Nervous System What allows you to perceive the world around you, to recognize the incoming stimuli and to react to the environment Sensory systems Motor systems Memory/learning
Nervous System Central Nervous System (CNS) Brain and Spinal Cord Peripheral Nervous System (PNS) All nervous tissue outside the CNS Somatic Nervous System (SNS)---voluntary Sensory and motor neurons to skeletal muscle Autonomic Nervous System (ANS)---Involuntary Sensory and motor neurons to viscera Sympathetic Division (increase heart rate) Parasympathetic Division (decrease heart rate)
Neurons (=nerve cells) general characteristics: Nervous System Neurons (=nerve cells) general characteristics: - can be very long---6 feet or more - conduct nervous impulses---communication - long lived---entire life span - high metabolic rate; high O2 and glucose needs---brain accounts for less than 10% of body mass, yet gets over 25% of body’s energy
Types of Neurons (functional classification) Motor Neurons--- carry info from brain to body Sensory Neurons--- carry info from body to brain Interneurons--- carry info within the Central Nervous System (CNS). These account for 90% of the neurons in the body Neuroglia---support cells Oligodendrocytes---CNS Schwann cells---PNS
Types of Neurons (structural classification) Multipolar---many processes located in CNS Bipolar---2 processes located in sensory organs (eye, ear & nose) Unipolar--1 process these are sensory neurons. The axon and dendrite fuse into one process. Interneurons---Named based on looks or after the person who first described them (fig. 12.5) Purkinje cells, Pyramidal cells
Anatomy of a `typical’ motor neuron nucleus
Anatomy of a `typical’ motor neuron nucleus cell body = soma = perikaryon
Anatomy of a `typical’ motor neuron nucleus Nissl bodies = rough endoplamic reticulum cell body = soma = perikaryon
Anatomy of a `typical’ motor neuron nucleus Nissl bodies cell body = soma = perikaryon Golgi apparatus
Anatomy of a `typical’ motor neuron other organelles: mitochondria lysosomes neurofilaments nucleus Nissl bodies cell body = soma = perikaryon Golgi apparatus
Anatomy of a `typical’ motor neuron neural processes: axon = nerve fiber dendrites
Anatomy of a `typical’ motor neuron Flow of Information: axon dendrites
Anatomy of a `typical’ motor neuron axon hillock (trigger zone) axon dendrites
Anatomy of a `typical’ motor neuron terminal branches= telodendria axon hillock axon dendrites
Anatomy of a `typical’ motor neuron terminal branches axon hillock axon axonal terminals = synaptic knobs = synaptic boutons dendrites
Anatomy of a `typical’ motor neuron terminal branches axon hillock axon axonal terminals = synaptic knobs = synaptic boutons dendrites
Anatomy of a `typical’ motor neuron axonal terminals = synaptic knobs = synaptic boutons
Anatomy of a `typical’ motor neuron synaptic vesicles with neurotransmitters
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Anatomy of a `typical’ motor neuron
Myelin Sheath Some Axons are myelinated Myelin Sheath (schwann cell in PNS and oligodendrocyte in CNS) axon Multiple layers wrapped around = myelin Cell body and cytoplasm (outer most layer) = Neurolemma
Anatomy of a `typical’ motor neuron myelination:
Anatomy of a `typical’ motor neuron myelination: Special Glial cells -- make up the myelin sheath
Anatomy of a ‘typical’ motor neuron Myelin
Anatomy of a `typical’ motor neuron nodes of Ranvier
Resting Membrane Potential Voltage across the membrane Electric potential energy Due to separation of ions All cells have a resting membrane potential
Resting Membrane Potential + - - + + + + - + - - + + - - -
Resting Membrane Potential + - + - + - - - - + + +
Resting Membrane Potential Amplifier Electrode Oscilloscope 0 mV
Resting Membrane Potential Amplifier Electrode Oscilloscope -70 mV
Resting Membrane Key Players Sodium-Potassium (Na+/K+) Pump Moves Sodium and Potassium against their concentration gradients Moves 3 Na+ out of the cell and 2 K+ into the cell
Resting Membrane Potential Key Players: Na+/ K+ Pump: 3 Na+ out Cell exterior cell membrane ATP NA/K pump establishes and maintains resting membrane potential Cell interior 2 K+ in
Na+ K+ Resting Membrane Potential Key Players: Leaky Channels K+ Na+ Cell exterior cell membrane Cell interior K+ Na+ Many K+ “leak” channels Few Na+ “leak” channels
