Lecture 23 Flashcards
What do sensory neurons carry
Afferent signals
- in and up
- info about the environment
What is neuron 1 in the somarosensory cortex
- This neuron starts at the sensory receptor in the body, such as in the skin.
- Its cell body resides in the dorsal root ganglion, which is located just outside the spinal cord.
- The peripheral fiber of neuron #1 carries sensory information from the receptor to the central nervous system.
- The central fiber of neuron #1 ascends towards the brain through the dorsal columns of the spinal cord white matter.
- Neuron #1 synapses on neuron #2 in the medulla oblongata.
Dendrites: ion Chanel location in sensory neurons
Chemically or mechanically gated ion channels ( Na+ and K+ )
What is the dendrities and cell body ion channel location in the intermediate and motor neurons
Chemically gated ion channels ( Na+ and K+ )
What is the axon ion channel location
Voltage gated ( Na+ and K+ ) channels
What is the Axon thermals, ion channel location
Voltage gated Ca2+ channels
What is the sensory neurons, somatic senses
Detected by the receptors in the skin, muscle and joints
What is the Visceral senses in the sensory neurons
Detected by recptors in the internal organs
What does sensory detection require
Stimulus transduction
What does transduction mean
Convert or change from one form to another
What is sensory transduction
Conversion of sensory stimulus into an action potential
Please tell me an example of stimulus transduction
• when you touch something with your finger
• …a mechanoreceptor in the skin of your fingertip gets squished.
• This deforms the membrane, opening mechanically-gated Na+ channels
• …allowing Na+ to enter and depolarise the membrane
…sending action potentials to the brain to make you aware of the touch.
What are the 4 types of information encoded by neural activity
- modality
- duration
- intensity
- location
What is modality
A type of stimulus detected by a specific type of receptor
Duration
Time period of which action potentials fire in afferrent neurons
Intensity
Rate ( frequency ) of action potential firing in afferent neurons
Location
Location of receptors withen the body. The somatosensory cortex has a map of locations from which it receives action potentials
What are the 4 examples of modality of stimulus
- thermoreceptor
- chemoreceptor
- there are 3 types of mechanoreceptors, 1) tactile receptors 2) proprioreceptor 3) baro receptor
- nociceptor
What is thermo receptor and give an example
This is for temperature, so a stimulus example is relative temperature ranges
What is chemoreceptor
Chemical and a stimulus examples is CO2, O2, H concentration in blood
What isn’t mechankreceptor
There are 3 basic mechano receptors
1) tactile receptor, this is for skin touch, SE: light touch, pressure, texture, vibration, stretch
2) propriceptor, this is propriception, SE: stretch or tension in skin, muscle and/or tendon
3) baro receptor this is pressure , SE: stench of visceral tubes ( eg: blood vessels, airways, intestines)
- Nociceptor! This is for PIAN, SE: excess temperature, chemical or mechanical stimuli
In depth of thermoreceptors
Thermorecetoes are nerve endings with temperature gated ion channels, they can sense a range of temperature and are sensitive to both increase and decrease of temperatures and are FAST ADAPTING.
Transduction of tempeture stimuli
Temperature stimuli opens temperature gated Na+ channels,
Allowing Na+ to enter and depolarise the membrane
If the threshold is reached in the thermoreceptor, an action potential will fire and propagate the brain.
In-depth of chemo receptors
These are specialised receptor cells with chemically gated ion channels
They respond to different chemical concentrations
Transduction of chemical stimuli
This is the same as the tempeture one:
Chemical stimuli bind and open chemically gated Na+ channels,
Allowing Na+ to enter and depolarise the membrane
If the threshold is reached in the thermoreceptor, an action potential will fire and propagate the brain.
