Chapter 17: The Chapter 17: The Nervous System Nervous System HST III HST III Spring Semester Spring Semester 2009 2009
Dec 26, 2015
Chapter 17: The Nervous Chapter 17: The Nervous SystemSystem
HST IIIHST III
Spring SemesterSpring Semester
20092009
The Brain has 4 regions:The Brain has 4 regions:
CerebrumCerebrum DiencephalonDiencephalon BrainstemBrainstem CerebellumCerebellum
Each hemisphere is subdivided Each hemisphere is subdivided into four sections:into four sections:
Parietal Lobe
Occipital Lobe
Frontal Lobe
Temporal Lobe
Neurons (Nerve Cells)Neurons (Nerve Cells)
Gray MatterGray Matter
Consist of aggregations of neuronal cell Consist of aggregations of neuronal cell bodiesbodies
Rims the surfaces of the cerebral Rims the surfaces of the cerebral hemispheres, forming the cerebral cortexhemispheres, forming the cerebral cortex
White MatterWhite Matter
Consists of neuronal axons that are Consists of neuronal axons that are coated with myelin.coated with myelin.
Myelin sheaths create the white color of Myelin sheaths create the white color of white matter, and allow nerve impulses white matter, and allow nerve impulses to travel more rapidly.to travel more rapidly.
Basal GangliaBasal Ganglia
Additional cluster of gray matter found Additional cluster of gray matter found deep in the brain.deep in the brain.
Affects movementAffects movement
Thalamus Thalamus
Additional cluster of gray matter found Additional cluster of gray matter found deep in the brain.deep in the brain.
Processes sensory impulses and relays Processes sensory impulses and relays them to the cerebral cortexthem to the cerebral cortex
HypothalamusHypothalamus
Additional cluster of gray matter found deep in Additional cluster of gray matter found deep in the brainthe brain
Maintains homeostasis and regulates body Maintains homeostasis and regulates body temperature, heart rate, and blood pressuretemperature, heart rate, and blood pressure
Affects the endocrine system and governs Affects the endocrine system and governs emotional behavior such as anger and sexual emotional behavior such as anger and sexual drivedrive
Hormones secreted from this area act directly Hormones secreted from this area act directly on the pituitary gland.on the pituitary gland.
Internal capsuleInternal capsule
White matter structure where myelinated White matter structure where myelinated fibers converge from all parts of the fibers converge from all parts of the cerebral cortex and descend into the cerebral cortex and descend into the brainstem.brainstem.
BrainstemBrainstem
Connects the upper part of the brain Connects the upper part of the brain with the spinal cordwith the spinal cord
Has three sections:Has three sections:
1.1. MidbrainMidbrain
2.2. PonsPons
3.3. MedullaMedulla
Reticular Activating (Arousal) Reticular Activating (Arousal) SystemSystem
Important structure in the diencephalon Important structure in the diencephalon and upper brainstemand upper brainstem
Plays an important role along with intact Plays an important role along with intact cerebral hemispheres in the level of cerebral hemispheres in the level of consciousness exhibitedconsciousness exhibited
The Spinal CordThe Spinal Cord
Encased within the bony vertebral column and Encased within the bony vertebral column and terminating at the first or second lumbar terminating at the first or second lumbar vertebra.vertebra.
Provides a series of segmental relays with the Provides a series of segmental relays with the periphery, serving as a conduit for information periphery, serving as a conduit for information flow to and from the brain.flow to and from the brain.
The motor and sensory nerve pathways relay The motor and sensory nerve pathways relay neural signals that enter and exit the cord neural signals that enter and exit the cord through posterior and anterior nerve roots through posterior and anterior nerve roots through the spinal and peripheral nerves.through the spinal and peripheral nerves.
