Download Nervous System and Senses - Avon Community School Corporation


Sensors- monitor external and internal
environment

Processing- receives information,
integrates it, and decided what to do

Effectors- carries messages to effectors
informing them what to do

Neurons- relay and process messages

Neuroglial- provide support to the
neurons

Microglial cells
› Scattered throughout CNS
› Phagocytize bacteria or cellular debris

Oligodendrocytes
› Along nerve fibers
› Provide myelin sheath (made of a fatty
substance called myelin) around axon in
CNS

Schwann cells
› Same as oligodendrocytes but in PNS

Astrocytes
› Provide connection between a neuron and
a blood vessel
› Provide support, help regulate ion
concentrations in tissue, make-up scar tissue
after injury

Ependymal cells
› Forms epithelial-like linings on the ousides of
specialized parts or lining cavities within the
CNS

Body Structure
› Cell Body
› Dendrites- carry messages to cell body
› Axons – carry messages away from cell body

Structures
› Large nucleus with easily seen nucleolus
› Chromatophilic substance- rough ER
› Neurofibrils- help support cell shape
Can be myelinated or unmyelinated
 PNS

› Schwann cells form myelin sheath
› Nodes of Ranvier- small breaks in myelin
sheath

CNS
› Oligodendrocytes form myelin
› Myelinated neurons form white matter
› Unmyelinated neurons form gray matter

Multipolar
› Many small branched dendrites
› One axon
› Found in CNS

Bipolar
› Two processes off of cell membrane (one axon
and one dendrite)
› Neurons in special sense organs

Unipolar
› One process off of cell body (one axon)
› Found throughout PNS

Sensory (afferent) neurons
› Have sensitive dendrites that are stimulated by
changes in environment
› Message is taken into CNS
› Usually unipolar or sometimes bipolar

Interneurons
› Transfer, direct, and process messages within
CNS
› Usually multipolar

Motor (efferent) neurons
› Carries message out of CNS to effoctors
› Usually multipolar

Inside the neuron
› High in K+
› High in negatively charged ions

Outside the neuron
› High in Na+

Result
› K+ tends to diffuse out of cell
› Na+ tends to diffuse into cell
› Negative ions cannot cross
Na/K pump- helps to restore
concentration gradient across the cell
membrane
 Resting potential- difference is electrical
charge across the membrane

› Established by concentration gradients of
various ions
› Inside of the membrane has a negative
charge of 70 mv
› Membrane is said to be polarized


Stimuli cause changes to the resting potential
by making the inside of the membrane less
negative
Once a stimulus happens
› The stimulus may not be strong enough to reach
threshold potential; cell membrane will return to
resting potential
› The stimulus may be strong enough to reach
threshold potential and start an action potential

Summation- if they occur close enough
together, stimuli that would be to small to
reach threshold potential add there effects
together to reach the threshold
Starts at trigger zone of axon
 Threshold stimulus open sodium channels
 Sodium moves into axon

› Because of the concentration gradient
› Because of the negative charge that
attracts the positive ions
This depolarizes the membrane as
negative charge diminishes
 Potassium channels open and potassium
moves out of the axon, repolarizing the
membrane

Action potential at the trigger zone
stimulates the next part of the axon to do
a action potential
 Potentials spread along the axon like a
wave
 Unmyelinated axons- wave continues
uninterrupted; relatively slow
 Myelinated axons- wave goes through
saltatory conduction (jump from one
node to the next); very fast

All-or-none- neuron does not react until
a threshold stimulus is applied, but once
it is applied it reacts fully
 Stimuli greater than threshold levels don’t
change the size of the response but its
frequency
 After a action potential, there is a brief
period of time called the refractory
period where the nerve cannot be
stimulated again.

The connection between two neurons
 Don’t touch, separated by synaptic cleft
 One-way communication between axon
of presynaptic neuron and dendrite of
postsynaptic neuron
 Neurotransmitters are made in the
synaptic knob of the axon, stored in
synaptic vesicles, and cross the cleft
when needed

A neurotransmitter that puts a neuron
closer to an action potential
(facillitation)or causes an action
potential is exitatory
 A neurotransmitter that moves a neuron
further away from an action potential is
inhibitory
 A neuron responds according to the sum
of all the neurotransmitters received at
one time

Acetylcholine
 Monoamines – modified amino acids
 Amino acids
 Neuropeptides- short chains of amino
acids
 Imbalances of neurotransmitters can
create disorders like depression
 Many drugs imitate neurotransmitters

When an action potential reaches the
end of an axon, Ca channels in the
neuron open
 Ca rushes in and cause the synaptic
vesicles to fuse with the cell membrane
and release the neurotransmitters into
the synaptic cleft
 After binding, neurotransmitters will either
be destroyed in the synaptic cleft or
taken back in to surrounding neurons
(reuptake)

