Sensorimotor Systems Flashcards
WHat is sensation, perception and modality
- Sensation = conscious or subconscious awareness of external and internal stimuli
- Perception = conscious awareness and intepretation of sensations
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Modality = uniqueness of each sensation; what distinguishes one sensation from another
- Each sensory neuron carries only one modality (type of message
- Ex: temperature, pain, pressure, touch, proprioception, hearing, vision, smell, etc
- General senses - both somatic (tactile, thermal, pain, proprioceptive) and visceral (internal organs - pressure, stretch, chemicals, nausea, hunger, temperature
- Special senses - smell, taste, vision, hearing, equilibrium
Where does sensation begin ?
Can be either a specilaised cell of the dendrites of a sensory neuron
A particular kind of stimulus (change in the environment) activates certain sensory receptors, while other sensory receptors respond only weakly or not at all (selectivity)
four a sensation to arise, qhat 4 events should normally happen?
- Stimulation of the sensory receptor - an appropriate stimulus must occur within the receptor receptive field, some change in environment must occur
- Transduction of the stimulus- a sensory receptor must detect and convert it (transduce it) into a graded potential
Recall that graded potentials (but not APs) vary in amplitude depending on the strength of stimulus that causes them, and are not propagated
3. COnduction - the nerve impulse must be carried to brain/cord
Occurds when sum of graded potentials reach the threshold in firts order neurons (1st neuron in specific tract- in this case from PNS to CNS)
4. Integration of sneosyr input - region of brain or spinal cord must trabslate the nerve impulse into sensation.
Occurs when partiuclar region of CNS integrates a number (and even variety) of snesory nerve impulses and results in ocnscious sensations or perceptions.
Neuron types
Several classes of snesoyr receptors
Sensory receptors can be grouped into several classes based ons tructural and functional characteristics
- Microscopic structure - free nerve endings vs encapsulated endings, for example:
- Free - bare dendrites, lack structural specialisation, pain, temperature, tickle, itch, touch
- Encapsulated - enclosed in connective tissue , pressure, vibration, tocuh
- Location - of the receptors and origin of stimulu that activate them
Exteroceptors - nesr ecternal surface
Interoceptiors (visceroreceptors)
- Type of stimulus detected (Nociceptors for pain, mechanioreceptord for pressure etc)
Characteristics of sensory receptors
- Selective- each sensosry receptor responds strongly to a certain kind of stimulus
- Some receptors are simple receptors - associated with general (somatic) senses (touch, itch, tickle, pressure, vibration, temp, pain, proprioceptors
- Some receptors are complex receptors - associated with special senses (smell, taste, vision, hearing, equilibrium)
- Most sensory receptors are adaptable: changes in sensitivity during long term stimulus:
- Eg, hot bath, you become less and less sensitive to heat
- SOme receptors can adapt more quickly than others (touch, smell etc)
- Some receptors adapt more slowly (remain snesitive to stimuus longer)… important in homeostasis: pain, proprioceptors, blood glucose etc.
Where are exteroreceptors, interoceptors and proprioceptors in the body
- Exteroceptors = lcoated near the surface of the body; detect changes in external environment (temp, touch, vision, smell, taste, pain, etc)
- Interoceptors = visceroreceptors - located in blood vessels and viscera; detect changes in internal enivronment. Mostly unconscious; occ/ pressur eor pain
- Proprioceptors = located in muscle,s tendons, joints, and internal ear; detect changes in body position, muscle tension etc.
Receptors can also denote the type of stimulus that excites them - Types environmental stimuli
Receptors named according to the mode of action
- Mechanoreceptors - detect stretching or mechanical pressure 9touch, pressure, proprioceptors, vibration, hearing, equilibrium, BP
- Thermoreceptors - detect changes in temperature
- Nociceptors - response to painful stimuli (tissue damage)
- Photoreceptors - activated by photons of light (detecting light striking retina of the eye)
- Chemoreceptors -detect chemicals in mouth (taste), nose (smell) and body fluids
- Osmoreceptors -detect osmotic pressure of body fluids.
