1

Mosby items and derived items © 2007, 2003 by Mosby, Inc.

Chapter 13Central Nervous System

2

Coverings of the Brain and Spinal Cord

Two protective coverings: Outer covering is bone Inner covering is the meninges

continues inside the spinal cavity beyond the end of the spinal cord

3

Coverings of the Brain and Spinal Cord

Meninges 3 membranous layers

Dura mater strong, white fibrous tissue outer layer of meninges and

inner periosteum of the cranial bones

Arachnoid mater delicate, cobwebby layer

between the dura mater and pia mater

4

Coverings of the Brain and Spinal Cord

Meninges 3 membranous layers (cont.)

Pia mater innermost, transparent layer adheres to the outer surface of the brain and spinal cord

5

6

Cerebrospinal Fluid

Functions Provides a supportive, protective cushion Reservoir of circulating fluid, which is monitored by the brain to

detect changes in the internal environment

Fluid spaces Cerebrospinal fluid— found around the brain and spinal cord

7

Cerebrospinal Fluid

Fluid spaces (cont.) Ventricles— fluid-

filled spaces within the brain; four ventricles within the brain

8

Spinal Cord

Structure of the spinal cord Oval cylinder that tapers slightly from above

downward Two bulges, one in the cervical region and

one in the lumbar region

9

10

Spinal Cord

Structure of the spinal cord (cont.) Nerve roots

Fibers of dorsal nerve root Carry sensory information into the spinal canal

Fibers of ventral nerve root Carry motor information out of the spinal cord

Interneurons are located in the spinal cord’s gray matter core

11

Dorsal (posterior) nerve root

Ventral (anterior) nerve root

12

Spinal Cord

Structure of the spinal cord (cont.)

Gray matter

Consists predominantly of cell bodies of interneurons and motor neurons

In transverse section, looks like an H

White matter

Surrounds the gray matter

consists of a large bundle of axons divided into tracts

13

Spinal Cord

Functions of the spinal cord Provides conduction routes to and from the brain

Ascending tracts (sensory)— conduct impulses up the cord to the brain

Descending tracts (motor)— conduct impulses down the cord from the brain

Bundles of axons compose all tracts

14

Spinal Cord

Functions of the spinal cord (cont.) Important ascending

(sensory) tracts = BLUE crude touch, pain, and

temperature pressure discriminating touch and

conscious kinesthesia (proprioception)

subconscious kinesthesia touch related to visual

reflexes

15

Spinal Cord

Functions of the spinal cord (cont.)Important descending (motor) tracts

voluntary movements on opposite side of the body

voluntary movements on same side of body maintain posture during movement transmit impulses that coordinate body movements and

maintenance of posture head and neck movements during visual reflexes coordination of posture and balance

Spinal cord— reflex center for all spinal reflexes reflex centers are located in the gray matter of the

cord

16

17

The Brain

Structures of the brainstem Medulla oblongata

Lowest part of the brainstem Composed of white matter and a network of gray and

white matter called the reticular formation Nuclei— clusters of neuron cell bodies located in the

reticular formation

18

The Brain Structures of the brainstem (cont.)

Pons Located above the medulla and below the midbrain Composed of white matter and reticular formation

Midbrain Located above the pons and below the cerebrum; forms the

midsection of the brain Composed of white tracts and reticular formation conduct impulses between the midbrain and cerebrum Red nucleus and substantia nigra (“black matter”)

clusters of cell bodies of neurons involved in muscular control

19

The Brain

Functions of the brainstem Performs sensory, motor, and reflex functions Nuclei in medulla— contain reflex centers

Of primary importance— cardiac, vasomotor, and respiratory centers

Nonvital reflexes— vomiting, coughing, sneezing, etc.

Pons— help regulate respiration

20

The Brain

Structure of the cerebellum Gray matter makes up the cortex, and white matter

predominates in the interior Cerebellum has numerous sulci (groove) and delicate,

gyri (raised areas)

21

The Brain

Functions of the cerebellum coordinates movements to produce the intended action General functions

produce skilled movements by coordinating the activities of muscles

maintains balance Controls posture smooth movements and make movements efficient and

coordinated Processes sensory information

22

Stand Up!

