Nervous System 2023 PDF

Nervous System Ch 16, 17, 18, & 19 1 Nervous Tissue Chapter 16 Controls and integrates all body activities within limits that maintain life Three basic functions  sensing changes with sensory receptors  interpreting and remembering...

Nervous System Ch 16, 17, 18, & 19 1 Nervous Tissue Chapter 16 Controls and integrates all body activities within limits that maintain life Three basic functions  sensing changes with sensory receptors  interpreting and remembering those changes  reacting to those changes with effectors muscular contractions glandular secretions 2  Nervous System Divisions Central nervous system (CNS)  consists of the brain and spinal cord Peripheral nervous system (PNS)  consists of cranial and spinal nerves  connects CNS to muscles, glands & all sensory receptors 3 Organization of the Nervous System CNS is brain and spinal cord PNS is everything else 4 Structures of the Nervous System The nervous system includes: o The brain o Cranial nerves (and their branches) o Spinal cord o Spinal nerves (and their branches) o Ganglia o Enteric plexuses o Sensory receptors 5  Subdivisions of the PNS Somatic (voluntary) nervous system (SNS)  neurons from receptors to the CNS  motor neurons to skeletal muscle tissue Autonomic (involuntary) nervous systems  sensory neurons from visceral organs to CNS  motor neurons to smooth & cardiac muscle and glands sympathetic division (speeds up heart rate) parasympathetic division (slow down heart rate) Enteric nervous system (ENS)  involuntary sensory & motor neurons control GI tract  neurons function independently of ANS & CNS 6 Structures of the Nervous System 7  Neurons Nerve cell Functional unit of nervous system Have electrical excitability Cell body  singlenucleus with prominent nucleolus Cell processes = dendrites & axons 8  Parts of a Neuron Neuroglial cells Nucleus with Nucleolus Axons or Dendrites Cell body 9 Dendrites Conducts impulses towards the cell body Surfaces specialized for contact with other neurons 10 Axons Conduct impulses away from cell body Swollen tips called synaptic end bulbs contain vesicles filled with neurotransmitters Synaptic end bulbs 11 Functional Classification of Neurons Sensory (afferent) neurons  transport sensory information to CNS  Motor (efferent) neurons  sendmotor nerve impulses to muscles & glands 12 Structural Classification of Neurons Based on number of processes found on cell body  multipolar = several dendrites & one axon most common cell type  bipolar neurons = one main dendrite & one axon found in retina, inner ear & olfactory  unipolar neurons = one process only are always sensory neurons 13 Neuroglia Neuroglia, glia, or glial cells constitute about half the volume of the CNS Neuroglia are smaller than neurons and 50X more numerous Glia o Do not generate or propagate nerve impulses o Have the ability to multiply and divide in the mature nervous system Six types of neuroglia: o Astrocytes, oligodendrocytes, microglia, and ependymal cells are found only in the CNS o Schwann cells (neurolemmocytes) and satellite cells are present in the PNS Copyright ©2017 John Wiley & Sons, Inc. 14 Neuroglia of the Central Nervous System (CNS) Copyright ©2017 John Wiley & Sons, Inc. 15  Astrocytes Star-shaped cells Form blood-brain barrier (BBB) by covering blood capillaries Provide strength Maintain the unique permeability characteristics of the endothelial cells In the embryo, astrocytes secrete Maintain the appropriate chemical chemicals that appear to regulate environment for the generation of the growth, migration, and nerve impulses interconnections among neurons Play a role in learning and memory in the brain by influencing the formation of neural synapses 16 Oligodendrocytes Most common glial cell type Each forms myelin sheath around more than one axons in CNS Analogous to Schwann cells of PNS 17 Microglia Small cells found near blood vessels Phagocytic role -- clear away dead cells, remove cellular debris and phagocytize microbes and damaged nervous tissue 18 Ependymal cells Ependymal cells line the ventricles of the brain and central canal of the spinal cord Functionally, ependymal