14.2 Sensorimotor systems

Question 1

What is sensation?

Answer 1

Conscious or subconscious awareness of external & internal stimuli

Question 2

What is perception?

Answer 2

Conscious awareness & interpretation of sensations

Question 3

What is modality?

Answer 3

The uniqueness of each sensation; what distinguishes one sensation from another sensation

• Each sensory neuron carries only one modality (type of message)*
• e.g. temperature, pain, pressure, touch*

Question 4

What are the types of general senses? (and give examples)

Answer 4

Somatic: tactile, thermal, pain and proprioceptive

Visceral: internal organs - pressure, stretch, chemicals, nausea, hunger, and temperature

Question 5

Give examples of special senses

Answer 5

Smell, taste, vision, hearing, and equilibrium

Question 6

Where does a sensation begin and how?

Answer 6

• Can be either a specialized cell or the dendrites of a sensory neuron
• A particular kind of stimulus (a change in the environment) activates certain sensory receptors, while other sensory receptors respond only weakly or not at all (a characteristic known as selectivity)

Question 7

For a sensation to arise what needs to happen?

Answer 7

1. Stimulation of the sensory receptor - an appropriate stimulus must occur within the receptor’s receptive field; some change in environment must occur
2. Transduction of the stimulus - a sensory receptor must detect and convert it (transduce it) into a graded potential (vary in amplitude depending on the strength of the stimulus causing them)
3. Conduction: The nerve impulse must be carried to the brain/cord
   
   • Occurs when the sum of graded potentials reach threshold in first-order neurons (the first neuron in a specific tract - in this case from the PNS into the CNS)
4. Integration of sensory input: A region of the brain or spinal cord must translate the nerve impulse into a sensation

Question 8

Briefly explain process through nervous system

Answer 8

Question 9

What are the classes of sensory receptors?

Answer 9

Based on:

1. Microscopic structure - free nerve endings vs encapsulated endings, for example

• Free - Bare dendrites: lack structural specialization; pain, temperature, tickle, itch, touch
• Encapsulated - enclosed in connective tissue; pressure, vibration, touch

1. Location…of the receptors and the origin of the stimuli that activate them
   
   • Exteroceptors near the external surface
   • Interoceptors (visceroceptors)
     
     • Tell us what’s happening inside the body
2. The type of stimulus detected (nociceptors for pain, mechanoreceptors for pressure, etc.)

Question 10

Explain how sensory receptors are selective

Answer 10

• Each sensory receptor responds strongly to one certain kind of stimulus
• Same receptor responds weakly or not at all to other stimuli
• Some receptors are simple receptors: associated with general (somatic) senses (touch, itch, tickle, pressure, vibration, temp., pain, proprioceptors , etc.)
• Some receptors are complex receptors: associated with special senses (smell, taste, vision, hearing, equilibrium)
• Most sensory receptors are adaptable: change in sensitivity during a long-term stimulus
  
  • Examples: hot bath, you become less & less sensitive to the heat
  • Adaptation, in which the generator potential or receptor potential decreases in amplitude during a sustained or constant stimulus
    
    • ​Frequency of nerve impulses travelling to the cerebral cortex DECREASES and the perception of sensation fades (EVEN though stimulus persists)
  • Receptors vary in how quickly they adapt
    • Rapidly adapting very quickly and specialized for signaling changes in a stimulus
    • Slowly adapting adapt slowly and continue to trigger nerve impulses as long as the stimulus persists; pain body position, chemical composition of blood

Question 11

What are the names of receptors according to their location?

Answer 11

• Exteroceptors: located near the surface of the body; detect changes in the external environment
  
  • (temp., touch, vision, smell, taste, pain, etc.)
• Interoceptors: visceroceptors = located in blood vessels & viscera; detect changes in the internal environment
  
  • Mostly unconscious; occ. pressure or pain
• Proprioceptors: located in muscles, tendons, joints (kinesthetic receptors), & internal ear; detect changes in body position, muscle tension, etc.
  
  • Convey nerve impulses about muscle tone, movement of body parts, & body position to the brain

Question 12

What are the names of sensory receptors according to their mode of activation?

