The Somatosensory Nervous System Flashcards
What are the general senses divided into and where?
*somatic - in skin, muscles + joints
*visceral - in internal organs
What are some examples of somatic senses?
*touch
*temperature
*pain
*pressure
*proreception
What are some examples of visceral senses?
*pain
*pressure
What do mechanoreceptors respond to?
ear, muscle and joints, skin and viscera,
cardiovascular
What do chemoreceptors respond to?
tongue, nose, skin and viscera
What do photoreceptors respond to?
eye
What do thermoreceptors respond to?
skin and CNS
What do notice receptors respond to?
respond to stimuli that result in
sensation of pain
Where are exoreceptors located and what do they respond to?
Exteroreceptors = body surface
* (pain, touch, pressure, temperature) and
special senses (vision, hearing, equilibrium ,
taste, smell)
Where are interoreceptors located and what do they respond to?
Interoreceptors (visceroreceptors) = within
the body,
* viscera and blood vessels (stretch,
temperature)
Where are propireceptors located and what do they respond to?
- Proprioreceptors = respond to internal
stimuli. - Skeletal muscle, joints, tendons,
ligaments and connective tissue.
Advise brain of body movements
What is a sensory unit?
A sensory unit is a single
afferent neuron and all of its
receptor endings
What might a sensory unit contain?
- Sensory receptors may be
- Neuron with free nerve
endings - Neuron with
encapsulated ending - Specialised receptor
cells closely associated
with neuron
Describe the process of a sensory response to the environment changing
- Environmental changes cause a change in membrane potential in
receptor - Receptor or generator potential : graded
- If this reaches threshold it will trigger an action potential, sensory
transduction - This information goes to the brain via
ascending fibres, primary then secondary
afferent nerve fibres - Each nerve may receive information from a
number of receptors in a particular area =
receptive field
How does stimulus intensity change threshold/ effect?
- The stronger the
stimulus, the larger
the graded receptor
potential, the more
frequent the action
potentials of the
afferent neuron, the
more
neurotransmitter is
released at the
synapse - AP is not graded
Describe what a receptive field is and how it differs + brain recgnition
- Region of space where the presence of a
stimulus will induce the production of a
signal in that neuron - Several sensory neurons may have
overlapping receptive fields - The smaller the receptive fields, the more
accurate a representation of the stimulus is
signaled to the brain - Brain cannot differentiate between two
stimuli acting on the same receptive field - Tested clinically to test for damage : Two
point discrimination task
Briefly summarise the somatosensory pathways
- Somatic nervous system - linked to skeletal muscles
- Gives us perception of touch, temperature, body position, pain
- Process stimuli received from receptors within the skin, muscles, and joints
- Mostly mechano, thermo- and chemoreceptors
- Responses voluntary AND involuntary
- Reflexes, breathing
- Pathways for Somatic Perception Project to the Cortex and Cerebellum
What are the sensory receptors in skin?
*free nerve endings
*merkel corpuscle
*meissners corpuscle
*pacinian corpuscle
*ruffini corpuscle
What do free nerve endings detect?
- Temperature, noxious
stimuli, hair movement - Dermis
What do the corpuscles detect?
- Merkel corpuscle
- Steady Pressure,
texture - Epidermal – dermal
junction - Meissners corpuscle
- Flutter, light pressure
- Dermis (papillary)
- Pacinian Corpuscles
- Vibrations
- Deep dermis/
subcutaneous - Ruffini corpuscles
- Stretch
- Dermis
Where do the somatosensory pathways take the signal?
Somatosensory pathways take the message
to the spinal cord and brain – somatosensory
cortex
- 2 Afferent pathways to the
brain - Sensory input enters the
spinal cord through the
dorsal horn - Dorsal column lemniscal for
fine touch, vibration and
position - Spinothalamic for crude
touch temperature, and
pain - Three neurons which
synapse in the spinal cord
(1) and in the thalamus (2) - Cross the midline in the
CNS/spinal cord - Terminate in the
somatosensory cortex - Somatotopic representation
How does the sensory homunculus work?
- The amount of space on the somatosensory cortex devoted to each body part is proportional to the
sensitivity of that part - Face fingertips tongue hands genitalia
2 Efferent pathways to the muscles
* Dorsolateral corticospinal tract
* To periphery (toes, hands):
* Ventromedial corticospinal tract
* To shoulders/neck/truck
* 2 neurons which synapse with each
other in the spinal cord
* Cross the midline in the spinal cord
* Terminate at the neuromuscular
junction with skeletal muscle
* Somatotopic representation in the
motor cortex
- A reflex pathway is commonly known as a reflex
- Simple somatic reflexes do not include the higher centres discussed for
conscious or voluntary aspects of movement. - An automatic, involuntary, consistent response
- Reflexes can be spinal or cranial, depending on the nerves and central
components that are involved. - Sensors detect external stimuli and sensory neurons sends an impulse to the
spinal cord. - Interneurons relay the information immediately back to the motor neurons
which causes movement. - No thought is involve
What are the five components to the sensory reflex arc?
*receptor
*afferent neurone
*integration centre
*efferent neurone
*effector organ
What is an example of a withdrawl reflex?
- ipsilateral (excites muscles on same side)