cells produce, possibly monitor, and assist in the circulation of cerebrospinal fluid (CSF) 19 Schwann Cell Schwann cells, also called neurolemmocytes, encircle PNS axons, form the myelin sheath around axons, and participate in axon regeneration, which is more easily accomplished in the PNS Each cell produces part of the myelin sheath surrounding an axon in the PNS 20 Satellite Cell Satellite cells surround the cell bodies of neurons of PNS ganglia and regulate the exchange of materials between neuronal cell bodies and interstitial fluid 21  Myelination in the CNS Oligodendrocytes myelinate axons in the CNS 22  Gray and White Matter White matter = myelinated processes (white in color) Gray matter = nerve cell bodies, dendrites, axon terminals, bundles of unmyelinated axons and neuroglia (gray color) 23 Multiple Sclerosis (MS) Autoimmune disorder causing destruction of myelin sheaths in CNS  sheaths becomes scars or plaques Symptoms include muscular weakness, abnormal sensations or double vision 24 Regeneration & Repair Plasticity maintained throughout life  sprouting of new dendrites  synthesis of new proteins  changes in synaptic contacts with other neurons Limited ability for regeneration (repair)  PNS can repair damaged dendrites or axons if the cell body remains intact  CNS little to no repair occurs even if the cell body is intact 25 Neurogenesis in the CNS Formation of new neurons from stem cells was not thought to occur in humans  1992 a growth factor was found that stimulates adult mice brain cells to multiply  1998 new neurons found to form within adult human hippocampus (area important for learning) Factors preventing neurogenesis in CNS  inhibition by neuroglial cells, absence of growth stimulating factors, lack of neurolemmas, and rapid formation of scar tissue 16-26 Hippocampus location 27 Repair within the PNS Axons & dendrites may be repaired if  neuron cell body remains intact  Schwann cells remain active and form a tube  scar tissue does not form too rapidly Chromatolysis  24-48 hours after injury, Nissl bodies break up into fine granular masses 16-28  Repair within the PNS By 3-5 days,  Wallerian degeneration occurs (breakdown of axon & myelin sheath distal to injury)  retrograde degeneration occurs back one node Within several months, regeneration occurs  neurolemma on each side of injury repairs tube (Schwann cell mitosis)  axonal buds grow down the tube to reconnect (1.5 mm per day) 16-29 Repair within the PNS Axons & dendrites may be repaired if  neuron cell body remains intact  Schwann cells remain active and form a tube  scar tissue does not form too rapidly 30 The Spinal Cord & Spinal Nerves Chapter 17 Together with brain forms the CNS Functions  spinalcord reflexes  highway for upward and downward travel of sensory and motor information 31 Spinal Cord 32 Structures Covering the Spinal Cord Vertebrae Epidural space filled with fat Dura mater  dense irregular CT tube Subdural space filled with interstitial fluid Arachnoid = spider web of collagen fibers Subarachnoid space = CSF Pia mater  thin layer 33 34 External Anatomy of Spinal Cord In adult ends at L1-L2 Nerve rootlets continue as cauda equina 31 pairs of spinal nerves branch from cord  PNS 35 Spinal tap or Lumbar Puncture Technique  long needle into subarachnoid space  safe from L3 to L5 Purpose  sampling CSF for diagnosis  injection of antibiotics, anesthetics or chemotherapy  measurement of CSF pressure 36  Inferior End of Spinal Cord Cauda equina (horse’s tail)  dorsal & ventral roots of lowest spinal nerves 37  Spinal Cord & Spinal Nerves Spinal nerves begin as roots Dorsal or posterior root is incoming sensory fibers  dorsal root ganglion (swelling) = cell bodies of sensory nerves Ventral or anterior root is outgoing motor fibers 38 Gray Matter of the Spinal Cord Gray matter is shaped like the letter H or a butterfly  contains neuron cell bodies, unmyelinated axons & dendrites  paired dorsal and ventral gray horns 39  White Matter of the Spinal Cord Anterior median fissure deeper than Posterior median sulcus Anterior, Lateral and Posterior White Columns contain axons that form ascending & descending