Unit 2 Flashcards
1
Q
Outer Ear
A
Pinna
2
Q
Part of external ear between pinna and tympanum
A
ear canal
3
Q
thin membranous tissue between external and middle ear
A
tympanic membrane
AKA eardrum
4
Q
a long air-filled cavity that connects the middle ear to the nasopharynx
what is its function?
A
Eustachian tube
AKA internal auditory canal
- equilibrates pressure in the middle ear during chewing, swallowing and yawning
5
Q
3 parts of middle ear
A
- tympanic membrane
- bony ossicles
- Eustachian tube
6
Q
what are the 3 bony ossicles in order from external to internal?
A
- Malleus
- Incus
- Stapes (touches oval window)
7
Q
What are the three parts of the internal ear and their sense functions?
A
- Cochlea (hearing)
- Vestibule (vertical and horizontal acceleration and tilting)
- Semicircular Canals (rotation of head in various planes)
8
Q
Where do the bony ossicles meet the internal ear and how do they function there?
A
- the stapes meets the cochlea at the oval window
- the ossicles transmit vibrations from the tympanic membrane to the oval window
9
Q
What are the three chambers of the cochlea (top to bottom)?
What separates them?
What do they contain?
A
scala vestibula - perilymph
Reissner’s membrane - btwn vestibula and media
scala media - endolymph (K+ rich), organ of Corti
basilar membrane - btwn media and tympani, below hair cells
scala tympani - perilymph
10
Q
What is the structure within the scala media that converts vibrations transmitted through the endolymph into graded potentials?
And how does it do this?
A
Organ of Corti
- Stereocilia on the hair cells bend as they are pushed up against the tectorial membrane
- This bending either opens or closes mechanically gated channels which allow K+ from endolymph in, causing depolarization or hyperpolarization.
- A slow, constant flow of neurotransmitter from the hair cell is either increased or decreased depending on which way the hairs are bent, sending correlating auditory signals to the brain.
11
Q
What percentage of K+ channels are open by default in hair cells of the organ of Corti?
A
10%
12
Q
What is the membrane that sits above the hair cells in the organ of corti and what is it made of?
A
Tectorial Membrane
- an acellular gel made of collagen and glycoproteins
13
Q
What are the cells in the organ of corti that create nerve signals from auditory vibrations?
How are they special?
A
Hair Cells
- modified neurons
- no mitosis
- no axon
- release neurotransmitter
14
Q
How are different frequencies of sound differentiated by the cochlea?
A
- by being picked up at different parts along the spiraled length of the cochlea depending on the thickness of the basilar membrane
- high frequencies vibrate the stiffer, thicker region of the membrane near the oval window
- low frequencies vibrate the thinner, more flexible region closer to the helicotrema (end)
15
Q
what nerve is formed from the axons of nerve cells exiting the cochlea?
A
Cochlear nerve
16
Q
What are the two parts of the vestibule and their functions?
What do they contain?
A
Utricle - sensing horizontal acceleration
Saccule - sensing vertical acceleration
- contain K+ rich endolymph
17
Q
What is the structure within the two parts of the vestibule that converts axial accelerations of the head into nerve signals?
And its parts?
A
Macula (of Utricle/Saccule)
- otolithic membrane (w/ crystals)
- hair cells (w/ stereocilia)
- solid membrane
18
Q
How are the two maculae of the vestibule oriented and how does this contribute to their function?
A
Saccule is vertically oriented
Utricle is horizontally oriented
- this allows them to pick up accelerations of the head on their respective planes
19
Q
what are the crystals that sit atop the maculae of the vestibule and contribute to its function by acting as a weight?
A
**Otoliths **
- made of calcium and proteins
20
Q
What inner ear organ detects rotational movements of the head?
A
the semicircular canals
21
Q
what is the structure within the semicircular canals where rotational movement is translated into action potentials?
A
Crista Ampullaris
22
Q
What is the gelatinous mass in the crista ampullaris?
A
cupula
23
Q
How does rotational movement affect the crista ampullaris and create an action potential?
A
1) as head turns, bony and membranous labyrinth walls move
2) inertia causes endolymph within to create drag, bending cupula against direction of rotation
3) Hair cell cilia embedded in the cupula are bent, opening K+ channels and causing depolarization. When bent back the opposite way, hyperpolarization occurs, also sending signals.
