Sensory systems Flashcards
what are the 3 common sense of sensory processing across all systems?
- requires a physical stimulus
- mechanical (movement of air particles, pressure, photons) - must transform stimulus into nerve impulses
- done by sensory receptors in PNS - evoke a response to the signal in the form of perception of sensation
- by CNS
what are sensory receptors?
- they can be whole cells, or proteins
- they take energy from the environment and transduce it into electrochemical signals
what are sensory receptor cells?
- respond with GPs
- can be primary afferent neurons, or can release neurotransmitter onto primary afferent neurons
what two forms can electrochemical signals take?
- Graded potentials
- a slow change in membrane potential
- graded depending on size of stimulus
- the smaller the stimulus, the smaller the graded potential - Action potential
GPs can be converted to APs
what are sensory receptor proteins?
- can be ionotropic or metabotropic
- how they are used, the morphology of the cell and where the cell is located determines their specialised function
what senses make up the 5 special sensors?
- vision
- smell
- taste
- hearing
- balance
(not touch as skin has multiple functions, not just for touch)
what is involved in vision?
the eye:
- one of the only places in the body (aside from skin) where light directly contacts cells
- pupils allow photons into the eye for absorption by photoreceptors
what is involved in smell?
the nose:
- nose is open to the external environment via nostrils
- chemicals can diffuse into it and activate olfactory receptor cells (neurons)
what is involved in taste?
tongue:
- specialised structures allow access into the mouth
- chemical stimuli can enter taste pores which allow taste receptor cells on tongue to bind to chemicals
what is involved in hearing and balance?
cochlea and semi-circular canals:
- specialised structures to detect mechanical movement of air
- both contain hair cells
the hair cells in these structures have different functions due to their anatomical structures and location
what is proprioception?
- allows us to understand how our body is positioned
- helps body adjust to changes e.g. when falling over
- maintains posture
- takes info from muscle spindles and Golgi tendon organs to see how stretched our muscles are
what are thermal senses?
- distinguishing between hot and cold stimuli
- free nerve endings in skin and viscera
- specific expression of receptor proteins (thermoreceptors)
what are pain senses?
- free nerve endings in skin and viscera
- specific expression of receptor proteins (nociceptors)
what is the general process of sensory transduction?
- stimulus activates a sensory receptor
- membrane permeability is altered in that receptor cell (usually increased)
- causes generation of GP
- GP causes opening of Ca2+ ion channels
- neurotransmitter is released and acts on afferent neuron terminals
- causes EPSP which summates to form AP in afferent terminal
- AP propagates to CNS in cranial nerves
- info is integrated in CNS
what is the difference between GP and AP?
- GPs can increase in size in response to increases in stimulus amplitude
- APs are always the same size, but have a threshold for activation
how are neurons activated in olfactory receptor cells?
- olfactory receptor cells contain cilia which project from dendritic cells into mucus
- mucus lines nasal cavity
- ion influx causes depolarisation and generation of GP in a cilium
- large enough GP causes depolarisation in cell soma, triggering EPSPs which form AP
- AP travels to olfactory bulb
how are neurons activated in taste receptors?
- ion influx causes depolarisation and generation of GP
- initiates synaptic vesicle fusion with membrane and neurotransmitter release
- neurotransmitter binds to postsynaptic receptors
- EPSP is generated in dendrite of afferent neuron
- EPSP summates to form AP
what 4 types of information can sensory receptors convey?
- Modality: type of stimulus
- Location: where did the stimulus come from
- Intensity: how strong is the stimulus
- Timing: when did the stimulus occur and how long did it last for
how is stimulus modality coded for?
by the labelled line code
what is the labelled line code?
- receptor is selective for one type of stimulus energy
- the axons of the receptor/associated afferent neuron acts a modality-specific line of communication
- axons from these neurons make connections with specific areas in the CNS
what does stimulation of afferent neurons in sensory systems lead to?
perception of the associated sensation:
- brain is wired so certain pathways correlate with certain senses
- e.g. stimulation of cochlea nerve causes brain to perceive a sound, even if there isn’t really a sound there
how does the cochlea identify the frequency of a sound?
via a tonotopic map:
- any stimulation at base of cochlea is high frequency sound
- any stimulation at apex of cochlea is low frequency sound
the tonotopic map travels through the brainstem and midbrain, up into the auditory cortex
what is synaesthesia?
fault in the labelled line code:
- when someone senses one type of modality but perceives it as a different modality e.g hearing colours
- abnormalities of genes in axonogenesis can cause cross-wiring of the labelled line code
how is stimulus location determined?
receptive fields:
- spatial arrangement of activated receptors gives info about the stimulus
in somatic system, a receptive field is the region of skin innervated by the terminals of the receptor neuron
in the visual system, a receptive field of a photoreceptor is the region of the visual field projected onto that receptor
how is stimulus intensity determined?
intensity = total amount of stimulus energy delivered to the receptor
- determined by the response amplitude of the receptor and thus the firing frequency of APs of afferent neurons
what is sensory threshold?
- the lowest stimulus strength that can be detected
how is stimulus timing determined?
onset timing:
- determined by when the stimulus energy is received by the receptor and causes it to fire
stimulus duration:
- determined by adaptation rates of receptors
what is adaptation?
- in response to continuous stimuli, the firing rate of APs decreases
what are slowly adapting neurons?
tonic receptors: respond to prolonged stimulation
what are rapidly adapting receptors?
phasic receptors: respond at beginning and end of a stimulus
what are the 3 types of sensory integration?
- divergence: primary afferent neurons signal to more than one relay neuron
- convergence: relay neuron has larger receptive fields than primary afferent neurons
- inhibitory neurons: ensures signal in the most active neuron is propagated
