__Cranial nerves attach to brain _Spinal nerves attach to spinal cord

____Cranial nerves attach to brain___Spinal nerves attach to spinal cord

Sensation:• The conscious or subconscious

awareness of external or internal stimuli.

Perception:• The conscious awareness and

the interpretation of meaning of sensations.

Peripheral sensory receptors

By location:

• Exteroceptors

– Sensitive to stimuli arising from outside body

• Interoceptors

– Or visceroreceptors, from internal viscera

• Proprioceptors

– Monitor degree of stretch in skeletal muscles, tendons, joints and ligaments

• Pain• Temperature• Light touch• Pressure• Sense of body

and limb position

• Taste• Smell• Vision• Hearing• Balance

General SensesGeneral Senses vs. vs. Special Special SensesSenses

• Mechanoreceptors

• Thermoreceptors

• Photoreceptors

• Chemoreceptors

• Nociceptors

• Osmoreceptors

skin, bones, internal organs, joints

Naked nerve endings surrounded by one or more layers

Pacinian corpuscle

Free nerve endings

Encapsulated Nerve Encapsulated Nerve

EndingsEndingsvs

Unencapsulated Unencapsulated

Nerve EndingsNerve Endings

Deeper tissue, muscles

Free Nerve Endings - Pain & Temperature

Merkel’s Discs - Light Touch & Pressure

Root Hair Plexuses - Light Touch

pain, light touch, and temperature

Pacinian Corpuscles - Deep Pressure

Meissner’s Corpuscles - Discriminative Touch in Hairless Skin Areas

Krause’s End-Bulbs - Discriminative Touch in Mucous Membranes

Ruffini’s Corpuscles - Deep Pressure & Stretch (Proprioception)

Merkel Cells- slow mechanoreceptors (basal layer)

Merkel cell

free nerve endings

root hair plexus

Meissner’s corpuscles

Pacinian corpuscles

Ruffini corpuscle

Merkel disc

Muscle Spindles - Skeletal Muscle StretchingGolgi Tendon Organs - Tendon StretchingJoint kinesthetic receptors – monitors stretch

in synovial joints; sends info to cerebellum and spinal reflex arcs

Proprioceptors

– to cerebrum, – cerebellum and – spinal reflex arcs

Peripheral motor endings

• Innervation of skeletal muscle

• Innervation of visceral muscles and glands

• Motor axons innervate skeletal muscle fibers at neuromuscular junctions = motor end plates

Motor unit: motor neuron & all the muscle fibers it innervates

All muscles in motor unit contract together when neuron fires

Stimulation of single motor unit causes weak contraction of entire muscle (spread out)

Innervation of visceral muscles & glands

• Near end organ visceral motor axon swells = presynaptic terminals (vesicles with neurotransmitters): action slow (NT diffuses)

Somatic Pain-results from injuries to skin, muscle, joints, tendon vs.Visceral Pain- pain in body organs

Referred Pain-felt on the body surface

• Mature neurons are amitotic• If the soma of a damaged nerve is intact, axon

will regenerate• Involves coordinated activity among:

– Macrophages—remove debris– Schwann cells—form regeneration tube and

secrete growth factors– Axons—regenerate damaged part

• CNS oligodendrocytes bear growth-inhibiting proteins that prevent CNS fiber regeneration

Figure 13.4 (1 of 4)

Endoneurium

Dropletsof myelin

Fragmentedaxon

Schwann cells

Site of nerve damage

The axonbecomesfragmented atthe injury site.

1


Schwann cell Macrophage Macrophagesclean out thedead axon distalto the injury.

