Signal Transduction Pathway • Reception, Transduction, Response • Ligand is the fancy word for signaling molecule. • Energy can be in the form of ions
Nervous System in Animals • Evolved from nerve net in Cnidarians • Brain evolves giving greater control. Includes a nerve cord. • Cephalization occurs- development of other sensory organs in the head.
Stimulus • A stimulus is a form of energy like light (electromagnetic) or pressure (mechanical), or sound waves.
Nervous System in Animals • 1. Sensory Input-Sensory receptors receive a stimulus and send it into the brain/ spinal cord. • 2. Integration- the CNS integrates/interprets/thinks about the sensory input (stimulus). • 3. Motor Output- Impulse sent from the brain to the muscles to respond. Effector cellsin muscles and glands will respond. • Peripheral Nervous System-has sensory receptors and motor nerves.
Neurons- nerve cells • Cell Body- receives stimuli from all dendrites, and creates one signal • Dendrites- carry stimuli into the cell body • Axon- carries signal away from cell body and towards next neuron. • Myelin Sheath- lipid covering over axon for insulation. Composed of Schwann cells (PNS) • Synaptic Terminal- end of axon • Synapse- gap between neurons or neuron and effector cell.
Other Nerve Terms • Ganglia- bundle of neurons in the PNS • Nuclei- bundle of neurons in the CNS • Glial Cells- give neurons support (framework) • Oligodendrocytes- aka Schwann Cells of the CNS
Multiple Sclerosis- MS- Schwann Cells die in CNS & PNS and causes the signal (electrical current) to burn muscles into permanent contractions. Schwann Cells OR Oligiodendrocytes Nodes of Ranvier Layers of myelin Axon Schwann cell Schwann cell Nucleus of Schwann cell Nodes of Ranvier Axon Myelin sheath 0.1 µm
Remember… • Ions can be considered ___________ • Concentration gradients are ________________ and so they can be considered _____________ • Active transport requires _______________ . • Diagram a cell pump.
Membrane Potential • Ability of the membrane to do work. • Created by electrical gradient (difference) on either side of the c.m. • Anions inside Cations outside
CYTOSOL EXTRACELLULAR FLUID [Na+] 150 mM [Na+] 15 mM Membrane Potential and ion concentrations [K+] 150 mM [K+] 5 mM [Cl–] 120 mM [Cl–] 10 mM [A–] 100 mM Plasma membrane
Resting Potential • Resting Potential- Unstimulated neuron, need to establish the [gradient] • 1. NaK Pump responsible for generating nerve impulse. • NaK Pumps are either ligand gated or voltage gated, which helps create gradient faster.
EXTRACELLULAR FLUID Na+ [Na+] high [K+] low Na+ Na+ Na+ Na+ Na+ Na+ Na+ Na+/K+ pumps ATP [Na+] low [K+] high P P Na+ CYTOPLASM ADP Phosphorylation causes the protein to change its conformation, expelling Na+ to the outside. Na+ binding stimulates phosphorylation by ATP. Cytoplasmic Na+ bonds to the sodium-potassium pump K+ K+ K+ K+ K+ P K+ P K+ is released and Na+ sites are receptive again; the cycle repeats. Loss of the phosphate restores the protein’s original conformation. Extracellular K+ binds to the protein, triggering release of the phosphate group.
Action Potential Steps • 1. Depolarization- destroys membrane potential, Na floods into cell • Depolarization is “graded” • Threshold potential-minimum Na that must enter to generate a nerve impulse • Action Potential- “Spike” electrical generated impulse, anaction will occur • 2. Repolarization- neuron pumps out K to try and return to resting potential.
Action Potential Steps • 3. Hyperpolarization- the cell will pull in some K to get back to resting potential. • Must Hyperpolarize so that the neuron can get back to resting potential, and to recreate the [gradient]/ polarity • 4. Refractory Period- neuron can’t make new impulse
Stimuli Stronger depolarizing stimulus Stimuli Resting Potential +50 +50 +50 Action potential 0 0 0 Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Threshold Threshold –50 –50 –50 Threshold Resting potential Resting potential Resting potential Depolarizations Hyperpolarizations –100 –100 –100 1 1 4 1 4 0 0 5 2 3 0 6 2 3 5 2 3 5 4 Time (msec) Time (msec) Time (msec) Graded potential hyperpolarizations Graded potential depolarizations Action potential
Propagation & Saltatory Conduction • Propagation: Impulse traveling down the axon. • Saltatory Conduction: impulse “hopping” over Schwann Cells. Ions are only exposed at the nodes. • The jumping makes impulse travel really quick.
Axon Action potential Propagation Na+ An action potential is generated as Na+ flows inward across the membrane at one location. Action potential K+ Na+ K+ The depolarization of the action potential spreads to the neighboring region of the membrane, re-initiating the action potential there. To the left of this region, the membrane is repolarizing as K+ flows outward. Action potential K+ Na+ K+ The depolarization-repolarization process is repeated in the next region of the membrane. In this way, local currents of ions across the plasma membrane cause the action potential to be propagated along the length of the axon.
