Week 4 - Efferant and Afferent Tracts/Pathways Flashcards
tacile receptors
coruscple of touch (meissner corpuscle)
hair root plexuses
type 1 cutaneous mechoreceptors (tactile disc)
type 2 cutaneous (ruffini corpuscle)
lamellated (pacinian) corpuscles
itch and tickle receptors
thermoreceptors
warm/cold receptors
location: free endings in skin/mucous membranous of mouth, vagina and anus
sensation: warmth or cold
rate: 1sr rapid then slow
pain receptors
nonciceptors
location: free nerve endings in every body tissue expect brain
sensation: pain
rate: slow
propriceptors
muscle spindles
tendon origin
joint kinesthetic recpetors
corpuscle of touch (meissner corpuscles)
location: caspule surronds mass of dendrite in dermal papillae of hairless skin
sensations: onset of otuch and low- frequency vibrations
rate: rapid
hair- root plexuses
structure/location: free nerve endingwrapped around hiar follicles in skin
sensatoin: movement on skin surface that disburbs hair
rate: rapid
type 1 cutaneous mechorecpetors (tacile discs)
saucer-shaped free- nerve endings make contact with tactile epithelilums cells in epidermal
senation: continous touch and pressure
rate: slow
type 2 citaneous mechoreceptors (ruffini corpsuslce)
location/sturcture: elongated capsule surronds dendrtire deep in dermis and ligament and tendons
sensation: skin stretching and pressure
rate: slow
lamellated (pacinian corspuscles)
location/structure: oval, layered capsule surronds dendrties presnt in dermis and subcutanoues layer, submucousal tissues, joints, periosteum and some viscera
sensation: high frequency vibrations
rate: rapid
itch and tickle receptors
location/structure: free nerve endings in skin and mucous membrane
sensation: itching and tickling
rate: rapid and slow
muscle spindles
location/senestion: sensory nerve endings wrap around central area of encapsulate intrafusal muscle fibres within most skeletal muscle
sensation: muscle length
rate: slow
muscle spindles
location/senestion: sensory nerve endings wrap around central area of encapsulate intrafusal muscle fibres within most skeletal muscle
sensation: muscle length
rate: slow
tendon organs
location/structure: capsules encloses collagen fibres and sesnroy nerve endings at junction of tendon and muscle
sensation: muscle tension
rate: slow
joint kinesthetic receptors
location/structure: lamallted corsusples, type 2 cuntanoues mechorecpetor, tendon organs, and free nerve endings
sensation: joint position and movement
reate: rapid
1st order neurons
- First-order (primary) neurons are sensory neurons that conduct impulses from somatic sensory receptors into the brainstem or spinal cord. All other neurons in a somatic sensory pathway are interneurons, which are located completely within the central nervous system (CNS). From the face, nasal cavity, oral cavity, teeth, and eyes, somatic sensory impulses propagate along the cranial nerves into the brainstem. From the neck, trunk, limbs, and posterior aspect of the head, somatic sensory impulses propagate along spinal nerves into the spinal cord.
2nd order neurons
Second-order (secondary) neurons conduct impulses from the brainstem or spinal cord to the thalamus. Axons of second-order neurons decussate (cross over to the opposite side) as they course through the brainstem or spinal cord before ascending to the thalamus.
3rd order neuron
- Third-order (tertiary) neurons conduct impulses from the thalamus to the primary somatosensory area on the same side. As
the impulses reach the primary somatosensory area, perception
of the sensation occurs. Because the axons of second-order neurons decussate as they pass through the brainstem or spinal cord,
somatic sensory information on one side of the body is perceived
by the primary somatosensory area on the opposite side of the
brain.
sensory receptors
Sensory receptors are activated by changes in the internal or external environment
A. Sensory receptors are specialized to respond to changes in their environment called stimuli.
- Activation of sensory receptors by a strong enough stimulus causes the production of graded
potentials that trigger nerve impulses along afferent pathways to the CNS.
