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Equine hippocampus 1 The Nervous system. Every living organism must be able to react appropriately to changes in its environment if it is to survive. The nervous system monitors and controls almost every organ system through a series of positive and negative feedback loops. The nervous system consists of brain, nerves and spinal cord. The nervous system pass messages around the body control the body. The brain also controls the senses. Vertebrates have complex sense organs and exhibit complex behaviors. These require a complex nervous system. The vertebrate nervous system is extremely cephalized. The nervous system can be subdivided several ways depending on if one is looking at function or location: In terms of function, Somatic NS voluntary muscles and reflexes vs Autonomic NS visceral/smooth and cardiac muscle Sympathetic NS increases energy expenditure prepares for action Parasympathetic NS decreases energy expenditure gains stored energy these have the opposite effects on the same organs --OR— In terms of location, Peripheral NS vs sensory and motor neurons Central NS (CNS) interneurons: brain and spine covered with three membranes, the meninges inflammation of these is called meningitis brain has gray matter on outside and white in center spine has white matter on outside and gray in center 2 The central nervous system (CNS) is the brain and spinal cord. The peripheral nervous system (PNS) is composed of the nerves and ganglia. Ganglia are clusters of nerve cell bodies outside the CNS. The nervous system consists of two types of cells. Nerve cells are called neurons. The typical neuron is an elongated cell that consists of a cell body, containing the nucleus. Various support cells are associated with the neurons, most typically, Schwann cells. The parts of a neuron include the dendrite which receives the impulse (from another nerve cell or from a sensory organ), the cell body (numbers of which side-by-side form gray matter) where the nucleus is found, and the axon which carries the impulse away from the cell. Wrapped around the axon are the Schwann cells, and the spaces/junctions between Schwann cells are called nodes of Ranvier. Collectively, the Schwann cells make up the myelin sheath (numbers of which side-by-side form white matter). Schwann cells wrap around the axon (like the camp food, “pigs in a blanket”). Having an intact myelin sheath and nodes of Ranvier are critical to proper travel of the nerve impulse. Diseases which destroy the myelin sheath (demyelinating disorders) can cause paralysis or other problems. Schwann cells are analogous to the insulation on electrical wires, and just as electrical wires short out 3 if there’s a problem with the insulation, so also, neurons cannot function properly without intact myelin sheaths. Autonomic Nervous System This part of the nervous system sends signals to the heart, smooth muscle, glands, and all internal organs. It is generally without conscious control. The autonomic nervous system uses two or more motor neurons: 4 The cell body of one of the motor neurons is in the CNS. The cell body of the other one is in a ganglion. Sympathetic Division-The sympathetic nervous system prepares the body to deal with emergency situations. This is often called the "fight or flight" response. Stimulation from sympathetic nerves dilates the pupils, accelerates the heartbeat, increases the breathing rate, and inhibits the digestive tract. The neurotransmitter is norepinephrine. Sympathetic nerves arise from the middle (thoracic-lumbar) portion of the spinal cord. Parasympathetic Division- When there is little stress, the parasympathetic system tends to slow down the overall activity of the body. It causes the pupils to contract, it promotes digestion, and it slows the rate of heartbeat. The neurotransmitter is acetylcholine. The actual rate of stimulus to each organ is determined by the sum of opposing signals from the sympathetic and parasympathetic systems. Parasympathetic nerves arise from the brain and sacral (near the legs) portion of the cord. Enteric Division- The enteric division contains neurons that control the digestive tract, pancreas, and gallbladder. Activity of the enteric division is usually regulated by the sympathetic and parasympathetic divisions. The nervous system has three basic functions: 1. sensory neurons receive information from the sensory receptors, 2. interneurons transfer and interpret impulses, and 3. Motor neurons send appropriate impulses/instructions to the muscles and glands. Meninges CNS is covered by meninges which is made up of three membranes viz. duramater, arachnoid