Neurophysiology Flashcards
1
Q
autonomic nervous system
A
= set of pathways to and from the CNS that innervate and regulate
- smooth muscle
- cardiac muscle
- glands
2
Q
three divisions of the ANS
A
- sympathetic
- parasympathetic
- enteric nervous systems
3
Q
parasympathetic NS features
- origin of preganglionic nerve
- preganglionic axon length
- nt to autonomic ganglia
- receptor type at ganglia
- postganglionic axon length
- nt to effector organ
- receptor type at effector organ
A
- origin of preganglionic nerve = CN 3, 7, 9, 10; spinal segments S2-S4 (craniosacral)
- preganglionic axon length: long
- nt to postganglionic: Acetylcholine (ACh)
- receptor type at ganglia: nicotinic
- postganglionic axon length: short
- nt to effector organ: ACh
- receptor type at effector organ: muscarinic
4
Q
sympathetic NS features
- origin of preganglionic nerve
- preganglionic axon length
- nt to autonomic ganglia
- receptor type at ganglia
- postganglionic axon length
- nt to effector organ
- receptor type at effector organ
A
- origin of preganglionic nerve = T1-12, L1-3 (thoracolumbar)
- preganglionic axon length: short (terminates in the paravertebral chain of ganglia)
- nt to postganglionic: ACh
- receptor type at ganglia: nicotinic
- postganglionic axon length: long
- nt to effector organ: norepinephrine (except sweat glands, which use ACh)
- receptor type at effector organ: alpha-1, alpha-2, beta-1, beta-2
5
Q
effector organs of the somatic nervous system
A
skeletal muscle
6
Q
neurotransmitter of the somatic NS
A
ACh
7
Q
receptor type of the somatic NS
A
nicotinic
8
Q
adrenal medulla and special anatomy
A
= specialized ganglion of the sympathetic nervous system; pregangllionic fibers synapse directly on chromaffin cells in the adrenal medulla–> secretion of epinephrine (80%) and norepinephrine (20%)
9
Q
pheochromocytoma
A
= tumor of the adrenal medulla that secrete excessive amts of catecholamines and is associated with increased excretion of 3-methyoxy-4-hydroxymandelic acid (VMA)
10
Q
adrenergic nerve fiber
A
= a neuron for which the neurotransmitter is either epinephrine, norepinephrine, or dopamine; usually norepinephrine
11
Q
cholinergic neuron
A
= a neuron for which the neurotransmitter is acetylcholine (ACh); present in both the sympathetic and parasympathetic NSs
12
Q
receptors types of the ANS
A
- adrenergic (nt = norepinephrine)
2. cholinergic (nt = ACh)
13
Q
special parasympathetic receptors of the GIT
A
= nonadrenergic, noncholinergic receptors of some postganglionic parasympathetic neurons in the GIT, which release
- substance P
- vasoactive intestinal peptide (VIP)
- nitric oxide (NO)
14
Q
types of adrenergic receptors
A
- alpha-1
- alpha-2
- beta-1
- beta-2
15
Q
two broad categories of cholinergic receptors (cholinoreceptors) and specific types of cholinergic receptors
A
categories of cholinergic receptors
- nicotinic receptors
- muscarinic receptors
specific types of cholinergic receptors
- Nm (N1)
- Nn (N2)
- M1
- M2
- M3
16
Q
alpha-1 receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location = 1. smooth muscle (vascular smooth muscle of the skin and splanchnic regions, GIT, and bladder sphincters), 2. radial muscle of the iris
- result of activation = excitation (contraction/constriction)
- nt sensitivity = equally responsive to norepi and epi but ONLY norepi released from adrenergic neurons is present in high enough concentrations to activate alpha-1 receptors
- G protein = Gq
- mechanism = Gq–> stimulation of phospholipase C–> increase IP3 and intracellular Ca2+
17
Q
alpha-2 receptors
- location
- result of activation
- nt sensitivity*
- G protein
- mechanism
A
- location: 1. walls of GIT (heteroreceptors), 2. sympathetic postganglionic nerve terminals (autoreceptors), platelets, fat cells
- result of activation: inhibition (relaxation/dilation)
- nt sensitivity*
- G protein: Gi
- mechanism: Gi–>inhibition of adenylate cyclase–> decrease in cAMP
18
Q
beta-1 receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: Heart (1. SA node, 2. AV node, 3. ventricular muscle)
- result of activation: excitation (increase HR, increase contraction velocity, increase contractility)
- nt sensitivity: equally sensitive to norepi and epi; more sensitive than alpha-1 receptors
- G protein: Gs
- mechanism: Gs–>activate adenylate cyclase–>increase cAMP
19
Q
beta-2 receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: smooth muscle (1. bronchial smooth muscle, 2. vascular smooth muscle of skeletal muscle, 3. walls of GIT and bladder)
- result of activation: relaxation (dilation of bronchioles, dilation of vascular smooth muscle, relaxation of the bladder wall)
- nt sensitivity: more sensitive to epi than norepi (epi>norepi); more sensitive to epi than alpha-1 receptors
- G protein: Gs
- mechanism: Gs–>activate adenylate cyclase–>increase cAMP
20
Q
Nm (N1) nicotinic cholinergic receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: skeletal muscle neuromuscular junction (somatic nervous system)
- result of activation: excitation
- nt: ACh or nicotine
- G protein: n/a
- mechanism: opening Na/K channels (because nicotinic ACh receptors are also ion channels for Na and K)
21
Q
Nn (N2) nicotinic cholinergic receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: autonomic ganglia (of both the sympathetic and parasympathetic NS); adrenal medulla
- result of activation: excitation
- n: ACh or nicotine
- G protein: n/a
- mechanism: opening Na/K channels
22
Q
M1 muscarinic cholinergic receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: CNS
- result of activation
- nt: ACh or muscarine
- G protein: Gq
- mechanism: Gq–>increase phospholipase C activity–>increase IP3/Ca
23
Q
M2 muscarinic cholinergic receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: heart
- result of activation: inhibition (decreased HR, decreased conduction velocity of the AV node)
