The Brain and Cranial Nerves

Cerebrum Largest part of brain Controls higher mental functions Divided into left and right cerebral hemispheres Surface layer of gray matter (neural cortex) Also called cerebral cortex Folded surface increases surface area Elevated ridges (gyri) Shallow depressions (sulci) Deep grooves (fissures)

Three Functional Principles of the Cerebrum Each cerebral hemisphere receives sensory information from, and sends motor commands to, the opposite side of the body The two hemispheres have different functions, although their structures are alike Correspondence between a specific function and a specific region of cerebral cortex is not precise

White Matter of the Cerebrum Association fibers connect within on hemisphere Arcuate fibers Short Connect one gyrus to another Longitudinal fasiculi Longer bundles Connect frontal lobe to other lobes in same hemisphere Commissural fibers connect two hemispheres Projection fibers link cerebral cortex with diencephalon, brain stem, cerebellum, and spinal cord

Motor and Sensory Areas of the Cortex Central sulcus separates motor and sensory areas

The percentages of total cerebral cortex volume for the different lobes are: frontal lobe = 41% temporal lobe = 22% parietal lobe = 19% occipital lobe = 18%

Hemispheric Lateralization Functional differences between left and right hemispheres Each cerebral hemisphere performs certain functions that are not ordinarily performed by the opposite hemisphere

The Basal Nuclei of the Cerebrum Also called cerebral nuclei Are masses of gray matter embedded in white matter of cerebrum Direct subconscious activities control of skeletal muscle tone coordination of learned movement patterns (walking, lifting)

Cerebellum Second largest part of brain Two hemispheres Covered with cerebellar cortex Coordinates repetitive body movements Adjusts postural muscles Fine-tunes conscious and subconscious movements

Diencephalon Located under cerebrum and cerebellum Links cerebrum with brain stem Made up of: Thalamus Relays and processes sensory information Hypothalamus Hormone production Emotion Autonomic function Pituitary Gland Major endocrine gland Interfaces nervous and endocrine systems

The Brain Stem Processes information between Includes Spinal cord and cerebrum or cerebellum Includes Mesencephalon Pons Medulla oblongata

Mesencephalon Pons Medulla oblongata Also called midbrain Processes sight, sound, and associated reflexes Maintains consciousness Pons Connects cerebellum to brain stem Is involved in somatic and visceral motor control Medulla oblongata Connects brain to spinal cord Relays information Regulates autonomic functions: heart rate, blood pressure, and digestion

Embryological Development Determines organization of brain structures Neural tube- origin of brain

Ventricles of Brain Origin Neural tube encloses neurocoel Neurocoel expands to form chambers (ventricles) lined with ependymal cells Each cerebral hemisphere contains one large lateral ventricle

Third ventricle Fourth ventricle Ventricle of the diencephalon Lateral ventricles communicate with third ventricle: via interventricular foramen (foramen of Monro) Fourth ventricle Extends into medulla oblongata Becomes continuous with central canal of the spinal cord Connects with third ventricle: via narrow canal in mesencephalon (aqueduct of midbrain)

Brain Protection and Support Physical protection Bones of the cranium Cranial meninges Cerebrospinal fluid Biochemical isolation Blood–brain barrier

The Cranial Meninges Dura mater Arachnoid mater Pia mater Inner fibrous layer (meningeal layer) Outer fibrous layer (endosteal layer) fused to periosteum Venous sinuses between two layers Arachnoid mater Covers brain Contacts epithelial layer of dura mater Subarachnoid space: between arachnoid mater and pia mater Pia mater Attached to brain surface by astrocytes

Cerebrospinal Fluid (CSF) Surrounds all exposed surfaces of CNS Interchanges with interstitial fluid of brain Functions of CSF Cushions delicate neural structures Supports brain Transports nutrients, chemical messengers, and waste products

CSF formation & circulation CSF circulates From choroid plexus through ventricles to central canal of spinal cord Into subarachnoid space around the brain, spinal cord, and cauda equina Reabsorbed by arachnoid granulations in subarachnoid space

Brain Protection and Support Blood–Brain Barrier Isolates CNS neural tissue from general circulation Allows chemical composition of blood and CSF to differ Astrocytes control blood–brain barrier by releasing chemicals that control permeability of endothelium Four Breaks in the BBB Portions of hypothalamus secrete hypothalamic hormones Posterior lobe of pituitary gland secretes hormones ADH and oxytocin Pineal glands for pineal secretions Choroid plexus where special ependymal cells maintain blood–CSF barrier

The Limbic System Establishes emotional states Links conscious functions of cerebral cortex with autonomic functions of brain stem Facilitates memory storage and retrieval

Four Categories of Brain Waves Alpha waves Found in healthy, awake adults at rest with eyes closed Beta waves Higher frequency Found in adults concentrating or mentally stressed Theta waves Found in children Found in intensely frustrated adults May indicate brain disorder in adults Delta waves During sleep Found in awake adults with brain damage Brain Waves are analyzed with the use of an EEG or electroencephalogram

Cranial Nerves 12 pairs connected to brain Four Classifications of Cranial Nerves Sensory nerves: carry somatic sensory information, including touch, pressure, vibration, temperature, and pain Special sensory nerves: carry sensations such as smell, sight, hearing, balance Motor nerves: axons of somatic motor neurons Mixed nerves: mixture of motor and sensory fibers