Chapter 7: Neutrons and Synapses

What is included in the CNS

Brain and spinal cord

Primary function of the CNS

Control and integration

What structures are included in the PNS

Cranial nerves and spinal nerves

What is the primary function of the peripheral nervous system

communication; it connects CNS to receptors, glands, etc.

What are the cell types in the nervous system

neurons and neuroglia

function of neurons

conduct electrical signals; basic cell or nervous system,

function of neuroglia

majority of all nerve tissues; supports neurons

where is the action potential generated on a neuron

the axon hillock

axonal transport

transporting things down the axon

what is the function of myelin

speed up signal transmission

All axons in the PNS, whether myelinated or unmyelinated, are surrounded by:

a continuous living sheath of Schwann cells

afferent neurons send signals:

into the CNS

Efferent neurons send signals

out of the CNS into the PNS

efferent and afferent neurons are part of the

PNS

interneurons are part of the

CNS

function of astrocytes

regulate the external environment of the neurons in the CNS

microglia function

migrate throughout the environment and help remove foreign substances —> can phagocytose foreign material and degenerative material

function of ependymal cells

epithelial cells that line the ventricles of the CNS; help support the cavity in which we house the brain and spinal cord; help control the composition of the fluid located in the CNS

can CNS axons regenerate

generally no

can PNS neurons regenerate

yes

what facilitates the regeneration of axons in the PNS

regeneration tube formed by Schwann cells that release chemicals calling other cells to help repair and regenerate

Schwann cells _NS

PNS; myelin-sheath former

Oligodendroytes _NS

CNS; myelin sheath former

at rest, neurons are relatively permeable to ___ ions

K+

at rest, neurons are relatively impermeable to ____ ions

Na+

depolarization

less negative than resting membrane potential

repolarization

membrane returning to the polarized resting potential

hyperpolarization

even more negative than the resting membrane potential

what happens during the depolarization of an action potential

voltage sensitive Na+ channels open as the membrane depolarizes —> when threshold is reached, more Na+ channels open

what happens during the peak of an action potential

Na+ channels become inactivated; Voltage gated K+ channels open

what happens during repolarization of an action potential

K+ leaves the neuron down the concentration gradient through the open K+ channels

What happens after hyperpolarization

K+ is still slowly leaving, and the cell returns to resting membrane potential

how are differences in stimulus intensity detected?

by the frequency of action potential generation

action potential refractory period description

due to INACTIVATED Na+ channels; if you apply a second stim. during that time, on that patch of neuron, no second action potential will be generated unless the membrane potential returns to almost zero

what is the relative refractory period due to

continued outward diffusion of K+; overshoot; need a strong stimulus to depolarize during this period

crossing the synapse sequence

action potential reaches the end of the axon terminals —> this causes gated calcium channels on the pre-synaptic cell to open —> calcium flows into the cell —> this causes the exocytosis of vesicles containing neurotransmitters —> neurotransmitters bind to the post synaptic cell —> gated sodium channels open on the post synaptic cell —> induces a synaptic potential in the postynaptic cell

what are the two types of synaptic potential

EPSP and IPSP

EPSP

excitatory post synaptic potential; results in depolarization of the post-synaptic membrane; if these signals are strong enough, an action potential occurs

IPSP

inhibitory post synaptic potential; postsynaptic membrane hyperpolarizes; opens Cl- channel, hyperpolarizing the cell

common neurotransmitters

• acetylcholine

• GABA

• Glutamate

• Glycine

• Norepinephrine and epinephrine

what type of neurotransmitter is ACH

excitatory

what type of neurotransmitter is GABA

inhibitory

what type of neurotransmitter is Glutamate

excitatory

what type of neurotransmitter is Glycine

inhibitory

what type of neutrotransmitters are norepinephrine and epinephrine

inhibitory/excitatory; just depends on the tissue

how do neurotransmitters act on postsynaptic cells

through controlling ion channels

ACh uses what type of receptor to open K+ channels

g-protein coupled channels

Norepinephrine uses what kind of receptors

G-coupled proteins that use cAMP as a secondary messenger

what is the function of acetylcholinesterase (AChE)

breaks ACh down into component parts, which are then taken back into the presynaptic cell for reuse

convergence

many presynaptic neurons converge onto one post-synaptic neuron

divergence

many post synaptic neurons diverge from one pre-synaptic neuron

Temporal summation explanation

signals occur more frequently —> theshold is reached

spatial summation

more axons are sending signals to the post-synaptic neuron