2


Fine axon sproutsor filaments

Aligning Schwann cellsform regeneration tube

3 Axon sprouts,or filaments,grow through aregeneration tubeformed bySchwann cells.


Schwann cell Site of newmyelin sheathformation

4 The axonregenerates anda new myelinsheath forms.

Single enlargingaxon filament

On Old Olympus Towering Tops A Fat Voracious German Viewed A Hop

1. Olfactory- smell2. Optic- vision3. Oculomotor- 4 of the 6 extrinsic eye muscles 4. Trochlear- extrinsic eye muscles5. Trigeminal- sensory fibers to the face and motor fibers to

the chewing muscles6. Abducens- controls eye muscles that turn the eye laterally7. Facial- facial expression8. Vestibulocochlear- hearing and balance9. Glosopharyngeal- tongue and pharynx10.Vagus- parasympathetic control of heart, lungs &

abdominal organs11.Accessory- accessory part of vagus nerve, neck & throat

muscles12.Hypoglossal- moves muscles under tongue

Olfactory

Optic

Oculomotor

Trochlear

Trigeminal

Abducens

VestibulocochlearGlossopharyngeal

VagusAccessory Hypoglossal

Facial

Olfactory bulbOlfactory tract

Olfactory receptor cell

Filaments of olfactory nerve

Abducensnerve

Lateral rectus muscle cut

Nerve Pathways into the Spinal Cord

Nerve Pathways into the Spinal Cord sensory

pathway

motor pathway

Spinal nerves

Spinal nerves• Dorsal roots – sensory fibers arising from cell bodies in dorsal root ganglia

• Ventral roots – motor fibers arising from anterior gray column of spinal cord

Ventral root ganglia

• Dorsal and ventral roots join in an intervertebral foramen forming spinal nerve

• Outside foramen, re-branch as rami (sing., ramus):Dorsal and ventral rami (somatic)Rami communicantes (visceral)

Spinal nerve

• Dorsal rami serve the muscles and skin of the posterior trunk– Back, from neck to sacrum, innervated in a

neatly segmented pattern: horizontal strip at same level as emergence from spinal cord

• Ventral rami serve the muscles and skin of the lateral and anterior trunk– In thorax only, a simple segmented pattern

as intercostal nerves– Also serve the limbs

Cross section of thorax showing main roots and branches of a spinal nerve– In the thorax, each ventral ramus

continues as an intercostal nerve

Dorsal ramus

Ventral ramus

Intercostal nerve

Nerve plexuses• Networks of

successive ventral rami that exchange fibers (crisscross & redistribute)

• Mainly innervate the limbs

• Thoracic ventral rami do not form nerve plexuses

Cervical Plexus

• Formed by ventral rami of C1–C4

• 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)

Brachial Plexus

• Formed by ventral rami of C5–C8 and T1 (and often C4 and T2)

• It gives rise to the nerves that innervate the upper limb

• Major branches of this plexus: – Roots—five ventral rami (C5–T1)– Trunks—upper, middle, and lower– Divisions—anterior and posterior – Cords—lateral, medial, and posterior

Figure 13.9 (a)

Upper

Middle Trunks

Lower

Roots (ventral rami):

Upper subscapular

Lower subscapular

Thoracodorsal

Medial cutaneousnerves of the armand forearm

Long thoracic

Medial pectoral

Lateral pectoral

Nerve tosubclaviusSuprascapular

Dorsal scapular

Posteriordivisions

Anteriordivisions

Lateral

PosteriorCords

Medial

Axillary

Musculo-cutaneousRadial

Median

Ulnar

Posteriordivisions

Trunks Roots

C4

C5

C6

C7

C8

T1

(a) Roots (rami C5 – T1), trunks, divisions, and cords

Brachial Plexus: Nerves• Axillary—innervates the deltoid, teres minor, and skin

and joint capsule of the shoulder• Musculocutaneous—innervates the biceps brachii and

brachialis and skin of lateral forearm• Median—innervates the skin, most flexors and

pronators in the forearm, and some intrinsic muscles of the hand

• Ulnar—supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand

• Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb

Figure 13.9 (c)

Median nerve

Musculocutaneous nerve

Radial nerveHumerus

Ulna

Ulnar nerveMedian nerve

Radius

Radial nerve (superficial branch)