PNS
The PNS includes all neural structures outside the brain and spinal cord: sensory receptors, peripheral
nerves and their associated ganglia, and efferent motor endings.
simple receptors
general senses and may be nonencapsulated or encapsulated dendritic endings.
nonencapsulated dendetritc end
free nerve endings and detect temperature, pain, itch,
light touch, or are located at the base of hair follicles.
encapsulated dendritic endings
consist of a dendrite enclosed in a connective tissue capsule
and detect discriminatory touch, initial, continuous, and deep pressure, and stretch of muscles,
tendons, and joint capsules.
somatosensory system
the part of the sensory system serving the body wall and limbs, receives
input from exteroreceptors, proprioreceptors, and interoreceptors.
There are three main levels of neural integration in the somatosensory system
: the receptor level,
circuit level, and perceptual level.
receptor level
- Processing at the receptor level requires a stimulus to excite a receptor within its receptive field,
causing generation of graded potentials in order for sensation to occur.
a. If the receptor is part of a sensory neuron, the graded potentials produced are generator
potentials that can cause the generation of action potentials on the sensory neuron.
b. If the receptor is a separate structure from the sensory neuron, the graded potentials
produced are receptor potentials that may cause generator potentials on the sensory neuron.
c. Many receptors exhibit adaptation, in which a constant stimulus results in a gradual decrease
in receptor sensitivity.
circuit level
- Processing at the circuit level involves delivery of impulses along first-, second-, and third-order
neurons to the appropriate region of the cerebral cortex for stimulus localization and perception.
processing at perceptual level
a. Perceptual detection sums input from several receptors and is the simplest level of
perception.
b. Magnitude estimation is the ability to detect stimulus intensity through frequency coding.
c. Spatial discrimination allows identification of the site or pattern of stimulation through spatial
discrimination.
d. Feature abstraction is the mechanism through which we identify complex features of a
sensation.
e. Quality discrimination involves the ability to differentiate specific qualities of a particular
sensation.
f. Pattern recognition is the ability to recognize a pattern in a complete scene.
visceral pain
results from stimulation of receptors within internal organs from stimuli such as extreme
stretch, ischemia, chemical irritation, and muscle spasms.
a. Visceral pain travels along the same fiber tracts as somatic pain impulses, giving rise to
referred pain that is in an area different from the affected area.
DCML
The dorsal column–medial lemniscus pathway (DCML) (also known as the posterior column-medial
lemniscus pathway, PCML) is a sensory pathway of the central nervous system that conveys
sensations of fine touch, vibration, two-point discrimination, and proprioception (position) from the
skin and joints.
decending motor pathways
Descending motor pathways can be divided into lateral and medial motor systems based on their
location in the spinal cord. The two lateral motor systems are the lateral corticospinal tract and the
rubrospinal tract, which control movements of the extremities.
The motor pathway, also called the pyramidal tract or the corticospinal tract, serves as the motor
pathway for upper motor neuronal signals coming from the cerebral cortex and from primitive
brainstem motor nuclei. There are upper and lower motor neurons in the corticospinal tract.
nerve
A. A nerve is a cord-like organ consisting of parallel bundles of peripheral axons enclosed by connective
tissue wrappings.
1. Each axon within a nerve is surrounded by a thin layer of loose connective tissue, the
endoneurium.
2. A perineurium is a connective tissue wrapping that bundles groups of fibers into fascicles.
3. An epineurium bundles all fascicles into a nerve.
peripheral nerves
Peripheral nerves, either cranial or spinal, are classified according to the direction in which they
transmit impulses.
1. Mixed nerves contain both sensory and motor fibers: Most nerves are mixed nerves.
2. Sensory, or afferent, nerves carry impulses only toward the CNS.
3. Motor, or efferent, nerves only carry impulses away from the
CNS
gangila
Ganglia are collections of neuron cell bodies associated with nerves in the PNS.
Ganglia associated with afferent nerve fibers are cell bodies of sensory neurons; ganglia associated
with efferent nerve fibers are mostly cell bodies of autonomic motor neurons.
damaged cns nerves vs pns nerves
Damaged CNS nerve fibers almost never regenerate, but if a PNS nerve fiber is cut or compressed,
and the cell body remains intact, axons can regenerate
schwann cells
Schwann cells participate in regenerating PNS axons, but in the CNS, oligodendrocytes have growthinhibiting proteins that do not support regrowth of axons.
cranial nerves summery
- Olfactory nerves (cranial nerve I) detect odors.
