Neuro summary Flashcards
1
Q
What are the cellular components of the nervous system
A
Neurones and glial cells
2
Q
What are glial cells
A
Neurone supporting cell, maintains environment. Both CNS and PNS
3
Q
What is the soma
A
Cell body
4
Q
What is the Nissl substance
A
Granules containing rough ER and free ribsomes. Site of protein synthesis in neurones
5
Q
Where are nissl granules found
A
Cell body/soma and dendrites
6
Q
Where is the axon potential initiated from
A
Axon hillock. The axon hillock has fast voltage gated sodium channels, the dendrites don’t
7
Q
What is the myelinating cell of CNS vs PNS
A
CNS = Oligodendrocytes
PNS = Schwann cells
8
Q
What is a key difference between oligodendrocytes and schwann cells
A
Oligodendrocytes can myelinate many axonal segments, schwann cells only 1
9
Q
What is the most numerous glial cell
A
Oligodendrocytes
10
Q
What are the functions of astrocytes
A
1) Storage of glycogen/lactate for neurones. Neurones do not store
2) Uptake of excess ions + neurotransmitters
3) Modulation of transmission. Release ATP which is converted to adenosine
4) Astrocyte end feet modulate blood flow
11
Q
What is adenosines function in the brain
A
Inhibitory neurotransmitter. Promotes sleep + supresses arousal
12
Q
What are gliotransmitters
A
Substances released from glial cells eg ATP from astrocytes which regulate neuronal synaptic transmission
13
Q
What is the origin of most glial cells
A
All are ectodermal in origin apart from microglia which are mesodermal
14
Q
What is the function of the microglia
A
Immune cells of the brain. Initiate phagocytosis + act as antigen presenting cells
15
Q
What is the function of ependymal cells
A
Produce CSF in choroid plexus. Have cilia to facilitate movement of CSF
16
Q
What are the 4 anatomically defined neurones
A
Multipolar, Bipolar, pseudounipolar, unipolar
17
Q
Where are multipolar neurones found
A
Brain and spinal cord (most common)
18
Q
Where are bipolar neurones found
A
Ganglia of CNVIII
Retina
Olfactory epithelium
19
Q
Where are pseudounipolar neurones found
A
Dorsal root ganglia
All CN ganglia apart from VIII
20
Q
Where are unipolar neurones found
A
Not in vertebrates
21
Q
Are cranial nerves peripheral or central?
A
Peripheral. Apart from the CN II Optic which is CNS. The optic nerve is ensheathed in all 3 meningeal layers
22
Q
What connective tissue surrounds peripheral nerves
A
Epineurium, perineurium, edoneurium
23
Q
What is ganglions
A
Collection of cell bodies
24
Q
What does white matter contain
A
Myelinated axons
25
What does gray matter contain
Cell bodies, dendrites, neuroglia
26
What are the components of the blood brain barrier
1) Tight junctions between endothelial cells + basement membrane
2) Pericytes
3) Astrocyte end feet
4) Microglia
27
Where is CSF produced
Choroid plexus. Covers the 2 lateral ventricles, and the roof of the 3rd + 4th ventricles
28
How much CSF is produced/day
500ml
29
How much CSF is present in the body at any given time
150ml
30
How is CSF produced
Ependymal cells form the blood-cerebral spinal fluid barrier. They secrete CSF
31
What is the osmolarity between CSF and blood
Have the same osmolarity
32
Where is CSF found
The ventricles, the subarachnoid space (between arachnoid mater and pia mater) and spinal canal
33
What do arachnoid granulations/villi do
Protrusions of arachnoid mater into the dura mater. Allow CSF to drain into the dural venous sinuses
34
What are the functions of CSF
1) Buoyancy
2) Protection
3) Homeostasis
4) Clearing waste
35
What is hydrocephalus
Abnormal increase of the volume of CSF within the ventricular system. Causes increased pressure
36
What are the 3 types of neurotransmitters based on function
Excitatory, inhibatory, neuromodulators
37
What do neuromodulators do
They alter the strength of the transmission between neurones by affecting the amount of neurotransmitter released
38
What is the most abundant neurotransmitter in the brain
Glutamate, excitatory
39
What is the main importance of glutamate
involved in learning and memory
40
Is acetylcholine excitatory or inhibatory
Excitatory
41
Is GABA excitatory or inhibitory
Inhibatory
42
Is glycine excitatory or inhibitory
Inhibitory
43
What are the divisions of the autonomic nervous system
Sympathetic, parasympathetic, enteric
44
