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
Inner ear details:
What are the 3 parts?
What is the canal filled of?
3 bony chambers
*Cochlea - hearing
*Vestibule - equilibrium
*Semicircular canals –equilibrium
*Filled with liquid called perilymph and endolymph fluids
What are the steps in the function of a sense?
Stimulus
Receptor
Change in membrane potential
Generation of action potential
Transmission to CNS
Integration of information by CNS
Where are exteroreceptors, interoreceptors and proprioreceptors located?
What are examples?
Exteroreceptors- body surface
*(pain, touch, pressure, temperature) and
special senses (vision, hearing, equilibrium ,
taste, smell)
Interoreceptors- Within the body
* viscera and blood vessels (stretch,
temperature)
Proprioreceptors- Respond to internal stimuli
* Skeletal muscle, joints, tendons,
ligaments and connective tissue.
Advise brain of body movements
How do sensory receptors function to trigger neuronal response?
- Environmental changes cause a change in membrane potential in receptor.
- Receptor or generator potential: graded
- If this reaches threshold it will trigger an action potential, sensory transduction
- This information goes to the brain via
ascending fibres, primary then secondary
afferent nerve fibres - Each nerve may receive information from a
number of receptors in a particular area =
receptive field
How do sensory receptors function to trigger neuronal response?
- Environmental changes cause a change in membrane potential in receptor.
- Receptor or generator potential: graded
- If this reaches threshold it will trigger an action potential, sensory transduction
- This information goes to the brain via
ascending fibres, primary then secondary
afferent nerve fibres - Each nerve may receive information from a
number of receptors in a particular area =
receptive field
Each neuron has a receptive field:
- What is a receptive field?
- Can sensory neurons have overlapping receptive fields?
- The smaller the receptive field, the more..
- Region of space where the presence of a
stimulus will induce the production of a signal in
that neuron - Yes
- Accurate a representation of the stimulus os signalled to the brain
Can the Brain differentiate between two stimuli
acting on the same receptive field?
No
What does the somatic nervous system control?
What does it process?
Are the responses voluntary or involuntary?
- Skeletal muscles
- Process stimuli received from receptors within the skin, muscles, and joints
( Mostly mechano, thermo- and chemoreceptors) - Both
What pathways does the somatic system lead to?
Pathways for Somatic Perception Project to the Cortex and Cerebellum
What are the cochlea? (shape)
What are they lined by?
Middle contains?
A hollow, spiral-shaped bone found in the inner ear that plays a key role in the sense of hearing and participates in the process of auditory transduction.
*Shaped like snail shell
2 canals extend from the oval window to the apex of the cochlea.
* from the apex back to the round window
* Lined on bottom channel by Basilar membrane
* Middle: cochlear canal -contains Organ of Corti
* Specialised sensory hair cells : stereocilia
* Seated on basilar membrane
* Reach to tectorial membrane
* Base of Hair cells attached to neuron
* Basilar membrane moves/vibrates when sound waves in periplymph move over it
What are the receptors in the ear called?
Mechanoreceptors
Organ of Corti
contains hair cells
– move due to pressure waves
* Hair cells sit on BM between BM
and TM
* embedded in TM
How is sound transmitted through the ear? (6)
- Sound waves vibrate tympanic
membrane - Auditory aussicles vibrate.
Amplification - Stapes connected to oval window,
sends vibrations into cochlea - Pressure wave pushes on basilar
membrane of cochlea duct. Energy waves
dissipate at round window - Hair cells bend, transmission of signal
- Neurotransmitter release activates
sensory neurones, action potentials to
brain.
Auditory pathway
- Vestibulocochlear nerve:
- Cochlear nerve -
portion involved in
hearing - Vestibular nerve is
involved in balance. - The cochlear nerve
sends axons to the
regions including - Auditory cortex in
temporal lobe
What are maculae?
Maculae- Hair cells, tips embedded in
gelatinous mass weighed down by
otoliths (protein and calcium
carbonate)
Equilibrium
*Vestibular apparatus : static
equibilbrium (movement and
position)
* 2 Chambers: Saccule and utricle
* Maculae
* Hair cells, tips embedded in
gelatinous mass weighed down by
otoliths (protein and calcium
carbonate)
* Otoliths moves in relation to
gravity bending hairs
* Upright : don’t move
* Hairs bend when tilted
* Depolarises receptor cells - action
potentials in associated neurons
travel to brain about head position
*Semi circular canals
* Dynamic equilibrium:
* Rotational acceleration in 3 planes
*3 canals : right angles
*Base: ampula
* Hair cells embedded in jelly cupula
* Floats in endolymph
*Movement:
* Endolymph tends to move in opposite direction
* Cupula and steroclia on hair cells bend
* Leads to action potential
*Vestibulocochlear nerve to cerebellum
What is the scotoma or blind spot?
Where the optic nerve leaves the eye
Where are the cochlea and organ of corti?
In the inner ear which is important for hearing and balance and is fluid filled
What does light have to pass to reach photoreceptor cells in the eye?
Ganglion and bipolar cells
What is the occipital lobe?
The visual cortex
What possess stereocilila?
Mechanoreceptors (receptor cells)
What is the temporal lobe?
The auditory centre
What are taste buds?
Sensory structures that detect taste stimuli
Receptor cells- sensitive to the chemicals contained within foods
Located on the tongue (papillae, palate, root of tongue, epiglottis )
What are papillae ?
What are the 4 types? (not assessed)
Swellings on tongue that make it feel rough.
Filiform, Fungiform, Circumvallate, Foliate
What is the structure of taste buds?
What is the sensory homunculus?
The amount of space of the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part.
What is a receptive field ?
Region of space where the presence of a stimulus will induce a production of a signal in that neuron
What are the sensory receptors in the skin? (not assessed)
Free nerve endings- important in pain
Merkel corpuscle
Meissners corpuscle
Pacinian Corpuscles
Ruffini corpuscles
What are the 2 Afferent pathways to the brain?
Dorsal column lemniscal for fine touch, vibration and position
Spinothalamic for crude touch temperature, and pain
Motor pathways Vs Somatosensory pathways
-Somatosensory pathways take the message to the spinal cord and brain – somatosensory cortex
-Motor pathways take the message to the spinal cord and muscles- motor cortex
What is a reflex?
An automatic, involuntary, consistent response
Sensors detect external stimuli and sensory neurons sends an impulse to the spinal cord.
Proprioceptors
Sense muscle length (stretch) and activate sensory neurones
Describe the 5 steps of the stretch reflex:
- Stretching of muscle stimulates muscle spindles
- Activating of sensory neuron
- Information processing at motor neuron
- Activating of motor neuron
- Contraction of muscle
