Lecture 3 Flashcards
What can influence pain?
Experience
Define pain
Protective mechanism triggered by nociceptors
What are the 3 types of pain receptors? What does each detect?
1) Mechanical nociceptors: cutting, crushing, pinching
2) Thermal nociceptors:
temperature, especially heat
3) Polymodal nociceptors:
Various stimuli, including chemicals from injured tissues
1) What sensitizes all nociceptors?
2) What causes these to be released? What does this do?
3) What inhibits these?
1) Prostaglandins
2) Tissue damage releases prostaglandins which enhances pain by lowering activation threshold of those receptors (among other causes)
3) NSAIDs inhibit prostaglandins
What are the two ways nociceptors transmit info to the CNS? Briefly describe each
1) A-delta fibers: fast pain pathway
2) C fibers: slow pain pathway
What fibers are the fast pain pathway?
A-delta fibers
1) What are A-delta fibers?
2) How fast are they? Are they myelinated or unmyelinated?
3) What receptors use these?
1) Fast pain fibers
2) 30m/s (myelinated)
3) Mechanical and thermal pain receptors
1) What are C fibers?
2) How fast are they? Are they myelinated or unmyelinated?
3) What do they involve?
1) Slow pain pathway
2) 12m/s (unmyelinated)
3) Bradykinin
1) What is bradykinin?
2) What does it do?
1) A normally inactive substance activated in the ECF by tissue damage
2) Causes pain, contributes to inflammatory response
What are the two best known neurotransmitters for pain?
1) Substance P
2) Glutamate
1) Is substance P unique?
2) What does it do?
1) Yes; unique to pain fibers
2) Activates ascending pathways to transmit pain signals for processing
What two things does glutamate bind to? Why?
1) Binds with AMPA receptors: to ultimately transmit pain signals
2) Binds with NMDA receptors: to sensitize injured area
Can chronic pain occur without tissue damage?
Yes
1) What causes chronic pain?
2) How does this happen?
1) Abnormal signaling of pain pathways
2) Neuronal response to pain becomes exaggerated and can lead to sensitive neurons even after tissue has healed
Define referred pain
Sensation of pain in a part of the body that is remote from the damaged tissue
Where is referred pain often seen? Why?
With visceral pain; bc chest and abdominal organs often have no sensory receptors except pain receptors
1) Define analgesic system; what 3 things does it descend from?
2) What does it do?
1) The descending pathway from periaqueductal gray matter, medulla, and reticular formation
2) Release enkalphin
What is enkalphin and what does it do?
An endogenous opioid that binds with opiate receptors, inhibiting substance P
What is periaqueductal gray matter?
Gray matter surrounding the cerebral aqueduct
Why is a conscious response to pain necessary?
So an organism can remove a noxious stimulus or remove itself from the environment to avoid further tissue damage
Give an example of subconscious pain response
Sitting for prolonged periods can cause tissue damage from lack of blood flow where the skin is compressed by the weight of the body (shifting weight)
What are the two divisions of the ANS? Describe each and where their fibers emerge
1) Sympathetic
-Responding to stress; fight or flight
-Fibers emerge from thoracic and lumbar regions of the spine
2) Parasympathetic
-Relaxed activities; rest and digest
-Fibers emerge from cranial and sacral regions
True or false: parasympathetic and sympathetic typically innervate same effector organs
True
What does the ANS consist of?
A two-neuron efferent pathway
1) Where is the first ANS neuron cell body? What does its axon do?
2) What does the second ANS neuron do?
1) In CNS; preganglionic fiber synapses with cell body of the second neuron
2) Innervates the effector organ
What is another name for presynaptic and postsynaptic neurons?
1st and 2nd neurons
1) What regions are the parasympathetic presynaptic (preganglionic) neurons and ganglia in?
2) What regions are the sympathetic presynaptic (preganglionic) neurons and ganglia in?
