Nervous System and Senses - Avon Community School Corporation
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Transcript 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)