Ch 48 – Nervous Systempt 2

P.

Neurons communicating with other cells Neurons communicate with other

cells at synapses

Electrical synapse- Direct communication from pre to post

synaptic cell Gap junctions connect cells and ion

currents flow between cells

Chemical Synapse Much more common in vertebrates &

most invertebrates Action potential reaches synaptic

terminal This depolarization causes Ca+ to

rush into neuron through voltage gated calcium channels

Chemical Synapse Synaptic vesicles fuse with

presynaptic membrane and release neurotransmitters.

Neurotransmitter diffuses across synaptic cleft and binds to ligand gated ion channels in second neuron.

Ligand gated ion channels open, generating a post-synaptic potential

Neurotransmitter is removed quickly – by enzymes or by surrounding cells uptake

Presynapticcell Postsynaptic cell

Axon

Presynapticmembrane

Synaptic vesiclecontainingneurotransmitter

Postsynapticmembrane

Synapticcleft

Voltage-gatedCa2 channel

Ligand-gatedion channels

Ca2

Na

K

2

1

3

4

Excitatory synapses

Some synapses are excitatory – they increase the likelihood that the axon of the postsynaptic neuron will generate an action potential

Opens channels that allow Na+ to enter & K+ to leave cell, so

EPSP – excitatory postsynaptic potentiial Electrical change caused by this binding

of neurotransmitter to receptor

Inhibitory synapses

Some synapses are inhibitory – they make it more difficult for the postsynaptic neuron to generate an action potential

Opens channels that allow K+ to rush out of cell and Cl- to enter cell, so

IPSP – inhibitory postsynaptic potentiial Electrical change caused by this binding

of neurotransmitter to receptor

Summation of postsynaptic responses A single EPSP is usually not enough

to produce an action potential Summation = the additive effect of

postsynaptic potentials The axon hillock is the neuron’s

integrating center Temporal summation Spatial summation

Indirect synaptic transmission In some synapses, a neurotransmitter

binds to a metabotropic receptor , not directly to an ion channel

Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a second messenger

Indirect synaptic transmission Compared to ligand-gated channels, the

effects of second-messenger systems have a slower onset but last longer

Neurotransmitters

Many different types – 5 main groups: Acetylcholine biogenic amines amino acids Neuropeptides gases

One neurotransmitter can have more than a dozen different receptors

Acetylcholine Acetylcholine is a common

neurotransmitter in vertebrates and invertebrates

It is involved in muscle stimulation, memory formation, and learning

Released at neuromuscular junctions Can be inhibitory or excitatory

Amino Acids & Gases Amino acid neurotransmitters are active in the

CNS and PNS Known to function in the CNS are

Glutamate Gamma-aminobutyric acid (GABA)- thought to

be transmitter at most inhibitory synapses in brain Glycine

Gases such as nitric oxide and carbon monoxide are local regulators in the PNS

Biogenic Amines

Biogenic amines are derived from amino acids

include Epinephrine Norepinephrine Dopamine Serotonin

They are active in the CNS and PNS

Neuropeptides Several neuropeptides, relatively short

chains of amino acids, also function as neurotransmitters

Neuropeptides include substance P and endorphins, which both affect our perception of pain

Opiates bind to the same receptors as endorphins and can be used as painkillers

Nervous system

Central Nervous system – Brain & spinal cord

Peripheral nervous system- nerves that communicate motor & sensory signals thru body

Vertebrate brain specialization

Cerebrum – 2 hemispheres, higher brain functions such as thought & action

Vertebrate brain specialization

Cerebellum – helps coordinate movement, posture, balance

Vertebrate brain specialization

Brainstem – controls homeostatic functions such as breathing rate, heart rate, blood pressure. Conducts sensory & motor signals between spinal cord & higher brain centers

Allan Jones: A map of the brain

http://www.ted.com/talks/allan_jones_a_map_of_the_brain.html

The mysterious workings of the adolescent brain

http://www.ted.com/talks/sarah_jayne_blakemore_the_mysterious_workings_of_the_adolescent_brain.html