Senses and Perceptions Flashcards
what are the main pieces of information needed to know about a sense?
what is it, how big is it, how long and where
what do specific sensory receptors do?
convert a stimulus into an electrical action potential and specific sensory pathways help transmit the information
in a sensory nerve cell what is released once the action potential reaches the CNS?
glutamate which activates the sensory neurons in the pathway
what is the structure of a sensory nerve cell?
receptor, axon and cell body
what are the different types of stimuli?
mechanical, thermal, noxious, chemical, light, sound, limb position, blood pressure
what are the different types of receptor?
mechanoreceptor, thermoreceptor, nociceptor, chemoreceptor, photoreceptor, proprioreceptor and baroreceptor
what are the different sensations?
touch, hot/cold, pain, taste/smell, sight/vision, hearing, spatial awareness
what does it mean if a receptor is modality specific
it only responds to a certain type of stimulus (vision, touch, pain etc.)
what is the transduction of a stimulus?
change to an electrical impulse
what are the stimulus properties?
quality, intensity, duration and location
what does coding of stimulus properties allow?
allows you to get a sense of the stimuli you get
what defines a neurons receptive field?
the distribution of the nerve endings (receptors) on the end of peripheral nerve branches
what do peripheral branches of the same axon do?
encapsulate a region of skin and if a stimulus falls into the region the neuron can generate a signal
why do receptor fields overlap?
for maximal coverage of sensation to skin regions
what happens to the receptor fields the further from the core?
the smaller they are and the greater degree of overlapping (e.g. more overlapping in fingers than upper arm)
what happens to the receptor fields if you move more proximally?
they are much larger and don’t overlap as much
what is two point discrimination?
the ability to discern two separate mechanical stimuli; a measure of spatial resolution and an indicative of receptive field size
what is the density of sensory input of small receptor fields?
high density of sensory input
what happens if a stimulus is applied in overlapping fields?
generation of two stimulus from two points
what happens if two stimuli are applied within the same receptor field?
the generation of action potentials in one sensory neuron which is perceived as being a single stimulus
comment on the receptor density around the mouth
there is a high density of receptors
what happens once a stimulus acts on an axon?
change in receptor membrane permeability - influx of cations - depolarisation: receptor potential - action potential
what happens once an action potential is generated?
it is converted centrally into CNS to innervate sensory pathways
what causes depolarisation?
molecular or ionic basis
what are the 2 mechanisms for signal transduction?
mechanoreceptors and chemoreceptors
describe mechanoreceptor activation
the pores are usually closed, they are joined to subellular structures that are bound to the membrane, a force is applied down on the membrane which pulls the subcellular structures (flexion of the cell membrane) and opens the pore
what is an ionotropic channel
direct passage of ions into and out of the cell
how are G-protein coupled channels activated?
the receptor ending is distal to the pore itself and the whole protein is interconnected, when the signal comes phosphorylation occurs which opes the channel
what chemoreceptor channel is easier to deactivate and what does this mean?
ionotropic are easier to deactivate meaning that the G-protein ones are more likely to stay on for longer
what are the two different types of chemoreceptor channel?
ionotropic and G-protein coupled
what is stimulus intensity coded by?
frequency of AP discharge, numbers of neurons activated
what does increased stimulus intensity mean in terms of AP frequency?
increased AP frequency
what is stimulus duration coded by?
duration of AP firing
what allows us to differentiate between different signals
the fact that different receptors have different thresholds
what type of pain does a slow adapting neuron give?
dull pain
what type of neuron fibre is slow adapting?
slow adapting C fibres
what type of pain does a rapidly adapting neuron give?
sharp pain
what type of neuron is a rapidly adapting neuron?
rapidly adapting nociceptors
what are the two different location types?
cortical and topographical
what is cortical representation
receptor fields lead to recruitment of cortical circuits in the brain region
what is topographical representation?
