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Questions and Answers
What type of sensation is primarily carried by the dorsal columns of the spinal cord?
What type of sensation is primarily carried by the dorsal columns of the spinal cord?
Which structure integrates temperature and pain information in the somatosensory pathway?
Which structure integrates temperature and pain information in the somatosensory pathway?
During hyperalgesia, what is the primary purpose of increasing pain sensitivity in the affected area?
During hyperalgesia, what is the primary purpose of increasing pain sensitivity in the affected area?
Which part of the nervous system is primarily involved in the dorsal column-medial lemniscus pathway?
Which part of the nervous system is primarily involved in the dorsal column-medial lemniscus pathway?
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Where do visceral and somatic pain afferents commonly synapse in the nervous system?
Where do visceral and somatic pain afferents commonly synapse in the nervous system?
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What type of mapping is used in the somatosensory cortex to represent different parts of the body?
What type of mapping is used in the somatosensory cortex to represent different parts of the body?
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Which pathway is primarily associated with temperature and pain sensations?
Which pathway is primarily associated with temperature and pain sensations?
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What characteristic is associated with a high acuity somatosensory map in the cortex?
What characteristic is associated with a high acuity somatosensory map in the cortex?
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What type of mechanoreceptor is responsible for detecting light stroking and fluttering?
What type of mechanoreceptor is responsible for detecting light stroking and fluttering?
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Which mechanoreceptor is categorized as slowly adapting and responds to pressure and texture?
Which mechanoreceptor is categorized as slowly adapting and responds to pressure and texture?
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What is the role of muscle spindles in somatic sensation?
What is the role of muscle spindles in somatic sensation?
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Which receptor is primarily responsible for sensing strong vibrations?
Which receptor is primarily responsible for sensing strong vibrations?
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What is the primary function of thermoreceptors?
What is the primary function of thermoreceptors?
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Which statement correctly describes Ruffini endings?
Which statement correctly describes Ruffini endings?
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What triggers the opening of ion channels in mechanoreceptors?
What triggers the opening of ion channels in mechanoreceptors?
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Which of the following correctly matches the receptor type with its function?
Which of the following correctly matches the receptor type with its function?
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Which type of sensory response is characterized by adaptation to fast stimulus changes?
Which type of sensory response is characterized by adaptation to fast stimulus changes?
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How does the size of a receptive field affect sensory acuity?
How does the size of a receptive field affect sensory acuity?
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What is the primary function of lateral inhibition in sensory perception?
What is the primary function of lateral inhibition in sensory perception?
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What does the term 'proprioception' refer to?
What does the term 'proprioception' refer to?
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In the context of sensory information processing, what roles do 'bottom up' and 'top down' mechanisms play?
In the context of sensory information processing, what roles do 'bottom up' and 'top down' mechanisms play?
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Which statement is true regarding the properties of overlapping receptive fields?
Which statement is true regarding the properties of overlapping receptive fields?
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What type of skin is associated with mechanoreceptors in touch sensation?
What type of skin is associated with mechanoreceptors in touch sensation?
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What is implied by a non-adapting sensory response?
What is implied by a non-adapting sensory response?
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Which type of response will likely show the ability to differentiate moderate stimulus changes?
Which type of response will likely show the ability to differentiate moderate stimulus changes?
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What is the role of presynaptic inhibition in sensory processing?
What is the role of presynaptic inhibition in sensory processing?
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Study Notes
Major Divisions of the Nervous System
-
Afferent (sensory input): Cell bodies outside the central nervous system (CNS)
- Cranial Nerves: Somatic, visual, olfactory, taste, auditory, vestibular
- Spinal Nerves: Somatic sensation (touch, temperature, pain) and visceral
-
Efferent (motor output): Cell bodies within the CNS
- Cranial Nerves
- Spinal Nerves: Somatic efferent (innervates skeletal muscle, excitatory—acetylcholine (ACh)); autonomic efferent (innervates smooth & cardiac muscle, excitatory & inhibitory).
