Module 3: The Peripheral Nervous System Flashcards
Identify key aspects to afferent neurons
- Small, round cell body
- Single long dendrite
- Short axons
Afferent nerve cell bodies are found in clusters called ___, found external to the spine
Ganglia
What is the primary purpose of the afferent division of the nervous system?
To carry nerve impulses from the peripheral receptors and special sense organs to the CNS
What is transduction?
The conversion of an environmental signal to an electrical signal
What do mechanoreceptors respond to?
Mechanical energy. Respond to vibration, acceleration, movement
Can neurons change the amplitude of an action potential? (T/F)
False! They cannot change amplitude of an action potential
How do neurons convey the strength of a stimulus?
They can code the intensity of a stimulus by firing a high frequency of action potentials
If a neuron conveys a high frequency of action potentials, will this illicit a strong or weak response?
Strong. High frequency of action potentials = stronger response
How does the brain identify the site of sensory stimulation?
It uses the location of the afferent nerves where the stimulation was picked up from
What is a receptive field?
A region of the environment where the neuron is sensitive to
How does the brain identify the location of a smell?
It uses gradients
What is receptor potential vs generator potential
The stimulation of a receptor that alters the membrane of the neuron to open nonselective cation channels. This is called receptor potential in specialized receptor cells and generator potential in the ending of an afferent neuron
What are the 4 properties that allow the CNS to differentiate between incoming signals
- Modality (receptor type, chemo/photo,etc)
- Intensity
- Location
- Duration
Describe tonic receptors
- Slow adapting or do not adapt at all
- Important in situations where a near constant signal from a stimulus is necessary
Describe phasic receptors
- Rapidly adapting
- The receptor will even stop rapidly generating action potentials even with the stimulus present
- Important for monitoring changes in stimulus intensity
What is an “off response”. What receptor is involved?
The depolarization of an action potential in a phasic receptor when a stimulus has been removed
What do mechanical nociceptors respond to?
Physical damage (cutting, crushing)
What do thermal nociceptors respond to?
Temperature, especially heat
What do chemical nociceptors respond to?
Noxious chemicals both external and internal to the body
Describe fast pain fibres
- Are a-delta fibres
- Perceived associated with these fibres are acute, sharp, and stabbing pain
Describe slow pain fibres
- are C-fibres
- Unmyelinated
- Perceived sensation associated is burning, aching and throbbing
How does glutamate and substance P aid in the sensation of pain?
- Is released from afferent pain fibre axons and is postsynaptic glutamate receptors on neurons on dorsal horn of spinal cord. Transmits the signal to higher levels for further processing
How are the hypothalamus and limbic system involved in the perception of pain?
- Allows for behavioural and emotional responses to the pain
How is the cortex involved in the perception of pain?
- Cortical somatosensory cortex processing localized pain to an area of the body where the stimulus has affected
How is the thalamus involved in the perception of pain?
- Allows for the perception of the pain stimulus
How is the reticular formation involved in the perception of pain?
- Increases the level of alertness and awareness of the painful stimulus
How does the activation of AMPA receptors affect the perception of pain?
- Activation of this receptor can lead to action potentials being generated in the dorsal horn and signals sent to higher brain centers
- Na+ is released and depolarizes the cell. When a certain level is reaches, Mg2+ is dislodged and the NMS channel is activated
How does the activation of NMDA receptors affect the process of pain perception?
- Allows calcium to enter the neuron once activated, which activates a second messenger pathway making the neuron more excitable than normal
- Can explain why injured areas are more sensitive
What is the endogenous analgesic system?
The CNS’s built in pain suppressing system
Describe the process of the endogenous analgesic system
- Activation of the descending pathways activate inhibitory neurons in the dorsal horn. These axons terminate on afferent fibre nerve terminals which release endogenous opiates that suppress the neurotransmitters being released from afferent pain fibres
What is the difference between endogenous opiates and exogenous opiates
- Endogenous opiates suppress the neurotransmitters being released from afferent pain fibres
- Exogenous opiates activate opioid receptors that decrease the perception of pain
Regulation of the muscles that control the constriction AND dilation of the pupil is controlled by what nervous system?
The autonomic nervous system
Describe pupillary constriction
- Caused by parasympathetic stimulation
- One set of muscles that is organized into a circular fashion constrict to make the pupil smaller
Describe pupillary dilation
- Caused by sympathetic stimulation
- One set of muscles that is organized in a radial fashion contract to dilate the pupil
What are the two refractive structures in the eye?
