Neurophysiology (Part 1) Flashcards
Sensory is synonymous with ___erent
afferent
Motor is synonymous with ___erent
efferent
What 2 things compose the CNS?
brain and spinal cord
What are the major divisions/structures of the CNS?
- spinal cord
- brainstem
- cerebellum
- diencephalon
- cerebral hemispheres
The spinal cord extends from the base of the skill to where?
the first lumbar segment
What are the 3 components of the brainstem?
- medulla
- pons
- midbrain
Which cranial nerves arise from the brainstem?
CN III-XII
What does the medulla contain?
- Autonomic centers that regulate breathing and blood pressure
- Centers that coordinate swallowing, coughing, and vomiting reflexes
What is the function of the pons?
Participates in balance and maintenance of posture, in regulation of breathing, and relays information from the cerebral hemispheres to the cerebellum
What does the midbrain do?
It participates in control of eye movements, and also contains relay nuclei of the auditory and visual systems
Where does the cerebellum lie?
Dorsal to the pons and medulla
What are the functions of the cerebellum?
Coordination of movement, panning and execution of movement, maintenance of posture, and coordination of head and eye movements.
What 2 structures make up the diencephalon?
the thalamus and hypothalamus
What information does the thalamus process?
Almost all sensory information going to the cerebral hemispheres and almost all motor information coming from the cerebral cortex
Where does the hypothalamus lie?
Ventral to the thalamus
What does the hypothalamus do?
It contains centers that regulate body temperature, food intake, and water balance
The hypothalamus is also a endocrine gland that controls what?
the secretions of the pituitary gland
How does the hypothalamus control secretions of the anterior pituitary gland?
It secretes releasing hormones and release-inhibiting hormones into hypophysial portal blood that causes release (or inhibition) if the anterior pituitary hormones
How does the hypothalamus control secretions of the posterior pituitary gland?
It contains the cell bodies of neurons of the posterior pituitary gland that secrete ADH and oxytocin
What are the 5 components of the cerebral hemispheres?
- cerebral cortex
- underlying white matter
- 3 deep nuclei:
> basal ganglia
> hippocampus
> amygdala
What are the functions of the cerebral cortex?
- perception
- higher motor functions
- cognition
- memory
- emotion
What are the 4 lobes of the cerebral cortex?
- frontal
- parietal
- temporal
- occipital
Primary areas of the cerebral cortex are the ____ direct and involve the ____ number of synapses.
most
fewest
Tertiary areas of the cerebral cortex require the ____ complex processing and involve the ____ number of synapses.
most
greatest
How are secondary and tertiary sensory and motor areas involved with more complex processing?
by connecting to association areas
What are the 3 deep nuclei of the cerebral hemispheres?
- basal ganglia
- hippocampus
- amygdala
What does the basal ganglia consist of?
The caudate nucleus, the putamen, and the globus pallidus
What do the basal ganglia do?
Receive input from all lobes of the cerebral cortex and have projections, via the thalamus, to the frontal cortex to assist in regulating movement
The hippocampus and amygdala are part of what system?
limbic
What is the hippocampus involved in?
memory
What is the amygdala involved in?
Emotions
It communicates with the autonomic nervous system via the hypothalamus to perceive these emotions through HR, pupil size, and hypothalamic hormone secretion
The nervous system uses synapses in ____ nuclei to integrate converging information.
relay
Relay nuclei contain what types of neurons?
local interneurons and projection neurons
Almost all information going and coming from the cerebral cortex is processed where?
in the thalamic relay nuclei
Topographic information in the somatosensory system is represented by what?
a sensory homunculus in the cerebral cortex
Topographic representation in the visual system is called what?
retinotopic
Topographic representation in the auditory system is called what?
tonotopic
Does all sensory and motor pathways cross from one side to the other side of the brain or spinal cord?
