Anatomy Notes
Class I – Sep 1
Anatomy of the CNS
Glial Cells
Structural, metabolic, functional support, transport nutrients, isolation axons, NGF/repair, composition of ECF
Astrocytes (nutrition):
• Provide structural support to neurons
• Maintain the blood–brain barrier (BBB)
• Regulate ion and neurotransmitter levels around synapses
• Play a role in repair (gliosis after injury)
Oligodendrocytes (insulation):
• Form the myelin sheath around CNS axons
• Each oligodendrocyte can myelinate multiple axons
• Myelin → increases speed of nerve conduction
Microglia (defense):
• The immune cells of the CNS (derived from mesoderm, unlike other glia)
• Act as phagocytes → remove debris, dead cells, and pathogens
• Important in neuroinflammation and repair
Ependymal cells (CSF circulation:
• Line the ventricles of the brain and central canal of the spinal cord
• Involved in producing and circulating cerebrospinal fluid (CSF)
• Found in the choroid plexus (where CSF is made)
CNS vs PNS
CNS Components: Brain + Spinal cord
Function: Processing, integration, and control center
Cell types: Neurons + CNS glial cells (astrocytes, oligodendrocytes, microglia, ependymal)
Protected by: Skull, vertebral column, meninges, CSF, BBB
Gray matter: Neuronal cell bodies (cortex, nuclei, horns)
White matter: Myelinated axons (tracts, columns)
PNS Components: All neural tissue outside CNS → cranial nerves, spinal nerves, peripheral ganglia
Function: Carries sensory info to CNS and motor commands from CNS
Cell types: Neurons + PNS glial cells (Schwann cells, satellite cells)
Subdivisions:
Somatic nervous system (SNS): Voluntary control of skeletal muscles
Autonomic nervous system (ANS): Involuntary control (sympathetic & parasympathetic)
Enteric nervous system (ENS): Independent gut control (sometimes considered part of ANS)
,Nerves
A nerve = bundle of axons in the PNS (in CNS they’re called tracts).
Surrounded by connective tissue:
Endoneurium → around individual axons
Perineurium → around fascicles (axon bundles)
Epineurium → around the whole nerve
Types of nerves:
Sensory (afferent) → carry impulses to CNS
Motor (efferent) → carry impulses from CNS to muscles/glands
Mixed nerves → contain both sensory and motor fibers (most spinal nerves)
Cranial Nerves
• 12 pairs (I–XII)
• Originate from the brain and brainstem
• Pass through foramina of the skull
• Can be sensory, motor, or mixed
• Functions mostly in the head and neck (except vagus nerve, which extends into thorax/abdomen)
https://www.youtube.com/watch?v=mowm8hPjTNU
1. Olfactory (I) – Sensory → Smell
2. Optic (II) – Sensory → Vision
3. Oculomotor (III) – Motor → Eye movement, eyelid elevation, pupil constriction
4. Trochlear (IV) – Motor → Eye movement (superior oblique muscle)
5. Trigeminal (V) – Mixed → Facial sensation & chewing muscles
6. Abducens (VI) – Motor → Eye movement (lateral rectus muscle)
7. Facial (VII) – Mixed → Facial expressions, taste (anterior 2/3 tongue), salivary & lacrimal glands
8. Vestibulocochlear (VIII) – Sensory → Hearing & balance
9. Glossopharyngeal (IX) – Mixed → Taste (posterior 1/3 tongue), swallowing, salivation
10. Vagus (X) – Mixed → Autonomic control (heart, lungs, gut), speech, sensation from viscera
11. Accessory (XI) – Motor → Sternocleidomastoid & trapezius (head & shoulder movement)
12. Hypoglossal (XII) – Motor → Tongue movement
Anatomical Protection of the Brain
1. Bony Protection
The skull (cranium) forms a hard, rigid case around the brain.
Cranial bones (frontal, parietal, temporal, occipital, sphenoid, ethmoid) protect against external trauma.
The base of skull has foramina for cranial nerves and blood vessels, but overall acts as a shield.
