Module 3 Flashcards
What is Afferent division
- Afferent neurons carry nerve impulses from pheripehral receptors to the CNS
- Have a long cell body with a single long dendrite and a short axon
- Once appropraite stimulus is reached
- conducts actions potentials twoards the cell bodys in the horn
- Found in clisters called ganglia immediately external to the spine
- Axons extend into the dorsal horn the spinal cord
What is receptor threshold
- Receptors are located at peripheral endings of afferent neurons responding to stims
- Both internal and external stimulu required threshold before they are activated
- to inform the CNS that the threshold stim has been reached
- Afferent neyrons use action potentials to propagate this signal
- Conversion of an environmental signal to an eelctrical signal is called transduction
What are the properteis of receptors
use 4 properties to allow the CNS to diffentiate them
MODALITY
* Each receptor is specialized to respond to a different type of energy or stimulus
* Photreceptors - respond to light
* Mechanoreceptors - Respond to mechanical energy. Skeletal muscles are sensitive to stretches and receptors in the ear contain fine heair cells that bend in response to sound waves
* Thermoreceptors - sensitive to heat
* Chemoreceptors - Sensitive to specific chemicals such as taste, smell, contents of the digestive tract
* Some sense the presence of oxygen in blood
LOCATION
* brain can sue identifiable sites to know activated afferent fibers
* Receptive field - each neuron has a region of the environment it is sensitive. This is called the receptive field, if a stim appears in the neurons field, the neuron will fire and the location is communicated
- Multiple sensors - Brain compares inputs from more than 1 sensor, eyes, ears
- Gradients - With smell we can determine location based on gradients
- if something smells we can move to its itensity. The more intense, that measn we are at the source
INTENSITY
* Action potentials are all ore nothing. Intensity is described are more frequent firings of the neurons
DURATION
* afferent neurons encode for different tupes of duration and communicate to the CNS
* Some cells fire only if the stim is present
* SOme cells fire as the stim goes on then stop and fire when the stim goes of
what is receptor transduction
- Receptors can be specialized endings of an afferent neurons or a seperate receptor cell closely associatd with the pheripher ending in the neuron
- Activation works the same
- Stim causes Ca2+ channels to open and allow it to enter
- They will depolarize the membrane
- This forces the exocytosis of neurotransmitters
What are receptors create graded potentials
- Receptor and generator potentials are graded potentials in that their aimplitide and duration can vary depending on the strength and duration of the stimulus
- If graded potentials are of sufficent magnitude theu will initaite an action potentail in the afferent neuron
- Specialized afferent endings - The receptor potential itself causes the afferent nerve fiber to reach threshold an trigger action potential
- Seperate receptor cell - When receptor potential is strong, it released a chemical messenger that diffuses to the afferent neuron and opens chemically gated sodium channels. If threshold is achieved, then the afferent nerve fiber will initiate and propagate an action potential
What is receptor adaptation
- Receptors themself also have the ability to regulate their responses and this is called adaptation
- Stim of same intensity does not always bring about the same magnitude of receptor potential
- In some stims, receptors adapt to the signal by enhancing or lessning their response
- There are two different types of receptors that vary in their speed of adaptation
What are tonic receptors
- Slow adapting or do not adapt at all
- Important where near constant signal from the stim is neccessary
- msucle stretch receptpr - as CNS constantly requires knowledge of the state of contraction of all skeletal muscles
- Pain receptors are also tonic, as CNS requires knowlege of pain and potentially dangerous stims
what are phasic receptors
- Rapidly adapting
- They work like a light switch. SIgnal when on, signal when off
- They stop generating action potentials even when the stim is still there
- When the stim is gone, They will signal once more
- Mechanoreceptors are an example of this
- Like wearing a watch or ring - initial wear will annoy u then u get used to it
- This happens from Rapidly adapting pacinian corpuscle
- Deformations in the corpuscle causes the potenials to be generated
- Because these receptors are constantly changing, oertime they will not be afected by the stimulus
What is a brief overview of pain
- Called nociceptors, and give an unpleasent sensation
- Defence to alert the CNS
- include external and internal events and can include percieved evemts that are observed
What are the types of nociceptors
- Mechanical nociceptors - Respond to physical damage such as cutting or crushing
- Thermal nociceptors - Respond to temperature, especially heat
- Chemical noiceptors - Respond to noxious chemicals which can be internal or external
- Nociceptors are specialized nerve endings on afferent fibers
- They are called pain fibers
- Two categories, sharp and dull, fast and slow
What are fast and dull Pain receptors
FAST pain fibers
* A-delta fibers are responsible for
* temperature
* chemical
* mechanical stims
* associated with sharp,stabbing intense pain from stimulation
SLOW pain fibers
* C-fibers
* Unmyelinated so they are slow
* SImilar to fast pain receptors
* Respond to chemical
* temperature
* mechanical
* Unlike A-delta fibers, they are polymordial receptors
* The sensation is burning, aching or throbbing
* associated with slow pain pathways is the bradykinin
* once activated, can directly stimulate noiceptors
* There is no adaptation to the stim, nociceptors are stimulated until the bradykinin is removed which explains the long lasting persistnt pain
How does the brain process pain
- When action potential reaches the end of afferent pain fiber axon
- Triggers the release of a neurotransmitter
- Substance P coexists with glutamate to activate ascending pathway
- Transmit the pain signals to higher levels for further processing
CORTEX
* Cortical somatosensory processing localized the painto a discrete body regions
* Locates the pain
THALAMUS
* Processing allows for the perception of pain
RETICULAR FORMATION
* Increases the level of alertness and awareness of painful stimuli
HYPOTHALAMUS/LIMBIC SYSTM
* Recieves input from the thalamus and reticular formation and allows for behaviour and emotional responses to the stimuli
What is Gluatamate
- Amino acids that also function as neurotransmitters
- released by nociceptor nerve endings
- activate post synpatic glutamate receptor on neurons
- Has two actions depending on which type of receptor on the dorsal horn neurons are activated.
