Download Chapter 12: The Central Nervous System

Chapter 14: The Brain and Cranial Nerves
Chapter Objectives
BRAIN ORGANIZATION
1. Introduce the principle parts of the brain in terms of their relative positions.
2. Describe the ventricles and where in the brain they are located
THE CEREBRUM
3. Define gyrus, sulcus, and fissure. Give the location of the Central sulcus and its
surrounding gyri.
4. Discuss the locations of the cerebral lobes.
5. Describe the cerebral cortex.
6. Define the location and purpose of the motor regions of the cerebral cortex including the
following regions: primary motor region, premotor area, Broca’s area, and primary eye
field area.
7. Define the location and purpose of the sensory regions of the cerebral cortex including
the following regions: somatosensory region, somatosensory association area, and the
primary sensory areas for the visual, auditory, gustatory, and olfactory systems.
8. Define the location and purpose of the association regions of the cerebral cortex
including the following regions: Prefrontal area and Wernicke’s area.
9. Describe the pathway destinations for the three types of white matter tracts within the
cerebrum (Association, Commissural, and Projection).
10. Identify the nuclei of the Basal nuclei (ganglia), describe the functions of the Basal nuclei
and describe one disorder associated with the Basal nuclei.
DIENCEPHALON
11. Discuss the structures of the Diencephalon and functions for each structure.
THE BRAIN STEM
12. List the structures that make up the brain stem.
13. Discuss the structures of the Midbrain and functions for each structure.
14. Describe the Pons.
15. Discuss the structures of the Medulla and functions for each structure.
16. Identify the vital reflex centers of the medulla oblongata and their functions.
CEREBELLUM
17. Describe the location of the Cerebellum and its functions.
FUNCTIONAL BRAIN SYSTEMS
18. List the component structures of the limbic system, and discuss their contribution to
behavioral responses and mental functions.
19. Indicate the distribution of nuclei that constitute the reticular formation and describe the
function of the reticular formation.
MENINGES
20. Identify the three layers of the meninges and their extensions that surround the brain and
spinal cord.
21. List the functions of CSF and where it is formed in the brain.
CRANIAL NERVES
22. Define a cranial nerve and identify the 12 pairs of cranial nerves by name, number, type,
which hole in the skull they pass through and function.
Chapter Lecture Notes
Regions of the Brain
Cerebrum (Fig 14.1 & Table 14.2)
Diencephalon
Brain Stem
Cerebellum
Ventricles
Ventricles – hollow chambers within the brain that are filled with cerebrospinal fluid and lined
with ependymal cells (Fig 14.3 & 14.4)
Four ventricles
Paired Lateral ventricles - cerebrum
Third ventricle - diencephalon
Fourth ventricle - brain stem
Cerebrum
Cerebrum - supported on brain stem and form bulk of brain (Fig 14.11)
Lateral ventricles
Cranial nerves 1 & 2
Surface features
Lobes - frontal, parietal, temporal, occipital
Gyrus - upfolds - increases surface area (surface area = 25 square feet)
Sulcus - shallow grooves
Central sulcus - divides parietal from frontal lobe
Precentral gyrus - motor in function
Postcentral gyrus - sensory in function
Lateral cerebral sulcus - divides frontal from temporal lobe
Fissures - deep grooves
Longitudinal fissure - divides the right from left hemispheres
Cortex (bark of tree) = outer gray - 2-4mm thick - 6 layers of cell bodies; divided into 3
functional areas (Fig 14.11 & 14.15)
EEG - electrical activity of cortex (Fig 14.16)
Motor - control voluntary muscle movements -in frontal lobe anterior to central sulcus
Primary motor area - precentral gyrus - controls muscle movement on opposite side of
body (pathway is pyramidal system) (Fig 16.8)
Premotor area - anterior to primary motor
Controls learned skilled movements - generates action potentials that enable specific
groups of muscles to contract in specific sequence like writing, typing,
playing musical instruments (deals with learned motor activities of a complex
and sequential nature)
Broca's area - generally on left side - in frontal lobe just superior to lateral cerebral sulcus
Broca's area programs motor cortex to move tongue, lips and speech muscles to
articulate words
Frontal eye field area - just anterior to premotor area
Controls voluntary scanning movements of eye - searching for a word in a dictionary
or looking for a book on a shelf or a person in a crowd
