Lecture 1: Sensation Flashcards
What is 4 steps of the scientific process?
- Observation
- Replication
- Interpretation
- Verification
What are lesions?
Zone of tissue with impaired function due to diesease or wounding
What are experimental ablation?
Experimental destruction to parts of brain to determine function (to excite or inhibit)
How does deep brain stimulation work?
By inserting electrodes into the brain to excite or inhibit something
What are the 5 steps of behaviour execution?
- Afferent input via receptors
- Spinal and brain stems -> induce reflexes
- Sensory cortex -> receives sensory AP
- Motor cortical areas
- Voluntary behaviour
(Repeats)
What are the 6 types of sensation?
- Physical
- Chemical (taste and small)
- Visual
- Auditory
- Vestibular
- Somatic (touch and pain)
What is sensory transduction?
process by which sensory receptors convert external stimuli (such as light, sound, or mechanical pressure) into electrical signals (nerve impulses) that can be interpreted by the brain.
What is involved in sensory transduction?
The influx of ions across channels
What are the 2 modality of sensation?
- Nature of stimulus
- Labeled line principle
What is labeled line principle ?
Describes the specificity of nerve fibres to transmit 1 modality of sensation to a specific area of the brain
What are the 4 ways an AP signal encode the property of stimulus?
- Modality
- Location
- Intensity
- Duration
What is receptive field defined as?
Region that when stimulated produces a change in activity of that neuron
Can receptive fields overlap?
Yes
What are the 2 ways Intensity of sensation can be propagated?
- Frequency code
- Population code
What is the relationship between strength of AP signal and frequency of impulses?
The stronger the AP, the higher the frequency impulses
What is the relationship between number of sensory receptors and intensity of signal?
More sensory receptors activated, the stronger the intensity of signal
What is temporal summation, and what is it under?
Temporal summation is when EPSP (EX1) excites a 2nd time before the 1st dies.
EX1 + EX1 = temporal summation.
It is under frequency code
What is spatial summation, and what is it under?
Spatial summation = EX1 + EX2
It is under population code
Duration of sensation depends on?
Adapting property of the receptor. There is slow (tonic) and rapid (phasic) adapting receptors
Describe tonic adapting receptors
- They are slow adapting receptors
- Active for duration of a stimulus. Response is maintained as long as stimulus is still present
- Good for monitoring situation throughout the duration
Describe phasic adapting receptors
- Active only during times of change. Response decreases despite stimulus maintained.
- Good in detecting changes in stimulation
Divergence pattern of signal flow leads to?
Loss of acuity
How to improve acuity? explain why it helps.
Via lateral inhibition. It enhances sensory input by inhibiting the activity of neighboring neurons, thus sharpening the contrast between the active neuron (which is responding to the stimulus) and the surrounding neurons.
Where is the primary somatosensory cortex (S1) location?
Post-central gyrus of parietal lobe
Primary somatosensory cortex (S1) is subdivided into how many areas ?
S1 is subdivided into four distinct Brodmann areas (areas 1, 2, 3a, and 3b)
Describe the 4 Broadmann areas
Brodmann Area 3a: Processes body position and movement from the muscles and joints.
Brodmann Area 3b: Processes tactile information from the skin, such as touch and pressure. A major part of S1 and plays a central role in processing cutaneous (skin) sensations.
Brodmann Area 1: Processed input from area 3b and specializes in texture perception and detecting the orientation of objects.
Brodmann Area 2: Integrates both tactile and proprioceptive information to give a sense of object shape and size.
The somatosensory cortex receives input from where?
The ventral posterior nucleus (VPN) of the thalamus. It processes and transmits sensory information to the primary somatosensory cortex (S1)
Which sensory receptor senses shapes/ surfaces?
Meissner corpuscles
Which sensory receptor senses indentations?
Merkel discs
Which sensory receptor senses stretching and shapes?
Ruffini endings
Which sensory receptors senses vibrations?
Pacinian corpuscles
Rank the depthness of the 4 sensory receptors in the skin. First being the most superficial.
- Merkel’s disc
- Meissner’s corpuscles
- Pacinian corpuscle
- Ruffini endings
What is the receptive field size and adaptation of Meissner’s corpuscle?
Small field size, rapid adaptation
What is the receptive field size and adaptation of Pacinian corpuscle?
Large field size, rapid adaptation
What is the receptive field size and adaptation of Merkel’s disc?
Small field size, slow adaptation
What is the receptive field size and adaptation of Ruffini’s endings
Large field size, slow adaptation
Axons from somatic sensory receptors enters spinal cord via which root?
Dorsal root
Sensory receptors from - skin
- muscles
- pain + tempt
- pain + tempt + itch
rank which one would AP travel the fastest. 1 being the fastest.
- Muscles
- Skin
- Pain + tempt
- Pain + tempt + itch
What is the Dorsal Column - Medial Lemniscal Pathway (DCML) for?
Neural pathway responsible for transmitting fine touch, vibration, pressure and proprioception to the brain.
Explain the DCML pathway
- Sensory receptors detect stimuli and the information travels through the axons of primary afferent neurons.
- The axons ascend ipsilaterally in the dorsal columns of the spinal cord
- These axons synapse onto 2nd order neurons located in the dorsal column nuclei of the medulla (nucleus gracilis, nucleus cuneatus)
- The axons of the 2nd order neurons decussate (cross over to the opposite side) in the medulla and form the medial lemniscus.
- The medial lemniscus then ascends and synapses onto 3rd order neurons in the ventral posterior (VP) nucleus of the thalamus.
- The 3rd order neurons project to specific regions of the primary somatosensory cortex
What is the trigeminal touch pathway for?
transmitting sensory information from the face to the brain
Explain the trigeminal touch pathway
- sensory information from is transmitted through the trigeminal nerve and enters the brain via the pons.
- Synapse onto 2nd Order Neurons in the Ipsilateral Trigeminal Nucleus in the pons.
- Axons Decussate in the pons, Project and Synapse onto 3rd Order Neurons in the Ventral Posterior (VP) Nucleus of the Thalamus
- VP Neurons then Project to Specific Regions of Primary Somatosensory Cortex (S1)
What is the spino-cerebellar pathway for?
for transmitting proprioceptive information about skeletal muscles, tendons and joints to the cerebellum
3 functions of spinocerebellar pathway
- Control muscle tone
- Regulate movements
- Regulate coordination
Is the spinocerebellar pathway a subconscious pathway?
Yes. Information from this pathway is not brought to our awareness.
Explain the spinocerebellar pathway
- 1st order axons synapse onto 2nd order neurons in dorsal horn of spinal cord
- Go into 2 diff tracts:
A) Posterior tract (no cross-over). 2nd order neurons in the posterior dorsal tract project ipsilaterally through the inferior cerebellar peduncle to reach the cerebellar cortex
B) Anterior tract (decussates). 2nd order neuron in the anterior ventral tract decussates and projects contralaterally through the superior cerebellar peduncle to reach the cerebellar cortex
