Chapter 10 Flashcards
Perception
The conscious interpretation of the world based on the sensory systems, memory, and other neural processes
Visceral afferents
Visceral receptors transmit info to the CNS by this class of afferent neurons
Chemoreceptors- monitor O2, CO2, H+ lvls in blood
Baroreceptors- certain vessels that monitor blood pressure
Mechanoreceptors- gastrointestinal that monitor stretch or distention
Somatosensory system
Necessary for perception of sensations in the skin(somesthetic) and position of limbs (proprioception) which depends on muscles and joint receptors
Sensations: pressure, temperature, pain, and body position
Special senses
Vision Hearing Balance Equilibrium Taste Smell
Adequate stimulus
The modality which a receptor responds best to
Sensory transduction
Receptors convert the energy of a sensory stimulus into changes in mem potential call receptor potential or generator potentials (opening and closing of ion channels)
Sensory receptor forms
1: specialized structure at the peripheral end of an afferent neuron uses mem potential to propagate action potentials
2: separate cell that communicates through a chemical synapse with an associated afferent neuron used the release of neurotransmitters
Slowly adapting or tonic receptors
Show little adaptation and can function in signaling the intensity of a prolonged stimulus
Best respond to pressure
Ex. Muscle stretch receptors
Rapidly adapting or phasic receptors
Adapt quickly and thus function best in detecting changes in stimulus intensity
Best responds to vibration
Off response- some show a second smaller response upon termination of a stimulus
Ex. Olfactory receptors, pacinian corpuscles, which detect vibration in the skin
Labeled lines
The specific neural pathways that transmit info pertaining to a particular modality, each modality follows its own line
Sensory unit
Comprises a single afferent neuron and all the receptors associated with it of the same type
Receptive field
The area over which and adequate stimulus can produce a response in the afferent neuron
First order neuron
The afferent neuron that transmits info from the periphery to CNS
They may diverge within the CNS and communicate with several interneurons
Interneurons may receive converging input from several first order neurons
Thalamus
Major relay nucleus for sensory input, consist of second order neurons
Third order neurons
Form synapses with second order neurons, and transmit info to the cerebral cortex for sensory perception
Sensory coding
How a sensory receptor determines the location, strength, and type of stimulus
Stimulus type- coded by receptor and pathway(s) activated
Sensory strength- coded by the frequency of action potential and number or receptor activated
Sensory location (tactile, proprioceptive, and visual stimuli)- coded by receptive fields
Acuity
Precision with which the location of a stimulus is perceived
Depends on size, number, and overlap of receptive fields called lateral inhibition
Localization is more accurate in places of smaller receptive fields, however done by the overlapping of fields
Lateral inhibition
A stimulus that strongly excites receptors in a given location inhibits activity in the afferent pathways of other nearby receptors
Synesthesia
May hear colors, see sounds, or taste shapes
Due to developmental anomalies in the wiring of CNS, where different pathways intertwine
Two point discrimination
Measure of tactile acuity, the ability of a person to perceive two fine points pressed against the skin as two distinct points
Two point discrimination threshold; The minimum distance between two points to be perceived as separate of two diff afferent neurons
Close areas: lips finger tips (great acuity)
Further apart: back, thigh, upper arm (low acuity)
Somatoreceptors
Proprioreceptors- muscles joints
Mechanoreceptors- pressure force vibration
Thermoreceptors- skin temp
Nociceptors- tissues damaging pain, noxious stimuli
Widest variety of Receptor types
Free nerve endings
Somatic sensory receptor types that lack identifiable specialized structures
Mechanoreceptors in skin
Superficial layers epidermis: Merkel’s disks and Meissner’s corpuscles ( only hairless glabrous areas)
Inner layer dermis: hair follicle receptors, pacinian corpuscles, Ruffini’s endings
Size of receptive fields vary greatly
Thermoreceptors in the skin
Respond to temp change around receptors and tissues not external air.