The Spinal Cord The Spinal Cord
Divided into five segments:Divided into five segments:
1.1. Cervical – C1 to C8Cervical – C1 to C8
2.2. Thoracic – T1 to T12Thoracic – T1 to T12
3.3. Lumbar – L1 to L5Lumbar – L1 to L5
4.4. Sacral – S1 to S5Sacral – S1 to S5
5.5. CoccygealCoccygeal
The Cranial NervesThe Cranial Nerves
I.I. Olfactory – Sense of smellOlfactory – Sense of smell
II.II. Optic – VisionOptic – Vision
III.III. Oculomotor – Pupillary constriction, Oculomotor – Pupillary constriction, opening the eyelid, and most opening the eyelid, and most extraocular movementsextraocular movements
IV.IV. Trochlear – Downward, internal Trochlear – Downward, internal rotation of the eyerotation of the eye
The Cranial NervesThe Cranial Nerves
V.V. TrigeminalTrigeminal
Motor – Temporal and masseter muscles Motor – Temporal and masseter muscles (jaw clenching), lateral jaw movement;(jaw clenching), lateral jaw movement;
Sensory – facialSensory – facial
1.1. OphthalamicOphthalamic
2.2. MaxillaryMaxillary
3.3. MandibularMandibular
The Cranial NervesThe Cranial Nerves
VI.VI. Abducens – Lateral deviation of the Abducens – Lateral deviation of the eyeeye
VII.VII. Facial Facial Motor – Facial movements, including those Motor – Facial movements, including those
of facial expression, closing the eye, of facial expression, closing the eye, and closing the mouthand closing the mouth
Sensory – taste for salty, sweet, sour, and Sensory – taste for salty, sweet, sour, and bitter substances on the anterior two bitter substances on the anterior two thirds of the tonguethirds of the tongue
The Cranial NervesThe Cranial Nerves
VIII.VIII. AcousticAcoustic
Hearing – Cochlear divisionHearing – Cochlear division
Balance – Vestibular divisionBalance – Vestibular division
IX.IX. GlossopharyngealGlossopharyngeal
Motor – PharynxMotor – Pharynx
Sensory – Posterior portions of the eardrum and Sensory – Posterior portions of the eardrum and ear canal, the pharynx, and the posterior ear canal, the pharynx, and the posterior tongue, including salty, sweet, sour, bittertongue, including salty, sweet, sour, bitter
The Cranial NervesThe Cranial Nerves
X.X. VagusVagusMotor – Palate, pharynx, and larynxMotor – Palate, pharynx, and larynxSensory – Pharynx and larynxSensory – Pharynx and larynxXI.XI. Spinal accessorySpinal accessoryMotor – The sternomastoid and upper Motor – The sternomastoid and upper
portion of the trapeziusportion of the trapeziusXII.XII. HypoglossalHypoglossalMotor - TongueMotor - Tongue
The Peripheral NervesThe Peripheral Nerves
Thirty one pairs of nerves attach to the Thirty one pairs of nerves attach to the spinal cord:spinal cord:
8 Cervical8 Cervical 12 Thoracic12 Thoracic 5 Lumbar5 Lumbar 5 Sacral5 Sacral 1 Coccygeal1 Coccygeal
Peripheral NervesPeripheral Nerves
Each nerve has:Each nerve has: Anterior (ventral) nerve root – contains Anterior (ventral) nerve root – contains
motor fibersmotor fibers Posterior (dorsal) nerve root – contains Posterior (dorsal) nerve root – contains
sensory fiberssensory fibers
These two roots merge to form a short These two roots merge to form a short spinal nerve, less than 5mm in length.spinal nerve, less than 5mm in length.
The Motor PathwaysThe Motor Pathways
Motor pathways are complex avenues, Motor pathways are complex avenues, extending from upper motor neurons ( in extending from upper motor neurons ( in the brain), to synapses with lower motor the brain), to synapses with lower motor neurons (in the spinal cord), and into the neurons (in the spinal cord), and into the periphery through peripheral nerve periphery through peripheral nerve structures.structures.
The Motor PathwaysThe Motor Pathways
There are three basic motor pathways:There are three basic motor pathways:
1.1. Corticospinal (Pyramidal tract)Corticospinal (Pyramidal tract)
2.2. Basal ganglia systemBasal ganglia system
3.3. Cerebellar systemCerebellar system
Corticospinal (Pyramidal) Corticospinal (Pyramidal) TractTract
Mediates voluntary movement and Mediates voluntary movement and integrate skilled, complicated, or delicate integrate skilled, complicated, or delicate movements by stimulating selected movements by stimulating selected muscular actions and inhibiting others.muscular actions and inhibiting others.
Carry impulses that inhibit muscle tone Carry impulses that inhibit muscle tone Originate in the motor cortex of the brainOriginate in the motor cortex of the brain Motor fibers travel down into the lower Motor fibers travel down into the lower
medulla, where they form an anatomical medulla, where they form an anatomical structure resembling a pyramid.structure resembling a pyramid.
Basal Ganglia SystemBasal Ganglia System
Includes motor pathways between the Includes motor pathways between the cerebral cortex, basal ganglia, brainstem, cerebral cortex, basal ganglia, brainstem, and spinal cordand spinal cord
Helps to maintain muscle tone and to Helps to maintain muscle tone and to control body movements, especially gross control body movements, especially gross automatic movements such as walkingautomatic movements such as walking
Cerebellar SystemCerebellar System
Receives both sensory and motor input Receives both sensory and motor input and coordinates motor activity, and coordinates motor activity, maintains equilibrium, and helps to maintains equilibrium, and helps to control posture.control posture.
