Neurons and Synapses in the Nervous System

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PNS Schwann cells form myelin sheaths around peripheral ______

axons

Microglia migrate through the CNS and phagocytose foreign and degenerated ______

material

Astrocytes help to regulate the external environment of neurons in the ______

CNS

Ependymal cells line the ventricles (cavities) of the ______

brain

Neural stem cells are involved in the maintenance of sympathetic ______

ganglia

The distal portion of an axon that is severed from the cell body degenerates and is phagocytosed by ______ cells

Schwann

Neurons are classified functionally and structurally; the various types of supporting cells perform specialized functions in the ______ system

nervous

The ______ nervous system includes the brain and spinal cord

central

The ______ nervous system includes the cranial nerves arising from the brain and the spinal nerves arising from the spinal cord

peripheral

Neurons are the basic structural and functional units of the ______ system

nervous

Neurons are specialized to respond to physical and chemical stimuli, conduct electrochemical impulses, and release chemical regulators enabling the perception of sensory stimuli, learning, memory, and the control of muscles and ______

glands

A neuron consists of a cell body, dendrites, and an ______

axon

Channels for ___ are always closed in the resting cell.

Na+

One type of ion channel is always open, whereas the other type is closed in the ___ cell.

resting

The event called the action potential, or nerve impulse, is due to changes in ___ and K+ diffusion.

Na+

A synapse is the functional connection between a neuron and a second ___ .

cell

Neurotransmitters then bind to specific receptor proteins that are part of the ___ membrane.

postsynaptic

The release of ___ is essential for the communication across the synapse.

neurotransmitter

Astrocytes appear to be needed for the formation of synapses in the CNS. Astrocytes induce the formation of the ______ barrier.

blood-brain

In electrical activity in axons, the permeability of the axon membrane to Na+ and K+ is regulated by ______, which open in response to stimulation.

gates

Brain capillaries are joined together by ______ junctions.

tight

Net diffusion of Na+ and K+ ions occurs in two stages: first Na+ moves into the axon, then K+ moves ______.

out

The resting membrane potential (rmp) of the axon may be reduced (depolarization) or increased ______.

(hyperpolarization)

Ions such as Na+, K+, and others pass through ion channels in the plasma membrane that are said to be ______ channels.

gated

Study Notes

Ion Channels and Action Potential

  • Ion channels are closed in the resting cell, making the plasma membrane less permeable.
  • When ion channels are open, the membrane is more permeable to ions like K+.
  • There are two types of K+ channels: one is always open, and the other is closed in the resting cell.
  • Na+ channels are always closed in the resting cell and open if the Na+ channel is opened first, then the K+ channel will open.

Synapses

  • A synapse is the functional connection between a neuron and a second cell.
  • In the CNS, the other cell is also a neuron.
  • In the PNS, the other cell may be a neuron or an effector cell within a muscle or gland.

Neurotransmitters and Synaptic Cleft

  • Neurotransmitters (like acetylcholine) are released from presynaptic axon terminals.
  • Neurotransmitters diffuse across the synaptic cleft and bind to specific receptor proteins on the postsynaptic cell membrane.
  • Receptor proteins have high specificity for their neurotransmitter (ligand).

Glial Cells

  • In the PNS, there are Schwann cells (form myelin sheaths) and satellite cells (support neuron cell bodies).
  • In the CNS, there are oligodendrocytes (form myelin sheaths), microglia (phagocytose foreign material), astrocytes (regulate neuron environment), and ependymal cells (line ventricles and central canal).

Axon Regeneration

  • When an axon in a peripheral nerve is cut, the distal portion degenerates and is phagocytosed by Schwann cells.
  • Schwann cells form a regeneration tube, and neurotrophins (like NGF, BDNF, and GDNF) promote neuron growth.

Astrocytes

  • Astrocytes take up K+ from the extracellular fluid.
  • Astrocytes take up some neurotransmitters released from axon terminals.
  • Astrocyte end-feet surrounding blood capillaries take up glucose from the blood.
  • Astrocytes are needed for the formation of synapses in the CNS and induce the formation of the blood-brain barrier.

Nervous System

  • The nervous system is composed of neurons (produce and conduct electrochemical impulses) and supporting cells (assist neuron functions).
  • The nervous system has a central nervous system (CNS) and peripheral nervous system (PNS).
  • Neurons are classified functionally and structurally, and supporting cells perform specialized functions.

Electrical Activity in Axons

  • Permeability of the axon membrane to Na+ and K+ is regulated by gated channels.
  • The flow of ions and changes in membrane potential constitute an action potential.
  • The resting membrane potential (rmp) of the axon can be reduced (depolarization) or increased (hyperpolarization).

Ion Gating in Axons

  • Ions like Na+, K+, and others pass through gated channels in the plasma membrane.
  • Ion channels are said to be gated channels.

Explore the composition of the nervous system, including neurons that produce and conduct electrochemical impulses, and supporting cells that assist neuron functions. Learn about the classification of neurons and the specialized functions of supporting cells within the central and peripheral nervous systems.

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