Transcript from somatic receptors to cerebral cortex (somatosensory area)

Sensation- conscious (perception)
or subconscious awareness
of changes in environment
Sensory modality- unique type of sensation
• general senses- somatic (tactile, thermal,
pain, proprioceptive) and visceral (internal
organs)
• special senses- smell, taste, vision, hearing,
equilibrium
Process of sensation
• begins with receptor (selective)stimulus produces potential at
threshold
• CNS integrates impulse
Three types of
receptors: free
nerve endings,
encapsulated
nerve endings,
separate cellssee figure 16.1
location
•
exteroceptor
s (external
surface of
body),
•
interoceptor
s (internal
environment
),
•
propriocepto
rs (muscles,
Can be grouped by stimulus
• mechanoreceptors (mechanical
stimuli)
• thermoreceptors (heat)
• nociceptors (pain)
• photoreceptors (light)
• chemoreceptors (chemicals)
• osmoreceptors (osmotic pressure)
Adaptation to
maintained,
constant
stimulus (can
be rapid or
slow)
A dog (red line) tracks a pheasant (yellow line). As the dog keeps
leaving the odour to prevent receptor adaptation, it zigzags.
Somatic sensations
• Tactile: touch, tickle, pressure, vibration, itch
(mechanoreceptors)
• touch: Meissner corpuscles and hair root plexuses are
rapidly adapting, Merkel discs and Ruffini corpuscles are
slowly adapting
• pressure and vibration: Meissner corpuscles, Merkel
discs, and lamellated corpuscles
• itch and tickle: stimulation of free nerve endings
• Thermal: free nerve endings, cold in epidermis, warmth in
dermis
• Pain: free nerve endings everywhere except the brain- very
little adaptation
• two types: fast ( sharp or prickling) and slow (aching or
throbbing)
• Proprioceptive: know where body parts are and control
equilibrium
Somatic Sensory Pathways- from somatic
receptors to cerebral cortex
(somatosensory area)
• First-order neuron- from somatic
receptor to brain stem (cranial) or spinal
cord (spinal nerves)
• Second-order neuron- from brain stem
or spinal cord to thalamus- decussate
(cross over to other side)
• Third-order neuron- from thalamus to
primary somatosensory area
Three pathways to cerebrum and
cerebellum- table 16.3
• posterior column-medial
lemmniscus: fine touch,
stereognosis (recognize by feel),
proprioception, vibration
• anterolateral: crude touch impulses,
pain, temperature
• spinocerebellar tracts:
proprioceptive to cerebellum
can map
somatosens
ory areas
(lips and
hands large
area, trunk
and limbs
small area)
Somatic Motor pathways- provide imput to lower
motor neurons
• Local circuit neurons- coordinate rhythmic
activity
• Upper motor neurons- planning, initiating,
and directing sequences of voluntary
movements
• Basal ganglia neurons- initiate and terminate
movements, suppress unwanted movement,
establish muscle tone
• Cerebellar neurons- monitor movement
(posture and balance)
• Direct (cerebral cortex- voluntary) and
indirect (brain stem) pathways
Integrative functions of the Cerebrum
• Wakefulness and sleep (circadian
rhthyms): recticular formation to cerebral
cortex
• Learning and memory: due to plasticity,
occurs in stages over time