chapter 13 Flashcards
Peripheral Nervous system
All neural structures outside the brain
- sensory receptors
- peripheral nerves and associated ganglia
- motor nerves
sensory receptors
- specialized to respond to changes in their environment (stimuli)
- activation results in graded potentials that trigger nerve impulses
- sensation (awareness of stimulus) and perception (interpretation of the meaning of the stimulus) occur in the brain
classification of receptors
Based on:
A) stimulus type (name indicates the type of stimulus: thermoreceptors)
B) Location (respond to either internal or external stimuli)
C)Structural complexity
- general senses-simple
- special senses- complex (vision, hearing, taste, smell)
Mechanoreceptors
respond to touch, pressure, vibration, stretch, and itch
thermoreceptors
sensitive to changes in temperature
photoreceptors
respond to light energy (e.g., retina)
chemoreceptors
respond to chemicals (e.g., smell, taste, changes in blood chemistry)
nociceptors
sensitive to pain-causing stimuli (e.g. extreme heat or cold, excessive pressure, inflammatory chemicals)
classification of receptors by location
- exteroceptors
- interoceptors-viscero
- proprioceptors
from sensation to perception
-survival depends upon sensation and perception
- sensation: the awareness of changes in the internal and external environment
- input comes from sensory receptors
- perception: the conscious interpretation of that stimuli
- this occurs in the brain
sensory integration
- receptor level- the sensor receptors. sensory reception and transmission to the CNS
- circuit level- ascending pathways (spinal cord and brain stem)
- perceptual level- neuronal circuits in the cerebral cortex. processing in cortical sensory centers
adaptation of sensory receptors
Adaptation: a change in sensitivity in the presence of a constant stimulus (bright light)
Phasic (fast-adapting) receptors signal the beginning or end of a stimulus, signals a change
Examples: receptors for pressure, touch, and smell (clothing)
Tonic receptors adapt slowly or not at all
Examples: nociceptors and most proprioceptor
structure of a nerve
- cordlike organ of the PNS
- Bundle of myelinated and unmyelinated peripheral axons enclosed by connective tissue
endoneurium
loose connective tissue that encloses axons and their myelin sheaths
perineurium
coarse CT that bundles fibers into fascicles
epineurium
tough fibrous sheath around a nerve
classification of nerve
most nerves are mixtures of afferent and efferent fibers:
- somatic afferent and somatic efferent
- visceral afferent and visceral efferent
->peripheral nerves are classified as cranial or spinal nerves
ganglia-collections of cell bodies in PNS
- dorsal root ganglia (sensory, somatic)
- autonomic ganglia (motor, visceral)
regeneration of peripheral nerve fibers
- mature neurons are amitotic
- if the soma(cell body) of a damaged nerve is intact, axon will regenerate
- CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration
what statement is correct about language and the brain
broca’s area is related to language expression and is located in the left inferior frontal gyrus
cranial nerves
- 12 pairs of peripheral nerves associated with the brain
- most are mixed in function; 2 pairs are purely sensory (I and II)
cranial nerve I and II
- CN I olfactory nerve: smell (just sensory)
- CN II optic nerve: vision (just sensory)
eye movements (CN 3,4,6)
- just motor
- cranial nerve III: oculomotor nerve
- cranial nerve IV: trochlear nerve
- cranial nerve VI- abducens nerve (abducts eye)
cranial nerve 5, 7, and 8
Cranial nerve V (5) - trigeminal nerve
- > sensation of face
- > motor of mastication
cranial nerve VII- facial nerve:
- > motor of face- facial expression
- > sensory taste
cranial nerve VIII- vestibulocohlear nerve
->hearing and balance
cranial nerve 9 and 10
cranial nerve IX (9)- glossopharyngeal nerve
-> “tongue and throat”- taste and swallowing
cranial nerve X- vagus nerve
- > “the wanderer”
- > only cranial nerve that leaves the head and neck
- > involved in parasympathetic nervous system
- > help regulate the heart, lungs, and abdominal viscera
cranial nerve 11 and 12
just motor
- cranial nerve XI-accessory nerve
- > moves head and neck (trapezius and SCM muscle)
- cranial nerve XII- hypoglossal nerve
- > “under tongue”-moves tongue
spinal nerves