- The cornea
- The lens
How does the cornea contribute to vision?
Contributes most to refractive ability of the eye
If someone has an astigmatism, what is wrong with their eye?
The surface of their cornea is uneven, meaning their refraction of light will be uneven
How does the lens contribute to vision
Has the ability to focus light rays on the retina because of its convex shape. Can also adjust to focus on something
The lens is controlled by what muscle and ligament?
The ciliary muscle and suspensory ligament
If the lens is relaxed, what would it look like? If the light source is close, what would it look like?
It would be a more flat, less convex shape if relaxed
If the light source was close, it would be more convex and the muscle would be contracted
Which structure in the eye has direct connection with the optic nerve?
The retina
What are the 3 main cells of the retina
Rods and cones
Bipolar cells
Ganglion cells
What is the function and location of rods and cones
- Cones are sensitive to colour
- Rods are responsible for vision in low lighting and peripheral vision
- The outermost layer of the retina
What is the function and location of bipolar cells
- Involved in transmission of signals from the rods and cones to the ganglion cells
- Middle layer in retina
Wha tis the function and location of ganglion cells in the eye
- Axons make up the optic nerve
- The neurons located on inner surface of retina
Describe the processing of vision
- Information of the optic nerve is transmitted to the visual pathway in the thalamus, where initial processing occurs and different visual stimuli (colour, form, depth, etc) is separated and relayed to appropriate zones in the cortex
If vision is captured on the right visual field, where is it processed in the brain?
On the left side of the brain
Why can we see farther than we can hear?
The vibrations of the air lose energy much faster as they move through the air than light waves
The pitch of a sound refers to what?
The tone. The frequency of vibrations. The greater the frequency, the higher the pitch
The intensity of a sound refers to what?
The loudness. The amplitude of the sound waves. Greater amplitude means louder sound
The timbre of sound refers to what?
Quality. The overtones that are superimposed on the pitch. allows us to distinguish between voices and instruments even if they are playing at the same loudness and pitch
What are the 3 parts to the external ear
- The pinna
- The ear canal
- The tympanic membrane
Describe the structure and function of the pinna
- The external skin covered cartilage that collects sound waves
- Essential for the location of sound
Describe the structure and function of the ear canal
- Conducts the sound waves towards the tympanic membrane
- Entrance of ear canal is guarded by hairs and wax to prevent airborne particles
Describe the structure and function of the tympanic membrane
- Stretches across the entrance to the middle ear
- Vibrates when hit by incoming sound waves
- Pressure on either side of tympanic membrane is similar
What are the three bones in the middle ear
The malleus, incus, and stapes
What is the purpose of the middle ear?
To take the movement of the tympanic membrane and amplify the sound as it is transmitted to the fluid of the inner ear
The bones in the middle ear act only as amplifiers? (T/F)
F. They can also act as a dampener of sound
What are the three parts to the inner ear?
The cochlea
The organ of Corti & basilar membrane
The inner hair cells
Sound waves are converted to __ energy as it passes through the oval window into the inner ear
mechanical
Describe the structure and function of the cochlea
- Spiral shape - kinda looks like a snail
- Responsible for the perception of hearing and aids in ability to determine pitch
Describe the structure/function/location of the organ of Corti and basilar membrane
- Contains hair cells, one row of inner hair cells and 3 rows of outer
- Found within the cochlea
- The action sense organ and is supported by the basilar membrane
- As fluid moves within the inner ear, the hair cells are moved and generate neuronal signals
Describe the function of the inner hair cells
- Transform the cochlear fluid vibrations into action potentials that send auditory messages to cortex
- Changes in membrane potential match the frequency of the original sound stimulus
Describe how pitch is discriminated within the ear
- Depends on the shape of the basilar membrane
- higher pitches are detected at the narrow end of the oval window and lower pitches are detected at the wider end.
- The stapes moves the oval window at a certain pitch where the wave travels to the part of the basilar membrane assoicated to that particular pitch
- Hair cells are deformed and give that mechanical information to the CNS
- That information is relayed to the brainstem and thalamus
Describe the function of the vestibular apparatus
- Provides information for equilibrium and coordination of movement by detecting changes in head movement
- Is fluid-filled and contains hair cells triggered by movement of the fluid
If someone is affected by motion sickness, what part of the ear corresponds to this
The vestibular apparatus. A sensitive one makes someone more susceptible to motion sickness
Taste receptors on the tongue are called ___ and are organized into clusters called ___
tastebuds; papillae
What are the 5 primary tastes?
