Biology Ch 4. The Nervous System Flashcards
Neurons
Highly specialized cells responsible for the conduction of impulses, communicate using both electrical and chemical forms
Electrical communication neurons
Electrical communication occurs via ion exchange in the generation of membrane potential’s down the length of an axon
Chemical communication neurons
Chemical communication occurs via neurotransmitters released from the presynaptic cell in the binding of these neurotransmitters to the postsynaptic cell
Dendrites
Appendages on the soma that receives signals from other cells
Soma
Cell body, the location of the nucleus as well as organelles such as the endoplasmic reticulum and ribosomes
Axon hillock
We are the cell body transitions from the soma to the axon and where the action potential’s are initiated
Axon
A long appendage down which an action potential travels
Nerve terminal
aka synaptic bouton, at the end of an axon from which neurotransmitters are released, enlarged and flattened to maximize transmission and ensure proper release of neurotransmitters
Synaptic bouton
aka nerve terminal, the end of an axon from which neurotransmitters are released, enlarged and flattened to maximize transmission and ensure proper release of neurotransmitters
Nodes of Ranvier
Exposed areas of myelinated axons that permit saltatory conduction, critical for rapid signal conduction
Synapse
Consist of the nerve terminal of the presynaptic neuron, the membrane of the postsynaptic cell, and the space between the two (synaptic cleft)
Synaptic cleft
Space between one neurons nerve terminal and the others membrane
Myelin
Insulating/fatty substance that prevents signal loss, created by oligodendrocytes in the CNS and Schwann cells in the PNS, prevents dissipation of the neural impulse and crossing of neural impulses from adjacent neurons, increases the speed of conduction in the axon
Oligodendrocytes
Creates myelin in the central nervous system
Schwann cells
Creates myelin in the peripheral nervous system
Nerves
What neurons can be bundled into in the PNS, may carry multiple types of information including sensory, motor, or both, cell bodies of the same type are clustered together into ganglia
Tracts
What neurons can be bundled into in the CNS, only contain one type of information, cell bodies of neurons in the same tract are grouped into nuclei
Ganglia
Where cell bodies of neurons of the same type on nerves cluster together in the PNS
Nuclei nerves
Where cell bodies of individual neurons within a tract cluster together in the CNS
Neuroglia
aka glial cells, other cells within the nervous system, 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 ingesting break down waste products and pathogens in the central nervous system
Resting membrane potential
Potential for all neurons, approximately -70 mV, maintained using selective permeability of Na+ and K+ and Na+/K+ ATPase
Na+/K+ ATPase
Times three sodium ions out of the cell for every two potassium ions pumped in
Excitatory signals
Cause depolarization of the neuron
Inhibitory signals
Cause hyperpolarization of the neuron
Temporal summation
The integration of multiple signals near each other in time
Spatial summation
The addition of multiple signals near each other in space
Action potential
Transmission of electrical impulses down the axon
Depolarization
Occurs from excitatory stimulation, raises membrane potential above resting, once the cell is depolarized to the threshold voltage, voltage gated sodium channels open
Threshold voltage
Voltage where voltage gated sodium channels open during cell depolarization
Electrochemical gradient during depolarization
Causes sodium to continue to flow into neuron, allows for depolarization to continue
Peak of the action potential
Approximately + 35 mV, the voltage were sodium channels are in activated and potassium channels open
Repolarization
After the peak of the action potential is reached, potassium channels open and potassium flows out of the cell due to a strong electrochemical gradient, potassium channel stay open long enough to overshoot the action potential resulting in a hyperpolarized neuron, then the potassium channels close
Hyperpolarization
Potassium channels stay open long enough to overshoot the resting membrane potential before the potassium channels close, Na+/K+ ATPase brings the neuron back to resting potential and restores gradients, causes refractory period
Refractory period
When the axon is hyperpolarized, causes the action option to propagate down the length of the axon in only one direction
Absolute refractory period
The cell is unable to fire another action potential
Relative refractory period
The cell requires a larger than normal stimulus to fire an action potential
Neurotransmitter release
When the action potential arrives at the nerve terminal, voltage gated calcium channels open, the influx of calcium causes fusion of vesicles filled with neurotransmitters with the presynaptic membrane, resulting in exocytosis of neurotransmitters into the synaptic cleft
Neurotransmitter uptake
Neurotransmitters bind to receptors on the postsynaptic cell, which maybe ligand gated ion channels or G protein coupled receptors
Stopping the propagation of a signal
Neurotransmitters must be cleared from the postsynaptic receptors, this can occur via the neurotransmitter being enzymatically broken down, the neurotransmitter being reabsorbed back into the presynaptic cell by reuptake channels, or the neurotransmitter diffusing out of the synaptic cleft
Reuptake channels
Channels that allow neurotransmitters to be reabsorbed back into the presynaptic cell from the synaptic cleft
Central nervous system matter
Either white or gray matter
White matter
Myelinated axons, in the brain deeper than grey matter, in the spinal cord less deep than grey matter
Grey matter
Unmyelinated cell bodies and dendrites, less deep than white matter in the brain, and deeper than white matter in the spinal cord
Three types of neurons
Motor/efferent, interneurons, sensory/afferent neurons
Reflex arcs
The ability of interneurons in a spinal cord to relay information to the source of a stimulus while simultaneously routing it to the brain
Monosynaptic reflex arc
The sensory neuron (afferent, presynaptic) fires directly onto the motor neuron (efferent, postsynaptic)
Polysynaptic reflex arc
At least one interneuron between the sensory (afferent) neuron and the motor (efferent) neuron
Myelin sheath
Coats most axons in mammalian nerve fibers, maintains the electrical signal within one neuron
Glial cells
aka neuroglia, play both structural and supportive rolls in the nervous system, cells that are not neurons, includes astrocytes, ependymal cells, microglia, oligodendrocytes, and Schwann cells
Impulse propagation
Uptake of Na in one segment causes depolarization of nearby segment allowing it to reach threshold, because one direction in refractory period, one way signal, CSA increase allows signal to go faster, longer length causes it to be slower
Saltatory conduction
Myelin insulation so effective that the membrane is only permeable to ion movement at the nodes of Ranvier, signal therefore hops from node to node
Effector
The postsynaptic cell if a neuron signals to a gland or a muscle
Supraspinal
Type of circuit that is used when input from the brain or brainstem is required
Spinal cord regions
Cervical, thoracic, lumbar, and sacral
Vertebral column
Protects the spinal cord, transmits nerves at the space between vertebrae
Dorsal root ganglia
Where cell bodies of sensory neurons that enter on the dorsal side of the spinal cord are found
Motor neurons and spinal cord
Exit the spinal cord ventrally, side closest to the front of the body
Autonomic nervous system neurons
Two neurons, work in series to transmit messages from the spinal cord, first is the preganglionic neuron (soma in CNS but axon in PNS), second is the postganglionic neuron
Somatic nervous system neurons
A motor neuron in the SNS goes directly from the spinal cord to the muscle without synapsing
Parasympathetic nervous system neurotransmitters
Both preganglionic and postganglionic neurons release acetylcholine
Sympathetic nervous system neurotransmitters
Preganglionic neuron releases acetylcholine, most postganglionic neurons release norepinephrine
