General Organization of Brainstem and its Division
Brain Organisation
● Brain / Encephalon (G. 'in + head')
○ Part of the central nervous system (CNS) located within the cranial cavity
○ According to both anatomical and clinical classifications, the brain is made up of:
■ Brain stem
■ Cerebellum
■ Cerebrum
Brain Stem
● The part of the neuroaxis between the spinal cord and the diencephalon
● From caudal to rostral:
1. Medulla oblongata
2. Pons
3. Midbrain
Medulla oblongata
● (L. 'middle + oblong-shaped')
● Also known as the bulb, abbreviated to medulla
● Continuous caudally with the spinal cord (at the foramen magnum)
● Continuous rostrally with the pons
● Many ascending and descending nerve fibres travel through the medulla
● Anteriorly: contains a pair of prominent pyramids
○ Each pyramid contains a major motor pathway for the opposite side of the body
○ Most fibres in the pyramids cross at the decussation of the pyramids in the lower
medulla
● Contains cranial nerve nuclei, including those for vital respiratory, cardiac, and
vasomotor centers
Pons
● (L. 'bridge')
● Continuous laterally with the middle cerebellar peduncles (L. 'little feet')
● Ventral aspect: basal pons, a bulge formed by transverse fibres passing to the
cerebellum
● Contains cranial nerve nuclei, as well as ascending and descending fibres
● Dorsal aspect of the pons and upper medulla: forms the floor of the fourth ventricle (L.
'little cavity')
,Midbrain
● Passes through the opening in the tentorium cerebelli
● Continuous rostrally with the diencephalon
● Anteriorly: V-shaped appearance with a pair of short, stout crura cerebri
● Many ascending and descending fibres travel through the midbrain
● Contains cranial nerve nuclei
● Surrounds the cerebral aqueduct (L. 'water + lead'), connecting the fourth ventricle
caudally to the third ventricle rostrally
Cerebellum
● (L. 'little brain')
● Consists of a pair of hemispheres united in the midline by the vermis (L. 'worm')
● Located in the posterior cranial fossa, dorsal to the brain stem
● Forms the roof of the fourth ventricle
● Separated from the cerebrum by a partition of dura mater, the tentorium cerebelli
Cerebrum
● Composed of:
○ Diencephalon
○ Telencephalon (expanded pair of cerebral hemispheres)
● The cerebral hemispheres are united across the midline by the corpus callosum (L.
'body + thick-skinned'), a large mass of fibres
● The falx cerebri (G. 'sickle') (dura mater) lies between the hemispheres
● Olfactory pathways (cranial nerve I) connect indirectly with the cerebral hemispheres
● Optic pathways (cranial nerve II) connect indirectly with the diencephalon
● Remaining ten pairs of cranial nerves arise directly from the brainstem
Diencephalon
● Rostral continuation of the brain stem
● Lies within the core of the cerebrum
● Seen in mid-sagittal section, enclosing the third ventricle
● Components:
○ Thalamus (G. 'chamber')
■ Paired ovoid masses on lateral walls of third ventricle
○ Hypothalamus
■ Connected by stalk to hypophysis (G. 'under + growth'), or pituitary gland
(L. 'phlegm')
○ Epithalamus
■ Includes the pineal gland (L. 'pinecone')
○ Subthalamus
■ Located between inferior surface of thalamus and tegmentum of midbrain
,Telencephalon
● (G. 'end + brain')
● Develops into large right and left cerebral hemispheres
● Connected via corpus callosum
● Surfaces:
○ Superolateral
○ Medial
○ Inferior
● Marked by:
○ Gyri (G. 'circles') – raised folds
○ Sulci (L. 'furrows') – grooves
● Some sulci are deep and separate the four main lobes:
○ Frontal
○ Parietal
○ Temporal
○ Occipital
● Insula (L. 'island')
○ An oval lobe of cortex remaining in the floor of the lateral sulcus during
development
○ Later covered by adjacent cortex from the frontal, parietal, and temporal lobes
Limbic System
● (L. 'edge')
● A collection of structures around the inferomedial cerebral hemisphere, encircling the
diencephalon
● Includes parts of the hypothalamus, thalamus, and deep temporal lobe structures
● Functions:
○ Controls autonomic nervous system and endocrine system
○ Referred to as the 'visceral brain'
○ Affects emotions, drives, motivation, mood, memory
Neuroectoderm
