Development of brain
Three to four-week embryo:
forebrain (prosencephalon)
midbrain (mesencephalon)
hindbrain (rhombencephalon)
Development of Brain
5-week embryo
telencephalon (cerebrum)
diencephalon (thalamus, hypothalamus & epithalamus)
mesencephalon (midbrain)
metencephalon (pons & cerebellum)
myelencephalon (medulla oblongata).
Forebrain
Midbrain
Hindbrain
Forebrain - Cerebrum & Diecephalon (3)
Midbrain & cebral aqueduct
Hindbrain - pons & cerebellum + medulla
Brain stem
consists of?
continuation of spinal cord
consists of medulla oblongato, pons & midbrain
second largest part of the brain.
posterior to brain stem
Cerebellum
Diencephalon
superior to brain stem
gives rise to thalamus, hypothalamus & epithalamus
largest part of brain
cerebrum
cranial meninges
dura mater - 2 layers (perieosteal & meningeal)
arachnoid mater
pia mater
(3) extensions of the dura mater separate parts of the brain:
1) falx cerebri - seperate the 2 cerebral hemispheres
2) falx cerebelli - seperate the 2 cerebellar hemispheres
3) tentorium cerebelli - seperate cerebrum from cerebellum
Extensions of the Dura Mater: Brain Blood Flow and the Blood-Brain Barrier
Brain receives approximately _____% of the total blood supply.
Internal __ & __ arteries carry blood to brain.
Internal _____veins return blood from the brain.
Blood-brain barrier (BBB) protects brain from?
20%
internal carotid & vertebral arteries - blood to brain
internal jugular veins return blood from brain
harmful substances.
Cerebrospinal Fluid (CSF)
clear, colourless fluid that protects CNS from chemical & physical injuries, absorbs shock, helps transport nutrients & wastes from blood & nervous tissue
circulates through cavities in brain (ventricles) & spinal cord (central canal) & in subarachnoid space
Ventricles
(3) & cerebral aqueduct
CSF-filled cavities within the brain.
1 lateral ventricles - in each hemisphere seperated byb septum pellucidum
third ventricle - along midline superior to hypothalamus
cerebral aqueduct - midbrain
fourth ventricle - between brain stem & cerebellum
CSF formation & circulation
formed in choroid plexuses of lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct (midbrain)→ 4rth ventricle → median aperture/lateral apertures (2) → subarachnoid space →central canal
Choroid plexus
networks of capillaries in the walls of the
ventricles.
Ventricles are lined by __ cells
ependymal
plasma is drawn from choroid plexuses through ependymal cells into ventricles to produce CSF
CSF is reabsorbed into blood by?
arachnoid villi - extensions of arachnoid that project into dural venous sinuses (sugerior sagittal sinnus)
Brain Stem (medulla, pons & midbrain) and Reticular Formation
Medulla Oblongata
continous with superior spinal cord
white matter tract contains all sensory & motor tracts between spinal cord & other parts of brain
white matter bulges on anterior - pyramids formed by large corticospinal tracts that pass from cerebrum to spinal cord
- common site of decussation of tracts - crossing over
Centers of the Medulla Oblongata
Vital centers:
cardiovascular
respiratory
also includes centers for vomiting, swallowing, sneezing, coughing and hiccupping.
houses 5 pairs of cranial nerves (VIII-XII)
portion of 3rd ventricle found here
Midbrain (mesencephalon)
Extends from the pons to the diencephalon.
Part of the ventricle found here- cerebral aqueduct - connects 3rd & 4rth ventricle
anterior part contains cerebral peduncles
posterior part - tectum
superior colliculli, inferior colliculi & substantia nigra
Cerebral Peduncles - paired bundles of axons in anterior part of midbrain
consists of?
Tectum
axons of the corticospinal, corticopontine and
corticobulbar tracts.
Tectum- situated posteriorly and contains 4 rounded elevations: 2
superior ones called superior colliculi and 2 inferior ones called inferior colliculi
Midbrain:
Substantia Nigra
large area with dark pigments. Help control subconscious muscle activities.
Loss of neurons here is associated with Parkinson disease.
Redc Nucleus of Midbrain
: Help control voluntary movements of the limbs
Midbrain contains cranial nerves....
III-IV
Reticular Formation
Extends from upper part of spinal cord, throughout brain stem & into
lower part of diencephalon.
Part of the reticular formation called the Reticular activating System (RAS) consists of?
consists of sensory axons that project to the cerebral cortex
S helps maintain consciousness.
Cerebellum
vermis
anterior & posterior lobes
flocculonodular lobe
cerebellar cortex
arbor vitae
2nd largest part of brain
central constricted area = vermis
anterior and posterior lobes control subconscious aspects of skeletal movement.
flocculonodular lobe - equilibrium & balance
cerebellar cortex - gray matter in form of parallel folds called folia
arbor vitae - tracts of white matter
Cerebellar peduncles
3 pairs - superior, middle & inferior
attach cerebellum to brain stem
functions: coordinate movements, regulate posture & balance
Thalamus
intermediate mass joins right & left sides of thalamus
(7) major nuclei: anterior, medial, lateral, ventral, intralaminar, midline, reticular
major relay station for most impulse reaching primary sensory areas
transmits info from cerebellum & basal nuclei to primary motor area
Hypothalamus
inferior to thalamus
consists of mammillary body, median eminence, infundibulum, and # of nuclei.