24
Q
What are the three tunics of the eye?
A
1) Fibrous
2) Vascular
3) Sensory
25
What are the two parts of the fibrous tunic?
- **Sclera** (whites of the eyes)
- **Cornea** (transparent front projection, covers iris, pupil and anterior chamber)
26
What are the 3 parts of the vascular tunic?
1) **Choroid** (vascular layer btwn retina and sclera)
2) **Ciliary Body** (ciliary muscle and processes)
3) **Iris** (colored part, controls pupil size)
27
What is the main part of the sensory tunic and its 3 types of cells?
**Retina**
## Footnote
1) **Photorecptor cells** (rods and cones)
2) **Bipolar cells** (trasmit photoreceptor APs to ganglion cells)
3) **Ganglion cells** (transmit APs to optic nerve and brain)
28
What are the different functions of the two different photoreceptor cells?
**Rods** - black and white, low light, and peripheral vision
**Cones** - sharp, color, high light vision
29
What are the visual pigments in both rods and cones?
In each one separately?
_In both_:
**Retinal** - binds to opsin, is straightened by light, causing it to fall off opsin (bleaching rods)
**Opsin** - transmembrane hourglass shape, binds retinal
_In rods only_:
**Rhodopsin** -** **
_In cones only_:
**Blue, Green and Red Pigments** -
30
Describe the process of shutting down rods in favor of cones in the presence of light.
1) in dark conditions, rods are slightly depolarized (**-40 mV**)
2) light photons hit **retinal** bound to **opsin** on **visual disc** membranes
3) **retinal**'s bent shape straightens, and it falls off of **opsin** (called "**bleaching the rods**")
4) "bleached" **opsin** activates **transducin** proteins nearby on membrane
5) transducin activates **phosphodiesterase**, breaking down **cGMP** which had been holding open **chemically-gated Na+ channels** on the rod cell membrane
6) Na+ flows in, hyperpolarizing rod to **-70 mV**
31
What is the name of the process of reaction to light in the eye?
transduction
32
What is the name of the clear gel that fills the eye between the lens and the retina?
vitreous humor
33
What is the small, oval, yellow-pigmented spot near the center of the retina?
What kinds of cells does it contain mostly?
What is the name of its center, which contains the highest concentration of these cells?
**Macula Lutea** - mostly cones
**Fovea Centralis** - highest concentration of cones, virtually no rods
34
In order, what structures, fluids and cells does light pass through before it hits photoreceptor cells?
1) **cornea**
2) **aqueous humor**
3) **pupil/iris** (then technically more aqueous humor)
4) **lens**
5) **vitreous humor**
6) **ganglion cells**
7) **bipolar cells**
... and finally photoreceptors
35
What are the two names for where neurotransmitters meet dendrites at synapses?
**_Ligands_**
Chemically-gated receptor proteins on dendrites
Opened by **neurotranmitters**, allowing **Na+** in
36
What is it called when a cell's resting charge increases due to influx of positive ions?
**Depolarization**
37
What is the entry of Na+ into a dendrite considered?
Why?
an **excitatory event**
because it depolarizes the cell, pushing it toward the creation of an action potential
38
What are the 3 methods of neurotransmitter removal at a synapse?
1) enzymatic breakdown
2) re-uptake into axon (endocytosis)
3) diffusion
39
What is a graded potential?
A variable strength signal that travels short distances and loses strength as it travels.
40
What are graded potentials used for?
What can they create?
What kinds are there?
Where and how do they start?
- short distance communication
- can lead to creation of action potentials
- can be **excitatory** (Na+ or Ca2+ inflow) or **inhibitory** (K+ outflow or Cl- entry)
- start at dendrites or cell bodies via localized changes in membrane permeability at chemically gated channels allowing in or outflow of ions
41
What is the major anion and cation in the intracellular fluid?
**K+ **and **Phosphate**
42
What is the major anion and cation in the extracellular fluid?
**Na+** and **Cl-**
43
What causes the difference in net charge between intra- and extracellular fluid?
- **intracellular fluid is electrically negative** because it contains protein anions without matching cations
- **extracellular fluid is electrically positive** because it contains some cations without matching anions
44
What is an **electrical gradient**?
a difference in net charge between two regions
45
What is an **electrochemical gradient**?
A combination of electrical and concentration gradients
46
What is the **resting membrane potential difference**?
