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Chapter 7 - Part 3
The Nervous System
The Reflex Arc
 Reflex – rapid, predictable, and involuntary
responses to stimuli
 Much like a one-way street – once a reflex
begins, it always goes in the same direction
 Reflex arc – direct route from a sensory
neuron, to an interneuron, to an effector
 The neural pathway where reflexes occur over
Simple Reflex Arc
Types of Reflexes and Regulation
1. Autonomic reflexes
 Regulate the activity of smooth muscles, the heart,
and glands.
 Regulate digestion, elimination, blood pressure,
and sweating.
 Examples: Secretion of saliva and changes in the
size of the eye pupils.
2. Somatic reflexes
 Include all reflexes that stimulate the skeletal
muscles.
 Examples: When you pull your hand away quickly
from a hot object.
CNS
 During embryonic
development, the
CNS first appears
as a simple tube, the neural tube
 The neural tube becomes the brain and
spinal cord
 The opening of the neural tube enlarges
and becomes the ventricles or chambers
 Four chambers within the brain
 Filled with cerebrospinal fluid
The Brain
• It weighs a little
over 3 lbs.
• It looks wrinkled
like a walnut and
with the texture of
cold oatmeal.
• Largest and most
complex mass of
nervous tissue in
the body.
Regions of the Brain
1. Cerebral
hemispheres
2. Diencephalon
3. Brain stem
4. Cerebellum
Cerebral Hemispheres (Cerebrum)
 Paired (left and
right) superior
parts of the brain
 Include more than
half of the brain
mass
 Encloses and
obscures much of
the brain stem
 How a mushroom
cap covers the
top of the stalk
Cerebral Hemispheres (Cerebrum)
 The surface
is made of
elevated
ridges (gyri)
and shallow
grooves
(sulci)
Lobes of the Cerebrum
 Fissures (deep grooves) divide the
cerebrum into lobes
 Surface lobes of
the cerebrum
1. Frontal lobe
2. Parietal lobe
3. Occipital lobe
4. Temporal lobe
Lobes of the Cerebrum
Specialized Areas of the Cerebrum
 Somatic sensory area – receives impulses
from the body’s sensory receptors
 Located in the parietal lobe
 Allows you to recognize pain, coldness, or a
light touch
 The body is represented in an upside down
manner in the sensory area
 The sensory pathways are crossed – the left
side of the cortex receives impulses from the
right side of the body
Sensory and Motor Areas of the
Cerebral Cortex
Specialized Areas of the Cerebrum
 Impulses from the special sense organs are
interpreted in other cortical areas.
 Visual area
 Located in the posterior part of the
occipital lobe
 Olfactory area
 Located deep inside the temporal lobe
Specialized Areas of the Cerebrum
 Primary motor area – sends impulses to
skeletal muscles
 Allows us to consciously move our skeletal
muscles
 Located in the frontal lobe
 The body is represented upside-down
 Pathways are crossed
 Most of the neurons in the this primary
motor area control body areas having the
finest motor control (face, mouth, hands)
Specialized Areas of the Cerebrum
 Broca’s area – involved in our ability to
speak
 Damage to this area causes inability to say
words properly (you know what you want
to say, but you can’t vocalize the words)
Specialized Areas of the Cerebrum
 Higher intellectual reasoning – believed to be
in the anterior part of the frontal lobe
 Complex memories – Appear to be stored in
the temporal and frontal lobes
 Language comprehension (word meanings) –
located in the frontal lobes
 Speech Area – allows one to sound out
words
 Located at the junction of the temporal,
parietal, and occipital lobes
Layers of the Cerebrum
 Gray matter
 Outer layer
 Composed mostly
of neuron cell
bodies
 Cerebral cortex –
the outermost
gray matter of the
cerebrum
Layers of the Cerebrum
 White matter
 The remaining,
deeper cerebral
hemisphere tissue
 Composed of fiber tracts
(bundles of nerve fibers)
carrying impulses to or from
the cortex
 The corpus callosum
(large fiber tract) connects
the cerebral hemispheres
 Allows the cerebral hemispheres to communicate with
one another
Layers of the Cerebrum
 Although most of the gray matter
is in the cerebral cortex, there are
several islands of gray matter
buried deep within the white matter.
 Basal nuclei – internal islands of gray matter
 Help regulate voluntary motor activities by
modifying sent instructions
 Individuals who have problems with their basal
nuclei are often unable to walk normally or
carry out other voluntary movements.
 Examples: Huntington’s disease and
Parkinson’s disease
Diencephalon
 Sits on top of the brain stem
 Enclosed by the cerebral hemispheres
 Made of three parts
1. Thalamus
2. Hypothalamus
3. Epithalamus
Diencephalon
Thalamus
 Surrounds the third
ventricle
 The relay station for
impulses
 Transfers impulses to the correct part of
the cortex for localization and
interpretation
Hypothalamus
 Under the
thalamus
 Important
autonomic nervous
system center
 Helps regulate body temperature
 Controls water balance
 Regulates metabolism
Hypothalamus
 Center for many drives and emotions
 An important part of the limbic system
(emotions)
 Thirst, appetite, sex, pain, and pleasure
centers are in the hypothalamus
 Regulates the pituitary gland (endocrine
organ) and produces two hormones of its
own.
 The pituitary gland hangs from the
anterior roof of the hypothalamus by a
slender stalk.
Epithalamus
 Forms the roof
of the third
ventricle
 Houses the
pineal body (an
endocrine gland)
 Includes the choroid plexus – knots of
capillaries within each ventricle that
forms the cerebrospinal fluid
Brain Stem
 Attaches to the spinal cord
 About the size of a thumb in
diameter and approximately
3 inches long
 Functions:
1. Provide a pathway for ascending and descending
tracts
2. Has many small gray matter areas (form cranial
nerves and control many vital activities)
 Parts of the brain stem:
1. Midbrain
2. Pons
3. Medulla oblongata
Brain Stem
Figure 7.15a
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.38b
Midbrain
 Mostly composed of tracts of nerve fibers
 Composed primarily of two bulging fiber tracts
– cerebral peduncles (literally, “little feet of
the cerebrum”)
 Function is to convey ascending and
descending impulses
 Has four rounded protrusions – corpora
quadrigemina
 These bulging nuclei are reflex centers
involved with vision and hearing
Pons
 The bulging
center part of the
brain stem
 Mostly composed of fiber tracts
 Includes nuclei involved in the control of
breathing
Medulla Oblongata




The lowest part of the brain stem
Merges into the spinal cord
Is an important fiber tract area
Contains important control centers
 Heart rate control
 Blood pressure
regulation
 Breathing
 Swallowing
 Vomiting
Reticular Formation
 Diffuse mass of gray matter along the
brain stem
 Involved in motor control of visceral
organs
 Reticular activating system (RAS)
plays a role in awake/sleep cycles and
consciousness
 Damage to this area can result in
permanent unconsciousness (coma)
Reticular Formation
Figure 7.15b
Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings
Slide 7.42b
Cerebellum
 Projects dorsally
from under the
occipital lobe
 It has two hemispheres and a
convoluted surface
 Has an outer cortex made up of gray
matter and an inner region of white
matter
Functions of the Cerebellum
 Involuntary
 Provides the
precise timing for
skeletal muscle
activity and
controls our
balance and
equilibrium
 Makes our body movements smooth
and coordinated
Damage to the Cerebellum
 If the cerebellum is damaged,
movements become clumsy and
disorganized.
 Cannot keep their balance and
appear to be drunk because of the
loss of muscle coordination.
 They are no longer able to touch their
finger to their nose with their eyes
shut.