- Enteric
Brain Anatomy
-
Cerebrum (cortex): Largest part of the brain
- Frontal: Located at the front of the brain
- Temporal: Located near the temples
- Parietal: Located behind the frontal lobe and above the temporal lobe
- Occipital: Located at the back of the brain
- Corpus callosum: Connects the two hemispheres of the cerebrum
- Thalamus: Filters and relays sensory information
-
Brainstem: Includes midbrain, pons, medulla
- Midbrain: Located above the pons
- Pons: Located above the medulla
- Medulla: Controls vital functions
- Cerebellum: Posterior to the brainstem; involved in balance, motor coordination and posture.
- Gyrus: A fold in the cerebral cortex
- Sulcus: A groove in the cerebral cortex
- Spinal cord: Connects to the brainstem
Brain Anatomy: Coronal Slice
- Gray matter: Darker tissue including neuron cell bodies
- White matter: Lighter tissue made of myelinated axons
- Ventricles: Fluid-filled spaces within the brain
- Basal nuclei (ganglia): Clusters of gray matter deep within the cerebrum
- Limbic system: Involved in emotions and memory
Divisions of the Spinal Cord
- Cervical nerves (8 pairs): Neck, shoulders, arms, and hands
- Thoracic nerves (12 pairs): Shoulders, chest, upper abdominal wall
- Lumbar nerves (5 pairs): Lower abdominal wall, hips, and legs
- Sacral nerves (5 pairs): Genitals and lower digestive tract
- Coccygeal nerves (1 pair):
Spinal Cord Anatomy
- Dorsal horn: Posterior portion of the gray matter
- Ventral horn: Anterior portion of the gray matter
- Central canal: A space within the spinal cord
- White matter: Composed of myelinated axons
- Dorsal root: Carries sensory information
- Ventral root: Carries motor information
- Dorsal root ganglion: Contains cell bodies of sensory neurons
- Spinal nerve: Contains both sensory and motor fibers
Twelve Cranial Nerves
- Olfactory nerve (smell)
- Optic nerve (vision)
- The other ten nerves are important but their naming isnt crucial for this exam
Brain Edema
- Increased intracranial pressure pushes the brain out the base of the skull
- Compresses the brainstem and cranial nerves, affecting pupillary response
Early Development of the Nervous System
- Blastocyst (week 1): Ball of cells
- Inner cell mass: Forms the embryonic disk
- Blastocyst (week 2-3): Developing into different cavities and where the action is happening
- Embryonic disk: Develops into the embryo
- Neural plate: Forms the neural tube
- Week 3: Neural plate turns into a neural tube
Development: The Neural Tube
- Ectoderm: Forms organs and muscles
- Mesoderm: Embryonic disk
- Endoderm: Digestive tract
- Neural crest: Becomes part of the peripheral nervous system (PNS)
- Neural tube: Becomes central nervous system (CNS) & part of PNS during week 4
- Dura mater: Outermost layer of the meninges
The Neural Tube
- Vesicles develop during week 4: Forebrain, midbrain, hindbrain
The Neural Tube Becomes the CNS
- Forebrain becomes Cerebral hemispheres and Thalamus
- Midbrain remains the Midbrain and Pons
- Hindbrain becomes the Medulla and Cerebellum
- Cavity becomes the ventricles and central canal
Ventricles
- Contain: 150 ml of cerebral spinal fluid (CSF)
- Lateral ventricles: The largest of the ventricles and contribute the most to CSF. Two lateral ventricles exist.
- Third ventricle: Connected to the lateral ventricles
- Fourth ventricle: Located between the brainstem and cerebellum
- Choroid plexus: Lining of the ventricles produces CSF.
Cerebrospinal Fluid (CSF)
- Formation: Produced by the choroid plexus (mostly the two lateral ventricles) at a rate of 500 ml/day, but the brain only retains 150 ml/day.
