Midterm 2 Flashcards
1
Q
Nervous system
define
general functions (3)
A
- A communication and control network that allows an organism to interact with its environment
- Sensory detection
- info processing
- expression of behaviour
2
Q
Central nervous system made up of
A
brain and spinal cord
3
Q
divisions of peripheral ns?
A
Afferent/sensory division
Afferent/motor division
4
Q
What makes up the nervous system? (4)
A
- Neurons - functional unit
- Neuroglial cells - microglial, astrocytes, dendrocytes
- Blood vessels - provide nutrients and energy
- Connective tissue - provide support
5
Q
Where does inhibitory and excitatory input go on neuron?
A
Inhibitory onto cell body and excitatory onto dendrites
6
Q
Features of:
cell body
soma
dendrites
axons
axon hillock
neural network
A
- contain organelles
- factory of cell - makes proteins + membrane structures
- input transmission - carry info to neuron
- output transmission
- Important for AP generation - contains all necesary ion channels
- APs fire along neural network to ensure that NS functions properly
7
Q
unpolar neurons dominant in
A
invertebrates
8
Q
Bipolar neurons extend to?
A
One end to CNS and one to PNS
Carry info from PNS to CNS
9
Q
pseudounipolar neurons
A
- develop from bipolar neurons
- One extension from cell body that divides
- One end to PNS and one to CNS
- Sensory neurons
10
Q
Multipolar neurons
A
- Dominant in vertebrates
- One axon that carries info to muscle cells
11
Q
Distribution of neurons in body
A
- 90% interneurons - multipolar, make connections
- 9% Motor neurons - mostly multipolar
- 1% sensory neurons - mostly bipolar and pseudounipolar. Carry info from receptor cells in sensory organ to upper level neurons
12
Q
Axonal tranport
Fast:
Slow:
Anterograde:
Retrograde:
Importance:
A
- Dast transport for membrane bound organelles and mitochondria
- Slow transport for proteins
- Anterograde - from soma toward terminals. Uses kinesin
- Retrograde - from terminals toward soma. Uses dynien
- Important for neurotransmission bc many structure in cell body need to get to nerve terminal that can’t do it through diffusion
13
Q
Why can Shingles affect the skn after many years latency?
A
- Caused by chicken pox firus
- Stays dormant in cells for many years after infection
- Virus can reactivate and will be transported from cell, down axon - affecting skin
14
Q
Supportive matrix of CNS
A
provides local environment for nearons to function (neuroglia)
15
Q
Neuroglia in CNS (list)
A
- Astrocytes
- Oligodendrocytes
- Microglia
- Ependyomal cells
16
Q
Astrocytes
A
Neuroglia in CNS
structural support, metabolic support, encourage NT uptake/release, nervous system repair, ion homeostasis, synaptic plasticity
17
Q
Oligodendroglia
A
Neuroglia in CNS
myelination of CNS axons
18
Q
Microglia
A
Neuroglia of CNS
- Immune defense => phagocytes
- Activated when CNS is injured, release factors to help with repair
19
Q
Ependymal Cells
A
Neuroglia of CNS
produce cerebrospinal fluid
20
Q
Neuroglia in PNS
A
- Satellite cells - function similarly to astrocytes (around the cell body)
- Schwaan cells - 1 group does myelin, other do debris clearance and nerve regeneration
21
Q
Myelination in CNS vs PNS
A
- CNS - oligodendroglia. Single oligodendrocyte myelinates many axons
- PNS - Schwann Cells - Each cell myelinates only one axon
22
Q
neurons vs neuroglia
A
Neurons
- Lots of brances, one long axon
- Can generate APs
- Cab regulate functions
- Can’t divide
Neuroglia
- Don’t branch extensively
- Not excitable
- Supporting unit of nerve cell
- Can divide - replication afected by tumors
23
Q
What cells can give rise to brain tumors in the adult brain?
In infants?
A
Atrocytoma, oligodendroglioma, ependyoma
In infants: neuroblastoma
24
Q
Grey matter
vs
white matter
A
soma and dendrites (axons, glial cells, capillaries)
acons (glial cells, capillaries). White bc of myelination
25
Why does grey matter have a higher metabolic rate?
Cell body located in grey matter. Factory for all proteins and cell components for neuron, therefore has higher metabolic rate.
26
Brainstem made up of
(not hypothalmus though it sits on top)
Midbrain
Pons
Medulla
27
Functions of the brainstem and its components
* _Brainstem_ - autonomic centres and relay nuclei
* _Midbrain:_ micturition, eye movement, auditory and visual systems
* _Pons:_ balance, maintenance of posture, breathing
* _Medulla:_ breathing, blood pressure, swallowing, coughing, vomiting reflexes
28
Cerebellum
location
functions
* Between cerebral cortex and spinal cord. Attached to brainstem and lies dorsal to pons and medulla
* Coordination of movement, maintenance of posture and balance
* Receives important info from spinal cord
29
Thalamus and hypothalamus
* Between cerebral hemispheres and brainstem - in **diencephalon** (meaning bt brain)
* Thalamus processes sensory information going to cerebral cortex and motor info coming from cerebral cortex to brainstem+spinal cord
* Hypothalamus regulates body temp, food intake, water balance, hormone secretions or pituitary
30
Cerebrum
location
structure
consists of
functions
* Located in anterior (front) portion of brain
* Divided into left and right hemispheres that are connected by **corpus callosum** (axon bundle)
* Cerebral himispheres consist of **cerebral cortex** (grey matter) and underlying what matter and 3 deep nuclei (basal ganglia, hippocampus, amygdala)
* _Functions:_ perception, higher motor functions, cognition, memory and emotion
31
3 deep nuclei in cerebrum
basal ganglia, hippocampus and amygdala
* Basal ganglia - base of forebrain, movement, parkinson's disease, huntington's disease
* Hippocampus - located in temporal lobe, memory
* Amygdala - In temporal lobe, emotion
32
Cerebral Cortex
gyrus
sulcus
lobe divisions
areas
functions
* _gyrus_ = ridges on cortex
* _sulcus_ = grooves on cortex
* Divides into frontal, parietal, occipital and temporal lobes
* Sylvian/lateral fissure divides frontal/temporal and parietal/temporal
* Longitudinal fissure divides the two hemispheres
* Areas: motor, sensory, association areas
* Functions: recieves and processes sensory information and integrates motor functions
33
Most of the brain is made up of associations areas (Eg the somatomotor cortex has the motor cortex and the association area of that cortex that is much larger)
why is this?
