1. The Central Nervous System
Chapter Marieb

2. Central Nervous System (CNS)
Composed of the brain and spinal cord
Spinal Cord
Central cavity surrounded by a gray matter core
External to which is white matter composed of myelinated fiber tracts
Brain
Similar to spinal cord but with additional areas of gray matter and outer cortex of gray matter
Cerebellum has gray matter in nuclei and cortex

3. Basic Pattern of the Central Nervous System
Figure 12.4

4. The Brain Composed of wrinkled, pinkish-gray tissue 4 major parts:
cerebral hemispheres
diencephalon
cerebellum
brain stem
Figure 12.3

5. Cerebral Hemispheres (Cerebrum)
Form the superior part of the brain and make up 83% of its mass
Contain ridges (gyri) and shallow grooves (sulci)
Contain deep grooves called fissures (large sulcus).
Are separated by the longitudinal fissure
Have three basic regions: cortex, white matter, and basal nuclei.

6. Hemispheres are not equal in function
Cerebral Cortex
The cortex – superficial gray matter; accounts for 40% of the mass of the brain
It enables sensation, communication, memory, understanding, and voluntary movements
Each hemisphere acts contralaterally (controls the opposite side of the body)
Hemispheres are not equal in function
No functional area acts alone; conscious behavior involves the entire cortex

7. Functional Areas of the Cerebral Cortex
The three types of functional areas are:
Motor areas – control voluntary movement
Sensory areas – conscious awareness of sensation
Association areas – integrate diverse information

8. Functional Areas of the Cerebral Cortex (not a required figure)
Figure 12.8a

9. Lateralization of Cortical Function
Lateralization – each hemisphere has abilities not shared with its partner
Cerebral dominance – designates the hemisphere dominant for language
Left hemisphere – controls language, math, and logic
Right hemisphere – controls visual-spatial skills, emotion, and artistic skills

10. Cerebral White Matter Consists of myelinated fibers and their tracts
It is responsible for communication between:
The cerebral cortex and lower CNS center, and between areas of the cortex
Types include:
Commissures – connect corresponding gray areas of the two hemispheres
Association fibers – connect different parts of the same hemisphere
Projection fibers – enter the hemispheres from lower brain or cord centers

11. Cerebral White Matter
Identify ventricles and fibers. Also the basal nuclei.

12. Basal Nuclei
Masses of gray matter found deep within the cortical white matter of the cerebral hemispheres
caudate nucleus
lentiform nucleus (putamen and globus pallidus)
Proposed functions of basal nuclei
Motor control -influence muscular activity
Regulate attention and cognition
Disorders of basal nuclei:
Huntington’s disease
Parkinson’s disease

13. Basal Nuclei
Figure 12.11a

14. Consists of three paired structures
Diencephalon
Consists of three paired structures
- thalamus
- hypothalamus
- epithalamus
Encloses the third ventricle

15. Label this with the book.

16. Thalamus
Paired, egg-shaped masses containing four groups of nuclei that project to and receive fibers from the cerebral cortex
Acts as a “relay station” for information entering the brain
Afferent impulses from all senses converge and synapse in the thalamus
All inputs ascending to the cerebral cortex pass through the thalamus
Impulses of similar function are sorted out, edited, and relayed as a group
Plays a key role in mediating sensation, motor activities, cortical arousal, learning, and memory

17. Located below the thalamus, it ‘caps’ the brainstem
Hypothalamus
Located below the thalamus, it ‘caps’ the brainstem
Infundibulum – stalk of the hypothalamus; connects to the pituitary gland
Functions:
Regulates blood pressure, rate and force of heartbeat, digestive tract motility, rate and depth of breathing, and many other visceral activities
Is involved with perception of pleasure, fear, and rage
Controls mechanisms needed to maintain normal body temperature
Regulates feelings of hunger and satiety
Regulates sleep and the sleep cycle

18. Most dorsal portion of the diencephalon
Epithalamus
Most dorsal portion of the diencephalon
Pineal gland – extends from the posterior border and secretes melatonin - hormone involved with sleep regulation, sleep-wake cycles, and mood

19. Consists of three regions
Brain Stem
Consists of three regions
- midbrain
- pons
- Medulla oblongata
Similar to spinal cord but contains embedded nuclei
Controls automatic behaviors necessary for survival
Exs. Heart rate, respiratory rate
Provides the pathway for tracts between higher and lower brain centers

20. Located dorsal to the pons and medulla
The Cerebellum
Located dorsal to the pons and medulla
Makes up 11% of the brain’s mass
Provides precise timing and appropriate patterns of skeletal muscle contraction, ie. coordinates movements
Cerebellar activity occurs subconsciously
Coordinating movement of the body.

21. Ventricles of the Brain
Contain cerebrospinal fluid
Continuous with the central canal of the spinal chord
The ventricles are:
The two C-shaped lateral ventricles
The third ventricle found in the diencephalon
The fourth ventricle dorsal to the pons

22. Ventricles of the Brain
Figure 12.5

23. Protection of the Brain
The brain is protected by bone, meninges, and cerebrospinal fluid
Harmful substances are shielded from the brain by the blood-brain barrier
CSF has protective and nutritive functions.

