Download CH 14 brain cranial nerves A and P 2017

Chapter 14
Brain and Cranial nerves
brain
brain integration
cranial nerves
the brain is very complex but scientists have located
- gross anatomical structures such as a lobe or gyrus
- internal structures for motor, sensory, or integrative functions
- specific area which deal with specific functions
- the role of the brain as a sensory and motor organ
some terms we should all know
fissure = cleft/groove dividing a structure, deeper than a sulcus
sulcus = shallow groove or furrow on the surface of a structure
gyrus = thick folds of tissue of the cerebrum and cerebellum
precentral gyrus = gyrus anterior to central sulcus (primary motor)
postcentral gyrus = gyrus posterior to central sulcus (primary sensory)
central sulcus = separates primary motor from primary sensory cortex
cerebrum = largest most superior part of brain (integration & thought)
cerebellum = area for balance, motor coordination, learned motor skills
medulla oblongata = connects cord to brain, site of many basic life needs
corpus callosum = connects left and right cerebrum at base of cerebrum
brainstem = medulla, pons, midbrain, diencephalon
gray matter = neurosomas, dendrites, synapses,
white matter = tracts, bundles of axons
brain development
- embryo made up of ecto, meso, and endoderm
- brain develops from ectoderm
- ecto  neural plate  neural groove  neural tube
 4th week becomes 3 dilations (fore, mid, & hindbrain)
 5th week forebrain becomes tele & diencephalon, mid
remains as one, and hindbrain becomes meta &
myelencephalon
- tele grows 2 lateral outpockets which become the cerebrums
- diencephalon has 2 outpockets which become optic vesicles
brain covering terms
- skull = bony covering for brain, compact and spongy bone
- dura periosteal layer = coats the inner surface of skull
- dura meningeal layer = inner layer which follows folds of brain
- arachnoid layer = thin fibrous layer separated from pia mater by fluid
filled space
- arachnoid granulations = reabsorb cerebral spinal fluid
- pia layer = thin fibrous layer which follows the contours of the brain
- gray matter = layer containing many neurosomas
- white matter = layer containing many axons in bundles and tracts
- sinuses = separation of dural layers which collect blood which
has left blood vessels
ventricles and CSF
- brain has 4 internal chambers called ventricles
- 2 lateral ventricles = ventricles 1 and 2 form a large arc in cerebrum
- interventricular foramen = connects 1 with2 and 1 & 2 to 3
- 3rd ventricle = narrow space below corpus callosum
- cerebral aqueduct = foramen leading down midbrain
-4th ventricle = small chamber between pons and cerebellum
- central canal = 4th narrows to small space which continues into cord
- choroid plexus = groups of small BV line ventricles and canals
- ependyma = neuroglial cells line ventricles and canals and make CSF
cerebrospinal fluid
- fills ventricles & canals & bathes external surfaces
- 500 ml made each day
- at any one time CNS has 100 to 160 ml of CSF
- 40% from subarachnoid space, 30% ependymal, 30% choroid
- CSF is a blood filtrate, modified by ependymal, Na,
potassium, calcium, glucose, and protein
- pulsations of blood moves CSF
- CSF provides buoyancy, allows for large brain, protection
- CSF provides regulation of chemical composition, removes wastes,
brain cant work without blood
- 2% of body weight but 15% of blood supply
- uses 20% of O2 , 20% of glucose
- no blood supply for 10 sec=faint, 1-2 m in=function, 4 min=irrev
- BBB regulates what leaves BV and gets to brain cells and fibers
- blood brain barrier has tight junctions for capillaries & ependymal
- circumventricular organ in 3rd & 4th ventricles, has direct access to
brain, cells here monitor glucose, pH, osmolarity, & other
parameters – disease?