AKA **membrane potential**
- an electrical gradient between extra- and intracellular fluid
* **"resting"** because it's in all living cells
* **"potential"** because it's a form of stored energy
* **"difference"** because it represents a difference in charge
47
What is the term for the membrane potential that exactly opposes the concentration gradient of an ion?
**equilibrium potential**
48
What is the resting membrane potential voltage of a typical cell?
**-70 mV**
49
How do cells maintain their resting membrane potential?
via active transport using **Na+-K+-ATPase** pumps
**2 K+ in for every 3 Na+ out**
50
What is the term for a decrease in potential difference between two regions?
**depolarization**
51
What is the term for a return to resting membrane potential?
**repolarization**
52
What is the term for an increase in potential difference between two regions?
**hyperpolarization**
53
What ions cause most changes in membrane potential?
And how?
**Na+, Ca2+, K+ and Cl-**
- permeability changes in a membrane relative to any of these ions allows them to move down their electrochemical gradient, changing charges inside and outside the cell
54
What happens if a cell becomes more permeable to calcium ions?
It tends to **depolarize** because Ca2+ concentration outside the cell is higher, so increased permeability means an influx of Ca2+.
55
What happens if a cell becomes more permeable to potassium ions?
It tends to **hyperpolarize** because K+ concentration is higher inside the cell, so increased permeability increases outflow of K+ and decreases net charge.
56
What happens if a cell becomes more permeable to sodium ions?
It tends to **depolarize**, because Na+ concentrations are higher outside the cell, so increased permeability creates an influx of Na+ and an increase in net charge.
57
What happens if a cell becomes more permeable to chloride ions?
It tends to **hyperpolarize** because Cl- concentrations are higher outside the cell so an increase in permeability means an influx of Cl- and a decrease in charge.
58
What are the 3 types of gating on ion channels?
**Mechanical** - in sensory neurons, open in response to physical forces such as pressure or stretch
**Chemical** - in most neurons, respond to various ligands such as extracellular NTs/neuromodulators or intracellular signaling molecules
**Voltage** - respond to change in membrane potential. important role in action potentials
59
Why are graded potentials considered "graded"?
Because their amplitude is directly proportional to the strength of the triggering event
60
What are the differences in signal type between graded potentials (GPs) and action potentials (APs)?
GP - input signal
AP - regenerating conduction signal
61
Where do GPs and APs usually occur?
**GP** - dendrites and cell body
**AP** - trigger zone thru axon
62
What types of gated ion channels are involved in GPs and APs?
**GP** - mechanically, chemically or voltage-gated
**AP** - voltage gated only
63
What ions are involved in GPs vs. APs?
**GP** - usually Na+, Cl-, Ca2+
**AP** - Na+ and K+
64
What type of signals are created in GPs vs. APs?
**GP** - de- or hyperpolarizing (Na+ or Cl-, respectively)
**AP** - depolarizing only
65
What is the difference in signal strengths between GPs and APs?
**GP** - depends on intial stimulus; can be summed
**AP** - all-or-nothing; can't be summed
66
What initiates signals in GPs vs. APs?
**GP** - entry of ions thru gated channels
**AP** - suprathreshold GP at trigger zone opens ion channels
67
What is the difference in stimulus needed to intiate GPs vs. APs?
**GP** - no minimum required
**AP** - _threshold stimulus_ (usually depolarization to -55 mV) required
68
Where do graded potentials sometimes form action potentials?
What is this place called and how is it different in efferent, inter-, and sensory neurons?
- APs are formed at the **trigger zone**
* Efferent and interneurons* - trigger zone is **axon hillock** and **initial segment** of axon
* Sensory neurons* - trigger zone **immediately adjacent to receptor**, where dendrites join axon
69
What is physiologically special about the trigger zone in comparison to the rest of the cell?
And how does this facilitate the creation of action potentials?
- it contains a **high concentration of voltage-gated Na+ channels**
- if GP depolarizes membrane to threshold, Na+ channels open, further depolarizing to create AP
70
What would a simple visual representation of a graded potential look like?
- sodium ions flowing in through dendrites and diffusing toward their lower concentration in the axon hillock where they may be able to induce an action potential
71
What are depolarizing graded potentials also called?
And why?
