Transcript The Central Nervous System

Central Nervous System
Brain and Spinal Cord
Central Nervous System
• The brain and spinal cord
• Control center of the body
• Receives, processes and
interprets the messages
then determines what
output occurs
The Brain
• Contains about 12 billion neurons and weighs about 3 pounds
• Wrinkled like a walnut and has a consistency of oatmeal
• Regions of the brain
– Cerebrum (cerebral hemispheres)
– Diencephalon
– Brain Stem
– Cerebellum
Cerebellum
Cerebrum (Cerebral Hemispheres)
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Superior part of the brain composed of two hemispheres
Has gray matter, white matter and basal nuclei
Largest mass of the brain (83%)
Responsible for voluntary or conscious activities
Allows us to remember the past, plan for the future, and
imagine things that have not happened
Cerebrum (Cerebral Hemispheres)
• Each hemisphere is divided
into regions called lobes
• Four lobes named for their
skull bones that cover them
– Frontal
– Parietal
– Temporal
– Occipital
Cerebrum (Cerebral Hemispheres)
• Gyri (gyrus)
– Elevated ridges of tissues
• Sulci (sulcus)
– Shallow grooves
• Fissures
– Deeper grooves
– Usually separate large parts of the
brain
• Some fissures and sulci are
used for anatomical landmarks
• Longitudinal fissure
– Separates right and left
hemispheres
• Transverse fissure
– Separates cerebrum and
cerebellum
Cerebrum (Cerebral Hemispheres)
• Central sulcus
– Separates frontal and
parietal lobes
• Parieto-occipital sulcus
– Separates occipital and
parietal lobes
• Lateral sulcus
– Separates temporal from
parietal and frontal lobe
– Outlines temporal lobe
• Precentral gyrus
– Anterior to central sulcus
• Postcentral gyrus
– Posterior to central sulcus
Cerebral Cortex “Conscious Mind”
• Cortex = outer layer composed
of gray matter
• Neuron cell bodies, dendrites,
and glia
• It has many convolutions that
triple the surface area
• Function: aware of
surroundings, communicate,
remember, understand and
initiate voluntary movements
• Alzheimer’s disease –
dementia producing lesions of
the cerebral cortex
Cerebral Cortex “Conscious Mind”
• Generalizations about the cerebral hemispheres
1. Three kinds of functional areas
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Sensory, motor, and association areas
2. Each hemisphere is concerned with the functions of
the opposite side of the body
3. Two hemispheres are not entirely equal in function
4. No functional area acts alone and conscious
behaviors involve the entire cortex
Cerebral Cortex “Conscious Mind”
• Functional regions can be seen using modern imaging
techniques
– PET scans show metabolic activity in the brain
– fMRI reveal blood flow
• Specific motor and sensory functional areas can be mapped
• Provide evidence that higher level thinking, memory and
language have overlapping areas
Motor Areas of the Cerebrum
• Control voluntary movements
• Located in the posterior part of the frontal lobes
1. Primary motor cortex
2. Premotor cortex
3. Broca’s area
Premotor cortex
Broca’s Area
Primary motor cortex
Motor Areas of the Cerebrum
• Primary motor cortex
– Precentral gyrus of the frontal
lobe of each hemisphere
– Allow us to consciously
control the precise, voluntary
movements of our skeletal
muscles
Motor Areas of the Cerebrum
• Primary motor cortex
– The entire body is
represented spatially in each
hemisphere
– Areas with greater need for
precise control are larger
– Damage to localized areas
paralyzes the voluntarily
controlled muscles of those
areas (left affects right side)
Motor Areas of the Cerebrum
• Premotor cortex
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Anterior to the precentral gyrus in the frontal lobe
Controls learned motor skills of a patterned nature
Coordinates the movement of several muscle groups
Involved in planning movements
Destruction results in a loss of the motor skills
programmed in that region
Motor Areas of the Cerebrum
• Broca’s area
– Anterior to the inferior region of the premotor area
(left side)
– Special motor speech area that directs the muscles
involved in speech planning and production
– People who suffer damage to this area usually have
aphasia – inability to create complete thoughts
verbally
Sensory Areas of the Cerebrum
• Concerned with conscious awareness of sensation
• Occur in the parietal, temporal and occipital lobes
– Primary sensory cortex
– Sensory association cortex
– Visual areas
– Auditory areas
– Olfactory cortex
– Gustatory cortex
Sensory Areas of the Cerebrum
• Primary sensory cortex
– Located in the postcentral gyrus of the parietal lobe
– Posterior to the primary motor cortex
– Neurons receive information from the general sensory
receptors in the skin and from proprioceptors in
skeletal muscles
– Identifies the body region being stimulated
Sensory Areas of the Cerebrum
• Primary Sensory Cortex - Homunculus Man
– The body is represented spatially and upside-down
according to the site of stimulus
– The right hemisphere receives input from the left side
of the body
– The amount of sensory cortex devoted to a body
region is related to the region’s sensitivity
– The face and fingertips are the most sensitive
Sensory Areas of the Cerebrum
• Sensory association cortex
– Posterior to the primary sensory cortex in the parietal lobe
– Integrates sensory inputs (temperature, pressure etc, not special
senses) from the primary sensory cortex
– Produces an understanding of an object being felt: its size, texture,
and the relationship of its parts
– Example: when you reach into your pocket, the stored memories of
the past sensory experiences perceive the objects you feel as coins
– Damage to this area would hinder recognition of these objects without
looking at them
Sensory Areas of the Cerebrum
• Primary visual cortex
– Posterior tip of the occipital lobe
– Receives visual information
– Damage to this area results in
functional blindness
• Visual association area
– Surrounds the primary visual cortex
– Uses past visual experiences to
interpret visual stimuli (color, form, and
movement)
– Enables us to recognize a flower and
appreciate what we are seeing
– People with damage to this area can
see but cannot comprehend what they
are looking at
Sensory Areas of the Cerebrum
• Auditory cortex
– Located in the superior margin of the temporal lobe
– Interpreted sounds as pitch, loudness and location
• Auditory association area
– Permits the perception of the sound
– Allows us to ‘hear’ a speech, screams, music, etc.