tracts 40 Tracts of the Spinal Cord Function of tracts  highway for sensory & motor information  sensory tracts ascend  motor tracts descend Naming of tracts  indicates position & direction of signal  example = anterior spinothalamic tract impulses travel from spinal cord towards brain (thalamus) found in anterior part of spinal cord 41  Spinal Reflexes Automatic response to change in environment Integration center for spinal reflexes is gray matter of spinal cord  somatic reflexes result in skeletal muscle contraction  autonomic (visceral) reflexes involve smooth & cardiac muscle and glands. heart rate, respiration, digestion, urination, etc. cranial reflexes involve cranial nerves 42  Reflex Arc Specific nerve impulse pathway 5 components of reflex arc  receptor  sensory neuron  integrating center  motor neuron  effector 43 Illustration of the Stretch Reflex 44 Clinical Considerations Checking a patient’s reflexes may help to detect disorders/injury Plantar flexion reflex -- stroke the lateral margin of the sole  normal response is curling under the toes  abnormal response or response of children under 18 months is called Babinski sign (upward fanning of toes due to incomplete myelination in child) 45  Spinal Nerves 31 Pairs of spinal nerves Named & numbered by the cord level of their origin  (C1 to C8)  (T1 to T12)  (L1 to L5)  (S1 to S5)  1 pair of coccygeal nerves Mixed sensory & motor nerves 46 A Nerve Plexus Joining of spinal nerves to form nerve networks or plexuses Found in neck, arm, low back & sacral regions No plexus in thoracic region  Intercostals 47 Cervical Plexus & Phrenic Nerve 48 C3, C4, C5 & Diaphragm 49 Branches off Brachial Plexus 50 Sacral Plexus L4-L5 & S1-S4 Anterior to the sacrum Supplies buttocks, perineum & part of lower limb Sciatic nerve = L4 to S3 supplies post thigh & all below knee 51 Branches of Sacral Plexus 52 Sciatic Nerve Branches Notice: Common Peroneal nerve and Tibial nerve behind the knee Notice: Sciatica pain extends from the buttock down the leg to the foot may be sign of herniated disc 53  Dermatomes & Myotomes Each spinal nerve contains both sensory & motor nerve fibers Dermatome  area of skin supplied by one spinal nerve  overlap prevents loss of sensation if one damaged  Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of the spinal cord. 54 Dermatomes Damaged regions of the spinal cord can be distinguished by patterns of numbness over a dermatome region 55 Referred Pain Skin area & organ are served by the same segment of the spinal cord.  Heart attack is felt in skin along left arm since both are supplied by spinal cord segment T1-T5 56 The Brain and Cranial Nerves Chapter 18 Largest organ in the body at almost 3 lb. Brain functions in sensations, memory, emotions, decision making, behavior 57 Cranial Nerves 58 Cranial Nerves and Functions Mnemonic to remember the I. Olfactory – Sensory names of the cranial nerves: II. Optic – Sensory Only One Of The Two Athletes III. Oculomotor – Motor Felt Very Good, Victorious, IV. Trochlear – Motor And Healthy. V. Abducens – Mixed Mnemonic to remember the VI. Trigeminal – Motor function of the cranial nerves: VII. Facial – Mixed Some Say Marry Money But VIII. Vestibulocochlear – My Brother Says Bad Sensory Business Marrying Money IX. Glossopharyngeal – *please note that Mixed refers to Mixed BOTH sensory and motor function so X. Vagus – Mixed Both is used in the mnemonic. S= sensory, M=motor B=both (mixed) XI. Accessory – Motor 59 XII. Hypoglossal – Motor Olfactory (I) Nerve Copyright ©2017 John Wiley & Sons, Inc. 60 Optic (II) Nerve Copyright ©2017 John Wiley & Sons, Inc. 61 Oculomotor (III), Trochlear (IV), and Abducens (VI) Nerves Copyright ©2017 John Wiley & Sons, Inc. 62 Trigeminal (V) Nerve Copyright ©2017 John Wiley & Sons, Inc. 63 Facial (VII) Nerve Copyright ©2017 John Wiley & Sons, Inc. 64 Vestibulocochlear (VIII) Nerve Copyright ©2017 John Wiley & Sons, Inc. 65 Glossopharyngeal (IX) Nerve Copyright ©2017 John Wiley & Sons, Inc. 66 Vagus (X) Nerve Copyright ©2017 John Wiley & Sons, Inc. 67 Accessory (XI) Nerve Copyright ©2017 John Wiley & Sons, Inc. 68 Hypoglossal (XII) Nerve Copyright ©2017 John Wiley & Sons, Inc. 69 Principal Parts of the Brain Cerebrum Diencephalon  thalamus & hypothalamus Cerebellum Brainstem  medulla, pons & midbrain 70 Protective Coverings of the Brain Bone, meninges & fluid Meninges same as around the spinal cord  dura mater  arachnoid mater  pia mater 71 Blood Supply to Brain Internal carotid and vertebral arteries supply most of the brain R and L Internal Carotid form Circle of Willis or Cerebral Arterial Circle Provide alternate routes to the brain if arteries damaged Uses 20% of our body’s oxygen & glucose needs Blood-brain barrier (BBB)  protects cells from some toxins and pathogens  astrocyte processes covering capillaries 72 Cerebrospinal Fluid (CSF) 80-150 ml (3-5oz) Clear liquid containing glucose, proteins, & ions Functions  mechanical protection  chemical protection  circulation 73  Origin of CSF Choroid plexus = capillaries covered by ependymal cells  2 lateral ventricles  roof of 3rd ventricle  fourth ventricle 74 Ventricles 75 Flow of Cerebrospinal Fluid 76  Reabsorption of CSF Reabsorbed through arachnoid villi 20 ml/hour reabsorption rate = same as production rate 77 Hydrocephalus Blockage of drainage of CSF Continued production cause an increase in pressure --- hydrocephalus Neurosurgeon implants a drain shunting the CSF to the veins of the neck or the abdomen 78 Brain Stem Composed of: o midbrain o pons o medulla oblongata 79  Medulla Oblongata Continuation of spinal cord Nuclei of 5 cranial nerves Cardiovascular center  force& rate of heart beat  diameter of blood vessels Respiratory center  medullary rhythmicity area sets basic rhythm of breathing Reflex centers for coughing, sneezing, swallowing, vomiting, hiccupping 80 Pons One inch long Pneumotaxic & apneustic areas help control breathing Middle cerebral peduncles carry sensory info to the cerebellum Cranial nerves 5 thru 8 81 Midbrain One inch in length Extends from pons to diencephalon Cerebral aqueduct connects 3rd ventricle above to 4th ventricle below Relays motor output from the cerebral cortex to the pons, relays sensory input from the spinal cord to the thalamus, coordinates movements of the eyes, and coordinates movements of the head and trunk to auditory stimuli 82 Cerebellum 2 cerebellar hemispheres and vermis Function  correct voluntary muscle contraction and posture based on sensory data from body about actual movements  sense of equilibrium 83 Cerebellum Transverse fissure between cerebellum & cerebrum Cerebellar cortex is grey matter Arbor vitae = tree of life = white matter 84 Diencephalon Surrounds 3rd Ventricle Surrounds 3rd ventricle Superior part of walls is thalamus Inferior part of walls & floor is hypothalamus 85 Thalamus 1 inch long mass of gray mater in each half of brain (connected across the 3rd ventricle by intermediate mass) Relay station for sensory information on way to cortex Crude perception of some sensations 86  Hypothalamus Dozen or so nuclei in 4 major regions  mammillary bodies are relay station for olfactory reflexes; infundibulum suspends the pituitary gland Major regulator of homeostasis  receives somatic and visceral input, taste, smell & hearing information; monitors osmotic pressure, temperature of blood 87 Functions of Hypothalamus Controls activities of the ANS which regulates smooth, cardiac muscle and glands Synthesizes regulatory hormones that control the anterior pituitary Regulates rage, aggression, pain, pleasure & arousal Feeding, thirst & satiety centers Controls body temperature Regulates daily patterns of sleep 88 Epithalamus Pineal gland  endocrine gland the size of small pea  secretes melatonin during darkness  promotes sleepiness & sets biological clock Habenular nuclei  emotional responses to odors 89  Cerebrum (Cerebral Hemispheres) Cerebral cortex is gray matter overlying white matter  2-4 mm thick containing billions of cells  grew so quickly formed folds (gyri) and grooves (sulci or fissures) Longitudinal fissure separates left & right cerebral hemispheres Corpus callosum is band of white matter connecting left and right cerebral hemispheres Each hemisphere is subdivided into 4 lobes 90  Longitudinal