the nervous system. divisions of the nervous system nervous system central nsperipheral ns afferent...
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The Nervous System
Divisions of the Nervous SystemNervous System
Central NSPeripheral NS
Afferent Efferent
Somatic Autonomic
Sympathetic Parasympathetic
Divisions of the Nervous System
Central Nervous System – made up of brain and spinal cord – sends instructions to the rest of the body, and processes incoming information.
Peripheral Nervous System – made up of peripheral nerves – delivers sensory info from rest of body to the CNS. It also carries (instructions) motor commands from CNS to peripheral nerves
Afferent (IN) division of PNS – delivers sensory info to CNS from receptors
Efferent (OUT) division of PNS – carries motor commands from CNS to target organs. (efferent has the effect)
Divisions of the Nervous System
Somatic nervous system – (Voluntary) part of efferent division that controls skeletal muscle contractions
Autonomic nervous system – (Involuntary) part of efferent division that regulates smooth muscle, cardiac muscle, and glandular secretions (subconscious)
Divisions of the Nervous System
Sympathetic – Activates the body for flight or fight response. Is at work when stressed or excited. (accelerator)
Parasympathetic – Activates the body for rest and digestion. Is at work when tired or relaxing. (brake)
Cells of the Nervous System
Neurons – receive and transmit stimuli, conduct action potentials
Neuroglia or glial cells – 4 functions1. Support and protect neurons. Sort of stick neurons
2. Provide nutrients and oxygen
3. Insulate with myelin which helps nerve signal travel faster
4. Protect by destroying pathogens
Functional Differences Among Neurons
Sensory neurons – (afferent neurons) carry nerve impulses from the body to the brain or spinal cord. Sense environment.
Interneuron – (association neurons) lie within the brain or spinal cord and transmit impulses from one part of the brain or spinal cord to another
Motor neurons – (efferent neurons) carry nerve impulses out of the brain or spinal cord; ex: stimulate muscles to contract and glands to release secretions. Cause the body to do respond.
Neuron Structure Body – contains nucleus and other organelles Dendrites – receive information and send impulses to the cell body Axons – send impulses away from the cell body Schwann cells & Oligodendrocyte –myelinate the axons of neurons
found in the PNS myelin sheath – fatty material that forms sheath-like covering around
some nerve fibers (axons); increases the speed of an impulse. Non-myelinated travel .5 m/sec; myelinated 125-150 m/sec nodes of Ranvier – gaps in myelin sheath Synapse – site where a neuron communicates with another cell (ends
of axons) Synaptic cleft – the space that separates the neuron and the cell it is
communicating with. Ex. Neuromuscular junction (muscle & nerve)
Neuron Structure
Conduction of a Nerve Impulse Resting Membrane Potential
the cell expends energy (uses ATP) to drive the Na+/K+ membrane pumps that actively transport the 3 Na+ ions out and 2 K+ ions into the cell. Every time this happens charge across membrane goes up 2, b/c more positives on outside.
many negative ions in cytoplasm; can’t move too big. There is an electrical difference between outside and
inside of cell. Overall electrical charge is - 70 millivolts: + outside/
- inside = polarized
Conduction of a Nerve Impulse Action Potential; step 1. Depolarization
a stimulus (temp. change, pressure change, etc.) causes Na+ channels to open.
rapid influx of Na+ due to open channels and attraction to negative ions inside cell
membrane becomes more - outside and more + inside = membrane is depolarized. +10 millivolts
Conduction of a Nerve Impulse Action Potential; Step 2 Repolarization
Need to reestablish negative inside K+ channels open causing rapid outward diffusion of
K+. Positives out = negatives in Repolarized back to around -70 millivolts. Na+/K+ pump continues to restore and maintain K+
and Na+ levels or resting potential refractory period – neuron cannot conduct another
impulse until it is repolarized.
Conduction of a Nerve Impulse
Summary: the rapid sequence of depolarization and repolarization takes about one-thousandth of a second and is an action potential—a bioelectric current that moves in a wave down a nerve fiber—the wave of action potentials along a nerve fiber constitutes a nerve impulse
Nerve impulse = Action Potential 1000 nerve impulses a sec are possible.
Slide 1Figure 12-13: The Generation of an Action Potential
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
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Activation of sodium channels and rapid depolarization
Inactivation of sodium channels and activation of potassium channelsThe return to normal permeability
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Depolarization to threshold
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RESTING STATE
Axon hillock
Initial segment
Slide 2
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12-13: The Generation of an Action Potential
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Initial segment
Slide 3
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12-13: The Generation of an Action Potential
Axon hillock
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Initial segment
Slide 4
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12-13: The Generation of an Action Potential
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Activation of sodium channels and rapid depolarization
–60 mV
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Depolarization to threshold
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RESTING STATE
Axon hillock
Initial segment
Slide 5
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12-13: The Generation of an Action Potential
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Activation of sodium channels and rapid depolarization
Inactivation of sodium channels and activation of potassium channels
–60 mV
Local
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Depolarization to threshold
–70 mV
RESTING STATE
Axon hillock
Initial segment
Slide 6
Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 12-13: The Generation of an Action Potential
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STEP1
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+10 mV+30 mV–90 mV
Activation of sodium channels and rapid depolarization
Inactivation of sodium channels and activation of potassium channelsThe return to normal permeability
–60 mV
Local
current
Depolarization to threshold
–70 mV
RESTING STATE
Axon hillock
Initial segment
Myelination Myelination speeds up nerve impulses because
myelin covers neuron membrane, not allowing the diffusion of ions.
This causes the action potential or wave of depolarization to be conducted through the cytoplasm
Action Potential, therefore, skips from Node of Ranvier (gaps in Myelin sheath) to Node of Ranvier.
This skipping of myelinated portions of neuron allows the nerve impulse to be conducted 300 times faster.
Pathway of a Nerve Impulse A nerve impulse travels along a neuron from the
dendrites, to the cell body, down the length of the axon. When the impulse reaches the axon; the synapse releases
neurotransmitters that diffuse across the synaptic cleft and stimulate the post-synaptic cell, causing a response.
Neurotransmitters stored in vesicles in synapse. 3 types of synaptic clefts.
1. Neuron – muscle; neuromuscular junction. Muscle contraction
2. Neuron – neuron; neuro-neuronal junction. Nerve impulse
3. Neuron – gland; neuroglandular junction. Gland releases hormones or enzymes
The Synapse
What you have all been waiting for the 7 step of nerve impulse!!!!!
Step 1 - Resting Membrane Potential – Na/K pump moves 3 Na out & 2 K in which along with many negative ions inside axon creates -70 mvolt charge.
Step 2 - stimulus stimulates neuron Step 3 - Depolarization - Na gate opens
allowing Na into cell causes voltage to become + 10 mvolt.
What you have all been waiting for the 7 step of nerve impulse!!!!!
Step 4 - Re-polarization – K gate opens allowing K out of the cell voltage returns to -70 mvolt
Step 5 - Na/K pump works to restore nerve to #1.
Step 6 - When Depolarization reaches synapse, neurotransmitter vesicles are released into synaptic cleft.
Step 7 - Neurotransmitters stimulate the post-synaptic cell.