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Vertebrate Nervous System Vertebrate Nervous System Synthesis Most complex, Rules over everything Functions are explained in a large part by the nervous system Set of parts that is responsible for nervous coordination and regulation of the different metabolic and physiological processes in your body Central processing or higher processing of the different things or stimuli from the environment Accessory functions that we don’t talk about often, we just think of nerve cells There are other types of cells that have a very impt role in the vertebrate nervous system like nerve cells of coordination but have other functions Divisions Central Nervous System (CNS) brain spinal cord centers for higher processing of nerve signals particularly the brain for that function Peripheral Nervous System (PNS) everything else, all nerves spinal nerves cranial nerves emerging from central nervous system With exception of the two: Optic nerves one of the cranial nerves, Part of the Peripheral Nervous system but considered to be still part of central nervous system Still covered in same meninges or layers that cover the brain Types of Cells Neurons Transmit nerve impulses Nerve cell body called perikaryon sometimes the soma where you have the nucleus Two sets of extensions: Axon - larger extension, pass on message to succeeding neurons Dendrites – much shorter but much more numerous, emerging directly from the cell body, receives impulses from preceding nerve cells, dendro means In some cases neurons may have neurosecretory (endocrine) serve like a gland, there are some neural cells/neurons that act as endocrine glands secretes products directly to the blood stream In the brain particularly the central nervous system you have a lot of cells that are neurons yet they produce hormones particularly the seratonin dopamin adrenalin oxytoxin collectively called neurotransmitters adrenalin epinephrine seratonin Aside from neurons Neuroglial cells (glia) Do not transmit impulses Other types of cells without neural function Astrocytes: look like stars, pass nutrients between blood capillaries and neurons Part of blood brain barrier – series of cells tissues that prevent blood and bacteria from leaking into cerebrospinal fluid, once you have bacteria that’s sepsis already and lead to very serious conditions Also pass nutrients between blood capillaries and neurons There’s a barrier against glycophilic substances, bacteria preventing from flowing from blood to csf via tight junctions of the cells Certain substances are allowed – Semi-permeability typical of cell membranes Nutrients are allowed Deposit or deliver inflammatory signals in cases where there is damage to part of the nervous system, to facilitate the immuno response, inflammation is a response Very important Microglia: engulf foreign material and bacteria, feeding on them, phagocytic elements of the nervous system Oligodendroglia/Schwann cells: insulate axons of nerve cells/ neurons, Axons have to be insulated, long extension of the nerve cell Axon acts like a wire carries electrical signals Nerve signals are electrical in nature, except in the part where they have to cross the synaptic gap in this case they are chemical in nature but while inside a neuron nerve signals are electrical in nature, if don’t have insulating agent electricity will difuse will not be able to travel from one part to the other, insulation keeps electric signal in place Myelin sheath – made of either schwann cells or oligodendroglia found in central nervous system Nerves cells in central nervous system axons of these nerve cells are wrapped in oligodendroglial cells Neurons in the peripheral nervous systems their axons are wrapped in Schwann cells Keep electric signal in place, nerves work on electric signals Same in terms of function Mechanism or machine that has an interface with nervous system Ependymal cells: line the central canal of brain and spinal cord When you dissect brain and spinal cord there’s a central canal or cavity joining to which the csf flows, lining that central canal are ependymal cells which are epithelial cells, they also function in producing the csf Neuron Soma or perikaryon, Line extensions of dendrites which receive nerve impulses from receding neurons and then signal transported via axon, insulated by myelin sheath, oligodendroglia if in cns or schwann cells if in pns, nerve signal transfer along the terminal regions of the axon, have to jump a space because the axon terminal buttons of the preceding neurons and dendrites of the succeeding neurons are not connected to each other, there’s a space between them, the signals has to pass and cross, cannot cross signal in the form of electric signal cause brain will be fried by the electricity has to be converted into a chemical signal first Neurotransmitters – nerve signals converted into chemicals/hormones, responsible for Serotonin – calming hormone, feel calm Oxytoxin - hugging hormone Endorphins – feeling of elation Astrocyte Have very extensive networks coming from astrocyte cell body these extensions provide the bridge between capillaries and neurons to exchange nutrients or other important products like inflammatory signal proteins Prevent passing on of materials that shouldn’t be passed off like bacteria lipids or larger substances like proteins Canal central canal of the spinal cord Ependymal cells lining Astrocytes not responsible only for transmitting nutrients but also inflammatory signals and neurotrophic and protective factor Important cell for normal functioning of the nervous system Without astrocytes you would have significant damage to your functions Microglia – phagocytosis Resting microglia and fully activated microglia Signals from damaged neurons are cascading into the interstitial fluid that initiates series of processes which includes astrocytes releasing inflammatory cells Information Transmission Electric signals Nerve impulses along plasma membranes of neurons Electrical in nature until they cross the synapse Action potential driving of nerve signal all or none nature, threshold that must be reached, when switch is off position light is closed Chemical signals Generated at synapses - gap between axon of preceding neuron and dendrites of the succeeding neuron Neurotransmitters – come in not all emotional Electrical signal converted into chemical signal carried by vesicles from one neuron to another, carrying electrical signal in the form of chemical Neurotransmitters have particular functions Regulatory mechanisms with regard to body temperature breathing, emotions Peripheral Nervous System Somatic vs. Visceral Distinction when talk about reflex arcs Somatic nerves found in muslce particularly skeletal muscle ones you can control Visceral nerves are found in the viscera smooth muscle parts of the body that you can’t actually move like the internal organs Afferent (sensory - dorsal) vs Efferent (motor - ventral) Roots of a nerve A particular nerve coming from the spinal cord would have an Afferent and Efferent root Afferent neuron – transmits nerve impulses toward the central nervous system Efferent – transmits signals from central nervous system to effector organ Receptor organ– body part that receives signal from particular part of the body whether muscle bundle of nerves, have both sensory and motor neurons Central nervous system bring response back to the organ Effector organ – organ that responds to the signal, neuron is the motor or efferent neuron Muscular system – fishes have a horizontal septum and spinal cord of the fish have a nerve there and there are two rami dorsal ramus supplying the hypaxial body mass ventral ramus supply the ventral body mass General vs Special Some nerves are very general for example vagus nerve supplies many diff. parts of the body from head to toe Has sensory and motor functions Receiving impulses and motor transmiting the response signal Autonomic Nervous System (ANS) Part of the PNS which you can’t regulate Sympathetic and Parasympathetic nervous system Independent of control Fight or flight response Adrenalin driven responses of the body governed by this Spinal Nerves Number sequentialy and named after vertebral section (Cervical vertebrae nerves C1 C2 C3,Thoracisc, Lumbar,Sacral) Dorsal afferent root or sensory root, ventral efferent root or motor root coming from the spinal chord Associated with ganglia which is diff. from the brain (just collection/masses of peripheral nerves) Brain is a true organ, we have several ganglia Responsible for a lot of diff. nervous processes Viscera reflex arch or autonomic reflex arch – ganglia sites of connection between primary motor neuron and secondary motor neuron before motor responds or motor signal is transferred to effector organ, sort of meeting place between successive neurons Cranial Nerves Emerging from the brain, already part of the peripheral nervous system or optic nerve but are found in the head region, not coming from the spine May be visceral/somatic, sensory/motor, general/special Terminal (0) – sensory (olfactory) zeroth nerve cause it’s the first nerve, not present in all vertebrates, prominent in fishes appearance is controversial in mammals, serves as sensory function, particularly for olfactory signals Olfactory (I) – sensory (olfactory), purely sensory nerve, for receiving signals from the outside environment Optic (II) – not a true nerve, controversial as well, for visual signals, still part of the central nervous system, covered in the same layers that normally cover the brain Oculomotor (III) – motor (extrinsic eye muscles), a lot of eye muscles, actual response of the body, if brain is intact you can see Trochlear (IV) – motor (extrinsic eye muscles), thin and found at the sides of the brain Trigeminal (V) – sensory & motor (skin of head, teeth, jaws), large 5th