Chapter 12 Flashcards
Everything done in NS involves (3) fundamental steps
1) sensory function detects internal & external stimuii
2) interpretation is made (analysis)
3) motor response occurs (reaction)
Divisions of the Nervous System (2)
CNS → brain & spinal cord
PNS → all nervous tissue outside CNS (includes nerves, ganglia, enteric plexuses & sensory receptors)
Most signals that __ muscles to ___ and __ to ___ originate in CNS
stimulate muscles to contract and glands to secrete originate in CNS
PNS is further divided into (3) ?
1) somatic sensory system (SNS)
2) autonomic nervous system (ANS)
3) enteric nervous system (ENS)
**SNS** consists of (3)?
1) somatic sensory (afferent) neurons
2) Somatic motor (efferent) neurons
3) Interneurons
SNS
1) somatic sensory (afferent) neurons
convey info from sensory receptors in head, body wall & limbs toward CNS
SNS
2) Somatic motor (efferent) neurons
conduct impulses from CNS to skeletal muscle under voluntary control in periphery
SNS
3) Interneurons
any neurons that conduct impulses between afferent and efferent neurons within the CNS
PNS → 2) ANS
consists of? (2)
1) Sensory Neurons
2) Motor Neurons
- sympathetic division
- parasympathetic division
*
- parasympathetic division
ANS → sensory neurons
convey info from :
autonomic sensory receptors mostly in visceral organs (stomach/lungs) → CNS
ANS → motor neurons
under involuntary control
conduct nerve impulses from CNS → smooth muscle, cardiac muscle & glands
ANS → motor neurons
- (2) branches
Sympathetic division
Parasympathetic division
Neurons
- gather info where?
- process info where?
- transmit info where?
1) gather info at dendrites
2) process info in dendritic tree & cell body
3) transmit info down axon to axon terminals
Synapse
site of communication between two neurons OR between a neuron & another effector cell
Synaptic Cleft
gap between pre & postsynaptic cells
Synaptic end bulbs & other varicosities on axon terminals of presynaptic neurons contain many?
tiny membrane-enclosed sacs (synaptic vesicles) that store packets of neurotransmitter chemicals.
→ many neurons even contain 2 or 3 types of neurotransmitters, each with different effects on postsynaptic cell
Like muscle fibers, neurons are electrically excitable
- communicate with each other using (2) types of electrical signals
1) Graded Potential
2) Action Potential
1) Graded Potential
used for short-distance communication only
only in dendrites & cell bodies
2) Action Potential
allow long-distance communication within body
at axon hillock
Producing electrical signals in neurons depends on ?
existance of resting membrane potential (RMP)
How is a cell’s RMP created?
created using ion gradients & variety of ion channels that open/close in response to specific stimuli
Prevalence of Ion Channels in Body
present in plasma membrane of all body cells but especially prominant part of NS
Steps of touching a pen → to CNS
touch → GP in sensory receptor of skin → triggers axon to form AP → along axon into CNS
→ causes release of neurotransmitters at synapse with interneuron → stimulates interneuron to form GP in dendrites & cell body (process repeats as interneurons in higher parts of brain [thalamus/cerebral cortex] are activated)
→ perception occurs when interneurons in cerebral cortex are activated
Steps of using a pen →
stimulus in brain → GP in dendrites/cell body of upper motor neuron → causes AP in axon → neurotransmitter release →GP in lower motor neuron → AP → neurotransmitter release at NMJ → stimulate muscle fibers → AP → contraction
When Ion channels are open, this allows..?
specific ions to move across plasma membrane down their electrochemical gradient
Electrochemical Gradient
concentration (chemical) difference plus an electrical difference
Chemical (concentration) part → ions move from areas of [high] to [low]
Electrical aspect → cations move toward negatively-charged area & anions move towards positively-charged area
Active channels open in response to?
stimulus (they are “gated”)
(3) types of active, gated channels
1) ligand-gated
2) voltage-gated
3) mechanically-gated
Ligand-gated Channels
respond to a neurotransmitter or hormone and are mainly concentrated at synapse
Voltage-gated Channels
respond to changes in transmembrane electrical potential & mainly located along neuronal axon
Mechanically-gated Channels
respond to mechanical deformation (applying pressure to receptor due to vibration, touch, stretch)
Leakage channels
gated but NOT active
- open & close randomly
RMP exists because of?
small buildup of negative ions in cytosol inside membrane & positive ions in ECF on surface
→ occurs very close to membrane, cytosol elsewhere is electrically neutral
Why is RMP slightly negative?
leakage channels favor gradient where more K+ leaks out than Na+ leaks in
(more K+ channels than Na+ channels)
- also large negatively charged proteins that always remain in cytosol