Senses and Perception Flashcards
what is tactile input
this is the type of mechanical stimulation on the skin
what is the quality of tactile input
the type of touch
what is the magnitude of tactile input
this is how big the input is
what is the duration of tactile input
this is how long and how often the stimulus lasts
where does most bodily innervation go as the first point of entry
the spinal cord
how do we convert a stimulus into an electrical signal
through modality specific sensory receptors
how is information transmitted faithfully to the central nervous system
through modality specific sensory pathways
wat is the first cell involved in the sensation pathway
the sensory neuron
what do sensory neurons do
they relay information from the periphery into the central nervous system
what is the morphology of the sensory neuron
pseudounipolar structure
describe the structure of the sensory neuron
cell body with two axons
first branch is in the periphery and innervates the skin, and a second brnach which projects into the central nervous system
what is found at the end of the peripheral branch of sensory neurons
receptor endings
what is found at the central terminal of sensory neurons
synaptic vesicles, which allow for synaptic release to recruit target neurons in the sensory pathway
list the events of a general stimulus on primary sensory receptors
- stimulus
- receptor endings activated
- action potential generated
- relayed centrally
- neurotransmitter released at central terminal
- recruitment of post synaptic targets
how are stimulus properties coded
according to quality, intensity, duration and location
what are the main stimulus types
mechanical
thermal
noxious
chemical
light
describe the stimulus and receptor for the sensation of touch
mechanical stimulus
mechanoreceptor
describe the stimulus and receptor for the sensation of temperature
thermal stimulus
thermoreceptor
describe the stimulus and receptor for the sensation of pain
noxious stimulus, nociceptor
describe the stimulus and receptor for the sensation of taste and smell
chemical stimulus, chemoreceptor
describe the stimulus and receptor for the sensation of vision
light stimulus
photoreceptor
which receptors are found on free nerve endings
nociceptors
what are the different mechanoreceptors found in the skin
meissners corpuscle
merkel disk
hair follicle receptor
pacinian corpuscle
ruffini ending
what is this
meissners corpuscle
mechanoreceptor in the skin
what is this
merkels disc
a mechanoreceptor found in the skin
what is this
hair follicle receptor
mechanoreceptor found in the skin
what is this
pacinian corpuscle
a mechanoreceptor found in the skin
what is this
ruffini ending
mechanoreceptor found in the skin
what features are found in all sensory neurons
cluster of peripheral nerve branches with its own receptor endings
what is a receptive field
this is the distribution of receptor endings found in each neuron
do receptive fields remain separate
they often overlap to allow for two point discrimination
how large are receptive fields in the periphery
small
how large are receptive fields in the trunk of the body
very large
what is two point discrimination
this is the ability to discern two separate mechanical stimuli
it is a measure of spatial resolution and an indication of the size of the receptive field
describe the temporal sequence of stimulus transduction
- stimulus
- change in receptor membrane permeability
- influx of cations
- depolarisation on the receptor potential
- action potential
what is the resting membrane potential on most cells
-70mV
what are the two subtypes of receptor
ionotropic and g protein coupled
describe the kinetics and modalities of ionotropic receptors
fast kinetics
mechanoreceptors and chemoreceptors
describe the kinetics of g protein coupled receptors
slow kinetics and chemoreceptors
describe signal transduction of ionotropic mechanoreceptors
- there is a lipid bilayer that has been interrupted by an ion channel
- the ion channel is tethered to the membrane by fibrils on the intracellular aspect of the membrane
- when inactive, the channel is closed
- when mechanical stimulus is applied, the deformation of the cell membrane pulls on the underlying fibrils which pulls the fibres away to open the channel
- potassium leaves and sodium enters
describe the signal transduction in ionotropic chemoreceptors
- ion channel is too narrow in the inactive state
- extracellular surface has ligand binding receptor sites
- this becomes active when the ligands bind
- conformational change allows the pore to open
- sodium and potassium can cross over
describe signal transduction in g protein coupled receptors
receptor is more complex as there are many proteins linekd to it.
the ligand binding site changes conformation to cause a response on the ion channel
when inactive, the channel is closed. the specific ligand will bind to the receptor, cause an intracellular signalling cascade, and then the channel can open.