- eitehr
- AMPA
- NMDA
what is AMPA
- Activation causes permeability that generates action potentials
- Dorsal horn neuron and send signal to higher brain centers
- the AMPA channel depolarization occurs only whe na certain level of depolarization is reached will the mG ion in the NMDA channel be dislodged and the NMDA channel will be activated
what is an NMDA receptor
- Once activated allows calcium to enter the neuron
- Mg2+ will block the receptor on default. It can be removed and it allows Ca to flow in
- Leads to the activation of a second messenger pathway that results in the neuron being more excitable than normal
- Explains why injured areas are more sensitive to a stim
- that would not normally cause pain
- Example is the pain felt when clothing rubs against a sunburn
What is the endogenous analgesic system
- After intial pain, there is a decrease in the receptor.
- Activation of a descing pathway that in turn activates inhibitory neurons in the dorsal horn
- The axons of these interneurons terminate on the afferent fibers of the nerve terminals
- They release endogenous opiates - pain killers produced by the body
- They supress neurotransmitters released from afferent pain fibers
- Exogenous opiates are not produces by the body like morphine, they activate the opioid receptor and decrease pain
What happens when light enters the eye
- Eye will regulate how much light can enter by expanding and contracting the iris
- Size can be adjusted by 2 contractions
- Controlled by the autonomic system
PUPILARY CONSTRICTION
* Causes by parasympthatic activity
* One set of muscles organized in circular fashion
* These muscles constrict to make the pullp smaller
PUPILLARY DILLATION
* Caused by sympathetic stimulation
* One set of muscles is organized in radial fashion
* These muscles contract to dillate and allow more light to go in
Why does light have to be focused
- Light waves radiate outwards from their source
- all incoming rays must be focused onto a single point to allow the eye to process them
- This processes of the light bending is called refraction
What does the cornea do
- Contributes to most of the reflective ability
- Large density difference at the air-cornea boundary
- The refractory ability of the cornea remains constant as the curve of the cornea cannot be altered
- In some persons, the cornea is uneven this is called astigmatism
What does the lens do
- Convex structire behind the pupil
- Allows light to focus futher on the retina
- Unlike the cornea it is adjustable
Lens accommodation
- The eye can adjust to maintain focus
- controlled bu the cilliary muscle
- When this muscle relaxes, the ligaments pull the lense int oa flatter, less convex shape
- When the muscles contract, it reduces the tension of the ligaments and the lens becomes more convex
- cilliary muscle contraction is also controlled by the ANS
DISTANT LIGHT SOURCES - When the light source is more than 6m away from the lens, the light rays enter parallel when they enter the eye
NEAR LIGHT SOURCES
* When the light is closer than 6m to the lens the light rays are diverging when they enter the eye
* The eye accommoodates by changing shape of the lens so it has a greater ability to bend light, allowung the eye to focus the image
* It will become wider and fatter
What is the retina
- an extension of the CNS
- Direct connection to the optical nerve
- each retina has 1mil nerve fibers into the brain
- The lens wants to focus light on the retina to convert light energy into electrical signals, sent to the CNS
- The structure of the retina is complex and has many layers. Can be divided into 3 layers of excitable cells
What are the rods and cones of the retina
- Contained on the outermost layer
- Cones see colours
- rods are for vision in low lighting
What are bipolar cells of the retina
- Middle layer cells
- involved in transmission of signals from the rods and cones to the ganglion cells