- nt: ACh or muscarine
- G protein: Gi
- mechanism: Gi–>inhibit adenylate cyclase–>decrease cAMP–>opening of K channels–>slowing of the rate of spontaneous phase 4 depolarization–>decreased heart rate
24
Q
M3 muscarinic cholinergic receptors
- location
- result of activation
- nt sensitivity
- G protein
- mechanism
A
- location: glands, smooth muscle
- result of activation: excitatory (increased GI motility, increased secretion)
- nt: ACh or muscarine
- G protein: Gq
- mechanism: Gq–>increase phospholipase C activity–>increase IP3/Ca
25
hexametonium
= ganglionic blocker in the autonomic ganglia but NOT at the neuromuscular junction (i.e. NOT the Nm (N1) nicotinic cholinergic receptors
26
atropine
= anticholinergic by blocking muscarinic cholinergic receptors
27
alpha-1 adrenergic receptor agonists (pro-sympathetic = sympathomimetic)
1. norepinephrine
| 2. phenylephrine
28
alpha-1 adrenergic receptor antagonists (anti-sympathetic = sympatholytic; parasympathomimetic)
1. phenoxybenzamine
2. phentolamine
3. prazosin
29
alpha-2 adrenergic receptor agonists (sympathomimetic)
clonidine
30
alpha-2 adrenergic receptor antagonists (sympatholytic; parasympathomimetic)
yohimbine
31
beta-1 adrenergic receptor agonists (sympathomimetic)
1. norepinephrine
2. isoproterenol
3. dobutamine
32
beta-1 adrenergic receptor antagonist (sympatholytic; parasympathomimetic)
1. propranolol
| 2. metroprolol
33
beta-2 adrenergic receptor agonists (sympathomimetic)
1. isoproterenol
| 2. albuterol
34
beta-2 adrenergic receptor antagonists (sympatholytic; parasympathomimetic)
1. propranolol
| 2. butoxamine
35
nicotinic cholinergic receptor agonists
1. ACh
2. nicotine
3. carbachol
36
nicotinic cholinergic receptor antagonists
1. curare (NMJ N1 (Nm) receptors
| 2. hexamethonium (ganglionic N2 (Nn) receptors
37
muscarinic cholinergic receptor agonists
1. ACh
2. muscarine
3. carbachol
38
muscarinic cholinergic receptor antagonists
1. atropine
39
Table 2.4
Effect of the ANS on organ systems - REVIEW
40
locations of ANS centers within the brainstem and hypothalamus
1. medulla - vasomotor center, respiratory center, swallowing/coughing/vomiting centers
2. pons - pneumotaxic center
3. midbrain - micturition center
4. hypothalamus - temperature regulation center; thirst and food intake regulatory centers
41
major divisions of the CNS
1. spinal cord
2. brain stem (medulla, pons, midbrain)
3. cerebellum
4. diencephalon (thalamus, hypothalamus)
5. cerebral hemispheres (cerebral cortex, basal ganglia, hippocampus, amygdala)
42
dendrites
= components that arise from the cell body and receive information from adjacent neurons
43
glial cells
= support cells for neurons
44
types of glial cells
1. astrocytes
2. oligodendrocytes and Schwann cells
3. microglial cells
45
astrocyte functions
1. supply metabolic fuels to neurons
2. secrete trophic factors
3. synthesize neurotransmitters
46
oligodendrocyte function
synthesize myelin in the CNS
47
Schwann cell function
synthesize myelin in the PNS
48
microglial cell function
proliferate following neuronal injury and serve as scavengers for cellular debris
49
sensory receptors
= specialized epithelial cells or neurons that transduce environmental signals into neuronal signals
50
environmental signals that can be detected by sensory receptors
1. mechanical force
2. light
3. sound
4. chemicals
5. temperature
51
4 types of sensory transducers (general categories)
1. mechanoreceptors
2. photoreceptors
3. chemoreceptors
4. nociceptors
52
5 types of mechanoreceptors
1. pacinian corpuscles
2. joint receptors
3. stretch receptors in muscle
4. hair cells in auditory and vestibular systems
5. baroreceptors in carotid sinus
53
2 types of photoreceptors
1. rods
| 2. cones of the retina
54
4 types of chemoreceptors
1. olfactory receptors
2. taste receptors
3. osmoreceptors
4. carotid body O2 receptors
55
sensation of nociceptors
extremes in pain and temperature
56
A-alpha fibers
- example
- sensory fiber types and examples
- diameter
- conduction velocity
- example: large alpha-motoneurons
- sensory fiber types and examples
1. Ia sensory fibers (e.g. muscle spindle afferents)
2. Ib sensory fibers (e.g. Golgi tendon organs)
- diameter: largest
- conduction velocity: fastest (because largest diameter)
57
A-beta fibers
- example
- sensory fiber types and examples
- diameter
- conduction velocity
- example: touch, pressure
- sensory fiber types and examples: II (e.g. secondary afferents of muscle spindles; touch and pressure)
- diameter: medium
- conduction velocity: medium
58
A-gamma
- example
- sensory fiber types and examples
- diameter
- conduction velocity
- example: gamma-motoneurons to muscle spindles (intrafusal fibers)
- sensory fiber types and examples: n/a
- diameter: medium
- conduction velocity: medium
59
A-delta
- example
- sensory fiber types and examples
- diameter
- conduction velocity
- example: touch, pressure, temperature, pain
- sensory fiber types and examples: III (e.g. touch, pressure, fast pain, and temperature)
- diameter: small
- conduction velocity: medium
60
B fibers
- example
- diameter
- conduction velocity
- example: preganglionic autonomic fibers
- diameter: small
- conduction velocity: medium
61
C fibers
- example
- sensory fiber types and examples
- diameter
- conduction velocity
- example: slow pain; postganglionic autonomic fibers
- sensory fiber types and examples: IV (e.g. unmyelinated pain and temperature fibers)
- diameter: smallest
- conduction velocity: slowest (because they have the smallest diameter and they are unmyelinated)
62
receptive field
= an area of the body that, when stimulated, changes the firing rate of a sensory neuron
63
excitatory receptive field
= the firing rate of the sensory neuron is increased
64
inhibitory receptive field
= the firing rate of the sensory neuron is decreased
65
steps in sensory transduction
