Ch. 18 Brain and Cranial Nerves Flashcards
Support and Protection of Brain
cranium
cranial meninges
cerebrospinal fluid (CSF)
blood-brain barrier
Meninges
dura matter, arachnoid mater, pia mater
- dura mater: periosteal and meningeal layers; spinal cord has only one
- dural venous sinuses: form between two dura matters; drain venous blood from the brain and deliver it into the internal jugular veins
- no epidural space around brain
Dura Mater
3 extensions of dura mater separate parts of the brain
- falx cerebri: separates the two hemispheres of the cerebrum
- falx cerebelli: separates the two hemispheres of the cerebellum
- tentorium cerebelli: separates the cerebrum from the cerebellum
Blood Brain Barrier
- allows glucose and oxygen into brain
- protects from harmful substances and pathogens
- proteins and antibodies cannot cross BBB
- oxygen, carbon dioxide, anesthetic drugs, and alcohol can cross BBB
- astrocytes are part of BBB
CSF
- clear, colorless that protects the brain and spinal cord against chemical, physical injuries and serve as shock absorber
- carries oxygen, glucose, and other needed chemicals from blood to neurons and neuroglia
- circulates through cavities in brain and spinal cord and around brain and spinal cord in the subarachnoid space
CSF Protection
- mechanical protection: CSF serves as shock-absorbing medium that protects the delicate tissues of the brain and spinal cord
- chemical protection: CSF provides chemical environment for accurate neuronal signaling in neurons that border the fluid
- circulation: medium for minor exchange of nutrients and waste products between blood and nervous tissue
CSF Production and Circulation
- lateral ventricle
- septum pellucidum: separate the lateral ventricles
- third ventricle: midline superior to hypothalamus and thalamus
- fourth ventricle: between brain stem and cerebellum
- choroid plexus
- interventricular formina: CSF formed in choroid plexuses flows into third ventricle through opening
Brain Stem: Medulla
- begins at foramen magnum and extends to inferior of pons
- Gray matter contains several nuclei that form 2 important centers:
cardovascular center: inhibitory and accelerator fibers control the rate of heart and blood pressure
respiratory center: controls rate and depth of breathing; centers of reflexes involved in sneezing, coughing, swallowing and vomiting
Internal Anatomy
Inferior Olivary Nucleus: relay impulses from proprioceptors to cerebellum
Gracile and Cutaneous Nuclei: touch, pressure, vibrations, and proprioception
White Matter of MO contains…
pyramids: sensory and motor axons that form the bulge within MO forms on anterior aspects of medulla
decussation of the pyramids: crossing of axons from right to left and vice-versa of spinal cord is decussation of pyramids
medial lemniscus: axons in a band of white matter that ascend from MP to the thalamus
gracile and cuneate nuclei: touch, conscious proprioception, pressure, and vibration
Cranial Nerves associated with MO
vestibulochoclear, glossopharyngeal, vagus, accessory, hypoglossal
Pons
- bridge that connects parts of the brain with one another
- connect right and left sides of cerebellum
ventral region: pontine nuclei: coordination between cerebellum and cerebrum
dorsal region: ascending and descending tract: between spinal cord and brain
pontine resp. group: - pneumotaxic and apneustic- control breathing
Pons contains nuclei associated with cranial nerves…
trigeminal, abducens, facial, vestibulocochlear
Midbrain
- cerebral aqueduct: passes through midbrain and connects third ventricle to fourth ventricle
- contains both tracts and nuclei
Anterior: - cerebral peduncles: pair of tracts in anterior part of the midbrain and contains axons of sensory neurons that extend from MO to thalamus; axons of corticospinal, coritcopontine, and corticobulbar motor neurons, which conduct nerve impulses from cerebrum to spinal cord, medulla, and pons
Posterior of Midbrain
superior colliculi: two superior elevations of midbrain
- reflex centers for certain visual activities; accommodation reflexes such as tracking movements with eyes
inferior colliculi: inferior elevations part of auditory reflex
- relaying impulses from receptors for hearing in the ear to the thalamus
substantia nigra (dopamine): contro subconscious muscle activities; loss of neurons causes Parkinson’s disease
red nuclei: axons of cerebellum and cerebral cortex form synapses in red nuclei
- functions with cerebellum to coordinate muscular movements
Cranial Nerves associated with Midbrain
oculomotor and trochlear
Reticular Formation
- broad region of white and gray matter
- sensory and motor function; RAS consists of sensory axons that project to cerebral cortex
- maintain consciousness, active during awakening from sleep and maintain attention and alertness
- descending portion of RAS maintain muscle tone
- helps regulates heart rate, bp, resp. rate
Cerebellum
cerebellar cortex: gray matter in series of slender, parallel ridges called folia
arbor vitae: tracts of white matter deep to gray matter
cerebellar nuclei: gray matter that give rise to axons carrying impulses from cerebellum to other brain centers and spinal cord
vermis: central constricted area
cerebellar hemispheres: separates two lobes
