1. General Properties of sensory systems

What is the role of the sensory nervous system?

To provide information about the internal and external environment of the body

What is sensory deprivation?

Absence or lack of perception of external stimuli

Why is sensory deprivation harmful?

Because the brain requires sensory input for normal function and perception

What is homeostasis?

Maintenance of stable internal conditions monitored by sensory pathways

Which sensory signals usually do not reach conscious perception?

Internal homeostatic signals such as blood pressure and pH

How does the body respond to sensory stimuli that do not reach consciousness?

Through subconscious reflexes

What is the difference between conscious and subconscious sensory processing?

Conscious processing reaches awareness while subconscious processing regulates internal parameters automatically

What is a sensory pathway?

A neural route that carries sensory information from receptors to the CNS

What are the basic components of a sensory pathway?

Stimulus receptor afferent neuron CNS integration efferent neuron effector response

What is the function of a sensory receptor?

To detect stimuli and convert them into electrical signals

What does sensory transduction mean?

Conversion of stimulus energy into a change in membrane potential

Why is transduction necessary?

Because the nervous system can only process electrical signals

What are the four main types of sensory receptors?

Chemoreceptors mechanoreceptors photoreceptors thermoreceptors

How are receptors classified?

By the type of stimulus they are most sensitive to

What are sensory hair cells?

Specialized receptor cells of special senses that synapse onto neurons

How do sensory hair cells differ from free nerve endings?

They release neurotransmitters onto neurons instead of generating action potentials directly

What is an adequate stimulus?

The form of energy a receptor is most sensitive to

Can receptors respond to non-adequate stimuli?

Yes if the stimulus intensity is high enough

What is a receptor threshold?

The minimum change in membrane potential required to trigger an action potential

What is a receptor potential?

A graded change in membrane potential produced by sensory transduction

Why are receptor potentials graded?

Because their size is proportional to stimulus strength

What happens if a receptor potential does not reach threshold?

The graded potential dies out and no action potential occurs

How does a receptor potential lead to an action potential?

By reaching threshold at the trigger zone of the neuron

What are graded potentials?

Variable-strength short-distance signals

Why are graded potentials important in sensory systems?

They allow stimulus intensity to be encoded

What is a receptive field?

The physical area where stimulation activates a sensory neuron

How does receptive field size affect sensitivity?

Smaller receptive fields increase sensitivity and localization accuracy

What is convergence in sensory pathways?

Multiple primary sensory neurons synapsing onto one secondary neuron

Why does convergence increase sensitivity?

Because subthreshold inputs can summate to reach threshold

Why does convergence reduce localization accuracy?

Because multiple stimuli are perceived as originating from one receptive field

What is two-point discrimination?

The ability to perceive two nearby stimuli as separate

What does poor two-point discrimination indicate?

Large receptive fields and high convergence

Why are fingertips more sensitive than the back?

They have smaller receptive fields and less convergence

What is a dermatome?

An area of skin innervated by one spinal nerve

How many spinal cord segments are there?

31

What do spinal nerves contain?

Both sensory and motor fibers

What is the difference between cranial and spinal nerves?

Cranial nerves originate from the brain while spinal nerves originate from the spinal cord

Where is the primary somatosensory cortex located?

In the parietal lobe of the cerebral cortex

What information is processed in the somatosensory cortex?

Touch temperature pain itch and proprioception

What is the somatosensory homunculus?

A cortical representation of body parts based on sensory sensitivity

Why do hands have a large representation on the homunculus?

Because they have high sensory receptor density

Where do pain and temperature pathways cross the midline?

In the spinal cord

Where do fine touch vibration and proprioception pathways cross?

In the medulla

Why do sensory pathways cross over?

So each cerebral hemisphere processes sensory input from the opposite side of the body

What are the four properties of a stimulus?

Modality location intensity duration

What is stimulus modality?

The nature or type of stimulus

How does the brain determine stimulus modality?

By the type of receptors activated and the brain region receiving the signal

What is labelled line coding?

A one-to-one association between a receptor pathway and a specific sensation

Why does labelled line coding explain why receptors always signal the same sensation?

Because stimulation of the same pathway is always interpreted the same way

What is stimulus location coding?

Identification of where a stimulus occurs based on which receptor fields are activated

Why can cortical stimulation feel like skin stimulation?

Because sensory perception depends on pathway activation not stimulus origin

What causes phantom limb pain?

Activation of secondary sensory neurons after loss of the primary sensory neurons

How is stimulus intensity encoded?

By the number of receptors activated and the frequency of action potentials

Why cannot action potential size encode intensity?

Because action potentials are all-or-none

How is stimulus duration encoded?

By the length of time action potentials are generated

What is sensory adaptation?

A decrease in receptor response during a sustained stimulus

What are phasic receptors?

Rapidly adapting receptors that respond to changes in stimulus

What are tonic receptors?

Slowly adapting receptors that continue firing while a stimulus persists

Why are pain receptors tonic receptors?

Because pain must continue to signal tissue damage

What is the functional purpose of sensory adaptation?

To allow the nervous system to focus on new or important stimuli