CH 10 REVIEW QUESTIONS Flashcards
List functions of the nervous system
- built to send and receive info
- sensory input, integration processing (decision making) and motor output are 3 main aspects of the nervous system
What are neurotransmitters?
- molecules that communicate signals thru the neuron
What are neuroglia?
- provide protection, support, insulation and nutrients for neurons
What are neuroglia?
- provide protection, support, insulation and nutrients for neurons
What is the main structure of the nervous system?
- CNS (brain + spinal cord)
- PNS (spinal + cranial nerves)
What are subdivisions of the PNS?
- afferent (sensory)
- efferent (motor)
What are subdivisions of the PNS?
- afferent (sensory)
- efferent (motor)
What are ganglia?
- located in the PNS
- clusters of neuron cell bodies located outside the brain and spinal cord
What are ganglia?
- located in the PNS
- clusters of neuron cell bodies located outside the brain and spinal cord
What is the function of the sensory (afferent) division of the PNS?
- converts info into impulses, which are conducted along the peripheral nerves to the CNS
What is the function of the motor (efferent) division?
- neurons that conduct impulses from the CNS to responsive structures called EFFECTORS carry out the motor functions of the nervous system
- these effects include muscles + glands and are mainly controlled by nerve activity
What 2 divisions can the motor portion of the PNS be divided into?
- somatic (voluntary)
- autonomic (involuntary)
What are 2 types of neural tissue?
- neurons that communicate electrical impulses
- neuroglia that protect, insulate, and nourish neurons
What 3 features do neurons share?
- cell body
- dendrites
- axons
What is the structure + function of the cell body?
- contains granular cytoplasm, mitochondria, lysosomes, a Golgi apparatus, and many microtubules
- contains network of fine threads called neurofilaments that extend into axon and support it
- contains membranous packets of NSSL bodies (chromatophilic substance) that consists of R.E.R
What is the structure + function of the cell body?
- contains granular cytoplasm, mitochondria, lysosomes, a Golgi apparatus, and many microtubules
- contains network of fine threads called neurofilaments that extend into axon and support it
- contains membranous packets of NSSL bodies (chromatophilic substance) that consists of R.E.R
What is the structure + function of dendrites?
- provide receptive surfaces which processes impulses from other neurons
What is the structure + function of axons?
- contains collaterals, axon hillock, synaptic cleft, and an axon terminal
- conducts impulses, conveys biochemicals and organelles, in a process called AXONAL TRANSPORTS, which is movement that occurs in both directions between the cell body and ends of axons
What is the structure + function of Schwann cells?
- located in the PNS
- type of neuroglia
- encase large axons in lipid-rich sheath and are composed of myelin layers (myelin sheath)
- neurilemma surrounds the myelin sheath and contains most of the cytoplasm and nuclei
What are characteristics of myelinated axons?
- impulses travel faster by leaping from the nodes of ranvier
- appear white underneath a microscope
What are characteristics of myelinated axons?
- impulses travel faster by leaping from the nodes of ranvier
- appear white underneath a microscope
- in the CNS myelin is produced by oligodendrocytes rather than Schwann cells, and do not have a neurilemma
What is the structure of multipolar neurons?
- has many processes arising from cell body; only one is an axon
- most neurons within the brain + spinal cord are this type
- some multipolar neurons are in ganglia associated with the autonomic nervous system
- others are found in specialized portions of the eyes
What is the structure of bipolar neurons?
- has only 2 processes, one arising from either end
- one is an axon, there other is a dendrite
- found in specialized parts of the eyes, nose, and ears
What is the structure of unipolar neurons
- has single process extending from cell body
- divides into 2 branches that function as a single axon
- one brain has dendrites near a peripheral body part
- the other branch enters the brain or spinal cord
- most are found in ganglia
What is the structure/function of sensory neurons?
- conduct impulses from peripheral body parts into the brain + spinal cord
- distal ends sense change
- when sufficiently stimulated, they trigger impulses that travel on sensory neuron axons into the brain or spinal cord
- most are unipolar
What is the structure + function of interneurons?
- brain + spinal cord
- multipolar and form links with other interneurons and relay info from one part of the brain + spinal cord to another
- transfer info across brain for processing + interpreting, whilst other info is sent to motor neurons
- aggregate in specialized masses called nuclei
What is the structure + function of motor neurons?
- multipolar + conduct impulses out of the brain or spinal cord to effectors
What are the 4 types of CNS neuroglia?
- astrocytes
- oligodendrocytes
- micoglia
- ependyma
What is the structure + function of astrocytes?
- provide structural support
- formation of scar tissue
- transport of substance between blood vessels and neurons
- communicate with one another and with neurons
- mop up excess ions and NTs
- induce synapse formation
How do astrocytes help repair injured neural tissue?
- form a special type of scar tissue, which fills spaces and closes gaps in the CNS
What is the structure + function of oligodendrocytes?
- form myelin sheaths in the brain + spinal cord
- produce nerve growth factors
What is the structure + function of microglia?
- provide structural support
- phagocytosis (immune protection)
What is the structure + function of ependyma?
- form a porous layer thru which substances diffuse between interstitial fluid of the brain + spinal cord and the cerebrospinal fluid
What are the neuroglia of the PNS?
