Chp 16 (Sensory, Motor, Integrative Systems)

Responsibilities of Spinal Cord, Brain Stem, Cerebral Cortex

Cord: reflexes

Stem: complex reflexes (eg; change in HR)

Cortex: conscious awareness of stimuli

Perception

Conscious awareness + interpretation of sensation

• Involves cortex and its memories

Sensation

Any stimuli body is aware of

• chemoreceptors, baroreceptors (pressure), themroreceptors, nociceptors (pain)

What sensations do we have but cant perceive?

Insulin levels, O2 saturation in blood

Receptors still sense things

Sensory Modality

= A specific type of sensation

• touch, pain, temp, hearing, vision, vibration

-a specific sensory neuron carries info for ONE modality (receptor specificity)

2 classes:

• general senses (somatic n visceral

• Special senses (smell, taste, vision, hearing, n equilibrium)

1st Step in Process of Sensation

1. Stimulation of Receptor

-sensory receptors demonstrate selectivity: respond to one stimuli

-can be dendrites on cell or specialized cells

-stimulus must occur in receptive field

2nd Step in Process of Sensation

2. Transduction (conversion)

-conversion of stimulus into GP: converts stimuli into electrical signal (open ion channels)

-vary in amplitude depending on stimulus strength and isnt propogated

3rd Step in Process of Sensation

3. Generation of Impulses

-generates when GP reaches threshold and sends it towards the CNS

-neurons that conduct impulses from PNS directly to the CNS are called first order neurons

4th Step in Process of Sensation

4. Integration of Sensory Input by CNS

3 Classifications of Sensory Receptors

1. Structural Classification

2. Receptor Location & Stimuli Origin

3. Type of Stimulus they detect

Structural Classification of Sensory Receptors

-receptor responds to stimulus by generating a receptor potential (RP)

• A GP that can lead to either generate an AP or release a ntm

• Amplitude of a RP varies with the intensity of stimulus

  • Frequency of NI or release of NTM conveys strength of stimulus

3 Types of Sensory Receptors (Structural)

Free Nerve Endings

• Bare dendrites

• Pain, temp, tickle, itch, light touch, smell

Encapsulated Nerve Endings

• dendrites enclosed in CT capsule (Eg; lamellar corpuscles)

• Pressure, vibration, deep touch

Separate Receptors Cells

• specialized cells, respond to stimuli w/ release of NTM

3 Types of Sensory Receptors (location)

Exteroceptors

• near surface of body

• External stimulus, vision, smell, taste, touch, temp, vibration, pressure

Interoceptors

• inside and monitor int. Environment (eg; vessels, muscles, nervous system)

Proprioceptors

• muscles, tendons, joints, inner ear

• Body position movement, equlibrium

6 Types of Sensory Receptors (Stimuli)

Mechanoreceptors

• mechanical stimuli (eg; deformation, stretching, bending)

• Touch, pressure, BP, proprioception, hearing, vibration

Thermoceptors: temp

Nociceptors: pain

Photoceptors: light

Chemoreceptors: detect molecules (taste, smell, changes in body fluid chemistry)

Osmoreceptors: osmotic pressure in fluids

Adaptation of Sensory Receptors

-most exhibit adaptation

• tendency for RP to dec. in amplitude during a constant stimulus

• With adaptation, perception of sensation may fade or disappear even though the stimulus persists

Rapidly Adapting Receptors (smell, pressure, touch)

• specialized for detecting changes in environment

Slowly Adapting Receptors (Pain, body position)

• AP continue as long as stimulus persists

Somatic Sensations

= stimulation of sensory receptors in skin, mucous membrane, muscles, and more

1. Tactile

2. Thermal

3. Pain

4. Proprioceptive

Tactile Sensations

-touch, pressure, vibration, itch, tickle

-tactile corpuscles, hair root plexuses, merkel’s discs, ruffini corpuscles, lamellar corpuscles, free nerve endings

Rapidly and Slowly Adapting Receptors (Touch)

Rapidly: tactile copuscles, hair root plexuses

Slowly: merkel’s discs, ruffini’s corpuscles

Tactile Corpuscles

-Dendrites enclosed in CT in dermal papillae of hairless skin

-touch + low frequency vibration

-rapidly

-generate impulses mainly at onset of touch

Hair Root Plexus

-free nerve endings found around follicles, detects hair movement

-rapidly

Merkel’s Discs

-flattened free dendrites touching cells of stratum basale

-slowly

-used in continuous touch n pressure

Bulbous Corpuscle

-encapsulated receptors found deep in dermis of skin, ligaments and tendons

-detect skin stretching, continuous touch, & pressure

Lamellar Corpuscle

-onion like CT capsule enclosing dendrites

-subq tissues + some viscera

-rapidly adapting

-deep pressure high frequency vibrations

Pressure

-sustained sensation felt over larger area than touch

-longer lasting, less intensity variation than touch, slowly adapting

Vibration

-result from rapidly repetitive sensory signals from tactile receptors

Itch and Tickle

-these receptors are free nerve endings

-stimulated by inflammation or chemicals (eg; histamine, mosquito saliva)

Thermal Sensations

-free nerve endings on skin surface/mucous membranes

-cold receptors in stratum basale respond to temps btw 10-35C

-warm receptors in dermis respond to temps btw 30-45C

-both rapidly at first, but continue to gen. Impulses at low frequency

-pain receptors are activated <10 and 45> (why u feel pain)

Pain Sensations

-signals tissue damaging conditions

• stretching prolonged muscular contractions, muscle spasms, ischemia

-nociceptors are free nerve endings that are located in all body tissue but brain

-little to no adaptation

-tissue injury releases chemicals that stimulate nociceptors (eg; potassium)

-pain can still remain after stimulus cuz chemicals are still present