1. stimulus arrives at the sensory receptor
2. ion channels are opened in the sensory receptor, allowing current to flow (usually inward current-->depolarization of the sensory receptor; EXCEPTION = photoreceptor - light-->DECREASED inward current-->hyperpolarization)
3. change in membrane potential produced by the stimulus = receptor potential (or generator potential)
4. if the receptor potential is large enough, the membrane potential will exceed threshold-->action potential in the sensory neuron
66
important point about receptor potentials
they are NOT action potentials; receptor potentials are graded in size depending on the size of the stimulus; if the receptor potential is depolarizing, it brings the membrane potential closer to threshold
67
two types of adaptations of sensory receptors
1. slowly adapting (tonic) receptors
| 2. rapidly adapting (phasic) receptors
68
examples of slowly adapting (tonic) receptors
1. muscle spindle receptors
2. pressure receptors
3. slow pain receptors
69
features of slowly adapting (tonic) receptors
1. respond repetitively to prolonged stimulus
| 2. detect a steady stimulus
70
examples of rapidly adapting (phasic) receptors
1. pacinian corpuscles
| 2. light touch
71
features of rapidly adapting (phasic) receptors
1. decline in action potential frequency with time in response to a constant stimulus
2. primarily detect onset and offset of a stimulus
72
general sensory pathway from sensory receptor to cerebral cortex
1. sensory receptor activated by environmental stimuli-->transduce the stimulus into electrical energy (i.e. receptor potential
2. first-order neurons
3. second-order neurons
4. third-order neurons
5. fourth-order neurons in the appropriate sensory area of the cerebral cortex
73
1st-order neurons
= the primary afferent neurons that receive the transduced signal and send info to the CNS; cell bodies are located in the dorsal root or spinal cord ganglia
74
2nd-order neurons
- location
- function
- location = spinal cord or brainstem
- function = receive information from one or more primary afferent neurons in relay nuclei and transmit it to the thalamus; **axons of 2nd order neurons may cross midline in a relay nucleus in the spinal cord before they ascend to the thalamus-->THEREFORE, sensory information originating on one side of the body ascends to the CONTRALATERAL thalamus
75
3rd-order neurons
- location
- function
- location = the relay nuclei of the thalamus
| - function = direct
76
4th-order neurons
- location
- function
- location = cerebral cortex
| - function = receives information of the stimulus and forms conscious proprioception
77
four senses of the somatosensory system
1. touch
2. movement
3. temperature
4. pain
78
two pathways of the somatosensory system
1. dorsal column system
| 2. anterolateral system
79
dorsal column system
- function
- fiber type
- course
- function: processes sensations of 1. fine touch, 2. pressure, 3. two-point discrimination, 4. vibration, 5. proprioception
- fiber type: group II fibers
- course: primary afferent neurons have cell bodies in the dorsal root; their axons ascend ipsilaterally to the nucleus gracilis and nucleus cuneatus of the medulla-->2nd orrder neurons cross midline and ascend to the contralateral thalamus where they synapse on 3rd order neurons-->3rd order neurons ascend to the somatosensory cortex, where they synapse on 4th order neurons
80
anterolateral system
- function
- fiber types
- course
- function: processes sensations of 1. temperature, 2. pain, 3. light touch
- fiber type: group III and IV fibers (terminate on dorsal horn)
- course: 2nd order neurons cross the midline to the anterolateral quadrant of the spinal cord-->ascend to the contralateral thalamus where they synapse on 3rd order neurons-->3rd order neurons ascend to the somatosensory cortex, where they synapse on 4th order neurons
81
sensation within the thalamus
is for the CONTRALATERAL side of the body; arranged somatotopically
82
four types of mechanoreceptors for touch and pressure
1. pacinian corpuscle
2. Meissner corpuscle
3. Ruffini corpuscle
4. Merkel disk
83
Pacinian corpuscle
- description
- sensation encoded
- adaptation
- description: onion-like structures in the SQ skin (surrounding unmyelinated nerve endings)
- sensation encoded: vibration, tapping
- adaptation: rapidly adapting
84
Meissner corpuscle
- description
- sensation encoded
- adaptation
- description: present in nonhairy skin
- sensation encoded: velocity
- adaptation: rapidly adapting
85
Ruffini corpuscle
- description
- sensation encoded
- adaptation
- description: encapsulated
- sensation encoded: pressure
- adaptation: slow adapting
86
Merkel disk
- description
- sensation encoded
- adaptation
- description: transducer is on epithelial cells
- sensation encoded: location
- adaptation: slowly adapting
87
largest areas of the sensory homunculus
1. face
2. hands
3. fingers
i. e. where precise localization is important
88
pain (nociceptors)
- receptors
- neurotransmitter
- receptors = free nerve endings in the skin, muscle, and viscera
- neurotransmitters for nociceptors = substance P
89
fast pain fibers
- fiber type
- features
- fiber type: group III fibers
| - features: rapid onset and offset; localized
90
slow pain fibers
- fiber type
- features
- fiber type: C fibers
| - features: aching, burning, throbbing that is poorly localized
91
referred pain
= pain of visceral origin that is referred to sites on the skin and follows the dermatome rule; innervated by nerves that arise from the same segment of the spinal cord
92
diopters definition
= the reciprocal of the distance
93
emmetropia
= normal; light focuses on the retina
94
hyperopia
= farsighted; light focuses behind the retina and is corrected with a convex lens
95
myopia
= nearsighted; light focuses in front of the retina and is corrected with a biconcave lens
96
astigmatism
