The Brain and Cranial Nerves PDF

The Brain and Cranial Nerves Ch 16 Intro The adult brain contains about 95% of the body's nervous tissue The Brain is far more complex than the spinal cord And responds to stimuli with greater adaptability This results from the number of neuronal pools and their complex interactions Excitatory and I...

The Brain and Cranial Nerves Ch 16 Intro The adult brain contains about 95% of the body's nervous tissue The Brain is far more complex than the spinal cord And responds to stimuli with greater adaptability This results from the number of neuronal pools and their complex interactions Excitatory and Inhibitory interactions ensure that our responses vary to meet changing conditions Embryology of the Brain The CNS begins as a hollow neural tube with a fluid filled internal cavity called the neurocoele This passageway enlarges to form the ventricles At week 4, the three areas expand rapidly forming the vesicles named for their positions: Prosencephalon, the forebrain Further divides to form the telencephalon (cerebrum) and diencephalon Mesencephalon, the midbrain Rhombencephalon, the hindbrain Further divides to form the metencephalon and myelencephalon Major Regions of the Brain There are 6 major regions in the Adult Brain: 1. 2. 3. 4. medulla Oblongata: Connects brainstem to spinal cord The pons: Connects the cerebellum to the brainstem The mesencephalon : also known as the Midbrain The diencephalon: Contains 3 regions 1. 2. 3. Epithalamus: Includes the Pineal Gland Thalamus Hypothalamus: Connected to Pituitary Gland 5. The cerebelum : 2nd largest part of brain, posterior to the pons and inferior to the cerebrum 6. Cerebrum: Largest part of the brain, divided int paired hemispheres Other Features The general organization of the gray matter in the brain resembles the distribution withing the SC However, the arrangement of gray and white in the brain is not as predictable as in the spinal cord There are 4 ventricles : All filled with CSF & lined with ependymal cells One in each cerebral hemisphere (2) A third in the diencephalon A fourth between the pons and cerebellum Meninges The brain lies within the cranium of the skull: This both protects the brain and is a source of potential damage Within the cranial cavity lie the meninges They protect the brain by acting as shock absorbers, preventing contact with the skull bones They are continuous with the spinal meninges and are divided into the same 3 layers Blood Brain Barrier Formed by capillary endothelial cells that are interconnected by tight junctions: Prevent materials from diffusion between cells Only lipid soluble materials will freely cross Passive or Active transport is required for the passage of water-soluble compounds In addition, astrocytes are in close contact with the capillaries of the CNS This further restricts the permeability of the endothelial cells within the brain There are 4 regions in the brain where the BBB is notable different: 1. 2. 3. 4. Portions of the hypothalamus Capillaries of the pineal gland Capillaries of the choroid plexus Capillaries of the posterior pituitary The hypothalamus, pineal gland, and pituitary all act either as parts of the endocrine system or are dependent on hormones for their functions The Choroid Plexus produces CSF CSF completely surrounds, supports, and cushions the brain It has several functions: Prevents contact between delicate neural structures and the bones Supports the brain: the brain “floats” within a chamber filled with CSF Transports nutrients, chemicals and waste into and out of the CNS The parts of the Brain A closer Look The Medulla Oblongata Connects the brain to the spinal cord and many of its functions are directly related to this The medulla incudes 3 groups of nuclei with various functions: 1. Relay stations and processing centers Many ascending tracts synapse with the sensory or motor nuclei of the medulla 2. Nuclei of cranial nerves Sensory and motor nuclei of 5 cranial nerves (viii-xii) are found within the medulla 3. Autonomic nuclei The reticular formation contains nuclei that are responsible for regulating essential autonomic functions including 2 major reflex centers: The cardiovascular Center-adjusts HR The respiratory Center-Sets basic rate of breathing The Pons Expands from the medulla to the mesencephalon and forms a prominent bulge on the brainstem The Pons contains: Sensory and motor nuclei of four cranial nerves (V-VIII) Nuclei regulating involuntary control of respiration (regulate the reflex center of the medulla) Nuclei that process and relay cereberall commands Ascending, descending and transverse tracts that interconnect the pons to other major brain areas The Mesencephalon The roof of the midbrain, the tectum, contains 2 pairs of sensory nuclei, the corpora quadragemina These relay stations are concerned with processing auditory and visual sensations superior Colliculi receive the visual information from the lateral geniculate Inferior Colliculi receive the auditory information from the medulla The mesencephalon also contains the major nuclei of the reticular formation This region is responsible for numerous involuntary muscle responses The Diencephalon The Epithalamus: Contains the Pineal gland, secretes the hormone melatonin The Thalamus: Contains most of the nerve tissue in the diencephalon Thalamic nuclei provide integration and relay centers for sensory and motor pathways All ascending sensory information from the SC and cranial nerves (except the olfactory nerve) synapse in the thalamus The Hypothalamus: Extends from the optic chiasm to the posterior margin of the bodies Contains a variety of important and integrative centers Functions include: Subconscious