Sensory - interpretation of sensory impulses; posterior to central sulcus
Postcentral gyrus - primary somatosensory (sensory) - localize points on body where
sensations such as touch, pressure, pain, taste, & temperature originate (Fig 16.8)
Somatosensory association area - Integrate and interpret sensations - permit you to
determine shape and texture of object without looking at it - store memories of
past experiences - can compare sensations with previous experience
Primary visual area = occipital lobe
Visual association area = relates present to past visual experience with recognition
and evaluation of what is seen
Primary auditory area - temporal lobe - interprets basic characteristics of sound such as
pitch and rhythm
Auditory association area - determines if sound is speech, music, or noise
Primary olfactory area - temporal lobe on medial side - interprets sensations related to
smell
Primary gustatory area - in parietal lobe at base of postcentral gyrus - interprets
sensations related to taste
Association areas - intellectual processes - occupies greater portions of lateral surfaces of
occipital, parietal, temporal, and frontal lobes anterior to motor areas
Association areas are concerned with memory, emotions, reasoning, will, judgment,
personality and intelligence
Prefrontal area – “executive decision area”
Allows moral judgments
Motivation and foresight to plan; also allows us to predict consequences of our
actions
Regulation of emotional behavior and mood
Functional center for aggression - one method used to eliminate uncontrollable
aggression in mental hospital was to surgically remove or destroy the
prefrontal regions (prefrontal lobotomy) - it eliminates aggression but also
eliminates motivation
Wernicke's area - stores information for speech content, arranges words of vocabulary
into meaningful speech according to rules of grammar; it plans what to say
Middle White Matter = tracts of myelinated nerve fibers (axons) (Fig 14.12)
Association fibers - connect and transmit nerve impulses between gyri in same hemisphere
Commissural fibers - transmit nerve impulses from gyri in one hemisphere to corresponding
gyri in opposite hemisphere
Example: corpus callosum
Projection fibers - form ascending and descending tracts that transmit impulses to and from
cerebrum to other parts of brain and spinal cord
Basal Nuclei - paired gray inner matter of cerebrum (Fig 14.13)
Technically it is nuclei but common usage is basal ganglia
Parts include:
Lentiform nucleus - receives input from substantia nigra in brain stem
Putamen
Globus pallidus
Caudate nucleus - receives input from substantia nigra
Substantia nigra (in midbrain) - inhibits unwanted motor activity from basal nuclei by
releasing dopamine
Basal nuclei help control muscle tone by inhibiting contraction of unwanted muscular
activity
Associated with control of large subconscious movements like swinging arms when
walking/facial expression
Basal nuclei coordinate slower contractions, whereas cerebellum is more involved with
coordination of quick movements
Disorder - Parkinson's - decrease in neurotransmitter dopamine from Substantia nigra to
Basal nuclei; result is tremors
Diencephalon
Thalamus - "inner room" - 2 oval masses joined by a bridge called intermediate mass
(interthalamic adhesion) (Fig 14.1 & 14.9)
2 masses form lateral walls of 3rd ventricle
Thalamus is bounded laterally by internal capsule
Gateway to cerebral cortex
Incoming sensory neurons are sorted, regrouped and then sent onto proper area of cerebral
cortex where interpretation is made
All sensory except olfactory synapse here before being relayed to sensory part of
cerebrum
Thalamus could also be referred to as the "sensory relay station"
Hypothalamus (Fig 14.1 & 14.10)
Connected to pituitary gland via infundibulum
Mammillary body - olfactory reflexes as related to emotions
Controls many functions related to homeostasis: (main visceral control center)
Controls autonomic nervous system
Mind over body phenomenon - extensive connections between hypothalamus and cortex thoughts influence our visceral functions - "the thought of __ makes me sick to
my stomach"
Serves as a link between nervous system and endocrine system
Control endocrine system: Stimulates anterior pituitary to release its hormones
Control endocrine system: Produces hormones found in posterior pituitary
Control body temperature - initiates sweating (cooling) or shivering (warming)
Governs eating habits
Governs thirst
Pacemaker to drive biological rhythms
Maintain waking state and sleeping patterns
