L8 Flashcards
what is sensation
detection of sensory stimulus
stimulus is a change in the external or internal environments
list some sensory stimuli
sight, sound, smell,
touch, pressure, taste, temperature, gravity,
position, pain etc.
what is perception
interpretation of the meanings of the
sensory stimuli
where do sensation and perception occur
in the brain
what are the special sensors
Taste, smell, vision, hearing & balance
where does each specialised sense organ project to in the brain
primary sensory cortex
where are the neurons for taste located
taste - lower end of postcentral gyrus
where are the neurons for smell located
smell - medial temporal (uncus) and orbitofrontal lobes
where are the neurons for vision located
vision - occipital lobe
where are the neurons for hearing located
hearing - superior temporal lobe
where are the neurons for equilibrium/balance located
equilibrium - mainly to the cerebellum
what nerves are involved in the special sensors
all of the cranial nerves
what are sensory receptors
are specialized receptors that respond to changes in their
environment
how are sensory receptors classified
the type of stimulus they detect
their body location
their structural complexity
what are mechanoreceptors
are sensitive to a mechanical force
e.g. touch, pressure, vibration, stretch & itch
what are thermoreceptors
are sensitive to temperature changes
what are photoreceptors
respond to light energy (the retina of the eye)
what are chemoreceptors
respond to chemicals in solution (molecules smelt or tasted, or changes in blood chemistry)
what are nociceptors
respond to potentially damaging stimuli that result
in pain eg burn or sting
noci = harm
what are exteroceptors
are sensitive to stimuli arising outside the body therefore they are located near or at the body surface
what are some examples of exteroceptors
touch, pressure, pain & temperature receptors (skin)
receptors of special senses (vision, hearing etc.)
what are interceptors/visceroceptors
are sensitive to stimuli within the body therefore they are located in the visceral organs & blood vessels
they monitor a variety of stimuli (eg. chemical changes, tissue stretch, temperature)
what are proprioceptors
are sensitive to internal stimuli
these are the receptors located in skeletal muscles, tendons, joints,
ligaments & in connective tissue coverings
of bones & muscles (located in the musculoskeletal system) (eg. joint kinesthetic receptors)
equilibrium receptors of the inner ear are
sometimes included in this class
their job is to constantly advise the brain of the body’s movement and location in space
where are complex receptors found
in the special sense organs
what is the somatosensory system
the part of the sensory system serving the
body wall & limbs
where does the somatosensory system receive inputs from
receiving inputs from exteroceptors &
proprioceptors
what are the 3 levels of the somatosensory system
the sensory receptors, ascending pathways and the cerebral neuronal circuits
describe processing at the receptor level
the receptors detect the stimuli –> then transduction happens (converting stimulus energy into changes in membrane potential in sensory axons) –> Propagation (generating nerve impulses)
describe processing at the circuit level
impulses are delivered to the appropriate regions of the cerebral cortex for
stimulus localization &
perception
or
impulses delivered to
the cerebellum
what is discriminative and non discriminative sensation
discriminative = fine touch/vibration and conscious proprioception
precise localization; only a few receptor types
non-discriminative = pain, temp, crude touch and pressure
what pathway does discriminative sensation take
dorsal column pathway
what pathway does non-discriminative sensation take
spinothalamic pathways
what is dissaspcated sensory loss
discriminative and non-discriminative sensation travel in different pathways therefore if you were to damage one pathway you would still have the other type of sensation
where is the first order neuron of the dorsal column pathway located
dorsal root ganglion
where is the second order neuron of the dorsal column pathway located
the nuclei gracilis and cuneatus
where is the 3rd order neuron of the dorsal column pathway located
the internal capsule (thalamus)
where does the dorsal column pathway decussate
the medulla
what is the role of the dorsal column medial lemniscus pathway
Transmits sensory impulses from general sensory
receptors of skin & proprioceptors (interpreted as discriminative touch &
conscious proprioception) to opposite somatosensory cortex
where does the gracile tract carry impulses from
Gracile tract carries impulses from lower limbs
& inferior body trunk
what information does the cuneate tract transmit
Cuneate tract transmits afferent impulses from
upper limbs, trunk & neck (not present in spinal cord below T6)
what do the gracile and cuneate tract form
the dorsal column pathway
what is a lemniscus
a bundle of axons
what is the role of the dorsal column medial lemniscus pathway
Transmits sensory impulses from general sensory receptors of skin & proprioceptors (interpreted as discriminative touch &
conscious proprioception) to opposite somatosensory cortex
what information does the gracile tract carry
impulses from lower limbs
& inferior body trunk
what information does the cuneate tract carry
transmits afferent impulses from upper limbs, trunk & neck (not present in
spinal cord below T6)
what does the lateral spinothalamic pathway detect
pain and temp
describe the lateral spinothalamic pathway
the first order neuron is in the dorsal root ganglion
synappes in the spinal cord
second order neuron is the dorsal horn neuron
crosses laterally in the spinal cord and then goes up to the thalamus. this is the location of the 3rd order neuron
from here the 3rd order neuron goes up though the internal capsule to the postcentral gyrus
where is the lateral tract located
lateral to the anterior horn (after it crosses over)
what kind of information does the anterior spinothalamic pathway transmit
Transmits impulses concerned with crude
touch & pressure to opposite somatosensory
cortex
what are spinocerebellar pathways
from the spinal cord to the cerebellum
these are NOT for conscious sensation
what information do the spinocerebellar tracts transmit
Transmit information about muscle or tendon
stretch to the cerebellum, which use this
information to coordinate skeletal muscle
activity
therefore they are responsible for unconscious proprioception
describe the pathway of the spinocerebellar tract
start in proprioceptor. the first order neuron is in the dorsal root ganglion
the 2nd order neuron is in the dorsal horn nucleus which then goes into the cerebellum
NOTE there is no 3rd order neuron because this tract does NOT decussate
this travels up the posterior lateral side of the spinal cord
how does the brain process perceptual information
Interpretation of sensory
input (stimulus location
and/or type) depends on the locations of the target neurons in the sensory cortex
Each sensory axon -
“labeled phone line”
telling brain “who” is
calling & from “where”
what would be the result of a dorsal column injury
Loss of fine touch and conscious proprioception on same side below the site of injury
what would be the result of an injury on the left anterolateral side
Loss of pain and temperature on right
side
what would be the result of an injury on the right posterolateral side
Loss of unconscious proprioception to the cerebellum from the right side of the body.