Answer 12

• Mechanoreceptors: detect stretching or mechanical pressure (touch, pressure, proprioceptors , vibration, hearing, equilibrium, BP)
• Thermoreceptors: which detect changes in temperature
• Nociceptors: which respond to painful stimuli (tissue damage)
• Photoreceptors: which are activated by photons of light (detect light striking the retina of the eye)
• Chemoreceptors: which detect chemicals in the mouth (taste), nose (smell) and body fluids
• Osmoreceptors: which detect the osmotic pressure of body fluids

Question 13

Explain cutaneous sensations

Answer 13

• Receptors located in skin, subcutaneous connective tissue, mucus membranes, & both ends of the Gl tract
• Some body sites contain more cutaneous receptors than other site (tongue, lips, fingertips, sex organs have many receptors; very sensitive)
• These cutaneous receptors may have:
  
  • Free nerve endings
  • A capsule (epithelial tissue or connective tissue)
• The steps in cutaneous receptors:
  
  • Cutaneous receptor → nerve impulse → somatic efferent neuron → spinal/cranial nerve → thalamus → somatosensory area of the parietal lobe of the cerebral cortex 

Question 14

What are touch sensations due to?

Answer 14

Due to stimulation of tactile receptors in upper levels of the skin (mechanoreceptors)

Question 15

What are the 2 main types of touch?

Answer 15

• Crude touch: ability to perceive that something has touched the skin (don’t know what it is)
• Discriminative touch: ability to recognize the exact point on body is touched

Question 16

What are the different receptors for touch?

Answer 16

1. Meissner’s corpuscles (Corpuscles of Touch)
   
   • Mass of dendrites surrounded by connective tissue
   • Located in the dermal papillae
   • Adapt rapidly (lose sensitivity to the stimulus)
   • Involved in discriminative touch
   • Location: fingertips, palms, soles, eyelids, tip of tongue
2. Hair root plexuses
   
   • Dendrites in networks around hair follicles
   • Movements of hair shaft stimulates these dendrites; these receptors detect movement along skin surface (crude touch)
   • Also, rapidly adapting receptors
3. Merkel discs: Type I Cutaneous Mechanoreceptors
   
   • Flattened dendrites near the stratum basale
   • Slowly adaptive (remain sensitive to stimulus longer)
   • Involved in discriminative touch
4. Ruffini corpuscles: Type II Cutaneous Mechanoreceptors
   
   • Located deeper in the dermis; detect heavy and/or continuous touch
   • Slowly adaptive (remain sensitive to stimulus longer)

Question 17

What is pressure sensation & what receptors pick up this sensation?

Answer 17

• Stimulation of tactile receptors deeper in tissues
• Pressure is longer-lasting than touch; also felt over larger area
• Receptors
  
  • Type II Cutaneous Mechanoreceptors
  • Pacinian Corpuscles: Lamellated corpuscles
    
    • 1 dendrite, surrounded by many layers of connective tissue (located in subcutaneous tissues)
    • Rapidly adapting (lose sensitivity to stimulus)

Question 18

What receptors pick up thermal sensation?

What is pain sensation & what receptors pick it up (describe them)?

Answer 18

• Thermal sensations:
  
  • Receptor: free nerve endings
  • Some of these thermal receptor respond to heat
  • Others respond to cold
• Pain sensations:
  
  • Vital sensation- danger alert signal
  • Nociceptors (pain receptors): free nerve endings
    
    • Located in nearly every tissue of the body
    • Tissue damage releases chemicals, which stimulate nociceptors
    • Little or no adaptation (remain sensitive for very long time)

Question 19

What are the types of pain?

Answer 19

• Acute pain: sharp, fast; felt in very localized area (message carried by large-diameter myelinated neurons)
• Chronic pain: slow pain which gradually increases
  
  • Aching; throbbing are examples of chronic pain
  • Message carried by small-diameter, unmyelinated neurons
• Superficial Somatic pain: due to stimulation of nociceptors in the skin
• Deep Somatic pain: stimulation of nociceptor in muscles, tendons, joints, etc.
• Visceral pain: stimulation of nociceptors in visceral organs
• Referred pain
  
  • With visceral pain, usually feel the pain in skin covering the organ (not the organ itself)
  • Cerebral cortex incorrectly identifies the area of pain stimulation
  • Usually, the area which is served by the same segment of spinal cord is where the pain is felt (same spinal nerves)
    
    • Example: heart attack (spinal nerves T1-T5) feel pain in skin over heart & left arm
• Phantom pain: sensation of pain from amputated limb
  
  • Brain receives impulses from the remaining (proximal ends) sensor neurons
  • Itching, tingling, pressure

Question 20

How is slow & fast pain different (receptors)?