**_Excitatory_ Post-Synaptic Potentials (EPSPs)**
- because they excite a cell, making it more likely to fire an action potential
72
What are hyperpolarizing graded potentials also called?
And why?
**_Inhibitory_ Post Synaptic Potentials (IPSPs)**
- because they further reduce the voltage of the intracellular environment, making it less likely to create an action potential
73
What is a phenomenon called that either occurs as maximal depolarization or does not occur at all?
**all-or-nothing**
74
How does summation differ in GPs vs. APs?
**GP** - two signals close in time will sum
**AP** - refractory period causes two signals close in time to not sum
75
How does stimulus strength affect GPs and APs?
**GP** - stimulus strength and GP _amplitude_ are directly proportional
**AP** - stimulus strength and AP _frequency_ are directly proportional (AP strength is constant)
stronger stimulus = stronger GP = higher frequency APs
76
What happens to a graded potential as it moves through the cell?
Why?
GPs **lose strength** as they move through cells due to two factors:
1. **Current leak** (open leak channels let + ions out)
2. **Cytoplasmic resistance** (cytoplasm resists flow of electricity)
77
What are the 3 phases of an action potential's voltage?
1) rising phase
2) falling phase
3) after-hyperpolarization phase
78
What is the threshold voltage for the creation of an action potential?
**-55 mV**
79
What initiates the rising phase of an AP?
- An **adequate GP depolarizes the trigger zone to threshold**, opening voltage-gated Na+ channels, causing an influx diffusion of Na+ ions due to their higher concentration outside the cell
80
What is the term for the portion of an AP above 0 mV?
**Overshoot**
81
What causes Na+ to keep moving into a cell once its voltage has become positive?
A remaining **concentration gradient** due to higher extracellular Na+ concentration
82
At what voltage does an action potential peak?
And what happens at this peak physiologically?
**+30 mV**
- Na+ channels close and K+ channels open, allowing outflow of K+ and repolarization
83
What initiates the falling phase of an action potential's voltage graph?
- **voltage-gated K+ channels open** in response to depolarization and Na+ channels close, causing outflow of K+ and repolarization
84
What properties of ion channels allow a neuron to depolarize?
- **K+ channels open more slowly than Na+ channels**, allowing a large influx of Na+ before a correspondingly large outflow of K+ can occur
85
What is another name for the after-hyperpolarization phase?
What voltage does it result in?
And why does it occur?
**Undershoot**
**-90 mV**
Because **voltage-gated K+ channels close slowly,** allowing more K+ to flow out after resting membrane potential has been reached
86
How big of a change in ion concentrations does ion movement in an action potential produce?
**Very little change**
only about 1 in 100,000 K+ ions must leave the cell to shift the voltage from +30 mV to -70 mV
87
How can an action potential's creation and self-propagation be visually represented?
- fast Na+ influx and slow K+ efflux channels opening and closing in response to voltage changes along the axon, allowing for fluctuation from resting voltage of -70 mV to threshold voltage of -55 mV, as high as +30 mV and then back down to -90 mV during hyperpolarization
88
What two major divisions of the nervous system are there?
And what does each contain?
**Central Nervous System (CNS)** - brain, spinal cord and CSF
**Peripheral Nervous System (PNS)** - sensory and efferent nerves, spinal nerves, ganglia
89
What are the 6 types of neuroglia cells?
Their function? Location?
Remember the acronym: **EMO-ASS**
## Footnote
**Ependymal** - CNS, creates/moves CSF, separates fluid compartments of CNS
**Microglia** - CNS, remove damaged cells/invaders
**Oligodendrocytes** - CNS, myelination, one cell for many axons
**Astrocytes** - CNS, BBB, take up/release chems at synapses, provide ATP substrates, take up K+ and H20
**Schwann** - PNS, myelination, many cells per axon
**Sattelite** - PNS, non-myelinating Schwann, support ganglial cell bodies
90
What are the three structural types of neurons and their location/function?
**Multipolar** - all motor nerves, have cell body with many extensions (branching dendrites and long axon)
**Bipolar** - rare sensory neurons (as in eye), 2 extensions: one to dendrites and one to axon
**Unipolar** - sensory nerves, single process with cell body off to side
91
What are the three functional types of neurons?
**Sensory (afferent) Neurons**- carry sense info to CNS
**Motor (efferent) Neurons** - carry motor signals to effectors
**Interneurons** - entirely within CNS, complex branching
92
What is the term for any stimulus that is too weak to create an action potential?
