Chapter 15 Sensory Pathways and the Somatic Nervous System

Anatomy and Phisiology 1

What are sensory receptors? 

specialized cells or cell processes that monitor specific conditions in the body or the external environment  

Where is somatic sensory information distributed to the brain?

the sensory processing centers (primary somatosensory cortex of the cerebral hemispheres or appropriate areas of the cerebellar hemispheres

Where is visceral sensory information distributed to the brain? 

to reflex centers in the brainstem and diencephalon

Voluntary or involuntary somatic motor commands control which peripheral effector? 

skeletal muscles

What is sensation?

sensory information arriving in the CNS

What is perception? 

the conscious awareness of sensation

What is the process of transduction?

When a sensory receptor detects an arriving stimulus and converts it into an action potential that can be propagated to the CNS

What is receptor specificity?

Each receptor has a characteristic sensitivity 

Which type of receptor has the least receptor specificity? 

free nerve endings 

Define receptive field. 

the area monitored by a single receptor cell 

What is the relationship between receptor field size and the ability to localize a stimulus? 

the size of the receptor potential depends on the strength of the stimulus 

What is a labeled line? 

sensory neurons that link specific peripheral receptors to specific cortical neurons  

What are tonic receptors?

are always active

What are phasic receptors?

usually not active and provide information about the intensity and rate of change of a stimulus 

adaptation

is a reduction of receptor sensitivity in the presence of a constant stimulus 

Are tonic receptors fast adapting or slow adapting?

slowing adapting

Are phasic receptors fast adapting or slow adapting?

fast adapting

Which of the following situations describe a phasic receptor? Which of the following situations describe a tonic receptor?  

jumping into a pool and feeling cold, but then quickly “getting used to” the temperature

phasic receptor

Which of the following situations describe a phasic receptor? Which of the following situations describe a tonic receptor?

burning your finger and feeling pain for the entire day

tonic receptor

Exteroceptors

provide information by location of the stimulus

Proprioceptors

report the positions and movements of skeletal muscles and joints 

Interoceptors

monitor visceral organs and functions

What general stimulus do nociceptors detect?

pain

What does the size of their receptive field indicate?  

have large receptive fields, as a result it is often difficult to determine the exact source of a pain sensation  

Type A

myelinated; fast pain (prickling pain) 

Type B

unmyelinated; slow pain (burning or aching pain) 

What is phantom limb syndrome? 

when pain is still felt in an amputated limb 

thermoreceptors

• Free nerve endings that detect temperature receptors 

• Located in the dermis, skeletal muscles, liver, and hypothalamus 

• Phasic  

What are mechanoreceptors sensitive to? 

physical stimuli that distort their plasma membranes  

What are the three classes of mechanoreceptors?

tactile receptors, baroceptors, proprioceptors

tactile receptors

provide the closely related sensations of touch, pressure, and vibration  

Baroceptors

detect pressure changes in the walls of blood vessels and in portions of the digestive, respiratory, and urinary tracts 

proprioceptors

monitor the positions of joints and skeletal muscles

Which tactile receptor is the only sensory receptor on the cornea of the eye? 

free nerve endings

Which tactile receptors are most abundant in the eyelids, lips, fingers, nipples, and external genitalia? 

tactile corpuscles

What kind of receptors monitor blood pressure in the carotid and aortic sinuses? 

baroreceptors  

What kind of receptors are involved in defecation and urination reflexes? 

stretch receptors

What are the three major groups of proprioceptors? 

muscle spindles, Golgi tendon organs, receptors in joint capsules

What are chemoreceptors and what do they detect? 

are specialoized nerve cells that detect small changes in the concentration of specific chemicals or compounds 

Which type of receptor monitors pH, and carbon dioxide and oxygen levels in arterial blood? 

chemoreceptors

Describe the function of a first-order neuron

A sensory neuron that delivers sensations directly to the CNS 

What is a second-order neuron?

interneuron in the spinal cord or brainstem  

In what part of the brain would you find a third-order neuron? 

thalamus

What is the process called when a second-order neuron crosses over to the opposite side of the CNS? 

decussation

Due to the decussation of second-order neurons, the right side of the thalamus receives information from which side of the body?  

the left side

List the three main somatic sensory pathways. 

the spinothalamic pathway, the posterior column pathway, and the spinocerebellar pathway 

What sensations are carried by the spinothalamic pathway? 

crude touch, pressure, pain, and temperature

Which sensory pathway is associated with phantom limb pain? 

spinothalamic pathway 

What is referred pain?

when a person can feel pain in an uninjured part of the body when the pain originates at another location 

Which sensory pathway is associated with referred pain?

spinothalamic pathway

What is a familiar example of referred pain that the book states? 

pain of a heart attack is frequently felt in the left arm

Which tracts in the spinothalamic pathway carry sensations of crude touch and pressure sensations? 

anterior spinothalamic tracts

Which tracts in the spinothalamic pathway carry pain and temperature sensations? 

lateral spinothalamic trcats

What sensations are carried by the posterior column pathway? 

fine touch, vibrations, pressure, and proprioception  

Which two spinal tracts are part of the posterior column pathway?

the left and right gracile fasciculus and the left and right cuneate fasciculus

What is a sensory homunculus? 

a functional map of the primary somatosensory cortex  

What information is conveyed by the spinocerebellar pathway? 

information about muscle, tendon, and joint positions from the spine to the cerebellum

Which tracts of the spinocerebellar pathway contain axons that do not cross over to the opposite side of the spinal cord? 

posterior spinocerebellar tracts  

Which tracts of the spinocerebellar pathway are dominated by axons that have crossed over to the opposite side of the spinal cord.

anterior spinocerebellar tracts  

Where is visceral sensory information primarily collected from? (ie: which body cavities) 

thoracic and abdominopelvic cavities  

Which nuclei function as major processing and sorting centers for visceral sensory information? 

solitary nucleus 

Somatic motor pathways always involve at least two motor neurons. What are they called? 

upper and lower motor neurons

upper motor neuron

whose cell body lies in a CNS processing center 

lower motor neuron

whose cell body lies in a nucleus of the brainstem or spinal cord

Conscious and subconscious motor commands control skeletal muscles by traveling over three integrated motor pathways. Name the motor pathways. 

the corticospinal pathway, the medial pathway, and the lateral pathway 

Which motor pathway carries motor command that provides voluntary control over skeletal muscles? 

the corticospinal pathway  

Name the three pairs of descending tracts of the corticospinal pathway.

the corticobulbar tracts, the lateral corticospinal tracts, and the anterior corticospinal tracts  

What is a motor homunculus?

functional map of the primary motor cortex

What do larger areas of the homunculus represent? 

the degree of fine motor control available

Which motor pathway is associated with the control of muscle tone and gross movements of the neck, trunk, and proximal limb muscles? 

medial pathway

Name four tracts that are part of the medial motor pathway. 

medial and lateral reticulospinal tracts, tectospinal tract, and vestibulospinal tract

Which motor pathway is associated with the control of muscle tone and more precise movements of the distal parts of the limbs? 

lateral pathway

The rubrospinal tract is part of which motor pathway? 

lateral pathway

What part of the brain contains the basal nuclei?

cerebrum

What part of the brain contains the basal nuclei?

cerebellum

What is the function of the cerebellum? 

monitors proprioceptive (position) sensations, visual information from the eyes, and vestibular (balance) sensations from the internal ear