12
Lecture Topic outline
Some fun facts
Division and function of component parts of the brain
Protective roles of meninges, CSF and cranial bones
Homeostatic disturbances
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The Brain - is wider than the Sky For - put them side by side The one the other will contain
With ease - and You - besideThe Brain is deeper than the sea For - hold them - Blue to Blue The one the other will absorb As sponges - Buckets - do
The Brain is just the weight of God For - Heft them - Pound for Pound And they will differ - if they do As syllable from Sound -
Emily Dickinson (1830-1886)
Dont know
FUN FACTS!
Average number of neurons in the human brain 100 billion
Rate of neuron growth during development of a fetus 250,000 n/minute
Longest axon of a neuron - around 15 feet
Giraffe primary afferent axon from toe to neck
Guess what?
There are more nerve cells in the human brain than there are stars in the
Milky Way.
What if we lined up all the neurons in our body? How long would that line
stretch?
Let's assume that one neuron is about 10 microns long. Remember, this is
just an example, because neurons come in all different sizes. So, if we line
up 100 billion neurons which are 10 microns long . . .
100,000,000,000 neurons x 10 microns=
1000 km/about 600 miles!
Regions of the brain
The brain is divided into three regions
Cerebrum
Cerebellum
Brainstem composed of:
medulla oblongata, pons, midbrain and diencephalon
Location and distribution of gray and white
matter
In the spinal cord
Central cavity - central canal
Gray matter - surrounds the cavity, internal to white matter
White matter - external to gray matter
Location and distribution of gray and white
matter
In the brain
Additional gray matter
Surface layer: outer cortex in the cerebral hemispheres and cerebellum
Stellate cells with dendrites projecting in all directions
Pyramidal cells with axon that passes out of the area
Deeper masses of gray matter: nuclei in other structures
Basal nuclei involved in movement
Location and distribution of gray and white
matter
Projection tracts
vertical from brain
internal capsule and
corona radiata
Commissural tracts
cross L to R
corpus callosum
Association tracts
Long - connect lobes
Short - connect gyri within one
hemisphere
Cerebrum
Largest part of the brain
Consists of two cerebral
hemispheres
Hemispheres are separated
externally by longitudinal fissure
Hemispheres are connected
internally by corpus callosum
Associated with higher brain
function = thought, language,
reasoning
The two hemispheres look mostly symmetrical, but have different functions
This is known as lateralization
Categorical - logic abilities
Representational- Creativity
The cerebral cortex is highly wrinkled.
Any guesses as to why this is important??
The brain is wrinkled because it makes the brain more efficient, by increasing the
surface area of the brain and the amount of neurons within it.
Shallow groove/s: sulcus/sulci
Deep groove/s: fissure/fissures
Bump/s : gyrus/gyri
The cerebral cortex is divided into sections called "lobes named for cranial bones
Frontal lobe
movement, parts of speech,
motor homunculus, personality
Parietal lobe
sensory perception,
sensory homunculus
Occipital lobe
visual processing
Temporal lobe
hearing, memory
Insula: little is
known
Cerebral cortex has 3 types of functional
areas
1. Sensory areas
Sensory signals from general senses
such as touch, pressure, pain,
vibration, temperature, travel up in
ascending tracts
Ascending tracts end in postcentral
gyrus (sensory homunculus) primary
sensory cortex
Sensory signals from special senses
project to other parts of cortex
Equilibrium to the cerebellum
!Taste is the only special sense projecting to postcentral gyrus
2. Motor areas
Primary motor cortex in the precentral gyrus (motor homunculus) of frontal
lobe controls voluntary movement of skeletal muscles
Pyramidal cells of precentral gyrus send signals to
muscles of contralateral side due to decussation
Motor homunculus is proportional to number
of muscle motor units in a region
3. Association areas
The Brainstem
Region that lies caudally to the cerebrum
Oldest region, in some ways most primitive
But structures here play very important roles
Medulla oblongata
Located just above
spine
Dont leave home without it!
Regulates critical life support systems, such as respiration, heart rate,
heart muscle contraction; also reflexes (e.g., vomiting)
Cardiovascular center (Cardiac center and Vasomotor center)
Respiratory center
Depressant drugs (heroin, alcohol) suppress activity
Medulla Oblongata
Houses part of 4th ventricle
Pyramids house the corticospinal tracts
(place of decussation)
Other descending/ascending tracts
nucleus cuneatus & gracile
Nuclei of cranial nerves
IX Glossopharyngeal
X Vagus
XI Accessory
XII Hypoglossal
Pons = bridge
Rostral to the medulla
Houses part of 4th ventricle
Consists of ascending & descending
tracts - cerebellar peduncles
important Plays role in sleep
regulation ( REM)
Nuclei of cranial nerves
V - trigeminal
VI - abducens
VII facial
VIII - vestibulocochlear
Midbrain = Mesencephalon
Has three parts:
Cerebral peduncles :corticospinal tract
Tegmentum connects to cerebellum
Tectum has corpora quadrigeminna
Cerebral aqueduct is surrounded by
periaqueductal gray matter
CN III oculomotor
Substantia nigra
releases dopamine, linked to basal nuclei
defficiency causes Parkinsons disease
Reticular Formation
Brain requires sensory stimulation in order to function properly
Sensory input not only provides specific information,
but also arouses cerebral cortex, prepares it to process information
System that enables this: Reticular Activating System (RAS) [aka Reticular
Formation)
Asleep, awake, alert, and attend (Williams, & Shellenberger, 1996).
