NURANP-Chap-7.pdf

CHAPTER 7: THE NERVOUS SYSTEM NURANP | First Semester - Midterms THE NERVOUS SYSTEM skeletal muscle MICROSCOPIC ANATOMY OF reflexes such...

CHAPTER 7: THE NERVOUS SYSTEM NURANP | First Semester - Midterms THE NERVOUS SYSTEM skeletal muscle MICROSCOPIC ANATOMY OF reflexes such as SKELETAL MUSCLE Functions of the Nervous System stretch reflex are Astrocytes Sensory Input initiated ○ abundant, star-shaped cells ○ gathering information involuntarily by ○ brace neurons ○ to monitor changes occurring inside same fibers ○ form barrier between capillaries and and outside the body Autonomic Nervous neurons and make exchanges ○ changes = stimuli System between the two Integration involuntary ○ control the chemical environment of ○ to process and interpret sensory nervous system the brain by capturing ions and input and decide if action is needed sympathetic and neurotransmitters Motor Output parasympathetic ○ a response to integrated stimuli divisions ○ the response activates muscles or glands Structural Classification of the Nervous System Central Nervous System (CNS) ○ brain and spinal cord Microglia ○ acts as integrating and command ○ spider-like phagocytes center ○ dispose of debris interpret incoming sensory dead cells and bacteria information and issue instructions based on past Organization of The Nervous System experiences and current conditions Peripheral Nervous System (PNS) ○ nerves outside the brain and spinal cord ○ link all parts of the body by carrying impulses to the CNS and back Ependymal Cells ○ line cavities of the brain and spinal Functional Classification of the Peripheral cord Nervous System ○ circulate cerebrospinal fluid with Sensory (Afferent) Division cilia ○ nerve fibers that carry information to the central nervous system Motor (Efferent) Division ○ nerve fibers that carry impulses away from the central nervous system Oligodendrocytes ○ Two Subdivisions ○ wrap their flat extensions tightly Somatic Nervous System around the nerve fibers voluntary nervous system 1  ○ produce myelin sheath around Neuron Cell Body Location nerve fibers in the central nervous most are found in the central nervous system system in clusters called nuclei bundles of nerve fibers in CNS = tracts ○ Gray Matter cell bodies and unmyelinated fiber ○ White Matter myelinated fibers bundels of nerve fibers in PNS = nerves Ganglia ○ collections of cell bodies outside the Satellite Cells central nervous system ○ protect neuron cell bodies Schwann Cells Axons and Nerve Impulses Functional Classification of Neurons ○ form myelin sheath in the peripheral axons end in axonal terminals Sensory (Afferent) Neurons nervous system axonal terminals contain vesicles with ○ cell bodies in a ganglion outside the neuroglia are not able to transmit nerve neurotransmitters CNS impulses but do not lose their ability to axonal terminals are separated from the next ○ carry impulses from the sensory divide, unlike neurons neuron by a gap receptors to CNS ○ Synaptic Cleft Cutaneous (Skin) Sense gap between adjacent Organs NERVOUS TISSUE: NEURONS neurons Proprioceptors neurons = nerve cells ○ Synapse detect stretch or cells specialized to transmit messages junction between nerves tension in Major Regions of Neurons muscle, tendon, ○ Cell Body Nerve FIber Coverings joints nucleus and metabolic Schwann Cells Motor (Efferent) Neurons center of the cell ○ produce myelin sheaths in jelly-roll ○ cell bodies found in the CNS ○ Processes like fashion ○ carry impulses from the central fibers that extend from the Nodes of Ranvier nervous system cell body ○ gaps in myelin sheath along the Interneurons (Association Neurons) axon ○ found in neutral pathways in the Neuron Anatomy central nervous system Cell Body cell bodies in the CNS ○ Nissl Substance ○ connect sensory and motor neurons specialized rough endoplasmic reticulum Neuron Classification ○ Neurofibrils intermediate cytoskeleton that maintains cell shape ○ nucleus, large nucleolus extensions outside the cell body ○ Dendrites conduct impulses toward the cell body ○ Axons conduct impulses away from the cell body 2 Structural Classification of Neurons the exchange of ions initiates an action How Neurons Communicate at Synapses Multipolar Neurons potential (nerve impulse) in the neuron ○ many extensions from the cell body Bipolar Neurons ○ one axon and one dendrite rare in adults in eye and ear only The Action Potential if the action potential (nerve impulse) starts, Unipolar Neurons it is propagated over the entire axon – The Reflex Arc ○ have a short, single process leaving all-or-none response Reflex the cell body porassium ions rush out of the neuron after ○ rapid, predictable, and involuntary axon conducts nerve sodium ions rush in, which repolarizes the responses to stimuli impulses both to and from membrane Reflex Arc the cell body the sodium-potassium pump restores the ○ direct route from a sensory neuron, original configuration to an interneuron, to an effector ○ this action requires ATP until repolarization occurs, a neuron cannot conduct another impulse Nerve Impulse Propagation the impulse continues to move toward the Simple Reflex Arc Functional Properties of Neurons cell body Two Main Functions impulses travel faster when fibers have a ○ Irritability myelin sheath ability to respond to stimuli ○ nerve impulse literally jumps from ○ Conductivity node to node because it cannot ability to transmit an cross myelin insulation impulse impulses are unable to cross the synapse to the plasma membrane at rest is polarized another nerve ○ fewer positive ions (usually K+) are ○ nurotransmitter is released from a inside the cell than outside the cell nerve’s axon terminal (usually Na+) ○ the dendrite of the next neuron has receptors that are stimulated by the Starting a Nerve Impulse neurotransmitter Depolarization ○ an action potential is started in the Types of Reflexes and Regulation ○ a stimulus depolarizes the neuron’s dendrites of the next neuron reflex arcs have a minimum five elements membrane transmission of an impulse is an ○ a sensory receptor a depolarized membrane allows sodium to electrochemical event reacts to stimuli flow inside the membrane ○ an effector receptor muscle or gland stimulated 3  ○ affferent and efferent neurons Lobes of the Cerebrum Sensory and Motor Areas of the Cerebral Cortex connecting the two fissures (deep grooves) divide the ○ the CNS integration center cerebrum into lobes surface lobes of the cerebrum CENTRAL NERVOUS SYSTEM (CNS) ○ named for cranial bone CNS develops from the embryonic neural over them tube – a simple tube Frontal Lobe ○ the neural tube becomes the brain Parietal Lobe and spinal cord Occipital Lobe ○ the opening of the neural tube Temporal Lobe becomes the ventricles four chambers within the cerebral areas involved in special brain senses filled with cerebrospinal ○ Gustatory Area (Taste) fluid ○ Visual Area ○ Auditory Area REGIONS OF THE BRAIN ○ Olfactory Area Cerebral Hemispheres interpretation areas of the cerebrum Diencephalon ○ speech/language region Brain Stem ○ language comprehension Cerebellum region ○ general interpretation area Specialized Areas of the Cerebrum Specialized Area of the Cerebrum somatic sensory area in parietal lobe ○ receives impulses from the body’s sensory receptors (except special senses) Cerebral Hemispheres (Cerebrum) ○ Occipital Lobe paired (left and right) superior parts of the vision and brain temporal lobe – include more than half of the brain mass auditory the surface is made of elevated ridges (gyri) and shallow grooves (sulci) ○ Primary Motor Area sends impulses Layers of the Cerebrum to skeletal Gray Matter muscles – frontal ○ outermost layer lobe ○ cerebral cortex ○ Broca’s Area ○ composed mostly of involved in our neuron cell bodies ability to speak – White Matter base of the ○ fiber tracts inside the gray precentral gyrus matter ○ Example: corpus callosum connects hemispheres 4  Basal Nuclei mostly composed of tracts of nerve ○ internal islands of gray fibers matter the cerebral aqueduct helps regulate voluntary motor ○ canal that connects the activities by modifying instructions 3rd ventricle of the sent to the skeletal muscles diencephalon to the 4th ventricle Diencephalon - Interbrain has two bulging fiber tracts sits on top of the brain stem ○ Cerebral Peduncles enclosed by the cerebral hemispheres convey Made of Three Parts: ascending and ○ Thalamus descending Cerebellum ○ Hypothalamus impulses two hemispheres with convoluted surfaces ○ Epithalamus has four rounded protrusions provides involuntary coordination of body ○ corpora quadrigemina movements Thalamus reflex centers for ○ of skeletal