hindbrain and midbrain
composed of the
medulla, pons,
reticular, and cerebellum
hindbrain
- myelencephalon becomes medulla oblongata
- metencephalon becomes pons & cerebellum
medulla oblongata (hindbrain)
- all nerves  or  pass through the medulla
- sensory nerves = 1st order from G&C fasiculito & C nucleus
- 2nd order decussate & go to medial lemiscus of pons then
go through pons - there 3rd order go to cerebrum
- motor = corticospinal tracts on anterior surface of medulla
- 90% decussate & control skeletal muscles below neck
- smaller tectospinal tract controls neck muscles
- 4 pair of cranial nerves 8, 9, 10, 11 originate in medulla
- inf olivary nuc relays info from brain to cerebellum
- reticular formation nuclei extend through medulla, pons & midbrain
& has centers for control of heart, lungs, & blood vessel tone
pons
- thick cerebellar peduncles connect pons & midbrain to cerebellum
- anterior ½ of pons tracts including transverse fascicles that cross
between left and right connect the two halves of the cerebellum
- longitudinal fascicles carry  &  signals up & down the brainstem
- cranial nerves 5, 6, 7, & 8 begin or end in the pons
- carry sensory info for hearing, equilibrium, taste, facial sensation,
touch, pain, & motor roles in facial expressions, chewing,
swallowing, urination, saliva, tears, & eye movements
- reticular formation in pons = nuclei for sleep, breathing & posture
midbrain
- a short segment of brainstem
- connects hindbrain to forebrain
- contains cerebral aqueduct
- continuations of medial lemniscus, reticular formation and
- motor nuclei for cranial nerves 3 & 4
- made up of the corpora quadrigemina
1 & 2= left and right superior colliculus (vision)
3 & 4= left and right inferior colliculus (inner ear)
plus
tectum, cerebral peduncles, substantia nigra, red nucleus
oculomotor nucleus, trochlear nerve, & cerebral crus
midbrain terms
tectum= post to aqueduct, contains corpora quadrigemina
reticular formation = runs from cord up through brainstem
tegmentum= to and from cerebellum for fine
motor control
sub nigra= melanin containing nuc, inhibitory center for
thalamus and basal nuc preventing unwanted
body movement
cerebral crus= tract connects cerebrum to pons and carries the
corticospinal nerve tracts,
red nuc= to & from cerebellum for fine motor control, many BV
medial lemniscus= carries fibers & from cord to cerebrum
reticular formation
- runs through entire brainstem, 100+ small nuclei,
- input from cord and senses to thalamus then cerebrum and - back to reticular system and down the spinal cord
-
reticular activating system
- controls sleep, waking, and attention
- a sophisticated filter
- creates a blind spot to junk
- acts as an executive assistant
- allows you to focus on what you value
- allows you to perceive a threat
- supports you when you set a goal
no mention made of reticular inactivating centers?
somatic motor control
- motor neurons axons from cerebrum to reticular form nuclei
- which give rise to the reticulospinal tract of cord
- which control muscle tone, tension, balance, & posture
- integrates signals from eyes & ears and sends to cerebellum
- other motor functions for gaze, patterns, breathing, & swallowing
other reticular system functions
- cardiac and vasomotor centers of medulla oblongata
- pain modulation,  & , analgesic pathways sent down to
stop or modulate pain sensory signals
- controls sleep & waking, injury = coma
- habituation body = learns to ignore repetitive unimportant
stimuli but nuclei remain sensitive to other stimuli,
these are called the reticular activating system
nuclei or extrathalamic cortical modulatory system
the cerebellum
- largest part of hindbrain & 2nd largest part of the brain
- right and left hemispheres connected by vermis
- surface exhibits masses of parallel folds called folia
- each hemisphere has 4 masses of gray matter (deep nuclei)
- all output from cerebellum originate from deep nuclei
- nuclei send information to thalamus which sends it to cerebrum
- 10% of mass but 50% of all brain neurons
- some estimate more cells than the rest of the brain
- 10% of brain mass but surface area equal to 60% of cerebrum
- cerebellum is connected to the brainstem by 3 peduncles
- a peduncle is a stem like projection
- inferior peduncles connects to medulla oblongata (spine in)
- middle peduncles connect to the pons (rest of brain in)
- superior peduncles connect to the midbrain (output)
- monitors muscle contraction
- monitors muscle coordination
- evaluates sensory information and coordinates with contraction
- tactile, spatial, 3D, timekeeper, temporal judgement
- football, music, ADHD
- lesions = moter, sensory, & emotional dysfunction
The forebrain made up of the
diencephalon and telencephalon
the diencephalon is made up of the