23

The Brain

Diencephalon Located between the cerebrum and the midbrain Consists of several structures: thalamus, hypothalamus, pineal

gland, and several others Thalamus

Dumbbell-shaped mass of gray matter made up of many nuclei plays role in processing auditory and visual input

24

25

The Brain

Thalamus (cont.)Serves as a major relay station for sensory impulses

on their way to the cerebral cortexPerforms the following primary functions:

Two parts for sensations: conscious recognition of the crude, less critical

sensations of pain, temperature, and touch Neurons relay all kinds of sensory impulses, except

possibly olfactory, to the cerebrum emotions by associating sensory impulses with feeling of

pleasantness and unpleasantness arousal mechanism

26

The Brain

Diencephalon (cont.) Hypothalamus

lies beneath (hypo) the thalamus Small but functionally important area of the brain,

performs many functions of greatest importance for survival and enjoyment

Links mind and body Links nervous system to endocrine system

27

The Brain

Hypothalamus (cont.) Summary of hypothalamic functions

Regulator and coordinator of autonomic activities Major relay station between the cerebral cortex and lower

autonomic centers crucial part of the route by which emotions can express

themselves in changed bodily functions maintaining water balance arousal mechanism regulating appetite maintaining normal body temperature

28

The Brain

Diencephalon (cont.) Pineal gland

Involved in regulating the body’s biological clock Produces melatonin as a “timekeeping hormone”

Melatonin is made from the neurotransmitter serotonin Melatonin levels increase when sunlight is absent and

decreases when sunlight is present, thus regulating the circadian (daily) biological clock (Figure 13-15)

Melatonin is the “sleep hormone”

29

30

The Brain

Structure of the cerebrum Cerebral cortex

Largest and uppermost division of the brain consists of right and left cerebral hemispheres each hemisphere is divided into four lobes:

Frontal lobe Parietal lobe Temporal lobe Occipital lobe

31

32

The Brain

Cerebral cortex (cont.)Cerebral cortex— outer surface made up of six

layers of gray matter Gyri— raised areas Sulci— shallow grooves

33

The Brain

Cerebral cortex (cont.) Fissures— deeper grooves, divide each cerebral

hemisphere into lobes Central sulcus— groove between frontal and parietal

lobes Lateral fissure— groove between temporal lobe below

and parietal lobes above

34

Structure of the cerebrum

Basal nuclei (or cerebral nuclei) Basal nuclei— islands of gray matter located deep

inside the white matter of each hemisphere Unsure of exact function but important in regulating

voluntary motor functions, especially repetitive actions Example: maintaining posture, walking

35

The Brain

Functions of the cerebral cortex Certain areas of

cortex have certain functions

Transverse gyrus— auditory area

Occipital lobe— visual areas

Precentral gyrus- somatic motor

Postcentral gyrus- somatic sensory

36

The Brain

Functions of the cerebral cortex (cont.) Sensory functions of the cortex

Cortex contains a “somatic sensory map” of the body

Senses send information to primary sensory areas, as well as to other parts of the brain

37

The Brain

Motor functions of the cortex For normal movements to occur,

many parts of the nervous system must function

Precentral gyrus primary somatic motor area controls individual muscles

Secondary motor area (premotor) in the gyrus immediately anterior

to the precentral gyrus activates groups of muscles

simultaneously

38

The Brain Integrative functions of the cortex

Consciousness State of awareness of one’s self,

one’s environment, and other beings

Depends on excitation of neurons from the reticular formation

Two about reticular activating system:

Functions as the alert system for the cerebral cortex

Its functioning is crucial for maintaining consciousness

39

The Brain

Integrative functions of the cortex (cont) Language

Ability to speak and write words AND ability to understand spoken and written words

Left cerebral hemisphere contains speech centers in approximately 90% of the population

FYI: Explains Broca’s and Wernicke’s area

40

The Brain Integrative functions of the cortex (cont.)

Emotions Limbic system— also known as the “emotional brain”

hippocampus Have primary connections with other parts of the

brain, such as thalamus, amygdaloid nucleus, and hypothalamus

FYI: removal of hippocampus causes inability to recall new info

41

The Brain

Integrative functions of the cortex (cont) Memory

One of the major human mental activities Cortex is capable of storing and retrieving both

short- and long-term memory Temporal, parietal, and occipital lobes are among

the areas responsible for short- and long-term memory

Cerebrum’s limbic system plays a key role in memory

42

The Brain

Right and left hemispheres of the cerebrum specialize in different functions

Both sides communicate with each other to accomplish complex functions

Left hemisphere is responsible for: Language functions Dominating control of certain hand movements

Right hemisphere is responsible for: Auditory Tactual perception Perceiving and visualizing spatial relationships

43

Cycle of Life: Central Nervous System

The development and degeneration of the CNS is the most obvious functional change over the life span

Development of the brain and spinal cord begins in the womb

Lack of development in the newborn is evidenced by lack of: Language- both speech and reading Comprehension of spatial relationships Complex motor skills- walking

44

Cycle of Life: Central Nervous System

Complex functions develop by adulthood Late adulthood— tissues degenerate

Profound degeneration— unable to perform complex functions

Milder degeneration— temporary memory lapse or difficulty with complex motor tasks

45

The Big Picture: The Central Nervous System and the Whole Body

Central nervous system ultimate regulator of the body essential to survival

Able to integrate bits of information from all over the body, make sense of them, and make decisions