CNS/Sensory Flashcards
What are spinal nerves responsible for?
Somatic sensation:
Touch
Temperature
Pain
What is the afferent system?
Sensory input, cell bodies out of CNS (axons out of CNS)
Efferent
Motor output
Cell bodies in CNS
What are the cranial nerves?
Somatic, visual, olfactory, taste, auditory, vestibular
Where do cranial nerves project to?
Brainstem or other parts of the brain
What is the motor output of the CNS called
Efferent (motor output)
Spinal Nerves functions
Somatic sensation
- touch
- temperature
- pain
What are somatic efferent nerves?
Innervate skeletal muscle, only excitatory, motor neurons
What are autonomic efferent part of nervous system do?
Innervates interneurons, smooth and cardiac muscle, excitatory and inhibitory (enteric nervous system)
What is the white matter in the spinal cord?
Axons running up and down the spinal cord
What is the purpose of the central canal?
Allow CSF to flow
Where are the cell bodies of the efferent neurons found?
In the gray matter
Where are the cell bodies of the neurons whose axons carry afferent signals into spinal cord?
In the dorsal root, more specifically dorsal root ganglion
How many cranial nerves are there?
12
How many cranial nerves enter or leave the brain stem?
10 (pairs, one per side) of 12
What are the only two nerves that do not enter or leave the brain stem called?
Olfactory and optic nerves
Steps of Nervous System development
- Fertilized egg (ovum)
- Ball of cells
- Blastocyst (week 1)
- Blastocyst (week 2)
- Blastocyst (week 3)
- Week 3
Week 1 Blastocyst develops
inner cell mass
Week 3 Blastocyst develops
embryonic disk
neural plate
What are the three layers that make up the embryonic disk, and their location.
Ectoderm (outermost layer)
Mesoderm (middle)
Endoderm (inner)
Neural groove
a shallow median groove of the neural plate between the neural folds of an embryo
What develops in week 4 of the neural tube
vesicles
Neural Crest becomes part of
PNS
Neural tube becomes
CNS and part of PNS
Neural Tube is composed of
Forebrain, Midbrain, Hindbrain
Forebrain becomes
Cerebal hemispheres and Thalamus
Midbrain becomes
Midbrain
Hindbrain becomes
Cerebellum, pons, medulla
Rest of Neural tube becomes
Spinal cord
Cavity becomes
the ventricles and central canal
What do ventricles contain (+amount)
150 ml of cerebral spinal fluid (CSF)
Where is CSF produced, and how much per day?
Produced in the choroid plexus (in the four ventricles, but mainly the two laterals), 500 ml/day
Describe the general composition of CSF?
Sterile, colorless, acellular fluid that contains glucose
Cerebrospinal spinal fluid function
1) Supports and cushions the CNS. Specific gravity of CSF and the brain are equal.
2) Provides nourishment to the brain.
3) Removes metabolic waste through
absorption at the arachnoid villi.
How is CSF circulated?
Passively , not pumped
Where does CSF enter?
The subarachnoid space
Hydrocephalus
an abnormal buildup of fluid in the ventricles (cavities) deep within the brain
Communicating Hydrocephalus
The flow of CSF is blocked after it exits the ventricles
Noncommunicating Hydrocephalus
The flow of (CSF) is blocked along one or more of the narrow passages connecting the ventricles.
Meninges cover the ____ and _____ ____
brain and spinal cord
What are the 3 meninges (membrane) of the CNS?
Dura mater, Arachnoid membrane, Pia mater
Where does CSF return to the blood?
at the dural sinus
What substrate is metabolized by the brain?
Usually only glucose
T/F: There is a lot of glycogen in the brain
F: Very little glycogen in the brain.
What does the brain need continuous supply of? (2)
glucose and oxygen
Glucose transport into the brain does not require ____
insulin
A few seconds of blood supply interruption can lead to
loss of consciousness
A few minutes of blood supply interruption can lead to
neuronal death (stroke)
What % of blood in circulation does the brain receive?
15%
Brain is __% of total mass
2
What is the use of the circle of willis?
SAFETY FACTOR - Able to ensure there is constant supply of blood to brain by ensuring that if one side is compromised, there is necessary blood flow.