1) Parasympathetic: Brainstem and sacrum
2) Sympathetic: Thoracic and lumbar
What do the preganglionic/ presynaptic endings of sympathetic fibers release? What about parasympathetic?
Preganglionic of both sympathetic and parasympathetic release Ach
What do the postganglionic/ postsynaptic endings of sympathetic fibers release? What about parasympathetic?
1) Parasympathetic: ACh
2) Sympathetic: NE
What two things mediate most effector organ responses?
Acetylcholine (ACh) and norepinephrine (NE)
What two types of structures release ACh? (nerves that supply what?)
1) Nerves that supply muscle and exocrine glands
2) Terminals of all motor neurons supplying skeletal muscle
What do the nerves that release norepinephrine (NE) affect?
Nerves supply smooth muscle, cardiac muscle, exocrine glands, CNS pathways for memory, mood, emotion, behavior, perception,sleep
1) What are fibers that release ACh called?
2) What does this include?
1) Cholinergic fibers
2) All autonomic preganglionic fibers and parasympathetic postganglionic fibers
1) What are fibers that release NE called?
2) What does this include?
1) Adrenergic fibers (NE aka noradrenaline)
2) Most sympathetic postganglionic fibers
What are the two exceptions to the general rules about what fibers release ACh and which release NE?
1) Sympathetic postganglionic fibers of sweat glands release ACh
2) Some autonomic fibers do not release either NE or Ach
Give two examples of dual innervation
1) When autonomic efferent output regulates visceral activities (E.g. circulation, digestion)
2) Most organs have sympathetic and parasympathetic fibers
True or false: Most organs have sympathetic and parasympathetic fibers
True
What two things does dual innervation do?
1) Allows for “opposite” effects in a particular organ
2) Enhances CNS control
Which fibers are the accelerators of the CNS? Which are the brakes?
1) Sympathetic: accelerators
2) Parasympathetic: brakes
1) When the heart is sympathetically stimulated, what happens?
2) What about when it’s parasympathetically stimulated?
1) S: Increases heart rate and increases force of contractions (entire heart)
2) P: Decreases heart rate and decreases force of contraction (atria only)
1) When most blood vessels are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Constricts(to increase BP)
2) P: Dilates vessels supplying the penis and clitoris only
1) When the lungs are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Dilates the bronchioles (airways)and inhibits mucous secretion (α)
2) P: Constricts the bronchioles and Stimulates mucus secretion
What 3 things does sympathetic stimulation do to the digestive system?
1) Decreases motility
2) Contracts sphincters (to prevent forward movement of contents)
3) Inhibits digestive secretions
What 3 things does parasympathetic stimulation do to the digestive system?
1) Increases motility
2) Relaxes sphincters (to permit forward movement of contents)
3) Stimulates digestive secretions
1) When the urinary bladder is sympathetically stimulated, what happens?
2) What about when it’s parasympathetically stimulated?
1) S: Relaxes
2) P: Contracts (emptying)
1) When the eyes are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Dilates the pupil (contracts radial muscle) for far vision
2) P: Constricts the pupil (contracts circular muscle) for near vision
1) When the liver is sympathetically stimulated, what happens to its glycogen stores?
2) What about when it’s parasympathetically stimulated?
1) S: Glycogenolysis (glucose is released)
2) P: Nothing
1) When the adipose cells are sympathetically stimulated, what happens?
2) What about when it’s parasympathetically stimulated?
1) S: Lipolysis (fatty acids are released
2) P: Nothing
1) When the pancreas is sympathetically stimulated, what happens to its exocrine secretions?
2) What about when it’s parasympathetically stimulated?
1) S: Inhibits pancreatic exocrine secretion
2) P: Stimulates pancreatic exocrine secretion (important for digestion)
1) When the sweat glands are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Stimulates secretion by sweat glands
2) P: Nothing
1) When the salivary glands are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Stimulates a small volume of thick saliva rich in mucus
2) P: Stimulates a large volume of watery saliva rich in enzymes
1) When the adrenal medulla is sympathetically stimulated, what happens?
