chemical, acetylene, is released from the nerve endings, stimulating the membranes of muscle fibers, and causing them to contract. COMMON DISEASES FROM THE NERVOUS SYSTEM SCHIZOPHRENIA The symptoms of schizophrenia include hallucinations and delusions, blunted emotions, distractibility, lack of initiative, and poverty of speech. The cause of schizophrenia is unknown, although the disease has a strong genetic component. There is an active effort to find the mutant genes that predispose a person to schizophrenia. Available treatments for schizophrenia focus on the use of dopamine as a neurotransmitter. Two lines of evidence suggest that this approach is suitable. First, amphetamine, which stimulates dopamine release, can produce symptoms identical to those of schizophrenia. Second, many of the drugs that alleviate the symptoms block dopamine receptors. Additional neurotransmitters may also be involved because other drugs successful in treating schizophrenia have stronger effects on serotonin and/or norepinephrine transmitters. The street drug PCP blocks glutamate receptors and induces strong schizophrenialike symptoms. Many current schizophrenia medications have severe side effects. Dopamine: It is an inhibitory neurotransmitter, which means that when it comes to its receptor sites, it blocks the tendency of that neuron to fire. Dopamine is associated with reward mechanisms in the brain. Severe deficiency and overabundance of this neurotransmitter can cause drastic results. It is often the neurotransmitter involved with drugs, like cocaine heroin, etc. People that suffer from Schizophrenia are often seen with vast amounts of dopamine in their system. People that suffer from Parkinson's disease are often seen with insufficient amounts of dopamine in their system. ALZHeimer’s disease Alzheimer’s disease is a mental deterioration or dementia. It is characterized by confusion, memory loss, and a variety of other symptoms. Its incidence is age related, rising from 10% at age 65 to 35% at age 85. The disease is progressive, with patients losing the ability to live alone and take care of themselves. There are also personality changes, almost always for the worse. It is difficult to diagnose Alzheimer’s disease while the patient is still alive. However, it results in characteristic brain pathology. Neurons die in huge areas of the brain, often leading to shrinkage of brain tissue. The diagnostic features are neurofibrillary tangles and senile plaques in the remaining brain tissue. Neurofibrillary tangles are bundles of degenerated neuronal and glial processes. Senile plaques are aggregates of ß-amyloid, an insoluble peptide that is cleaved from a membrane protein normally found in neurons. Membrane enzymes, called secretases, catalyze the cleavage, causing ß-amyloid to accumulate outside the neurons and to aggregate in the form of plaques. The plaques seem to trigger the death of the surrounding neurons. Parkinson’s disease Approximately 1 million people in the United States suffer from Parkinson’s disease, a motor disease characterized by difficulty in initiating movement, slowness of movement, and rigidity. Parkinson’s disease results from death of neurons in a midbrain nucleus called the substantia nigra. These neurons normally release dopamine from their synaptic terminals in the basal nuclei. The degeneration of dopamine neurons is associated with the accumulation of protein aggregates containing a protein typically found in presynaptic nerve terminals. The consensus among scientists is that it results from a combination of environmental and genetic factors. At present, there is no cure for Parkinson’s disease, although various approaches are used to manage the symptoms, including brain surgery; deep-brain stimulation; and drugs such as L-dopa, a dopamine precursor that can cross the blood-brain barrier. One potential cure is to implant dopamine-secreting neurons, either in the substantia nigra or in the basal ganglia. Embryonic stem cells can be stimulated or genetically engineered to develop into dopamine-secreting neurons. Transplantation of these cells into rats with an experimentally induced condition that mimics Parkinson’s disease has led to a recovery of motor control. It remains to be seen whether this kind of regenerative medicine will work in humans. MULTIPLE CHOICE QUESTIONS 1. The function of a Schwann cell is to a) Produce esterases to break down neurotransmitters b) Form the myelin sheath around the axon of a neuron c) Act as an interneuron in the spinal cord d) Receive impulses and send them to the neuron e) Act as an effector for a neuron 2. Which of the following are the parts of neurons? a) Brain, spinal cord, and vertebral column b) Sensory and motor c) Dendrite, axon, and cell body d) Cortex, medulla, and sheath e) Sympathetic and parasympathetic http://www.youtube.com/watch?v=m7wRMlThMik http://www.youtube.com/watch?v=UabDiuTtU0M