control of skeletal muscle contractions Control of autonomic functions Coordinates activities of the nervous and endocrine systems Secretes hormones Produces emotions and behavioral drives Coordination between voluntary and autonomic functions Regulation of body temp Controls circadian rhythms The Cerebellum Has two cerebellar hemispheres, each with highly folded surfaces Folds are termed Folia The 2 lobes of each hemisphere are termed anterior and posterior and are separated by the primary fissure Along the midline the vermis separates the two hemispheres The cortex contains huge, highly branched Purkinje cells Have a massive pear-shaped cell body Axons from the basal portions project deep into the white matter Reach the cerebellar nuclei Internally the white matter branches, resembles a tree Called arbor vitae: Tree of Life The cerebellum receives proprioception information from the SC Monitors all proprioceptive, visual, tactile, balance, and auditory sensations received by the brain Most sensory axons do not synapse withing the cerebellar nuclei Instead, they pass to the cortical surface and synapse with the purkinje cells The Cerebrum Much of the cerebrum is involved in the processing of somatic sensory and motor information somatosensory info reaches our conscious awareness Cerebral neurons exert direct (voluntary) or indirect (involuntary) control over somatic motor units A thick layer of superficial gray matter (The Cerebral Cortex) covers the paired cerebral hemispheres The cortical surface is marked by gyri (folds) and Sulci (grooves) The cortex performs the most complicated neural functions Cerebral Lobes The deep longitudinal fissure separates the L/R hemispheres Each hemisphere is divided into lobes names after the bones of the skull Each lobe contains functional regions whose boundaries are not well defined Some process sensory info while others generate motor commands In general, cerebral lobes: Receive sensory information from and send motor commands to the contralateral side of the body Have some functional differences Assigning function to a single region is imprecise as one region may have several different functions Higher Order Functions Are performed by the cerebral cortex Involve complex interconnection and interaction between areas withing the cortex and with other areas of the brain Involve both conscious and unconscious information Are not part the “wiring” of the brain Functions subject to modification over time Integrative centers receive information from many areas and direct extremely complex motor actions and analytical functions Centers such as the prefrontal cortex, Broca’s area, and Wernicke’s area are concerned with processes like mathematics, speech, writing and spatial relationships Prefrontal Cortex The prefrontal cortex of the frontal lobe coordinates information relayed from all the cortical association areas Does not fully develop until mid 20’s It performs such abstract functions as predicting the consequences of events or actions Feelings of frustration, tension, and anxiety are generated as a result of the prefrontal cortex’s interpretation of ongoing events Hemispheric Lateralization Each of the 2 hemispheres is responsible for specific functions that are not performed by the opposite hemisphere In most people the left hemisphere contains specialized language areas of the brain (reading, writing, and speaking) Also important in analytical tasks and logical decision making The right hemisphere analyzes sensory information and relates the body to the sensory environment Permits you to identify familiar objects by sight, touch, taste, or smell The Cranial Nerves There are 12 pairs of Cranial Nerves Each contain one of 5 axon types: 1. Special sensory Taste, Vision, Smell 2. Somatic Motor Synapse on motor neurons of the head region 3. Visceral Motor Synapse on smooth muscle in the head, chest, digestive tract and cardiac muscle 4. Somatic Sensory Sense touch, temp, pain in te head and face 5. Visceral Seonsory Touch, temp, pain from lungs, digestive ract, heart OOOT TAF AG VAH The olfactory Nerve (I) Function: Special Sensory Origin: Olfactory Epithelium Destination: Olfactory Bulb The optic Nerve (II) Function: Special Sensory Origin: Retina of eye Destination: Diencephalon The oculomotor Nerve (III) Function: Motor Origin: Mesencephalon Destination: Superior, Inferior, Medial Rectus, Inferior Oblique The trochlear Nerve (IV) Function: Motor Origin: Mesencephalon Destination: Superior Oblique The trigeminal Nerve (V) Function: Mixed (Sensory and Motor) Origin: 3 Branches with sensory information from the head and face Ophthalmic-sensory only Maxillary-sensory only Mandibular-motor only Destination: Muscles of mastication The abducens Nerve (VI) Function: Motor Origin: Pons Destination: Lateral Rectus The facial Nerve (VII) Function: Mixed Origin: Taste Receptors on the Anterior 2/3 of tongue Destination: Pons The vestibulochchlear (Acousticovestibular) Nerve (VIII) Function: Special Sensory Origin: Inner Ear Destination: Vestibular and Cochlear Nuclei of the Pons and Medulla The glossopharyngeal Nerve (IX) Function: Mixed Origin: Sensory: Posterior 1/3 of tongue Destination: Motor: Muscles of pharynx involved in swallowing The vagus Nerve (X) Function: Mixed Origin: Sensory: Pharynx, Outer Ear, Visceral Organs of the abdomen Motor: Medulla Destination: Somatic Motor: Muscles of the palate and pharynx Visceral Motor: Lungs, Heart, Digestive Organs The accessory Nerve (XI) Function: Motor Origin: Medulla Destination: Muscles of the palate, pharynx and larynx, sternocleidomastoid and trapezius muscles The hypoglossal Nerve (XII) Function: Motor Origin: Medulla Destination: Muscles of the Tongue