1. Chapters 48 & 49 Neurons and the Nervous System

2. Three Functions
1. Sensory input: signals conducted from sensory cells in body (heat, touch, hearing, balance, vision, smell, taste, etc.)
2. Integration: information interpreted and processed (in brain and spinal cord).
3. Motor output: signals carried to muscles and glands.

3. Two Parts
Central nervous system (CNS) – processes information; brain and spinal cord.
Spinal cord incased in vertebral column; simple stimuli and responses (reflexes); carries info to brain.
Peripheral nervous system (PNS) – network of neurons which carry information into and out of the CNS.

4. Nervous system cells
1. Neurons – nerve cells made up of dendrites (receive signals), cell body (contains organelles), and axons (carries signals away from cell body).
a. Sensory neurons gather sensory info.
b. Motor neurons carry out action signals.
c. Interneurons integrate input and output.
Synapses “connect” neurons by electrical or chemical means (neurotransmitters).

8. Nervous system cells cont.
2. Supporting cells -- help neurons function (nourishment, organization); times more than neurons.
a. Glial cells found in CNS; form blood-brain barrier and myelin sheath.
b. Schwann cells found in PNS; form myelin sheath.

11. Nerve Impulse Nerve impulses are electrical signals.
Depends on flow of ions across the neuron’s cell membrane.
Neuron at rest has higher numbers of Na+ outside, higher number of K+ inside, and high numbers of Cl- outside.
Membrane potential is about –70 mV (polarized).
Sodium-potassium pump keeps ions in these concentrations so neuron can be ready to fire.

12. Nerve impulse cont.
Electrical stimulus at the dendrites causes a shift in the ion balance as Na+ enters the cell (depolarization).
When membrane potential rises to about -55 mV, the action potential is triggered.
Na+ continues into the cell and K+ exits the cell as protein channels open (more depolarization); total +100 mV change. (positive feedback loop)
Action potential moves like a wave down the axon to the end of the cell (hundreds per second).
Membrane proteins will then reset the Na+/K+ balance (repolarization).

13. Animations
Nerve impulse
Synapse
Bozeman: Action Potential

14. Neurotransmitters Can be stimulatory or inhibitory.
Acetylcholine – released by vertebrate neurons when they synapse with muscle cells, causing them to contract. (Nicotine also stimulates ACh receptors; botulinum toxin inhibits release of ACh.)
Other stimulant neurotransmitters: Epinephrine (adrenaline), dopamine.
Acetylcholine animation
Botox animation

16. Neurotransmitters cont.
Inhibitor neurotrans-mitters include: Serotonin, GABA, endorphins.

17. Brain Structure
Forebrain: cerebrum right and left hemispheres (center of intelligence; integration) connected by corpus callosum; thalamus (sensory relay station); hypothalamus (regulates temp and pituitary hormones).
Midbrain/Hindbrain (brain stem): medulla (controls heart and breathing); cerebellum (balance and coordination); pons (connects cerebellum to cerebrum)