body map corresponding to particular regions in the brain
what are receptors
peripheral endings of sensory neurons
where do axons of sensory neurons go?
they enter the CNS and connect to other neurons
what are neurons with the same functions grouped into?
bundles or pathways
what are primary receiving areas?
areas in the brain where the neural pathways terminate
where do pain fibres recruit their circuits from?
outer parts of the brain
where do touch fibres recruit their circuits from?
inner parts of the brain
what does a peripheral nerve do?
innervate specific body regions
what axons does a peripheral nerve contain?
some contain only sensory axons and others also have motor axons
where is the brachial plexus and what does it do?
found in the shoulder and is responsible for the innervation of the upper limb
what are the branches of the brachial plexus?
axillar, musculocutaneous, radial, ulnar, median
where is the epineurium and what does it do?
it touches the outer connective tissue and allows mechanical protection
where is the perineurium?
surrounding the axons inside the fascicle
what are the different peripheral nerves?
A alpha, A beta, A delta and C
describe the A alpha nerve
thickest, conduction of AP happens really quickly
what does the A alpha nerve do?
innervate muscle and relay sensory information from muscles about muscle tension
describe the A beta nerve
the myelin sheath is a bit thinner so the conduction is not as quick as A alpha
what is the A beta nerve involved in?
perception of mechanosensation of the skin
describe the A delta nerve
small axon diameter, thinnest myelination so very slow conduction
what does the A delta nerve do?
convey dull aching pain
describe the C nerve
no myelin sheath, small diameter, very slow transduction
what does the C nerve do?
convey dull aching pain
where do sensory axons enter the CNS?
via dorsal roots
where are the cell bodies of sensory axons located?
in the dorsal root ganglia
where do motor axons exit the CNS?
via the ventral roots
what parts of the trigeminal nerve are for sensory functions only?
ophthalmic branch and maxillary branch
what part of the trigeminal nerve has sensory and motor functions?
mandibular branch
what sense does the mechanoreception pathway serve?
touch
what sense does the nociception pathway serve?
pain
what neurons compose the sensory neuron pathway?
3 interconnected neurons - primary sensory, secondary sensory and tertiary sensory
where does the primary sensory neuron in the sensory pathway sit?
it sits in the periphery but projects into the CNS
describe the mechanoreception (somatic) pathway that the neurons take on the way to brain
primary sensory neuron sends a side branch to the dorsal horn but the axon continues up and terminates in the brainstem - secondary sensory neuron projects to the side before projecting to thalamus where it synapses and connects to third sensory neuron
what is the difference between somatic mechanoreception and mechanoreception in the trigeminal nerve
with the trigeminal nerve, the primary nerve goes straight to the brainstem and not the spinal cord
what is the medial lemniscal pathway?
the dorsal column that the primary neuron travels up towards the brainstem
what is the trigeminothalamic pathway?
the pathway that the trigeminal nerve takes to get to the brainstem
describe the nociception (somatic) pathway that the nerve takes on the way to the brain
primary sensory neuron goes straight to spinal cord and synapses to the secondary neuron which goes to the brain and synapses in the thalamus to the third neuron
what is the spinothalamic pathway?
the pathway that the somatic nociception neurons follow - with the first synapse being in the spinal cord rather than the brainstem
what is the difference between somatic nociception and trigeminal nerve nociception?
with trigeminal nerve nociception the primary neuron goes straight to the brainstem where it synpases with the secondary neuron
what is the difference between the posterior and the anterior trigeminothalamic pathways?
the anterior is for nociception (perception of pain on the face) and the posterior is for mechanoreception (touch)
what is the sensory homunculus?
the brains perceptions of senses
why is the brain image of senses distorted?
the more sensory neurons that supply an area, the more brain space allocated in the cortex, areas with high density of receptors are represented more widely in the cortex
what is stereognosis?
the ability to recognise objects by the feel alone
what does stereognosis involve
requires a 3D mental image and the need to compare with previous experiences
