Neurons, Synapses, and Signaling Chapter 48 Neurons, Synapses, and Signaling

Information Processing 1) Detection of stimuli (senses) 2) Sensory input (from peripheral to central nervous system) 3) Integration 4) Motor output (effector)

Neurons Sensory – can detect changes in/out of the body Interneuron – process the signal and pass it on to the next neuron Motor – cause the response: move a muscle, stimulate gland, etc.

More Vocabulary Ganglia – in peripheral nervous system, collection of neuron cell bodies Nuclei – in the central nervous system, collection of neuron cell bodies

Parts of a neuron Dendrites – receive signal, carry it towards cell body Nodes of Ranvier – (PNS) the parts of the axon without myelin (between the myelin sheaths) Cell body – have the nucleus and organelles Neuroglia – (CNS) Axon – carries impulse away from the cell body Astrocytes: surround capillaries in the brain; blood brain barrier Synapse – space between the neurons Oligodendrocytes: myelin makers Schwann cells – (PNS) makes myelin which insulates axon, helping the signal move faster

Vertebrates vs Invertebrates Single longitudinal vertebrae Spinal cord is dorsally located Hollow spinal cord Division of ganglia is not as apparent Brain controls body more than the spinal cord Paired longitudinal vertebrae Spinal cord is ventrally located Solid spinal cord Division of ganglia is apparent Spinal cord can control the body without brain

Nerve impulse Electrical signal that depends on the flow of ions K+ (inside), Na+ (outside), Cl- (outside), Large anions like proteins (inside) Resting Membrane Potential: -70 mV (more negative outside) Cells have a higher permeability to potassium (more channels), so when potassium leaves, the inside will become more negative. Sodium (which was on the outside) moves into the cell to balance the negative/positive difference, the inside becomes more positive. Sodium-potassium pump restores to resting membrane potential

Continued Two cells that can change membrane potential because of stimulus: neurons and muscle cells. Hyperpolarizing stimuli- open potassium ion channels (becomes more negative) Depolarizing stimuli- open sodium ion channels (becomes more positive)

All or none Threshold: if you reach about -50mV, then you have an action potential Action potential: maximum membrane potential, depolarized to the max Stimulus If gentle stimulus, then lower frequency of impulse firing If harsh stimulus, then higher frequency of impulse firing

The whole process now… Animation: http://highered.mheducati on.com/sites/007249585 5/student_view0/chapter 14/animation__the_nerve _impulse.html

Transmission The larger the diameter of the axon, the faster the transmission Saltatory conduction – myelin aids in faster transmission, because the impulse “jumps” from Node to Node of Ranvier

Synapse Electrical synapse – don’t really need to know, ex. Sticking finger into electrical outlet Chemical synapse – Calcium ions (in pre-synaptic neuron) help move neurotransmitter in vesicles, neurotransmitters are dumped into the synaptic cleft, sodium ion channels open on post-synaptic neuron. (Animation) Excitatory post-synaptic potentials = sodium ion channels open Inhibitory post-synaptic potentials = potassium ion, chloride ion channels open Summation: Temporal – dependent on time, needs to be very quick to sum up Spatial – dependent on space, multiple potentials come in and sum up (or cancel each other if there are excitatory and inhibitory potentials) Figure 48.16

Neurotransmitters Acetylcholine Amino acids Excitatory in muscles Amino acids GABA – most abundant inhibitory neurotransmitter Endorphins – natural opiates, block out pain Gases Nitric oxide – ex. erections in penis