Functions of the Nervous System 1. Sensory input – gathering information monitor changes both inside and outside the body Changes = stimuli 2. Integration -- process and interpret sensory input 3. Motor output A response to integrated stimuli The response activates muscles or glands Changes include environmental temp, light, dangers. External. Internal: salt, CO2, O2 concentration, BP, pathogens. Glucose levels. Essential for maintaining homeostasis is to be able to sense current status of all these conditions. Integration- without processing, nothing more than an electrical signal. On or off. Meaning is based on frequency of signal and on location, as denoted by particular neuron that transmitted the signal. Interpretation of signals is learned, f r many signals.

Components of the Nervous System Central Nervous System brain, spinal cord Peripheral NS Sensory - input afferent (approach) Motor - output efferent (exit) Components of nervous system: CNS = brain, spinal cord Peripheral - Nerves outside the brain and spinal cord . Sensory (afferent)/ APPROACH - Nerve fibers that carry information TO the central nervous system = input. Sensory neurons with specialized dendrite endings, set up to detect specific stimuli: chemical (taste, smell), light (vision), pressure (touch, deep pressure). . pain receptors = plain nerve endings. Warn us of body damage. Propriorecptors in muscles and tendons Motor (efferent/EXIT) division Nerve fibers that carry impulses away from the central nervous system = output. Several targets, so different systems for each output targe:. Somatic - controls skeletal muscle Autonomic - controls smooth, cardiac muscle and glands. No conscious control. imprt in maintaining homeostasis among organ systems in body. Note that divisions are artificial. System works together. Division is for ease of study. Figure 11.1

Organization of the Nervous System Motor (efferent) division Somatic nervous system = voluntary Autonomic nervous system = involuntary Note that divisions are artificial. System works together. Division is for ease of study. Motor: autonomic w/ 2 types, imprt in maintaining homeostasis among organ systems in body. Sympathetic “Strong”= flight or fight responses Parasympathetiic “peaceful”= return to normal life maintenance. - works in opposition to maintain homeostasis. Figure 7.2

Communication Cells of System Neurons: specialized cells for communication Types: sensory interneurons motor neurons Neurons = nerve cells Cells specialized to transmit messages Sensory - stimulated to send electrical impulse when detects light, pressure, specific stimulus, chemical, light, pressure. Input to CNS Interneuron - connect 2 other neurons within CNS. Carry signal.impt for integration of input. Motor - carry impulses away from CNS , out to all body tissues. Efferent neurons, cell bodies are ALWAYS located in CNS. Means that individual neurons can extend quite a ways to appendage.

Neuron Anatomy Cell body Dendrites Axon Neuroglial cells: support and protect neurons Schwann cells Wrap around axon Signal transmitted along axon -. Typical cell organelles in cell body: nucleus, nucleolus and metabolic center of the cell. Mito, other organelles. No centrioles, corresponds to lack of cell division in neurons specialized rough endoplasmic reticulum = Nissl substance Neurofibrils - intermediate cytoskeleton that maintains cell shape Processes - Extensions outside the cell body Dendrites – conduct impulses toward the cell body; receive signals Axons – conduct impulses away from the cell body. long thin tube with little cytoplasm. Designed to transmit electrical impulse. Axon ends in small branches celled axon terminals, each w/ axon bulb. Neuroglial - make up about 80% of cells in the nervous system. several types; one of these is Schwann. Wrap around axon and produce fatty substance = myelin. Serves as insulation (electrical type). Gaps in btw = nodes of Ranvier. Physical support, protection. Help provide appropriate amts of chemicals. DO NOT send impulses. Figure 7.4a–b

