L39 - Central Nervous System

What are the Two Functional Divisions of the Vertebrate Nervous System?

1. Central nervous system (CNS)

2. Peripheral nervous system (PNS)

What is a Major Feature of the Vertebrate Brain?

It is highly organized and specialized, and evolved from the spinal cord

Why is the vertebrate CNS considered highly protected?

It is protected by:

1. Bone

2. Meninges

3. Cerebrospinal fluid (CSF)

4. Blood-brain barrier

What is the basic hierarchical flow of information through the nervous system?

Sensory input → Association → Decision → Motor output

What occurs in an Ascending Pathway?

Stimulus → Sensory fibers → CNS → filtering → cerebral interpretation/association

What occurs in a Descending Pathway?

Decision/behavior → Motor pathways → lower motor neurons → Effector

What is Gray matter primarily composed of?

Neuronal cell bodies (somata)

What is a Cortex?

Gray matter in which neuronal cell bodies are organized into layers/laminae

What are Examples of Cortical organization?

• Cerebral cortex

• Cerebellar cortex

• Hippocampus

What is a CNS nucleus?

A cluster of neuronal cell bodies located deep within the cerebral hemispheres or brainstem

What is White matter primarily composed of?

Axons/fibers

What is a Tract?

A bundle of axons within the CNS

Why does White matter appear white?

Many axons are surrounded by lipid-rich myelin

What are the Major Functions of the Cerebral cortex?

1. Sensory interpretation

2. Voluntary/skilled movement

3. Intellectual/emotional processing

What does the Cerebral cortex do with sensory information?

Localizes and interprets sensory input

What does Gyrencephalic mean?

A folded/convoluted cerebral cortex

What is a Gyrus?

A fold of the cerebral cortex.

What is a Sulcus?

A groove between folds

What is a Fissure?

A deeper groove

What does Lissencephalic mean?

A smooth, non-convoluted cerebral cortex

What are the Three Types of Cerebral White matter Fibers?

1. Association

2. Commissural

3. Projection fibers

What do Association fibers connect?

Areas within the same cerebral hemisphere

What do Commissural fibers connect?

The two opposite cerebral hemispheres

What do Projection fibers connect?

The cerebrum with lower CNS regions, including the brainstem and spinal cord.

What is the Major Function of the Basal nuclei?

Refine and regulate voluntary skeletal muscle movement

1. Eye movement

2. Habit formation

3. Procedural learning

4. Conditional learning

What is the Major Function of the Thalamus?

Acts as a relay station for sensory impulses to the cerebral cortex

• Relays information between the cerebral motor cortex and motor centers and participates in memory processing

What is the Hypothalamus?

The chief integration center of the autonomic nervous system

What Functions does the Hypothalamus regulate?

1. Temperature

2. Food intake

3. Water balance

4. Thirst

5. Biological rhythms

6. Drives,

7. Hormonal output

How does the Hypothalamus Function as an Endocrine organ?

It produces posterior pituitary hormones and regulates anterior pituitary output

What Three Structures form the Brainstem?

1. Midbrain

2. Pons

3. Medulla oblongata

What are Major Functions of the Midbrain?

1. Visual/auditory reflexes

2. Subcortical motor control

3. Projection pathways

What is a Major Functions of the Pons?

1. Relays information from the cerebrum → cerebellum

2. Cooperates with medullary respiratory centers

What are Major Functions of the Medulla oblongata?

1. Relays ascending sensory information

2. Contains visceral nuclei

3. Relays information to the cerebellum

What important crossing occurs in the Medulla?

Pyramidal decussation

What information does the Cerebellum process?

Input from the:

• Motor cortex

• Proprioceptors

• Equilibrium

• Visual pathways

What is the Major Functional Role of the Cerebellum?

Coordination of:

1. Movement

2. Balance

3. Posture

What are the Two Major Functions of the Spinal cord?

Links the brain and PNS and acts as an integration center for spinal reflexes

What do Ascending Spinal cord Pathways carry?

Sensory information → brain

What do Descending Spinal cord Pathways carry?

Motor information → body

What three functional brain systems are emphasized in the lecture?

1. Reticular activating system (RAS)

2. Limbic system

3. Neocortex

What is the general Role of the RAS?

Integrates and relays information needed for vital survival functions

• Sleep

• Arousal

• Consciousness

What neurotransmitters are associated with the RAS?

