Flashcards in Sensory Nervous System and Special Senses Deck (102):
From which peripheral nervous systems do sensory nerves innervate and collect information from?
Somatic (vol) NS - Sensory nerves innervate and collect information from skeletal muscles, skin and joints.
Autonomic (unvol) NS - Sensory nerves innervate and collect information from smooth muscles, cardiac muscle and glands.
What is the common pathway for the detection of senses?
1) Detection from a receptor
3) Change in membrane potential
4) Firing of action potential to the CNS.
Do ions move readily across the cell membrane, if not, what do they use in order to get across?
Ions will use specifically-gated channels and protein pumps in order to move across the membrane (via facilitated diffusion).
What do ions depend on in order to move across the membrane?
1) Concentration differences (high to low)
2) Voltage differences (positive - negative v/v)
Across an ELECTROCHEMICAL gradient
What is the somatosensory cortex the same as?
The somatosensory cortex is another name for the sensory area (a lobe in the cerebral hemisphere - parietal lobe just past the central sulcus)
Describe the somatosensory pathway:
1) A stimulus is detected by a specific receptor
2) The 1st order neurone transmits sensory information to the 2nd order neurone in the spinal cord.
3) The 2nd order neurone (afferent neurone) will synpase with the 3rd order neurone in the Thalamus
4) The 3rd order neurone transmits the sensory information to the cerebral cortex.
5) The cell bodies in the somatosensory area of the cerebral cortex processes this sensory information (concious perception of the stimulus)
In what nervous systems are the order neurones (in the somatosensory pathway)?
1st order (PNS)
2nd order and 3rd order (CNS)
Which nerves are contained in the dorsal and which nerves are contained in the ventral roots (coming from the spinal cord)?
Dorsal - Sensory afferent nerves
Ventral - Motor efferent nerves
Where do the ventral roots extend out of the spinal cord from?
The anterior of the spinal cord (white matter - nerve fibres)
Where do the dorsal roots enter the of the spinal cord from?
The posterior of the spinal cord (white matter)
After the ventral root nerves leave the spinal cord and before the dorsal root nerves enter the spinal cord, what happens?
The ventral root and dorsal root will clump together in order to form the MIXED NERVE FIBRE.
What are dermatones?
Areas of skin that are innovated by a branch of sensory nerve fibres that come from a single spinal nerve. They are able to detect different stimuli from these areas of the skin.
Does each spinal nerve (31 spinal nerves) have a branch of sensory nerve fibres innervated an area of the skin, in order to create dermatones?
Yes - each spinal cord does!
Why are dermatones useful?
They are a useful diagnostic tools - in order to discover the origin of injury or infection in a spinal nerve or dorsal root nerve.
What is referred pain?
If you have a disturbance in the spinothalamic tract (1st, 2nd or 3rd order neurone) it can feel like the pain is coming from where this path originated from (the 1st order neurone - sensory ending).
The sensory nerve endings of the 1st order neurones can either be:
1) Encapsulated (with connective tissue or GLIAL cells)
2) Unencapsulated (without connective tissue)
If a sensory nerve ending is encapsulated then...
it is more sensitive to a stimulus
What are the 4 main receptors that sense touch (2 that sense steady pressure and 2 that sense vibrations):
Steady Pressure: 1) Ruffini endings 2) Merkel endings
Vibrations: 1) Pacinian corpuscles 2) Meissner corpuscles
What is noiciception?
The feeling or perception of pain
What are noiciceptors?
Free nerve endings that signalsTISSUE DAMAGE
How are noiciceptors stimulated?
When a tissue is damaged they will release inflammatory mediators (histamines, cytokines and chemokines) which will stimulate the noiciceptors
What is a noxious stimulus?
Explain how the pain intensity changes and which noiciceptor is responsible for this perception of different pain intensities?
1st pain = sharp, quick, localised pain (caused by the A-delta noiciceptors)
2nd pain = long, nagging, diffuse pain (caused by the C noiciceptors)
What is the difference between A-delta fibres and C-fibers?
A-delta = myelination (transmission of AP is fast)
C fibres = un-myelinated
What are the 4 different types of pain:
1) Noiceptive pain: Pressure, chemical, hot, cold
2) Inflammation pain: tissue pain
3) Neuropathic pain: Neural lesion
4) Dysfunctional pain: Abnormal processing of information by the nerve
What is important to remember about neuropathic and dysfunctional pain?
The pain is caused by the nerve itself rather than an external stimulus
An example of how neural lesions can occur?
A Herniated disc can cause a neural leision in a spinal nerve - this causes neuropathic pain anywhere along this spinal nerve tract
How is referred pain caused?
1) A visceral organ and area of skin share the same dermatone (i.e. a branch of nerve fibres innovates the skin and visceral organ and this branch leads to the same single nerve).
2) Tissue damage occurs in the visceral organ.
3) Noiciceptors detect the pain and information is sent along the branch of nerve fibres to the single spinal nerve.
4) As the brain doesn't normally detect pain from this nociceptor - it wrongly assumes that the pain is coming from the skin (as these nociceptors are normally stimulated).
