Neurology Flashcards
What are 5 main functions of the NS?
1) Sensation
2) Motor capability
3) Cognition
4) Homeostasis
5) Emotions
What are the 5 main parts of a neuron?
1) Dendrites
2) Soma / cell body
3) Axon hillock
4) Axon
5) Presynaptic terminal
What are the 4 lobes of the brain and what are their functions?
1) Frontal – personality, motor planning, motor cortex
2) Parietal – integration of multiple sensory systems, somatosensory cortex
3) Occipital – visual cortex
4) Temporal – auditory processing
What are the 3 regions of gray matter?
1) Dorsal horn
2) Lateral horn
3) Ventral horn
What is found in the dorsal horn?
Cell bodies of interneurons upon which afferent neurons terminate
What is found in the lateral horn?
Cell bodies of autonomic efferent nerve fibres
What is found in the ventral horn?
Cell bodies of somatic efferent neurons
Is Na+ more concentrated in the ICF or ECF?
ECF
Is K+ more concentrated in the ICF or ECF?
ICF
Is Cl- more concentrated in the ICF or ECF?
ECF
Is Ca2+ more concentrated in the ICF or ECF?
ECF
Is Mg2+ more concentrated in the ICF or ECF?
ECF
What direction is the passive flow of Na+ and K+?
Na+ flows in and K+ flows out
What direction is the active transport of Na+ and K+?
K+ transported in and Na+ transported out
What is the net movement at equilibrium potential?
Zero
What is equilibrium potential?
The membrane which would produce an electrical force that would be equal to and in the opposite direction to the chemical force produced by the ion concentration gradient
What should be assumed when considering equilibrium potentials?
100% permeability
Why is resting membrane potential not equal to Ek?
At rest, the cell is not completely permeable to K+ ions and there is a small permeability to Na+ ions
What forces act on Na+ ions at the point of threshold?
Chemical and electrical
What happens before reaching ENa+?
The voltage-dependent Na+ channels inactivate
What other channel beside K+ channels contribute to afterhyperpolarization?
Ca2+ activated K+ channels
What is the effect of a drug that opens Na+ channels?
Depolarization
What is the effect of a drug that opens K+ channels?
Hyperpolarization
What is the effect of a drug that opens Na+ and K+ channels?
Depolarization (Na+ wins)
What is the most important intracellular cation?
Potassium
What is the function of potassium?
Maintain cellular osmolarity and membrane potential inside the cell
What is the concentration of K+ in normal plasma?
3.5 - 5 meq
What is hyperkalimia?
When the concentration of K+ in plasma is greater than 5 meq
Why will injecting a high concentration of potassium into the ECF cause death?
Ek will depolarize, which causes neurons and muscle cells to depolarize, meaning that muscle contraction and the heart stay in contraction
Where does synaptic transmission occur?
Over the dendrites, soma, and axon hillock
What are the 7 events of chemical synaptic transmission?
1) Action potential propagation
2) Depolarization of presynaptic terminal
3) Opening of vdep Ca2+ channels
4) Ca2+-induced fusion of vesicles with presynaptic membrane
5) Binding of transmitter to postsynaptic receptor
6) Postsynaptic action
7) Termination of transmitter action
What 2 events happen when calcium enters the presynaptic terminal?
- Triggers the fusion of vesicles with presynaptic membrane
- Releases transmitters into synaptic cleft
How much calcium is needed for synaptic function?
Very little
What is an analogy that can describe the relationship between transmitters and receptors, and what describe the transmitters in this analogy?
- Lock in key
- Transmitters are the key
What are 2 classifications of transmitters?
1) Small fast-acting
2) Large slow-acting
What are 3 examples of small fast-acting transmitters?
1) Acetylcholine
2) Dopamine
3) GABA
What is one example of a large slow-acting transmitter?
Endorphins
What is the main excitatory neurotransmitter?
Glutamate
What are the 2 main inhibitory neurotransmitters?
1) Glycine
2) GABA (gamma-ammobutyric acid)
What are 2 ways that the postsynaptic terminal can be excited?
1) Na+ entry into the cell by opening Na channels (depolarization)
2) Close K+ channels, causing less positive ions to leave (depolarization)
What is central inhibition?
Inhibitory neurotransmitters bind to a receptor that causes ion channels to open and produce a postsynaptic hyperpolarization
What 2 things cause central inhibition?
1) K+ leaving postsynaptic cell
2) Cl- entering
What is an excitatory response?