**Subthreshold Stimulus**
93
What is the term for the minimum stimulation necessary to create an action potential?
**threshold stimulus**
94
What phenomenon causes a 1-2 msec delay between action potentials?
Explain the physiology of this.
**Absolute Refractory Period**
- double-gated Na+ channels must reset to their original position, so a second action potential cannot occur before the first has finished
95
What is the phenomenon that allows summation of adequately strong GPs?
Explain its physiology.
**Relative Refractory Period**
- some Na+ channels have reset, K+ channels are still open for repolarization
- because K+ efflux is offsetting Na+ influx, a stronger-than-normal GP can stimulate an AP of decreased amplitude
- occurs from about 2-4 msec after start of intial AP
96
What are the two types of conduction along an axon and what causes them to differ?
**Continuous Conduction**
**Saltatory Conduction**
- myelination allows for saltatory conduction
97
Explain continuous conduction.
Draw it.
Continuous conduction occurs in unmyelinated axons because the axon is uninsulated and every Na+/K+ channel along its length must open and close as conduction occurs.
98
Explain saltatory conduction.
Draw it.
Myelinated axons are insulated by either oligodendrocytes (CNS) or schwann cells (PNS).
This insulation helps AP signals to jump between insulated segments to the _nodes of Ranvier_, where unmyelinated axon membrane allows for opening and closing of ion gates.
99
What are the two methods through which neurotransmitters interact with synapses?
Briefly describe them.
**Direct Method** - faster, NT opens chem-gated ion channels
**Indirect Method** - slower, NT reacts w/ receptor to create chemical chain reaction that ends in opening of ion channels
100
Describe the "Direct Method" of NT interaction at a neuronal synapse.
NTs open chemically-gated ion channels on the post-synaptic cell and create rapid, short-acting fast synaptic potentials.
101
Describe the "Indirect Method" of NT interaction at neuronal synapses.
1) Neurotransmitters react with **G-Protein Coupled Receptors (GPCRs)**
2) These receptors activate **G-proteins**
3) G-proteins activate **enzymes**
4) Enzymes create **secondary messengers**
5) Secondary messengers open/close ion channels
All of this is slower than the direct method but can have longer-lasting effects.
102
What are the two main secondary messengers involved in the indirect method of NT stimulation of post-synaptic neurons?
**cyclic AMP** and **cyclic GMP**
both made by enzymatic breakdown of ATP
103
Describe summation.
What does it allow subthreshold stimuli to do?
Summation is the **adding together of multiple signals from pre-synaptic neurons** to create one potential in the postsynaptic cell.
It allows multiple subthreshold stimuli to create a suprathreshold stimulus in the postsynaptic cell, triggering an action potential.
104
What are the two kinds of summation?
Describe them.
**Spatial Summation** - multiple GPs from different locations (usually dendrites) create one AP
**Temporal Summation** - multiple GPs from a single presynaptic neuron that arrive at the trigger zone close together in time
105
What receptors react with acetylcholine?
What are the two types and their actions?
**Cholinergic Receptors**
## Footnote
1) **Nicotinic** - excitatory, don't use secondary messengers
2) **Muscarinic** - inhibitory, postganglionic parasymp, G-protein coupled receptors (indirect method)
106
What receptors react with epinephrine and norepinephrine?
What are the two kinds?
**Adrenergic Receptors** (all G Protein-coupled)
## Footnote
1) **Alpha**
2) **Beta**
107
What are the 4 major regions of the brain?
**Cerebrum **
**Diencephalon**
**Brain Stem**
**Cerebellum**
108
What are some general functions of the brain stem?
Midbrain - **eye movement**
Pons - **cerebral/cerebellar relay, breathing**
Medulla - **involuntary functions**
Reticular Formation - **arousal, sleep, muscle tone, pain modulation**
109
What are some general functions of the diencephalon?
**Homeostasis**
thalamus - **information relay**
hypothalamus - **behavior, hunger, thirst, autonomic/endocrine control**
pineal gland - **melatonin release**
pituitary gland - **hormone production/secretion**
110
What are some general functions of the cerebrum?
**sense perception**
**motor control**
"association areas" that **integrate information** and direct movement
111
What are some general functions of the cerebellum?
**process sensory info** and **coordinate movement**
112
What are the main lobes of the cerebrum?
