Week 1: Tuesday Flashcards
what does the autonomic nervous system do
- innervates viscera - unconscious control
- mediates homeostasis
- visceral sensory and visceral motor neurons that function in visceral reflexes
- takes 2 motor neurons in series to innervate organs
- parasympathetic and sympathetic
- dual innervation of organs
what is homeostasis
maintenace of critical physiological parameters of the internal environment within the limits comparible with life
what are the functions of the parasympathetic divistion
- conserves and restores energy reserves (anabolic)
- promotes digestion, absorption, and storage
- protective - miosis - contriction of pupil
- rest and digest
where does the parasympathetic nervous system originate
- from a restricted part of brain and spinal cord (cranial-sacral)
- has own set of peripheral ganglia
what are the functions of the sympathetic division
- prepares body for action
- mobilizes energy stores (catabolic)
- mediates responses to stress
- fight or flight
where does the sympathetic nervous system originate
- from restricted part of spinal cord (thoracolumbar)
- has own set of peripheral ganglia
what is dual innervation
- many organs have a sympathetic and a parasympathetic innervation (one excites and other inhibits)
- some organs don’t (skin, sweat glands, arrector pili muscle, vascular smooth muscle, adrenal gland and adipose tissue) - only sympathetic
resting membrane potential
- net negative charge inside the cell membrane
- ion pumps maintain concentration gradient
what are contractile cardiac cells
- generate force
- not autorhythmic, but do conduct action potentials
what are autorhythmic cardiac cells
- provide a pathway for spreading excitation through the heart (pacemaker cells, conduction fibers)
- don’t generate much contractile force
what are fast-response action potentials
- contractile cardiac cells
- Na+ driven (fast Na+ channels)
what are slow-response action potentials
- autorhythmic cardiac cells
- Ca2+ driven (L-type Ca2+ channels)
- pacemaker potentials lead to spontanous action potentials
- due to hyperpolarization-activated cyclic nuceotide-gated (HCN) channels (funny current) and T-type calcium channels
what are the 3 steps in action potentials in contractile cardiac cells
- rapid depolarization
- plateau
- repolarization
what are the 6 important membrane currents in contractile cardiac cells
- INa: sodium current
- ICa: L-type Ca current
- Ito: transient outward K current
- IKr: rapidly activated delayed rectifying K current
- IKs: slowly activating delayed rectifying K current
- IK1: inward rectifying K current
what membrane currents are in phase 4 of autorhythmic cells
- If: funny current, HCN channel
- ICa2+ (T): T-type voltage gated channel
what membrane currents are in phase 0 of autorhythmic cells
ICa2+ (L): L-type voltage gated channel
what phases are absent in autorhythmic cells
phase 1 and 2
what membrane currents are in phase 3 of autorhythic cells
IK: potassium current, dlayed rectifier potassium
what membrane current is important for parasympathetic regulation of HR
IKACh: rectifying potassium current
what happens at intercalated disks
- desmosomes provide structural strength
- cells linked by gap junctions
what do gap junctions allow the cell to behave as
a functional syncytium
during a heartbeat where is the first action potential initiated
the SA node
what is the AV node
the only pathway through which the signal can pass between the atria and ventricles
slight delay from SA to AV node
why is there a delay between the SA and AV node
reduction of gap junctions and reduction of diamter of cells
what does the delay allow
allows the heart to be “topped off”by the atrial contractions
what does the AV node provide
unidirectional passage of action potential through the atria to ventricles
what can the AV node act as if needed
an auxiliary pacemaker
if any pacemaker/conduction cell can initiate its own action potential, then why is the SA node the heart’s pacemaker
because of the hierarchy of normal automaticity (inate firing rate) and the concept of overdrive suppression
what is tachycardia
abnormally high heart rate (based on site of origin)
what is bradycardia
abnormally low heart rate
what is sick sinus syndrome
dysfunction of the SA node
what is afterdepolarizations
depolarizations during the refractory period
* eary afterdepolarizations (phase 2-3)
* delayed afterdepolarizations (phase 4)
what is a block
a conduction pathway is blocked from transmitting the action potential
what is a block caused by
- trauma
- toxins
- infections
- heart defects
what is a third degree block
- a complete block
- no atrial action potentials conducted to ventricles
what is a second degree block and the two types
- some atrial action potentials conducted to ventricles
- type one: time from atria to ventricular depolarization gets longer and skip happens
- type two: delay in communication but delayis random
what is a first degree block
- all atrial action potential transmitted to ventricles
- delay at the AV node is abnormally long
what is reentry
abnormal signaling through the heart
what is the most common mechanism of arrythmias
reentry
what is reentry caused by
a block and/or slowed conduction
how can reentry be defined (two ways)
- anatomically defined
- functionally defined
what is an electrocardiogram
external measure of electrical activity of the heart
what is the body
EKG
a conductor
the length and amplitude of waves depend on what two factors
- size of the sum of potentials
- synchronicity of potentials
what is an electrical dipole
a pair of electrical charges separated by a distance
ex: flashlight battery (+ and - end)
what happens when a dipole is placed into a conductive medium
ionic currents will flow through medium and relative differences in polarity can be detected
what does the P wave mean
atrial depolarization
what does the Q wave mean
early ventricular depolarization
what does the R wave mean
ventricular depolarization
due to left side bigger than right
what does the S wave mean
late ventricular depolarization
what does thr T wave mean
ventricular repolarization
what is Einthoven’s Law
any two of the three bipolar limb leads determine the third one
* lead 1 + lead 3 = lead 2
