A&P II Chapter 15 - The Brain + Somatic Nervous System

Sensory Pathways

series of neurons that relay sensory information from receptors to the CNS

Sensory Receptors

specialized cells/neuron processes that monitor specifi conditions in the body/external environment

What happens when a receptor is stimulated?

action potentials are generated that are propagted along sensory pathways

What are the afferent divisions of the nervous system?

somatic + visceral sensory pathways

Somatic Information

sensory processing centers in the cerebral cortex

Visceral Information

primarily brainstem + diencephalon

What is the efferent division of the nervous system?

somatic motor pathways that control peripheral effectors

Where do motor commands travel from?

motor centers in the brain along somatic motor pathways

What can motor commands be modified by?

higher-order functions in the brain

What are effectors considered?

skeletal muscles

Sensation

sensory information arriving in the CNS

Perception

concious awareness of a sensation

Transduction

conversion of an arriving stimulus into an action potential by a sensory receptor

What are considered general senses? (6)

temperature, pain, touch, pressure, vibration, proprioception (body position)

What are considered special senses? (5)

olfaction (smell), gustation (taste), vision, equilibrium, hearing

Special Sensory Receptors

provide the sensations; located in sense organs (ex: eye, ear)

What is the specificity of sensory receptors?

each receptor has a charactersitic sensitivity

What is the field of a sensory receptor?

the area monitored by a single receptor cell

What does a larger receptive field mean?

harder to localize stimulus

What varies vs stays consistent with sensory receptors?

nature of stimuli varies but receptors always convert stimulus into an action potential

Where do action potentials travel to after being converted?

the CNS through transduction

Receptor Potential

stiulus changes receptor membrane potential

What happens when receptor potential is depolarized?

membrane is brought closer to threshold; aka generator potential

What happens when receptor potential is hyperpolarized?

membrane is moved further away from threshold

What is the size of receptor potential dependent on?

stimulus strength

What are receptors of the special senses considered?

specialized cells that communicate with sensory neurons at synapses

Where does receptor potential occur?

receptor cell

Where does generator potential occur?

sensory neuron

What does sensory iformation use to arrive at a specific site of the cerebral cortex?

location + nature of stimulus

Labeled Line

sensory neurons that link specific peripheral receptors to specific cortical neurons

What information does each labeled line carry about?

one modality or type of stimulus (ex: touch or light)

Sensory Coding

strength, duration, + variation of stimulus determines frequency + pattern of APs

What does perception of stimulus depend on?

the labeled line it uses

What is the difference between tonic + phasic receptors?

always active vs inactivated until there’s a stimulus

What does an increase/decrease in stimulation cause for tonic receptors?

an increase/decrease in the frequency of action potentials

What information do phasic receptors provide?

intensity + rate of change of a stimulus

What does stimulation cause in phasic receptors?

burst of action potentials that end when stimulus stops/doesn’t change in intensity

Adaptation

reduction of receptor sensitivity in the presence of a constant stimulus

What does the nervous system quickly adapt to?

painless, constant stimulu

What occurs in the PNS when the level of receptor activity changes?

peripheral adaptation

Fast-Adapting Receptors

respond strongly at first but then activity decreases - phasic (ex: temperature)

Slow-Adapting Receptors

show little peripheral adaptation - tonic (ex: pain)

What does central adaptation in the CNS involve?

inhibition of nuclei along a sensory pathway

Where is most incoming sensory information processed?

in centers along the spinal cord, brainstem, or thalamus before it reaches the cerebral cortex

What are tuning out background noise + listening carefully examples of?

concious + subconcious increase/decrease of sensory awareness

Exetroceptor

sensory receptor that provides information about external environment

Proprioceptors

sensory receptors that provide information about position of skeletal muscles + joints

Interoceptors

sensory receptors that provide information about visceral organs + functions

Nociceptors

sensory receptors the detect pain

What are nociceptors considered?

free nerve endings with large receptive fields

Where are nociceptors common?

superficial skin, joint capsules, periosteum of bones + around walls of blood vessels

What are nociceptors sensitive to?

temperature extremes, mechanical damage, dissolved chemicals (released by injured cells)

what central adaptation of nociceptors do?

reduce perception of pain

What may explain the difference in perception of pain in nociceptors?