Answer 20

• Fast pain (acute, well localized) occurs rapidly because the nerve impulses propagate along medium-diameter, myelinated A fibers
• Slow pain begins after a stimulus is applied and gradually increases in intensity over a period of several seconds or minutes.
  
  • Impulses for slow pain conduct along small-diameter, unmyelinated C fibers and this type of pain may be excruciating and often has a burning, aching, or throbbing quality

Question 21

What can be done to relieve pain?

Answer 21

• Anesthesia: blocks sensations of pain, touch, etc.; don’t allow the messages to reach the brain
  
  • General anesthesia = removes all sensations; also causes unconsciousness
  • Spinal anesthesia = removes all sensations below injection site (into subarachnoid space)
• Analgesia: decrease or block sensations of pain
  
  • Can block production of prostaglandins, which stimulate nociceptors
  • Can block impulse conduction down neurons
  • Can change the perception of pain by the brain

Question 22

Explain the different orders of neurons

Answer 22

• First-order neurons conduct impulses from somatic receptors into the brain stem or spinal cord
  
  • Cranial nerves: into brain stem
  • Spinal nerves: into spinal cord
• Second-order neurons conduct impulses from the brain stem and spinal cord to the thalamus where the neurons decussate (cross to the opposite side)
  
  • Thus, all somatic sensory information from one side of the body reaches the thalamus on the opposite side
• Third-order neurons conduct impulses from the thalamus to the primary somatosensory area of the cortex on the same side

Question 23

What do posterior column tracts do? (and what’s in them)

Answer 23

• Carry impulses for:
  
  • Proprioception
  • Discriminatory touch
  • Pressure
  • Vibrations
• 2 tracts

1. Cuneate fasciculus - nerve impulses from upper limbs, upper trunk, neck and posterior head
2. Gracile fascicules - nerve impulses from lower trunk and lower limbs

Question 24

What do the spinothalamic tracts do? (what are the types)

Answer 24

• Lateral & Anterior Columns
• Carry impulses to cerebral cortex for:
  
  • Pain
• Temperature
  
  • Itch & tickle
• From limbs, trunk, neck and posterior head
• To primary sensory motor cortex on the opposite side the site of stimulation

Question 25

What do the **trigeminothalamic tracts** do?

Answer 25

* Carries nerve impulses for: * *Touch* * *Pressure* * *Vibration* * *Pain* * *Temperature* * *Itch/Tickle* * From *face*, *nasal cavity*, *oral cavity*, and *teeth* * To *primary sensory motor cortex* on the *opposite side the site of stimulation*

Question 26

What do the **spinocerebellar tracts** do? (what are the types)

Answer 26

* ***Anterior*** and ***posterior*** * Nerve impulses for: * *_Proprioception_* * From *trunk* and *lower limbs* * From one side of the body to the same side of cerebellum * Allows for *coordination*, *posture* and *balance*

Question 27

Explain the **distribution** of *sensory neurons*

Answer 27

* ***Somatic sensory neurons*** are _not_ _distributed_ evenly in the body * *Relative size of these regions* in the ***_somatosensory_*** area are *proportional* to the *_number of specialized sensory receptors_* in the corresponding body parts - ***_sensory homunculus_*** (**cerebral Cortex**)

Question 28

Explain how **motor activity** begins

Answer 28

* *_Motor activity_* begins in the *primary motor* areas of the ***_precentral gyrus_*** and other cerebral integrative centers (motor homunculus) * Any *motor neuron* that is _not_ directly responsible for *stimulating target muscles* is called an **_upper motor neuron (UMN)_** * ***UMNs*** connect the *brain* to the *appropriate level in the spinal cord* * All *_excitatory_* and *_inhibitory_* signals that control movement converge on ***_second-order motor_*** neurons known as ***lower motor neurons (LMNs)*** that *descend to innervate skeletal muscle* * Since only **LMNs** provides *output* from the *CNS* to *skeletal muscle fibers* they are also called the ***final common pathway***