CSF moves from
______ to _____ through _____ to _____ through _____ to _____ to _____ back to _____
Heart
Chorioid plexus
ventricles subarachnoid space archnoid villi dural sinus venous system Heart
Blood moves from
______ to either _____ arteries or _____ arteries.
The _____ arteries moves straight to _____ whereas the ______ arteries moves through _____ to _____. Then to the _____ to the ______ system back to _____
Heart
vertebral arteries
carotid arteries carotid arteries circle of willis vertebral arteries basilar artery circle of willis brain venous system heart
Blood-brain barrier
capillary wall
Function of astrocytes (glia) (4)
- provide strucutral support
- induce tight juctions
- glutamate K+
- phagocytosis of debris
Sensation
Awareness of sensory stimulation.
Perception
The understanding of a sensation’s meaning
T/F: We perceive energy of a sensory stimulus directly
F: We do not perceive the “energy” of a sensory stimulus directly.
T/F: We only perceive the neural activity that is produced by sensory stimulation.
T: We only perceive the neural activity that is produced by sensory stimulation.
How do tight junctions impact the effects of the capillary wall of endothelial cells?
It heavily controls diffusion of things across capillary wall
What properties do drugs need to be able to move from blood to extracellular space?
Lipid-soluble or hitch a ride with active transport mechanism
What is the law of specific nerve energies?
Regardless of how a sensory receptor is activated, the sensation felt corresponds to that of which the receptor is specialized
What is the law of projection?
Regardless of where in the brain you stimulate a sensory pathway, the sensation is always felt at the sensory receptor location
(Law of specific nerve energies/projection):
Rub your eyes hard and you will see light.
Law of specific nerve energies
Penfield electrically stimulated somatic sensory cortex and patients perceived somatic sensation in the body
Law of projection
(Law of specific nerve energies/projection): Phantom limb pain after amputation.
Law of projection:
What is the labeled line principle?
The brain knows the modality and location of every sensory afferent
6 sensory systems:
Visual, Auditory, Vestibular, Somatosensory, Gustatory, Olfactory
Modality of Vestibular
Balance
Modality of Somatosensory
Somatic Senses
4 Somatic Senses
Touch
Pain
Proprioception
Thermal
Taste stimulates
Sweet
Sour
Salt
Bitter
Umani
Stimulus Energy of Somatosensory system
Mechnical, thermal, chemical
Stimulus Energy of Vestibular sensory system
Gravity, Acceleration
What is transduction?
Transduction in the nervous system typically refers to stimulus-alerting events wherein a physical stimulus is converted into an action potential, which is transmitted along axons towards the central nervous system for integration
What is responsible for the different afferent responses to constant stimulation?
Because of adaptation where non changing stimulus does not lead to constant stimulus (ie putting clothes on in the morning and not feeling them after a while)
Stimulus Energy of Gustatory sensory system
Chemical
Stimulus Energy of Olfactory sensory system
Chemical
Receptor class of Visual sensory system
Photorecptors
Receptor class of Auditory sensory system
Mechanoreceptors
Receptor class of Vestibular sensory system
Mechanoreceptors
Receptor class of Somatosensory system
Mechanoreceptors
Chemoreceptors
Thermoreceptors
Nociceptors
Receptor class of Gustatory sensory system
Chemoreceptors
Receptor class of Olfactory sensory system
Chemoreceptors
Which of sensory systems use photoreceptors?
Visual
Which of sensory systems use mechanoreceptors?
Auditory
Vestibular
Somatosensory
Which of sensory systems use chemoreceptors?
Somatosensory
Gustatory
Olfactory
Which of sensory systems use thermoreceptors?
Somatosensory
Which of sensory systems use nociceptors?
Somatosensory
Modaility
General class of a stimulus
Steps of sensory receptors (5)
- Stimulus energy
- receptor membrane
- transduction
- ion channel activation
- afferent
For stimulus energy there must be
adequate stimulus (specificity)
Stimulus energy is converted into
afferent activiity
Steps of stimulus energy being converted into afferent activity (5)
- Stimulus energy
- receptor potential
- action potentials
- propagation of action potentials
- release of neurotransmitters
What are the types of afferent response adaptations?
Non-adapting (encodes stimulus intensity and slow changes)
slowly adapting (some stimulus intensity and moderate stimulus changes)
rapidly adapting (fast stimulus changes)
Magnitude of receptor potential
determines the frequency with which action potentials are generated
Afferent adaption allows us to be
sensitive to changes in sensory input
Receptive field
The region in space that activates a sensory receptor or neuron
stimuilus location
Overlapping RFs produce a
population code
Acuity
ability to differentiate one stimulus from another
High/Low acuity location: Lips
High
High/Low acuity location: Back
Low
High/Low acuity location: Hands
High
Small RF means ____ acuity
High
Large RF means ____ acuity
Low
What is the purpose of lateral inhibition?