and piamater. Outer most being duramater and innermost piamater with 5 arachnoid in between. Cranial meninges are closely united with endosteum of cranial cavity. Epidural space is the space between spinal meninges and the periosteum. This space is used for epidural anaesthesia. The brain contains fluid-filled ventricles that are continuous with the central canal of the cord. Fluid within the ventricles and central canal originates from the blood. It slowly circulates, carrying nutrients and wastes from cells. The fluid eventually returns to the circulatory system and is replaced by fresh fluid. Brain- it is enclosed in cranial part of skull. During embryonic development, the brain first forms as a tube, the anterior end of which enlarges into three hollow swellings that form the brain, and the posterior of which develops into the spinal cord. Brain can de divided: three different ways to sub-divide the brain. 1) Embryonic division; telen- , dien-, mesen-, meten-, myelin- cephalon. 2) Gross anatomy divisions; cerebrum, cerebellum (part of meten-), brain stem (dien-, mesen-, pons, myelin- cephalon.). 3) Clinically useful divisions; forebrain (telen-, dien- cephalon), hind brain (meten- and myelin- cephalon). But for our better understanding the Brain is divided into forebrain, midbrain and hindbrain. 1) Forebrain is made up of cerebrum, mammillary body, pineal body, thalamus and hypothalamus. 2) Midbrain consists of a small area that serves as a connection between forebrain and hindbrain. 3) Hindbrain consists of medulla oblongata, pons and cerebellum. Convoluted part of brain is called gyrus and the depression between gyri is called fissure. 6 Parts of the brain as seen from the middle of the brain. Brain stem Medulla Oblongata 7 Arachnoid Longitudinal fissure Cerebral hemisphere Forebrain 1) Thalamus- Like the midbrain of mammals, the thalamus serves as a relay area to the cerebrum from other parts of the spinal cord and brain. For example, it receives sensory input (except smell) and sends to appropriate areas of the cerebral cortex. The Thalamus contains part of the reticular formation (see below). Reticular Formation- The reticular formation is a net of nerve cells extending from the thalamus through the brain stem (midbrain, pons and medulla oblongata) to the spinal cord. It acts as a filter to incoming stimuli and discriminates important from unimportant. Hundreds of millions of sensory receptors flood the brain; the brain does not have the capacity to deal with even a small fraction of this information, so much of it must be ignored. The reticular activating system (RAS) is the part of the reticular formation that controls wakefulness. 8 Sleep centers are located in the reticular formation. Neurons in one sleep center secrete serotonin, a chemical that inhibits the RAS and thus causes drowsiness and sleep. Another sleep center secretes factors that counteract serotonin and bring about wakefulness. Damage to these centers can lead to unconsciousness or coma. 2) Hypothalamus- The hypothalamus regulates the endocrine system by controlling the secretions of the pituitary gland or by producing some of the hormones that are secreted by the pituitary. These hormones affect the body or affect other glands in the body. Their overall affect is to maintain homeostasis. The hypothalamus also contains neurons associated with the limbic system (below). Limbic System- The limbic system contains neural pathways that connect portions of the cortex, thalamus, hypothalamus, and basal nuclei (several areas deep within the cerebrum). It causes pleasant or unpleasant feelings about experiences (rage, pain, pleasure, sorrow). This helps guide the individual into appropriate behavior that is more likely to be beneficial. 3) Cerebrum- the largest part of the brain is divided into left and right hemispheres. The hemispheres are covered by a thin layer of gray matter known as the cerebral cortex and it is divided into four lobes: occipital, temporal, parietal, and frontal lobes. Figure below show lobes of cerebrum. The cerebrum became greatly enlarged as evolution progressed from the 9 earliest vertebrates to mammals. In reptiles and mammals, it receives sensory information and coordinates motor responses. Motor responses to the skeletal muscles originate in the cerebrum but are refined and coordinated by the cerebellum. Olfactory Bulbs- The anterior parts of the cerebral hemispheres are called the olfactory bulbs. It receives input from the olfactory nerves (smell). The olfactory bulbs of primitive vertebrates comprise a large proportion of the cerebrum. Cerebral Cortex- Over evolutionary