thalamus, hypothalamus, and epithalamus
the telencephalon derives from two paired vesicles
which give rise to the paired cerebral hemispheres
the thalamus
- paired structures on the superior end of the brainstem
- account for 80% of diencephalon
- has at least 23 nuclei and more are being discovered
- anterior, posterior, medial, lateral, & ventral
- info for taste, smell, hearing, equilibrium, vision, touch, pain,
pressure, heat, and cold pass through on way to cerebrum
- motor signals from cerebellum to cerebrum go through thalamus
- involved in memory and emotions
-feedback loop between cerebrum, basal ganglia & cerebellum
- memory and emotion linked to limbic system, coordinates muscle
action in light of sensory input from in and out of the body
- has both motor and sensory centers
- gateway to the cerebrum
the hypothalamus
- lies under the thalamus
- forms the floor and walls of the 3rd ventricle
- pituitary gland attached by infundibulum which is anterior to
optic chiasma and posterior to mammillary bodies
- relays info from limbic to thalamus
- control center for endocrine and autonomic nervous system
- homeostatic center for virtually every organ and system
- controls many visceral functions
secretes hormones that control the anterior pituitary thus
regulating growth, metabolism, reproduction, and stress
-secretes two hormones that are stored in the post pituitary
which are involved with labor contractions,
lactation, and water conservation
- ANS effects = integration center, sends fibers to lower
brainstem to coordinate heart rate, blood pressure,
gastric secretions, gastric mobility, and pupil diameter
- thermal regulation = collection of nuclei especially the
preoptic nucleus monitor body temperature
- when body temperature deviates from a set point the
hypothalamus activates mechanisms to bring it to
normal
- food and water intake = arcuate nucleus and others are
stimulated by hormones which increase hunger and
energy use
- other hormones have an inhibitory affect on both
- other hormones have a long term affect on body mass
- osmoreceptors monitor blood osmolarity and affect water
intake or salt and water loss along with antidiuretic hormone
sleep and circadian rhythms = the caudal part of the hypothalamus
is a continuation of the reticular formation which along with
the suprachiasmatic nucleus controls our 24 hour circadian
rhythms, mother was correct you need sleep
memory = the memory center of the brain, the hippocampus, send
info to the thalamus by passing through the mammillary
bodies, hypothalamic lesions cause memory deficits
sex and hormones = anger, aggression, fear, pleasure,
contentment, sex drive, libido, copulation, and orgasm are
functions whose actions involve one or more hypothalamic
nuclei
the epithalamus
- small mass of tissue made up of the pineal gland and the
habenula which forms the roof of the third ventricle
and relays information from limbic system to the
midbrain
the cerebrum
- embryo telencephalon cerebrum
- frontal lobe = voluntary muscle function, motivation, planning,
foresight, memory, mood, emotion, social
judgement, aggression
- parietal lobe = general senses, taste, some visual, & pathways
- occipital lobe = primary visual cortex
- temporal lobe = hearing, smell, learning, memory, some
vision and emotion
- insula = small mass deep in lateral sulcus, spoken language,
taste, integration of visceral receptors
the majority of the cerebrum is composed of three kinds of
fiber tracts of glial coated or myelin coated, white fibers which
send signals back and forth between various areas of the
cerebrum and between the cerebrum and lower brain centers,
these centers are multimodal
the results of this interaction is a complex system of integration
which allows us to do the many things we are able to do, the
many factors we use when making a decision, and the many
things stored in our brain and made accessible when we need
the information
cerebrum fiber tracts
projection tracts = & between higher and lower brain and
cord, among the basal ganglia are two internal
capsules carrying fibers into the cerebrum which then
spread out to their specific areas of importance
commissural tracts = enable left and right hemispheres to
communicate through ant, post, and corpus callosum
association tracts = short fibers connect gyri in same lobe, long
fibers connect different lobes of a hemisphere, aids
perception and memory
the cerebral cortex
- gray outer and white inner layers, 6 layers called the neocortex
- site of complex neural integration between
- cortex, cerebellum, basal nuclei, and limbic system
- cortex 2-3 mm thick containing 14-16 billion neurons
- contains two types of cells stellate and pyramidal
- stellates have multiple short projections in all directions
