Lesson 1 General Senses Flashcards
what are the two kinds of receptors?
- Receptors with bare nerve endings
Or - True sense organ
what are receptors?
Structure specialized to detect a stimulus
what are sense organs?
A structure that combines nerve tissue that is surrounded by other tissues; which enhances response to certain types of stimulus.
what is accessory tissue?
The extra tissue that surrounds sense organ nerve tissue, that aids in response to stimuli.
- type of tissue includes epithelium, muscular tissue, and connective tissue.
what is transduction?
Conversion of energy from one form to a different form.
What is the fundamental purpose of any sensory receptor?
Is to convert electrical energy into nerve signals
what are the two stages in the sensory process?
1.) Sensation= sensory receptor detection
2.) Perception= conscious experience
what is receptor potential?
A small localized electrical change
- if the stimulation is strong enough then the neuron fires AP and nerve signals to the brain.
- part of the sensation stage in the sensory process
what are the kinds of information sensory receptors transmit?
1.) Modality
2.) Locations
3.) Intensity
4.) Duration
what is modality?
A type of stimulus or the perception it produces.
what is location?
where the stimulus is located
- Encoded by which nerve fibers are firing
what is a labeled line?
A chain of neurons that sends information to the CNS.
- separates different information from one and other
what is a receptive field?
A single sensory neuron area of detection for stimuli.
- Size determines resolutions (ability to distinguish between two close-together stimuli
what is intensity?
strength of stimulus
-Ex: whether a sound is loud or soft
How is intensity encoded?
1.) Which fibers respond
2.) How many fibers respond
3.) How fast the fibers are firing
what is duration?
How long the stimulus last
- encoded by changes in firing frequency over time
what is sensory adaptation?
If a stimulus is prolonged, the firing of the neuron slows down over time, and we become less aware of the sensation.
- stop responding
what is phasic receptors?
- adapt quickly
- bursts of signals when the stimulus starts, then stops in the middle, finally when the stimulus stops signals begin again
-Ex: smell, hair movement - llllllllll———–llllllll
what are tonic receptors?
- adapt slowly
- AP continue steadily while stimulus is present
-Ex: body position, muscle tension, and pain - lllllllllllllll
what are the classification by stimulus modality
1.) Photoreceptors= located in eyes and responds to light
2.) Thermoreceptors= responds to heat and cold
3.) Nociceptor= respond to tissue injury, activation of these receptors produces the feeling of pain
4.) Chemoreceptors= respond to chemicals
- Ex: oders, tastes, body fluid composition
5.) Mechanoreceptors= respond to physical deformation
- vibration, touch, pressure
- organs of hearing and balance use mechanoreceptors
what is analgesia?
inability to feel pain
what is hypergesia?
increase in sensitivity to pain
what are type-A axons?`
large myelinated fibers
- sends signal fast
- prickling/fast pain
- Ex: deep cut, injection
- reaches CNS fast to trigger somatic reflexes before reaching primary somatosensory cortex.
what are type-C axons?
small unmyelinated fibers
- slow
- sends burning/aching/slow pain
- activates reticular formation and thalamus
- not specific to exact location of affected area
what are carotid bodies? what do they do?
located near the origin of the internal carotid arteries on each side of the neck
- blood going to brain
what are Aortic bodies? what do they do?
Located between the major branches of the aortic arch
what is the pain sensation pathway?
1.) Reticular formation in brainstem
2.) Thalamus
3.) Primary sensory cortex
what are the three classes of Mechanoreceptors?
1.) Tactile receptors
2.) Baroreceptors
3.) Proprioceptors
what are mechanoreceptors?
Receptors that respond to stimuli the physically distort the receptor’s plasma membrane; contains mechanically-gated ion channels that open and close in response to stretching, compression, and twisting.
what are Tactile receptors?
- Mechanoreceptors
Fine touch and pressure receptors
- very sensitive
- narrow receptive field
provides sensory information like:
- exact location
- shape
- size
- texture
- movement at the location
Also include crude touch and crude pressure receptors
- less sensitive
- large receptive field
- gives little information about stimulus
What are Baroreceptors?
- Mechanoreceptors
Monitors change in pressure
- has free nerve endings that branch with elastic tissues
- Location: walls of distensible organs like blood vessels and digestive organs
- Phasic receptors
What are Proprioceptors?
- Mechanoreceptors
- Monitors position of joints
- Monitor tension in tendons and ligaments
- Monitor the amount of skeletal muscle contraction
what are the three major groups of Proprioceptors?