Higher brain function = perception
34
The ventricular system
* The system that the cerebrospinal fluid runs through
* 4 ventricles in brain
* Connected by foramina:
* Interventricular foramina connects ventricles 1 + 2
* cerebral aqueduct connects 3 + 4
*
35
cerebrospinal fluid
what is it?
produced by
can be sampled by
function
Liquid that fills and circulates within the ventricular system of brain
* Produced by choroid plexus
* Can be sampled by a *lumbar puncture (lumbar cistern)*
* Distributes nutritive materials to and removes waste from nervous tissue; protection of the brain
36
hydrocephalus
* Abnormal accumulation of cerebrospinal fluid in ventricles
* Increased pressure that causes disease
37
Nervous system reaction to injury
1. **Degeneration**
* Effector denervated
* Wallerian degeneration - axon pulls up toward the cell body
* Chromatolysis = dissolution of nissl bodies in cell body
2. **Regeneration** - in PNS but not in CNS
* Severed axon begins to srpout and can allow regeneration
3. Axon growth = trophic factors (NGF, neurotrophin, CNF)
38
Nissl Body
large granular body founf in neurons. Rough ER with free ribosomes and parts of golgi. Seen in soma and dendrites. Not axon.
39
Non-traditional senses
* Nocicpetion - pain, helps you avoid damage
* Equilibrioception - body balance when walking/standing
* Proprioception - Sense of relative body parts
* Thermoception - sense of temperature around skin
40
Sensory receptors are
3 types
specialized structure activated by stimuli, that convert a stimulus into neuronal activity (electrical activity)
## Footnote
they are one of:
1. **Endings** - most simple. Nerve terminal of afferent neurons (somatosensory and olfactory systems)
2. **Specialized epithelial cells** adjacent to an afferent neuron (visual, taste and auditory systems)
3. **Specialized structure** associated with nerve terminals (Pacinian corpuscule)
41
Mechanoreceptors
modality
receptor
location
* Touch (pressure), audition, vestibular
* Pacinian corpuscule, hair cell
* Skin, organ of Corti, semicircular canal
42
Photoreceptors
modality
receptor
location
* Vision
* Rods + cones
* Retina
43
Chemoreceptors
Modality
Receptor
Location
* Olfaction, arterial oxygen levels, oH of cerebrospinal fluid
* Olfactory receptor
* Olfactory mucosa, carotid and aortic bodies, ventrolateral medulla
44
Thermoreceptors
Modality
Receptor
Location
* Temperature
* Cold receptor, warn receptor
* Skin
45
Nociceptors
modality
receptor
location
* Stimuli causing tissue damage
* Thermal nociceptor, mechanical nociceptor, polymodal nociceptor
* Skin
46
*A stimulus is converted to electrical energy by opening and closing of ion channels in sensory receptors, which results in receptor potentials*
47
receptor potential
* graded change in membrane potential of the sensory receptor.
* Can be depolarizing or hyperpolarizing
* *Depolarizing* receptor potential spreads within afferent neuron until it reaches a region with high density VGSCs
* If receptor potential threshold is reached, AP generated
48
Receptor potential vs action potential
Receptor potential is a graded potential. The amplitude is graded with stimulus intensity. These potentials cannot propogate, only spread along the membrane.
Receptor potential can be hyperpolarizing or depolarizing
AP can only be triggered by a depolarizing current
49
Sensory Unit
* *Primary sensory neuron and all sensory receptors (endings or associated sensory receptor cells*)
* The smallest unit of sensory response
* If the sensory receptor is a neuron terminal, then the sensory neuron is a sensory unit. If there is some associated epithelial cell + sensory neuron, then that is the sensory unit
50
Receptive Field
* An area of the body surface that when stiumlated results in a change in firing of a sensory neuron.
* vary in size
* Smaller receptive field = more precise sensation
* Higher order of CNS neuron, more complex receptive field
* Receptive field can be excitatory or inhibitory depending on the change in firing rate
51
Sensory systems mainly code which 4 aspects of a stimulus?
