NERVOUS SYSTEM, THE BRAIN, AND THE SENSORY ORGANS

BY: 6TH GRADE

SCA STUDENTS

2017-18

MODIFIED FROM

COPYRIGHT © 2003

PEARSON EDUCATION,

INC. PUBLISHING AS

BENJAMIN CUMMINGS

Functions of the Nervous System1. Sensory input – gathering information

• To monitor changes occurring inside and outside the body (changes = stimuli)

2. Integration –

• to process and interpret sensory input and decide if action is needed.

3. Motor output

• A response to integrated stimuli

• The response activates muscles or glands

Structural Classification of the Nervous System

• Central nervous system (CNS)

• Brain

• Spinal cord

• Peripheral nervous system (PNS)

• Nerve outside the brain and spinal cord

Functional Classification of the PNS

• Sensory (afferent) division

• Nerve fibers that carry information to the CNS (spinal cord and brain)

• Motor (efferent) division

• Nerve fibers that carry impulses away from the CNS

• Motor (efferent) division

• Two subdivisions

• Somatic nervous system = voluntary

• Autonomic nervous system = involuntary

Organization of the Nervous SystemNeuron (Nerve Cell) Anatomy❖ Neurons = nerve cells

➢ Cells specialized to transmit messages

❖ Major regions of neurons

• Cell body – nucleus and metabolic center of the cell

• Processes – fibers that extend from the cell

body (dendrites and axons)

❑ Cell body

➢ Nucleus

➢ Large nucleolus

❑ Extensions outside the

cell body

➢ Dendrites – conduct impulses

toward the cell body

➢ Axons – conduct impulses away

from the cell body

Neuron Cell Body Location• Most are found in the central nervous system

• Gray matter – cell bodies and unmyelinated (not insulated) fibers

• Nuclei – clusters of cell bodies within the white matter of the CNS

• Ganglia – collections of cell bodies outside the CNS

Functional Classification of Neurons

• Sensory (afferent) neurons

• Carry impulses from the sensory receptors

• Cutaneous sense organs

• Proprioceptors – detect stretch

or tension

• Motor (efferent) neurons

• Carry impulses from the CNS

The Reflex Arc• Reflex – rapid, predictable, and involuntary responses to stimuli

• Reflex arc – direct route from a sensory neuron, to an interneuron, to an effector

Simple Reflex Arc

Types of Reflexes and Regulation• Autonomic reflexes

• Smooth muscle regulation

• Heart and blood pressure regulation

• Regulation of glands

• Digestive system regulation

• Somatic reflexes

• Activation of skeletal muscles

Central Nervous System (CNS)• CNS develops from the embryonic neural tube

• The neural tube becomes the brain and spinal cord

• The opening of the neural tube becomes the ventricles (brain chambers)

• Four chambers within the brain

• Filled with cerebrospinal fluid

Regions of the Brain

o Cerebrum

o Cerebellum

o Brain stem

o Diencephalon

*each region is subdivided into lobes

Cerebral Hemispheres (Cerebrum)• Paired (left and right) superior parts of the brain

• Include more than half of the brain mass

• The surface is made of ridges

(gyri) and grooves (sulci)

• Fissures (deep grooves) divide

the cerebrum into lobes

• Surface lobes of the cerebrum

• Frontal lobe

• Parietal lobe

• Occipital lobe

• Temporal lobe

• Somatic sensory area – receives

impulses from the body’s sensory

receptors

• Primary motor area – sends

impulses to skeletal muscles

• Broca’s area – involved in our

ability to speak

Lobes of the Cerebrum

Sensory and Motor Areas of the Cerebral Cortex

Specialized Area of the Cerebrum• Interpretation areas of the cerebrum

• Speech/language region

• Language comprehension region

• General interpretation area

•Cerebral areas involved in special senses

•Gustatory area (taste)

•Visual area

•Auditory area

•Olfactory area

Brain Stem• Attaches to the spinal cord

• Parts of the brain stem

• Midbrain, Pons, and

Medulla oblongata

Midbrain• Mostly composed of tracts

of nerve fibers

• Reflex centers for vision

and hearing

• Cerebral aquaduct

connects the 3rd and 4th ventricles to allow flow of cerebral fluid

Pons• The bulging center part of the brain stem, mostly composed of fiber tracts, that

includes nuclei involved in the control of breathing

Medulla Oblongata• The lowest part of the brain stem, that merges into the spinal cord, includes

important fiber tracts, and contains important control centers for…..