Myelin Sheath on Neuron Myelin sheath: Schwann cells in PNS Functions: Saves the neuron energy Speeds up the transmission of impulses Helps damaged or severed axons regenerate Saves energy by preventing leakage of Na, K across membrane. Active transport to reestablish Saltatory conduction impulse jumps from node to node rather than linear transmission across axon. Spreads current without having to undergo membrane changes all along axon membrane. Jumps to next node. Analogy w/ car ride vs. airplane puddle-jumping. Saltare = to dance. Saltimbocca - jump into the mouth Speed of action potential transmission goes from 5 mph to 250 mph. 50X faster. Damaged neurons can regenerate axons thru guide of myelin sheath. Days to months. Disease multiple sclerosis involves scar tissue replacing sheaths. Slows, blocks impulses. Muscle weakness, visual impairment. ALS - amylotrophic lateral sclerosis. Spinal cord sclerosis. So muscles affected first. Resp failure.

Nervous Tissue: Support Cells Oligodendrocytes - protection in CNS Produce myelin sheath around nerve fibers in the central nervous system Flat extensions of these cells wrapped tightly around neurons, produce fatty layer of myelin sheath. In CNS. Demo model. Glial cells are NOT able to transmit nerve impulses. Serve as electrical insulation, much like rubber coating on wires. In brain and spinal cord, sheaths produced by oligod break down if axon dies, so no regeneration of axon occurs. So spinal injuries can be permanent. Glial cells can divide, unlike neurons. So,this ability helps when recovering from nerve damage. Also means that brain tumore are the result of glia dividing, not neurons. Support cells for PNS of two types: Multiple Sclerosis = hardening (sclerosis) of myelin sheaths, interferes with nerve transmission. Each case of MS can differ, dept on which nerves are affected. Autoimmune disease: a protein of the myelin is attacked. Lorenzo’s oil - rare disease in which extra-long fatty acid chains lead to loss of myeliin sheath. Parents try to understand how hid diet affects production of these fatty acids. Myelin sheath part of many other neural diseases. Figure 7.3d

Maintenance of the Resting Membrane Potential Neuron that is not sending a signal. Resting state. Na, K constantly leak down their gradients and at equal rate, are pumped back. More Na outside than K inside, so slight negative charge -70 mV. Size of symbol indicates relative concentration of Na, K. PLAY Press to play Active Transport video Figure 11.4

Neurons Initiate Action Potentials Na-K pump: maintains resting potential Graded potential: alters resting potential, either to depolarize or hyperpolarize Graded potential created by incoming signals from other neurons. They alter the potential of this neuron, either more neg or less neg (in either positive or neg direction). Not all by the same amount = graded. Various quantities. Occur at single sites on neuron. Many (100s) at once. Analogy of waves in pond surface. Lots of pebbles thrown in, each creating its own little ripple that dies away as it travels. Key pt - these can sum up. If large enough, will trigger an action potential.

Resting Membrane Potential, Graded Potentials, and an Action Potential Graded potentials can reach threshold and trigger an action potential Action potential - a sudden reversal of membrane voltage. Temporary. How? Voltage-sensitive ion channels which open when threshold potential is reached. Ions flow into cell, changing electrical potential. Action potential moves down axon membrane. This is the only signal that a neuron can make. ON?OfF. Meaning is contained in where the signal came from and where it goes. 3 parts of action potential, next pg. Figure 11.5

Action Potential Depolarization: sodium moves into the axon Repolarization: potassium moves out of the axon Re-establishment of the resting potential: the normal activity of the sodium-potassium pump 1. When threshold potential is reached, Na channels open and Na flows into cell. Causes reversal of voltage of membrane. From neg to pos, so depolarization. 2, Repolarization; change in voltage causes K channel to open and K diffuses out of cell. Rebalances the voltage. 3. Resting potential - K channels close, a bit slowly so voltage overshoots. Then Na/K pump resets gradients. On/off - same voltage changes each time. Only frequency can vary. From once to 100s per second.

