Chapter 13 Flashcards
Peripheral Nervous System (PNS)
Provides links from and to world outside of body
All neural structures outside brain
Example
-Nerves
Sensory Receptors
Specialized to respond to changes in environment (stimuli)
Activation results in graded potentials that trigger nerve impulses
Sensation Vs. Perception
Sensation- Sensory Nerves- Touch
-Awareness of changes in environment
Perception- Either Brain or Spinal Cord- Thought
-Interpretation of changes in environment
Classification by Stimulus Type
Mechanoreceptors Thermoreceptors Photoreceptors Chemoreceptors Nociceptors
Mechanoreceptors
Movement, Pressure
Thermoreceptors
Temperature
Photoreceptors
Light
Chemoreceptors
Chemicals, Taste, Smell
Nociceptors
Pain, Spicy, Too Hot
Sensory Integration
Somatosensory system- part of sensory system serving body wall and limbs
Receives inputs from:
-Exteroceptors
-Proprioceptors
-Interoceptors
Input relayed toward head, but processed along way
Levels of Sensory Integration
Receptor Level
Circuit Level
Perceptual Level
Receptor Level
Sensory Receptors
Circuit Level
Processing in ascending pathways
Perceptual Level
Processing in cortical sensory areas
Processing at Receptor Level
To produce sensation -Receptors activation -Stimulus location -Transduction occurs Graded potentials must reach threshold
Adaptation of Sensory Receptors
Adaptation is change in sensitivity in presence of constant stimulus
- Receptor membranes become loss responsive
- Receptor potentials decline in frequency or stop
Processing at the Circuit Level
Pathways of 3 neurons conduct sensory impulses upward to appropriate cortical regions
First Order Sensory Neurons
Second Order Sensory Neurons
Third Order Sensory Neurons
First Order Sensory Neurons
From receptor to second neuron
Second Order Sensory Neurons
From spinal cord to third region
Third Order Sensory Neurons
Thalamus to perception or somatosensory system
Perception of Pain
To recognize outside threat- to warn us of danger
Pain Tolerance
Tolerance not threshold
“Sensitive to pain” means low pain tolerance, not low pain threshold
Genes help to determine pain tolerance
Response to pain medications
Hyperalgesia
Long lasting intense pain.
Same intensity but feels like hyper-stimulated
Phantom Limb Pain
Felt in a limb that is no longer present, like feeling a hand on the distal end of an amputated arm
Referred Pain
Pain from one body region perceived from different region
Example:
-Heart Attack- heart pain but felt in left arm and jaw
-Neck and shoulder pains
Structure of a Nerve
Connective Tissue Coverings
- Endoneurium- loose connective tissue
- Perineurium- coarse connective tissue
- Epineurium- tough fibrous sheath
Ganglia
Contain neuron cell bodies associated with nerves in PNS
Afferent nerve fibers- sensory neurons
Efferent nerve fibers- autonomic motor neurons
Regeneration of New Fibers
PNS- yes if cell body is intact
CNS- no
Cranial Nerves
12 Pairs; mixed nerves, numbered from 1 to 12
Olfactory Nerves
Smell: Olfactory Bulbs to Olfactory Cortex
Optic Nerves
Sight: Retinas to Thalamus Occipital Cortex
Vagus Nerves
Only Cranial Nerve that extend beyond head and neck region
- Heart
- Lungs
- Abdominal Functions
Compostition of Cranial Nerves
Some mixed nerves contain both somatic and autonomic fibers
Spinal Nerves
31 Pairs of mixed nerves named for point of issue from spinal cord
- 8 Cervical (only 7 cervical vertebrae, 1 exits canal below 7)
- 13 Thoracic
- 5 Lumbar
- 5 Sacral
- 1 Coccygeal
Spinal Nerves: Roots
Each spinal nerve connects to spinal cord with two roots
- Ventral
- Dorsal
Ventral Roots
Contain efferent fibers from ventral horn motor neurons
Fibers innervate skeletal muscles
Dorsal Roots
Contain afferent fibers from sensory neurons in dorsal root ganglia
Conduct impulses from peripheral receptors
Brachial Plexuses
5 Nerves
- Axillary
- Musculocutaneous
- Median
- Ulnar
- Radial
Axillary
Innervates much of shoulder region
Musculocutaneous
Innervates much of upper arm
Median
Innervates much of the forearm flexors
Ulnar
Innervates forearm flexors and intrinsic hand
Radial
Innervates forearm extensors
Lumbar Plexus
Innervates thigh, abdominal wall
L1 to L4
Femoral Nerve
Innervates anterior and medial thigh
Obturator Nerve
Innervates adductor muscles
Sacral Plexus
Innervates buttocks, lower limb, pelvis, and perineum
L4 to S4
Sciatic Nerve
Longest, thickest nerve of body Innervates posterior/medial thigh and most muscles in leg and foot Composed of 2 nerves -Tibial -Fibular
Dermatome
Area of skin supplied to one spinal nerve
All spinal nerves except C1 participate in dermatomes
Extent of spinal cord injuries ascertained by affected dermatomes
Overlapping areas
Innervation of Skeletal Muscle
- Takes place at neuromuscular junction
- Neurotransmitter acetylcholine (ACh) released when nerve impulses reaches axon terminal
- ACh binds to receptors, resulting in:
- Movement of Na+ and K+ across membrane
- Depolarization of muscle cell
- At end plate potential, which triggers an action potential- muscle contraction
Reflexes
Rapid, voluntary, predictable motor response to stimulus
Learned/acquired reflexes result from practice or repetition
Reflex Arc
- Receptor
- Sensory Neuron
- Integration Center
- Motor Neuron
- Effector
Reflexes: Functional Classification
Somatic Reflexes
Autonomic (visceral) reflexes
Spinal Nerves: Plexuses
Within plexus fibers criss-cross
- Each branch contains fibers from several spinal nerves
- Fibers from ventral ramus go to body periphery via several routes
- -Each limb muscle innervated by more than one spinal nerve
Cervical Plexus and the Neck
Formed by ventral rami of C1 to C4
Most branches form cutaneous nerves
-Innervate skin of neck, ear, back of head, and shoulders
-Other branches innervate neck muscles
Phrenic Nerve
Major motor and sensory nerve of diaphragm (receives fibers from C3 to C5
Irritation= hiccups
Brachial Plexus and Upper Limb
Formed by ventral rami of C5 to C8 and T1 (and often C4 and T2)
Gives rise to nerves that innervate upper limb
Numerous major branches of the plexus
Somatic Reflexes
Activate Skeletal Muscle
Autonomic (Visceral) Reflexes
Activate visceral effectors (smooth or cardiac muscle or glands
Spinal Somatic Reflexes
Integration Center: Spinal Cord
Effectors: Skeletal Muscle
Testing of somatic reflexes allow assessment of nervous system
If exaggerated, distorted, or absent- degeneration/pathology of specific nervous system regions
Stretch and Tendon Reflexes
To smoothly coordinate skeletal muscle nervous system must receive proprioceptor input regarding
- Length of muscle
- Amount of tension in muscle
Muscle Spindles
Contracting muscle reduces tension on muscle spindle
Stretch Reflex
Maintains muscle tone in large postural muscles, and adjusts it reflexively
-Causes muscle contraction in response to increased muscle length (stretch)