Yes
What are the crossings of sensory and motor pathways in the spinal cord and brain called?
decussations
Areas of the brain that only contain decussating axons are called what?
commissures
What is the commissure that connects the 2 cerebral hemispheres?
the corpus callosum
What are nerve fibers classified according to?
their conduction velocity, which depends on the size of the fibers and the presence or absence of myelinaton
What are the 2 types of nerve classification systems?
- both sensory and motor nerve fibers use lettered nomenclature of A, B, and, C
- sensory nerve fibers only use a Roman numeral nomenclature of I, II, III, and IV
What are the 5 steps involved in transmitting sensory information
1) sensory receptors are activated by stimuli in the environment and this information is converted into electrochemical energy called the receptor potential via sensory transduction
2) the first-order neuron begins the transmission of this information through the CNS
3) the first-order neuron synapses with the second-order neuron in relay nuclei in the brain or spinal cord and when in route to the thalamus they decussate either in the spinal cord or in the brain stem
4) In the thalamus the second-order neuron synapses with the fourth-orderneuron
5) Fourth-order neurons transmit information to the appropriate sensory area of the cerebral cortex which the information is processed
What are the 5 types of receptors?
- mechanoreceptors
- photoreceptors
- chemoreceptors
- thermoreceptors
- nociceptors
What activates mechanoreceptors?
Pressure or changes in pressure
What are a few examples of mechanoreceptors?
- pacinican corpuscles in subcutaneous tissue
- Meissner’s corpuscles in nonhairy skin
- baroreceptors in the carotid sinus
- hair cells on the organ of Corti and semicircular canals
What activates photoreceptors and what are they involved in?
Photoreceptors are activated by light and are involved in vision
What activates chemoreceptors and what are they involved in?
Chemoreceptors are activated by chemicals and are involved in olfaction, taste, and detection of oxygen and carbon dioxide in the control of breathing
What activates nociceptors?
Extremes of pressure, temperature, and noxious chemicals
What is sensory transduction?
The process by which an environmental stimulus activates a receptor and is converted into electrical energy
What does sensory transduction typically involve?
Opening or closing of ion channels in the receptor membrane, which leads to a flow of ions across the membrane
This current flow then leads to a change in what?
receptor potential
What are the steps involved when a stimulus activates a mechanoreceptor?
1) a mechanical stimulus causes movement of the mechanoreceptor
2) this change causes ion channels in the sensory receptor membrane to open or close, which results in a change in current flow
3) receptor potential is generated based on whether the current flow is inward or outward (inward = depolarization; outward = hyperpolarization)
4) if the receptor potential is sufficient enough, an action potential will be generated
What are receptor potentials?
Graded electronic potentials, whose amplitude correlates with the size of the stimulus
If current flow is inward __polarization occurs and the membrane potential is moved ____ threshold which _____ the likelihood of an action potential will occur.
If current flow is outward __polarization occurs and the membrane potential is moved ____ threshold which _____ the likelihood of an action potential will occur.
depolarization; towards; increases
hyperpolarization; away; decreases
What is a receptive field?
An area of the body that when stimulated results in a change in firing rate of a sensory neuron
What are the 2 classifications of receptive fields?
- excitatory: produces an increase in the firing rate of a sensory neuron
- inhibitory: produces a decrease in the firing rate of a sensory neuron
The _____ the receptive field, the more precisely the sensation can be localized or identified
smaller
The ______ the order of the CNS neuron, the more complex the receptor field. Why?
higher
Since more neurons converge in relay nuclei on each level
Describe the concept of lateral inhibition
Lateral inhibition is the capacity of an excited neuron to reduce the activity of its neighbors. In other words it disables the spread of action potentials from excited neurons to neighboring neurons in the lateral direction.
Lateral inhibition creates a contrast in stimulation that allows _____ sensory perception
Increased
What are the 6 features of a stimulus that can be encoded?
- Sensory modality
- Spatial location
- Threshold
- Intensity
- Frequency
- Duration of stimulus
Describe the concept of sensory modality
Information transmission depends on receptor type such as light, sound, temperature, taste, pressure, and smell. The type and location of the sensory receptor activated by the stimulus plays the primary role in coding the sensation.
