Quiz 1 (suzanne's) Flashcards
Two major classes of cells:
Neurons: carry/ transmit information by the conduction of electrical impulses / action potentials.
Glia or neuroglia (“glue”) cells: provide support and maintenance functions for neural tissue.
Remember: Glia cells are unable to transmit potentials.
Glia or neuroglia (“glue”) cells
provide support and maintenance functions for neural tissue.
Remember: Glia cells are unable to transmit potentials.
Neurons: 3 types
Motor/ Efferent (descending): they are coming out from the CNS and PNS to the effector organs and tissues. They “make things happen”.
Sensory/ Afferent (ascending). They bring information from the effector organs and tissues to the PNS/ CNS for interpretation.
Associative / interneurons: compile a “balance sheet”. You can consider them “middle men”. They are majority of neurons. Integrate sensory information elicit motor response.
Efferent
Motor neurons
Descending
they are coming out from the CNS and PNS to the effector organs and tissues. They “make things happen”.
Afferent
Sensory neuron
Ascending
They bring information from the effector organs and tissues to the PNS /CNS for interpretation.
Associative
Interneurons
compile a “balance sheet”. You can consider them “middle men”.They are majority of neurons.
Central Nervous System (CNS)
Interneurons
compile a “balance sheet”. You can consider them “middle men”.They are majority of neurons.
Glia cells: 6 types
- Schwann cells: insulating (organized into myelin), and assist regeneration/ repair of axons within PNS.
- Oligodendrocytes: insulating and resist regeneration within CNS.
- Astrocytes (CNS): form blood-brain barrier
- Microglia (CNS): a “sanitation department” macrophages of brain and spinal cord, clear cellular debris and dead neurons through phagocytosis, first line of immune defense for cns.
- Satellite cells (PNS): provide support within ganglia (clusters of functionally united neurons)
- Ependymal cells (CNS): Secrete CSF within brain ventricles; provide brain-CSF barrier.
Somatic Nervous System:
controls and innervates-
The external lining and internal lining (peritoneum) of the body wall : sensory and motor
Extremities: sensory and motor
Special senses: smell, taste, vision, hearing, equilibrium
NOTE: There are two exceptions on the body wall and extremities:
- Erector pili muscles (“goose bumps”) they are smooth muscles
- Sweat glands
- Both are controlled by ANS
Peripheral Nervous System (PNS)
Somatic Nervous System (SNS)
Autonomic Nervous System (ANS)
Enteric Nervous System (ENS)
clusters of related neurons (cell bodies or soma) are called:
GANGLIA (GANGLION)
bundles of related axons: NERVE(S).
Autonomic Nervous System:
Motor Innervation of “internal body”
Cardiac muscle, smooth muscle, secretory glands
Subdivisions: Sympathetic and Parasympathetic
Enteric Nervous System
Chains of ganglia (plexi/ plexus) along several layers of gastro-intestinal tube / alimentary canal.
Responsible for peristalsis and secretion of GI “juices”.
The neurons of the ENS are collected into two types of ganglia: myenteric (Auerbach’s) and submucosal (Meissner’s) plexuses.[10] Myenteric plexuses are located between the inner and outer layers of the muscularis externa, while submucosal plexuses are located in the submucosa.
Dendrites
Receivers
Branches-most efficient receiving part in neuron for impulses and information.
Soma
Perikaryon-around the nucleus
Major control place
Produces building blocks
Enables neurons to communicate with other neurons
Node of ranvier
Gaps in the myelin sheath.
Appear at intervals along the axon.
Neurons
carry/ transmit information by the conduction of electrical impulses / action potentials.
Axon
Axis of a neuron.
Propagates nerve impulse toward another neuron, muscle fiber or gland cell.
Synaptic end bulbs
Tips of some axon terminals
Chemical synapses found here
Nissl bodies
Rough endoplasmic reticulum
Found in the soma
( neuronal cell bodies contain free ribosomes and prominent clusters of rer)
Resting membrane potential
The membrane potential is an electrical voltage difference across the membrane.
VOLTAGE IS ALSO TERMED THIS.
Neurons are electrically excitable and communicate with one another using 2 types of electrical signals.
- Action potentials.
- Graded potentials.
