Download Peripheral nervous system

Nervous system
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Central nervous system
Peripheral / autonomous nervous system
Brain functions
Neurons and drugs
evolution of vertebrate brain - sponges are only multicellular
animals w/o nerves
• cnidarians - have simplest nervous systems (nerve net)
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no control/association
• flatworms - simplest animals w/ association in nervous system
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bigger mass of nervous tissue (beginnings of brain) >>
complex control
• interneurons/tracts added to brain as it evolved (interneurons
- complex, high-level neurons found in brain/spinal cord)
Hindbrain (rhombencephalon) - extension of spinal cord
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coordinates motor reflexes
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cerebellum (“little cerebrum”) - controls balance, body
position
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pons - controls automatic functions, links
cerebellum/medulla oblongata w/ other parts of brain
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medulla oblongata - contains respiration, circulation
Midbrain (mesencephalon) - consists of mostly optic lobes that
receive/process visual information
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controls eye/ear reflex
Forebrain (prosencephalon) - processes most of sensory
information
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diencephalons - thalamus, hypothalamus
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thalamus - relays info between spinal cord and cerebrum
hypothalamus - controls emotions, pituitary gland
cerebrum (telencephalon) - dominant part of mammalian
brain
• ascending tracts - carry sensory info to brain
• descending tracts - carry impulses from brain to motor neurons
Human forebrain - divided into 2 hemispheres connected by
corpus callosum
• each hemisphere receives info from opposite side
Cerebral cortex - layer of gray matter on outer surface of
cerebrum
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contains 10% of all neurons in brain
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folded/wrinkled to increase surface area
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primary motor cortex - right in front of central sulcus
(crease), controls mov’t
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primary somatosensory cortex - right behind central
sulcus, receives info from sensory neurons of
skin/muscles
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auditory cortex - in temporal lobe
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visual cortex - in occipital lobe
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association cortex - used for higher mental activities
Basal ganglia - collections of cell bodies, dentrites that produce
gray matter islands
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receives info from ascending tracts, motor commands
from cerebrum/cortex
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sends info to spinal cord to control mov’t
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damaged ganglia >> Parkinson's
Thalamus - main area of senses (especially pain)
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receives visual, auditory, somatosensory info
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relays info to occipital (visual), temporal (auditory),
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parietal (somatosensory) lobes
Hypothalamus - controls instinct
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regulates body temperature, hunger, thirst, emotion
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controls pituitary gland (regulates other endocrine glands)
Limbic system - responsible for emotional responses
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includes hypothalamus, hippocampus (may control
memories), amygdala
Spinal cord - cable of neurons going from brain through
backbone
• protected by vertebral column and meninges (membrane
layers that also cover the brain)
• inner zone (gray matter) - consists of interneuron, motor
neuron, neuroglia cell bodies
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unmyelinated cell bodies
• outer zone (white matter) - consists of sensory axons (in
dorsal column) and motor axons (in ventral column)
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myelinated axons
• controls reflexes (sudden involuntary muscle mov’t)
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doesn’t require higher level processing of info
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only uses a few neurons >> very fast
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monosynaptic reflex arc - simplest reflex (like kneejerk reflex), sensory nerve connects directly to motor
neuron
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most reflexes usually involve an interneuron between
sensory/motor neurons
• regeneration - implanted nerve axons can’t penetrate spinal
cord tissue
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factor in spinal cord inhibits nerve growth
use of fibroblast growth factor shows limited improvement
in neuron regeneration ability
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Peripheral nervous system
Nerves, ganglia
Nerve
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- collections of axons (myelinated/unmyelinated)
separates into motor/sensory parts at origin
dorsal root - sensory axons
ventral root - motor axons
Ganglia - groups of neuron cell bodies outside the central
nervous system
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dorsal root ganglia - contains cell bodies of sensory
neurons
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motor neuron cell bodies found inside spinal cord
• somatic motor neurons stimulate skeletal muscles to contract
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for each muscle stimulated to contract, its antagonist
must be inhibited by hyperpolarizing the motor neuron
Autonomic nervous system
contains sympathetic/parasympathetic areas, medulla oblongata
• autonomic neurons control smooth muscles, cardiac muscles,
glands
• medulla oblongata - controls the system
• 2 neurons used for each pathway (1 has cell body in central
nervous system, other has cell body in autonomic ganglion)
• Preganglionic neuron - 1st neuron, releases Ach at synapse
• Postganglionic neuron - releases Ach in parasympathetic
division, norepinephrine in sympathetic division
• Sympathetic division - stimulates the adrenal gland to
secrete epinephrine
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prepares the body for fight or flight
norepinephrine released at postganglionic neuron
synapses
Parasympathetic division - slows down heart, increases
secretions
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regulates organs by releasing Ach
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ACh causes G proteins to open up ion channels >>
hyperpolarization >> slows down cell
Neuroglia - cells that support neurons
• supplies neurons w/ nutrients, gets rid of waste, provides
immunity
