Transcript Ch. 13 Central Nervous System

Ch. 13 Central Nervous
System
Lindsey Bily
Anatomy & Physiology
Austin High School
The Central Nervous System
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Consists of the brain and
spinal cord.
Processes all of the
information received from
the body and outside
world.
Coverings of the Brain and Spinal
Cord
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The brain and spinal cord are very delicate and so
vital. They are well protected.
Outer covering: bone (cranial bones and vertebrae)
Inner covering: membranes called meninges which
have 3 layers…
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Dura mater: strong white fibrous tissue (outer)
Arachnoid membrane: delicate cobweb layer (middle)
Pia mater: transparent and sticks to the surface of the
brain and spinal cord and contains blood vessels
(innermost)
Meninges
Meningitis
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Inflammation of the meninges.
Usually involves the arachnoid layer and the pia
mater.
Most often caused by bacteria, but can also be viral,
fungal, or due to tumors.
Symptoms are fever and severe headaches as well as
neck stiffness and pain.
Can be fatal.
Spinal meningitis only occurs in the spinal cord.
Cerebrospinal Fluid
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Cerebrospinal fluid (CSF)
cushions and bathes the
brain and spinal cord.
Found in the subarachnoid
space around the CNS and
within cavities or canals
within the CNS.
Ventricles: large fluid filled
spaces within the brain.
There are 4.
Cerbrospinal Fluid
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Formed by separation of fluid from blood in
ventricles.
Circulates through the ventricles and into the
central canal and subarachnoid spaces.
Absorbed back into the blood
The average adult has 140 mL in the CNS.
Hydrocephalus
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Condition that interferes with the circulation
of CSF.
Usually a tumor has blocked off flow.
Blood clots or hemorrhage may occur.
In an infant, the head may swell since the
cranium is not fused.
A tube may be inserted to drain the fluid, but
it can lead to brain damage, coma, or death.
Hydrocephalus
Hydrocephaly
normal
Spinal Cord
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About 18 inches long and extends from the
foramen magnum in the skull to the first
lumbar vertebra.
The spinal cavity includes the cord, meninges,
CSF, adipose tissue, and blood vessels.
Provides conduction routes to and from the
brain and serves as an integrator, or reflex
center or spinal reflexes.
Functions of the Spinal Cord
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Ascending tracts: conduct sensory impulses up the cord to the
brain.
Descending tracts: conduct motor impulses from the brain
down the spinal cord.
All of the axons from any tract originate from neuron cell
bodies located in the same area of the CNS and they
terminate in the same structure elsewhere in the CNS and
they serve one general function.
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EX: All of the axons in the spinothalamic tract originate from neuron
cell bodies located in the spinal cord and terminating in the thalamus.
All of the axons transmit impulses that produce sensations of crude
touch, pain and temperature.
Spinal Cord
Human cadaver
Brain
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One of the largest organs in the adult. Weighs about 3
pounds.
Attains its full size by age 18, but grows rapidly only until
about age 9.
There are six major divisions of the brain that you need to
know….
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Medulla oblongata
Pons
Midbrain
Cerebellum
Diencephalon
cerebrum
Brainstem
Divisions of the Brain
(cerebrum)
Structure of the Brainstem
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Three divisions make up the brainstem (pons,
medulla oblongata, midbrain)
Medulla Oblongata
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Attaches to the spinal cord.
About an inch in length.
Has cardiac, respiratory and vasomotor control
centers (vital centers).
Also controls non-vital reflexes such as vomiting,
coughing, sneezing, hiccupping and swallowing.
An injury or disease of the medulla is often fatal
(blows to the base of the skull or bulbar
poliomyelitis cause death because they interrupt
impulse conduction)
Pons
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Just above the medulla oblongata.
Has an arching, bridgelike appearance.
Contains control centers for reflexes mediated by the 5th, 6th,
7th, & 8th cranial nerves. (More on that in later chapters)
Midbrain
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Forms the midsection of the brain.
Lies above the pons and below the cerebrum.
Contains auditory and visual centers as well as muscle
control.
Cerebellum
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2nd largest part of
the brain
Has a distinctive
pattern similar to a
leaf.