• Heart rate control, blood pressure regulation, breathing, swallowing, and vomiting

Cerebellum• Two hemispheres with convoluted surfaces

• Provides involuntary coordination of body movements

Protection of the CNS• Scalp and skin

• Skull and vertebral column

• Meninges

• Cerebrospinal fluid

• Blood brain barrier

Traumatic Brain Injuries (TBI)▪ Concussion

▪ Slight or mild brain injury

▪ Bleeding & tearing of nerve fibers happened

▪ Recovery likely with some memory loss

▪ Contusion

▪ A more severe TBI

▪ Nervous tissue destruction occurs

▪ Nervous tissue does not regenerate

▪ Cerebral edema

▪ Swelling from the inflammatory response

▪ May compress and kill brain tissue

▪ Cerebral edema

▪ Swelling from the inflammatory response

▪ May compress and kill brain tissue

▪ Subdural hematoma

▪ Collection of blood below the dura (this is a bruise on the brain)

Cerebrovascular Accident (CVA)• Commonly called a stroke

• The result of a ruptured blood vessel supplying a

region of the brain

• Brain tissue supplied with oxygen from that blood

source dies

• Loss of some functions or death may result

Alzheimer’s Disease• Progressive degenerative brain disease

• Mostly seen in the elderly, but may begin in middle age

• Structural changes in the brain include abnormal

protein deposits and twisted fibers within neurons

• Victims experience memory loss, irritability, confusion

and ultimately, hallucinations and death

Spinal Cord• Extends from the medulla oblongata to the T12 region

• Below T12 is the cauda equina (a collection of spinal

nerves)

• Enlargements occur in the cervical and lumbar regions

Peripheral Nervous System• Nerves and ganglia outside the CNS

• Nerve = bundle of neuron fibers

• Neuron fibers are bundled together by connective tissue that strengthens and

insulates the neurons

Spinal Nerves• There is a pair of spinal nerves

at the level of each vertebrae.

• The spinal nerves connect the

CNS to all of the other areas of

the body.

Autonomic Nervous

System• The involuntary branch of the nervous

system

• Consists of only motor nerves

• Divided into two divisions: Sympathetic

division & Parasympathetic division

• Sympathetic – “fight-or-flight”

• Response to unusual stimulus

• Takes over to increase activities

• Remember as the “E” division =

exercise, excitement, emergency,

and embarrassment

• Parasympathetic – housekeeping

activities

• Conserves energy

• Maintains daily necessary body

functions

• Remembered as the “D” division -

digestion, defecation, and diuresis

Comparison of Somatic and Autonomic Nervous Systems

✓ The eye is the organ of vision.

✓ It has a complex structure consisting of a

transparent lens that focuses light on the retina.

✓ The retina is covered with two basic types of

light-sensitive cells-rods and cones.

✓ The cone cells are sensitive to color and are located

in the part of the retina called the fovea, where the

light is focused by the lens.

✓ The rod cells are not sensitive to color, but have greater sensitivity to light than the cone cells.

✓ Rodare located around the fovea and are responsible for peripheral vision and night vision.

✓ The eye is connected to the brain through the optic nerve.

✓ The point of this connection is called the "blind spot" because it is insensitive to light.

✓ Experiments have shown that the back of the brain (visual cortex) maps the visual input from the

eyes.

✓ Being nearsighted or farsighted depends on the length of your eye.

✓ People with blue eyes all share a common ancestor.

✓ Your eyes actually see everything upside down, but your brain sorts it out.

✓ Your eyes can get sunburned too.

✓ We blink 28,000 times per day.

✓ 20/20 vision isn't perfect vision, it's just normal.

✓ The human eye can detect over 10 million different colors.

✓ The ear is the organ of hearing.

✓ The outer ear protrudes away from the head and

is shaped like a cup to direct sounds toward the

tympanic membrane, which transmits vibrations to

the inner ear through a series of small bones in the

middle ear called the malleus, incus and stapes.

✓ The inner ear, or cochlea, is a spiral-shaped chamber

covered internally by nerve fibers that react to the

vibrations and transmit impulses to the brain via the auditory nerve.

✓ The brain combines the input of our two ears to determine the direction and distance of sounds.

✓ Your ears contain the three smallest bones in the human body: the malleus, incus, and stapes

✓ Ears help the body maintain equilibrium.

✓ The outside of the ear is called the pinna which acts as a funnel, collecting and amplifying sound

for the inner ear.

✓ Your ability to hear high frequencies deteriorates as you get older, because the hair cells closest

to your outer ear begin to break down.

✓ Sound travels at roughly 770 miles per hour through our atmosphere.

✓ Earwax is used to catch dirt and debris.

✓ The hardest bone in the human body is the temporal bone and it shapes the inner ear where its

shape helps process sounds in the ear.

✓ The receptors for taste, called taste buds, are

situated chiefly in the tongue, but they are also

located in the roof of the mouth and near the pharynx.

