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147 terms

Chapter 14

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rostral
toward the forehead
caudal
toward the spinal cord
average weight of brain
Brain weighs about 1,600g (3.5 lb) in men, and 1,450g in women
three major portions of the brain
cerebrum
cerebellum
brainstem
Cerebrum
83% of brain volume; cerebral hemispheres, gyri and sulci, longitudinal fissure, corpus callosum
Brainstem
the portion of the brain that remains if the cerebrum and cerebellum are removed; diencephalon, midbrain, pons, and medulla oblongata
Cerebellum
contains 50% of the neurons; second largest brain region, located in posterior cranial fossa
Longitudinal fissure
deep groove that separates cerebral hemispheres
Corpus callosum
thick nerve bundle at bottom of longitudinal fissure that connects hemispheres
Sulci
shallow grooves
Gyri
thick folds
Brainstem
what remains of the brain if the cerebrum and cerebellum are removed

Major components
-Midbrain
-Pons
-Medulla oblongata
Major components of the brainstem
-Midbrain
-Pons
-Medulla oblongata
Gray matter
—the location of neuron cell bodies, dendrites, and synapses
-Forms surface layer (cortex) over cerebrum and cerebellum
-Forms nuclei deep within brain
White matter
-bundles of axons
-Lies deep to cortical gray matter, opposite relationship in the spinal cord
-Pearly white color from myelin around nerve fibers
-Composed of tracts (bundles of axons) that connect one part of the brain to another or connect the cortex to the spinal cord
tracts
bundles of axons
ectoderm
outermost tissue layer of the embryo
-where the nervous system develops
Neuroectoderm
early into the third week of development, dorsal streak appears along the length of embryo
what does the neruoectoderm thicken to form?
the neural plate
neural plate
-what the neuroectoderm thickens to form
-Destined to give rise to most neurons and all glial cells except microglia, which come from mesoderm
as thickening of the neural plate progresses...
Neural plate sinks and its edges thicken
Forming a neural groove with a raised neural fold on each side
Neural folds fuse along the midline
Beginning in the cervical region and progressing rostrally and caudally
where do the neural folds fuse?
along the midline. Beginning in the cervical region and progressing rostrally and caudally
by the fourth week of embryonic development, what is formed?
neural tube
neural tube
hollow channel formed by the fourth week
4th week of embryonic development
-Neural tube separates from overlying ectoderm
-Sinks deeper
-Grows lateral processes that later will form motor nerve fibers
-Lumen of neural tube becomes fluid-filled space
-Central canal in spinal cord
-Ventricles of the brain
Neural crest
formed from ectodermal cells that lay along the margins of the groove and separate from the rest forming a longitudinal column on each side
-Gives rise to the two inner meninges, most of the peripheral nervous system, and other structures of the skeletal, integumentary, and endocrine systems
what does the neural crest give rise to?
the two inner meninges, most of the peripheral nervous system, and other structures of the skeletal, integumentary, and endocrine systems
three anterior dilations (primary vessicles) that the neural tube exhibits by the fourth week...
Forebrain (prosencephalon)
Midbrain (mesencephalon)
Hindbrain (rhombencephalon)
what happens during the fifth week of embryonic development?
it subdivides into five secondary vessicles:
-telencephalon
-diencephalon
-mesencephalon
-metencephalon
-myelencephalon
what two vessicles does the hindbrain divide into during the fifth week of embryonic development?
metencephalon
myelencephalon
what two vessicles does the forebrain divide into during the fifth week of embryonic development?
Telencephalon—becomes cerebral hemispheres
Diencephalon—has optic vesicles that become retina of the eye
The midbrain during the fifth week of embryonic development
remains undivided.
called: mesencelphalon
The medulla oblongata
Cardiac center: Adjusts rate and force of heart

