Week 13 somatosensory nervous system

Question 1

Intro

Answer 1

Senses: information on your surroundings
Processed in the CNS -> consciously or unconsciously
Somatic -> touch, pressure, proprioception, temperature

Question 2

Senses : function

Answer 2

Stimulus ->
Receptor ->
Change in membrane potential
->
Generation of action potential ->
Transmission to CNS ->
Integration of information by CNS

Question 3

Receptors

Answer 3

Can be defined by;
-The type of stimuli they respond to
-Location of receptor

Question 4

Type of stimuli they respond to;

Answer 4

Main types of stimuli:
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

Question 5

Location of recpetor

Answer 5

-Exteroreceptors = body surface
(pain, touch, pressure, temperature) and special senses (vision, hearing, equilibrium , taste, smell)
-Interoreceptors (visceroreceptors) = within the body -> viscera and blood vessels (stretch, temperature)
Proprioreceptors = respond to internal stimuli -> skeletal muscle, joints, tendons, ligaments and connective tissue. Advise brain of body movements

Question 6

Receptors and sensory units

Answer 6

-A sensory unit is a single afferent neuron and all of its receptor endings
Sensory receptors may be:
->Neuron with free nerve endings
->Neuron with encapsulated ending
->Specialised receptor cells closely associated with neuron

Question 7

Simple receptors

Answer 7

Are neurons with free nerve endings

Question 8

Complex neural receptors

Answer 8

Have nerve endings enclosed in connective tissue capsules

Question 9

Special sense receptors

Answer 9

Most Special sense receptors are cells that release neurotransmitters onto sensory neurons, initiating an action potential

Question 10

Sensory receptors function to trigger neuronal response

Answer 10

->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
->Sensory transduction converts stimuli into graded potentials, action potentials transmit the information to the brain

Question 11

Stimulus threshold – intensity

Answer 11

-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

Question 12

Each neuron has a receptive field

Answer 12

->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

Question 13

Somatosensory NS

Answer 13

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

Question 14

Sensory receptors in skin

Answer 14

Variety of different receptors for different sensations;

Question 15

Ascending sensory pathways

Answer 15

-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

Question 16

Sensory homunculous

Answer 16

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

Question 17

Motor dividison

Answer 17

Motor pathways take the
message to the spinal cord and muscles:
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

Question 18

Reflexes

Answer 18

-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 involved

Question 19

Five components to the reflex arc

Answer 19

1)Receptor
2)Afferent Neurone
3)Integration Centre
4)Efferent Neurone
5)Effector organ

Question 20

Withdraw reflex

Answer 20

Ipsilateral (excites muscles on same side)