Physiology Flashcards
What is the length constant? How can it be increased?
- length constant (lambda) is the length a passive process can be spread before it diminished to 0.
- increase axon diameter
- myelin sheaths
What is the most common excitatory and inhibitory NT?
- excitatory: glutamate (cation, Na+ channels)
- inhibitory: GABA/glycine (anion, Cl-)
Describe the responses of ACh in the nervous system (ionotropic, metabotropic).
- ionotropic (direct, fast response) - binds Na/K channels
- metabotropic (indirect, slow) - binds GPCR, then M-type K channels
Describe the concept of [neuronal] adaptation.
Describes whether sensory units change their firing velocity
- in response to stimuli of changing intensity
- not at all (constant)
Describe the concept of receptive field.
The target territory from which a sensory unit can be excited. Inverse to sensory acuity.
Name the sensory neurones, their relative conduction velocity (e.g., fastest, 2nd, 3rd, slowest) and which laminae they synapse in.
- A[alpha]: fastest; proprioception; laminae VII - IX
- A[beta]: 2nd; mechanoreceptors; laminae III - VI
- A[delta]: 3rd; pain / temp; laminae I-II
- C: slowest; pain / temp / itch; laminae I-II
Describe the concept of lateral inhibition.
Active sensory neurones inhibit their neighbours via inhibitory interneurones.
This sharpens stimulus perception.
Name the features associated with the Brodmann areas.
- cutaneous mechanoreceptors
- joint afferents, Golgi tendon organs, deep tissues
3a. proprioceptors
3b. cutaneous receptors, touch, texture, shape, stimulus size
Describe the general structure of a central pattern generator (CPG).
- Strategy [neocortex, BG]
- Tactics [motor cortex, cerebellum; to lateral descending tract]; controls voluntary movement of distal musculature and discrete skilled movement
- Execution [brainstem, spinal cord, to ventromedial tract]; controls posture and locomotion
Define the motor unit and the motor neurone pool.
Unit - an alpha MN and all the skeletal muscle it innervates
Pool - collection of alpha MNs that innervate a single muscle
What is the function of gamma MNs?
yMNs innervate the motor spindle - a sensory organ within muscle
Describe the 3 main types of muscle.
- type I: slow oxidative; fatigue resistant and rich in myoglobin
- type IIa: oxidative phosphorylation, fast contraction, fatigue resistant
- type IIx: glycosis, fast contraction, not fatigue resistant
What is the Henneman principal?
Susceptibility of an alpha MN to discharge APs is a function of its size; smaller units have a lower threshold to fatigue.
Describe the myotatic reflex.
- skeletal muscle is pulled
- muscle spindle (yMN) registers change in length
- monosynaptic reflex arc ensues
What is the purpose of assessing reflexes? How may they be enhanced clinically?
- assesses functional integrity of the spinal cord at specific levels
- Jendressik maneouvre
Describe how the hair cell produces a signal.
- cell body releases glutamate onto efferent nerve endings
- cilia tip links gate the TMC1 channel, opening with tilt
- hair cell K+ current is INWARD (endolymph conc. is high)
- thus mutations to K channels can cause deafness
- prestin changes cell length
Describe how the vestibular system produces a signal.
- otoconia sit on top of the otolithic membrane
- cupula contains stereocilia
- changes in orientation moves cupula and stereocilia, causing depolarisation
Name and describe the three main vestibular reflexes.
- vestibulocular: keep eyes still in space when head moves
- vestibulocolic: keeps head still/on a level plane when walking
- vestibulospinal: adjust posture for rapid changes in position.
Describe the organisation of cells in the LGN (visual pathway).
- M cells (movement): layers 1-2 of LGN (-> IVCa of PVC)
- P cells (colour/shape): layers 3-6 of LGN (-> IVCB of PVC)
- K cells (colour, ocular dominance) (-> II + III in PVC)
Define sleep and REM.
- sleep is a normal, recurring, reversible state, with loss of ability to response to the external environment
- REM sleep occurs mainly at the end of the night. there is marked muscle atonia (except for the diaphragm and extraocular muscles).
- REM sleep is most likely useful for early brain development [neonates sleep 15hr/day 50% of which is REM, down to 27% in future sleep]
How much time is spent in NREM sleep in young adulthood? What physiological changes occur in this time?
- 75% of sleep, most important type of sleep
- synchronised rhythmic EEG activity, partial muscle relaxation
- decreased cerebral blood flow, HR, BP, TV
- some non-narrative images
Describe the three critical responses that occur with sleep onset.
- homeostatic: the longer you are awake, the sleepier you become
- emotional (e.g., difficult to fall asleep when excited)
- Circadian rhythm: adults are most sleepy at 2pm and 3/4am. lasts 25hr
