Chapter 16 - Sensory, Motor & Integrative Systems Flashcards
Sensation
Awareness of body conditions
Perception
Conscious awareness of sensation
Modality
Any specific sensory entity
4 Components of Sensation
- Stimulation
- Transduction
- Conduction
- Integration
Stimulation
- Events caused by a stimulus
- Stimulus = environmental change which activates sensory neurons
Transduction
- When a sensory receptor/sensory organ converts one kind of signal/stimulus into another
- Can be caused by a generator potential or a receptor potential
- Can result in either depolarization or hyperpolarization
Generator Potential
Depolarization of dendrites of 1st order sensory neuron
Receptor Potential
Graded change in membrane potential due to receptor stimulation
Conduction
When an action potential (caused by generator/receptor potential) travels towards the CNS
Integration
When action potentials are translated into sensations in the CNS
Sensory Coding
When a type of sensation is identified by which fiber carries the incoming message to the CNS
Sensory Receptors
- Only respond well to one type of stimulus (due to selectivity)
- Receptive field = area monitored by receptor cell
Adaptation
- Decreased receptor sensitivity caused by constant stimulus
- 2 mechanisms: peripheral adaptation & central adaptation
2 Receptor Types Based on Adaptation
- Tonic Receptors = Slow adapting; always sending signals to CNS for as long as they’re being stimulated
- Phasic Receptors = Fast adapting; Only activated when their monitored signals change, then quickly adapt
2 Receptor Types Based on Complexity
- Simple Receptors
2. Complex Receptors
Simple Receptors
- Associated w/ general senses: temperature, pain, tactile sense & proprioception
- 2 Types: Free nerve endings (sense pain, temperature, & touch) & Encapsulated nerve endings (sense touch & vibration)
- Distributed throughout body
- Cutaneous sensations = Combo of temperature, pain, & tactile sense
Complex Receptors
- Associated w/ special senses: olfaction, gustation, vision, equilibrium & audition
- All utilize special sensory receptor cells (except olfaction)
- Olfactory receptors = bipolar neurons w/ olfactory hairs
3 Receptor Types Based on Location
- Exteroceptors
- Interoceptors
- Proprioceptors
Exteroceptors
Receptors that receive stimuli from outside the body
Interoceptors
- Receptors that receive stimuli from inside the body (not usually conscious)
- Examples: baroreceptors & chemoreceptors
Proprioceptors
- Receive info from muscles, tendons, joints & inner ear labyrinth
- Are tonic receptors
- Send brain info on muscle tension, weight discrimination, movements & position of body + body parts
- 3 different types
3 Types of Proprioceptors
- Muscle Spindles
- Golgi Tendon Organs
- Joint Kinesthetic Receptors
Muscle Spindles
- Intrafusal fibers wrapped by sensory neuron’s dendrites
- Functions: monitor muscle length, perform stretch reflexes & set muscle tone
Golgi Tendon Organs
- Protect tendons & muscles from excessive stretch
- Capsule w/ CT fibers wrapped by dendrites of sensory neuron
- Located in tendons
Joint Kinsethetic Receptors
Cause joint muscles to relax under excessive stress
6 Receptor Types Based on Stimulus
- Mechanoreceptors
- Thermoreceptors
- Nociceptors
- Photoreceptors
- Chemoreceptors
- Osmoreceptors
Mechanoreceptors
- Respond to physical distortion of their cell membranes
- 3 subtypes
3 Subtypes of Mechanoreceptors
- Tactile Receptors
- Baroreceptors
- Proprioceptors
Tactile Receptors
- Receptors that detect touch, pressure &/or vibration
- 4 different examples
5 Examples of Tactile Receptors
- Hair Root Plexus
- Meissner’s Corpuscle
- Merkel’s Tactile Disc
- Ruffini’s Corpuscle
- Pacinian Corpuscles
Hair Root Plexus
- Found around hair follicles
- Detect movement of hair strands
Meissner’s Corpuscle
- Located in dermal papillae
- Detects discriminative touch & vibration
- Rapidly-adapting/phasic
Merkel’s Tactile Disc
- Contact Merkel cells of stratum basale
- Detect discriminative touch & pressure
- Slowly-adapting/tonic
- AKA “Type 1 Cutaneous Mechanoreceptors”
Ruffini’s Corpuscle
- Found in palms & soles
- Detect heavy touch & pressure
- Slowly-adapting/tonic
- AKA “Type 2 Cutaneous Mechanoreceptors”
Pacinian Corpuscles
- Located in various body parts
- Detect pressure & vibration
Itch & Tickle Receptors
- Free nerve endings
- Function as inflammatory mediators (e.g., histamine & bradykinin)
Baroreceptors
- Respond to pressure changes in walls of hollow organs
- Rapidly-adapting/phasic in blood vessels
- Help coordinate reflex activities in visceral organs (e.g., reflex peristalsis in GI Tract)
Thermoreceptors
- Free nerve endings
- Rapidly-adapting/phasic
- Separate receptors for warm & cold. Cold (10-40 C) in stratum basale; warm (32-48 C) in dermis.