Vasomotor center: Adjusts blood vessel diameter

Respiratory centers: Control rate and depth of breathing

Reflex centers: For coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head
Cardiac center
Adjusts rate and force of heart
Vasomotor center
Adjusts blood vessel diameter
Respiratory centers
Control rate and depth of breathing
Reflex centers
For coughing, sneezing, gagging, swallowing, vomiting, salivation, sweating, movements of tongue and head
The midbrain
-Mesencephalon becomes one mature brain structure, the midbrain
-Short segment of brainstem that connects the hindbrain to the forebrain
-Contains cerebral aqueduct
-Contains continuations of the medial lemniscus and reticular formation
-Contains the motor nuclei of two cranial nerves that control eye movements: CN III (oculomotor) and CN IV (trochlear)
what two cranial nerves that control eye movement does the midbrain contain?
CN III (oculomotor) and CN IV (trochlear)
Tectum
-rooflike part of the midbrain posterior to cerebral aqueduct
-Exhibits four bulges, the corpora quadrigemina
-Upper pair, the superior colliculi, function in visual attention, tracking moving objects, and some reflexes
-Lower pair, the inferior colliculi, receives signals from the inner ear
-Relays them to other parts of the brain, especially the thalamus
Tegmentum
-Dominated by the red nucleus
-Pink color due to high density of blood vessels
-Connections go to and from cerebellum
-Collaborates with cerebellum for fine motor control
Substantia nigra
-Dark gray to black nucleus pigmented with melanin
-Motor center that relays inhibitory signals to thalamus and basal nuclei preventing unwanted body movement
-Degeneration of neurons leads to tremors of Parkinson disease
Cerebral peduncles
-Bundle of nerve fibers that connect the cerebrum to the pons
-Carries corticospinal tracts
Meninges
—three connective tissue membranes that envelop the brain
-Lies between the nervous tissue and bone
-As in spinal cord, they are the dura mater, arachnoid mater, and the pia mater
-Protect the brain and provide structural framework for its arteries and veins
Dura mater
-Most superficial of the 3 layers
-In cranial cavity; is actually composed of two layers
-An Outer periosteal—equivalent to periosteum of cranial bones
-An Inner meningeal—continues into vertebral canal and forms dural tissue that surrounds the spinal cord
-Cranial dura mater is pressed closely against cranial bones
-No epidural space
-Few blood vessels trapped between outer dura and cranial cavity
-Layers separated by dural sinuses—collect blood circulating through brain
Falx cerebri
separates the two cerebral hemispheres
Tentorium cerebelli
separates cerebrum from cerebellum
Falx cerebelli
separates the right and left halves of cerebellum
what does the dura mater do?
Folds inward to extend between hemispheres of the brain
-falx cerebri
-tentorium cerebelli
-falx cerebelli
Arachnoid mater
-Transparent membrane over brain surface
-Subarachnoid space separates it from pia mater below
-Subdural space separates it from dura mater above in some places
Pia mater
Very thin membrane that follows contours of brain, even dipping into sulci
Not usually visible without a microscope
Ventricles
four internal chambers within the brain
-2 lateral ventricles
-third ventricle
-fourth ventricle
Two lateral ventricles
: one in each cerebral hemisphere
Interventricular foramen—a tiny pore that connects to third ventricle
Interventricular foramen
a tiny pore that connects to third ventricle
Third ventricle
single narrow medial space beneath corpus callosum
Cerebral aqueduct runs through midbrain and connects third to fourth ventricle
Cerebral aqueduct
runs through midbrain and connects third to fourth ventricle
Fourth ventricle
-small triangular chamber between pons and cerebellum
-Connects to central canal, runs down through spinal cord
Choroid plexus
spongy mass of blood capillaries on the floor of each ventricle
Ependyma
-neuroglia that lines the ventricles and covers choroid plexus
-Produces cerebrospinal fluid
ventricles and CSF
-CSF continually flows through and around the CNS
-Driven by its own pressure, beating of ependymal cilia, and pulsations of the brain produced by each heartbeat
-CSF secreted in lateral ventricles flows through intervertebral foramina into third ventricle
-Then down the cerebral aqueduct into the fourth ventricle
-Third and fourth ventricles add more CSF along the way
what is CSF reabsorbed by?
arachnoid villi
arachnoid villi
Cauliflower-shaped extension of the arachnoid meninx
Protrudes through dura mater
Into superior sagittal sinus
CSF penetrates the walls of the villi and mixes with the blood in the sinus
Small amount of CSF fills the central canal of the spinal cord
All escapes through three pores
Median aperture and two lateral apertures
Leads into subarachnoid space of brain and spinal cord surface
Cerebrospinal fluid (CSF)
-clear, colorless liquid that fills the ventricles and canals of CNS
-Bathes its external surface
how much CSF does the brain produce/absorb per day?
-Brain produces and absorbs 500 mL/day
-100 to 160 mL normally present at one time