2. Meninges (Protective Membranes)
Three connective tissue layers between brain and skull:
Dura mater (outermost, “tough mother”)
Strong, fibrous; has 2 layers (periosteal + meningeal)
Forms dural folds (falx cerebri, tentorium cerebelli) → help anchor brain in place
,Contains dural venous sinuses (for venous drainage)
Arachnoid mater (middle layer, “spider-like”)
Thin, web-like
Subarachnoid space beneath it contains cerebrospinal fluid (CSF) and blood vessels
Pia mater (innermost, “gentle mother”)
Very delicate, adheres closely to brain surface, following gyri & sulci
Contains small vessels that nourish the brain
3. Cerebrospinal Fluid (CSF)
Clear fluid produced by choroid plexus in ventricles
Functions:
Cushions the brain (shock absorption)
Provides buoyancy (reduces effective weight of brain)
Circulates nutrients & removes waste
Flows through ventricles → subarachnoid space → absorbed into venous sinuses via arachnoid granulations
4. Blood–Brain Barrier (BBB) (physiological protection, but linked to anatomy)
Formed by endothelial tight junctions, basement membrane, astrocyte end-feet
Prevents toxins, pathogens, and many drugs from entering brain tissue
Allows selective passage of nutrients (e.g., glucose, oxygen)
5. Additional Features
Cranial sutures & fontanelles (in infants) → allow flexibility and growth
Cranial base fossae (anterior, middle, posterior) → cradle different brain parts
Venous sinuses in dura → drain blood, prevent pressure buildup
Gray Matter in the CNS
Gray matter = areas rich in neuronal cell bodies, dendrites, and synapses (little myelin).
In the brain:
• Forms the cerebral cortex (outer surface of hemispheres).
• Also forms deep nuclei (clusters of cell bodies inside white matter, e.g., basal ganglia, thalamic nuclei).
In the spinal cord:
• Located centrally (H-shaped), with dorsal horns (sensory), ventral horns (motor), and lateral horns
(autonomic).
Buralara geri gelcem
, Subdivisions of the CNS (5 brain vesicles)
Brain vesicles are the bulges (fluid-filled expansions) that appear in the developing neural tube during embryonic
development. They are the precursors of the major regions of the adult brain.
1. Telencephalon: Cerebral hemispheres (cortex, basal ganglia, hippocampus, amygdala, olfactory bulb)
2. Diencephalon: Thalamus, hypothalamus, epithalamus, retina
3. Mesencephalon: Midbrain (tectum, tegmentum, cerebral peduncles)
4. Metencephalon: Pons + Cerebellum
5. Myelencephalon: Medulla oblongata
Neural Development (Neurulation)
1. Neural Plate (from surface ectoderm)
• Around day 18–19 of embryonic development.
• The ectoderm (outer germ layer) thickens in the dorsal midline, forming the neural plate.
• This is the first sign of the developing nervous system.
2. Neural Folds & Neural Groove
• The lateral edges of the neural plate elevate → neural folds.
• A depression forms in the middle → neural groove.
• Neural folds gradually move toward each other.
3. Neural Tube Formation
• The neural folds fuse in the midline → forming the neural tube.
• Fusion begins in the middle of the embryo and proceeds cranially (head) and caudally (tail).
• Openings remain temporarily:
• Cranial neuropore (closes ~day 25)
• Caudal neuropore (closes ~day 27)
• Once closed → the neural tube detaches from the ectoderm and sinks beneath the surface.
4. Neural Crest Cells
• Special cells at the tips of the neural folds break away → form neural crest cells.
• They migrate extensively → give rise to much of the PNS (dorsal root ganglia, autonomic ganglia, Schwann
cells, melanocytes, adrenal medulla, craniofacial structures).
5. Brain Vesicle Formation (Rostral Neural Tube)
• The anterior part of the neural tube enlarges → forms primary brain vesicles:
o Prosencephalon (forebrain)
o Mesencephalon (midbrain)
o Rhombencephalon (hindbrain)
These subdivide into the five secondary vesicles:
o Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon
Spina bifida
occulta (hidden form)
o Mildest & most common.
o Just failure of vertebral arch fusion; spinal cord and meninges remain in place.