The Sensory PathwaysThe Sensory Pathways
Give rise to conscious sensation, calibrate Give rise to conscious sensation, calibrate body position in space, and helps regulate body position in space, and helps regulate internal autonomic functions like blood internal autonomic functions like blood pressure, heart rate, and respirationspressure, heart rate, and respirations
Relays impulses from the skin, mucous Relays impulses from the skin, mucous membranes, muscles, tendons, and membranes, muscles, tendons, and visceraviscera
The Sensory PathwaysThe Sensory Pathways
Fibers conducting the sensations of pain and Fibers conducting the sensations of pain and temperature pass into the posterior horn of the temperature pass into the posterior horn of the spinal cord and synapse with secondary spinal cord and synapse with secondary sensory neuronssensory neurons
Fibers conducting crude touch both without Fibers conducting crude touch both without accurate localization also pass into the accurate localization also pass into the posterior horn and synapse with secondary posterior horn and synapse with secondary neuronsneurons
The secondary neurons then cross to the The secondary neurons then cross to the opposite side and pass upward in the opposite side and pass upward in the spinothalamic tract into the thalamus spinothalamic tract into the thalamus
The Sensory PathwaysThe Sensory Pathways
Fibers conducting the sensations of Fibers conducting the sensations of position and vibration pass directly into position and vibration pass directly into the posterior columns of the cord and the posterior columns of the cord and travel upward to the medulla, together travel upward to the medulla, together with fibers transmitting fine touchwith fibers transmitting fine touch
At the thalamic level, the general quality At the thalamic level, the general quality of sensation is perceived , but fine of sensation is perceived , but fine distinctions are not made.distinctions are not made.
The Sensory PathwaysThe Sensory Pathways
For full perception, a third group of For full perception, a third group of sensory neurons sends impulses from the sensory neurons sends impulses from the thalamus to the sensory cortex of the thalamus to the sensory cortex of the brain.brain.
Lesions at different points in the sensory Lesions at different points in the sensory pathways produce different kinds of pathways produce different kinds of sensory losssensory loss
DermatonesDermatones
The band of skin innervated by the The band of skin innervated by the sensory root of a single spinal nerve. sensory root of a single spinal nerve.
Knowledge and testing of dermatones Knowledge and testing of dermatones help localize a lesion to a specific spinal help localize a lesion to a specific spinal cord segment.cord segment.
Deep Tendon Reflexes (Muscle Deep Tendon Reflexes (Muscle Stretch Reflexes)Stretch Reflexes)
Relayed over structures of both the Relayed over structures of both the central and peripheral nervous systemscentral and peripheral nervous systems
A reflex is an involuntary stereotypical A reflex is an involuntary stereotypical response that may involve as few as two response that may involve as few as two neurons, one afferent (sensory) and one neurons, one afferent (sensory) and one efferent (motor), across a single synapseefferent (motor), across a single synapse
Deep Tendon ReflexesDeep Tendon Reflexes
Each deep tendon reflex involves specific Each deep tendon reflex involves specific spinal segments, together with their spinal segments, together with their sensory and motor fibers, an abnormal sensory and motor fibers, an abnormal reflex can help you to locate a pathologic reflex can help you to locate a pathologic lesionlesion
Deep Tendon Reflexes Deep Tendon Reflexes
Ankle reflex – Sacral 1 primarilyAnkle reflex – Sacral 1 primarily
Knee reflex – Lumbar 2, 3, 4Knee reflex – Lumbar 2, 3, 4
Supinator (Brachioradialis) reflex – Supinator (Brachioradialis) reflex – Cervical 5, 6Cervical 5, 6
Bicep reflex – Cervical 5, 6Bicep reflex – Cervical 5, 6
Tricep reflex – Cervical 6, 7Tricep reflex – Cervical 6, 7
Cutaneous Stimulation Cutaneous Stimulation ReflexesReflexes
Reflexes may be initiated by stimulating Reflexes may be initiated by stimulating skin as well as muscle:skin as well as muscle:
Abdominal reflexes – upper – Thoracic 8, Abdominal reflexes – upper – Thoracic 8, 9, 109, 10
Lower – Thoracic 10, 11, Lower – Thoracic 10, 11, 1212
Plantar responses – Lumbar 5, Sacral 1Plantar responses – Lumbar 5, Sacral 1
Anal reflex – Sacral 2, 3, 4Anal reflex – Sacral 2, 3, 4
HeadacheHeadache
Be sure to ask about severity, location, Be sure to ask about severity, location, duration, and any associated symptoms duration, and any associated symptoms such as visual changes, weakness, or loss such as visual changes, weakness, or loss of sensationof sensation
Ask if the headache is affected by Ask if the headache is affected by coughing, sneezing, or sudden movement coughing, sneezing, or sudden movement of the head, which can increase of the head, which can increase intracranial pressureintracranial pressure
HeadacheHeadache
Dull headache affected by the previous Dull headache affected by the previous actions listed, could be a sign of a large actions listed, could be a sign of a large brain lesion or abscessbrain lesion or abscess
Subarachnoid hemorrhage may present Subarachnoid hemorrhage may present as “the worst headache of my life”as “the worst headache of my life”
Complaint of a severe headache could be Complaint of a severe headache could be a sign of meningitisa sign of meningitis
DizzinessDizziness
Defined as a loss of balance, light-Defined as a loss of balance, light-headedness, or sensation that one is headedness, or sensation that one is unsteady and may fallunsteady and may fall
May result from heart palpitations, May result from heart palpitations, vasovagal stimulation, low blood vasovagal stimulation, low blood pressure, febrile illness, and other pressure, febrile illness, and other conditions.conditions.
