The Nervous System Structures and Processes Central Nervous System Peripheral Nervous System.
Nervous system
description
Transcript of Nervous system
Nervous system
Nervous system• 2 main parts
– 1) Central Nervous System (CNS)
– Brain: central processing center
– Spinal cord: extends down back below brain
Nervous system• 2 main parts
– 2) Peripheral Nervous System (PNS)
– Connects CNS to muscles, sensory cells, etc.
– 12 pairs of cranial nerves (attached to brain)
– _________ pairs of spinal nerves (attached to spinal cord)
Nervous system• Functions:
– 1) Monitors changes in external and internal environment
– Receptors: gather information
Nervous system• Functions:
– 1) Monitors changes in external and internal environment
– Receptors: gather information– 2) Sends messages in response to information
gathered– Effectors: cells that respond to message
(glands, muscles)
Nervous system• 3 types of nerve cells (neurons)
– Sensory neurons (act as receptors)• Found in skin, organs. Cell body of neuron outside of CNS.
Long dendrites, ____________ axons
Nervous system• 3 types of nerve cells (neurons)
– Motor neurons (carry message to effectors) • Cell bodies contained within CNS. Short dendrites, long axons
Nervous system• 3 types of nerve cells (neurons)
– Association neurons (often link sensory and motor neurons)
• Cell bodies in CNS. Connect motor and sensory neurons. Connect sensory neurons to ____________
The neuron• Functional unit of nervous system• Neuron: dendrite (incoming messages), cell
body, axon (outgoing message)
Neuroglia• Neuroglia (supporting cells)• Schwann cells (PNS) and oligodendrocytes (CNS)• Form myelin sheath, Nodes of Ranvier
Neuroglia• Myelinated axons are whitish: called white matter
in nerves/spinal cord/brain• Unmyelinated axons/dendrites and cell bodies are
grayish: called gray matter
Neuroglia• Secrete myelin (80% ___________)• Cells wrap axon in a whitish “jelly roll”:
myelin sheath
Neuroglia• Functions:
– 1) support and protect nerve cell from injury– 2) nourish nerve cell (lies between blood
vessels and neurons)– 3) electrical insulator: increases rate of impulse,
insulates against firing of other neurons– 4) aids in regeneration of sensory nerves after
______________
Neuroglia• Example of importance:
Multiple Sclerosis (MS)• 2 million people worldwide• Body’s immune system attacks
myelin sheaths• Result: poor nerve impulse
conduction. Lose ability to _____________ muscles
• Cause? Uncertain: genetics, viral infection
How a nerve works• Nerve impulse:
– electrochemical signal– great speed: up to _________ miles per hour– resting nerve has charge difference across membrane:
membrane “polarized”– impulse: wave of depolarization caused by sudden
influx of Na+ into axon– followed by repolarization: return to original
polarized state
How a nerve works• Resting neuron
– Lots Na+ outside membrane and K+ on inside– Charge is + outside and - inside due to Cl- and
proteins on inside of membrane– Maintained by Na-K pumps
How a nerve works• Resting neuron
– Neuron said to be polarized– Charge difference across membrane called _________
potential. About -70 millivolts (mV)
How a nerve works• Resting neuron movie
QuickTime™ and aCinepak decompressor
are needed to see this picture.
How a nerve works• Firing neuron
– stimulus arrives– if stimulus is enough, causes neuron to fire– firing is production of an action potential across
membrane: change in _____________ distribution– goes from -70 mV (resting potential) to +30 mV (at
peak of action potential)
How a nerve works• Firing neuron
– 1) membrane channels open to allow Na+ to rush in– 2) extra K+ channels open and lots of K+ flows out– This repolarizes membrane– 3) Refractory period: time during which original state
is regenerated by Na-K pumps. During this time, neuron __________ fire again.
How a nerve works• The firing neuron movie
QuickTime™ and aCinepak decompressor
are needed to see this picture.
