The
Nervous
System
Chapters 10 and 11
Nervous System
• Master controlling and
communicating system
Interesting Facts
• A 1999 study of Einstein’s brain, based on photographs taken of it after
he died in 1955, showed that the parietal lobes, which are linked to math
ability, appear 15% wider than normal. But the size of his brain was a
little smaller than average.
• We may be the smartest creatures on the planet, but others have bigger
brains. Larger brains are needed partly to control larger muscles. A
sperm whale's brain weighs about 17 pounds and an elephant's weighs a
little more than 10 pounds.
• Your brain is only about 2% of your body weight, but brain cells use
twice as much energy as other cells in your body. Brain cells are always
active, even when you sleep.
• Studies suggest that your brain is aware of subliminal, or hidden,
messages even when you aren't. Human faces that express emotions,
such as smiling or frowning, seem to have the strongest impact.
• Researchers believe that sleep gives the brain time to process and store
memories. People who don’t get enough sleep have trouble concentrating
and recalling memories.
• Brain cells are the longest living cells in the body. Research shows that
some parts of the brain may be able to grow new neurons as we age. But
most of our brain cells are present from birth to death. The wiring of
these cells changes constantly through our lives.
Basic Functions
1. Sensory input – gather information
2. Integration – process and interpret sensory
input
3. Motor output – response by muscles and
glands
Organization
A. Central Nervous System (CNS)
▫ Brain & spinal cord
▫ Integrative and control centers
B. Peripheral Nervous System (PNS)
▫ Nerves (spinal nerves, cranial nerves)
▫ Communication lines between CNS and rest of body
▫ Two Divisions:
1. Sensory (afferent) Division: Sensory receptors
 CNS
2. Motor (efferent) Division: CNS  effectors
(muscles & glands)
Motor Division
• Somatic nervous system (voluntary) –
control skeletal muscles
• Autonomic nervous system (ANS)
(involuntary) – regulate smooth muscles,
cardiac, glands
▫ Subdivisions:
 Sympathetic: primary process is stimulating the
body's fight-or-flight response; constantly active at
a basic level to maintain homeostasis
 Parasympathetic: serves to slow the heart rate,
increase intestinal and glandular activity, and
relax the sphincter muscles
Brain Anatomy
Brain Anatomy…
• Brain: mass of 100-120 billion neurons and
neuroglial cells weighing approximately 3 pounds,
protected by cranial bones
• Cerebrum: largest mass of brain (83% of brain
mass); responsible for higher mental functions and
distribution of impulses
▫ Cerebral medulla: white matter, conduction
pathways
▫ Cerebral cortex: outer layer of gray matter; short
and long term memory
Cerebrum
• Divided into right and left
hemispheres
▫ left side governs right side of body
▫ right side governs left side of body
• Lobes
▫ Frontal: learning, planning,
organizing, behavior, emotion,
language production/comprehension
 Motor Cortex: voluntary movement
▫ Parietal: sensory (pain/pressure),
distance, size, shape,
cognitive/intellectual processes
▫ Occipital: vision, visual memory
▫ Temporal: memory, auditory,
olfactory, speech, judgment, reasoning,
will power, emotion
Brain Anatomy
• Gyrus (gyri): elevated
ridges/folds
• Sulcus (sulci): shallow
grooves
• Fissures: deep grooves
▫ Longitudinal: separates
right and left hemispheres;
corpus callosum (large fibers
that connect the two
hemispheres)
▫ Transverse: separates
cerebrum from cerebellum
▫ Fissure of Rolando:
divides frontal and parietal
lobes at coronal suture
▫ Fissure of Sylvan/lateral
fissure: divides frontal and
temporal lobes
cerebellum
• Below and posterior to
cerebrum
▫ Outer gray, inner white
forms arbor vitae
▫ Function is to
coordinate and regulate
muscular activity
▫ Damage produces
ataxia (lack of
coordination due to
errors in speed, force,
direction of movement
• Damage = coma
▫ Controls: heart rate and
blood pressure, smell and
taste, eye movement,
appetite, vision, balance
▫ 3 Parts:
 Midbrain: Short section
of the brain stem between
the diencephalon and the
pons
 Cerebral aqueduct: CSF
 Pons: The rounded bulge
on the underside of the
brain stem, where it
separates the midbrain
from the medulla
oblongata.
 Medulla oblongata:
Portion of the brain
between the pons and the
spinal cord.
Brain Stem
Diencephalon
• Diencephalon: area between
cerebrum and midbrain
▫ Composed of the thalamus,
hypothalamus, subthalamus,
and epithalamus
▫ Thalamus: gray matter, relay
station for sensory incoming and
motor outgoing impulses;
damage - increased sensitivity to
pain, loss of consciousness
▫ Hypothalamus: forms floor of
third ventricle
 Regulates autonomic control
 Cardiovascular control,
temperature control, appetite,
water balance, GI control,
emotional states
▫ Epithalamus: part of the
forebrain including the pineal
gland and a region in the roof of
the third ventricle of the brain.
Anatomy of the Brain
Nervous System ~ Part 2
White vs. Grey Matter
• The CNS is made up of two types of tissue: grey
matter and white matter.
• Grey matter is mainly composed of neuron cell
bodies, glial cells, and unmyelinated axons
▫ Axons are the processes that extend from neuronal
cell bodies, carrying signals between those bodies.
▫ In grey matter, these axons are mainly
unmyelinated, meaning they are not covered by a
whitish-colored, fatty protein called myelin.
▫ Color comes from greyish hue of the neurons and
glial cells combining with the red of the capillaries to
give this tissue its greyish-pink color
• The grey matter serves to process information in
the brain; process signals generated in the
sensory organs or other areas of the grey matter.
