The brain and cranial nerves Flashcards
Cerebrum
-weighs 1.3kg
-100 billion neurones
-outer layer= grey matter, accounts 80% weight
-inner= white matter
-vulnerable to injury through inter cranial pressure
-lobes of cerebrum correspond to bone names of skull
Cerebrum structure
-grey matter develops quicker than white matter causes cortical region to roll and fold in on itself
-ridges= gyri
-deepest ridges= fissures
-longitudinal fissure- divides R and L hemispheres
-central sulcus- divides frontal and parietal lobes
Frontal lobe
-largest lobe
-higher cognitive activity
-thinking, reasoning, understanding, language
-gives us our personality- auto biographical memory
-inhibited by alcohol and recreational drugs
Damage to frontal lobe
-increased display of combativeness
-abusive attitude
-inappropriate sexual activity
Areas of cerebral cortex
Brodmann’s areas -numbered regions of cortex that have been mapped to specific cognitive functions
Sensory areas- perception of sensory info
Motor areas- control execution of voluntary movements
Association areas- complex integrative functions eg. memory, personality, traits
Primary somatosensory area
-parietal lobe
-in postcentral gyrus
-receive nerve impulses for sensations of touch, pressure, vibration, temperature, pain
-impulse depends on number of neurones present not size of the body part
Parietal lobe
-supplied by large arteries
-where most strokes occur causing motor/ sensory paralysis
Sensory homunculus
describes the way the somatosensory area is distorted as the impulse is dependent on the number of neurones not the size of the body part
eg. larger region of the somatosensory area receives impulses from the lips/ fingers compared to the thorax/ hip- more receptors in lips
Motor area
-located in precentral gyrus of frontal lobe
-controls voluntary contractions of muscles
-homunculus map, more area devoted to muscles involved with skilled, complex or delicate movement
Location primary visual area
-located at posterior tip of occipital lobe
-mainly on medial surface
Primary gustatory area (taste) location
-located inferior to primary somatosensory areaP
Primary auditory area location
-superior part of the temporal lobe
Primary olfactory area location
-inferior medial temporal lobe
White matter in cerebrum and tracts
-consists primarily of myelinated axons in 3 types of tract:
1. association tracts- conduct impulses between gyri in the same hemisphere
2. commissural tracts- conduct impulses between gyri from one hemisphere to another
3. projection tracts- conduct impulses to lower parts of the CNS or vice versa
Corpus callosum
-one of the 3 important groups of commissural tracts
-thick band axons connects hemispheres
Basal nuclei
-part of grey matter
-conspicuous centres of cell bodies deep in cortex
-3 basal nuclei help initiate and terminate movements
-control subconscious contractions of skeletal muscles eg. swinging arms when walking
Limbic system
-3 integrated systems
-3 integrated systems
-1 and 2= limbic system
1.Reptilian brain- primary instincts and body functions, ANS
2.Mammalian brain- emotions, sexual desire, relationships, learning, memory
3.Cerebral cortex- neo cortex of homo sapiens
Limbic system function
-doesn’t represent one part of the brain, its multiple parts that work together
-motivates feelings of primitive nature
-feeding, fighting, flight, sexual activity
-inhibited by frontal lobe
Diencephalon
gives rise to hypothalamus and thalamus
Medulla oblongata structure
-extends from pons above and continuous with spinal cord below
-2.5cm long
-pyramid shape, base upwards
-lies just within cranium
Medulla oblongata functional centres
Cardiovascular centre- rate, force, diameter vessels
Respiratory rhythmicity centre- rate and rhythm breathing
Vomiting, coughing and sneezing centres
Pyramids medulla
-2 external bulges formed by motor tracts
-axons from left pyramid cross to the right and vice versa
-decussation of pyramids- so left hemi of brain controls right side muscles and vice versa
Pons varolii
-above medulla
-connects spine with brain
Mid brain
2 parts
Tectum
-contains colliculus- important route for sensory info
-filters unnecessary info so can concentrate on stimulus
Substantia nigra
-largest nuclear mass in mid brain
-involved automatic movement of skeletal muscle
-failure of this causes parkinson’s
Reticular formation
-maintain consciousness, alert, aware
-inactivation of RAS produces sleep, state partial consciousness
-prevents sensory overload by filtering insignificant info
Cerebellum location
-2nd largest part of brain
-inferior to cerebrum and posterior to brain stem
Cerebellum function
-compares intended movements with what is happening with skeletal muscles
-regulates posture, equilibrium and balance
Hypothalamus
-area of diencephalon
-control ANS
-coordinates between NS and endocrine system
-body temperature
-regulates hunger/ thirst
-assists with circadian rhythm
Cranial meninges
Function, location, layers
-helps protect brain
-continuous with spinal meninges
-tough outer dura mater
-spidery arachnoid mater
-thin, delicate pia mater
Brain blood flow
-consumes 20% of o2 and glucose even when resting
-anteriorly (front), internal carotid arteries supply blood to brain
-posteriorly(back), via vertebral arteries
-internal jugular veins are the venous return
Vascular endothelium
-differs in brain capillaries compared to other organs
-forms tight junctions with end feet of nearby astrocytes
-this forms a blood brain barrier which isolates the parenchyma of the brain from blood and substances within it
Cerebral spinal fluid
Function
-circulates through cavities in brain= brain ventricles and spinal cord
-absorbs shock and protects brain and spinal cord
-helps transport of nutrients and waste
Flow of CSF
-flows continuously between pia mater and arachnoid that is tightly attached to outer dura
-constant pressure
-rate of reabsorption matches rate formation at 20ml per hour
CN I
olfactory nerve
CN II
optic nerve
CN III, IV, VI
-innervate extraocular muscles, allow us to move eyes
-CN III- supply motor input to eyelid muscles and facilitates pupillary constriction
CN V
-trigeminal nerve
-major sensory nerve of face
-3 branches which supply area of face:
1.ophthalmic
2.maxillary
3.mandibular
CN VII
-facial nerve
-5 somatic branches which innervate muscle of facial expression
-also carries some taste sensations
-paralysis of nerve called bell’s palsy and leads to loss of ability to close eyes, impairment of taste
CN VIII
-vestibulocochlear nerve
-vestibular component carries info on balance
-cochlear component enables hearing
-damage causes vertigo, ringing in ears, deafness
CN IX
-glossopharyngeal nerve
-taste sensations as well as ANS impulses to salivary glands
CN X
-vagus nerve
-carries most of parasympathetic motor efferent to the organs of thorax and abdomen
CN XI
-spinal accessory nerve
-supplies somatic motor innervation to the trapezius and sternocleidomastoid muscles ( neck and shoulders)
CN XII
-hypoglossal nerve
-solely for tongue
-chew, talk, swallow
