Anp

(1) by the type of stimulus they detect;

(2) by their body location; and

(3) by their structural complexity.

respond to mechanical force such as touch, pressure (including blood pressure), vibration, and stretch.

such as those of the retina of the eye, re-spond to light

respond to chemicals in solution (mol-ecules smelled or tasted, or changes in blood or interstitial fluid chemistry

respond to potentially damaging stimuli that result in pain. For example, searing heat, extreme cold, excessive pressure, and inflam-matory chemicals are all interpreted as painful. These signals stimulate subtypes of thermoreceptors, mechanoreceptors, and chemoreceptors

are sensitive to stimuli arising outside the body (extero5 outside), so most extero-ceptors are near or at the body surface. They include touch, pressure, pain, and temperature receptors in the skin and most receptors of the special senses (vision, hearing, equilib-rium, taste, smell

also called visceroceptors, respond to stimuli within the body (intero= inside), such as from the internal viscera and blood vessels. Interoceptors monitor a variety of stimuli, including chemical changes, tissue stretch, and temperature. Sometimes their activity causes us to feel pain, discomfort, hunger, or thirst. However, we are usually unaware of their workings.

A key player in detecting painful stimuli is a plasma membrane protein

non-encapsulated

which lie in the deepest layer of the epidermis, function as light touch receptors. Certain free nerve endings associate with enlarged, disc-shaped epidermal cells (tactile or Merkel cells) to form tactile discs

non encapsulated

free nerve endings that wrap basket-like around hair follicles, are light touch receptors that detect bending of hairs. The tickle of a mosquito landing on your skin is mediated by hair follicle receptors.

are small recep-tors in which a few spiraling sensory terminals are sur-rounded by Schwann cells and then by a thin egg-shaped connective tissue capsule. Tactile corpuscles are found just beneath the epidermis in the dermal papillae and are espe-cially numerous in sensitive and hairless skin areas such as the nipples, fingertips, and soles of the feet. They are recep-tors for discriminative touch, and apparently play the same role in sensing light touch in hairless skin that hair follicle receptors do in hairy skin.

also called Pacinian corpuscles, are scattered deep in the dermis, and in subcutaneous tissue underlying the skin. Although they are mechanoreceptors stimulated by deep pressure, they respond only when the pressure is first applied, and thus are best suited to monitor-ing vibration (an “on/off ” pressure stimulus). They are the largest corpuscular receptors. Some are over 3 mm long and half as wide and are visible to the naked eye as white, egg-shaped bodies. In section, a lamellar corpuscle resembles a cut onion. Its single dendrite is surrounded by a capsule con-taining up to 60 layers of collagen fibers and flattened sup-porting cells.

Ruffini endings, which lie in the dermis, subcutaneous tissue, and joint capsules, contain a spray of receptor endings enclosed by a flattened capsule. They bear a striking resemblance to tendon organs (which moni-tor tendon stretch) and probably play a similar role in other dense connective tissues where they respond to deep and continuous pressure.

are fusiform (spindle-shaped) propriocep-tors found throughout the perimysium of a skeletal muscle. Each muscle spindle consists of a bundle of modified skel-etal muscle fibers, called intrafusal fibers (in0trah-fu9zal), enclosed in a connective tissue capsule (Table 13.1). Muscle spindles detect muscle stretch and initiate a reflex that resists the stretch. We will consider the details of their innervation later when we describe the stretch reflex

are proprioceptors located in tendons, close to the skeletal muscle insertion. They consist of small bun-dles of tendon (collagen) fibers enclosed in a layered capsule, with sensory terminals coiling between and around the fi-bers. When muscle contraction stretches the tendon fibers, the resulting compression of the nerve fibers activates the tendon organs. This initiates a reflex that causes the contract-ing muscle to relax

are propriocep-tors that monitor stretch in the articular capsules that enclose synovial joints. This receptor category contains at least four receptor types: lamellar corpuscles, bulbous corpuscles, free nerve endings, and receptors resembling tendon organs. To-gether these receptors provide information on joint position and motion (kines5 movement), a sensation of which we are highly conscious

(awareness of changes in the internal and external environments)

conscious interpretation of those stimuli

When the receptor region is part of a sensory neuron (as with free dendrites or the encapsulated receptors of most general sense receptors), the graded potential is called a gen-erator potential because it generates action potentials in a sensory neuron.