Center for emotional response and behavior - it lies at the "heart" of the limbic system
Pleasure center
Rage and aggression
Pineal gland - reproductive function in most animals; in humans it produces melatonin that helps
regulate sleep/wake cycle and some aspects of mood
Brain Stem
Brain stem - control of involuntary function
Midbrain - cranial nerves 3, 4 (Fig 14.7)
Corpora quadrigemina - Posterior side (tectum = roof)
Superior colliculi - reflex center for movement of eye, head, neck and trunk in
response to visual stimuli (contains fibers from optic tract)
Inferior colliculi - reflex center for movement of eye, head, neck and trunk in
response to auditory stimuli (contains fibers from auditory tract)
Cerebral aqueduct - connects 3rd and 4th ventricles
Cerebral peduncles - Anterior side
Contain motor and sensory tracts and are the main connections for tracts between
upper parts of brain and lower parts of brain and spinal cord
Peduncles were thought to form vertical pillars that seem to hold up cerebrum; hence
"little feet" that hold up the cerebrum
Red nucleus - has numerous blood vessels that give it red color
Center for integrating information about muscle tone and posture
Substantia nigra - pigmented nuclei included as part of basal nuclei
Pons - connects medulla with midbrain and connects cerebellum with cerebrum (Fig 14.1)
Cranial nerves 5-8
4th ventricle
Medulla (Fig 14.6)
Cranial nerves 8-12
Pyramids – Anterior side
Pyramids are composed of largest motor (descending) tracts that pass from cerebral
cortex to spinal cord
Decussation of pyramids – crossing of tracts from one side to another (80% of motor
tracts cross in medulla)
Contains all sensory (ascending) tracts that connect the spinal cord & brain
Vital reflex centers of medulla:
Cardiac center - regulate heart rate and force of contraction
Respiratory center - controls rate and depth of respiration
Vasomotor center - adjusts blood vessel diameter to regulate blood pressure
Nonvital centers:
Swallowing, vomiting, coughing, sneezing, hiccupping
Cerebellum
Coordinates movement of skeletal muscle, especially quick movements (Fig 14.8)
Maintenance of balance and equilibrium
Helps in maintenance of posture
Processes input from sensory receptors - through connections with cerebral cortex, cerebellum
refines and coordinates muscle movements
Does not initiate movement
Not involved in sensory perception
Injury or removal of cerebellum results in impairment of muscle coordination and not
paralysis
Hand-eye coordination is one example of cerebellum function
Functional Brain Systems
Functional Brain Systems - networks of neurons that work together but span large distances
within brain, so cannot be localized to a specific region
Limbic system - mostly interconnected gray matter that includes components of cerebrum and
diencephalons (Fig 14.14)
Wishbone shaped and encircles brainstem (limbus = ring)
Limbic system has extensive connections to the prefrontal cortex
Sometimes called emotional brain
Functions in emotional aspects of behavior related to survival
Limbic system associated with pleasure, pain, rage, fear, aggressiveness
Communication between the cerebral cortex and limbic system explains why emotions
sometimes overrides logic and conversely why reason can stop us from
expressing emotions in inappropriate situations
Plays role in memory processing
Because of relationship of memory to emotions, events that cause strong emotional
response are remembered more efficiently that those that do not
Parts include:
Hippocampus - (sea horse) gyrus of the temporal lobe - in floor of the lateral ventricle
Hippocampus along with cortex function in memory
Amygdala - end of caudate nucleus - role in memory
Fornix - tracts that link the limbic system together, specifically connects hypothalamus to
hippocampus (fornix = arch)
Cingulate gyrus - above the corpus callosum (cingulate = belt)
Olfactory bulb
Mammillary bodies - part of hypothalamus (odors can trigger memory)
Parts of thalamus and hypothalamus
Pathway from limbic system project into hypothalamus and exert widespread effect
on body via autonomic nervous system and endocrine system (most limbic
output is relayed through hypothalamus)
Since the hypothalamus is clearinghouse for emotional response and autonomic
nervous system, it is not surprising that some people under unrelenting
emotional stress fall prey to emotional-induced illness such as increased blood
pressure, irritable bowel syndrome, heartburn
Reticular formation - gray matter interspersed among white fibers that are found in spinal cord,