How a nerve works• Nerve firing:
– All or none response. A nerve either fires or it doesn’t
– Very brief. Lasts about ________ millisecond– Transmitted along sections of axon like “the wave” in
a stadium
How a nerve works• Myelin sheaths speed impulse movement
– allow action potential to jump between nodes– action potential only produced at nodes, not in
between
How a nerve works• Myelin sheaths speed impulse movement
– like stadium with sections of empty seats. “Wave” jumps to next filled section
– called saltatory conduction
How a nerve works• Note speed of myelinated axons• Note also that axon diameter influences speed of
impulse. Larger axon, ___________ speed.
Neuron to neuron transmission• 2 neurons usually don’t touch• Share synapse: tiny intercellular space (synaptic
cleft)
Neuron to neuron transmission• Chemical transmission of impulse:
– 1)Action potential in firing axon stimulates release of synaptic vesicles into synapse
Neuron to neuron transmission• Chemical transmission of impulse:
– 2) Vesicles contain neurotransmitters– 3) Neurotransmitters diffuse across cleft to _________
proteins in postsynaptic membrane (dendrite of other neuron or muscle cell as shown here)
Neuron to neuron transmission• Chemical transmission of impulse:
– 4) Receptor proteins cause start of action potential in postsynaptic membrane
– 5) Enzymes ______________ neurotransmitters when transmission is completed. Prepares synapse for the next impulse.
Neurotransmitters• Vital substances in transfer of messages between
neurons
Neurotransmitters• 2 main types
– 1) excitatory transmitters: cause depolarization of postsynaptic membrane
– 2) inhibitory transmitters: stabilize membrane against depolarization
Neurotransmitters• Acetylcholine: Neurotransmitter between motor
nerve axon and skeletal muscle cell• Example of excitatory neurotransmitter• Causes depolarization of muscle cell membrane
and stimulation of ________________
Neurotransmitters• How stop stimulus? Acetylcholinesterase:
enzyme breaks down acetylcholine• What happens if acetylcholinesterase inhibited?
Muscle contraction uncontrolled.
• This is _________......• Some chemicals designed to kill by inhibiting
acetylcholinesterase
Neurotransmitters• Nerve gas: works by inhibiting acetylcholinesterase• Example, VX gas featured in “The Rock”
VX gas spheres in “The Rock”
Neurotransmitters• Nerve gas: works by inhibiting acetylcholinesterase• Example, sarin gas• Used in Tokyo subway attack by religious cult in
1995 (12 dead)
Neurotransmitters• Nerve gas: works by inhibiting acetylcholinesterase• Example, sarin gas• Used by Saddam Hussein and his pal “Chemical
Ali” in 1988 against Kurds at Halabjah (5,000 killed)
Neurotransmitters• Nerve gas: works by inhibiting
acetylcholinesterase• Example, sarin gas• US Army used incinerator at Anniston AL to
destroy some sarin gas (Sept. 2003)
Neurotransmitters• GABA: an inhibitory neurotransmitter• Allows ________ into neuron membrane,
making it even more negative inside.• Thus harder to develop action potential
Neurotransmitters• Some sedatives take advantage of GABA
mechanism• Ex, Valium: enhances binding of GABA to its
receptors. Harder for neurons to fire.