-Production begins with the filtration of blood plasma through the capillaries of the brain
-Ependymal cells modify the filtrate, so CSF has more sodium and chloride than plasma, but less potassium, calcium, glucose, and very little protein
Functions of the CSF
Buoyancy
Protection
Chemical stability
Functions of the CSF: Buoyancy
Allows brain to attain considerable size without being impaired by its own weight
If it rested heavily on floor of cranium, the pressure would impede impulse flow of neurons and kill the nervous tissue
Functions of the CSF: Protection
Protects the brain from striking the cranium when the head is jolted by decreasing the velocity of the brains movements
Functions of the CSF: Chemical Stability
Flow of CSF rinses away metabolic wastes from nervous tissue and homeostatically regulates its chemical environment
Blood Supply and the Brain Barrier System
-Brain is only 2% of the adult body weight, and receives 15% of the blood
750 mL/min.

-Neurons have a high demand for ATP, and therefore, oxygen and glucose, so a constant supply of blood is critical to the nervous system

-A 10-second interruption of blood flow may cause loss of consciousness
-A 1- to 2-minute interruption can cause significant impairment of neural function
-Going 4 minutes without blood causes irreversible brain damage
what can blood also be a source of?
Blood is also a source of antibodies, macrophages, bacterial toxins, and other harmful agents
Brain barrier system
strictly regulates what substances can get from the bloodstream into the tissue fluid of the brain

Two points of entry must be guarded
-Blood capillaries throughout the brain tissue
-Capillaries of the choroid plexus
Two points of entry must be guarded in the blood brain barrier system
Blood capillaries throughout the brain tissue
Capillaries of the choroid plexus
Blood-brain barrier
-protects blood capillaries throughout brain tissue
-Consists of tight junctions between endothelial cells that form the capillary walls
-Astrocytes reach out and contact capillaries with their perivascular feet
-Induce the endothelial cells to form tight junctions that completely seal off gaps between them
-Anything leaving the blood must pass through the cells, and not between them
-Endothelial cells can exclude harmful substances from passing to the brain tissue while allowing necessary ones to pass
Blood-CSF barrier
—protects the brain at the choroid plexus
-Forms tight junctions between the ependymal cells
-Tight junctions are absent from ependymal cells elsewhere
-Important to allow exchange between brain tissue and CSF
what is blood barrier system permeable to?
Blood barrier system is highly permeable to water, glucose, and lipid-soluble substances such as oxygen, carbon dioxide, alcohol, caffeine, nicotine, and anesthetics

Slightly permeable to sodium, potassium, chloride, and the waste products urea and creatinine
Crainal nerves
Brain must communicate with rest of body
-most of the input and output travels by way of the spinal cord
-12 pairs of cranial nerves arise from the base of the brain
-Exit the cranium through foramina
-Lead to muscles and sense organs located mainly in the head and neck
where do the 12 pairs of cranial nerves arise?
the base of the brain
where do the 12 pairs of cranial nerves exit?
through foramina
motor fibers of the cranial nerves
Most motor fibers of the cranial nerves begin in nuclei of brainstem and lead to glands and/or muscles
Sensory fibers of the cranial nerves
Sensory fibers begin in receptors located mainly in head and neck and lead mainly into the brainstem
cranial nerve impulses (sensory or motor)
Most cranial nerve impulses (sensory or motor) are generally ipsilateral
-i.e Lesion in left brainstem causes sensory or motor deficit on same side

-Exceptions: optic nerve where half the fibers decussate, and trochlear nerve where all efferent fibers lead to a muscle of the contralateral eye
Cranial nerve classification
Some cranial nerves are classified as motor, some sensory, others mixed

-Sensory (I, II, and VIII)

-Motor (III, IV, VI, XI, and XII)
-Stimulate muscle but also contain fibers of proprioception

-Mixed (V, VII, IX, X)
-Sensory functions may be quite unrelated to their motor function
-Facial nerve (VII) has sensory role in taste and motor role in facial expression
The Olfactory Nerve (I)
Sensory only
Sense of smell (olfaction)
The Optic Nerve (II)
Sensory only
Provides vision
Neurons project to the primary visual cortex in the occipital lobe
The Oculomotor Nerve (III)
Motor only
Controls muscles that turn the eyeball up, down, and medially, as well as controlling the muscle of the iris, lens, and upper eyelid
Damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing, and inability to move eye in certain directions
The Trochlear Nerve (IV)
Motor only
Eye movement (superior oblique muscle)
The Trigeminal Nerve (V
Mixed motor and sensory
Largest of the cranial nerves