= curvature of the lens is not uniform and is corrected with a cylindrical lens
97
presbyopia
= a result of loss of the accommodation power of the lens that occurs with age; the near point moves farther from the eye and is corrected with a convex lens
98
near point
= the closest point on which one can focus by accommodation of the lens
99
listed layers of the retina
1. pigmented epithelial cells
2. receptor cells (rods and cones)
3. bipolar cells
4. horizontal and amacrine cells
5. ganglion cells
100
pigmented epithelial cell function
1. absorb stray light and prevent scatter
| 2. convert 11-cis retinal to all-trans retinal
101
blind spot
= the optic disc where there are no rods or cones
102
rods
- sensitivity to light
- acuity
- dark adaptation
- color vision
- sensitivity to light: sensitive to low-intensity light; adapted for night vision
- acuity: lower visual acuity; not present in fovea
- dark adaptation: rods adapt later
- color vision: no
103
cones
- sensitivity to light
- acuity
- dark adaptation
- color vision
- sensitivity to light: sensitive to high-intensity light; day vision
- acuity: higher visual acuity; present in fovea
- dark adaptation: cones adapt first
- color vision: yes
104
bipolar cells
= the receptor cells onto which rods and cones synapse; bipolar cells then synapse on ganglion cells
105
structure of rod and cone synapses on bipolar cells
- cones: few cones synapse on a single bipolar cell-->synapses on a single ganglion cell-->basis for high acuity and low sensitivity of cones
- rods: many rods synapse on a single bipolar cells-->less acuity in the rods than in the cones, but greater sensitivity in the rods bc light striking any one of the rods will activate the bipolar cell
106
function of horizontal and amacrine cells
form local circuits with the bipolar cells
107
ganglion cells
receive input from the bipolar cells; are the output cells of the retina (axons of the ganglion cells form the optic nerve-->optic tract-->lateral geniculate body of the thalamus)
108
fovea
= point of highest acuity where the ratio of cones to bipolar cells is 1:1; NO rods located in the fovea
109
optic chiasm
= location where fibers from each nasal hemiretina cross (vs. the fibers from each temporal hemiretina remain ipsilateral)
110
geniculocalcarine tract
= fibers from the lateral geniculate body that pass to the occipital lobe of the cortex
111
```
lesions:
- cutting the optic nerve-->
- cutting the optic chiasm-->
- cutting the optic tract-->
cutting the geniculocalarine tract-->
```
- cutting the optic nerve-->blindness in the ipsilateral eye
- cutting the optic chiasm-->heteronymous bitemporal hemianopia?? blindness of the outer vision?
- cutting the optic tract-->homonymous contralateral hemianopia
cutting the geniculocalarine tract-->homonymous hemianopia with macular sparing
112
rhodopsin
= the photosensitive element in the rods; composed of opsin (a protein) belonging to the superfamily of GPCRs and retinal (an aldehyde of vitamin A)
113
steps in photoreception in the rods
1. light on the retina converts 11-cis retinal to all-trans retinal (= photoisomerization); a series of intermediates then forms, one of which is metarhodopsin II
2. metarhodopsin II activates the G protein called transducin (Gt), which-->activates a phosphodiesterase
3. phosphodiesterase catalyzes the conversion of cyclic guanosine monophosphate (cGMP) to 5'-GMP and cGMP levels decrease
4. decreased levels of cGMP-->closure of Na channels, decreased inward Na current, and as a result-->hyperpolarization of the photoreceptor membrane
5. when the photoreceptor is hyperpolarized, there is decreased release of glutamate (= an excitatory neurotransmitter)
114
two types of glutamate receptors on bipolar and horizontal cells (which determines whether the cell is excited or inhibited)
1. inotropic glutamate receptors = excitatory
| 2. metabotropic glutamate receptors = inhibitory
115
inotropic glutamate receptors
= excitatory; decreased release of glutamate from the photoreceptors actin on ionotropic receptors-->hyperpolarization (inhibition) because there is decreased excitation
116
metabotropic glutamate receptors
= inhibitory; decreased release of gluamate from photoreceptors actin on metabotropic receptors-->depolarization (excitation) bc there is decreased inhibition
117
on-center, off-surround
= one pattern of ganglion cell receptive feed in which light striking the center of the receptive field-->depolarizes (excites) the ganglion cell vs. light striking the surround of the receptive field-->hyperpolarizes (inhibits) the ganglion cell
118
possible patterns of a ganglion cell receptive field
1. on-center, off-surround
| 2. off-center, on-surround
119
features detected by neurons in the visual cortex
1. shape
| 2. orientation of figures
120
three cortical cell types involved in the visual cortex
1. simple cells
2. complex cells
3. hypercomplex cells
121
simple cells
- center-surround, on-off patterns
- elongated rods rather than concentric circles
- respond best to: bars of light that have the correct position and orientation
122
complex cells respond best to
moving bars or edges of light with the correct orientation
123
hypercomplex cells respond best to
lines with particular length and to curves and angles
124
components of the middle ear
1. tympanic membrane
2. auditory ossicles (malleus, incus, stapes)
3. oval window = a membrane between the middle ear and the inner ear
* air filled
125
mechanisms of sound amplification
1. the lever action of the ossicles
| 2. the concentration of sound waves from the large tympanic membrane onto the smaller oval window
126
components of the inner ear
1. bony labyrinth (= semicircular canals + cochlea + vestibule)
2. membranous labyrinth
3. perilymph = fluid outside the ducts; high Na concentration
4. endolymph = fluid within the ducts; high K concentration
