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Nervous System
Chapters 48 and 49
Nervous System Diversity
• Cnidarians – (hydra, sea stars), have nerve
nets that control the gastrovascular cavity
• Cephalization – shows greater complexity
of the nervous system
• Annelids/Anthropods – (segmented worms),
have ganglia (clusters of neurons), have
small brains
Nervous System Diversity
Info Processing
Info Processing: Sensory input, integration and
motor output
Types of Neurons
• Sensory Neurons – transmit info from sensors
(that detect internal or external stimuli) to
interneurons (the CNS)
• Interneurons – either the spinal cord or brain,
integrate the sensory input and send message the
motor neurons
• Motor Neurons – send message from interneurons
to effector cells (muscles or endocrine cells)
“Knee Jerk” Reflex
Describe the function of each in the reflex arc:
sensors, sensory neurons, interneurons, motor
neurons, effector cells
The Neuron
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Cell Body – contains nucleus
Dendrites – branches that receive signals
Axon – extension that transmits signals
Axon Hillock – conical region of axon where it joins cell body
Myelin Sheath – lipid layers around axons
Nodes of Ranvier – spaces between myelin sheath
Synaptic Terminal – branches of axon, send neurotransmitters
Neuron Diversity
Glia Cells
• Supporting cells of the neuron
• Ex: astrocytes, radial glia, oligiodendrocytes and
schwann cells
• Astrocytes: structural support, form blood-brain
barrier, stem cells
• Radial Glia: form tracks for newly formed neurons
to move from neural tube, stem cells
• Oliodendrocytes (CNS) and Schwann Cells
(PNS): form myelin sheaths which insulate axon
and allow for faster impulses
Schwann Myelin
Multiple Sclerosis- autoimmune disease, T
cells destroy myelin sheaths
Resting Potential = -70mV
The electrical potential difference between the outside and
inside of a plasma membrane is called the membrane
potential. A membrane potential of a cell at rest is -70mV
Resting Potential
• Resting Potential (when a neuron is not signaling)
is -70mV
• The inside is negative relative to the outside
• Maintained by the sodium potassium pump, which
pumps 3 Na+ out of the cell for every 2 K+ it
pumps in, and K+ ion channels that allow for the
diffusion of K+ out of the cell
• Na+ is not allowed in (the Na+ ion channels are
closed)
Stimulating a Neuron
• The membrane potential changes from its
resting value when the membrane’s
permeability to ions changes – triggers
signaling
• Types of Ion Channels: Stretch Gated,
Ligand Gated and Voltage Gates Ion
Channels
Depolarization
• When the resting potential becomes less
negative due to the opening of Na+ ion
channels (which let Na+ into the cell)
• Threshold – when a stimulus changes the
membrane potential enough to cause a
response, or action potential
Action Potential
Production of Action Potential
• 1. Resting potential: Na+ gates closed, some K+ gates
open (move out) and Na-K pump active
• 2. stimulus Na+ channels open, causing depolarization
• 3. When threshold is met, membrane is in rising phase
• 4. The Na+ channels close and K+ channels open- falling
phase
• 5. Because more K+ are open than usual, the membrane
potential is more neg – undershoot
• 6. More K+ close returning the potential to normal
Production of Action Potential
Refractory Period
• Na+ channels remain closed during falling
phase and undershoot, therefore a second
stimulus could not trigger stimulation
during this time
Conduction
• The Na+ changes at
one part of the neuron
stimulate the
depolarization of the
neighboring section
(like dominoes)
• Because of the
refectory period, the
impulse can only
move in one direction
Saltatory Conduction
The action potentials are not generated at the
myelin sheath, only at nodes; causing action
potential to jump from node to node
Synapses
• 2 kinds – electrical and chemical
• Electrical – gap junctions between two
neurons that allow for direct flow of the
electrical current from one neuron to the
next
• Chemical – involve the release of
neurotransmitters from synaptic vesicles
Chemical Synapse
Neurotransmitters
• Released by exocytosis through the synaptic
cleft
• Can cause excitatory (excitatory
postsynaptic potentials- EPSP) or inhibitory
(inhibitory postsynaptic potentials – IPSP)
effects
• Ex: acetylcholine, epi, dopamine,
serotonin, nitric oxide
Central Nervous System
• Brain and spinal
cord
• Filled with
cerebrospinal fluid
• White matter –
axons (myelin)
• Gray matter dendrites
Peripheral Nervous System
• Gives and receives info from CNS – sensory and
motor neurons
• Cranial and spinal nerves
• 2 systems – somatic and autonomic
• Somatic – carries signals to and from skeletal
muscles, responds to external stimuli
• Autonomic – regulates internal environment,
controls smooth and cardiac muscles
The CNS and
the PNS
Divisions of the PNS
Autonomic Nervous System
• 3 parts-sympathetic, parasympathetic and
enteric
• Sympathetic – increases metabolism, ex:
increases heart beat, etc.