• Schwann cells - produce myelin sheaths in peripheral nervous
system
oligodendrocytes - produce myelin sheaths in central
nervous system
Brain Function
Sleep/arousal - reticular formation in brain stem controls
consciousness
• less stimuli >> less active reticular formation >> easier to
sleep
• sleep = active process, not lack of consciousness
Electroencephalogram (EEG) - records electrical activity in the
brain
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alpha waves - 8-13 hertz, found in relaxed/awake people
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beta waves - 13-30 hertz, found in alert people
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theta/delta waves - found in sleeping people
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REM sleep - rapid eye mov’t sleep
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EEG like that of relaxed, awake person
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difficult to wake up
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when dreams occur
Language/spatial recognition - hemispheres each responsible
for different jobs
• left hemisphere = dominant language area for 9/10 of righthanded people, 2/3 of left handed people
• Wernicke’s area - found in parietal lobe between
auditory/visual areas
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controls language comprehension, formation of thoughts
• Broca’s area - found near motor cortex controlling the face
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controls motor skills needed for language communication
• aphasias - language disorder where words lack meaning, due to
damage in Wernicke/Broca areas
• right hemisphere = nondominant hemisphere, good at spatial
reasoning and musical ability
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damaged inferior temporal cortex >> inability to
recognize faces
memory/learning - doesn’t take place in any specific part
• short-term memory - temporary memory
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possibly stored electrically as neural excitation
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can be forgotten w/ electrical shock
• long-term memory - involves structural changes in neural
connections
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converted from short-term memory by
hippocampus/amygdala
• long-term potentiation (LTP) - frequently used neurons become
more sensitive after each transmission
Alzheimer disease - condition where memory/thought
processes become dysfunctional
• nerve cells either killed from outside in or inside out
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• beta-amyloid peptides - external proteins that could plaque and
fill in brain when mutated
• tau protein - internal protein that normally maintain transport
microtubules
could cause tangles when mutated
Membrane potential –
difference in charge across the membrane
• cytoplasm = negative, extracellular matrix = positive
• Fixed anions - negatively charged molecules too large to
diffuse out of the cell
• leak channels and sodium-potassium pump keep positively
charged ions out of the cell
• Equilibrium potential - point where electrical/chemical forces
balance out for a certain ion
graded potentials - small changes in membrane potentials
• casued by activation of gated ion channels (can open in
response to stimuli like hormones)
• Chemical (ligand) gated channel - open when chemicals bind
to them
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channels open >> change in membrane permeability >>
different ions can get in/out
• depolarization >> membrane potential becomes less negative
• hyperpolarization >> membrane potential becomes more
negative
• Summation - ability of graded potentials to combine
• threshold - amount of depolarization needed to create action
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potential
Action potential - nerve impulse once voltage-gated ion
channels open
• Voltage-gated ion channel - opens/closes depending on
membrane potential
• Na+ gates open first, before K+ gates
• Na+ enters cell (depolarization) >> K+ exits cell
(repolarization) >> possible undershoot if K+ channels stay
open (hyperpolarization)
• cannot combine w/ other action potentials
• either occurs completely or none at all
• can depolarize another area of the membrane, starting a chain
of action potentials
• Saltatory connection - action potentials jumping from node
to node in myelinated axons
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speeds up nervous transmissions
• myelinated + larger axon diamter >> fast action potential
transmission
Synapse
Intercellular junction between dendrites and soma
• electrical synapse - uses direct cytoplasmic connections
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usually found in invertebrate systems
• chemical synapse - accounts for majority of synapses
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synaptic cleft - narrow space that separates 2 cells
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synaptic vesicles - contains neurotransmitters
action potential at end of axon >> Ca++ channels open
>> depolarization >> vesicles bind to membrane >>
neurotransmitters released through exocytosis, bind
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to receptor proteins on other cell
• neurotransmitters recycled into cell by transporters, but most
go back to cell body before being used again by vesicles
• excitatory postsynaptic potential (EPSP) - depolarization
• inhibitory postsynaptic potential (IPSP) - hyperpolarization
• synaptic integration - EPSP’s and IPSP’s working together to
bring about overall effect on cell
Neurotransmitters
• dopamine - used to control body mov’ts
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deficiency causes Parkinson’s disease
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excess causes schizophrenia
• norepinephrine - adds on to the effect of epinephrine,
secreted by adrenal gland
• serotonin - regulates sleep/emotion
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deficiency can cause depression
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drug LSD blocks serotonin receptors >> depression
• substance P - neuropetide that responds to pain stimuli
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pain won’t be felt w/o it
• nitric oxide - 1st gas discovered to act as regulatory molecule
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cannot be stored (diffuses through membranes)
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causes smooth muscles to relax
Drugs - decreases the sensitivity of receptors, mimics the effects
of neurotransmitters
Habituation - receptors lost ability to respond if exposed to
constant stimulus for long time
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number of receptor proteins decrease
• blocks transporters >> excess of neurotransmitters in synapse
cleft >> # of receptors decrease due to over-stimulation
>> addiction
• body adjusts to conditions when drug is present >> withdrawal
symptoms occur when drug no longer used
Agonist - acts like the neurotransmitter
Antagonist - blocks the receptor for a neurotransmitter
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