Chapter 15 SNS Flashcards
Visceral sensory information is primarily distributed to what brain regions?
reflex centers of the brain stem and diencephalon
Transduction
sensory receptors detect arriving stimulus, translate it into an action potential which conducts it to the CNS.
Receptive field
The area monitored by a single receptor cell.
Generator potential
A depolarizing receptor potential in a neural receptor
Labeled line
The link between a peripheral receptor and cortical neuron which consists of axons carrying information about modality (touch, pressure, light and sound)
Sensory coding
the translation of complex sensory information into meaningful patterns.
Tonic receptors
Are always active
Phasic receptors
Usually not active, provide information about intensity and rate of change in stimuli
Adaptation
A reduction in the pressure of a constant stimuli
Includes slow and fast adapting receptors
Fast- adapting receptors
Peripheral adaptation that occurs when the level of receptor activity changes. They respond strongly at first then gradually decrees-phasic (thermoreceptors)
Slow-adapting receptors
Tonic fibers, show little peripheral adaptation they include pain receptors (nociceptors)
General sensory receptors are classified by
the type of stimuli that excites them
Exteroceptors
Provide information about the external environment
Proprioceptors
Report the position and movement of skeletal muscles
Interoceptors
Monitor visceral organs and their functions
Detailed classification of 4 types of receptors by stimulus that excites them
Nociceptors
Thermoreceptors
Mechanoreceptors
Chemoreceptors
Nociceptors
Pain receptors that are especially common in the superficial skin, in joints, in periostea, and round artery walls
Maybe sensitive to:
1. extremes in temperature
2. mechanical damage
3. dissolved chemicals
Type A fibers carry fast pain (pricking)
Type C fibers carry slow pain (burning and aching)
Endorphins and enkephalins are neuromodulators that
inhibit activity along pain sensations
Thernoreceptors
free nerve endings located in the skin and skeletal muscles, in the liver and hypothalamus. Consist of hot and cold but cold are 3-4 times more numerous
Mechanoreceptors
Contain mechanically gated ion channels that close in response to stretching, compression, twisting or other distortions of their membrane. 3 classes are: 1. Tactile 2. Baroreceptors 3. Proprioceptors
Tactile receptors
Provide sensations of touch, pressure and vibration
- free nerve endings: in epidermal cells and the cornea
- root hair plexus: adapt rapidly
- tactile discs/merkle: fine touch
- tactile corpuscle/meissner’s: recieve fine touch pressure and vibration
- lamellated corpuscle/pacinian: deep pressure
- ruffini corpuscle: located in deep dermis and show little adaptation
Baroreceptors
Monitor changes in pressure in an organ and walls of major blood vessels. (carotid sinuses and aortic sinuses) Also in the lungs.
Respond immediately to changes in pressure
Proprioceptors
Monitor the position of joints, tendons and skeletal muscles
3 types are:
1. Muscle spindles: monitor stretch
2. Golgi tendon organs: joint between skeletal muscles and tendons
3. Receptors in joint capsule
Do not adapt and constantly send information to the CNS
Chemoreceptors
Detect small changes in specific chemicals or compounds . Generally only respond to water or lipid soluble compounds.
Monitor pH and CO2 levels in the blood
3 order neurons in ascending order
first order: delivers sensation to the CNS (meaning spinal cord) second order: interneuron that maybe located in the spinal cord or brain third order (if sensation is to reach awareness the 2nd order synapses with a 3rd order)
3 major somatic sensory pathways
- Spinothalamic
- Posterior column pathway
- Spinocerebellar
Spinithalamic pathway
Provides conscious sensation of poorly localized (crude) touch, pain and pressure.
1st: synapses in posterior grey horn with 2nd
2nd: Interneurons cross the spinal cord before ascending to the thalamus
3rd synapses with the primary motor cortex
Posterior column pathway
Carries fine touch sensations of touch pressure vibration and propioception. Contains the faciculus gracilis and fasciculus cuneatus.
1st: enters through dorsal root ganglion and ascends to synapse in the medulla with the 2nd
2nd: which then crosses the medulla and ascends to the thalamus to synapse with the 3rd
3rd: enters the primary sensory cortex
Spinocerebellar pathway
1sr: synapse in the posterior grey horns, the anterior tract crosses over and the posterior tract does not.
2nd: ascend to the cerebellum.
Does not reach our awareness
“double cross” so they synapse on the same side as the original stimulous
Our ability to recognize stimulus depends on
projection of information from the thalamus to the primary sensory cortex
Two motor neurons that are always involved in somatic motor pathways
Upper motor neurons: cell body lies in the CNS processing center
Lower motor neurons: cell body lies in a nucleus of the brain stem of spinal cord
Descending tracts of the spinal cord
Corticospinal pathway
Lateral pathways
Medial pathways
Corticospinal pathway (3 pairs of descending tracts)
Corticobulbar tracts
Lateral corticospinal
Medial corticospinal
Corticobulbar tracts
Synapse on the lower motor neuclei of cranial nerves III, IV, V, VI, VII, IX, XII. Provide conscious control over these regions and innervate the motor centers of the medial and lateral pathways
Medial pathway
Helps control gross motor motor movements of the trunk and proximal limbs. They include 3 tracts:
- vestibulospinal
- tectospinal
- reticulospinal
Lateral pathway
Contols distal limb muscles and more precise movements
Cross over and descend the spinal cord through the rubrospinal tracts
Basal neucleiq
Provide back ground patterns of movement involved in voluntary movement patterns by:
Cerebellum
Monitor proprioception, visual information, and balance.,
