Cerebrum
Brain Organization
Brain (encephalon)
● part of the central nervous system (CNS)
● located within the cranial cavity
● anatomical and clinical classifications: consists of brain stem, cerebellum, cerebrum
Brain stem
● part of the neuroaxis between spinal cord and diencephalon
● from caudal to rostral: medulla oblongata, pons, midbrain
Cerebellum (L. 'little brain')
● consists of a pair of hemispheres united in the midline by the vermis (L. 'worm')
● situated in posterior cranial fossa, dorsal to brain stem
● forms roof of the fourth ventricle
● partition of dura mater (tentorium cerebelli) located between cerebellum inferiorly and
cerebrum superiorly
Cerebrum (L. 'brain')
● consists of diencephalon and telencephalon
● telencephalon: expanded pair of cerebral hemispheres
○ united across midline by large body of fibres (corpus callosum)
○ corpus callosum located below partition of dura mater (falx cerebri) between
cerebral hemispheres
Olfactory pathways
● via cranial nerve I, olfactory bulbs and tracts
● indirectly continuous with cerebral hemispheres
Optic pathways
● via cranial nerve II, optic chiasma and tracts
● indirectly continuous with diencephalon
Remaining ten pairs of cranial nerves
● arise directly from brainstem
, Developmental classification (caudal to rostral)
● hindbrain (medulla, pons, cerebellum)
● midbrain
● forebrain (diencephalon, cerebral hemispheres)
Rostral end forms vesicles
that undergo proliferatio n .
J
N
, Merginga
Neuraubegia
Brain Development
Brain and spinal cord
● both derived from ectoderm
● during development, neural plate of neuroectoderm on each side separated from general
ectoderm by transitional cells termed neuroectodermal junction
● neural plate: longitudinal midline thickening of ectoderm along dorsum of embryo
● cellular proliferation of neural plate forms neural groove
Neural groove and neural folds
● neuroectodermal junctions become neural folds
● neural groove deepens and eventually forms neural tube
● neural folds join each other, creating islands of cells called neural crest
Origins of CNS and PNS components
● entire central nervous system (CNS) develops from neural tube
● peripheral nervous system (PNS) primarily develops from neural crest, with some
contribution (efferent fibres) from neural tube
Neural tube
● expanded cranial end develops into brain
● narrow caudal part develops into spinal cord
Neural crest derivatives
● sensory (afferent) fibres, sensory ganglia, Schwann cells within PNS
● autonomic cells and enteric nervous system
● melanocytes (in skin)
● suprarenal medulla (modified sympathetic ganglion)
● odontoblasts of dental pulp
● inner two membranes covering CNS (arachnoid mater and pia mater)
Neural tube derivatives (within PNS)
● motor neurons with cell bodies in CNS:
○ somatic motor neurons
○ preganglionic autonomic motor neurons
● axons extend into PNS as components of peripheral nerves
, Ventricular System
Cranial end of neural tube subdivided into three primary brain vesicles:
● from caudal to rostral:
○ rhombencephalon (hindbrain)
○ mesencephalon (midbrain)
○ prosencephalon (forebrain)
Secondary brain vesicles form subsequently:
● Rhombencephalon (G. 'rhomboid-shaped + brain'):
○ elongates and divides into:
■ myelencephalon
■ metencephalon
● Prosencephalon (G. 'before + brain'):
○ expands and divides into:
■ diencephalon
■ telencephalon
Myelencephalon (G. 'marrow + brain'):
● develops into medulla oblongata
Metencephalon (G. 'after + brain'):
● develops into pons and cerebellum
Mesencephalon (G. 'middle + brain'):
● short connection between diencephalon and rhombencephalon
● no further expansion in humans; remains primitive as midbrain
Diencephalon (G. 'through + brain'):
● develops into:
○ thalamus
○ hypothalamus
○ epithalamus
○ subthalamus
Telencephalon (G. 'end + brain'):
● develops into:
○ large right and left cerebral hemispheres
○ connecting structures between hemispheres