Nociceptors
- Respond to painful stimuli
- Damaged tissues release of prostaglandins, kinins &/ or K+ (Non-steroidal Anti-inflammatory Drugs; NSAIDs)
- Located everywhere in the body except the brain
- Slowly-adapting/tonic
4 Different Types of Pain
- Fast Pain
- Slow Pain
- Somatic Pain
- Visceral Pain
Fast Pain
- Carried by myelinated A fibers
- Occurs only in skin
- Generally localized
Slow Pain
- Carried by unmyelinated C fibers
- Tends to increase in intensity over time
- Occurs typically in deeper tissues
Somatic Pain
- Found superficially in the skin
- Also found in skeletal muscles, joints, tendons & fascia
Visceral Pain
-Pain exclusively found in visceral organs
Referred Pain
Visceral pain felt in a site other than the place of origin
*Mechanism: The same spinal cord segment(s) serves place of origin & site where pain referred
Photoreceptors
- Receptors stimulated by light
- Examples: rods & cones found in the retinae of eyes
Chemoreceptors
- Found in mouth & nose
- Also found in carotid & aortic bodies
- Info goes to respiratory control centers
- Monitor chemical composition of body fluid
Osmoreceptors
Monitor solute/solvent ratio of biological fluids
Posterior column-Medial lemniscus (PCML) pathway
- Conducts sensory info for tactile sensation (discriminative touch, pressure & vibration) & proprioception
- Origin of sensations include limbs, trunk, neck & posterior head
Route of PCML
- 1st order relay neuron travels along Posterior root ganglion -> Posterior white column (Gracile fasciculus & cuneate fasciculus) -> Medulla (Gracile & cuneate nuclei)
- 2nd order relay neuron decussates, then ascends via medial lemniscus -> Ventral posterior nucleus
- 3rd order relay neuron (ventral nucleus) -> Primary somatosensory cortex
- Gracile tract conducts sensory info from lower limbs & trunk to cuneate tract
- Cuneate tract conducts sensory info from upper limbs, trunk, neck & posterior head
Anterolateral (AKA “Spinothalamic”) Pathways
- Conducts sensory info fro pain, temperature, tickle, itch, crude touch & deep pressure
- Origins of sensation include limbs, trunk, neck & posterior head
Route of Spinothalamic Pathway
- 1st order sensory neuron travels along posterior root ganglion -> Spinal cord (Posterior gray horn)
- 2nd order relay neuron decussates, then ascends spinal cord in spinothalamic tracts -> Ventral posterior nucleus
- 3rd order relay neuron (Ventral posterior nucleus) -> Primary somatosensory cortex
Trigeminothalamic Pathway
- Conducts sensory info for tactile sensations, pain & temperature
- Origin of sensations include face, oral & nasal cavities & teeth
Route of Trigeminothalamic Pathway
- 1st order sensory neuron travels via trigeminal nerve -> cell body in trigeminal ganglion, which projects -> Nuclei of pons/ medulla
- 2nd order relay neuron from pons/ medulla nuclei decussates, then ascends via trigeminothalamic tract -> Ventral posterior nucleus
- 3rd order relay neuron from ventral posterior nucleus -> Primary somatosensory cortex
Sensory Pathways to the Cerebellum
- Anterior & Posterior Spinocerebellar tracts are responsible for conduction
- Travel to lateral white columns in spinal cord
- Conducts sensory info on unconscious proprioception from muscles, joints & tendons of lower limbs & trunk required by cerebellum
Simple & Complex Motor Pathways
- Simple Pathways: Upper Motor Neuron & Lower Motor Neuron
- Complex Pathways: UMNs + interneurons + LMNs
