Exam 1 Flashcards
Nervous System
- CNS (brain & spinal cord)
- Peripheral NS:
– (ANS) Sympathetic NS & Parasympathetic NS - Somatic NS
– Muscle, skin, organs - Enteric NS
–Gastrointestinal tract
–“Gut-brain”
• Neurotransmitters and neurons that help coordinate the digestion of food
• Muscle coordinated movements to move digested food to the small intestine for absorption and then moves into large intestine/ movement has to be coordinated by neurons
• Serotonin – 80-90% is in Enteric Nervous System
o Reason why people who experience anxiety often have stomach aches
Brainstem: parts and function
o Consists of: Medulla –> Pons –> Midbrain
Ascending and descending tracts* between spinal cord and thalamus, cerebellum, cortex
o Reticular activating system* (RAS)
Neurons located throughout brainstem
Activates thalamus, hypothalamus, neocortex for arousal* from sleep
Help keeps one alert* during day
The midbrain* portion is particularly critical* for cortical activation^
Injury* leads to problems* with arousal, alertness, coma*
oAxons* from specialized clusters of cell bodies* project to the brain, spinal cord, and autonomic nervous system (ANS)
Release neurotransmitters* to regulate respiration, ANS (e.g. cardiovascular activity) consciousness, alertness
o Some axons from cell bodies throughout the brainstem release serotonin^ (5-HT)
o Other axons from cell bodies in the mesencephalon (midbrain) release dopamine^ (DA)
o Other axons from cell bodies in the pons release norepinephrine^ (NE)
o Other axons from cell bodies in the upper brainstem release acetylcholine^ (ACh)
Cerebellum
Cerebellum’s function?
o Nonconscious modulation of complex movements, posture, muscle tone, gait, visuomotor coordination*
o Performs error correction* of movements
o Speeds up* movements, prepares motor systems
o Acquiring/maintain smooth, coordinated motor skills
ANS: Viscera (internal organs) are influenced by two interdependent systems
Neural: uses neurotransmitters, synapses
- Responses are faster to develop, shorter-term, reach limited* number of cells
Endocrine: uses hormones via bloodstream
- Responses are slower to develop, more prolonged, reach greater number of cells
- Responses travel through hormones which is why
responses are slower and travels to a greater amount of cells/ bloodstream can go to every cell in the body
ANS: Endocrine and Neural systems
o Neural and Endocrine system both involved in neuro-conscious “automatic” and homeostatic* processes, including:
Cardiovascular* - heart beats, blood pressure, exc.
Respiratory- how fast and deeply we breathe
Digestive
Urinary*
Reproductive*
o Neural and Endocrine both controlled by the CNS (primarily hypothalamus) also amygdala
o Neural and Endocrine both are affected by emotional factors and sensory input* from inside and outside the body
ANS* is the neural* system
• Innervates smooth muscle, cardiac muscle, glandular epithelium
Sympathetic Nervous System (SNS)*
• “Fight or flight” – extreme excitement, exertion, stress* causes global* activation of SNS*
o Increase* release of NE* (stress hormone) in tissues
• Increases:
o Rate ND STRENGTH of heart beating*
Pt may feel this (palpitations* )
o Blood pressure*
o Blood flow to skeletal muscles*
o Blood glucose level*
o Sweating*
o Pupil size*
• Concurrently decreases*
- Gut mobility
- Digestive gland selection
- Blood flow to abdominal viscera, skin
- SNS acts in a global manner (all aroused at once)
Parasympathetic Nervous System
• “Rest and digest”
• Increase* release of ACh* in tissues
• Increases* food digestion* by increasing gut
mobility and digestive gland secretion
• Slows heart rate*
- PNS works in a localized (the entire system does not need to work all at once/ at the same time)
SNS and PNS
the SNS and PNS have opposite* effects
o Overall balance* is critical
o Each must become temporarily dominant* for a specific situation
• Emotional dysfunction* may cause/worsen disease* if SNS* is hyperactive and chronic*
Neurons
• Neurons*: basic signaling unit, information processors, computation devices, CPUs
