Lecture #16 Chapter 10 Flashcards
What is the function of the nervous system?
Detect changes, make decisions, stimulate muscles and glands to response, and maintain homeostasis
What are the two cell-types of the nervous system?
Neurons and Neuroglia
What are the two functions of Neurons?
-React to changes
-Relay nerve impulses for communicating to other parts of the body
What are the two functions of neuroglia?
-Surround and support neurons
-Help maintain blood-brain barrier (BBB)
What are the two branches of the nervous system?
Central nervous system (CNS) and peripheral nervous system (PNS)
What comprises the CNS?
Brain and spinal cord
What comprises the PNS?
Cranial and spinal nerves
What are the two divisions of the PNS?
Sensory division and motor divison
What type of neurons does the sensory division have?
Afferent neurons
What type of neurons does the motor division have?
Efferent neurons
What are the two divisions of the motor division?
Somatic nervous system and autonomic nervous system
What does the somatic nervous system control?
Skeletal muscle
What 3 things does the autonomic nervous system control?
-Smooth muscle
-Cardiac muscle
-Glands
What are the three general functions of the nervous system?
-Sensory
-Integration
-Motor response
During the general function of sensory in the nervous system, what 2 things occur?
-Nervous system utilizes sensory receptors to receive information
-Relays information to the CNS
During the general function of integration in the nervous system, what 3 things occur?
-Coordinates of sensory information
-Creates sensations, memories, and thoughts
-Informs decision-making in response to sensations
During the general function of motor response in the nervous system, what 2 things occur?
-Decision is put into action
-Impulses are carried to effectors (muscles/glands)
What does the somatic nervous system do?
Voluntary instruction to skeletal muscle
What does the autonomic nervous system do?
Transmits involuntary instruction to smooth muscle, cardiac muscle, and glands
What are the 4/8 parts of a nerve cell?
-Cell body
-Dendrites
-Axon
Axon hillock
Synaptic knob
-Schwann Cells
Myelin
Myelin Sheath
What is a Schwann cell?
A type of glial cell that encases peripheral axon in a sheath of lipoprotein called myelin
What are nodes of ranvier?
Gaps between myelin clusters
What is myelin?
A lipid material that forms a sheath-like covering around some axons
How does myelination occur in the PNS?
A series of Schwann cells along the length of an axon
What is the purpose of myelin?
Increases conduction velocity of a nerve impulse
What are unmyelinated PNS axons encased in?
Schwann cell cytoplasm
How are neurons classified?
By the number of extension radiating from their cell body
What are the three types of neurons?
-Multipolar
-Bipolar
-Unipolar
What type of neuron is most common?
Multipolar (99% of all neurons)
What type of neurons does the CNS mostly have?
Multipolar neurons
Where would bipolar neurons be found?
Special senses such as eyes, ears, and nose
What would be the function of a unipolar neuron?
Sensory
What are the three types of neurons by function?
-Sensory neurons
-Interneurons
-Motor neurons
What is another name for sensory neurons?
Afferent neurons
What do sensory neurons do?
Carry impulses to the CNS
What do interneurons do?
Link neurons together
Where are interneurons located?
Within the CNS
What is another name for motor neurons?
Efferent neurons
What do motor neurons do?
Carry impulses away from the CNS/deliver signals to effectors
What are the 5 roles of neuroglia?
-Provide structural support for neurons
-Guide embryonic neurons into position
-Produce growth factors to nourish neurons
-Clear excess ions and neurotransmitters
-Assist in formation of synapses
What are the 4 neuroglia of the CNS
-Astrocytes
-Oligodendrocytes
-Microglia
-Ependyma
What are the 5 functions of astrocytes?
-Connect neurons to blood vessels
-Exchange nutrients and growth factors
-Form scar tissue
-Regulate ion concentration
-Part of BBB
What are the 2 function of oligodendrocytes?
-Myelinate CNS axons
-Provide structural support
What are the 2 function of microglia?
-Phagocytic cell
-Provide structural support
Where are ependyma cells found?
