The Nervous System

Divisions of the Nervous System Nervous 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. 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 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 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) 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 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) 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) 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) 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 Neurons – receive and transmit stimuli, conduct action potentials Neuroglia or glial cells – 4 functions Neuroglia or glial cells – 4 functions 1. 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. 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 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. 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 Body – contains nucleus and other organelles Dendrites – receive information and send impulses to the cell body Dendrites – receive information and send impulses to the cell body Axons – send impulses away from the cell body Axons – send impulses away from the cell body Schwann cells & Oligodendrocyte –myelinate the axons of neurons found in the PNS 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. 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 m/sec Non-myelinated travel.5 m/sec; myelinated m/sec nodes of Ranvier – gaps in myelin sheath nodes of Ranvier – gaps in myelin sheath Synapse – site where a neuron communicates with another cell (ends of axons) 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) 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 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. 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. many negative ions in cytoplasm; can’t move too big. There is an electrical difference between outside and inside of cell. There is an electrical difference between outside and inside of cell. Overall electrical charge is - 70 millivolts: + outside/ - inside = polarized Overall electrical charge is - 70 millivolts: + outside/ - inside = polarized

Conduction of a Nerve Impulse Action Potential; step 1. Depolarization Action Potential; step 1. Depolarization a stimulus (temp. change, pressure change, etc.) causes Na+ channels to open. 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 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 membrane becomes more - outside and more + inside = membrane is depolarized. +10 millivolts

Conduction of a Nerve Impulse Action Potential; Step 2 Repolarization Action Potential; Step 2 Repolarization Need to reestablish negative inside Need to reestablish negative inside K+ channels open causing rapid outward diffusion of K+. Positives out = negatives in K+ channels open causing rapid outward diffusion of K+. Positives out = negatives in Repolarized back to around -70 millivolts. Repolarized back to around -70 millivolts. Na+/K+ pump continues to restore and maintain K+ and Na+ levels or resting potential 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. 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 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 Nerve impulse = Action Potential 1000 nerve impulses a sec are possible nerve impulses a sec are possible.

Slide 1 Figure 12-13: The Generation of an Action Potential

Slide 2 Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13: The Generation of an Action Potential –––– – – – – – –70 mV RESTING STATE Axon hillock Initial segment

Slide 3 Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13: The Generation of an Action Potential Axon hillock

Slide 4 Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13: The Generation of an Action Potential

Slide 5 Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13: The Generation of an Action Potential

Slide 6 Copyright ©2005 Pearson Education, Inc., publishing as Benjamin Cummings Figure 12-13: The Generation of an Action Potential

Myelination Myelination speeds up nerve impulses because myelin covers neuron membrane, not allowing the diffusion of ions. 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 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. 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. 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. 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. 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. Neurotransmitters stored in vesicles in synapse. 3 types of synaptic clefts. 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 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 2 - stimulus stimulates neuron Step 3 - Depolarization - Na gate opens allowing Na into cell causes voltage to become + 10 mvolt. 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 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 5 - Na/K pump works to restore nerve to #1. Step 6 - When Depolarization reaches synapse, neurotransmitter vesicles are released into synaptic cleft. Step 6 - When Depolarization reaches synapse, neurotransmitter vesicles are released into synaptic cleft. Step 7 - Neurotransmitters stimulate the post- synaptic cell. Step 7 - Neurotransmitters stimulate the post- synaptic cell.