Neutron depolarizes and if it reaches threshold an AP is initiated
What is an inhibitory response?
Neutron hyperpolarizes and APs are harder to elicit
Define ionotropic
Receptor is linked to an ion channel and opens/closes the channel
Define metabotropic
Receptor is linked to a G protein, which can activate second messengers
What can metabotropic synapse-activated second messenger channels do?
- Open/close channels
- Activate enzymatic pathways
Define motoneuron
A motor neuron that innervates muscles
What is the transmitter released by motoneurons?
Acetylcholine
What are 4 attributes of a stimulus?
1) Modality
2) Intensity
3) Location
4) Duration
What are the 4 types of mechanoreceptors that convey touch?
1) Meissner’s corpuscle
2) Merkel cells
3) Pacinian corpuscle
4) Ruffini endings
What is special about Meissner’s corpuscle and Merkel cells?
- Closer to surface
- Finer discrimination
- Smaller receptive field
What is special about Pacinian corpuscle and Ruffini endings?
- Courser discrimination
- Larger receptive field
- Further away from surface
Which touch mechanoreceptors are rapidly adapting and which are slowly adapting?
Rapidly adapting – Merkel cells and Ruffini endings
Slowly adapting – Meissner’s corpuscle and Pacinian corpuscle
Define proprioception
Knowing where your body is in space
What kind of fibres control proprioception?
Large diameter myelinated sensory fibres
What are muscle spindles?
Specialized sensory organs
What 3 structures make up muscle spindles?
1) Intrafusal muscle fibres
2) Ia sensory fibres
3) Group 2 sensory fibres
What is the function of Ia sensory fibres in muscle spindles?
Sensitive to muscle stretch (change in length)
What is the function of group 2 sensory fibres?
Convey static length of muscle
What innervates intrafusal muscle fibres?
Gamma-motoneurons
What is the function of gamma motoneurons?
Regulate spindle length so spindles stay responsive for a range of muscle lengths
What would happen if a muscle body was shortened by alpha motoneurons activation?
Spindle would go slack and Ia fibres would be unresponsive
What is the benefit to activating alpha and gamma motoneurons together?
Keeps spindles responsive
What does the dorsal column system mediate?
Fine touch and proprioception
What does the dorsal column system convey and from where?
Afferent info from large diameter afferent myelinated sensory fibres
What 2 sections are found in the parietal lobe?
1) Postcentral gyrus
2) Parietal association cortex
Where is the postcentral gyrus found?
Immediately behind central sulcus
What is the postcentral gyrus?
Primary sensory cortex
Where is the sensory homunculus found?
Across the postcentral gyrus
What is the parietal association cortex responsible for?
Awareness of body and environment
What is pain?
A perception, not a sensation
When is pain felt?
In the absence of activation of nociceptors
Define nociceptor
Sensory receptor that when activated, pain would normally be perceived
What are 2 examples of what can produce pain?
1) Tissue injury
2) Disturbed central sensory transmission
Define paraesthesia
Abnormal sensation (ex: burning, pricking, tingling) sometimes due to “central” pain syndrome following a stroke
Define phantom limb
Sensation that an amputated limb is still present, often with painful paraesthesia
Define causalgia
Burning pain following nerve damage that persists long after tissue has healed
Define allodynia/hyperalgesia
A non-painful stimulus becomes painful
What are 3 immediate effects of pain?
1) Local burn
2) APs in sensory fibres
3) Reddening, swelling
What are 2 medium effects of pain (soon after immediate effects)?
1) Active compounds released from sensory nerves cause release of histamine and other substances
2) Flare – further reddening and hyperalgesia
What are 2 long-term effects of pain?
1) Secondary hyperalgesia due to receptor sensitization and changes in CNS transmission
2) Pain sensation lingers beyond tissue damage
What is nociception mediated by?
Unmyelinated or small diameter myelinated sensory fibres
Describe the gate theory of pain transmission
Activity in non-nociceptive afferents activates inhibitory interneurons that inhibit ascending spinothalmic tract neurons and decrease transmission through the nociceptive pathway
What can cause allodynia?
Loss or disruption of large diameter fibres
What happens when the inhibitory interneuron is not activated in the gate theory of pain transmission?
The 2nd order (ascending) spinothalmic tract neuron becomes more active
Describe the endogenous opioid system
Stimulation around the cerebral aqueduct produces long lasting pain reduction
What causes referred pain (perception of pain in a location other than the site of origin)?