4. Then sends projections into wide regions of cerebral cortex
3. Extends through midbrain
2. Extends through pons
1. Begins in medulla
Receives input from most sensory systems
Projections to cortex release neurotransmitters
Sensitizes neurons they reach; these neurons more likely to become
active in response to specific inputs
RAS plays important role in determining general level of arousal
(consciousness)
Suppression of activity (e.g., from blow to head) can >>
unconsciousness
Also plays role in habituation
Is inhibited by alcohol and sleep-inducing drugs
Homeostatic imbalance: ADHD - poor attention and distractibility
and/or hyperactive and impulsive behaviors.
Is a functional system
Pineal Gland
Diencephalon
orms the walls & floor of 3rd ventricle
.Epithalamus
Pineal gland secretes melatonin hormone
2. Thalamus - oval mass of gray matter beneath cerebral hemispheres
Is the gateway to cortex
Interconnected to limbic system = emotions & memory
3. Hypothalamus
Main visceral control center
Hypothalamus
Called a neuroendocrine organ
Autonomic NS control
BP, HR, contractility, GI motility
Controls the endocrine system
Pituitary gland
Secretes ADH and Oxytocin
Regulates
Temperature
Food and water intake
Center for emotional response
Part of limbic system: rage, pleasure, fear, sex drive
Limbic System Functional system
MRI of the brain reveals a smaller amygdala in cocaine-addicts
Connected with cortex and hypothalamus
Represents our emotional center
facilitates memory storage and retrieval
associated with smell
Cerebellum
2nd largest region of the brain
Caudal to cerebrum in posterior cranial fossa
Separated by transverse cerebral fissure
Sits atop the 4th ventricle
White matter forms arbor vitae
Gray matter forms folia
Motor coordination and control
Receives signals from the motor cortex and sensory receptors
Coordinates force, direction, extent of muscle contraction
Compares intentions with performance of the body
Maintains posture
Meninges
Layers covering CNS
Same layers in brain and spinal cord from superficial to deep
Dura mater
Arachnoid mater
Pia mater
Functions
Cover and protect the nervous tissue
Protect blood vessels and enclose venous sinuses
Contain cerebrospinal fluid CSF
In the skull: form partitions
Dura mater = tough mother
In the brain: double layer membrane
Outer periosteal attached to bone
Inner meningeal = dural sheath
Forms partitions
falx cerebri
tentorium cerebelli
falx
cerebelli
In the spinal cord: one layer membrane
Forms the dural sheath
Not attached to bone
Has epidural space filled with adipose
tissue
Arachnoid and pia mater
Subarachnoid space
contains CSF
Arachnoid mater
spider web loose lining of dura mater
Has arachnoid villi protrude through the dura mater into the superior
sagital sinus and return CSF into circulatory system
Pia mater = gentle mother
Highly vascular, clings tightly to the brain and spinal cord
Forms denticulate ligament and filum terminale in spinal cord
Meningitis
Inflammation of the meninges
Can be bacterial or viral
Infection by nose and throat
affects pia mater & arachnoid
Disease of infancy and childhood mostly
3 months 2 years
High fever, stiff neck, headache,
drowsiness, rash, coma
Cerebrospinal fluid (CSF)
CNS has spaces lined by ependymal cells
The brain has ventricles
The spinal cord has a central canal
These spaces are filled with CSF
Clear, colorless liquid similar to blood plasma
Gives buoyancy to brain and spinal cord
Protects the tissue from trauma
Transports nutrients, hormones, wastes
About 500 ml/day produced
About 150 ml of CSF fills the ventricles and central canal
On the roof of lateral ventricles blood capillaries enclosed by pia
mater and covered by ependymal cells form the choroid plexus
Blood-brain barrier (BBB)
Selectively permeable mechanism that maintains constant environment for
neurons
Absent in circumventricular organs in 3rd & 4th ventricles
HTA and vomiting center
Consists of
1. endothelium of capillaries with tight junctions
2. basal lamina
3. astrocytes
Many substances diffuse freely: H2O, glucose, CO2, caffeine, nicotine