muscles, balance and surrounds the third ventricle of the vision and equilibrium brain hearing Automatic Pilot the relay station for sensory ○ continually comparing brain’s impulses passing upward to the Pons intentions with actual body sensory cortex the bulging center part of the brain performance transfers impulses to the correct stem part of the cortex for localization mostly composed of fiber tracts PROTECTION OF THE CENTRAL and interpretation includes nuclei involved in the NERVOUS SYSTEM control of breathing Scalp and Skin Hypothalamus Cerebrospinal Fluid an important part of the limbic Medulla Oblongata Skull and Vertebral Column system (emotions) – the lowest part of the brain stem Blood Brain Barrier emotional-visceral brain merges into the spinal cord Meninges the pituitary gland is attached to includes important fiber tracts and regulated by the hypothalamus contains important control centers ○ Heart Rate Control Epithalamus ○ Blood Pressure Regulation forms the roof of the third ventricle ○ Breathing houses the pineal body (an ○ Swallowing endocrine ○ Vomiting gland) includes the choroid plexus Reticular Formation ○ forms cerebrospinal fluid diffuse mass of gray matter along Meninges the brain stem Dura Mater Brain Stem involved in motor control of visceral ○ double-layered external covering attaches to the spinal cord organs the brain Parts of the Brain Stem reticular activating system plays a Periosteum ○ Midbrain role in awake/sleep cycles and attached to ○ Pons consciousness surface of the ○ Medulla oblongata damage here results in a skull permanent coma Midbrain 5  Meningeal Layer outer covering of Alzheimer’s Disease the brain and progressive degenerative brain disease continues as the mostly seen in the elderly, but may begin in dura matter of the middle age spinal cord structural changes in the brain include ○ folds inward in several areas that abnormal protein deposits and twisted fibers attaches the brain to cranial cavity within neurons Arachnoid Layer victims experience memory loss, irritability, ○ middle layer that is web-like confusion and ultimately, hallucinations and Pia Mater death ○ internal layer that clings to the surface of the brain following every SPINAL CORD fold Blood Brain Barrier extends from the medulla oblongata to the Subarachnoid Space filled with includes the least permeable capillaries of region of T12 Cerebrospinal Fluid the body below T12 is the cauda equina (a collection ○ Arachnoid Villi ○ only H2O, glucose, and essential of spinal nerves) projections of arachnoid amino acids get through enlargements occur in the cervical and membrane protruding excludes many potentially harmful substance lumbar regions through the dura matter useless against some substances ○ Fats and Fat Soluble Molecules Cerebrospinal Fluid ○ Respiratory Gases similar to blood plasma composition ○ Alcohol ○ less protein, more vitamin C, ○ Nicotine different ions ○ Anesthesia formed by the choroid plexus forms a watery cushion to protect the brain TRAUMATIC BRAIN INJURIES circulated in arachnoid space, ventricles, and Concussion central canal of the spinal cord ○ slight brain injury dizzy or lose Ventricles and Location of the Cerebrospinal Fluid consciousness briefly ○ no permanent brain damage Contusion ○ nervous tissue destruction occurs does not regenerate ○ if cortex is damaged, coma for hours or life Cerebral Edema ○ swelling from the inflammatory response ○ may compress and kill brain tissue Cerebrovascular Accident (CVA) commonly called a stroke the result of a clot or a ruptured blood vessel supplying a region of the brain brain tissue supplied with oxygen from that blood source dies loss of some functions or death may result 6 Spinal Cord Anatomy groups of fibers are bound into fascicles by ○ motor fiber to eye muscles Internal Gray Matter perineurium (movement) ○ mostly cell bodies that surround the fascicles are bound together by epineurium V Trigeminal Nerve central canal of the cord ○ sensory for the face; motor fibers to ○ Dorsal (Posterior) Horns chewing muscles ○ Anterior (Ventral) Horns VI Abducens Nerve contains motor neurons of ○ motor fibers to eye muscles the somatic nervous (rotation) system, which send their VII Facial Nerve axons out the ventral root ○ for taste; motor fibers to the face ○ together, they fuse to