1.) Receptors in joint capsules= free nerve endings that detect pressure, tension, movement at joints.
2.) Golgi tendon organs= located between skeletal muscle and its tendon. Monitor external tension generated during skeletal muscle contraction. Stimulated by tension in the tendon.
3.) Muscle spindles= Monitor skeletal muscle length; used to trigger stretch reflex.
What are the 6 classes of Tactile receptors?
1.) Tactile (Merkel) discs
2.) Hair receptors (root hair plexuses)\
3.) Tactile (Meissner) corpuscles
4.) End bulbs (Krause end bulbs)
5.) Bulbous (Ruffini) corpuscles
6.) Lamellar (Pacinian) corpuscles
Which Tactile receptors are unencapsulated nerve endings?
1.) Free nerve endings
2.) Tactile (Merkel) discs
3.) Hair receptors (root hair plexuses)
Definition of Free nerve endings?
They are Tonic receptors with small receptive fields that are bare dendrites.
- detect temperature and pain
- abundant in skin and mucous membranes
Definition of Tactile (Merkel) discs?
Tonic receptors with small receptive field that are flattened nerve endings; which end at a tactile cell located in basal layer of epidermis.
- sensitive
- detects light touch, texture, edges, and shapes
Definition of Hair receptors (root hair plexuses)?
Phasic receptors that are dendrites coiled around hair follicle and respond to movement of the hair
- very sensitive
What are Encapsulated nerve endings?
Nerve fibers wrapped in Glial cells (support cells) or connective tissue; the wrapping enhances sensitivity or selectivity of response.
1.) Tactile (Meissner) corpuscles
2.) End bulbs (Krause end bulbs)
3.) Bulbous (Ruffini) corpuscles
4.) Lamellar (pacinian)corpuscles
Definition of Tactile (Meissner) corpuscles?
2 or 3 nerve fibers within a fluid-filled capsule of flattened schwann cells. (PNS)
- Phasic receptors
- detect fine/light touch and texture
- Location: edges of dermal papillae, hairless areas of skin (fingertips, palms, eyelids, nipples, and genitals)
Definition of End Bulbs (Krause end bulbs)
Sensory nerve fibers that are surrounded by connective tissue.
- Location: Mucous membranes
- similar to Tactile corpuscles
Definition of Bulbous (Ruffini) corpuscles?
Flattened, elongated capsules containing a few myelinated axons in an incomplete fibrous capsule.
- Tonic receptors
- Location: reticular layer of dermis (bottom layer under papillary layer)
- Detects heavy touch, pressure, stretching of skin, deformation of fingertips, and joint movement.
Definition of Lamellar (pacinian) corpuscles?
Large, ovoid receptors with a single dendrite surrounded by layers of flattened schwann cells and fibroblasts (support cells).
- Phasic receptors
- detects deep pressure and vibration
- sensitive to pulsing or high-frequency vibrations
- Location: periosteum of bone, joint capsules, some viscera, and deep in dermis (especially on hands, feet, breasts, and genitals)
Classification of receptors by origin of stimuli.
- what are the three origins of stimuli?
1.) Exteroceptors= sense stimuli external to the body.
- receptors for vision, hearing, taste, smell, and cutaneous sensations like touch, heat, cold, pain
2.) Interoceptors= detect internal stimuli
- stomach and intestines
3.) Proprioceptors= sense body position and movements, purely somatic sensation
- location: muscle, tendons, and joint capsules
Classification of receptors by distribution
- what are the two form of receptor distribution?
1.) General (somatosensory, somesthetic) senses= widely distributed in skin, muscles, tendons, joints, viscera.
- some are simple, and some are just bare dendrites
- touch, pressure, stretch, temp, pain, blood pressure/composition.
2.) Special senses= limited to head, innervated by cranial nerves, and involve complex sense organs
- uses the brain structures specialized for vision, hearing, equilibrium, taste and smell
what are Nerves?
bundle of axons located in the PNS
what are Nuclei?
cluster of cell bodies located in the CNS
what are Tracts?
bundle of axons located in the CNS
what is the definition of a sensory pathway?
The delivering of somatic or visceral sensory information to their final destination inside the CNS using tracts, nuclei, and nerves.
what is the Somatic Nervous System (SNS)?
Motor neurons and pathways that provides voluntary control of skeletal muscles.