Functions of the Hypothalamus
Control of the ANS
production of hormones
regulation of emotion & behavioral patterns, eating & drinking, body temp, circadian rhythms
Epithalamus
small region superior to thalamus
consists of pineal gland that secretes melatonin which induces sleep
Cerebrum
seat of intelligence
cerebral cortex - gray matter
Gyri
Sulci
longitudinal fissure
cerebral hemispheres
Cerebrum
Gyri
Sulci
longitudinal fissure
cerebral hemispheres
Gyri - folds of cortical region
Sulci - shallow grooves between folds
longitudinal fissure - seperates cerebrum into right & left halves (contains falx cerebri)
cerebral hemispheres- connected internally by corpus callosum
Lobes of the cerebrum (4)
frontal
parietal
temporal
occipital
Cerebral white matter consists of ?
myelinated axons in (3) types of tracts
1) association
2) commissural
3) projection
myelinated axons in (3) tracts of cerebral white matter
1) association - axons conduct nerve impulses between gyri in same hemisphere
2) commissural - axons conduct nerve impulses to corresponding gyri in opposite hemisphere
3 groups - corpus callosum, anterior & posterior commissure
3) projection - axons conduct nerve impulses from cerebrum to lower CNS (thalamus, brain stem & spinal cord)
Basal Nuclei
(3) nuclei (masses of gray matter) deep within each cerebral hemisphere
LENTIFORM NUCLEUS:
globus pallidus - lateral to thalamus
putamen - closer to cerebral cortex
CAUDATE NUCLEUS
corpus striatum = caudate + lentiform
Basal Nuclei
functions
Help initiate and terminate movements, suppress unwanted movements & regulate muscle tone.
Limbic system
A ring of structures on inner border of cerebrum and floor of diencephalon
emotional brain - governs emotional aspects of behavior
also involved in olfaction & memory
Components of the limbic system
Limbic lobe - cingulate, parahippocampal gyrus & hippocampus
dentate gyrus
amygdala
septal nuclei
mammillary bodies
anterior & medial nucleus
olfactory bulbs
Functional Organization of the Cerebral Cortex: Sensory Areas
(5)
Primary somatosensory area-
Primary visual area-
Primary auditory area-
Primary gustatory area-
Primary olfactory area-
Cerebrum
central sulcus
precentral gyrus
postcentral gyrus
central sulcus - seperates frontal & parietal lobes
precentral gyrus - frontal: primary motor area
postcentral gyrus - parietal: primary somatosensory area
- Primary somatosensory area- ___ gyrus.
- Primary visual area- ____________lobe.
- Primary auditory area- ____________lobe.
- Primary gustatory area- base of the __ gyrus.
- Primary olfactory area- ____________lobe
-
postcentral gyrus
- occipital
- temporal
-
postcentral gyrus
- temporal
Functional Organization of Cerebral Cortex: Motor Areas
primary motor area - precentral gyrus
Broca's speech area - left cerebral hemisphere (speech production)
Functional Organization of the Cerebral Cortex: Association Areas
Somatosensory association area- behind 1° somatosensory area.
Visual association area- occipital lobe.
Auditory association area- temporal lobe.
Wernick's area- left temporal & parietal lobes (speech comprehension)
Prefrontal cortex- anterior portion of frontal lobe.
Cranial Nerves
12 pairs
sensory, motor & mixed
name & roman numberic number to identify
Olfactory (I) Nerve
Sensory nerve.
Sense of smell.
Olfactory cells converge to become olfactory nerve that end in olfactory bulb.
Optic (II) Nerve
sensory
vision
ganglion cells in retina join to form optic nerve
Oculomotor (III) Nerve
motor cranial
originates in midbrain
supply extrinsic eye muscles to control movement of eye & upper eyelid
Trochlear (IV) Nerve
motor cranial nerve
smallest
originate in midbrain
controls movement of eyeball
Trigeminal (V) nerve
largest cranial nerve
mixed
(3) branches: ophthalmic, maxillary & mandibular
deal with sensation of touch, pain & temperature.
motor axons supply muscles of mastication
Abducens (VI) Nerve
motor cranial
originates in pons
cause abduction of the eyeball (lateral rotation)
Facial (VII) Nerve
mixed cranial
sensory portion - from taste buds of anterior 2/3 of tongue
motor - arises from pons & deal with facial expression
Vestibulocochlear (VIII) Nerve
sensory cranial
originates in inner ear
vestibular branch - impulses for equilibrium
cochlear branch - impulses for hearing
Glossopharyngeal (IX) Nerve
mixed cranial
sensory: taste buds of posterior 1/3 of tongue
motor: arise from medulla & deals with release of saliva
Vagus (X) Nerve
mixed cranial
distributed from head & neck into thorax & abdomen
sensory: sensations - proprioception & stretching
motor - arise from medulla & supply muscles of pharynx, larynx & soft palate that are involved swallowing & vocalization
Accessory (XI) Nerve
Motor cranial nerve.
Divided into cranial accessory and spinal accessory nerves.
Supplies sternocleidomastoid & trapezius muscles to coordinate head movements.
Hypoglossal (XII) Nerve
motor cranial
conduct nerve impulses for speech & swallowing
