Chapter 16: Lecture midterm II Flashcards
Sensation
conscious or subconscious awareness of changes in the external or internal environment
perception
conscious interpretation of sensation performed mainly by the cerebral cortex
General senses
- refer to both somatic and visceral senses
Somatic senses include:
- tactile sensations such as touch, pressure, vibration, itch and tickle, thermal sensations, pain sensations and proprioceptive sensations
Visceral senses
provide information about changes within internal organs; for example; pressure, stretch, chemical nausea, hunger, or temperature
Special senses:
include sensory modalities for smell, taste, vision, hearing and equilibrium or balance
What are the events that occur for sensation:
- stimulation of sensory receptor
- transduction of stimulus
- generation of nerve impulses
- integration of sensory input
What is stimulation of sensory receptor:
An appropriate stimulus must occur within the sensory receptors receptive field, that is, the body region where stimulation activates the receptor and produces a response
What is transduction of stimulus:
- a sensory receptor converts the energy in the stimulus to a graded potential
What is generation of nerve impulses
when a graded potential in a sensory neuron reaches threshold, and it triggers one or more nerve impulses which propagate towards the CNS
Sensory neurons that conduct nerve impulses from the PNS to CNS are known as…
first-order neurons
What is integration of sensory input
- a particular region of the CNS recieves and integrate (processes) the sensory nerve impulse
- conscious sensations or perceptions are integrated in the cerebral cortex
free nerve endings:
- bare dendrites associated with pain, thermal, itch, tickle and some touch sensations
encapsulated nerve endings
- dendrites enclosed in connective tissue capsule for pressure, vibration and some touch sensations
separate cells:
receptor cells that synapse with first-order sensory neurons; located in the retina, inner ear or taste buds
exteroceptors
- located at or near the surface of the body; sensitive to stimuli coming from outside of the body
- conveys: visual, smell, taste, touch, pressure, vibration, thermal and pain sensations
interoceptors
- located in blood vessels, visceral organs, and nervous system; provide information about internal environment
- impulses are usually not consciously perceived but may be felt as pressure or pain
proprioceptors
located in muscles, tendons, joints and inner ear; provide information about body position an motion of joints and equilibrium
mechanoreceptors
detect mechanical stimuli: provide sensations of touch, pressure, vibration, proprioception and hearing and equilibrium
thermoreceptors
detect changes in temp
nociceptors
respond to painful stimuli
photoreceptors
detect light that strikes the retina of the eye
chemoreceptors
detect chemicals in mouth (taste), nose (smell) and body fluids
osmoreceptors
sense osmotic pressure of body fluids
areas with highest density of somatic sensory receptors are;
- tip of the tongue
- lips
- fingertips
What are the four modalities for somatic sensations
- tactile
- thermal
- pain
- proprioceptive
Deep somatic pain:
skeletal muscles, joints, tendons and fascia
Visceral pain:
stimulation of pain sensory in visceral organs
- usually presents in or just deep into the skin that overlies the stimulates organ
Muscle spindles:
- type of proprioceptor found in skeletal muscles, that monitors muscle length and are involved in some stretch reflexes
Tendon organs
- type of proprioceptor found at the junction of a tendon and a muscle
- protects muscles and tendons from damage due to overstretching
Joint kinesthetic receptors
- exist in and around the joint capsule of synovial joints and they respond to pressure, acceleration, deceleration during movement to help protect against excessive strain
What are the different tactile receptors:
- tactile corpuscles
- hair root plexus
- non-encapsulated sensory corpuscles
- bulbous corpuscle
- lamellar corpuscle
- itch and tickle receptors
Tactile corpuscles:
- capsule surrounds mass of modified schwann cels and nerve endings in dermal papillae of hairless skin
- sensations: onset of touch and low frequency vibrations
Hair root plexus:
- free nerve endings wrapped around hair follicles in skin
- sensations: movements on skin surface that disturb hairs
Non- encapsulated sensory corpuscles:
- saucer-shaped free nerve endings make contact with tactile epithelial cells in dermis
- sensations: continuous touch and pressure
Bulbous corpuscles:
- elongated capsule surrounds nerve endings and schwann cells deep in dermis and ligaments and tendons
- Sensations: skin stretching and pressure
Lamellar corpuscles:
- oval, layered capsule surrounds nerve endings; present in dermis and subcutaneous tissue, submucosal tissues, joints, periosteum, and some viscera
- Sensations: high frequency vibrations
Itch and tickle receptors:
- free nerve endings in skin and mucous membranes
- Sensations: itch and tickle
somatosensory pathways relay information from somatic sensory receptors in the skin, muscles and joints to the …
primary somatosensory cortex
where is the primary somatosensory cortex located
(postcentral gyrus) in the parietal lobe of the cerebrum and the cerebellum
first - order (primary) neurons
- conduct nerve impulses from somatic sensory receptors into the brainstem or spinal cord
second - order (secondary) neurons
- conduct nerve impulses from the brainstem or spinal cord to the thalamus
- axons of second order neurons decussate as they course through the brainstem or spinal cord before ascending to the thalamus
third - order (tertiary) neurons
- conduct nerve impulses from the thalamus to the primary somatosensory cortex on the same side
- as the impulses reach the primary somatosensory cortex, perception of the sensation occurs
Posterior column-medial lemniscus pathway conveys impulses from the
limbs, trunk, neck and posterior head
Posterior column-medial lemniscus’s first order neurons extend from peripheral sensory receptors to the…
spinal cord
Once the Posterior column-medial lemniscus pathway’s first-order neurons have entered the spinal cord they..
ascend to the medulla via tracts known as the posterior columns
the first-order neurons of the Posterior column-medial lemniscus pathway synapse with second order neurons at the…
medulla
Axons of the second-order neurons of the Posterior column-medial lemniscus pathway decussate at the —— and enter the
the medulla, the medial lemniscus
what is the medial lemniscus
thin ribbon like projection that extends from the medulla to the thalamus
Once the second-order neurons synapse with third order neurons from the Posterior column-medial lemniscus pathway at the —–, they project the sensations to the
thalamus, primary somatosensory cortex of the cerebrum