1. _Stimulus Modality_ - type of stimulus
2. _Stimulus Intensity_
3. _Stimulus location_
4. _Stimulus duration_: adaption
52
Adequate stimulus
Each sensory receptor is particularly sensitive to one stimulus type
53
Labeled line
* The distinct anotomical pathways from sensory receptors to a specific region of the CNS associated with a particular stimulus modality
* The attachment from the sensory receptor + higher level neurons + eventually to a specific region of the cerebral cortex = labeled line
54
Stimulus intensity encoded by
1. Number of receptors that are activated
2. Differences in firing rates of sensory neurons in a pathway. Increased Stim = increased AP frequency
3. Activating different types of receptors (eg nociceptors as well)
55
Acuity
* precision of stimulus location
* Dense arrangement of sensory units =\> better acuity
* Large receptive field =\> bad acuity
* Lips and hands have good acuity
56
Lateral inhibition
* The capacity of an excited neuron to reduce the activity of its neighbors
* Further enhance sensory **acuity**
In image - firing frequency is decreased in all 3 secondary neurons, but the middle is suppressed less.
57
Adaption
Sensory receptors decrease in sensitivity to a stimulus of constant strength (AP frequency decreases)
* **Phasic** = rapidly adapting sensory receptor. Generates RP and AP on onset, but quickly stops responding. Detects CHANGES in stimulus
* **Tonic** = slowly adapting sensory receptor. Encodes DURANTION AND INTENSITY of a stimulus
58
Microneurography
Invasive method for visualizing normal traffic of nerve impulses
* Can map receptove field of a neuron
* Whenever a stimulus brings about a neuronal response, the response can be trecorded by an amplifyer
59
General features of sensory system (4)
1. Synaptic relays
2. Topographic organization
3. Decussation
4. Different types of nerve fibres
60
General feature of the Sensory System:
Synaptic relays
* **Relay nuclei** in the thalamus integrate converging info from neurons in CNS. One neuron tends to get info from many lower neurons
* Relay nuclei contain interneurons and projection neurons
* _Interneurons_ have important role in analyzing converging info/perception =\> association neurons
* _Projection neurons_: sit along axon + send to higher order CNS. Carry info from relay nuclei to other parts of the brain
61
General Features of the Sensory System:
## Footnote
**Topographic Organization**
* Neural maps
* *Somatotopic Map* in somotosensory system (*Sensory Homunculous)*
* Retinotopic map in visual system
* Tonotopic map in the auditory system
62
General Features of the Sensory System
## Footnote
**Decussation**
* Crossing of sensory (and motor) pathways in the spinal cord
* *Comissure* - contains only axons (eg corpus callosum)
* *Optic Chiasma*
* Most sensory info will be conveyed to contralateral side of the brain
63
Convergence and divergence of ascending pathways
* **Divergence** = one primary neuron synapses onto many higher order neurons
* **Convergence** = A higher order sensroy neurons recieves input from more than 1 primary sensory neuron
64
Sensory processing in the Cortex (General)
1. Ascending pathways terminate in specific sensory areas (eg innervation at eyes ==\> visual cortex)
2. Further processing occurs in associational areas where complete integration occurs
3. Perception- understanding of sensations
4.
65
Inhibition of ascending pathways by descending pathways
* Directly or indirectly
* Form of controlling ascending pathways
* Not all sensory information reaches consciousness
66
Subdivisions of the Somatosensory System
1. Proprioceptive division
2. Enteroceptive division
3. **Exteroceptive division** - responsible for providing information about contact of skin with objects in external world
67
3 major receptors of exteroceptive division of somatosensory system
1. Mechanoreceptor
2. Thermoreceptor
3. Nociceptors
68
Somatosensory modalities
Information about touch, position, pain and temperature
69
Meissner's corpunscule
location
adaption
sensation encoded
* Mechanoreceptor
* Only located in non-hairy skin
* rapid adaption
* Point discrimination, tapping, flutter
70
Pacinian Corpunscule
## Footnote
location
adaption
sensation encoded
* Hairy and non hairy skin, intramuscular
* very rapidly adapting
* vibration, tapping
71
Hair follicles (mechanoreceptors)
## Footnote
location
adaption
sensation encoded
* Hair skin
* rapid adaption
* Velocity, direction of movement
72
Ruffin's corpunscule
* hairy and non hairy skin
* Slow adaption
* stretch, joint rotation
73
Merkel's receptors
## Footnote
location
adaption
sensation encoded
* Nonhairy skin
* slowly adapting
* verticle identification of skin, light touch
74
Tactile disks (mechanoreceptors)
## Footnote
location
adaption
sensation encoded
* Hairy skin
* slow
* verticle identation of skin
75
Operation of thermoreceptors
* Respond to temperature change
* Slowly adapting
* Cold and warm receptors
* Nociceptors activated by extreme heat
* At body temp, both acting equally
76
TRP Channels
what are they
how many
structure
what ions
* Associated with thermosensation. Responsible for some nociception
* 27 types, 6 groups - respond to diff temps and chemicals
* 6 TM domains and 1 imbedded domain between 5 and 6
* Permeable to Na and Ca
77
Why does spicy food make you feel hot? Why does mint make you feel cool?
TRPV1 can be activated by spicy things and it's also a heat receptor. TRPM8 activated by menthal and also a cold receptor.