How many neurones make up the efferent (motor) limb of the autonomic nervous system
Generally 2. Preganglionic with a cell body in the CNS and post ganglionic with a cell body in the periphery
45
What neurotransmitters do the sympathetic vs parasympathetic nervous systems use
Sympathetic = acetylcholine, norepinepherine
Parasympathetic = acetylcholine, acetylcholine
46
What vertebrae do sympathetic neurones arise from
T1 - L2/3
47
What are the exceptions to the 2 neurone rule of the ANS
For sympathetic innervation of the chromaffin cells of the adrenal medulla, the preganglionic neurone synapses directly - 1 neurone. Acetylcholine is the neurotransmitter
48
What are the length differences of the 2 ANS neurones
Sympathetic = short, long
Parasympathetic = long, short
49
Do efferent fibres exit the spinal cord anteriorly or posteriorly
Anteriorly
50
Where are the cell bodies of sympathetic preganglionic neurones located
In the grey matter on the spinal cord
51
What does the white rami communicans do?
Carries preganglionic nerve fibres from the spinal cord to the sympathetic trunk
52
Are the sympathetic neurones ipsilateral or contralateral?
Ipsilateral, the fibres do not decussate
53
After the sympathetic preganglionic neurones emerge from T1-L2/3, they enter the sympathetic chain. What can happen then?
1) Ascend/descend the symp trunk then synapse with a symp postganglionic neurone
2) Synapse on that level with a symp post ganglionic neurone. Join the grey rami communicans, then a spinal nerve
3) Travel through the sympathetic chain without synapsing --> becomes a splanchnic nerve
4) Single preganglionic neurone to adrenal medulla
54
D) Paravertebral ganglia
Sympathetic chain. String of synapses adjacent to the spinal cord
55
What are the two main divisions of splanchnic nerves
1) Cardiopulmonary
2) Abdominopelvic
56
What receptor type does acetylcholine bind to
Cholingernic receptors --> usually muscarinic
57
What receptor type does norepinephrine bind to
Adrenergic receptors --> alpha 1,2 and beta 1,2,3
58
What is the sympathetic innervation of the head + neck
Cervical ganglia -
1) superior = head, arterial smooth m
2) middle = neck, arterial smooth m
3) inferior = heart, arterial smooth m
59
What is the enteric nervous system
(Arguably) division of the ANS which controls digestion
60
What are the two plexuses of the enteric nervous system
- Myenteric (Auerbach's)
- Submucosal (Meissner's)
61
What sets up the resting membrane potential
Na+/K+ ATPase pump
62
What is the resting membrane potential of neurones
-70 mV
63
What are the ion concentrations inside vs outside the neurone
Inside = K+ and organic ions
Outside = Na+ and Cl-
64
What ion has the greatest influence on resting membrane potential
K+
65
What is the Na+/K+ ATPase pump
Actively transports 3 sodium ions out and 2 potassium ions in against a concentration gradient
66
D) Equilibrium potential
The point at which the rate of ions leaving a cell down a concentration gradient is equal to the rate at which ions enter via an electrochemical gradient
67
What is the Nernst equation
The Nernst equation is used to calculate the value of the equilibrium potential for a particular cell for a particular ion
68
What is hyperkalaemia and what does this cause
High blood K+ level. Means that the diffusion of K + out of cells is reduced (less conc gradient). So the RMP is closer to the threshold for an action potential
--> neurones are more easily excitable
69
What is the refractory period
The period of time after an action potential when sodium channels close
70
What are the divisions of the refractory period
- Absolute refractory period
- Relative refractory period
71
D) Absolute refractory period
When the sodium channel are closed after an action potential and cannot be reopened, regardless of the strength of the stimulus
72
D) Relative refractory period
When the sodium channels begin to come out of inactivation. Another action potential can be generated, if the stimulus is strong enough
73
D) Local current
The diffusion of sodium ions in an axon down a concentration gradient. This diffusion depolarises the membrane at the next node so the threshold potential is reached and another action potential is generated
74
What factors dictate the distance of a local current at which the threshold is no longer reached