time, gray matter developed over the cerebrum. This is the cerebral cortex and it is an information-processing center. It increased in size more rapidly than the skull so that it has become folded (convoluted) in order to fit in the skull. Intelligence, emotion, creativity, learning, and memory are localized in the cerebral cortex. Lobes of the cerebral cortex The cerebral cortex is divided into four lobes; each receives information from particular senses and processes the information into higher levels of consciousness. Lobe Frontal Function motor functions; permits conscious control of skeletal muscles; contains the primary motor cortex conscious thought Parietal sensory areas from the skin; contains the primary sensory cortex Occipital The primary visual cortex is located within the occipital lobe. Temporal hearing and smell Primary Sensory and Primary Motor Cortex- The primary sensory cortex is a narrow band of cortex tissue that extends from one side of the cortex near the ear over the top of the brain to the other side. Information from sensory receptors in the skin arrives at this area. The motor cortex is a band of cortex tissue directly anterior (in front) of the primary sensory cortex. Signals that control the skeletal muscles originate in this area. 10 Corpus Callosum- The corpus callosum contains neurons that cross from one side of the brain to the other, allowing each half to communicate with each other. Corpus callosum Hindbrain 1. Medulla oblongata- The medulla controls vital functions such as breathing, heart rate, and blood pressure. It also contains reflexes such as vomiting, coughing, sneezing, hiccupping, swallowing, and digestion. Information that passes between the spinal cord and the rest of the brain must pass through the medulla. In the medulla, sensory and motor axons on the right side cross to the left side and axons on the left side cross to the right side. As a result, stimuli passing through from the left side of the body are sent to the right side of the brain and signals passing through from the right side of the brain stimulate the left side of the body. 2. Cerebellum- The cerebellum coordinates and refines complex muscle movements. Movement information that is initiated in higher brain centers 11 (the cerebral cortex) is compared to the actual position of the limbs. The cerebellum then adjusts and refines the movement. It is large in birds because flight requires considerable coordination. 3. Pons- The pons is involved in some of the same activities as the medulla. For example, it assists the medulla in controlling breathing. The pons functions as a connection between higher brain regions, the cerebellum, and the spinal cord. Midbrain The midbrain receives some sensory information and sends it to the appropriate part of the forebrain. The midbrain originally functioned for reflexes associated with visual input. It is the most prominent part of the brain in fishes and amphibians and has major control of the body. The midbrain of reptiles and mammals controls visual reflexes such as the pupil response to light intensity but the forebrain of these vertebrates processes the visual information (see diagram below). The midbrain also controls some auditory reflexes and helps control posture. 12 Brainstem The medulla oblongata, pons, and midbrain look like the spinal cord and appear to connect the rest of the brain to the spinal cord. They are collectively referred to as the brainstem. Summary of Brain Structure Brain Structure Function Vital functions such as breathing, heart rate, and blood pressure Medulla oblongata Reflexes such as vomiting, coughing, sneezing, hiccupping, swallowing, and digestion Neurons cross Pons Breathing, connects spinal cord, cerebellum and higher brain centers Cerebellum Motor coordination Receives visual, auditory, and tactile information Midbrain In mammals, this information is sent to the thalamus and higher brain centers. In lower vertebrates, the information is further 13 processed in the midbrain. Thalamus Hypothalamus Cerebrum Relays sensory information to the cerebral cortex. Contains part of the reticular formation (controls arousal). Maintains homeostasis, regulates the endocrine system Contains part of the Limbic system (controls emotion) Processes sensory information and produces signals that move the skeletal muscles. This is the outer layer of the cerebrum. Cerebral Cortex Thinking, intelligence, and cognitive functions are located here. Processing of sensory information and motor responses Spinal cord The spinal cord runs along the dorsal side of the body and links the brain to the rest of the body. Vertebrates have their