A stimulus/sensory modality is often encoded by what?
labeled lines, which consist of pathways of sensory neurons dedicated to that modality
What is stimulus location encoded by?
the receptive field of sensory neurons
What is stimulus threshold?
The minimum stimulus that can be detected
What are the 3 ways in which stimulus intensity is encoded?
- by the number of receptors that are activated
- differences in firing rates of sensory neurons in the pathway
- activating different types of receptors
Some stimulus information that is encoded in the pattern of nerve impulses are based on what 3 things?
- mean discharge frequency
- duration of firing
- temporal firing pattern
Stimulus duration is encoded by what?
the duration of firing of sensory neurons
Stimulus information is also encoded in ____ maps.
neural
What forms a neural map?
Arrays of neurons receiving information from different locations on the body, from different locations on the retina, or different sound frequencies
What are the 2 types of receptor adaptations?
- phasic
- tonic
Phasic receptors adapt ____ to the stimulus, whereas tonic receptors adapt ____ to the stimulus.
rapidly
slowly
What is an example of a phasic receptor?
pacinian corpuscles
What do phasic receptors typically detect?
the onset and offset of a stimulus and a changing stimulus
What is an example of a tonic receptor?
mechanoreceptors such as Merkel’s disks
What 2 things do tonic receptors typically encode?
- stimulus duration: the longer the stimulus, the longer the period in which the receptor potential exceeds threshold
- stimulus intensity: the greater the intensity, the larger the depolarizing receptor potential and the more likely APs are to occur
What type of information does the somatosensory system process?
touch
position
pain
temperature
What are the 3 types of somatosensory receptors
- mechanoreceptors
- thermoreceptors
- nociceptors
How many different types of mechanoreceptors are there and how are they divided?
There are six different types found in either nonhairy or hairy skin
What are the 2 mechanoreceptors found in nonhairy skin
- Meissner’s corpuscle
- Merkel’s receptors
Describe Meissner’s corpuscles
They are rapidly adapting receptors found in the dermis of nonhairy skin that encode point discrimination, precise location, tapping, and flutter
Where are Meissner’s corpuscles usually found?
on the fingertips and lips
Describe Merkel’s receptors
They are slow adapting receptors found in nonhairy skin that detect vertical indentation of the skin
What are the 3 mechanoreceptors found in hairy skin
- hair follicle receptors
- Ruffini’s corpuscle
- tactile discs
Describe hair follicle receptors
They are rapidly adapting array of nerve fibers surrounding a hair follicle in hairy skin that detect the velocity and direction of hair displacement
Describe Ruffini’s corpuscle
They are slow adapting receptors found in the dermis of hairy skin and in joint capsules that respond to stretch and joint rotation
Describe tactile discs
They are slow adapting receptors found in hairy skin that detect vertical indentation of the skin
Same as Merkel’s except in hairy skin
What type of mechanoreceptors are found in the subcutaneous layers of nonhairy and hairy skin and in muscle?
Pacinian
Describe Pacinian corpuscles
They are very rapidly adapting receptors that detect changes in stimulus velocity and encode the sensation of vibration
What are thermoreceptors?
Slowly adapting receptors that detect changes in skin temperature
What are the 2 classes of thermoreceptors?
Warm and Cold
At what temperature are both warm and cold receptors active?
36 degrees Celsius
At what temperature do warm thermoreceptors become inactive and nociceptors take over?
45 degrees Celsius
What do nociceptors respond to?
noxious stimuli that can produce tissue damage
What are the 2 major classes of nociceptors?
- thermal or mechanical nociceptors
- polymodal nociceptors
Thermal/mechanical nociceptors are supplied by what?
Finely myelinated A-delta afferent nerve fibers
What do thermal/mechanical nociceptors respond to?
sharp, pricking pain
Polymodal nociceptors are supplied by what?
Unmyelinated C fibers
What do polymodal nociceptors respond to?
high-intensity mechanical or chemical stimuli and hot/cold stimuli
What chemical directly activates nociceptors?
