chapter 15 sensory pathways & somatic nervous system Flashcards
what are the 3 sensory receptor types
1) exteroreceptor: monitor external environment
2) interoreceptor: monitor visceral orgnas/ internal environment
3) proprioreceptor: monitor position of skeletal muscles & joints
Where in the brain does this sensory info & visceral sensory info go to?
- the sensory info goes to “cerebrum” & cerebellum
- the visceral sensory info goes to brain stem & diencephalon
how does the sensory pathway work in somatic nervous system?
the tract:
1. general sensory receptor goes to sensory pathways and the sensory processing in centers in brain (afferent)
2. concious and subconscious motor centers in brain to motor pathways (efferent)
- somatic nervous system (SNS)»_space; skeletal muscles
- autoomic nervous system (ANS)»_space; visceral effectors (smooth muscles, glands, cardiac muscle,a dipocytes etc)
what are sensory receptors?
Structures that monitor changes in specific variabels inside & outside the body
- usually specific receptors are at end of an afferent neuron
- each receptor responds to specific type of stimulus
= receptor specificitiy (e.g. pressure receptors are stimulated by pressure)
- you have 2 types of senses: general & special
what are general senses?
temeprature, pain, touch, pressure, vibration & proprioception (muscle stretch)
general sense receptors: are usually teh dendrites ends of an affernet (sensory) neuron in dermis or in stratum basale (the deepest epidermis layer)
the types of general sense receptors
- free nerve endings: pain, touch, pressure, temp (e.g. tactile receptors)
- root hair plexus
- merkal cells and tactile discs: fine touch & pressure
- tactile corpuscle (Meissner’s) [=little body]: light touch & pressure
- lamellated corpuscle (pacinian): deeper pressure/ wrapped by fibrobalst
- ruffini corpuscle (bulbous): distortion
What are special senses?
olfaction (smell), vision, gustation (taste), equilibrium (balance), hearing
- receptors are more complex; & are located in sense organs (e.g. eye, ear and tongue)
what is a detection of the stimulus
an adequate stimulus acting on a sensory receptor causes a change in the membrane’s permeability
- which leads to the generation of the receptor cell’s graded depolarizaiton/ hyperpolarization = receptor potential
- Generator potential = a depolarization of the sensory neuron (= the receptor cell in general senses, 2nd cell in special senses)
- transduction = process of translating stimulus into an action potential (change the chemical info into electrical info)
where is stimulli detected in general senses
in general senses:
- stimuli detected at the receptive endings of sensory neruons
- unipolar
where is stimuli detected in special senses
in special senses:
- specialized receptor cells are required
- receptive endings of olfactory neruons (smell)
what is range of detection
- the number and type of sensory receptors we have limit what we can sense and become aware of
- each of us is unique in our sensory abilities
what is a receptive field?
area of body monitored by “one” particular afferent neuron and all its receptors
- 2-point discrimination test: to assess if the patient is able to identify 2 close points on a small area of skin, how fine the baility to discriminate this are
3 interpretation types of sensory information: sensation, perception and not perceived
to generate conscious sensations, sensory info must be transmitted to the cortex (cerebral cortex):
- sensation: raw experience; may be unconscious/ activity in any & all sensory neurons
(every sense coming into brain)
- perception: SNS (1% of all sensation); interpretation, meaning given to sensation, conscious awareness of sensation / activity in cerebral cortex and not just spinal cord & brain stem
not perceived: visceral sensory info delivered to diencephalon, spinal cord & brain stem only (reflex)
- labelled line: pathway that conducts sensory info from a receptor to specific neurons in cortex
what is modality interpreted by?
modailty (type) of stimulus (e.g. touch, pressure, temp., sound) is interpreted by labelled line
- information ab the type, strength, duration and variation of the stimulus is coded by:
1) type of sensory receptor cell activated
2) the rate of action potentials generated (e.g. frequency, how long the sensation lasted)
e.g. the harder/ stronger the stimulus, the more action potentials generated (APs are more frequent)
where does sensory conding begin at?