- Function: Supports and cushions the CNS, provides nourishment to the brain, and removes metabolic waste via absorption in arachnoid villi.
- Composition: Sterile, colorless, acellular fluid with glucose
- Circulation: Passive (not pumped)
CSF Circulation
- Foramen of Monro: Connects the two lateral ventricles to the third ventricle
- Cerebral aqueduct: Connects the third ventricle to the fourth ventricle
- Foramina of Lushka & Magendie: Two lateral foramina that connect the fourth ventricle to the subarachnoid space
- Subarachnoid space: Space surrounding the brain and spinal cord, filled with CSF
- Arachnoid villi: Absorb CSF and return it to the blood.
Meninges
- Meninges cover the brain and spinal cord
- Dura mater: Outer layer, attached to bone
- Arachnoid membrane: Middle layer, web-like structure
- Pia mater: Inner layer, adheres to the surface of the brain and spinal cord
Dural (Venous) Sinus
- CSF returns to the blood at dural sinuses
Blood Supply to the Brain
- Glucose is the main energy source for the brain
- Brain has little glycogen
- Brain needs continuous supply of glucose and oxygen
- Blood supply interruption can lead to loss of consciousness or neuronal death (stroke)
- Brain receives 15% of total blood (2% of total mass)
Blood Supply: Front View
- Internal carotid artery: Base of the brain
- Vertebral artery: Joins to form the basilar artery
- Common carotid artery: Where killers sometimes slay all the blood
- Circle of Willis: Protective network of arteries to preserve blood circulation
Cerebral Circulation: CSF and Blood
- CSF is another extracellular fluid that dumps into the heart and gets filtered
- Flows from the ventricles to the dural sinus
Blood-Brain Barrier (Capillary Wall)
- Protects the brain from harmful toxins in the blood
- Tight junctions between endothelial cells of the capillaries, preventing large, diffusible substances from passing through.
- Lipid-soluble substances (like alcohol, nicotine, caffeine) can cross
- Blood-brain barrier only lets lipid soluble substances
Blood-Brain Barrier: Astrocytes (Glia)
- Supporting cells in the brain
- Phagocytize debris
- Regulate ion concentrations
- Maintain suitable environment for neuronal function
Sensory Modalities
-
Sensory System:
- Modality: General class of stimulus.
- Stimulus energy: Energy that activates the receptor.
- Receptor class: Type of receptor that responds to the stimulus.
Perception of the External World
- Sensation: Awareness of sensory stimulation
- Perception: Understanding of a sensation's meaning
- Laws of specific nerve energies: The sensation that a receptor produces is determined by its location and type, and not the source of stimulation
Sensory Receptors
- Stimulus energy: External energy that activates the receptor
- Receptor membrane: Contains ion channels
- Receptor activation: Stimulus energy causes a receptor to change its membrane potential
- Transduction: Converts stimulus energy into a receptor potential in the receptor membrane
- Afferent pathway: Carries the receptor potential to the CNS
Stimulus Intensity and Afferent Response
- Intensity: Higher stimulus intensity corresponds to a higher frequency of action potentials and a greater magnitude of neurotransmitter release by afferent neurons.
Adaptation of Afferent Response
- Adaptation: The change in afferent neuron activity even if the stimulus intensity remains constant
Receptive Field (RF)
- Area of space that activates a sensory neuron.
- Sensory responses vary across an RF, strongest near the central point of the RF.
Receptive Fields Overlap
- Multiple neurons' RF overlap to create an intricate pattern of overlapping sensory information from the receptive field
Stimulus Acuity and RF Size
- High acuity: smaller RF sizes (e.g., on fingertips
- Low acuity: larger RF sizes (e.g., on the back)
Lateral Inhibition
- Sharpens sensory acuity by inhibiting the activity of neurons with receptors located near a stimulated receptor.
Descending Pathways Modulate Sensory Inputs
- Sensory information may be modulated or influenced by descending mechanisms (e.g., top–down processing).
