Chapter 9: Nervous Tissue Flashcards
What are the functions of the nervous system?
- Sensory
- senses changes within the body and environment
- Motor
- initiates muscle movements or glandular secretion
- Integrative
- interprets sensory info and decides the appropriate motor response.
What is the function of the afferent neurons?
Conducts impulses from sensory cells to central nervous system (CNS).
What are the 2 subdivisions of the autonomic nervous system?
- Sympathetic
2. Parasympathetic
What is the function of microglia?
Acts as phagocytotic cells.
What are ependymal cells?
Epithelial cells (often ciliated) that line the ventricles of the brain.
What do ependymal cells produce?
Cerebrospinal Fluid (CSF)
Describe the structure of a myelin sheath.
Consists of many layers of phospholipid membrane that belongs to schwann cells.
–the sheath wraps around axons on the myelinated neurons.
What are dendrites?
Extensions of the cell body that transmit impulses to the cell body.
White Matter
Groupings of myelinated processes of many neurons
What does Grey Matter contain?
Contains nerve cell bodies, dendrites, and axon terminals of unmyelinated axons and neuroglia.
Ganglia
Clusters of nerve cell bodies outside the CNS.
Resting Potential
The potential difference that exists across a nerve cell membrane when it is not conducting an impulse
– usually about -70 millivolts.
What is the role of the sodium-potassium pump?
Actively carries sodium out of the cell and potassium into the cell.
What is the sodium-potassium pump powered by?
ATP
How does a neuron become depolarized?
The rapid influx of sodium ions through the nerve cell membrane causes depolarization.
Refractory Period
The period of time following an initial stimulus, during which a neuron cannot be stimulated to conduct a second impulse.
What is a threshold stimulus?
A stimulus that causes the membrane of a neuron to depolarize to a critical level (-55 mV) to generate an action potential?
What is the advantage of saltatory conduction?
Its very fast and required less energy expenditure of the sodium-potassium pump.
Why does the synaptic conduction of an impulse occur only in one direction?
Transmission must be unidirectional
- because neurotransmitters are released only from presynaptic terminals, and
- because only postsynaptic membranes have appropriate neurotransmitter receptors.
Neurotransmitter
A chemical released by a presynaptic neuron for the purpose of stimulating or inhibiting the postsynaptic neuron.
What type of nervous system is the sympathetic nervous system part of?
Autonomic Nervous System (ANS)
What neuroglia produces myelin in CNS?
Oligodenfrocyte
What gated ion channel opens to a change in membrane potential?
Mechanical Pressure
What are the most important factors that determine the speed of impulse propagation??
- Fiber diameter
- Presence or absence of myelin sheath
What doe the peripheral nervous system (PNS) consist of?
- Cranial and spinal nerves with sensory (afferent) and motor (efferent) components
- Ganglia
- Sensory receptors
What does the somatic nervous system (SNS) consist of?
- Neurons that conduct impulses from cutaneous and special sense receptors to CNS
- Motor neurons that conduct impulses from CNS to skeletal muscle tissue.
What does the autonomic nervous system (ANS) consist of?
- Sensory Neurons from visceral organs.
- Motor neurons that convey impulses from CNS to smooth muscle tissue, cardiac muscle tissue, and glands.
What does the enteric nervous system (ENS) consist of?
Neurons in the enteric plexuses that extend the length of gastrointestinal (GI) tract.
What are subdivisions of PNS?
- Somatic (voluntary)
- Autonomic (involuntary)
- Enteric nervous systems
What is the function of a dendrite?
Conducts impulses from receptors or other neurons to cell body.
What is the function of a axon?
Conducts nerve impulses:
- from neuron to dendrite
- to cell body of another neuron
- to an effector organ of the body.
What are the different types of neuroglia and their functions?
- Astrocyte = blood brain barrier
- Oligondendrocyte = support
- Microglia = phagocytosic
- Ependymal Cells = cerebrospinal fluid production
- Schwann Cells = myelin production
- Satellite cells = support
What do voltage-gated ion channels respond to?
A direct change in membrane potential.
What does ligand-gated ion channels respond to?
A specific chemical stimulus
What do mechanically-gated ion channels respond to?
Mechanical vibration or pressure
What is the typical value for the resting membrane potential?
- 70 mV
- —meaning its polarized
Action Potential (AP)
A sequence of rapidly occurring events that decrease and eventually reverse the membrane potential (depolarize).
What can an action potential also be called?
An impluse
What happens during the refractory period?
- Another impulse cannot be generated
(absolute refractory period) OR - Can be triggered only by a suprathreshold stimulus (relative refractory period)
What do Action Potential do?
Conducts or propagates (travels) from point to point along the membrane.
Nerve impulse
Traveling action potentials
How are neurotransmitters removed from the synaptic cleft?
- Diffusion
- Enzymatic Degradation
- Uptake into cells (neurons and glia)
