Anatomy Chapter 13- Peripheral Nervous System Flashcards
Peripheral Nervous System
Provide the brain with sensory input and allows for motor output to reach the effector organs
General structures of the PNS
Sensory receptors
Afferent fibers
Efferent fibers
Sensory receptors
The environment could be internal or external
Afferent fibers
Sensory information being carried
Efferent fibers
Carries impulses away from the CNS
Subdivisions of the PNS
Afferent Division
Efferent division
Afferent Division
Carry impulses from the body to the central nervous system (sensory)
Efferent Division
Carry impulses to the body from the central nervous system (motor)
Can be somatic or autonomic
Somatic Division
Skeletal muscle tissue is the effector
Autonomic divison
Cardiac muscle, smooth muscle and glands
Stimuli
Specialized structures that respond to changes in the environment
Classification of sensory receptors
- Stimulus type- what change in the environment activates the receptor
- Location- either location in the body or the location of the source of the stimulus (inside or outside the body)
- Receptor structure- non encapsulated or encapsulated
Stimulus Types (5)
- Mechanoreceptors
- Thermoreceptors
- Photoreceptors
- Chemoreceptors
- Nociceptors
Mechanoreceptors
Respond to mechanical force
When own form is being physically distorted or changed
Example- When bent, it will respond
Thermoreceptors
Respond to temperature changes (hot or cold)
Photoreceptors
Respond to light
Highly localized/only found in the eye
Chemoreceptors
Respond to chemicals in solution
Can be body-wide or localized
Keeping track of blood pH as well
Nociceptors
Respond to damaging stimuli
Pain sensations
Extreme temperature, extreme, pressure, too much chemicals, etc.
Classification by location
- Exteroceptors
- Interoceptor
- Proprioceptors
Exteroceptors
Mostly found at or near the body surface
Close or near the skin
Examples- photoreceptors, mechanoreceptors
Interoceptors
Found deeper in the body
Closer to the visceral receptors
Proprioceptors
Found in skeletal muscle, tendon, joints, ligaments
Highly localized, body position in space, coordinate movements, etc.
Nerve Endings
Modified gendritic endings of sensory neurons
Types of nerve endings
Nonencapsulated (free)
Encapsulated
Non-encapsulated (free) nerve endings
Dendritic ends of sensory receptors have no covering on them
Abundant in epithelia and connective tissue (anywhere)
Respond to pain and temperature (noci and thermo)
Sensations allowed by free (nonencapsulated) nerve endings
- Itch - histamine
- Light Pressure - Merkel cells (hair stimulates free nerve endings - bug on skin)
- Light touch specifically for hair (mechanoreceptor) - hair follicle where nerve endings wrap around it and respond to changes in hair and hair follicle
Encapsulated nerve endings
Densritic endings are enclosed in a capsule
Sensations allowed by encapsulated nerve endings
- Tactile corpuscles
- Lamellar Corpuscles
- Bulbous corpuscles
- Muscle Spindles
- Tendon Organs
- Joint Kinesthetic Receptor
Tactile corpuscles
Found in dermal papillae of hairless skin
Important for light touch sensation
Lamellar Corpuscles
Located deep in dermis
Stimulated by onset of deep pressure
Bulbous corpuscles
Located in dermis, subcutaneous tissue and joint capsules
Respond to deep, continuous pressure
Muscle spindles
proprioceptors found in tissue wrapped around skeletal muscle
Detect muscle stretch and initiates reflexes to resist excessive stretching
Tendon organs
Proprioceptors of tendons
Initiates reflex that eelaces skeletal muscle to prevent damage to tendon
Responsible for monitoring the stretch found in the tendon
Joint kinesthetic receptor
Proprioceptor monitoring stretch in joints
Provide information about joint position and motion
Prevents dislocation
Sensation
Awareness of a change in external/internal environment
Perception
How we interpret the stimuli
Somatosensory system
Sensory system that specifically serves body wall and limbs
Input from exteroceptors, proprioceptors, and interoceptors
Levels of somatosensory system
- Receptor level
- Circuit level
- Perceptual level
Receptor level
Sensation will only occur if a stimulus activates a receptor and if the action potentials reach the CNS
1. Stimulus must match receptor specificity
2. Stimulus must be applied within receptor’s receptive field
3. Stimulus energy must be converted to a graded potential
4. Graded potentials must reach threshold for sensory receptor to generate an action potential
Receptive field
How large or small the field is depends on what part of the body it is and what sensation its responsible for changing to
Circuit level
Delivering impulses to appropriate region of the cerebral cortex
Perceptual level
Sensory input is interpreted at the cerebral cortex
Identifying the sensation depends on the target neurons of the cerebral cortex
Types of pain
Sharp- occurs at onset of injury (small, myelinated fibers - message sent very quickly to brain)
Burning- Occurs after sharp pain (small, unmyelinated fibers - message sent slowly to the brain)
Endorphins/Enkaphalins
Suppress feling of pain
Visceral pain
Noxious stimulation of receptors of the thorax and abdominal cavity
Example- Extreme stretching of tissue
Referred pain
Pain stimuli arising from one part of the body are perceived as coming from another part
Nerve
Cordlike organ that is part of the peripheral nervous system consisting of parallel bindles of peripheral axons enclose by connective tissue wrappings
Classification of nerves
Afferent
Efferent
Mixed
Afferent nerves
Sensory
Efferent nerves
Motor
Mixed nerves
Sensory and motor
to and from the sensory nervous system
Endoneurium
Axons wrapped with this connective tissue that prevents unauthorized sending of information
Fascicles
Groups of axons that are bundled together by perineuron
Epineurium
Fascicles bundled together to form the true nerve