* fluid-filled
127
structure of the cochlea
= three tubular canals
1. scala vestibuli
2. scala tympani
3. scala media
- scala vestibuli and scala tympani contain perilymph
- scala media contains endolymph
128
basilar membrane
borders the scala media; the site of the organ of Corti (the cell bodies of the hair cells contact the basilar membrane while the cilia of the hair cells are embedded in the tectorial membrane
129
Organ of Corti structure
= contains the receptor cells (inner and outer hair cells) for auditory stimuli; cilia protrude from the hair cells and are embedded in the tectorial membrane
130
inner vs. outer hair cells
- inner hair cells: arranged in single rows; few in number
| - outer hair cells: arranged in parallel rows; great in number
131
spiral ganglion
contains the cell bodies of the auditory nerve (cranial nerve 8), which synapses on the hair cells
132
steps in auditory transduction by the organ of Corti
1. sound waves cause vibration of the organ of Corti (NOTE: because the basilar membrane is more elastic than the tectorial membrane, vibration of the basilar membrane causes the hair cells to bend by shearing force as they push a against the tectorial membrane)
2. bending of the cilia-->changes in K+ conductance of the hair cell membrane (bending in one direction causes depolarization vs. bending in the other direction causes hyperpolarization)-->cochlear microphonic potential (oscillating potential)
3. the oscillating potential of the hair cells causes intermediate firing of the cochlear nerves
133
note about frequency and hair cell location
the frequency that activates a particular hair cell depends on the location of the hair cell along the basilar membrane
134
base of the basilar membrane (near the oval and round windows) features
stiff and narrow; responds best to high frequencies
135
apex of the basilar membrane (near the helicotrema) features
wide and compliant; responds best to low frequencies
136
central auditory pathway
1. fibers ascend through the lateral lemniscus-->
2. inferior colliculus-->
3. medial geniculate nucleus of the thalamus-->
4. auditory cortex
fibers may be crossed or uncrossed-->a mixture of ascending auditory fibres represents BOTH ears at all higher levels
137
lesions of the cochlea of one ear-->
unilateral deafness
138
central unilateral lesions-->
bilateral deafness
139
features detected by the vestibular system
1. angular acceleration of the head
| 2. linear acceleration of the head
140
vestibular organ structure
= a membranous labyrinth consisting of
1. three perpendicular semicircular canals
2. utricle
3. saccule
141
function of the semicircular canals
contain endolymph and bathed in perilymph; detect angular acceleration or rotation
142
functions of the utricle and saccule
detect linear acceleration
143
receptors of the vestibular organ
hair cells located at the end of each semicircular canal; the cilia are embedded in a gelatinous structure (= the cupula); kinocilium = a single long cilium; stereocilia = smaller cilia
144
steps in vestibular transduction of angular acceleration
1. during counterclockwise rotation of the head (left), the horizontal semicircular canals and its attached cupula also rotate to the left - initially the cupula moves more quickly than the endolymph-->the cupula is DRAGGED through the endolymph-->the cilia on the hair cell bend to the right toward the kinocilium-->the hair cell depolarizes
2. after several seconds, the endolymph "catches up" with the movement of the head and the cupula-->cilia return to their upright position and are no longer depolarized or hyperpolarized
3. when the head stops moving, the endolymph continues to move counterclockwise (left), dragging the cilia in the opposite direction-->therefore if the hair cell was depolarized with the initial rotation, it will now hyperpolarize and if it was hyperpolarized initially (e.g. the ones on the right), it will depolarize
145
if the stereocilia are bend away from the kinocilium-->
the hair cell hyperpolarizes (inhibition)
146
nystagmus
= when the eyes slowly move in the OPPOSITE direction to maintain visual fixation and when the limit of eye movement is reached, the eyes rapidly snap back (nystagmus) then move slowly again
147
definition of nystagmu
defined by the fast phase; therefore, the nystagmus occurs in the same direction as head rotation
148
postrotatory nystagmu
occurs in the OPPOSITE direction of the head rotation
149
receptor cells of the olfactory pathway
= located in the olfactory epithelium; true neurons that conduct action potentials into the CNS
150
basal cells of the olfactory epithelium
undifferentiated stem cells that continuously turn over and replace the olfactory receptor cells (neurons)
151
axon features of the olfactory nerves
= unmyelinated C fibers (smallest and slowest in the nervous system)
152
2 innervations of the olfactory epithelium
1. CNI
| 2. CN V (trigeminal) - detects noxious or painful stimuli (e.g. ammonia)
153
fractures of the cribriform plate-->
sever input to the olfactory bulb and reduce (hyposmia) or eliminate (anosmia) the sense of smell; NOTE the response to ammonia will be INTACT because the response is carried by CN V
154
mitral cells of the olfactory bulb
= 2nd order neurons; output forms the olfactory tract, which projects to the prepiriform cortex
155
steps in transduction in the olfactory receptor neurons
1. odorant molecules bind to specific olfactory receptor proteins on the cilia of the olfactory receptor cells
2. when receptors are activated, they activate G proteins (Golf), which in turn activate adenylate cyclase
3. adenylate cyclase-->increase in cAMP-->opens Na channels in the olfactory receptor membrane-->depolarizing receptor potential
4. the receptor potential depolarizes the initial segment of the axon to threshold, and action potentials are generated and propagated