nerve, supplies and innervates the skin of the head, teeth and jaws Abducens (VI) – motor (extrinsic eye muscles), small thin tendency to remove them accidentaly, infront of the medulla oblungata Facial (VII) – sensory (taste buds) & motor (2nd hyoid arch) Auditory (VIII) – aka vestibulocochlear; sensory (inner ear) hearing Glossopharyngeal (IX) – sensory (taste buds, gill pouches) & motor (3rd hyoid arch) Vagus (X) – sensory & motor (mouth, pharynx, viscera) Spinal Accessory (XI) – motor (mastoids, trapezius) Hypoglossal (XII) – motor (hyoid and tongue muscles) below tongue Telencephalon and Diencephalon both part of the forebrain/procencephalon Mesencephalon – middle Metencephalon – hindbrain Myelencephalon Cerebral peduncle – where you have oculomotor nerve Pons – you can see abducens here in the actual ventral surfaces Trochlear thin nerves emerging at the side Trigeminal Nerve Facial Auditory Glossopharyngeal spinal accessory and hypoglossal - succeeding nerves which are the smallest Spinal Reflexes (knee jerk response tendon of patella, hitting a bundle of nerves in quadriceps) When have nerve signals transmitted but the brain is not involved In normal responses brain is involved, reflex arc is faster When touch a hot object Still goes to the Central Nervous System but only till spinal chord, signal still go to brain but after effector muscle relax, late notice by the brain Somatic relfex arcs Usually involve three neurons (sensory, interneuron,motor) for skeletal muscles, jerking hand away from hot Visceral reflex arcs Usually involve four neurons (sensory, interneuron between bridging the two, two motor neurons: preganglionic and postganglionic) Peristaltic motion Ganglia meeting of 1 primary motor neuron and secondary motor neuron Primary and secondary meet at a ganglion Primary pre ganglionic going into the ganglion Second motor neuron is the postganglionic coming from ganglion going to the effector, not as fast, no control, can’t be regulated by the body Ganglion – meeting or cluster, between motor and motor Stimulus is received by the receptor organ which is the muscles of the hand palm muscle, sensory neuron or afferent dorsal neuron is activated by the signal go to the dorsal root then go into the spinal cord, sensation is eventually relayed to the brain after the effector muscles did the act Butterfly shape in spinal cord dorsal wings are for sensory the ventral wings are for motor Sensory signal being processed very quickly by the spinal cord Motor response is transferred by the ventral or efferent root into the effector organ, in this case the effector is the biceps Viscera Basic difference addition of motor neuron have a second one, postganglionic and preganglionic axon Reflexes that body goes through that you can see are somatic, don’t see the viscera Knee jerk response reaction When you tap the tendon of the patella you strike a bundle of nerves in the quadriceps thus the receptor organ then signal will travel via the afferent then to the interneuron then to the efferent into the hamstrings and quadriceps but a separate set of interneurons affect the hamstrings, not a direct effect but makes or blocks signals going into the hamstrings so that it will stay relaxed, when hamstrings are contracted your leg is flexed A knee jerk stretches its leg against your will same time that the motor or efferent root At the same time that the motor or efferent root is stimulating the quadriceps to extend the length set of interneurons is blocking nerve signals toward the hamstrings so that they relax thus causing the leg to move forward not just as simple as 1 muscle is just being affected, other muscles are also being affected Autonomic Nervous System Sympathetic nervous system Adrenaline rush – during certain circumstances something will drive you to exert more effort Such processes are generally stimulatory for instance burst of strength Thoracolumbar as you can see the sympathetic nervous system branches are found in the thorax and lumbar area Adrenergic the primary hormone or neurotransmitter responsible for a lot of the functions is Adrenalin or epinephrine Stimilatory functions like speeding of the heart rate Fight or flight response when facing the threat to yourself, pumped up with adrenaline, flight is for survival Relaxation of the digestive muscles Parasymphathetic nervous system Generally inhibitory/resting Craniosacral cervical and sacral Cholinergic primary neurotransmitter is acetyl cholin Certain functions that are stimulatory What one does the other one does the opposite of Central Nervous System Spinal Cord Brain Origins Meninges – mostly ectodermal (dura mater) Layer that covers the central nervous system for protection Mostly ectodermal have the Dura mater Pia mater and Arachnoid mater Mater means mother Pia is gentleman Arachnoid means spiderlike Dura mater Pia Arachnoid Only the dura mater is not from dermal because it comes from the