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Essentials of Human Anatomy & Physiology Elaine N. Marieb Seventh Edition The Nervous System Modified by S.Mendoza 1/2014 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Functions of the Nervous System Sensory input – gathering information Uses sensory receptors to monitor changes (stimuli) occurring inside and outside the body Integration To process and interpret sensory input and decide if action is needed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.1a Functions of the Nervous System Slide 7.1b Motor output A response to integrated stimuli The response activates muscles or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Neuroglia “Cell Glue” Generally assist, segregate, and insulate neurons Neuroglia can replicate but cannot conduct Neurofibromatosis Overproduction of Schwann cells Nervous Tissue: Neurons Neurons = nerve cells Cells specialized to transmit messages – can conduct but cannot replicate Have 3 specialized characteristics Longevity: with nutrition, can live as long as you do Amitotic: unable to reproduce themselves (so cannot be replaced) High metabolic rate: require continuous oxygen & glucose (due to lots of activity) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.8 Neuroglia vs. Neurons Neuroglia divide. Neurons do not. Most brain tumors are “gliomas.” Involve the neuroglia cells, not the neurons. As neuroglia grow out of control, they press on the neurons impairing their function Neurolemma Why is the plasma membrane (neurolemma) of a neuron so important? It is the site of electrical signaling – plays a crucial role in cell to cell interactions during development as well Major Regions of Neurons Cell body Contains the metabolic/biosynthetic center of the cell (location of the nucleus) Does not contain centrioles (reflects amitotic nature) but has the other organelles Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.8 Neuron Anatomy Dendrites hundreds per cell – diffusely branched – close to cell body Receptive sites conduct impulses toward the cell body Immense surface area for reception Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Neuron Anatomy Axons Transmit impulses away from cell body Vary in length and diameter Larger diameter = faster conduction Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Neuron Anatomy Axons Axon collaterals – right angle branches connecting other neurons Axon terminals located at end of axon branches Figure 7.4a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.10 Axon terminals Contain vesicles with neurotransmitters – chemicals which transmit electrical impulses Axonal terminals are separated from the next neuron or effector by the Synaptic cleft Synapse -junction between nerves Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.11 Myelin Sheath Function: Protects & insulates fibers Increases speed of transmission Formed by Schwann Cells (add to notes) Figure 7.5 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.12 Functional Classification of Neurons Sensory (afferent) Nerve fibers that carry information from sensory receptors to the central nervous system (CNS) Ends of dendrites associated with specialized receptors – know examples in your notes! Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Sensory Receptors Ends of dendrites are associated with specialized receptors Cutaneous receptors: pressure, pain, heat, cold Proprioceptors: muscles & tendons: amount of stretch or tension Specialized receptors in sense organs: sight, hearing, smell, taste, equilibrium Functional Classification Motor (efferent) division Nerve fibers that carry impulses from the central nervous system to muscles & glands Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3b Functional Classification Association or Interneurons • Responsible for integration & reflex – connect motor & sensory neurons • Make up over 99% of neurons End of Quiz #1 Material Study for quiz!!! Functional Properties of Neurons Two major functional properties of neurons resulting in electrochemical event Irritability - ability to respond to stimuli & convert it into a nerve impulse Conductivity – ability to transmit an impulse to other neurons, muscles, or glands Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.17 Synapse – know the diagram Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.11 Stages of the Chemical Event The action potential (electrical signal) reaches the axon terminals Neurotransmitter is released into the synaptic cleft when the vesicle fuses with the membrane (presynaptic neuron) NT diffuses across the cleft and binds to the receptors on the dendrite of the next neuron (postsynaptic neuron) Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 Stages of the Chemical Event An action potential is started in the next neuron (or muscle or gland) In order to prevent continuous stimulation, NT is removed from the synapse through: Re-uptake Enzymatic breakdown Synapse Animation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.21 Development Aspects of the Nervous System As you learn: Axon terminal gets wider so more NT can be released (more surface area) Synaptic cleft get narrower More NT gets across to receptors Faster & more efficient process Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide Reflex Activity – page 438 Reflex: rapid predictable motor response to stimuli that the body is programmed to do Unlearned, unpremeditated, involuntary Withdrawal from pain Learned or acquired reflexes result from repetition or practice. Example: experienced driver drives a car Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.58 Reflex Activity Two types: Autonomic: regulate the activity of smooth muscles, the heart, and glands Examples: salivary reflex, pupilary reflex, digestion, blood pressure Somatic reflexes: skeletal muscle reflexes Example: knee jerk reflex Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.58 Reflex – define 5 elements of Know your diagram Regeneration Mature neurons are incapable of mitosis. However, PNS axons can regenerate if cell body is not destroyed. The uninjured cell body gets larger in order to synthesize proteins needed for