fissure (green) Lobes and Fissures Frontal lobe Central sulcus (yellow)  precentral & postcentral gyrus Parietal lobe Occipital lobe Lateral sulcus (blue) Temporal lobe 91 Primary Motor Cortex Precentral gyrus initiates voluntary movement Cells are called upper motor neurons Muscles represented unequally (according to the number of motor units) More cortical area is needed if number of motor units in a muscle is high  vocal cords, tongue, lips, fingers & thumb 92 Somatosensory Map of Postcentral Gyrus Relative sizes of cortical areas  proportional to number of sensory receptors  proportional to the sensitivity of each part of the body Can be modified with learning  learn to read Braille & will have larger area representing fingertips 93 Limbic System Parahippocampal & cingulate gyri & hippocampus Emotional brain--intense pleasure & intense pain Strong emotions increase efficiency of memory 94 The Autonomic Nervous System Chapter 21 Regulate activity of smooth muscle, cardiac muscle & certain glands Receives input from limbic system and other regions of the cerebrum 95 Autonomic vs Somatic NS Somatic nervous system  consciously perceived sensations  excitation of skeletal muscle Autonomic nervous system  unconsciously perceived visceral sensations  involuntary inhibition or excitation of smooth muscle, cardiac muscle or glandular secretion 96 Autonomic versus Somatic NS Notice that the ANS pathway is a 2 neuron pathway while the Somatic NS only contains one neuron. 97 Divisions of the ANS 2 major divisions  parasympathetic  sympathetic Dual innervation  one speeds up organ  one slows down organ 98 Sources of Dual Innervation Sympathetic (thoracolumbar) division Parasympathetic (craniosacral) division CN III, VII, IX, X S2-4 99 Pathways of Sympathetic Fibers Spinal nerve route  out same level Sympathetic chain route  up chain & out spinal ganglion route 100 ANS Neurotransmitters Classified as either cholinergic or adrenergic neurons based upon the neurotransmitter released Adrenergic Cholinergic 101  Sympathetic Responses Dominance by the sympathetic system is caused by physical or emotional stress -- “E situations”  emergency, embarrassment, excitement, exercise Alarm reaction = flight or fight response  dilation of pupils  increase of heart rate, force of contraction & BP  decrease in blood flow to nonessential organs  increase in blood flow to skeletal & cardiac muscle  airways dilate & respiratory rate increases  blood glucose level increase 102  Parasympathetic Responses Enhance “rest-and-digest” activities Mechanisms that help conserve and restore body energy during times of rest Normally dominate over sympathetic impulses SLUDD type responses = salivation, lacrimation, urination, digestion & defecation and 3 “decreases”--- decreased HR, diameter of airways and diameter of pupil Paradoxical fear when there is no escape route or no way to win  causes massive activation of parasympathetic division  loss of control over urination and defecation 103 Comparison: PNS Somatic Sensory (afferent) neurons  Skin and special senses  Pain, thermal, tactile, proprioceptive, and the special sense Motor (efferent) neurons  Most motor are a single axon extending to skeletal muscle  Skeletal muscle (ACh) 104 Comparison: PNS Autonomic (Visceral) Autonomic sensory (afferent) neurons  Viscera interoreceptors  Chemoreceptors, mechanoreceptors, etc. Autonomic motor (efferent) neurons  Inhibit or excite effector tissues 1. Cardiac muscle 2. Smooth muscle 3. Glandular tissue Most ANS motor consist of two motor neurons  One cell body in CNS, second in autonomic ganglia 105 Autonomic Motor (Efferent) Pathway End in varicosities (swellings) versus synapse  Release many NT over large area of innervated organ Preganglionic neuron  Originate in brain or spinal cord  Myelinated axon exits as cranial or spinal nerve  Travel to autonomic ganglion Postganglionic neuron  Cell body in autonomic ganglion  Unmyelinated fibers 106 107 Sympathetic Division Thoracolumbar  Cell bodies in lateral horns of gray matter  Originate from T1 to L2 Ganglia locations  Sympathetic Trunk (Paravetebral) ganglion Vertical row on either side