2) What about when it’s parasympathetically stimulated?
1) S: Stimulates epinephrine and norepinephrine secretion (cholinergic)
2) P: Nothing
1) When the pancreas is sympathetically stimulated, what happens to its endocrine functions?
2) What about when it’s parasympathetically stimulated?
1) S: Inhibits insulin secretion; stimulates glucagon secretion
2) P: Stimulates insulin and glucagon secretion
1) When the genitals are sympathetically stimulated, what happens?
2) What about when they’re parasympathetically stimulated?
1) S: Controls orgasmic contractions (both sexes)
2) P: Controls erection (penis in males and clitoris in females)
1) When the brain is sympathetically stimulated, what happens to brain activity?
2) What about when it’s parasympathetically stimulated?
1) S: Increases alertness (receptors unknown)
2) P: None
What is tone?
The idea that although one system may dominate, usually sympathetic and parasympathetic systems are active to varying degrees
Give an example of how the balance of sympathetic and parasympathetic tone can vary between organs
Sympathetic dilation of the eye’s pupil in dim light while in a relaxed state
What does sympathetic dominance do?
Prepares the body for strenuous activity or response to stressful situations
What are the body’s responses to sympathetic dominance?
Fight-or-flight responses:
1) Heart pumps more forcefully and rapidly
2) Blood vessels constrict
3) Airways dilate
4) Pupils dilate
5) Digestive and urinary activities inhibited (“postponed”)
-Not essential in addressing the threat
What does parasympathetic dominance do?
-In quiet, relaxed situations, it causes rest-and-digest
-“General housekeeping/maintenance”
What are the 3 exceptions to dual innervation?
1) Blood vessels (except for in penis and clitoris)
2) Sweat glands
3) Salivary glands (kinda)
1) What innervates blood vessels? (excluding vessels of penis and clitoris)
2) How does it/ do they control their function?
1) Only sympathetic fibers
2) Vasoconstriction and dilation regulated by adjusting fire rate of the fibers
Why do the penis and clitoris blood vessels receive both sympathetic and parasympathetic fibers?
More precise vascular control
1) What innervates sweat glands?
2) What else is unusual here?
1) Only innervated by sympathetic nerves
2) These nerves secrete ACh rather than NE
Are salivary glands dual innervated? Explain
Dual innervated but not in an antagonistic fashion; both stimulate secretion of different volume and composition
1) What is the adrenal medulla?
2) Where are the adrenal glands?
3) What is the outer portion of the adrenal glands called?
4) What is the inner part called?
1) A modified part of the sympathetic nervous system
2) Lie above the kidneys
3) Outer: adrenal cortex
4) Inner: adrenal medulla
Describe the control of the adrenal medulla
-Modified sympathetic ganglion
-Does not have postganglionic fibers; instead, secretes catecholamine hormones (ACh and NE) upon stimulation by preganglionic fiber
1) What is the output of the adrenal medulla?
2) What does it/ do they do?
1) 20% output is NE; 80% is adrenaline (epinephrine)
2) Both enhance sympathetic activity
There are only so many NTs for all the autonomic effects in the body, so where does the variety of effects come from?
Different types of receptors in the tissues
What are the two main types of receptors in the tissues? List their two types as well
1) Cholinergic receptors:
Nicotinic and muscarinic
2) Adrenergic receptors: Alpha 1 &2 and beta 1 &2
What are the two types of cholinergic receptors?
Nicotinic and muscarinic
1) Where are nicotinic receptors found? In parasympathetic or sympathetic?
2) Where are muscarinic receptors found? In parasympathetic or sympathetic?
1) Nicotinic: On postganglionic cell bodies in all autonomic ganglia; sympathetic and parasympathetic
2) Muscarinic: On effector organs for parasympathetic system
1) What do alpha receptors have an affinity for?