-31 pairs of mixed nerves named according to their point of issue from the spinal cord
- > 8 cervical (C1-C8)
- > 12 thoracic (T1-T12)
- > 5 lumbar (L1-L5)
- > 5 sacral (S1-S5)
- > 1 coccygeal (C0)
spinal nerves: roots
-each spinal nerve connects to the spinal cord via 2 roots
ventral roots:
- > contain motor (efferent) fibers from the ventral horn motor neurons
- > fibers innervate skeletal muscles
spinal nerve: roots
Dorsal roots:
- contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia
- conduct impulses from peripheral receptors
-dorsal and ventral roots unite to form spinal nerves
spinal nerves: rami
-each spinal nerve branches into mixed rami
- > dorsal ramus
- > larger ventral ramus
- > rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region
- roots- lie medial to spinal nerve-either motor or sensory
- rami- lie lateral to spinal nerve- mixed
spinal nerves: rami
- all ventral rami except T2-T12 form nerve networks called PLEXUSES (cervical, brachial, lumbar, and sacral)
- the back is innervated by dorsal rami via several branches
cervical plexus
- formed by ventral rami of C1-C5
- innervates skin and muscles of the neck, ear, back of head, and shoulders
phrenic nerve
- major motor and sensory nerve of the diaphragm (receives fibers from C3-C5)
- irritation of phrenic nerve causes hiccups
brachial plexus
- formed by ventral rami of C5-C8
- gives rise to the nerves that innervate the upper limb
- major nerves from the branches: axillary, musculocutaneous, median, ulnar, and radial
brachial plexus injury
-Erb’s palsy: stretching of upper trunk of brachial plexus
Klumpke’s paralysis: injury to lower roots of plexus (claw hand)
lumbar plexus
- arises from L1-L4
- innervates the thigh, abdominal wall, and psoas muscle
- femoral nerve
- obturator nerve
femoral nerve
innervates quadriceps and skin of anterior thigh and medial surface of leg
obturator nerve
innervate adductor muscles (groin muscles)
sacral plexus
- arises from L4-S4
- serves the butt, lower limg, pelvic structures, and perineum
sciatic nerve
sciatic nerve
(part of sacral plexus)
- longest and thickest nerve of body
- innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot
- composed of 2 nerves: tibial and common fibular
reflexes
- inborn (intrinsic) reflex: a rapid, involuntary, predictable motor response to a stimulus
ex: splashing hot water from pot on your arm - learned (acquired) reflexes: result from practice or repetition
ex: driving skills
pathway:
- receptor
- sensory neuron
- integration center
- motor neuron
- effector
reflex arc
components of a reflex arc (neural path):
- RECEPTOR: site of stimulus action
- SENSORY NEURON: transmits afferent impulses to the CNS
- INTEGRATION CENTER: either monosynaptic or polysynaptic region within the CNS
- MOTOR NEURON: conducts efferent impulses from the integration center to an effector organ
- EFFECTOR: muscle fiber or gland cell that responds to the efferent impulses by contracting or secreting
spinal reflexes
- Spinal somatic reflexes
- > integration center is in the spinal cord
- > effectors are skeletal muscle
include: stretch, flexor, and crossed-extensor
stretch reflexes
How a stretch reflex works:
-> stretch activates the muscle spindle (receptor)
- > sensory neurons synapse directly with alpha motor neurons in the spinal cord
- > alpha motor neurons cause the stretched muscle to contract
- all stretch reflexes are monosynaptic and ipsilateral- ( the reflex occurs on the same side of the body as the stimulus.)
ex: the patellar (knee jerk) reflex
flexor and crossed-extensor reflexes
Flexor (withdrawal) reflex:
- > initiated by a painful stimulus
- > causes automatic withdrawal of the threatened body part
- > ipsilateral and polysynaptic
however, descending signals from brain can override flexor reflexes (ie. pin prick)
flexor and crossed-extensor reflexes
Crossed extensor reflex:
-> occurs with flexor reflexes in weight-bearing limbs to maintain balance
- > consists of an ipsilateral flexor reflex and a contralateral extensor reflex
- the stimulated side is withdrawn (flexed)
- the contralateral side is extended
superficial reflexes (cutaneous)
Plantar reflex (babinski reflex) ->stimulus: stroking lateral aspect of the sole of the foot
*normal response: downward flexion of the toes
tests for function of corticospinal tracts
