Physiology

Question 1

What is the length constant? How can it be increased?

Answer 1

• length constant (lambda) is the length a passive process can be spread before it diminished to 0.
• increase axon diameter
• myelin sheaths

Question 2

What is the most common excitatory and inhibitory NT?

Answer 2

• excitatory: glutamate (cation, Na+ channels)

- inhibitory: GABA/glycine (anion, Cl-)

Question 3

Describe the responses of ACh in the nervous system (ionotropic, metabotropic).

Answer 3

• ionotropic (direct, fast response) - binds Na/K channels

- metabotropic (indirect, slow) - binds GPCR, then M-type K channels

Question 4

Describe the concept of [neuronal] adaptation.

Answer 4

Describes whether sensory units change their firing velocity

• in response to stimuli of changing intensity
• not at all (constant)

Question 5

Describe the concept of receptive field.

Answer 5

The target territory from which a sensory unit can be excited. Inverse to sensory acuity.

Question 6

Name the sensory neurones, their relative conduction velocity (e.g., fastest, 2nd, 3rd, slowest) and which laminae they synapse in.

Answer 6

• 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

Question 7

Describe the concept of lateral inhibition.

Answer 7

Active sensory neurones inhibit their neighbours via inhibitory interneurones.
This sharpens stimulus perception.

Question 8

Name the features associated with the Brodmann areas.

Answer 8

1. cutaneous mechanoreceptors
2. joint afferents, Golgi tendon organs, deep tissues
   3a. proprioceptors
   3b. cutaneous receptors, touch, texture, shape, stimulus size

Question 9

Describe the general structure of a central pattern generator (CPG).

Answer 9

• 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

Question 10

Define the motor unit and the motor neurone pool.

Answer 10

Unit - an alpha MN and all the skeletal muscle it innervates

Pool - collection of alpha MNs that innervate a single muscle

Question 11

What is the function of gamma MNs?

Answer 11

yMNs innervate the motor spindle - a sensory organ within muscle

Question 12

Describe the 3 main types of muscle.

Answer 12

• 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

Question 13

What is the Henneman principal?

Answer 13

Susceptibility of an alpha MN to discharge APs is a function of its size; smaller units have a lower threshold to fatigue.

Question 14

Describe the myotatic reflex.

Answer 14

• skeletal muscle is pulled
• muscle spindle (yMN) registers change in length
• monosynaptic reflex arc ensues

Question 15

What is the purpose of assessing reflexes? How may they be enhanced clinically?

Answer 15

• assesses functional integrity of the spinal cord at specific levels
• Jendressik maneouvre

Question 16

Describe how the hair cell produces a signal.

Answer 16

• 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

Question 17

Describe how the vestibular system produces a signal.

Answer 17

• otoconia sit on top of the otolithic membrane
• cupula contains stereocilia
• changes in orientation moves cupula and stereocilia, causing depolarisation

Question 18

Name and describe the three main vestibular reflexes.

Answer 18

• 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.

Question 19

Describe the organisation of cells in the LGN (visual pathway).

Answer 19

• 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)

Question 20

Define sleep and REM.

Answer 20

• 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]

Question 21

How much time is spent in NREM sleep in young adulthood? What physiological changes occur in this time?

Answer 21

• 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

Question 22

Describe the three critical responses that occur with sleep onset.

Answer 22

• 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