Chapter 43- The Nervous System Flashcards
Sensory receptors
Detect stimulus
Motor effectors
Responds to stimulus
Sensory neurons (afferent neurons)
They carry impulses to the central nervous system
Motor neurons (efferent neurons)
They carry impulses from the central nervous system to the effectors (muscles and glands)
Interneurons (association neurons)
They provide more complex reflexes and associative functions (learning and memory)
What supports the neurons both structurally and functionally?
The Neuroglia
What produce myelin sheaths surrounding the axons?
Schwann Cells and oligodendrocytes
What is bundled in the peripheral nervous system to form nerves?
Myelinated axons
What form white matter in the central nervous system?
Myelinated axons
Membrane potential
A voltage across the cell’s plasma membrane
What is the membrane potential of a neuron not sending signals?
The resting potential
What ion concentration is the highest inside the cell?
K+
What ion concentration is the highest outside the cell?
Na+
How are these K+ and Na+ gradients maintained?
The sodium-potassium pumps use the energy of ATP to maintain them
Where is chemical potential converted to electrical potential?
In the opening of ion channels in the plasma membrane
In a resting neuron, the currents of K+ and Na+ are what?
Equal and opposite
Graded potentials
Small continuous changes to the membrane potential
Selective
Action potential
A massive change in membrane voltage
With depolarization, it brings a neuron closer to the threshold
Hyperpolarization does the opposite
Why do action potential arise?
It is due to voltage-gated channels opening or closing
Why do changes in membrane potential occur?
It is due to neurons contain gated ion channels that open and close in response to stimuli
Voltage-gated channels lead to what?
They lead to action potentials
Ligand-gated channels lead to what?
They lead to graded potentials
Ligand gated channel
They are hormones or neurotransmitters
Induce opening and cause changes in cell membrane permeability
Hyperpolarization
An increase in magnitude of the membrane potential
Makes the membrane more positive
Depolarization
A reduction in the magnitude of the membrane potential
Makes the membrane more negative
The diffusion of K+ out, making the inside of the cell more negative is an example of what?
Hyperpolarization
Na+ channels open and Na+ diffuses into the cell is an example of what?
Depolarization
Integration of EPSPs (depolarization) and ISPSs (hyperpolarization) occurs on what?
Neuronal cell body
What are the two ways that the membrane can reach the threshold voltage?
Spatial and temporal summmation
Spatial summation
Many different dendrites produce EPSPs
Temporal summation
One dendrite produces repeated EPSPs
What is a refractory period?
It is a result of a temporary inactivation of the Na+ channels and a second action potential cannot be initiated
Negative pole is located where?
Cytoplasmic side
Positive pole is located where?
Extracellular fluid side
What does a sodium-potassium pump do?
It brings two K+ into cell for every three Na+ it pumps out
What does ion leakage channels do?
They allow more K+ to diffuse out than Na+ to diffuse in
What are the two major forces that act on ions in establishing the resting membrane potential?
Electrical potential and concentration gradient
Electrical potential is produced by what?
It is produced by unequal distribution of charges
Concentration gradient is produced by what?
It is produced by unequal concentrations of molecules from one side of the membrane to the other.
Which concentration is higher? The K+ or Na+?
K+
Equilibrium potential
Balance between diffusional force and electrical force
What is summation?
The ability of graded potentials to combine
Voltage-gated Na+ Channels
Activation and inactivation gate
At rest, activation gate closed, and inactivation gate open
Transient influx of Na+ causes the membrane to depolarize
Voltage-gated K+ channels
Single activation gate that is closed in the resting state
K+ channel opens slowly
Efflux of K+ repolarizes the membrane
What are the three phases of action potential?
Rising, falling, and undershoot
Action potentials are always ___________
“separate, all-or-none events with the same amplitude.”
In the rising phase of the action potential, what does it reflect?
Each reflects a reversal in membrane polarity.
What causes the positive charge to depolarize the adjacent region of the threshold?
Na+
What are the two ways to increase velocity of conduction?
The axon has to have a large diameter or it has to be myelinated
How does the Axon having a large diameter increase the velocity of conduction?
There would be less resistance to the current flow
How does the Axon being myelinated help increase the velocity of conduction?
It causes the impulse jumps from node to node and it is a saltatory conduction
Synapses
“Intercellular junctions with the dendrites of other neurons, with muscle cells, or with gland cells”
What cell transmits the action potential and what cell receives it?