Upper Motor Nuerons (UMNs)
- UMNs arising from motor cortex initiate voluntary skeletal muscle activity
- UMNs arising from red nucleus, vestibular nucleus, superior colliculus/ reticular formation control muscle tone, posture & balance
- Receives inputs from basal nuclei & cerebellum
- Most UMNs synapse indirectly w/ LMNs via local circuit nuerons
Lower Motor Neorons (LMNs)
- LMNs arising from brainstem extend axons via cranial nerves to skeletal muscles of face & head
- LMNs arising from spinal cord extend axons via a spinal nerve to skeletal muscles of limbs & trunk
Spastic Paralysis
- Occurs due to UMN injury
- Symptoms include exaggerated reflexes & increased muscle tone
Flaccid Paralysis
- Occurs due to LMN injury
- Symptoms include absent reflexes & decreased/absent muscle tone
Pyramidal Cells
UMNs of motor cortex
3 Parts of the Motor Cortex
- Primary Motor Cortex
- Premotor Cortex (Includes premotor area, Broca’s motor speech area & frontal eyefield area)
- Supplementary Motor Area (Found midline atnerior to precentral gyrus; involved in planning & coordination)
*Pyramidal cell axons form tracts that project to nuclei of brainstem & spinal cord where they synapse w/ LMNs, either directly/ via local circuit neurons
Function of the Motor Cortex
To regulate muscle tone & coordinate skilled movements
2 Types of Direct (AKA “Pyramidal”) Motor Pathways
- Corticobulbar Pathway
2. Corticospinal Pathway
Corticbulbar Pathway
- Location of UMNs: Motor Cortex (Pyramidal Cells)
- Destination: Motor nuclei of cranial nerves 3-7 & 9-12 in the brainstem
- Site of cross-over: Brainstem
- Actions: Voluntary control over skeletal muscles of eye, jaw, tongue, face, pharynx & some neck muscles
Corticospinal Pathway (Lateral & Anterior)
- Location of UMNs: Motor Cortex (Pyramidal Cells)
- Destination: Anterior gray horns of spinal cord
- Site of decussation: Inferior end of medulla (forms LATERAL corticospinal tracts) OR passing through the medulla (forms ANTERIOR corticospinal tracts; crosses over via anterior white commissure)
- Actions: Voluntary control over skeletal muscles of contra-lateral limbs & trunk (Lateral -> Controls distal limb parts; Anterior -> Controls trunk & proximal limb parts)
Indirect (AKA “Extrapyramidal”) Motor Pathways
- Axons of UMNs w/ cell bodies in brainstem nuclei
- Location: Anterior & lateral white columns
4 Types of Indirect (AKA “Extrapyramidal”) Motor Pathways
- Rubrospinal Tracts
- Tectospinal Tracts
- Vestibulospinal Tracts
- Lateral & Medial Reticulospinal Tracts
Rubrospinal Tracts
- Location of UMNs cell bodies: Red nucleus
- Destination of UMN axons: Anterior gray horns of spinal cord
- Site of decussation: Brainstem
- Actions: Voluntary movements of distal upper limb muscles
Tectospinal Tracts
- Location of UMNs cell bodies: Superior colliculus
- Destination: Anterior gray horns of cervical spinal cord
- Site of decussation: Brainstem
- Actions: Involuntary regulation of contralateral skeletal muscle activity (Moves eyes, head neck + trunk in response to visual & auditory stimuli)
Vestibulospinal Tracts
- Location of UMNs cell bodies: Vestibular nuclei of pons & medulla
- Destination: Anterior gray horns of spinal cord
- Site of decussation: None
- Actions: Involuntary control of ipsilateral trunk & proximal limb skeletal muscles (Balance + posture in response to head movements)
Lateral & Medial Reticulospinal Tracts
- Location of UMNs cell bodies: Reticular formation
