Sensorimotor systems Flashcards
LOs
- Demonstrate a systematic and coherent knowledge of the anatomical and physiological functioning of the sensory and motor systems
- Appraise the implications of any alteration in the normal function of the sensorimotor system
- Discuss and analyse structure- function relationships of the sensory motor pathways and CNS
- Recognise the basic neurological processes inculked in sensation
- Describe the mechanism of voluntary and involuntary movements, recognise the important centres involved
levels of sensation:
sensation
perceprtion
modality
Sensation- conscious or subconscious awareness of external and internal stimuli
Perception- conscious awareness and interpretation of sensations
Modality- the uniqueness of each sensation; what distinguishes one sensation from another sensation
each sensory neurone can carry how many modalities? (type of message)
1
examples of somatic and visceral senses
what are the special senses (5)
somatic- tactile, thermal, pain and proprioception
visceral- internal organs- pressure, stretch, chemicals, nausea, hunger and temperature
Special senses: Smell, taste, vision, hearing, and equilibrium
what 2 kinds of structure can detect stimuli?
what is selectivity?
specilised receptor cell
sensory neurone (e.g., olfactory sensory neurones)
selectivity- A particular kind of stimulus (a change in the environment) activates certain sensory receptors, while other sensory receptors respond weakly or not at all
for a sensation to arise there has to be 4 events typically happen
3 general kind of neurone
Sensory
Interneurone
Motor
3 ways of grouping sensory neurones
-
microscopic structure- free nerve endings vs encapsulated endings for example a) Free- bare dendrites; lack structural specialisation, pain, temperature, tickle, itch, touch
* b) Encapsulated*- enclosed in CT, pressure, touch, vibration -
Location… of receptors and the origin of the stimuli that activate them
a) Exteroceptors near the external surface
b) Internoceptors (visceroceptors) - The Type of stimulus detected (nociceptors for pain, mechanoreceptors for pressure, etc.)
characteristics of sensory receptors (2)
1) selective-
- Each sensory receptor responds strongly to one certain kind of stimulus
- Some receptors respond weakly or not at all to other stimuli
- Some are simple whereas others are complex (special senses)
2) Adaptable-
- in which the generator potential or receptor potential decreases in amplitude during a sustained or constant stimulus
- Because there is an accommodation response at the receptor level, the frequency of nerve impulses traveling to the cerebral cortex decreases and the perception of the sensation fades even though the stimulus persists
- Receptors vary in how quickly they adapt
- Rapidly adapting for signaling changes in a stimulus
- Slowly adapting continue to trigger nerve impulses as long as the stimulus persists; pain body position, chemical composition of blood
receptors named according to their location:
exteroceptors
interoceptors
proprioceptors
- 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
- Proprioceptors- located in muscles, tendons, joints, & internal ear; detect changes in body position, muscle tension, etc.
Receptors named according to their mode of activation
- mechanoceptors
- thermoreceptors
- nociceptors
- photoreceptors
- chemoreceptors
- osmoreceptors
- mechanoceptors- 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
general somatic senses
where are they classically felt
collect info about cutaneous sensation
Somatic senses (“soma” means body) detect touch, pain pressure, temperature, and tension on the skin and in internal organs.
Receptors located in skin, subcutaneous connective tissue, mucus membranes, & both ends of the Gl tract.
cutaneous receptors are? they come in which 2 forms?