Presynaptic cell transmits while postsynaptic cell receives it.
Electrical synapses
They involve direct cytoplasmic connections between the two cells formed by gap junctions.
Chemical synapses
The have a synaptic cleft between the two cells
End of the presynaptic cell contains synaptic vesicles packed with neurotransmitters
What does the chemical synapse’s action potential trigger?
It triggers an influx of Ca2+
What are the steps to chemical synapses?
The synaptic vesicles fuse with cell membrane
Neurotransmitterr is released by exocytosis
Diffuses to other side of cleft and binds to chemcial- or ligand-gated receptor proteins
Produces graded potentials in the postsynaptic membrane
Neurotransmitterr action is terminated by enzymatic cleavage or cellular uptake
What are the function(s) of Acetylcholine (ACh)?
It binds to the receptor in the postsynaptic membrane
It causes ligand-gated ion channels to open
It produces a depolarization called an excitatory postsynaptic potential (EPSP)
It stimulates muscle contraction
What is gluttamate?
It is a major excitatory neurotransmitter in the vertebrate CNS (Central nervous system)
Name the inhibitory transmitters and define what they do
Glycine and GABA (y-aminobutyric acid)
They open ligand-gated channels for Cl- and produce a hyperpolarization called an inhibitory postsynaptic potential
Which biogenic amines are responsible for the “fight or flight” response?
Epinephrine (adrenaline) and norepinephrine
Which biogenic amine is used in some areas of the brain that control body movements?
Dopamine
Which biogenic amine is involved in the regulation of sleep?
Serotonin
What is released from sensory neurons when activated by a painful stimuli?
Substance P
What perceives the intensity of pain?
Enkephalins and endorphins
What gas causes smooth muscle relaxation?
Nitric oxide
Habituation
Prolonged exposure to a stimulus may cause cells to lose the ability to respond to it
What does Cocaine affect?
Affects neurons in the brain’s “pleasure pathways” (limbic system)
Binds dopamine transporters and prevents the reuptake of dopamine
What does Nicotine affect?
Bind directly to a specific receptor on postsynaptic neurons of the brain
Binds to a receptor for acetylcholine
What major phylum does not have nerves?
Sponges
What are the three basic divisions for all vertebrate brains?
Hindbrain or rhombencephalon
Midbrain or mesencephalon
Forebrain or prosencephalon
What are the two elements of the forebrain?
The diencephalon and the telecephalon
What is the purpose of the diencephalon?
Thalamus - integration and relay center
Hypothalamus - participates in basic drives and emotions, controls pituitary gland
What does the telencephalon do?
It is devoted largely to associative activity
Called the cerebrum
What is the right and left cerebral hemispheres connected by?
They are connected by a tract called the corpus callosum
What are the hemispheres divided into?
The frontal, the parietal, the temporal, and the occipital lobes
Cerebral cortex
Outer layer of the cerebrum
Highly convoluted surface
What does the primary motor cortex control?
Movement
What does the primary somatosensory cortex control?
Sensory
What does the association cortex control?
Higher mental functions
Basal ganglia
Aggregates of neuron cell bodies
Participate in the control of body movement
What is the limbic system responsible for?
Emotional response
Reticular-activating system
Controls consciousness and alertness
Electroencephalogram (EEG)
Records electrical activity
What are the two proposed causes to Alzheimer disease?
Nerve cells are killed from the outside in
Nerve cells are killed from the inside out
Inner zone of the spinal cord
Gray matter
Consists of the cell bodies of interneurons, motor neurons, and neuroglia
Outer zone of the spinal cord
White matter
Contains cables of sensory axons in the dorsal columns and motor axons in the ventral columns
Somatic Nervous System
Stimulate the skeletal muscles to contract
Automatic Nervous System
Composed of the sympathetic and parasympathetic divisions, plus the medulla oblongata
Has 2 neurons: Preganglionic neuron and postganglionic neuron
Preganglionic neuron
Exits the CNS and synapses at an autonomic ganglion
Postganglionic neuron
Exits the ganglion and regulates visceral effectors
Sympathetic division
Preganglionic neurons originate in the thoracic and lumbar regions of the spinal cord
Most axons synapse in two parallel chains of ganglia right outside the spinal cord
Parasympathetic division
Preganglionic neurons originate in the brain and sacral regions of spinal cord
Axons terminate in ganglia near or even within internal organs