**Frontal**
**Parietal**
**Temporal**
**Occipital**
113
What are some functions of the **frontal lobe**?
- **skeletal muscle movement** (motor cortex and motor association)
- **coordinates info from other areas** (prefrontal association area)
114
What are some functions of the **parietal lobe**?
- **receive sensory input** from skin, musculoskeletal system, viscera, taste buds
115
What are some functions of the **temporal lobe**?
**hearing** (auditory cortex & association area)
116
What are some functions of the occipital lobe?
**Vision** (visual cortex and association area)
117
What and where is gray matter?
**unmyelinated nerve cell bodies, dendrites and axon terminals**
found in **cerebral cortex** (outer layer) and **spinal "horns"** (inner, butterfly-like part of spinal cord)
118
What and where is white matter?
**myelinated axons** with very few cell bodies
found in deeper parts of cerebrum and superficial parts of spinal cord
119
What is the fluid that surrounds the central nervous system tissues?
Function?
Where is it made?
**Cerebrospinal Fluid**
- salty solution with little protein and no blood cells (low K+, higher H+)
- **physically and chemically protects the CNS** via buoyancy, cushioning and creation of a regulated extracellular environment
- made in **choroid plexus** of ventricles
120
What is the mechanism that separates the brain from regular bloodflow?
Its function?
And what makes it up?
the **Blood-Brain Barrier**
- protects brain from toxins and fluctuations in hormones, ions and neuroactive substances in blood
- made up of two components:
1) **tight endothelial junctions** in brain capillaries
2) **astrocyte foot processes** that surround the capillaries
121
What areas of the brain lack BBB?
And why?
**Hypothalamus/Pituitary -** because it releases hormones that must pass into the capillaries of the hypothalamic-hypophyseal portal system
**Medulla Oblongata** - contains neurons that monitor for toxic substances in blood and induce vomiting
122
What is a nerve?
a bundle of axons
123
What is a reflex?
an automatic response to a stimulus
124
What are the two kinds of reflexes?
**Somatic** - using skeletal muscle
**Autonomic** - everything else (smooth/cardiac)
125
What are the parts of a reflex arc in order from stimulus to response?
**Receptor** (senses stimulus)
**Sensory nerve** (transmits sensed stimulus via AP)
**Interneuron** (within SC, transmits signal to motor nerve)
**Motor nerve** (stimulates effector to respond to stimulus)
**Effector** (responds to stimulus)
126
What is a reflex that also affects the opposite side of the body from the stimulus?
a **crossed extensor reflex**
127
What is special about stretch reflexes?
they involve only two neurons (one synapse): **sensory neurons** from a muscle spindle and **motor neurons** to that muscle
128
What are the two divisions of the nervous system?
Their differing characteristics?
**Somatic** (voluntary, skeletal muscle)
**Autonomic** (involuntary, smooth/cardiac muscle)
129
What are the two branches of the autonomic nervous system?
**Sympathetic** - "fight or flight"
**Parasympathetic** - "rest and digest"
130
What is the similarity between the sympathetic and parasympathetic nervous systems?
2 neurons in a series
131
How many neurons are involved in efferent innervation in the somatic vs. autonomic NS?
**somatic** - one neuron/axon to the target organ
**autonomic** - 2 neuron series (1st melinated, 2nd not)
132
What is the difference in myelination betwen ANS and SNS?
**Somatic** - heavy myelination throughout
**Autonomic** - 1st axon in series is myelinated, 2nd is not
133
What is the difference in neurotransmitters used between the SNS and ANS?
**Somatic** - always acetylcholine
**Autonomic** - acetycholine at ganglion, Ach, Epi or Norepi at postganglionic synapse
134
Where does the nerves of the sympathetic and parasympathetic NS originate from?
**Sympathetic** - Thoracic and Lumbar spine
**Parasympathetic** - Brainstem and Sacrum
135
What is the difference between the lengths and structure of pre and post ganglionic nerves in the parasympathetic vs. sympathetic NS?
**Sympathetic** - short myelinated pre-, long unmyelinated post-
**Parasympathetic** - long myelinated pre-, short unmyelinated post-
136
What does the sympathetic ganglionic chain allow for?
innervation of multiple organs at once due to the interconnection of the chain
137
how many pairs of spinal nerves are there?
31
138