what are the 2 general types of receptors
sensory conding begins at the sensory receptors
1. tonic receptors: always acticve; provide info about
- background level of stimulation
- changes indicated by frequency of action potentials generated
- called **slow adapting **receptors because they show little peripheral adaptation
- phasic receptors: not always active fire, only when stimulated, provide information ab:
- intensity and rate of ahcnge of stimulus
- called fast-adapting receptors becuase they respond strongly at first & then show decline in activity = peripheral adaptation
tonic receptor: e.g. the stimulation for pain; never be adapated
the receptors catagorized as tonic receptors
- ruffini corpuscle (pain receptors)
- merkel tactile receptors
- nociceptors
- joint capsule proproceptor
- muscle spindle (stretch centres)
the receptors categorized as phasic receptors
- pacinian corpuscles
- meissner’s corpuscles
- thermoreceptors
- root hair plexuses
what are the difference between peripheral/ central adaptations?
adaptation: reduction in sensitivity of nervous system to constant stimulus
1) perpheral adaptation: phasic sensory receptors become less responsive (e.g. become used to background noise, feeling of clothing, room temp)
2) central adaptation: receptors still responding but central adaptation, involved inhibition at various nuclei
- sensory info may still generate reflex responses, but no conscious sensation or perception; awareness is reduced (e.g. you get used to new odours in a room)
=higher centers can increase receptor sensitivity or facilitate transmission (e.g. RAS heightens awareness - listen carefully)
why does adaptation take place?
it’s theory!!!
: so that the brain is not overwhelmed and is not using up resources paying attention tothings that are not important»_space; allows the brain to focus on more important things
4 types of receptors of general senses
1) nociceptors: pain receptor
2) thermoreceptors: temperature monitor
3) mechanoreceptors: cell membrane (e.g. ion channel) stimuli
4) chemoreceptors: detect changes in pH, [O2], [CO2]
what is nociceptors?
= pain receptors, free nerve ending (dendrites)
location: superficial skin, joint capsules, periostea of bones, around the walls of blood vessels (pain)
respond to: extreme temp, mechanical damge, dissolved chemicals (e.g. chemicals released by damged cells)
- very strong stimuli will excite all 3 receptor types and lead to awareness of the same sensation: “burning feeling”
- slow adapting: tonic, feeling will last as long as stimuli
2 axon types carry pain info
1) type A fibers (faster, myelinated): prickling pain
2) type C fibers (slower, unmyelinated): burning/ aching pain
what is a themoreceptor?
= free nerve endings in the dermis, liver & hypothalamus- info sent along lateral spinothalamic pathway to thalamus and reticular formation (same as with nociceptors)
what is a mechanoreceptor?
respond to: stimuli that distort cell membrane, and mechanically open ion channel
1) tactile receptor: detect touch, pressure & vibration
2) baroreceptors: free nerve endings within elastic tissue, detect pressure changes in walls of blood vessels and in portions of the digestive, reproductive & urinary tract
3) proprioceptors: detect position of joints & muscles
- muscle spindles
- golgi tendon organs
- receptors in joint capsules = free nerve endings that detect pressure, tension & movement
what is a chemoreceptor?
detect changes in pH, [O2] and [CO2]
the orders of sensory pathways organization
1) first order neuron: afferent, sensory neurons that bring sensroy info into CNS
- location of cell body: dorsal root
2) second order neurons: interneuron
- location of cell body: medulla oblongata or posterior/ dorsal horn then cross to opposite side of CNS from source of stimulus
3) third order neurons
- location of cell body: thalamus
- third order neurons synapse with neurons located: cerebrum (somatosensory cortex)
how location of sensation is interpreted: corresponds to specific area of primary cortex stimulated
what are 2 types of sensory pathways
A) somatic sensory pathways
- sensory info from skin, skeletal muscles, joints
- info sent to cerebrum & cerebellum
B) visceral sensory pathways
- sensory ifo from visceral tissues and organs
- info sent to brainstem & dencephalon
what are visceral tissue sand organs?