- pyramydals small and large collect information from the gray
matter accumulate integrative information from
stellate cells and pass out efferent fibers which
leave the cerebrum
- all fibers which leave the cortex arise from layers 3, 5, and 6
- not all areas have 6 layers
- paleocortex has 1 to 5 layers in insula and smell area of temporal
- archiocortex for memory in hippocampus has 3 layers
- neocortex has 6 layers (last to evolve)
limbic system
- emotion and learning
- ring structure on medial side of cerebral hemisphere
encircling the corpus callosum and thalamus, the
hippocampus, amygdala, mammillary bodies, and basal
nuclei form the limbic system
- most prominent feature is the cingulate gyrus
- all parts are interconnected (smell, emotions, memory,
gratification, and aversion
- the basal nuclei are gray matter buried deep in the
lateral thalamus
integrative functions of the cerebrum
- one of the tools used to investigate higher brain functions is
the EEG
- by measuring the EEG when areas are active or dormant and
when signals are measured to or from an area
functional maps of the brain have been developed
- probably no function is localized to one area of the cerebrum
-some of the functions where the electro encephalograms
have been used are sleep, cognition, memory,
emotion, sensation, special senses, general senses,
motor control, language, and cerebral lateralization
beta waves = continued input, thinking 14 -30 cps (Hz)
alpha = resting, eyes closed, no real concentration 8 – 13 cps
theta = drowsy or sleepy state, common in kids, 4 – 7 cps
delta = deep sleep, less than 3.5 cps
stage 1 = drowsy, close eyes, relax, thoughts come and go, drifting,
easily awakened, alpha waves
stage 2 = light sleep, EEG declines, amplitude increases, 1 or 2
spindles appear, from interaction between with
thalamus
stage 3 = moderate to deep sleep, theta and delta appear, muscles
relax, vital signs fall
stage 4 = slow wave sleep, muscles relaxed, vitals at lowest level,
difficult to awaken
- 4 or 5 times a night a sleeper goes from stage 3 or 4 back to
stage 2 and go into rapid eye movement sleep (REM)
- eyes move back and forth under eyelids as if watching a
movie screen, vital signs increase, brain uses more oxygen
- sleep paralysis occurs (it is very difficult to awaken the
person) it is thought that this prevents people from acting
out their dreams,
- dreams can occur in REM and non REM sleep
- REM dreams more vivid and longer
-parasympathetic ns very active during REM
- pupils constrict, penis and clitoris erect,
- sleep involves interaction of cortex, thalamus, hypothalamus,
the reticular formation and the suprachiasmatic nucleus
- a neuropeptides orexins from the hypothalamus stimulates
wakefulness and increased metabolic rates
- a second system inhibits the orexin receptors thus inducing
sleep
- it is thought that sleep is a period of growth and repair for the
physical and emotional body
- during sleep the body releases the most HGH, memories are
consolidated or purged
cognition
- how we get new knowledge
- scattered throughout the cerebrum are association areas for
- senses, thought, reasoning, judgement, memory, imagination, and
intuition
- this is the least understood area of brain research
parietal lesions = unaware of objects even your own limbs or body
temporal lesions =unable to recognize names of objects, or faces
frontal lesions = personality disorders, socially inappropriate
memory
-hippocampus of limbic system is an important center
- does not store memories but organizes sensory and cognitive
experiences into a unified long term memory (whatever
that is)
– memories of faces, words & objects resides in the superior
temporal lobes
- memories for plans & social roles are in the prefrontal cortex
- lesions in many areas cause amnesia
- loss of hippocampi and other temporal tissue causes inability to
form new memories
- cerebellum is involved in learning motor skills and the amygdala has
a role in emotional memory
emotion
- interaction between prefrontal cortex and diencephalon
- studies from injuries, surgeries, lesions, and ablations
- prefrontal seat of judgement, intent, control over expressions
of our emotions
- amygdala gets sensory input from general senses, vision,
hearing, taste, and smell and info used to mediate a
response to the sensory input
- amygdala sends info hypothalamus and lower brainstem to
influence skeletal and cardiac muscle responses
- also info to prefrontal cortex for conscious response
- lesions , ablations cause removal of inhibition of responses
- median forebrain bundle seems to be a gratification center
sensation
- primary sensory cortex
- area where sensory input is 1st perceived and becomes conscious
- there are special senses – vision, hearing, etc.
