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 and
shallow grooves:
 Gyri - Elevated
ridges
 Sulci – Shallow
grooves
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 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
Layers of the Cerebrum
 The corpus callosum (large fiber tract)
connects the cerebral hemispheres
 Allows the cerebral
hemi-spheres 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.
Layers of the Cerebrum
 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