- each hemisphere consists of lobes separated by deep and distinct fissures
Cerebellum Anatomy
Flocculonodular lobe: contribute to equilibrium and balance
superior and middle cerebellar peduncles: bundles of axons that conduct impulses between the cerebellum and other parts of the brain
inferior peduncles: carries sensory info from the vestibular apparatus and proprioception into the cerebellum
anterior and posterior lobe: govern subconscious aspects of skeletal muscle movements
Diencephalon
- contains nuclei involved in sensory and motor processing between higher and lower brain centers
- extends from brain stem to cerebrum and surrounds the third ventricle; includes the thalamus, hypothalamus, and epithalamus
- projecting is hypophysis, or pituitary gland; optic tracts carrying neurons from the retina enter this region of the brain
Thalamus
- bridge of gray mater celled intermediate mass (interthalamic adhesion) joins the right and left halves of the thalamus
functions: serve as major relay station, relays sensory impulses from spinal cord, brain stem, and midbrain to primary sensory area of cerebral cortex - transmits info from cerebellum and basal ganglia to primary motor area of cerebral cortex
- plays a role in regulation of autonomic activities and maintenance of consciousness
- crude perception of painful, thermal, and pressure sensations arise at the level of the thalamus
7 Groups of Nuclei on each side of thalamus
anterior nucleus: emotions, alterness and memory
medial nuclei: emotions, memory, awareness, and cognition
lateral nuclei: expression of emotions
ventral group: contains five nuclei and contribute to motor functions such as movement planning
intralaminar nuclei: pain perception, integratin of sensory and motor info and arousal
midline nucleus: memory and olfaction
reticular nucleus: surround lateral aspect of thalamus next to internal capsule; monitors, filters, and integrates activities of other thalamic nuclei
Hypothalamus (4 major regions)
mammillary: relay station for reflexes related to sense of smell
tuberal region: widest part; include stalk called infundibulum, which connects pituitary gland to hypothalamus
supraoptic region: superior to optic chiasm and contains paraventricular nucleus, supraoptic nucleus, anterior hypothalamic nucleus, and suprachiamastic nucleus; forms hypothalamohypophyseal tract to posterior pituitary
preoptic region anterior: region contains medial and lateral preoptic nuclei; participate with hypothalamus to regulate certain autonomic activities
Hypothalamus Functions
- control of ANS
- production of hormones
- regulation of emotional and behavioural patterns
- regulation of eating and drinking
- control of body temperature
- regulation circadian rhythms and state of consciousness
Epithalamus
- posterior to thalamus, consists of pineal gland and hebenular nuclei
- halbenular nucleus involved in olfaction (emotional response)
- pineal gland is part of endocrine system by secreting melatonin
- melatonin promotes sleepiness and contribute to set body’s biological clock by inducing sleep and help body adjust to jet lag
Circumventricular Organs
- part of diencephalon called circumventricular organs lie in wall of third ventricle and monitor chemical changes in blood because they lack a blood-brain barrier
- include part of hypothalamus, pineal gland, pituitary gland, and few other nearby structures
- coordinate homeostatic activities of endocrine and nervous systems such as blood pressure, hunger, thirst, fluid balance
- site of HIV entrance in brain
Cerebrum
- cerebral hemispheres that are separated by falx cerebri
- outer rim of gray matter and internal white matter and gray matter deep within white matter
- outer rim of gray matter is cerebral cortex
- folds are called gyri or convolutions
- deepest grooves between folds are known as fissures; shallower grooves between folds are termed sulci
Lobes of Cerebrum
frontal, parietal, temporal, occipital lobes
- central sulcus: separates frontal from parietal
- precentral gyrus: located anterior to central sulcus and contains primary motor area of cortex
- postcentral gyrus: lies posterior to central sulcus, contains primary somatosensory area of cerebral cortex
- lateral cerebral sulcus: separates frontal lobe from temporal lobe
- parieto-occipital sulcus: separates parietal lobe from occipital lobe
Cerebral White Matter
- consists primarily of myelinated axons in three types
- association tracts: contains axons that conduct nerve impulses between gyri in same hemisphere
- commissural tracts: contain axons that conduct nerve impulses from gyri in one cerebral hemisphere to other gyri in other cerebral hemisphere; three important groups: corpus, anterior commissure, and posterior commissure
- projection tracts: contain axons that conduct nerve impulses from cerebrum to lower parts of CNA or from lower parts of CNS to cerebrum
Functional Areas of Cerebrum (Telencephalon-forebrain)
cerebrum:
- motor areas: primary motor area; motor speech area
- sensory areas: primary somatosensory area; primary visual, auditory, gustatory, olfactory area
- association areas: somatosensory association area, visual and auditory association area, Wernicke’s area, gnostic area