spinal cords encased in a series of (usually) bony vertebrae that comprise the vertebral column. The gray matter of the spinal cord consists mostly of cell bodies and dendrites. The surrounding white matter is made up of bundles of interneuronal axons (tracts). Some tracts are ascending (carrying messages to the brain), others are descending (carrying messages from the brain). The spinal cord is also involved in reflexes that do not immediately involve the brain. Function of spinal cord is summarized below. Spinal Cord the spinal cord receives information from skin, joints, and muscles sends back signals for both voluntary and reflex movements transmits signals from internal organs to the brain and from the brain to internal organs connects the brain to peripheral organs and tissue in addition, the spinal cord contains ascending pathways through which sensory information 14 reaches the brain descending pathways that relay motor commands from the brain to motor neurons 15 The Spinal Cord-The vertebrae surround and protect the spinal cord. Cerebrospinal fluid within the central canal functions to cushion the spinal cord. Many sensory - motor reflex connections are in the spinal cord. Interneurons often lie between sensory and motor neurons. White matter- White matter contains tracts that connect the brain and the spinal cord. The white colour is due to the myelin sheaths. Gray matter- Gray matter looks gray because it is unmyelinated. It contains the short interneurons that connect many sensory and motor neurons. Sensory neurons enter the gray matter and the axons of motor neurons leave the gray matter. The cell bodies of these motor neurons are located in the gray mater. Piamater White mater Gray mater T/S: spinal cord of mammalian Peripheral nervous system (PNS) PNS are made up of cranial nerves, spinal nerves and autonomic nervous system. Each of this is described on their function as below: Nerve 16 A nerve is an enclosed, cable-like bundle of nerve fibers or axons. Based on its origin a nerve can be cranial or spinal. Cranial nerves originate from the brainstem, and mainly control the functions of the anatomic structures of the head. There are 12 pairs of cranial nerves that originate from various parts of brain and supply different sense organs in head. Number Name Function I Olfactory Nerve Smell II Optic Nerve Vision III Oculomotor Nerve Eye movement; pupil dilation IV Trochlear Nerve Eye movement V Trigeminal Nerve Somatosensory information (touch, pain) from the face and head; muscles for chewing. VI Abducens Nerve Eye movement VII Facial Nerve Taste (anterior 2/3 of tongue); somatosensory information from ear; controls muscles used in facial expression. VIII Vestibulocochlear Nerve Hearing; balance IX Glossopharyngeal Nerve Taste (posterior 1/3 of tongue); Somatosensory information from tongue, tonsil, pharynx; controls some muscles used in swallowing. X Vagus Nerve Sensory, motor and autonomic functions of viscera (glands, digestion, heart rate) 17 XI Spinal Accessory Nerve Controls muscles used in head movement. XII Hypoglossal Nerve Controls muscles of to tongue Spinal Nerves Spinal nerves take their origins from the spinal cord. They control the functions of the rest of the body. In cattle, there are 37 to 39 pairs of spinal nerves: 8 cervical, 13 thoracic, 6 lumbar, 5 sacral and 5 -7 coccygeal. The naming convention for spinal nerves is to name it after the vertebra immediately above it. Thus the fourth thoracic nerve originates just below the fourth thoracic vertebra. This convention breaks down in the cervical spine. The first spinal nerve originates above the first cervical vertebra and is called C1. This continues down to the last cervical spinal nerve, C8. There are only 7 cervical vertabra and 8 cervical spinal nerves. Spinal nerve is made up of dorsal and ventral root and its branches. Dorsal root emerges from dorsal portion of spinal cord and carries afferent (sensory) impulses to the spinal cord from peripheral parts of body. Ventral root emerges from the ventral part of spinal cord and carries efferent (motor) impulses from spinal cord to the effector (muscles). Figure below show components of spinal nerve. Functional unit Neuron or a nerve cell is an anatomic and physiologic unit of nervous system. It is made up of cell body and processes dendrites and axon. A process is called dendrite if it carries impulse towards cell body and an axon if it carry impulses out of cell body. Axon is called nerve fiber and membrane covering the axon is called axolemma. In a myelinated axon axolemma is surrounded by myelin sheath called neurilemma, at regular interval there is myelin free gaps called nodes of Ranvier that facilate faster conduction of impulses. A group of nerve cell bodies in CNS (brain and spinal cord) is called nucleus while group of nerve cell bodies outside CNS is called ganglion. Bundle of neuron fibers within the CNS is called a tract while bundle of neuron fibers outside CNS is called nerve. Figure below show the neuron. 