What is adaption and how quickly can receptors adapt?
- Adaption = generator potential or receptor potential decreases in amplitude during sustained or constant stimulus
- Because there is an accomodation sponse at receptor level, the frequence of nerve impulses travelling to cerebral cortex decreases and the perception of sensation fades even though stimulus persists.
- Receptors can vary how quickly they adapt:
- Rapidly adapting - v quick, specialised signalling changes in stimulus
- SLowly adapting - adapt slowly and continue to trigger nevre impulses as long as stimulus perists, pain body position, chemical composition of blood
Cutaneous sensations - where are the receptors and the characteristca of receptors
- Receptors are located in the skin, subcutaneous connective tissue, mucus membranes and both ends of gI tract
- Some body sites contain more cutaneous receptors than other site (tongue, lips, fingertips, sex organs have many receptors, very sensitive.
- CUtaneous receptors - dendrites of sensory neurons, may be free nerve endings, may have capsule (epithelial tissue or CT)
- Cutaneous receptor -> nerve impulse -> somatic efferent neuron -> spinal./ cranial nerve -> thalamus -> somatosensory area of parietal lobe of cerebral cortex.
WHat are touch sensations due to the stimulation of?
Touch sensations are due to the stimulation of tactile receptors in upper layers of skin (mechanoreceptors)
The 2 types touch and the types receptors for touch
- Crude touch - ability to perceive that something has touched the skin (dont know what it is)
- Discriminative touch - ability to recognise the exact point on body is touched
- Receptors for touch:
Meissner’s corpuscles (Corpuscles of touch) ->
- Mass of dnedirtes surrounded my CT
- Located in dermal papillae
- Adapt rapidly (loose sensitivity to stimulus)
- Inovlved in discriminative touch
- Location - fingertips, palms, soles, eyelids, tip of tongue.
Hair root plexuses
- Dendrites - in networks around hair follicles
- movements of hair shaft stimulates these dendrites, these receptors detect movements along skin surface (crude touch)
- Also, rapidly adapting receptors
Merkel Discs
Type I cutaneous mechanoreceptors
- Flattened dendrites near stratum basala
- Slowly adaptive (remain sensitive to stimulus longer)
- Involved in discriminative touch
Ruffini corpuscles
Type II cutaneous mechanoreceptors
- Lopcated deeper in dermis, detect heavy and or continuous touch
- Slowly adaptive (remain snesitive to stimulus longer
Effect of pressure sensation and receptors invovled
- Pressure sensations = stimulation of tactile Receptors deeper in tissues
- Pressure is longer-lasting than touch, also felt over larger area
- Receptors:
- Type II Cutaneous Mechanoreceptors
- Pacinian Corpuscles - Lamellated corpuscles:
- 1 dendrite, surrounded by many layers of connective tissue (located in subcutaneous tissues)
- Rapidly adapting (lose sensitivity to stimulus)
Thermal Sensations
- Receptor - free nerve endings
- Some of these thermal receptors respond to heat
- Others respond to cold
Pain Sensations
- Vital sensation - danger alert signal
- Nociceptors (pain receptors): free nerve endings
- Located in nearly every tissue of the body
- Tissue damage releases chemicals that stimulate nociceptors
- Little or no adaption (remain sensitive for very long time)
Types of Pain
- Acute pain - sharp, fast, felt in very localised area (Message carried by large diameter myelinated neurons)
- Chronic pain - slow pain which gradually increases - aching (throbbing), message carried by small diameter, unmyelinated neurons
- Superficial somatic pain - due to sitmulation of nociceptors in skin
- Deep somatic pain - stimulation of nociceptors in muscles, tendons, joints etc
- Viscerla pain - stimulation of nociceptors in visceral organs
- Referred pain
- Phantom pain - sensation of pain from amputated limb
Nociception - Common patterns of referred visceral pain
Common patterns of referred visceral pain
Describe fast vs slow pain?