Class I – Sep 1
Anatomy of the CNS
Glial Cells
Structural, metabolic, functional support, transport nutrients, isolation axons, NGF/repair, composition of ECF
Astrocytes (nutrition):
• Provide structural support to neurons
• Maintain the blood–brain barrier (BBB)
• Regulate ion and neurotransmitter levels around synapses
• Play a role in repair (gliosis after injury)
Oligodendrocytes (insulation):
• Form the myelin sheath around CNS axons
• Each oligodendrocyte can myelinate multiple axons
• Myelin → increases speed of nerve conduction
Microglia (defense):
• The immune cells of the CNS (derived from mesoderm, unlike other glia)
• Act as phagocytes → remove debris, dead cells, and pathogens
• Important in neuroinflammation and repair
Ependymal cells (CSF circulation:
• Line the ventricles of the brain and central canal of the spinal cord
• Involved in producing and circulating cerebrospinal fluid (CSF)
• Found in the choroid plexus (where CSF is made)
CNS vs PNS
CNS Components: Brain + Spinal cord
Function: Processing, integration, and control center
Cell types: Neurons + CNS glial cells (astrocytes, oligodendrocytes, microglia, ependymal)
Protected by: Skull, vertebral column, meninges, CSF, BBB
Gray matter: Neuronal cell bodies (cortex, nuclei, horns)
White matter: Myelinated axons (tracts, columns)
PNS Components: All neural tissue outside CNS → cranial nerves, spinal nerves, peripheral ganglia
Function: Carries sensory info to CNS and motor commands from CNS
Cell types: Neurons + PNS glial cells (Schwann cells, satellite cells)
Subdivisions:
Somatic nervous system (SNS): Voluntary control of skeletal muscles
Autonomic nervous system (ANS): Involuntary control (sympathetic & parasympathetic)
Enteric nervous system (ENS): Independent gut control (sometimes considered part of ANS)
,Nerves
A nerve = bundle of axons in the PNS (in CNS they’re called tracts).
Surrounded by connective tissue:
Endoneurium → around individual axons
Perineurium → around fascicles (axon bundles)
Epineurium → around the whole nerve
Types of nerves:
Sensory (afferent) → carry impulses to CNS
Motor (efferent) → carry impulses from CNS to muscles/glands
Mixed nerves → contain both sensory and motor fibers (most spinal nerves)
Cranial Nerves
• 12 pairs (I–XII)
• Originate from the brain and brainstem
• Pass through foramina of the skull
• Can be sensory, motor, or mixed
• Functions mostly in the head and neck (except vagus nerve, which extends into thorax/abdomen)
https://www.youtube.com/watch?v=mowm8hPjTNU
1. Olfactory (I) – Sensory → Smell
2. Optic (II) – Sensory → Vision
3. Oculomotor (III) – Motor → Eye movement, eyelid elevation, pupil constriction
4. Trochlear (IV) – Motor → Eye movement (superior oblique muscle)
5. Trigeminal (V) – Mixed → Facial sensation & chewing muscles
6. Abducens (VI) – Motor → Eye movement (lateral rectus muscle)
7. Facial (VII) – Mixed → Facial expressions, taste (anterior 2/3 tongue), salivary & lacrimal glands
8. Vestibulocochlear (VIII) – Sensory → Hearing & balance
9. Glossopharyngeal (IX) – Mixed → Taste (posterior 1/3 tongue), swallowing, salivation
10. Vagus (X) – Mixed → Autonomic control (heart, lungs, gut), speech, sensation from viscera
11. Accessory (XI) – Motor → Sternocleidomastoid & trapezius (head & shoulder movement)
12. Hypoglossal (XII) – Motor → Tongue movement
Anatomical Protection of the Brain
1. Bony Protection
The skull (cranium) forms a hard, rigid case around the brain.
Cranial bones (frontal, parietal, temporal, occipital, sphenoid, ethmoid) protect against external trauma.
The base of skull has foramina for cranial nerves and blood vessels, but overall acts as a shield.