It sharpens sensory acuity
Enhances the profile of activity of the efferent, and we are able to tell more accurately where the input is coming from
Lateral Inhibition
- Sharpens sensory acuity
- Process by which stimulated neurons inhibit the activity of nearby neurons by interneurons
2nd order neurons
carry signals from the spinal cord to the thalamus
Interneurons
Found only in CNS
It also connects to other interneurons, allowing them to communicate with one another.
What do top-down, or descending pathways do?
They modulate sensory inputs and can actually inhibit sensory input
Sensory information is shaped by both
“bottom up” and “top down” mechanisms
Touch
Mechanoreceptors with specialized end organs that surround the nerve terminal. These end organs allow only selective mechanical information to activate the nerve terminal.
What are Meissner’s Corpuscles?
Fluid-filled structure enclosing the nerve terminal (tip of finger, ex). They are rapidly adapting -> light stroking and fluttering
What is the Merkel disk?
Small epithelial cells surround the nerve terminal. They are slowly adapting -> pressure and texture
Superficial layers receptors:
Merkel disk, Meissner’s corpuscle
What are pacinian corpuscles?
Deep layer structure, Large concentric capsule of connective tissue surround the nerve terminal -> rapidly adapting, strong vibrations
Deep layers receptors:
Pacinian corpuscle, Ruffini endings
What are Ruffini endings?
Deep layer, nerve endings wrap around a spindle-like structure, slowly adapting -> stretch and bending of the skin (shape of object)
How are mechanoreceptors activated?
Stretching the cytoskeletal strands
Proprioception
Muscle spindles provide sense of static position and movement of limbs and body.
Describe thermoreceptors?
Free nerve endings containing ion channels that respond to difference temperature ranges
They do not have specialized nerve ending like mechanoreceptors
What can activate cold afferents, without actual cold?
Menthol
What can activate a warm afferent, without heat?
capsaicin and ethanol
Extreme temperatures activate
pain receptors
What are the receptors responsible for pain?
Nociceptors, free nerve ending containing ion channels that open in response to intense mechanical deformation, excessive temperature, or chemicals.
How are nociceptors activated?
Response to intense mechanical deformation, excessive temperature or chemicals
What is special about pain afferents?
They are highly modulated (enhanced or suppressed)
What are visceral pain receptors and what are they activated by?
Nociceptors on internal environments, such as organs, and are activated by inflammation
Describe the pathway of nociceptors used to signal pain to the brain?
Stimulus occurs, nociceptors become activated and the signal travels up the nociceptive afferent, which fires APs, reaches the spinal cord and release Substance P (neurotransmitter), which activates second order neurons that carries information up to brain
How are nociceptors modulated and enhanced?
Enhancement of surrounding nociceptors by injured tissue and afferent feedback onto mast cells -> dilation of nearby blood vessels -> pain the next day signals to you to avoid use of injured part
Nociceptors are enhanced by many
mediators
What is the enhancement of nociceptors following an injury called?
Hyperalgesia
Describe the pathway a signal takes from the tip of finger to brain?
Afferent of mechanoreceptors (cell bodies found in dorsal root ganglion) extend their axon towards the spinal cord, enter through dorsal root, and move to dorsal column (which carries axons up and down), towards the brain stem (medulla)
What is ipsilateral and contralateral?
Same side and opposite side
Touch and Proprioception route
Dorsal Root ganglion
Dorsal columns
Medulla
Medial lemniscus
Thalmus
Somatosensory cortex
Dorsal columns (senses)
Touch and Proprioception
(Contralateral or Ipsilateral) Touch and proprioception
Ipsilateral
(Contralateral or Ipsilateral) Temperature and Pain
Contralateral
Temperature and Pain route
Dorsal Root ganglion
Dorsa, horn
Anterolateral column
Branches into the reticular formation
Thalamus
Somatosensory cortex
Commonly synapse on the same neurons in the spinal cord
Visceral & somatic pain afferents
Heart attacks commonly produce pain
in the left arm
What is referred pain?
Referred pain is pain perceived at a location other than the site of the painful stimulus/ origin. It is the result of a network of interconnecting sensory nerves, that supplies many different tissues
Analgesia
Reduction of pain through presynaptic inhibition
Opiate neurotransmitters
Presynaptic inhibition
Stop substance P from being released in spinal cord
How do descending pathways reduce pain?
