Midbrain mesencephalon One inch in length Extends from

Midbrain (“mesencephalon”) • One inch in length • Extends from pons to diencephalon • Cerebral aqueduct connects 3 rd ventricle above to 4 th 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– 8 a

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– 7 a

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– 7 b

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– 5 a

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– 10 a

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 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 p. H 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, CO 2, • 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 depends on CO 2 more than O 2 concentration • High CO 2 increased blood flow • Low CO 2 decreased blood flow Hyperventilation blow off CO 2 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

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