1) Membrane capacitance (ability to store charge - low is better)
2) Membrane resistance (number of open ion channels - low number so high resistance is better)
--> low cap, high mem
75
How does the myelin sheath increase the speed of conduction
- Increases membrane resistance and decreases membrane capacitance
--> saltatory conduction
76
What are the two main classes of receptors found on neurones
Metabotropic and inotropic
77
What is a metabotropic receptor
A membrane receptor which when activated uses secondary messengers to change the cells activity
78
What is an inotropic receptor
A ligand-gated ion channel
79
What is the Post synaptic potential
Change in the membrane potential of a post synaptic neurone as a result of excitatory/inhibitory neurotransmitters. If the post synaptic potential is great enough, the threshold will be reached and an action potential generated
80
Is the neurotransmitter dopamine excitatory or inhibitory
Both, it depends on which receptor it binds to
81
How do excitatory neurotransmitters eg glutamate work
- Glutamate binds to an a receptor resulting in the opening on non-selective cation channels
- Na+ enters, K+ leaves slowly. Na + will be more significant
- The membrane potential increases
82
How do inhibitory neurotransmitters eg GABA work
- GABA binds to receptors resulting in the opening chloride ion channels
- Chloride ions enter the post synaptic neurone causing hyperpolarisation
83
What is spatial summation
Neurotransmitters are released from several presynaptic neurones at once
84
What is temporal summation
A presynaptic neurone releases neurotransmitters within short time intervals
85
What happens in an epileptic seizure
A sudden excess increase in electrical activity. Can be as a result of increased excitatory neurotransmitters or reduced inhibitory
86
What is Guillain-Barre syndrome
Autoimmune damage to the myelin sheaths of the peripheral nerves resulting in rapid muscle weakness
87
What is synaptic plasticity
The ability of synapses to change over time (become stronger/weaker or form/eliminate) in response to an increase or decrease in their activity
'fire together wire together'
88
D) Neuropeptides
Large neurotransmitters that are produced in the cell body and are then packaged into secretory granules and sent to the axon terminal
89
What is the speed of response for inotropic vs metabotropic receptors
Fast for inotropic, slow for metabotropic
90
How are neurotransmitters removed
1) Re uptake by presynaptic neurone
2) Breakdown by enzyme
3) Diffusion into surrounding area --> astrocytes
91
D) Ascending pathways
the sensory pathways - both CNS and PNS
92
D) Sensory transduction
The process of converting a sensory signal into an electrical signal
93
What are the two main types of sensory receptors
Tonic and phasic receptors
94
What do tonic receptors do
Slow adapting. They fire as long as the stimulus is present = info about the length of the stimulus
95
What do phasic receptors do
Fast adapting. They stop firing upon continuous stimulation = quick info about changes to the stimulus
96
D) Nociceptors
Receptors which respond to noxious stimuli, resulting in the sensation of pain
97
What are examples of mechanoreceptors
Pacinian corpuscles (phasic), muscle spindles, golgi tendon organs
98
Are cold or hot thermoreceptors more common
Cold
99
Are thermoreceptors phasic or tonic
Initially phasic but then switch to tonic - adapting to environment
100
What are the conscious ascending tracts
1) Dorsal column-medial lemniscal (DCML)
2) Anterior and lateral spinothalamic tracts
101
What information does the DCML relay
Fine touch, vibration, proprioception, 2 point discrimination
102
DCML: Where do signals from the upper limb (T6 and above) travel
Travel in the fasciculus cuneatus (lateral dorsal column), then synapse onto the nucleus cuneatus of the medulla
103
DCML: Where do signals from the lower limbs (lower than T6) travel
Travel in the fasciculus gracilis (medial dorsal column), then synapse onto the nucleus gracilis of the medulla
104
DCML: Where do second order neurones originate and end
In the cuneatus/gracilis nuclei of medulla, decussate go to the thalamus
105
DCML: When do the DCML fibres decussate
