A&P 1 Lecture - Ch. 13 PNS

sensory receptors

specialized dendritic endings that respond to changes in environment (stimuli)

mechanoreceptors

respond to touch, pressure, vibration, stretch, and itch

thermoreceptors

respond to changes in temperature

photoreceptors

respond to light

ex: rods and cones in our retina

chemoreceptors

respond to chemicals (e.g., smell, taste, changes in blood chemistry)

nociceptors

pain receptors that are sensitive to tissue damage causes by extreme heat or cold, excessive pressure, inflammatory chemicals, etc.

exteroreceptors

respond to stimuli outside the body

include receptors of the skin that respond to touch, pressure, pain and temperature

interoreceptors

respond to stimuli from internal visceral organs and blood vessels; sensitive to chemical, temperature, stretch and pressure changes

proprioreceptors

Respond to stretch in skeletal muscles, tendons, joints, ligaments, and connective tissue coverings of bones and muscles; inform the brain of movements and body position

general senses

tactile sensations (touch, pressure, stretch, vibration), temperature, pain, and proprioception

special senses

vision, hearing, taste, smell, equilibrium; housed in complex sense organs

receptor adaptation

can occur when a constant stimulus causes a decrease in sensitivity in a receptor

phasic receptors

•Receptor sensitivity is fast-adapting

•Send impulses at beginning and/or end of stimulus

•Examples: receptors for pressure, touch, and smell

tonic receptors

•Receptor sensitivity adapts slowly or not at all

•Examples: nociceptors and most proprioceptors

Nonencapsulated (free) nerve endings characteristics

•Abundant in epithelia and connective tissues

•Most are nonmyelinated

•Small-diameter group C fibers (slow)

•Distal terminals have knoblike swellings

Respond mostly to temperature, pain, or light touch

nonencapsulated (free) nerve endings types

•Thermoreceptors

•Nociceptors

•Tactile (Merkel) discs

•Hair follicle receptors

Tactile (Merkel) discs

function as light touch receptors; located in deeper layers of epidermis

Hair follicle receptors

•Free nerve endings that wrap around hair follicles

•Act as light touch receptors that detect bending of hairs

Tactile (Meissner's) corpuscles

•Small receptors involved in discriminative touch

•Found just below skin, mostly in sensitive and hairless areas (nipples, external genitalia, fingertips, soles of feet, eyelids)

Lamellar (Pacinian) corpuscles

•Large receptors that respond to deep pressure and vibration

•Located in deep dermis, hypodermis, tendons, ligaments, joint capsules

Bulbous corpuscles (Ruffini endings)

proprioceptors located in deep dermis and joint capsules

nerve

a cordlike organ composed of a bundle of axons (nerve fibers)

endoneurium

loose connective tissue that encloses axons and their myelin sheaths

perineurium

coarse connective tissue that bundles fibers into fascicles

Epineurium

tough fibrous sheath around the outside of a nerve

afferent neurons

transmit sensory impulses from receptors to the CNS

efferent neurons

transmit motor impulses from CNS to effectors

mixed nerves

nerves carrying both sensory and motor fibers

ganglia

Collection of nerve cell bodies found outside the CNS

dorsal root ganglia

contain nerve cell bodies of somatic sensory neurons

Olfactory nerves

cranial nerve I

sensory only

functions in the sense of smell

Optic nerves

cranial nerve II

sensory only

functions in vision

crosses over at optic chiasma and forms optic tracts

oculomotor nerves

cranial nerve III

motor only

functions in raising the eyelid, directing the eyeball, constricting the iris to control pupil diameter, controlling the lens shape

trochlear nerves

cranial nerve IV

motor only

functions in directing the eyeball

trigeminal nerves

cranial nerve V

largest cranial nerve

both sensory and motor

3 divisions - ophthalmic, maxillary, mandibular

sensory input from ophthalmic and maxillary regions

motor output to the mandibular region controlling mastication (chewing)

abducens nerves

cranial nerve VI

motor only

innervates lateral rectus muscle of the eye causing lateral eye movements

facial nerves

cranial nerve VII

both sensory and motor

5 major branches: temporal, zygomatic, buccal, mandibular, cervical

motor: facial expression, produce tears at lacrimal glands and saliva at salivary glands

sensory: taste from anterior 2/3 of tongue

vestibulocochlear nerves

cranial nerve VIII

2 sensory divisions

1. cochlear division innervates hearing receptors

2. vestibular division innervates equilibrium (balance) receptors

glossopharyngeal nerve

Cranial nerve IX.

Sensory and motor nerve

sensory: taste and general sensation from tongue and pharynx; chemoreception and baroreceptor (pressure) from the carotid artery

motor: tongue and pharynx for swallowing, and parotid salivary glands

vagus nerve

cranial nerve X

sensory and motor

only cranial nerve that extends beyond the head and neck

sensory: taste from posterior tongue and pharynx, sensation from thoracic and abdominal organs

motor: innervates and regulates visceral organs providing parasympathetic control

accessory nerve

cranial nerve XI

motor only

innervates sternocleidomastoid and trapezius muscle causing movements of the head and neck

hypoglossal nerve

cranial nerve XII

motor only

innervates muscles of the tongue for chewing, swallowing and speech

ventral roots

contain motor (efferent) fibers from ventral horn motor neurons that innervate skeletal muscles

dorsal roots

contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors

spinal nerves are short (1-2cm) and quickly branch into...

dorsal rami

ventral rami

dorsal rami

branch off of spinal nerves and innervate the skin and muscles of the posterior body trunk

ventral rami

branch off of spinal nerves and innervate the skin and muscles of the anterior trunk and limbs via nerve plexuses

intercostal nerves

originate from thoracic spinal nerves T1-T12 and innervate the body trunk

nerve plexuses

a complex network of nerves formed by all ventral rami except those forming the intercostal nerves