● Brain and spinal cord derive from ectoderm
● Neural plate: thickened ectoderm along the embryo’s dorsal midline
○ Separated from general ectoderm by neuroectodermal junction
○ Forms the neural groove through cellular proliferation
● Neuroectodermal junctions become neural folds
○ Folds meet and form the neural tube
○ Cells that break off form the neural crest
, Neural Tube and Neural Crest
● Neural tube: gives rise to entire central nervous system (CNS)
● Neural crest: gives rise to most of the peripheral nervous system (PNS)
○ Sensory (afferent) fibres
○ Sensory ganglia
○ Schwann cells
○ Autonomic cells
○ Enteric nervous system
○ Melanocytes
○ Suprarenal medulla
○ Odontoblasts (dental pulp)
○ Inner two CNS meninges
● Motor neurons (somatic and preganglionic autonomic):
○ Cell bodies in CNS (from neural tube)
○ Axons in PNS (as part of peripheral nerves)
Brain Vesicles
● Neural tube’s cranial end subdivides into primary brain vesicles:
○ Rhombencephalon (hindbrain)
○ Mesencephalon (midbrain)
○ Prosencephalon (forebrain)
● Secondary vesicles develop:
○ Rhombencephalon (G. 'rhomboid-shaped + brain') →
■ Myelencephalon: medulla oblongata (G. 'marrow + brain')
■ Metencephalon: pons and cerebellum (G. 'after + brain')
○ Mesencephalon (G. 'middle + brain') → midbrain (no further subdivision)
○ Prosencephalon (G. 'before + brain') →
■ Diencephalon: thalamus, hypothalamus, epithalamus, subthalamus
■ Telencephalon: cerebral hemispheres and connections
Structural Overview of the Brain and Spinal Cord
● The brain and spinal cord consist of:
○ Neurons (excitable cells)
○ Neuroglia (non-excitable support cells)
● On fresh sectioning:
○ Grey matter: appears greyish; dominated by neuron cell bodies
○ White matter: appears whitish due to myelinated nerve fibres
● Both grey and white matter contain:
○ Neuroglia
○ Endothelial cells of blood capillaries
Brain Organisation
● Brain / Encephalon (G. 'in + head')
○ Part of the central nervous system (CNS) located within the cranial cavity
○ According to both anatomical and clinical classifications, the brain is made up of:
■ Brain stem
■ Cerebellum
■ Cerebrum
Brain Stem
● The part of the neuroaxis between the spinal cord and the diencephalon
● From caudal to rostral:
1. Medulla oblongata
2. Pons
3. Midbrain
Medulla oblongata
● (L. 'middle + oblong-shaped')
● Also known as the bulb, abbreviated to medulla
● Continuous caudally with the spinal cord (at the foramen magnum)
● Continuous rostrally with the pons
● Many ascending and descending nerve fibres travel through the medulla
● Anteriorly: contains a pair of prominent pyramids
○ Each pyramid contains a major motor pathway for the opposite side of the body
○ Most fibres in the pyramids cross at the decussation of the pyramids in the lower
medulla
● Contains cranial nerve nuclei, including those for vital respiratory, cardiac, and
vasomotor centers
Pons
● (L. 'bridge')
● Continuous laterally with the middle cerebellar peduncles (L. 'little feet')
● Ventral aspect: basal pons, a bulge formed by transverse fibres passing to the
cerebellum
● Contains cranial nerve nuclei, as well as ascending and descending fibres
● Dorsal aspect of the pons and upper medulla: forms the floor of the fourth ventricle (L.
'little cavity')
,Midbrain
● Passes through the opening in the tentorium cerebelli
● Continuous rostrally with the diencephalon
● Anteriorly: V-shaped appearance with a pair of short, stout crura cerebri
● Many ascending and descending fibres travel through the midbrain
● Contains cranial nerve nuclei
● Surrounds the cerebral aqueduct (L. 'water + lead'), connecting the fourth ventricle
caudally to the third ventricle rostrally
Cerebellum
● (L. 'little brain')
● Consists of a pair of hemispheres united in the midline by the vermis (L. 'worm')
● Located in the posterior cranial fossa, dorsal to the brain stem
● Forms the roof of the fourth ventricle
● Separated from the cerebrum by a partition of dura mater, the tentorium cerebelli
Cerebrum
● Composed of:
○ Diencephalon
○ Telencephalon (expanded pair of cerebral hemispheres)
● The cerebral hemispheres are united across the midline by the corpus callosum (L.
