Exam Revision Flashcards
Name the 3 receptor types.
- Free nerve endings
- Encapsulated receptors
- Specialise receptors
What 4 steps are necessary for a signal to be sent from a receptor to the CNS?
- Stimulation of the receptor
- Transduction of stimulus - energy converted to graded potential
- generation of nerve impulse - if graded > threshold -> AP
- Integration of sensory input - specific regions of cortex
What are the characteristics of free nerve endings and name 3 different receptors which are free nerve ending receptors.
- Bare dendrites, no structural specialisation
- Pain
- Thermal
- Touch
What are the characteristics of encapsulated receptors, and name 1 receptor of this type and what does it detect.
- Dendrites enclosed in connective tissue capsule
- Capsules enhance specificity or sensitivity of the receptor
- Pacini corpuscles - deep pressure and vibrations
Name 2 examples of specialised receptors.
- gustatory receptors
- photoreceptors
What do specialised receptors synapse with?
1st order neurons.
Name two types of graded potential.
- generator potential
- receptor potential
Where do generator potentials occur?
- free nerve endings
- encapsulated receptors
Where do receptor potentials occur?
- specialised receptor cells - eg photoreceptor cells
What happens if free nerve ending receptors or encapsulated receptors are stimulated?
If graded potential > threshold then an action potential is generated in the 1st order neuron
What happens if a specialised receptor is stimulated?
- If receptor potential > threshold then pre-synaptic membrane depolarises.
- VOC open, Ca2+ enter, neurotransmitter release
- diffuses across cleft
- Neurotransmitter binds to receptors causing ligand gated sodium channels to open causing depolarisation of post-synaptic membrane
- if enough channels open -> AP in 1st order neuron
What is normal membrane potential ?
- 70mV
What is threshold potential ?
About 50 mV
What is the approximate size of an epsp?
1mV
How can graded potentials be summated ?
- temporally
- spacially
How does adaptation of receptors occur?
Amplitude of generator/receptor potential decreases with maintained constant stimulus.
What effect does adaptation to stimulus have on action potentials in 1st order neurons.
Decreases their frequency
What effect does adaptation to a stimulus have on the perception of that stimulus?
Perception of sensation fades even though stimulus continues.
Do all receptors adapt at the same speed?
No some adapt more quickly than others.
Name a receptor that adapts quickly and give an example of that occuring.
- temperature sensor
- temperature of bath water
Where do 1st order neurons relay messages from/to?
From receptor to brain or spinal cord
Where do 2nd order neurons relay impulses from/to?
From brain stem or spinal cord to thalamus
What happens to 2nd order neurons before reaching the thalamus?
They decussate before ascending to ventral nucleus of the thalamus
Where do 3rd order neurones go from/to?
From thalamus to primary somatosensory area of the cortex
Somatosensory information ascends to the CNS via 3 pathways, name these.
- posterior column-medial pathway
- spinothalamic pathway
- trigeminthalamic pathway
What sensory information is carried by the posterior column-medial pathway?
- touch
- pressure
- vibration
What sensory information ascends to the CNS via the spinogeminal pathway?
- pain
- temperature
What sensory information ascends to the CNS via the trigeminothalamic pathway?
Most somatic sensations from the face, pain, touch etc.
What are the 5 consequences of haemorrage on heart?
- decreased blood volume
- decreased venous return
- decreased stroke volume
- decreased cardiac output
- decreased arterial pressure
How does the heart compensate for haemorrhage?
- reduced firing of baroreceptors
- detected via. Cardiovascular centre in medulla
- decreased parasympathetic to heart
- increased sympathetic to heart, veins and arterioles.
What is the effect of increased sympathetic activity to the heart?
- increased contractility
- increased stroke volume
- increased cardiac output