Motor Area (right frontal lobe)
primary motor area: located in precentral gyrus of frontal lobe
- neurons of this area control voluntary skeletal muscle activity
Left frontal lobe
motor speech area (broca’s area): located in inferio-lateral portion of left frontal lobe
- regulates patterns of breathing
- control muscular movement necessary for vocalization
Sensory Area
primary somatosensory area: located postcentral gyrus area of the parietal lobe
- receives somatic sensory info from touch, pain, pressure, proprioceptors
primary visual: located in occipital lobe; recieves and processes incoming visual info
primary auditory: located in temporal; auditory info
primary gustatory: located in insula area; processes taste info
primary olfactory area: temporal lobe; provides conscious awareness of smells and olfactory perception
Association Areas
somatosensory area: located in parietal lobe and posterior to prim. somatosensory cortex
- integrates and interprets sensations to determine texture, temp., pressure, and shapes of objects
- storage of memories of past experiences
Visual: occipital lobe and surrounds primary visual area; process visual info by analyzing color, movement and form
auditory: temporal lobe; interprets characterisitics of sound and store memories of sound
Wernicke;s: located in left hemisphere; recognizing, understanding and comprehending spoken or written language
Integrative: parietal, occipital and temporal lobes; integrates all sensory, visual and auditory info being processed by association area
Limbic System
- olfaction and memory
- “emotional brain”
- damage causes memory impairment
Cranial Nerves
- 12 pairs of cranial nerves
- five are mixed nerves because they contain axons of both sensory and motor neurons
- cell bodies of motor neurons lie in neuclei within the brain; cranial nerves 3, 4 and 6 include both somatic and autonomic motor axons
- cell bodies of sensory neurons are located in ganglia outside the brain
Origin of Cranial Nerves
forebrain: 2 pairs (1&2) brainstem: - midbrain 2 pairs (3&4) - MO 5 pairs (8,9,10,11,12) - pons 3 pairs (5,6,7)
Olfactory Nerve
- sensory
- axons that conduct nerve impulses for olfaction
- end in brain in paired masses of gray matter called olfactory bulbs, two extensions of the brain that rest of cribriform plate
- within bulbs, axon terminals of olfactory receptors form synapses with dendrites
- make up olfactory tracts, which extend posteriorly from olfactory bulbs
Optic Nerve
- sensory
- contains axons that conduct nerve impulses for vision
- two optic nerves merge at optic chiasm; axons on medial hald cross and lateral half remain on same side
- most axons in optic tract end in lateral geniculate nucleus of thalamus
Oculomotor Nerve
- motor
- axons in superior innervate superior rectus and levator palpebrea superior
- axons inferior supply medial rectus, inferior rectus, and inferior oblique muscles (extrinsic muscles)
Trochlear Nerve
- motor; only one that arises from posterior aspect of brain stem
- somatic motor axons innervate superior oblique muscle of eyeball
- proprioceptive sensory axons from superior oblique muscle begin in 3 nerve but leave nerve to join opthalmic branch of 5 nerve
Abducens
- motor
- originates in abducens nucleus in pons
- somatic motor axons extend from nucleus to lateral rectus muscle of eyeball
- abducens nerve is named so because nerve impulses cause abduction of eyeball
Trigeminal Nerve
- mixed cranial nerve and largest
- 3 branches: ophthalmic, maxillary, and mandibular
- ophthalmic nerve: smallest branch passes into orbit via superior orbital fissure
- maxillary nerve: in intermediate size between ophthalmic and manipular nerves and passes through foramen rotunda
- mandibular nerve: largest branch, passes through foramen ovale
Facial Nerve
- mixed cranial nerve
- nerve impulses propagating along these axons cause contraction of facial expression muscles plus stylohyoid muscle, posterior belly of digastric and stapedius muscle
Vestibulocochlear Nerve
- sensory cranial nerve and two branches; vestibular branch and cochlear branch
- vestibular branch carries impulses for equilibrium and cochlear branch carries impulses for hearing
Vagus
- mixed cranial nerve that is distributed from head and neck into thorax and abdomen
- originate from medulla oblongata
- axons of autonomic motor neurone (para.) in vagus nerve originate in nuclei and medullar and end in lungs and heart
- vagal para. axons also supply glands of GI tract and smooth muscle of rest. passageways, esophagus, stomach, gallbladder, small intestine, most large intestine
Accessory Nerve
- mixed cranial nerve
- cranial portion part of vagus nerve
- motor axons arise in anterior gray horn of first five segments of cervical portion of spinal cord
- conveys motor impulses to sternocleiodmastoid and trapezius muscles to coordinate head movements
Hypoglossal Nerve
- motor cranical nerve
- comatic motor axons originate in hypoglossal nucelus in medulla oblongata, pass through hypoglossal canal and supply tongue muscles
- axons conduct nerve impulses for speech and swallowing; sensory axons originate from proprioceptors in tongue muscles begin course toward brain in hypoglossal nerve and end in medulla oblongata