Brain Organization
Brain (encephalon)
● part of the central nervous system (CNS)
● located within the cranial cavity
● anatomical and clinical classifications: consists of brain stem, cerebellum, cerebrum
Brain stem
● part of the neuroaxis between spinal cord and diencephalon
● from caudal to rostral: medulla oblongata, pons, midbrain
Cerebellum (L. 'little brain')
● consists of a pair of hemispheres united in the midline by the vermis (L. 'worm')
● situated in posterior cranial fossa, dorsal to brain stem
● forms roof of the fourth ventricle
● partition of dura mater (tentorium cerebelli) located between cerebellum inferiorly and
cerebrum superiorly
Cerebrum (L. 'brain')
● consists of diencephalon and telencephalon
● telencephalon: expanded pair of cerebral hemispheres
○ united across midline by large body of fibres (corpus callosum)
○ corpus callosum located below partition of dura mater (falx cerebri) between
cerebral hemispheres
Olfactory pathways
● via cranial nerve I, olfactory bulbs and tracts
● indirectly continuous with cerebral hemispheres
Optic pathways
● via cranial nerve II, optic chiasma and tracts
● indirectly continuous with diencephalon
Remaining ten pairs of cranial nerves
● arise directly from brainstem
, Developmental classification (caudal to rostral)
● hindbrain (medulla, pons, cerebellum)
● midbrain
● forebrain (diencephalon, cerebral hemispheres)
Rostral end forms vesicles
that undergo proliferatio n .
J
N
, Merginga
Neuraubegia
Brain Development
Brain and spinal cord
● both derived from ectoderm
● during development, neural plate of neuroectoderm on each side separated from general
ectoderm by transitional cells termed neuroectodermal junction
● neural plate: longitudinal midline thickening of ectoderm along dorsum of embryo
● cellular proliferation of neural plate forms neural groove
Neural groove and neural folds
● neuroectodermal junctions become neural folds
● neural groove deepens and eventually forms neural tube
● neural folds join each other, creating islands of cells called neural crest
Origins of CNS and PNS components
● entire central nervous system (CNS) develops from neural tube
● peripheral nervous system (PNS) primarily develops from neural crest, with some
contribution (efferent fibres) from neural tube
Neural tube
● expanded cranial end develops into brain
● narrow caudal part develops into spinal cord
Neural crest derivatives
● sensory (afferent) fibres, sensory ganglia, Schwann cells within PNS
● autonomic cells and enteric nervous system
● melanocytes (in skin)
● suprarenal medulla (modified sympathetic ganglion)
● odontoblasts of dental pulp
● inner two membranes covering CNS (arachnoid mater and pia mater)
Neural tube derivatives (within PNS)
● motor neurons with cell bodies in CNS:
○ somatic motor neurons
○ preganglionic autonomic motor neurons
● axons extend into PNS as components of peripheral nerves
, Ventricular System
Cranial end of neural tube subdivided into three primary brain vesicles:
● from caudal to rostral:
○ rhombencephalon (hindbrain)
○ mesencephalon (midbrain)
○ prosencephalon (forebrain)
Secondary brain vesicles form subsequently:
● Rhombencephalon (G. 'rhomboid-shaped + brain'):
○ elongates and divides into:
■ myelencephalon
■ metencephalon
● Prosencephalon (G. 'before + brain'):
○ expands and divides into:
■ diencephalon
■ telencephalon
Myelencephalon (G. 'marrow + brain'):
● develops into medulla oblongata
Metencephalon (G. 'after + brain'):
● develops into pons and cerebellum
Mesencephalon (G. 'middle + brain'):
● short connection between diencephalon and rhombencephalon
● no further expansion in humans; remains primitive as midbrain
Diencephalon (G. 'through + brain'):
● develops into:
○ thalamus
○ hypothalamus
○ epithalamus
○ subthalamus
Telencephalon (G. 'end + brain'):
● develops into:
○ large right and left cerebral hemispheres
○ connecting structures between hemispheres