5) In this way the brain perceives pain in the skin
What are the 5 different differences between chronic pain and acute pain?
1) Chronic pain is caused by no specific injury/disease whereas acute pain is caused by a specific injury/disease
2) Chronic pain serves no biology function whereas acute pain does serve a biological function.
3) Chronic pain is associated with psychological functioning whereas acute pain is associated with the F/F responses of the sympathetic NS.
4) Chronic pain can last up to more than 6 months, whereas acute pain is short lasting
5) Chronic pain is hard to treat and acute pain is easier to treat.
What 3 things can cause an absence of pain perception?
What 2 things control pain?
1) Chemicals (Analgesics or endogenous opiods - e.g. endorphins)
2) The Gate Theory of Pain
What 4 things are involved in the gate theory of pain?
1) Inhibitory neurones
2) Projection neurones
3) C-fibres (nociceptive)
4) alpha-beta fibres (non-nociceptive)
What happens when the alpha-beta fibres are stimulated in the gate theory of pain?
1) The inhibitory neurones are stimulated - which inhbits the projection neurone from projecting the pain.
2) The projection neurones are stimulated - so the inhibited pain is projected.
No pain is percieved.
What happens when the C fibres are stimulated in the gate theory of pain?
1) The inhibitory neurones are inhibited - so the projection of pain isn't inhibited by the inhibitory neurones, and so pain is projected
2) The projection neurones are stimulated.
Pain is percieved.
What happens when the alpha-beta fibres and the C fibres are both stimulated in the gate theory of pain?
It is more likely that the inhibitory neurones will be stimulated by alpha-beta fibres than inhibited by the C fibres. Therefore, less pain or no pain is perceived.
Does the detection of an itch use the same pathway as pain?
Which areas of the brain are stimulated in order to detect an itch?
The areas associated with:
1) Disagreeable feelings
2) Irresistible urges
What are special senses?
Detect information about the external environment and send this information to the CNS.
What are the 4 special senses?
What stimulus do the eyes detect?
The eyes detects visible light in the form of different colours
Why are eyelashes important?
Prevent foreign material from entering the eye
What is the important of eyelids?
Allows us to blink to produce tears that lubricate the eye and keeps dust out
What is the pupil?
Dark circle in the centre of the eye that lets light in. The pupil can dilate to allow more light in or constrict to allow less light in
What is the iris?
The coloured region around the pupil
What is the conjunctiva?
It is the mucus epithelial membrane that lines the outer surface of the eye and the inner surface of the eyelid.
What is the role of the lacrimal gland and nasolacrimal duct?
Lacrimal glands continuously produce tears and push them across the eye. Tears are collected in the nasolacrimal duct and into the eyeball.
What is the importance of the lacrimal gland producing tears?
Keeps the conjunctiva clean and moist
What is conjunctivitis?
Inflammation of the conjunctivitis caused by infection or physical abrasion.
What is the name of the bony casing that protects the eyeball?
What is the eyeball divided up into?
2 fluid filled cavities. Posterior and Anterior
What seperates the 2 fluid filled cavities of the eyeball?
What is the name of the 3 TUNIC layers making up the wall of the eyeball?
1) Neural tunic (retina)
2) Vascular tunic
3) Fibrous tunic
(inside - out)
What is contained in the neural tunic of the eyeball (retina)?
All of the photoreceptors (rods and cones) that detect light.
Rods - more sensitive to light (enable us to see at night)
Cones - less sensitive to light (but enable us to see different colours)
Which photoreceptor is more numberous in the retina?
What forms the optic nerve?
The photoreceptors (rods and cons) in the retina will synapse with sensory receptors and sensory receptors will converge to form the optic nerve
What instrument can be used to view the retina through the pupil?
What is the optic disc?
The optic disc is located in the middle of the eye. It is where the optic nerve leaves the eye and blood vessels enter/leave the eye.
What is the optic disc sometimes referred to as?
The blind spot. As the optic disc is part of the retina that doesn't contain photoreceptors.
What is special about the MACULA LUTEA in the retina?
In the centre of the Macula Lutea contains the FOVEA CENTRALIS.
In the Fovea Centralis, there are ONLY cone cells. This is because most of the light is focused on the fovea centralis and cone cells are less sensitive to light so need all the light they can get.
How does vision become blurry when someone suffers from Diabetic Retinopathy?
As their blood glucose is high. This damages the retinal blood vessels. They become more permeable. Plasma fluid leaks out = oedema. This causes blurry vision.
What is contained in the vascular tunic?
1) Blood Vessels
2) Smooth Muscle
2) Ciliary Body
What does the iris contain and what is its function?
The iris is a pigmented area. It contains smooth muscle fibres.
If the smooth muscle fibres contract = the pupil dilates
If the smooth muscle fibres relax = the pupil constricts
What is the function of the ciliary body?
It holds the lens in place
What is the Choroid?
The Choroid is the largest part of the eyeball and it contains blood vessels.
What are the 2 parts of the fibrous layers of the eyeball?
What is the cornea?
The transparent layer covering the iris and pupil
What is the sclera?
The white part of the eye. Muscle is connected to the sclera and pulls on the sclera in order for the eye to move in different directions.