Groups of highly interconnected neurons
that work together in the CNS
 Convergence- axons from different
parts of the nervous system connect to
the same neuron combining their affects
 Divergence- a message from one
neuron is sent to many neurons at once;
amplifies message

Nerves are made of bundled axons,
called nerve fibers
 Nerve fibers

› Sensory (afferent)- carry messages to CNS
› Motor (efferent)- carry messages from CNS
to effectors

Nerves- same definitions hold true, but
most nerves contain both types of fibers
and are called mixed nerves
A nerve fiber (axon) is surrounded with
endoneurium
 Nerve fibers are bundled togther and
surrounded with perineurium to form a
fascicle
 Fascicles are bundles together and
surrounded with epineurium to form a
nerve

Path that the message takes through the
body
 Includes

› Sensor
› Sensory neuron
› Interneuron
› Motor neuron
› Effector
Simplest nerve pathway is a reflex
 Reflexes without pain

› Involve only sensory and motor neurons
› Ex: knee-jerk reflex

Reflexes with pain
› Involve interneurons in CNS
› Ex: withdrawal reflex

Central nervous system

Consists of brain and spinal cord

Made of both gray and white matter

Covered in meningies
Cranial Bone
 Dura mater- first layer; tough, fibrous
connective tissue; forms inner periosteum
of crania bone; folds into the cranium in
some places to form division walls in the
brain
 Arachnoid mater- web-like membrane
over CNS; does not dip into crevices

Subarachnoid space- below arachnoid
layer; contains cerebrospinal fluid
 Pia mater- lower layer of meninges; forms
a tight covering over brain; does dip into
crevaces


Same exept:
› Vertebrae
› Epidural space- filled with loose connective
and adipose tissue
› Dura mater
› All other are the same
Flows through ventricles (spaces in
brain), in the subarachnoid space, and
through the central canal of the spinal
cord
 Fluid is made by the choroid plexus

Stretches from brain to intervertebral disk
between first and second lumbar
vertebrae
 31 pairs of spinal nerves come of the
cord
 Gray matter core surrounded by white
matter

Responsible for communication between
brain and body and spinal reflexes
 Ascending tracts- nerves that send info
to brain
 Descending tracts- nerves that send into
to effectors

Made up off about 100 billion neurons
 Four main sections

› Cerebrum- nerves for processing sensory and
motor function; higher functions like
reasoning
› Diencephalon- processes sensory
information
› Brainstem- regulates certain body functions
like breathing
› Cerebellum- coordinates skeletal muscle
movements
Divided into two hemispheres (right and
left)
 Corpus callosum- connects the two sides
 Other structures

› Convolutions- ridges
› Sulcus- shallow groove
› Fissure- deep groove
Frontal lobe
 Parietal lobe
 Temporal lobe
 Occipital lobe
 Insula
 Each lobe has unique functions

Cerebral cortex- thin layer of gray matter
surrounding cerebral hemisphere;
contain most of the cell bodies in the
cerebrum
 Inner part of the cerebrum is mainly
made of white matter


Motor areas
› Primarily in frontal lobe
› Send information out to effectors

Sensory areas
› Interpret information from sensors
› Area in parietal, temporal, and occipital
lobes

Association areas
› Analyze information from sensors
› Located in areas in all lobes mentioned
above
Located between the cerebral
hemispheres above the brainstem
 Contains

› Thalamus
› Hypothalamus
› Pituitary gland
› Pineal gland
Thalamus- routes sensory impulses to the
correct region of the cerebrum
 Hypothalamus- monitors many internal
conditions, link between nervous and
endocrine system
 Limbic system (thalamus, hypothalamus,
and basal nuclei)- controls experience
and expression (feelings)

Connection between spinal cord and
the rest of the brain
 Contains

› Midbrain
› Pons
› Medulla oblongata
Located between diencephalon and
pons
 Contains some visual and auditory reflexs
 Serves as the main connection for motor
neurons between spinal cord and upper
part of brain

Rounded bulge between midbrain and
medulla oblongata
 Relays impulses between medulla and
cerebrum or between cerebrum and
cerebellum

Lowest part of brain, connect to spinal
cord
 All ascending and descending tracts run
through the oblongata
 Serves as a control center for many vital
function like heart rate, blood pressure,
and respiratory center

Located in the lower back part of the
brain
 Structured liked cerebrum with inner
white matter core and gray matter
covering
 Controls posture and complex skeletal
movements

Peripheral Nervous system
 Includes

› 12 pairs of cranial nerves
› 31 pairs of spinal nerves

Divided into
› Somatic nervous system- controls conscious
activities; connects to skin and skeletal
muscles
› Autonomic nervous system- controls
unconscious activities; connects to internal
organs or structures