The 2nd order neurones decussate in the medulla
106
DCML: Where do the 3rd order neurones originate + end
They originate in the thalamus, travel through the internal capsule and terminate in the primary sensory cortex
107
What information does the anterior spinothalamic tract relay
Crude touch and pressure
108
What information does the lateral spinothalamic tract relay
Pain and temperature
109
Spinothalamic tract: Where do 1st order neurones originate + end
They enter the spinal cord and synapse at the tip of the dorsal horn in the substantia gelatinosa
110
Spinothalamic tract: Where do the fibres decussate
The 2nd order neurones decussate in the spinal cord a couple of vertebral levels above entry, to form the anterior and lateral spinothalamic tracts
111
Spinothalamic tract: Where do the 2nd order neurones originate + end
Start in the substantia gelatinosa, decussate then go up to the thalamus
112
What information do the spinocerebellar tracts relay
Unconscious proprioception, they help the brain to coordinate and refine movements
113
What is the input to the spinocerebellar tracts
Muscle spindle, golgi tendon organ, joint capsule
114
Where does the spinocerebellar tract end
**Ipsilateral** cerebellum
115
Where do the conscious sensory tracts end
**Contralateral** primary sensory cortex
116
Will damage to the DCML in the spinal cord cause an ipsilateral or contralateral loss of fine touch, proprioception etc
Ipsilateral as fibres decussate in the medulla
117
Will damage to the Spinothalamic tract in the spinal cord cause an ipsilateral or contralateral loss of crude touch, pain etc
Contralateral as fibres decussate in the spinal cord
118
What is Brown-Sequard syndrome
The hemi section of the spinal cord
= Ipsilateral DCML
= Contralateral spinothalamic
= Ipsilateral hemiparesis (descending)
119
Will damage to the spinocerebellar tract cause ipsilateral or contralateral loss of muscle coordination
Ipsilateral. Usually there is also descending motor tract damage which will be more 'relevant'
120
D) Descending tract
Neural pathways by which motor signals are transmitted to the lower motor neurones
121
D) Upper motor neurones
Neurones which synapse onto interneurones (relay) or lower motor neurones
122
D) Lower motor neurones
Neurones which directly innervate muscles/glands
123
What are the main 2 descending tract groups
Pyramidal and extrapyramidal
124
D) Pyramidal tracts
Tracts which cause voluntary control of muscles. Originates in the cerebral cortex
125
D) Extrapyramidal tracts
Tracts which cause the involuntary/autonomic control of muscles. Originates in the brainstem
126
What is the clinical significance of the internal capsule
Conscious ascending and descending tracts pass through it. It is susceptible to compression from haemorrhagic strokes = lacunar
127
What are the 2 types of pyramidal tracts + their function
Corticobulbar = head and neck
Corticospinal = body
128
D) Pain (important def)
An unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage
129
D) Nociception
The neural processes involved in producing a sensation of pain
130
D) Nociceptor
First order afferent sensory neurones that are activated by noxious stimuli + have free nerve endings
131
D) Acute pain
Less than 12 weeks
132
D) Chronic pain
More than 12 weeks or greater than the tissue healing time
133
D) Nociceptive pain + feeling
Pain as a result of damage to non-neural tissue, activation of nociceptors
- Aching, localised
134
D) Neuropathic pain + feeling
Pain causes by damage to the somatosensory nervous system
- Shooting, burning
135
D) Nociplastic pain
Pain that is neither nociceptive or neuropathic in nature
136
Allodynia vs hyperalgesia
Pain from a stim that normally does not cause pain vs increased pain from a painful stim
137
What sensory tract transmits pain
Lateral spinothalamic
138
139
Pain: What are the features of the first order neurones
- Pseudounipolar
- Un encapsulated
- Cell body in the dorsal root ganglion
140
Pain: What are the features of the 2nd order neurones
- Cell body in the rexed laminae of the spinal cord
- Decussate in **anterior white commisure** of spinal tract to form a + lateral spinothalamic --> Lateral is for pain
141
Pain: What are the features of the 3rd order neurones
- Cell body located in the ventral posterolateral nucleus of thalamus