78
TRP channels activated by high body temp and high external temp
TRP V1 and TRPV2
79
Thermal or mechanical nociceptors
* Fast conducting
* Adelta nerve fibres
* Respond to mechanical or thermal stimuli such as sharp pricking pain
* Fast first pain
80
polymodal nociceptor
* Slow-conducting C fibres
* Respond to high intensity mechanical, chemical and thermal stimuli
* Slow second pain
81
Hyperalgesia
an amplified response to a noxious stimuli
sensitization of pain
82
Allydonia
A painful response to a normally innocuous stimuli (like taking a bath when you have a sunburn)
83
Inflammatory soup
Peptides, lipids, NTs, cacitonin gene-related protein and neurotrophins that are released by damaged tissue to help with repair
84
Extreme cold TRP channels
TRPM8
TRP A1
85
Innervation of the body by primary sensory neurons located in the \_\_\_\_\_\_\_\_\_\_\_
dorsal root ganglion
86
Dermatomal organization
* Certain dorsal nerves arrive from ganglia in skin dermatomes
* 31 nerve haris and 30 dermatomes (no dermatome for C1)
* 1 dermatome = 1 dorsal nerve and the visceral and skin area that it innervates
87
Shingles disease
* After chicken pox infection, virus remains in dorsal rooted ganglion
* When reactivated, virus transported along dorsal root axons to the area of skin in the dermatome
88
Innervation of the face
by primary sensory neurons located in the trigeminal ganglion
89
Dorsal column medial leminscus system
functions and process
* _Sensations_: fine touch, pressure, two point discrimination, vibration
* _Graphthesia_: the ability to recognize numbers or letters when traced on skin
* **1st** order neuron: large, myelinated (Aa, AB)
* Fibres stay ipsilateral in spinal cord
* **2nd** order neuron in nucleus gracilis (upper body) or nucleus cuneatus (lower body) in the medulla
* Decussation
* **3rd** order neuron in ventral posterior lateral nucleus of the thalamus
* **4th** order neuron in somatosensory cortex
90
Anterolateral/Spinothalamic Pathway
* Pain, temperature, crude touch
* **1st** order neuron - small, lightly myelinated and unmyelinated axons (Group III/IV). Synpase in grey matter.
* **2nd** order neuron in spinal cord
* Decussation
* **3rd** order neuron in ventral postinferior nucleus of thalamus
91
Damage to the sensory pathways
Damage below decussation will lead to loss of sensation on same side of lesion
Damage above decussation will lead to contralateral deficits
92
Somatosensory Homunculous
Represents each part of the body in proportion to its number of sensory neural connections, but not its actual size
93
Nociceptor fibres
* Ad and C
* Fast/first pain from Ad
* Rapid onset and offset
* Precisely located
* Serves as warning signal
* Slow/second pain from C fibres
* More prologued, less intense
* Poorly localized
* More complex emotional response
94
3 types of pain
nociceptive
inflammatory
neuropathic
95
Nociceptive Pain
1. Sensory neuron
2. Site
3. Involvement of TRP channels
4. Clinical Setting
5. Function
6. Pain sensitivity
1. Noxious
2. Nociceptor
3. PNS
4. Yes TRP
5. Acute Trauma
6. Protective
7. High Threshold
96
Inflammatory Pain
1. Sensory neuron
2. Site
3. Involvement of TRP channels
4. Clinical Setting
5. Function
6. Pain sensitivity
1. Inflammation
2. nociceptor and non-nociceptor (high motor neurons involved)
3. PNS and CNS
4. Yes TRP
5. Post operative pain and arthritis
6. Healing/repair
7. Low threshold
97
Neuropathic pain
1. Sensory neuron
2. Site
3. Involvement of TRP channels
4. Clinical Setting
5. Function
6. Pain sensitivity
1. neural damage to nerve passage or ectopic firing
2. nociceptor and non-nociceptor
3. PNS and CNS
4. TRP unclear
5. PNS and CNS lesions, diabetic neuropathy, lumbar radioculopathy, spinal cord injury
6. Pathological
7. Low threshold
98
What type of pain for trigeminal neuralgia?
Trigger?
Treatment?
* Can happen to elderly; Chronic pain
* Neuropathic because artery gives a mechanical stimulus
* Not because of inflammation or trauma
* Treated by displacing the artery
99
Gate control theory of pain
* Innocuous stimuli are able to suppress pain
* Mechanism: activation of inhibitory interneurons by innocuous stimuli applies to AB fibres results in inhibitiion of pain signals transmitted via C fibres to CNS
* Eg patting head
100
Referred Pain
* Sensation of pain that is experienced at a site other than the injured tissue
* Visceral origin - neurons in dorsal ganglia innervate sensory receptors in skin and visceral organs
* Pain referred to a structure that originates from the same dermatome as the source of pain
* Eg referred pain from heart to left arm
101
Endogenous Analgesia System
* Sensory information can be modiefied by your emotion
* opioids released by NS bind to receptors that activate pathways that reduce pain via inhibitory interneurons
* Morphine is an agonist for opioids receptors
102
opioid examples
enkephalin, endorphins, dynorphin
103
Treating Morphine OD
Naloxone - antagonist
104
How does morphine relieve pain?
* Morphine mimics opioids functions by activating endogenous analgesia system.