Histamine released by mast cells
What is hyperalgesia and what is its significance in nociceptor activation?
It is the process by which the axons of nociceptors release substances that sensitize them to stimuli that were not previously noxious or painful which reduces one’s pain threshold
What are the 2 pathways for transmission of somatosensory information to the CNS?
- dorsal column system
- spinothalmic/anterolateral system
What type of information does the dorsal column system transmit?
discriminative touch, pressure, vibration, two-point discrimination, and proprioception
The dorsal column system consists mainly of what type of nerve fiber?
group I and II nerve fibers
Where are the cell bodies of first-order neurons in the dorsal column system found?
in the dorsal root ganglion or in cranial nerve ganglion cells
Discriminative information that comes from the lower limb ascend the dorsal column system ipsilaterally to the nucleus _____ in the medulla.
gracilis
Discriminative information that comes from the upper limb ascend the dorsal column system ipsilaterally to the nucleus _____ in the medulla.
cuneatus
Describe the path discriminative information takes after it exits the nucleus gracilis/cuneatus.
First-order neurons synapse with second-order neurons and cross the midline in the medulla. The second-order neurons then ascend to the contralateral thalamus, where they synapse on the third-order neurons, which ascend to the somatosensory cortex and synapse on fourth-order neurons.
What type of information does the anterolateral/spinothalmic system transmit?
pain, temperature, and light touch
The anterolateral/spinothalmic system consists mainly of what type of nerve fiber?
group III and IV (slowest) nerve fibers
Where are the cell bodies of first-order neurons in the anterolateral/spinothalmic system found?
dorsal horn of the spinal cord
Where do first-order neurons of the anterolateral/spinothalmic system get their information from?
thermoreceptors and nociceptors in the skin
Where do first-order neurons synapse with the second-order neurons in the anterolateral/spinothalmic system ?
in the spinal cord
Describe the pathway through the anterolateral/spinothalmic system after the first and second-order neurons synapse in the spinal cord
The second-order neurons cross the midline and ascend to the contralateral thalamus where they synapse with third-order neurons which ascend to the somatosensory cortex and synapse on fourth-order neurons.
____ pain has a rapid onset and offset, and is precisely localized
Fast
Fast pain is carried on what types of fibers?
A delta, group II, and group III fibers
____ pain is characterized as aching, burning, or throbbing pain that is poorly localized.
Slow
Slow pain is carried on what type of fibers?
C fibers
Referred pain is of _____ origin
visceral
Referred pain is “referred” according to what?
dermatomal pattern
Where do the following refer pain to?
Heart
Gallbladder
Kidney
Heart: chest and shoulder
Gallbladder: abdomen
Kidney: lower back
What 2 qualities of light can the eye distinguish?
- brightness
- wavelength
Wavelengths between ___ and ___ nanometers are called visible light
400-750
The wall of the eye consists of how many layers?
3 concentric layers
Describe the outer layer of the wall of the eye and what contains
It is fibrous and includes the cornea, corneal epithelia, the conjunctiva, and the sclera
Describe the middle layer of the wall of the eye and what contains
It is vascular and includes the iris and choroid
Describe the inner layer of the wall of the eye and what contains
It is neural and contains the retina
The functional portions of the eye cover the entire posterior eye except for what area?
The blind spot which is the optic disc (head of the optic nerve)
Where is visual acuity highest?
at a central point of the retina called the macula in which light is focused at a depression called the fovea
What are the 2 fluids of the eye and what areas do they fill?
- aqueous humor: fills anterior chamber
- vitreous humor: fills posterior chamber
What are the sensory receptors for vision called and where are they located?
Photoreceptors on the retina
What are the 2 types of photoreceptors?
Rods and Cones
Describe what type of light rods are sensitive to
They have low thresholds, are sensitive to low-intensity light, and function well in darkness
Describe what type of light cones are sensitive to
They have a higher threshold, not sensitive to low-intensity light, and operate best in daylight
____ have low acuity. _____ provide higher visual acuity.
Rods
Cones
Visual information is received and transduced by photoreceptors on the retina and thin is carried to the CNS via the axons of what type of cells?
retinal ganglion
Which of the photoreceptors are involved in color vision?
cones
What are the 3 types of retinal cells?