regeneration Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.14b Regeneration Axons regenerate at a rate of 1.5 mm/day The greater the distance between severed nerve endings, the less chance of recovery. Axonal sprouts may grow into surrounding areas and form a mass called a neuroma. Surgical realignment can help. Retraining may be necessary once the connection is completed Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.14b Neuroma Acoustic neuroma MRI Regeneration PNS vs CNS In PNS axon regeneration, macrophages clean out the debris from the injury. Schwann cells will form a tunnel of neurolemma to guide severed nerve ending together. A growth factor is also released In CNS – No Schwann cells to do this.Slide Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings 7.14b End of Quiz #2 Material Don’t forget to complete your Quiz review for EC Organization of Nervous System Memorize the info on the chart provided you need to understand how it all fits together Classification of the Nervous System Central nervous system (CNS) Brain & Spinal cord Integrative & control centers Peripheral nervous system (PNS) Cranial & Spinal Nerves (outside the brain and spinal cord) Communication lines between the CNS and the rest of the body Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.2 Distribution of Cranial Nerves Figure 7.21 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.59 Spinal Nerves Figure 7.22a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.64 Functional Classification of the Peripheral Nervous System Motor (efferent) division Two subdivisions Somatic nervous system = voluntary Conducts impulses to skeletal muscles Autonomic nervous system = involuntary Conducts impulses to cardiac muscle, smooth muscle, & glands Figure 7.1 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.3c Functional Classification of the Peripheral Nervous System Autonomic nervous system Has 2 subdivisions Sympathetic division Fight or flight system Speeds up HR, respiration rate, increases cardiac output, deactivates digestive system Parasympathetic division Resting system Activates digestive, slows other systems Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Organization of the Nervous System Figure 7.2 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.4 Central Nervous System Protection of the CNS Scalp, hair, and skin- Cushions Bone: Skull and vertebral column – Surrounds & Protects Meninges – membranes fig 7.16 Figure 7.16a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Meninges Epidural space: Found around spine only-contains fat & CT Dura mater – “tough mother” Double-layered external covering fused together except where dural sinuses are enclosed Dural sinuses – venous blood collected from brain and shunted into internal jugular vein Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.45a Meninges Subdural space Contains serous fluid Arachnoid layer Middle layer Spider web-like Subarachnoid space Contains CSF & major arteries & veins Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.45b Meninges Pia mater: “little mother” Internal layer of delicate CT Clings directly to the surface of the brain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.45b Blood Brain Barrier Function: ensures stable environment by endothelial tight junctions(the least permeable capillaries of the body) Excludes many potentially harmful substances and metabolic waste products Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.48 Blood Brain Barrier Useless against some substances Fats and fat soluble molecules Respiratory gases Alcohol Nicotine Anesthesia Medical Implication (add to notes): Hard to get antibiotics through BBB so hard to treat brain infections Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.48 Blood Brain Barrier Not identical in all regions In the hypothalamus region, the BBB is almost non-existent so chemical composition of blood can be monitored Different in newborns vs. adult Kernicterus: description on next page Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.48 Kernicterus – copy BLUE into notes Hemoglobin is released into blood as RBC’s recycle Hemoglobin breaks down into bilirubin which is normally cleared from the body by the liver Newborns have an immature liver so bilirubin will build up and cause jaundice of body and of brain Infant will have diminished reflexes, lethargy, reduced muscle tone, and a high pitched abnormal cry as external symptoms. UV light treatment helps dissolve excess bilirubin. Cerebrospinal Fluid Function: Support, protect, & exchange of materials Forms a watery cushion to protect the brain Circulates to monitor levels of CO2, O2 , pH – triggers feedback mechanism if necessary Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.46 Cerebrospinal Fluid Similar to blood plasma composition Location: subarachnoid space and 4 ventricles in brain and central canal of SC Formed by the choroid plexus (network of capillaries) in brain ventricles: seeps from capillaries into ventricles ~800 ml formed daily Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.46 Circulation of CSF: Memorize Choroid plexus lateral (1st & 2nd) ventricles interventricular foramen 3rd ventricle cerebral aqueduct 4th ventricle subarachnoid space & central canal of SC Hydrocephalus •Define: something blocks Slide 7.47b circulation/drainage of CSF, fluid accumulates & puts pressure on brain •Adult:skull bones are fused, fluid compresses BV and soft brain tissue – result is brain damage •Child:skull bones not fused, head may enlarge, brain damage still a possibility •Treatment: insert a shunt to go around blockage Figure 7.17b Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Hydrocephalus Do not need to copy this info Shunt drains excess fluid from ventricles into abdominal cavity where body can reabsorb it. Pressure then does not build up in the brain Brain Development (CNS) CNS develops from the embryonic neural tube The neural tube becomes the brain and spinal cord The opening of the neural tube becomes the ventricles Malformations of neural tube lead to several defects such as spina bifida Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Major Regions of the