dendrites of sensory neurones
a) free nerve endings
b) may have a capsule (e.g., in epithelial tissue or CT)
touch sensations are due to which kind of receptor
what is:
- crude touch
- discriminative touch
stimulation of tactile receptors in upper levels of the skin (mechanoreceptors)
Crude touch- ability to perceive something has touched the skin
Discriminative touch- ability to recognize the exact pints on the body that is touched
receptors for touch (4)
- Meissner’s corpuscle
- hair root plexuses
- merkel discs
- ruffini corpuscles
Meissner’s corpuscles
- 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 movements 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)
what is pressure
how is it different to touch
what are its receptors like
stimulation of tactile receptors deeper in tissues
Pressure is longer-lasting than touch; also felt over a larger area
Receptors:
Type II cutaneous mechoreceptors
Pacinian corpuscles- lamellated corpuscles
1 dendrite, surrounded by many layers of CT (located in subcutaneous tissues)
Rapidly adapting (lose sensitivity to stimulus)
thermal sensations
receptor
Receptor: free nerve endings
Some of these thermal receptors 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)
types of pain
- Acute pain
- Chronic pain
- Superficial somatic pain
- Deep somatic pain
- Visceral pain
- Referred pain
- Phantom pain
- Acute pain- sharp, fast; felt in a very localised area (message carried my large diameter myelinated neurones
- Chronic pain- slow pain which gradually increases Aching and throbbing are examples
- Superficial somatic pain- due to stimulation of nociceptors in the skin
- Deep somatic pain- stimulation of nociceptors in muscles, tendons, joints etc
- Visceral pain- stimulation of nociceptors in visceral organs
- Referred pain- with visceral pain, usually feel the pain in skin/ peritoneum covering the organ (not the organ itself)
• 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
7. Phantom pain- sensation of pain from amputated limb
- Brain receives impulses from the remaining (proximal ends) sensor neurons
- Itching, tingling, pressure
Nociception- 2 types:
Fast pain- acute well localised, occurs rapidly because the nerve impulses propagate along medium-diameter, myelinated A fibres
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
relief of pain
anaesthesia
analgesia
Anaesthesia- 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 neurones
Can change the perception of pain by the brain
proprioceptive sensations receptors
Located in skeletal muscles (muscle spindles)
Tendons, in and around joints kinesthetic receptors and in the internal ear
These proprioceptors convey nerve impulses bout muscle tone, movement of body parts, & body position to the brain
somatic senory pathways are made of how many neurones?
3
primary, secondary and third order neurones
what is a first order neurone
conduct impulses from somatic receptors into the brain stem or spinal cord
- Cranial nerves: into brain stem
- Spinal nerves: into spinal cord
Second order neurone
conducts 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
Posterior column tracts
Carry impulses for: proprioception, Discriminatory touch, Pressure, Vibrations
made up of 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
spinothalamic tract (lateral and 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
trigeminothalamic tract
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 of the site of stimulation
spinocerebellar tract (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 co-ordination, posture and balance
somatic sensory distribution
not distributed evenly in the body
relative sizes of these regions are proportional to the number of specialised sensory receptors in the corresponding body part- making a sensory homunculus (cerebral cortex)
where does motor activity begin?
in the primary motor areas of the precentral gyrus + other cerebral integrative centres
what is the name of the motor neurone that is not directly responsible for stimulating target muscles?
what do they do?
upper motor neurone
UMNs connect the brain to the appropriate level in the spinal cord
what is the purpose of second order/ lower MNs?
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
direct/ pyramidal tracts
part of the UMN system and are a system of efferent nerve fibers that carry signals for precise, volunatry movements from the cerebral cortex to either the brainstem or the spinal cord. It divides into two tracts: the corticospinal tract and the corticobulbar tract
lateral and anterior corticospinal 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
The neurons that travel in the corticospinal tract are referred to as upper motor neurons; they synapse on neurons in the spinal cord called lower motor neurons, which make contact with skeletal muscle to cause muscle contraction.
Corticobulbar pathway
Impulses for the control of skeletal muscles in the head
Associated with cranial nerves
Indirect and extra/pyramidal tracts (lateral and anterior columns)
- Originate in the midbrain (unconscious)
- Nerve impulses for involuntary movements, muscle tone, posture and balance
- Five major tracts
what are the 5 indirect/ extra pyramidal 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 balancr in response to head movements
• Lateral & Medial reticulospinal- maintaining posture and regulating muscle tone in response
to ongoing body movements
Sleep and wakefullness are functions of what part of the brain?
what are they controlled by?
integrative functions of the cerebrum
Controlled by the “reticular activating system” (RAS)
what is the reticular formation
how does the RAS system work?
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
- When the RAS is stimulated by nociceptors, touch, proprioceptors signals, bright light, or
sound, it sends impulses through 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
during sleep the activity of the RAS is very low
what is sleep?
2 kinds of 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
Two types of normal sleep:
- 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
definitions of
- learning
- memory
- plasticity
- short term memory
- long term memory
- amnesia
Learning- ability to acquire new information or skills through instruction or experience
Memory- process by which information acquired through learning is stored and retrieved
Plasticity- capability for change associated with learning (structural and functional changes in the brain)
short term memory- lasts longer than immediate but still short lived
long term memory
amnesia anterograde (new) and retrograde (past)
