Chapter 7
The Nervous System:
Neurons and Synapses
Nervous System
n 2 types of cells in the nervous system:
n 1.
n 2.
n Nervous system is divided into:
n Central nervous system (CNS):
n
n
n Peripheral nervous system (PNS):
n .
n .
Neurons
n Basic structural and functional units of the nervous system.
n ______by mitosis.
n Respond to ______and ______stimuli.
n Produce and conduct electrochemical impulses.
n Release ______regulators.
n Nerve:
n Bundle of axons located outside CNS.
n Most composed of both ______and ______fibers.
Neurons (continued)
n Cell body:
n “______.” – area where ______synthesis occurs
n “______”
n Dendrites:
n Information ______area.
n ______electrical impulses to ______.
n ______processes that branch repeatedly
n Axon:
n Conducts impulses ______from ______
n Information transmitting
n Usually ______leaving nerve cell body
n ______than dendrites (1 meter in some animals)
n Lack ______– therefore no ______synthesis
Functional Classification of Neurons
n Based upon direction impulses conducted.
n ______:
n Conduct impulses from sensory receptors into ______.
n Motor or efferent:
n Conduct impulses ______of CNS to ______organs.
n Association or interneurons:
n Located ______the CNS.
n Serve an integrative function.
Structural Classification of Neurons
n Based on the # of processes that extend from cell body.
n ______:
n Short single process that branches like a T.
n Sensory neurons.
n Bipolar neurons:
n Have 2 processes.
n ______.
n Multipolar:
n Have several dendrites and 1 axon.
n ______.
Neurons (continued)
PNS Supporting Cells –
n Myelin Sheath:
n Made up of ______:
n Specialized ______cells wrapped around axon
n Glial “Greek for glue”
n Structural component – no ______
n Successive wrapping of the cell membrane.
n ______.
n Nodes of Ranvier:
n Unmyelinated areas between adjacent Schwaan cells that produce nerve impulses.
CNS Supporting Cells
n ______:
n Process occurs mostly postnatally.
n Each has extensions that form myelin sheaths around several axons.
n Insulation.
n ______–
n Migrate through CNS
n ______foreign and degenerated material
Nerve Regeneration
n ______:
n Act as ______, as the ______neuronal portion degenerates.
n Surrounded by basement membrane, ______:
n Serve as guide for ______.
n Send out ______that attract the growing axon.
n ______tip connected to cell body begins to grow towards destination.
Nerve Regeneration (continued)
n ______has limited ability to regenerate:
n Absence of continuous ______.
n ______molecules inhibit neuronal growth.
CNS Supporting Cells (continued)
n ______:
n Most abundant ______cell.
n Vascular processes terminate in ______that surround the ______.
n Stimulate ______, contributing to ______barrier.
n Regulate external environment of K______.
n Other extensions adjacent to synapses.
CNS Supporting Cells (continued)
n ______:
n Secrete ______.
n Line ______.
n Function as ______cells.
n Can divide and progeny ______.
Blood-Brain Barrier
n Capillaries in brain ______have pores between adjacent endothelial cells.
n Joined by ______.
n Molecules within brain capillaries moved selectively through endothelial cells by:
n ______.
n Active transport.
n ______.
n Exocytosis.
Electrical Activity of Axons
n All cells maintain a resting membrane potential (RMP) which is a electrical charge across the cell membrane.
n Potential voltage difference across membrane.
n Electrical ______between (____) charge inside the membrane and (______) charge ______
n Limited diffusion of positively charged inorganic ions.
n Permeability of cell membrane:
n Electrochemical gradients of ______+ and K+.
n Na+/K+ ATPase pump.
n Excitability/irritability:
n Ability to produce and conduct ______.
Electrical Activity of Axons (continued)
n Inside cell is ______millivolts below outside
n Extracellular fluid is set at ______millivolts
n ______:
n Potential difference reduced (become more positive).
n ______:
n Return to resting membrane potential (become more negative).
n ______:
n More negative than RMP.