– Memories of sounds are stored here
Sensory Areas of the Cerebrum
• Primary olfactory (smell) cortex
– Medial aspect of the temporal lobe
– Conscious awareness of different odors
– Very involved in memory and emotion
• Gustatory (taste) cortex
– Located deep to the temporal lobe
– Involved in the perception of taste
• Wernicke’s Area
– Only in left parietal lobe
– Comprehension of written and
spoken language
Association Areas of the Cerebrum
• Analyzes sensory inputs from multiple senses
• Sends outputs to multiple motor areas
• Where sensations, thoughts, and emotions become
conscious
• Information flows from:
– Sensory receptors  primary sensory cortex 
sensory association cortex  motor cortex
• Association cortex
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Allows us to give meaning to the information that we receive
Store memories
Tie messages to previous experiences and knowledge
Decide what action to take
Relay it to the motor cortex
Association Areas of the Cerebrum
• Prefrontal cortex
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Anterior part of frontal lobe
Thought, intelligence, motivation, personality
Sets humans apart from other animals
Tumors can cause wide mood swings, loss of attentiveness,
initiative and judgment
– Prefrontal lobotomy is a surgical technique to treat severe mental
illness (rare)
Association Areas of the Cerebrum
• Affective language areas
– Right side of frontal lobe
– Opposite Broca’s area and Wernicke’s area
– Involved in nonverbal, emotional components of
language
Lateralization of Cerebrum
• Division of labor between hemispheres
• Both cerebral hemispheres appear identical and are
used for almost every activity
• Each hemisphere has unique abilities not shared by its
partner – lateralization
Lateralization of Cerebrum
• Each half of the cerebrum deals mainly with the
opposite side of the body
– Sensations from the left side of the body go to the
right hemisphere of the cerebrum and vice versa
• One hemisphere tends to be more dominant for
language, speech, logic and analytical skills – cerebral
dominance
• The other hemisphere is more free-spirited, involved in
visual-spatial skills, emotion and creativity
Lateralization of Cerebrum
• 90% of people are left
hemisphere dominant and are
usually right-handed
• 10% of people are right
hemisphere dominant and are
usually left-handed and male
– Some “lefties” have a cerebral
cortex that functions bilaterally are
ambidextrous
• The two hemispheres have
perfect and almost instantaneous
communication with one another
via connecting fiber tracts –
corpus collusum
Hemisphere Inventory
LEFT BRAIN FUNCTIONS
uses logic
detail oriented
facts rule
words and language
present and past
math and science
can comprehend
order/pattern perception
knows object name
reality based
forms strategies
practical
safe
RIGHT BRAIN FUNCTIONS
uses feeling
"big picture" oriented
imagination rules
symbols and images
present and future
believes
appreciates
spatial perception
knows object function
fantasy based
presents possibilities
impetuous
risk taking
Cerebral White Matter
• White matter deep to the cortical gray matter is
responsible for communication between cerebral areas,
cerebral cortex and lower CNS centers
• White matter consists largely of myelinated fibers bundled
into large tracts
Cerebral White Matter
• Fiber tracts are classified according to the direction in
which they run
– Commisures connect corresponding gray areas of two
hemispheres enabling them to function as a whole
• The largest is the corpus collosum
– Association fibers connect different parts of the same hemisphere
– Projection fibers connects the cerebrum and lower brain areas
• Sensory information reaches the cerebral cortex and motor
output leaves it through these fibers
Basal Nuclei
• Gray matter (group of nuclei) deep within the white matter
• Receives input from entire cerebral cortex
• Output initiates and controls muscle movements directed
by primary motor cortex
• Necessary to perform several activities at once
• Disorders result in too much or too little movements like in
Parkinson’s disease
Diencephalon, Brain Stem and
Cerebellum
Diencephalon
• Extends from the brain stem
• Surrounded by the cerebrum
• Regions of the diencephalon
– Thalamus
– Hypothalamus
– Epithalamus
– Pituitary gland
Diencephalon
• Thalamus “inner room”
– Location
• Superior, egg shaped portion
– Composition
• Gray matter
– Functions
• Gateway to the cerebral cortex
• Relay station for sensory inputs
and motor outputs
• Sorts out and groups inputs
together
– Imbalance
• Damage to the area causes
increase in sensitivity to pain and
loss of consciousness
Diencephalon
• Hypothalamus
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Location