Gila (gilal cells)
Support cells (structural, functional support) for neurons
Neurotransmitters* (NTs)
Made inside neurons
o Neurons make NTs and release at a proper time
o NT does not cross the membrane that surrounds cells
• A neuron is named after the main NT of that neuron
o i.e. dopaminergic neuron makes and releases dopamine (NT)
Steps in NT function:
- NT is synthesized* and stored in synaptic vesicles* until needed
- NT is released* when an action potential reaches the terminal
- Activation* occurs when an NT binds to a specific binding site on a specific receptor* (protein in postsynaptic membrane)
This causes one of two events:
• 1. Excitation
• 2. Inhibition
Deactivation*
o Primarily by two mechanisms- Reuptake* is the most common* type
– NT * is taken by a presynaptic transporter*
(“reuptake pump”)
– Most is stored in vesicles for reuse and to protect
from enzymatic degradation - Enzymatic degradation* (monoamine oxidase)
- Reuptake* is the most common* type
Resting Potential
• At rest* a neuron has an electrical potential (charge across its membrane) of -70 mV (inside negative relative to outside) due to unequal distribution of charged particles (ions, proteins)
• It is said to be polarized*
• Resting potential* created by semipermeable
membrane
o Hard for Na+* (sodium) to pass into neuron (but some
leak)
o Proteins (mostly with a negative charge) are kept
inside due to size and charge
o K* (potassium) can pass freely through channels
o Na-K pump exchanges three Na* from inside for
every two K* from outside
o Result is 10 times more Na* outside than inside
Synapse
Synapse^: site of functional contact Consists of: presynaptic membrane with active zone Synaptic cleft – space between neurons Postsynaptic membrane with receptors
NTs influence neurons via …
receptors
Two of the most common families of receptors are…
ionotropic receptors (ligand-gated ions) and Metabotropic (G-protein linked receptors)
Ionotropic (ligand-gated ion channels) receptors
o Allow ions* to move across the membrane through a channel that opens when NT binds
Rapid change in membrane potential (msecs)
o Mediate fast* behavior
o May be excitatory* or inhibitory*
Graded potentials
- is a gradual change in the resting potential membrane
EPSP
•Excitatory^ postsynaptic^ potential^ (EPSP*)
- Neuron becomes depolarized; Excited and closer to firing threshold of -50mV
Graded potential: excited
Gradual change in the resting potential membrane
When excited…
Charge becomes less^ negative^ or depolarized^; is excited^
• Why excited? Because now closer* to firing threshold* of -50 mV^
Graded potential: inhibited
If CI- or K+ channels open, CI-enters or K+ exists…
Change becomes more^ negative^, or hyperpolarized^; is inhibited^
Now further from firing threshold -50 mV^
o Graded potentials occur in msecs for fast changes
IPSP
Inhibitory^ postsynaptic^ potential
- Neuron becomes hyperpolarized; Inhibited and further from firing potential -50 mV
Action Potential
Action Potential^; “firing” of the neuron
• If summation* at the axon hillock (where axon begins) reaches the firing threshold* (-50 mV), it fires^ (action potential occurs)
• At firing threshold, voltage sensitive Na+ channel* (VSSC) opens – even more Na+ enters
o Changes potential to +30 mV
o Voltage-sensitive K+ channel opens slowly
• When potential reaches +30 mV, Na+ channel
closes and K+ channel is fully opened
o Let K+ exit, which reverses potential—causes slight
hyperpolarization
o Then back to resting potential
- The amplitude^ (distance from bottom to peak) is constant^ for all action potentials (all-or-none)
- Occurs quickly and lasts about 5 msecs
Propagation
• Na+ that came into the neuron during action potential depolarizes the adjacent area
o Triggers its channels to open
- The action potential is then propagated* (action signals travels down; “domino effect”) along entire axon
- When the impulse reaches its terminal, it releases NT, and the whole process may be continued in the next neuron
