Chapter 12 nervous tissue Flashcards
What is the CNS?
Brain and spinal cord
What is the PNS?
- cranial nerves
- spinal nerves
- Enteric plexuses in small intestine
- sensory receptors in skin
What is the sensory function of the nervous system?
Detect changes through sensory receptors
What is the integrative function of the nervous system?
Analyze incoming sensory information, store some aspects, and make decisions regarding appropriate behaviors
What is the motor functions of the nervous system?
Respond to stimuli via effectors
What are some aspects of neurons?
- electrically excitable
- nerve impulse is called action potential
What are the cellular structures of the neuron ?
- cell body
- dendrites
- axon
Neurons can be classified based on the number of what?
Processes extending from the cell body
Neurons can be classified based on what?
Direction of nerve impulse propagation
What are three types of neurons?
- sensory/ afferent neurons
- Motor/ efferent neurons
- Interneurons/ association neurons
What does the sensory/ afferent neurons do?
Conveys information to the CNS
What do Motor/ efferent neurons do?
Convey action potential from the CNS
What does interneurons/ association neurons do?
Process sensory information and elicit motor response
What are neuroglia?
- not electrically excitable
- make up about half the volume of the nervous system
- can multiply and divide
- 6 kinds total (4 in CNS, 2 in PNS)
Electrical cells communicate with each other how?
Action potentials or graded potentials
Action potentials allow communications over what kind of distances?
Short and long distances
Graded potentials allow for communications over what distance?
Short distance only
Production of an AP or GP depends on what ?
The existence of a resting membrane potential and the existence of certain ion channels
What are leak channels?
They alternate between open and closed
Between K channels and Na channels which one is more numerous?
K are more numerous than Na+ channels
What are ligand-gated channels?
Channels that respond to chemical stimuli (ligand binds to receptor)
Mechanically gated channels respond to what?
Mechanical or pressure stimuli
Voltage gated channels respond to what?
Direct changes in membrane potential
Where are leak channels located?
Nearly all cells, and dendrites, cells bodies, and axons of all types of neurons
Where are ligand- gated channels located?
Dendrites of some sensory neurons such as pain receptors and dendrites and cell bodies of interneurons and motor neurons
Where are mechanically gated channels located?
Dendrites of some sensory neurons such as touch receptors, pressure receptors, and some pain receptors
Where are voltage-gated channels located?
Axons of all types of neurons
What happens during resting membrane potential
Electrical potential between the extracellular fluid and the cytosol is the same
What are action potentials?
sequence of rapidly occurring events that decrease and eventually reverse the membrane potential and eventually restore it to the resting state
What are the two phases of action potentials?
- depolarization
- Repolarization
What is the depolarizing phase?
When membrane potential of axon reaches threshold, the NA channel activation gates open. As Na ions move through these channels into the neuron, a buildup of positive charges forms along inside surface of membrane and the membrane becomes depolarized
What is the repolarizing phase?
Na channel inactivation gates close and K channels open. The membrane starts to become repolarized as some K ions leave the neuron and a few negative charges begin to build up along the inside surface of the membrane
Where does graded potentials originate?
Mainly in dendrites of cell bodies
What types of channels do graded potentials have?
ligand-gated or mechanically gated ion channels
What kind of conduction does graded potentials have?
Decremental, permit communication over short distances
What does the amplitude of graded potentials look?
Depending on strength of stimulus, varies from less then 1mv to more then 50 mv
What is the duration of graded potentials?
typically longer, ranging from several milliseconds to several minutes
What is the polarity of graded potentials?
May be hyperpolarizing or depolarizing
What is the refractory period of graded potentials?
Not present; summation can occur
What is origin of nerve impulses?
Arise at trigger zones and propagate along axon
What are the types of channels in nerve impulses?
Voltage gated channels for Na+ and K+
What is the conduction of nerve impulses?
Propagate and thus permit communication over longer distances
What is the amplitude of nerve impulses?
All or none; typically about 100mv
What is the duration of nerve impulses?
Shorter, ranging from 0.5 to 2 msec
What is the polarity of nerve impulses?
Always consist of depolarizing phases followed by repolarizing phase and return to resting potential
What is the refractory period of nerve impulses?
Present; summation cannot occur
In order for communication to occur from one body part to another what must happen?
Action potentials must travel from where they arise at the trigger zone to the axon terminals
Action potentials do not die out, why?
They keep their strength as they spread across the membrane of a neuron
What affects propagation speed?
- Axon diameter
- amount of myelination
- temperature
A synapse is the junction between what?
Neurons or between neuron and an effector
What is an electrical synapse?
They are gap junctions which connect cells and allow the transfer of information to synchronize the activity of a group of cells
What is a chemical synapse?
One way transfer of information from a presynaptic neuron to a post synaptic neuron
What are some small molecule neurotransmitter?
- Acetylcholine
- Biogenic amines
What are three types of biogenic amines?
- Norepinephrine
- Dopamine
- Serotonin