1. Norepinephrine from locus coeruleus

2. Serotonin from raphe nuclei

What Major Structures are included in the Limbic system?

1. Cingulate region

2. Hippocampus

3. Amygdala

4. Associated structures

What is the general Function of the Limbic system?

Emotion, memory, learning, social processing, motivation, and reward

What other body systems does the Limbic system influence?

The endocrine and autonomic nervous systems

What is the Mammalian Neocortex?

A six-layered neuronal cortex involved in higher-order brain functions

What Functions are associated with the Neocortex?

Sensory perception, motor commands, attention, spatial reasoning, complex behavior, and cognition

Do birds have the same six-layer neocortex as mammals?

No

• Birds have a differently organized pallium but can still perform complex cognitive behaviors.

What are the Four Major forms of CNS protection?

1. Bone

2. Meninges

3. CSF

4. Brain barriers

What bone protects the Brain?

The cranium, specifically the cranial vault

What protects the Spinal cord?

The vertebrae

What are the Three Meninges from Outermost → Innermost?

1. Dura mater

2. Arachnoid mater

3. Pia mater

What is the Dura mater?

The outermost, fibroelastic meningeal layer

• Permeable to fluid

What is the Arachnoid mater?

The middle, fluid-impermeable meningeal layer

What is the Subarachnoid space?

Space between arachnoid and pia mater containing CSF

What are Arachnoid villi?

Protrusions into dural venous sinuses involved in CSF reabsorption

What is the Pia mater?

The innermost meningeal layer that closely follows the CNS contour

What is CSF?

A clear, colorless, low-protein fluid that protects and nourishes the CNS

Where is CSF produced?

Choroid plexus

Where does CSF circulate?

Through the Ventricular system and Subarachnoid space

Where is CSF reabsorbed?

Into Dural venous sinuses via Arachnoid villi

How does CSF compare with plasma?

CSF has…

• Very little protein

• Less glucose

• Lower K⁺/Ca²⁺

• Similar osmolarity and Na⁺

• Slightly lower pH

What Cells line the Ventricles and Central canal?

Ependymocytes

What are Tanycytes?

Specialized ependymocytes located at the third ventricle

What are Choroid Epithelial cells?

Specialized ependymocytes forming the choroid plexus epithelium

What percentage of CSF is produced by the choroid plexus according to the lecture?

About 80%

What is the Pathway of CSF Circulation?

1. Lateral ventricles

2. 3rd ventricle

3. Cerebral aqueduct

4. 4th ventricle

5. Central canal/subarachnoid space

6. Arachnoid drainage

7. Dural venous sinuses

8. Venous circulation

What is Internal hydrocephalus?

CSF accumulation within the ventricular system

What is External hydrocephalus?

CSF accumulation primarily within the subarachnoid space

How does an Obstruction produce Hydrocephalus?

1. Blocked CSF circulation →

2. CSF accumulation →

3. Ventricular enlargement

What commonly causes Congenital Obstructive Hydrocephalus?

Stenosis of the mesencephalic/cerebral aqueduct

• Internal hydrocephalus

What can cause Acquired Obstructive Hydrocephalus?

Internal hydrocephalus

• Tumor

• Injury

• Inflammation/disease

• Dural fibrosis

• Occipital bone hypoplasia

Congenital obstructive hydrocephalus vs. Acquired obstructive hydrocephalus SUMMARY

Type	When does obstruction develop?	Examples from your lecture	Result
Congenital obstructive hydrocephalus	During early development	Most commonly mesencephalic aqueduct stenosis	CSF blocked → accumulates in ventricles → internal hydrocephalus
Acquired obstructive hydrocephalus	After development due to disease/injury	Neoplasia, ependymal inflammation (FIP/bacterial meningoencephalitis), dural fibrosis, occipital bone hypoplasia	CSF flow obstructed → ventricular expansion → internal hydrocephalus

What are the Three Brain Barriers?

1. Blood-CSF

2. Arachnoid-CSF

3. Blood-brain barriers

Where is the blood-CSF barrier located and what does it do?

Choroid plexus

• Selective transport/filtration

What can occur if the blood-CSF barrier is damaged?

↑ protein in CSF

Where is the arachnoid-CSF barrier and what does it do?