Most important sensory nerve of the face

Forks into three divisions:
-Ophthalmic division (V1): sensory
-Maxillary division (V2): sensory
-Mandibular division (V3): mixed
The Abducens Nerve (VI)
Motor only
Provides eye movement (lateral rectus m.)
The Facial Nerve (VII)
Mixed motor and sensory
Motor—major motor nerve of facial muscles: facial expressions; salivary glands and tear, nasal, and palatine glands
Sensory—taste on anterior two-thirds of tongue
Damage produces sagging facial muscles and disturbed sense of taste (no sweet and salty)
The Vestibulocochlear Nerve (VIII)
Sensory only
Nerve of hearing and equilibrium
Damage produces deafness, dizziness, nausea, loss of balance, and nystagmus (involuntary rhythmic oscillation of the eyes from side to side)
The Glossopharyngeal Nerve (IX)
Mixed motor and sensory
General sensation form the pharynx
Taste from posterior one-third of tongue
Damage results in loss of bitter and sour taste and impaired swallowing
Relays sensory input for Swallowing, salivation, gagging, control of BP and respiration
The Vagus Nerve (X)
Mixed motor and sensory
Most extensive distribution of any cranial nerve

Relays sensory information regarding cardiac, pulmonary, digestive, and urinary function to the brain

Motor - Swallowing, speech, regulation of viscera

Damage causes hoarseness or loss of voice, impaired swallowing, and fatal if both are cut
The Accessory Nerve (XI)
Motor only
Swallowing; head, neck, and shoulder movement
Damage causes impaired head, neck, shoulder movement; head turns toward injured side
The Hypoglossal Nerve (XII)
Motor only
Tongue movements for speech, food manipulation, and swallowing
If both are damaged: cannot protrude tongue
If one side is damaged: tongue deviates toward injured side; see ipsilateral atrophy
cerebral peduncles- 3 main components
-tegmentum
-substantia nigra
-cerebral crus (crus cerebri)
the cerebellum
The largest part of the hindbrain and the second largest part of the brain as a whole

Consists of right and left cerebellar hemispheres connected by vermis

Has an outer cortex of gray matter with folds (folia) and four deep nuclei in each hemisphere
Cerebellar peduncles
three pairs of stalks that connect the cerebellum to the brainstem
Consist of thick bundles of nerve fibers that carry signals to and from the cerebellum
Inferior peduncles
connected to medulla oblongata
Most spinal input enters the cerebellum through inferior peduncle
Superior peduncles
-connected to the midbrain
-Carries cerebellar output
Middle peduncles
connected to the pons
Most input from the rest of the brain enters by way of middle peduncle
Forebrain consists of two parts
-Diencephalon
Encloses the third ventricle