* Use naloxone to treat overdose because it can bind to receptors and counter the effects of morphine
105
* descending pathways can inhibit (directly or indirectly) the transduction of sensory information to the brain*
* ==\> not all sensory information reaches consciousness*
106
Efferent division of PNS divides into
Somatic NS
Autonomic NS
107
Somatic Nervous System
voluntary control of body movements via skeletal muscles
voluntary nervous system
108
Autonomic Nervous System
Involuntary controls of visceral organs via smooth muscles, cardiac muscles and glands
109
Somatic NS
1. Control type
2. Number of neurons in pathway
3. Cell body location
4. Effectors
5. Neurotransmitter and receptor
1. Voluntary
2. Single (motorneuron)
3. CNS
4. Skeletal muscles
5. ACh/nAChR
110
Autonomic NS
1. Control type
2. Number of neurons in pathway
3. Cell body location
4. Effectors
5. Neurotransmitter and receptor
1. Involuntary
2. Two (preganglionic and post ganglionic)
3. CNS (preganglionic neuron) and autonomic ganglion (post ganglionic neuron)
4. Cardiac muscles, smooth muscles, glands
5. * Preganglionic neuron: ACh/nAChR
* Postganglionic neuron: ACh/mAChR and norepinephrine/a1, a2, B1, B2
111
Autonomic nervous system divides into
1. Sympathetic (fight or flight)
2. parasympathetic (rest and digest, sexual arousal and salivation)
most organs innervated by both
112
Sympathetic Divsion
1. Set up
2. Origin of preganglionic nerve
3. Location of ganglia
4. Length of preganglionic nerve
5. Length of Postganglionic nerve
1. 2 neurons in series connect the spinal cord and the effector
2. **Thoracolumbar**
3. Far from effector organs
4. Short
5. Long
113
Adrenal Gland
* Specialized sympathetic ganglion
* Cell bodies of adrenal gland's preganglionic neurons are located in the **thoracic** spinal cord
* Axons of preganglionic neurons pass through the sympathetic chain and the celiac ganglion without synapsing and travel to the adrenal medulla where they synapse on **chromaffin cells**
114
Parasympathetic nervous System
1. Set up
2. Origin of preganglionic nerve
3. Location of ganglia
4. Length of preganglionic nerve
5. Length of Postganglionic nerve
1. Two neurons in series connect CNS and effector organs
2. **Craniosacral**
3. Near or within effector organs
4. Long pre-ganglionic neurons
5. Short postganglionic neurons
115
Neuromuscular Junction
Arrangement
Innervation
NT Storage Sites
Postsynaptic receptors
* Discrete, organized structure called motor end plate
* A skeletal muscle fibre is innervated by a single motor neuron
* Nerve terminals
* Postsynaptic receptors are located in the motor end plate
116
Neuroeffector Junction
arrangement
innervation
NT storage sites
postsynaptic receptors
* Diffuse, branching network
* Target tissues may be innervated by many post ganglionic neurons
* Varicosities
* Postsynaptic receptors are widely distributed on target tissue
117
Adrenergic neurons
adrenoreceptors
neurons that synthesize and release norepinephrine
a1, a2, B1, B2 - activated by norepinephrine or epinephrine
118
Cholinergic neurons
Cholinoreceptors
neurons that synthesize and release ACh
nicotinic AChR, muscarinic AChR - activated by ACh
119
120
A substantial amount of nicotine consumption will cause?
1. Increased sympathetic response
2. Increased parasympathetic response
121
Non classical NTs for sympathetic NS and parasympathetic NS?
Para: VIP and NO
Sympa: ATP and Neuropeptice Y
122
G Protein Couples Receptors
* Autonomic receptors are couples to G Proteins
1. Ligand binds
2. GDP on a subunit is switched for GTP
3. a + GTP dissociates, does a job
4. GTP hydrolysis
5. Return to a+B+Y inactive state
123
Gs does
stimulates adenylyl syclase =\> more cAMP + more PKA
124
Gi does
inhibits Adenylyl Cyclase =\> less cAMP, less PKA
125
Gq does
Activates Phospholipase C =\> more IP3 + more DAG
IP3 =\> Ca2+
DAG =\> PKC
126
a1 receptor does what with 2nd messengers?
stimulates PLC/IP3 =\> Ca2+ + PKC
127
a2 receptor does what
inhibits AC/cAMP
smooth muscle of GI and blood vessels
128
B1 and B2 autonomic receptors do what with second messengers?
where is B1/function
where is B2/function
stimulate AC and CAMP =\> PKA
SA node in heart, slivary glands, kidney / salivation etc
Smooth/skeletal muscle GI/bladder / relaxation and dilation
129
Autoreceptor on sympathetic presynaptic regions
inhibits further release of norepinephrine from the same terminals
-ve feedback
130
Heteroreceptor present on parasympathetic presynaptic regions
inhibits the release of ACh from parasympathetic postganglionic nerve terminals
131
**mAChR**
activates PLC =\> IP3 + DAG =\> Ca2+ + PKC
Coupled to PLC and Gq protein
132
**nAChR**
postganglionic neurons of the ANS
chromaffin cells
motor end plate of skeletal muscles
133
Dual innervation by sympathetic and parasympathetic divisions
* Most organs are dually innervated
* Usually antagonistic
* Sweat glands, adrenal medulla and blood vessels all only have sympathetic innervation
134
Pupil
Dilates under sympathetic innervation due to increased NE release, a1 receptor activity in radial muscle -\> mydriasis
135
What is the pathophysiology of Horner's Syndrome?
* Miosis (pupil constriction). Less sweating, droopy eyelid. Damage to sympathetic nerves.
136
Servomechanism
a control system uses -ve feedback to operate another system =\> eg vasomor centre in blood pressure regulation
137
Temperature regulation by
central thermoceptors in anterior hypothalamus
138
What is the mechanism for a fever?