Warm receptors: respond to 30°C-45°C TRPV
Cold receptors: respond to 35°C-20°C TRPM, TRPA
Actions potentials frequency increases to 45°C, then decrease rapidly
Free nerve endings with temp sensitive ion channels called (TRP) channels
Transient receptor potential channels (TRP)
Some Open or close solely in response to thermal stimuli, others to chemical stimulus include with thermal and pain transduction
7 subfamilies of TRP receptors
TRPV1-4 activated by heat
TRPM TRPA activated by cold
TRPV1+TRV2 respond to 43°C + found in nociceptors
TRPV3 and TRPV4 respond to 27°C-42°C found in warm receptors
TRPM8 responds to temp less than 25°C
TRPA1 responds to temp less than 17°C
Chemical responses to TRP receptors
TRPV3- responds to warm inducing sensations from using camphor
TRPM8 responds to methanol and eucalyptus oil causing cold sensation
TRPA1 receptors respond to mustard oil, garlic, and cinnamon
TRPV1 receptors responds to acid and capsaicin (chilli)
Nociceptors in the skin
Mechanical nociceptors: responds to intense mechanical stimuli
Thermal nociceptors: respond to intense heat 44°C+
Polymodal nociceptors: respond to all of the above and chemicals released by damaged tissue
*chemicals released from damaged tissue: histamine, bradykinin, and prostaglandins
The somatososensory cortex
Where somatic sensations from all over body originate
Vertical columns are organized according to sensory modality such as vibration cold pressure etc
Somatosensory pathways
Transmit info from peripheral sensory info to the thalamus, then to primary somatosensory cortex
1: Dorsal column medial lemniscal pathway
2: Spinothalamic tract
Both pathways enter the spinal cord on one side and cross to the other before reaching the thalamus right
Dorsal column medial lemniscal pathway
Transmits info from mechanoreceptors and proprioceptors to the thalamus, crosses to other side of CNS in medulla oblongata
1st order neurons originate in periphery and enter dorsal horn of spinal cord, terminate in medullary dorsal column nuclei to form synapses with 2nd order neurons
2nd order neurons cross over to contralateral side of medulla (medulla lemnicus) then ascends to thalamus
3rd order synapses with 2nd, transmitting info from thalamus to somatosensory cortex
Axon ascends from spinal cord to ipsilateral brainstem in the dorsal columns
The spinothalamic tract
Transmits info from thermoreceptors and nociceptors to the thalamus; crosses over to other side of CNS in spinal cord before brain
First order neurons originate in the periphery at thermo or nociceptors and enter dorsal horn of spinal cord, may ascend or descend within Lissauers tract
2nd order neurons cross over to contralateral side of spinal cord,ascend in anterolateral quadrant of spinal cord thru brainstem and terminate in thalamus
3rd order form synapses with 2nd in thalamus that ascend to the somatosensory cortex
Response to pain
Autonomic responses- blood pressure heart rate, dilation of pupil, ^ blood glucose
Emotional responses- fear and anxiety
Reflexive withdrawal from the stimulus
Fast pain
Perceived as a sharp pricking sensation that can be easily localized
Transmitted by A-delta fibers, thin lightly myelinated axons 12-30m/sec
Slow pain
Perceived as a poorly localized dull aching sensation; transmitted by C fibers, thin unmyelinated axons 0.2-1.3 m/sec
How pain is transducted
A-delta or C fibers, form synapses with 2nd order neurons (dorsal horn of spinal cord)
1st and 2nd order communicate with neurotransmitters substance P and Glutamate from 1st order neuron
2nd order neurons ascend to the thalamus via spinothalamic tract to the reticular formation of the brainstem, hypothalamus, and limbic system
Referred pain
Activation of nociceptors in viscera
Due to second order neurons also receiving input from somatic afferents
Gate control theory
States that somatic signals of non painful sources can inhibit signals of pain at the spinal level
The basis for using transcutaneous electrical nerve stimulation (TENS) to treat pain
TENS: a small current applied through skin overlying a nerve activated large diameter afferents which relieves pain
Endogenous analgesia system
Activated by an area in the midbrain called periqueductal gray matter, which communicates with the nucleus raphe magnus and lateral reticular formation in medulla
Neurons Descend to spinal cord where they block communication between nociceptors afferent neurons and 2nd order neurons
Inhibitory neurons release endogenous opiate neurotransmitter enkaphalin, can inhibit the release of substance P