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Below the thalamus and caps the brain stem
Functions
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Main visceral control center of the body
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Vitally important in overall homeostasis
1. Autonomic control center
– Regulates cardiac and smooth muscle and
secretion of glands
– Influences blood pressure, rate and force of
heart beat, digestive tract motility, eye pupil
size, etc
2. Center for emotional response – “heart” of the
limbic system
– Nuclei involved in perception of pleasure,
fear, rage and biological rhythms and drives
– Initiates the physical expressions of emotion
through the ANS
Diencephalon
• Hypothalamus
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Controls body temperature
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Body’s thermostat is hypothalamus
Monitor blood temperature and
receive input from thermoreceptors
Initiates cooling (sweating) and
heating (shivering) as needed
Regulates food intake
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Responds to changing blood levels of
certain nutrients of hormones by
regulating feelings of hunger
Regulates water balance and
thirst
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Osmoreceptors regulate the
concentration of water
Neurons trigger the release of
antidiuretic hormone (ADH) from the
pituitary gland to retain water
Stimulates thirst center to drink more
Diencephalon
• Hypothalamus
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Regulates sleep-wake cycles
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Controls endocrine system
functioning
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Sets the timing of the sleep cycle in
response to daylight-darkness cues
received from visual pathways
Acts as the helmsman of the
endocrine system by releasing and
inhibiting hormones of the pituitary
gland
Imbalance
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Disorders include severe body wasting,
obesity, sleep disturbances, dehydration,
emotional imbalances
Diencephalon
• Epithalamus
– Location: most dorsal portion of diencephalon
– Components and function
• Pineal gland
– Secretes the hormone melatonin
– Responsible for body rhythms (biological clock)
• Choroid plexus
– Forms cerebrospinal fluid (CSF)
Diencephalon
• Pituitary Gland
– Part of the endocrine system but located in the brain
– Controlled by the hypothalamus
– Secretes regulatory hormones
Brain Stem
• Location
– Between the cerebrum and the spinal cord
• Composition
– Deep gray matter surrounded by white matter fiber tracts
– Three regions
1. Midbrain
2. Pons means “bridge”
3. Medulla oblongata
• Functions
– Provides a pathway for fiber tracts running between higher
and lower neural centers
– Produces the programmed, automatic behaviors necessary
for survival
– Associated with 10 of the 12 cranial nerves – provides the
main motor outputs and sensory inputs of the face and neck
Brain Stem
• Midbrain
– Location
• Between the diencephalon and the pons
• Superior part of brain stem
– Functions
• Pain suppression
• Link between the fear perceiving
amygdala and ANS pathways that
control “fight or flight” response
• Visual reflexes that coordinate head and
eye movement
• Auditory relay from the hearing
receptors to the auditory cortex
• Startle reflex which causes you to turn
you head toward and unexpected sound
Brain Stem
• Midbrain
– Substantia nigra
• High content of melanin a
precursor for dopamine
• Linked to the basal nuclei
• Releases dopamine
• Controls subconscious motor
movements
• Degeneration of dopaminereleasing neurons cause
Parkinson’s disease
Brain Stem
• Pons “bridge”
– Location
• Bulging brain stem region
• Wedged between the midbrain and the medulla oblongata
– Composition
• Conduction tracts oriented in two opposite directions
• Deep projection fibers run longitudinally and complete the pathway
between higher brain centers and spinal cord
• Superficial ventral fibers run transversely and dorsally and connect
the pons bilaterally with the two sides of the cerebellum dorsally
• Cranial nerve pairs = trigeminal, abducens, and the facial nerve
– Functions
• Controls normal rhythm of breathing
• Relays impulses from one side of the cerebellum to the other and
between the medulla and midbrain
Brain Stem
• Medulla Oblongata
Medulla
Oblongata
– Location
• Most inferior part of the brain stem
• Blends into the spinal cord at the foramen magnum
– Composition
• Made of white and gray fibers called reticular formation
• Above medulla- spinal cord junction fibers cross over to the
opposite side before traveling to the spinal cord
– Functions
• Relays sensory information from spinal cord to sensory cortex
• Autonomic reflex center for body homeostasis