✓ They are able to detect four basic tastes: salty, sweet,

bitter, and sour.

✓ The tongue also can detect a sensation called "umami“

from taste receptors sensitive to amino acids.

✓ Generally, the taste buds close to the tip of the tongue

are sensitive to sweet tastes, whereas those in the back

of the tongue are sensitive to bitter tastes.

✓ The taste buds on top and on the side of the tongue are sensitive to salty and sour

✓ Your taste buds have a lifespan that can last from 10 days to two weeks. It is possible to kill your

taste buds by burning your tongue, but they regenerate rather quickly. However, smoking can

actually reduce taste bud “pods” (called papillae) and therefore dull your taste buds more

permanently.

✓ Taste buds are made up of microvilli, which are microscopic hairs that send signals to the brain

to tell us how to process and identify how things taste.

✓ Your taste buds need the help of your nose’s olfactory senses to send the correct message to

the brain about how something tastes. The flavor of something is determined by the taste and

the smell senses.

✓ When you smell an odor you are also tasting it.

✓ The nose is the organ responsible for the sense

of smell.

✓ The cavity of the nose is lined with mucous

membranes that have smell receptors connected

to the olfactory nerve.

✓ The smells themselves consist of vapors of

various substances.

✓ The smell receptors interact with the molecules of these vapors and transmit the sensations to

the brain.

✓ The nose also has a structure called the vomeronasal organ whose function is being sensitive to

pheromones that influence the reproductive cycle.

✓ The sense of smell is sometimes temporarily lost when a person has a cold.

✓ The sense of smell comes about through the stimulation of specialized cells in our nasal cavities

— cells that are similar to the sensory cells of the antennae of invertebrates. The human

olfactory system works when odorant molecules bind to specific sites on the olfactory receptors,

which are used to detect the presence of smell.

✓ And it all comes together at the glomerulus, a structure which transmits signals to the olfactory

bulb — a part of the brain directly above the nasal cavity and below the frontal lobe. The end

result is the subjective experience we call smell.

✓ The smell receptors are sensitive to seven types of sensations that can be characterized into 10

categories: Fragrant (e.g. florals and perfumes) Fruity (all non-citrus fruits)

Citrus (e.g. lemon, lime, orange) Woody and resinous (e.g. pine or fresh cut grass)

Chemical (e.g. ammonia, bleach) Sweet (e.g. chocolate, vanilla, caramel)

Minty and peppermint (e.g. eucalyptus and camphor) Toasted and nutty (e.g popcorn, peanut butter, almonds)

Pungent (e.g. blue cheese, cigar smoke) Decayed (e.g. rotting meat, sour milk)

✓ The sense of touch is distributed throughout the body.

✓ Nerve endings in the skin and other parts of the body

transmit sensations to the brain.

✓ Some parts of the body have a larger number of

nerve endings and, therefore, are more sensitive.

✓ Four kinds of touch sensations can be identified: cold,

heat, contact, and pain.

✓ Hairs on the skin magnify the sensitivity and act as an early warning system for the body.

✓ The sense of touch is the first to develop in humans at about 8 weeks into the gestation period.

✓ Touch stimulates the brain to release endorphins.

✓ The skin is your body’s largest organ and contains more than 4 million sensory receptors.

✓ Among the body’s most sensitive areas are the lips, the back of the neck, the fingertips, and the

soles of the feet.

✓ The least sensitive area of your body is the middle of your back.

✓ Being touched can reduce stress, by lowering levels of hormones like cortisol, which can reduce

blood pressure and heart rate.

✓ Pain is the body’s warning system and that’s why people have more receptors for pain than for

any other sensations.

✓ Thermoreceptors perceive sensations related to temperature, but they may be stimulated when

the surface of the skin drops below 41° (which is why your skin starts to feel numb in icy

temperatures) or rises above 113° (at which point pain receptors take over to avoid burns).

Resources

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InnerBody.com, Jan. 2018, www.innerbody.com/htm/body.html.

“Human Body Systems.” Carolina Biological Supply: World-Class Support for Science &

Math, Carolina Biological Supply, Mar. 2018, www.carolina.com/teacher-

resources/Interactive/human-body-systems/tr40161.tr.

“Nervous System." Fact Monster. © 2000–2017 Sandbox Networks, Inc., publishing as

Fact Monster. May 2018.

<https://www.factmonster.com/dk/encyclopedia/science/Nervous-system/>.

Dowshen, Steven. “Body Basics.” Rady Children's Hospital-San Diego, The Nemours

Foundation/KidsHealth., Mar. 2012, www.rchsd.org/health-articles/nervoujs-system/.