- somatic motor commands start in the motor center in the brain and follows the somatic motor pathway of:
- Motor Nuclei= in the CNS
- Tracts= in the CNS
- Neurons= in the PNS
what is the Autonomic Nervous system (ANS)?
sends involuntary commands to viscera. Two divisions
1.) sympathetic
2.) parasympathetic
Definition of Sensory Projection?
transmission of information from receptors to specific location in cerebral cortex. These signals travel along projection pathways.
What are the three ways somatosensory signal travel?
1.) First-order neuron
2.) Second-order neuron
3.) Third-order neuron
What are First-order neurons?
- Signals travel from brain through cranial nerves and into either the pons or medulla (signal start in brain)
- Signals from below the head, enter into the posterior horn (spinal cord) via dorsal root
- Body signal –> dorsal root–> posterior horn
- touch, pressure, and proprioception fibers= large, myelinated, fast
- temp fibers are small and unmyelinated, slower
What are Second-order neurons?
Decussate (cross) to opposite side (contralateral) in spinal cord, medulla, or pons
- ends in the thalamus, except for proprioception, which ends in cerebellum
What are Third-order neurons?
Thalamus to primary somatosensory cortex of cerebrum.
What are the three major somatic sensory pathways?
1.) Spinothalamic pathway
2.) Posterior column pathway
3.) Spinocerebellar pathway
What is the Spinothalamic pathway?
Provides conscious sensation of poorly localized (crude) touch, pressure, pain, and temp.
What is the Posterior Column pathway?
Carries highly localized fine touch, pressure, vibration, and proprioception.
What is the Spinocerebellar pathway?
Carries proprioceptive information from skeletal muscles, tendons, and joints.
- information terminates at the cerebellum for processing.
What diseases cause loss of pain perception?
- Leprosy
- Diabetes mellitus
- Nerve damage (peripheral neuropathy) results in neglect of injuries
what are two types of Pain?
1.) Nociceptive pain= stems from tissue injury; occurs when nociceptors are activated
2.) Neuropathic pain= stems from injuries to nerves, spinal cord, meninges, brain
what are the three origins of Nociceptive pain?
1.) Visceral pain= comes from internal organs
- diffuse, dull, hard to locate
- sensations of squeezing, cramping, nausea
- caused by stretch, chemical irritation, ischemia
2.) Deep somatic pain= comes from bones, joints, and muscles
- Ex: arthritis, sprains, bone. fractures
3.) Superficial somatic pain= usually comes from the skin
- Ex: pain from cuts, burns, insect stings
What are the two types of nerve fibers involved in pain responses?
1.) Fast pain= immediate, sharp, localized pain
- type A, myelinated, large
- also called discriminative pain because we can tell exactly where its coming from
2.) Slow pain= burning, dull, aching pain
- type C, unmyelinated, small
- longer-lasting and more diffuse pain
What is Referred pain?
Pain in viscera often perceived as originating from superficial sites (such as skin)
- caused from convergence of neural pathways in CNS
- Brain can not distinguish source
- Ex: heart pain felt in shoulder or arm because both send pain input to spinal cord segments T1 to T5
what is analgesic?
pain-relieving mechanisms in the CNS
What is endogenous opioids?
Analgesic peptides secreted by CNS, pituitary, digestive tract, and others.
- act as neuromodulators that block pain and give pleasure
- Ex: Enkephalins, endorphins, and dynorphins
what is spinal gating?
How opioids block pain
- stops pain signals at posterior horn of spinal cord
- interneurons stimulated to release enkephalins
- inhibit second-order pain neurons
what are the somatic motor pathway disorders we went over?
1.) Amyotrophic Lateral Sclerosis (ALS)
2.) Cerebral palsy (CP)
what is Amyotrophic Lateral Sclerosis (ALS)
A progressive degenerative disorder affecting motor neurons in the spinal cord, brain stem, and cerebral hemisphere.
- Death of these motor neurons causes atrophy in associated skeletal muscles
- Genetic 5-10% other unknown
-TREATMENT= oral medications such as Riluzole (does not reverse damage) mitigate symptoms
what is Cerebral palsy (CP)?
Number of disorders affecting voluntary motor control, motor skills, posture/balance, memory, speech, learning
- dysfunction is not progressive it is consistent throughout life
- appear during infancy or childhood
- Possible causes: unusually stressful birth, maternal exposure to drugs, genetic defect affecting the motor pathways
- Treatment: medication, muscle relaxants and pain relievers, therapies
