A&P Chapter 16 - Sensory and Motor Pathways

• always sensory and afferent
• carry info from receptors up to brain and spinal cord
• begin at a sensory receptor that is acted on by a stimulus
• AP travels to spinal cord, up to cerebrum or cerebellum

• always motor and efferent
• carry info from brain out out effectors
• begin in frontal lobe motor cortex
• AP travels down cord out to muscle or gland

• all fibers in a tract have similar origins, destinations, functions
• fibers usually decussate in tract
• if they cross, response is contralateral

• every sensory tract contains 3 neurons: FON, SON, TON
• 3 specific pathways: posterior column medial lemniscus/fasciculus gracilis, fasciculus cuneatus

• begins at sensory receptor, ends at brain stem or spinal cord
• BS: sensations from mouth, teeth, eyes (via cranial nerves)
• SC: sensations from posterior head, neck, everywhere else (via spinal nerves)

• begins at BS/SC, ends at thalamus
• decussation in medulla pyramids

begins at thalamus, ends at cerebrum (rarely cerebellum)

• sensory pathway
• conveys sensations of touch to the cerebrum
• contralateral
• discriminative touch, stereognosis, proprioception, weight discrimination, vibration, kinesthesia

• part of posterior column medial lemniscus pathway
• conveys info from lower part of body

• part of posterior column medial lemniscus pathway
• conveys info from upper part of body

ability to perceive the form of an object by using the sense of touch

awareness of the position of the body without looking

awareness of the movement of the body without looking

• sensory pathway
• anterior: conveys sensations of itch, tickle, pressure, and crude touch
• lateral: conveys sensations of pain and temperature

• sensory pathway
• balance, posture, muscle tone, skilled body movements

• always begin in frontal lobe of brain and end in muscle or gland
• 2 types: direct and indirect

• aka pyramidal
• 2 neurons: upper motor neuron and lower motor neuron
• produces precise, voluntary contraction of a muscle
• almost all fibers decussate (95%)
• 3 pathways: lateral corticospinal, anterior corticospinal, corticobulbar

• begins in motor cortex, ends in BS/SC
• synapses with lower motor neuron

begins in BS/SC, ends in muscle or gland

• direct motor pathway
• all fibers decussate
• voluntary movement of the arms, hands, legs, feet

• direct motor pathway
• 90% of fibers decussate
• voluntary movement of the neck, trunk, axial skeleton

• direct motor pathway
• all fibers decussate
• voluntary contraction of the muscles of the head, face, neck

• aka extrapyramidal
• more complicated than direct (extra neuron)
• begins in motor cortex with association neuron -> UMN -> LMN
• produces involuntary responses
• 5 tracts: tectospinal, rubrospinal, vestibulospinal, lateral reticulospinal, medial reticulospinal

• indrect motor pathway
• involuntary movement of the eyes and head in response to rapid auditory, visual, or tactile stimulation

• indirect motor pathway
• involuntary movement of fingers and toes

• indirect motor pathway
• no fibers cross
• muscle tone, posture, balance

• indirect motor pathway
• controls reflexes associated with pain (withdrawal reflex)

• indirect motor pathway
• inhibits withdrawal reflex

a conscious or subconscious awareness of internal or external stimulus

the way a sensation is interpreted

• a unique sensations (such as taste, smell, etc)
• a neuron can carry only one modality
• 2 classes: general senses, special senses

touch, pressure, temperature

vision, hearing, taste, smell

• sensory receptors
• exposed dendrites that respond to pain, temp, itch, tickle, light touch

• sensory receptors
• dendrites enclosed in connective tissue capsule (pressure receptors)

• sensory receptors
• hearing and vision receptors

receptors on body surface that respond to external stimuli

• aka visceroceptors
• receptors inside body around blood vessels that respond to stretch, pressure, and pain

receptors in muscles, tendons, joints, inner ear that respond to body position, movement, balance

temperature receptors

light receptors

chemical receptors

pain receptors

long term and constant pain

pain perceived in a structure that was amputated

deep pain projected to a surface site that shares the same spinal nerve

• long lasting stimulus will cause a sensation to decrease until it is no longer perceived
• 2 receptors: phasic and tonic

rapidly adapting receptors (temp, smell, touch)

slowly adapting receptors (pain, chemical)

• heart and blood vessels
• respond to changes in BP

• inner ear
• maintain balance

• muscles
• prevent muscle damage if muscle has been stretched

• hair follicle
• makes hair sensitive to touch

touch receptors in the dermis

• pressure receptors in the dermis
• respond to heavy and continuous touch