Action Potentials All or none: individual neuron thresholds; when this threshold is reached, it fires Self-propagating: electrical current reaches threshold throughout axon during spread of the action potential Any indl neuron can either fire or not. On /off signal only. All or none. No tag backs: Absolute Refractory period - while Na is moving in, cannot start another action potential. Relative refractory period - while K is moving out of cell. Takes extra strong stimulation to cause another AP. NOT due to lack of Na or K. Only a small fraction is moved w/ each AP. But does prevent AP from traveling in more than one direction. Ie, NO TAG BACKS. Self propagating = depolarization in one area triggers it in adjacent areas. Frequency of firing, target is only other means by which info is communicated.

Summary of Synaptic Transmission How does ON/OFF signal create a graded potential? AP moves Ca ++ into bulb Ca++ causes vesicles to release neurotransmitter 3. Neurotransmitter binds to receptor, causing Na+ channel to open. 4. Na+ flows into cell, creating graded potential how does an electric signal create a graded potential? Ie, an on/off switch becomes a quantitative stimulus. OVERALL, CHANGE OF IMPULSE FROM ELECTRICAL TO CHEMICAL. 1., 2. As in diagram. 3, Note this Na channel is chemically gated, not voltage gated. Switch is now quantitative, not on/off. Na flows into post synaptic cell; amount of Na+ creates graded potential. Graded potential result of neurotransmitter plus chemically sensitive ion channel, (not voltage sensitive as for AP.) Integrate and process info, b/c chemical stimulation is NOT all or none. Quantities of Neurotransmitter make a difference. Only if threshold is reached will neuron trigger AP. Result is ability to screen messages, ignore minor ones. So, to increase stimulus: many neurons send signals to one neuron = convergence. Graded responses add up to AP. OR sgl neuron fires very rapidly to reach threshold. To decrease - use Neurotransmitterthat is inhibitory, counteracts stimulatory Neurotransmitter. Divergence - one neuron stim many other neurons. Muscle cells with only one neuron. All or none response by muscle; must obey neuron, no editing. Also, neuromuscular junction is large, ensures threshold is reached. Figure 11.7

Neurotransmitters Excitatory - depolarize postsynaptic cell. Acetylcholine - muscle cells Norepinephrine - areas of brain and spinal cord ANS Glutamate - major excitatory transmitter in brain Inhibitory - hyperpolarize postsynaptic cell. Serotonin - areas of brain, spinal cord. involved in sleep, appetite, moods Dopamine - brain, parts of PNS. Involved in emotions. Endorphins - brain, spinal cord. Natural opiates that inhibit pain Somatostatin - brain, pancreas. Inhibits pancreatic release of growth hormone. Neurotransmitter can be excitatory; depolarize postsynaptic cell. Ex. acetylcholine on muscle cells, norepinephrine on certain targets Or inhibitory; hyperpolarize postsynaptic cell ex. dopamine on brain cells, serotonin on brain, spinal cord. action of Neurotransmitter depends on receptors in target cells. Fate of Neurotransmitter: taken up again and reused, broken down in synaptic cleft, diffuses away. Drugs can affect by interfering w/ processing of Neurotransmitter. Acetylcholine - communicate with muscle cells, also used by autonomic nervous system Norepinephrine; Serotonin - Usly inhibitory, Dopamine - Glutamate - brain, spinal cord. Major excitatory transmitter in brain endorphins - brain, spinal cord. Natural opiates that inhibit pain G-amino butyric acid = brain, spinal cord. Main inhibitory transmitter in brain Somatostatin -.

Peripheral Nervous System Nerves and ganglia outside the central nervous system Nerve = bundle of neuron fibers Nerves: carry signals to and from CNS Cranial nerves: connect directly to brain Spinal nerves: connect to spinal cord Ganglion - collection of nerve cell bodies OUTSIDE the CNS. Nerve = bundle of neurons. Signals go both ways within one nerve, both afferent and efferent neurons. Wrapped in connective tissue. Each neuron has specific connections, th4 specific info it communicates. Cranial nerves - 12 pairs, connect directly to brain. Receptors for cranial senses, thoracic and abdominal inputs. Outputs to facial muscles and head, thoracic abdominal muscles. Spinal nerves (31 pairs) connect via spinal cord, each vertebra has incoming and outgoing paths. Dorsal root = sensory nerves. Ventral root = motor nerves. So each spinal nerve carries both incvoming and outgoing signals.