heart/ lungs/ adrenen gland/ thyroid gland etc - anything soft internal organs of the body
the types of somtatic sensory pathways
a) posterior column path way “PFPV”
- carries sensation of: highly localized pressure, fine touch, vibration, & proprioception
b) anterior spinothalamic pathway “CAP”
- carries sensations of: crude touch & pressure. (deeper touch/ pressure)
c) lateral spinothalamic pathway “LPT”
- carries sensations of: pain & temperature
d) spinocerebellar
- no conscious senstation (doesn’t go to cortex)
what is a posterior column pathway?
PFPV
- highly localized pressure, fine touch, vibration and proprioception
- origin of second order neuron: medulla oblongata
- ascend: posterior column
- site of decussation (crossing over): medulla oblongata
what is an anterior spinothalamix pathway?
CAP
- crude touch & pressure (deeper)
- origin of 2nd order neuron: posterior/ odrsal horn of spinal segment
- ascends: anterior column (anterior spinothalmic tract) = ascending
- site of decussation: 2nd order neuron crosses in spinal cord
what is a lateral spinothalamic pathway?
LPT
- carries sensations of: pain & temperature
- origin of 2nd order neuron: posterior/ dorsal horn of spinal segment
- ascends: lateral column (lateral spinothalmic tract)
- site of decussationL 2nd order neuron crosses in spinal cord
what is a spinocerebellar pathway?
- no conscious sensation: doesn’t go to cortex
= conveys proprioceptive info ab position of muscles, joints & tendons to cerebellum - origin of 2nd order neurons: dorsal gray horns
(some axons decussate, some dont) - termination of 2nd order neurons: cortex of cerebellum
what is the effect of a partial spinal lesion at T10?
- loss of a ll sensation on right side in dematone T10
- loss of pain and tem sense
- loss of touch and vibration sense
- no loss of sensation
- posterior column pathway
- lateral spinothalmic pathway
what is referred pain? p28
due to convergence of afferent neurons on same interneuron 1
a) first theory: pain generated by one part of the body, but experienced in another b/c the affected visceral organs are innervated by the same spinal segments as specific regions of the body surface
b) second theory: nocleptors from several locations converage on a single, ascending tract in the spinal cord.
- pain signals from the skin are more common that pain from internal organs and the brain associates activation of the pathway with pain in the skin.
the components of each pathway (e.g. posterior column, spinocerebellar, spinothalamic pathways)
posterior column pathways:
- fasciculus gracilis (localized pressure, fine touch, vibration and proprioception)
- fasciculus cuneatus (superior half of body)
spinocerebellar pathways
- posterior spinocerebellar tract (muscle spindle)
- anterior spinocerebellar tract (golgi tendon organs)
spinothalamic pathway
- lateral spinothalamic tranct (paint & temperature)
- anterior spinothalamic tract
What is visceral sensory pathways & visceral reflex arcs
??????
Interoreceptors monitor visceral tissues & organs (e.g. smooth muscle, cardiac muscle, glands, mouth & throat)
- synapse directly on motor neurons in the spinal cord = visceral spinal refelx arc
- or travel up the spinal cord and synapse on motor neurons in the solitary nucleus of the medullar oblongata
typicially, there is no conscious awareness of cisceral sensation
what are 2 motor neruons involved in somatic motor pathways
somatic nervous system controls skeletal muscles
somatic motor pathways involves at least 2 motor neurons:
1. upper motor neuron (UMN)/ cell body; in CNS processing center
2. lower motor neuron (LMN)/ cell body; in brain stem or spinal cord
= each LMN activates a single motor unit in skeletal muscle
what is a motor homunculus
different parts of primary motor cortex control different regions of body
what are the three somatic system motor pathways? (somatic nervous system)
- corticospinal pathway (pyramidal tracts): provides voluntary control over skeletal muscle
- corticobulbar tract
- lateral corticospinal tract
- anterior corticospinal tract - medial pathways (extraphyramidal tracts)
- tectospinal
- vestibulospinal
- reticulospinal - lateral pathway (extrapyramidal tracts)
= rubrospinal tracts
what are the three tracts of corticospinal pathway
corticospinal pathway: provides voluntary control over skeletal muscle
= uppoer motor neurons originate in the primary motor cortex
- corticobulbar tract (cortext to bulb;upper motor neuron): corosses over in brain stem
- lateral corticospinal: descends on opposite side to synapse with LMNs in 85 anterior gray horns
- anterior corticospinal: crosses over in spinal cord
what is a medial pathway?