2) Where are A1 receptors? What do they do?
3) Where are A2 receptors? What do they do?
1) Affinity for NE over Epinephrine
2) A1: on most sympathetic tissues; excitatory response
2) A2: digestive organs; inhibitory response
1) Where are B1 receptors? What do they have an affinity for and what do they do?
2) Where are B2 receptors? What do they have an affinity for and what do they do?
1) B1: heart; equal affinity for NE and E; excitatory
2) B2: smooth muscles of arterioles and bronchioles; only bind with Epinephrine; inhibitory
What can drugs do to autonomic responses?
Can selectively alter autonomic responses of a receptor type
Define agonist and antagonist in the context of drugs
1) Agonist: binds to NT’s receptor and causes same response the NT would
2) Antagonist: binds with receptor but doesn’t produce response, “blocking” it
What does albuterol do?
Actives B2 adrenergic receptors, dilating bronchioles in asthma without stimulating the heart excessively
What does metoprolol do?
Blocks B1 adrenergic receptors, decreases blood pressure by decreasing heart rate and force without affecting bronchioles
(a beta blocker)
True or false: Many regions of the CNS are involved in control of autonomic activities
True
Give four examples of CNS control of autonomic activity
1) Spinal-cord integration (autonomic reflexes) for urination, defecation, erection
2) Medulla of brainstem controls cardiovascular, respiratory, and digestive autonomic activity
3) Hypothalamus controls various autonomic, somatic, and endocrine responses
4) Prefrontal association cortex controls emotional expression (like blushing)
1) What is spinal cord integration in control of?
2) What’s the caveat here?
1) Urination, defecation, erection
2) Higher levels of consciousness can become involved in these
What does the medulla of the brainstem do in terms of autonomic responses?
Controls cardiovascular, respiratory, and digestive autonomic activity
What does the hypothalamus control in terms of autonomic responses?
Various autonomic, somatic, and endocrine responses
What does the prefrontal association cortex control in terms of autonomic responses? Give an example
Controls emotional expression (E.g. blushing when embarrassed)
1) What do motor neurons do?
2) What do their axons make up?
1) Supply skeletal muscle to bring about movement
2) The somatic nervous system
How are the axons of motor neurons different from the two-neuron chain of autonomic fibers?
Unlike two-neuron chain, the axons of motor neurons continue to their endings on skeletal muscle
1) Where do motor neurons go?
2) What do they release?
1) Axons continue to their endings on skeletal muscle
2) Release ACh
What is the somatic nervous system also called?
The motor nervous system
1) What is the only way the CNS can influence skeletal muscle?
2) What presynaptic inputs do motor neurons receive?
1) By acting on motor neurons
2) Motor neurons receive many presynaptic inputs
-Excitatory and inhibitory inputs
Is the somatic nervous system voluntary? Explain
Somatic system is under voluntary control, but much of the skeletal muscle activity is subconsciously maintained
(posture, walking, balance)
Give examples of subconscious maintenance of the somatic nervous system
Posture, walking, balance
1) What links motor neurons and skeletal muscle fibers?
2) What happens?
1) Neuromuscular junctions
2) Action potential in motor neuron propagates along axon
1) Does the nerve and the muscle cells come into direct contact?
2) Describe what happens at motor neuron-to-muscle synapses (called neuromuscular junctions)
1) No
2) The space between is too large for electrical transmission, so ACh is the neuromuscular junction neurotransmitter
What is the neuromuscular junction neurotransmitter?
ACh
True or false: Each terminal button of a motor neuron contains thousands of ACh vesicles
True
List the 5 steps of a motor neuron releasing its neurotransmitter
1) Action potential triggers opening of voltage-gated calcium channels in all of the terminal buttons of a motor neuron
2) Calcium triggers ACh vesicles to be released.