of vertebrae  Prevertebral ganglion Anterior to vertebral column close to large abdominal arteries 108 109 White Communicating Rami Preganglionic axons leave spinal cord through anterior rootlets of spinal nerve  Myelinated sympathetic axons pass into anterior ramus and into a white ramus communicans Move into nearest sympathetic trunk ganglia and terminate in several ways 110 Sympathetic Axon Collateral Branches: 1. Synapse in the first ganglion at entry level 2. Pass up or down sympathetic trunk 3. Pass through sympathetic trunk without terminating 1. Exit splanchnic nerves (viscera) 2. Terminate in prevertebral ganglia 4. Pass through both ganglia and extend to chromaffin cells of suprarenal medullae 111 112 Parasympathetic Division Craniosacral  CN 3, 7, 9, 10 and S2, 3, 4 Terminal ganglia located close to or within the wall of a visceral organ  No parasympathetic fibers to extremities, skin, or subcutaneous tissues!  Parasympathetic tend to have localized singular response, opposed to sympathetic 113 114 Neurons and Receptors Cholinergic neurons release ACh  All symp and parasymp preganglionic  Symp postganglionic that innervate sweat glands  All parasymp postganglionic Adrenergic neurons release NE  Most symp postganglionic Epinephrine and NE also released by chromaffin cells into bloodstream 115 Hypothalamus and ANS Major control and integration center of ANS  Input from visceral functions, olfaction, gustation, temperature, etc. and emotions from limbic system  Output influences centers for CV, saliva, swallowing, vomiting, urination, defecation, etc. Connected to both symp and parasymp through cell bodies in nuclei and axons in tracts  Posterior and lateral = sympathetic  Anterior and medial = parasympathetic 116 Brachial Plexus Musculocutaneous nerve (C5-C7)  Flexion at elbow of the anterior arm compartment Radial nerve (C5-T1)  Extension at elbow of posterior arm compartment Median and Ulnar nerve (C5-T1, C8-T1)  Flexors of wrist and hand Radial nerve (C5-T1)  Extensors of wrist and hand 117 Lumbar and Sacral Plexus Obturator nerve (L2-L4)  Adducts medial thigh compartment Femoral nerve (L2-L4)  Extensors of anterior thigh compartment Sciatic nerve (L4-S3)  Flexorsof posterior thigh compartment  (Hamstrings) 118 Sacral Plexus Common Fibular (L4-S2)  Deep fibular nerve Extensors of anterior leg compartment Dorsiflexion  Superficial fibular nerve Flexors of lateral leg compartment Eversion (foot) Tibial nerve (L4-S3)  Flexors of posterior leg compartment  Plantar flexion 119 Cranial Nerve Review CN I Olfactory  Special sensory, olfaction CN II Optic  Special sensory, vision CN III Oculomotor  Somatic movement of eyeballs and upper eyelid Levator palpebrae superioris  ANS adjust lens and constriction of pupil 120 Cranial Nerve Review CN IV Trochlear  Somatic movement of eyeballs Superior oblique CN V Trigeminal V1 Ophthalmic branch V2 Maxillary branch V3 Mandibular branch  Touch, pain, thermal from scalp, face, and oral (ant 2/3)  Mastication and control of middle ear muscle 121 Cranial Nerve Review CN VI Abducens  Movement of eyeballs (abduction) Lateral rectus CN VII Facial  Taste(ant 2/3)  Muscles of facial expression and middle ear  ANS salivary glands and lacrimation 122 Cranial Nerve Review CN VIII Vestibulocochlear  Special sensory, hearing and equilibrium CN IX Glossopharyngeal  Taste (post 1/3)  Swallowing, blood pressure and CO2/O2 levels of blood near carotid arteries  Touch, pain, thermal from external ear and upper pharynx  ANS saliva from parotid salivary 123 Cranial Nerve Review CN X Vagus  Taste from epiglottis, proprioception of throat and voicebox, blood pressure and CO2/O2 in carotid sinus  Touch, pain, thermal from external ear  Sensation from thoracic and abdominal organs  Swallowing, vocalization, coughing  ANS digestion, constriction of resp passageways, decrease in heart rate 124 Cranial Nerve Review CN XI Accessory (Spinal)  Proprioceptionand pain from trapezius and sternocleidomastoid  Movement of head and pectoral girdle CN XII Hypoglossal  Speech, manipulation of food, swallowing  Skeletal to all “-glossus” muscles of tongue except palatoglossus 125