- Destination: Anterior gray horns of spinal cord
- Site of decussation: None
- Actions: Involuntary control of ipsilateral trunk & proximal limb skeletal muscles (Responsible for posture + muscle tone in response to ongoing movement)
2 Integrative Functions of the Cerebrum
- Sleep
2. Learning + Memory
Sleep
- Arousable state of partial unconsciousness
- Functions to maintain mental health, memory & learing
- Dominated by the parasympathetic division of the ANS
Mechanism of Sleep
- Blockade of ACh-releasing neurons of the Reticular Activating System
- May be caused by adenosine binding to A1 receptors
- Methylxanthines (Caffeine & thephylline) prevent adenosine binding to A1 receptors
- RAS blockade also by melatonin
2 Components of Sleep
- Non-Rapid Eye Movement (NREM) Sleep
2. Rapid Eye Movement (REM) Sleep
NREM Sleep
- Stage 1: Transition between wakefulness & sleep (Possible hypnagogic hallucinations
- Stage 2: Light sleep
- Stage 3: Moderately deep sleep, growth hormone released (+Delta waves emitted)
- Stage 4: Deep sleep; growth hormone released; body repairs; possible sleepwalking, night-terrors
3 Parts that Control NREM Sleep
- Pre-optic Area
- Basal forebrain
- Medulla
REM Sleep
- Occurs about every 90 mins.
- 3 to 5 times/night
- REM sleep duration lengthens w/ each cycle
- Dreaming also occurs
- Eyeballs move rapidly back & forth w/ eyelids closed
- High brain blood flow & O2 yse
- Function: To help w/ brain development
Typical Sleep Cycle
NREM1 -> NREM2 -> NREM3 -> NREM4 -> NREM3 -> NREM2 -> REM -> NREM1 -> Wake or repeat
Learning
Acquisition of new information, behaviors, or skills
Memory
Ability to store, retain & retreive learned info
4 Brain Parts Contributing to Memory
- Frontal, parietal, temporal + occipital lobes
- Limbic system
- A. Hippocampus stores spatial + explicit memory
- B. Amygdala stores emotional memory - Cerebellum & basal nuclei store procedural + implicit memory
- Anterior & Medial thalamic nuclei
3 Types of Memory
- Immediate (AKA “Sensory”) Memory
- Short-term Memory
- Long-term Memory
Immediate (AKA “Sensory”) Memory
- Very short-term retention of sensory input received by brain
- Electro-chemical events occurring in the hippocampus, mammillary bodies, and thalamic nuclei
Short-term Memory
- Info retained for a few minutes
- Limited capacity
- Electro-chemical events occurring in the hippocampus, mammillary bodies, and thalamic nuclei
- Converted to long-term memories by reinforcement
Long-term Memory
- More permanent memory
- Frequent memory retrieval will reinforce it (“Memory consolidation”)
- If memory not consolidated, eventually lost
- Newly-formed long-term memory lost following general anaesthesia, brain hypoxia, and ECT
Mechanism of Long-term Memory
- Structural/functional changes occur in neural circuitry due to plasticity of the brain
- Changes include increased:
1. Protein synthesis
2. No. of Pre-synap. terminals
3. Size of synaptic end bulbs
4. Quantity of neurotransmitter stored
5. No. of dendritic branches + “spines”
6. No. of synaptic connections
Calpain
Proteolytic enzyme; degrades spines of dendrites, thus, leading to memory loss
Long-term Potentiation (LTP)
- Persistent enhancement of neural transmission caused by high-frequency stimulation of chemical synapses in hippocampus
- Glutamate causes N.O. release from post-synaptic neuron
- N.O. diffuses into pre-synap. neuron -> circuitry changes
- LTP important for learning & memory