156
note about taste receptors
they are NOT neurons, unlike olfactory receptors
157
features of the anterior 2/3 of the tongue
- papillae
- tastes detected
- innervation
- papillae: fungiform
- tastes detected: salty, sweet, umami
- innervation: CN7
158
features of the posterior 1/3 of the tongue
- papillae
- tastes detected
- innervation
- papillae: circumvallate and foliate
- tastes detected: sour, bitter
- innervation: CN9
NOTE: the back of the throat and epiglottis are innervated by CNX
159
taste pathway
CN7, 9, and 10 enter the medulla-->ascend in the solitary tract-->terminate on 2nd order taste neurons in the solitary nucleus-->project, primarily ipsilaterally to the ventral posteromedial nucleus of the thalamus-->taste cortex
160
steps in taste transduction
1. taste chemicals bind taste receptors-->produce depolarizing receptor potential in the receptor cell
161
components of a motor unit
single motoneuron + the muscle fibers it innervates
162
fine control motor unit components
= single motoneuron innervates only a few muscle fibers
163
larger movement motor unit components
= single motoneuron innervates thousands of muscle fibers
164
motoneuron pool
= a group of motoneurons that innervates fibers within the same muscle
165
force of muscle contraction determinant
graded by recruitment of additional motor units (size principle)
166
size principle
= as additional motor units are recruited, more motoneurons are involved and more tension is generated
167
features of small motoneurons
- innervate a FEW muscle fibers
- have the LOWEST thresholds = fire first
- generate the smallest force
168
features of large motoneurons
- innervate MANY muscle fibers
- have the HIGHEST thresholds = fire last
- generate the largest force
169
types of muscle sensors
1. muscle spindles
2. Golgi tendon organs
3. pacinian corpuscles
4. free nerve endings
170
muscle spindles
- fiber groups
- structure
- detect
- fiber groups: group Ia and II afferents
- structure: arranged in parallel with extrafusal fibers
- detect: both static and dynamic changes in muscle length
171
Golgi tendon organs
- fiber groups
- structure
- detect
- fiber groups: Ib afferents
- structure: arranged in series with extrafusal muscle fibers
- detect: muscle tension
172
Pacinian corpuscles
- fiber groups
- structure
- detect
- fiber groups: group II afferents
- structure: distributed throughout the muscle
- detect: vibration
173
Free nerve endings
- fiber groups
- detect
- fiber groups: III and IV afferents
| - detect: noxious stimuli
174
types of muscle fibers
1. extrafusal fibers
| 2. intrafusal fibers
175
extrafusal fibers
- definition
- innervation
- function
- definition = the bulk of the muscle
- innervation = alpha-motoneurons
- function = provide the force for muscle contraction
176
intrafusal fibers
- definition
- innervation
- structure
- function
- definition = smaller than extrafusal muscle fibers
- innervation = gamma-motoneurons
- structure = encapsulated in sheaths to form muscle spindles; run in parallel with extrafusal fibers but not for the entire length of the muscle
- function = too small to generate significant force; used for fine movement?
177
types of intrafusal fibers in muscle spindles
1. nuclear bag fibers
| 2. nuclear chain fibers
178
nuclear bag fibers
- detect
- innervation
- structure
- detect: rate of change in muscle length (fast, dynamic changes)
- innervation: group Ia afferents
- structure: nuclei collected in a central "bag" region
179
nuclear chain fibers
- detect
- innervation
- structure
- detect: static changes in muscle length
- innervation: group II afferents
- structure: nuclei arranged in rows
* more numerous than nuclear bag fibers
180
how the muscle spindle works
- muscle spindle reflexes oppose (correct for) increases in muscle length (stretch)
- sensory information about muscle length is received by group Ia (velocity) and group II (static) afferent fibers
- when a muscle is stretched, the muscle spindle is stretched-->stimulating group Ia and II afferents-->stimulates alpha-motoneurons to the spinal cord-->contraction and shortening of the muscle
181
function of gamma-motoneurons
innervate intrafusal muscle fibers and adjust the sensitivity of the muscle spindle so that it will respond appropriately during muscle contraction
182
three types of muscle reflexes
1. stretch reflex (knee-jerk)
2. Golgi tendon reflex (clasp-knife)
3. flexor withdrawal reflex (after touching a hot stove)
183
stretch reflex = knee jerk reflex
- number of synapses
- stimulus
- afferent fibers
- pathway
- response
- number of synapses: monosynaptic
- stimulus: stretching of muscle
- afferent fibers: Ia
- pathway: stretching of muscle-->stimulates group Ia afferent fibers-->group Ia afferents synapse directly on alpha-motoneurons in the spinal cord that innervate the homonymous muscle-->contraction in the muscle that was stretch - ALSO synergistic muscles are activated and antagonistic muscles are inhibited
- response: contraction of the stretched muscle
184
Golgi tendon reflex (inverse myotactic)
- number of synapses
- stimulus
- afferent fibers
- pathway
- response
= the inverse (opposite) of the stretch reflex
- number of synapses: disynaptic
- stimulus: active muscle contraction
- afferent fibers: Ib
- pathway: active muscle contraction-->stimulates the Golgi tendon organs and group Ib afferent fibers-->group Ib afferents stimulate inhibitory neurons in the spinal cord-->inhibit alpha-motoneurons-->relaxation of the muscle that was originally contracted
- response: relaxation of the muscle
185
myotactic reflex
= the stretch reflex
186
alpha-motoneurons versus gamma-motoneurons
Alpha motor neurons control muscle contraction involved in voluntary movement, whereas gamma motor neurons control muscle contraction in response to external forces acting on the muscle.