Superficial branch of ulnar nerveDorsal branch of ulnar nerve

Digital branch of ulnar nerveMuscular branchDigital branch

(c) The major nerves of the upper limb

Axillarynerve

Anteriordivisions

Posteriordivisions

Trunks Roots

Note distribution of cutaneous nerves

Sensory innervation, palm

1. Ulnar nerve

2. Median nerve

3. Radial nerve

• T3-T12• 11 intercostal nerve• 1 subcostal nerve

Lumbar Plexus

• Arises from L1–L4

• Innervates the thigh, abdominal wall, and psoas muscle

• Femoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of leg

• Obturator nerve—passes through obturator foramen to innervate adductor muscles

Sacral Plexus

• Arises from L4–S4

• Serves the buttock, lower limb, pelvic structures, and perineum

• Sciatic nerve– Longest and thickest nerve of the body– Innervates the hamstring muscles, adductor

magnus, and most muscles in the leg and foot– Composed of two nerves: tibial and common

fibular

Functional Divisions of the Peripheral Nervous System

Afferent Division– Sensory (advances) neuron –

goes toward CNSEfferent Division

– Motor (exits) neuron- leaves CNS– Somatic Nervous System– Autonomic Nervous System

REFLEXES

• Rapid, predictable response to a stimulus.

• Unlearned, involuntary, "hard-wired" into our neuroanatomy at the cellular & tissue level.

The simplest type of nerve circuit regulates a reflex (or autonomic response) and is called a reflex arc.

Methods of Classifying Reflexes

• Innate reflexes–Result from connections that form

between neurons during development

• Acquired reflexes–Learned, and typically more

complex

Reflex classifications

• Cranial reflexes–Reflexes processed in the brain

• Spinal reflexes–Interconnections and processing

events occur in the spinal cord

More reflex classifications

• Somatic reflexes–Control skeletal muscle

• Visceral reflexes (autonomic reflexes)–Control activities of other

systems

still more reflex classifications

• Monosynaptic reflex– Sensory neuron synapses directly on a

motor neuron

• Polysynaptic reflex– At least one interneuron between sensory

afferent and motor efferent

– Longer delay between stimulus and response

and more reflex classifications

Spinal Reflex Arc

Spinal Reflex Arc

patellar ligament

stretch receptor

motor neuron

sensory neuron

motor neuron

interneuron

+ Excitatory synapse– Inhibitory synapse

Quadriceps strongly contracts. Golgi tendon organs are activated.

Interneurons

Spinal cord

Quadriceps(extensors)

Golgitendon

organHamstrings

(flexors)

1



Afferent fibers synapse with interneurons in the spinal cord.

Interneurons

Spinal cord


Golgitendon

organHamstrings

(flexors)

1 2




Interneurons

Spinal cord


Golgitendon

organHamstrings

(flexors)

1 2

3a The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending theknee.




Interneurons

Spinal cord


Golgitendon

organHamstrings

(flexors)

1 2

3a 3b

The interneurons (green) make inhibitory synapses with ventral horn neurons (purple) that prevent the antagonist muscles (hamstrings) from resisting the contraction of the quadriceps.

The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending theknee.

The motor neurons (red) send activating impulses to the quadriceps causing it to contract, extending theknee.

Reflex Arc

Baby Reflexes

• Palmar Grasp reflex• Suckling reflex• Rooting reflex• Babinski/plantar reflex

Pupillary Reflex

Mammalian Dive Reflex

An automated response system for diving in cold water (less than about 21C / 70F).

1. Bradycardia2. Vasoconstriction to extremities3. Apnea

INQUIRY

1. What is a reflex?2. Damage of the spinal cord

above C3 can result in_____?

3. In which portion of the spinal cord do the interneurons lie?

4. What kind of peripheral nerve fiber carries motor impulses outward to smooth muscles and glands of internal organs?

Documents

____Cranial nerves attach to brain ___Spinal nerves attach to spinal cord

__Cranial nerves attach to brain _Spinal nerves attach to spinal cord