4 types: cervical, brachial, lumbar, sacral

significance of nerve plexuses

Fibers crisscross so that each branch contains fibers from several different spinal nerves; that means muscles are innervated by more than one spinal nerve, so damage to one does not cause complete paralysis

cervical plexus

give rise to cutaneous nerves that innervate the skin of the neck, ear, back of head, and shoulders; provide motor fibers to neck muscles for movement

phrenic nerve

arises from the cervical plexus

innervates the diaphragm - the major muscle for breathing

irritation of the nerve causes hiccups

Ansa cervicalis

nerve of the cervical plexus that innervates muscles involved with swallowing and speech

brachial plexus

gives rise to the nerves that innervate the upper limb

ulnar

median

axillary

radial

musculocutaneous

Ulnar nerve

important for fine motor control of the hand

Median nerve

innervates anterior forearm muscles of wrist flexion and pronation and innervates thumb muscles for opposition

Axillary nerve

innervates deltoid and teres minor and associated skin

Radial nerve

innervates the triceps brachii, supinator and forearm extensor muscles

Musculocutaneous nerve

innervates the biceps brachii and brachialis for forearm flexion and coracobrachialis for arm flexion

Carpel tunnel syndrome

caused by compression of the median nerve at the anterior wrist

Ape hand

Damage to the median nerve; deformity in which people cannot move thumb away from rest of hand.

Claw hand

ulnar nerve injury

Funny bone

a sensation caused by hitting the ulnar nerve at the medial epicondyle

Wrist drop

radial nerve injury

Erb's palsy

damage to the brachial plexus when an infant's head and neck are pulled on while passing through the birth canal

What nerve innervates the quadriceps?

femoral nerve

Largest nerve of lumbar plexus

femoral nerve

Saphenous nerve

Branch of femoral nerve; provides sensory information for medial aspect of entire leg and foot

Obturator nerve

passes through obturator foramen to innervate adductor muscles

Largest nerve in the body

sciatic nerve

What plexus does the sciatic nerve belong to?

sacral plexus

What does the sciatic nerve branch into?

tibial nerve and common fibular (peroneal) nerve

What nerve innervates the hamstrings?

sciatic nerve

Pudendal nerve

Supplies sensation to external genitalia and perineum

allows for bladder and bowel control

Tibial nerve

•Plantar flexion (gastrocnemius, soleus, tibialis posterior)

•Toe flexion (flexor digitorum longus, flexor hallucis longus)

•Sural nerve (sensory for calf)

Common fibular nerve

•Dorsiflexion (tibialis anterior)

•Toe extension (extensor digitorum longus)

•Ankle eversion (peroneus muscles)

Sciatica

•inflammation or injury to the sciatic nerve that causes radiating pain or numbness down the entire lower leg

Dermatomes

•an area of skin that is primarily supplied by the sensory fibers of a single spinal nerve

clinically significant because they can help identify the location of nerve or spinal cord injuries.

Myotomes

•group of muscles primarily innervated by the motor fibers of a single spinal nerve, which controls specific muscle movements

•Clinically significant in assessing and diagnosing nerve injuries, spinal cord injuries, and certain neurological conditions.

Reflexes

•involuntary, nearly instantaneous movements of the body in response to specific stimuli without the input of higher brain centers

Major reflex centers

spinal cord and brainstem

Reflex arc

neural pathway that controls a reflex action without involving the brain, ensuring a rapid reaction to potentially harmful stimuli without conscious thought

includes a receptor, sensory neuron, interneuron, motor neuron, effector

Muscle spindles

•specialized sensory receptors in the muscle that detect muscle stretch and the rate of stretch; this proprioception is continuously sent to the spinal cord and brain

Muscle spindle (stretch) reflex

• a rapid, protective response that helps maintain muscle tone, posture, and balance

•The reflex ALSO protects muscles from excessive or sudden stretching that could result in damage

Muscle spindle (stretch) reflex causes muscles to _____________ to prevent excessive stretching of muscle.

contract

Golgi tendon organs

•specialized sensory receptors located at the junctions between muscle fibers and tendons

•They sense tension within tendons, particularly when a muscle contracts and pulls on its tendon

•They provide proprioception to the CNS, which can make fine adjustments to enhance motor control and precision

Golgi tendon reflex

reflex causes the muscle to relax in response to excessive tension in tendons to prevent potential injury

Flexor (withdrawal) reflex

Causes automatic withdrawal of threatened body part

Crossed extensor reflex

opposite limb supports body during withdrawal of injured limb

Amitotic

cells are unable to divide

CVA

cerebrovascular accident (stroke)

occurs when blood flow to the brain is blocked, cells are starved of oxygen and glucose and die

Multiple Sclerosis (MS)

autoimmune disease resulting in demyelination of CNS axons

Amyotrophic Lateral Sclerosis (ALS)

degeneration of motor neurons, leading to muscle weakness, paralysis, and eventually loss of function

Alzheimer's Disease

death of neurons and synapses in the brain, causing memory loss and cognitive decline

Parkinson's Disease

degeneration of dopamine-producing neurons in the brain, leading to motor control issues

Diabetic neuropathy

•type of nerve damage in diabetics due to the direct effects of chronic high blood glucose on peripheral axons

causes numbness, tingling, pain, muscle weakness, autonomic issues

Can axons of PNS neurons regenerate?

yes regeneration is possible

carried out by schwann cells

Can axons of CNS neurons regenerate?

NO regeneration, oligodendrocytes prevent it