- Schwann cells
- Satellite cells
What is the function of Schwann cells?
- produce the myelin on peripheral myelinated neurons
What is the function of satellite cells?
- provide nutritional support + help regulate the concentrations of ions around neuron cell bodies within ganglia
How do axons regenerate?
- damaged PNS axons may regenerate
- if disease or injury separates an axon in PNS nerve from its cell body, the distal portion of the axon + the myelin sheath deteriorate within a few weeks, but the Schwann cells + neurilemma remain
- macrophages remove the fragments of myelin + other cellular debris
- the proximal end of the injured axon develops sprouts shortly after the injury
- influenced by nerve growth factors that nearby neuroglia secrete, one of these sprouts may grow into a tube formed by remaining Schwann cells
- Schwann cells along the length of the regenerating portion form new myelin around the growing axon
What is a membrane potential?
- a charge that is inside of a cell that indicates that there is potential for charges to move across the cell membrane
What is resting membrane potential?
- 70 mv
- this is when a cell is at rest, or inactive
What affect charges within the cell?
- K+ ions that are usually in higher concentration on the inside of a neuron
- the inside is usually negatively charged due to anions such as phosphate and sulfate that are impermeable to “leaky K+ channels”
- sodium is in higher concentration outside the cell
What manages the concentration gradient during RMP?
- the K+ and Na+ ability to be excited and rapidly get back to rest
How does permeability affect charges within a cell?
- in a neuron, before the membrane potential is established, K+ ions diffuse out of the cell faster than Na+ ions diffuse
- a net loss of positive charge from the cell results
- the membrane potential, negative on the inside of the membrane, aids sodium diffusion into the cell, and opposes potassium diffusion out of the cell
- as a result, slightly more Na+ ions enter the cell than K+ ions leave
- The sodium/potassium pump balances these movements and maintains the concentrations of these ions, and the RMP
What does the sodium/potassium pump do?
- manages the concentration gradients within a cell
- for every 3 Na+ ions that enter a cell, 2 K+ move outside the cell
How is action potential reached?
- if Na+ or K+ channels open, more of that particular ion will cross the cell membrane, altering the RMP.
- the channels open in response to a NT, that allows more Na+ into the cell, causing it to become more positive. (depolarization)
- if the membrane potential reaches -55mv, it reaches an all or nothing threshold, and starts the action potential
What is polarization?
- the charges within a membrane are balanced
What is a graded potential?
- when a localized part of the membrane is triggered, ion channels open (typically sodium ions)
- local area becomes depolarized (graded potential is produced) and spreads to adjacent areas of the membrane
- usually graded potentials die out across the membrane
- however, if the graded stimuli is strong enough, it can cause the membrane to reach -55 mv, and the voltage gated sodium channels open at the trigger zone
What is action potential?
- when voltage-gated sodium channels open @ the trigger zone, and the charge hits an all-or-nothing threshold and rapidly rises to +30 mv, beginning an action potential
- starts with depolarization, because the inside + outside of the neuron now each possess a positive charge
- after depolarization, there is a quick return that results in an “overshoot,” and brief hyperpolarization occurs, before the membrane repolarizes at the resting rate.
How is a membrane re-polarized after an action potential?
- thru sodium/potassium pumps
What is a refractory period?
- period following stimulation during which a neuron or muscle fiber will not respond to another threshold stimulus
- has two parts called ABSOLUTE REFRACTORY PERIOD + RELATIVE REFRACTORY PERIOD
- ensures that an action potential is conducted in only one direction, down the axon, because the area upstream where the action potential just occurred is still in refractory period
What happens during absolute refractory period?
- the axon’s voltage-gated sodium channels are temporarily not responsive at all, and the axon cannot be stimulated
What happens during the relative refractory period?
- RMP is re-established, and during this time, re-polarization is still incomplete, however a stimulus of higher than usual intensity may trigger an impulse
What happens during the relative refractory period?
- RMP is re-established, and during this time, re-polarization is still incomplete, however a stimulus of higher than usual intensity may trigger an impulse
What is impulse conduction?
- an action potential in one region stimulates the adjacent region, and the action potential is propagated along the axon
What are the events leading to impulse conduction?
- nerve cell maintains RMP by diffusion of Na+ and K+ down their concentration gradients as the cell pumps them up the gradients
- neurons receive stimulation, causing local potential changes, which may sum to reach threshold
- if threshold is reached, Na+ channels in the trigger zone of the axon open
- sodium ions diffuse inward, depolarizing the membrane
- potassium channels in the membrane open
- potassium ions diffuse outward, depolarizing the membrane
- the resulting action potential causes an electric current that stimulates adjacent portions of the membrane
- the action potential propagates along the length of the axon
How does impulse conduction differ in myelinated + unmyelinated axons?
- unmyelinated neurons conduct impulses continuously down the entire surface of their axons
- myelinated neurons conduct impulses by a process called SALTATORY CONDUCTION
- action potentials only occur at the nodes of ranvier, which causes them to leap down the axon from node to nodes; this occurs more quickly than continuous propagation
What is the presynaptic neuron?
- the neuron before the synapse
What is a postsynaptic neuron?
the neuron after the synapse