- Optic nerves (cranial nerve II) are responsible for vision.
- Oculomotor, trochlear, and abducens nerves (cranial nerves III, IV, and VI) allow movement of the
eyeball. - Trigeminal nerves (cranial nerve V) allow sensation of the face and motor control of chewing muscles.
- Facial nerves (cranial nerve VII) allow movement of muscles creating facial expression.
- Vestibulocochlear nerves (cranial nerve VIII) are responsible for hearing and balance.
- Glossopharyngeal nerves (cranial nerve IX) control the tongue and pharynx.
- Vagus nerves (cranial nerve X) control several visceral organs.
- Accessory nerves (cranial nerve XI) have a relationship with the vagus nerves.
- Hypoglossal nerves (cranial nerve XII) innervate muscles of the tongue
how many pairs of spinal nerves
31
how is spinal cord connected
Each spinal nerve connects to the spinal cord by a ventral root, containing motor fibers, and a dorsal
root, containing sensory fibers.
rami
- Rami lie distal to and are lateral branches of the spinal nerves that carry both motor and sensory
fibers. - The back is innervated by the dorsal rami with each ramus innervating the muscle in line with the
point of origin from the spinal column. - Only in the thorax are the ventral rami arranged in a simple segmental pattern corresponding to that
of the dorsal rami. - The cervical plexus is formed by the ventral rami of the first four cervical nerves.
dermatome
The area of skin innervated by the cutaneous branches of a single spinal nerve is called a dermatome
a. Dermatomes on the trunk are relatively uniform in width, run horizontally, and are in direct
line with their spinal nerves.
b. Dermatomes in the upper limbs are innervated by ventral rami from C5–T1, while
dermatomes of the lower limbs are innervated by lumbar nerves (anterior surface), or sacral
nerves (posterior surface).
peripheral motor endings connect nerves to their effectors
A. Peripheral motor endings are the PNS element that activates effectors by releasing
neurotransmitters.
B. The terminals of the somatic motor fibers that innervate voluntary muscles form elaborate
neuromuscular junctions with their effector cells and they release the neurotransmitter acetylcholine.
C. The junctions between autonomic motor endings and the visceral effectors involve varicosities and
release either acetylcholine or epinephrine as their neurotransmitter
segmental level of motor control
A. The segmental level is the lowest level on the motor control hierarchy and consists of the spinal cord
circuits.
1. Circuits that control locomotion or repetitive motor activity are called central pattern
generators (CPGs) and consist of inhibitory and excitatory neurons that produce rhythmic or
alternating movements.
projection level of motor control
B. The projection level has direct control of the spinal cord and acts on direct and indirect motor
pathways.
1. Upper motor neurons produce voluntary movement of skeletal muscles.
2. Brain stem motor nuclei help control reflex and CPG controlled motor actions.
pre-command level
C. The pre-command level is made up of the cerebellum and the basal nuclei and is the highest level of
the motor system hierarchy.
1. The cerebellum acts on motor pathways through projection areas of the brain stem, and on
the motor cortex via the thalamus.
2. The basal nuclei receive inputs from all areas of the cortex and send output to premotor and
prefrontal cortices via the thalamus.
reflexes
A. Reflexes are unlearned, rapid, predictable motor responses to a stimulus and occur over highly
specific neural pathways called reflex arcs.
1. Inborn, or intrinsic, reflexes are unlearned, unpremeditated, and involuntary.
2. Learned, or acquired, reflexes result from practice, or repetition.
Reflexes are functionally classified as somatic, which activate skeletal muscle, or autonomic, which
activate visceral effectors.
reflec arc
A reflex arc is a very specific neural path that controls reflexes and has five components: a receptor, a
sensory neuron, an integration center, a motor neuron, and an effector.
stretch and tendon reflexes
- In the stretch reflex, the muscle spindle is stretched and excited by either an external stretch
or an internal stretch. - The tendon reflex produces muscle relaxation and lengthening in response to contraction.
The Flexor and Crossed Extensor Reflexes
- The flexor, or withdrawal, reflex is a polysynaptic ipsilateral reflex initiated by a painful
stimulus, causing automatic withdrawal of the threatened body part from the stimulus. - The crossed-extensor reflex is a complex spinal reflex consisting of an ipsilateral withdrawal
reflex and a contralateral extensor reflex.