3 Determinants of Resting Potential
n 1. ______
n 3 Na+ out / 2 K+ in
n Neuron cannot store either
n If deprived of either = neurological problems
n 2. ______
n More permeable to K than N ions
n Therefore – more K diffuse out (down gradient) = buildup of + charge outside membrane
n Very impermeable to Na
n 3. ______
n Ex: ______
n Synthesized by neuron are to large to diffuse across the membrane
Ion Gating in Axons
n Changes in membrane potential caused by ______flow through ion channels.
n Voltage gated (VG) channels open in response to ______in membrane potential.
n ______channels are part of ______that comprise the channel.
n Can be open or closed in response to change.
n 2 types of channels for K+:
n ______always open.
n ______closed in resting cell.
n Channel for Na+:
n Always ______in resting cells.
n Some Na+ does leak into the cells.
Ion Gating in Axons (continued)
Action Potentials (APs)
n Stimulus causes ______to threshold.
n VG Na+ channels open.
n Electrochemical gradient inward.
n ______feedback loop.
n Rapid reversal in membrane potential from –70 to + 30 mV.
n VG ______channels become inactivated.
n VG K+ channels open.
n Electrochemical gradient outward.
n ______feedback loop.
n Restore original ______.
Membrane Permeabilites
n AP is produced by an ______.
n After short delay, ______.
Action Potentials (APs) (continued)
n Depolarization and repolarization occur via ______, do not require active transport.
n Once AP completed, Na+/K+ ATPase pump extrudes Na+, and recovers K+.
n ______:
n When threshold reached, maximum potential change occurs.
n Duration is the same, only open for a fixed period of time.
n Coding for Stimulus Intensity:
n Increased ______of AP indicates ______strength.
n Recruitment:
n Stronger ______can activate more axons with a higher threshold.
Refractory Periods
n Absolute refractory period:
n ______.
n Relative refractory period:
n VG ion channel shape alters at the molecular level.
n ______
n Axon membrane can produce another action potential, but requires ______.
Cable Properties of Neurons
n Ability of neuron to ______charge through ______.
n Axon cable properties are poor:
n High ______.
n Many charges leak out of the axon through membrane.
n An ______does not travel down the entire axon.
n Each ______is a stimulus to produce another AP in the next region of membrane with VG channels.
Conduction in an Unmyelinated Axon
n Cable spread of depolarization with influx of ______depolarizes the adjacent region membrane, propagating the ______.
n Conduction rate is slow.
n AP must be produced at every fraction of micrometer.
n Occurs in ______direction; previous region is in its refractory period.
Conduction in Myelinated Axon
n ______prevents movement of Na+ and K+ through the membrane.
n Interruption in ______contain VG Na+ and K+ channels.
n AP occurs only at the nodes.
n AP at 1 node depolarizes membrane to reach threshold at next node.
n ______.
n Fast rate of conduction.
Synapse
n .
n Transmission in ______direction only.
n Axon of first (______) to second (______) neuron.
n Synaptic transmission is through a ______channel.
n Presynaptic terminal (______) releases a ______(NT).
Electrical Synapse
n Impulses can be regenerated without interruption in adjacent cells.
n ______:
n Adjacent cells electrically coupled through a channel.
n Each gap junction is composed of 12 connexin proteins.
n Examples:
n ______
Chemical Synapse
n ______is separated from postsynaptic cell by ______.
n NTs are released from ______.
n Vesicles fuse with axon membrane and NT released by ______.
n Amount of NTs released depends upon frequency of ______
Synaptic Transmission
n NT release is rapid because many vesicles form ______at “docking site.”
n AP travels down axon to ______.
n VG Ca2+ channels open.
n ______enters bouton down concentration gradient.
n Inward diffusion triggers rapid fusion of synaptic vesicles and release of ______
n Ca2+ activates ______, which activates ______.
n Protein kinase phosphorylates ______.
n ______aid in the fusion of synaptic vesicles.
Synaptic Transmission (continued)
n NTs are released and diffuse across ______.
n NT (ligand) binds to specific receptor proteins in postsynaptic cell membrane.
n Chemically-regulated gated ion channels open.
