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Nervous System & Neurons

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Presentation on theme: "Nervous System & Neurons"— Presentation transcript:

1 Nervous System & Neurons
Chapter 29, Section 2 Of your textbook

2 Central Nervous System (CNS)
Brain & spinal cord Brain – controls complex behavior Spinal cord -- controls simple responses Receives information from the peripheral nervous system & interprets it

3 Peripheral Nervous System (PNS)
All nerves & neurons outside of the CNS, Cranial nerves (originate in brain) Spinal nerves (originate in spinal cord) Divided into sensory & motor divisions

4 Sensory & Motor Divisions (of PNS)
Incoming neurons that convey info from receptors to CNS Picks up info from both internal and external environments Motor: Outgoing neurons that convey signals from CNS to muscles & glands Divided further into the somatic & autonomic systems

5 Somatic vs. Autonomic Nervous System (Motor Division of PNS)
Carries signals to skeletal muscles Generally, controls voluntary actions because it is under conscious control Includes reflexes Autonomic: Carries signals to smooth & cardiac muscles, major organ systems and glands Generally controls involuntary actions & responses

6 Types of Neurons Sensory Neurons Interneurons Motor Neurons
Receive info from inside / outside of body Send signals to brain / spinal cord Interneurons Located in brain / spinal cord Relay info between sensory & motor neurons Motor Neurons Take messages from brain / spinal cord to muscles / glands

7 Reflex Arc

8 Neuron (animation) The neuron is the structural and functional unit of the nervous system Dendrites: receive information into cell body; highly branched Cell Body: contains the nucleus and organelles Axon: one long extension that transmits an info/impulse away from cell body

9 Neuron Myelin sheath: made of Schwann cells; insulates the axon
Nodes of Ranvier: tiny gaps in the myelin sheath Axon terminals, aka synaptic terminals: branched ends of the axon Drag and Drop Quiz – Neuron Structure

10 Neurons and Signaling A neuron uses an electrical signal to transmit messages down its axon A neuron uses a chemical signal – neurotransmitters – to transmit messages across the synapse (either to another neuron or to a muscle / gland)

11 Resting Potential When a neuron is at rest, the inside is negative compared to the outside. There are more sodium (Na+) ions OUTside. There are more potassium (K+) ions INside.

12 Sodium-Potassium Pump
Helps the neuron maintain resting potential by pumping Na+ out for every K+ it pumps in Uses active transport Needs energy (ATP) Moves substances against their concentration gradient

13 Action Potential When a neuron is stimulated, membrane channels open & Na+ rushes into the cell. This makes the inside become positive (and the outside becomes negative).

14 An action potential is a moving electrical impulse.
It is generated by a stimulus. Na+ enters, and cell becomes positively charged. K+ leaves, and the area of positive charge moves. An action potential only travels one-way down the axon (from dendrites/cell body toward terminals/synapse). Animation

15 An action potential has multiple phases.
As the inside of the membrane becomes more positive, it depolarizes. As the inside becomes less positive / more negative, it is repolarizing.

16 An action potential travels faster down a myelinated axon because the impulse jumps from node to node (the gaps along the myelin sheath).

17 Signals at the Synapse When the action potential reaches the axon / synaptic terminals, the electrical signal cannot jump the synapse (the tiny gap between one neuron and the next). A chemical signal – in the form of a neurotransmitter – passes from one neuron to another (or onto a muscle or gland).

18 These neurotransmitters stimulate the next cell.
If it is another neuron, then that neuron may also have an action potential. If it is a muscle, then the muscle may contract. If it is a gland, then the gland may release a hormone.

19 The neurotransmitters are picked up by special receptor proteins in the post-synaptic cell.
When enough neurotransmitters are received, the message is carried forward. Review animation area of detail

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