3) ACh binds to nicotinic receptors of muscle fiber membrane,
4) Triggers channels to open, Na+ influx, depolarization
5) As this spreads throughout the muscle fiber membrane, the fiber contracts
Motor neuron stimulation needs to be switched off quickly for purposeful coordinated movement, so what is the “off” switch?
Acetylcholinesterase
What ends ACh activity at the neuromuscular junction?
Acetylcholinesterase
What 5 major components coordinate movement? What else is involved?
1) Cerebral cortex
2) Brainstem
3) Spinal cord
4) Basal ganglia
5) Cerebellum
-Afferent muscle innervation provides feedback for motor control
1) What provides feedback for motor control?
2) What is the final common path for motor control?
1) Afferent muscle innervation
2) Lower motor neurons
1) Where are lower motor neurons?
2) Where are upper motor neurons?
1) Lower: Located in the ventral horns [of spinal cord]
2) Upper: in the cortex and brainstem
What are the 5 places upper motor neurons can be found in the cortex and brainstem?
1,2) Corticospinal and corticobulbar tracts
3,4,5) Rubiospinal, vestibulospinal and reticulospinal tracts
1) What does spinal motor anatomy correlate with? Where are the LMNs?
2) What does the spinal cord mediate? Give examples
1) Function; LMNs are grouped into ventral horns
2) Reflex activity (exs: Myotatic (muscle stretch), Flexor withdrawal)
What modifies spinal cord pathways? Give an example
Descending motor pathways (ex: sitting)
Brainstem is the origin of what descending tracts?
The ones that influence posture and movement
What influences posture and movement?
The brainstem’s descending tracts
What are 3 descending motor tracts from the brainstem? Where is each located and what do they do?
1) Rubrospinal Tract: Red nucleus receives input from cerebellum and cerebral motor areas
-Descend on the contralateral side
-Mainly upper limbs
2) Vestibulospinal Tracts
-Pons and medulla
-Position and movements of the head
-Ipsilateral side
3) Reticulospinal Tracts
-Reflexes, truck/limb muscles, posture control
-Both ipsilateral and contralateral
True or false: Terminations of the brainstem motor tracts correlate with their functions
True
1) What controls posture?
2) What do central generator programs do?
3) What produce upper motor neuron sign?
1) Sensory and motor systems work together to control posture
2) Help control rhythmic motor behaviors
3) Injuries to the motor cortex or corticospinal tract
What does abnormal posturing result from?
Damage to descending [brainstem] motor tracts
What are two kinds of abnormal posturing? Define each
1) Decerebrate Posturing: rigid extension
2) Decorticate Posturing: abnormally flexed
True or false: Several distinct cortical areas participate in voluntary movement
True
What is the primary efferent path from the cortex?
Corticospinal tract
1) Where is the primary motor cortex?
2) What does it do?
3) What simplifies its representation?
1) Frontal lobe in the precentral gyrus
2) Initiate voluntary movements
3) Somatotopic organization (homunculus)
1) How does the corticospinal tract descend?
2) What is it responsible for?
1) Contralateral side
2) Rapid, skilled, discrete movements of the hands
What is responsible for the preparation and initiation of [conscious] movement?
A group of subcortical nuclei in the basal ganglia
True or false: Basal ganglia nuclei are extensively interconnected
True
1) Give examples of basal ganglia nuclei interconnections
2) What are functions of the basal ganglia partially revealed by? What does this do
1) Limbic, association, oculomotor and motor channels
2) Disease; leads to hypo or hyperkinesis
What are two diseases of the basal ganglia?
Parkinson’s and Huntington’s
1) What does Parkinson disease cause?
2) What does Huntington disease cause?
1) Parkinson Disease: Hypokinetic movement
2) Huntington Disease: Hyperkinetic movement
1) What is another name for the cerebellum?
2) What does it control?
3) How is it organized?