– Cardiovascular center = adjusts force and rate of heart rate
– Vasomotor center = regulates blood pressure
– Respiratory center = controls rate and depth of breathing
– Regulates vomiting, hiccupping, swallowing, coughing and
sneezing
Cerebellum
• Second largest part of the brain
• Location
– Dorsal to the pons and medulla
– Protrudes under the occipital lobes
– Below and posterior to the cerebrum
• Composition
– Outer gray matter and inner white forms arbor vitae
Cerebellum
• Functions
– Subconscious aspects of skeletal movements
– Provides precise timing of skeletal muscle contraction
– Compares intended movements with what is actually happening
to smooth, skilled movements
– Regulates posture, equilibrium and balance
• Imbalance
– Damage produces ataxia (lack of coordination due to errors in
speed, force, direction of movement
Functional Brain Systems
• Limbic System
– Associated with emotional brain
– Emotional brain is the functional system involving cerebral and
diencephalon structures that mediates emotional response
– Interacts with the cerebral cortex
– Hypothalamus is gatekeeper of responses
– Communications between the cerebral cortex and the limbic
system also permit us to refrain from acting out our emotions
when reason warns that a particular response would be unwise
– Structures within the limbic system
• Hippocampus
• Amygdala – incorporates and store sensory perceptions into
fact memory; oversees the memory system
• Mammillary bodies – olfaction and swallowing reflexes
– Damage to the hippocampus and amygdala causes amnesia
Brain Bank
http://video.nationalgeographic.com/video/player/science/health-human-bodysci/human-body/brain-bank-sci.html
Central Nervous System
• Brain and spinal cord are in
three layers of connective
tissue called the meninges
• Three layers
– Dura mater – double-layered
external covering
– Arachnoid - middle layer
– Pia mater – internal layer;
clings to the surface of the
brain
• Meningitis – bacterial/viral
inflammation of meninges,
causes headache, fever,
sore throat, back and neck
pain
Cerebrospinal Fluid
• Filled between the meninges and
the CNS
• Similar to blood plasma composition
• Clear, colorless and composed of
water, 40-60% glucose, NaCl, K,
protein and a few white blood cells
• Bathes skull, brain and spinal cord
• Serves as a shock absorber for the
brain and spinal cord
• Provides nutrients and waste
removal for brain tissue
• 400-500 mL produced daily, only
140 mL is circulating at any time
• Circulates through the ventricles and
into the central canal and
subarachnoid spaces and is
absorbed back into the blood
Ventricles
• Cerebrospinal fluid filled spaces of
the brain
• Formed by the choroid plexus
• Four ventricles
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Right lateral ventricle
Left lateral ventricle
Foramen of Monro – connects
lateral ventricles with third ventricle
Cerebral aqueduct - connects third
with fourth ventricle
In the roof of the fourth ventricle
are openings that allow CSF to
move into the cisterna magna
• Hydrocephalus – increased
accumulation of CSF within the
ventricles, causes cranium to
enlarge unless treated with a shunt
to remove excess fluid
Blood Brain Barrier
• Protective mechanism that helps ensure
that the brain’s tissue remains stable
• Brain cannot be subjected to drastic
variations in hormones, amino acids, ions
– Could result in uncontrolled neural activity
• Permeable to water, nutrients, and fatty
acids
• Includes the least permeable capillaries of
the body
• Excludes many potentially harmful
substances
• Useless against some substances
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Fats and fat soluble molecules
Respiratory gases
Alcohol
Nicotine
Anesthesia
Homeostatic Imbalances
• Cerebrovascular Accidents (CVA) – Stroke
– Caused by hemorrhage from cessation of blood
flow through cerebral blood vessels
– Blood circulation to a brain area is blocked
(blood clot, hemorrhage) and vital brain tissue
dies
– Can cause injury to upper motor neurons
• Transient Ischemic Attack (TIA)
– 5-30 minutes of paralysis
– Numbness, impaired speech
– Ischemia = loss of blood to any tissue
Homeostatic Imbalances
• Dementia – “forgetfulness”
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Loss of brain function that occurs with certain diseases
General term of destruction of neurons of brain
Degenerative - nonreversible
Affects memory, language, attention span, intellect, personality,
cognitive skills
– Most common type is Alzheimer’s
– Parkinson’s disease, multiple sclerosis, or Huntington’s disease
are a few other diseases that can lead to dementia
Homeostatic Imbalances
• Epilepsy
– Seizures caused by tumors or
chemical imbalances
– Treated with drugs that block
synaptic transmission