[14.5] control of heart rate Flashcards
what does the autonomic nervous system control?
involuntary activities of internal muscles and glands
what are the 2 subdivisions of the ANS?
- sympathetic nervous system
- parasympathetic nervous system
what does the sympathetic nervous system do?
- stimulates effectors so speeds up any activity
- helps us cope with stressful situations by heightening awareness and preparing us for activity (fight or flight response)
what does the parasympathetic nervous system do?
- inhibits effectors so slows down any activity
- controls activities in normal resting conditions
- wants to conserve energy and replenish body’s reserves
in what way are the actions of the sympathetic and parasympathetic nervous systems antagonistic?
- normally oppose one another
- if one system contracts a muscle, the other relaxes it
- activities of internal glands and muscles are regulated by a balance of the two systems
describe the muscle of the heart
- known as cardiac muscle
- myogenic (contraction is initiated from within muscle itself)
what 4 features of the heart that are involved in heart rate?
- sinoatrial node (SAN)
- atrioventricular node (AVN)
- purkyne fibres (PFs)
- bundles of his (BoH)
what is the SAN and where is it found?
cluster of neurons embedded in wall of right atrium (top left corner of RA)
why is the SAN known as the pacemaker?
has a basic rhythm of stimulation that determines the beat of the heart
what does the SAN do?
sends a wave of depolarisation across both atria, causing them to contract (systole)
why does the SAN’s wave not cross to the ventricles?
there is a layer of non-conductive tissue (atrioventricular septum) that prevents this
where is the AVN?
bottom right corner of RA, between the atria
what does the AVN do?
- picks up wave of excitation
- brief pause
- conveys a wave of electrical excitations between the ventricles along PFs which make up BoH
what are the BoH and where are they found?
collection of neurons in the septum
what is the role of the BoH?
conducts wave through atrioventricular septum to base of ventricles, where they branch into PF
what are PFs and where are they found?
neurons in muscle wall at base of ventricles
what is the role of the PFs?
- wave of excitation is released from purkyne tissue
- causes ventricles to contract from base of heart upwards, forcing blood in that direction
what are changes to heart rate controlled by?
region of brain called medulla oblongata
what 2 coordinators in the medulla oblongata control heart rate?
- cardio-acceleratory centre
- cardio-inhibitory centre
what does the cardio-acceleratory centre do?
sends impulses to SAN via sympathetic motor neurons
what does the cardio-inhibitory centre do?
sends impulses to SAN via parasympathetic motor neurons
what 2 receptors control heart rate?
- chemoreceptors
- pressure receptors
what do chemoreceptors do?
- detect changes in blood pH due to excess production of carbon dioxide from aerobic respiration
- pH becomes more acidic so is lower
- increased frequency of impulses to centres medulla oblongata
where are chemoreceptors and pressure receptors found?
aortic and carotid bodies (clumps of cells in walls of aorta and carotid arteries)
what do pressure receptors do?
- detect changes in blood pressure
- sends more impulses to centres in medulla oblongata based on this
why is having too high or low blood pressure bad?
- high = damage to tissues and cells
- low = interrupts delivery of blood to parts of body