24. Major functions of the meninges
Three connective tissue membranes lie external to the CNS – dura mater, arachnoid mater, and pia mater
Major functions of the meninges
Cover and protect the CNS
Protect blood vessels
Contain cerebrospinal fluid (CSF)
CSF is between A and P.

25. Meninges Figure12.24 Dura outside, Arachnoid middle, Pia inside.
DAP. From outside to inside.
Figure 12.23a
Figure12.24

26. Cerebrospinal Fluid (CSF)
Watery solution similar in composition to blood plasma except it contains less protein and different ion concentrations
Nourishes the brain and carries chemical signals throughout it
Forms a liquid cushion that gives buoyancy to the CNS organs
prevents the brain from crushing under its own weight
protects from trauma
Liquid cushion, absorbs some of the shock.

27. Blood-Brain Barrier
Protective mechanism that helps maintain a stable environment for the brain
Selective barrier that allows nutrients to pass freely
Is ineffective against substances that can diffuse through plasma membranes
Bloodborne substances are separated from neurons by:
endothelium of capillary walls
thick basal lamina
bulbous “feet” of astrocytes
Allows most nutrients, and most hydrophobic, but a lot of big hydrophilic molecules can not pass.
Astrocytes cover the capillaries. Thick basal lamina makes it a selective barrier.
Extensions of the astrocytes are the bulbous feet, large pseudopodia that surround the blood vessel.
Has to pass two layers of plasma membrane, so must be very hydrophobic to pass through both.

28. Brain Waves
Normal brain function involves patterns of continuous electrical activity- brain waves
An electroencephalogram (EEG) records this activity-wave frequency expressed as Hertz (Hz)
Each person’s brain waves are unique
Brain waves change with age, sensory stimuli, brain disease, and the chemical state of the body
EEGs can be used to diagnose and localize brain lesions, tumors, infarcts, infections, abscesses, and epileptic lesions
A flat EEG (no electrical activity) is clinical evidence of death
EEG’s aren’t perfect usually need other devices. When an EEG is flat, life is essentially over. Even in a coma you have EEG patterns. Needs to be a certain amount of time though.
Alpha waves – regular and rhythmic, low-amplitude, slow, synchronous waves indicating an idling brain.
Beta waves – rhythmic, more irregular, more frequent.
Adults lose theta waves. Theta waves are more irregular than alpha.

29. Involves simultaneous activity of large areas of the cerebral cortex
Consciousness
Encompasses perception of sensation, voluntary initiation and control of movement, and capabilities associated with higher mental processing
Involves simultaneous activity of large areas of the cerebral cortex
Is superimposed on other types of neural activity
Is holistic and totally interconnected
Clinical consciousness is defined on a continuum that grades levels of behavior – alertness, drowsiness, stupor, coma
Very unknown, kind of a philosophical question. Coma would be probably the lowest state of consciousness.

30. Spinal Cord
CNS tissue enclosed within the vertebral column; Provides two-way communication to and from the brain
Protected by bone, meninges, and CSF
Epidural space – space between the vertebrae and the dural sheath (dura mater) filled with fat and a network of veins
Spinal nerves – 31 pairs attach to the cord by paired roots
Cervical and lumbar enlargements – sites where nerves serving the upper and lower limbs emerge
Spinal cord is the CNS material within the spinal column, including epidural space and the spinal nerves. Bones that protect are the vertebrae, also protected by CSF/meninges.
Nerves from upper and lower limbs meet in the cord.

31. Spinal Cord
Figure 12.28a
12.29

32. Cross-Sectional Anatomy of the Spinal Cord
dorsal
Notice epidural space has fat
THIS IS ON THE EXAM
Enter dorsal horn through dorsal root ganglia.
Once the nerves travel to outside of spinal cord, outward, they become part of the PNS.
Dorsal horn
Ventral horn
ventral
Dorsal root
Ventral root
12.31a
Figure 12.30a

33. Gray Matter and Spinal Roots
Gray matter consists of somas, unmyelinated processes, and neuroglia
Dorsal segment (dorsal horns)– sensory (afferent)
Afferent fibers from sensory neurons form dorsal roots
Sensory neuron somas found in dorsal root ganglia (PNS)
Ventral segment (ventral horns)– motor (efferent)
Axons of motor neurons leave spinal cord through ventral roots
Dorsal and ventral roots fuse laterally to form spinal nerves
Enter spinal cord, enter through dorsal roots. Leave spinal cord, leave through ventral roots.

34. Gray Matter and Spinal Roots (not a required figure)
Different areas of the white matter, don’t really worry about it for this course. Different regions of white matter, have different nuclei.
12.31b
Figure 12.30b

35. White Matter in the Spinal Cord
Fibers (axons) run in three directions – ascending, descending, and transversely
Fiber tracts are composed of axons with similar functions
Ascending tracts send impulses to the sensory cortex
Descending tracts send impulses that ultimately control muscles and visceral organs
Ascending up into brain, sends impulses to cortex. (Afferent).
Descending down into the bodies muscles and organs.