facilitation of neurons in the pain pathway

What inhibit pain pathways in the CNS?

endorphins + enkephalins

Fast Pain (prickling)

pain similar to that caused by injection or deep cut

What carries fast pain?

myelinated type a fibers

What happens when fast pain sensation reaches the CNS quickly?

it often triggers somatic reflexes

What is fast pain relayed to and what does it receive?

primary somatosensory cortex + concious attention

Slow Pain

burning + aching pain

What is slow pain carried by?

unmyelinated type c fibers

What does slow pain cause?

generalized activation of reticular formation + thalamus

How do we feel slow pain?

you’re aware of it but only the general idea of affected area

Thermoreceptors

detect temperature

What are thermoreceptors considered?

free nerve endings

Where are thermoreceptors located?

dermis, skeletal muscles, liver, + hypothalamus

Where are thermoreceptor sensations conducted?

along the same pathways that carry pain sensations

Where are thermoreceptor sensations sent to?

reticular formation, thalamus, + (to a lesser extent) the primary somatosensory cortex

What do thermoreceptors do since they are phasic receptors?

respond most to temperature changes + then adaptation occurs

Mechanoreceptors

a sensory receptor that detects physical distortion like touch

What are mechanoreceptors sensitive to?

physical stimuli that distort their plasma membranes

What kind of channels do mechanoreceptor membranes have?

mechanically-gated ion channels

What do mechanoreceptor membrane channels respond to?

stretching, compression, twisting, + other distortions of the membrane

Tactile Receptors

a mechanoreceptor that detects touch (shape/texture), pressure (degree of mechanical distortion) + vibration (pulsing pressure)

What do fine touch + pressure receptors provide?

detailed information about the source, location, shape, size, direction of stimulus (extremely sensitive with narrow receptive fields)

What do crude touch + pressure receptors provide?

poor localization + little information about the stimulus (large receptive fields)

Free Nerve Endings

a type of tactile receptor, tonic with small fields that go to touch + pressure sensations

Where are free nerve endings located?

between epidermal cells

Root Hair Plexus

a type of tactile receptor, nerve endings that monitor distortions + movements around body surface with hairs

What are characteristics of root hair plexus?

they adapt rapidly + they’re best at detecting initial contact + subsequent movements

Tactile Discs

a type of tactile receptor, very sensitive tonic receptors for fine-touch + pressure

What are characteristics of tactile discs?

sensitive to shape + texture, small receptive fields

Bulbous Corpuscles (ruffini corpuscles)

a type of tactile receptor, tonic receptors sensitive to pressure/distortion of skin

What are characteristics of bulbous corpuscles?

located in reticular dermis, show little if any adaptation

Lamellar Corpuscles (pacinian corpuscles)

a type of tactile recptor, fast-adapting receptors sensitive to deep pressure

What are characteristics of lamellar corpuscles?

most sensitive to pulsing/high-frequency vibrations, consists of single dendrite within a series of concentric layers of collagen

Tactile Corpuscles (meissner corpuscles)

a type of tactile recepter, large fast-adapting receptors sensitive to fine touch, presure, + low frequency vibration

Where are tactile corpuscles most abundant?

eyelids, lips, fingertips, nipples, + external genitalia

Baroreceptors

a type of mechanoreceptor that detects pressure changes in blood vessels + portions of the digestive, respiratory, + urinary tracts

What are baroreceptors considered?

free nerve endings that branch within elastic tissues in walls of distensible organs

What is an example of a barorecepor?

blood vessel

How do baroreceptors respond + adapt?

immediately respond to change in pressure but adapt rapidly

Propioceptors

a type of mechanoreceptor that monitors position of joints + skeleal muscles

Proprioception

only a somatic sensation so no proprioceptors in visceral organs

Muscle Spindles

a type of proprioceptor that monitors skeletal muscle length + triggers stretch reflexes

Golgi Tendon Organs

a type of proprioceptor that acts as a junction between skeletal muscle + its tendon as well as monitors tension during muscle contractions

Receptors in Joint Capsules

a type of proprioceptor that has free nerve endings that detect pressure, tension, + movement at a joint

Chemoreceptors

a mechanoreceptor that detects chemical concentration in response to water-soluble + lipid-soluble substances dissolved in body fluids

What do chemoreceptors exhibit?

fast peripheral adaptation