Download Nervous System

Nervous System
3 stages in processing information by NS:
1. sensory input
2. integration
3. motor output
 Neuron: basic cell of nervous system
 cell body contains nucleus and organelles
 axon: long process conducting impulses away from cell
body
- usually single and very long relative to cell
 dendrites: receive impulses from stimulus from other
neurons
- usually many, short relative to cell
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 synapse: junction between axon of one neuron and
dendrite of next
- presynaptic cell = transmitting neuron
- postsynaptic cell = receiving cell
 chemical messengers = neurotransmitters =
communication between the pre- and post-
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 sensory neurons:
- receive information from body and senses
- transmit to spinal cord and brain
 motor neurons:
- transmit information from brain and spinal cord
- control muscles and glands
 interneuron: between sensory and motor neurons; in
brain.
 glial: support cells for neurons
 Schwann cells (PNS): wrap peripheral axons of one
and/or many neurons in myelin sheath = nerve
- Lipid; faster, more efficient conduction
(insulation)
o Nodes of Ranvier: gaps between the myelin
sheaths
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- Action potential only occur at these nodes and
travels to the next node = Saltatory
conduction
 Transmission of Impulses in Neurons
 membrane potential: inside of neuron negative
relative to outside (outside = + ; inside = -)
 “+” ions (cations) on inside and outside cell, but “-“
inside due to “-“ proteins and other anions (“-“)
inside cell that cannot cross cell membrane.
 resting potential: not transmitting signal (about
—70 mV = refers to the inside of the membrane)
- we’ll get back to this after …
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 ACTION POTENTIAL (AP): signals that carry info.
along axon
 It’s all about Na+ AND K+
 reversal in membrane potential (outside = - ;
inside = +) = depolarization
How?
- controlled by gated protein channels in the
membrane
- stimulus
small depolarization triggers opening of
Na+ ion channels
- if stimulus causes enough Na+ to move in =
threshold: a stimulus causes minimum depolarization
required to trigger an AP
- increases permeability to Na+ - rushes into cell
o Domino affect = one Na+ opening triggers the
next and so on…
 causes membrane potential increases to +35 mV
(outside = - ; inside = +)
• all or none principle: all the way to +35 mV or
not
o So long as they can reach the threshold of the cell,
strong stimuli produce no stronger action potentials
than weak ones, just more of them.
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o So, the strength of the stimulus is encoded in the
frequency of the action potentials that it generates.
 Na+ gated channel closes
- inactivated: will not reopen until resting
potential restored
How?
 repolarization:
- K+ ion gated channels open = K+ migrates out
It keeps on moving down the axon…propagation of action
potential: movement of impulse down neuron
• influx of Na+ depolarizes adjacent membrane
• impulse travels with AP
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Now what is the problem here? Hummmm
 We have resting membrane potential again after
repolarization (outside = + ; inside = -), but…
Na+ and K+ are on the wrong sides of the membrane!
How to fix it…
 Na+/K+ pump: 3 Na+ out for every 2 K+ pumped
in
 High energy cost! (1/3 of daily energy!)
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Now, let’s go back to how the stimulus is received…
 Synapses
Synapses located at branches of axons (terminal end) of
presynaptic cell and cell body or dendrite of postsynaptic
cell
 electrical synapses: transmit action potential directly
between neurons
- formed by gap junctions between cells
 **chemical synapses: use chemicals to transfer
impulses when action potentials are not transmitted
from one neuron to the next, directly…needs a
“communicator” = neurotransmitter (NT)
- Located in vesicles of neuron
- Binds to receptor portion of gated channels of
postsynaptic cell
 most common = **Acetylcholine (Ach)
 others:
 Norepinephrine & Epinephrine (also act as
hormones – adrenal glands) = increases
heart rate; therefore blood flow
 Dopamine & Serotonin = affect sleep, mood,
attention, and learning
 And more…
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Where are the NT’s released?…
- synaptic cleft (synapse): space between neurons
HOW?
incoming potential:
 AP ends at presynaptic terminal of presynaptic cell
- This depolarization of presynaptic terminal opens
gated channels for Ca2+ (Ca2+ in synapse) = =
enters presynaptic terminal
 Ca2+ in - triggers fusion of synaptic vesicles with
presynaptic membrane
 NT released into synaptic cleft via exocytosis
 NT bind to receptors on gated channels in
postsynaptic membrane
- specific ion channels opened by binding
• EPSP: Excitatory PostSynaptic Potential
- Na+ ion channels open on postsynaptic
membrane
- Bring membrane potential of postsynaptic
neuron to threshold = membrane
depolarization
AP
If an inhibitory NT is released…
• IPSP: Inhibitory PostSynaptic Potential
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- K+ ion channels open and leaves cell
- Causes the interior to be more negative
- increases polarization (hyperpolarization) =
inhibits impulse propagation = no AP
- due to membrane moving away from threshold
o Gives, AP “a break”
- Need twice the amount of Na+ rushing into
get AP to go again.