VertigoVertigo
Vertigo is defined as the sensation of the Vertigo is defined as the sensation of the room spinning or rotatingroom spinning or rotating
Caused typically by inner-ear conditions, Caused typically by inner-ear conditions, or possibly a brainstem tumoror possibly a brainstem tumor
WeaknessWeakness
Focal weakness may arise from ischemic, Focal weakness may arise from ischemic, vascular, or mass lesions in the central nervous vascular, or mass lesions in the central nervous system;system;
May arise from peripheral nervous system May arise from peripheral nervous system disorders, neuromuscular disorders, or diseases disorders, neuromuscular disorders, or diseases in the muscles themselvesin the muscles themselves
Question patients what “weakness” means to Question patients what “weakness” means to them, in order to rule out paralysis, or the them, in order to rule out paralysis, or the inability to move a part or side of the bodyinability to move a part or side of the body
Loss of SensationLoss of Sensation
Absence of feeling in limb or body partAbsence of feeling in limb or body part May be described as numbnessMay be described as numbness Paresthesia – described as a peculiar sensation Paresthesia – described as a peculiar sensation
without obvious stimulus; commonly occur without obvious stimulus; commonly occur when an arm or leg “goes to sleep”when an arm or leg “goes to sleep”
Dysethesias – are distorted sensations in Dysethesias – are distorted sensations in response to a stimulus and may last longer than response to a stimulus and may last longer than the stimulus itself; a person may perceive a the stimulus itself; a person may perceive a light touch or pinprick as a burning or tingling light touch or pinprick as a burning or tingling sensationsensation
Loss of SensationLoss of Sensation
Paresthesia and dysethesias may be Paresthesia and dysethesias may be present in central lesions in the brain and present in central lesions in the brain and spinal cord, as well as disorders of spinal cord, as well as disorders of peripheral sensory roots and nervesperipheral sensory roots and nerves
Paresthesia of the hands and around the Paresthesia of the hands and around the mouth may be present in mouth may be present in hyperventilationhyperventilation
Burning pain may be felt in painful Burning pain may be felt in painful sensory neuropathysensory neuropathy
Loss of Consciousness Loss of Consciousness (Fainting)(Fainting)
Syncope is the sudden but temporary loss Syncope is the sudden but temporary loss of consciousness and postural tone that of consciousness and postural tone that occurs in decreased blood flow to the occurs in decreased blood flow to the brain brain
Presyncope – feeling faint, light-headed, Presyncope – feeling faint, light-headed, or weak, without losing consciousnessor weak, without losing consciousness
Loss of ConsciousnessLoss of Consciousness
Young people with emotional stress and Young people with emotional stress and warning symptoms of flushing, warmth, warning symptoms of flushing, warmth, or nausea may have vasovagal syncope of or nausea may have vasovagal syncope of slow onset, slow offsetslow onset, slow offset
Cardiac syncope from arrhythmias, are Cardiac syncope from arrhythmias, are more common in older adults, often with more common in older adults, often with sudden onset, sudden offsetsudden onset, sudden offset
SeizureSeizure
A paroxysmal disorder caused by sudden A paroxysmal disorder caused by sudden excessive electrical discharge in the excessive electrical discharge in the cerebral cortex or its underlying cerebral cortex or its underlying structuresstructures
Seizures can be of varying typesSeizures can be of varying types Tonic-clonic motor activity, bladder or Tonic-clonic motor activity, bladder or
bowel incontinence, and postictal state bowel incontinence, and postictal state suggest a generalized seizuresuggest a generalized seizure
Tremors Tremors
Involuntary movements that occur with Involuntary movements that occur with or without additional neurologic or without additional neurologic manifestationsmanifestations
An example is the tremor, rigidity, and An example is the tremor, rigidity, and bradykinesia (slow movement) are seen bradykinesia (slow movement) are seen in Parkinson’s diseasein Parkinson’s disease