Question 29

What do **direct/pyramidal tracts** do? (what are the types)

Answer 29

* ***_Direct/Pyramidal Tracts_*** * Carry nerve impulses for *precise*, *voluntary movements* from cerebral cortex (conscious) * Axons of *LMNs* extend through *cranial nerves* to the skeletal muscles of the face and head, and through spinal nerves to innervate skeletal muscles of the limbs and trunk * Two of the major LMN tracts * ***_Lateral corticospinal tracts_*** - responsible for *precise, agile*, and *higher skilled movements* of the *hands* and *feet* * ***_Anterior corticospinal tracts_*** - control movements of the *trunk* and *proximal parts of the limbs*

Question 30

What do the **corticobulbar pathways** do?

Answer 30

* Impulses for the *control* of *skeletal muscles* in the *_head_* * Associated with ***cranial nerves***

Question 31

What do the **indirect/extrapyramidal tracts** do? (columns & tracts)

Answer 31

*Indirect*/*Extrapyramidal* tracts (***Lateral*** & ***Anterior*** Columns) * Originate in *midbrain* (unconscious) * Nerve impulses for *involuntary movements*, *muscle tone*, *posture*, & *balance* (equilibrium) * Five major tracts * ***Rubrospinal***- precise, *voluntary movement* of *distal* parts of *upper* *limbs* * ***Tectospinal***- reflexively move *head*, *eyes*, and *trunk* in response to *visual* and *auditory* *stimulus* * ***Vestibulospinal***- maintaining *posture* and *balance* in response to *_head movements_* * ***Lateral*** & ***Medial*** ***reticulospinal***- maintaining *posture* and *regulating* *muscle* *tone* in response to ongoing body movements

Question 32

What **controls** *sleep* & *wakefulnes?*

Answer 32

Controlled by the “***Reticular Activating System (RAS)***” * Reticular Formation: patches of gray matter scattered in the white matter of brainstem, spinal cord, and diencephalon * A portion of the Reticular Formation is the RAS * *RAS acts as an alerting system to "_wake up_" the cerebral cortex* * *​*During sleep *RAS* is _VERY_ low * When the RAS is stimulated by *nociceptors*, *touch*, proprioceptors signals, *bright light*, or *sound*, it sends *impulses* thru the thalamus, where the message gets dispersed to many areas of the cerebral cortex * The RAS is responsible for arousal from deep sleep, and for *maintaining a general state of _wakefulness_/_consciousness_*

Question 33

What is **sleep** & explain it

Answer 33

* ***Sleep***: state of *altered* *consciousness* or *partial* *unconsciousness*, from which the person can be aroused * Neurotransmitters which cause *sleep*: ***Serotonin*** & ***Norepinephrine*** * Each is produced by *specific nuclei* in the brain stem

Question 34

What are the **2 types** of **normal sleep**? (& the steps)

Answer 34

* ***Non-rapid eye movement sleep (NREM)***: *slow* wave sleep (4 stages) * ***REM sleep***: most *dreaming* occurs; *very high 02* consumption by the brain during REM * First go to sleep → ***NREM***; about every 90 minutes, ***REM*** period occurs; each episode of ***REM*** lasts *longer* than the *previous one*

Question 35

What is **learning**?

Answer 35

***Learning*** - ability to *acquire* *_new information_* or *_skills_* through *instruction* or *experience*

Question 36

What is **memory**?

Answer 36

***Memory*** - process by which *information* *acquired* through *learning* is *_stored*_ and _*retrieved_*

Question 37

What is **plasticity**?

Answer 37

***Plasticity*** - capability for *change* associated with *learning* (*structural* and *functional* *changes* in the *brain*)

Question 38

What is ... - **I****mmediate memory** - **S****hort term memory** - **L****ong term memory**

Answer 38

* ***Immediate memory*** - extremely *short lived* * ***Short term memory*** - lasts longer than immediate but still *short lived* * ***Long term memory*** - transfer the information from *short term* to *long term* by *_rehearsal*_, _*consolidation_*, _mnemonic_

Question 39

What is **amnesia** & the types

Answer 39

**Amnesia** - form of memory loss Can be: * ***Anterograde*** (new) * ***Retrograde*** (past)