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The Nervous System
• A network of billions of nerve cells linked
together in a highly organized fashion to
form the rapid control center of the body.
• Functions include:
– Integrating center for homeostasis,
movement, and almost all other body
functions.
– The mysterious source of those traits that we
think of as setting humans apart from animals
Performance of normal voluntary movement,
the integrity of two sets of neurons is important
Upper motor neurones
Neurons originating in the cerebral cortex and the
brain stem
Synapse directly or indirectly with the anterior horn
cells or with the motor neurones of the cranial nerves
Grouped into pyramidal and extrapyramidal systems
Lower motor neurones
Motor cranial nuclei and their axons, i.e. motor fibres
of the cranial nerves (3rd, 4th, 5th, 6th, 7th, 9th, 10th,
11th and 12th)
In the spinal cord they include the anterior horn
motor neurones and their axons, i.e. the motor
nerves to skeletal muscles
Basic Functions of the Nervous System
1. Sensation
•
Monitors changes/events occurring in and
outside the body. Such changes are known as
stimuli and the cells that monitor them are
receptors.
2. Integration
•
The parallel processing and interpretation of
sensory information to determine the appropriate
response
3. Reaction
•
Motor output.
– The activation of muscles or glands (typically
via the release of neurotransmitters (NTs))
Nervous vs. Endocrine System
• Similarities:
– They both monitor stimuli and react so as to
maintain homeostasis.
• Differences:
– The NS is a rapid, fast-acting system whose
effects do not always persevere.
– The ES acts slower (via blood-borne chemical
signals called H _ _ _ _ _ _ _) and its actions
are usually much longer lasting.
Organization of the
Nervous System
•
2 big initial divisions:
1. Central Nervous System
• The brain + the spinal cord
– The center of integration and
control
2. Peripheral Nervous System
• The nervous system outside of
the brain and spinal cord
• Consists of:
– 31 Spinal nerves
» Carry info to and from the
spinal cord
– 12 Cranial nerves
» Carry info to and from the
brain
Brain Regions
1.
2.
3.
4.
Cerebrum
Diencephalon
Brainstem
Cerebellum
Cerebellum
Cerebral
Cortex
•
3 types of functional areas:
1. Motor 
2. Sensory 
3. Association 
Control voluntary
motor functions
Allow for conscious
recognition of stimuli
Integration
Cortical Motor Areas
1. Primary Motor
Cortex
2. Premotor Cortex
3. Broca’s Area
4. Frontal Eye Field
2.Premotor cortex
4.Frontal
Eye Field
3.Broca’s Area
1.Primary motor
cortex
Primary (Somatic) Motor Cortex
• Located in the precentral gyrus
of each cerebral hemisphere.
• Contains large neurons
(pyramidal cells) which project to
SC neurons which eventually
synapse on skeletal muscles
– Allowing for voluntary motor
control.
– These pathways are known
as the corticospinal tracts or
pyramidal tracts.
Primary
(Somatic) Motor
Cortex
• Somatotopy
– The entire body is
represented spatially in
the primary motor cortex,
_ i.e., in one region we have
neurons controlling hand
movements and in
another region leg
movements, etc.
• What does it mean to say
that motor innervation is
contralateral?
Sensory Areas
•
Found in the parietal, occipital, and
temporal lobes.
1.
2.
3.
4.
5.
6.
7.
Primary somatosensory cortex
Somatosensory association cortex
Visual areas
Auditory areas
Olfactory cortex
Gustatory cortex
Vestibular cortex
Primary Somatosensory Cortex
• Found in the
postcentral gyrus.
• Neurons in this
cortical area
receive info from
sensory neurons
in the skin
• and from
proprioceptors
which monitor joint
position.
• Contralateral input.
Somatosensory Association
Cortex
• Found posterior to the
primary
somatosensory cortex
and is neurally tied to
it.
• Synthesizes multiple
sensory inputs to
create a complete
comprehension of the
object being felt.
– How would damage
to this area differ
from damage to the
primary
somatosensory
Basal Nuclei
• Info arrives at the caudate nucleus and the putamen from
sensory, motor, and association areas of the cortex.
• Processing and integration occurs w/i the nuclei and then
info is sent from the globus pallidus to the motor cortex
via the thalamus.
• The basal nuclei alter motor commands issued by the
cerebral cortex via this feedback loop.
Parkinson’s Disease
• Each side of the midbrain contains a nucleus called
the substantia nigra.
• Neurons in the substantia nigra inhibit the activity of
basal nuclei by releasing dopamine.
Damage to SN
neurons
Appearance of symptoms of
Parkinson’s disease: tremor, slow
movement, inability to move, rigid
gait, reduced facial expression
Decrease in
dopamine secretion
Increased activity of
basal nuclei
Gradual increase in
muscle tone
Diencephalon
•
•
Forms the
central core
of the
forebrain
3 paired
structures:
1. Thalamus
2. Hypothalam
us
3. Epithalamus
All 3 are gray matter