When the receptor is a separate cell (as in most special senses), the graded potential is called a receptor potentialbecause it occurs in a separate receptor cell. The receptor po-tential changes the amount of neurotransmitter released by the receptor cell onto the sensory neuron. The neurotransmit-ters then generate graded potentials in the sensory neuron

are fast adapting, often giving bursts of im-pulses at the beginning and the end of the stimulus. Phasic re-ceptors report changes in the internal or external environment. Examples are lamellar and tactile corpuscles

provide a sustained response with little or no adaptation. Nociceptors and most proprioceptors are tonic receptors because of the protective importance of their information.

is the ability to detect that a stimulus has occurred. This is the simplest level of perception. As a general rule, inputs from several receptors must be summed for perceptual detection to occur

is the ability to detect how intense the stimulus is. Perceived intensity increases as stimulus inten-sity increases because of frequency coding

is the mechanism by which a neuron or circuit is tuned to one feature, or property, of a stimulus in preference to others. Sensation usually involves an interplay of several stimulus features.

is the ability to differentiate the sub-modalities of a particular sensation. Each sensory modality has several qualities, or submodalities. For example, taste is a sen-sory modality and its submodalities include sweet and bitter

is the ability to take in the scene around us and recognize a familiar pattern, an unfamiliar one, or one that has special significance for us. For example, we can look at an image made of dots and recognize it as the portrait of a familiar face. We can listen to music and hear a melody, not just a string of notes

Within a few hours, the axon and its myelin sheath distal to the injury site begin to disintegrate because they cannot receive nutrients from the cell body.

1.The axon fragments. Almost immediately, the separated ends seal themselves off and then swell as substances be-ing transported along the axon accumulate in the sealed ends.

2.Macrophages clean out the dead axon.

3.Axon filaments grow through a regeneration tube.

4. The axon regenerates and a new myelin sheath forms.

Oligodendrocytes are studded with growth-inhibiting pro-teins. Consequently, the neuronal growth cone collapses and the fiber fails to regrow. Moreover, astrocytes at the site of in-jury form scar tissue rich in chondroitin sulfate that blocks axonal regrowth

sensory only

smell

sensory only

carries afferent nerves for vision

motor nerves

somatic motor fibers to four of the six extrinsic eye muscle that help direct eyeball , cause pupil to constrict,

The name oculomotor means “eye mover.” This nerve supplies four of the six extrinsic muscles that move the eyeball in the orbit

motor nerve

somatic motor fibers to one of the extrinsic eye muscles

The term trochlear means “pulley” and it inner-vates an extrinsic eye muscle that loops through a pulley-shaped ligament in the orbit

inferolaterally

superior oblique muscle,

Largest cranial nerve

both/ mixed sensory and motor

three divisions (trigemina5 threefold): ophthalmic, maxillary, and mandibular divisions. As main general sensory nerves of face, transmit afferent impulses from touch, temperature, and pain receptors. Cell bodies of sensory neurons of all three divisions are located in large trigeminal ganglion

The mandibular division also contains motor fibers that innervate chewing muscles

motor

supply somatic motor fibers to lateral rectus muscle an extrinsic muscle of the eye

moves eye laterally

This nerve controls the extrinsic eye muscle that abducts the eyeball (turns it laterally

A large nerve that innervates muscles of facial ex-pression (among other things)

Mixed nerves that are the chief motor nerves of face. Five major branches: temporal, zygomatic, buccal, mandibular, and cervical

Sensory only nerve for hearing and balance was formerly called the auditory nerve

Mixed nerves that innervate part of tongue and pharynx. Provide somatic motor fibers to, and carry proprioceptor fibers from, a superior pharyngeal muscle called the stylopharyngeus, which elevates the pharynx in swallowing. Provide parasympathetic motor fibers to parotid salivary glands (some of the nerve cell bodies of these parasympathetic motor neurons are located in otic ganglion).

Sensory fibers conduct taste and general sensory (touch, pressure, pain) impulses from pharynx and posterior tongue,

Mixed/Both nerve

The only cranial nerves to extend beyond head and neck region.

Nearly all motor fibers are parasympathetic efferents, except those serving skeletal muscles of pharynx and larynx (involved in swallowing). Parasympathetic motor fibers supply heart, lungs, and abdominal viscera and are involved in regulating heart rate, breathing, and digestive system activity. Transmit sensory impulses from thoracic and abdominal viscera, from the aortic arch baroreceptors (for blood pressure) and the carotid and aortic bodies (chemoreceptors for respiration), and taste buds on the epiglottis. Carry proprioceptor fibers from muscles of larynx and pharynx.