form the spinal nerves VIII Vestibulocochlear Nerve ○ nerves leave at the level of each ○ for balance and hearing vertebrae IX Glossopharyngeal Nerve Dorsal Root Ganglion ○ sensory for taste; motor fibers to ○ where cell bodies of sensory the pharynx neurons, whose fibers enter the X Vagus Nerves cord by the dorsal root are found ○ sensory and motor fibers for Classification of Nerves damage to this area causes sensation from pharynx, larynx, and viscera classified according to the direction in which the body area served to be lost XI Accessory Nerve they transmit impulses Exterior White Mater – Conduction Tracts ○ motor fibers to neck and upper back Mixed Nerves ○ posterior, lateral, and anterior XII Hypoglossal Nerve ○ carry both sensory and motor fibers columns ○ motor fibers to tongue – spinal nerves each contains a number of Afferent (Sensory) Nerves fiber tracts make up of Spinal Nerves ○ carry impulses toward the CNS axons with the same there is a pair of spinal nerves at the level of Efferent (Motor) Nerves destination and function each vertebrae for a total of 31 pairs ○ carry impulses away from the CNS central canal filled with cerebrospinal fluid spinal nerves are formed by the combination of the ventral and dorsal roots of the spinal Cranial Nerves cord 2 pairs of nerves that mostly serve the head spinal nerves are named for the region from and neck which they arise numbered in order, front to back ○ names reveal structures they control most are mixed nerves, but three are sensory only ○ Optic, Olfactory, and Vestibulocochlear PERIPHERAL NERVOUS SYSTEM nerves and ganglia outside the central Cranial Nerves nervous system I Olfactory Nerve nerve = bundle of neuron fibers ○ for smell neuron fibers are bundled by a connective II Optic Nerve tissue sheath ○ for vision III Oculomotor Nerve Structure of a Nerve ○ motor fiber to eye muscles endoneurium surrounds each fiber (position) IV Trochlear 7  Differences between Somatic and Autonomic pass through a ramus communications, to Anatomy of Spinal Nerves Nervous Systems enter a sympathetic chain ganglion at the spinal nerves divide soon after leaving the sympathetic chain (trunk) (near the spinal spinal cord cord) ○ Dorsal Rami SOMATIC AUTONOMIC short pre-ganglionic neuron and long serve the skin and postganglionic neuron transmit impulse from muscles of the posterior NERVES one motor neuron preganglionic and CNS to the effector trunk – axons extend postganglionic norepinephrine and epinephrine are ○ Ventral Rami all the way to the nerves neurotransmitters to the effector organs forms a complex of skeletal muscle networks (plexus) for the they serve Sympathetic Pathways anterior, which serve the motor and sensory needs EFFECTOR skeletal muscle smooth muscle, of the limbs ORGANS cardiac muscle, and glands NEUROTRA always use use acetylcholine, NSMITTERS acetylcholine epinephrine, or norepinephrine Comparison of Somatic and Autonomic Nervous Systems Examples of Nerve Distribution Anatomy of the Autonomic Nervous System AUTONOMIC NERVOUS SYSTEM Anatomy of the Parasympathetic Division the involuntary branch of the nervous system originates from the brain stem and S2 – S4 consists of only motor nerves neurons in the cranial region send axons out Divided into Two Divisions: in cranial nerves to the head and neck ○ Sympathetic Division organs mobilizes the body they synapse with the second motor neuron ○ Parasympathetic Division in a terminal ganglion allows body to unwind terminal ganglia are at the effector organs always uses acetylcholine as a neurotransmitter originates from T1 through L2 reganglionic axons leave the cord in the ventral root, enter the spinal nerve, then 8 Autonomic Functioning Sympathetic ○ “fight-or-flight” ○ response to unusual stimulus ○ takes over to increase activities ○ remember as the “E” division exercise, excitement, emergency, and embarrassment Parasympathetic ○ housekeeping activities ○ conserves energy ○ maintains daily necessary body functions ○ remember as the “D” division digestion, defecation, and diuresis 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 – contains centers for regulating body temperature no more neurons are formed after birth, but growth and maturation continues for several years largely due to myelination the brain reaches maximum weight as a young adult 9