Midbrain
(“mesencephalon”)
• One inch in length
• Extends from pons
to diencephalon
• Cerebral aqueduct
connects 3rd
ventricle above to
4th ventricle below
Structures of the
Mesencephalon
• Tectum:
• 2 pairs of sensory nuclei (corpora
quadrigemina):
– superior colliculus (visual)
– inferior colliculus (auditory)
Relationship of mesencephalon
to pons and cerebellum
Structures of the
Mesencephalon
• Tegmentum:
– red nucleus (many blood vessels)
– substantia nigra (pigmented gray matter)
Structures of the
Mesencephalon
• Cerebral peduncles:
– nerve fiber bundles on ventrolateral
surfaces
– contain:
• descending fibers to cerebellum
• motor command (pyramidal) fibers
Mesencephalon in Section
• Red nucleus-- rich blood supply & iron-containing pigment
• Substantia nigra---helps controls subconscious muscle
activity
– cortex & cerebellum coordinate muscular movements by sending
information here from the cortex and cerebellum
• Cerebral peduncles---clusters of motor & sensory fibers
The Mesencephalon
Figure 14–8a
Midbrain
(“mesencephalon” of the brainstem)
Summary: The Mesencephalon
Table 14-4
Reticular Formation
(Don’t forget this diffuse
structure!)
Motor function: helps regulate muscle
movements
Sensory function: Reticular activating system
(RAS)
Stimulation  increased cortical activity
Inactivation  sleep
Reticular Activating System
• RAS filters out repetitive, weak, irrelevant
stimuli.
• LSD removes the filtering effect  sensoryoverload.
Head Trauma (eg., lightweight boxers)
 concussion (mild, transient loss of
consciousness)
 coma (loss of consciousness, hours to
lifetime).
The Cerebellum
Figure 14–7a
Cerebellum
1.Adjusts
postural
muscles
2.Fine-tunes
conscious
and
subconscious
movements
Cerebellar Peduncles
• Three paired fiber tracts
• Superior peduncles connect the cerebellum to
the midbrain
• Middle peduncles connect the pons to the
cerebellum
• Inferior peduncles connect the medulla to the
cerebellum and carry ascending and descending
cerebellar tracts from the spinal cord.
• All fibers in the cerebellum are ipsilateral
Structures of the Cerebellum
Figure 14–7b
Cerebellum
Arbor Vitae
Arbor Vitae
• Highly branched, internal white matter
of cerebellum
• Cerebellar nuclei:
– embedded in arbor vitae
– relay information to Purkinje cells
Purkinje Cells
• Large, branched cells
• Found in cerebellar cortex
• Receive input from up to 200,000
synapses
Disorders of the
Cerebellum
• Ataxia:
– damage from trauma or
stroke
– intoxication (temporary
disturbance)
– disturbs muscle
coordination
Summary: The Cerebellum
Table 14-3
What are the main components
of the diencephalon
and their functions?
The Diencephalon
• Integrates sensory
information and
motor commands
• Filters ascending
sensory information for
primary sensory cortex
• Relays information
between basal nuclei
and cerebral cortex Figure 14–5a
The Diencephalon
• Thalamus,
epithalamus, and
hypothalamus
Figure 14–9
The Third Ventricle
• Separates left thalamus and right
thalamus
• Intermediate mass:
– projection of gray matter
– extends into ventricle from each side
Thalamic Nuclei
• Lateral geniculate nucleus: relays visual
information
• Medial geniculate nucleus: relays auditory
information
• Lateral group: involved in emotional states
and integration of sensory information
Summary: Thalamic Nuclei
Table 14-5
Hypothalamus
• Located below the thalamus
it caps the brainstem and
forms the inferolateral walls
of the third ventricle
• Mammillary bodies
– Small, paired nuclei;
Relay station for olfactory pathways
– control reflex eating movements
• Infundibulum – stalk of the hypothalamus;
connects to the pituitary gland
Diencephalon
The Diencephalon
Hypothalamus
The Hypothalamus
• Lies below thalamus
Figure 14–10a
8 Functions of the Hypothalamus
1. Provides subconscious control of
skeletal muscle
2. Controls autonomic function
3. Coordinates activities of nervous and
endocrine systems
Functions of the Hypothalamus
4. Secretes hormones:
–
–
antidiuretic hormone (ADH) by
supraoptic nucleus
oxytocin (OT) by paraventricular nucleus
Functions of the Hypothalamus
5. Produces emotions and behavioral
drives:
–
–
the feeding center (hunger)
the thirst center (thirst)
Functions of the Hypothalamus
6. Coordinates voluntary and autonomic
functions
7. Regulates body temperature:
–
preoptic area of hypothalamus
Functions of the Hypothalamus
8. Controls circadian rhythms (day–night
cycles):
–
suprachiasmatic nucleus
Summary: The Hypothalamus
Table 14-6
Epithalamus
Pineal Gland
• Above the thalamus
• Pineal gland
– secretes melatonin:
a hormone involved with sleep regulation,
sleep-wake cycles, and mood
Questions?