18 Cell body Dendrites Axon Myelin sheath Node of Ranvier Terminal bulb Figure A Figure B Amyelinated (A) and Myelinated (B) neurons Synapse Junction between two nerve terminals is called synapse. There is no physical contact between the neurons instead there is space in between, across which impulse is conducted through chemicals. Impulse conduction For effective conduction of nerve impulse there are three stages viz. resting potential, depolarization and repolarization. Membrane Potentials Membrane potentials were first demonstrated using the giant axons of a squid (1mm dia). An oscilloscope measured the electrical difference by placing one electrode outside the neuron and the other inside the neuron. Resting potential The sodium-potassium pump pumps out 3 sodium ions (Na+) for each 2 potassium ions (K+) pumped into the neuron. This results in more potassium ions inside and more sodium ions on the outside. 19 Unequal pumping (3 Na+ out to 2K+ in) results in more positive charge on the outside compared to the inside. The membrane is polarized. Some K+ channels are open so K+ tends to leak out. This contributes to the negative charge inside. The charge difference prevents further leakage. The charge difference is measured in millivolts. Gated Channels The membrane contains channels that open or closes, allowing the polarity of the membrane to change as ions pass through the channel. Ligand-gated channels are found in the synapses on postsynaptic cells. They open when bound to specific ligands (molecules or ions) such as specific neurotransmitters. 20 Voltage-gated channels open when the membrane becomes depolarized. For example, sodium gates open and then close slowly when the membrane is depolarized but remain closed when it is polarized. When the sodium channel is open, sodium can pass through. In a resting (polarized) neuron, sodium gates are closed. A slight depolarization will not cause the gates to open but if the depolarization is greater than a threshold value, the gates will open. Propagation of an Action Potential Stimulation of the neuron causes Na+ gates open allowing Na+ to rush in. This results in depolarization of the membrane in the area where the stimulation occurred. Depolarization of an area of membrane stimulates more Na+ gates in adjacent areas to open, thus spreading the depolarization. Immediately after depolarization, then Na+ ions channels close and K+ channels open causing K+ to flow out. This process returns positive charge to the area just outside the membrane, thus restoring the resting polarity. The depolarization and repolarization events described above are called an action potential. During an action potential, the depolarization spreads all the way to the 21 action terminal where the axon joins another cell. The action potential is "all or nothing." The intensity of an action potential does not diminish as it spreads along an axon. The sodium-potassium pump operates continuously to restore the ionic gradient. In the diagram below, depolarization caused by the influx of sodium can be seen spreading to the right. 22 Refractory Period The action potential cannot reverse its direction because membrane that has just been depolarized cannot be depolarized again until after a brief recovery (called refractory) period. During this period, the membrane is insensitive to stimulation. The diagram below shows the voltage difference across the membrane as an action potential proceeds. Initially, the inside of the membrane is approximately -65 or 70 millivolts compared to the outside. When sodium gates open and sodium ions rush in, the inside temporarily becomes positively charged. Potassium gates then open and potassium ions rush out, restoring the negative charge. 