- Fast pain = acute, well localised, occurs rapidly because the nerve impulses propagate along medium-diameter, myelinated A fibres
- Slow pain = begins after stimulus applied and gradually increases in intensity over period of several seconds or minutes
Impulses for slow pain are conducted along small-diameter, unmyelinated C fibres and this type of pain may be excruciating and often has a burning, aching or throbbing quality
Pre-op, intra-op, post-op anaestheisa and analgesic methods
Proprioceptive sensations - the receptors and how come about
- Recptors = located in skeletal muscle (Muscle spindles)
- Tends (tendon organs) in and aorund joints kinesthetic receptors (Joint kinesthetic receptors) and in the internal ear
These proprioceptors convey nerve impulses about muscle tone, movenebt of body parts and boyd position to the brain
Summary of receptors for somatic sensations
Somatic sensory pathways briefly
- First order neurons - conduct impulses from somatic receptors into the brain stem or spinal cord.
- Cranial nerves - into brain stem
- Spinal nerves - into spinal cord
- Second order neurons - conduct impulses from brain stem and spinal cord to thalamuc where neurons decussate (cross to opp side)
- This, all somatic sensory information form one side of body reaches thalmaus on opp side
- third order neurons - conduct impulses from thalamus to primary somatosensory area of cortex on same side
Posterior Column Tracts
Spinothalamic tract
Trigeminothalamic
Carries nerve impulses for: touch, pressure vibration, pain, temperature, itch/tickle
- From face, nasal cavity, oral cavity, and teeth
- To primary sensory motor cortex on the opposite side the site of stimulation
Spinocerebellar
Spinocerebellar (anteiror and posterior):
- Nerve impulses for: proprioception
- From trunk and lower limbs
- From one side of body to same side cerebellum
- Allows for coordination, posture and balance
How are somatic sensory neurons distributed>
- Somatic sensory neurons are not distributed evenly in the body
- • Relative size of these regions in the somatosensory area are proportional to the number of specialized sensory receptors in the corresponding body parts - sensory homunculus (cerebral Cortex)
Where does motor activity begin in somatic sensory pathways?
- Motor activity begins in the primary motor areas of the precentral gyrus and other cerebral integrative centers (motor homunculus)
- Any motor neuron that is not directly responsible for stimulating target muscles is called an upper motor neuron (UMN)
- UMNs connect the brain to the appropriate level in the spinal cord
Somatic Motor pathway
Anterior an dlateral corticospinal pathway diagram
Corticobulbar pathway
- Impulses for the control of skeletal muscles in the head
- Associated with cranial nerves
Indirect/ Extra pyramidal tracts (Lateral and anteiror columns)
▪ Originate in midbrain (unconscious)
▪ Nerve impulses for involuntary movements, muscle tone, posture, & balance (equilibrium)
▪ Five major tracts
• Rubrospinal- precise, voluntary movement of
distal parts of upper limbs
• Tectospinal- reflexively move head, eyes, and
trunk in response to visual and auditory stimulus
• Vestibulospinal- maintaining posture and balance
in response to head movements
• Lateral & Medial reticulospinal- maintaining
posture and regulating muscle tone in response
to ongoing body movements
Sleep and wakefullness - integrative functions of cerebrum
▪ Controlled by the “Reticular Activating System (RAS)”
• Reticular Formation: patches of gray matter scattered in the white matter of brainstem,
spinal cord, and diencephalon
- A portion of the Reticular Formation is the RAS
- RAS acts as an alerting system to “wake up” the cerebral cortex
- When the RAS is stimulated by nociceptors, touch, proprioceptors signals, bright light, or
sound, it sends impulses thru the thalamus, where the message gets dispersed to many areas
of the cerebral cortex
• The RAS is responsible for arousal from deep sleep, and
for maintaining a general state of wakefulness/consciousness
REM sleep
