Ascending sensory pathways Flashcards
sensation
detection of sensory stimuli
sensory stimulus
a change in the internal or external environments. this includes sight, sound, smell, touch, pressure, taste, temperature, etc.
perception
the interpretation of the meanings of sensory stimuli
special senses
taste, smell, vision, hearing and balance
Where is the taste sensory cortex
the lower end of the postcentral gyrus
where is the smell sensory cortex
medial temporal (uncus) and orbitofrontal lobes
where is the vision sensory cortex
occipital lobe
where is the hearing sensory cortex
superior temporal lobe
where is the balance sensory cortex
cerebellum
mechanoreceptors
sensitive to a mechanical force
thermoreceptors
sensitive to temperature changes
photoreceptors
respond to light energy
chemoreceptors
responds to chemicals in solution
nociceptors
respond to potentially damaging stimuli that result in pain
exteroceptors
are sensitive to stimuli arising outside the body. these are located near or at the body surface.
includes: touch, pressure, pain and temp receptors, as well as receptors of special senses
interoceptors or interoceptors
are sensitive to stimuli within the body. they are located in the visceral organs or blood vessels. they monitor a variety of stimuli
proprioceptors
are sensitive to internal stimuli. they are located in skeletal muscles, tendons, joints, ligaments and in connective tissue. balance receptors of the inner ear may be included
complex receptors
located in the special sense organs
simple receptors
detect tactile sensation, temperature, pain, muscle senses
types of nerve endings for simple receptors
free nerve endings
encapsulated nerve endings
free nerve endings
detects pain and temperature. they are located in epithelial tissue
encapsulated nerve endings
tactile corpuscles - fine touch
lamellate corpuscles - pressure
General organisation of the somatosensory system
sensory receptors at the receptor level
ascending pathways at the circuit level
cerebral neural circuits at the perceptual level
processing at the receptor level
involves receptors detecting stimuli, transduction of the stimuli into membrane potentials and propagation of nerve impulses to be send to the brain
processing at the circuit level
impulses are delivered to the appropriate regions of the cerebellar cortex for stimulus localisation and perception, or to the cerebellum
dorsal column pathway (function)
is for discriminative sensation. this pathway is for fine touch/vibration, conscious proprioception and precise localisation.
the medial lemniscus pathway
transmits sensory impulses from general sensory receptors of skin and proprioceptors to opposite somatosensory cortex.
it has two tracts - the graciel and cuneate tract
the graciel tract
carrier impulses from the lower limbs and inferior body trunk
the cuneate tract
transmits afferent impulses from the upper limbs, trunk and neck
the spinothalamic pathways (function)
is it non-discriminative sensation. these pathways detect pain and temperature, crude touch and pressure.
the dorsal column pathway
sensory neurons are connected to the first-order neuron, which has its cell body in the dorsal root ganglion. the first-order neuron sends the signal through the dorsal column and synapses onto the second-order neuron, which has its cell body in the medulla. decussation occurs. the second-order neuron synapses onto the third-order neuron, which is located in the thalamus. this neuron sends the information up to the post-central gyrus through the medial lemniscus pathway.
the spinothalamic pathway
the first order neuron is connected to the sensory receptor. it has its body in the dorsal root ganglion. the first-order neuron synapses with the second-order neuron at the dorsal horn neuron. this is where decussation occurs. the second-order neuron sends information up through the lateral column of the spinal cord, and synapses with the third-order neuron at the thalamus. the third-order neuron sends the information to the post central gyrus.
the lateral spinothalamic pathway
transmits impulses concerned with pain and temperature to the opposite somatosensory cortex
the anterior spinothalamic pathway
transmits impulses concerned with cruse touch and pressure to opposite somatosensory cortex
the spinocerebellar pathway (function)
do not contribute to conscious sensation. they transmit information about muscle or tendon stretch to the cerebellum, which uses this information to coordinate skeletal muscle activity. it is responsible for unconscious proprioception
the spinocerebellar pathway
the receptor is a proprioceptor, which connects with the first-order neuron in the dorsal root ganglion. it synapses with the second-order neuron in the dorsal horn neuron. the second-order neurons send information up to the cerebellum.
processing at the perceptual level
involves interpretation of sensory input. it depends on the locations of the target neurons in the sensory cortex. each sensory axon tells the brain the action and its location.
dorsal column injury
results in loss of fine touch and conscious proprioception on the same side below the site of injury.
injury on the left anterolateral side of the spinal cord
results in loss of pain and temperature on the right side
injury on the right posterolateral side on the spinal cord
results in loss of conscious proprioception to the cerebellum on the right side of the body