The Reflex Arc Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector Crossed extensor reflex, stretch reflex, flexor Reflex – rapid, predictable, and involuntary responses to stimuli Somatic reflexes Activation of skeletal muscles. Here, response to sharp object.= flexor reflex = withdrawal. Input to motor neurons. Note that output goes on 2 sides of efferent nerves, one to each different muscle needed for response. One leg lifts, another straightens for balance. Coordinated response. Called crossed extensor reflex. Does not involve processing by brain before response. Other signal keep brain informed. Stretch reflex - when muscle is stretched, signals trigger a contraction. Opposite muscle is relaxed. Helps with balance, posture. Ex. Pateller reflex. Tests whether spinal cord, brain reflex centers are working. Autonomic reflexes Smooth muscle regulation Heart and blood pressure regulation Regulation of glands Digestive system regulation

Organization of the Nervous System Motor (efferent) division Somatic nervous system = voluntary Autonomic nervous system = involuntary Note that divisions are artificial. System works together. Division is for ease of study. Motor: autonomic w/ 2 types, imprt in maintaining homeostasis among organ systems in body. Voluntary: conscious control of skeletal muscles Involuntary: spinal reflexes; flexor (withdrawal), crossed extensor, stretch The involuntary branch of the nervous system Consists of only motor nerves Divided into two divisions Sympathetic = flight or fight responses Parasympatheitic = return to normal life maintenance Figure 7.2

Differences between Somatic and Autonomic NS Differences include Nerves: Neorotransmitters Effector organs. Somatic one motor neuron Acetylcholine skeletal muscle Autonomic preganglionic and postganglionic nerves use acetylcholine, epinephrine, or norepinephrine smooth muscle, cardiac muscle, and glands

Autonomic Nervous System Sympathetic – “fight-or-flight” “E” division = exercise, excitement, emergency, and embarrassment Autonomic Nervous System Parasympathetic – housekeeping activites Conserves energy necessary body functions “D” division - digestion, defecation, and diuresis Originates from T1 through L2 Ganglia are at the sympathetic trunk (near the spinal cord) Sympathetic: Short pre-ganglionic neuron and long postganglionic neuron transmit impulse from CNS to the effector Norepinephrine and epinephrine are neurotransmitters to the effector organs Parasympathetic Originates from the brain stem and S1 through S4 Terminal ganglia are at the effector organs Always uses acetylcholine as a neurotransmitter Function in opposition. Sympathetic NS will stimulate adrenal glands to release epinephrine and norepinephrine, which continue stimulation of flight or fight response for several minutes. Systems work to balance body systems. Blood pressure (affected by heart rate, blood vessel dilation) Respiration (rate, depth) Digestion Relaxation (eye pupils close down, skin warm, digestion and enzymes) Figure 7.25

Central Nervous System CNS protection Bone: skull and vertebrae Meninges: dura mater, arachnoid, and pia mater Cerebrospinal fluid: carries nutrients and waste for CNS Blood-brain barrier: Spinal cord: relays information through nerve tracts in white matter 3 layers of membranes. Meningitis when infected. Very rare but dangerous. Inflammation puts pressure on brain cells, spinal cord cells. Cbrospinal fluid produced by blood. Secreted only from capillaries within 4 ventricles of brain. Shock absorber. Circulates thru brain and spinal cord. carries nutrients and waste for CNS BB barrier due to tight leakproof cappls. Only lipid soluble molecules get thru membrs. All else must be actively transported. So, alcohol, many drugs, incl cocaine, nicotine, caffeine go thru readily. Many antibiotics do not. Glial cells help screen chemicals, too. In brain, oligodendrocytes.