so it is a lot slower because the pathway is more complex than in ionotropic receptors
what is the stimulus property for type of receptor
quality
what is the stimulus property for action potential frequency
magnitude or intensity
what is the stimulus property for number of neurons activated
magnitude or intensity
what is the stimulus property for duration of action potential firing
duration or timing
what is the stimulus property for receptive field
location
what does the quality of the receptor depend on
type of receptor
what does the magnitude of the stimulus depend on
the action potential frequency and the number of neurons that has been activated
what does the duration of the stimulus depend on
duration of the action potentia firing
what does the location of the stimulus depend on
the receptive field
what does an increase in stimulus intensity do to the action potential
increases the action potential frequency
describe the coding of receptive fields
each one is coded by a particular sensory neuron which activates a pathway that prokects and ends in a discrete region in the brain
each one has its own cortical region in the brain
what does the sensory homunculus show
the distinct structures of the cerebral cortex that are responsible for different nerve functions
what are the main principles of receptive fields
size
distribution
density
where is the cortical representation for the brain
the homunculus
what do peripheral nerves contain
axons from two functionally distinct types of nerve cells
what are afferents
sensory neurons
what are efferents
motor neurons
how do axons exit the spinal cord
via the peripheral nerves
what is the function of the epineurium
mechanical protection and support to the neuron
what surrounds the individual fascicles in the neurons
perineurium connective tissue
are unmyelinated axons larger
no
why are there blood vessels within the nerves connective tissue
conduction of action potentials is metabolically demanding and needs blood supply to remove by products and provide oxygen and glucose
describe myelinated axons in the peripheral nervous system
they have a series of schwann cells lined up along the axon, each having a wrapped coating of myelin insulating the axon
describe unmyelinated axons in the peripheral nervous system
encased by schwann cells cytoplasm, but there is no wrapped coating of myelin around the axons
which axon types are myelinated
A alpha
A delta
A beta
which axon types are unmyelinated
C fibres
describe A alpha axons from the skin
thickest axon and thickest myelin sheath
very fast conduction speed of 80-120 metres a second
what are the sensory receptors with A alpha axons
proprioreception in skeletal muscle
describe A beta cells
thick axon and thick myelin sheath
fast conducting speed at 35-75 metres a second
which type of sensory receptors have a beta axons
mechanoreceptors of the skin
describe a delta fibres
thin diameter and a conduction speed of 5-30 metres a second
which type of sensory neurons have A delta fibres
pain and temperature sensation
what is the diameter of A alpha axons
13-20 micrometers
what is the diameter of a beta axons
6-12 micrometers
what is the diameter of a delta fibres
1-5 micrometers
what is the diameter of c fibres
0.2 -1.5 micrometers
what is the speed of c fibres
0.5 - 2 metres a second
which axons are associated with sensation of pain and temperature
A delta and C
what can spinal cord grey matter be divided into
dorsal horn
intermediate horn
ventral horn
what is the target of peripheral nerves
the spinal cord
how many dorsal root ganglia are there
31 pairs
what is the dorsal root
this is the medial portion of the sensory nerve that goes from the root ganglia into the spinal cord
what is the dorsal root made up of
only the centrally projecting axons, no myelin
where do sensory neurons enter the spinal cord
dorsal horn
where are the cell bodies of motor neurons found
the ventral horn of the grey matter
how do motor neurons exit the spinal cord
through ventral roots, to innervate muscle in appropriate regions
can a peripheral nerve carry both afferent and efferent information
yes they all do
describe how the spinal cord is arranged along the torso and what this gives rise to
it has a segmental arrangement and this gives rise to dermatomes, which are strip like structures along the body that indicate specific spinal segments that receive information from them
which branches of the trigeminal nerve are sensory only
the opthalmic division and the maxillary division
which branches of the trigeminal nerve are both sensory and motor
the mandibular branch, as it gives general sensation but also innervates the muscles of mastication
what is the principle innervation for sensation on the face
the trigeminal nerve
what does the opthalmic division of the trigeminal nerve innervate
most of the scalp and forehead, and the dorsum of the nose
what does the maxillary division of the trigeminal nerve supply
