Sensory Systems Flashcards
1
Q
What is the process of a specialised afferent nerve ending being propagated toward the CNS?
A
- In sensory receptors that are specialised afferent neuron endings, stimulus opens stimulus-sensitive channels, permitting net Na+ entry that produces receptor potential
- Local current flow between depolarised receptor ending and adjacent region opens voltage-gated Na+ channels
- Na+ entry initiates action potential in afferent fibre that self-propagates to CNS
2
Q
Provide some information about hair receptors
A
- afferent neuron endings spiral around the base of hair follicles
- stimuli: mechanical displacement of the hair leads to receptor potential
- fast adapting (phasic) receptor
- sustained stimulation does not produce further action potentials
- respond best to moving objects and signal the direction and speed of the moving object
- discriminative touch
3
Q
Discuss features of the merkel cell-neurite complex
A
- found in hairy and not hairy skin in basal layer of the epidermis
- comprised of two receptor types, Markel cell and Merkel disk
- specialised receptor cell
- enlarged afferent neuron endings from Merkel disk
- respond to fine tactile stimuli and slow vibration
- force applied to skin leads to distortion of the cell receptor potential = neurotransmitter release
- Merkel cell leads to action potential in Merkel disk
- each afferent neuron innervated by up to 90 Merkel cells in a discrete patch of skin
- small receptive fields in fingers, larger in palm of hand and legs
- slowly adapting
- responds best to steady pressure from small objects
4
Q
What is the Meissner complex?
A
- encapsulated receptor found within the dermal papillae in non-hairy skin
- most sensitive to flutter and movement
- stack of epithelial cells with afferent fibre endings interspersed between the cells
- force applies to skin causes epithelia cells to slide past each other = distortion of membranes of axon terminals = receptor potential
- single afferent neuron forms many Meissner corpuscles
- rapidly adapting response
- small receptive field
- respond best to rubbing against skin, movement across a surface
5
Q
What is the Ruffini corpuscle?
A
- encapsulated mechanoreceptor
- sensitive to skin stretch, sustained pressure
- found deep in the skin, in joint ligaments and capsules
- touch and proprioceptor
- contains strands of collagenous fibres, continuous with connective tissue
- afferent fibre branches within the capsule, endings are intertwined with collagenous fibres
- tugging or stretching in the dermis detected
- slowly adapting receptor
- monitor slippage of object (modulation of grip)
6
Q
What is the Pacinian corpuscle?
A
- encapsulated (onion shaped with layers of epithelial cells surrounding afferent neuron endings)
- sensitive to vibratory pressure, deep touch
- in subcutaneous tissue beneath the dermis, connective tissues of bone, body wall and body cavity = cutaneous and proprioceptive function
- epithelial cells contain fluid that is displaced when force is applied, movement of fluid dissipates force
- mechanical deformation = opening of pressure sensitive channel = receptor potential
- fast adapting
- function (grasping, releasing objects, surface texture discrimination)
7
Q
List some features of free nerve endings, including where in the body they are located as well as what they are receptors for.
A
- found throughout the body (skin, muscles, tendons, cornea, viscera, etc.)
- receptors for crude touch, pain and temperature
- morphologically very similar but different functions, each with its own ascending pathway
- adaption depends on specific functional type, but mostly slow adapting
- small unmyelinated fibres
8
Q
Contrast fast and slow pain
A
Fast:
- occurs on stimulation of mechanical and thermal nociceptors
- carried by small, myelinated A-delta fibres
- produces sharp, prickling sensation
- easily localised
- occurs first
Slow:
- occurs on stimulation of polymodal nociceptors
- carried by small, unmyelinated C fibres
- produces dull, aching, burning sensation
- poorly localised
- occurs second, persists for longer time, more unpleasant
9
Q
What are the two best known pain neurotransmitters>
A
- Substance P (activates ascending pathways that transmit nociceptive signals to higher levels for further processing)
- Glutamate (major excitatory neurotransmitter)
10
Q
How does the analgesic system of the CNS work?
A
- CNS suppresses transmission in pain pathways as they enter spinal cord
- depends on presence of opiate receptors (endogenous opiates - endorphins, enkephalins, dynorphin)
11
Q
Describe ‘equilibrium’
A
- sense of body orientation and motion
- body orientation with respect to gravity
- discriminate self-generated movements from external forces
- activates reflex pathways - compensatory body movements
- also activates pathways that project to the cortex
12
Q
What is the vestibular apparatus comprised of?
A
- semicircular canals (rotational equilibrium)
- otolith organs (gravitational equilibrium)
13
Q
Describe the semicircular canals
A
- fluid filled canals (endolymph(
- detect rotational or angular acceleration or deceleration
- canals are perpendicular to each other (map 3D space)
- receptors (hair cells) are located in the cristae ampullaris within the ampulla of each cell
- hairs are embedded in gelatinous material called the cupula
14
Q
What structures are involved in transduction?
A
- hair cell - separate receptor cell
- hair cell consists of 1 kinocilium and 20-50 stereocilia (microvilli)
- hairs are connected by tip links
- mechanically gated ion channels open/close depending on direction of bending
15
Q
Describe the process of transduction with specific mention of how it works when the head is turning.
A
- when head is turned, endolymph lags behind due to inertia
- endolymph (in the canal that is in the same plane as the movement) pushes on cupula and bends hair cells in the opposite direction of head movement = appropriate signal
- if head movement continues in same direction, endolymph moves at the same speed as the head movement, no force in the cupula = hair cells are no longer bent
- if head movement stops, the reverse happens