This is the actual nerve
Damage in CNS and PNS
CNS- cannot regenerate and die
PNS- Capable of regeneration IF cell body isn’t damaged and the severed ends are close together (will not be as good as before)
Axon Regeneration Steps in the PNS
- Injury occurs- Axon is damaged and distal portions will degenerate
- Clean-up- Macrophages invade the area and dying portions are destroyed
- Axon regeneration begins- hairs coming together with both ends - Schwann cells release growth factor to stimulate growth and form a “tube” to fuse with one another properly
- Completion of regeneration - Form complete axon and Schwann cells form the myelin sheath around new axon (smaller diameter)
Cranial Nerves
Olfactory - S
Optic - S
Oculomotor - M
Trochlear - M
Trigeminal - B
Abducens - M
Facial - B
A/Vestibulocochlear - S
Glossopharyngeal - B
Vagus - B
Spinal accessory - M
Hypoglossal - M
Olfactory
nerves associated with olfaction (smell)
Optic
nerves associated with vision
Vision, light intensity
From retina
Oculomotor
supplies four of the six extrinsic eye muscles the move the eyeball
Trochlear
innervates extrinsic eye muscle that depresses the eye and turns it laterally (superior oblique)
Trigeminal
supplies sensory fibers to the face and motor fibers to the chewing muscles
Pain, touch, and temperature on our faces
Abducens
controls extrinsic eye muscle that abducts the eye (the lateral rectus muscle)
Abduct the eye (turning towards the temple)
Facial
innervates muscle for facial expression, contributes to taste
Tongue (2/3rds)
Vestibulocochlear
Hearing and balance
Auditory nerve
Glossopharyngeal
innervates tongue for taste & general senses, innervates pharynx for general senses, innervates muscles of the pharynx for swallowing
Innervate muscle from the pharynx for swallowing foods or liquids
Vagus
fibers extend to and supply sensory & motor fibers to the organs of the thorax and abdomen
Spinal Accessory
supplies motor fibers to muscles that move the head and neck
Hypoglossal
innervates muscles of the tongue and under the tongue to allow movement of the tongue for chewing, speech, swallowing
Dorsal Ramus
Provides sensory and motor fibers to tyhe skin and muscles of the back
Ventral ramus
Provides sensory and motor fibers to lateral and ventral walls and to the upper and lower limbs
Nerve Plexuses
Ventral rami branch to form these nerve networks
Cervical Plexus
cutaneous nerves that supply the neck, ear, back of the head, and shoulders
C1 - C4
Brachial Plexus
provides fibers that supply the upper body limbs
C5-C8, T1
Lumbosacral Plexus
Lumbar plexus and sacral plexus have large degree of overlap
Anterior and medial portion of the leg
Lumbar Plexus
innervates parts of abdominal wall muscle, major branches innervate anterior & medial thigh
Sacral Plexus
innervates buttocks and posterior aspect of lower limbs, pelvic structures and perineum
Lumbosacral trunk function
Lumbosacral trunk
Some fibers of lumbar plexus contribute to the sacral plexus through this passage
Anterolateral Thorax and Abdominal Wall
Ventral rami in the thorax do not form plexuses but are arranged in a segmental pattern
serve intercostal muscles between ribs, skin of anterolateral thorax, and most of abdominal wall (arranged segmentally)
Back
Dorsal rami innervate posterior body trunk in segmental pattern
each dorsal ramus innervates narrow strip of muscle & skin at same area where it emerges from spinal column
Dermatomes
Area of skin innervated by a single spinal nerve
Provides sensory details of the skin to the brain
Types of reflexes
- Intrinsic
- Acquired
Intrinsic reflex
Unlearned, unpremeditated, and involuntary
Built in responses
Making fast adjustments to body posture after losing balance
Acquired reflex
Results form practice or repetition
learned responses
Driving a car
Components of a reflex arc
- Receptor - site of stimulus action
- Sensory neuron - transmits afferent impulses to the CNS
- Integration center - Synpases found in the CNS (spinal cord)
- Motor neuron - Conducts efferent impulses from the integration center to effector organ
- Effector - muscle fiber or gland that responds to the impulse
Spinal Reflex
Any somatic reflex that is mediated by the spinal cord
Types of spinal reflexes
- Stretch
- Tendon
- Flexor and Cross-Extension Reflexes
Stretch Reflex
Ensures that a muscle stays at its optimal length
prevents damage to muscle and tendon by causing a muscle to contract when the muscle is stretched too far
Monosynaptic
Stretch reflex
Have only a single synapse between the sensory neuron and a motor neuron
Ipsalateral
Stretch reflex
The stimulus and response occur on the same side of the body
Muscle spindles
Provide information about the length of a particular muscle
Function as proprioceptors
When stretched, muscle spindle sends impulses at higher frequency
Knee-Jerk Reflex
- Tap the patellar ligament
- Send a sensory impulse straight to the spinal cord
- Motor response sent back out through fibers in the quadriceps muscle
Quadricep contracts (knee extends)
Neural fibers go to the hamstring muscle as well and it will cause the knee to go back so that the quadricep does not overextend the knee
Antagonistic
Tendon Reflex
prevents damage to muscle by causing the muscle to relax when tension force (during muscle contraction) becomes so great it can damage the muscle
Tendon organs
Provide information about the amount of tensin in a muscle and its associated tendons
Muscles relax and lengthen in response to an action
Prevents damage due to excessive stretch
Polysynaptic
Tendon reflex
Involve multiple synapses with chains of interneurons
Flexor reflex
Initiated by painful stimuli
Protection/survival mechanism
Crossed-Extensor reflex
Often accompanies flexor reflex
maintaining balance on the other side of the body
Contralateral
Crossed-Extensor reflex
The stimulus and response occur on opposite sides of the body