Spinal Cord Connects PNS to brain; reflex center Extends from the brain to lumbar region 31 pairs of nerves Connector or PNS to brain Also contains neurons for reflexes Spinal cord extends only to T12;, nerves separate below that into “horse tail” before exiting spinal column. Surrounded by meninges, triple layer of membranes. Damage to neurons can immobilze or block sensation from various body parts, depending on where damage occurs. Epidural anesthetic - blocks sensory input in lower half of body during childbirth. Figure 7.18

Spinal Cord Anatomy Exterior white mater – conduction tracts Internal gray matter - mostly cell bodies Central canal filled with cerebrospinal fluid Meninges cover the spinal cord Nerves leave at the level of each vertebrae Dorsal root Associated with the dorsal root ganglia – collections of cell bodies outside the central nervous system Ventral root Figure 7.19

Brain: Major Divisions Hindbrain: coordinates basic, automatic, vital functions Medulla oblongata: controls automatic functions of internal organs Cerebellum: coordinates basic movements Pons: aids flow of information Pons - The bulging center part of the brain stem Mostly composed of fiber tracts Includes nuclei involved in the control of breathing Medulla oblongata - The lowest part of the brain stem Merges into the spinal cord Includes important fiber tracts. Swiftest info flow from left side to rights side, vice-versa. By means of 2 large nerve tracts. Contains important control centers - critical role in maintaining homeostasis of body. Heart rate control Blood pressure regulation Breathing, Swallowing Vomiting - some neurons outside of the blood-brain barrier. Allows chemicals in blood to be detected and trigger vomit response if they are toxic. Cerebelllum - control of basic movements. Such as antagonistic muscles. sequences of skilled movements: stored and recalled w/out thought. Alcohol acts on cerebellum, disrupts balance.

Hindbrain, Midbrain Midbrain: coordinates muscles related to vision & hearing Input from vision, hearing, relays it to other parts of the brain. Controls reflexes of vision, hearing. Conscious muscles, turn towards source of sound, for ex. Controls conscious muscle movement to smooth motion.

Brain: Processes and Acts on Information Forebrain: receives and integrates information concerning emotions and conscious thought Hypothalamus: helps regulate homeostasis Thalamus: receiving, processing, and transfer center Limbic system: neuronal pathways involved in emotions and memory Cerebrum/cerebral cortex: higher functions Hypothalamus: receives input re: vision, smell, taste, noise, body temp. Regulates homeostasis of body temp, water, solute balance (thirst), hunger, carbon metabolism. HYPOTHALAMUS - key role in homeostasis. Important autonomic nervous system center Helps regulate body temperature Controls water balance Regulates metabolism, hormones Thalamus - transfers info onwards. Limbic system - memory, emotions. Set of neuron pathways. Details later. Cerebrum - language, decision making, complex thought. Largest part of brain. cerebral cortex = Outer portion is gray, only 6 mm thick. Contains cell bodies. Inner portion is white = myelinated axons, connections btw various parts of brain.

Specialized Areas of the Cerebrum Cerebrum - 2 large hemispheres. Right and Left. Connected by large tract, corpus callosum. Ridges on surface., some shallow, some deep. Correlation of specific areas with functions. Occipital, temporal, parietal, frontal lobes. Broca’s area – involved in our ability to speak. On one side of the brain only, usly left side. Separate from area which lets us understand language. Frontal lobes - reasoning, social behavior, complex memories. Special senses Gustatory (taste), visual, auditory, olfactory areas Interpretation areas Speech/language region Language comprehension region General interpretation area Somatic sensory area – receives impulses from the body’s sensory receptors, crossed pathways, left goes to right brain, vice versa. Primary motor area – sends impulses to skeletal muscles What is memory? Series of nervous impulses (action potentials) that enable you to recall information. Short term memory is in limbic system; pathway of recently fired neurons easy to re-excite. Long term - cerebrum. Involves physical or chemical change in neurons that make this path more easily activated in the future. Figure 7.13c

