Download CH 48 Nervous systemnotes2010

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CH 48: Nervous system
Overview of nervous system
Three main processes of the nervous system
sensory receptor provides sensory input
information is integrated/processed in brain
sensory output can be motor output to an effector cell
Nervous Systems
central nervous system (CNS) consists of brain + spinal cord in vertebrates
peripheral nervous system (PNS) which consists of the rest of nervous system in the body- nerves
the neuron
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structure
1.
cell body – large part of structure containing the nucleus
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axon – long skinny part along which the message travels and ends in synaptic terminal /when a
message travels through axon and the synaptic ends and to the target cell or another nerve cell it is
called a synapse
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dendrites – finger-like projections from which message travels to the target tissue/cells
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myelin sheath – insulating cover over axon to increase efficiency of nerve cell in sending the
message
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Schwann cells – cells of the myelin sheath in the PNS
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ganglia – area consisting of clusters of nerve cell bodies allows for quick response without involving
brain ex. knee jerk response
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glia-supporting cells that are essential for structure and functioning of neurons
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astrocytes-supports neurons and regulate concentrations of ions and neurotransmitters
9. oligodentrocytes- glia that form the myelin sheaths
B.
three types of neurons
1. sensory neuron receives information from the internal or external environment and transmits the signals
to the central nervous system
2. interneuron- a nerve cell within the central nervous system responsible for the integration of neural
input and output
3. motor neuron transmits signals from the brain or spinal column to muscles or glands
How do nerve cells send impulses along itself? All deals with membrane potentials
it’s the voltage measured across a plasma membrane
created by solute concentration on either side being different due to plasma membrane selectivity in what
goes through inside cell primarily Na+ and Cl- outside cell primarily K+
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membrane potentials can be controlled with gated ion channels which allow for certain ions to pass through
the membrane
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hyperpolarization – increasing the electrical gradient ex. opening the K+ channel to create a more
negative environment in nerve cell
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depolarization – decreasing the gradient ex. opening the Na+ channel to allow Na+ into the nerve
cell to balance out the exiting of K+
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action potential – when depolarization reaches some threshold (becomes positively charged inside
cell to some point), there is a big jump in depolarization (lots of Na+ coming in) through voltage
gated ion channels (positive feedback) and this is called the action potential and is what sends the
nerve impulse
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Steps
a.
Resting stage -both channels are closed (no K+ or Na+ movement)
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Threshold is the maximum membrane voltage before an action potential is triggered
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Action potential- signals conducted by axons when the threshold is exceeded and a nerve
impulse is sent
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depolarization phase- only Na+ channels open, increasing positive charge in nerve cell
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creates action potential (large peak) and sending of nerve impulse
repolarization phase- Na+ channels close and K+ channels open to allow K+ to leave cell
too much K+ leaving causes an undershoot (much more negative in cell than resting phase)
all or nothing – the strength of the stimulus is not a factor. Impulses do not increase or
decrease in intensity, they simply increase or decrease in action potentials sent.
E.
ways to increase nerve impulse speed?
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larger axon diameter  less resistance (ex. like a electrical wire)
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salutatory conduction- myelinated axons act as insulation preventing loss of current while
breaks in the sheath (nodes of Ranvier) are where action potentials take place (where the channels are),
so impulse jumps along axons making the impulse faster
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Synapsis – how it happens
(between two neurons = axon terminal ends to dendrites or cell bodies) transmitting neuron called the presynaptic
cell and the receiving cell called the postsynaptic cell
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terms to know
1. presynaptic cell- the end of the axon of the first cell containing
2. post synaptic cell- the receiving dendrites of the second cell
3. synaptic vesicles- vesicles with neurotransmitters that either increase or decrease the transmission of
the impulse
4. What happens at a synapse?
b.
