Somatic sensory Flashcards by Casi Jones

Functional divisions of the nervous system

CNS
PNS

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Sensation is detected by receptors

Senses: Information on your surroundings
Processed in the CNS

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Receptor types / Type of stimuli they respond to

Mechanoreceptors

Chemoreceptors

Photoreceptors

Thermoreceptors

Nociceptors

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Mechanoreceptors

ear, muscle and joints, skin and viscera, cardiovascular

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Chemoreceptors

tongue, nose, skin and viscera

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Photoreceptors

eye

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Thermoreceptors

skin and CNS

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Nociceptors

respond to stimuli that result in sensation of pain

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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

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SENSES - broken down

GENERAL > SOMATIC {touch, pressure, temperature, pain, proprioception} + VISCERAL { pain, pressure}

SPECIAL > smell, taste, sight, hearing, balance

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Where is the Somatic senses located?

skin, muscles, joints

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Where is the Visceral senses located?

internal organs

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Where is the general senses disturbed?

over a large part of the body

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Where is the receptors located for special senses?

Receptors localised within specific organs

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Receptors and Sensory units

A sensory unit is a single afferent neuron and all of its receptor endings.

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Sensory receptors may be…

1) Neuron with free nerve endings

2) Neuron with encapsulated ending

3) Specialised receptor cells closely associated with neuron

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Sensory receptors function to trigger neuronal response

Environmental changes cause a change in membrane potential in receptor

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Receptor or generator potential

GRADED

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What happens if the signal reaches threshold?

It will trigger an action potential

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This information goes to the brain via ascending fibres; what type of fibres?

afferent nerve fibres

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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

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is AP graded?

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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

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What is unique about the receptive fields in the sensory neurones?

Several sensory neurones may have overlapping receptive fields

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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?

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)