Sensory and Motor Areas of the Cerebral Cortex Nerve tract called corpus callusom is the major connection btw R, L cerebrum. Switching of motor control, so that L brain controls R motor nerves. Figure 7.14

Sleep Sleep center: reticular activating system (RAS) Stages: based on electroencephalograms (EEGs) Stage 1-4 RAS = a group of neurons in hindbrain. Releases serotonin, which inhibits activity in neurons of brain. Involves pineal gland. Stage 1: transitional, random small waves on EEG Stage 2: skeletal muscles relax, little eye or body movement, EEG shows sleep spindles Stage 3: heart and respiration slower, EEG shows slow wave sleep Stage 4: difficult to awaken, heart and respiration slowest, body temperature decreased REM (rapid eye movement) Sleep: dreaming, EEG same as awake

Limbic System: Emotions of Fear, Anger, Sorrow, Love Limbic = border b/c forms the base of the cerebrum. Direct connection to sense of smell. Strongest memories often involve smell. Collection involves hypothalamus, thalamus, integrted in cerebrum, controls action on our raw feelings. Hooked up to basic urges of thirst, hunger, and love, emotional pain. Figure 11.18

Psychoactive drugs Affect consciousness, emotions, behavior Cross blood-brain barrier Affect action of neurotransmitters Ex. Cocaine blocks reuptake of dopamine Psychological dependence Tolerance Action: affects higher brain functions Psychological dependence: user craves the feeling associated with the drug Tolerance: takes more of the substance to achieve the same affect Addiction: the need to continue obtaining and using a substance; no free choice Withdrawal: physical symptoms that occur upon stopping the drug

Disorders of the Nervous System Trauma: concussion, stroke, spinal cord injuries Infections: encephalitis, meningitis, rabies Neural and synaptic transmission: epilepsy Parkinson’s disease Alzheimer’s disease Brain tumors - growth of glial cells Concussion Slight brain injury No permanent brain damage Contusion Nervous tissue destruction occurs Nervous tissue does not regenerate Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue = a stroke Due to ruptured blood vessel in the brain Brain tissue dies from lack of oxygen Loss of some functions or death may result Alzheimer’s disease Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons. Theory that transport of materials along axons in the problem. “Plaques and tangles” cause or symptom? Victims experience memory loss, irritability, confusion, appear to lose motor abilities in reverse order of acquisition as infants. and ultimately, hallucinations and death Mostly seen in the elderly, but may begin in middle age.

Alzheimer’s Disease Progressive, degenerative brain disease Structural changes in the brain include abnormal protein deposits and twisted fibers within neurons Parkinson’s - lack of dopamine, such that certain neurons are overactive, cause jerky muscle contractions Progressive degenerative brain disease Parkinson’s - caused by degeneration of dopamine-releasing neurons of the substantia nigra, such that basal nuclei (groups of grey matter within cerebrum that regulate voluntary muscle) no longer get dopamine, become overactive. Result is tremors, other characteristic jerky movements. Treatment - -dopa, deprenyl, embryonic stem cells. Huntingdon’s - degeneration of basal nuclei. Genetic cause. Eventually, degradation of entire cerebral cortex. Opposite of Parkinson’s, as this is overstimulation, not understimulation of muscles. 15 yrs progression to death.

Development Aspects of the Nervous System The nervous system is formed during the first month of embryonic development Any maternal infection can have extremely harmful effects The hypothalamus is one of the last areas of the brain to develop No more neurons are formed after birth, but growth and maturation continues for several years The brain reaches maximum weight as a young adult

Where Do You Stand Among Your Peers? Table 11.3

Cerebrum