• Parasympathetic – antagonistic to
sympathetic, ex: slows heart beat
• Enteric- control organ secretions
Sympathetic and Parasympathetic
Systems
The Brain
• Embryonic development – 3 parts of the
brain: forebrain, midbrain and hindbrain
• Forebrain cerebrum, diencephalon
• Midbrain  midbrain (brainstem)
• Hindbrain cerebellum, pons, medulla
The Brain Stem
• “lower brain”
• 3 parts: medulla oblongata, pons and
midbrain
• Maintain homeostasis (breathing, heart beat,
etc), coordination, and conduction of info to
higher brain centers
Cerebellum
• Coordination-motor, perception and
learning (cognitive function)
Diencephalon
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Epithalamus, thalamus and hypothalamus
Epithalamus: pineal gland
Thalamus: input sensory info to cerebrum
Hypothalamus: regulates homeostasis
Cerebrum
• Outer gray, inner white
• Analyzes sensory info, motor command and
language generation
• Neocortex – cerebral cortex – more convoluted the
more intelligent the animal is
• Corpus Callosum- band of axons that enables
communication between left and right brain (right
brain : spatial, patterns “big picture”; left brain:
language, math, logic)
Corpus Callosum
Cerebral Cortex
Limbic System
Sensory Receptors
• Mechanoreceptors – pressure, stretch, touch
• Chemoreceptors – solutes
• Electromagnetic Receptors – light
electricity
• Photoreceptors - light
• Thermoreceptors – heat, cold
• Pain Receptors - damage
Hearing
• Convert the
energy of
pressure
waves
traveling
through air
into nerve
impulses
• Three bones of the middle ear transmit the
vibrations to the oval window, a membrane on the
cochlea’s surface
• The vibration against the oval window creates
pressure waves in the fluid
• Waves travel through the vestibular canal, pass
around the tip of the cochlea and move through
the tympanic canal and hit the round window
Transduction in the cochlea
Bending of the hairs increases the frequency of action
potentials in the sensory neurons – the neurons carry
sensations to the brain through the auditory nerve
Muscles
• Skeletal muscle
• Muscle fibers are made up
of myofibrils which are
made up of thin (actin)
and thick filaments
(myosin)
• Sarcomere – basic
contractile unit of the
muscle
• Muscle contraction is
when the sarcomere
shortens by the filaments
slide past each other
Actin/Myosin
• 1. myosin binds to ATP
• 2. it changes ATP into
ADP
• 3. myosin head binds to
actin
• 4. myosin pulls the thin
filament
• 5. Binding to ATP again
releases the myosin head
Calcium
• Tropomyosin – regulatory proteins that blocks the
myosin binding sites on the thin filaments
• Depolarization of neuron allows Ca+ in the cell.
• Ca+ binds to troponin complex which controls the
position of the tropomyosin on the thin filaments,
uncovering the binding sites – allowing
contraction
The Eye
The Structure of the Eye
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Sclera- white outer layer, connective tissue
Choroid – thin inner layer
Conjunctiva- mucous membrane
Cornea – transparent sclera
Iris-color of eye, regulates light into pupil
Pupil – hole in center of iris
Retina – inner layer, photoreceptors
Aqueous Humor – liquid between cornea and iris
Rods – sensory receptor for light
Cones- sensory receptors for color
Opsin – contains retinal, found in cones – absorbs light
Rhodopsin – found in rods