Through presynaptic inhibition. Descending pathways from brainstem release opiate neurotransmitters (presynaptic inhibition) which blocks the release of substance P in spinal cord -> pain is not perceived
What does morphine do?
Binds to presynaptic opiate receptors and block release of substance P
Visual perception is dependent on
context
What is a Brown-Sequard Lesion?
Brown-Sequard syndrome (BSS) is a rare neurological condition characterized by a lesion in the spinal cord which results in weakness or paralysis (hemiparaplegia) on one side of the body and a loss of sensation (hemianesthesia) on the opposite side
Lens (purpose)
refracts (bends) light to a single point
Light is refracted by
the cornea and lens
What refracts more light: Cornea or lens
Cornea
What accommodates near vision?
The lens accommodates for changes in object location,
conformation changes of lens are controlled by ciliary muscles
What is meant when we say the eye is myopic and what structural difference is responsible?
Nearsightedness, eyeball is too long
What is meant when we say the eye is hyperopic and what structural difference is responsible?
Farsighted, eyeball too short
Nearsightedness is corrected by a ____ lens
concave
Farsightedness is corrected by a ____ lens
convex
Cataract
changes in lens colour (more opaque)
What is presbyopia?
The lens gets stiff and unable to accommodate for near vision
What is astigmatism?
The lens or the cornea is misshapen, cornea is not spherical
Fovea centralis
the retinal circuitry is shifted out of the way
What is visual transduction?
Visual phototransduction is the sensory transduction of the visual system. It is a process by which light is converted into electrical signals in the rod cells, cone cells and photosensitive ganglion cells of the retina of the eye
Bipolar cells
only neurons that connect the outer retina to the inner retina
Horizontal cells
Help integrate and regulate the input from multiple photoreceptor cells
Amacrine cells
the major carriers of rod signals to the ganglion cells in the retina
Ganglion cells
Make up the optic nerve
Rods/Cones:
High sensitivity, night vision
Rods
Rods/Cones:
Low sensitivity, day vision
Cones
Rods/Cones:
More rhodopsin, captures more light
Rods
Rods/Cones:
High amplification, single photon closes many Na+ channels
Rods
Rods/Cones:
Slow response time
Rods
Rods/Cones:
Faster response time
Cones
Rods/Cones:
Lower amplification
Cones
What is found binded to rhodopsin?
Chromophore
Rods/Cones:
Less opsin
Cones
Rods/Cones:
More sensitivity to scattered light
Rodes
Rods/Cones:
Most sensitive to direct axial rays
Cones
Rods/Cones system:
Low acuity: not present in central fovea, highly convergent
Rod System
Rods/Cones system:
High acuity: concentrated in fovea, less convergent
Cone system
Rod/Cone system:
Achromatic: one type opsin
Rod System
Rods/Cones system:
Chromatic: three types of opsin
Cone system
When bright light goes to dark
Temporary blindness until rods “re-activate” and take over
What activates the opsin molecule and what happens?
Light (photons) activate the opsin molecule, and as it is activated, the opsin and chromophore separate
When dark goes to bright light
Rods are initially saturated. Temporary blindness until
rods “inactivate” and cones take over
T/F: It takes time to put the chromophore and opsin back together
T
Retina reports relative/absolute intensity of light
relative
Retinal ganglion cells
signal the relative differences of the light (contrast) across their receptive fields
- B/W
- Colour
Photoreceptors are sensitive to ________
wavelength
The opsin molecule determines
the chromatic sensitivity of the photoreceptor
The output of the retina encodes
relative values of brightness and colour
What activates the G-protein cascade, and what does the cascade do?
The separated opsin activates the g-protein cascade, which convert cGMP to GMP
What happens when there is no more cGMP in the cell?
Na+ channels close
What does light cause in the photoreceptors?
Hyperpolarize
Optic tract
both eyes with contralateral visual field
Optic nerve
one eye with both visual fields
What do retinal ganglion cells do?
Retinal ganglion cells signal the relative difference of the light (contrast) across the receptive fields
Cervical Nerves
- body part
- pairs
Neck, shoulders, arms and hands
8
Thoracic Nerves
- body part
- pairs
Shoulders, chest, upper abdominal wall
12
What happens at the optic Chiasm?
The axons of the retinal ganglion cells that are closest to nose (nasal half) cross
The axons of the retinal ganglion cells from the peripheral halves do not cross
Lumbar Nerves
- body part
- pairs
Lower abdominal wall, hips, and legs
5
Sacral Nerves
- body part
- pairs
Genitals and lower digestive tract
5
