14.2 Sensorimotor systems Flashcards
1
Q
What is sensation?
A
Conscious or subconscious awareness of external & internal stimuli
2
Q
What is perception?
A
Conscious awareness & interpretation of sensations
3
Q
What is modality?
A
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*
4
Q
What are the types of general senses? (and give examples)
A
Somatic: tactile, thermal, pain and proprioceptive
Visceral: internal organs - pressure, stretch, chemicals, nausea, hunger, and temperature
5
Q
Give examples of special senses
A
Smell, taste, vision, hearing, and equilibrium
6
Q
Where does a sensation begin and how?
A
- 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)
7
Q
For a sensation to arise what needs to happen?
A
- Stimulation of the sensory receptor - an appropriate stimulus must occur within the receptor’s receptive field; some change in environment must occur
- 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)
-
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)
- Integration of sensory input: A region of the brain or spinal cord must translate the nerve impulse into a sensation
8
Q
Briefly explain process through nervous system
A
9
Q
What are the classes of sensory receptors?
A
Based on:
- 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
-
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
- The type of stimulus detected (nociceptors for pain, mechanoreceptors for pressure, etc.)
10
Q
Explain how sensory receptors are selective
A
- 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
11
Q
What are the names of receptors according to their location?
A
-
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
12
Q
What are the names of sensory receptors according to their mode of activation?
A
- 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
13
Q
Explain cutaneous sensations
A
- 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
14
Q
What are touch sensations due to?
A
Due to stimulation of tactile receptors in upper levels of the skin (mechanoreceptors)
15
Q
What are the 2 main types of touch?
A
- 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
16
Q
What are the different receptors for touch?
A
-
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
-
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
-
Merkel discs: Type I Cutaneous Mechanoreceptors
- Flattened dendrites near the stratum basale
- Slowly adaptive (remain sensitive to stimulus longer)
- Involved in discriminative touch
-
Ruffini corpuscles: Type II Cutaneous Mechanoreceptors
- Located deeper in the dermis; detect heavy and/or continuous touch
- Slowly adaptive (remain sensitive to stimulus longer)
17
Q
What is pressure sensation & what receptors pick up this sensation?
A
- 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)
18
Q
What receptors pick up thermal sensation?
What is pain sensation & what receptors pick it up (describe them)?
A
-
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)
20
Q
How is slow & fast pain different (receptors)?
A
- 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
22
Q
Explain the different orders of neurons
A
-
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
23
Q
What do posterior column tracts do? (and what’s in them)
A
- Carry impulses for:
- Proprioception
- Discriminatory touch
- Pressure
- Vibrations
- 2 tracts
- Cuneate fasciculus - nerve impulses from upper limbs, upper trunk, neck and posterior head
- Gracile fascicules - nerve impulses from lower trunk and lower limbs
24
Q
What do the spinothalamic tracts do? (what are the types)
A
- 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
25
Q
What do the trigeminothalamic tracts do?
A
- 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
26
Q
What do the spinocerebellar tracts do? (what are the types)
A
- 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
27
Q
Explain the distribution of sensory neurons
A
- 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)
28
Q
Explain how motor activity begins
A
-
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
29
Q
What do direct/pyramidal tracts do? (what are the types)
A
-
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
30
Q
What do the corticobulbar pathways do?
A
- Impulses for the control of skeletal muscles in the head
- Associated with cranial nerves
31
Q
What do the indirect/extrapyramidal tracts do? (columns & tracts)
A
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
34
Q
What are the 2 types of normal sleep? (& the steps)
A
- 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