Somatic (Bodily) Sensation
- Several receptor types mediate somatic sensations:
- Touch
- Temperature
- Pain
- Proprioception
Thermoreceptors
- Cold afferents: Respond to temperatures between 0 and 35°C (activated by menthol).
- Warm afferents: Respond to temperatures between 30 and 50°C (activated by capsaicin and ethanol).
Pain
- Nociceptors and pain afferents are modulated.
Nociceptors
- Enhanced by certain mediators released by injured tissues and afferent feedback onto mast cells.
- Chemicals like bradykinin, histamine, 5-HT, prostaglandin, and substance P can induce inflammation and sensitization of pain.
- Blood vessel dilation assists in tissue healing.
Dorsal Columns Pathway
- Carries information from touch and proprioception. Information remains on the same side of the body during transmission to the brain
Anterolateral Pathway
- Carries information from temperature and pain; cross over to the other side of the body during transmission to the brain.
Somatosensory Cortex
- Somatotopic mapping: A specific area of the somatosensory cortex corresponds to a body part
- Contralateral representation: Sensory information from one side of the body is processed in the opposite side of the brain
- High acuity (e.g., lips) vs. lower acuity (e.g., legs)
Referred Pain
- Visceral and somatic pain afferents may synapse on the same neurons in the spinal cord
Descending Pathways Regulate Nociceptive Information
- Periaqueductal gray matter (midbrain) & Reticular formation (medulla): Pain modulation areas in the brain
- Dorsolateral funiculus: Pathway for descending control over pain
Reduction of Pain Through Presynaptic Inhibition
- Opiate neurotransmitters from the brainstem block the release of substance P in presynaptic inhibition
Visual System
- Anatomy: Retina, vitreous humor, lens, iris, pupil, cornea, sclera, fovea centralis, optic disk, blood vessels.
- Refraction: Cornea and lens refract light and focus it on the fovea
- Accommodation: Ciliary muscles change lens shape to focus on objects at different distances
- Common optical defects: Nearsightedness (myopia), farsightedness (hyperopia), astigmatism, presbyopia, cataracts
Visual Perception.
- Depends on context
Organization of the Retina
- Rods and cones
- Bipolar cells
- Horizontal cells
- Amacrine cells
- Ganglion cells
Phototransduction
- Light actives rhodopsin
- G-protein cascade
- cGMP is hydrolyzed to GMP (closes channels)
- Photoreceptor hyperpolarizes, generating an electrical signal
- Four different opsin molecules (rhodopsin is found in rods)
Differences Between Rods and Cones
- Rods: High sensitivity to light, night vision, low acuity, achromatic, one type of opsin
- Cones: Moderate sensitivity to light, day vision, high acuity, chromatic, three types of opsin (Blue, Green, Red)
Light and Dark Adaptation
- Dark adaptation: Gradual increase in rod sensitivity after exposure to dim light (Takes time to rebuild)
- Light adaptation: Gradual decrease in cone sensitivity after exposure to bright light (rapid recovery).
Retina and Relative Light Intensity
- The retina reports relative intensity of light
Retinal Ganglion Cells: Center-Surround Receptive Fields
- Bright center, dark surround or dark center, bright surround
- Signals relative differences in light (contrast)
Photoreceptors and Wavelength Sensitivity
- Opsin molecules determine chromatic sensitivity
Perception of Color
- Depends on context
Retinal Ganglion Cells: Color-Opponent Receptive Fields
- Encode relative values of brightness and color
Color Blindness
- Problem with retina receptors’ sensitivity (issues with the opsins or photoreceptors)
Flow of Visual Information in the Brain
- Optic nerve: Carries visual information from the eye to the brain
- Optic chiasm: Point where nasal fibers cross to the opposite side of the brain.