Pyrogens increase the temp regulation set point in the hypothalamus
139
Regulation of food intake
regulation of water intake?
glucoreceptors in hypothalamus
osmoreceptors in hypothalamus
140
B1 activation; 5 outcomes
SA node - increased heart rate
AV node - increased conduction velocity
ventricular muscle = contraction
salivary gland - secretion
kidney - secrene renin
141
corda equina
less nerve trunks near bottom of spinal cord so they come out in bundles that look like horse tails
142
*sympathetic nerves come out on the right side and segmental nerves on the other side*
143
Functions of the CNS
1. **Input of information** - from external and internal environment
2. **Output of information** to muscles, glands and control of some sense organs
3. **Integration** **of information** - input +memory =\> output (behaviour)
1. simple reflexes to complex behaviour
144
Cranial nerves
Oh Oh Oh to touch and feel a girls vagina, ah heavan
1. Olfactory
2. Optic
3. Oculomotor
4. Trochlear (eye motor)
5. Trigeminal (face sensory)
6. Abducens (eye motor)
7. Facial (face motor)
8. Auditory (hearing balance)
9. Glossopharyngeal (mouth sensory
10. Vagus (autonomic)
11. Accessory (neck motor)
12. hypoglassal (tongue motor)
145
Spinal cord function
input, output, local reflexes, modification of ascending and descending info
146
Brainstem function
midbrain, pons, medulla
control of respiration, cardiovascular system, arousal, posture, visual reflexes, micturition, some auditory processing
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Cerebellum function
coordiantor of movement, balance
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diencephalon function
Thalamus, hypothalamus, pineal
control of sensory input, autonomic regulation
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Cerebrum functions
higher functions, speech, vision, end of sensory flow, start of motor flow
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corpus callosom function
major pathway for information bt the two hemispheres.
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Large axons are ___________ to stimulate
Easier.
A small stiumulus will exite mainly Aa efferects (motor neurons) or Ia afferents (from muscle spindles)
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*Below 1um it isn't energetically worth myelinating an axon*
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*Afferents are bipolar with cell bodies in dorsal root ganglion*
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Outputs
Alpha
Gamma
Autonomic
Alpha - motorneurons to skeletal muscle
Gamma - motorneurons to muscle spindles
Autonomic - to visceral muscles and glands
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Inputs
Cutaneous
Muscle
Joints
Visceral
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Dorsal column medial leminscus system
Summary
* Carries accurate touch, vibration and conscious proprioceptive information
* Uses large diameter, faster conducting axons
* Axons ascend ipisilaterally in the spinal cord to dorsal column nuclei in medulla
* Second order neurons cross to the contralateral side before synapsing in the thalamus
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Anterolateral system summary
* Carries pain and temp information
* Neurons synpase in spinal cord
* 2nd order neurons cross immediately and ascend contralaterally before synapsing in the thalamus
* Third order neurons ascend to the somatosensory cortex and cingulate cortex (pain)
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Brown Sequard syndrome
damage to one side of the spinal cord causes loss of touch to one side of body and loss of pain and temperature to the other side
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Spinocerebellar system
* Afferents from muscle and joint receptors
* Large diameter, faster conduction axons
* 1st order afferents synapse in the Clarke's nucleus in spinal cord
* 2nd order neurons ascend ipsilaterally in Clarke's column and pass from brainstem to cerebellum
* Cerebellum involved in movement, coordination, balance
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lateral tracts for which pathways
medial tracts?
corticospinal (pyramidal) and midbrain (rubrospinal) pathways
Include corticospinal and pathways from medulla, pons and vestibular
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Corticospinal System
Pyramidal System
* fastest motor system - only 2 neurons from cortex to muscle
* 80-90% corticospinal axons cross over at the front of brainstem and form **pyramids**
* **fine discriminatory movements of distal digits**
* Damage causes weakness, but primarily fingers affected
* other 10-20% axons don't cross over. They descend in the medial tract and cross over before synapsing on motor neurons
* Analogous corticobulbar tract gives fine control of lower face muscles, including tongue + lips
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Extrapyramidal System
* Any motor pathway that is not in corticospinal (pyramidal) system is in the extrapyramidal system
* Pathways all start in the motor cortex and synpase at least once before proceeding to spinal cord
* Older system (fish, birds, reptiles)
* Posture, intiation and repetition of movement
* Pyramidal develops slowly so this is what babies use
* Psychotropic drugs have effects here leading to extrapyramidal symptoms
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Muscle Tone
what is it
upper and lower motor neurons
hypertonia
spasticity
hypotonicity
* The resistance of a muscle to stretch. When a person tries to move a limb, there ar etwo parts: *viscoelastic properties* of the must and *a-motorneuron activity*
* Upper motorneurons are actually interneurons descending to the "lower" a-motorneurons that inneravate
* **Hypertonia** = too much tone. Increased motorneuron activity often caused by decreased inhibition of motorneurons or change in postsyn sensitivity by damage to upper motorneurons
* **Spasticity** = hypertonicity after muscle stretch. A brief contraction. Any longer is a cramp
* **Hypotonicity** = too little tone, flaccid. Can be caused by lower motorneuron damage, neuromuscular junction or muscle disease
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Upper motorneuron damage
* Damage to upper motorneurons in pyramidal tract often caused by stroke, ALS etc
* Consequence of **flaccid paralysis** (like spinal shock)
* Followed by spastic hemiplegia or hemiparesis (paresis = weak)
* Rapid movement of muscles causes greated increase in tone
* Clasp knife reflex - pushing hard on joint =\> collapse, probably due to golgi tendon organ inhibition
* Stretching may cause **clonus** = rapid, rhythmic contraction
* Normal reflexes may increase or decrease
* **Babinski sign** - upturb of big toe and fanning of toes on plantar stimulation (in babies bc their pyramidal tract isn't full myelinated)
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afferents from skin vs muscle
afferents from the skin have many different connections - **polysynaptic**
monosynaptic are mainly from muscle receptors. These are the largest axons - fastest etc.
