Chapter 12 Study- Nervous Tissue Flashcards
What are the two anatomical subdivisions of the nervous system? Which ones houses the brain and spinal cord?
Central nervous system (CNS)—brain and spinal cord
Peripheral nervous system (PNS)—nerves and ganglia
What are the 2 divisions of the PNS?
- Sensory (afferent) division—carries signals from receptors (sense organs) to CNS
- Motor (efferent) division—carries signals from CNS to effectors (glands and muscles that carry out the body’s response)
Compare somatic to visceral
Somatic motor division—carries signals to skeletal muscles; causes voluntary muscle contraction and automatic reflexes
Visceral motor division (autonomic nervous system, ANS)—carries signals to glands, cardiac and smooth muscle; no voluntary control; responses called visceral reflexes
What are the 3 functional classes of neurons? Compare afferent (sensory) neurons to efferent (motor)
- Sensory (afferent) neurons—detect stimuli and transmit information about them toward the CNS
- Interneurons—receive signals from other neurons, process this information, and make resulting “decisions”
- Motor (efferent) neurons—send signals out to muscles and gland cells (the effectors)
the next cell
Be able to differentiate between multipolar, bipolar, unipolar, and anaxonic neurons.
Multipolar neuron—one axon and multiple dendrites; most common type in body, most neurons in CNS
*Bipolar neuron—one axon and one dendrite; examples include olfactory cells, some neurons of retina, sensory neurons of ear
*Unipolar neuron—single process leading away from cell body, splits into peripheral process and central process
Both processes comprise the axon; only short receptive endings of peripheral process are considered dendrites
*Anaxonic neuron—many dendrites but no axon; found in brain, retina, and adrenal gland
Compare anterograde to retrograde transport
Anterograde transport—movement away from cell body, down the axon
Retrograde transport—movement up the axon toward the cell body
List the 6 neuroglial cells and each of their functions. Which are found in the CNS and which are found in the PNS?
1. Oligodendrocytes—form myelin sheaths in CN
- Oligodendrocytes—form myelin sheaths in CNS
- Ependymal cells—line internal cavities of brain; secrete and circulate cerebrospinal fluid (CSF)
- Microglia—macrophages; engulf debris, provide defense against pathogens
- Astrocytes—most abundant type; wide variety of functions
PNS
1 . Schwann cells—envelop axons of PNS, form myelin sheath, and assist in regeneration of damaged fibers - Satellite cells—surround nerve cell bodies in ganglia of PNS; provide insulation around cell body and regulate chemical environment
What is myelin? Which cells secrete this? What are the gaps between myelin called?
spiral layers of insulation around an axon
What is MS?
Multiple sclerosis (MS) -Oligodendrocytes and myelin sheaths in CNS deteriorate
How does size and myelin effect how fast signals travel down an axon?
Diameter: larger axons have more surface area and conduct signals more rapidly (faster the signal)
Presence or absence of myelin: myelin speeds signal conduction
Define RMP. How does the ICF of a resting cell compare to the ECF
Resting membrane potential (RMP)—charge difference across plasma membrane intracellular fluid (ICF) becomes relatively negative to the extracellular fluid (ECF)
Compare depolarization to hyperpolarization
Depolarization- Polarity is reduced, voltage is less negative
Hyperpolarization- (membrane more negative) is inhibitory—makes a neuron less likely to produce an action potential
Define action potential
Action potential—rapid up-and-down change in voltage produced by the coordinated opening and closing of voltage-gated ion channels
Describe the 3 important characteristics of action potentials listed
All-or-none law—if threshold reached, neuron fires up to maximum voltage; if threshold not reached, it does not fire
Non decremental—do not get weaker with distance
Irreversible—once started, an action potential travels all the way down the axon cannot be stopped
Compare the absolute refractory period to the relative refractory period
Refractory period—period of resistance to stimulation; has two phases:
Absolute refractory period—no stimulus of any strength will trigger another AP
*Caused by inactivation of voltage-gated Na+ channels
Relative refractory period—an unusually strong stimulus is needed to trigger a new AP
*During hyperpolarization, a larger depolarization (local potential) is required to reach threshold
Compare conduction in unmyelinated and myelinated axons
Unmyelinated axons and continuous conduction: Slower
Unmyelinated axons have voltage-gated channels along their entire length
Chain-reaction continues down axon
Myelinated axons and saltatory conduction: Faster
Action potentials can only be generated at the nodes, where voltage-gated ion channels are concentrated
Electrical signal must spread passively between nodes
Action potential seems to “jump” from node to node
What molecules link 2 neurons together across the cleft?
Each neuron has cell-adhesion molecules (CAMs) reaching into the cleft
Describe the functions of a neurotransmitter. Compare the 3 different examples of synapses
Some neurotransmitters are excitatory, others inhibitory, and sometimes a transmitter’s effect differs depending on type of receptor on postsynaptic cell
Example1: An excitatory cholinergic synapse
Cholinergic synapse—acetylcholine (ACh) is the neurotransmitter
Example 2: An inhibitory GABA-ergic synapse
Example 3: An excitatory adrenergic synapse
Adrenergic synapse—norepinephrine (NE) is the neurotransmitter
List 3 ways that neurotransmitter can be cleared from a synaptic cleft.
Neurotransmitter degradation—enzyme in synaptic cleft breaks down neurotransmitter
Reuptake—neurotransmitter or its breakdown products reabsorbed into axon terminal
Diffusion—neurotransmitter or its breakdown products simply away from synapse into nearby ECF
What is a neuromodulator? List an example
Neuromodulators—chemicals secreted by neurons that have long term effects on groups of neurons
Exsample: Relaxing smooth muscle
Compare EPSPs to IPSPs
Excitatory postsynaptic potential (EPSP)—voltage change from the RMP toward threshold
Inhibitory postsynaptic potential (IPSP)— voltage becomes more negative that it is at rest
Compare temporal summation to spatial summation
Temporal summation—a single synapse generates EPSPs so quickly that each is generated before the previous one fades
Spatial summation—EPSPs from several different synapses add up to threshold at an axon hillock
Compare presynaptic facilitation to inhibition
Presynaptic facilitation—occurs when one presynaptic neuron enhances another one
Presynaptic inhibition—occurs when one presynaptic neuron suppresses another on
Identify the 4 different neural circuit types
Diverging circuit—one nerve fiber branches and synapses with several postsynaptic cells
Converging circuit—input from many different nerve fibers can be funneled to one neuron or neural pool
Reverberating circuit—neurons stimulate each other in linear sequence but one or more of the later cells restimulates the first cell to start the process all over
Parallel after-discharge circuit—input neuron diverges to stimulate several chains of neurons
Compare serial and parallel processing
Serial processing—neurons and neural pools relay information along pathway in relatively simple linear fashion
Parallel processing— information is transmitted along diverging circuits through different pathway that act on it simultaneously, for different purposes
driving steering and vision (looking around)
Can process only one flow of information at a time
Serial processing—neurons and neural pools relay information along pathway in relatively simple linear fashion
Read a book or watch a television movie—you cannot do both simultaneously
May jump back and forth between one and the other, or only half understanding each
Compare AD to Parkinson disease.
Alzheimer disease (AD)
Memory loss, moody, combative, and lose ability to talk, walk, and eat
Acetylcholine (ACh) and nerve growth factor (NGF) deficiencies
Parkinson disease (PD)—progressive loss of motor function due to degeneration of dopamine-releasing neurons
Dopamine normally prevents excessive activity in motor centers (basal nuclei