- Salty
- Sour
- Sweet
- Bitter
- Umami
Describe the process of olfaction
- Chemicals that can be “smelled” dissolve in the mucous layer and interact with cilia on olfactory receptors
- Budding of an odorant activates G proteins and mobilizes cAMP that leads to opening of Na+ channel.s These depolarize the cell and cause an action potential
The “fight or flight” nervous system
The sympathetic nervous system
The “rest and digest” nervous system
The parasympathetic nervous system
Describe the nerves in the sympathetic nervous system
- Have a short preganglionic fibre
- Have a long postganglionic fibre
- Releases acetylcholine from preganglionic fibre
- Releases nonephinephrine and epinephrine from post-ganglionic fibre
- Adrenergic fibre type
Describe the nerves in the parasympathetic nervous system
- Have a long preganglionic fibre
- Have a short postganglionic fibre
- Releases acetylcholine from preganglionic fibre
- Releases acetylcholine from postganglionic fibre
- Cholinergic fibre type
Describe the nerve origin and termination in sympathetic nerves
- Originate in the thoracic and lumbar regions of the spinal cord
- Preganglionic fibres terminate in ganglia by the spinal cord and postganglionic fibres terminate on the effector organ
Describe the nerve origin and termination in parasympathetic nerves
- Originate from the brain or lower spinal cord
- Preganglionic fibres terminate in ganglia located close to the effector organ
What is dual innervation?
Input from both the sympathetic and parasympathetic nervous system
Describe the effect sympathetic stimulation has on specific organs (heart, eye, digestive tract, blood vessels, lungs, urinary bladder)
Heart: increases rate and force of contraction
Eye: Dilation of the pupil, adjustment of eye for far vision
Digestive tract: Decreased motility, inhibition of digestive secretions
Blood vessels: Constriction
Lungs: Dilation of bronchioles, inhibition of mucous secretion
Urinary bladder: Relaxation
Describe the effect parasympathetic stimulation has on specific organs (heart, eye, digestive tract, blood vessels, lungs, urinary bladder)
Heart: decreased rate and decreased force of contraction in atria only
Eye: Adjustment of eye for near vision
Digestive tract: Increased motility, stimulation of digestive secretions
Blood vessels; Dilation of vessels supplying penis and clitoris only
Lungs: Constriction of bronchioles and stimulation of mucous secretion
Urinary bladder: Contraction (emptying)
Provide an example of an exception to dual innervation. Describe
Arterioles and veins:
Receive only sympathetic stimulation and are regulated by increasing/decreasing sympathetic activity
Sweat glands:
Receive only sympathetic innervation
How does the adrenal gland affect the ANS
Amplifies sympathetic system when activated by sympathetic stimulation
What are cholinergic receptors?
Receptors that respond to neurotransmitter acetylcholine
What are adrenergic receptors?
Receptors that respond to epinephrine and norepinephrine. All activate G proteins
What are the two types of cholinergic receptors? What differs between them?
Muscarinic receptors and nicotinic receptors.
Muscarinic receptors are found on effector cell membranes
Nicotinic receptors are found on cell bodies of postganglionic cells in all autonomic ganglia
What are the two types of adrenergic receptors?
Alpha and beta receptors
Describe the properties of alpha (1) receptors
- Greater sensitivity for norepinephrine compared to epinephrine
- Activates Ca2+ second messenger system
- Is inhibitory
- Targets smooth muscle cells of digestive system, causing relaxation
Describe the properties of alpha (2) receptors)
- Greater sensitivity for norepinephrine compared to epinephrine
- Suppresses cAMP pathway
- Is excitatory
- Targets smooth muscle cells in blood vessels causing constriction
Describe the properties of beta (1) receptors
- Equally responsive to nonephinephrine and epinephrine
- Enhances the cAMP pathway
- Excitatory
- Primarily targets heart
Describe the properties of beta (2) receptors
- Greater affinity for epinephrine
- Enhances the cAMP pathway
- Inhibitory
- Primarily targets smooth muscle, cells of arterioles, and respiratory airway
Describe the properties of beta (3) receptors
- Found only in adipose tissue
Describe the somatic nervous system
- Comprised of axons that innervate skeletal muscle under voluntary control
- Cell bodies for motor neurons are found in the ventral horn of the spinal cord and the axons terminate directly on the effector
- There is no inhibition of skeletal muscle, only excitation