mesoderm and its outermost Pia and arachnoid are ectodermal (neural plate) Spinal cord and brain – ectodermal (neural plate) How parts of the nervous system are formed Invagination above the notochord forms first from mesodermal conglomeration Invagination to create the neural plate that is ectoderm Eventually, there will be a paging off to create a tube made of ectoderm which becomes the spinal cord Meninges and Cerebrospinal Fluid For protection of spinal cord and brain In fishes, only one primary meninx In tetrapods, with secondary meninx (arachnoid and pia mater, primary meninx is dura mater) Cerebrospinal Fluid (CSF) Common medium that doctor gets for diagnosis Detect various pathogens for example when you have meningitis When CSF swelling under the arachnoid Protection of the spinal cord Produt of choroid plexus (blood vessels) associated with ependymal cells This tells me that they are like lymph, excess tissue fluid, produced by hydrostatic pressure from blood vessels Has a high rate of producing For cushioning of spinal cord and brain watery medium In fishes, there is just 1 primary menyx The fish is surrounded in water so it has a habitat that is naturally protective In tetrapods, there is secondary menyx Outside water, brain has to be surrounded with fluid environment Made of arachnoid and pia mater Dua mater – outermost Pia mater and arachnoid mater – responsible for keeping in place the csf, it flows sin these two, if there is a damage you will have severe implications 150mL in humans Spinal Cord Butterfly shape in the middle Gray matter nerves are there but the ones in the middle where you find the nerve cell bodies perikaryon and soma White matter where you have the axons, surrounded by the myelin sheath Dorsal efferent root Ventral efferent root Central canal where csf will flow Ganglion part where two motor neurons will meet Brain Made of three distinct regions Responsible for a particular set of functions Forebrain – procencephalon divided into two: Telencephalon are the cerebral vesicles embryologically but they eventually become the cerebral cortex main part of the brain higher processing units of the brain for various types of signals you receive Speech centers of the brain: Broca’s anterior part of the brain if damaged, Actual physical speech is affaced by Broca’s Wernicke’s posterior - Ablity to understand, able to speak normally but not able to analyze deeper meaning very well Aphasia – speech defects may be related to damage of broca’s or wernicke’s Diencephalon still part of the forebrain part where you have the thalamus and hypothalamus Cerebrum part of the telencephalum Cerebrum part of the Telencephalon Hypothalamus found below the thalamus connected to a very impt gland called pituitary gland which produces 9 different hormones Thalamus is a relay center responsible for bridging between diff. areas of the brain for processing of nerve signals, also responsible for various autonomic functions Hypothalamus impt in interacting w/ the pituitary gland, impt functions in regulating body temperature also hunger thirst Still part of the forebrain, ventral part of the midbrain is the tegmentum and tegtum superior and inferior folliculi Tegmentum responsible for various autonomic functions Tectum primary responsible for auditory and visual signals Both part of the diencephalon Still part of the procencephalon or forebrain Another part is the limbic system not just a part but consists of many diff. parts including the hypo and hippocampus responsible for memory Amygdla for feelings of fear, if you want to not feel fear remove this Limbic memory fear and hunger, sexual drive Midbrain mesencephalon Hindbrain collective term is rhombencephalon Divided into two distinct sections Metencephalon is the cerebellum smaller lobe behind the cerebrum, for coordinated muscular movement and depth perception Myelencephalon fons reading center for nervous signals and medulla oblongata or brainstem is for houskeeping functions like heart breathing and respiration, when deprived of oxygen high levels of carbon dioxide will tell your medulla oblongata to signal body to breathe Marine mammals don’t have very carbon dioxide sensitive medulla oblongata tells body when to take breaths, when damaged fatal To kill a zombie – shoot it in medulla oblongata See some variations in birds and mamalls large cerebral cortex or telencephalon needed for higher processing Bony fishes have very prominent mid brain or mesencephalon or tectum in particular for visual signals, visual cortex large, large for bony fishes tectum Sharks have small brains, tectum tegmentum and visual cortex, use ampullae of lorenzini for electrical signals, sense of smell chemoreception Not so much on visual signals, bigger olfactory Brains of vertebrates differ in terms of enlargement depending on what they require Mammals – cerebellum for more coordinated movement Aquatic animals not very well developed