187
flexor withdrawal reflex
- number of synapses
- stimulus
- afferent fibers
- pathway
- response
- number of synapses: polysynaptic
- stimulus: pain (e.g. stepping on a hot stove)
- afferent fibers: II, III, and IV
- pathway: pain-->stimulates the flexor reflex afferents of groups II, III, and IV-->the afferent fibers synapse polysynaptically (via interneurons) onto motoneurons in the spinal cord
* on the ipsilateral side-->flexors are stimulated (contract) and extensors are inhibited (relax)-->arm is pulled away from the stove
* on the contralateral side-->flexors are inhibited and extensors are stimulated (contract)-->crossed extension reflex to maintain balance
- response: ipsilateral flexion; contralateral extension
188
homonymous muscle
= the same muscle that was stimulated
189
convergence
= when a single alpha-motoneuron receives its input from many muscle spindle group Ia afferents and produces spatial and/or temporal summation
190
divergence
= when the muscle spindle group Ia afferent fibers project to all of the alpha-motoneurons that innervate the homonymous muscle
191
Renshaw cells
= inhibitory cells in the ventral horn of the spinal cord
192
recurrent inhibition
= when Renshaw cells receive input from collateral axons of motoneurons and, when stimulated, negatively feedback (inhibit) the motoneuron
193
two major tracts controlling posture
1. pyramidal tracts
| 2. extrapyramidal tracts
194
pyramidal tracts
= pass through the medullary pyramids
1. corticospinal
2. corticobulbar
195
extrapyramidal tracts
1. rubrospinal
2. pontine reticulospinal
3. medullary reticulospinal
4. lateral vestibulospinal tract
5. tectospinal tract
196
rubrospinal tract
- origin
- projection
- stimulus
- origin: red nucleus
- projection: to interneurons in the lateral spinal cord
- stimulus: -->stimulation of flexors and inhibition of extensors
197
pontine reticulospinal tract
- origin
- projection
- stimulus
- origin: nuclei in the pons
- projection: to ventromedial spinal cord
- stimulus: -->general stimulatory effect on both flexors and extensors, with predominant effect on extensors
198
medullary reticulospinal tract
- origin
- projection
- stimulus
- origin: medullary reticular formation
- projection: to spinal cord interneurons in the intermediate gray area
- stimulus: -->general inhibitory effect on both extensors and flexors, with predominant effect on extensors
199
lateral vestibulospinal tract
- origin
- projection
- stimulus
- origin: dieters nucleus
- projection: to ipsilateral motoneurons and interneurons
- stimulus: -->powerful stimulation of extensors and inhibition of flexors
= OPPOSITE function of the rubrospinal tract
200
tectospinal tract
- origin
- projection
- stimulus
- origin: superior colliculus
- projection: to cervical spinal cord
- stimulus: involved in control of neck muscles
201
spinal shock
= initial loss of reflexes; immediately after transection, there is loss of the excitatory influence from alpha and gamma motoneurons; limbs become flaccid and reflexes are absent
202
lesion at C7-->
loss of sympathetic tone to the heart-->decrease HR and arterial BP
203
lesion at C3-->
stops breathing
204
effects of transection at lesions above the lateral vestibular nucleus
-->decerebrate rigidity = extensor posturing = exaggerated extensor contraction of all extremities
205
lesions resulting in decerebrate rigidity
1. lesions above the lateral vestibular nucleus
| 2. lesions above the pontine reticular formation and below the midbrain
206
lesion above the red nucleus
-->decorticate posturing (flexion of arms and wrists) and intact tonic neck reflexes
207
three functional sections of the cerebellum
1. vestibulocerebellum
2. pontocerebellum
3. spinocerebellum
208
role of vestibulocerebellum
= control of balance and eye movement
209
role of pontocerebellum
= planning and initiation of movement
210
role of spinocerebellum
= synergy = control of rate, force, range, and direction of movement
211
layers of the cerebellar cortex
1. granular layer
2. Purkinje cell layer
3. molecular layer
212
granular layer
- location
- contains
- location: innermost layer
- contains
1. granule cells
2. golgi type II cells
3. glomeruli = within which axons of mossy fibers form synaptic connections on dendrites of granular and golgi type II cells
213
purkinje cell layer
- location
- contains
- output
- location: middle layer
- contains: purkinje cells
- NOTE output of the Purkinje cell layer is always inhibitory
214
molecular layer
- location
- contains
- location: outermost layer
- contains
1. stellate cells
2. basket cells
3. dendrites of purkinje and golgi type II cells
4. parallel fibers (= axons of granule cells)
215
inputs into the cerebellar cortex
1. climbing fingers
| 2. mossy fibers
216
climbing fingers
- origin
- synapses
- function
- origin: single region of the medulla (inferior olive)
- synapses: multiple synpses onto Purkinje cells-->high frequency bursts or complex spikes
- function: condition the purkinje cells (role in cerebellar motor learning)
217
mossy fibers
- origin
- synapses
- function
- origin: many centers in the brainstem and spinal cord; includes vestibulocerebellar, spinocerebellar, and pontocerebellar afferents
- synapses: multiple synapses on Purkinje fibers via interneurons
- function:
1. synapses on Purkinje cells-->simple spikes
2. synapses on granule cells in glomuli
218
output of the cerebellar cortex
Purkinje cells = ONLY output of the cerebellar cortex and the output of the purkinje cells is ALWAYS INHIBITORY; neurotransmiitter = GABA