Brain Cerebral hemisphere Diencephalon Brain stem Cerebellum Figure 7.12 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.27 Cerebrum The surface is made of ridges (gyri) and grooves (sulci) Purpose: triple surface area Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.28b Figure 7.13a Lobes of the Cerebrum Fissures (deep sulci) divide the cerebrum into lobes Longitudinal fissure: separates 2 hemispheres Transverse fissure: separates cerebellum Lateral fissure:on side of brain Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Lobes of Brain Surface lobes of the cerebrum Frontal lobe Parietal lobe Occipital lobe Temporal lobe Lobes of the Cerebrum Figure 7.15a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.29b The Cerebrum Cerebral cortex: Gray matter: cell bodies 1/16” thick, ~40% of brain mass Voluntary motion Higher order thinking skills Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.30 Sensory and Motor Areas of the Cerebral Cortex Figure 7.14 Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.31 Layers of the Cerebrum White matter Fiber tracts inside the gray matter Example: corpus callosum connects hemispheres & allows them to communicate Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Figure 7.13a Slide 7.33b Layers of the Cerebrum Basal nuclei – internal islands of gray matter w/in white matter Indirectly helps initiate and control slow stereotyped muscle movement When impaired, postural disturbances, muscle tremors uncontrolled contractions result Figure 7.13a Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.33c Cerebral Nuclei Diencephalon Sits on top of the brain stem Enclosed by the cerebral hemispheres Made of three parts Thalamus Hypothalamus Epithalamus Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.34a Brain Stem Attaches to the spinal cord Rigidly programmed automatic behaviors necessary for survival Parts of the brain stem Midbrain Pons Medulla oblongata - If damaged severely, death will result Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.38a Cerebellum Two hemispheres with convoluted surfaces Provides involuntary smooth, coordinated body movements Likened to the control system of an automatic pilot to constantly monitor and adjust muscle functioning Ataxia Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.43a End of Quiz #3 Information Also need to study Brain Diagram Brain Disorders You need to have a basic description & understanding of the following disorders – so read everything but copy down every blue detail Hemispherectomy to control seizures Developmental Aspects of the Nervous System Cerebral palsy Lack of oxygen to developing (in utero) infant May be caused by: mother who smokes, mother who gets German measles, problems during labor & delivery, etc. Cerebral palsy symptoms Alzheimer’s Disease Progressive degenerative brain disease Mostly seen in the elderly, but may begin in middle age(early onset) Structural changes in the brain include abnormal protein deposits (plaques) and twisted fibers within neurons Victims experience memory loss, irritability, confusion and ultimately, hallucinations and death Parkinson’s disease Age 50s to 60s Degeneration of dopamine releasing neurons in nuclei of brain stem – cause is unknown Tremors, stiff facial expression, slow in movement Treatment: L-dopa, deep brain stimulation through implanted electrodes Huntington’s chorea Dominant genetic disorder Degeneration of basal nuclei and cerebral cortex Strikes during middle age – usually fatal within 15 years Wild, jerky motions Treated with drugs that block dopamine but no cure Disorders Meningitis Inflammation of the meninges Can be bacterial or viral Bacterial is worse due to the toxins excreted by bacteria Encephalitis Brain inflammation Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.45b Traumatic Brain Injuries Cerebral edema Swelling from the inflammatory response May compress and kill brain tissue Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.49 Cerebrovascular Accident (CVA) Commonly called a stroke The result of a ruptured blood vessel or a clot in a BV supplying a region of the brain Ischemia: Tissue death – lack of 02 Brain tissue supplied with oxygen from that blood source dies Loss of some functions or death may result Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Slide 7.50 CVA TIA Transient ischemic attacks Last from 5-50 minutes Symptoms: numbness, temporary paralysis, impaired speech Not permanent BUT warning sign of impending stroke Multiple sclerosis Demyelinating disorder – form scleroses (hardened deposits) Autoimmune Onset 20-40 years of age –more common in women Incurable – treatments based on slowing progression Multiple sclerosis Disorders Hemiplegia Paralysis of left or right side of body – due to brain injury/stroke rather than spinal cord injury Spinal Cord Approximately 17 inches long and extends from the foramen magnum to the 1st/2nd lumbar vertebrae. It is about the size (diameter) of your thumb for most of its length Meningeal coverings extend to the 4th sacral vertebrae Spinal Cord Lumbar puncture aka spinal tap Purpose: to obtain a CSF sample for testing Location: level of L4 or L5 - since spinal cord ends at L1 or L2 – this reduces the chance of puncturing the spinal cord Patient must remain lying down for 6-12 hours since withdrawal of fluid decreases internal pressure which may cause an excruciating headache until body regulates itself. Lumbar (spinal) tap Terms to Know Flaccid paralysis – No voluntary muscle motion possible – muscles will atrophy Spastic paralysis – affected muscles stay healthy due to reflex activity but motions are involuntary and uncontrolled Terms to Know Quadriplegic: all four limbs are affected Paraplegic: only the legs are affected Spina Bifida Spina bifida-incomplete formation of vertebrae – folic acid reduces risk Occulta-no external manifestations Cystica-saclike cyst protrudes from spine Meningocele-cyst contains meninges & CSF Myelomeningocele-cyst also contains portions of spinal cord and nerve roots Spina Bifida Types Milder forms of SB Occulta Cystica Spina Bifida Myelomeningocele Fetal Surgery Study proves benefits of spina bifida surgery (02/10/11)