Week 3: Heart Beat Control Flashcards
There are other examples of CPG other than
locomotion in lamprey like control the heartbeat of leeches
The heartbeat control system of
medicinal leech has been studied intensively for over three decades
The leech has two tubular hearts running the
length of the body and moving blood through its closed circulatory system
The beating pattern of leeches (beat period of 4 to 10s) is asymmetric with one heart and the other… (2)
with one heart generating high systolic pressure through a front-directed peristaltic wave (peristaltic coordination mode) along its length]
, and the other generating low systolic pressure through near-synchronous constriction (synchronous coordination mode) along its length.
The peristaltic heart moves
blood forward,
As compared to peristaltic heart, the synchronous heart has been hypothesized mainly to
push blood into the peripheral circulation and supports rearward (towards the back) blood flow
After descriving peristaltic and synchronous
After about 20 – 40 beats (switch period ~100 – 400 s)
the hearts switch roles
The two heart tubes leech has receives which is located in (2)
excitatory input from an ipsilateral member of a pair of segmental heart (HE) motor neurons,
located in each midbody segmental ganglion,
The firing pattern of heart motor neurons (i.e., fictive motor pattern is (2)
one side firing while other side
bilaterally asymmetric, with motor neurons on one side firing with a rear-to-front progression
while those on the other side fire nearly synchronously with appropriate side-to-side coordination of these two firing patterns (they swithc)
The heart motor neurons are controlled and coordinated by the heartbeat CPG through
rhythmic inhibitory drive (period 5-12 s).
Nine pairs of identified segmental heart (HN) interneurons (plus one pair of unidentified pair) compose the
CPG
The core CPG consists of
index (2)
seven pairs of these interneurons located in
the first seven midbody ganglia of the nerve cord and are indexed by ganglion number and body side (HN(L,1) – HN(R,7))
Rhythmic activity in the CGP network is paced by a
highly interconnected timing network consisting of coordination (HN(1) and HN(2) interneurons) and oscillator interneurons (HN(3) and HN(4) interneurons).
The firing pattern of the interneurons (and particularly of the front (HN(3) and
145 HN(4)) and the middle (HN(6) and HN(7)) premotor interneuron) of this core CPG has been
extensively characterized and is also bilaterally asymmetric like that of
147 the heart motor neurons and with appropriate side-to-side coordination.
The asymmetry in firing patterns is not permanent, however; there are regular (every 200-400 s) side-to-side switches in the CGP network
peristaltic and synchronous patterns in the heart interneurons that underlie
the changes in both the motor pattern and the rhythmic constriction patterns of the heart tubes.
These switches in coordination are mediated by the HN(5) switch interneurons in CGP network
which link the timing network to the middle premotor interneurons by bilateral inhibitory connections; only one of this pair of interneurons is rhythmically active at a time the other is silent.
Premotor interneurons and motor neurons on the side of the active switch interneuron are coordinated synchronously, while
those on the on the side of the silent switch interneuron are coordinated peristaltically.
Order of explaining new CPG (15)
- Leech has 2 hearts
- Beating pattern, peristaltic and other synchronous
- Peristaltic heart…
- Synchronous heart ….
- After 20-40 heart beat….(switch)
- Two heart receive excitation from HE motor neurons
- HE firing pattern
- HE controlled via heartbeat CPG through….
- 9 pairs of HN compromise heartbeat CGP
- Core CGP consist of
- Rhythmic activity in CGP network paved by…
- Firing pattern of HN neurons
- Asymmetry not permanent
- Switched in CGP that are mediated by..
- Pre motor interneurons
The heartbeat central pattern generator (CPG) in medicinal leeches controls blood flow
This circuit (2)
within a closed circulatory by programming the constrictions of two parallel heart tubes
This circuit reliably produces a stereotyped fictive pattern of activity and has been extensively characterized.