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Facilitation
Stimulate things seperately you get a small response. If you stimulate them together you get a response that is bigger than their individual responses
= facilitation
**Subliminal fringe** = a neuron that doesn't fire when stimulated by A or B. It must be stimulated by both to fire.
The longer you wait after A firing to fire B, the smaller the facilitated sum reponse will be.
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Occlusion
* Stimulate either strongly and you get a strong response
* Innervate A and B together and you get a weaker response than the sum of their individual responses
* sublinear summation is due to occlusion
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Spinal animal
Cut at spine
The higher you cut, the more function you get
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Spinal reflexes
bahviour produced entirely within the spinal cord
Two types of reflexes based on afferent input:
1. Muscle receptor reflexes (muscle spindles, tendon organs)
2. Cutaneous reflexes (skin pressure or pain)
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Spinal Shock
Spinal cord sextion outcomes
* Following cut of spinal cord, no activity in spinal cord for about 2 weeks (**flaccid paralysis**), then reflexes resume and are often hyperactive.
* probably due to loss of descending pathways and growth of new local synapses
1. Plegia - paralysis
2. Paresis - weakness
3. Anaesthesia - loss of sensation
4. Paresthesia - abnormal sensation (pins and needles)
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Spindles - explanation
* Short, fusiform (spindle shaped), multinucleated, varied density
* Some muscles so dense with them that their main job is sensation
* Contribute to conscious sense of limb position (proprioception) and movement (kinesthesia)
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The spindle, muscle, motorneuron set up
* a-motorneurons innervate muscle fibres
* muscle fibres put out gamma motorneurons to spindles
* **Trail** y-motorneuron ends go to **chain** spindles (nuclei in row)
* **Plate** y-motorneuron ends go to **bag** spindles (nuclei in bag in middle)
* Bag spindles have Ia afferents
* Chain spindles have Ia afferents and II afferents
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Muscle spindle afferent firing (3)
1. Increasing load = stretching muscle = increases firing
2. Increasing a-motor neuron activity = contraction = less y firing
3. Increasing y motorneuron activity stretches nuclei and increases firing
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Spindles.
Statis and dynamic
* **Ia** (primary) are dynamic response. Respond to changing length
* **II** (secondary) are static response. Respond to contant length
* y - dynamic increases dynamic sensitivity (probably on bag spindles)
* y-static increases static sensitivity (probably on chain spindles)
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Muscle spindles are responsible for the stretch reflex
* Tendon jerk
* Stretch muscle rapidly and it contracts
* Stimulating the Ia afferent in a loop that stimulates the a motorneuron to contract
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reciprocal connections
* **Synergistic muscles** work together
* **Antagonistic muscles** work against each other
* At the joint there are flexors and extensors. Two flexors are synergistic, one of each are antagonistic
* Reciprocal innervation =\> antagonistic muscles to opposit things
* Common to many reflexes/stretch reflex
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co-activation
* activating a-motorneurons shortens the muscle and the spindles relax and reduce firing
* CNS then turns up y firing so that spindles don't relax and can still detect changes in length due to external load
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Servo controls of stretch reflex
They usd to think that only y-motor neurons did the stretch reflex, but then they realized that the circle of innervation means that the a-motorneurons are also helping which makes the function more stable.
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Golgi Tendon Organ Reflexes
mechanism
recent finding
* Inhibit a-motorneuron activity at muscle as well as at neigbouring synergistic muscles.
* Several muscle affected
* Muscles are synergistic - acting together
* Disynaptic reflex - two synapses (needs an interneuron because one neuron can do inhib and excit)
* Extensor phase of walking had golgi tendon activity that excited motor neurons so reflex behaviour is plastic - can change during activities such as walking
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Flexion Reflex
* In a spinal animal, noxious stim on distal limb leads to flexion of stimulated limb and extension of other limb
* many muscles involved
* Synergistic and antagonistic muscles
* Man synapses - polysynaptic reflexes
* Slow reflex
* Temporal smmation - one stimulus does nothing, but several elecit a response
* Spatial summation
* Protective role and supportive role
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Positive supporting reaction
extensory thrust reflex
light pressure to spread toes leads to extension of limb
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Scratch reflex
Stimulate the skin on an animal's side and they scartch same location
* complex behaviour
* Temporal summation
* Spatial summation
* Long latency
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Central pattern generators
Currently under research
rhythmic patterns that seem to have roots in the spinal cord
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Postural reflexes
balance against gravity requires information from (we need 2):
1. Vestibular righting reflexes - signals from the vestibular system about the direction of gravity
2. Optical righting reflexes - vision is enough if there is light
3. Cutaneous righting reflexes - pressure on skin and proprioception from joints and muscles indicates gravity
Muscle and jiont receptors in neck provide reflex control of flexor and extensor muscles in the limbs to keep body upright. These reflexes are coordinated with the other righting reflexes.
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Romberg test
Subject stands with feet together and closes eyes
If their vestibular and proprioceptive inputs are comprimised the subject will sway or fall.