Together creates -70 mV Resting Membrane Potential K+ 2 K+ K+ ATP K+ 2 K+ Pumps 3 Na+ K+ Leak Channels 2 K+ K+ _ + K+ 3 Na+ Na+ Together creates -70 mV Resting Membrane Potential 3 Na+ 2 K+ Na+ Leak Channels Na+
Resting Membrane Potential Voltage across the membrane Electric potential energy Due to separation of ions All cells have a resting membrane potential
Electrical Signaling Through Changes in Membrane Potential Describing Changes in Membrane Potential Graded Potentials Action Potentials Propagation of Action Potentials
Two Types of Change: Depolarizing Hyperpolarizing -70 mV 0 mV -90 mV Depolarizing reduce membrane potential make inside less negative Na+ move into cell -70 mV 0 mV -90 mV Hyperpolarizing increase membrane potential make inside more negative K+ move out of cell
Signals produced by a change in membrane potential Graded potentials Short lived Local Signaling Either depolarizing or hyperpolarizing
Graded Potentials are the first step in neuronal communication are essential in initiating action potentials typical of dendrites and cell body (NOT axons)
Graded Potentials “graded” because - magnitude of the potential change varies directly with the strength of the stimulus Can be hyperpolarizing or depolarizing -70 +70 weak hyperpolarized strong depolarized
Graded Potentials Cause current flow that decreases in magnitude with distance (Signal dies out with distance) due to leaky membrane Distance (mm) Membrane Potential (mV) Site of stimulus -70
Graded Potentials Cause current flow that decreases in magnitude with distance (Signal dies out with distance) due to leaky membrane
How are graded potentials produced? Changing the membrane’s permeability to different ions by opening/closing ion channels
Na+ How are graded potentials produced? Changing the membrane’s permeability to different ions by opening/closing ion channels Triggering a depolarizing graded potential Na+ cell membrane + + + - - - Resting Depolarized - - - -70 mV e.g., +30 mV + + + + + + Na+ Open chemically-gated or voltage gated channels for cation (Na+) flow INTO cell depolarization
Cl– How are graded potentials produced? hyperpolarization Changing the membrane’s permeability to different ions by opening/closing ion channels Triggering a hyperpolarizing graded potential Open channels for cation (K+) flow OUT of cell Open channels for anion (Cl-) flow INTO cell K+ Cl– e.g., -90 mV -70 mV + + + - - - Resting - - - - - - - - Hyperpolarized hyperpolarization
Signals produced by a change in membrane potential Graded potentials Action potentials All or None Self Propagating Long distance communication
Action Potential Key Players: Voltage gated ion channels Channel is blocked by one or more ‘gates’ Membrane Potential hits a threshold voltage and ‘gate’ opens
Concept of Threshold Graded potentials that are not large enough to depolarize a large area of the axon hillock, fade away and never reach threshold A stimulus that is large enough to depolarize a large enough section of the axon hillock hit threshold ( -55mV), causes an ACTION POTENTIAL Threshold Stimulus Stimulus Strength Sub-threshold Stimuli Supra-Threshold -70 Membrane Potential (mV) -55 30 threshold
Why? Many Voltage gated Na+ channels located at trigger zone If graded potential is strong enough to hit threshold when it reaches the axon hillock, it will trigger an Action Potential Why? Many Voltage gated Na+ channels located at trigger zone On soma & dendrite : 50-75 / um2 membrane At trigger zone : 350-500 / um2 membrane
Action Potential Key Players: Voltage gated ion channels Voltage gated Na+ activation gate closed at resting inactivation gate open at resting Voltage gated K+ Single gate closed at resting
Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + + Remember that due to Resting Membrane Potential: there is a large diffusional gradient inward for Na+ as well as a large electrical gradient inward for Na+ There is a large diffusional gradient outward for K+
Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + + Depolarization that reaches threshold opens the Na+ activation gates and Na+ RUSHES into the cell
Action Potentials and the membrane potential Depolarizes ... Amplifier Electrode -70 mV Oscilloscope and the membrane potential Depolarizes ...
Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + + As membrane potential peaks at about 30 mV, the Na+ inactivation gates close and Na+ can no longer enter the cell K+ channels open and K+ RUSHES out of the cell
Action Potentials Return to resting membrane potential Amplifier Electrode +30 mV -70 mV Oscilloscope Return to resting membrane potential
+ + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Action Potentials + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + As membrane potential approaches resting potential the Na+ activation gate closes and the inactivation gate opens K+ gate closes
Stages of the action potential 1) Depolarization +30 2) Repolarization Membrane Potential (mV) 3) Hyperpolarization -70 1 2 3 Time (msec) Notice the Time scale……
Stages of the action potential 1) Depolarization Initially, depolarization is a local current until it reaches threshold (-55 to -50 mV) Na+ activation & inactivation gates are opened; K+ gates are closed Na+ rushes into cell Membrane Potential (mV) -70 1 2 3 Time (msec)
Stages of the action potential 2) Repolarization Sodium inactivation gates close Membrane permeability to Na+ declines to resting levels Voltage-gated K+ channels open K+ exits the cell and internal negativity of the resting neuron is restored Membrane Potential (mV) -70 1 2 3 Time (msec)
Stages of the action potential 3) Hyperpolarization Potassium gates are slow to close, causing an excessive outflow of K+ This outflow causes hyperpolarization of the membrane (undershoot) Na+ Activation gates close Na+ inactivation gates open Membrane Potential (mV) -70 1 2 3 Time (msec)
Refractory Periods Absolute RP Relative RP Na+ channels open Na+ channels inactivated No new action potential possible Relative RP Some Na+ channels still inactivated New action potential possible, but it requires a stronger than normal stimulus Membrane Potential (mV) -70 Time (msec)
Action Potentials are ALL-or None Once we hit threshold the voltage gated channels are ‘popped’ and the Na+ rushes in We have an Action Potential Threshold Stimulus Stimulus Strength Sub-threshold Stimuli Supra-Threshold -70 Membrane Potential (mV) -55 30 threshold (Its like firing a gun)
Action Potentials are Self-Propagating + + + + + + + + + + + + + + + + + + + + + +
Action Potentials are Self-Propagating + + + + + + + + + + + + + + + + + + + + + + +
Action Potentials are Self-Propagating + + + + + + + + + + + + + + + + + + + + + + +
Action Potentials are Self-Propagating + + + + + + + + + + + + + + + + + + + + + +
Action Potentials are Self-Propagating + + + + + + + + + + + + + + + + + + + + + +
Action Potentials are Self-Propagating Continuous Conduction: the action potential moves down the entire length of the axon Trigger Zone Graded Potentials Action Potentials
Action Potentials are Self-Propagating What about myelinated axons?
Action Potentials are Self-Propagating Myelinated Axons Myelin Sheath (each made by a Schwann cell) Nodes of Ranvier
Action Potentials are Self-Propagating Myelinated Axons
Action Potentials are Self-Propagating Myelinated Axons
Action Potentials are Self-Propagating Myelinated Axons Action Potentials are Self-Propagating Myelinated Axons
Action Potentials are Self-Propagating Myelinated Axons Action Potentials are Self-Propagating Myelinated Axons
Action Potentials are Self-Propagating Myelinated Axons
Action Potentials are Self-Propagating Myelinated Axons Saltatory conduction: action potential jumps from one node of Ranvier to another -- speeds up conduction in Vertebrates WOW! APs in unmyelinated = 1m/sec in myelinated = 150m/sec
An Action Potential is an Action Potential…… If there are no BIG Action Potentials for BIG stimuli…… how do we tell the difference?
Frequency Coding for Stimulus Intensity
Graded Potentials vs Action Potentials “the magnitude of the potential varies directly with the intensity of the stimulus” magnitude decreases with distance from the source Action Potentials All-or None do not decrease in magnitude with distance
Graded Potentials vs Action Potentials Are generated in Dendrites and cell body in response to stimuli Travel toward the axon hillock Action Potentials Are generated at Axon hillock when depolarization reaches threshold Are Propagated down the axon Continuous conduction Saltatory conduction Refractory Period Absolute Relative
Chemical Synaptic Transmission
Chemical Synaptic Transmission
Chemical Synaptic Transmission
Chemical Synaptic Transmission [239]
Chemical Synaptic Transmission [239]
Chemical Synaptic Transmission Synaptic Cleft [239]
Chemical Synaptic Transmission Synaptic Cleft [239]
Synaptic Cleft [239] Ca++ Chemical Synaptic Transmission calcium channels open Ca++ Synaptic Cleft [239]
Synaptic Cleft [239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell Ca++ Synaptic Cleft [239]
Synaptic Cleft [239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell Ca++ Synaptic Cleft [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ [239]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction [239]
[240] Ca++ Excitatory Postsynaptic Potential =EPSP EPSP Na+ Na+ neurotransmitter - receptor interaction opening of post-synaptic ion channels [240]
K+ K+ [240] Ca++ Inhibitory Postsynaptic Potential =IPSP IPSP neurotransmitter - receptor interaction opening of post-synaptic ion channels [240]
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction opening of post-synaptic ion channels [239] degradation of neurotransmitter
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction opening of post-synaptic ion channels [239] degradation of neurotransmitter
[239] Ca++ Chemical Synaptic Transmission calcium channels open calcium moves into presynaptic cell synaptic vesicles fuse with membrane exocytosis of neurotransmitter neurotransmitter diffuses across cleft Ca++ neurotransmitter - receptor interaction opening of post-synaptic ion channels [239] degradation of neurotransmitter
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Temporal Summation threshold [241]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [242]
Spatial Summation threshold [243]
Spatial Summation (+) threshold (+) (-) [243]