Two branches
› Parasympathetic- control under more
normal conditions
› Sympathetic- control under stress or
emergency conditions (fight or flight)
› Usually these two have antagonistic effects
or any one organ or structure; either might
be utilized to maintain homeostasis
Chemoreceptors- respond to changes in
chemical concentrations
 Pain receptors- respond to tissue
damage
 Thermoreceptors- respond to
temperature changes
 Mechanoreceptors- respond to changes
in pressure or movement
 Photoreceptors- respond to light

The brain is where sensations come from;
impulses are interpreted based on what
area of the brain they end up in
 The brain projects the sensation back to
the sensor so the person feels the
sensation at the sensor


Ability of the PNS or CNS to block sensory
impulses that it deems unimportant or
has become used to
Sensors are widely spread throughout
body and are fairly simple
 Include

› Touch
› Pressure
› Temperature
› Pain

Three kinds of receptors
› Free nerve endings- sensations of touch and
pressure
› Meissner’s corpuscles- provide sensations of
light touch, usually located in regoins of skin
without hair
› Pacinian corpuscles- respond to heavy
pressure, located in deeper tissues
Warm and cold receptors (free nerve
endings)
 Extreme temperatures stimulate pain
receptors
 Receptors adapt very fast

Sensations arise from free nerve ending
throughout body except brain
 Pain receptors adapt poorly
 Visceral pain- referrers pain to areas on
the skin

Sensations arise from specially adapted
sensors
 Includes

› Smell
› Taste
› Hearing
› Equilibrium
› Sight
Olfactory receptors are located in small
patches along the roof of the nasal
cavity
 They are chemoreceptors so incoming
gases must dissolve in the mucous
covering the nasal cavity
 Dissolved particle interact with the cilia
and may stimulate an action potential

Taste buds- located primarily on tongue,
although some found on roof of mouth
and sides of the throat
 Each taste bud has many gustatory
receptors and tiny cilia projections
 These are chemoreceptors so incoming
foods must be dissolved in saliva to be
tasted


Four main taste areas
› Sweet- concentrated on the tip of the
tongue
› Sour- concentrated along the margins of the
tongue
› Bitter- concentrated along the back of the
tongue
› Salty- spread throughout
Sound waves are directed into the ear
by the external auricle
 They travel down the external acoustic
meatus
 Bounce against tympanic membrane
(eardrum) and make the eardrum move

Occurs in the tympanic cavity
 Has three small auditory ossicles
 Vibrations at the tympanic membrane
cause the three bones to vibrate
 The final bone vibrates against the oval
window of the inner ear
 The bones amplify the sound
 Eustachian tube- connects middle ear to
throat, equalizes pressure for eardrum


Includes two labyrinths
› Osseous labyrinth- bony canals
› Membranous labyrinth- membrane-bound
tube inside the bony canals
› Perilymph separates the two
› Endolymph is found inside the membranous
labyrinth

Two parts to the labyrinth
› Semicircular canals- used in equillibrium
› Cochlea – organ for hearing
Vibrations at the oval window cause
vibrations in the perilymph of the scala
vestibuli
 Vibrations pass through vestibular
membrane into endolymph
 Vibrations than pass through basilar
membrane to perilymph of scala
tympani
 Organ of Corti- found in basilar
membrane, contains hearing sensors
with hairs; vibrations cause hairs to move


Two divisions
› Static Equilibrium- senses posture while at rest
 Occurs in vestibule
 Position of head is determined by hairs on the
macula, hairs respond to shifting of otoliths
› Dynamic Equilibrium – maintaining balance
during movement
 Occurs in the semicircular canals, in particular
the ampulla
 Movements cause the perilymph to stimulate
hairs in the ampulla
Visual receptors located in eye
 Accessory organs aiding eye

› Eyelids
› Lacrimal apparatus- gland that produces
tears to cleanse and protect eye and ducts
to carry the tears to the nasal cavity
› Muscle- move the eye

Posterior portion
› Sclera- tough fibrous covering
› Choroid coat- contains melanocytes to help
darker the inside of the eye
› Retina- thin complex inner layer that is
continuous with the optic nerve and
contains the receptors
› Vitreous humor- jelly-like fluid filling internal
eye

Anterior portion
› Cornea- transparent covering
› Aqueous humor- fluid that is made between
the iris and lens but can move to between
the cornea and the iris through the pupil
› Iris- pigmented layer containing smooth
muscle to control size of pupil
› Aqueous humor
› Lens- layer that focuses the image on the
retina; can change shape to change focus

Contains receptors
› Rods- black-and-white vision; more indistinct
image; pigment is rhodopsin
› Cones- color vision; refined image; pigments
are sensitive to red, green, and blue hues
Fovea centralis- part of retina containing
high concentration of cones; area with
sharpest focus
 Optic disc- area of retina with
connection to optic nerve; lacks
receptors (blindspot)
