REFLEX PHYSIOLOGY & GENERAL SENSES

Reflex

automatic response to a stimulus

Maintain balance and posture, Protect us from danger or injury, Carry out routine activities like chewing or walking

most neural reflexes are designed to

Reflex Arc

1.Receptor

2.Sensory Relay

3.Integration

4.Motor Command Relay

5.Effector

1st step of reflex arc

receptor

2nd step of reflex arc

sensory relay

3rd step of reflex arc

integration

4th step of reflex arc

motor command relay

5th step of reflex arc

effector

monosynaptic

fast and integrated in the spinal cord

polysynaptic

contain at least one interneuron, most reflexes

knee jerk

example of monosynaptic

monosynaptic v polysynaptic

based on the number of neurons involved

somatic

voluntary and involves skeletal muscle

autonomic

involuntary and involves smooth muscles, glands, or visceral organs

Acquired Reflexes

learned through experience, ex driving walking and skiing

general stimuli

temperature, pH, pressure

special stimuli

vision, hearing, equilibrium, taste, smell

Exteroceptors

monitor external conditions, (heat, cold, touch, pain, pressure)

Interoceptors

monitor internal conditions (chemoreceptors, visceral stretch receptors, proprioceptors)

Chemoreceptors

interoceptor that monitors blood PH

Visceral Stretch Receptors

interoceptor thats a distension of visceral organs

Proprioceptors

interoceptor that deals with postural information

TWO broad classes of receptors

general and special

Free (naked) Nerve Endings

Dendrites terminate in epidermis/dermis junction of skin and mucosal epithelium, Detect pain (extreme temperature)

Merkel Cells

associated with free nerve endings, located in the stratum germinitivum (basale), detect light touch/ sustained pressure

Encapsulated Receptors

Ex. Meissner’s Corpuscles, Pacinian Corpuscle

Meissner’s Corpuscle

type of encapsulated receptor, more superficial, detects light touch

Pacinian Corpuscle

type of encapsulated receptor, more deep, detects forceful pressure, vibration

Free nerve endings

—•terminate basically at the surface of skin or mucosa and detect pain (more superficial and detect pain)

merkel cells

—reside at the deepest layer of the epidermis and detect touch (deeper and detect touch)

Meissner’s Corpuscles

superficial

Pacinian Corpuscles

deep (since they are deeper it takes more force to activate)

1

merkel disk

2

ruffini corpuscle

3

Pacinian Corpuscle

4

Nociceptor (free nerve endings)

5

Meissner’s corpuscle

6

Root Hair Plexus

7

Krause End Bulb

Muscle Spindle

uMonitor muscle position

uEnsure muscles are not overstretched

muscle spindle

Purpose of — is to monitor muscle position based on its state of stretch (prevents overstretching)

Intrafusal & Extrafusal Fibers

TWO types of muscle fibers in muscle spindle

intrafusal fibers

—-(proprioceptors): have a contractile and non-contractile region

extrafusal fibers

have contractile regions

intrafusal fibers

—located within extrafusal skeletal muscle fibers

sensory region

Intrafusal fiber innervated by sensory neuron dendrites wrapped around —

a-motor neurons

—innervate contractile region of extrafusal fibers

y-motor neurons

innervate contractile region of intrafusal fiber

sensory neurons

—sends continual impulses to CNS which sends signals back to extrafusal fibers via α-motor neurons

spindle is compressed

Muscle is contracted and —: frequency slows

fewer impulses

—sent to α-motor neurons and skeletal muscles relax

spindle is stretched

Muscle is extended and —: frequency increases

more impulses

—sent to α-motor neurons and skeletal muscles contract

willful muscle contraction

Brain sends impulse to γ-motor neurons in order to contract the intrafusal fibers which relieves compression of spindle

spindle length

determines frequency that alpha-motor neuron fires

intrafusal, extrafusal

We can willfully contract — fibers to reduce compression on spindle when we want to contract the — fibers

trandsucers

receptors are:

action potentials

the nervous system only speaks the “language” of ——- so we need to convert stimuli into ——.

Destination in the brain

How do we distinguish between action potentials?

Receptive fields

How do we distinguish stimuli?

2 point discrimination test

Ability for a person to detect two distinct points of contact on the skin as separate stimuli

Transducers

Convert stimuli to action potentials

destination

Action potentials are distinguished as unique by their ——- in the brain

action potentials

Different regions of the brain interpret ——- differently (pain vs. touch)

receptor fields

The smaller and denser the fields, the more sensitive (Hands, feet, face, genitals)

adaptation

Desensitization to constant stimuli is called 

1

Secondary sensory endings (type 2 fiber)

2

Primary sensory endings (type 1a fiber)

3

muscle spindle

4

connective tissue capsule

5

intrafusal muscle fiber

6

extrafusal muscle fiber

7

efferent motor fiber to extrafusal muscle fibers

8

efferent motor fiber to spindle