Schwann cell Saltatory Conduction Depolarized region (node of Ranvier) Cell body Myelin sheath Axon
Reflex Arc-Simplest Neural Pathway • 1. Sensory Neuron- receive stimulus • 2. Interneuron- in CNS (spinal cord) takes sesoryimput and gives signal to motor neuron • 3. Motor Neuron- carries energy to effector cell. ( ________/__________) • This is why you don’t think about a reflex, the signal never made it to the brain for integration.
Remember • Diffusion is _________ and uses no ________ • Ligands bind to receptor proteins and cause a: • Do you think all ligands cause the same response?
Draw 2 neurons & label the synapse • Where are synapses located? ______&________
Synapses and Nerve Impulses • 2 Types of Synapses • 1. Electrical- direct cell contact, in brain • 2. Chemical- most common in animals- requires a neurotransmitter (chemical ligand)
Chemical Synapses • The impulse is Electrical energy chemical energy electrical energy • Nerve Impulse Conversion in Chemical Impulses: 1. Depolarization- down to the axon terminal of presynaptic neuron. • 2. Ca rushes into presynaptic cell due to impulse hitting the axon terminal. • 3. Neurotransmitter vesicles fuse with pre-syn. cell membrane.
Nerve Impulse cont. • 4. Neurotransmitter released into synapse • 5. Neurotransmitter binds to receptor protein on post syn cell and causes a CSC • 6. Na floods into post syn. Cell and causes depolarization.
Postsynaptic cell Presynaptic cell Synapse at the axon terminal Na+ Neuro- transmitter K+ Synaptic vesicles containing neurotransmitter Presynaptic membrane Postsynaptic membrane Ligand- gated ion channel Voltage-gated Ca2+ channel Postsynaptic membrane Ca2+ Synaptic cleft Ligand-gated ion channels
EPSP & IPSP • IPSP & EPSP • Excitatory Post Synaptic Potential- causes Post syn. Cell to do act or keep impulse going • Inhibitory Post Synaptic Potential- causes Post syn. Cell to stop impulse transmission • Summation- adding of all dendrite stimuli to reach threshold potential
Neurotransmitters • Neurotransmitters- chemical ligands produced by neuron to transmit the signal across the synapse. • Neurotransmitters are released from a pre-synaptic cell (neuron) and received by a postsynaptic cell (neuron or effector cell).
Neurotransmitters • Acetylcholine- (ACh)makes muscles contract in PNS, can be excitatory or inhibitory in CNS. • Cholinesterase breaks down ACh • Biogenic Amines • 1 & 2. Epinephrine and norepinephrine- fight or flight, speeds up body functions • 3.Dopamine=happy • 4. Serotonin=sleep *both out of whack in ADD/Schiz
Neurotransmitters • Amino Acids • 1. Substance P- relays pain stimulus • 2. Endorphins- block Substance P “second wind” • Gases- work by diffusion • 1. NO • 2. CO • *both inhibit nerve signaling and muscle contractions
Stimuli Stronger depolarizing stimulus Stimuli Can you explain these? +50 +50 +50 Action potential 0 0 0 Membrane potential (mV) Membrane potential (mV) Membrane potential (mV) Threshold Threshold –50 –50 –50 Threshold Resting potential Resting potential Resting potential Depolarizations Hyperpolarizations –100 –100 –100 1 1 4 1 4 0 0 5 2 3 0 6 2 3 5 2 3 5 4 Time (msec) Time (msec) Time (msec) Graded potential hyperpolarizations Graded potential depolarizations Action potential
Sense Perception • 1. Sensation- action potential is at the brain, and senses a nerve impulse. • 2. Perception- integration of sensation by brain
Sensory Reception • Special neurons detect stimuli. • Stimuli will be detected by their ____________. • Stimuli is defined as _________________ • That will cause a _ _ _
Sensory Transduction Pathway • 1. Summation will cause Threshold potential to be reached. • 2. Amplification can occur on the way to the CNS. • 3. Saltatory conduction is responsible for signal propagation. • 4. Integration by CNS for appropriate response.
Sensory Adaptation • Decrease in continuous stimulus coming into the CNS. • CLOTHING DETECTED BY BODY, BUT IS NOT RESPONDING.
Types of Sensory Receptors 1. Internorepectors- detect internal stimuli- pressure, balance, homeostasis 2. Externoreceptors- external stimuli • Mechanoreceptors- detect bend/stretch of membranes/hairs • Nociceptors-detect pain using Substance P • Thermoreceptors- detect cold • Chemoreceptors-detect cheimicals: osmo-water, gustatory-taste, olfactory-smell • Electromagnetic receptors-detect photo-light, electro- electrical, magno-magnetic
Cold Hair Pain Heat Light touch Stimulus receptors Epidermis Dermis Hypodermis Strong pressure Hair movement Connective tissue Nerve