medulla, pons, midbrain and diencephalon; has both sensory and motor functions (over
90 separate nuclei) (Fig 14.7)
Fibers (axons) make extensive connections to diencephalon, cerebellum, cerebrum
RAS - reticular activating system - control general wakefulness or alertness of brain
Injury to formation results in unconsciousness or deep coma (coma can result from
poison, hypoxia, hypoglycemia, ischemia, infection, acid-base disorder, trauma)
Alerts cerebral cortex to incoming sensory signals from ears, eyes and skin to activate
person
Filters sensory impulses entering the brain and accepts and enhances relay of certain
sensory impulses to cerebrum while rejecting others
Protects brain from constant barrage of sensory "noise" that would be overwhelming
(being aware of all stimuli in environment; colors, shapes, odors, sounds)
Filters out 99% of sensory and enhance only important
Hyperactivity in children is due in part to inability to filter out unnecessary sensory
input
Meninges
Dura mater – outermost layer that is double membraned where it surrounds skull (Fig 14.2)
Periosteal layer - outer layer - adheres to inner surface of skull (does not exist around spinal
cord)
Meningeal layer - inner layer - forms true external covering of brain and continues around
cord
Dura layers are fused together except where they form the dural sinuses that collect venous
blood from brain and cerebrospinal fluid from arachnoid villi and then direct the
blood and cerebrospinal fluid into the internal jugular of neck
Meningeal dural mater extends inward to form flat septa (wall) that anchor brain to skull
Falx cerebri (falx = sickle) - dips into longitudinal fissure between cerebrum (attached to
crista galli of the ethmoid)
Falx cerebelli – between cerebrum and cerebellum
Arachnoid mater – middle layer
Weblike extensions of collagen and elastic fibers
never dips into sulcus
Arachnoid villi protrudes through the dura mater and into dural sinuses
Pia mater – innermost layer composed of delicate connective tissue and is richly invested with
tiny blood vessels
clings tightly to brain and into sulcus
Subarachnoid space – space between arachnoid mater and pia mater
contains cerebrospinal fluid (CSF) and blood vessels serving brain
Cerebrospinal fluid - cushions, protects and nourishes brain and spinal cord
contains O2, glucose, proteins, Na+, K+, Ca2+, ClChoroid plexus in the brain ventricles form cerebrospinal fluid (Fig 14.4)
Circulates from ventricles, through and around the spinal cord and back to the brain where it
is reabsorbed at the superior sagittal sinus
Volume - 150 ml (1/2 cup)
Replaced every 3 - 4 hours
Clear fluid
Cranial Nerves
12 pairs - know names, numbers, functions and where they pass through the skull
Oh, Oh, Oh, To Touch And Feel Very Green Vegetables – AH (Fig 14.5 & Table 14.4)
On Old Olympic Towering Tops A Finn And German Viewed Some Hops
I. Olfactory (Fig 14.17)
Passes through cribriform plate
Sensory - Smell
II. Optic (Fig 14.18)
Passes through optic foramen
Sensory - Sight
III. Oculomotor (Fig 14.19)
Passes through superior orbital fissure
Motor - Eye movement
IV. Trochlear (Fig 14.19)
Passes through superior orbital fissure
Motor - Eye movement
V. Trigeminal (Fig 14.20)
Ophthalmic - passes through superior orbital fissure
Maxillary - passes through foramen rotundum
Mandibular - passes through foramen ovale
Mixed
Sensory - facial sensations
Motor- chewing - (masseter/temporalis)
VI. Abducens (Fig 14.19)
Passes through superior orbital fissure
Motor - Eye movement
VII. Facial (Fig 14.21)
Passes through stylomastoid foramen
Mixed
Sensory - anterior 2/3 taste
Motor – salivation and facial expression
VIII. Vestibulocochlear (Auditory) (Fig 14.22)
Passes through internal auditory (acoustic) meatus
Sensory
Vestibular - for equilibrium
Cochlear- for hearing
IX. Glossopharyngeal (Fig 14.23)
Passes through jugular foramen
Mixed
Sensory - posterior 1/3 taste
Motor – salivation and swallowing
X. Vagus (vagrant) (Fig 14.24)
Passes through jugular foramen
Mixed
Sensory – monitors functioning of the organs of thorax and abdomen
Motor – parasympathetic regulation of the organs of the thorax and abdomen
XI. Accessory (Spinal) (Fig 14.25)
Passes through jugular foramen
Motor - Controls the Trapezius and Sternocleidomastoid muscles
XII. Hypoglossal (Fig 14.26)
Passes through hypoglossal canal
Motor - Tongue movements during speech and swallowing
III, IV, VI, XI, XII are primarily motor but have a sensory part that is for proprioception