23 Most action potentials last a few milliseconds and there may be as many as several hundred action potentials per second. Saltatory Conduction The gap between the Schwann cells in the myelin sheath is called a node of Ranvier. Gated channels are concentrated in this area and not in the area under the myelin sheath. The action potentials jump from node to node (saltatory conduction). This increases the speed at which a neuron can conduct a signal. Sodium-potassium pumps require a substantial amount of energy to pump the ions, so the presence of insulation reduces the amount of membrane that requires active sodium-potassium pumps, thus saving energy. The diameter of the neuron also is related to the speed of conduction. Larger diameter axons conduct faster. Synaptic Potentials Synapses A synapse is a junction between a neuron and another cell. It is separated by a synaptic cleft. In most synapses, the axon terminal of the presynaptic cell contains numerous synaptic vesicles with neurotransmitter stored within them. The action potential causes calcium channels to open in the plasma membrane of the presynaptic cell. The calcium ions (Ca++) diffuse into the neuron and activate enzymes, which in turn, promote fusion of the neurotransmitter vesicles with the plasma membrane. This process releases neurotransmitter into the synaptic cleft. Neurotransmitter molecules diffuse across the cleft and stimulate the postsynaptic cell, causing Na+ channels to open. Depolarization of the postsynaptic cell results. The depolarization of the postsynaptic cell is referred to as a synaptic potential. The magnitude of a synaptic potential depends on: 24 The amount of neurotransmitter The electrical state of the postsynaptic cell. If it is already partially depolarized, an action potential can be produced with less stimulation by neurotransmitters. If it is hyperpolarized, it will require more stimulation than normal to produce an action potential. After the neurotransmitter is released into the synaptic cleft, it must be quickly removed or inactivated to prevent the postsynaptic cell from being continuously stimulated and to allow another synaptic potential. In some cases there may be enzymes present in the synaptic cleft that break down the neurotransmitter immediately. For example, acetylcholinesterase breaks down the neurotransmitter acetylcholine. In other cases, the axon terminal may reabsorb neurotransmitter and repackage it into vesicles for reuse. Excitatory and inhibitory postsynaptic potentials - A synaptic potential can be excitatory (they depolarize) or inhibitory (they polarize). Some neurotransmitters depolarize and others polarize. There are more than 50 different neurotransmitters. In the brain and spinal cord, hundreds of excitatory potentials may be needed before a postsynaptic cell responds with an action potential. Synaptic integration- Synaptic integration is the combining of excitatory and inhibitory signals acting on adjacent membrane regions of a neuron. In order for an action potential to occur, the sum of excitatory and inhibitory postsynaptic potentials must be greater than a threshold value. 25 Synapses closest to the trigger zone will have the greatest influence. Temporal and Spatial Summation The effect of more than one synaptic potential arriving at a neuron is additive if the time span between the stimuli is short. This is called temporal summation. The summation effect is greatest when the time interval between stimuli is very short. The effect of more than one synaptic potential arriving at a given region of a neuron can also be additive. This is called spatial summation. The summing effect is greater if multiple stimuli all arrive at nearby areas of a membrane. The effect is less if they stimulate separate, distant areas. Direction of Impulse 1 Figure sowing the direction of impulse and synapse 26 Autonomic nervous system (ANS) The organs (the "viscera") of our body, such as the heart, stomach and intestines, are regulated by a part of the nervous system called the autonomic nervous system (ANS). The ANS is part of the peripheral nervous system and it controls many organs and muscles within the body. In most situations, we are unaware of the workings of the ANS because it functions in an involuntary, reflexive manner. For example, we do not notice when blood vessels change size or when our heart beats faster. The ANS is most important in two situations: 1. In emergencies that cause stress and require us to "fight" or take "flight" (run away) and 2. In nonemergencies that allow us to "rest" and "digest" The ANS regulates: Muscles o in the skin (around hair follicles; smooth muscle) o around blood vessels (smooth muscle) o in the eye (the iris; smooth muscle) o in the stomach, intestines and bladder (smooth muscle) o of the heart (cardiac muscle) Glands . The ANS is divided into two parts: The sympathetic nervous system The parasympathetic nervous system 27 The autonomic nervous system is responsible for controlling involuntary muscular and metabolic activities within the body such as heart rate, peristalsis, vascular constriction and dilation, etc. Different emotional states can have a direct impact on the types of