Nociceptive afferents from viscera enter spinal cord at the same spinal segment as nociceptive afferents from skin/muscle/joints
What are 7 strategies for managing pain?
1) Deliver anesthetic to avoid unwanted sites of action
2) Tailor the treatment to the pain
3) Target peripheral sensitization
4) Use Gate theory
5) Activate endogenous opioid system
6) Recognize potential “central pain”
7) Try to prevent pain rather than treat it
What are the 5 special senses?
1) Olfaction (smell)
2) Vision
3) Taste
4) Hearing/audition
5) Vestibular function
What sensory receptor does olfaction use?
CN 1, olfactory nerve
What sensory receptor does vision use?
CN 2, optic nerve
What sensory receptor does taste use?
- CN 7, facial nerve – lateral border and anterior 2/3 of tongue
- CN 9, glossopharyngeal nerve (posterior 1/3 of tongue)
What sensory receptor does hearing use?
CN 8, vestibulocochlear
What sensory receptor does vestibular function use?
CN 8, vestibulocochlear
Define myopia
Nearsightedness
What causes myopia?
Eyeball too long or lens too strong
What corrects myopia?
Concave )( lenses
Define hyperopia
Farsightedness
What causes hyperopia?
Eyeball too short or lens too weak
What corrects hyperopia?
Convex () lenses
Define presbyopia
Loss of lens accommodation after age 40 (longer focal distance)
What corrects presbyopia?
Reading glasses or bi/trifocals for those with myopia corrective lenses
What is the function of the external ear?
Funneling/focusing of sound waves
What is the function of the middle ear?
Mechanical conversion of sound waves to pressure waves
What is the function of the inner ear?
Pressure waves converted to neural signal
What is the function of the cochlea?
Changes pressure waves to vibrations of the basilar membrane
What are the mechanoreceptors of the ear?
Organ of Corti hair cells
How are organ of Cortia hair cells activated?
By the movement of the basilar membrane
What can lead to irreversible hearing loss?
Overstimulation of hair cells
- Too high sound levels
- Some drugs that are toxic to receptor cells
Define conductive deafness
When there is a failure in the transmission of the sound wave in the middle or inner ear
What are 2 examples of causes of conductive deafness?
1) Bone calcification
2) Basilar membrane damage
Define central deafness
When there is damage to the neural pathways such as the cochlear nerve, brainstem, or cortex via lesion or disease
What causes acoustic neuroma and what does it result in?
- Caused by tumor growing around CN 8
- Results in hearing loss and vestibular dysfunction symptoms
What are the semicircular canals?
3 canals at right angles to each other
What do the semicircular canals detect?
Rotational and angular acceleration or deceleration of the head
How do the semicircular canals detect rotation?
Through movement of fluid in canal
- Movement is detected by hair cells
- Fluid stays stationary while head rotates
What are the 2 otolith organs?
Utricle and saccule
What do the otolith organs detect?
The position of head relative to gravity
What are 3 functions of the vestibular system?
1) Keeps us upright
2) Tells us where we are relative to gravity
3) Senses acceleration and spinning
What structures of the body does the vestibular system effect?
- Muscles of body and neck
- Eye movements
Define vertigo
Dizziness; sensation of spinning
What are 2 examples of causes of vertigo?
1) Inappropriate activation of semicircular canal hair cells
2) Imbalance between the 2 sides
Define nystagmus
Rhythmic vertical or horizontal eye movements triggered by vestibular stimulus
What are 2 examples of causes of nystagmus?
1) Normal response (after spinning)
2) Spontaneously as a sign of underlying neuropathology (episodes of vertigo)
What are rods specialized for?
Capturing light
What are rods the primary photoreceptors for?
Conveying vision in dim/dark conditions
What are the 3 types of cones?
1) Red
2) Blue
3) Green
What is needed for an image to be sharp?
It must be focused on the retina
When do images appear blurred?
When they come into focus ahead of or behind the retina
Define glaucoma
Increased internal pressure in the eye
Define cataracts
Clouding of normally clear lens, resulting in blurred or distorted vision
Define dry eye
Not enough tears, or tears of the wrong composition
Define colour blindness
Usually poor red and green discrimination
What is the cause of cataracts?
Cause is unknown
What is the auditory pathway?
- Cochlea
- CN 8
- Brainstem nuclei of contralateral side
- Auditory cortex (temporal lobe)
