中樞神經系統

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Functional Organization of
The Central Nervous System
丁慶華
[email protected]
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CNS
Organization
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CNS
Role
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The Brain
Brief facts
 Weighs about 1600g in ♂
and about 1400g in ♀
 Has about 1012 neurons, each
of which may receive as
many as 200,000 synapses –
how about integration!
 Although these numbers
connote a high level of
complexity, the CNS is
actually quite orderly.
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Gray and White Matters
 Microscopically, the CNS contains
2 neural elements:
 Neuron cell bodies (clusters are
known as nuclei)
 Nerve fibers (axons) in bundles
called tracts.
 Viewed macroscopically, CNS
tissues can be distinguished by
color:
 Gray matter consists of somas,
dendrites, and unmyelinated axons.
 White matter consists primarily of
myelinated axons.
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Brain Regions
 Cerebrum
 Responsible for the initiation and coordination of all voluntary activity
in the body.
 Governs the functioning of lower parts of the nervous system.
 Cortex is the seat of all intelligent behaviour.
 Diencephalon
 Functions as signal relay.
 Brainstem
 Sensory, motor, and reflex functions
 Cerebellum
 Acts with the cerebral cortex to produce killed movements by
coordinating the activities of groups of muscles.
 Helps control posture by making movements smooth.
 Maintains equilibrium by controlling skeletal muscles.
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Cerebrum
 Allows for sensation,
voluntary movement, selfawareness, communication,
recognition, and more.
 Gray matter!
 40% of brain mass, but only
2-4 mm thick.
 Each cerebral hemisphere is
concerned with the sensory
and motor functions of the
opposite side of the body.
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Cerebral Layers
The cerebral cortex
has 6 layers.
Each layer composes
of millions of axon
terminals with
millions of dendrites
and cell bodies other
neurons.
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Cerebrum
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Functional Areas of the Cortex
3 types of functional areas:
 Motor 
Control voluntary
motor functions
 Sensory 
Allow for conscious recognition of
stimuli
 Association  Integration
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Functions of the Cerebral Cortex
No part of the brain functions alone. It requires coordination of many parts of
the CNS to function normally.
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Cortical Motor Areas
1.
2.
3.
4.
Primary Motor Cortex
Premotor Cortex
Broca’s Area
Frontal Eye Field
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Primary motor
cortex
Premotor cortex
Frontal Eye
Field
Broca’s Area
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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.
 Neurons controlling movement
of different body regions do not
intermingle.
 Look at the motor homunculus.
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Sensory Functions of the Cortex
Somatic senses include sensations of touch,
pressure, temperature, body position, and
perceptions that do not require complex sensory
organs.
Special senses include vision, hearing, and other
perceptions that require complex sensory organs.
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Cerebral Sensory Areas
Found in the parietal, occipital, and temporal
lobes.
 Primary somatosensory cortex
 Somatosensory association cortex
 Visual areas
 Auditory areas
 Olfactory cortex
 Gustatory cortex
 Vestibular cortex
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Functions of the Cerebral Cortex
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Somatosensotry Cortex
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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LEFT
RIGHT
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LEFT
RIGHT
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Somatosensory Association Cortex
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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Visual Cortex
Largest of the sensory
cortices.
 What does this suggest?
Contralateral input.
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Visual Association Area
 Surrounds the primary
visual cortex.
 Basically vision is the
sensation of bars of light
on our retinal cells.
 The primary visual cortex
tells which cells are being
stimulated and how.
 The association area lets us
“see” what we’re looking
at.
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Auditory Cortex
 Found in the superior
margin of the temporal
lobe, next to the lateral
sulcus.
 Sound waves excite
cochlear receptors in the
inner ear which send info
to the auditory cortex.
 There is also an auditory
association area which lets
us interpret and remember
sounds.
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Olfactory Cortex
 Receptors in the olfactory
epithelium extend
through the cribriform
plate and are excited by
the binding of oderants.
They then send their info
to the olfactory cortex.
 Very much involved in
memory and emotion.
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Olfactory Pathway
Olfactory Sensor
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Gustatory and Vestibular Cortices
Gustatory cortex is involved in taste and is in the
parietal lobe just deep to the temporal lobe.
Vestibular cortex is involved in balance and
equilibrium and is in the posterior insula
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Association Areas
 Allows for analysis of
sensory input.
 Multiple inputs and outputs.
Why?




Prefrontal cortex
Language areas
General interpretation area
Visceral association area
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Prefrontal Cortex
Involved in analysis,
cognition, thinking,
personality, conscience, &
much more.
Look at its evolution
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Language Areas
 Large area for language understanding
and production surrounding the lateral
sulcus in the left (language-dominant)
hemisphere
 Includes:
 Wernicke’s area  understanding
oral/written words
 Broca’s area  speech production
 Lateral prefrontal cortex 
language comprehension and
complex word analysis
 Lateral and ventral temporal cortex
 integrates visual and auditory
stimulate
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Cerebellum
 2nd largest region of the brain.
 10% of the brain by volume, but it contains 50% of its neurons
 Has 2 primary functions:
1. Adjusting the postural muscles of the body
 Coordinates rapid, automatic adjustments, that maintain
balance and equilibrium
2. Programming and fine-tuning movements controlled at the
subconscious and conscious levels
 Refines learned movement patterns by regulating activity of
both the pyramidal and extrapyarmidal motor pathways of the
cerebral cortex
 Compares motor commands with sensory info from muscles
and joints and performs any adjustments to make the
movement smooth
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Cerebellum
The cerebellum can be
permanently damaged by
trauma or stroke or
temporarily affected by
drugs such as alcohol.
These alterations can
produce ataxia – a
disturbance in balance.
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Diencephalon
Forms the central
core of the forebrain
3 paired structures:
1. Thalamus
2. Hypothalamus
3. Epithalamus
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Thalamus
 80% of the diencephalon
 Sensory relay station
where sensory signals can
be edited, sorted, and
routed.
 Also has profound input
on motor (via the basal
ganglia and cerebellum)
and cognitive function.
 Not all functions have
been elucidated.
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Hypothalamus
 Functions:
 Autonomic regulatory center
 Influences HR, BP, resp. rate,
GI motility, pupillary diameter.
 Can you hold your
breath until you die?
 Emotional response
 Involved in fear, loathing, pleasure
 Drive center: sex, hunger
 Regulation of body temperature
 Regulation of food intake
 Contains a satiety center
 Regulation of water balance and thirst
 Regulation of sleep/wake cycles
 Hormonal control
 Releases hormones that influence hormonal
secretion from the anterior pituitary gland.
 Releases oxytocin and vasopressin
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Epithalamus
Above the thalamus
Contains the pineal gland
which releases melatonin
(involved in sleep/wake
cycle and mood).
Contains a structure
called the habenula –
involved in food and
water intake
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Somatic Sensory Pathways in the
Central Nervous System
 Sensory pathways to the cerebral cortex are crossed
pathways.
 Impulses are conducted to its sensory areas by way of relays of
neurons referred to as sensory pathways.
 Each side of the brain registers sensations from the opposite side
of the body.
 General sensations of the right side of the body are
predominantly experienced by the left somatic sensory area.
 General sensations of the left side of the body are predominantly
experienced by the right somatic sensory area.
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left
right
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Somatic Motor Pathways in the
Central Nervous System
Impulses are conducted from its motor areas to
skeletal muscles by relays of neurons referred to
as somatic motor pathways.
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