Transcript Chapter 14: The Brain and Cranial Nerves

Principal Parts of the Brain
• Cerebrum
• Diencephalon
– thalamus
– hypothalamus
• Cerebellum
• Brainstem
– midbrain
– pons
– medulla
Brain – midsagital section
(photograph)
• Largest organ in the body at almost 3 lb.
• Brain functions in sensations, memory, emotions,
decision making, behavior
Hydrocephalus
and CSF Shunt
Ventricles of the Brain
Figure 14–2
Origins of Ventricles
• Neural tube encloses neurocoel space,
which expands to form chambers
(ventricles) lined with ependymal cells
Embryology of the Brain
Table 14-1
CSF flow
1.
2.
3.
4.
5.
6.
lateral ventricles (R and L)
inter-ventricular foramen
3rd ventricle
cerebral aqueduct
4th ventricle
median and lateral
apertures
7. subarachnoid space
Arachnoid villi reabsorb CSF.
Summary
Why all this
!$^%&*!
trouble?
Skin
Galea Aponeurotica
Fascia
Bone
Dura Mater
Arachnoid mater
Pia mater
Protection of the
brain
and three
related disorders
Reabsorption of CSF: Arachnoid
Villi
• Grapelike clusters (arachnoid granulations)
penetrate inner (“endosteal”) layer of dura into
venous blood of the venous sinus
• 20 ml/hour
Reabsorption rate = Production rate
The Cranial Meninges: Review
• 3 layers:
– dura mater
– arachnoid mater
– pia mater
• Continuous with spinal meninges
• Protects the brain from cranial trauma
Pia Mater
• Deepest layer composed of delicate
connective tissue that clings tightly to the
brain.
• Contains tiny blood vessels that enter the
brain tissue.
• Attached to brain surface by astrocytes
Arachnoid Mater
• Arachnoid mater:
– middle meningeal layer is
separated from dura mater by
the “subdural space”
• Subarachnoid space:
– between arachnoid mater and pia mater
– CSF and large blood vessels
– web-like extensions span the space and secure it to
the underlying pia mater
• CSF gets into the subarachnoid space from 3
foramina (openings) in the roof of the 4th
ventricle
Dura Mater
Dura mater:
– irregular connective
tissue
– inner fibrous layer
(meningeal layer)
– outer fibrous layer
(endosteal layer)
fused to periosteum
– venous sinuses
between 2 layers
• Superior Sagital Sinus
The Dural
• Inferior Sagital Sinus
Sinuses
• Straight Sinus
• R and L Transverse Sinuses
• R and L Sigmoid Sinuses
…. R and L jugular veins and back to heart.
Dural Folds
• falx cerebri
• falx
cerebelli
• tentorium
cerebelli
Figure 14–3b
Dural Folds
• inner layer of dura
mater (folded)
• extend into cranial
cavity
• support brain
• contain collecting
veins (dural sinuses)
Don’t confuse the “arachnoid villi”
of dural sinus with the “choroid
plexus” of the ventricles!
Review: Principal Parts of the Brain
• 750 to 2100 cc
• about 98% of the
body’s neural
tissue
• about 1.4 kg
(3 lb)
Endocrine
Preview:
Pituitary
Gland
• Connects to hypothalamus by thin
double stalk (infundibulum)
