the nervous system a network of billions of nerve cells linked together in a highly organized...
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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
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Performance of normal voluntary movement, Performance of normal voluntary movement, the integrity of two sets of neurons is importantthe integrity of two sets of neurons is important
Upper motor neuronesUpper motor neuronesNeurons originating in the cerebral cortex and the Neurons originating in the cerebral cortex and the brain stembrain stemSynapse directly or indirectly with the anterior horn Synapse directly or indirectly with the anterior horn cells or with the motor neurones of the cranial nervescells or with the motor neurones of the cranial nervesGrouped into pyramidal and extrapyramidal systemsGrouped into pyramidal and extrapyramidal systems
Lower motor neuronesLower motor neuronesMotor cranial nuclei and their axons, i.e. motor fibres Motor cranial nuclei and their axons, i.e. motor fibres of the cranial nerves (3of the cranial nerves (3rdrd, 4, 4thth, 5, 5thth, 6, 6thth, 7, 7thth, 9, 9thth, 10, 10thth, 11, 11thth and 12and 12thth))In the spinal cord they include the anterior horn In the spinal cord they include the anterior horn motor neurones and their axons, i.e. the motor motor neurones and their axons, i.e. the motor nerves to skeletal musclesnerves to skeletal muscles
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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))
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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.
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Organization of the Nervous System
• 2 big initial divisions:1. Central Nervous System
• The brain + the spinal cord– The center of integration and
control2. 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
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Brain Regions
1. Cerebrum
2. Diencephalon
3. Brainstem
4. Cerebellum
Cerebellum
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Cerebral Cortex
• 3 types of functional areas:1. Motor Control voluntary
motor functions
2. Sensory Allow for conscious recognition of
stimuli
3. Association Integration
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Cortical Motor Areas
1. Primary Motor Cortex
2. Premotor Cortex
3. Broca’s Area
4. Frontal Eye Field
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1.Primary motor cortex
3.Broca’s Area
2.Premotor cortex
4.Frontal Eye Field
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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.
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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?
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Sensory Areas• Found in the parietal, occipital, and
temporal lobes.
1. Primary somatosensory cortex2. Somatosensory association cortex3. Visual areas4. Auditory areas5. Olfactory cortex6. Gustatory cortex7. Vestibular cortex
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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.
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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 cortex ?
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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.
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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
Decrease in dopamine secretion
Increased activity of basal nuclei
Gradual increase in muscle tone
Appearance of symptoms of Parkinson’s disease: tremor, slow movement, inability to move, rigid
gait, reduced facial expression
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Diencephalon
• Forms the central core of the forebrain
• 3 paired structures:
1. Thalamus
2. Hypothalamus
3. Epithalamus
All 3 are gray matter
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