Superficial reflexes are elicited by gentle cutaneous stimulation.
- The plantar reflex is used to evaluate the proper functioning of the lower spinal cord.
- The abdominal reflex tests the proper function of the spinal cord and ventral rami from T8–
T12.
Developmental Aspects of the Peripheral Nervous System
A. The spinal nerves branch from the developing spinal cord and adjacent neural crest and exit between
the forming vertebrae, ending at the adjacent muscle mass: Cranial nerves innervate muscles of the
head in a similar way.
B. Cutaneous nerves develop in a similar pattern: The trigeminal nerves innervate most of the face and
scalp, and spinal nerves supply branches to specific dermatomes.
C. Sensory receptors atrophy to some degree with age, and there is a decrease in muscle tone in the
face and neck; reflexes occur a bit more slowly.
efferent pathways and gangila
- In the somatic nervous system, the cell bodies of the neurons are in the spinal cord and their
axons extend to the skeletal muscles they innervate. - The ANS consists of a two-neuron chain in which the cell body of the first neuron, the
preganglionic neuron, resides in the spinal cord, and synapses with a second neuron, the
postganglionic neuron, residing within an autonomic ganglion outside the CNS.
neurotransmitter effects
- The neurotransmitter released by the somatic motor neurons is acetylcholine, which always
has an excitatory effect; the neurotransmitters released by the ANS are epinephrine and
acetylcholine, and both may have either an excitatory or an inhibitory effect.
cranial part of parasymmpathic divsion
- Parasympathetic fibers of the oculomotor nerve control pupil constriction and lens shape.
- Facial nerves carry parasympathetic fibers to nasal glands, lacrimal glands, and submandibular
and sublingual salivary glands. - Glossopharyngeal parasympathetic fibers activate parotid salivary glands.
- The vagus nerve carries parasympathetic fibers to the cardiac plexus to innervate the heart,
the pulmonary plexus to airways of the lungs, and the esophageal plexus, serving the esophagus
and stomach.
sacral part of parasympathic
- The distal half of the large intestine and the pelvic organs are served by the sacral part, which
arises from neurons located in the lateral gray matter of spinal cord segments S2−S4.
visceral reflex arcs
Visceral reflex arcs have the same five components as somatic reflex arcs
A. Visceral reflex arcs differ from somatic motor reflex arcs, in that they have two consecutive neurons
in their motor components, and afferent fibers are visceral sensory neurons.
1. The visceral sensory neurons are the first link in autonomic reflexes, sending information concerning
chemical changes, stretch, and irritation of the viscera.
Acetylcholine and norepinephrine are the major ANS neurotransmitters
- Nicotinic cholinergic receptors are found on all postganglionic neurons, hormone-producing
cells of the adrenal medulla, and skeletal muscle cells at the neuromuscular junction, bind
acetylcholine, and are always excitatory. - Muscarinic receptors occur on all parasympathetic target organs, and a few sympathetic
targets, such as eccrine sweat glands, bind acetylcholine, and may be excitatory or inhibitory.
adrenergic receptors
- There are two classes of adrenergic receptors, alpha (α) and beta (β) that bind norepinephrine, and
produce either excitatory or inhibitory responses.
The parasympathetic and sympathetic divisions usually produce opposite effects
mechanoreceptors
detect mechanical stimuti: provide sensations of touch, pressure, vibration, proproropetors, and hearong and equilibrium:; also mointor stretching of blood vessel and interal organs
chemoreceptors
detect chemical in mouth (taste) and nose (smell) and body fluids
osorecpetors
sense osmotic pressure of body fluids
photoreceptros
detects light that strikes retina
THERMORECEPTORS
DETECTS CHANGES IN TEMP
exteroceptors
located near body surface, senstistive stimuli orginating outside body: provide information about external enironment: convey visual , smell, taste, touch, pressure, vibration, pain and thermal sensation
interoceptors
located in blood vessels, visceral organs, and neurons system; provideinformation about internal enironment impulses usuallt arent subcunous but occasionallt may be felt with pain/pressure
prorioceptor
located in muscle tenods joints and inner ear: provide information about body position, muscle length and tension. position and motion of joints and qualilibrium (balance