2. Meninges (Protective Membranes)
Three connective tissue layers between brain and skull:
Dura mater (outermost, “tough mother”)
Strong, fibrous; has 2 layers (periosteal + meningeal)
Forms dural folds (falx cerebri, tentorium cerebelli) → help anchor brain in place
,Contains dural venous sinuses (for venous drainage)
Arachnoid mater (middle layer, “spider-like”)
Thin, web-like
Subarachnoid space beneath it contains cerebrospinal fluid (CSF) and blood vessels
Pia mater (innermost, “gentle mother”)
Very delicate, adheres closely to brain surface, following gyri & sulci
Contains small vessels that nourish the brain
3. Cerebrospinal Fluid (CSF)
Clear fluid produced by choroid plexus in ventricles
Functions:
Cushions the brain (shock absorption)
Provides buoyancy (reduces effective weight of brain)
Circulates nutrients & removes waste
Flows through ventricles → subarachnoid space → absorbed into venous sinuses via arachnoid granulations
4. Blood–Brain Barrier (BBB) (physiological protection, but linked to anatomy)
Formed by endothelial tight junctions, basement membrane, astrocyte end-feet
Prevents toxins, pathogens, and many drugs from entering brain tissue
Allows selective passage of nutrients (e.g., glucose, oxygen)
5. Additional Features
Cranial sutures & fontanelles (in infants) → allow flexibility and growth
Cranial base fossae (anterior, middle, posterior) → cradle different brain parts
Venous sinuses in dura → drain blood, prevent pressure buildup
Gray Matter in the CNS
Gray matter = areas rich in neuronal cell bodies, dendrites, and synapses (little myelin).
In the brain:
• Forms the cerebral cortex (outer surface of hemispheres).
• Also forms deep nuclei (clusters of cell bodies inside white matter, e.g., basal ganglia, thalamic nuclei).
In the spinal cord:
• Located centrally (H-shaped), with dorsal horns (sensory), ventral horns (motor), and lateral horns
(autonomic).
Buralara geri gelcem
, Subdivisions of the CNS (5 brain vesicles)
Brain vesicles are the bulges (fluid-filled expansions) that appear in the developing neural tube during embryonic
development. They are the precursors of the major regions of the adult brain.
1. Telencephalon: Cerebral hemispheres (cortex, basal ganglia, hippocampus, amygdala, olfactory bulb)
2. Diencephalon: Thalamus, hypothalamus, epithalamus, retina
3. Mesencephalon: Midbrain (tectum, tegmentum, cerebral peduncles)
4. Metencephalon: Pons + Cerebellum
5. Myelencephalon: Medulla oblongata
Neural Development (Neurulation)
1. Neural Plate (from surface ectoderm)
• Around day 18–19 of embryonic development.
• The ectoderm (outer germ layer) thickens in the dorsal midline, forming the neural plate.
• This is the first sign of the developing nervous system.
2. Neural Folds & Neural Groove
• The lateral edges of the neural plate elevate → neural folds.
• A depression forms in the middle → neural groove.
• Neural folds gradually move toward each other.
3. Neural Tube Formation
• The neural folds fuse in the midline → forming the neural tube.
• Fusion begins in the middle of the embryo and proceeds cranially (head) and caudally (tail).
• Openings remain temporarily:
• Cranial neuropore (closes ~day 25)
• Caudal neuropore (closes ~day 27)
• Once closed → the neural tube detaches from the ectoderm and sinks beneath the surface.
4. Neural Crest Cells
• Special cells at the tips of the neural folds break away → form neural crest cells.
• They migrate extensively → give rise to much of the PNS (dorsal root ganglia, autonomic ganglia, Schwann
cells, melanocytes, adrenal medulla, craniofacial structures).
5. Brain Vesicle Formation (Rostral Neural Tube)
• The anterior part of the neural tube enlarges → forms primary brain vesicles:
o Prosencephalon (forebrain)
o Mesencephalon (midbrain)
o Rhombencephalon (hindbrain)
These subdivide into the five secondary vesicles:
o Telencephalon, Diencephalon, Mesencephalon, Metencephalon, Myelencephalon
Spina bifida
occulta (hidden form)
o Mildest & most common.
o Just failure of vertebral arch fusion; spinal cord and meninges remain in place.
