Chapter 7 - Part 3 The Nervous System

The Reflex ArcThe Reflex Arc Reflex – rapid, predictable, and involuntary

responses to stimuli Much like a one-way street – once a reflex

begins, it always goes in the same direction Reflex arc – direct route from a sensory

neuron, to an interneuron, to an effector The neural pathway where reflexes occur over

Simple Reflex ArcSimple Reflex Arc

Types of Reflexes and RegulationTypes of Reflexes and Regulation

1. Autonomic reflexes Regulate the activity of smooth muscles, the heart,

and glands. Regulate digestion, elimination, blood pressure,

and sweating. Examples: Secretion of saliva and changes in the

size of the eye pupils.

2. Somatic reflexes Include all reflexes that stimulate the skeletal

muscles. Examples: When you pull your hand away quickly

from a hot object.

CNSCNS

During embryonic development, the CNS first appears as a simple tube, the neural tube The neural tube becomes the brain and

spinal cord The opening of the neural tube enlarges

and becomes the ventricles or chambers Four chambers within the brain Filled with cerebrospinal fluid

The BrainThe Brain

• It weighs a little over 3 lbs.

• It looks wrinkled like a walnut and with the texture of cold oatmeal.

• Largest and most complex mass of nervous tissue in the body.

Regions of the BrainRegions of the Brain

1. Cerebral hemispheres

2. Diencephalon

3. Brain stem

4. Cerebellum

Cerebral Hemispheres (Cerebrum)Cerebral Hemispheres (Cerebrum) Paired (left and

right) superior parts of the brain

Include more than half of the brain mass

Encloses and obscures much of the brain stem How a mushroom

cap covers the top of the stalk

Cerebral Hemispheres (Cerebrum)Cerebral Hemispheres (Cerebrum)

The surface is made of elevated ridges (gyri) and shallow grooves (sulci)

Lobes of the CerebrumLobes of the Cerebrum

Fissures (deep grooves) divide the cerebrum into lobes

Surface lobes of the cerebrum

1. Frontal lobe

2. Parietal lobe

3. Occipital lobe

4. Temporal lobe

Lobes of the CerebrumLobes of the Cerebrum

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Somatic sensory area – receives impulses from the body’s sensory receptors Located in the parietal lobe Allows you to recognize pain, coldness, or a

light touch The body is represented in an upside down

manner in the sensory area The sensory pathways are crossed – the left

side of the cortex receives impulses from the right side of the body

Sensory and Motor Areas of the Sensory and Motor Areas of the Cerebral CortexCerebral Cortex

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Impulses from the special sense organs are interpreted in other cortical areas. Visual area

Located in the posterior part of the occipital lobe

Olfactory area Located deep inside the temporal lobe

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Primary motor area – sends impulses to skeletal muscles Allows us to consciously move our skeletal

muscles Located in the frontal lobe The body is represented upside-down Pathways are crossed Most of the neurons in the this primary

motor area control body areas having the finest motor control (face, mouth, hands)

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Broca’s area – involved in our ability to speak

Damage to this area causes inability to say words properly (you know what you want to say, but you can’t vocalize the words)

Specialized Areas of the CerebrumSpecialized Areas of the Cerebrum

Higher intellectual reasoning – believed to be in the anterior part of the frontal lobe

Complex memories – Appear to be stored in the temporal and frontal lobes

Language comprehension (word meanings) – located in the frontal lobes

Speech Area – allows one to sound out words Located at the junction of the temporal,

parietal, and occipital lobes

Layers of the CerebrumLayers of the Cerebrum

Gray matter

Outer layer

Composed mostly of neuron cell bodies

Cerebral cortex – the outermost gray matter of the cerebrum

Layers of the CerebrumLayers of the Cerebrum White matter

The remaining, deeper cerebral hemisphere tissue

Composed of fiber tracts (bundles of nerve fibers) carrying impulses to or from the cortex

The corpus callosum (large fiber tract) connects the cerebral hemispheres

Allows the cerebral hemi-spheres to communicate with one another

Layers of the CerebrumLayers of the Cerebrum

Although most of the gray matter is in the cerebral cortex, there are several islands of gray matter buried deep within the white matter. Basal nuclei – internal islands of gray matter

Help regulate voluntary motor activities by modifying sent instructions

Individuals who have problems with their basal nuclei are often unable to walk normally or carry out other voluntary movements. Examples: Huntington’s disease and

Parkinson’s disease

DiencephalonDiencephalon

Sits on top of the brain stem

Enclosed by the cerebral hemispheres

Made of three parts

1. Thalamus

2. Hypothalamus

3. Epithalamus

DiencephalonDiencephalon

ThalamusThalamus

Surrounds the third ventricle

The relay station for impulses

Transfers impulses to the correct part of the cortex for localization and interpretation

HypothalamusHypothalamus

Under the thalamus

Important autonomic nervous system center Helps regulate body temperature

Controls water balance

Regulates metabolism

HypothalamusHypothalamus Center for many drives and emotions

An important part of the limbic system (emotions) Thirst, appetite, sex, pain, and pleasure

centers are in the hypothalamus

Regulates the pituitary gland (endocrine organ) and produces two hormones of its own. The pituitary gland hangs from the

anterior roof of the hypothalamus by a slender stalk.

EpithalamusEpithalamus

Forms the roof of the third ventricle

Houses the pineal body (an endocrine gland)

Includes the choroid plexus – knots of capillaries within each ventricle that forms the cerebrospinal fluid

Brain StemBrain Stem Attaches to the spinal cord

About the size of a thumb in diameter and approximately 3 inches long

Functions: 1. Provide a pathway for ascending and descending

tracts

2. Has many small gray matter areas (form cranial nerves and control many vital activities)

Parts of the brain stem:1. Midbrain

2. Pons

3. Medulla oblongata

Brain StemBrain Stem

Slide 7.38bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 7.15a

MidbrainMidbrain

Mostly composed of tracts of nerve fibers Composed primarily of two bulging fiber

tracts – cerebral peduncles (literally, “little feet of the cerebrum”) Function is to convey ascending and

descending impulses Has four rounded protrusions – corpora

quadrigemina These bulging nuclei are reflex centers

involved with vision and hearing

PonsPons

The bulging center part of the brain stem

Mostly composed of fiber tracts

Includes nuclei involved in the control of breathing

Medulla OblongataMedulla Oblongata The lowest part of the brain stem Merges into the spinal cord Is an important fiber tract area Contains important control centers

Heart rate control Blood pressure

regulation Breathing Swallowing Vomiting

Reticular FormationReticular Formation

Diffuse mass of gray matter along the brain stem

Involved in motor control of visceral organs

Reticular activating system (RAS) plays a role in awake/sleep cycles and consciousness

Damage to this area can result in permanent unconsciousness (coma)

Reticular FormationReticular Formation

Slide 7.42bCopyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

Figure 7.15b

CerebellumCerebellum

Projects dorsally from under the occipital lobe

It has two hemi- spheres and a convoluted surface

Has an outer cortex made up of gray matter and an inner region of white matter

Functions of the CerebellumFunctions of the Cerebellum

Involuntary

Provides the precise timing for skeletal muscle activity and controls our balance and equilibrium

Makes our body movements smooth and coordinated

Damage to the CerebellumDamage to the Cerebellum

If the cerebellum is damaged, movements become clumsy and disorganized.

Cannot keep their balance and appear to be drunk because of the loss of muscle coordination.

They are no longer able to touch their finger to their nose with their eyes shut.