Cerebrospinal Fluid (CSF)
• 80-150 ml (about ½ cup)
• Clear liquid containing glucose, proteins, &
ions
• Functions
– mechanical protection
• floats brain & softens impact with bony walls
– chemical protection
• optimal ionic concentrations for action potentials
– circulation
• nutrients and waste products to and from blood
CSF Composition
Differs from plasma:
no (or very few) cells
protein is lower
ionic concentrations are different
pH  affects brain blood flow &
respiratory rate.
Blood Brain Barrier
Ependymal cells around choroid plexus
(which produce CSF) have tight junctions.
Capillaries of brain tissue have tight
junctions between endothelial cells.
Astrocytes wrap the small vessels.
Many antibiotics and chemotherapy agents
can not pass from blood to brain.
Blood Brain Barrier – details to know
Break-Down
radiation, infection, neoplasm (cancer), manitol
(intentional disruption)
facilitated diffusion
glucose, amino acids
simple diffusion
Small, neutrally charged molecules (i.e., lipid soluble
molecules) pass easily.
•
Water, CO2, O2,
•
alcohol, caffeine, nicotine, heroin
•
“general” anesthetics
Brain Blood Flow
Sources:
2 internal carotids (R and L)
2 vertebral arteries and “Circle of Willis”
(Study in more detail in lab.)
14% of cardiac output, and uses 20% of
oxygen used by body
Brain Blood
Flow
Brain Blood Flow
Flow depends on CO2 more than O2 concentration
• High CO2  increased blood flow
• Low CO2  decreased blood flow
Hyperventilation  blow off CO2  low blood flow
 dizzy spell
Other Factors:
extreme blood pressures
intracranial pressure
blood viscosity
Brain Blood Flow: Clinical
Issues
• Low blood sugar (eg., too much insulin)
starves neurons
• Mass (tumor, blood clot)  decreased flow
• Heart attack  decreased flow and
confusion
• 10 seconds without blood  pass out
• 4 minutes  permanent brain damage
• lysosomes release enzymes
Medical Example:
Subdural Hematoma
An subdural hematoma
is a blood collection
Between the dura and
arachnoid mater
(external to the brain)
Since the skull cannot
expand, the brain shifts
across the midline.
Clinical Cases:
Bleeding in the Brain
• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal
Bleed
Clinical Cases:
Bleeding in the Brain
• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal
Bleed
Clinical Cases:
Bleeding in the Brain
• Epidural Bleed
• Subdural Hematoma
• Intraparenchymal
Bleed(s)
Medical
Examples
• Meningitis is
inflammation of
the meninges due
to bacterial or
viral infection.
• Encephalitis is
inflammation of
the brain
Parkinson’s Disease
• Unknown cause.
• Basal ganglia involved.
• Tremor, rigidity.
• New therapy….
Basal Ganglia
• Connections to red nucleus, substantia nigra &
subthalamus
• Input & output with cerebral cortex, thalamus &
hypothalamus
• Control large automatic movements of skeletal muscles
The Electroencephalogram
Figure 14–17
Seizure
• Is a temporary cerebral disorder
• Changes the electroencephalogram
• Symptoms depend on regions affected
4 Categories of Brain Waves
1. Alpha waves:
–
found in healthy, awake adults at rest
with eyes closed
2. Beta waves:
–
–
higher frequency
found in adults concentrating or
mentally stressed
4 Categories of Brain Waves
3. Theta waves:
–
–
–
found in children
found in intensely frustrated adults
may indicate brain disorder in adults
4. Delta waves:
–
–
during sleep
found in awake adults with brain damage
Synchronization
• A pacemaker mechanism:
– synchronizes electrical activity between
hemispheres
• Brain damage can cause
desynchronization
Herpes Virus
CN V (trigeminal)
Dermatomes
Next time:
• Special Senses and Cranial Nerves (not
on pre-midterm)
• Review of somatic sensory and motor
pathways
• Integration areas of the brain
• Limbic system
• Learning and Memory
end