What is the posterior part of the eye filled with and what is its function?
Jelly-like substance that maintains the pressure of the eye.
What is the anterior part of the eye filled with and what is its function?
Water-like substance that nourishes the lens and cornea.
How often is the aqueous chamber replaced in the anterior cavity?
What is the name given to the part where the 2 optic nerves join together?
Describe the visual pathway?
1) Light comes in through the iris.
2) Light is focused on the retina by the lens.
3) Photoreceptors in the retina will detect the light stimulus.
4) Action potentials will occur in the optic nerve.
5) The 2 optic nerve connect (forming the Optic Chiasm).
6) The axons from each eye (contained within each of the optic nerves) either enter the brain on the same side or cross in the optic chiasm to the other side of the brain.
7) The axons will synapse at the vision area of the cerebral cortex (in the occupitial lobe)
What is the sense of smell a response to?
Oderants entering the nasal cavity
What doe the sense of smell also affect?
Where is the olfactory epithelium located?
In the upper regions of the nasal cavity
What cells are contained in the olfactory epithelium?
Pseudo-stratified ciliated columner goblet cells (that produce mucous) and olfactory cells (sensors)
Describe the smell pathway:
1) Oderants enter the nasal cavity and stick to the mucus (produced by the olfactory epithelium).
2) The oderants stimulate the olfactory cells (sensors).
3) Action potentials are sent down axons (axons combine to form the olfactory nerve)
4) These axons synapse with axons in the OLFACTORY BULB.
5) Axons from the olfactory bulb will synapse with axons that run down the OLFACTORY TRACT.
6) The axons are taken to the olfactory area of the cerebral cortex (in the temporal lobe).
Name the 4 locations where taste buds are found?
1) Soft Palette
What do taste buds contain?
1) Taste cells - with hair-like projections, that extend out on the surface of the taste pores
2) Taste pores
3) Axons leaving the basal end of the taste pore
4) Sensory receptors - on the hair-like projections of the taste cells.
The pathway for taste to be detected and perceived?
1) Tastants will bind to the sensory receptors on the hair-like projections.
2) This will stimulate an action potential down the sensory neurones, that leave the taste pore at the basal end.
3) 3 nerves are able to carry this action potential to the brain:
- Facial nerve
- Glossopharyngeal nerve
- Vegus nerve
4) These nerves will take this information to the taste centre of the cerebral cortex (in the temporal lobe).
What are the 5 basic tastes:
All taste buds, will have receptors that sense all tastes. However, some will have more receptors specific to a particular taste.
Sweet - front
bitter - back
Sour - sides
(of the tongue)
The ear is the organ or hearing and...
What is the ear divided up into?
1) Outer ear
2) Middle ear
3) Inner ear
What are the 3 components of the outer ear?
2) External acoustic meatus
3) Tympanic membrane
What is the Auricle?
Fleshy outer membrane of the ear, supported by elastic cartlidge
What is the external acoustic meatus?
A pathway through the temporal bone.
It contains CERUMINOUS GLANDS and hairs.
The ceruminour glands produce ear wax (CERUMEN).
The ear wax and hairs will prevent any foreign objects from reaching the tympanic membrane
What is the tympanic membrane?
(aka ear drum)
When vibrations hit the ear drum, the ear drum will vibrate.
It seperates the outer ear from the middle ear.
What is the middle ear?
Air filled cavity that is seperated from the outer ear by the tympanic membrane and the inner ear by the oval and round windows.
What 3 temporal ossicles (ear drums) are found in the middle ear?
What is the function of the temporal ossicles?
To transmit the vibrations from the tympanic membrane to the oval window.
What happens if a sound is really loud and the tympanic membranes vibrations are hard?
Muscles (attached to the temporal ossicles) will pull on the temporal ossicles away from the tympanic membrane. So, the vibrations are not transmitted to the oval window.
What tube connects the middle ear with the nasopharynx?
What is the function of the auditory tube?
To equalise pressure
What does the inner ear contain?
1) Semi-circular canals
4) Vestibulocochlear nerve
What are the semi-circular canals and vestibule concerned with?
What is the cochlear concerned with?
What is the role of the vestibulocochlear nerve?
It is connected to the semi-circular canals, vestibule and cochlear - and transmits this information to the brain.
Describe the sound transmission process?
1) Sound is collected by the auricle and transmitted down the external acoustic meatus.
2) The sound waves causes the tympanic membrane to vibrate.
3) This causes the auditory ossicles to vibrate (malleus, incus and stape)
4) This causes the oval window to vibrate
5) This causes the FLUID in the cochlear to vibrate.
6) This stimulates the sensory receptors
7) Action potentials are sent down the cochlear axons (in the vestibulocochlear nerve).
8) Action potentials are transmitted to the cochlea nucleus in the brain stem.
9) Action potentials are sent from the cochlea nucleus to the auditory area of the cerebral cortex (at the top of the temporal lobe).
What does the vestibule contribute to balance perception?
It is concerned with the position of the head (static equillibrium)
What does the semi-circular canals contribute to balance perception?
It is concerned with the movements of the head and the rate of these movements (kinetic equillibrium)