extrapyramidal tracts: tectospinal, vestibulospinal & reticulospinal
: controls gross movements of trunk & proximallimb muscles and eye, head & neck and allows reflexes. reticulospinal is involed in locomation and posture control.
- conveys motor commands generated at: a subconscious level
- UMN cell bodies located in brain stem & most axons cross over immediately (except reticulospinal don’t cross; some vestibulospinal decussate in medulla & some stay ipsilateral)
- synapse with LMNs that are also innervated by corticospinal pathway
- modify voluntary muscular contraction via facilitation & inhibition of LMNS
Three tracts of medial pathways
- tectospinal (eye)
UMN starts intectum
= superior colliculus
= eye &head reflexes to flash of light, puillary reflex, corneal/ bink reflex, doll’s eye reflex, accommodation reflex
(inferior colliculus is involved in eye/ head reflex to noise) - vestibulospinal (ear): UMN starts in vestibular nuclei in region where pons meet medulla oblongata
= balance info from inner ear (vestibule) allows for righting reflex - reticulospinal: UMN starts in RAS = reticular activating system/ formation
what is lateral pathway
controls learned & precise movements of distal upper limbs, but not fine finger movements
(extrayramidal tracts): rubrospinal tract
- convey motor commands generated at a subconscious level (using input from cerebrum & cerebellum)
- UMN cell bodies located in midbrain & axons cross over immediately
synapse with LMNs that are also innervated by corticospinal pathway - modify voluntary muscular contraction via facilitation & inhibition of LMNs
what is a balsal nuclei
somatic motor pathways are also oversee by basal nuceli and cerebellum
basal nuclei: deep within cerebral hemispheres
(functions)
- provide background patterns of activity in voluntary movements
- operate by: adjusting activities of upper or lower motor neurons
2 major pathways of basal nuclei operations:
1. influences thalamic neurons which influences premotor cortex to adjust upper motor neurons = indirect pathway
2. influences centrer in brain stem which influence excitability of lower motor neurons
The roles of the basal nuclei in modifying movements
sensory areas (in cerebral cortex)
1. receptors sens signals into sensory areas,
2. the information on body position and the output of motor areas of the cerebral cortex in sensory areas (cerebral cortex) is passed to basal nuclei (into caudate nucelus and putamen)
3. basal nuclei processes and integrate within the basal nuceli and globus pallidus (one of the basal nuclei) directs control over movements
4. through red nucleus, superior and inferior colliculi, reticular formation, it faciliates ongoing movement of unconscious adjustments in muscle tone and limb position
(3.a) globus pallidus also passes the signal of indirect modification of movement to motor areas
- motor areas: subconscious adjustment and modification of voluntary motor commands
(3.b) through thals, premotor, SMA & UMN of primary motor cortex, and through corticobulbar & corticospinal pathways, eventually results in voluntary skeletal muscle movement
what is the function of cerebllum in somatic motor system
receives sensory info from proprioceptors and the eyes; also receives info ab balance from inner ear
function: modifies activities of upper motor neurons to aggenerate smooth, accurate movements & maintains balance
- improves with repetition; e.g. fine tunes movements of athletes
- damaged/ impaired by drugs and alcohol, causing reduced motor control (e.g. ataxia)
ataxia: A! taxi! Ahhhh!!!!1
