The Central Nervous System

1
The Central Nervous System

• Brain Spinal cord

2
Development of the CNS

• Similar in all "Amniotes"
• Blastoderm over yolk sac
• three "germ layers"
• Ectoderm ("outside skin")
• Mesoderm ("middle skin")
• Endoderm ("inner skin")

3
Nervous System Development

• Develops from Ectoderm
• Rising of neural folds
• Sinking of neural plate forms neural groove
• Folds fuse to complete neural tube

4
Nervous System Development

• Neural tube forms CNS (esp. spinal cord)
• Expands anteriorly to form brain
• Peripheral nerves develop from lateral "neural
  crest" cells

5
Expansion of Brain

• Primary
• Forebrain
• Midbrain
• Hindbrain

6
Expansion of Brain

• Secondary
• Forebrain
• Telencephalon
• Diencephalon
• Midbrain
• remains just midbrain
• Hindbrain
• Cerebellum
• Brain stem

7
Expansion of Brain

• Final development
• Telencephalon cerebrum
• Diencephalon thalamus hypothalamus
• Cerebellum
• Brain stem Midbrain pons medulla oblongata

8
Protection Nutrition of CNS
9
Protection

• Bone
• Cranial bones vertebral arches
• Meninges
• Dura mater
• Arachnoid mater
• Pia mater
• Cerebrospinal fluid (CSF)

10
Meninges

• Dura mater
• Arachnoid mater
• Pia mater

11
Cerebrospinal fluid (CSF)

• Filtered from blood plasma in choroid plexuses

12
Cerebrospinal fluid (CSF)

• Filtered from blood plasma in choroid plexuses
• Circulates in through ventricles, canals,
  between meninges
• Returned to blood at superior sagittal sinus

13
Ventricles of the Brain

• 2 Lateral ventricles (1, 2) in cerebral
  hemispheres
• Third ventricle (3) between hemispheres
• Fourth ventricle (4) in midbrain and medulla

14
Cerebrospinal fluid (CSF)

• Supports (buoys) mass
• Cushions CNS - like waterbed
• Nourishes brain tissue
• Contains proper electrolytes for CNS

15
Blood supply Nutrition

• Brain is highly vascular
• blood delivers O2 and glucose supply
• Can't be deprived of O2. No capacity for
  anaerobic respiration.
• Brain cells die w/in 5-6 minutes when deprived
• Requires glucose (or ketone bodies) as fuel
• Can't use fats, amino acids.

16
Blood-brain barrier

• CNS is sensitive to chemicals
• Capillaries have thicker, non-leaky walls.
• Protects brain from drugs, metabolites, toxins

17
BRAIN

• Largest part of CNS
• Center of consciousness, communication
• Integrates sensory input
• Coordinates complex responses to environment
• Center of homeostatic regulation of nearly all
  physiological processes.
• Breathing, Heartbeat, Hunger/Satiety
• Reproductive "drive," Musculoskeletal coordination

18
Parts of the Brain

• In order evolved, from lower posterior to higher
  anterior.

19
Brain Stem

• Superior continuation of spinal cord
• Medulla oblongata
• Pons (bridge)
• Midbrain
• Reticular formation

20
Medulla oblongata

• Conduction region for motor and sensory pathways
  to from brain
• Decussation
• Crossing of tracts/fibers to opposite sides
• Left brain controls right motor activity.
• Regulation of heartbeat force of contraction,
• " " breathing rhythm,
• " " blood flow through
  arteries,
• " " equilibrium (sense of
  balance).
• Origins of cranial nerves VIII - XII

21
Pons (bridge)

• Connections to other parts of brain
• transverse fibers to/from cerebellum
• longitudinal fibers to above/below
• Regulation of breathing
• Origins of cranial nerves V - VIII

22
Midbrain

• Conveys impulses to/from cerebrum
•  Superior Inferior colliculi
• Reflex centers for movements of eyes, head,
  torso in response to visual auditory stimuli
• Tracking of moving objects
• Origins of cranial nerves III, IV

23
Reticular formation

• Deep structure of whole brain stem
• Reticular Activating System
• Regulates alertness, wakefulness sleep