This tissue directs sensory (motor) stimuli to
nerve cells in the central nervous system where
synapses induce a response to the stimuli.
• White matter is mainly composed of long-range
myelinated axons (that transmit signals to the
grey matter) and very few neuronal cell bodies.
▫ Myelin forms a protective coating around these
axons, insulating them and improving their
transmission of neuronal signals.
Meninges of the Brain
Brain is protected by the skull and 3 layers of membranes called
meninges
Meninges
• DURA MATER (literally means “tough mother”)
▫ Tough outer layer
• ARACHNOID MATER (literally means “spider
mother”)
▫ Beneath and stuck to the dura mater
▫ Stringy, web-like
▫ Space under the arachnoid, the subarachnoid
space, is filled with cerebrospinal fluid and
contains blood vessels.
• PIA MATER (means “tender mother”)
▫ Thin transparent membrane that follows the
contour of the ridges (gyri) and valleys (sulci) of
the brain.
Corpus
Callosum
• Broad
band of nerve fibers
joining the two hemispheres
of the brain
▫ largest white matter
structure in the brain
• This bundle of nerve tissue
contains over 200 million
axons
▫ This neural tissue facilitates
communication between the
two sides of the brain
Cerebellar Vermis
• The cerebellar vermis receives information
from the spinal cord about the sense of touch
and proprioception.
▫ Proprioception is the ability to sense or
perceive the spatial position and movements of
your body.
CSF and
Ventricles
• The ventricles of the
brain are a communicating network of
cavities filled with cerebrospinal fluid (CSF)
• Functions of CSF:
▫ Protection –cushion for the brain, limiting neural damage in
cranial injuries
▫ Buoyancy –being immersed in CSF reduces weight of brain
and prevents excessive pressure on the base of the brain.
▫ Chemical stability – creates an environment to allow for
proper functioning of the brain.
• The ventricular system is composed of:
▫
▫
▫
▫
Lateral ventricles (2)
Third ventricle
Cerebral aqueduct
Fourth ventricle
• The choroid plexuses located in the ventricles produce
CSF, which fills the ventricles and subarachnoid space,
following a cycle of constant production and reabsorption.
Additional Anatomical
Structures…
• Pineal gland: Produces the hormone melatonin at
night which helps maintain circadian rhythm and
regulate reproductive hormones
• Mamillary bodies: serve as relay stations for
impulses; important in forming and recalling
memories
▫ Destruction or injury to these portions of the brain is
often associated with amnesia
• Inferior Colliculi: main auditory (sound) center for
the body; acts as the channel for almost all auditory
signals in the human body (reflex center – midbrain)
• Superior Colliculi: movement of eyes, head and
neck in response to visual stimuli (reflex center –
midbrain)
• Infundibulum: connection between the
hypothalamus and the posterior pituitary; pituitary
stalk
System
Cranial Nerves and Dissection Preparation
Part 3
Cranial Nerves I and II
• Olfactory Nerve (I): responsible for smell
▫ Olfactory bulb: Structure located in the forebrain that
receives neural input regarding smell
• Optic Nerve (II): transfer of visual information from
retina to visual centers of the brain
▫ Optic chiasma: X-shaped structure on the underside of
the brain formed by a partial crossing over of optic nerves
Cranial Nerves 3-6
• Oculomotor nerve (III): enable
movements of the eye and eyelid
• Trochlear nerve (IV): smallest
to service the eye; moves the
superior oblique muscle of the eye
• Trigeminal nerve (V):
responsible for sensation in the
face and motor functions (biting,
chewing)
• Abducens nerve (VI): controls
the movement of the lateral
rectus muscle of the eye
Cranial Nerves 7-10
• Facial Nerve (VII): supplies the
muscles of facial expression
• Vestibulocochlear Nerve (VIII):
responsible for both hearing and balance
and brings information from the inner
ear to the brain
• Glossopharyngeal Nerve
(IX): receives general sensory from the
tonsils, the pharynx, the middle ear and
the posterior 1/3 of the tongue; taste
• Vagus Nerve (X): involuntary nervous
system and commands unconscious body
procedures, such as keeping the heart
rate constant and controlling food
digestion
Cranial Nerves 11
and 12
• Accessory Nerve (XI):
neck muscle movements
• Hypoglossal Nerve (XII):
controls movements of the
tongue
Arbor Vitae
• White matter of the cerebellum
• Named as much due to its branch-like
appearance
• Brings sensory and motor info to and from the
cerebellum
Human vs. Sheep Brain (ctd.)
• The convolutions and sulci comprises of a larger surface
area than sheep brains
▫ Sheep brains have less ridges and contours.
• Human behavior and motor control is typically
controlled by the cerebellum
▫ Sheep brains have a much smaller cerebellum than the
human brain, which, in comparison with humans and
their complex learned behaviors, have less motor control
and less learning abilities.
• The olfactory bulb is larger in the sheep’s brain than
that of the human brain
▫ Animals usually rely more upon their senses and abilities
of smell than humans do.
▫ Humans rely more upon other senses, such as sight and
hearing, rather than smell like sheep and other animals.
Human vs. Sheep Brain
• A sheep’s brain is elongated in shape, whereas a
human brain is rounded.
• The human brain stem is towards the backbone and
downwards, because in the human body the
backbone is vertical;
▫ Sheep’s backbone which is horizontal, and its brain is
directed outwards.
• The human brain is not only larger, but heavier
than a sheep’s brain,
▫ Sheep brain is roughly 140 grams compared to the
human brain, and is only about one third as long.
Human vs. Sheep Brain (ctd.)
• The pineal gland is responsible for controlling
reproduction and circadian rhythms
▫ Larger in the sheep’s brain when compared to
the human brain, that has less basic instinctual
behavior controls.
• Human hind brain positioning
▫ Different from the sheep because of the human’s
erect position.