- Terminate in primary sensory cortex
142
Where do pain fibres decussate
In the anterior white commissure a few levels above point of entry to form anterior + lateral spinothalamic
143
D) Free nerve endings
Unencapsulated cutaneous receptors
144
How does the size of the receptive field of a nociceptor relate to the pain felt
The smaller the size of the receptive field, the greater the **sensory acuity** so the more sensitive the area will be
145
Do receptive fields overlap
Yes, overlapping receptive fields reduce the precision of perception
146
How does the size of the receptive field relate to the representation in the somatosensory cortex
The smaller the receptive field, the greater the cortical representation
147
Where are nociceptors not found
In the brain
148
Are nociceptors specific or generalised
- There are different nociceptors for different stimuli but also polymodal nociceptors which respond to multiple types
149
Pain: How are signals transmitted from the nociceptors to the dorsal horn of the spinal cord
Specific nociceptors = type A delta fibres
Polymodal nociceptors = type C fibres
150
Pain: What are features of type Alpha delta fibres
- Myelinated, fast conduction
- Responsible for initial localised pain
- Small receptive field
151
Pain: What are features of type C fibres
- Unmyelinated, slow conduction
- Responsible for dull, throbbing secondary pain
- Large receptive field
152
Pain: What is the difference in firing threshold for A delta vs C type fibres
- A delta fibres have a lower threshold but C fibres can be sensitised eg hyperalgesia
153
Pain: Where do 1st order neurones terminate + what neurotransmitter is released
A delta type = Rexed laminae I, glutamate
C type = Rexed laminae II, substance P+ glutamate
154
Why does substance P cause long lasting pain
Remains bound to the receptor for a longer period of time
155
How can sensitisation (hyperalgesia) occur
1) Peripheral sensitisation
2) Central sensitisation --> increase in the number of NMDA receptors which respond to glutamate
= hyperexcitatability
156
D) Descending modulation of pain
- The hypothalamus and cortical regions process painful stimuli and cause the release of endogenous opioids
157
D) What are the endogenous opioids
B endorphins
Dynorphins
Enkephalins
158
How do opioid receptors work
Presynaptic membrane of 1st order = reduce neurotransmitter release
Postsynaptic membrane of 2nd order = cause hyperpolarisation
--> reduces pain signal transmission
159
What is the Gate control theory of pain
A non-painful input can close the ‘gate’ to painful inputs, so prevents pain sensations from being perceived and felt
160
What factors affect 2 point discrimination
The density of sensory receptors + the size of neuronal receptive fields
161
D) Sensory acuity
How accurately a stimulus can be located
162
What does UMN refer to in clinical practice
The descending pyramidal tracts
163
What neurotransmitter is used by upper motor neurones
Glutamate
164
What does the motor homunculus show
That areas of the body that have greater precision of motor control have greater cortical representation
165
Symptoms of UMN damage
- Muscle weakness/paralysis
- Hypertonia due to reduced descending inhibition
- Hyperreflexia as UMN limits reflexes
- Spasticity = increased muscle tone on passive movement in a velocity dependent manner
- Positive babinski sign = splayed toes
- Clonus = involuntary muscle contraction
166
Is a lower motor neurones' cell body in the PNS or CNS
CNS - in the ventral horn or brainstem for motor cranial nerves
167
What are the 2 types of lower motor neurones
- Alpha motor neurones
- Gamma motor neurones
168
What do alpha motor neurones do
Cause the contraction of muscle fibres that they innervate (extrafusal)
169
How are lower motor neurones (both alpha and gamma) organised in the ventral horn
Somatotopically - medial innervates more proximal
170
What does LMN refer to in clinical practice
Alpha motor neurones
171
What do gamma motor neurones do
The regulation of muscle tone and allow non-conscious proprioception to be maintained - goes from extrapyramidal tract
172
What do gamma motor neurones innervate
The intrafusal muscle spindle
173
What are the two components of the muscle that allow for unconscious proprioception