1) “Little brain”
2) Muscle coordination, balance and posture, and motor learning
3) Structural divisions of the cerebellum correlate with function
List the 3 divisions of the cerebellum and what each does
1) Vestibulocerebellum (flocculonodular lobe):
Maintaining balance and eye movements
2) Spinocerebellum (midline vermis +intermediate zone): Coordinating complex voluntary movements
3) Cerebrocerebellum (Lateral zone): Planning and coordinating movements by providing input to cortical motor areas
1) What regulates the intrinsic circuitry of the cerebellum?
2) Is this excitatory or inhibitory?
3) Why/ what neurotransmitter is involved?
1) Purkinje cells
2) Inhibitory.
3) GABA
How do cerebellar lesions reveal functions of the cerebellum?
Through the consequences of cerebellar lesions: ataxia, hypotonia, dysdiadochokinesia, dysarthria, decrease in motor learning, intention tremor
1) Define ataxia
2) Define hypotonia
1) Impaired movement
2) Muscle flaccidity
1) Define dysdiadochokinesia
2) Define dysarthria
1) Rapid alternating movements
2) Garbled speech
1) What can cause intention tremor? What is it?
2) What can cause a decrease in motor learning?
1) Cerebellar lesion; when you’re thinking about it it gets worse (reaching to grab a cup).
2) Cerebellar lesion
1) What does the cerebellum do besides motor function?
2) Give examples of what’s being researched about the cerebellum
1) Plays a role in several nonmotor cognitive functions
2)
-Working memory
-Learning
-Attention
-Executive control
-Language
-Emotion
-Addiction
-Pain
1) What does poliovirus do microscopically?
2) What does that cause?
1) Selectively destroys cell bodies of motor neurons
2) Paralysis of the affected muscles
1) What does ALS stand for?
2) What does ALS do microscopically?
3) What does that cause?
1) Amyotrophic lateral sclerosis (ALS)
2) Degeneration of motor neurons
3) Gradual loss of motor control, progressive paralysis, and death within 3-5yrs
What is the cause of ALS?
The cause is uncertain, but there are ideas:
1) Neurofilaments blocking axonal transport
2) Extracellular glutamate accumulation to toxic levels
3) Mitochondrial dysfunction
1) What does black widow venom do microscopically?
2) What does this cause?
1) Causes explosive release of ACh at all cholinergic sites, causing prolonged depolarization so the muscle cannot relax
2) Potential respiratory failure as diaphragm cannot relax
1) What does Botulinum toxin do microscopically?
2) What can this lead to?
3) Does it have any clinical applications?
1) Blocks ACh release from motor neuron terminal buttons, so muscles do not respond to nerve impulses 2) Can cause inability to contract diaphragm
3) Highly lethal, but miniscule amounts can temporarily paralyze muscles and alleviate wrinkles (botox)
1) Where do afferent neurons carry info?
2) Where is their receptor ending?
3) Where do they terminate?
4) What excites them?
1) Information to the CNS
2) Receptor ending is in the periphery
3) Terminates onto interneuron
4) Receptor potential induced by a stimulus
1) Where do efferent autonomic neurons carry info?
2) Where does the preganglionic neuron originate?
3) Where does the postsynaptic fiber terminate?
4) What do they do to the target organ? How?
5) What is this system called?
1) Info from CNS to effector organs
2) Preganglionic: originates in CNS
3) Postganglionic: terminates onto effector organ
4) Excites or inhibits target organ via sympathetic or parasympathetic activity
5) Two-neuron chain
1) Where do efferent somatic neurons carry info?
2) Where is the cell body of the motor neuron? Where does its axon terminate?
3) Can they be both excitatory and inhibitory? Explain
1) Carries info from CNS to skeletal muscles
2) Cell body of motor neuron in spinal cord; axon terminates onto skeletal muscle
3) The motor neuron can be excited or inhibited, but in terms of its action on the muscle it can only excite, not inhibit
List 3 exocrine glands
1) Pancreas’s exocrine functions
2) Sweat glands
3) Salivary glands