- photoreceptors
- interneurons (bipolar cells, horizontal cells, and amacrine cells)
- ganglion cells
The main visual pathway is through what pathway of the thalamus?
dorsal lateral
What leads to higher visual acuity and lower sensitivity in cones?
What leads to lower visual acuity and higher sensitivity in rods?
The arrangement in which a few cones synapse on a single bipolar cell
The arrangement in which many rods synapse on a single bipolar cell
What are the 8 layers of the retina? Describe what can be found in each layer
1) pigment cell layer: absorb stray light and prevent light from scattering
2) photoreceptor layer: contains the rods and cones
3) outer nuclear layer: contains nuclei of the photoreceptors
4) outer plexiform layer: contains presynaptic and postsynaptic elements of retinal interneurons
5) inner nuclear layer: contains the cell bodies of the retinal interneurons
6) inner plexiform layer: contains presynaptic and postsynaptic elements of retinal interneurons
7) ganglion cell layer: contains the cell bodies of ganglion cells, which are the output cells of the retina
8) optic nerve layer: contains axons of retinal ganglion cells which form the optic nerve
Where are the outer and inner segments of photoreceptors located?
In the photoreceptor layer of the retina
Where are the nuclei of photoreceptors located?
in the nuclear layer of the retina
Where are the synaptic terminals of photoreceptors located?
in the outer plexiform layer of the retina
What is rhodopsin?
A light sensitive pigment found in both rods and cones
Describe the structure of the outer segment in rods
They are long and consist of stacks of free-floating double-membrane discs containing large amounts of rhodopsin
Describe the structure of the outer segment in cones
They are short and cone-shaped and consist of infoldings of surface membrane that contains a small amount of rhodopsin
The greater the amount of rhodopsin (photopigment) the _____ the sensitivity to light
greater
This accounts for the greater light sensitivity in rods
What connects the inner and outer segments in rods and cones?
a single cilium
What do the inner segments contain?
mitochondria and other organelles
Where is synthesized in the inner segment?
rhodopsin
Describe how rhodopsin is incorporated into the membranes of the outer segments in rods
It is inserted in new membrane discs, which are displaced toward the outer segment and eventually shed
Describe how rhodopsin is incorporated into the membranes of the outer segments in cones
It is incorporated randomly into membrane folds, with no shedding process
What are the 6 steps in photoreception?
1) light strikes the retina which initiates photoisomerization which converts rhodopsin into metarhodopsin II
2) this metarhodopsin II activates transducin which results in an increased breakdown of cyclic GMP
3) depending on whether there is an increase or decrease in cyclic GMP levels will produce a Na+ inward current or outward current which will either result in depolarization or hyperpolarization of the photoreceptor membrane
4) If hyperolarization occurs than there is a decrease in the release of either an excitatory or inhibitory NT
5) if the NT is excitatory, than the bipolar or horizontal cells become hyperpolarized
6) if the NT is inhibitory, than the bipolar or horizontal cells become depolarized
Increased levels of cyclic GMP levels occurs in the ____ which produces an _____ flow of sodium and __polarization will occur.
dark
inward
depolarization
Decreased levels of cyclic GMP levels occurs in the ____ which produces an _____ flow of sodium and __polarization will occur.
light
outward
hyperpolarization
When light hits a photoreceptor they are always hyperpolarized. Therefore if an excitatory NT is released the bipolar cell will be _____ and if an inhibitory NT is released the bipolar cell will be _____.
inhibited
excited
What is cochlear microphonic potential?
the oscillating receptor potential generated in the hair cells of the organ of Corti in response to acoustic stimulation.
What structure is sensitive to horizontal movement?
the utricle
What structure is sensitive to vertical acceleration (elevator)?
saccule
What is the statoconia?
The otolith mass