Golgi tendon organs
Muscle spindle
174
What is the sensory innervation of the muscle spindle and golgi tendon organs
Group A alpha)
175
What do golgi tendon organs do
Sensory receptor that senses muscle tension. Transmits info to the spinocerebellar tracts
176
What do muscle spindle do
Allows muscle to remain sensitive to stretch and involved in muscle stretch reflexes. Sensory via la sensory afferents, motor innervation by gamma motor neurones
177
What can the GTO do under extreme tension
Under extreme tension, the GTO can inhibit the muscle from contracting via temporarily inhibiting muscle spindle activity
178
What are signs of LMN damage
- Hyporeflexia
- Hypotonia/atonia
- Muscle weakness/paralysis
- Fasciculations = when alpha motor neurones are damaged, they can cause random contractions of motor units resulting in twitching
- Muscle atrophy from loss of neurotrophic factors from alpha motor neurones
179
Disuse atrophy
Caused by UMN damage
180
D) Motor unit
A single alpha motor neurone and all the muscle fibres it innervates
181
D) Motor pool
All the lower motor neurones (both alpha and gamma) that innervate a single muscle
182
What is spinal muscular atrophy
Autosomal recessive resulting in the loss of lower motor neurones. There are 4 types
183
What cartilage is the pinna
elastic
184
What makes up the external acoustic meatus
1/3 elastic cartilage, 2/3 temporal bone
185
What are the auditory ossicles
Maleus, incus and stapes
186
What does the stapes attach to
The oval window
187
What is the structure of the cochlear
2.5 turns of bony tube filled with fluid. Has 2 openings - oval window and round window
188
What are the three compartments of the cochlear
scala vestibuli, scala media, scala tympani
189
What fluid is found in the scala vestibuli and tympani vs media
Scala vestibuli + tympani = perilymph (basically ECF, lots of Na+)
Scala media = endolymph (lots of K+)
190
What structure connects the scala vestibuli and tympani
the helicotrema
191
What is the hearing process up until the oval window
1) Outer ear directs sound to tympanic membrane
2) Ossicles conduct and amplify sound due to smaller SA
3) Stapes vibrates the membrane of the oval window
192
What is the hearing process from the oval window onwards
1) Vibrations are passed to the perilymph of the scala vestibuli
2) Vibrations pass round to the scala tympani via the helicotrema
3) The vibrations cause the elastic basillar membrane to move up and down
4) Inner hair cells (sterocilia) push against the stiff tectoral membrane
5) Shearing forces cause mechanically gated K+ channels to open --> depolarisation of auditory fibres
193
Inner vs outer hair cells
Inner hair cells = do mechanical transduction, afferent fibres
Outer hair cells = do fine tuning, efferent fibres
194
What is the ratio of inner: outer hair cells
1:3
195
How does the structure of the basilar membrane relate to hearing
Base (start of cochlea) = stiffer, thinner, higher frequency
Apex (final turn) = wider, floppier, lower frequency
196
What are the two possible auditory pathways
1) Primary (lemniscal) pathway = main pathway, conscious. Auditory information goes to primary auditory cortex
2) Non-lemniscal pathway = involved in unconscious perception. Attention, emotional response, reflexes
197
After the organ of corti, what is the auditory pathway
- Inferior colliculus (midbrain)
- Medial geniculate body (thalamus)
--> primary auditory cortex only for main pathway
198
Nicotinic vs Muscarinic receptors
- Nicotinic receptors are found at neuromuscular junctions (inotropic)
- Muscarinic receptors are found at smooth muscle + glands (metabotropic)
199
D) Association fibres
Fibres that link cortical regions in one hemisphere
200
D) Commissural fibres
Fibres that link similar functional areas in the two cortical hemispheres
201
D) Projection fibres
Fibres that link the cortex with subcortical structures
202
Example of commissural fibre
Corpus callosum
203
Example of projection fibres
Internal capsule, corona radiata
204
Do the peripheral limbs have commissural fibres
no
205
What artery supplies brocas area
the middle cerebral
206
What artery supplies wernickes area
the middle cerebral
207
What are the key points of the sensory/motor homunculus
Lateral = tongue/lips
Medial = foot