steps
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when an action potential depolarizes the presynaptic cell’s terminal ends, Ca+ enters this
cell
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the Ca+ causes vesicles containing neurotransmitter molecules to fuse to the presynaptic
cell’s membrane and release these molecules
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these neurotransmitter molecules bind the postsynaptic cell’s ion channel and opens them
to allow Na+ to enter and create an action potential in this cell (increase positive charge in this
cell)
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eventually enzymes from the synaptic cleft and/or postsynaptic membrane degrade the
neurotransmitter molecules and the ion channels close stopping the nerve impulse until
this all happens again
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Types of neurotransmitters – can be excitatory (E) or Inhibitory (I) or both
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acetylcholine – the most common type in verts/inverts, can cause both excitation (ex. skeletal muscle
contraction) or inhibitory (ex. cardiac muscle contraction)
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norepinephrine – can also function as hormones (adrenaline) it can be either E or I
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dopamine – can be both but mostly excitatory (ex. Parkinson’s disease due to lack of it while
overproduction  schizophrenia)
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serotonin – inhibitory
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endorphins – inhibitory (ex. pain killers)
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Organization of the nervous system
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Simplest to most complex
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nerve net – ex in cnidarians (hydra, jellyfish) is a system of branched nerves throughout the body (no
centralization)
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nerve ring with radial nerves – ex. starfish
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dorsal brain with ventral nerve cord – ex. planaria, insects, mollusks, squid, also may have longitudinal
nerve cords and ganglia
VI.
Vertebrate nervous system
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CNS contains white matter (holds motor and sensory axons) and grey matter (holds cell bodies, dendrites,
unmyelinated axons)
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Cerebrospinal fluid – caused by filtering the blood, and this filtrate surrounds the brain and enters the
central canal of the spinal cord bringing in needed nutrients, hormones, and wbc/also acts as cushion for
brain
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Nervous system can be separated into two categories
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somatic nervous system – carries signals from CNS to skeletal muscles in response to external
stimuli/is voluntary
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autonomic nervous system – carries signal from CNS to internal environment (ex. smooth/cardiac
muscles for digestion, cardiovascular, excretory and other systems that are involuntary)
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autonomic nervous system can be of the parasympathetic division – used for activities
that gain/conserve energy
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or the sympathetic division – increase energy and prepare individual for fight/flight
response
VII. Brain structures/functions
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brainstem – has three parts, medulla oblongata (control many autonomic functions), pons (same), and and
the midbrain (accepts sensory info and processes it, ex. hearing/vision)
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reticular formation is the region of the brainstem that regulates being awake or asleep
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cerebellum – used for coordination of movement/balance/hand eye coordination
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thalamus/hypothalamus – for sensory info processing and endocrine system functions respectively
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cerebrum – divided into right and left cerebral hemispheres, each hemisphere is covered in grey matter (aka
the cerebral cortex), many functions associated with it and functions differ between left and right
hemispheres
1. lateralization- different parts of the cerebrum becomes more efficient at different tasks and the right
hemisphere and left hemisphere specialized
2. Boca’s region and Wernicke’s area control the network of brain regions involved in language
3. limbic system control primary emotions and their associated behaviors- crying when sad etc
memory –short term memory and long term memory are located in frontal lobes of the brain and the
hippocampus. Most long term memories or actions are repeated events. Habits are hard to break or
unlearn. Accents, gestures are individual and are recognized by others.
F. CNS diseases or injuries
1. schizophrenia- lose ability to distinguish what is real and what is not- hallucinations, voices and
delusions are common symptoms- is not a split personality. It can be inherited. PCP can mimic
schizophrenic symptoms
2. bipolar disorder- mood swings from high to low ; can cause increased bouts of energy with creative
ideas, overtalking, increased risk behaviors ( some famous artists and musicians were believed to have p
produced their best work during this manic phase). The depressive stage lowers ability to feel pleasure,
and includes loss of interest , loss of sleep, some even consider or attempt suicide during this stage.
3. major depression- low mood all the time. Can affect 5% of the population. Some drugs used to treat
other diseases such as TB and heart disease are used to treat depression
4. Alzheimer’s disease- mental deterioration which is age related. Can be confused with dementia
another age related disease. ( as medicines keep people alive longer, the incidence of AD increases)
AD is caused by the death of neurons in large areas of the brain. Post mortem an AD patient has large
tangles of glia cells and a plaque caused by an abnormal insoluble protein.
5. Parkinson’s disease – motor disorder characterized by difficulty in moving, slowness of movements
Patients have tremors, poor balance, weakness. Parkinson’s disease is progressive. Can be both genetic
and environmental in cause. Treatment to control tremors can be with dopamine, lacking in Parkinsons
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