changes that are exerted by the ANS at any particular time. The sympathetic system, which originates from ganglia outside the thoracic and lumbar regions of the spinal cord, is responsible for exciting the various systems in the body in what is often called the "fight or flight" response. The parasympathetic system, on the other hand, is responsible for maintaining routine metabolic functions and quieting the body after being stimulated by the sympathetic system. The two systems work antagonistically and are functioning at all times 28 The sympathetic nervous system It is a nice, sunny day...you are taking a nice walk to Gomchen’s restaurant. Suddenly, an angry bear appears in your path. Do you stay and fight OR do you turn and run away? These are "Fight or Flight" responses. In these types of situations, your sympathetic nervous system is called into action - it uses energy - your blood pressure increases, your heart beats faster, and digestion slows down. Notice in the picture below that the sympathetic nervous system originates in the spinal cord. Specifically, the cell bodies of the first neuron (the preganglionic neuron) are located in the thoracic and lumbar spinal cord. Axons from these neurons project to a chain of ganglia located near the spinal cord. In most cases, this neuron makes a synapse with another neuron (post-ganglionic neuron) in the ganglion. A few preganglionic neurons go to other ganglia outside of the sympathetic chain and synapse there. The post-ganglionic neuron then projects to the "target" - either a muscle or a gland. Two more facts about the sympathetic nervous system: the synapse in the sympathetic ganglion uses acetylcholine as a neurotransmitter; the synapse of the post-ganglionic neuron with the target organ uses the neurotransmitter called norepinephrin The parasympathetic nervous system It is a nice, sunny day...you decided to listen to your favourite music and lie on your bed and relax. This calls for "Rest and Digest" responses. Now is the time for the parasympathetic nervous system to work to save energy - your blood pressure decreases, your heart beats slower, and digestion can start. Notice in the picture below, that the cell bodies of the parasympathetic nervous system are located in the spinal cord (sacral region) and in the medulla. In the medulla, the cranial nerves III, VII, IX and X form the preganglionic parasympathetic fibers. The preganglionic fiber from the medulla or spinal cord projects to ganglia very close to the target organ and makes a synapse. This synapse uses the neurotransmitter called acetylcholine. From this ganglion, the post-ganglionic neuron projects to the target organ and uses acetylcholine again at its terminal. Here is a summary of some of the effects of sympathetic and parasympathetic stimulation. Notice that effects are generally in opposition to each other. 29 The Autonomic Nervous System Structure Sympathetic Stimulation Parasympathetic Stimulation Iris (eye muscle) Pupil Dilation Pupil Constriction Salivary Glands Saliva production reduced Saliva production increased Oral/Nasal Mucosa Mucus production reduced Mucus production increased Heart Heart rate and force increased Heart rate and force decreased Lung Bronchial muscle relaxed Bronchial muscle contracted Stomach Peristalsis reduced Gastric juice secreted; motility increased Structure Sympathetic Stimulation Parasympathetic Stimulation Small Intestine Motility reduced Digestion increased Large Intestine Motility reduced Secretions and motility increased Liver Increased conversion of glycogen to glucose Conversion of glucose into glycogen Kidney Decreased urine secretion Increased urine secretion Adrenal medulla Norepinephrine and epinephrine secreted No hormone secreted Bladder Wall relaxed Sphincter closed Wall contracted Sphincter relaxed Senses Input to the nervous system is in the form of our five senses: pain, vision, taste, smell, and hearing. Vision, taste, smell, and hearing input are the special senses. Pain, temperature, and pressure are known as somatic senses. Sensory input begins with sensors that react to stimuli in the form of energy that is transmitted into an action potential and sent to the CNS. Ear, eye, nose, skin and tongue are the five senses of organs. References 1) http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Nervous %20System/nervous1.htm 2) Notes for Diploma (by Dr. Penjor and Nidup) 3) http://images.google.com/imgres?imgurl=http://www.fao.org/docrep/T0690E/t0690e05.gif&imgre furl=http://www.fao.org/docrep/T0690E/t0690e04.htm&h=317&w=412&sz=4&hl=en&start=6&u m=1&tbnid=Zte8D7dY6_GG8M:&tbnh=96&tbnw=125&prev=/images%3Fq%3Dthe 30