-Telencephalon
Develops chiefly into the cerebrum
Diencephalon
Encloses the third ventricle
Has three major subparts
-Thalamus
-Hypothalamus
-Epithalamus
Diencephalon: Thalamus
-ovoid mass on each side of the brain perched at the superior end of the brainstem beneath the cerebral hemispheres
-Constitutes about four-fifths of the diencephalon
-Two thalami are joined medially by a narrow intermediate mass
-Composed of at least 23 nuclei; to consider five major functional groups
-"Gateway to the cerebral cortex": nearly all input to the cerebrum passes by way of synapses in the thalamic nuclei, filters information on its way to cerebral cortex
Hypothalamus
—forms part of the walls and floor of the third ventricle
-Major control center of autonomic nervous system and endocrine system
-Plays essential role in homeostatic regulation of all body systems
Infundibulum
—a stalk that attaches the pituitary gland to the hypothalamus
Functions of hypothalamic nuclei
Hormone secretion
Autonomic effects
Thermoregulation
Food and water intake
Rhythm of sleep and waking
Memory
Emotional behavior
Hormone secretion in hypothalamus
Controls anterior pituitary
Regulates growth, metabolism, reproduction, and stress responses
Controls anterior pituitary
Regulates growth, metabolism, reproduction, and stress responses
Autonomic effects in hypothalamus
Major integrating center for autonomic nervous system
Influences heart rate, blood pressure, gastrointestinal secretions, motility, etc.
Thermoregulation in hypothalamus
Hypothalamic thermostat monitors body temperature
Activates heat-loss center when temp is too high
Activates heat-promoting center when temp is too low
Food and water intake in hypothalamus
Hunger and satiety centers monitor blood glucose and amino acid levels
Produce sensations of hunger and satiety
Thirst center monitors osmolarity of the blood
Rhythm of sleep and waking in hypothalamus
Controls 24-hour (circadian) rhythm of activity
Memory in hypothalamus
Mammillary nuclei receive signals from hippocampus
Emotional behavior in hypothalamus
Anger, aggression, fear, pleasure, and contentment
Epithalamus
—very small mass of tissue composed of:
Pineal gland: endocrine gland
Cerebrum
—largest and most conspicuous part of the human brain
Seat of sensory perception, memory, thought, judgment, and voluntary motor actions
Two cerebral hemispheres divided by longitudinal fissure
Connected by white fibrous tract, the corpus callosum
Gyri and sulci: increase amount of cortex in the cranial cavity
Gyri increases surface area for information-processing capability
Some sulci divide each hemisphere into five lobes named for the cranial bones overlying them
what are the two cerebral hemispheres divided by?
longitudinal fissure
5 parts of the cerebrum
frontal lobe
parietal lobe
occipital lobe
temporal lobe
insula
Frontal lobe
Voluntary motor functions
Motivation, foresight, planning, memory, mood, emotion, social judgment, and aggression
Parietal lobe
Receives and integrates general sensory information, taste processing
Occipital lobe
Primary visual center of brain
Temporal lobe
Areas for hearing, smell, learning, memory
Insula (hidden by other regions)
Understanding spoken language, taste and sensory information from visceral receptors
The Cerebral White Matter
Most of the volume of cerebrum is white matter
Glia and myelinated nerve fibers transmitting signals from one region of the cerebrum to another and between cerebrum and lower brain centers
three types of tracts in cerebral white matter
projection tracts
commissural tracts
association tracts
Projection tracts
Extends vertically between higher and lower brain and spinal cord centers
Carries information between cerebrum and rest of the body
Commissural tracts
Cross from one cerebral hemisphere through bridges called commissures
Most pass through corpus callosum
Enables the two sides of the cerebrum to communicate with each other
Association tracts
Connect different regions within the same cerebral hemisphere
-Long association fibers—connect different lobes of a hemisphere to each other
-Short association fibers—connect different gyri within a single lobe
Long association fibers
connect different lobes of a hemisphere to each other
Short association fibers
connect different gyri within a single lobe
Cerebral gray matter found in three places
Cerebral cortex
Basal nuclei
Limbic system
Neural integration
is carried out in the gray matter of the cerebrum
Cerebral cortex
-layer covering the surface of the hemispheres
-Only 2 to 3 mm thick
-Cortex constitutes about 40% of brain mass
-Contains 14 to 16 billion neurons
two principal types of neurons in cerebral cortex
stellate cells
pyramidal cells
Stellate cells
Have spheroid somas with dendrites projecting in all directions
Receive sensory input and process information on a local level
Pyramidal cells
Tall, and conical, with apex toward the brain surface
A thick dendrite with many branches with small, knobby dendritic spines
Include the output neurons of the cerebrum
Only neurons that leave the cortex and connect with other parts of the CNS.
Basal nuclei
masses of cerebral gray matter buried deep in the white matter, lateral to the thalamus
Receives input from the substantia nigra of the midbrain and the motor areas of the cortex
Send signals back to both these locations
Involved in motor control
three brain centers form basal nuclei
Caudate nucleus
Putamen
Globus pallidus
Lentiform nucleus
putamen and globus pallidus collectively
Corpus striatum
putamen and caudate nucleus collectively
Parkinson's disease
stiff, "frozen" limbs & rigid muscles
hypokinesia = slowness of movement
arises from dopamine depletion
Huntington's disease (chorea)
excessive motion, & flailing limbs
hyperkinesia = excess movement
arises from degeneration of caudate nucleus
Primary sensory cortex
sites where sensory input is first received and one becomes conscious of the stimulus
Association areas
nearby to sensory areas that process and interpret that sensory information
Sensory homunculus
-diagram of the primary somesthetic cortex which resembles an upside-down sensory map of the contralateral side of the body
-Shows receptors in the lower limbs projecting to the superior and medial parts of the gyrus
-Shows receptors from the face projecting to the inferior and lateral parts
Somatotopy
point-to-point correspondence between an area of the body and an area of the CNS