Ch. 4: The Nervous System Flashcards
Neurons
Highly specialized cells responsible for the conduction of impulses
- Communicate both electrically and chemically
Electrical Communication
Via ion exchange and the generation of membrane potentials down the length of the axon
Chemical Communication
Via neurotransmitter release from the presynaptic cell and the binding of these neurotransmitters to the postsynaptic cell
Dendrites
Appendages that receive signals from other cells
Soma
Cell body; location of the nucleus as well as organelles such as the endoplasmic reticulum and ribosomes
Axon hillock
Where the cell body transitions to the axon and where action potentials are initiated
Axon
Long appendage down which an action potential travels
Nerve terminal or Synaptic Bouton
End of the axon from which neurotransmitters are released
Nodes of Ranvier
Exposed areas of myelinated axons that permit saltatory conduction (signals hop from node to node)
Synapse
Consists of the nerve terminal of the presynaptic neuron, the membrane of the postsynaptic cell, and the space between the two
Synaptic Cleft
Space between the nerve terminal of the presynaptic neuron and the membrane of the postsynaptic cell
Myelin:
Many axons are coated in myelin; an insulating substance which prevents signal loss– prevents dissipation of the neural impulse and crossing of neural impulses from adjacent neurons
Oligodendrocytes
Create myelin in the central nervous system
Schwann cells
Create myelin in the peripheral nervous system
Nerves
- individual axons and bundled into nerves or tracts
- a single nerve may carry multiple types of info including sensory, motor, or both
- cell bodies of neurons of the same type within a nerve cluster in ganglia in the peripheral nervous system
Tracts
- individual axons and bundled into nerves or tracts
- tracts contain only one type of info
- cell bodies of the individual neurons within a tract cluster in nuclei in the central nervous system
Neuroganglia or Glial Cells
Other cells within the nervous sys in addition to neurons. Include astrocytes, ependymal cells, microglia, oligodendrocytes, and Schwann cells
Astrocytes
Nourish neurons and form the blood-brain barrier, which controls the transmission of solutes from the bloodstream into nervous tissue
Ependymal cells
Line the ventricles of the brain and produce cerebrospinal fluid, which physically supports the brain and serves as a shock absorber
Microglia
Phagocytic cells that ingest and break down waste products and pathogens in the central nervous system
Resting membrane Potential
70 mV; maintained using selective permeability of ions as well as the Na+/K+ ATPase
Na+/K+ ATPase
Pumps 3 Na ions out of the cell for every 2 K+ ions pumped in; K+ leak channel leaks K+ ions out causing negative potential
Excitatory signals
Cause depolarization of the neuron
Inhibitory signals
Cause hyperpolarization of the neuron
Temporal Summation
Refers to the addition of multiple signals near each other in time
Spatial Summation
Refers to the addition of multiple signals near other in space
Action Potential
Used to propagate signals down the axon. Relay electrical impulses down the axon to the synaptic bouton
Depolarization
When enough excitatory stimulation occurs, the cell is depolarized to the threshold voltage and voltage gated sodium channels open
Sodium Flow
Sodium flows into the neuron due to its strong electrochemical gradient to continue depolarizing the neuron
Peak of the Action Potential
+35 mV; sodium channels are inactivated and potassium channels open
Potassium Flow
Potassium flows out of the neuron due to its strong electrochemical gradient, repolarizing the cell. Potassium channels stay open long enough to overshoot the action potential, resulting in a hyperpolarized neuron; then the potassium channels close
Return to Resting Potential
Na+/K+ ATPase bring the neuron back to the resting potential and restores the sodium and potassium gradients
Refractory Period
While the axon is hyperpolarized
Absolute Refractory Period
Cell is unable to fire another action potential
Relative Refractory Period
The cell requires a larger than normal stimulus to fire an action potential
How does an impulse propagate down the length of an axon?
The influx of sodium in one segment of the axon brings the subsequent of the axon to threshold. The fact that the preceding segment of the axon is in its refractory period means that the action potential can only travel in one direction
Nerve Terminal
Site where neurotransmitters are released into the synapse; when the action potential arrives at the nerve terminal, voltage gated calcium channels open. The influx of calcium causes fusion of vesicles filled w neurotransmitter with the presynaptic membrane, resulting in exocytosis of neurotransmitter into the synaptic cleft. Neurotransmitters bind to receptors on the postsynaptic cell which may be ligand-gated ion channels of G protein-coupled receptors
Stopping the Propagation of the signal
Neurotransmitters must be cleared from the postsynaptic receptors to stop the propagation of the signal. Neurotransmitter can be enzymatically broken down. Neurotransmitter can be absorbed back into the presynaptic cell by reuptake channels. Neurotransmitter can diffuse out of the synaptic cleft
Types of neurons in the nervous system
Motor (efferent) neurons, Interneurons, and sensory (afferent) neurons
Sensory neurons
Transmit sensory info from receptors to the spinal cord and brain
Motor neurons
Transmit motor information from the brain and spinal cord to muscles and glands
Interneurons
Found between other neurons and are the most numerous of the 3 types. Located in the mostly brain and spinal cord and are often linked to reflexive behavior
The nervous system is made up of
Central nervous system (CNS) and the Peripheral Nervous system (PNS)
Central Nervous system
Brain and spinal cord, white matter and gray matter
White Matter
Consists of myelinated axons; in the brain, white matter is deeper than gray matter. In the spinal cord gray matter is deeper than white matter.
Gray matter
Unmyelinated cell bodies and dendrites
Peripheral Nervous System
Cranial and Spinal nerves; Divided into somatic (voluntary) and autonomic (involuntary) nervous systems
Autonomic nervous system
Further divided into parasympathetic (rest and digest) and sympathetic (fight or flight) branches
Reflex Arcs
Use the ability of interneurons in the spinal cord to relay info to the source of a stimulus while simultaneously routing it to the brain
Monosynaptic reflex arc
Sensory (afferent, presynaptic) neuron fires directly onto the motor (efferent, postsynaptic) neuron
Polysynaptic reflex arc
The sensory neuron may fire onto a motor neuron as well as interneurons that fire onto other motor neurons