219
clinical disorders of the cerebellum
1. ataxia
2. dysdiadochokinesia
3. intention tremor
4. rebound phenomenon
220
components of basal ganglia
1. striatum
2. globus pallidus
3. subthalamic nuclei
4. substantia nigra
221
function of the basal ganglia
modulates thalamic outflow to the motor cortex to plan and execute smooth movements (i.e. control of movements); many synaptic connections are INHIBITORY and use GABA as the neurotransmitter
222
two pathways of the striatum to the thalamus and cerebral cortex
1. indirect = inhibitory
| 2. direct = excitatory
223
neurotransmitter btwn striatum and substantia nigra
dopamine = inhibitory in the Indirect pathway (D2 receptors) and excitatory on the direct pathway (D1 receptors); the OVERALL action of dopamine is EXCITATORY
224
lesions of the globus pallidus-->
inability to maintain postural support
225
lesions of the subthalamic nucleus
- cause
- result
- cause: release of inhibition on the contralateral side
| - result: wild, flinging movements (hemiballismus)
226
lesions of the striatum
- caused by
- result
- caused by: release of inhibition
- result = quick, continuous uncontrollable movements
occurs in patients with Huntington disease
227
lesions of the substantia nigra
- caused by: destruction of dopaminergic neurons (since dopamine INHIBITs the INDIRECT (inhibitory) pathway and excites the direct (excitatory; D1) pathway, destruction of the dopaminergic neurons is, overall, inhibitory
- result: lead-pipe rigidity, tremor, and reduced voluntary movement
occurs in patients with Parkinson disease
228
function of supplementary motor cortex
programs complex motor sequences and is active during "mental rehearsal" for a movement
229
primary motor cortex (area 4)
- function
- organization
- function: the execution of movements
| - organization: somatotopically (motor homunculus)
230
predominant EEG wave in awake adult with eyes open
beta waves
231
predominant EEG wave in awake adult with eyes closed
alpha waves
232
predominant EEG wave during sleep
slow waves
233
driver of circadian periodicity
suprachiasmatic nucleus of the hypothalamus; input from the retina
234
features of REM sleep
1. rapid eye movements
2. loss of muscle tone
3. pupillary constriction
4. penile erection
235
factors that decrease duration of REM sleep
1. benzodiazepines
| 2. increasing age
236
functions of the right cerebral cortex hemisphere
1. facial expression
2. intonation
3. body language
4. spatial tasks
237
functions of the left cerebral cortex hemisphere
1. language
238
lesions of the left hemisphere-->
aphasia
239
damage to the Wernicke area-->
sensory aphasia = difficulty understanding written or spoken language
240
damage to the Broca area-->
motor aphasia = speech and writing are affected but understanding is intact
241
short term memory
involves synaptic changes
242
long term memory
involves structural changes in the nervous system; is more stable
243
lesions that block ability to form new long-term memories
bilateral lesions of the hippocampus
244
components of the blood-brain barrier BBB
1. endothelial cells of the cerebral capillaries
| 2. choroid plexus epithelium
245
transport across the BBB
- freely movable and equilibrate = lipid soluble substances (CO2, O2) and water
- carriers = other substances
composition of the CSF is approximately the same as the interstitial fluid of the brain but differs significantly from blood
246
CSF versus blood:
- equal in
- CSFblood
- equal in: Na, Cl, HCO3, osmolarity
| - CSFblood: Mg, creatinine
247
functions of the BBB
1. maintains a constant environment for neurons
2. protects the brain from endogenous or exogenous toxins
3. prevents escape of neurotransmitters from their functional sites in the CNS into general circulation
248
heat-generation mechanisms
1. thyroid hormone-->increase metabolic rate and heat production by stimulating Na-K-ATPase
2. cold temperatures activate the sympathetic nervous system and beta receptors in brown fat-->increase metabolic rate and heat production
3. shivering (orchestrated by the hypothalamus)
249
most potent mechanism for increasing heat production
shivering
250
heat loss mechanisms
1. radiation
2. convection
orchestrated by the anterior hypothalamus
3. evaporation (depends on activity of sweat glands, which are under sympathetic muscarinic control)
251
hypothalamic set point for body temperature
- anterior hypothalamus compares detected core temperature to set point temperature
- posterior hypothalamus is responsible for heat generating or heat loss mechanisms
252
pyrogens
increase the set-point temperature by increasing production of IL-1 by phagocytic cells-->IL-1 and other cytokines cross the BBB-->IL-1 acts on the anterior hypothalamus to increase production of prostaglandin E2-->prostaglandins increase the set-point temperature
253
aspirin MOA
inhibits cyclooxygenase-->inhibits production of prostaglandins-->decreases set point temperature-->decreases fever
254
steroid MOA
block the release of arachidonic acid from brain phospholipids, thereby preventing the production of prostaglandins
255
heat exhaustion
caused by excessive sweating-->blood volume and arterial blood pressure decrease-->syncope occurs
256
heat stroke
occurs when body temperatures increase to the point of tissue damage; sweating is impaired and core temperature increases further
257
malignant hyperthermia
characterized by massive increase in O2 consumption and heat production by skeletal muscles-->rapid rise in body temperature