Chemical Synapses
n Excitatory postsynaptic potential
n EPSP: ______
n Increase change of action potentials
n Inhibitory postynaptic potential
n IPSP: ______.
n Decrease likelihood of action potential
n ______.
Acetylcholine (ACh) as NT
n ACh is both an excitatory and inhibitory NT, depending on organ involved.
n Causes the opening of chemical gated ion channels.
n ______:
n Found in autonomic ganglia and ______muscle fibers.
n ______:
n Found in the plasma membrane of ______muscle cells, and in cells of particular ______.
Acetylcholinesterase (AChE)
n Enzyme that ______.
n Present on postsynaptic membrane or immediately outside the membrane.
n Prevents ______.
ACh in CNS
n ______:
n Use ACh as NT.
n Axon ______synapses with dendrites or cell body of another neuron.
n First VG channels are located at axon hillock.
n EPSPs spread by cable properties to initial segment of axon.
n Gradations in strength of EPSPs above threshold determine frequency of APs produced at ______.
ACh in PNS
n ______motor neurons synapse with ______muscle fibers.
n Release ______from boutons.
n Produces end-plate potential (EPSPs).
n Depolarization opens VG channels adjacent to ______.
Monoamines as NT
n Monoamine NTs:
n ______.
n ______.
n ______.
n ______.
n Released by exocytosis from ______vesicles.
n Diffuse across the ______.
n Interact with specific receptors in postsynaptic membrane.
Mechanism of Action
n Monoamine NT do not directly open ion channels.
n Act through ______, such as cAMP.
n Binding of ______stimulates dissociation of G-protein alpha subunit.
n Alpha subunit binds to ______, converting ATP to cAMP.
n cAMP activates ______, phosphorylating other proteins.
n Open ion channels.
Serotonin as NT
n NT (derived from ______) for neurons with cell bodies in raphe nuclei.
n Regulation of ______.
n SSRIs (serotonin-specific reuptake inhibitors):
n Inhibit reuptake and destruction of serotonin, prolonging the action of NT.
n Used as an ______.
n Reduces appetite, treatment for anxiety, treatment for migraine headaches.
Dopamine an NT
n ______for neurons with cell bodies in midbrain.
n Axons project into:
n Initiation of ______movement.
n Parkinson’s disease: degeneration of neurons in substantia nigra.
n Can inhibit ______
n Involved in ______.
Norepinephrine (NE) as NT
n NT in both ______and ______.
n PNS:
n Smooth muscles, cardiac muscle and glands.
n Increase in ______.
n CNS:
n ______.
Amino Acids as NT
n ______and ______:
n Major excitatory NTs in CNS.
n Glutamic acid:
n NMDA receptor involved in ______.
n Glycine:
n Inhibitory, produces ______.
n Opening of Cl- channels in postsynaptic membrane.
n ______
n Helps control skeletal movements.
n GABA (gamma-aminobutyric acid):
n Most prevalent ______in brain.
n Inhibitory, produces IPSPs.
n Hyperpolarizes postsynaptic membrane.
n Motor functions in cerebellum.
Polypeptides as NT
n CCK:
n Promote ______following meals.
n Substance P:
n Major NT in sensations of ______
n Synaptic plasticity (neuromodulating effects):
n Neurons can release classical NT or the polypeptide NT.
Polypeptides as NT
n Endogenous ______:
n Brain produces its own analgesic endogenous morphine-like compounds, blocking the release of substance P.
n Beta-endorphin, enkephalins, dynorphin.
n ______:
n Most abundant neuropeptide in brain.
n Inhibits ______in hippocampus.
n Powerful stimulator of ______.
n NO:
n Exerts its effects by stimulation of cGMP.
n Macrophages release ______to helps kill bacteria.
n Involved in memory and learning.
n ______.
Endogenous Cannabinoids, Carbon Monoxide
n Endocannabinoids:
n Bind to the same receptor as THC.
n Act as ______.
n Function as retrograde NT.
n Carbon monoxide:
n Stimulate production of cGMP within neurons.
n Promotes ______adaptation in olfactory neurons.
n May be involved in neuroendocrine regulation in hypothalamus.