Sensory Pathways and the Somatic Nervous System

Question 1

Neural pathways

Answer 1

• Information arrives by sensory receptors
• Information ascends within the afferent division
• Motor commands descend and are distributed by the efferent division

Question 2

Sensory receptor

Answer 2

Specialised cell or cell process that monitors the specific conditions within the body or in the external environment

Question 3

Sensation

Answer 3

Arriving information

Question 4

Perception

Answer 4

Awareness of a sensation

Question 5

General senses

Answer 5

Sensitivity to temperature, pain, touch, pressure, vibration, and proprioception

Question 6

Special senses

Answer 6

Located in specific sense organs

Structurally more complex than general senses

Question 7

Receptive field

Answer 7

Each receptor cell monitors a specific receptive field

Question 8

Transduction

Answer 8

Begins when a large enough stimulus depolarises the receptor potential or generator potential to the point where action potentials are produced

Question 9

Labeled line

Answer 9

A link between a peripheral receptor and a cortical neuron

Question 10

Tonic receptors

Answer 10

• Always active

- Slow-adapting receptors

Question 11

Phasic receptors

Answer 11

Provide information about the intensity and rate of change of a stimulus

Question 12

Adaptation

Answer 12

• A reduction in sensitivity in the presence of a constant stimulus
• Fast-adapting receptors

Question 13

Nociceptors

Answer 13

Provide information of pain as related to extremes of temperature, mechanical damage and dissolved chemicals

Question 14

Myelinated type A fibres

Answer 14

Carry fast pain

Question 15

Unmyelinated type C fibres

Answer 15

Carry slow pain

Question 16

Thermoreceptors

Answer 16

Found in the dermis

Question 17

Mechanoreceptors

Answer 17

• Sensitive to distortion of their membranes

- Include tactile receptors (6 types), baroreceptors, proprioceptors (3 types)

Question 18

Chemoreceptors

Answer 18

Include carotid bodies and aortic bodies

Question 19

First-order neurons

Answer 19

Sensory neurons that deliver sensation to the CNS

Question 20

Second-order neurons

Answer 20

In the brainstem and spinal cord

Question 21

Third-order neurons

Answer 21

In the thalamus

Question 22

Spinothalmic pathway

Answer 22

Carries poorly localised (“crude”) sensations of touch, pressure, pain and temperature

Axons involved decussate in the spinal cord and ascend within the anterior and lateral spinothalmic tracts to the ventral nuclei of the thalamus

Question 23

Phantom limb syndrome

Answer 23

Caused by abnormalities along spinothalmic pathway

Painful sensations that are perceived despite a missing limb and referred pain

Question 24

Referred pain

Answer 24

Inaccurate localisations of the source of pain

Question 25

Posterior column pathway

Answer 25

Carries fine touch, pressure and proprioceptive sensations

Axons ascend within the gracile fasciculus and cuneate fasciculus and relay information to the thalamus by the medical lemniscus

Question 26

Decussation

Answer 26

Before the axons enter the medical lemniscus, they cross over to the opposite side of the brainstem

Question 27

Spinocerebellar pathway

Answer 27

• Includes posterior and anterior spinocerebellar tracts

- Carries sensations to the cerebellum concerning the position of muscles, tendons, and joints

Question 28

Visceral sensory pathways

Answer 28

• Carry information collected by interocceptors
• Sensory information from cranial nerves V, VII, IX, and X is delivered to the solitary nucleus in the medulla oblongata
• Posterior roots of spinal nerves T1-L2 carry visceral sensory information from organs between the diaphragm and the pelvic cavity
• Posterior roots of spinal nerves S2-S4 carry sensory information from more inferior structures

Question 29

Somatic motor

Answer 29

Involve an upper motor neuron (whose cell body lies in a CNS processing centre) and a lower motor neuron (whose cell body is located in a nucleus of the brainstem or spinal cord)

Question 30

Pyramidal cells

Answer 30

Neurons of the primary motor cortex

Question 31

Corticospinal pathway

Answer 31

Provides voluntary skeletal muscle control

Question 32

Corticobulbar tracts

Answer 32

• End at the cranial nerve nuclei
• Synapse on lower motor neurons in the anterior horns of the spinal cord
• Visible along the medulla oblongata as a pair of thick bands called pyramids, where most of the axons decussate to enter lateral corticospinal tracts. Those that do not cross over enter the anterior corticospinal tracts
• Provides a rapid, direct mechanism for controlling skeletal muscles

Question 33

Medial and lateral pathways

Answer 33

Include several other centres that issue motor commands as a result of processing performed at subconscious level

Question 34

Medial pathways

Answer 34

• Primarily controls gross movements of the neck, trunk and proximal limbs
• Includes the vestibulospinal, tectospinal, and medial and lateral reticulospinal tracts

Question 35

Vestibulospinal tracts

Answer 35

Carry information related to maintaining balance and posture

Question 36

Tectospinal tracts

Answer 36

Commands carried by tectospinal tracts change position of the head, neck, and upper limbs in response to bright lights, sudden movements, or loud noises

Question 37

Reticulospinal tracts

Answer 37

• Makes up the lateral pathway

- Primarily control muscle tone and movements of the distal muscles of the upper limbs

Question 38

Basal nuclei

Answer 38

Adjust the motor commands issued in other processing centres and provide background patterns of movement involved in voluntary motor activities

Question 39

Cerebellum

Answer 39

• Monitors proprioceptive sensations, visual information, and vestibular (balance) sensations
• Precise control of movement