Ch 15 Sensory pathways and the somatic nervous system Flashcards
Describe the receptive field. (Figure 15-2)
The area receptive to stimuli monitored by a single receptor cell.
General sense receptors are typically the
dendrites of sensory neurons.
The conversion of a sensory input to a change in membrane potential in the receptor is known as
transduction
A reduction in sensitivity in the presence of a constant stimulus is referred to as
adaptation
How do we become aware of the sensation of touch?
General sensory receptors send information to the primary somatosensory cortex.
Receptor specificity can arise from __________.
the presence of accessory cells
the structure of the receptor cell
the presence of structures that protect the receptor cell
You cannot tell when your small intestines shift position as food enters because you do not have any ________ there.
proprioceptors
Receptors in your stomach that determine when food enters because the pH changes would be classified as
chemoreceptors
Mechanoreceptors that respond to changes in blood pressure are called
baroreceptors.
We are constantly bombarded by a variety of stimuli inside and outside of our bodies. Why are we not overwhelmed by sensory information?
A very tiny percentage of incoming sensory information is received by the cerebral cortex.
Pain is to ________ as cold is to _______
nociceptors; thermoreceptors
Receptive characteristics
- Specificity
- Field
- Tonic (slow) + phasic (fast)
- Transduction (convert stimulus to change in membrane potential which leads to AP)
Classification of receptor
• stimulus type => name usually define what it is
• location => where stimulus arise
What impact the specificity of receptors & how?
Structural complexity
• Free nerve endings
• connective tissue layers around nerve endings
• accessory structures
Define Receptive field?
It’s the size that localize the stimulus.
E.g: two-point discrimination
Generator potential
If receptor is sensory neuron and when depolarization reach threshold AP generated
Receptor potential
When receptor is other type of cell and not neuron in this case graded potential can alter the rate Of NTs release by sensory receptor cell
Key features of neural pathways
- multi-neural-> 2-3 to relay info
- Spatial relationships among fibers
- Most decussate (cross sides)
- Paired symmetrically both R & L sides
Immediate involuntary response
Processing centers in the spinal cord or brainstem may direct an immediate reflex response even before sensations reach the cerebral cortex.
Voluntary response
The voluntary response, which is not immediate, can moderate, enhance, or supplement the relatively simple involuntary reflexive response.
next half start at 21 deck
Key features for neural pathways
=> multi-neural (2-3)
=> Most exhibit spatial relationships
among fibers that reflect mapping
=> Most decussate (cross sides) at
some point
=> Pathways are paired symmetrically
define immediate involuntary response
Processing centers in the spinal cord or brainstem may direct immmediate reflex response even before sensation reach cerebral cortex
voluntary response
it is not immediate, can moderate, enhance, or supplement the relatively simple involuntary response.
name the three pathways for somatic sensory information (SSP)
Posterior column pathway
Spinocerebellar pathway
–posterior/anterior tracts
spinothalamic pathway
–lateral/ anterior
explain somatic sensory pathways
- Ascending tracts
- Associated with white matter of spinal
cord - Two have 3rd order neurons
what are the stimulus for spinothalamic pathway
-provide sensation from the poorly localized touch, pain, and pressure
explain the pathway for spinothalamic
First-order neuron => enter spinal cord at the posterior horns on second-order neuron
second => the interneuron cross to the opposite side of the spinal cord.
Third => the interneuron synapse in the primary somatosensory cortext
define somatotopy
the functional mapping of the somatosensory cortex. also called ‘homunculus’ mean ‘‘little man’’
how map area is divided for different regions in the somatosensory cortex.
like caricature => size of the devoted region for body parts is proportional to the density of the sensory input received from that region.
Posterior column pathway
It carries highly localized fine touch, pressure, vibration, and proprioception. also known as posterior column- medial lemniscus pathway
bague explanation of spinothalamic
- Inputs come from many
different types of sensory
receptors - May make multiple synapses
in brainstem - Aware of stimulus, but have
difficulty localizing precisely
vague explanation of posterior column pathway
- Inputs come from a single or a
few related types of sensory
receptor - Information sorted by 1)
nature of stimulus and 2)
body region involved - Localize stimulus
precisely on body surface
Spinocerebellar pathway
The cerebellum receives proprioceptive information about the position of the skeletal muscles, tendons, and joints along this pathway.
Posterior spinocerebellar tract
it contains the axons that do not cross over the opposite side of the spinal cord.
It reach to cerbellar cortex by the inferior cerebellar peduncle of that side.
Anterior spinocerebellar pathway
these are dominated by axons that have over to the opposite side of the spinal cord.
Adaptation of SSP
it can reduce the amount of sensory
information reaching the CNS (peripheral adaptation) and cerebral cortex (central adaptation)
Frequency and pattern of action potentials of SSP
it provides information about the stimulus such as strength duration and variation
labeled lines and preception about SSP
- The labeled line that is activated tells the brain about the type of stimulus and where it is coming from
- Your perception of the nature of the stimulus depends on the path it takes in the CNS
Visceral sensory pathway
- Visceral sensory information is collected by
interoceptors monitoring visceral tissues and organs:
(Primarily within thoracic and abdominopelvic cavities
=> goes to medulla oblongata
what are the interoceptors
Interoceptors include:
nociceptors,
baroreceptors,
thermoreceptors,
tactile receptors,
chemoreceptors
Referred pain
not localised enough as many neurons from multiple places merge into one neuron.
visceral pain info travel similae route as somatic pain info.
key features of somatic motor pathways SMP
- contraction of skeletal muscles
- centers in cerebrum, diencephalon, and brainstem.
- conscious or unconscious reflexive control
what motor neurons include in SMP
- Upper motor neuron – cell body in CNS
processing center - Lower motor neuron – cell body in
brainstem or spinal cord, axon extends out
of CNS
major Somatic motor pathways
=> corticospinal pathway
=> Lateral Pathway
=> Medial Pathway
Corticospinal Pathway
=> Upper motor neuron descend to spinal cord without synapsing
=> associated with fine and fast skilled movements
=> axons in the corticospinal tracts cross to the opposite side either in brainstem or spinal cord.
=> heavily myelinated
Lateral pathways
=> related to limbs
=>helps control distal limb muscles
that perform precise movements
=> it controls subconscious movements of muscle tone & body posture.
Medial pathways
=> helps control gross movements
of trunk and proximal limb
muscles
=> lower limbs and head position
Basal ganglia
Subconscious adjustment and modification of voluntary motor commands
cerebellum
=> Coordinates complex somatic motor patterns
=> adjust out of the other somatic motor centers in brain and spinal cord.
role of cerebellum and basal ganglia in the somatosensory/motor pathways
Adjusting the activity of motor pathways
often involves stimulating or inhibiting
1) motor nuclei
2) the primary motor cortex