– venous connection (anterior pituitary)
– axonal connection (posterior pituitary)
Major Regions and Landmarks
PLAY
3D Peel- Away of the Brain
Figure 14–1
Lobes and Fissures
• Longitudinal fissure (green)
• Frontal lobe
• Central sulcus (yellow)
– precentral & postcentral gyrus
•
•
•
•
•
•
Parietal lobe
Parieto-occipital sulcus
Occipital lobe
Lateral sulcus (blue)
Temporal lobe
Insula ?
Insula within
Lateral Fissure
• Gray matter
– cell bodies,
dendrites,
unmyelinated
axons
– cortex and
deep nuclei
• White matter
– primarily
myelinated
axons
– X-Y-Z
connections
Gray
vs.White
Matter
Gray vs. White Matter
Projection Fibers
• Pass through
diencephalon
•  brain stem,
cerebellum, and
spinal cord
• In lab: see the
internal capsule
– ascending and
descending
projection fibers
Review: Cerebral White
Matter
• Projection fibers form descending & ascending tracts
• Commissural fibers from one hemisphere to other
• Association fibers between gyri in same hemisphere
Association
Fibers
• within each hemisphere:
– arcuate fibers:
• are short fibers, connect 1 gyrus to another
– longitudinal fasciculi:
• longer bundles, connect frontal lobe to other
lobes (in same hemisphere)
Commissural Fibers
• Bands of fibers
connecting 2
hemispheres:
– corpus callosum
– anterior
commissure
Cortical Area Summary: Sensory (1 of 2)
Cortical Areas
SENSORY
Function
Primary Sensory
Cortex
Conscious awareness of
sensation
Receives tactile information from
the body
Somatic Sensory
Association Area
Processing of multisensory
information
Visual Cortex
Detection of simple visual stimuli
Visual Association Complex processing of visual
Area
information
Cortical Area Summary: Sensory (2 of 2)
Cortical Areas
Function
Auditory Cortex
Detection of sound quality
(loudness, tone)
Auditory Association
Area
Complex processing of
auditory information
Olfactory Cortex
Awareness of different odors
Gustatory Cortex
Perception of taste stimuli
Vestibular Cortex
Awareness of balance and
the position of the head
Cortical Area Summary: Motor
Cortical Areas
MOTOR
Function
Controls voluntary movement
Primary Motor
Cortex
Premotor Cortex
Initiation of voluntary movement
Motor Association
Cortex
Coordination of complex
movement
Speech Center
(Broca's Area)
Frontal Eye Field
Speech production and
articulation
Voluntary eye movements
Controls learned motor skills
Cortical Area Summary: Integration
Cortical Areas
Function
Integrative Centers
Integrates information for
purposeful action
Prefrontal Cortex
Problem Solving, Emotion,
Complex Thought
General Interpretation Integrates all signals into a
Area
single thought
Wernicke's Area
Language comprehension
Visceral Association
Area
Perception of visceral
sensations
Cortical Motor Areas
Premotor
cortex
Frontal
Eye Field
Broca’s Area
Primary motor
cortex
Primary (Somatic) Motor
Cortex


