Transcript Chapter_15_Neural_Integration_I

Anatomy
and
Physiology
Biology 2401
Chapter-15
Neural Integration I
Four Principal Functions of the Nervous System
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Carry information from receptors to the brain: sensation
Integrate the sensory information: association
Transmit motor responses to effectors
Memory
Sensation
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Conscious or unconscious awareness of both
external and internal stimuli
Perception: conscious awareness and
interpretation of sensations
Process of sensation
1. Stimulation (change in the environment) of sensory
receptor
2. Transduction of the stimulus: conversion of stimulus
into an electrical potential
3. Generation of a impulse and conduction: if the
electrical potential reaches threshold, an action
potential is produced and travels to the CNS
4. Integration of the sensory input: the action potential
is translated into a sensation
Sensory Modality
• The way one sensation is distinguished from
another
• Two major classes of modalities: general and
special senses
• General senses subdivided into
– Visceral: provide information about conditions of
internal organs
– Somatic: provide information about external stimuli
affecting the skin and its accessory structures as well as
proprioceptive information from the joints
• Special senses are smell, taste, vision, hearing and
equilibrium
Types of Sensory Receptors
• A first order neuron acts as the receptor. Primary
receptor.
– Free nerve endings: naked dendrites of the neuron act as the
receptor. Pain, heat, cold
– Encapsulated nerve endings: connective tissue layers surround
the dendrites of the first order neuron
• Sensory receptor cells synapse with a first order neuron.
Secondary receptor.
Types of Sensory Receptors
Types of Receptors Based on Location
• Exteroceptors: used to interpret stimuli that come from
the external environment and that are at or near the
surface of the body. Touch, pressure, vibration,
temperature, pain, hearing, vision, smell, taste.
• Interoceptors: used to interpret stimuli that are produced
internally. Found in organs such as blood vessels and the
viscera. Perceived as pain or pressure
• Proprioceptors: receptors that recognize the position of
the body and about body position, muscle tension or
activity of joints. Stretch receptors in muscles, tendons,
and joints. Equilibrium receptors in inner ear
Types of Receptors Based on Type of
Stimulus Detected
• Mechanoreceptors: touch, pressure, vibration,
proprioception, hearing and equilibrium
• Thermoreceptors: changes in temperature
• Nocioceptors: respond to physical or chemical
damage to tissues. Results in pain perception
• Photoreceptors: light striking the retina
• Chemoreceptors: taste, smell, oxygen, carbon
dioxide
• Osmoreceptors: monitor relative concentrations
of salt and water in body fluids
Adaptation in Sensory Receptors
• Tendency for generator or receptor potentials to
decrease in amplitude during a maintained,
constant stimulus
• Rapidly adapting (phasic): pressure, touch,
smell. Specialized for signaling changes in a
particular stimulus.
• Slow adapting (tonic): Monitor stimuli associated
with pain, body position, and chemical
composition of the blood
THE SOMATIC SENSATIONS
• Tactile
• Thermal
• Pain
• Proprioception
Thermal Sensations
• Free nerve endings in skin and in mucous membranes of
mouth, vagina, and anus
• Separate thermoreceptors respond to hot and cold
stimuli
• Adapt rapidly initially, then more slowly
Pain Sensations
• Nocioceptors: free nerve endings. Located in every tissue
of the body except the brain.
• Adaptation is slight if at all
• Provides individual with information about tissue
damage. Also, used as a sign during diagnosis of disease
or injury.
Types of Pain
• Fast: recognized rapidly and is described as acute, sharp,
or prickly
• Slow: begins several seconds after the stimulus and
increases in intensity. Described as chronic, burning,
aching, or throbbing
• Superficial: arises from the skin
• Deep: arises from skeletal muscle, joints and tendons
• Chronic: not a response to immediate, direct tissue injury.
– Hypothetical causes: cerebrum and thalamus may
misinterpret discomfort as pain or brain as a whole
may not properly regulate how much pain stimulation
is allowed to penetrate the cerebral cortex.
– Migraine, back pain.
– Often associated with depression, frustration,
helplessness, hopelessness
Types of Pain, cont.
• Phantom pain: sensations of pain in a limb that has been
amputated
• Brain interprets sensations from the remaining part of the
limb as sensations from the amputated part OR neurons
in the brain that received input from the missing limb are
still firing
THE VISCERAL SENSATIONS
• Pain and pressure if they are
intense enough to reach
conscious perception
• Referred pain: sensation in
one region of body that is not
the source of the stimulus.
– Organ pain usually referred to
skin
– Both the organ and that region
of the skin input to the same
spinal segment and converge on
the same ascending neurons
• Stretch receptors located in
muscles (muscle spindles) and
tendons and joints (tendon
organs or Golgi tendon organs)
• Receptors for equilibrium
(kinesthetic sense) in inner ear
• Convey information about muscle
tone, precise position of a body
part, rate of movement of a body
part, weight of an object held in
the hand, range of movement of
a joint, and balance
Proprioceptive
Sensation
Mapping of Sensory Areas on Postcentral Gyrus
Primary Somatosensory Area
• Specific areas of the cerebral
cortex receive somatic
sensory input from particular
parts of the body.
• Homunculus maps the
destination of somatic
sensory signals from different
parts of the body. The
relative sizes of the regions in
the somatosensory area are
proportional to the number
of specializes sense receptors
within the corresponding
part of the tissue
INTEGRATIVE FUNCTIONS OF THE
CEREBRUM
• Wakefulness and sleep
• Learning and memory
Wakefulness and Sleep
• Reticular activating system (RAS): control and integrate
wakefulness and sleep
• Awakening (arousal) comes about because of increased
activity of the RAS. Activation of RAS causes activation
of the cerebrum leading to consciousness
• Sleep: state of altered consciousness or partial
unconsciousness from which an individual can be
aroused by a number of stimuli. RAS activity is very low
• Two types of sleep: non-rapid eye movement sleep
(NREM) and rapid eye movement sleep (REM)
Indirect Motor Pathways
• All somatic motor
tracts other than the
corticospinal and
corticobulbar tracts
• Involve the motor
cortex, basal ganglia,
thalamus, cerebellum,
reticular formation
and nuclei in the brain
stem
Sleep
• NREM: four stages, each
of which gradually merges
into the next
• REM: dreaming
• Patterns of stages change
over the course of 8 hours
of sleep, with body
temperature changes
(warmer means longer
periods of REM), and with
age (older people exhibit
shorter and fewer
episodes of REM)
Learning and Memory
• Learning: ability to acquire new knowledge or skills
through instruction or experience
• Memory: process by which learned knowledge is retained
over time
• Brain exhibits plasticity: capability for change with
learning. Memories are represented by persistent
functional changes in the brain
Types of Memory
• Immediate: ability to recall something for a few seconds
• Short-term memory: ability to recall bits of information
for seconds or hours. Electrical and chemical events occur
in the brain.
• Long-term memory: ability to recall information from
days to years. Anatomical and biochemical changes at
synapses.
Amnesia
• Loss of memory
• Anterograde: loss of memory for events that occur after a
trauma (inability to form new memories)
• Retrograde: loss of memory for events that occur before a
trauma (inability to recall past events)