W7 The Somatosensory Nervous System (NS 6) Flashcards
Inc: The somatosensory nervous system Sensory physiology
What are these receptors found?
Mechanoreceptors
Chemoreceptors
Photoreceptors
Thermoreceptors
Nocicoreceptors
Mechanoreceptors- ear, muscle and joints, skin and viscera, cardiovascular
Chemoreceptors- Tongue, nose, skin and viscera
Photoreceptors- eye
Thermoreceptors- skin and CNS
Nociceptors- respond to stimuli that result in sensation of pain
What are the Sensory receptors in the skin?
- Free nerve endings (learn this)
- Temperature, noxious stimuli, hair movement
- Merkel corpuscle
- Steady Pressure,
texture - Meissners corpuscle
- Flutter, light
pressure - Pacinian Corpuscles
- Vibrations
- Ruffini corpuscles
Stretch
What is the name for the topographical representation of the sensory input to the somatosensory cortex?
Homunculus
What is a sensory unit?
What are the 3 types?
An afferent neurone and its receptor endings
(An afferent neurone goes to the brain, and efferent goes away)
Sensory receptors may be:
* Neuron with free nerve endings (unmyelinated)
* Neuron with encapsulated ending
* Specialised receptor cells closely associated with neuron
Which of the following are graded potentials?
Receptor/generator potentials
Action potentials
Receptor/generator potentials
The stronger the stimulus, the larger the graded receptor potential which leads to…
An increase in frequency of action potentials of the afferent neurone so more neurotransmitter is released at the synapse.
Action potential is not graded
What are the 5 components to the reflex?
Receptor
Afferent neurone (Sensory neuron)
Integration centre (CNS)
Efferent neurone (Motor neurone)
Effector organ
What are the special senses?
- Sight (Visual system)
- Hearing (Auditory system)
- Taste (Gustatory system)
- Smell (Olfactory system)
The eye
Contains photoreceptors (rods and cones)
*Vision is the dominant sense in humans
*Eye protected by orbit and cushion of fat
*Accessory Structures
* Eyebrows
* Eyelids or palpebrae
* Blink
* Eyelashes
* Conjunctiva
* transparent mucous membrane
- Lacrimal apparatus
- Lacrimal gland: Responsible for tears (PNS) (on outer corner of eyelid)
- mucus, antibodies and lysozyme
- nasolacrimal duct →nasal cavity
- Extrinsic Eye Muscles
- Movement
Anatomy of the eye ball
Three Tissue Layers (Tunics) of the eye wall* Fibrous Layer (Outer)
* Sclera: white of the eye
* Cornea: front of the eye (transparent)
* Vascular layer
* Choroid
* Dark: melanin containing cells
* Absorbs light
* Ciliary body
* Cilliary muscles
* Change thickness of Lens
* Iris
* Coloured part of eye
* Highly vascularised
* Pupil size controlled by muscles of the iris
* Light passes through pupil
* Nervous tissue layer (inner most)
* Retina
* Outer Pigmented retina
* Prevents light reflection
* Inner sensory retina
Anatomy of the eye:
What are its Chambers?
Anterior Segment / cavity
* Anterior chamber
* chamber between cornea and iris
* Posterior chamber
* chamber between iris and lens
* Aqueous humor: Fills Anterior Segment
* Watery liquid, replaced continuously
* Filtered through ciliary body and returned to blood via venous synus
* Nutrients
* Refracts light
* Maintains pressure
Posterior segment/cavity
* Vitreous chamber
* Vitreous humor: in posterior segment
* Jellylike
* Maintains pressure and refracts
* Forms in embryo and doesn’t circulate 8
Vision
* The iris allows light into the eye
* Focused by the cornea, lens, and humors onto the retina
* The light striking the retina produces action potentials that
are relayed to the brain via optic nerve
Retina: 2 Layers
- Outer thin pigmented layer: * Melanocytes (prevent light scattering), contains melanin
- Inner thicker neural/sensory layer* Three main type of neurons:* Photoreceptors
- Rods
- Cones
- Bipolor cells
- Ganglion cells
Regions of (posterior) retina
* Macula (5.5mm)
* High-resolution, color vision (lots of rods and cones)
* Within this is the fovea (1.5mm)
* Where light is most focused when the eye is looking directly at an object
* Highest density of cones
* Optic disc
* Blood vessels enter the eye
* Axons from the retina meet, pass through the layers and exit the eye as the optic nerve
* No photoreceptors
Why are there only cone cells in the fovea?
They provide detailed colour vision
What are the 2 types of Photoreceptors?
1.Which are more sensitive to light?
2. Which have only black and white vision?
3. Which have high visual acuity and colour vision?
Rod cells and Cone cells
1. Rod cells
2. Rod cells
3. Cone cells
Rod cells
* More sensitive to light - vision permitted in dim light but only gray and fuzzy
* Only black and white and not sharp
* Rhodopsin (opsin & retinal)
Cone cells
* High acuity NEED bright light
* Colour vision
* 3 sub-types:
* blue, red and green light cones
* found in macula lutea,
* operate in bright light, colour vision
Why is the back of the eye dark?
To prevent scattering light
Why is the back of the eye dark?
To prevent scattering light
What do ciliary muscles do?
They change/control the thickness of the lens
What are the parts of the ear called?
Outer (external) ear
Middle ear (ossicles) for hearing
Inner ear (labyrinth)
What are the parts of the outer ear?
- Pinna
- External auditory canal
External and middle: conduct sound waves toward the inner ear - hearing only,
What are the parts of the middle ear called?
- Tympanic membrane
- Malleus (hammer)
- Incus (anvil)
- Stapes (stirrup)
External and middle: conduct sound waves toward the inner ear - hearing only,
What are the parts of the inner ear called?
Why is it important?
Mechanoreceptor for hearing and balance
* Vestibular apparatus
* Semicircular canals
* Cochlea
* Organ of Corti
Inner ear: both hearing and balance
Details of middle ear :
- Air filled
- Oval and round window connect to inner
ear - TM causes ossicles in air filled middle ear
to move: - Malleus (hammer) (attached to TM)
- Incus (anvil)
- Stapes (stirrup) (touches oval window)
- Ossicles form a lever system
- Amplifies and transmits the vibratory motion
of the TM to fluids of inner ear cochlea via
oval window - Auditory canal open to pharynx