Transcript Chapter 17: The Nervous System - Practicum-Health-Science-I

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