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 Types of Nervous Systems (Evolutionary Trends)
o nerve net: no central control (Cnidarians)
o ganglia: clusters of nerve cells (other many inverts.)
o cephalization: nerve centers and sense organs at
anterior end
- flatworms: simple brain with two nerve trunks
- annelids & arthropods: obvious brain plus
ventral nerve cord
The Vertebrate Nervous System
 Central Nervous System (CNS) = includes brain
and spinal cord
BRAIN
 Gray matter on outside – mostly unmyelinated axons
o modulates the distribution of action
potentials
 White matter on inside – myelinated axons
o Function: tissue through which messages pass
between different areas of gray matter;
o affects how the brain learns and dysfunctions
 4 ventricles in deep interior
• Contains cerebrospinal fluid – formed from
filtrate of blood; drains into veins
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• Contains nutrients, oxygen, hormones, NT’s,
and cellular waste.
• Cushions the brain (& spinal cord)
Breaking it down into parts:
1. Cerebrum (forebrain): processing and integration
of sensory information, speech, and emotion.
• includes: cerebral cortex – divided into 2 halves;
R. & L. sides = cerebral hemispheres
o corpus callosum: connects halves of cerebral
cortex; communication between right and
left cerebral hemispheres
- R. side of brain controls L. side of body
- L. side of brain controls R. side of body
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o thick bands of axons
(mammals: integration of vision)
2. hypothalamus (forebrain): regulation of
homeostasis, endocrine sys.
3. Brainstem (midbrain and hindbrain): axons extend
into the cerebral cortex
- Midbrain = sends sensory info to forebrain
o Auditory center (hearing) – localizes sound
o optic lobe: visual centers
(mammals: coordinate visual reflexes)
- hindbrain
o cerebellum: coordination of movement
o medulla oblongata: control of autonomic
functions = breathing, heartbeat, vessel
activity, digestion, swallowing, vomiting
o pons: helps regulate the medulla oblongata
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SPINAL CORD
o carries information to and from brain
o simple reflexes (knee jerk, etc.)
reflex arc:
• sensory neuron brings afferent signal to spinal cord
• impulse synapses to motor neuron
• motor neuron delivers efferent impulse to effector
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 Peripheral Nervous System (PNS)
o Divided into 2 regions:
1. somatic (voluntary)
2. autonomic (involuntary)
 sensory: inputs signals to brain (afferent)
- somatic: senses external stimuli, [from] skeletal
muscles
ex. Step on sharp rock
- autonomic: senses organs, [from] involuntary
muscles
ex. Bolus in esophagus
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 motor: relays commands from brain (efferent)
- somatic: voluntary muscles
ex. Move foot off sharp rock
- autonomic: involuntary muscles and organs
ex. Peristaltic contractions moving bolus
to stomach.
More on the 2 regions:
1. Somatic NS
- carries signals to and from skeletal muscles
2. Autonomic NS
- Regulates internal environment: peristalsis, heart,
other organs
- Divided into 3 regions (we’re looking at 2 of them):
1.
sympathetic: generally prepares body for action
(“fight or flight”)
- increases heart rate, raises metabolism
**[What part of the endocrine system would this
control?]**
2.
parasympathetic: generally relaxes and rebuilds
- stimulating digestion, slowing heart
3. (enteric: controls digestive tract, pancreas and
gallbladder) [don’t worry about this]
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 Receptors and Effectors
 receptors: receive information from external or
internal environment from reception to perception:
 Types of Receptors
 mechanical: pressure, touch, stretch, balance, sound
- bending/stretching membrane increases
permeability to Na+ & K+
 depolarization generates AP
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- hair cells: detect motion (sound and balance,
pressure in fish)
 chemical: taste and smell, osmolarity, pheromones in
insects
- chemicals bind to membrane receptor molecules
- changes membrane permeability
 thermal: separate responses to heat and cold
- hypothalamus receptors regulate body temp
 pain: response to excess heat, pressure or chemicals
- comprised of naked dendrites
 electromagnetic: visible light, infrared, electricity,
magnetism
- earth’s magnetic fields aid in migration
Sensory Receptors of
Human Skin:
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