Ion Channels
The main paths for flow of current across the membrane are ion channels.
When ion channels are open, they allow specific ions to move across the plasma membrane down their electrochemical gradient.
- Ions move from greater areas of concentration to lesser areas of concentration.
- Positively charged cations move towards negatively charged area and negatively charged anions move towards a positively charged area.
- As they move, they change the membrane potential.
Types of Ion Channels
There are several types of ion channels.
Leakage channels - gates randomly alternate between open and closed positions.
Voltage-gated channels - open in response to change in membrane potential (voltage).
Ligand-gated channels - open and closes in response to a specific chemical stimulus.
Mechanically gated channels - open or closes in response to mechanical stimulation.
Light gated channels-open, when affected by entering light(eye retina)
Resting Membrane Potential
In neurons, the resting membrane potential ranges from -40 to -90 mV.
Typically -70 mV.
The minus sign indicates that the inside of the cell is negative compared to the outside.
Graded Potentials
A graded potential is a small deviation from the resting membrane potential.
- It makes the membrane either more polarized (more negative inside) or less polarized (less negative inside).
- Most graded potentials occur in the dendrites or cell body.
Hyperpolarizing graded potential.
Depolarizing graded potential.
Graded potentials occur when ligand-gated or mechanically gated channels open or close.
- Mechanically gated channels are present in sensory neurons.
- Ligand-gated channels are present in interneurons and motor neurons.
Action Potentials
known as an impulse.
- Depolarizing phase - the resting membrane potential decreased towards zero.
- Repolarizing phase - restores the resting membrane potential.
Threshold - depolarization reaches a certain level (about -55 mV), voltage gated channels open.
arise according to an all or none principal.
Depolarizing Phase
A depolarizing graded potential or some otherstimulus causes the membrane to reach threshold
• Voltage-gated ion channels open rapidly
• The inflow of positive Na ions changes the
membrane potential from -55mv to 30 mV.
About 20,000 Na enter through the gates.
Millions are present in the surrounding fluid.
Repolarizing Phase
When all sodium channels are open, they will start slowly to close.
Potassium voltage channels will begin to open.
• K channels allow outflow of K ions.
• The closing of Na channels and the slow opening of K channels allows for repolarization.
Refractory Period
The period of time after an action potential begins during which an excitable cell cannot generate another action potential.
Neurotoxins
Neurotoxins produce poisonous effects upon the nervous system.
• Local anesthetics are drugs that block pain and other somatic sensations.
• These both act by blocking the opening of voltage-gated Na channels and preventing propagation of nerve impulses.
Continuous and Saltatory Conduction
Continuous conduction - step-by-step depolarization and repolarization of adjacent segments of the plasma membrane.
• Saltatory conduction - a special mode ofimpulse propagation along myelinated
axons.
Few ion channels are present where there is myelin.
• Nodes of Ranvier - areas where there is no myelin - contain many ion channels.
• The impulse “jumps” from node to node.
- This speeds up the propagation of the impulse.
- This is a more energy efficient mode of conduction.
Signal Transmission at Synapses
Presynaptic neuron - the neuron sending the signal.
Postsynaptic neuron - the neuron receiving the message.
- Axodendritic - from axon to dendrite.
- Axosomatic - from axon to soma.
- Axoaxonic - from axon to axon.
Types of Synapses
Electrical synapse
Chemical synapse
Chemical Synapses
The plasma membranes of a presynaptic and postsynaptic neuron in a chemical synapse do not touch one another directly.
The space between the neurons is called a synaptic cleft which is filled with interstitial fluid.
A neurotransmitter must diffuse through the interstitial fluid in the cleft and bind to receptors on the postsynaptic neuron.
The synaptic delay is about 0.5 msec.
Axon hillock
Cone shaped elevation where the cell body is joined
Axon terminal
Where the axon and collaterals end.
Enteric plexus of meissner
Secretion
myenteric plexus of auerbach
Motility
What do ions produce
Electrical current
Absolute refractory period
a second action potential cannot be initiated, even with a very strong stimulus.
Relative refractory period
an action potential can be initiated, but only with a larger than normal stimulus
Electrical Synapses
Action potentials conduct directly between adjacent cells through gap junctions.