'body + thick-skinned'), a large mass of fibres
● The falx cerebri (G. 'sickle') (dura mater) lies between the hemispheres
● Olfactory pathways (cranial nerve I) connect indirectly with the cerebral hemispheres
● Optic pathways (cranial nerve II) connect indirectly with the diencephalon
● Remaining ten pairs of cranial nerves arise directly from the brainstem
Diencephalon
● Rostral continuation of the brain stem
● Lies within the core of the cerebrum
● Seen in mid-sagittal section, enclosing the third ventricle
● Components:
○ Thalamus (G. 'chamber')
■ Paired ovoid masses on lateral walls of third ventricle
○ Hypothalamus
■ Connected by stalk to hypophysis (G. 'under + growth'), or pituitary gland
(L. 'phlegm')
○ Epithalamus
■ Includes the pineal gland (L. 'pinecone')
○ Subthalamus
■ Located between inferior surface of thalamus and tegmentum of midbrain
,Telencephalon
● (G. 'end + brain')
● Develops into large right and left cerebral hemispheres
● Connected via corpus callosum
● Surfaces:
○ Superolateral
○ Medial
○ Inferior
● Marked by:
○ Gyri (G. 'circles') – raised folds
○ Sulci (L. 'furrows') – grooves
● Some sulci are deep and separate the four main lobes:
○ Frontal
○ Parietal
○ Temporal
○ Occipital
● Insula (L. 'island')
○ An oval lobe of cortex remaining in the floor of the lateral sulcus during
development
○ Later covered by adjacent cortex from the frontal, parietal, and temporal lobes
Limbic System
● (L. 'edge')
● A collection of structures around the inferomedial cerebral hemisphere, encircling the
diencephalon
● Includes parts of the hypothalamus, thalamus, and deep temporal lobe structures
● Functions:
○ Controls autonomic nervous system and endocrine system
○ Referred to as the 'visceral brain'
○ Affects emotions, drives, motivation, mood, memory
Neuroectoderm
● Brain and spinal cord derive from ectoderm
● Neural plate: thickened ectoderm along the embryo’s dorsal midline
○ Separated from general ectoderm by neuroectodermal junction
○ Forms the neural groove through cellular proliferation
● Neuroectodermal junctions become neural folds
○ Folds meet and form the neural tube
○ Cells that break off form the neural crest
, Neural Tube and Neural Crest
● Neural tube: gives rise to entire central nervous system (CNS)
● Neural crest: gives rise to most of the peripheral nervous system (PNS)
○ Sensory (afferent) fibres
○ Sensory ganglia
○ Schwann cells
○ Autonomic cells
○ Enteric nervous system
○ Melanocytes
○ Suprarenal medulla
○ Odontoblasts (dental pulp)
○ Inner two CNS meninges
● Motor neurons (somatic and preganglionic autonomic):
○ Cell bodies in CNS (from neural tube)
○ Axons in PNS (as part of peripheral nerves)
Brain Vesicles
● Neural tube’s cranial end subdivides into primary brain vesicles:
○ Rhombencephalon (hindbrain)
○ Mesencephalon (midbrain)
○ Prosencephalon (forebrain)
● Secondary vesicles develop:
○ Rhombencephalon (G. 'rhomboid-shaped + brain') →
■ Myelencephalon: medulla oblongata (G. 'marrow + brain')
■ Metencephalon: pons and cerebellum (G. 'after + brain')
○ Mesencephalon (G. 'middle + brain') → midbrain (no further subdivision)
○ Prosencephalon (G. 'before + brain') →
■ Diencephalon: thalamus, hypothalamus, epithalamus, subthalamus
■ Telencephalon: cerebral hemispheres and connections
Structural Overview of the Brain and Spinal Cord
● The brain and spinal cord consist of:
○ Neurons (excitable cells)
○ Neuroglia (non-excitable support cells)
● On fresh sectioning:
○ Grey matter: appears greyish; dominated by neuron cell bodies
○ White matter: appears whitish due to myelinated nerve fibres
● Both grey and white matter contain:
○ Neuroglia
○ Endothelial cells of blood capillaries