Neurotransmitters• Serotonin: Involved in sleep regulation and
emotional states• Insufficient serotonin production involved in
depression, Parkinson’s disease
Neurotransmitters• Prozac: blocks reabsorption of serotonin to make
up for _________ of production
Neurotransmitters• Serotonin• LSD: blocks serotonin receptors
in portion of brain to produce hallucinations or “trip”
Neurotransmitters• Cocaine: Affects neurons in brain’s “pleasure
pathways” (limbic system)
Neurotransmitters• Slows reabsorption of transmitters, so pleasure
messages intensified
Neurotransmitters• Addiction: body adjusts to drug. Example, cocaine• Decrease number of neurotransmitter receptors• When drug removed, synapse _________ sensitive
Neurotransmitters• Addiction example, nicotine
Neurotransmitters• Nicotine binds to brain receptors that normally
bind acetylcholine• Influences a number of other neurotransmitters
and their receptors• Result is stimulating
Neurotransmitters• Problem: brain cells adjust numbers and
sensitivities of many brain receptors • If nicotine removed (stop smoking), system
unbalanced. Effects unpleasant
Neurotransmitters• Example, nicotine• Takes time to recover
Synaptic Integration• Recall that there are two types of
neurotransmitters: excitatory and inhibitory• So, synapses can be either excitatory or
inhibitory, depending on the neurotransmitter produced
• CNS neurons often receive input from many other neurons
Synaptic Integration• Example, 1 spinal cord motor neuron might have
50,000 synapses!• Action of that neuron depends on the total effect
of both excitatory (red) and inhibitory (blue) inputs
Parts of the Nervous System• Central nervous system: brain and spinal cord
Parts of the Nervous System• Brain: Hindbrain
– 1) Medulla oblongata: continuation of spinal cord. Pathway to higher brain centers (traffic controller)
– Contains reflex centers that control: breathing, heart rate, blood pressure, swallowing
– Damage to this area is __________!
Parts of the Nervous System• Brain: Hindbrain
– 2) Pons: carries impulses from one side of ______________ to other. Regulates chewing, salivation, facial expressions, eye movements
Parts of the Nervous System• Brain: Hindbrain
– 3) Cerebellum: receives information from sense organs, muscles, cerebrum
– Involved in equilibrium, coordination of muscles
Parts of the Nervous System• Brain: Midbrain
– 4) Small area in humans: midbrain connects hindbrain to forebrain
5) Brain: Forebrain– Cerebrum: Main processing center. Regulates vision,
speech, hearing, olfaction, memory, logic, consciousness, etc.
5) Brain: Forebrain– Thalamus: analyzes sensory information and relays it
to cerebrum– Hypothalamus: regulates sleep, metabolism, body
temperature, water balance, appetite, thirst, pleasure– Note connection of hypothalamus to _____________
gland
Brain comparisons• Humans with highly developed cerebrum: largest
portion of brain
Parts of the Nervous System• Spinal cord: cable of neurons running down
back. Information highway!• Inner zone: gray matter. Interneurons and cell
bodies of motor neurons• Outer zone: white matter. Axons and dendrites
of neurons.
Parts of the Nervous System• Spinal cord: also contains reflex arcs• Very fast responses because information doesn’t
travel to _______________ for processing
Parts of the Nervous System• 2 neuron arc: has only sensory and motor neuron
involved. Example, knee jerk reflex
Parts of the Nervous System• 3 neuron arc: has sensory and motor neuron, but
________________ present also. Example, cutaneous spinal reflex
Parts of the Nervous System• Brain to spinal cord mass ratio• Gives rough measure of intelligence• Fish/amphibians 1:1• Cat 4:1• Tailed monkey 15:1• Human 55:1• ____________ 61:1• Who’s more intelligent??
Parts of the Nervous System• Peripheral Nervous System
– Afferent system: carry impulse from sensory neuron to CNS. Sensory pathways.
– Efferent system: carry impulses from CNS to muscles (effectors). Motor pathways.
Parts of the Nervous System• Peripheral Nervous System
– Efferent system: carry impulses from CNS to muscles (effectors). Motor pathways.
• Somatic: CNS to skeletal muscles (_________________)• Autonomic: CNS to smooth muscles (involuntary)
Parts of the Nervous System• Peripheral Nervous System
– Autonomic: CNS to smooth muscles (involuntary)– Made of two antagonistic subdivisions (have
__________ effects)• 1) Sympathetic• 2) Parasympathetic
Parts of the Nervous System• Autonomic
– 1) Sympathetic (on edge). Speed up body functions and activities to prepare for defense
– Increase heart rate, glucose release, decrease blood to digestive system, more blood to muscles
Parts of the Nervous System• Autonomic
– 2) Parasympathetic (laid back)– _________________ of sympathetic system