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neck reflexes
The neck muscles have many muscle spindles. Moving the head causes reflex limb movements aimes at keeping the head upright
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Postural reflexes depend on:
* centres above the spinal cord
* spinal animal doesn't have posture
* posture reflexes reappear if the cut is made higher
* decebrate animal can right itself when placed on its back
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Primary motor cortex set up
* Somatotopic representation of the body - motor homunculous
* Stimulating a region on the map stimulates that region on the body. Relative to each other like on the body. Big regions for race and hand and tongue
* Damage to part of the motor cortex leads to paralysis in the appropriate region - can recover if another part takes over its function
* Complex connections bt diff motor areas that are also somatotopically organized
* These areas are all involved in creating movements, but we don't know how the movements are initiated
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Supplementary motor area
premotor area
cingulate motor area
* Also involved in movement and somatotopically organized
* Stimulating this areas also produces movements that tend to be more complex involving more muscles around a joint.
* Premotor area also somatotopically organized; clear seperation of uppler/lower limbs; produces movement, but stronger stim is needed
* Damage to supplementary and premotor areas leads to complex problems like **apraxia**
* Cingulate motor area linked to the drive required to move and the reward acquired from moving.
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Apraxia
difficulty putting together complex movements like screwing in a lightbulb as a result of damage to the premotor cortex and the supplementary motor cortex
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basal ganglia
* Complex connections between the cerebral cortex, basal ganglia, thalamus and spinal cord
* Basal ganglia is part of an old system and is the only motor system in birds and lower vertebrates
* Damage to the motor circuits involving basal ganglia cause some common movement disorders like Parkinsons:
*
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Parkinson's Disease
* Akinesia/bradykinesia - no movement or slow movement
* Rigidity - increased muscle contraction or tone
* Tremor - oscillation of the limbs at 4-5 per second
* caused by loss of cells in substantia nigra that release dopamine
* L-DOPA a precursor of dopamine that can cros BBB has therapeutic value, but it decreases as the disease progresses
* Surgical treatment either destroys over-active areas in brain permanently (pallidotomy) or inhibit them temporarily (deep brain stimulation)
* Stimulation can sometimes bring wrong effect.
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Ballismus
Athetosis
Chorea
Basal ganglia movement disorders
* Ballistic movements of limbs, often rotary, usually unilaterally so it is called hemiballismus.
* Seems to be caused by damage (often strokes) to the subthalamic nuclei
* Slow, writhing movements
* Brisk, dancing movements
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Huntington's disease
* Best known chorea
* Caused by excessive (40) repeats of CAG that lead to cell death in basal ganglia
* Disease onset 30-50 yrs or earlier with more repeats
* Causes chorea, later rigidity and akinesia (also dementia).
* Might have been responsible for some of the salem witch trials
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Cerebellum inputs and outputs
The oldest part
* Inputs:
* Cutaneous (from spinal cord and brain stem)
* Visual and auditory cells (via the cerebral cortex)
* Vestibular (direct fand via the brain stem)
* Muscle and joint receptors (from spinal cord)
* Outputs: brainstem nuclei (nothing goes directly to spinal cord)
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Cerebellum
contralateral or ipsilateral?
flocculonodular lobe
* Connections are generally ipsilateral (in contrast to cerebrum). many pathways cross midline twice)
* **Flocculondodular lobe**
* Closely associated w vestibular system
* Mainly involved in controlling eye movements, head position, posture relative to gravity
* Damage causes difficulty with eye and head position and balance. Patients stand with legs far apart to improve balance
* They can still control their head eyes and limbs, just can't correct them based on vestibular input
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Cerebellum - spinocerebellum
* Central region is older - **spinocerebellum**
* Recieves input from afferents of spinal cord (tracts), particularly from muscle and joint receptors
* Somatotopically organized sensory maps of body surface - trunk at centre, outwards toward distal limbs
* modulates descending motor pathways in brain stem and cerebral cortex
* helps control movements by anticipation
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Lateral regions of the cerebellum
* much larger in man than in apes
* Call the cerebrocerebellum or pontocerebellum
* recieves a wide range of sensory information (including vision and hearing) via cerebrum
* Functions are still being discovered and include planning and adjusting movement based on sensory information, cognitive tasks useful for movements, and learning motor tasks
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Disorder caused by cerebellar damage
* **Hypotonia** - reduction of muscle tone, reduced resistance to passive movement, ascillation after the stretch reflex
* **Ataxia** - lack of coordination, Delay in starting a movement
* **Dysmetria** (error in size of movement), errors in rate and regularity of repeated movement
* Movement decomposition
* **Intention tremor** - oscillation that increases with movement (in contrast to resting tremor in Parkinson's)
* **Loss of plasticity** in controlling movements, such as learning to throw darts while wearing prism glasses
* Not paralysis!
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Ataxia and Tremors
* **Ataxia** = range in diseases causing bad movement coordination.
* Commonly caused by cerebellar damage (malnutrition, virus, genetic mutation, stroke, alcohol, drugs)
* **Postural tremor** = small oscillation, particularly when extending hands is common. Can be caused by genetic factors, anxiety, drug or alcohol withdrawal
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eyes
* Superior/inferior rectus move eyes up and down
* Lateral/medial rectus move eyes sideways
* Superior/inferior oblique roll eyes around visual axis
* Occulomotor nerve drives all except Superior oblique and Lateral rectus
* **Saccades** = quick, darting, normal eye movements
* Superior colliculou (top of midbrain) has a topographic map of visual world, invovles front eye fields and posterior parietal lobe
* **Tracking movements** slower and smooth, follow an object
