Control of Heart Rate Flashcards
What does autonomic mean?
Self-governing
What does the autonominc nervous system controls?
The involutonaty (subscious) activities of internal muscles and glands
What are the two divisions of autonomic nervous system?
- Sympathetic nervous sytem
- Parasympathetic nervous sytem
What is the sympathetic nervous system?
- Stimulates effectors and speeds up anxiety
- It acts rather like an emergency controller
- It controlls effectors when we execise stimultaneous or experience powerful emotion
- In other words, it helps us to cope with stressful situations by heightening our awareness and preparing us for activity (fight or flight response)
What is the parasympathetic nervous sytem?
- In general it inhibts effectors and slow down any activity
- It controls activities under normal resting conditions
- It is concerned with conversing energy and replenishing body’s reserves
How is sympathetic and parasympathetic nervous systems antagonistic?
They oppose each other
one system contracts a muscle and other releaxes
The activities of internal glands and muscles therefore regulated by a balance of two systems
e.g control of heart rate
What is caradiac muscle?
Muscle of heart
Why is the caradiac muscleis myogenic?
The contraction is initiated from the muscle itself rather than by nervous impulses from outside (neurogenic) as it with case with other muscles
Where is the SAN?
In the right atrium
What is SAN 9sinoartial node)
It is from here that inital stimulus for contraction originates
It has a basic rhythm of stimulation that determine the beat of heart
This is why it is referred to a pace maker
Sequence of events that control heart rate
- A wave of electrical excitation spreads from sinortial node across both atria causing them to contract
- A layer of non-conductive tissue (atrioventricular septum) prevents the wave crossing to ventricles
- Wave of excitation leads to a second group of cells AVn
- AVN conveys a wave of electrical excitiation between ventricles along purkyne tissue
- Bundle of His conducts a wave through AV septum to base of ventricles where bundle branches into smaller fibres of purkyne tissue
- A wave of excitation released from purkyne tissue causing the ventricles to contract quickly from bottom of heart and upwards
What does AVN stand for?
Atrioventricular node lies between atria
What is purkyne tissue?
Collectively makes up structure of bundle of His
What is the resting heart rate of a typical adult human?
70 beats per minute
however essential this rate altered to meet varying demands of oxygen e.g exercise the resting heart rate more than double
What is medulla oblongata?
Changes to hert rate is controleld by this part of region in the brain
What are the two centres in the medulla oblongata that concerned with heart rate?
- A centre that icnreases heart rate linked with sinoartial node by sympathetic nervous sytem
- A centre that decreases heart rate linked with sinoartial node linked with parasympathetic system
How do these centres in the medulla oblongata depend upon?
Nerve impulses which recieve two types of receptor which respond to stimuli or either chemical or pressure changes in the blood
Where are chemoreceptors found?
In the wall of carotid arteries (arteries serve the brain)
Whar are chemoreceptors sensitive to?
Changes to the blood as a result of changes in carbon dioxide concenrration insolution
carbon dioxide forms an acid therefore lowers pH levels
Control by chemoreceptors:
- Increased msucular/metabolic acitivtiy
- More carbon dioxide produced in tissue from icnreased respiration
- Blood pH is lowered
- Chemical receptors in carotid artieres increase frequency of impulses to medulla oblongata
- Centrein medulla oblongata speeds heart rate and increases frequency of impulses to SA node via sympathetic nervous system
- SA node increases heart rate
- Increased blood flowremovescarbon dioxide faster
- Carbon dioxide concentration returns to normal
What happens when blood pressure is higher than normal?
- Pressure receptors transmit more nervous impulses to centre of medulla oblongata to decrease heart rate
- This centre sends impulses via parasympathetic nervous sytem to sinoartial node of heart
- Leads to decrease rate of heart beats
What happens when blood pressure is lower than normal
- Pressure receptors transmit more nervous impulses to the centre of medulla oblongata that increase heart rate
- This centre sneds impulses via sympathetic nervous system to sinoartial node which increases heart beat