Has numerous
grooves (sulci)
and raised areas
(gyri).
Functions of the Cerebellum
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Performs 3 general functions that control the
skeletal muscles.
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1. Acts with the cerebral cortex to produce skilled
movements by coordinating the activities of
groups of muscles.
Helps control posture. Makes movements smooth,
steady and efficient instead of jerky, trembling,
and awkward.
Controls skeletal muscles to maintain balance.
Functions of the Cerebellum
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Impulses from the cerebrum start motor
action, but also travel to the cerebellum. The
cerebellum compares the motor commands of
the cerebrum to the information coming from
receptors in the muscle.
It compares the intended movement with the
actual movement.
Cerebellar Disease
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Abscess, hemorrhage, tumors or trauma to the
cerebellum cause certain symptoms.
Ataxia (muscle incoordination), hypotonia,
tremors, disturbances of gait and balance.
Diencephalon
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Literally means
“between brain”.
Contains the
thalamus and
hypothalamus,
optic chiasma,
pineal body, and
other small
structures.
Thalamus
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Dumbbell shaped mass of gray matter made
up of many nuclei (cell bodies and
unmyelinated axons)
Large numbers of axons conduct impulses
into the thalamus from the spinal cord,
brainstem, cerebellum, cerebral nuclei and
various parts of the cerebrum.
Major relay station for sensory impulses on
their way to the cerebral cortex.
Thalamus
Thalamus
1.
2.
3.
4.
Once certain sensory impulses get to the thalamus,
we become conscious of the crude, less critical
sensations of pain, temperature and touch.
Plays a part in emotions. Associates sensory
impulses with feelings of pleasantness and
unpleasantness.
Plays a part in the arousal or alerting mechanism.
Plays a part in mechanisms that produce complex
reflex movements.
Hypothalamus
Hypothalamus
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Lies beneath the thalamus. “hypo” means low.
Weighs about 7 grams, but it is super
important for survival and the enjoyment of
life.
Functions as the link between the body and
the mind (soma and psyche).
Links the nervous system to the endocrine
system.
Hypothalamus Functions
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Regulator and coordinator of autonomic activities,
“Mind Body Link”: It is the major relay station between the cerebral
cortex and the lower autonomic centers; crucial part of the route by which
emotions can express themselves in bodily functions.
Synthesizes hormones secreted by the posterior pituitary gland and plays
an essential role in maintaining water balance because it makes a hormone
that is involved in amount of urine excreted.
Some neurons function as endocrine glands. The axons secrete releasing
hormones which cause the anterior pituitary to release certain hormones.
Plays a crucial role in the arousal mechanism. Sleepiness disorders can be
due to problems with the hypothalamus.
Involved in the mechanism regulating appetite.
Involved in the mechanism regulating body temperature. It has neurons
whose fibers connect with autonomic centers for vasoconstriction,
dilation, sweating and somatic centers for shivering.
Pineal Body (Gland)
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Named so
because it
resembles a
tiny pine cone.
Involved in
regulating the
biological
clock.
Produces
melatonin
Structure of the Cerebrum
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Cerebrum is the largest and uppermost division of
the brain and has two halves… left and right cerebral
hemispheres.
The surface of the cerebrum is 2-4mm thick and is
gray matter. Called the cerebral cortex.
Five lobes:
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Frontal lobe
Parietal lobe
Temporal lobe
Occipital lobe
insula
Cerebral Lobes
The insula lobe
is not visible.
You have to
separate the
temporal and
frontal lobes
to see it.
Cerebrum
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Mostly white matter, but
areas of gray matter
embedded are called
cerebral nuclei.
The corpus callosum
connects the left and
right hemispheres.
Parkinson Disease
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Normally neurons from the midbrain lead to the
cerebral nuclei and secrete dopamine.
Dopamine inhibits the excitatory effects of
acetylcholine.
In Parkinson disease, these neurons degenerate, so
you don’t have the dopamine.
The cerebral nuclei produce excess signals that affect
the voluntary muscles.
Overstimulation of the postural muscles of the neck,
trunk, and upper limbs produces tremors and
abnormal gait.
