Chapter 17 Flashcards
What are the two divisions of the nervous system in animals?
Central nervous system (Brain and spinal cord) and peripheral nervous system (nerve tissue outside of the brain and spinal cord).
What are the two types of cells in nervous tissue?
Neurons which transmit nerve impulses, and neuroglia which support and nourish neurons.
What are the neurons of the peripheral nervous system?
Sensory, afferent, and efferent.
Describe sensory neurons.
Connected to receptor cells, may have specialized endings. Detect a change in stimuli and conduct and electrical impulse which then travels to CNS.
Describe afferent neurons.
Take info from sensory neurons and move it to spinal column or CNS.
Describe efferent neurons.
After central nervous system has dealt with message that was sent from sensory neurons.
What is an effector?
Efferent neurons send messages to an effector. It is an organ, muscle, or gland that receives messages from CNS via efferent neurons.
Describe an interneuron.
Lie entirely within the CNS- the spinal column. Receive input from sensory neurons. They create circuits to parts of CNS that make decisions.
What type of neuron plays a role in reflex reactions?
Interneurons.
Describe motor neurons.
Cell body is in a spinal column, fiber may be outside. Given processed CNS message from interneurons. Then, motor neurons then give message to efferent neurons which then go on to an effector.
What are the 3 parts of a neuron.
Cell body: Contains the nucleus and other organelles.
Dendrites: extensions that receive signals from other neurons.
Axon: Conducts nerve impulses away from the cell body toward other neurons or effectors.
What is a myelin sheath?
Some axons are covered by a myelin sheath in the PNS. Myelin, a lipid substance which wraps around axons to act as an electrical insulator.
Describe the nodes of Ranvier.
The myelin sheath isn’t continuous. The nodes of Ranvier are gaps in the myelin sheath that play a role in ions diffusing in/out enhancing electrical conduction.
What are schwann cells?
A type of neuroglia that surround axons and deposit lipids. These create the myelin sheath around axons.
What happens if the axon is severed in the PNS and CNS?
PNS: sheath helps with new fiber construction or regeneration.
CNS: myelin sheath doesn’t help with regeneration of severed axons.
What are the 2 types of nervous tissue the CNS is composed of?
Gray matter, white matter.
Describe gray matter.
Contains cell bodies and short, non-myelinated fibres. In the surface layer of the brain, related to senses, emotions, and decision making, also in central part of spinal cord where it is related to muscle movement.
Describe white matter.
Contains myelinated axons that run in tracts. The high myelin content gives the white color. It is deep in the brain, surrounds gray matter in spinal cord. The white matter conducts the messages pass to the different gray matter areas.
What happens when an axon is not conducting an impulse.
The inside of the axon is negative compared to the outside. There is unequal distribution of ions across membrane, more sodium (NA+) outside than inside, and more potassium (K+) inside than outside.
How is resting potential maintained?
Sodium-potassium pump. It actively transports Na+ out and K+ in. The membrane is somewhat permeable to Na+ and K+, tends to diffuse toward lesser concentration.
What is the polarity of a membrane based on?
Generally, more (+) ions outside the membrane than inside. Large, negatively-charged organic ions inside.
What is action potential?
A rapid change in polarity across axonal membrane as impulse occurs. (All-or-none), requires two types of gated channel proteins.
What are the two types of gated channel proteins?
Sodium gated channels, potassium gated channels.
What happens first in the action potential?
Sodium gates open first. Sodium flows down the concentration gradient into the axon. Membrane potential changes from -65 mV to +35 mV. It is called depolarization because inside changes from negative to positive.
Discuss the threshold in action potential.
Axon will fire if the depolarization reaches -55 mV. If it goes more to +35 mV it won’t make the impulse stronger, will just make it happen more often.
What happens second in action potential?
Potassium gates open second. Potassium flows down its concentration gradient out of the axon. Brings potential back to -65mV. Called repolarization because it returns to original negative polarity as K+ exits axon. Goes back to resting potential.
Describe conduction of an action potential in nonmyelinated axons.
Action potential travels down an axon one small segment at a time, as soon as an action potential has moved on, and the previous section undergoes a refractory period… during this period the sodium gates are unable to reopen.
Describe the refractory period.
For a short period, Na+ channels are inactivated. New stimuli won’t make them open, will go to resting potential. When able to open, Na+ rushes in again and depolarize and can work again.