A PH sensitive cell is an example of,e of an chemoreceptor
In depth about Mechaoreceptos
They are nerve endings with mechanical,t gated ion channels
They respond to physical forces that distort the plasma membrane ( deformation
Transduction of mechanical stimuli
Mechanical stimuli deform the membrane causing mechanically gated Na+ channels to open
This allows Na+ to move in and depolarise the membrane
And is the threshold is reached in the menchnoreceptor, an action potential will fire and propagate to the brain
Mechanoreeceptors: tactile receptor
- responds to light touch, pressure, vibration and stretch of skin
- Some are tonic ( slow adapting )
- some are phasic ( fast adapting )
Me hnoreceptors: proprioceptors
- respond to stretch, tension in receptors
- inform about limb position
- are tonic ( slow adapting )
Mechanicoreceptors: baro receptors
- detect pressure in/strech of tubes ( eg:blood sugar )
In depth of Nociceptors
- this is a Nerve ending that responds to noxious stimuli ( harmful, painful ) and is tippically caused by tissue damage
- They have either temperature gated, chemically gated or mechicallt gated ions channels responding to extreme stimuli
- are tonic ( slow adapting )
Transduction of noxious stimuli
Noxious stimuli causes ion channels to open allowing Na+ to enter and depolarise the membrane
If the threshold is reached in the nociceptor, an action potential will fire and propagate to the brain
Duriation of stimulus, tonic receptors
Tonic receptors are continually active, providing a continuous signal to the central nervous system (CNS) that reflects the background level of stimulation.
- These receptors maintain a relatively constant firing rate over time, even in the presence of a sustained stimulus.
- The action potential (AP) frequency may change when the intensity of the stimulus changes, but the receptors continue to respond as long as the stimulus is present.
- Tonic receptors are associated with slowly adapting responses, meaning they continue to respond for a prolonged duration to sustained stimuli.
- Examples include muscle spindles involved in proprioception (sensing body position and movement) and nociceptors responsible for detecting pain.
Duration of stimuli, phasic receptors
- Phasic receptors, on the other hand, respond rapidly to changes in the stimulus but adapt quickly to sustained stimuli.
- They are characterized by a burst of activity when the stimulus is first applied but then rapidly decrease their firing rate, becoming less responsive over time if the stimulus remains constant.
- Phasic receptors are associated with fast-adapting responses, meaning they quickly adapt to sustained stimuli and may stop firing even if the stimulus is still present.
- Examples include receptors for touch, vibration, and pressure, which are crucial for detecting changes in the environment but may become less responsive to constant stimuli.
Intensity of stimulus, action potential frequency
NO AP = NO SENSATION
SOME AP = SOME SENSATION
MORE AP = MORE INTENSE SWNSATION
Intensity of stimulus, Ap frequency plus number of neurons activated
- below threshold there is no response in afferent neuron
- increasing stimulus increases action potential frequency
- stronger stimuli can also activate more receptors and action potentials in more sensory axons
Location of stimulus, receptive Feilds
• The area of skin with receptive endings for a single sensory neuron
• 1 receptive field to 1 sensory neuron
Size and density of receptive fields affect discriminatory touch (sensitivity) and ability to localize a stimulus.
Location of stimulus - size and density of receptive Feilds - sensitivity and localisation
Large and more widely spaced receptive fields provide:
• less sensitivity and
• less accurate localization
• e.g. in arms, legs, torso
Small and densely packed receptive fields provide:
• More sensitivity (better two- point discrimination)
• more accurate localization
e.g. hand, fingers and lips
Location of stimulus - sometorsensory cortex map
Somatic sensory neurons send signals from different parts of the body and Up axons within the dorsal column pathway to the somatosensory cortex of the brain Creating a somatotopic map
Location of stimulus , receptive Feilds and the somatopic map. TRUNK TORSO AND LIMBS
• Areas of skin with larger receptive fields so this has less representation in the brain because there are fewer neurons involved
Remember: 1 sensory neuron per receptive field
Location of stimulus : lips and hands, receptive Feilds and somatopic map
• Areas of skin with smaller receptive fields
• have more representation in the brain because there are more neurons involved
Remember: 1 sensory neuron per receptive field