- there are general senses – spread over the body
vision – posterior occipital is the primary visual cortex, while the
anterior occipital is a visual association area as are the posterior and
inferior temporal areas
hearing – superior temporal lobe and insula are the primary
auditory cortex, the association area is in the inferior and deep
temporal lobe, this is where we become capable of recognizing
spoken words, pieces of music, and voices without seeing a face
equilibrium – signals from inner ear to cerebellum and
brainstem, for head and eye movements, signals are sent to
the lower end of the central sulcus which is the seat of
consciousness for body movements and orientation in space
taste and smell – sensory info for taste goes to the primary
gustatory cortex located in the inferior postcentral gyrus of the
parietal lobe and the anterior insula,
sensory info for smell goes to the primary olfactory cortex in
the medial temporal lobe and inferior surface of the frontal
lobe
the orbitofrontal cortex is a multimodal association area for
taste and smell
the general senses
somatosensory, somesthetic, somatic senses
- distributed over the entire body
- use simple sensory receptors
- touch, pressure, movement, heat, cold, and pain
- from the head mostly via the trigeminal nerve
- rest of body use sensory tracts of the spinal cord
- both paths decussate at the thalamus
- fibers go to the postcentral gyrus (primary somatosensory cortex)
- next to it is the somatosensory association area where cognitive
sense is made so decisions are made based on many inputs
motor control
- info about the need or intent to move a skeletal muscle
arrives at the motor association premotor area
- here info is integrated with info from the cerebellum, limbic
system and sensory cerebrum
- the integrated info is then sent to the precentral gyrus
(primary motor area)
- which send info down to brainstem, spinal cord, and muscles
- the pre and post central gyri are somatotopy
- amount of cortex is proportional to the number of muscles
and motor units in a region
- fibers from the precentral gyrus are called upper motor
neurons as are the fibers arising from the basal nuclei
- fibers leaving the cord to initiate movement are called lower
motor neurons
- some of the upper motor neurons decussate in the lower medulla
(pyramidal decussation) and form the lateral corticospinal
tract
- the remaining fibers continue as the anterior corticospinal tract
and decussate in spinal cord
- each precentral gyrus thus controls the contralateral side of the
body
-the role of the cerebellum in motor functions are increasing
- people are capable of repetitive motor skills which are done
at a rate which defies thought
- it is thought that the cerebellum is involved in allowing such
things as typing 200 words a minute
- cerebellum is involved with muscle tone, posture, coordinate
eye and hand movements and joints movements
- compares what you intend to do with what your body is
doing, the Purkinje cells compare the two and adjust the
output of muscles to match your intent
language
reading, writing, speaking, understanding words
- Wernicke area (posterior to lateral sulcus) spoken & written words (left)
- receives input from visual, auditory, and somatosensory cortex
- the integrated info is sent to the Broca area in inferior prefrontal cortex
- sends motor signals for all muscles involved in speech or signing to the
primary motor cortex which executes the program
- emotions of language from right brain Wernike and Broca areas in the
affective language area it also examines other’s speech for emotions
- lesions result in flat emotionless speech and not understanding others
emotional speech such as anger and jokes
cerebral lateralization
- the left and right lobes look identical but they are not
- this difference is called cerebral lateralization
- but left and right need this difference in information to
properly integrate information to form a correct
interpretation of sensory info or for motor control
- left hemisphere = categorical brain (spoken & written
language, sequential & analytical reasoning, linear thinking
- right hemisphere = representational brain (imagination,
insight, music, artistic, patterns, spatial, comparison of special
senses, holistic integration
- right handed = 96% have left as categorical, 4% have right
- left handed = 70% have left as categorical, 15% have right,
other 15% have neither hemisphere is specialized
cranial nerves
- sensory fibers mainly from head and neck go to brainstem
- fibers carry info for special senses, proprioception, & touch
- most motor fibers begin in nuclei of brainstem and lead to
glands and muscles
- most cranial nerves involve ipsilateral receptors & effectors
- exception is optic nerves where half the fibers decussate and
cranial nerve IV which all efferents go to contralateral eye
cranial nerves I, II, VIII are sensory
cranial nerves III, IV, VI, IX, XII are motor
cranial nerves V, VII, IX, X are mixed
sensory = 128
motor = 346912
mixed = 57910
should know function, composition, origin, path to termination