Arachnoid region

• Controls CSF movement/drainage

What can occur if the arachnoid-CSF barrier is damaged?

External hydrocephalus

Where is the blood-brain barrier (BBB)?

At the neurovascular unit

What is the major property of the BBB?

Restrictive permeability

Why is restrictive BBB permeability clinically important?

Some drugs, antibiotics, and other substances may have difficulty reaching CNS tissue

What happens when inflammation or disease damages the BBB?

↑ permeability → abnormal leakage into CNS tissue

Gray Matter vs. White Matter SUMMARY

Feature	Gray Matter	White Matter
Primarily contains	Neuronal cell bodies (somata)	Axons/fibers
Main organization	Cortex or nuclei	Tracts/fibers
Cortex	Somata arranged in layers/laminae	—
Nucleus	Cluster of neurons deep in CNS	—
Tract	—	Bundle of axons
Why white?	—	Lipid-rich myelin around many axons

Cerebral White Matter Fibers SUMMARY

Fiber Type	Connects	Easy Reminder
Association fibers	Areas within the SAME hemisphere	Associate within one side
Commissural fibers	OPPOSITE hemispheres	Cross hemispheres
Projection fibers	Cerebrum ↕ brainstem/spinal cord	Project up/down

Major CNS Regions SUMMARY

CNS Region	Main Function
Cerebrum	Sensation, interpretation, association, motor planning
Brainstem	Reflexes, relay pathways, visceral functions
Cerebellum	Proprioception, balance, coordinated movement
Spinal cord	Ascending sensory + descending motor pathways; spinal reflexes

Brainstem Regions SUMMARY

Region	Key Functions
Midbrain	Visual/auditory reflex centers; subcortical motor centers; projection fibers
Pons	Cerebrum → cerebellum relay; assists respiratory centers
Medulla oblongata	Sensory relay; visceral control; cerebellar relay; pyramidal decussation

Thalamus vs. Hypothalamus vs. Basal Nuclei SUMMARY

Structure	Main Function	Think...
Thalamus	Relay station for sensory impulses to cortex	Sensory relay
Hypothalamus	Chief ANS integration center; homeostasis + endocrine regulation	Homeostasis
Basal nuclei	Refines/regulates voluntary skeletal muscle movement	Refine movement

Functional Brain Systems SUMMARY

System	Major Role	Important Functions
Reticular Activating System (RAS)	Instinct/survival	Sleep, arousal, consciousness; vital functions
Limbic system	Emotion + motivation	Emotion, memory, learning, social processing, motivation, reward
Neocortex	Higher-order processing	Sensory perception, motor commands, attention, spatial reasoning, cognition

Meninges SUMMARY

Layer	Position	Key Feature
Dura mater	Outermost	Fibroelastic; permeable to fluid
Arachnoid mater	Middle	Impermeable to fluid
Pia mater	Innermost	Closely follows CNS contour
Subarachnoid space	Between arachnoid + pia	Contains CSF
Arachnoid villi	Extend into dural venous sinuses	CSF reabsorption

CSF — Production, Circulation & Reabsorption SUMMARY

Step	Location
Production	Choroid plexus
↓	Lateral ventricles
↓	Third ventricle
↓	Cerebral/mesencephalic aqueduct
↓	Fourth ventricle
Circulation	Central canal + subarachnoid space
Reabsorption	Arachnoid-associated drainage
↓	Dural venous sinuses
Return	Venous circulation

Ependymal-Related Cells SUMMRY

Cell	Location/Role	Key Feature
Ependymocytes	Line ventricles + central canal	Microvilli + cilia
Tanycytes	Third ventricle	Contact blood vessels + hypothalamic neurons
Choroid epithelial cells	Choroid plexus	Specialized ependymocytes; CSF production

CNS Barriers SUMMARY

Barrier	Location	Main Function	If Damaged
Blood-CSF	Choroid plexus	Selective transport/filtration	↑ Protein in CSF
Arachnoid-CSF	Arachnoid region	Controls CSF movement/drainage	External hydrocephalus
Blood-brain (BBB)	Neurovascular unit	Restrictive permeability	Abnormal leakage into brain

Internal vs. External Hydrocephalus SUMMARY

Type	Where Does CSF Accumulate?
Internal hydrocephalus	Inside ventricular system
External hydrocephalus	Primarily within subarachnoid space