Chapter 17: The Nervous System HST III Spring Semester 2009.

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


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


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


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


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


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


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.


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

Chapter 17: The Nervous System HST III Spring Semester 2009.

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