Lining the central canals of the spinal cord and the ventricles of the brain
What are ependyma cells made of?
Ciliated cuboidal/columnar cells
What is the function of ependyma cells?
Regulate composition of cerebrospinal fluid (CSF)
What are the two types of neuroglia in the PNS?
-Schwann cells
-Satellite cells
What do Schwann cells do?
Produce the myelin sheath found on some peripheral axon to speed up nerve impulse transmission
What do satellite cells do?
Support clusters of neuron cell bodies (ganglia)
Mature neurons do not ____?
Divide
If the cell body of a neuron is injured, then the neuron usually ____?
Dies
What are the 3 steps for a neuron to regenerate in the PNS?
-Distal axon will degenerate
-Schwann cells and neurilemma remain (provides guiding sheath for growing axon)
-Newly formed axon reconnects with the proximal portion
Why is the regeneration of CNS neurons unlikely?
CNS axons lack neurilemma to act as a guiding sheath and oligodendrocytes do not proliferate after an injury
What is a synapse?
The site at which a neuron transmits a nerve impulse to another neuron
What is a postsynaptic neuron?
A neuron on the receiving side of a synapse
What is a presynaptic neuron?
A neuron releasing a neurotransmitter at the synapse
What is the synaptic cleft?
A narrow extracellular space between the cells of a synapse
A synapse is a ________ transfer of information?
One-way
How are neurotransmitters released?
When the impulse reaches the synaptic knob, it causes an influx of Ca++ ions. This then causes the realise of neurotransmitter via exocytosis
Neurotransmitters can either be ____ or ____?
Inhibitory or excitatory
What is cell membrane potential?
Stored electrical energy across a cell membrane due to the unequal distribution of positive and negative ions on the two sides of the membrane
What is the cell membrane potential in mV?
-70 millivolts
Is the inside or the outside of a nerve cell negative?
The inside of the cell is negative
The resting membrane potential is said to be a ____ membrane?
Polarized
What is the threshold for an action potential to result?
-55mV
What is the resting membrane potential becoming less negative called?
Depolarization
What is depolarization?
The membrane of a neuron becoming less negative (more positive) than the resting potential
What is the threshold stimulus?
The level of potential at which an action potential is triggered in a neuron or muscle fiber
Neurons are ___ cells?
Excitable
What are the 8 steps of an impulse conduction?
- Nerve cell membrane maintains resting potential (diffusion of Na+ and K+ down their concentration gradients as the cell pumps them up the gradients)
- Neurons receive stimulation causing local potential which may sum to reach the threshold
- Sodium channels in the trigger zone open
- Sodium ions diffuse inward, depolarizing the membrane
- Potassium channels in the membrane open
- Potassium ions diffuse outward, repolarizing the membrane
- The resulting action potential causes an electric current that stimulates adjacent portion of the membrane
- Action potential occur sequentially along the length of the axon
What does all-or-none response mean?
A response that occurs completely or not at all.
All impulses on an axon are the ____ ____?
Same strength
Stimulus of greater intensity produces ____ ____ of action potentials (impulses/sec), not stronger impulses?
Higher frequency
What are the two parts of the refractory period?
Absolute refractory period and relative refractory period
What is the absolute refractory period?
The time when threshold stimulus cannot generate another action potential due to voltage-gated Na+ channels being unresponsive
What is the relative refractory period?
The time when only high-intensity stimulus can generate another action potential due to repolarization not being complete
What does the refractory period limit?
The number of action potentials generated per second
What is saltatory conduction?
Impulse conduction along a myelinated axon that seems to jump form one node to the next
The speed of impulse conduction varies with ____?
Myelination
Myelin is rich in ____, and prevents water and water soluble substances (such as ions) from crossing the ____ ____; it acts as an ____ ____?
Lipids, cell membrane, electrical insulator
____ ____ also affect conduction speed?
Axon diameter
Thick, myelinated axons: ____ m/sec?
Thin, unmyelinated axon: ____ m/sec?
120
0.5
What is faster-unmyelinated axon conduction or saltatory conduction?
Saltatory conduction
