Somatic sensory Flashcards
Functional divisions of the nervous system
CNS
PNS
Sensation is detected by receptors
Senses: Information on your surroundings
Processed in the CNS
Receptor types / Type of stimuli they respond to
Mechanoreceptors
Chemoreceptors
Photoreceptors
Thermoreceptors
Nociceptors
Mechanoreceptors
ear, muscle and joints, skin and viscera, cardiovascular
Chemoreceptors
tongue, nose, skin and viscera
Photoreceptors
eye
Thermoreceptors
skin and CNS
Nociceptors
respond to stimuli that result in sensation of pain
step by step; functions of senses
1) Stimulus
2) Receptor
3) Change in membrane potential
4) Generation of action potential
5) Transmission to CNS
6) Integration of information by CNS
SENSES - broken down
GENERAL > SOMATIC {touch, pressure, temperature, pain, proprioception} + VISCERAL { pain, pressure}
SPECIAL > smell, taste, sight, hearing, balance
Where is the Somatic senses located?
skin, muscles, joints
Where is the Visceral senses located?
internal organs
Where is the general senses disturbed?
over a large part of the body
Where is the receptors located for special senses?
Receptors localised within specific organs
Receptors and Sensory units
A sensory unit is a single afferent neuron and all of its receptor endings.
Sensory receptors may be…
1) Neuron with free nerve endings
2) Neuron with encapsulated ending
3) Specialised receptor cells closely associated with neuron
Sensory receptors function to trigger neuronal response
Environmental changes cause a change in membrane potential in receptor
Receptor or generator potential
GRADED
What happens if the signal reaches threshold?
It will trigger an action potential
This information goes to the brain via ascending fibres; what type of fibres?
afferent nerve fibres
The stronger the stimulus the ________ the graded receptor potential, the more frequent the action potentials of the afferent neurone the more neurotransmitter is released at the synapse
larger
is AP graded?
No
Each Neuron Has A Receptive Field
Region of space where the presence of a stimulus will induce the production of a signal in that neuron
What is unique about the receptive fields in the sensory neurones?
Several sensory neurones may have overlapping receptive fields
What is unique about the receptive fields in the sensory neurones?
Several sensory neurones may have overlapping receptive fields
The smaller the receptive fields, the more ______ a representation of the stimulus is signaled to the brain
accurate
Brain cannot differentiate between two stimuli acting on the same receptive field
Tested clinically to test for damage : Two point discrimination task
Somatosensory NS - pathways
many different paths
Somatic nervous system
Linked to skeletal muscles
What does somatic nervous system do?
Gives us perception of touch, temperture, body position and pain
External - somatic NS role
Process stimuli received from receptors within the skin muscles and joints
Are responses voluntary or involuntary?
Both =
Reflexes & Breathing
Pathways for Somatic Perception Project to the _______ and _______
a) Cortex
b) Cerebellum
Sensory Receptors in skin - more superficial
1) Free nerve endings
2) Merkel corpuscle
3) Meissners corpuscle
4) Pacinian Corpuscles
5) Ruffini corpuscles
1) Free nerve endings
Temperature, noxious stimuli, hair movement
2) Merkel corpuscle
Steady Pressure, texture
3) Meissners corpuscle
Flutter, light pressure
4) Pacinian Corpuscles
Vibrations
5) Ruffini corpuscles
Stretch
Free nerve endings are important in ___
Pain - deeper
Different types of sensory neurons for different types of ______
receptors
Most neurones are _____ for electrical insulation.
myelinated
If neurone is myelinated they have a high?
NCV - Nerve conduction velocity (higher speed)
Ascending sensory pathways
Somatosensory pathways take the message to the spinal cord and brain – somatosensory cortex
Ascending sensory pathways
Somatosensory pathways take the message to the spinal cord and brain – somatosensory cortex
How many afferent pathways to the brain?
2
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)
The amount of space on the somatosensory cortex devoted to each body part is proportional to the sensitivity of that part
The bigger amount of space are in the
- Face fingertips tongue hands genitalia
Motor pathways take the message to the spinal cord and muscles
2 neurons which synapse with each other in the spinal cord
Cross the midline in the spinal cord
Terminate at the neuromuscular junction with which muscle?
Skeletal muscle
Somatotopic representation in the _____ cortex.
motor
Reflexes
A reflex pathway is commonly known as a reflex
Simple somatic reflexes ___ ___ include the higher centres discussed for conscious or voluntary aspects of movement.
do not
How would you describe a reflex?
An automatic, involuntary, consistent response
Sensors detect external stimuli and sensory neurones sends an impulse to:
the spinal cord
Interneurons (spine) relay the information immediately back to the motor neurons which causes:
movements
reflexes is involuntary- generally
NO THOUGHT is involved - this is for protection of your body
The Five Components to the Reflex Arc
1) Receptor
2) Afferent neurone [which takes message to spinal chord]
3) Intergration Centre (sometimes)
4) Efferent neurone
5) Effector organs (where action has been taken - muscle)
Stretch Reflex
Involves Muscle spindle
Muscle Spindles are
Proprioceptors
Muscle spindles are specialised muscle fibres surrounded by a capsule inside skeletal muscle
Runs parallel to muscle and causes
a contraction
Proprioceptors
sense muscle length (stretch) and activate sensory neurones
When does stretch reflex occur?
when muscle proprioceptors detect the stretch and tension of a muscle
send messages to the spinal cord to contract it.
Stretch reflex increases muscle tension to
counter stretching
What are stretch reflex properties?
Allows fluidity of movement
Vital for bearing body weight, etc.
Step by step = stretch reflex
5 steps
1) stretching
Stretching of muscle stimulates muscle spindles
2) activation
Activation of sensory neurone
3) Information processing
Info processing at motor neurone
4) activation of neurone
Activation of MOTOR neurone
5) contraction
Contraction of muscle
step 5 > 1
opposes / prevents it from happening
Golgi Tendon Organs:
Control of muscle contraction
Proprioceptors:
between muscle and tendon sense tension and activate sensory neurones (type Ib)
Axons synapse onto inhibitory spinal
interneurones
These inhibit α motorneurones (using GABA/glycine) and reduce
contraction
What is voluntary movement is controlled by
the brain
The primary motor cortex in
the frontal lobe
Brain - Integrates information from the
somatosensory cortex BUT doesn’t work alone
What is the role of the Cerebellum/
Associated with balance and coordination
Examples: clapping hands, speaking, writing,
Inhibited in ethanol intoxication
Where is the cerebellum located in the brain?
The outer layer (pink)