- Optic tract: Carries information to the thalamus
- Lateral geniculate nucleus (LGN): Relay station in the thalamus
- Optic radiations: Project to the visual cortex in the occipital lobe; the visual cortex in the occipital lobe processes information from both eyes
Anatomy of Visual Field Deficits
- Loss of vision in ipsilateral or contralateral visual field or in both visual fields
Cortical Representation of the Visual World
- Polymodal: Visual information combined with other sensory information.
- Parietal visual stream: Involved in spatial features and motion
- Temporal visual stream: Involved in object recognition (e.g. faces)
- Primary visual cortex: Simple image features, orientation of line segments
Model of V1 Orientation Selective Responses
- Retina and LGN center-surround responses project to V1
The Pupillary Reflex
- Light in one eye causes both pupils to constrict.
- 3rd cranial nerve transmits information from the retina to the midbrain.
- 4 cranial nerve relays to the ciliary sphincter muscles in the other eye
Auditory System
- Anatomy: Pinna (outer ear), external auditory canal, tympanic membrane, malleus, incus, stapes, cochlea, eustachian tube (and more)
- Sound transduction: Sound waves cause vibrations across the eardrum
- Cochlear amplifier: Outer hair cells adjust basilar membrane vibration, thus enhancing the response.
Motion of Basilar Membrane
- High-frequency vibrations produce motion near the base of the cochlea, and low-frequency vibrations produce motion near the apex
Basilar Membrane in Action
- Vibrations cause shearing of hair cells' stereocilia
Cochlear Amplifier
- Outer hair cells change length, generating and amplifying vibrations on the basilar membrane
Clinical Implications of Outer Hair Cell 'Electromotility'
- Otoacoustic emissions (reflex) are used to assess hearing in newborns
Hair Cells
- Contain mechanoreceptors (stereocilia)
Movement of Hair Cell Stereocilia
- Sound vibrations cause stereocilia to move
Tip Links
- Connect stereocilia, causing nearby ion channels to open during movement.
Mechano-transduction at Tip Links
- Activation of afferent neurons
Clinical Implications (Ringing in Ears - Tinnitus)
- Transient (< 24 hours): Usually loud noise. Excessive mechanical energy; often resolves.
- Chronic: Many causes, usually but not always loud noise. Can be either inner ear, nerve, or central issues.
Visual versus Auditory Transduction
- Visual: Photons, High energy, slow (G protein pathway)
- Auditory: Sound waves, Low energy, fast (channel activation)
Cochlear Implant
- Implants electrodes in the scala tympani in the inner ear
- Stimulation of different parts of the cochlea provides sound perception.
- Usually has ~12 electrodes
Central Auditory Pathways
- Auditory information travels through multiple brain regions (pathway) to the auditory cortex.
Vestibular Organs
- Semicircular canals and utricle & saccule assist with spatial orientation
Vestibular Ocular Reflex (VOR)
- Rotational movements of the eyes in the opposite direction of the head.
- Helps retain visual focus during head movement
Organization of Semicircular Canals
- Ampulla
- Cupula
- Stereocilia
- Hair cells
Utricle and Saccule
- Detect linear acceleration
- Contain otoliths that shift causing stereocilia bending
Taste (Gustation)
- Anatomy: Taste buds on tongue; taste cells connect to cranial nerves
- Transduction: Chemicals activate taste cells causing ion channels to change
- Various G-protein cascades (salty, sour, sweet, bitter, umami)
Central Taste Pathways
- Information routed to the brainstem which then travels to the thalamus
Olfaction (Smell)
- Anatomy: Olfactory receptors in nasal cavity connected to the olfactory bulb
- Signal transduction: Odorants bind to receptors, activating G protein pathways
Central Olfactory Pathways
- Signals route to the limbic system
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Description
Test your knowledge on the somatosensory pathways, including the dorsal column-medial lemniscus pathway and the mechanisms of pain and temperature sensations. This quiz covers various aspects such as receptors, brain structures, and the roles of different pathways in sensory perception.