Functions of the Cerebral Cortex
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Certain areas of the cortex engage in
predominately one function. However, this
can vary from person to person and at
different times in an individual when the brain
is damaged. (cerebral plasticity)
The function of each region depends on the
structures that is communicates with.
No part of the brain functions alone and they
work together to function normally.
Sensory Functions of the Cortex
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The cortex integrates separate bits of sensory
information into whole perceptions.
For example, that someone put an ice cube in your
hand. You would see it and sense something cold
touching your hand. You would also know it was an
ice cube because you would perceive a total
impression compounded of many sensations such as
temperature, shape, size, color, weight, texture, and
movement and position of your hand and arm.
Fig. 13-17
Primary somatic sensory (A) and
motor (B) areas of the cortex. The
body parts illustrated here show
which parts of the body are "mapped"
to specific areas of each cortical area.
The exaggerated face indicates that
more cortical area is devoted to
processing information to/from the
many receptors and motor units of
the face than for the leg or arm, for
example.
Integrative Functions of the Cortex
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Consciousness
Use of language
Emotions
Memory
Consciousness
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The state of awareness of one’s self, one’s environment, and
other beings.
Very little is known about the neural mechanisms that
produce consciousness.
Depends on excitation of cortical neurons by impulses
conducted to them by a network of neurons known as the
reticular activating system.
The reticular activating system lies in the brainstem and
receives impulses from the spinal cord and relays them to the
thalamus then to all parts of the cortex.
If the neurons are not excited, you are unconscious.
Drugs that depress the activating system decrease your
alertness and put you to sleep (barbiturates).
Drugs such as amphetamines stimulate the center.
Consciousness
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We exhibit certain levels of consciousness at
different times.
Sometimes we are relaxed and nonattentive,
sometimes we are alert and attentive.
During sleep, we cycle from Slow Wave Sleep
(SWS) and Rapid Eye Movement (REM) sleep.
SWS has slow frequency, high voltage brain waves
and it’s dreamless.
REM has dreams.
States of Consciousness
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Anesthesia: reversible lack of awareness.
Coma: state of unconsciousness, lasting more than 6
hours in which a person cannot be awakened, fails to
respond normally to painful stimuli, light or sound,
lacks a normal sleep-wake cycle and does not initiate
voluntary actions.
Meditation: waking state but the person is highly
relaxed but also highly alert. Takes training and
practice.
Language
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Ability to speak and write words and to
understand spoken and written words.
Language centers are located in the frontal,
parietal, and temporal lobes almost
exclusively on the left side of the brain.
Lesions in speech centers give rise to
language defects (aphasias)
Emotions
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Controlled by the limbic system (emotional brain) in
the cerebrum.
Allows us to feel many emotions– anger, fear, sexual
feelings, pleasure, sorrow, etc.
However, other parts of the cortex control the normal
expression of these emotions.
Limbic activity without modulation by the cortex
may bring on attacks of abnormal, uncontrollable
rage.
Limbic System
Limbic System is also
involved in learning
and memory. We
are able to
recognize other’s
feelings and
associate emotions
with memories.
Memory
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Short-term memory: storage of information
for a few seconds or minutes. Short term
memories can be consolidated and stored as
long term memories days, months or weeks
later.
Temporal, parietal, and occipital lobes are
involved.
Left and Right Brain
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Left: talking, speaking, language, hand
movements (skilled and gesturing).
Right: Perception of non-speech sounds.
Melodies, coughing, crying, laughing. Better
at tactual perception and visualizing spatial
relationships.
Both sides of the brain communicate with
each other via the corpus callosum to perform
a task however.
Diseases
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Stroke: hemorrhage or clot in the brain causes destruction of
motor neurons in the cerebrum. May see paralysis.
Cerebral palsy: Damage to motor control areas of the brain
that is present at birth or occurs shortly after. May be caused
by prenatal infection, disease of the mother, lack of oxygen to
the brain.
Dementia: Degeneration of the neurons in the brain. Affects
memory, attention span, intellectual capacity, personality and
motor control.
Seizures: sudden bursts of abnormal neuron activity that
result in temporary changes in brain function.