brain & cranial nerves

BRAIN & CRANIAL NERVES

The brain and spinal cord develop from ectoderm

The brain and spinal cord develop from the neural tube

• Prosencephalon (Forebrain)• Mesencephalon ( Midbrain)• Rhombencephalon (Hindbrain)

• Primary brain vesicles are present around the 3rd week of development

Prosencephalon (forebrain)

• Differentiates in 5th week into:• Telencephalon

–cerebral hemispheres

• Diencephalon–thalamus; hypothalamus–pineal gland

Midbrain

• Mesencephalon remains the same• Brainstem = midbrain

Rhombencephalon

• Metencephalon–cerebellum, pons

• Myelencephalon–medulla oblongata

Meninges

• Dura mater–dural septa (extensions): falx cerebri, falx

cerebelli, tentorium cerebelli

• Arachnoid• Pia mater

• Cavities–subarachnoid space, subdural space

4 Ventricles filled with CSF

• Lateral ventricles (paired)–Interventricular foramen – connects to 3rd

ventricle• Third ventricle

–Cerebral aqueduct – connects 3rd and 4th ventricles

• Fourth ventricle–Connects with central canal of spinal cord

Cerebrospinal Fluid

• Clear, colorless fluid that protects brain

• Formed by the choroid plexus• Absorbed by arachnoid villi

Parts of the Brain

Medulla oblongata• Major reflex center for the cardiovascular and

respiratory system– vasomotor, vasoconstriction

• Pyramids - decussation (crossing) center for motor `tracts

• Non-vital center for coughing, hiccuping, swallowing, vomiting

• Ascending/descending fibers pass through• Cranial nerves VIII-XII arise here

PONS• Acts as a bridge connecting the

spinal cord to the brain• Major relay center for voluntary

skeletal movements from the cerebral cortex to the cerebellum

• Coordinates with the medulla to regulate respiration

• Cranial nerves V-VIII emerge here

Midbrain

• Corpora quadrigemina–Visual and auditory reflex centers

• Cerebral peduncles - containing large fiber tracts going to and from the brain

• Houses the cerebral aqueduct• Cranial Nerves III-IV emerge here

Thalamus

• Two halves connected by the intermediate mass

• Relay center for ALL sensory cranial and spinal nerves

• Interpretation center for crude awareness of pain, temperature and pressure

• Location of 3rd ventricle

Hypothalamus• Links the nervous system and

endocrine system• Major regulator of homeostasis• Regulates many ANS functions• Regulates appetite, water balance,

thirst, body temperature• Emotional part of brain - pleasure,

fear, rage

Cranial Nerves• 12 Pairs

• 1 Olfactory - smell

• 2. Optic - sight

• 3. Oculomotor - eye movements

• 4. Trochlear - eye movements

• 5. Trigeminal - eyes & face, chewing

• 6. Abducens - eyes

• 7. Facial - facial expression, taste

• 8. Vestibulocochlear - equilibrium, hearing• 9. Glossopharyngeal - tonge & swallowing• 10. Vagus - heart, visceral organs• 11. Accessory - neck & back• 12. Hypoglossal - tongue

Cranial Nerves (continued)

Cerebellum• Second largest area of the brain• 2 cerebellar hemispheres• Arbor vitae - branchlike pattern• Vermis - wormlike structure that

connects left & right side• Major coordination of skeletal muscle

contraction• Assists with posture and balance

Cerebrum

• Cerebral cortex - outer layer of gray matter• Two hemispheres separated by longitudinal

fissure• Gyri - ridges on surface• Sulci - grooves on surface• Fissures • Septum pellucidum - thin wall between

ventricles

Lobes of the Brain

• Frontal• Parietal• Occipital• Temporal• Central sulcus• Lateral sulcus

Cerebral Dominance

• Left hemisphere–Language–Logic–Math

• Right Hemisphere–Artistic–Musical–Creative

Cerebral Cortex Specialization• Motor Areas

–Control opposite side of body–Control voluntary motor functions

• Sensory Areas–Detect sensations from opposite side of

body• Association Areas

–Integrate diverse information into purposeful action

Association Areas

• Prefrontal Cortex – intellect, learning, & personality

• Language Areas–Wernicke’s area – sounding out new words–Brocas’s area – speech

• General Interpretation• Visceral Interpretation

Basal Ganglia

• Cerebral nuclei• Islands of gray matter located deep within the

white matter• Function: controls large automatic skeletal

muscle movements and produce dopamine

White Matter

• Commissural fibers (corpus callosum) - connect corresponding parts of two hemispheres

• Association fibers - connect within the same hemisphere

• Projection fibers (higher centers to lower ones)

Limbic System

• Includes part of thalamus, hypothalamus, and cerebrum

• Emotional brain• Associated with memory• Involuntary behavior for survival• Pleasure and pain centers - fear, sorrow,

affection

Reticular Formation

• RAS System - reticular activating system• Network of gray matter extending from the

medulla, pons, midbrain into the cortex• Maintains consciousness• Awaken from sleep• Alerts brain of incoming sensory signals