Motor

motor fibers to trapezius and sternocleidomastoid muscles which together moved head and neck

Motor

Hypoglossal nerve control allows tongue movements that mix and manipulate food during chewing, and contribute to swallowing and speech

contain motor (efferent) fibers that arise from ventral horn motor neurons and extend to and innervate the skeletal muscles.

contain sensory fibers that arise form sensory neurons in the dorsal rot ganglia and conduct impulses form peripheral receptors to the spinal cord.

quite short (only 1–2 cm). Almost im-mediately after emerging from its foramen, it divides into a small dorsal ramus (ra9mus; “branch”), a larger ventral ramus, and a tiny meningeal branch (me ̆ -nin9je-al) that reenters the vertebral canal to innervate the meninges and blood vessels within. Each ramus, like the spinal nerve itself, is mixed.Special rami called rami communicantes, which contain au-tonomic (visceral) nerve fibers, attach to the base of the ventral rami of the thoracic spinal nerves

cervical plexus

most important

receives fiber from C3,C4,C5

supplies both motor and sensory fibers to the diaphragm which is the chief muscle causing breathing movement

femoral nerve

obturator nerve

Lateral femoral cutaneous

Iliohypogastric

Ilioinguinal

Genitofemoral

sciatic nerve- The sciatic nerve is actually two nerves—the tibial and common fibular

In the vicinity of the knee, the tibial nerve gives off the sural nerve, which serves the skin of the posterolateral leg.■At the ankle the tibial nerve divides into the medial and lat-eral plantar nerves, which serve most of the foot.

Superior/inferior gluteal

Posterior femoral cutaneous

Pudendal

Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint.

length of muscle spindles

each muscle spindle consists of three to ten modified skeletal muscle fibers called intrafusal muscle fibers (intra5 within; fusal5 the spindle) enclosed in a connective tissue capsule

effector fibers of the muscle, called extrafusal muscle fibers.

amount tension in the muscle

Anulospiral endings (also called primary sensory endings) are the endings of large axons that wrap around the spindle center. They are stimulated by both the rate and degree of stretch.

Flower spray endings (also

called secondary sensory end-ings) are formed by smaller axons that supply the spindle ends. They are stimulated only by degree of stretch.

ex. knee jerk reflex

monosynaptic and ipsilateral. In other words, they involve a single synapse and motor activity on the same side of the body. Stretch reflexes are the only monosynaptic reflexes in the body.

Muscles relax and lengthen in response to tension.

Afferent impulses are transmitted to the spinal cord, and then to the cerebellum, where the information is used to adjust muscle tension. Simultaneously, motor neurons in spinal cord circuits supplying the contracting muscle are inhibited and antagonist muscles are activated, a phenomenon called recipro-cal activation. As a result, the contracting muscle relaxes as its antagonist is activated

Flexor reflexes are ip-silateral and polysynaptic,

automatic withdrawal of the threatened body part from the stimulus

often accompanies the flexor reflex in weight-bearing limbs and is particularly important in maintaining balance. It is a complex spinal reflex consisting of an ipsilateral withdrawal reflex and a contralateral extensor re-flex.

The ipsilateral response causes you to quickly lift your cut foot, while the contralateral response ac-tivates the extensor muscles of your opposite leg to support the weight suddenly shifted to it.

are elicited by gentle cutaneous stimula-tion, such as that produced by stroking the skin with a tongue depressor. These clinically important reflexes depend both on functional upper motor pathways and on cord-level reflex arcs. The best known are the plantar and abdominal reflexes

tests the integrity of the spinal cord from L4to S2 and indirectly determines if the corticospinal tracts are functioning properly. To elicit the plantar reflex, draw a blunt object downward along the lateral aspect of the plantar surface of the sole of the foot.

problem- Babinski’s sign, in which the great toe dorsiflexes and the smaller toes fan laterally.

Stroking the skin of the lateral abdomen above, to the side, or below the umbilicus induces a reflex contraction of the abdomen muscles in which the umbilicus moves toward the stimulated site

check the integrity of the spinal cord and ventral rami from T8 to T12

skeletal muscles derive from paired blocks of mesoderm (somites) distributed segmentally down the posteromedial aspect of the embryo