the lateral region of the face and under the eyes, cheeks
where is the temporalis muscle found
in the temporal fossa on the lateral aspect of the face above the ear
what sensation is touch
mechanreception
what sensation is pain
nociception
is the facial innervation pathway the same as the spinal nerve pathway
no
what are sensory pathways comprised of
three interconnected neurons - the primary, secondary and tertiary neurons
describe the general sensory pathway with its interconnecting pathways
- primary sensory neurons are the first and they deliver information from the periphery along the peripheral nerve into the central nervous system
- they target the secondary sensory neuron to relay information along the axon toward the axon terminal, which triggers the release of neurotransmitter
- this recruits the tertiary sensory neuron which projects into the cerebral cortex to the appropriate region
where is most of the primary sensory neuron found
the periphery
is the information relayed by sensory pathways relayed to the sensory cortex on the same or the opposite side of the body
the opposite - there is a cross over in the thalamus when the information goes to the secondary neuron
what is cortical representation
this is how every sensory neuron’s receptive field is represented in the cortex, as there are body regions with higher sensory innervation due to a higher density of receptor endings, and these regions have greater cortical representation
what is somatic mechanoreception
perception of innoxious tactile sensation
what is the brain stem continuous with
the cerebral hemispheres
describe the route of the primary sensory neuron in the dorsal column medial lemniscal pathway
when information goes to the spinal cord, there is a small branch that terminates in the spinal cord and another that ascends up the spinal cord to the medulla oblongata
describe the route of the secondary sensory neuron in the dorsal column medial lemniscal pathway
axon crosses over to the other side of the body before it relays through the brainstem toward the thalamus
once it reaches the thalamus it synapses with the tertiary neuron
describe the route of the tertiary neuron in the dorsal column medial lemniscal pathway
goes from the thalamus to the cerebral cortex
describe the posterior trigeminothalamic pathway
- sensory neuron project into the brainstem via the trigeminal nerve
- cell body of trigeminal afferents in the trigeminal ganglia
- axon projects into the brainstem where it synapses with the second order sensory neuron
- crosses to the opposite side and projects into the thalamus where it connects with the tertiary neuron
- crosses to the cortex and terminates here
describe the spinothalamic pathway
- free nerve endings coalsce to form an axon
- projects via peripheral nerve into the spinal cord
- into the dorsal horn of the spinal cord
- synapse with second order sensory neuron
- sends an axon to the opposite side of the body at the same segmental level
- then is ascends the spinal cord to the thalamus
- via a white matter bundle
- to synapse with tertiary sensory neuron in thalamus
- to go to cerebral cortex
- perception received
what is the anterior trigeminothalamic pathway describing
pain in the face
what is the dorsal trigeminothalamic pathway describing
somatic mechanoreception ie general sensation in the face
what is the spinothalamic pathway describing
somatic nociception ie pain
what is the dorsal column medial lemniscal pathway describing
somatic mechanoreception - general sensation
what is sensation
the process of sensing our environment by activation of sensory receptors and associated sensory pathways
what are some different sensations
touch
taste
sight
smell
what is perception
this is the interepration of sensory input, and requires a high degree of cortical processing
what is stereognosis
mental perception of objects referenced by touch - it is our ability to generate a mental perception of objects from touch stimuli only
what is involved in the cortical processing of stereognosis
- integration of information on several aspects of touch like texture, weight and size
- ability to retrieve previous experiences
- generate a 3D mental image without having seen the object
what is stimulating in the sensory cortex during stereognosis
hippocampus
basal ganglia
motor cortex
what is proprioception
this is the sense of self movement and body position, otherwise known as kinesthesia
describe the integration of mechanosensory input in kinesthesia
- balance organs in the inner ear
- muscle receptors and joint receptors
- mechanoreceptors
- periodontal receptors
what are the balance organs in the inner ear
utricle
saccule
semi circular canals
why are muscle receptors and joint receptors used during kinesthesia
for muscle length and tension
joint position
how are axon fibres classified
according to their:
- myelination
- diameter
- conduction velocity
- sensory modality
