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Nervous System.

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Presentation on theme: "Nervous System."— Presentation transcript:

1 Nervous System

2 Nervous System Overview
Sensory input Sensory receptors Collect info Integration Interpretation of stimuli Occurs in CNS (brain & spinal cord)

3 Nervous System Overview
Motor Output Conduction of signal from CNS to effector cells Carry out response to stimuli Muscles & glands Signal conducted by nerves CNS PNS (outside of CNS)

4 Nervous System Overview

5 Nervous System Overview
Nerve Circuit Simplest: automatic (reflex arc) Sensory neuron interneuron of spinal cord  motor neuron  effector cell


7 Nervous System Overview
Ganglion: cluster of nerve cell bodies with similar functions in PNS Cluster within brain: nuclei Supporting cells :glia “Glue” neurons together Helps embryonic development of CNS

8 Nervous System Overview
Astrocytes: provide support for neurons, induce tight junction formation for cells lining capillaries of brain Blood-brain barrier Restricts passage of substances into brain

9 Nervous System Overview
Oligodendrocytes (in CNS) [Schwann cells in PNS] Form insulating lipid sheath around neuron axon Increase speed of nerve impulse Deterioration of: MS


11 Membrane Potential Nerve signals: changes in voltage across plasma membrane of nerve cells Caused by ion movement More anions inside; more cations outside Membrane now electrically polarized -50 to –100 mV in resting state (unstimulated)


13 Membrane Potential Inside: cations are mostly K+, some Na+ (anions are proteins, a.a., sulfate, P, Cl-) Outside: cations are mostly Na+, some K+ (anions are mostly Cl-) Ions only pass through selective protein channels Most cells more permeable to K+ than Na+ Internal anions too large to cross


15 Membrane Potential Tendency for K+ to diffuse out, Na+ in
Through channels that are always open (ungated) Sodium-potassium pump uses ATP to bring K+ in & Na+ out Maintains ionic gradient – keep potential


17 Membrane Potential Cells that generate changes in potential – excitable cells When unexcited: resting potential When stimulated, gated ion channels open - allow specific ion through


19 Membrane Potential Some stimuli trigger hyperpolarization – inc in voltage across membrane (K+ out  cell more negative) Some trigger depolarization (Na+ in  cell less negative) Strong enough stimuli trigger action potential (nerve impulse)



22 Action Potential All or nothing Few milliseconds
In between stimuli: refractory period More intense stimuli – repeated action potentials with refractory period in between Action potential at one point of axon triggers next action potential


24 Action Potential Speed of action potential influenced by:
Diameter of axon (larger = faster) Myelination of axon Action potential only occurs at nodes (between Schwann cells) Appears to “jump” – saltatory conduction


26 Synapses Cell junctions between neurons, receptors, effectors
Two types Electrical synapses Action potential spreads directly from cell to cell Cells connected by gap junctions

27 Synapses Chemical synapses Gap (synaptic cleft) separates cells
Action potential cannot be directly transmitted Conversion of electrical signal to chemical signal that bridges gap Action potential at end of neuron releases Ca2+ into neuron


29 Synapses This causes synaptic vesicles to release chemicals (neurotransmitters) into synaptic cleft Receptors on next neuron receive chemicals – opens ion channels – allows K+, Na+, Cl- across – impulse continues


31 Neurotransmitters Figure 48.1

32 Nervous System Diversity

33 Vertebrate Nervous System



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