deck_2769174 Flashcards
Define Sensation
Is a conscious or sub-conscious awareness of an external or internal stimulus
Define sensory modalities
The different types of senses that cause a response in receptors
What are the different types of senses?
General somatic- tactile, thermal, pain, proprioceptionGeneral visceral Special senses
Describe sensory receptors
Receptors which are specialised to detect stimuli, usually found throughout the layers of skin. There are many different types of sensory receptors and are often specific to a modality.
What components make up a sensory receptor?
Free nerve endingEncapsulated nerve endingSpecialised cell
What is a sensory quality?
A subdivision of modalitye.g. sweet and sour are qualities of the taste modality
Describe proprioceptors
These are sensory receptors found in muscles and joints which provide an awareness of where our body is in space.
Describe the receptors involved in proprioception
Muscle spindles - info about length of the muscleGolgi tendon organ - measures the tension in the tendons
What is sensory transduction?
The ability of a stimulus to be converted into an action potential and for to travel along to the brain control centres.
Describe the process of signal transduction.
- Stimulus stimulates a receptor and evokes a change in the permeability of the ions in the receptor membrane at the peripheral axon, in proportion to the size of the stimulus. 2. A receptor potential is generated due to ion movement across the membrane3. If the stimulus is great enough, the combination of receptor potentials will reach threshold level and generate an action potential which can propagate along the nerve.
What things determine the strength of an action potential stimulus?
Frequency coding - the rate of action potential stimulus. There will be a greater rate of firing with a greater stimulus. Activation of neighbouring cells can occur with a stronger stimulus.
What are the two different adaptations that receptors have?
Tonic receptorsPhasic receptors
Describe tonic receptors
Slowly adapting receptors which keep firing as long as they are being stimulated by a stimulus
Where do you find tonic receptors?
They are joint receptors and pain receptors
Describe phasic receptors
These rapidly adapting receptos respond maximally and briefly to a stimulus
What kind of receptors are phasic receptors?
Touch receptors
Define sensory acuity
The precision by which a stimulus can be located.
What things determine sensory acuity?
Lateral inhibitionTwo point discriminationSynaptic convergence and divergence
Describe lateral inhibition
Inhibitory neurones will prevent the transmission of action potentials which do not have a maximum stimulus. This means that only maximally stimulated neurones will fire, leading to a sharpening of sensory acuity.
How does lateral inhibition work?
Inhibitory interneurons act on the neurones which have not been stimulated to inhibit the transmission of their action potentials.
Describe two point discrimination
There is a minimum distance that needs to be between two points so that you are able to distinguish between them.
How does two point discrimination vary?
In areas which have a high density of sensory receptors and a small neuronal field (fingers) you are able to distinguish between two points which are closer together compared to an area such as the forearm which has a lower sensory receptor density and larger neuronal field.
Describe synaptic convergence
Several 1st order neurones converge onto a single 2nd order neurone.
What effect does synaptic convergence have?
It decrease sensory acuity
Describe synaptic divergence
A single 1st order neurone divergse to several 2nd order neurones
What effect dose synaptic divergence have?
It amplifies the signal
What is a receptive field?
This is an area where a stimulus will alter the firing of that neurone- the smaller the receptive field, the higher the receptor density
Describe the structure of a receptive field
Found at the end of an axonDetermines where an axon can sense stimuli. Vary on size and densityCan overlap with neighbouring fields
Where do you feel sensation?
In the thalamus- have crude localisation and discrimination of a stimulus- have highly organised projections to the cortex
Describe the somatosensory cortax
Is located at the post central gyrusHave somatotrophic representation - each area of the body is mapped to a specific part of the cortex.
What does the somatosensory cortex do?
It allows for the sharp localisation and recognitions of the different qualities of modalities. Relays information to other cortical and subcortical areas. The choice to respond to a stimulus is taken but the cortical areas.
Define the sensory homunculus
This is a contralateral representation of specific body areas. Each area of the cortex is mapped to a body areas and the relative size of the area depends on the degree of sensory acuity associated with it.
Define perception
The awareness of stimuli and our ability to discriminate between different types of stimuli.
Describe synesthesia
A neurological disorder whereby the stimulation of one sense gives rise to an automatic response from a second sense.
Describe the pathology of shingles
Caused by the varicellar zoster virusPrimary infection causes chicken pox but the virus stays in the dorsal root ganglia and is reactivated to cause shingles
How does shingles cause pain?
Increases the sensitivity of the dorsal root neurones, triggering burning and tingling sensation. The skin of the affected dermatome becomes red and blisters and it is extremely painful.
Why does shingles only affect one or two dermatomes?
The infection is restricted to one or two dorsal root ganglia.