Located in precentral gyrus of the frontal
lobe
“upper motor neurons” (pyramidal cells)
may follow more than one pathway to
“lower motor neuron” that controls
contralateral skeletal muscles
 corticospinal tracts

Old terminology – “pyramidal tract”
Cerebrum
Primary (Somatic) Motor
Cortex

Somatotopy


body map = “motor
homunculus”
Strokes that are
localized result in
precise deficits.

cortex lesion
 contralateral
side paralyzed
Cerebrum
Premotor
Cortex



anterior
to the primary
motor cortex
planning of movements
“skills”


Learned motor patterns
Neurons project through corticospinal
tract.
Medical Example
• Stroke affecting the premotor cortex will
cause loss of motor skills
• Muscle strength and ability to perform
individual movements are not hindered
• If you damage the area controlling typing,
you would not be able to type at the regular
speed, but you could make the same
movements. You would need to relearn the
rhythmic movements.
Broca’s Area




Speech production
and articulation
anterior to the premotor area of frontal lobe
unilateral (usually the left hemisphere)
motor speech area

“planning” speech mechanics including direction
of the tongue
Medical Example:
Broca’s Aphasia

A stroke to Broca’s area of
the brain makes patients
unable to speak.



They are still able to
understand speech
…..frustrating!!!
Give them a pad and pencil;
they can still write the
words!
Frontal Eye Field
• Controls voluntary eye movements.
Preview: Brain Pathways of Vision
synapse in thalamus
& visual cortex
Visual fields
• Left occipital lobe
receives visual images
from right side of an
object through
impulses from nasal
1/2 of the right eye and
temporal 1/2 of the left
eye
• Left occipital lobe sees
right 1/2 of the world
• Fibers from nasal 1/2
of each retina cross in
optic chiasm
Sensory Association Areas
• Visual association area:
– occipital lobe
– interprets activity in primary visual cortex
• Auditory association area:
– temporal lobe
– monitors auditory cortex
• Somatic sensory association area:
– interprets input to primary sensory cortex
(e.g., recognizes and responds to touch)
Somatosensory Cortex
• anterior part of
parietal lobe
• somatotopy
– spatial
discrimination
Somatic
Sensory
Association
Cortex
• posterior to the primary sensory cortex
• Synthesizes multiple sensory inputs to create
a complete comprehension of the object being
felt.
Example: Touch a coin in your pocket; this area
would help you identify a small coin as a dime
Gustatory and Vestibular Cortex
• Gustatory cortex
– taste
– parietal lobe
• Vestibular cortex
– Cranial Nerve VIII (8)
– balance and equilibrium (position of head)
– posterior part of the insula (deep to the
temporal lobe)
Cerebrum
Olfactory Cortex
• Cranial Nerve I (1)
– Receptors in the
olfactory epithelium
extend through the
cribriform plate and
send their info to the
olfactory cortex.
– frontal lobe above the
orbits, medial temporal
lobe
• linked to “limbic
system” for memory
and emotion
Limbic System
• Emotional brain--intense pleasure & intense pain
– Strong emotions increase efficiency of memory
– arahippocampal & cingulate gyri & hippocampus
More Cerebral Functions later
• Start at the spinal cord
and work our way back
up to the cerebrum…
The Medulla Oblongata
• Continuous with spinal
cord
Medulla
• Controls visceral functions
– Coordinates complex autonomic reflexes
• Hard blow to the back of the head  fatal
Nuclei in the
Medulla
• Autonomic nuclei:
visceral activities
• Sensory and motor
nuclei:
cranial nerves
• Relay stations:
sensory and motor
pathways
Figure 14–6b
Medulla Nuclei
• Cardiovascular control center:
– force and rate of heart contraction
(can override the autorhythmic
pacemaker cells of the heart)
• Vasomotor center:
– tone of vascular smooth muscle
• Respiratory rhythmicity centers:
– rate and depth of breathing
• Additional Centers:
– Emesis, coughing, choking,
hiccupping, and sneezing
Sensory and Motor Nuclei
• Associated with 5 of 12 cranial nerves
(VIII, IX, X, XI, XII)
• Can you match their names to their
basic functions?
Relay Stations
• Nucleus gracilis and nucleus
cuneatus:
– pass somatic sensory information to
thalamus (lower and upper
extremities, respectively)
• Solitary nucleus:
– receives visceral sensory information
• Olivary nuclei (olives):
– relay information about somatic
motor commands (descending
pathway)
– Some somatic motor command do
NOT cross here.
Medulla:
Decussation of
the Pyramids
• Lateral
corticospinal
tract (i.e., not
all motor fibers)
cross to the
opposite side in
the medulla.
Summary: The Medulla Oblongata
Table 14-2
The Pons
• Link cerebellum to
mesencephalon
(midbrain),
diencephalon,
cerebrum, and
spinal cord
• somatic and
visceral motor
control
Figure 14–6c
The Pons: 4 Groups
1. Sensory and motor nuclei of cranial
nerves V, VI, VII, VIII
2. Nuclei involved with respiration:
–
–
apneustic center and pneumotaxic
center
modify respiratory rhythmicity center
activity
The Pons: 4 Groups
3. Nuclei and tracts:
–
process and relay information to and
from cerebellum
4. Ascending, descending, and
transverse tracts:
–
transverse fibers (axons)
• link nuclei of pons with opposite cerebellar
hemisphere
continues with part 2