Sensory Systems Flashcards
(39 cards)
What is a sensory system?
Part of the nervous system responsible for processing sensory information
The sensory system consists of?
- sensory receptors that receive stimuli
- neural pathways that conduct information from receptors to CNS
- parts of the brain that deal with primarily processing of the information
What is sensation?
Sensation is the conscious or subconscious awareness of external or internal stimuli
- Detection of physical energy (a stimulus) from the environment and converting it into neural signals
- Sensory impulses that reach the cerebral cortex allows us to precisely locate and identify specific sensations
What is perception?
Perception is the conscious awareness and the interpretation of meaning of sensations
- Selection, organization, and interpretation of our sensations
- We have no perception of some sensory impulses because they never reach the cerebral cortex
e.g. sensory receptors that constantly monitor blood pressure propagate to the cardiovascular centre in the medulla oblongata
What are sensory modalities?
• Refers to each type of sensation
e.g. pain, hearing, vision, touch
• A given sensory neuron carries information for one modality only
What are classes of sensory modalities?
- General senses: Include both somatic and visceral senses (tactile, thermal, pain, proprioceptive sensations)
- Special senses: Include modalities of smell, taste, vision, hearing, and balance
What are sensory receptors?
Sensory receptors can either be a specialised cell or dendrites of a sensory neuron that monitors particular condition (stimuli) in the internal or external environment
How can different receptors be excited to cause receptor potentials?
- by mechanical deformation of the receptor, which stretches the receptor membrane and opens ion channels
- by application of a chemical to the membrane, which also opens ion channels
- By change of the temperature of the membrane, which alters the permeability of the membrane
- by the effects of electromagnetic radiation, such as light on a retinal visual receptor
What is signal transduction?
• Conversion of a stimulus into a receptor potential (depolarization or hyperpolarization)
• In special senses, stimulus from specialised receptor cells trigger release of an excitatory neurotransmitter onto the sensory neuron that leads to generation of action potential
How is an impulse generated?
• When graded potential in a sensory neuron (1st order neuron) reaches threshold, it triggers one or more action potentials that propagate impulses from the PNS into the CNS
What happens to the sensory input?
A particular Region of the CNS receives and integrates the sensory nerve impulses
How are sensory receptors classified based on structure?
- Free nerve endings
- Encapsulated nerve endings at the dendrites
- Specialized separate cells
Describe sensory receptors with free nerve endings?
bare dendrites that often have no visible structural specialisation
e.g. receptors for pain, thermal, tickle, itch
Describe sensory receptors with encapsulated nerve endings?
dendrites are enclosed in a connective tissue capsule that has distinct microscopic structure
e.g. lamellated (Pacinian) corpuscles, receptors for somatic and visceral sensations like touch, pressure and vibration are encapsulated
Describe the sensory receptors that have specialized separate cells?
Sensory receptors for the special senses of vision (photoreceptors), hearing and equilibrium (hair cells), and taste (gustatory receptor cells) consists of specialised separate cells that synapse with first order neurons
Names and describe sensory receptors classified on location?
- Exteroreceptors
- Located in or near the external surface of the body and detect changes in the external environment
e.g. receptors for touch (Meissner’s corpuscles, Merckel’s discs), cold, heat and pain, vision, smell, vision, vibration etc. - Interoreceptors
- Transmit impulses from the visceral organs, blood vessels
- Usually not consciously perceived - Telereceptors (distance receptors)
- Detect stimuli reaching us from remote sources
e.g. smell, sound - Proprioceptors
- Supply info containing movements and position of the body in space
e.g. Golgi tendon organs, muscle spindles, and hair cells in the labyrinth of the inner ear
Name and describe sensory receptors classified based on their stimulus type?
- Mechanoreceptors - Mechanical forces
e.g. Touch, pressure, stretch, vibrations - Thermoreceptors - temperature changes
- Chemoreceptors - Chemicals in solution: Detect chemicals in the mouth and body fluids
e.g. Taste, smell, blood chemistry - Photoreceptors - Respond to light
- Nociceptors - Harmful stimuli (pain) from physical or chemical damage to tissue
Describe sensory receptors classified based on their distribution?
- General senses
- Scattered throughout the body, simple in structure
e.g. Temperature, pain, touch, pressure, proprioception, chemicals in blood - Special senses
- Receptors located in sense organs in the head where they are protected by surrounding tissues
e.g. Olfaction (smell), vision, gustation (taste), equilibrium (balance) and hearing
What is sensory adaptation?
adaptation either partially or completely to any constant stimulus after a period of time
- When a continuous sensory stimulus is applied, the receptor responds at a high impulse rate at first and then at a progressively slower rate until finally the rate of action potentials decreases to very few or often to none at all
• E.g. cutaneous cold receptors when taking a cold shower
What is peripheral adaptation?
When receptors or sensory neurons alter their level of activity
i.e. reduces amount of info that reaches the CNS
What is central adaptation?
• Occurs in the CNS
• Involves inhibition of nuclei along a sensory pathway
Describe the sensory receptors classified based on response?
- Tonic receptors adapt slowly and inform about the presence and strength of a stimulus
- always active and adapt little or not at all
e.g. pain receptors, proprioceptors - Phasic receptors adapt rapidly and therefore inform about the rate of change of a stimulus
- normally inactive and become active for a short time when stimulus strength changes
e.g. temp, touch receptors
Describe the function of first order neurons?
• Conduct impulses from sensory receptors to the CNS
• Cell bodies are located in dorsal root ganglion if the spinal cord
• Impulses from the face, mouth, eyes, teeth propagate along cranial nerves into brainstem
• Impulses from the neck, trunk, limbs and posterior aspect of head propagate along spinal nerves into spinal cord
What are dermatomes?
• Each spinal nerve contains sensory* neurons that serve a specific predictable segment of the body
• A dermatome is the area of the skin that provides sensory input to the CNS via one pair of spinal nerves
• There are 8 cervical nerves (note C1 has no dermatome), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves.
• The nerve supply in the adiacent dermatomes overlap
• Knowing which spinal cord segments supply each dermatome makes it possible to locate damaged regions of spinal cord e.g. from radiculopathy (pinched nerve)