Because this one never crossed over
describe the general organisation of the motor systems
the premotor cortex is always planning movement. this signal goes to the cerebellum which works out the best way to do the movement and sends it to the thalamus
the signal waits in the thalamus until a signal from the premotor cortex removes the brake from the basal ganglia
from the thalamus it goes back up to the primary motor cortex
from here it goes to the brain stem via the dirrect pathway and then from the brainstem to the spinal cord via the indirect pathway
it then goes through the spinal cord to the skeletal muscles
what is the hierarchy of motor control
the highest level contains the premotor cortex, basal ganglia and the cerebellum
the middle level is the primary motor cortex
the lowest level is the spinal cord
what is the name of the highest level of hierarchy of motor control
(theres 2 names)
precommand level
or pre action level
what is the name of the middle level of hierarchy of motor control
projection level
what is the name of the lowest level of hierarchy of motor control
segmental level
what is the orientation of neurons at the segmental level
there are interneurons in the dorsal horns of the spinal cord
ventral horns contain motor and inter neurons
what are central pattern generators
the segmental circuits in the spinal cord that control
locomotion (eg. walking)
& other specific & oft-repeated motor activity
what do central pattern generators consist of
consists of a network of local interneuron and motor neurons, on both sides of the spinal cord, that work together to generate
a rhythmic pattern of motor activity
what initiates and modulates central pattern generators
a “switch” consisting of the brainstem command neurons, particularly reticulospinal neurons
Upper Motor Neurons in the primary cortical motor areas & brainstem directly control what
the spinal cord
The cortical motor areas produce the direct
(pyramidal) system
Brainstem motor areas oversee the indirect
(multineuronal, extrapyramidal) system
describe the pathway of the pyramidal tract (direct pathway)
the primary motor cortex transmits its signal through the posterior limb of the internal capsule to the cerebral peduncle in the medulla. from here it goes through the pons to the pryimid (medulla)
it crosses over at the pyramidal decussation (at the level of the medulla spinal cord junction) into the lateral corticospinal tract where it descends in the lateral column to the lateral intermediate zone and the lateral motor nuclei
what are the 3 parts of the internal capsule
the anterior limb, genu and the posterior limb
what tract runs through the posterior limb of the internal capsule
the corticospinal tract
there are body regions sitting within the internal capsule. what are these
most anteriorly is the face
then upper extremity –> trunk –> and lower extremity most posteriorly
the corticospinal tract breaks into 3 parts at the decussation. what are these
90% goes into the lateral corticospinal tract
8% becomes the anterior corticospinal tract
2% never crosses over and becomes the uncrossed lateral corticospinal tract
what does the corticospinal tract regulate
fast and skilled movements
what does the corticospinal tract control
reflex motor output and modifying sensory input
what does damage to the corticospinal tract cause
damage at any level leads to paralysis of target muscles
eg If lesion above pyramidal decussation on right –> paralysis of left upper limb and lower limb muscles
If lesion below the pyramidal decussation in the left lateral T10 spinal cord paralysis of left
lower limb muscles.
what are the corticobulbar tracts
they go from the cortex to the bulb (brainstem). these have bilateral synappes and are mainly on the contralateral side
these then go into the crainial nerve
what is the indirect (extrapyramidal) system
Motor axons arise from several brainstem nuclei
what are the 4 major nuclei/regions of the extrapyramidal system
Superior colliculus, located in tectum or roof of midbrain
Red nucleus in the midbrain
Reticular formation in pons & medulla
Vestibular nuclei in medulla
what are the 4 major pathways of the extrapyramidal system
Tectospinal tracts – move head & neck, visual input
Rubrospinal tracts – maintain muscle tone
Reticulospinal tracts – initiates CPG in spinal cord
Vestibulospinal tracts – maintain balance
what are the Tectospinal tracts responsible for
move head & neck, visual input
what are the Rubrospinal tracts responsible for
maintain muscle tone
what are the Reticulospinal tracts responsible for
initiates CPG in spinal cord
what are the Vestibulospinal tracts responsible for
maintain balance
summery
what is the projection level
The pyramidal tracts
- originate from the primary motor cortex
- synapse either with interneurons or with
ventral horn motor neurons in spinal cord
- concerned with voluntary, discrete, skilled
movements
The command neurons in the brainstem nuclei can function to start, stop or modify the basic rhythm of CPGs of the spinal cord
through the indirect pathways
The command neurons in the brainstem nuclei also
regulate muscle tone (posture) and balance
summery
what is the precommand level
Includes the premotor cortex, cerebellum & basal
ganglia
Premotor cortex responsible for initiating plan for next intended movement
innervates Basal ganglia to
release brake to start a specific movement
innervates Cerebellum which precisely calculates the best way to achieve
coordinated synergistic movements across multiple
limb joints = sends this “blueprint” to the primary
motor cortex, which then starts the intended
movement. also monitors muscle tone and balance
what is the effect of a stroke in the internal capsule
the function of the face, upper extremity, truck, and lower extremity would be effected
